The Illustrated Dictionary of Electronics - Loscha

TheIllustrated Dictionary ofElectronics

This page intentionally left blank.

TheIllustrated Dictionaryof ElectronicsEighth EditionStan GibiliscoEditor-in-ChiefMcGraw-HillNew York Chicago San Francisco Lisbon London MadridMexico City Milan New Delhi San Juan SeoulSingapore Sydney Toronto

Cataloging-in-Publication Data is on file with the Library of CongressMcGraw-HillabcCopyright © 2001 by The McGraw-Hill Companies, Inc. All rights reserved. Printed in the United States ofAmerica. Except as permitted under the United States Copyright Act of 1976, no part of this publicationmay be reproduced or distributed in any form or by any means, or stored in a data base or retrieval system,without the prior written permission of the publisher.1 2 3 4 5 6 7 8 9 0 AGM/AGM 0 9 8 7 6 5 4 3 2 1P/N 0-07-137237-7ISBN 0-07-137236-9The sponsoring editor for this book was Scott Grillo, and the production supervisor was Pamela Pelton. Itwas set in Bookman by Techbooks.Printed and bound by Quebecor/Martinsburg.McGraw-Hill books are available at special quantity discounts to use as premiums and sales promotions, orfor use in corporate training programs. For more information, please write to the Director of Special Sales,McGraw-Hill, Two Penn Plaza, New York, NY 10121-2298. Or contact your local bookstoreInformation in this book has been obtained by the publisherfrom sources believed to be reliable. However, neither thepublisher nor the authors guarantee the accuracy or completenessof any information published herein. Neither the publishernor the authors shall be responsible for any errors, omissions, ordamages arising out of use of this information. This work is publishedwith the understanding that the publisher and authorsare supplying information but are not attempting to render professionalservices in any way, shape or form. If such services arerequired, the assistance of an appropriate professional shouldbe sought.This book is printed on recycled, acid-free paper containing a minimum of 50 percent recycledde-inked fiber.

To Tony, Tim, and Samuelfrom Uncle Stan

This page intentionally left blank.

ContentsPreface ixAcknowledgmentsxiDictionary 1Appendix A Schematic Symbols 773Appendix B Tables and Data 787Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

This page intentionally left blank.

PrefaceThe Illustrated Dictionary of Electronics—8th Edition has been revised, clarified, and updated,reflecting technological advances of recent years. New definitions have been added inthe fields of wireless technology, robotics, and artificial intelligence. Every effort has beenmade to be concise and accurate, without “talking down” to the reader.Many definitions contain cross references (indicated in ALL CAPITALS); these providerecommended additional information or allow comparison with related terms. Expressions ofspecial significance are printed in italics. Electronics abbreviations are included in the text;the full terms are stated as definitions.While an effort has been made to avoid superfluous mathematics, equations are sometimesnecessary to completely and effectively define a term. Mathematics beyond the highschoollevel has not been used.Appendix A contains the standard symbols used in electrical and electronic diagrams.These symbols are used in illustrations throughout this dictionary. Appendix B contains thefollowing data tables:1. Conversion between electrical systems2. Greek alphabet3. Mathematical functions and operations4. Prefix multipliers5. Resistor color codeSuggestions for future editions are welcome.Stan GibiliscoEditor-in-ChiefCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

This page intentionally left blank.

AcknowledgmentsIllustrations in this book were generated with CorelDRAW. Some clip art is courtesy of CorelCorporation, 1600 Carling Avenue, Ottawa, Ontario, Canada K1Z 8R7.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

This page intentionally left blank.

TheIllustrated Dictionary ofElectronics

This page intentionally left blank.

2 abhenry • absolute errorand is the inductance across which a currentthat changes at the rate of 1 abampere per secondinduces a potential of 1 abvolt.ABL Abbreviation of Automated Biology Laboratory(NASA).abmho The obsolete unit of conductance and ofconductivity in the cgs electromagnetic system.Replaced with ABSIEMENS.abnormal dissipation Power dissipation higher orlower than the customary level, usually an overload.abnormal oscillation 1. Oscillation where none isdesired or expected, as in an amplifier. 2. Oscillationat two or more frequencies simultaneouslywhen single-frequency operation is expected.3. Oscillation at an incorrect frequency. 4. Parasiticoscillation.abnormal propagation 1. The chance shifting ofthe normal path of a radio wave, as by displacementsin the ionosphere, so that reception is degraded.2. Unintentional radiation of energy fromsome point other than the transmitting antenna.3. Propagation over a path or in a direction notexpected.abnormal reflections Sharp, intense reflections atfrequencies higher than the critical frequency ofthe ionosphere’s ionized layer.abnormal termination The shutdown of a runningcomputer program or other process. Caused bythe detection of an error by the associated hardwarethat indicates that some ongoing series ofactions cannot be executed correctly.abnormal triggering The false triggering or switchingof a circuit or device, such as a flip-flop, bysome undesirable source instead of the true triggersignal. Electrical noise pulses often cause abnormaltriggering.abohm The unit of resistance and of resistivity inthe cgs electromagnetic system. One abohmequals 10 –9 ohms and is the resistance acrosswhich a steady current of 1 abampere produces apotential difference of 1 abvolt.abort To deliberately terminate an operation, experiment,process, or project before it has run itsnormal course.AB power pack 1. A portable dry-cell or wet-cellarray containing both A and B batteries in onepackage. 2. An ac-operated unit in one packagefor supplying A and B voltages to equipment normallyoperated from batteries.abrasion machine An instrument for determiningthe abrasive resistance of a wire or cable.abrasion resistance A measure of the ability of awire or wire covering to resist mechanical damage.ABS A basic programming abbreviation for the absolutevalue (of a number, variable, or expression).abscissa 1. The independent variable in a function.2. The axis (usually horizontal) on the graph of afunction that indicates the independent variable.absence-of-ground searching selector A rotaryswitch that searches for an ungrounded contactin a dial telephone system.absiemens The unit of conductance or conductivityin the cgs electromagnetic system. Oneabsiemens equals 10 9 siemens and is theconductance through which a potential of 1 abvoltforces a current of 1 abampere.absolute 1. A temperature scale in which zero representsthe complete absence of heat. Units of measureare same as units on Celsius and Fahrenheitscales. See ABSOLUTE SCALE. 2. Independent ofany arbitrarily assigned units of measure or value.absolute accuracy The full-scale accuracy of a meterwith respect to a primary (absolute) standard.absolute address In a digital computer program,the location of a word in memory, as opposed tolocation of the word in the program.absolute code A computer code in which the exactaddress is given for storing or locating the referenceoperand.absolute coding In computer practice, coding thatuses absolute addresses.absolute constant A mathematical constant thathas the same value wherever it is used.absolute delay The time elapsing between thetransmission of two synchronized signals fromthe same station or from different stations, as inradio, radar, or loran. By extension, the time intervalbetween two such signals from any source,as from a generator.absolute digital position transducer A digital positiontransducer whose output signal indicatesabsolute position. (See ENCODER.)absolute efficiency The ratio X x /X s , where X x isthe output of a given device, and X s is the outputof an ideal device of the same kind under thesame operating conditions.absolute encoder system A system that permitsthe encoding of any function (linear, nonlinear,continuous, step, and so on) and supplies a nonambiguousoutput.absolute error The difference indicated by the approximatevalue of a quantity minus the actual

absolute error • absolute tolerance 3value. This difference is positive when the approximatevalue is higher than the exact value,and it is negative when the approximate value islower than the exact value. Compare RELATIVEERROR.absolute gain Antenna gain for a given orientationwhen the reference antenna is isolated in spaceand has no main axis of propagation.absolute humidity The mass of water vapor perunit volume of air. Compare RELATIVE HUMID-ITY.absolute instruction A computer instruction thatstates explicitly and causes the execution of aspecific operation.absolute magnitude For a complex number quantity,the vector sum of the real and imaginarycomponents (i.e., the square root of the sum ofthe squares of those components). Also see AB-SOLUTE VALUE and IMPEDANCE.absolute maximum rating The highest value aquantity can have before malfunction or damageoccurs.absolute maximum supply voltage The highestsupply voltage that can be applied to a circuitwithout permanently altering its characteristics.absolute measurement of current Measurementof a current directly in terms of defining quantities.1. TANGENT GALVANOMETER method:Current is proportional to the tangent of the angleof deflection of the needle of this instrument.Deflection depends on torque, resulting from themagnetic field produced by current in the galvanometercoil acting against the horizontalcomponent of the earth’s magnetic field.2. ELECTRODYNAMOMETER method: With this2-coil instrument, current is determined fromthe observed deflection, the torque of the suspensionfiber of the movable coil, and the coil dimensions.absolute measurement of voltage Measurementof a voltage directly in terms of defining quantities.1. CALORIMETRIC method: A currentcarryingcoil immersed in water raises thetemperature of the water. The difference ofpotential that forces the current through the coilthen is determined in terms of the equivalent heatenergy. 2. Disk-electrometer method: In thissetup, a metal disk attached to one end of abalance beam is attracted by a stationary diskmounted below it, the voltage being applied to thetwo disks. The other end of the beam carries apan into which accurate weights are placed. Atbalance, the voltage is determined in terms of theweight required to restore balance, the upper-diskarea, and the disk separation.absolute minimum resistance The resistance betweenthe wiper and the nearer terminal of a potentiometer,when the wiper is as close to thatterminal as physically possible. All potentiometershave two such specifications, one for eachend terminal.absolute Peltier coefficient The product of theabsolute Seebeck coefficient and absolute temperatureof a material.absolute pitch A tone in a standard scale, determinedaccording to the rate of vibration, independentof other tones in the range of pitch.absolute pressure Pressure (force per unit area) ofa gas or liquid determined with respect to that ofa vacuum (taken as zero).absolute-pressure transducer A transducer actuatedby pressure from the outputs of two differentpressure sources, and whose own output is proportionalto the difference between the two appliedpressures.absolute scale 1. A scale in which the zero valueindicates the lowest physically possible value thata parameter can attain. 2. A standard scalefor measurement of a quantity. 3. A universallyagreed-upon scale for the determination of a variablequantity. 4. The Kelvin temperature scale.5. The Rankine temperature scale.absolute Seebeck coefficient The quotient, as anintegral from absolute zero to the given temperature,of the Thomson coefficient of a material dividedby its absolute temperature.absolute spectral response The frequency outputor response of a device in absolute power units(such as milliwatts) as opposed to relative units(such as decibels).absolute system of units A system of units inwhich the fundamental (ABSOLUTE) units arethose expressing length (l), mass (m), charge (q),and time (t). All other physical units, includingpractical ones, are then derived from these absoluteunits.absolute temperature Temperature measured oneither the Kelvin or Rankine scales, where zerorepresents the total absence of heat energy.absolute temperature scale 1. The Kelvin temperaturescale, in which the divisions are equal insize to 1° Celsius, and the zero point is absolutezero, the coldest possible temperature, approximately–273.16° Celsius. 2. The Rankine temperaturescale, in which the divisions are equal insize to 1° Fahrenheit, and the zero point is absolutezero or approximately –459.7° Fahrenheit.absolute tolerance The value of a component as itdeviates from the specified or nominal value. It isusually expressed as a percentage of the specifiedvalue.

4 absolute units • A-B testabsolute units Fundamental physical units (seeABSOLUTE SYSTEM OF UNITS) from which allothers are derived. See, for example, AMPERE,OHM, VOLT, and WATT.absolute value The magnitude of a quantity withoutregard to sign or direction. The absolute valueof a is written |a|. The absolute value of a positivenumber is the number itself; thus, |10|equals 10. The absolute value of a negative numberis the number with its sign changed: |-10|equals 10.absolute-value circuit A circuit that produces aunipolar signal in response to a bipolar input andin proportion to the absolute value of the magnitudeof the input.absolute-value computer A computer in whichdata is processed in its absolute form; i.e., everyvariable maintains its full value. (Compare toINCREMENTAL COMPUTER.)absolute-value device In computer practice, a devicethat delivers a constant-polarity outputsignal equal in amplitude to that of the inputsignal. Thus, the output signal always has thesame sign.absolute zero The temperature –273.16°C(459.7°F and 0 Kelvin). The coldest possibletemperature, representing the complete absenceof heat energy.absorbed wave A radio wave that dissipates in theionosphere as a result of molecular agitation.This effect is most pronounced at low andmedium frequencies.absorptance The amount of radiant energy absorbedin a material; equal to 1 minus the transmittance.absorption The taking up of one material or mediumby another into itself, as by sucking orsoaking up. Also, the retention of one medium (ora part of it) by another medium, through whichthe first one attempts to pass. See, for example,ABSORBED WAVE, ABSORPTION COEFFI-CIENT, DIELECTRIC ABSORPTION. CompareADSORPTION.absorption band See ABSORPTION SPECTRUM.absorption circuit A circuit that absorbs energyfrom another circuit or from a signal source—especiallya resonant circuit, such as a wavemeteror wavetrap.absorption current In a capacitor, the current resultingfrom absorption of energy by the dielectricmaterial.absorption dynamometer A power-measuring instrumentin which a brake absorbs energy from arevolving shaft or wheel.absorption fading Fading of a radio wave, resultingfrom (usually) slow changes in the absorptionof the wave in the line of propagation.absorption frequency meter See WAVEMETER.absorption line See ABSORPTION SPECTRUM.absorption loss 1. Transmission loss caused bydissipation of electrical energy, or conversion of itinto heat or other forms of energy. 2. Loss of all orpart of a skywave because of absorption by theionosphere. Also called ionospheric absorption oratmospheric absorption.absorption marker A small blip introduced ontoan oscilloscope trace to indicate a frequencypoint. It is so called because it is produced by theaction of a frequency-calibrated tuned trap, similarto an absorption wavemeter.absorption modulation Amplitude modulation of atransmitter or oscillator by means of an audiofrequency-actuatedabsorber circuit. In its simplestform, the modulator consists of a few turns of wirecoupled to the transmitter tank coil and connectedto a carbon microphone. The arrangementabsorbs energy from the transmitter at a varyingrate as the microphone changes its resistance inaccordance with the sound waves it receives.absorption spectrum For electromagnetic waves, aplot of absorption coefficient (of the medium ofpropagation) versus frequency. Also called EMIS-SION SPECTRUM.absorption trap See WAVETRAP.absorption wavemeter A resonant-frequency indicatinginstrument that is inductively coupled tothe device under test.absorptivity In audio and microwave technologies,a measure of the energy absorbed by a given volumeof material.A-B test Comparison of two sounds by reproducingthem in alternating succession.

abvolt • accentuation 5abvolt The unit of potential difference in the cgselectromagnetic system. One abvolt equals 10 –8 Vand is the difference of potential between any twopoints when 1 erg of work is required to move 1abcoulomb of electricity between them.abwatt The unit of power in the cgs electromagneticsystem. One abwatt equals 10 7 W and is thepower corresponding to 1 erg of work per second.ac 1. Abbreviation of ALTERNATING CURRENT.2. Abbreviation of ATTITUDE CONTROL. 3. Abbreviationof AERODYNAMIC CENTER. 4. A suffixmeaning AUTOMATIC CALCULATOR orAUTOMATIC COMPUTER.a/c 1. Abbreviation of AIRCRAFT. 2. Abbreviationof AIR CONDITIONING.Ac Symbol for ACTINIUM.ACA Abbreviation of automatic circuit analyzer.ac base current Symbol, I B(ac) . The ac component ofbase current in a bipolar transistor.ac base resistance Symbol, R B (ac) . The dynamicbase resistance in a bipolar transistor.ac base voltage Symbol, V B(ac) . The ac componentof base voltage in a bipolar transistor. It is the acinput signal voltage in a common-emitter amplifieror emitter-follower amplifier.ac bias In a tape recorder, the high-frequency currentthat passes through the recording head tolinearize operation.acc 1. Abbreviation of AUTOMATIC CHROMI-NANCE CONTROL. 2. Abbreviation of AUTO-MATIC COLOR COMPENSATION. 3. Abbreviationof ACCELERATION.ac cathode current Symbol, I K(ac) . The ac componentof cathode current in an electron tube.ac cathode resistance Symbol, R K(ac) . The dynamiccathode resistance in an electron tube. R K(ac)equals dV K /dI K for a constant value of V G .ac cathode voltage Symbol, V K(ac) . The ac componentof cathode voltage in an electron tube. It isthe ac output signal voltage in cathode-followerand grounded-grid amplifiers.accelerated life test A test program that simulatesthe effects of time on devices or apparatus,by artificially speeding up the aging process.accelerated service test A service or bench test inwhich equipment or a circuit is subjected to anextreme condition in an attempt to simulate theeffects of average use over a long time.accelerating conductor or relay A conductor orrelay that prompts the operation of a succeedingdevice in a starting mode according to establishedconditions.accelerating electrode In a cathode-ray tube orklystron, the electrode to which the acceleratingvoltage is applied.accelerating time The elapsed time that startswhen voltage is applied to a motor, and endswhen the motor shaft reaches maximum speed.accelerating voltage A positive high voltage appliedto the accelerating electrode of a cathode-ray tubeto increase the velocity of electrons in the beam.acceleration at stall The angular acceleration of aservomotor at stall, determined from the stalltorque and the moment of inertia of the motor’srotor.acceleration derivative Acceleration (a) expressedas the second derivative of distance (s) with respectto time (t): a equals d 2 s/dt 2 .acceleration potential See ACCELERATINGVOLTAGE.acceleration switch A switch that operates automaticallywhen the acceleration of a body towhich it is attached exceeds a predetermined ratein a given direction.acceleration time The time required by a computerto take in or deliver information after interpretinginstructions. Compare ACCESS TIME.acceleration torque During the accelerating periodof a motor, the difference between the torquedemanded and the torque actually produced bythe motor.acceleration voltage The potential between acceleratingelements in a vacuum tube, the value ofwhich determines average electron velocity.accelerometer A transducer whose output voltageis proportional to the acceleration of the movingbody to which it is attached.accentuation The emphasis of a desired band offrequencies, usually in the audio-frequency spectrum.

6 accentuator • accuracy ratingaccentuator A circuit or device, such as a filter,tone control, or equalizer, used to emphasize aband of frequencies, usually in the audiofrequencyspectrum. Also see ACCENTUATION.acceptable-environmental-range test A test todisclose the environmental conditions that equipmentcan endure while maintaining at least theminimum desired reliability.acceptable quality level Abbreviation, AQL. A percentagethat represents an acceptable average ofdefective components allowable for a process, orthe lowest quality that a supplier is permitted toregularly present for acceptance.acceptance sampling plan A probabilistic methodof sampling a quantity of units from a lot, and determiningfrom the sample whether to accept thelot, reject the lot, or perform another sampling.acceptance test A test performed on incomingequipment or on submitted samples to determineif they meet tester’s or supplier’s specifications.acceptor 1. Any device or circuit, such as a seriesresonantcircuit, that provides relatively easytransmission of a signal, in effect accepting thesignal. 2. A hole-rich impurity added to a semiconductorto make the latter p-type. It is so calledbecause its holes can accept electrons. CompareDONOR.acceptor circuit See ACCEPTOR, 1.acceptor impurity See ACCEPTOR, 2.access 1. To gain entrance to something, such asthe interior of the cabinet of a high-fidelity amplifier.2. In a computer, the action of going to a specificmemory location for the purpose of dataretrieval. 3. A port or opening into a piece ofequipment, placed there to make the equipmenteasy to maintain and repair.access arm A mechanical device that positions theread/write mechanism in a computer storage unit.access control register A register that is part of acomputer protection system that prevents interferencebetween different software modules.access method A method of transferring informationor data from main storage to an input/outputunit.access right The access status given to computersystem users that indicates the method of accesspermitted (e.g., read a file only or write to a file).access time The time required by a computer tobegin delivering information after the memory orstorage has been interrogated.accidental error An unintentional error committedby a person making measurements andrecording data.accidental triggering The undesired chanceoperationof a flip-flop or other switching circuitcaused by a noise pulse or other extraneous signal.ac collector current Symbol, I C(ac) . The ac componentof collector current in a bipolar transistor.ac collector resistance Symbol, R C(ac) . The dynamiccollector resistance of a bipolar transistor.R C(ac) equals dV C /dI C for a constant value of basecurrent I B (in a common-emitter circuit) or emittercurrent I E (in a common-base circuit).ac collector voltage Symbol, V C(ac) . The ac componentof collector voltage in a bipolar transistor.The ac output signal voltage in a common-emitteror common-base amplifier.accompanying audio channel The RF signal thatsupplies television sound. Also called Cochannnelsound frequency.ac component In a complex wave (i.e., one containingboth ac and dc), the alternating, fluctuating,or pulsating part of the combination.Compare DC COMPONENT.accordion A printed-circuit connector contact witha Z-shaped spring that allows high deflectionwith low fatigue.ac-coupled flip-flop A flip-flop that is operated bythe rise or fall of a clock pulse.ac coupling Transformer coupling or capacitivecoupling, which transmit ac, but not dc. CompareDIRECT COUPLING.accumulator 1. In a digital computer, a circuit orregister device that receives numbers, totalsthem, and stores them. 2. Storage battery.accuracy 1. Precision in the measurement ofquantities and in the statement of physical characteristics.2. Degree of precision. Usually expressed,in terms of error, as a percentage of thespecified value (e.g., 10 V plus or minus 1%), as apercentage of a range (e.g., 2% of full scale), or asparts (e.g., 100 parts per million).accuracy rating The maximum error in an instrument,given as a percentage of the full-scalevalue.

accw • ac magnetic bias 7accw Abbreviation of ALTERNATING-CURRENTCONTINUOUS WAVE.ac/dc Abbreviation of ALTERNATING CURRENT/DIRECT CURRENT. Pertains to equipment thatwill operate from either ac utility power or a dcpower source. A notebook computer is a good example.ac directional overcurrent relay A relay thatworks on a specific value of alternating overcurrentthat is rectified for a desired polarity.ac drain current Symbol, I D(ac) . The ac componentof drain current in a field-effect transistor.ac drain resistance Symbol, R D(ac) . The dynamicdrain resistance in a field-effect transistor; R D(ac)equals dV D /dI D for a constant value of gate voltageV G .ac drain voltage Symbol, V D(ac) . The ac componentof drain voltage in a field-effect transistor. The acoutput signal voltage in a common-source FETamplifier.ac dump The removal of all ac power from a systemor component.ac emitter current Symbol, I E(ac) . The ac componentof emitter current in a bipolar transistor.ac emitter resistance Symbol, R E(ac) . The dynamicemitter resistance of a bipolar transistor; R E(ac)equals dV E /dI E for a constant value of base currentI B (in an emitter-follower circuit) or collectorvoltage V CC (in a common-base circuit).ac emitter voltage Symbol, V E(ac) . The ac componentof emitter voltage in a bipolar transistor. Theac input signal voltage in a common-base amplifier;the ac output signal voltage in an emitterfolloweramplifier.ac equipment An apparatus designed for operationfrom an ac power source only. Compare DCEQUIPMENT and AC/DC.ac erasing In tape recording, the technique of usingan alternating magnetic field to erase materialalready recorded on the tape.ac erasing head Also called ac erase head. In tapeand wire recording, a head that carries alternatingcurrent to erase material already recorded onthe tape or wire. Also see AC ERASING.acetate Cellulose acetate, a tough thermoplasticmaterial that is an acetic acid ester of cellulose. Itis used as a dielectric and in the manufacture ofphotographic films.acetate base 1. The cellulose acetate film thatserved as the base for the magnetic oxide coatingin early recording tape. Most such tapes todayare of polyester base. 2. The cellulose acetatesubstrate onto which certain photosensitive materialsare deposited for lithographic reproduction.Also see ACETATE and ANCHORAGE.acetate tape Recording tape consisting of a magneticoxide coating on a cellulose acetate film.Also see ACETATE BASE.ac gate voltage Symbol, V G(ac) . The ac componentof gate voltage in a field-effect transistor. The acinput signal voltage.ac generator 1. A rotating electromagnetic machinethat produces alternating current (e.g., adynamo or alternator). 2. An oscillator or combinationof an oscillator and an output amplifier.ac grid voltage Symbol, V G(ac) . The ac componentof control grid voltage in an electron tube. The acinput signal voltage in a common-cathode amplifieror cathode follower.A channel The left channel of a two-channel stereosystem.achieved reliability A statement of reliability basedon the performance of mass-produced parts orsystems under similar environmental conditions.Also called OPERATIONAL RELIABILITY.achromatic 1. Without color. In a TV image, thetones from black through gray to white. The termoccasionally refers to black-and-white television,although MONOCHROMATIC is more often usedin this sense.achromatic locus Also called achromatic region.An area on a chromaticity diagram that containsall points, representing acceptable referencewhite standards.achromatic scale A musical scale without accidentals.ACIA Abbreviation of asynchronous communicationsinterface adapter.acicular Pertaining to the shape of magnetic particleson recording tape. Under magnification,these particles look like thin rods.acid A substance that dissociates in water solutionand forms hydrogen (H) ions (e.g., sulfuric acid).Compare BASE, 2.acid depolarizer Also called acidic depolarizer.An acid, in addition to the electrolyte, used insome primary cells to slow the process of polarization.ac line A power line that delivers alternating currentonly.ac line filter A filter designed to remove extraneoussignals or electrical noise from an ac powerline, while causing virtually no reduction of thepower-line voltage or power.ac line voltage The voltage commonly deliveredby the commercial power line to consumers. Inthe United States, the two standards are 117 Vand 234 V (~ about 5 percent). The lower voltageis used by most appliances; the higher voltage isintended for appliances and equipment thatdraws high power, such as electric ovens, cookingranges, clothes dryers, and amateur-radioamplifiers. In Europe, 220 V is the commonstandard.aclinic line Also called magnetic equator. An imaginaryline drawn on a map of the world or of anarea that connects points of zero inclination (dip)of the needle of a magnetic compass.ACM Abbreviation for Association for ComputingMachinery.ac magnetic bias See AC BIAS.

8 ac meter • acoustic feedbackac meter A meter that is intended to work only onalternating current or voltage. Such meters includeiron-vane and rectifier types.ac noise 1. Electromagnetic interference originatingin the ac power lines. 2. Electrical noise of arapidly alternating or pulsating nature.ac noise immunity In computer practice, the abilityof a logic circuit to maintain its state, despiteexcitation by ac noise.acous Abbreviation for ACOUSTIC.acoustic Pertaining to audible sound disturbances,usually in air (versus audio-frequencycurrents or voltages).acoustic absorption The assimilation of energyfrom sound waves passing through or reflected bya given medium.acoustic absorption loss That portion of soundenergy lost (as by dissipation in the form of heat)because of ACOUSTIC ABSORPTION.acoustic absorptivity The ratio of sound energyabsorbed by a material to sound energy strikingthe surface of the material.acoustic attenuation constant The real-numbercomponent of the complex acoustical propagationconstant, expressed in nepers per unit distance.acoustic burglar alarm An alarm that receives thenoise made by an intruder. The alarm device respondsto the impulses from concealed microphones.acoustic capacitance The acoustic equivalent ofelectrical capacitance.acoustic clarifier In a loudspeaker system, a set ofcones attached to the baffle that vibrate to absorband suppress sound energy during loud bursts.acoustic communication Communications bymeans of sound waves. This can be through theatmosphere, or it can be through solids or liquids,such as a taut wire, a body of water, or theearth.acoustic compliance COMPLIANCE in acoustictransducers, especially loudspeakers. It is equivalentto electrical capacitive reactance.acoustic consonance An effect that occurs whentwo objects are near each other but not in physicalcontact, and both have identical or harmonicallyrelated resonant frequencies. An example is shownby two tuning forks with identical fundamental fre-quencies. If one fork is struck and then broughtnear the other, the second fork will begin vibrating.If the second fork has a fundamental frequencythat is a harmonic of the frequency of the first fork,the second fork will vibrate at its own resonantfrequency. See HARMONIC, RESONANCE.acoustic coupling Data transfer via a sound linkbetween a telephone and a pickup/reproducer.Was once common in computer terminals andfacsimile machines. This scheme has been largelyreplaced by hard wiring and optical coupling.acoustic damping The deadening or reduction ofthe vibration of a body to eliminate (or cause todie out quickly) sound waves arising from it.acoustic delay line Any equivalent of a specialtransmission line that introduces a useful timedelay between input and output signals. In oneform, it consists of a crystal block or bar with aninput transducer at one end and an output transducerat the other. An electrical input signal inthe first transducer sets up sound waves thattravel through the interior of the crystal; thepiezoelectric reaction of the crystal to sound vibrationssets up an output voltage in the secondtransducer. The delay is caused by the time requiredfor the acoustic energy to travel the lengthof the crystal bar.acoustic depth finder A direct-reading device fordetermining the depth of a body of water, or forlocating underwater objects via sonic or ultrasonicwaves transmitted downward and reflectedback to the instrument.acoustic dispersion Variation of the velocity ofsound waves, depending on their frequency.acoustic elasticity 1. In a loudspeaker enclosure,the compressibility of air behind the vibratingcone of the speaker. 2. In general, the compressibilityof any medium through which soundpasses.acoustic electric transducer A transducer, suchas a microphone or hydrophone, that convertssound energy into electrical energy. CompareELECTRICAL/ACOUSTIC TRANSDUCER. Alsosee ACOUSTIC TRANSDUCER.acoustic feedback A usually undesirable effectthat occurs when sound waves from a loudspeaker(or other reproducer) reach a microphone(or other input transducer) in the same system.

acoustic feedback • acoustic radiator 9This can cause an amplifier to oscillate, with a resultantrumbling, howling, or whistling.acoustic filter Any sound-absorbing or transmittingarrangement, or combination of the two, thattransmits sound waves of desired frequency whileattenuating or eliminating others.acoustic frequency response The soundfrequencyrange as a function of sound intensity.A means of describing the performance of anacoustic device.acoustic generator A device that produces soundwaves of a desired frequency and/or intensity.Examples are electrical devices (headphones orloudspeakers operated from a suitable oscillator,buzzer, bell, or flame) and mechanical devices(tuning forks, bells, string, or whistles).acoustic grating A set of bars or slits that are parallelto one another and arranged a fixed distanceapart so that an interference pattern forms assound passes through. Used to determine thewavelength of acoustic waves.acoustic homing system 1. A system that uses asound signal for guidance purposes. 2. A guidancemethod in which a missile homes in onnoise generated by a target.acoustic horn A tapered tube (round or rectangular,but generally funnel-shaped) that directssound and, to some extent, amplifies it. So calledto distinguish it from a microwave horn.acoustic howl See ACOUSTIC FEEDBACK.acoustician 1. A person skilled in acoustics (anacoustics technician). 2. An AUDIOLOGIST.acoustic impedance Unit, ACOUSTIC OHM. Theacoustic equivalent of electrical impedance. Likethe latter, acoustic impedance is the total oppositionencountered by acoustic force. Also like electricalimpedance, acoustic impedance hasresistive and reactive components: ACOUSTICRESISTANCE and ACOUSTIC REACTANCE.acoustic inductance Also called inertance. Theacoustic equivalent of electrical inductance.acoustic inertance See ACOUSTIC INDUCTANCE.acoustic inhibition See AUDITORY INHIBITION.acoustic intensity See SOUND INTENSITY.acoustic interferometer An instrument that evaluatesthe frequency and velocity of sound wavesin a liquid or gas, in terms of a standing wave setup by a transducer and reflector as the frequencyor transducer-to-reflector distance varies.acoustic labyrinth A loudspeaker enclosurewhose internal partitions form a maze-like pathor “tube” lined with sound-absorbing material.The tube effectively runs from the back of thespeaker down to where it terminates in a MOUTHor PORT that opens at the front of the enclosure.The labyrinth provides an extremely efficient reproductionsystem because of its excellent acousticimpedance-matching capability.acoustic lens A system of barriers that refractssound waves the way that an optical lens doeswith light waves.acoustic line Baffles or other such structureswithin a speaker that act as the mechanical equivalentof an electrical transmission line to enhancethe reproduction of very low bass frequencies.acoustic load A device that serves simultaneouslyas the output load of an amplifier and as a transducerof electrical energy into acoustic energy(e.g., headphones or a loudspeaker).acoustic memory In a computer, a volatile memoryelement employing an acoustic delay line, oftenincorporating quartz or mercury as thetransmission and delay element.acoustic mirage A type of sound distortion inwhich the listener experiences the illusion of twosound sources when there is only one. The phenomenonis caused by the effect of a large temperaturegradient in the air or water throughwhich the sound passes.acoustic mode Crystal-lattice vibration withoutproducing an oscillating dipole.acoustic noise Interferential (usually disagreeable)sounds carried by the air (or other propagationmedium) to the ear or to an acoustic transducer.This is in contrast to electrical noise, which consistsof extraneous current or voltage impulsesand is inaudible until converted into sound.acoustic ohm The unit of acoustic resistance, reactance,or impedance. One acoustic ohm equalsthe volume velocity of 1 cm/s produced by asound pressure of 1 microbar (0.1 Pa). Also calledacoustical ohm.acoustic phase constant The imaginary-numbercomponent of the complex acoustic propagationconstant expressed in radians per second or radiansper unit distance.acoustic phase inverter A bass reflex loudspeakerenclosure.acoustic pressure 1. The acoustic equivalent ofelectromotive force, expressed in dynes persquare centimeter; also called acoustical pressure.2. Sound pressure level.acoustic propagation The transmission of soundwaves, or subaudible or ultrasonic waves, as adisturbance in a medium, rather than as an electriccurrent or electromagnetic field.acoustic radiator A device that emits soundwaves. Examples are the cone of a loudspeaker,the diaphragm of a headphone, and the vibratingreed of a buzzer.

10 acoustic radiometer • ac plate resistanceacoustic radiometer An instrument for measuringthe intensity of a sound wave (see SOUND IN-TENSITY) in terms of the unidirectional steadystatepressure exerted at a boundary as a resultof absorption or reflection of the wave.acoustic reactance Unit, ACOUSTIC OHM. Theimaginary-number component of ACOUSTICIMPEDANCE. It can take the form of ACOUSTICCAPACITANCE or ACOUSTIC INDUCTANCE.acoustic reflectivity The ratio F r /F i , where F r isthe rate of flow of sound energy reflected from asurface and F i is the rate of flow of sound energyincident to the surface.acoustic refraction The deflection of sound wavesbeing transferred obliquely between media thattransmit sound at different speeds.acoustic regeneration See ACOUSTIC FEEDBACK.acoustic resistance Unit, ACOUSTIC OHM. Thereal-number component of ACOUSTIC IMPE-DANCE. The opposing force that causes acousticenergy to be dissipated in the form of heat. It isattributed to molecular friction in the mediumthrough which sound passes. See ACOUSTICOHM.acoustic resonance In an enclosed chamber withwalls that reflect sound waves, resonance that occursat certain wavelengths because the echoescombine in and out of phase. Speaker enclosuresalmost always have resonance at certain frequencies.This effect can be used to an advantage whenit is necessary to get good bass (low-frequency)response from a relatively small speaker.acoustic resonator 1. A chamber, such as a box,cylinder, or pipe, in which an air column resonatesat a particular frequency. 2. A piezoelectric, magnetostrictive,or electrostrictive body that vibratesat a resonant audio frequency that is governed bythe mechanical dimensions of the body when anaudio voltage at that frequency is applied.acoustics 1. The physics of sound. The study andapplications of acoustic phenomena. 2. The qualitiesof an enclosure or sound chamber (room,auditorium, or box) that describe how soundwaves behave in it.acoustic scattering The spreading of a soundwave in many directions as a result of diffraction,reflection, or refraction.acoustic suspension A loudspeaker design thatallows exceptional low-frequency reproductionfor a fairly small physical size. An airtight enclosureis used to increase the tension on thespeaker cone.acoustic system 1. A coordinated array of acousticcomponents (e.g., acoustic filters, resonators,etc.) that responds to sound energy in a predeterminedmanner. 2. An audio-frequency system inwhich sound energy is converted into electricalenergy, processed, and then reconverted intosound energy for a clearly defined purpose.acoustic telegraph A telegraph that gives audiblesignals, as opposed to visual signals or printedmessages.acoustic transducer 1. Any device, such as headphonesor a loudspeaker, for converting audiofrequencyelectrical signals into sound waves. 2.Any device, such as a microphone, for convertingsound waves into alternating, pulsating, or fluctuatingcurrents.acoustic transmission The direct transmission ofsound energy without the intermediary of electriccurrents.acoustic transmission system A set of componentsdesigned to generate acoustic waves.acoustic transmissivity Also called acoustictransmitivity. The ratio e t /e i , where e t is thesound energy transmitted by a medium, and e i isthe incident sound energy reaching the surface ofthe medium. Acoustic transmissivity is proportionalto the angle of incidence.acoustic treatment Application of sound-absorbingmaterials to the interior of an enclosure orroom to control reverberation.acoustic wave The traveling vibration, consistingof molecular motion, via which sound is transmittedthrough a gas, liquid or solid. Usuallyrefers to sound waves in air.acoustic wave filter See ACOUSTIC FILTER.acoustoelectric effect The generation of a voltageacross the faces of a crystal by sound waves travelinglongitudinally through the crystal.acoustoelectronics A branch of electronics concernedwith the interaction of sound energy andelectrical energy in devices, such as surface-wavefilters and amplifiers. In such devices, electricallyinduced acoustic waves travel along the surfaceof a piezoelectric chip and generate electrical energy.Also called praetersonics and microwaveacoustics.ac plate current Symbol, I P(ac) . The ac componentof plate current in a vacuum tube.ac plate resistance Symbol, R P(ac) . The dynamicplate resistance of an electron tube. R P(ac) equalsdE P /dI P , where E P is the plate voltage and I P is theplate current, for a constant value for grid voltageE G .

ac plate voltage • active chord mechanism 11ac plate voltage Symbol, E P(ac) . The ac componentof plate voltage in an electron tube. The ac output-signalvoltage in a common-cathode amplifier.ac power Symbol, P ac . Unit, watt (W). The poweracting in an ac circuit, P ac equals EI cos q, whereE is in volts, I in amperes, and q is the phase angle.Compare DC POWER. Also see POWER.ac power supply A power unit that supplies aconly (e.g., ac generator, vibrator-transformer, oscillator,or inverter). Compare DC POWERSUPPLY.acquisition 1. The gathering of data from transducersor a computer. 2. Locating the path of anorbiting body for purposes of collecting telemetereddata. 3. Orienting an antenna for optimumpickup of telemetered data.acquisition and tracking radar An airborne orground radar, which locks in on a strong signaland tracks the body that reflects (or transmits)the signal.acquisition radar A radar that spots an oncomingtarget and supplies position data regarding thetarget to a fire-control or missile-guidance radar,which then tracks the target.acr 1. Abbreviation of AUDIO CASSETTE RE-CORDER. 2. Abbreviation of AUDIO CASSETTERECORDING SYSTEM.ac reclosing relay The controlling component inan alternating-current circuit breaker. It causesthe breaker to reset after a specified period oftime.ac relay A relay designed to operate on alternatingcurrent without chattering or vibrating.ac resistance Pure resistance in an ac circuit. Unlikereactance and impedance, which are alsoforms of opposition to the flow of current, ac resistanceintroduces no phase shift.acronym A word formed from letters or syllablestaken from other applicable words of a multiwordterm. Acronyms are convenient for naming newdevices and processes in electronics. Usually, aterm is considered an acronym only when it isspelled in all-capital letters; once the term is acceptedand popularized, it is written as a conventionalword and is no longer thought of as anacronym. For example, LASER was once anacronym for light amplification by the stimulatedemission of radiation. By the popularization process,the acronym became a conventional wordfrom which other terms (such as the verb “lase”)were derived.acrylic resin A synthetic resin used as a dielectricand in electronic encapsulations. It is made fromacrylic acid or one of its derivatives.ACS Abbreviation of automatic control system.ac source current Symbol, I S(ac) . The ac componentof source current in a field-effect transistor.ac source resistance Symbol, R S(ac) . The dynamicsource resistance in a field-effect transistor; R S(ac)equals dV S /dI S for a constant value of V G .ac source voltage Symbol, V S(ac) . The ac componentof source voltage in a field-effect transistor.The ac output-signal voltage in a source-follower(grounded-drain) FET amplifier.acss Abbreviation of analog computer subsystem.ac time overcurrent relay A device with a certaintime characteristic, which breaks a circuit whenthe current exceeds a certain level.actinic rays Short-wavelength light rays in the violetand ultraviolet portion of the spectrum thatgive conspicuous photochemical action.actinism The property whereby radiant energy(such as visible and ultraviolet light, X-rays, etc.)causes chemical reactions.actinium Symbol, Ac. A radioactive metallic element.Atomic number, 89. Atomic weight, 227.actinodielectric Exhibiting a temporary rise inelectrical conductivity during exposure to light.actinoelectric effect The property whereby certainmaterials (such as selenium, cadmium sulfide,germanium, and silicon) change theirelectrical resistance or generate a voltage on exposureto light. Also see ACTINODIELECTRIC.actinometer An instrument for measuring the directheating power of the sun’s rays or the actinicpower of a light source.action current A small transient current thatflows in a nerve in the human body as a result ofstimulation.activate To start an operation, usually by applyingan appropriate enabling signal.activation 1. Supplying electrolyte to a battery cellto prepare the cell for operation. 2. Causing theacceleration of a chemical reaction.activation time In the activation of a battery cell(see ACTIVATION, 1), the interval between additionof the electrolyte and attainment of full cellvoltage.activator A substance added to an accelerator (seeACCELERATOR, 3) to speed the action of the accelerator.active Pertaining to a circuit or device that requiresa power supply for its operation. This differsfrom a passive circuit or device, whichoperates with no external source of power.active antenna An antenna that uses a smallwhip, loop, or ferrite loopstick with a high-gainamplifier for receiving at very-low, low, medium,and high radio frequencies (approximately 9 kHzto 30 MHz).active area The forward-current-carrying portionof the rectifying junction of a metallic rectifier.active arm See ACTIVE LEG.active balance In telephone repeater operation, thesum of return currents at a terminal network balancedagainst the local circuit or drop resistance.active chord mechanism Abbreviation, ACM. Inrobots, an electromechanical gripper capable ofconforming to irregular objects. It has a structuresimilar to the human spine, with numeroussmall, rigid links connected by hinges.

12 active communications satellite • active repair timeactive communications satellite A satellite containingreceivers (which pick up beamed electromagneticsignals from a ground point and amplifythem) and transmitters (which send signals backto the surface of the earth). Also called activecomsat. Compare PASSIVE COMMUNICATIONSSATELLITE.active component 1. A device capable of some dynamicfunction (such as amplification, oscillation,or signal control) that usually requires apower supply for its operation. Examples includebipolar transistors, field-effect transistors, andintegrated circuits. Compare PASSIVE COMPO-NENT. 2. In an ac circuit, a quantity that containsno reactance so that the current is in phasewith the voltage.active component of current See ACTIVE CUR-RENT.active computer A computer in an installation ornetwork that is processing data.active comsat See ACTIVE COMMUNICATIONSSATELLITE.active control system A device or circuit thatcompensates for irregularities in the operatingenvironment.active current In an ac circuit, the current componentthat is in phase with the voltage. This is incontrast to reactive current, which is not in phasewith the voltage, and is “inactive,” with respect topower in the circuit. The active current is equal tothe average power divided by the effective voltage.active decoder An automatic ground-station devicethat gives the number or letter designation ofa received radio beacon reply code.active device 1. An electronic component, such as atransistor that needs a power supply, and/or thatis capable of amplifying. 2. Broadly, any device (includingelectromechanical relays) that can switch(or amplify) by application of low-level signals.active electric network A network containing oneor more active devices or components, usuallyamplifiers or generators, in addition to passivedevices or components.active element The driven or RF-excited elementin a multielement antenna or antenna array.active file A computer file in use (i.e., one that isbeing updated or referred to).active filter A bandpass, bandstop, highpass orlowpass filter, consisting of resistors, capacitors,and operational amplifiers, arranged to pass a desiredfrequency response. Commonly used at audiofrequencies.active infrared detection Detection of infraredrays reflected from a target to which they werebeamed.active jamming Transmission or retransmissionof signals for the purpose of disrupting communications.active junction A pn junction in a semiconductordevice that has been created by a diffusion process.active leg An element within a transducer thatchanges one or more of its electrical characteristicsin response to the input signal of the transducer.Also called active arm.active lines In a U.S. television picture, the lines(approximately 488) that make up the picture.The remaining 37 of the 525 available lines areblanked and are called INACTIVE LINES.active material 1. In a storage cell, the chemicalmaterial in the plates that provides the electricalaction of the cell, as distinguished from the supportingmaterial of the plates themselves. 2. A radioactivesubstance. 3. The phosphor coating of acathode-ray tube screen. 4. The material used tocoat an electron-tube cathode.active mixer A signal mixer using one or more activecomponents, such as transistors or integratedcircuits. An active circuit providesamplification, input-output isolation, and highinput impedance, in addition to the mixing action.Compare PASSIVE MIXER.active modulator A modulator using one or moreactive components, such as transistors or integratedcircuits. An active circuit provides gain,input-output isolation, and high input impedance,in addition to modulation. Compare PAS-SIVE MODULATOR.active network See ACTIVE ELECTRIC NET-WORK.active pressure The electromotive pressure thatproduces a current in an ac circuit.active pull-up An arrangement using a transistoras a pull-up resistor replacement in an integratedcircuit, providing low output impedance and lowpower consumption.active RC network 1. A resistance-capacitance(RC) circuit that contains active components(transistors or integrated circuits), as well as passivecomponents (capacitors and resistors). 2. AnRC network in which some or all of the resistorsand capacitors are simulated by the action of activecomponents.active repair time The time during which maintenanceis done on a system and the system is outof operation.

active satellite • adapter 13active satellite See ACTIVE COMMUNICATIONSSATELLITE.active sensor In an electronic security system, atransducer that generates an electromagneticfield or acoustic-wave field, and detects changesin the field resulting from the presence or movementof objects in the vicinity.active substrate In an integrated circuit, a substrateconsisting of single-crystal semiconductormaterial into which the components are formed;it acts as some or all of the components. This is incontrast to a substrate consisting of a dielectric,where the components are deposited on the surface.active system A radio and/or radar system thatrequires transmitting equipment to be carried ina vehicle.active tracking system A system in which atransponder or responder on board a vehicle retransmitsinformation to tracking equipment(e.g., azusa, secor).active transducer 1. A transducer that containsan active device, such as a transistor or integratedcircuit, for immediate amplification of thesensed quantity. 2. A transducer that is itself anactive device.active wire In the armature of a generator, a wireexperiencing induction and, therefore, is deliveringvoltage.activity 1. Intensity of, as well as readiness for, oscillationin a piezoelectric crystal. 2. Radioactiveintensity. 3. Intensity of thermal agitation. 4.Thermionic emission of electrons.activity ratio The ratio of active to inactive recordsin a computer file.ac transducer A transducer that either requires anac supply voltage or delivers an ac output signal—evenwhen operated from a dc supply.ac transmission The use of an alternating voltageto transfer power from one point to another, usuallyfrom generators to a distribution center, andgenerally over a considerable distance.actual ground The ground as “seen” by an antenna.The actual ground surface is not necessar-ily in the same physical location as the trueground surface (i.e., the earth itself ). An actualground can be an artificial ground plane, such asthat provided in some antenna structures. Actualground can also be modified by nearby rooftops,buildings, guy wiring, and utility wiring.actual height The highest altitude where radiowave refraction actually occurs.actual power Also called active or AVERAGEPOWER. Symbol, P avg . In a resistive circuit undersine-wave conditions, average power is the productof the rms voltage and the rms current. It isalso equal to half the product of the maximumcurrent and maximum voltage.actuating device A device or component that operateselectrical contacts to affect signal transmission.actuating system 1. An automatic or manuallyoperated system that starts, modifies, or stops anoperation. 2. A system that supplies energy forACTUATION.actuating time Also called actuation time. Thetime interval between generation of a control signal,or the mechanical operation of a control device,and the resulting ACTUATION.actuation1. The starting, modification, or terminationof an operation or process. 2. Activation ofa mechanical or electromechanical switching device.actuatorAn electromechanical device that useselectromagnetism to produce a longitudinal or rotarythrust for mechanical work. It is often theend (load) device of a servosystem.ACU Abbreviation of automatic calling unit.ac voltage A voltage, the average value of which iszero, that periodically changes its polarity. In onecycle, an ac voltage starts at zero, rises to a maximumpositive value, returns to zero, rises to amaximum negative value, and finally returns tozero. The number of such cycles per second istermed the ac frequency.ac voltmeter See AC METER.acyclic machine Also called ACYCLIC GENERA-TOR. A dc generator in which voltage induced inthe active wires of the armature is always of thesame polarity.A/D Abbreviation for ANALOG-TO-DIGITAL. SeeANALOG-TO-DIGITAL CONVERSION.Ada A microcomputer language designed primarilyfor use in multi-computer systems, where eachsmall computer communicates with the others,providing some of the advantages of a larger computer.Adam A communications code word sometimesused for phonetic verbalizing of the letter A. Morecommonly, ALPHA is used.adapter 1. A fitting used to change either the terminalscheme or the size of a jack, plug, or socketto that of another. 2. A fitting used to provide atransition from one type or style of conductor toanother (e.g., waveguide to coaxial line). 3. An

14 adapter • address generationauxiliary system or unit used to extend the operationof another system (e.g., a citizens-bandadapter for a broadcast receiver).adaptive communication A method of communicationthat adjusts itself according to the particularrequirements of a given time.adaptive suspension vehicle Abbreviation, ASV.A specialized robot that moves on mechanicallegs, rather than on wheels. It generally has sixlegs and resembles an insect. It is designed tomove over extremely irregular or rocky terrain,and to carry a human passenger.adaptivity The ability of a system to respond to itsenvironment by changing its performance characteristics.adc Abbreviation of ANALOG-TO-DIGITAL CON-VERTER.Adcock antenna A directional antenna systemconsisting of two vertical antennas, spaced insuch a way that the whole array behaves like aloop antenna. Its members are connected and positionedso that it discriminates against horizontallypolarized waves, and delivers output that isproportional to the vector difference of signal voltagesinduced in the two vertical arms.Adcock direction finder A radio direction-findingsystem based on the directivity of the ADCOCKANTENNA.Adcock radio range A radio range system withfour ADCOCK ANTENNAS situated at the cornersof a square, and a fifth antenna at the center ofthe square.add-and-subtract relay A stepping relay that canbe switched either uprange (add) or downrange(subtract).addend In a calculation, any number to be addedto another. Compare AUGEND.addend register In a digital computer, the registerthat stores the addend.adder 1. In a digital computer, the device or circuitthat performs binary addition. A HALF ADDER isa two-input circuit that can produce a sum outputand a carry output, but it cannot accommodatea carry signal from another adder. A FULLADDER can accommodate a carry input, as wellas two binary signals to be added. Also see ANA-LOG ADDER. 2. A circuit in a color TV receiverthat amplifies the receiver primary matrix signal.additive 1. The character or characters added to acode to encipher it. 2. In a calculation, an itemthat is to be added. 3. An ingredient, usually in asmall quantity, added to another material to improvethe latter in quality or performance.additive color A color formed by combining therays from two or three primary-colored lightsonto a single neutral surface. For example, byprojecting a red and a green beam onto a neutralscreen, a yellow additive color results.additive primaries Primary colors that form othercolors in a mixing of light (see ADDITIVE COLOR),but are not themselves formed by mixing otheradditive primaries. For example, red, green, andblue are the additive primaries used in color television.Through appropriate mixing, these colorscan be used to generate an unlimited variety ofother colors. Compare SUBTRACTIVE PRI-MARIES, which form the color spectrum by mixingpigments rather than lights. In additivesystems, each superimposed primary color increasesthe total light output from the reflecting(viewing) surface; in subtractive systems, each superimposedprimary decreases the total reflectivity.Thus, equal combination of additive primariesproduces gray or white, and equal combination ofsubtractive primaries produces gray or black.addition record An extra data store created in acomputer during processing.address 1. In computer operations, a usually numericalexpression designating the location ofmaterial within the memory or the destination ofsuch material. 2. The accurately stated locationof information within a computer; a data pointwithin a grid, matrix, or table; a station within anetwork. 3. In computer operations, to select thelocation of stored information.address comparator A device that ensures thatthe address being read is correct.address computation In digital computer operations,the technique of producing or modifyingonly the address part of an instruction.address field In a computer, the part of the instructionthat gives the address of a bit of data (ora word) in the memory.address generation The programmed generationof numbers or symbols used to retrieve recordsfrom a randomly stored direct-access file.

address indirect • adjusted decibels 15address indirect An address that specifies a storagelocation that contains another address.address memory The memory sections in a digitalcomputer that contain each individual register.address modification In computer operations,altering only the address portion of an instruction;if the command or instruction routine isthen repeated, the computer will go to the newaddress.address part In a digital computer instruction, thepart of an expression that specifies the location.Also called ADDRESS FIELD.address register In a computer, a register in whichan address is stored.add/subtract time In a computer, the time requiredto perform addition or subtraction, excludingthe time required to get the quantitiesfrom storage and to enter the sum or differenceinto storage.add timeIn computer operations, the time requiredto perform addition, excluding the time requiredto get the quantities from storage and toenter the sum into storage.a/d converter A device that changes an analogquantity into a digital signal. See ANALOG-TO-DIGITAL CONVERSION.ADF Abbreviation of AUTOMATIC DIRECTIONFINDER.ADI Abbreviation of ALTERNATE DIGIT INVER-SION.adiabatic damping In an accelerator (see ACCEL-ERATOR, 1), reduction of beam size as beam energyis increased.adiabatic demagnetization A technique using amagnetic field to keep a substance at a low temperature,sometimes within a fraction of a degreeof absolute zero.adjacencyA character-recognition condition inwhich the spacing reference lines of two charactersprinted consecutively in line are closer thanspecified.adjacent- and alternate-channel selectivity Theselectivity of a receiver or radio-frequency (RF)amplifier, with respect to adjacent-channel andalternate-channel signals. That is, the extent towhich a desired signal is passed, and nearby unwantedsignals are rejected.adjacent audio channel See ADJACENT SOUNDCHANNEL.adjacent channel The channel (frequency band)immediately above or below the channel of interest.adjacent-channel attenuation The reciprocal ofthe selectivity ratio of a radio receiver. The selectivityratio is the ratio of the sensitivity of a receiver(tuned to a given channel) to its sensitivityin an adjacent channel or on a specified numberof channels removed from the original.adjacent-channel interference In television orradio reception, the interference from stationson adjacent channels. A common form arisesfrom the picture signal in the next higher channeland the sound signal in the next lowerchannel.adjacent-channel selectivity The extent to whicha receiver or tuned circuit can receive on onechannel and reject signals from the nearest outlyingchannels.adjacent sound channel In television, the radiofrequency(RF) channel containing the soundmodulation of the next lower channel.adjacent video carrier In television, the radiofrequency(RF) carrier containing the picturemodulation of the next higher channel.adjustable component Any circuit componentwhose main electrical value can be varied at will(e.g., a variable capacitor, inductor, resistor, orload).adjustable instrument 1. An instrument whosesensitivity, range, or response can be varied atwill (e.g., multirange meter or wideband generator).2. An instrument that requires adjustmentor manipulation to measure a quantity (e.g.,bridge, potentiometer, or attenuator).adjustable motor tuning An arrangement that allowsthe motor tuning of a receiver to be confinedto a portion of the frequency spectrum.adjustable resistor A wirewound resistor in whichthe resistance wire is partially exposed to allowvarying the component’s value.adjustable voltage divider A wirewound resistorwith terminals that slide on exposed resistancewire to produce various voltage values.adjusted circuit A circuit in which leads that arenormally connected to a circuit breaker areshunted so that current can be measured undershort-circuit conditions without breaker tripping.adjusted decibels Noise level (in decibels) above areference noise level (designated arbitrarily aszero decibels) measured at any point in a systemwith a noise meter that has previously been adjustedfor zero (at reference), according to specifications.

16 admittance • affirmativeadmittance Symbol, Y. Unit, siemens (formerlymho). The property denoting the comparativeease with which an alternating current flowsthrough a circuit or device. Admittance is the reciprocalof impedance (Z ): Y = 1/Z.adp 1. Abbreviation of AMMONIUM DIHYDROGENPHOSPHATE, a piezoelectric compound used forsonar crystals. 2. Abbreviation of AUTOMATICDATA PROCESSING.adsorption Adhesion of a thin layer of molecules ofone substance to the surface of another withoutabsorption. An example is adsorption of water tothe surface of a dielectric. This term is often confusedwith ABSORPTION because the spellings ofthe two words are almost identical. Compare AB-SORPTION.adu Abbreviation of automatic dialing unit.advanced-class license An amateur-radio licenseconveying all operating privileges, except for a fewsmall bands that are allocated to extra-class licensees.The second-highest class of amateur license.advance information Data published prior to theactual production or availability of a manufacturedcomponent, circuit, or system. Advance informationis often only an approximate reflectionof the expected characteristics of a device.advance wire A resistance wire used in thermocouplesand precision applications. It is an alloy ofcopper and nickel, which has high resistivity anda negligible temperature coefficient of resistance.aeolight A glow lamp using a cold cathode and amixture of inert gases. Because its illuminationcan be regulated with an applied signal voltage, itis sometimes used as a modulation indicator formotion-picture sound recording.aerial See ANTENNA.aerial cable A wire or cable run through the air, usingsupport structures, such as towers or poles.aerodiscone antenna A miniature discone antennadesigned for use on aircraft.aerodynamics The science dealing with forces exertedby air and other gases in motion—especiallyupon bodies (such as aircraft) moving throughthese gases.aerogram See RADIOGRAM.aeromagnetic Pertaining to terrestrial magnetism,as surveyed from a flying aircraft.aeronautical advisory station A civil defense andadvisory communications station in service forthe use of private aircraft stations.aeronautical broadcasting service The specialservice that broadcasts information regarding airnavigation and meteorological data pertinent toaircraft operation.aeronautical broadcast station A station of theaeronautical broadcasting service.aeronautical fixed service A fixed radio servicethat transmits information regarding air navigationand flight safety.aeronautical fixed service station A station thatoperates in the aeronautical fixed service.aeronautical ground station A land station thatprovides communication between aircraft andground stations.aeronautical marker-beacon signal A distinctivesignal that designates a small area above a beacontransmitting station for aircraft navigation.aeronautical marker-beacon station A land stationthat transmits an aeronautical markerbeaconsignal.aeronautical mobile service A radio service consistingof communications between aircraft, andbetween aircraft and ground stations.aeronautical radio-beacon station An aeronauticalradio-navigation land station that transmitssignals used by aircraft and other vehicles to determinetheir position.aeronautical radionavigation services Servicesprovided by stations transmitting signals used inthe navigation of aircraft.aeronautical radio service A service that encompassesaircraft-to-aircraft, aircraft-to-ground,and ground-to-aircraft communications importantto the operation of aircraft.aeronautical station A station on land, and occasionallyaboard ship, operating in the aeronauticalmobile service.Aeronautical Telecommunication Agency Theagency that administers the operation of stationsin the aeronautical radio service.aeronautical telecommunications Collectively,all of the electronic and nonelectronic communicationsused in the aeronautical service.aeronautical utility land station A ground stationin an airport control tower that providescommunications having to do with the control ofaircraft and other vehicles on the ground.aeronautical utility mobile station At an airport,a mobile station that communicates with aeronauticalutility land stations and with aircraftand other vehicles on the ground.aerophare See RADIO BEACON.aerospace 1. The region encompassing the earth’satmosphere and extraterrestrial space. 2. Pertainingto transport and travel in the earth’s atmosphereand in outer space. This includesaircraft, orbiting space vessels, and interplanetaryspacecraft.AES Abbreviation for Audio Engineering Society.AEW Abbreviation of airborne (or aircraft) earlywarning.aF Abbreviation of ATTOFARAD.AF Abbreviation of AUDIO FREQUENCY.AFC 1. Abbreviation of AUTOMATIC FREQUENCYCONTROL. 2. Abbreviation of AUDIO-FRE-QUENCY CHOKE.affirmative In voice communications, a word oftenused for “yes”—especially when interference ispresent or signals are weak.

AFIPS • aircraft bonding 17AFIPS Acronym for American Federation of InformationProcessing Societies.afpc Abbreviation of automatic frequency/phasecontrol.AFSK Abbreviation of AUDIO-FREQUENCY-SHIFTKEYING.afterglow The tendency of the phosphor of a cathode-ray-tubescreen to glow for a certain time afterthe cathode-ray beam has passed. Also seePERSISTENCE.afterpulse An extraneous pulse in a multiplierphototube (photomultiplier), induced by a precedingpulse.AF transformer See AUDIO-FREQUENCY TRANS-FORMER.a/g Abbreviation of AIR-TO-GROUND.AGC Abbreviation of AUTOMATIC GAIN CONTROL.AGE Abbreviation of AEROSPACE GROUNDEQUIPMENT.agent An active force, condition, mechanism, orsubstance that produces or sustains an effect.Thus, a sudden voltage rise is a triggering agentin certain bistable circuits; arsenic is a dopingagent in semiconductor processing; the slow coolingof a heated metal to improve ductility is anANNEALING AGENT.aging 1. An initial run of a component or circuitover a certain period of time shortly after manufactureto stabilize its characteristics and performance.2. The changing of electricalcharacteristics or of chemical properties over aprotracted period of time.agonic line An imaginary line connecting points onthe earth’s surface at which a magnetic needleshows zero declination (i.e., points to true geographicnorth).AGREE Acronym for Advisory Group on Reliabilityof Electronics Equipment.Ah Abbreviation of AMPERE-HOUR. Depending onthe standard used, the abbreviation can be amphr,a-h, a-hr, or A-h.aH Abbreviation of ATTOHENRY.aided tracking In radar and fire control, a systemin which manual correction of target tracking errorautomatically corrects the rate of movementof the tracking mechanism.AIEE Abbreviation for American Institute of ElectricalEngineers, now consolidated with the IRE,forming the IEEE.AIP Abbreviation for American Institute of Physics.air The mixture of gases that constitutes theearth’s atmosphere and figures prominently inthe manufacture and operation of numerouselectronic devices. By volume, air contains about21 percent oxygen, 78 percent nitrogen, andlesser amounts of argon, carbon dioxide, helium,hydrogen, krypton, neon, and xenon. It also containsvarying amounts of water vapor, and insmoggy areas, carbon monoxide and the oxides ofsulfur and nitrogen.airborne intercept radar A type of short-rangeradar used aboard fighter and interceptor aircraftfor tracking their targets.airborne long-range input Equipment aboard aircraft,for the purpose of facilitating the use oflong-range missiles.airborne noise See ACOUSTIC NOISE.airborne radar platform Surveillance and altitude-findingradar used aboard aircraft.air capacitor A capacitor in which air is the dielectricbetween two sets of conductive plates. Alsocalled air-dielectric capacitor.aircarrier aircraft station On an aircraft, a radiostation that is involved in carrying people for hireor in transporting cargo.air cell A primary electrochemical cell in which thepositive electrode is depolarized by reduced oxygenin the air.air cleaner See DUST PRECIPITATOR.air column The open space inside an acousticchamber, pipe, or horn.air-cooled component A component, such as apower transistor, that is cooled by circulating air,compared with one cooled by a circulating liquid,such as water or oil.air-cooled transistor A transistor (particularly apower transistor) from which the heat of operationis drawn away, through radiation and convection,into the surrounding air. The transistoris usually mounted on a heatsink or fitted withfins.air-cooled tube An electron tube from which heatis drawn away, mainly via convection, into thesurrounding air. A device called a chimney can beplaced around the tube, through which air isblown by a fan. Cool air enters through the bottomof the assembly, and hot air escapes from thetop.air-core inductor A coil of wire wound around ahollow cylindrical form or in a loop, designed tointroduce inductive reactance into a circuit orsystem. In practice, the maximum attainable inductanceis approximately 1 mH. This type of inductoris used in some wireless transmitters,receivers, and antenna networks. The componentcan be designed for high current-carrying capacityby using heavy-gauge wire and a large windingradius. The magnetic lines of flux extend considerablybeyond the interior of the coil, especiallyalong the winding axis. This increases the likelihoodof mutual inductance between the coil andsurrounding electrical components, devices, orcircuits.air-core transformer A transformer without a ferromagneticcore, so called because air is the onlymaterial at the center of (and immediately surrounding)the transformer coils.aircraft bonding The practice of solidly connecting,for electrical purposes, the metal parts of anaircraft, including the engine.

18 aircraft flutter • airwavesaircraft flutter Rapid, repetitive fading and intensifyingof a received radio or television signal, resultingfrom reflections of the signal by passingaircraft.aircraft station A nonautomatic radio communicationsstation installed on an aircraft.air-dielectric coax A special type of COAXIAL CA-BLE designed to have minimum loss. The spacebetween inner and outer conductors is mostlyempty (i.e., air-filled). Some such cables aresealed and filled with an inert gas. The inner conductoris held away from the inner wall of theouter conductor by beads, washers, or a spiralwoundfilament of high-grade dielectric material,such as polyethylene.air environment Pertaining to communicationsequipment aboard aircraft.airflow The path or movement of air in, through, oraround an electronic device or piece of equipment—especiallypertaining to an AIR-COOLEDCOMPONENT.air gap 1. A narrow space between two parts of amagnetic circuit (e.g., the gap in the core of a filterchoke). Often, this gap is filled with a nonmagneticmaterial, such as plastic, formechanical support. 2. The space between two ormore magnetically coupled or electrostaticallycoupled components. 3. A device that gets itsname from the narrow gap between two smallmetal balls, needle points, or blunt rod tipstherein. When an applied voltage is sufficientlyhigh, a spark discharges across the gap.air/ground control radio station A station foraeronautical telecommunications related to theoperation and control of local aircraft.air-insulated line 1. An open-wire feeder or transmissionline. Typically, the line consists of twoparallel wires held apart by separators (bars orrods of high-grade dielectric material) situated atwide intervals. 2. AIR-DIELECTRIC COAX.air-moving device A mechanical device, such as aspecially designed fan or blower, used to facilitateair cooling of electronic components.airport beacon A radio or light beacon that marksthe location of an airport.airport control station A station that providescommunications between an airport controltower and aircraft in the vicinity.airport surveillance radar An air-traffic-controlradar that scans the airspace within about 60miles (approximately 100 kilometers) of an airport,and displays in the control tower the locationof all aircraft below a certain altitude and allobstructions in the vicinity.air-position indicator An airborne computer systemthat, using airspeed, aircraft heading, andelapsed time, furnishes a continuous indicationof the position of the aircraft. The indication isaffected by high-altitude winds. CompareGROUND-POSITION INDICATOR.air-to-air communication Radio transmissionfrom one aircraft to another in flight. CompareAIR-TO-GROUND COMMUNICATION andGROUND-TO-AIR COMMUNICATION.air-to-ground communication Radio transmissionfrom an aircraft in flight to a station locatedon the ground. Compare AIR-TO-AIR COMMUNI-CATION and GROUND-TO-AIR COMMUNICA-TION.air-to-ground radio frequency The carrier frequency,or band of such frequencies, allocated fortransmissions from an aircraft to a ground station.airwaves 1. Radio waves. The term is slang, but iswidely used. It probably came from the public’s

airwaves • aliasing noise 19mistaken notion that radio signals are propagatedby the air. 2. Skywaves.Al Symbol for ALUMINUM.alabamine See ASTATINE.alacratized switch A mercury switch in which thetendency of the mercury to stick to the parts hasbeen reduced.alarm 1. An electronic security system. 2. A silentand/or audible alert signal transmitted by anelectronic security system when an intrusion occurs.3. A silent and/or audible signal that informspersonnel of the occurrence of anequipment malfunction.alarm circuit A circuit that alerts personnel to asystem malfunction, a detected condition, or anintruder.alarm condition 1. An intrusion or equipmentmalfunction that triggers an alarm circuit. 2. Theoperation of an alarm circuit that occurs in responseto an intrusion or equipment malfunction.alarm hold A device that keeps an alarm soundingonce it has been actuated.alarm output The signal sent from an alarm circuitto a siren, buzzer, computer, or other externaldevice to alert personnel to an ALARMCONDITION.alarm relay A relay that is actuated by an alarmdevice.A-law A form of companding law frequently used inEuropean electronics (the mu-law is more oftenused in North America). A nonlinear transfercharacteristic in companding circuits. It can becontinuous, or can be a piecewise linear approximationof a continuous function.A-law companded Companding by means of an 8-bit binary code following the A-LAW, a specificcompanding function.albedo For an unpolished surface, the ratio of reflectedlight to incident light. It can vary from 0.0to 1.0, or from 0 to 100 percent.albedograph An instrument for measuring thealbedo of planets.ALC Abbreviation of AUTOMATIC LEVEL CON-TROL.alerting device An audible alarm that includes aself-contained solid-state audio oscillator. Poweredfrom the ac line or a battery, the device producesa raucous noise when actuated.Alexanderson antenna A very-low-frequency(VLF) and low-frequency (LF) vertically polarizedantenna, designed to minimize ground losses instructures of manageable height. It usually consistsof several wires, each quarter-wave resonantwith a loading coil, and all connectedtogether at the apex of a tower. The antenna isfed between the ground and the base of one ofthe wires.Alford antenna A loop antenna, in a square configuration,with the corners bent toward the centerto lower the impedance at the current nodes.algebraic adder In computer operations, an adderthat provides the algebraic sum, rather than thearithmetic sum, of the entered quantities.algebraic operation A form of electronic calculatoroperation, in which the keystrokes proceed in anintuitive sequence, following the way in which thecalculation is written down. Compare REVERSEPOLISH NOTATION.algebraic sum The sum of two or more quantitieswith consideration of their signs. CompareARITHMETIC SUM.algorithm A step-by-step procedure for solving aproblem, (e.g., the procedure for finding thesquare root of a number). It can be expressed in aline-by-line instruction set or as a flowchart.algorithmic language A computer language usedto describe a numeral or algebraic process.alias A label that is an alternate term for items ofthe same type; a label and several aliases canidentify the same data element in a computerprogram.aliasing 1. In analog-to-digital (A/D) conversion, afalse output signal that results from a samplingrate that is too slow. Ideally, the sampling rate is atleast twice the highest input signal frequency. 2.Sawtooth-like irregularities, also called jaggies,which are sometimes introduced into a bit-mappedcomputer image when it is changed in size.aliasing noise A form of signal distortion causedby a signal with an excessive bandwidth.

20 align • alloy diodealign 1. To adjust (i.e., to preset) the circuits of anelectronic system, such as a receiver, transmitter,or test instrument, for predetermined response.2. To arrange elements in a certainprecise orientation and spacing, relative to eachother, as in a Yagi antenna. 3. To orient antennasso that they are in line of sight, with respect toeach other.alignment The process of ensuring that equipment,components, or systems are adjusted, bothphysically and electronically, for the most efficientpossible performance.alignment chart A line chart for the simple solutionof electronic problems. It is so called becauseits use involves aligning numerical values on variousscales, the lines intersecting at the solutionon another scale. Also called nomograph.alignment pin A pin or protruding key, usually inthe base of a removable or plug-in component, toensure that the latter will be inserted correctlyinto a circuit. Often, the pin mates with a keyway,notch, or slot.alignment tool A specialized screwdriver orwrench (usually nonmagnetic) used to adjustpadder or trimmer capacitors or inductor cores.alive See LIVE.alkali See BASE, 2.alkali metals Metals whose hydroxides are bases(alkalis). The group includes cesium, francium,lithium, potassium, rubidium, and sodium.alkaline battery 1. A battery composed of alkalinecells and characterized by a relatively flat dischargecurve under load.alkaline cell A common non-rechargeable electrochemicalcell that employs granular zinc forthe negative electrode, potassium hydroxide asthe electrolyte, and a device called a polarizer asthe positive electrode. Produces approximately1.5 volts under no-load conditions. The geometryof construction is similar to that of the zinc–carbon cell, but it can deliver current effectivelyat lower temperatures. Cells of this type haveshelf lives longer than zinc–carbon cells; they alsohave greater energy-storage capacity per unitvolume, but they are more expensive than zinc–carbon cells. They are used in calculators, transistorradios, and cassette tape and compact-discplayers. Compare ZINC–CARBON CELL.alkaline-earth metals The elemental metals barium,calcium, strontium, and sometimes beryllium,magnesium, and radium, some of which areused in vacuum tubes.alkaline earths Substances that are oxides of thealkaline-earth metals. Some of these materialsare used in vacuum tubes.all-diffused A type of INTEGRATED CIRCUIT inwhich both active and passive elements havebeen fabricated by diffusion and related processes.Allen screw A screw fitted with a six-sided (hexagonal)hole.Allen wrench A tool used to tighten or loosen anAllen screw. It is a hexagonal rod and is availablein various sizes.alligator clip A spring-loaded clip with jaggedteeth, designed to be used for temporary electricalconnections.allocate 1. To assign (especially through legislation)operating frequencies or other facilities orconditions needed for scientific or technical activity;see, for example, ALLOCATION OF FRE-QUENCIES. 2. In computer practice, to assignlocations in the memory or registers for routinesand subroutines.allocated channel A frequency channel assignedto an individual or group.allocated-use circuit 1. A circuit in which one ormore channels have been authorized for the exclusiveuse of one or more services. 2. A communicationslink assigned to users needing it.allocation of frequencies See RADIO SPECTRUM.allocator A telephone system distributor associatedwith the finder control group relay assembly.It reserves an inactive line-finder for another call.allophone A variation in the sound of a phoneme,depending on what comes before and/or after thephoneme in the course of speech. Important inspeech recognition and synthesis. There are 128different phoneme variations in the English language.See PHONEME.alloter relay A telephone system line-finder relaythat reserves an inactive line-finder for the nextincoming call from the line.allotropic Pertaining to a substance existing intwo forms.alloy A metal that is a mixture of several other metals(e.g., brass from copper and zinc), or of ametal and a nonmetal.alloy deposition In semiconductor manufacture,depositing an alloy on a substrate.alloy-diffused transistor A transistor in which thebase is diffused and the emitter is alloyed. Thecollector is provided by the semiconductor substrateinto which alloying and diffusion areaffected. Compare ALLOY TRANSISTOR andDIFFUSE TRANSISTOR.alloy diode A junction-type semiconductor diodein which a suitable substance (such as p-type) isalloyed into a chip of the opposite type (such as

alloy diode • alternating-charge characteristic 21n-type) to form the junction. Also called alloyjunctiondiode.alloy junction In a semiconductor device, a positive/negative(pn) junction formed by alloying asuitable material (such as indium) with the semiconductor(silicon or germanium).alloy transistor A transistor whose junctions arecreated by alloying. Also see ALLOY JUNCTION.all-pass filter Also called all-pass network. A filterthat (ideally) introduces a desired phase shift ortime delay, but has zero attenuation at all frequencies.all-relay central office In telephone service, anautomatic central-office switchboard that usesrelay circuits to make line interconnections.all-wave Pertaining to a wide operating-frequencyrange. Few systems are literally all-wave. For example,a so-called “all-wave radio receiver” mightcover 500 kHz to 30 MHz only.all-wave antenna An antenna that can be operatedover a wide frequency range with reasonable efficiencyand preferably without needing readjustment.Examples are the DISCONE ANTENNA andthe LOG-PERIODIC ANTENNA.all-wave generator A signal generator that willsupply output over a wide range of frequencies.all-wave receiver A radio receiver that can betuned over a very wide range of frequencies, suchas 10 kHz to 70 MHz.allyl plastics Plastics, sometimes used as dielectricsor for other purposes in electronics, based onresins made by polymerization of monomers (suchas diallyl phthalate) that contain allyl groups.alnico Coined from the words aluminum, nickel,and cobalt. An alloy used in strong permanentmagnets, it contains the constituents noted plus(sometimes) copper or titanium.alpha 1. Symbol, α. The current gain of a commonbase-connectedbipolar transistor. It is the ratio ofthe differential of collector current to the differentialof emitter current; α = dI C /dI E . For a junctiontransistor, alpha is always less than unity, butvery close to it. 2. In voice communications, thephonetic representation of the letter A.alphabet The set of all characters in a natural language.alphabetic coding In computer practice, an abbreviationsystem for coding information to be fedinto the computer. The coding contains letters,words, and numbers.alphabetic-numeric Also called alphabeticalnumericaland alphanumeric. In computer operations,pertaining to letters of the alphabet andspecial characters, and to numerical digits.alpha cutoff frequency Also called alpha cutoff. Ina bipolar transistor circuit, the frequency atwhich the alpha (current gain) becomes 0.707(70.7 percent) of its value at 1 kHz. A bipolartransistor can have considerable gain at its alphacutoff. This specification denotes how rapidly atransistor loses gain as the frequency increases,an important consideration in the design of radiofrequency(RF) amplifiers. See ALPHA. CompareGAIN BANDWIDTH PRODUCT.alpha decay The decay of a substance in which thenuclei of the atoms emit alpha particles, resultingin a change of the atomic number and atomicweight of the substance over a period of time.alphanumeric See ALPHABETIC-NUMERIC.alphanumeric code In computer operations or incommunications, a code composed of, or using,both letters and numbers.alphanumeric readout A type of digital readoutthat displays both letters and numerals.alpha particle A nuclear particle bearing a positivecharge. Consisting of two protons and two neutrons,it is given off by certain radioactive substances.Compare BETA RAYS and GAMMA RAYS.alpha system An alphabetic code-signaling system.alphatron An ionizing device in which the radiationsource is an emitter of alpha particles.alteration An inclusive-OR operation.alternate channel In communications, a channelsituated two channels higher or lower than agiven channel. Compare ADJACENT CHANNEL.alternate-channel interference Interferencecaused by a transmitter operating in the channelbeyond an adjacent channel. CompareADJACENT-CHANNEL INTERFERENCE.alternate digit inversion In multiplex equipment,a method of switching the binary signals to theopposite state, in accordance with A-law companding.alternate frequency A frequency allocated as analternative to a main assigned frequency andused under certain specified conditions.alternate-mark inversion signal A signal thatconveys bits in which the successive signals areof opposite polarity (positive, then negative, thenpositive, etc.). They are equal in absolute valueamplitude.alternate mode The technique of displaying severalsignals on an oscilloscope screen by rapidlyswitching the signals in sequence at the end ofeach sweep.alternate routing A secondary, or backup, communicationspath, used when primary (normal)routing is impossible.alternating-charge characteristic In a nonlinearcapacitor, the relationship between the instanta-

22 alternating-charge characteristic • amateur extra-class licenseneous charge and the instantaneous value of analternating voltage.alternating current Abbreviation, ac. A current thatperiodically reverses its direction of flow. In one cycle,an alternation starts at zero, rises to a maximumpositive level, returns to zero, rises to amaximum negative level, and again returns to zero.The number of such cycles completed per second istermed the ac frequency. Also see CURRENT.alternating-current continuous wave An amplitude-modulatedsignal resulting from the operationof an oscillator or RF amplifier with raw acvoltage.alternating current/direct current See AC/DC.alternating-current erasing head See AC ERAS-ING HEAD.alternating-current pulse A short-duration acwave.alternating-current transmission 1. The propagationof alternating currents along a length ofconductor—especially for power-transfer purposes.2. A means of picture transmission inwhich a given signal strength produces a constantvalue of brightness for a very short time.alternating voltage Also called alternating-currentvoltage. See AC VOLTAGE.alternation In ac practice, a half cycle. In a completecycle, there are two alternations, one in the positivedirection and one in the negative direction.alternative denial A NOT-AND operation.alternator Any mechanically driven machine forgenerating ac power. Sometimes specifically onehaving a permanent-magnet rotor, such as amagneto.altimeter station An airborne transmitter whosesignals are used to determine the altitude of aircraft.altitude 1. The vertical distance of an object abovesea level. 2. The vertical distance of an objectabove the earth’s surface. 3. The angle, measuredin degrees, with respect to the horizon, at which ahighly directional antenna is pointed.altitude delay In a plan-position-indicating type ofradar, the sync delay introduced between transmissionof the pulse and start of the trace on theindicator screen to eliminate the altitude circle inthe display.ALU Abbreviation of ARITHMETIC AND LOGICUNIT.alumel An alloy used in the construction of onetype of THERMOCOUPLE. It is composed ofnickel (three parts) and aluminum (one part).alumina An aluminum-oxide ceramic used in electrontube insulators and as a substrate in thefabrication of thin-film circuits.aluminum Symbol, Al. An elemental metal. Atomicnumber, 13. Atomic weight, 26.98. Aluminum iswidely used in electronics, familiar instances beingchassis, wire, shields, semiconductor doping,and electrolytic-capacitor plates.aluminum antimonide Formula, AlSb. A crystallinecompound useful as a semiconductor dopant.aluminized screen A television picture-tubescreen with a thin layer of aluminum depositedon its back to brighten the image and reduce ionspotformation.Am Symbol for AMERICIUM.A/m Abbreviation of ampere per meter: the SI unitof magnetic field strength.AM 1. Abbreviation of amplitude modulator. 2. Abbreviationof AMPLITUDE MODULATION.amalgam An alloy of a metal and mercury. Loosely,any combination of metals.amateur1. A nonprofessional, usually noncommercialdevotee of any technology (i.e., a hobbyist).2. A licensed radio operator legallyauthorized to operate a station in the AMATEURSERVICE.amateur band Any band of radio frequencies assignedfor noncommercial use by licensed radioamateurs (see AMATEUR, 2). In the UnitedStates, numerous such bands are above 1.8 MHz(160 meters). Also see AMATEUR SERVICE andAMATEUR STATION.amateur call letters Call letters assigned by a governmentlicensing authority—especially to amateurstations. Call-letter combinations consist ofa letter prefix denoting the country in which thestation is situated, plus a number designatingthe location within the country, and two or moreletters identifying the particular station. For example:W6ABC: W (or K) = United States, 6 = California,and ABC = identification of individuallicensee (issued alphabetically, except under specialcircumstances).amateur callsign See AMATEUR CALL LETTERS.amateur extra-class license The highest class ofamateur-radio operator license in the UnitedStates. It conveys all operating privileges.

amateur radio • AM/FM tuner 23amateur radio 1. A general term, referring to thepractice of operation, experimentation, and otherwork in and related to the amateur service. 2. Thehardware that comprises an amateur radio station.3. A radio receiver, transmitter, or transceiverthat is specifically designed for operation in theamateur bands.amateur radio operator Also called radio ham orham radio operator. An individual licensed totransmit radio signals in the amateur service.amateur service A two-way radio service, existingpurely for hobby purposes (i.e., without pecuniaryinterest).amateur station A radio station licensed in theAMATEUR SERVICE.amauroscope An electronic aid to the blind, inwhich photocells in a pair of goggles receive lightimages. Electric pulses proportional to the lightare impressed upon the visual receptors of thebrain through electrodes in contact with nervesabove each eye.amber A yellow or brown fossil resin that is historicallyimportant in electronics. It is the first materialreported to be capable of electrification byrubbing (Thales, 600 BC). Also, the words electricity,electron, and electronics are derived fromthe Greek name for amber, elektron.ambience The acoustic characteristic of a room, interms of the total amount of sound reaching a listenerfrom all directions.ambient An adjective meaning “surrounding.” Oftenused as a noun in place of the adjective-noun combination(thus, “10 degrees above ambient,” insteadof “10 degrees above ambient temperature”).ambient humidity The amount of moisture in theair at the time of measurement or operations inwhich dampness must be accounted for.ambient level The amplitude of all interference(acoustic noise, electrical noise, illumination,etc.) emitted from sources other than that of asignal of interest.ambient light Also called ambient illumination.Room light or outdoor light incident to a locationat the time of measurement or operations.ambient-light filter In a television receiver, a filtermounted in front of a picture-tube screen to minimizethe amount of ambient light reaching thescreen.ambient noise 1. In electrical measurements andoperation, background electrical noise. 2. Inacoustical measurements and operations, audiblebackground noise.ambient pressure Surrounding atmospheric pressure.ambient temperature The temperature surroundingapparatus and equipment (e.g., room temperature).ambient-temperature range 1. The range overwhich ambient temperature varies at a given location.2. The range of ambient temperature thatwill cause no malfunction of, or damage to, a circuitor device.ambiguity 1. Any unclear, illogical, or incorrect indicationor result. 2. The seeking of a false null bya servo. 3. In digital computer operations, an errorresulting from improper design of logic.ambiguous count In digital counters, a clearly incorrectcount. See ACCIDENTAL TRIGGERING.ambisonic reproduction A close approximation ofthe actual directional characteristics of a sound ina given environment. The reproduced sound almostexactly duplicates the sound in the actualenvironment in which it was recorded.American Morse code (Samuel F. B. Morse, 1791–1872). Also called Railroad Morse. A telegraphcode, at one time used on wire telegraph lines inthe United States. It differs from the Continentalcode, also called the International Morse Code,which is used in radiotelegraphy. Compare CON-TINENTAL CODE.American National Standards Institute Acronym,ANSI. An industrial group in the UnitedStates that encourages companies to manufacturedevices and equipment in accordance withcertain standards. The objective is to minimizehardware incompatibility problems.American Radio Relay League A worldwide organizationof amateur radio operators, headquarteredin Newington, Connecticut. The officialpublications are the monthly magazines, QSTand QEX. They also publish numerous books andother educational materials.American Standards Association Abbreviation,ASA. At one time, the name of the national associationin the U.S. devoted to the formation and disseminationof voluntary standards of dimensions,performance, terminology, etc. See ANSI.American wire gauge Abbreviation, AWG. Alsocalled Brown and Sharpe gauge or B & S gauge.The standard American method of designatingwire sizes. Wire is listed according to gauge numberfrom 0000 (460 mils diameter) to 40 (3.145mils diameter).americium Symbol, Am. A radioactive elementalmetal first produced artificially in the 1940s.Atomic number, 95. Atomic weight, 243.AM/FM receiver A radio set that can receive eitheramplitude-modulated or frequency-modulatedsignals. Usually, a band switch incorporates thedemodulation-selection circuitry so that as thefrequency range is changed, the appropriate detectoris accessed.AM/FM transmitter A radio transmitter whoseoutput signal can be frequency- or amplitudemodulatedby a panel selector switch.AM/FM tuner A compact radio receiver unit thatcan handle either amplitude- or frequencymodulatedsignals, and delivers low-amplitudeoutput to a high-fidelity audio power amplifier.Compare AM TUNER and FM TUNER.

24 AMI • Amperian whirlCharacter Symbol Character SymbolA . — U . . —B — . . . V . . . —C . . . W . ——D — . . X . — . .E . Y . . . .F . — . Z . . . .G ——. 1 .——.H . . . . 2 . . — . .I . . 3 . . . — .J — . — . 4 . . . . —K — . — 5 ———L —— 6 . . . . . .M —— 7 ——. .N — . 8 — . . . .O . . 9 — . . —P . . . . . 0 ——Q . . — . period . . ——. .R . . . comma . — . —S . . . question — . . — .T — markAmerican Wire Gauge (AWG) DiametersAWG Millimeters Inches1 7.35 0.2892 6.54 0.2573 5.83 0.2304 5.19 0.2045 4.62 0.1826 4.12 0.1637 3.67 0.1448 3.26 0.1289 2.91 0.11510 2.59 0.10211 2.31 0.090912 2.05 0.080713 1.83 0.072014 1.63 0.064215 1.45 0.057116 1.29 0.050817 1.15 0.045318 1.02 0.040219 0.912 0.035920 0.812 0.0320AWG Millimeters Inches21 0.723 0.028522 0.644 0.025423 0.573 0.022624 0.511 0.020125 0.455 0.017926 0.405 0.015927 0.361 0.014228 0.321 0.012629 0.286 0.011330 0.255 0.010031 0.227 0.0089432 0.202 0.0079533 0.180 0.0070934 0.160 0.0063035 0.143 0.0056336 0.127 0.0050037 0.113 0.0044538 0.101 0.0039839 0.090 0.0035440 0.080 0.00315AMI See ALTERNATE-MARK INVERSION SIGNAL.A-minus Also, A-. The negative terminal of an Abattery, or pertaining to the part of a circuit connectedto that terminal.ammeter An instrument used to measure theamount of current (in amperes) flowing in a circuit.ammeter shunt A resistor connected in parallel withan ammeter to increase its current range. Also seeAYRTON-MATHER GALVANOMETER SHUNT.ammeter-voltmeter method The determination ofresistance or power values from the measurementof voltage (E) and current (I). For resistance,R = E/I; for power, P = EI.ammonium chloride Formula, NH 4 Cl. The electrolytein the carbon-zinc type of primary cell.Also called SAL AMMONIAC.AMNL Abbreviation of AMPLITUDE-MODULATIONNOISE LEVEL.amortisseur winding 1. A winding that actsagainst pulsation of the magnetic field in an electricmotor. 2. A winding that acts to prevent oscillationin a synchronous motor.amorphous substance A noncrystalline material.amp 1. Slang for AMPERE. 2. Slang for AMPLIFIER—especially in audio high-fidelity applications.ampacity Current-carrying capacity expressed inamperes.amperage The strength of an electric current (i.e.,the number of amperes).ampere (Andre Marie Ampere, 1775-1836). Abbreviations,A (preferred), a, amp. The SI base unit ofcurrent intensity (I). The ampere is the constantcurrent that, if maintained in two straight parallelconductors of infinite length and of negligible circularcross section and placed 1 meter apart in avacuum, would produce between the conductors aforce of 2 × 10 –7 newton per meter. One ampereflows through a 1-ohm resistance when a potentialof 1 volt is applied; thus I = E/R. Also see MI-CROAMPERE, MILLIAMPERE, NANOAMPERE,and PICOAMPERE.ampere balance A device consisting of two conductorsin which the force between them (causedby current) is balanced against the gravitationalforce exerted on an object in the gravitationalfield of the earth. Used for the precise determinationof current of large dimension, or of the size ofthe ampere.ampere-hour Abbreviations: Ah, amp-hr. Thequantity of electricity that passes through a circuitin one hour when the rate of flow is one ampere.Also see BATTERY CAPACITY.ampere-hour meter An instrument for measuringampere-hours. It contains a small motor driven bythe current being measured and which moves apoint on an ampere-hour scale. The motor speed isproportional to the current. The position of thepointer is proportional to current and elapsed time.Ampere’s law Current flowing in a wire generatesa magnetic flux that encircles the wire in theclockwise direction when the current is movingaway from the observer.ampere-turn Symbol, NI. A unit of magnetomotiveforce equal to 1 ampere flowing in a single-turncoil. The ampere-turns value for any coil is obtainedby multiplying the current (in amperes) bythe number of turns in the coil.Amperian whirl The stream of electrons in asingle-turn, current-conducting wire loop actingas an elementary electromagnet.

amp-hr • amplify 25WireaxisDirection offlux flowDirectionof currentAmpere’s Lawamp-hr One style of abbreviating AMPERE-HOUR.Also, Ah.amplidyne A dynamo-like rotating dc machinethat can act as a power amplifier because the responseof the output voltage to changes in fieldexcitation is quite rapid. Used in servo systems.amplification 1. The process of increasing themagnitude of a signal. This entails an input signalcontrolling a local power supply to produce alarger output signal. Depending on the kind of inputand output signals, amplification can be categorizedas CURRENT, VOLTAGE, POWER, orsome combination of these. 2. The qualitative signalincrease resulting from the process in 1. 3.The quantitative signal increase (resulting fromthe process in 1), expressed as a factor (such as100) or in terms of decibels (dB). See AMPLIFICA-TION FACTOR and DECIBEL.amplification factor 1. The ratio of the outputvoltage, current, or power to the input voltage,current, or power of an AMPLIFIER circuit. Forvoltage or current, this ratio has meaning onlywhen the input and output impedances are iden-tical. 2. The number of decibels by which an AM-PLIFIER circuit increases the amplitude of a signal.For voltage or current, this figure hasmeaning only when the input and outputimpedances are identical. See DECIBEL. 3. TheALPHA or BETA of a bipolar transistor. 4. Inthe operation of an electron tube, the ratio ofthe derivative (instantaneous rate of change) ofthe plate voltage to the derivative of the grid voltage,for zero change in plate current.amplified ALC Abbreviation, AALC. An automaticlevel-control(ALC) system that uses the amplificationof the fed-back control signal. It is used inRF power amplifiers, particularly single-sideband(SSB) linear amplifiers, to prevent overmodulationand nonlinearity.amplified back bias A declining voltage developedacross a fast-time-constant circuit in an amplifierstage and fed back into a preceding stage.amplifier Any device that increases the magnitudeof an applied signal. It receives an inputsignal and delivers a larger output signal that, inaddition to its increased amplitude, is a replicaof the input signal. Also see CURRENT AMPLI-FIER, POWER AMPLIFIER, and VOLTAGE AM-PLIFIER.amplifier diode Any semiconductor that can provideamplification in a suitable circuit or microwavesystem. See DIODE AMPLIFIER.amplifier distortion A change in the waveform of asignal, arising within an amplifier that is operatedin compliance with specified conditions.amplifier input 1. The terminals and section of anamplifier that receive the signal to be amplified.2. The signal to be amplified.amplifier noise Collectively, all extraneous signalspresent in the output of an amplifier when noworking signal is applied to the amplifier inputterminals.amplifier nonlinearity A condition in which theamplifier output signal does not exhibit a linearrelationship to the corresponding input signal.Some amplifiers are designed to operate in a linearmanner at all times, but many amplifier typesneed not function in this manner to be effective.Also see AMPLIFIER DISTORTION and LINEARAMPLIFIER.amplifier output 1. The terminals and section ofan amplifier that deliver the amplified signal forexternal use. 2. The amplified signal.amplifier power The power level of the output signaldelivered by an amplifier (also called OUTPUTPOWER), or the extent to which the amplifier increasesthe power of the input signal (also calledPOWER AMPLIFICATION).amplifier response The performance of an amplifierthroughout a specified frequency band. Factorsusually included are gain, distortion,amplitude versus frequency, and power output.amplify To perform the functions of amplification(see AMPLIFICATION, 1).

26 amplifying delay line • amplitude selectionamplifying delay line A delay line that causes amplificationof signals in a circuit intended forpulse compression.amplistat A self-saturating magnetic amplifier.amplitron A backward-wave amplifier used in microwavecircuits.amplitude The extent to which an alternating orpulsating current or voltage swings, positivelyand negatively, from zero or from a mean value.amplitude-controlled rectifier A thyratron- orthyristor-based rectifier circuit.amplitude density distribution A mathematicalfunction giving the probability that, at a given instantin time, a fluctuating voltage has a certainvalue.amplitude distortion In an amplifier or network,the condition in which the output-signal amplitudeexhibits a nonlinear relationship to the input-signalamplitude.amplitude error 1. The error in measuring the amplitudeof a signal, normally expressed as a percentageof signal amplitude or as a percentage offull scale. 2. The frequency at which the outputamplitude of a signal is in error by 1% with amplitudeat 10% of full scale.amplitude factor For an ac wave, the ratio of thepeak value to the rms value. The amplitude factorof a sine wave is equal to the square root of 2 =1.4142136.amplitude fading In the propagation of electromagneticwaves, a condition in which the amplitudesof all components of the signal (i.e., carrierand sidebands) increase and decrease uniformly.Compare SELECTIVE FADING.amplitude/frequency response Performance ofan amplifier throughout a specified range, as exhibitedby a plot of output-signal amplitude versusfrequency for a constant-amplitude inputsignal.amplitude gate A transducer that transmits onlythose portions of an input wave that lie withintwo close-spaced amplitude boundaries; alsocalled slicer.amplitude limiter A circuit, usually with automaticgain control (AGC), that keeps an amplifieroutput signal from exceeding a certain level, despitelarge variations in input-signal amplitude. Adc-biased diode performs passive limiting actionvia clipping.amplitude-modulated generator A signal generatorwhose output is amplitude modulated. Usually,this instrument is an RF generator that ismodulated at an audio frequency.amplitude-modulated transmitter A radiofrequencytransmitter whose carrier is varied inamplitude, according to the rate of change ofsome data-containing signal (such as voice, music,facsimile, television pictures, control signals,or instrument readings).amplitude modulation Abbreviation, AM. Amethod of conveying intelligence in wireless communicationsand broadcasting. The modulatingsignalenergy appears at sideband frequenciesabove and below, and very close to, the carrierfrequency. These sideband signals carry all theinformation. The extent of modulation is expressedas a percentage, from 0, which representsan unmodulated carrier, to 100, which representsfull modulation. In a signal modulated 100percent, one-third of the power is used to conveythe data; the other two-thirds is consumed by thecarrier. This form of modulation is essentiallyoutmoded, although it is still used in the standardbroadcast band from 535 to 1605 kHz. SeeFREQUENCY MODULATION, PHASE MODU-LATION, SINGLE SIDEBAND.amplitude-modulation noise Spurious amplitudemodulation of a carrier wave by extraneous signalsand random impulses, rather than by the intendeddata-containing signal.amplitude noise In radar, amplitude fluctuationsof an echo returned by a target. This noise limitsthe precision of the system.amplitude of noise The level of random noise in asystem. The amplitude of noise is measured inthe same way that signal amplitude is measured.amplitude range The maximum-to-minimum amplitudevariation of a signal. It can be expressedas a direct numerical ratio or in decibels.amplitude response The maximum output obtainableat various frequencies over the range of aninstrument operating under rated conditions.amplitude selection The selection of a signal, accordingto its correspondence to a predeterminedamplitude or amplitude range.

amplitude separator • analog integrator 27amplitude separator In a television receiver, a circuitthat separates the control pulses from thecomposite video signal.amplitude suppression ratio The ratio of an undesiredoutput of a frequency-modulated (FM) receiverto the desired output, when the test signalis amplitude modulated and frequency modulatedsimultaneously.amplitude-versus-frequency distortion Distortionresulting from varying gain or attenuation of anamplifier or network, with respect to signal frequency.AMTOR A form of amateur-radio data communications,in which the accuracy of a group of charactersin a message is checked periodically by thereceiving station. If an error appears likely, thenthe receiving station sends an instruction to thetransmitting station to retransmit that particulargroup of characters. Characters are sent inbunches with pauses for possible inquiries fromthe receiving station.AM tuner A compact radio receiver unit that handlesamplitude-modulated signals and deliverslow-amplitude audio output to a high-fidelity amplifier.Compare AM/FM TUNER and FM TUNER.amu Abbreviation of atomic mass unit.amusement robot An electromechanical robot, oftencomputer-controlled, that is intended for useas a toy.AN- A prefix designator used by American militaryservices to indicate commonality.anacoustic Pertaining to the lack of sound or absenceof reverberation or transmission of sonicwaves.analog 1. A quantity that corresponds, point forpoint or value for value, to an otherwise unrelatedquantity. Thus, voltage is the analog of waterpressure, and current is the analog of water flow.2. Varying over a continuous range and, therefore,capable of attaining an infinite number ofvalues or levels. Compare DIGITAL.analog adder An analog circuit or device that receivestwo or more inputs and delivers an outputequal to their sum.analog adder/subtracter An analog circuit or devicethat receives two or more inputs and deliversan output equal to their sum or difference (in anycombination), as desired.analog channel In an ANALOG COMPUTER, an informationchannel in which the extreme limits ofdata magnitude are fixed, and the data can haveany value between the limits.analog communications Any form of communicationsin which a carrier, generally an electromagneticwave or high-frequency current, is varied ina continuous and controlled way by a datacontainingsignal. See ANALOG, 2.analog computer A computer in which input andoutput quantities are represented as points oncontinuous (or small-increment) scales. To representthese quantities, the computer uses voltagesor resistances that are proportional to the numbersto be worked on. When the quantities arenonelectrical (such as pressure or velocity), theyare made analogous by proportional voltages orresistances.analog data 1. Data represented in a quantitativelyanalogous way. Examples are the deflectionof a movable-coil meter, the positioning of a slideron a slide rule, and the setting of a variable resistorto represent the value of a nonelectrical quantity.Also see ANALOG. 2. Data displayed along asmooth scale of continuous values (as by amovable-coil meter), rather than in discrete steps(as by a digital meter).analog differentiator An analog circuit or devicewhose output waveform is the derivative of theinput-signal waveform, with respect to time.analog divider An analog circuit or device that receivestwo inputs and delivers an output equal totheir quotient.analog electronics Electronic techniques andequipment that is based on uniformly changingsignals, such as sine waves, and often havingcontinuous-scale indicators, such as D’Arsonvalmeters. Compare DIGITAL ELECTRONICS.analog information Approximate numerical information,as opposed to digital information, whichis assumed to be exact.analog integrator An analog circuit or devicewhose output waveform is the integral of the inputsignal waveform, with respect to time.

28 analog inverting adder • AND circuitanalog inverting adder An analog adder that deliversa sum with the opposite sign to that of theinput quantities.analog meter An indicating instrument that usesa movable-coil arrangement or the equivalent,causing a rotating pointer to indicate a particularvalue on a graduated printed scale. CompareDIGITAL METER.analog multiplexer 1. A multiplexer used withanalog signals (see MULTIPLEXER). 2. An analogtime-sharing circuit.analog multiplier An analog circuit or device thatreceives two or more inputs and delivers an outputequal to their product.analog network A circuit that permits mathematicalrelationships to be shown directly by electricor electronic means.analogous pole In a PYROELECTRIC MATERIAL,the end or face having the positive electric charge.analog output An output quantity that variessmoothly over a continuous range of values,rather than in discrete steps.analog record Also called analog recording. Arecord or recording method in which some propertyof the recorded material, such as displacementor magnetization, varies over a continuousrange that is relative to time and/or physical position.analog recorder Any recorder, such as a recordingoscillograph, potentiometric recorder, electroencephalograph,electrocardiograph, or lie detector,that produces an analog record. The counterpartis a digital recorder, which produces a readout indiscrete numbers (printed or visually displayed).analog representation Representation of informationwithin a smooth, continuous range, ratherthan as separate (discrete) steps or points.analog signal A signal that attains an infinitenumber of different amplitude levels, as opposedto one that can attain only a finite number of levelsas a function of time.analog subtracter An analog circuit or device thatreceives two inputs and delivers an output equalto their difference.analog summer See ANALOG ADDER.analog switch A switching device that will onlypass signals that are faithful analogs of transducerparameters.analog-to-digital conversion 1. A process inwhich an analog signal (such as a voice waveform)is changed into a digital or binary signalthat conveys the same information. This processis commonly used in digital computers to encodesounds and images. It is also used in communicationssystems to improve efficiency, minimizethe necessary bandwidth, and optimize the signal-to-noiseratio. 2. A process in which continuousmechanical motion is encoded into a digitalor binary electronic signal.analog-to-digital converter Any circuit or devicethat performs ANALOG-TO-DIGITAL CONVER-SION.analysis1. The rigorous determination of the constantsand modes of operation for electronicequipment. Compare SYNTHESIS. 2. A branch ofmathematics dealing with point sets, relations,and functions.analytical engine A primitive mechanical calculatingmachine, invented in 1833 by Charles Babbage.analyzer 1. Any instrument that permits analysisthrough close measurements and tests (e.g., distortionanalyzer, WAVE ANALYZER, or gas analyzer).2. A computer program used for debuggingpurposes; it analyzes other programs and summarizesreferences to storage locations. 3. Ananalysis interface to an oscilloscope.anastigmatic yoke Also called full-focus yoke. In atelevision (TV) receiver, a deflection yoke with acosine winding for better focus at the edges of thepicture.anchorage In plastic recording tape, the adhesionof the magnetic oxide coating to the surface of thetape.ancillary equipment Equipment that does not directlyenter into the operation of a central system.Examples are input/output components of a computerand test instruments attached to a system.AND circuit In digital systems and other switchingcircuits, a logic gate whose output is high (logic 1)only when all input signals are high. Otherwisethe output is low (logic 0). Compare OR CIRCUIT.

Anderson bridge • angle of beam 29Anderson bridge An ac bridge circuit with siximpedances, permitting the value of an unknowninductance to be determined in terms of a standardcapacitance.AND gate 1. AND circuit. 2. In a TV receiver, anAND circuit that holds the keyed-AGC signal offuntil a positive horizontal flyback pulse and ahorizontal sync pulse appear simultaneously atthe input.android A sophisticated robot built in humanoidform. Usually, it propels itself by rolling onwheels or on a track drive. A rotatable head containsposition sensors, a machine vision system,and/or a machine hearing system. Mechanicalarms are equipped with end effectors to performvarious tasks. The most advanced androids haveself-contained computer control systems.anechoic Pertaining to the absence of echoes. Examples:ANECHOIC CHAMBER, anechoic enclosure,or anechoic room.anechoic chamber An enclosure that does not reflectsound waves that approach its walls. Such achamber is used to test certain audio devices.anemograph An electromechanical device thatproduces a recording of wind speed versus time.Generally, it consists of an ANEMOMETER connectedto a PEN-AND-INK RECORDER via a suitableelectronic interface.anemometer An instrument that measures orindicates wind speed, or speed and direction (velocity).angel 1. An extraneous image, usually of short duration,on a cathode-ray-tube (CRT) display. Theterm applies particularly to anomalies in a radarimage caused by low-atmospheric reflection,birds, or other mobile objects. 2. Air-deployedmetallic debris, also known as chaff, designed tocreate radar echoes as a decoy or diversion tactic.angle jamming A radar jamming technique inwhich the return echo is jammed with a signalcontaining improper azimuth or elevation anglecomponents.angle modulation Variation of the angle of a sinewavecarrier in response to the modulatingsource, as in FREQUENCY MODULATION andPHASE MODULATION.angle noise In radar reception, the interference resultingfrom variations in the angle at which anecho arrives from the target.angle of arrival The angle which the line of propagationof an incoming radio wave makes with thesurface of the earth. Compare ANGLE OF DE-PARTURE.angle of azimuth The horizontal angle betweenthe viewer and object or target, usually measuredclockwise from north.angle of beam The angle enclosing most of thetransmitted energy in the radiation from a directionalantenna. It is usually measured betweenthe half-power points in the main lobe of the directionalpattern. This angle can be measured inthe horizontal (azimuth) plane or in the vertical(elevation) plane.

30 angle of conduction • anhysteresisangle of conduction 1. Also called angle of flow.The number of degrees of an excitation-signal cycleduring which output (drain, collector or plate)current flows in an amplifier circuit. 2. The numberof degrees of any sine wave at which conductionof a device (e.g., a diode) begins.angle of convergence 1. In any graphical representation,the angle formed by any two lines orplots that come together at a point. 2. The angleformed by the light paths of two photocells focusedon the same object.angle of declination The angle between the horizonand a descending line. Compare ANGLE OFELEVATION.angle of deflection In a cathode-ray tube, the anglebetween the electron beam at rest and a newposition resulting from deflection.angle of departure The angle, relative to thehorizon, made by the line of propagation of atransmitted radio wave. Compare ANGLE OFARRIVAL.angle of depression See ANGLE OF DECLINA-TION.angle of divergence In a cathode-ray tube, the angleformed by the spreading of an undeflectedelectron beam as it extends from the gun to thescreen.angle of elevation The angle that an ascendingline subtends, with respect to the horizon. CompareANGLE OF DECLINATION.angle of flow See ANGLE OF CONDUCTION.angle of incidence The angle, measured relative tothe perpendicular (orthogonal) to a surface orboundary, subtended by an approaching ray.Compare ANGLE OF REFLECTION and ANGLEOF REFRACTION.angle of lag The phase difference (in degrees or radians)whereby one component follows another intime, both components being of the same frequency.Compare ANGLE OF LEAD. Also seePHASE ANGLE.angle of lead The phase difference (in degrees orradians) whereby one component precedes anotherin time, both components being of the samefrequency. Compare ANGLE OF LAG. Also seePHASE ANGLE.angle of radiation 1. The angle, measured with respectto the horizon, at which the principal lobe ofan electromagnetic wave leaves a transmittingantenna. 2. The angle, measured relative to thehorizon, of a receiving or transmitting antenna’soptimum sensitivity.angle of reflection The angle, measured relative tothe perpendicular (orthogonal) to a surface, subtendedby a ray leaving the surface after havingbeen reflected from it. Compare ANGLE OF INCI-DENCE.angle of refraction The angle, measured relativeto the perpendicular (orthogonal) to a boundarybetween two different media, subtended by a rayleaving the boundary after having been refractedthereat. Compare ANGLE OF INCIDENCE.angle tracking noise Noise in a servo system thatresults in a tracking error.angstrom (Anders J. Angstrom, 1814 –1874). Aunit of length used to describe certain extremelyshort waves and microscopic dimensions; 1angstrom equals 10 –4 microns (10 –10 meters).angular deviation loss The ratio of microphone orloudspeaker response on the principal axis of responseto the response at a designated angle fromthat axis. Expressed in decibels.angular difference See PHASE ANGLE.angular displacement In an ac circuit, the separation,in degrees, between two waves. See PHASEANGLE.angular frequency The frequency of an ac signal,expressed in radians per second (rad/sec) and approximatelyequal to 6.28f, where f is the frequencyin Hertz.angular length Length, as along the horizontalaxis of an ac wave or along the standing-wavepattern on an antenna, expressed as the productof radians and wavelength.angular-mode keys On a calculator or computer,the DEG, RAD, and GRAD keys for expressing orconverting angles in DEGREES, RADIANS, andGRADS, respectively.angular phase difference For two sinusoidalwaves, the phase difference, expressed in degreesor radians.angular rate In navigation, the rate of bearingchange, expressed in degrees or radians.angular resolution The ability of a radar to distinguishbetween two targets by angular measurement.angus pen recorder An instrument that makes apermanent record of the time whenever a channelis used.anharmonic oscillator An oscillating device inwhich the force toward the balance point is notlinear, with respect to displacement.anhysteresis The magnetization of a material by aunidirectional field containing an alternating fieldcomponent of gradually decreasing amplitude.

anhysteretic state • anomalous propagation 31anhysteretic state The condition of a substanceafter it has been subjected to a strong magneticfield, the intensity of which alternates in directionand diminishes gradually to zero.animism A belief or philosophy, held especially inEastern civilizations, such as Japan, that allthings contain an essence of life. This theory rendersirrelevant the question of whether or not machines,such as computers and robots can be“alive.”anion A negative ion. Also see ION.anisotropic Pertaining to the tendency of somematerials to display different magnetic and otherphysical properties along different axes.ANL Abbreviation of AUTOMATIC NOISE LIMITER.anneal To heat a metal to a predetermined temperatureand let it cool slowly. The operation preventsbrittleness and often stabilizes electricalcharacteristics.annealed laminations Core laminations for transformersor choke coils that have been annealed.annealed shield A magnetic shield for cathode-raytubes, that has been processed by annealing.annealed wire Soft-drawn wire that has been subjectedto annealing.annotations 1. Marking on copies of original engineering-installationdocuments to show changesmade during the installation. 2. Any set of commentsor notes accompanying a program, anequipment or system, or a process.annular 1. Pertaining to the region between twoconcentric circles that lie in the same plane; ringshaped.2. Pertaining to two or more concentriccircles that lie in a common plane.annular conductor A number of wires stranded inthree concentric layers of alternating twistsaround a hemp core.annular transistor A mesa transistor in which thebase and collector take the form of concentricrings around a central emitter.annulling network A subcircuit that shunts a filterto cancel reactive impedance at the extremeends of the pass band of the filter.annunciation relay A relay that indicates whetheror not a circuit is carrying current.annunciator A device that produces loud soundand/or conspicuous light to attract attention(e.g., the electronic siren in an automotive securitysystem).anode 1. The positive electrode of a vacuum tubeor solid-state device (i.e., the electrode towardwhich electrons move during current flow). 2. Inan electrochemical cell, the electrode that loseselectrons by oxidation. This is usually the negativeelectrode.anode balancing coil Mutually coupled windingsused to maintain equal currents in parallel anodesoperating from a common transformer terminal.anode current Current flowing in the anode circuitof a device.anode efficiency Also called plate efficiency. In apower amplifier using an electron tube, the ratioP o /P i , where P o is the output power in watts and P iis the dc anode power input in volt-amperes.anode power input Symbol, P A(input) . The product ofanode current and anode voltage.anode power supply The ac or positive dc powersupply unit that delivers current and voltage tothe anode of a device.anode saturation The point beyond which a furtherincrease in anode voltage does not producean increase in anode current.anode strap In a multicavity magnetron, a metalstrap connecting the anodes.anode terminal 1. In a diode, the terminal towhich a positive dc voltage must be applied forforward bias. Compare CATHODE TERMINAL. 2.In a diode, the terminal at which a negative dcvoltage appears when the device is used as an acrectifier. Compare CATHODE TERMINAL. 3. Theterminal that is connected internally to the anodicelement of any device.anode voltage Symbol, E A or V A . The difference in potentialbetween the anode and cathode of a device.anodic Pertaining to the anode of a device, or toanode-like effects.anodizing An electrolytic process in which a protectiveoxide film is deposited on the surface of ametallic body acting temporarily as the anode ofthe electrolytic cell.anomalous dispersion Dispersion of electromagneticradiation that is characterized by a decreasein refractive index with increase in frequency.anomalous propagation 1. The low-attenuationpropagation of UHF or microwave signals through

32 anomalous propagation • antenna currentatmospheric layers. 2. Unusual, bizarre, or unexplainableelectromagnetic-wave propagation (e.g.,apparent F-layer ionospheric effects in the FMbroadcast band). 3. Rapid fluctuation of a sonarecho because of variations in propagation.anoxemia toximeter An electronic instrument formeasuring or alerting against the onset of anoxemia(deficiency of oxygen in the blood)—especiallyin airplane pilots.AN radio range A navigational facility entailing fourzones of equal signal strength. When the aircraftdeviates from course, an aural Morse-code signal,A (DIT DAH) or N (DAH DIT) is heard; but when theaircraft is on course, a continuous tone is heard.ANSI Acronym for American National Standards Institute.AN signal The signal provided by an AN radio rangeto apprise aircraft pilots of course deviation.answerback The automatic response of a terminalstation to a remote-control signal.answer cord In a telephone system, the cord usedfor answering subscribers’ calls and incomingtrunk calls.answering machine A device that automaticallyanswers a telephone and records an audio messagefrom the caller.answer lamp A telephone switchboard lamp thatlights when an answer cord is plugged into a linejack; it switches off when the telephone answersand lights when the call is completed.ant Abbreviation of ANTENNA.antenna In a communications system, a specializedtransducer that converts incoming electromagneticfields into alternating electric currentshaving the same frequencies (receiving antenna),or converts an alternating current at a specificfrequency into an outgoing electromagnetic fieldat the same frequency (transmitting antenna). Anantenna can be a simple wire or rod, or a complicatedstructure. Thousands of geometries andspecifications are possible. The optimum antennatype for a given situation depends on the communicationsfrequency, the distance to be covered,and various other factors.antenna ammeter An RF ammeter, usually of thethermocouple type, employed to measure currentflowing to a transmitting antenna.antenna amplifier 1. A radio-frequency amplifier,often installed at the antenna, used to boost signalsbefore they reach a receiver (also called anRF preamplifier). 2. Occasionally, the first RF amplifierstage of a receiver, also known as the frontend.antenna array See ARRAY.antenna bandwidth The frequency range throughoutwhich an antenna will operate at a specifiedefficiency without needing alteration or adjustment.antenna beamwidth A measure of the extent towhich a directional antenna focuses a transmittedelectromagnetic field, or focuses its responseto incoming electromagnetic fields. Expressed asthe angle in degrees between opposite half-powerpoints in the main lobe of the directional pattern.Usually determined in the horizontal plane, butoccasionally in the vertical plane.antenna coil The primary coil of the input RFtransformer of a receiver, or the secondary coil ofthe output RF transformer of a transmitter.antenna coincidence The condition in which twodirectional antennas are pointed directly towardeach other.antenna-conducted interference Extraneous signalsgenerated in a transmitter or receiver andpresented to the antenna, from which they are radiated.antenna core A ferrite rod or slab around which acoil of wire is wound to act as a self-contained antenna,usually in a miniature receiver.antenna coupler A device consisting of an inductor,RF transformer, or a combination of inductor(s)and capacitor(s), used to match theimpedance of an antenna to that of a transmitteror receiver. Also known as a transmatch or antennatuner.antenna coupling Inductive and/or capacitivecoupling used to optimize the transfer of energyfrom an antenna to a receiver, or from a transmitterto an antenna.antenna current 1. Radio-frequency current flowingfrom a transmitter into an antenna. 2. Radiofrequencycurrent flowing from a receivingantenna into a receiver.

antenna ground system The earth, counterpoise,guy wires, radials, and/or various conducting obantennadetector • antenna pattern 33antenna detector A circuit that warns aircraftpersonnel that they are being observed by radar.It picks up the radar pulses and actuates a warninglight or other device.antenna diplexer A coupling device that permitsseveral transmitters to share one antenna withouttroublesome interaction. Compare ANTENNADUPLEXER.antenna directivity The directional characteristicsof a transmitting or receiving antenna, usuallyexpressed qualitatively (e.g., omnidirectional,bidirectional, or unidirectional). A more preciseexpression is ANTENNA BEAMWIDTH.antenna director In a directional antenna, a PAR-ASITIC ELEMENT situated in front of the radiatorand separated from it by an appropriate fractionof a wavelength. Its function is to intensify radiationin the direction of transmission. CompareANTENNA RADIATOR and ANTENNA REFLEC-TOR.antenna duplexer A circuit or device permittingone antenna to be shared by two transmitterswithout undesirable interaction.antenna effect The tendency of wires or metallicbodies to act as antennas (i.e., to radiate or receiveradio waves).antenna efficiency The ratio of radio-frequencyenergy supplied to a wireless transmitting antenna,to the energy radiated into space. Electrically,the radiation resistance of the antenna (R R )appears in series with loss resistance (R L ). The efficiencyEff of the antenna can be determined bythe following formula:Eff = R R /(R R + R L )As a percentage,Eff % = 100 (R R /(R R + R L )The efficiency is always less than 1 (100 percent)because, in practice, the loss resistance cannever be reduced to zero.antenna factor A factor (in decibels) added to anRF voltmeter reading to find the true open-circuitvoltage induced in an antenna.antenna field The electromagnetic field immediatelysurrounding an antenna.antennafier Low-profile antenna/amplifier device,sometimes used with portable communicationssystems. Also called an active antenna.antenna front-to-back ratio For a directional antenna,the ratio of field strength in front of the antenna(i.e., directly forward in the line ofmaximum directivity) to field strength in back ofthe antenna (i.e., 180 degrees from the front), asmeasured at a fixed distance from the radiator. Itis usually specified in decibels.antenna gain For a given antenna, the ratio of signalstrength (received or transmitted) to that obtainedwith a comparison antenna, such as asimple dipole. Generally specified in decibels.jects in the vicinity of an antenna which, takentogether, form the radio-frequency (RF) groundsystem against which the antenna operates.Some antennas require an extensive ground systemto function efficiently; others need no groundsystem.antenna/ground system An arrangement embodyingboth an antenna and a low-resistanceconnection to the earth, as opposed to an antennasystem that involves no connection toearth.antenna height 1. The height of an antenna abovethe surface of the earth immediately beneath thedriven element(s). 2. The height of an antennaabove the effective radio-frequency (RF) groundimmediately beneath the driven element(s). 3.The height of an antenna above average terrain,determined against the mean altitude of a numberof points on the earth’s surface that lie withina certain radius of the antenna structure. Alsocalled height above average terrain (HAAT).antenna impedance The complex-number impedancethat an antenna presents to a transmissionline. It can vary over a tremendous range,and depends on the antenna type, antenna size,antenna height, operating frequency, and variousother factors.antenna-induced potential Also called antennainducedmicrovolts. The voltage across the opencircuitedterminals of an antenna.antenna lens Also called lens antenna. A radiatordesigned to focus microwave energy in much thesame manner that an optical lens focuses lightrays. Lens antennas are made from dielectric materialsand/or metals.antenna loading 1. The insertion of inductance inantenna elements to lower the resonant frequencyof the system without necessarily makingthe system physically larger or the elementslonger. 2. The insertion of capacitance in antennaelements to raise the resonant frequency of thesystem without necessarily making the systemphysically smaller or the elements shorter.antenna lobe A well-defined region in the radiationpattern of an antenna in which radiation is mostintense, or in which reception is strongest. Alsosee ANTENNA PATTERN.antenna matching The technique of establishing asatisfactory relationship between the antennaimpedance and the transmission-line or transmitter-outputimpedance, for maximum transferof power into the antenna. Also, the matchingof antenna impedance to receiver-input impedance,for delivery of maximum energy to thereceiver.antennamitter An antenna/oscillator combinationthat serves as a low-power transmitter.antenna pattern A polar plot of antenna performancethat shows field strength versus angle ofazimuth, with the antenna at the center. It isusually specified in the horizontal plane.

34 antenna polarization • anthropomorphismantenna polarization The orientation of electriclines of flux, with respect to the surface of theearth, for which an antenna is most efficient. Avertical antenna radiates and receives verticallypolarized waves. A horizontal antenna radiatesand receives horizontally polarized waves broadsideto itself, and vertically polarized waves athigh elevation angles off its ends. In other directions,the polarization is slanted at various angles.antenna power Symbol, P ant . The RF power developedin an antenna by a transmitter; P ant equalsI 2 R, where I is the antenna current and R is theantenna resistance at point I is measured.antenna power gain The ratio of the maximum effectiveradiated power (ERP) from a wirelesstransmitting antenna to the ERP from a referenceantenna, expressed in decibels (dB). If the ERPfrom an antenna under test is P T watts and theERP from the reference antenna is P R watts, thenthe gain G dB is:G dB = 10 log 10 (P T /P R )Power gain is always measured in the direction inwhich the test antenna performs the best. Thereference antenna, usually a dipole, is chosenwith a gain assumed to be unity, or 0 dB. Gainrelative to a dipole is expressed in dBd (decibelsrelative to a dipole). Alternatively, the referenceantenna can be an isotropic radiator, in whichcase the gain is expressed in dBi (decibels relativeto an isotropic radiator). Gain figures in dBd anddBi differ by a constant amount as follows:G dBi = 2.15 + G dBdantenna preamplifier A highly sensitive amplifierused to enhance the gain of a receiver. It is usuallyused at the very high frequencies and above.antenna radiation The propagation of radio wavesby a transmitting antenna.antenna radiator The element of an antenna thatreceives RF energy from the transmitter and radiateswaves into space. Also known as the drivenelement. Compare ANTENNA DIRECTOR and AN-TENNA REFLECTOR.antenna range 1. The frequency band, communicationdistance characteristically covered, orother continuum of values that specify the operatinglimits of an antenna. 2. The region immediatelysurrounding an antenna in which tests andmeasurements usually are made. Sometimescalled ANTENNA FIELD.antenna reflector In a directional antenna, a PAR-ASITIC ELEMENT situated behind the radiatorand separated from the latter by an appropriatefraction of a wavelength. Its function is to intensifyradiation in the direction of transmission.Compare ANTENNA DIRECTOR and ANTENNARADIATOR.antenna relay In a radio station, a low-loss, heavydutyrelay that enables the antenna to beswitched between transmitter and receiver.antenna resistance The resistive component ofANTENNA IMPEDANCE.antenna resonant frequency The frequency, ornarrow band of frequencies, at which an antenna’simpedance appears resistive.antenna stage 1. The first RF amplifier stage of areceiver. 2. Occasionally, the final RF amplifier ofa transmitter.antenna switch In a radio station, a low-loss,heavy-duty switch that enables the antenna to beconnected to transmitter, receiver, or safetyground.antenna system Collectively, an antenna and all ofthe auxiliary electrical and mechanical devicesneeded for its efficient operation, including couplers,tuners, transmission lines, supports, insulators,and rotator.antenna terminals 1. The points at which a transmissionline is attached to an antenna. 2. The signalinput terminals of a receiver. 3. The signaloutput terminals of a transmitter.antennaverter An antenna and converter combinedinto a single circuit, intended for connectionto the antenna terminals of a receiver toallow operation on frequencies outside the bandfor which the receiver has been designed.antenna wire 1. The radiator element of a wiretypeantenna. 2. A strong solid or stranded wire(e.g., hard-drawn copper, copper-clad steel, orphosphor-bronze) used for antennas.anthropomorphism The perception, by people, ofmachines as having human qualities. This can

anthropomorphism • antiparticle 35lead to emotional attachment to hardware, suchas computers and robots. The more sophisticatedthe apparatus, in general, the more powerful thisperception can become.antialiasing filter A low-pass or bandpass filterthat limits the bandwidth of an input signal toprevent aliasing and its effects. See ALIASING, 1.anticapacitance switch A switch whose membersare thin blades and stiff wires widely separated tominimize capacitance between them.anticathode The target electrode of an X-ray tube.Anticipatory Sciences A group of futurists, peoplewho attempt to predict the course of technology.Some futurists believe that progress will continueuntil, for example, homes become fully automatedand artificial intelligence reaches a level comparableto human intelligence. Other futurists believethat such things are highly improbable.anticlutter circuit A supplementary circuit in aradar receiver that minimizes the effect of extraneousreflections that would obscure the image ofthe target.anticlutter gain control In a radar receiver, a circuitthat automatically raises the gain of the receiverslowly to maximum after each transmitterpulse to reduce the effect of clutter-producingechoes.anticoincidence Noncoincidental occurrence oftwo or more signals. Compare COINCIDENCE.anticoincidence circuit In computers and controlsystems, a circuit that delivers an output signalonly when two or more input signals are not receivedsimultaneously. Compare COINCIDENCECIRCUIT. Also see NAND CIRCUIT.anticoincidence operation An exclusive-OR operation.anticollision radar A vehicular radar system thatis used to minimize the probability of a collisionwith another vehicle, whether or not that othervehicle has a similar system.antiferroelectric 1. Pertaining to the propertywherein the polarization curve of certain crystallinematerials shows two regions of symmetry.2. A material that exhibits the aforementionedproperty.antiferromagnetic Pertaining to the behavior ofmaterials in which, at low temperatures, themagnetic moments of adjacent atoms point in oppositedirections.antihunt The condition in which hunting is counteracted,usually by removing overcorrection inautomatic control or compensation systems.antihunt circuit 1. A circuit that minimizes oreliminates hunting. Also see ANTIHUNT. 2. In atelevision (TV) receiver, a circuit that stabilizes anautomatic frequency control (afc) system.antijamming Pertaining to communications systemsthat are resistant to, or that counteract, theeffects of jamming.antilogarithm Abbreviated, antilog or log –1 . Thenumber corresponding to a given logarithm. Forexample, log 10,000 = log 10 4 = 4, and thus antilog4 = 10 4 = 10,000.antilogous pole In a PYROELECTRIC MATERIAL,the end that becomes negatively charged as thetemperature rises.antimagnetic Pertaining to materials having extremelylow RETENTIVITY.antimatter Pertaining to particles that are thecounterparts of conventional particles (i.e.,positrons instead of electrons, antineutrons insteadof neutrons, and antiprotons instead ofprotons). When a particle meets its antiparticle,the two annihilate, releasing energy. Also see AN-TIPARTICLE.antimicrophonic See NONMICROPHONIC.antimony Symbol, Sb. A metalloidal element.Atomic number, 51. Atomic weight, 121.76. Oftenused as n-type dopant in semiconductor manufacture.antineutrino The antiparticle of the NEUTRINO,emitted as a result of radioactive decay.antineutron An uncharged particle with a massequal to that of the neutron, but with a magneticmoment in the direction opposite that of the neutron.antinode A point of maximum amplitude in astanding wave.antinoise carrier-operated circuit A circuit thatcuts off the audio output of a receiver while thestation transmitter is in use. This can be accomplishedin the automatic-gain-control (AGC) circuitof the receiver, or in the speaker or audioline. The circuit is actuated by energy from thetransmitted signal.antinoise microphone Any microphone that discriminatesagainst acoustic noise (e.g., a lip microphoneor throat microphone).antinucleon A particle with the mass of a nucleon,but with the opposite electrical charge and directionof magnetic moment. Compare NUCLEON.antioxidant A material, such as a lacquer coat oran inactive oxide layer, that prevents or slows oxidationof a material exposed to air.antiparticle A subatomic particle opposite in characterto conventional particles, such as electrons,neutrons, protons. Antiparticles constituteantimatter. Also see ANTINEUTRINO, ANTI-NEUTRON, ANTINUCLEON, ANTIPROTON, andPOSITRON.

36 antiphase • A plusantiphase The property of being in phase opposition(180 degrees out of phase).antipincushioning magnets In some television(TV) receivers, a pair of corrective magnets in thedeflection assembly on the picture tube that eliminatepincushion distortion (disfigurement of theraster so that it resembles a pincushion—a rectanglewith its sides bowed in).antiproton A subatomic particle with a mass equalto that of the proton, but with opposite electricalcharge.antiquark An ANTIPARTICLE of a QUARK.antirad substance A material that protects againstdamage caused by atomic radiation.antiresonance 1. Parallel resonance. 2. The conditionof being detuned from a resonant frequency.antiresonant circuit See PARALLEL-RESONANTCIRCUIT.antiresonant frequency 1. The resonant frequencyof a parallel-resonant circuit. 2. In apiezoelectric crystal, the frequency at whichimpedance is maximum (as in a parallel-resonantcircuit).antisidetone Pertaining to the elimination in telephonecircuits of interference between the microphoneand earphone of the same telephone.antistickoff voltage The low voltage applied to thecoarse synchro control transformer rotor windingin a dual-speed servo system to eliminate ambiguousbehavior in the system.antitransmit/receive switch Abbreviated ATR. Ina radar installation, an automatic device to preventinteraction between transmitter and receiver.antivirus program A computer program or utilitydesigned to detect and eliminate viruses and Trojanhorses in a computer system.antivoice-operated transmission Radio communicationsthat use a voice-activated circuit as atransmitter interlock during reception on thecompanion receiver.apc 1. Abbreviation of automatic picture control. 2.Abbreviation of AUTOMATIC PHASE CONTROL.aperiodic Characterized by a lack of predictablerepetitive behavior. For example, the sferics or“static” electromagnetic interference caused bylightning.aperiodic current The unidirectional current thatfollows an electromagnetic disturbance in an LCRcircuit, in which R is equal to or higher than thecritical circuit resistance.aperiodic damping Damping of such a high degreethat the damped system, after disturbance,comes to rest without oscillation or hunting.aperiodic discharge A discharge in which currentflowing in an LCR circuit is unidirectional, ratherthan oscillatory. For this condition, 1/LC is lessthan or equal to R 2 /4L 2 .aperiodic function A nonrepetitive function (e.g.,a hyperbolic trigonometric function).aperture 1. The larger, normally open end of ahorn antenna or horn loudspeaker. 2. An openingin an opaque disk or mask that passes a predeterminedamount of light or other radiant energy.3. The portion of a directional antenna throughwhich most of the radiated energy passes.aperture angle For an antenna or telescope or microscope,the half angle formed by the radius ofthe detecting instrument, as viewed from thesource.aperture antenna An antenna whose beamwidthdepends on the size of a horn, reflector, or lens.aperture compensation In a television (TV) camera,the minimizing of APERTURE DISTORTIONby widening the video-amplifier passband.aperture distortion In a television (TV) cameratube, a form of distortion that occurs when thescanning beam covers several mosaic elementssimultaneously. This condition, caused by excessivebeam thickness, results in poor image resolution.aperture mask In a three-gun color picture tube, athin, perforated sheet mounted behind the viewingscreen to ensure that a particular color phosphorwill be excited only by the beam for thatcolor. Also called shadow mask.aperture synthesis In telescopes, a method of obtaininghigh resolution using several small antennasseparated by great distances. The smallantennas are moved around to simulate the resolvingpower of a much larger antenna thatwould, in practice, be impossible or impractical toconstruct.aphelion 1. The point at which a solar-orbitingsatellite attains its highest altitude. It occursonce for every complete orbit. At this point, thesatellite travels slower than at any other point inthe orbit. 2. The altitude, measured from thesun’s surface or the sun’s center, of a solarorbitingsatellite at its most distant point.APL Abbreviation for A Programming Language. Ahigh-level computer language designed for ease ofuse, and characterized by the requirement for aspecial character set.apl 1. Abbreviation of average picture level. 2. Abbreviationof automatic phase lock.A plus Also, A+. The positive terminal of an A battery.Also, pertaining to the part of a circuit connectedto that terminal.

apogee • arc cosecant 37apogee 1. The point at which an earth-orbitingsatellite attains its highest altitude. It occursonce for every complete orbit. At this point, thesatellite travels slower than at any other point inthe orbit. 2. The altitude, measured from theearth’s surface or the earth’s center, of an earthorbitingsatellite at its most distant point.A power supply A term sometimes used to denotethe unit that supplies energy to a vacuum-tubefilament. Compare B POWER SUPPLY.apparent bearing In radio-direction finding, theuncorrected direction from which a signal appearsto arrive.apparent power In an ac circuit, the power valueobtained by multiplying the current by voltage (Pequals IE), with no consideration of the effects ofphase angle. Compare TRUE POWER.apparent power loss The loss in an ammeter orvoltmeter, caused by the imperfection of the instrument.At full scale, the ammeter has a certainvoltage across its terminals; the apparent powerloss is the current multiplied by this voltage. Avoltmeter carries a small current; the apparentpower loss is the product of the current and theindicated voltage.appearance potential The potential throughwhich an electron must move to produce a certainion from the atom with which it is associated.applause meter An instrument consisting essentiallyof a microphone, audio amplifier, and indicatingmeter (reading directly in sound level). It isso called because of its familiar use in measuringaudience response, as indicated by loudness ofapplause.Applegate diagram For a velocity-modulated tube,a plot of the positions of electron bunches in thedrift space versus time.Appleton layer Collectively, the F1 and F2 layersof the ionosphere, at a height between 150 and400 kilometers above the surface of the earth.apple tube A color picture tube, used in television,with the red, blue, and green phosphor in verticalstrips.appliance Electrical equipment in general. Thismight include any home-operated device.application A task or job for which an electronicdevice or system is used. It especially pertains topersonal-computer software that has practicalusefulness.application factor A factor involved in determiningthe failure rate of a circuit or system affectedby unusual operating conditions.application schematic diagram A diagram of pictorialsymbols and lines that illustrate the interrelationshipof functional circuit blocks in aspecific program mode.applicators 1. In dielectric heating, the electrodesbetween which the dielectric body is placed andthe electrostatic field developed. 2. In medicalelectronics, the electrodes applied to a patientundergoing diathermy or ultrasonic therapy.applied voltage The voltage presented to a circuitpoint or system input, as opposed to the voltagedrop resulting from current flow through an element.applique circuit A circuit for adapting equipmentto a specialized job.approach-control radar A radar installation servinga ground-controlled approach (GCA) system.approximate data 1. Data obtained through physicalmeasurements. Such data can never be exact;all measurements are subject to error. 2.Loosely estimated data or imprecise calculations.AQL Abbreviation of ACCEPTABLE QUALITYLEVEL. A statistically defined quality level, definedin terms of percent defective, accepted onan average of 95 percent of the time.Aquadag A tradename for a material that consistsof a slurry of fine particles of graphite. Aquadagforms a conductive coating on the inside and outsidewalls of some cathode-ray tubes.aqua pura Pure water; in most instances, distilledwater. Formula, H 2 O. Pure water is a nonconductorwith a dielectric constant of about 81.Ar Symbol for ARGON.arbitrary function fitter A circuit or device, suchas a potentiometer, curve changer, or analogcomputer element, providing an output currentor voltage that is some preselected function of theinput current or voltage.arc 1. A luminous sustained discharge betweentwo electrodes. Because it is sustained, ratherthan intermittent, an arc is distinguished from aspark discharge, the latter being a series of discharges(sparks)—even when it appears continuous.2. In graphical presentations, a section ofcurved line, as of a circle.arc angle The angle in degrees traced out by a circulararc if the center point of the circle is consideredto be the vertex of an angle formed bytwo rays intersecting the arc at designatedpoints.arc cosecant Abbreviated arc csc or csc –1 . 1. Theinverse of the cosecant function. 2. The angle, in

38 arc cosecant • area coderadians or degrees, corresponding to a givencosecant.arc cosine Abbreviated arc cos or cos –1 . 1. The inverseof the cosine function. 2. The angle, in radiansor degrees, corresponding to a given cosine.arc cotangent Abbreviated arc cot or cot –1 . 1. Theinverse of the cotangent function. 2. The angle, inradians or degrees, corresponding to a givencotangent.arc failure 1. Damage to, and/or failure of, insulationor a dielectric as a result of ARCOVER. 2.Failure of make-and-break contacts throughdamage caused by arcover.arc function An inverse trigonometric function. SeeARC COSECANT, ARC COSINE, ARC COTAN-GENT, ARC SECANT, ARC SINE, and ARC TAN-GENT.arc furnace A high-temperature electric furnace inwhich heat is produced by one or more electricalarcs.architecture The functional design elements of acomputer—especially the components of the centralprocessing unit (CPU) and the manner inwhich these elements interact.archived file A computer file stored on somebackup medium, such as magnetic tape, diskette,or CD-ROM (compact disk, read-only memory),rather than being held on the hard disk.Such a file will be apart from the operating system’scatalog of current files, but can be reconstitutedas needed.archives A complete, periodically updated set ofARCHIVED FILES.arcing See ARCOVER.arcing contacts Make-and-break contacts betweenwhich an arc occurs when they are separated.arcing ring A metal ring placed around an insulatorin a high-voltage electrical system. This keepsan arc from charring or breaking the insulator.arcing time The elapsed time between the breakingof contacts and the end of the arc between thecontacts.arc lamp An electric lamp in which a brilliant arcjumps between the tips of two rods (originally carbon).arc length The length along a given arc, usually apart of the circumference of a circle. If the circlehas circumference C and the arc measures x degrees,then the arc length is Cx/360 units.arc minute See MINUTE.arc oscillation Oscillations that can occur whenopening relay contacts arc.arcover The occurrence of an electrical ARC betweenelectrodes, contacts, or capacitive plates.arcover voltage The voltage at which disruptivedischarge occurs, typically accompanied by anarc.arc resistance The ability of a material, usually adielectric, to resist damage from arcing. Thisproperty is commonly expressed as the length oftime between the start of the arc and the establishmentof a conductive path through the material.arc secant Abbreviated arc sec or sec –1 . 1. The inverseof the secant function. 2. The angle, in radiansor degrees, that corresponds to a givensecant.arc second See SECOND.arc sensor A device for detecting visible arcs andexcessive reflected power in microwave systems.arc sine Abbreviated arc sin or sin –1 . 1. The inverseof the sine function. 2. The angle, in radians ordegrees, that corresponds to a given sine.arc suppression Extinguishing an arc discharge.Disruptive arcs in electronic circuits are suppressedby means of auxiliary diodes or resistorcapacitornetworks.arc-suppressor diode A semiconductor diode usedto prevent arcing between make-and-break contacts.arc tangent Abbreviated arc tan or tan –1 . 1. Theinverse of the tangent function. 2. The angle, inradians or degrees, corresponding to a given tangent.arcthrough The puncturing of a material by anarc.area code In the United States, a three-digitnumber that indicates the location, according tospecified assigned districts, of a telephone sub-

area code • arithmetic symmetry 39scriber. When making a long-distance call, thearea code of the desired station must be given inaddition to the seven-digit telephone number.area protection Coverage of a defined region, interms of area or volume, by an alarm system.area redistribution A scheme to determine the effectiveduration of an irregularly shaped pulse. Arectangle is constructed whose height is equal tothe peak height of the pulse, as displayed on anoscilloscope. The rectangle width is adjusted untilthe area of the rectangle is the same as thearea under the curve representing the pulse. Thewidth of the rectangle then represents the effectiveduration of the pulse.area search The scanning of a large group of computerrecords for those of a major category orclass.area sensor A transducer, used with an alarm system,that protects a defined region or volume,such as an office or bedroom.Argand diagram Named after Jean Robert Argand,(1768-1822) of Geneva, for his work on thegraphical representation of complex numbers. Agraphical illustration of a complex number in theform A + jB, where the real-number (A) axis isperpendicular to the imaginary-number ( jB) axis.The value j is the square root of -1, the unit imaginarynumber. The axes are perpendicular, usuallywith the A axis horizontal. The length of theline from the point (0,0) to the point (A,jB) is theamplitude of the vector X = A + jB. The directionis specified as the angle, in degrees or radians, ofthe vector measured counterclockwise from the Aaxis.argon Symbol, Ar. An inert gaseous element.Atomic number, 18. Atomic weight, 39.94. Argon,present in small amounts in the earth’s atmosphere,is used in various specialized devices,such as lasers.argon laser A laser whose tube is filled with argongas. It generates coherent light at specific wavelengthsthat are characteristic of elemental argon.argument 1. The direction angle of a polar vector.2. An independent variable whose value determinesthe value of a function.arithmetic address An address obtained by performingan arithmetic operation on another address.arithmetic and logic unit Abbreviation, ALU. Thepart of a digital computer containing the circuitsthat perform calculations and logic operations;distinguished from mass storage, input/output,and peripheral units.arithmetic circuit Also called arithmetic element.In a digital computer, a circuit that is involved inthe execution of calculations. Included areadders, storage registers, accumulators, subtracters,and multipliers.arithmetic mean The average of a group of quantities,obtained by dividing their sum by the numberof quantities.arithmetic operation In digital computer practice,a numerical process performed: addition,subtraction, multiplication, division, comparison.arithmetic progression A mathematical series inwhich each term following the first is obtained byadding a constant quantity to the preceding one.For example, S = 1, 2, 3, 4, . . . n. Compare GEO-METRIC PROGRESSION.arithmetic shift In a digital computer, the multiplicationor division of a quantity by a power ofthe base used in the notation.arithmetic sum The sum of two or more quantitiesdisregarding their signs. Compare ALGEBRAICSUM.arithmetic symmetry A filter response that is exactlysymmetrical about the center frequencywhen the frequency scale is linear.

40 arm • arsenicarm 1. Any of the distinct branches of a circuit ornetwork. Also called leg. 2. A movable element in adevice, usually containing a contact for switching.armature 1. The rotating member of a motor. 2.The rotating member of some types of electro-mechanicalgenerator. 3. The movable member of arelay, bell, buzzer, or gong. 4. The movable memberof an actuator. 5. The soft-iron keeper placedacross the poles of a permanent magnet to conservepower.armature coil A coil of insulated wire wound on aferromagnetic core to provide the electromagneticproperties of an armature. In a motor or generator,the armature coil is distinguished from theFIELD COIL.armature core The ferromagnetic core upon whichthe armature coil of a motor or generator iswound.armature gap 1. In a motor or generator, the spacebetween an armature core and the pole of a fieldmagnet. 2. In a relay, the space between the armatureand the relay-coil core.armature hesitation A momentary delay in themovement of a relay.armature-hesitation contact chatter Undesired(usually rapid, repetitive) making and breaking ofrelay contacts. Generally caused by armaturehesitation.armature-impact contact chatter Undesired(usually rapid, repetitive) making and breaking ofrelay contacts, caused by contact bounce whenthe armature strikes the relay core (closure) orbackstop (opening).armature relay A relay that uses an electromagnetto pull a lever toward or away from a set of fixedcontacts.armature travel The distance traveled by an armatureduring relay operation.armor A protective metal cable covering.Armstrong FM system (Edwin H. Armstrong,1890 –1954). A phase-shift method of frequencymodulation. See PHASE MODULATION.armature voltage control A means of controllingmotor speed by changing the applied armaturewinding voltage.armchair copy An amateur radio term for receptionof exceptionally clear signals.arming the oscilloscope sweep Enabling an oscilloscopeto trigger on the next pulse by closing aswitch.Armstrong oscillator (Edwin H. Armstrong,1890–1954). An oscillator circuit that uses inductivefeedback between the output and input.Either the output coil or the input coil can betuned to set the oscillator frequency. The amountof positive feedback is controlled by varying thecoupling between the coils.Armstrong superheterodyne circuit See SUPER-HETERODYNE CIRCUIT.Armstrong superregenerative circuit See SU-PERREGENERATIVE CIRCUIT.ARPA Acronym for Advanced Research ProjectsAgency, a subsidiary of the U.S. Department ofDefense.array 1. A directive antenna that consists of an assemblyof properly dimensioned and spaced elements,such as radiators, directors, andreflectors. 2. A coordinated group or matrix ofcomponents, such as diodes, resistors, memorycells, etc., often enclosed in one capsule. 3. Subscriptedvariables representing data arranged sothat a program can examine the array and extractdata relevant to a particular subscript.array device A group of similar or identical componentsthat are connected together in a certainfashion, to perform a specific task.arrester 1. A device used to protect an installationfrom lightning. It consists of a varistor or an airgap connected between an antenna or power lineand an earth ground. The device passes little orno current under ordinary conditions, but passesheavy current to ground during a lightningstroke. Also called LIGHTNING ARRESTER. 2. Aself-restoring protective device used to reducevoltage surges on power lines.ARRL Abbreviation for American Radio RelayLeague.arrowhead A wideband, log-periodic antenna withlinear polarization.ARS Abbreviation of Amateur Radio Service.arsenic Symbol, As. A metalloidal element. Atomicnumber, 33. Atomic weight, 74.91. Arsenic is familiaras an n-type dopant in semiconductor processing.

ARSR • assemble 41ARSR Abbreviation of air route surveillance radar.articulation A measure of the effectiveness of voicecommunications, expressed as the percentage ofspeech units understood by the listener when theeffect of context is negligible.artificial antenna See DUMMY ANTENNA.artificial ear A microphone-type sensor, equivalentto the human ear, used to measure soundpressures.artificial echo 1. In radar practice, the reflectionsof a transmitted pulse returned by an artificialtarget. 2. A signal from a pulsed radio-frequency(RF) generator, delayed to simulate an echo.artificial ground The effective ground provided bythe radials or disk of a ground-plane antenna, asopposed to actual ground (the earth itself ). CompareTRUE GROUND.artificial horizon In aircraft instrumentation, adevice that displays lines showing the position ofthe aircraft in flight, with reference to the horizon.artificial intelligence Abbreviation, AI. 1. A specializedfield of computer science overlappingwith electronics, biology, physiology, and othersciences, concerning attempts to develop advancedcomputer systems that can emulate theprocesses of the human mind. 2. The ability of acomputer to learn from its mistakes, refine itsown processes, and perhaps ultimately reason ina humanlike manner.artificial ionization An artificial reflecting layerthat is created in the atmosphere to provide askip condition.artificial language A language that is not commonlyused, but has been devised for efficiency ina particular situation—especially in a computersystem.artificial life 1. The ultimate endpoint of ARTIFI-CIAL INTELLIGENCE, wherein machines acquirequalities, such as wisdom and the capability tofeel emotions. The state of the art is currentlynowhere near this point. 2. A hypothetical machineor set of machines with lifelike qualities, includinghuman-level intelligence, wisdom, andemotion.artificial stimulus An electronic method of robotguidance and navigation using radar, sonar, visionsystems, edge detection, and/or beacons.artificial transmission line A network of capacitorsand inductors with characteristics similar tothose of the more bulky transmission line it replacesin tests and measurements. It also servesas a time-delay or phase-shift device and as apulse-forming network.artificial voice A device used to test and calibratenoise-canceling microphones, consisting essentiallyof a small loudspeaker that has a bafflewhose acoustical properties simulate those of thehuman head.artos stripper A machine that cuts and strips wirefor the fabrication of multiconductor cables.artwork 1. In the manufacture of printed circuits,the scaled drawings from which the mask or etchpattern is obtained photographically. 2. Collectively,the illustrations depicting an electronic circuit,device, or system.As Symbol for ARSENIC.ASA Abbreviation of AMERICAN STANDARDS AS-SOCIATION.asbestos A nonflammable fibrous material consistingof calcium and magnesium silicates that isused for high-temperature insulation.A-scan A radar-screen presentation in which thehorizontal time axis displays distance or range,and the vertical axis displays the amplitude ofsignal pulse and echo pulses.ascending node For a satellite orbiting the earth oranother planet, any point at which the groundtrackcrosses the equator as it moves from thesouthern hemisphere into the northern hemisphere.This node generally changes for eachsucceeding orbit, because the earth or planet rotatesunderneath the orbit of the satellite. CompareDESCENDING NODE.ascending pass For a specific point on the earth’ssurface, the time during which an artificial communicationssatellite is accessible when its latitudeis moving northward. The duration ofaccessibility depends on the altitude of the satellite,and on how close its groundtrack comes tothe earth-based point. Compare DESCENDINGPASS.ASCII Acronym (pronounced “ask-ee”) for AmericanStandard Code for Information Interchange.ASI Abbreviation for American Standards Institute.A-scope A radar system that displays an A-SCAN.Askarel A synthetic, nonflammable liquid dielectric.aspect ratio The width-to-height ratio of a videoimage, generally three units high by four unitswide.asperities On the surface of an electrode, tinypoints at which the electric field is intensified andfrom which discharge is highly probable.ASR 1. Abbreviation of AIRBORNE (or AIRPORT)surveillance radar. 2. Abbreviation of AUTO-MATIC SEND/ RECEIVE.ASRA Acronym for automatic stereophonic recordingamplifier.assemble 1. To gather subprograms into a completedigital computer program. 2. To translate a

42 assemble • astrionicsSymbols for ASCII teleprinter codeFirstLast three signalsfoursignals 000 001 010 011 100 101 110 1110000 NUL DLE SPC 0 P / p0001 SOH DC1 ! 1 A Q a q0010 STX DC2 " 2 B R b r0011 ETX DC3 # 3 C S c s0100 EOT DC4 $ 4 D T d t0101 ENQ NAK % 5 E U e u0110 ACK SYN & 6 F V f v0111 BEL ETB ' 7 G W g w1000 BS CAN ( 8 H X h x1001 HT EM ) 9 I Y i y1010 LF SUB * : J Z j z1011 VT ESC + ; K [ k {1100 FF FS , < L / l /1101 CR GS – = M ] m }1110 SO RS . > N n ~1111 SI US | ? O - o DELACK: acknowledgeBEL: bellBS: back spaceCAN: cancelCR: carriage returnDC1: device control no. 1DC2: device control no. 2DC3: device control no. 3DC4: device control no. 4DEL: deleteDLE: data link escapeENQ: enquiryEM: end of mediumEOT: end of transmissionESC: escapeETB: end of transmissionblockETX: end of textFF: form feedFS: file separatorGS: group separatorHT: horizontal tabLF: line feedNAK: do not acknowledgeNUL: nullRS: record separatorSI: shift inSO: shift outSOH: start of headingSPC: spaceSTX: start of textSUB: substituteSYN: synchronous idleUS: unit separatorVT: vertical tabsymbolic program language into a machine (binary)language program by substituting operationcodes and addresses.assembly 1. A finished unit that can be either apractical working model or a dummy, a prototype,or a final model; an integrated aggregationof subunits. 2. A low-level computer source-codelanguage that uses crude mnemonics that areeasier to remember than the machine-languageequivalents.assembly language A source code that usesmnemonic instructions. (See ASSEMBLY, 2.)assembly program The program that operates ona symbolic-language program to produce a machinelanguage program in the process of assembly.Also called assembler.assembly robot A form of industrial robot that putshardware together. Such a robot is generally acomponent of an automated integrated manufacturingsystem (AIMS). The robot can do repetitivework at high speed and precision for long periodsof time.assign To reserve part of a computing system for aspecific purpose, normally for the duration of aprogram run.assigned frequency The radio carrier frequency orband of frequencies designated for a transmittingstation by a licensing authority. Also see RADIOSPECTRUM.associative memory Computer memory in whichlocations are identified by content, rather than byspecific address.assumed decimal point A decimal point that doesnot occupy an actual computer storage space,but is used by the computer to align values forcalculation; the decimal point is assumed to be atthe right unless otherwise specified.astable Having two temporary states; BISTABLE.astable circuit A circuit that has two unstablestates, and whose operation is characterized byalternation between those states at a frequencydetermined by the circuit constants.astable multivibrator A free-running multivibrator.The common circuit uses two bipolar or fieldeffecttransistors, their inputs and outputs beingcross coupled. Conduction switches alternatelybetween the two.astatic 1. Without fixed position or direction. 2. Ina state of neutral equilibrium.astatic galvanometer A galvanometer with a movableelement consisting of two identical magnetizedneedles mounted nonparallel on the samesuspension. Each needle is surrounded by a coil.The coils are wound in opposite directions, andare connected in series to the current source. Alarge permanent magnet provides the fieldagainst which the needle assembly rotates. Theinstrument functions independently of the geomagneticfield.astatine Symbol, At. A radioactive elemental halogenproduced from radioactive decay. Atomicnumber, 85. Atomic weight, 210. Formerly calledalabamine.A station One of the two stations in the transmittingsystem of LORAN (long-range navigation).astigmatism A focusing fault in a cathode-raytube (CRT), in which electrons in different axialplanes focus at different points.ASTM Abbreviation for American Society for Testingand Materials.astrionics The design, production, and applicationof electronic devices and systems for use in spacevehicles and space navigation.

astronomical unit • atmospheric absorption noise 43astronomical unit Abbreviation, AU. A unit of distanceequal to 1.496 × 10 8 kilometers (9.296 × 10 7miles). Approximately equal to the mean distancebetween the earth and the sun.A supply See A POWER SUPPLY.asymmetrical cell A photocell exhibiting ASYM-METRICAL CONDUCTIVITY.asymmetrical communications 1. Two-way communicationsin which the volume of transmitteddata is much greater in one direction than in theother. 2. Two-way communications in which thespeed of transmitted data is much greater in onedirection than in the other. Compare SYMMET-RICAL COMMUNICATIONS.asymmetrical conductivity A condition in whicha device conducts well in one direction, but poorlyin the other direction. A rectifier diode is a commonexample of a component that exhibits thiseffect.asymmetrical distortion In a binary system,lengthening or shortening of one of the states, bycomparison to the theoretical or ideal duration.asymmetrical FET A FIELD-EFFECT TRANSIS-TOR in which the source and drain cannot be interchangedwithout degrading performance.asymmetrical multivibrator An unbalanced multivibrator(i.e., one in which the circuit halves arenot identical). If the time constants of the halvesare different, the output pulses will be short andwidely separated.asymmetrical sideband See VESTIGIAL SIDE-BAND.asymmetrical sideband transmission See VESTI-GIAL SIDEBAND TRANSMISSION.asymmetrical wave A wave whose upper (positivehalf-cycle) and lower (negative half-cycle) portionshave different amplitudes or shapes. Alsocalled asymmetric wave.asymmetry control An adjustment in a device intendedfor measuring the pH (acidity/alkalinity).This corrects the inaccuracies that results fromthe differences between the electrodes.asymptote In analytical geometry, a fixed straightline or ray L with a special relationship to acurve or part of a curve K that recedes to infinity.As the distance from the origin (0,0) increaseswithout limit, the separation between Kand L approaches zero, but K and L never actuallymeet.asymptotic breakdown voltage A voltage that willcause dielectric breakdown if applied continuouslyfor a sufficiently long time.asymptotic expression An expression having avery small error in terms of percentage.asynchronous 1. Not synchronous, i.e., nonrecurrent(as in out-of-phase waves). 2. A mode ofcomputer operation in which the completion ofone operation starts another.asynchronous device A device not regulated bythe system in which it is used, as far as its operatingfrequency or rate is concerned.asynchronous input In digital circuitry, any flipflopinput at which a pulse can affect the outputindependently of the clock.asychronous motor An ac motor whose speed isnot proportional to the supply frequency.asynchronous transmission Data transmissionin which each character or symbol begins with astart signal and ends with a stop signal. Thiseliminates the need for the data to be sent at auniform speed.asynchronous vibrator In a vibrator-type portablepower supply, a vibrator that only makes andbreaks the primary circuit of the step-up transformer.This is in contrast to the synchronous vibrator,which also makes and breaks thesecondary circuit in synchronism with the primary.Also called NONSYNCHRONOUS VIBRA-TOR.AT A quartz crystal cut wherein the angle betweenthe x-axis and the crystal face is 35 degrees.At Symbol for astatine.AT-cut crystal A piezoelectric crystal cut at a 35-degree angle, with respect to the optical axis ofthe quartz. The frequency of such a crystal doesnot appreciably change with variations in temperature.atmosphere 1. The gas surrounding a planet, particularlythe air sheathing the earth. 2. Abbreviation,atm. A unit of pressure equal to 1.013 × 10 6dynes per square centimeter (about 14.7 poundsper square inch).atmospheric absorption 1. The conversion ofelectromagnetic energy into heat, with resultingloss, as the energy passes through the earth’s atmosphere.The extent of this effect depends onthe wavelength. 2. See ABSORPTION LOSS, 2.atmospheric absorption noise Noise, principallyabove 1 GHz, resulting from atmospheric absorption(see ABSORPTION LOSS, 2).

44 atmospheric bending • atomic radiationatmospheric bending The refraction or reflectionof electromagnetic waves by the troposphere orionosphere. See ATMOSPHERIC REFLECTION.atmospheric duct A tropospheric stratum, oftenassociated with temperature inversions, lake effects,or weather fronts, through which electromagneticenergy at ultra-high and microwavefrequencies is efficiently propagated for long distances.atmospheric electricity Static electricity presentin the atmosphere, which evidences itself in disturbanceof radio communications and in displaysof lightning.atmospheric noise Receiver noise resulting fromATMOSPHERIC ELECTRICITY. Also called sfericsor static.atmospheric pressure Abbreviation, atm press. 1.The pressure exerted by the earth’s atmosphere,as indicated by a barometer at sea level; normallybetween 29 and 31 inches of mercury. 2. A pressureof 1.013 × 10 6 dynes per square centimeter.See ATMOSPHERE, 2.atmospheric radio wave See SKYWAVE.atmospheric radio window The band of frequencies(approximately 10 MHz to 10 GHz), includingradio waves that can penetrate the earth’s troposphereand ionosphere.atmospheric reflection The return of a radio waveto earth, resulting from reflection by an ionizedportion of the atmosphere.atmospheric refraction 1. Downward bending ofradio waves as a result of variations in the dielectricconstant of the troposphere. 2. Downwardbending of radio waves in the ionosphere, resultingin long-range propagation at high frequencies.atmospheric scatter 1. The scattering of very-highfrequency ( VHF) and ultra-high frequency (UHF)radio waves by the lower atmosphere. 2. Communicationvia scattering of VHF and UHF radiowaves in the lower atmosphere.atmospherics See ATMOSPHERIC NOISE.atom 1. The smallest material particle that displaysthe unique characteristics and properties ofan element. Atoms consist of a dense, positivelycharged central nucleus, around which less-massive,negatively charged electrons “swarm” at definitelevels called shells. Also see BOHR ATOMand RUTHERFORD ATOM. 2. In a computercompilingoperation, an operator or operand.atomechanics The physics of electron movement.atomic battery A battery in which atomic energy isconverted into electrical energy.atomic charge The electrification (i.e., the electroncharge) exhibited by an ion.atomic clock Also called atomic time standard. Ahighly accurate electronic clock, driven by thecharacteristic oscillations of certain atoms.atomic energy Energy released by the FUSION orFISSION of atomic nuclei. Also see ATOMICPOWER.atomic fission See FISSION.atomic frequency The natural vibration frequencyof an atom.atomic fusion See FUSION.atomic pile See REACTOR, 2.atomic mass unit Abbreviated amu. A unit thatexpresses the relative mass of an elemental isotope.One amu is equal to 1⁄12 of the atomic massof carbon 12 (C12). A neutron has a mass ofroughly one amu.atomic migration The transfer or “wandering” of avalence electron between or among atoms in asingle molecule.atomic number The number of protons in the nucleusof an atom. Also, the number of electrons ifthe atom is electrically neutral. For example, theatomic number for copper is 29, indicating 29protons in the nucleus. An electrically neutralatom of copper has 29 electrons. The atomicnumber uniquely identifies an element.atomic radiation The emission of radiant energyby radioactive substances.

atomic reactor • attracted-disk electrometer 45atomic reactor See REACTOR, 2.atomic theory The scientific theory that all matter iscomposed ultimately of atoms, which are the smallestparticles retaining the identity of an element.Atoms combine to form molecules, the smallestparticles that retain the identity of a compound.Atoms themselves contain minute subatomic particles,some of which carry electric charges. SeeBOHR ATOM and RUTHERFORD ATOM.atomic time 1. A means of time determinationthat makes use of the resonant vibrations of certainsubstances, such as cesium. 2. Synchronizedastronomical time, as determined by anATOMIC CLOCK.atomic unit of energy In a hydrogen atom, the potentialenergy of the electron in the lowest-energyshell, as averaged over a certain length of time.The shell represents the mean energy of the electron.atomic weight 1. The mass of a particular atom inATOMIC MASS UNITS (amu). 2. A number characterizingthe average mass of individual atomsfor a specific isotope of an element. Thus, carbon12 (C12) has an atomic weight of 12, oxygen 16(O16) has an atomic weight of approximately 16,and uranium 238 (U238) has an atomic weight ofabout 238.atomistics The science of the atom and atomic energy.Also called atomics.attack 1. The rise of a pulse from zero to maximumamplitude. 2. The time required for a pulse to risefrom zero to maximum amplitude. 3. The initializationof a circuit voltage or current for a certainpurpose, such as an automatic gain control. 4.The rise of a musical note from zero to full volume.attenuate To reduce in amplitude.attenuation A reduction of signal amplitude.attenuation characteristic Also called attenuationconstant. 1. In an amplifier, network, or component,the decrease in signal amplitude as afunction of frequency, usually expressed in decibelsper octave. 2. In a transmission line, the decreasein signal amplitude per unit length.Usually expressed in decibels per 100 feet, decibelsper mile, or decibels per kilometer.attenuation constant See ATTENUATIONCHARACTERISTIC.attenuation distortion A type of distortion characterizedby variation of attenuation with frequencywithin a given frequency range.attenuation equalizer An equalizer that stabilizesthe transfer impedance between two ports at allfrequencies within a specified frequency band.attenuation-frequency distortion Distortioncharacterized by the attenuation of the frequencycomponents in a complex waveform. FrequencysensitiveRC networks (such as a Wien bridge) exhibitthis type of distortion when they attenuate afundamental and each harmonic unequally.attenuation network A combination of components(R, C, or L singly or in any necessarycombination) that provide constant signalattenuation with negligible phase shift throughouta frequency band.attenuation ratio The ratio indicating a relativecurrent, voltage, power or energy decrease. Forexample, for voltage, E input /E output = 6/2 = 3:1 = 3.attenuator A device for reducing signal amplitudein precise, predetermined steps, or smoothly overa continuous range. A network of resistors, capacitors,or both. The simplest attenuator consistsof one or more noninductive resistors.attack time The time required for an applied signalthat suddenly increases in amplitude to reach63.2 percent of its final, stable value.attemperator An automatic temperature-controllingdevice; a thermostat.attention display A computer-generated chart orgraph, displayed as an alert signal concerning aparticular situation.attitude The position of an aircraft or space vehiclerelative to a (usually terrestrial) reference point,often determined with electronic instruments.atto- Abbreviated, a. A prefix meaning 10 –18 ormultiplication by 10 –18 .attofarad Abbreviation, aF. An extremely smallunit of low capacitance; 1 aF equals 10 –18 F.attracted-disk electrometer A device to measurepotential difference consisting of two parallelmetal disks—one of which is connected to a tensionspring. The force between the disks indicatesthe magnitude of the electric field.

46 attraction • audio-frequency filterattraction The drawing together or pulling toward,as in the attraction between electric charges ormagnetic poles. Dissimilar charges and poles attracteach other (electric plus to minus, magneticnorth to south). Compare REPULSION.ATV Abbreviation of amateur television, used in theAmateur Radio Service.AU Abbreviation of ASTRONOMICAL UNIT.Au Symbol for GOLD.audibility The quality of being detectable by thehuman ear. In a healthy listener, the threshold ofaudibility is extremely low; at the threshold, thepressure of a sound wave varies from normal byapproximately 10 -4 pascal. The frequency rangeof human audibility extends roughly from 20 Hzto 20 kHz.frequency section). 3. A radio channel of fixed frequencythat is reserved for voice communications.audio clipping Brute-force limiting of the amplitudeof an audio signal, usually accomplished usingsemiconductor diodes to prevent the positiveand negative peak amplitudes from exceeding acertain level.SoundAudibility (dB)Threshold of hearing 0Whisper 10–20Electric fan at 10 feet 30–40Running water at 10 feet 40–60Speech at 5 feet 60–70Vacuum cleaner at 10 feet 70–80Passing train at 50 feet 80–90Jet at 1000 feet altitude 90–100Rock band on stage 110–120Air hammer at 5 feet 130–140audibility tableaudibility curve A graph (such as the Fletcher-Munson curve) that depicts the range of humanhearing in terms of frequency versus the soundpressure at the threshold of AUDIBILITY.audible Detectable by the human ear.audible alarm device An ANNUNCIATOR thatproduces an easily identifiable sound in responseto an ALARM CONDITION in a securitysystem.audible frequency See AUDIO FREQUENCY.audible tone A vibration of air molecules that canbe detected by the human ear, and with periodicproperties, such as a sine-wave vibration.audio 1. Pertaining to the spectrum of frequenciescorresponding to the human hearing range(about 20 Hz to 20 kHz), or to equipment or performanceassociated with that spectrum. 2. Anydisturbance, such as a current or compressionwave, falling within the range of about 20 Hz to20 kHz. 3. AUDIO FREQUENCY.audio amplifier See AUDIO-FREQUENCY AMPLI-FIER.audio band The range (band) of audio frequencies.audio channel 1. The portion of a complex signalor waveform used to convey audio information exclusively.2. The audio-frequency section of atransmitter or receiver (as opposed to the radioaudiocomponent The audio-frequency portion ofany wave or signal.audio converter A circuit in which a received radio-frequency(RF) signal is heterodyned with alocal RF oscillator signal to produce an audiofrequency(AF) beat-note output. The beat note isthen amplified by an AF amplifier. It is used especiallyby amateur radio operators in the receptionof continuous-wave (CW) radiotelegraphy,radioteletype, and packet radio at high frequencies.audio frequency A frequency lying within the audiblespectrum. Abbreviated AF. See AUDIO-FREQUENCY SPECTRUM.audio-frequency amplifier An amplifier that operatesin part or all of the frequency range 20 Hz to20 kHz. High-fidelity amplifiers function over asomewhat wider range (e.g., 10 Hz to 50 kHz).audio-frequency choke An inductor (usually havinga ferromagnetic core) that blocks audio-frequencycurrent, but passes direct current.audio-frequency feedback 1. Electrical FEED-BACK (positive and/or negative) that affects audiofrequencycircuits. 2. ACOUSTIC FEEDBACK.audio-frequency filter A filter of any type that operateson any part of the frequency range 20 Hz to20 kHz.

audio-frequency meter • audio mixer 47audio-frequency meter An instrument to measurefrequencies in the audio-frequency spectrum (approximately20 Hz to 20 kHz). Three types arecommonly used:• Analog Gives direct indications of frequency onthe scale of a D’Arsonval meter; the usual rangeis 20 Hz to 100 kHz.• Digital Gives direct indications of frequency bymeans of readout lamps; the usual range is 1 Hzto 15 MHz. This instrument is useful also as aradio-frequency meter.• Bridge Consists of a frequency-sensitive bridge,such as a Wien bridge, with a null-indicatingmeter. The operator balances the bridge andreads the unknown frequency from the dial ofthe balance control.audio-frequency noise Any electrical noise signalcausing interference within the audio-frequencyspectrum.audio-frequency oscillator See AUDIO OSCILLA-TOR.audio-frequency peak limiter Any circuit or device,such as a biased diode, that performs thefunction of audio limiting.audio-frequency-shift keying Abbreviation, AFSK.Frequency-shift keying that is done at audiofrequencies (below approximately 20 kHz) ratherthan at radio frequencies. There are two audiosine-wave signals, one for logic 1 (high or mark)pulses and the other for the logic 0 (low or space)pulses. This scheme is commonly used withtelephone modems where the signal bandwidth isseverely limited by circuit characteristics. Attypical data speeds in twisted-pair telephonelines (usually 28.8 or 57.6 kbps), signals of thistype sound like a hiss or roar. CompareFREQUENCY-SHIFT KEYING.audio-frequency-shift modulator A modulator foraudio-frequency-shift keying of a signal.audio-frequency spectrum The band of frequenciesextending from roughly 20 Hz to 20 kHz.High-fidelity component specifications extendthis range somewhat in both directions (e.g., from10 Hz to 50 kHz).audio-frequency transformer Abbreviation, AFtransformer. A device used for the purpose ofmatching impedances at frequencies within therange of human hearing (up to approximately 20kHz). This ensures the most efficient possibletransfer of power between stages of audio amplification,between an amplifier and a speaker orheadset, or between a microphone and an audiopreamplifier. These transformers are availablewith various power ratings and impedancematchingratios. Some devices are tailored tohave a certain attenuation-versus-frequency response.At audio frequencies, transformers arephysically similar to the alternating-currenttransformers used in power supplies. They arewound on laminated or powdered-iron cores.Compare RADIO-FREQUENCY TRANSFORMER.audio-frequency transistor A transistor that isusually used only at audio frequencies.audiogram A graph used to rate hearing, used byaudiologists and audiometrists.audio image In a direct-conversion receiver, a responseto a signal on one side of (above or below)the local-oscillator (LO) frequency, when the operatoris listening to a signal on the other side ofthe LO frequency. These responses are reducedor eliminated in single-signal receivers.audio-level meter An ac meter for monitoring signalamplitude in an audio-frequency system. Itcan indicate in volts, decibels, volume units (VU),or arbitrary units, and is often permanently connectedin the circuit.audio limiter A limiter or clipper operated in theaudio-frequency (AF) channel of a receiver ortransmitter to hold the output-signal amplitudeconstant, or to minimize the effect of noise peaks.audiologist A person skilled in testing hearing (i.e.,in using audiometers and other electronic instruments)and evaluating their indications for thefitting of hearing aids.audiometer An instrument used for hearing tests,which consists of a specialized audio-frequency(AF) amplifier with calibrated attenuators, outputmeter, and signal source.audiometrist A person skilled in the use of audiometersand other electronic instruments thatmeasure sound and human hearing, and whodeals with attendant health and behavior problems.Compare ACOUSTICIAN and AUDIOLOGIST.audio mixer An amplifier circuit for blending twoor more audio-frequency (AF) signals, such asthose delivered by microphones or receivers.

48 audio oscillator • auroral propagationaudio oscillator 1. An oscillator that delivers anoutput signal in the frequency range 20 Hz to 20kHz. 2. An audio-frequency (AF) signal generator.Some instruments of this type operate above andbelow the limits of the common audio-frequencyspectrum (e.g., 1 Hz to 1 MHz).audio output The output of an audio-frequencyoscillator or amplifier. It can be measured interms of peak or rms volts, amperes, or watts.audiophile A sound-reproduction hobbyist.audio power Alternating-current power at frequenciesroughly between 20 Hz and 20 kHz. Whenused in connection with transmitters and othermodulated radio-frequency (RF) equipment, theterm refers to modulator power output.audio response unit A device that links digitizedresponses, held in computer storage, to a telephoneset or line to answer incoming calls and inquiries.audio signal generator See AUDIO OSCILLA-TOR, 2.audio spectrum The range of sine-wave frequenciesdetectable by the human ear when they occuras acoustic vibrations. This range is about 20Hz to 20 kHz.audio squelch A squelch circuit that operates onlyon the audio channel of a receiver.audio system 1. The portion of any electronic assemblythat is used to process sound. 2. Specialcomputer equipment capable of storing and processingdigitized audio-frequency (AF) data.audiotape Magnetic tape for the recording and reproductionof data in the audio-frequency (AF)range.audio taper In potentiometers, a semilogarithmicvariation of resistance versus rotation. Used involume and tone controls for audio circuits. Atmidposition (the halfway point), the counterclockwiseportion of the device has about 1⁄10 theresistance of the clockwise portion. A listener willhear sound at half-volume because of the logarithmicnature of the human audibility curve.audio-visual Pertaining to a combination of soundand sight (e.g., television and sound motion pictures).auditory backward inhibition A subjective phenomenon,in which a sound is erased from thememory of a listener by a second sound arrivingabout 60 milliseconds later.auditory inhibition The tendency of sound wavesto be partially or totally canceled by theears/mind of a listener, depending on the waves’intensity, relative phase, and/or direction of impact.auditory mirage See ACOUSTIC MIRAGE.audit trail A history of the processes relating to arecord, transaction, or file in a computer system.Created during the routine processing of data,the trail is stored as a file. The audit trail allowsauditing of the system or the subsequent recreationof files.augend In a calculation, the number to which anotheris to be added. Compare ADDEND.augend register In a digital computer, the registerthat stores the augend. Compare ADDEND REG-ISTER.aural Pertaining to sound actually heard, as opposedto sound that exists only as audiofrequencycurrents or waves.aurora A phenomenon sometimes called the northernlights or southern lights, as seen in the nightsky. In the Northern Hemisphere, it is known asAurora Borealis; in the Southern Hemisphere, itis called Aurora Australis. It generally occurs afew hours after a solar flare, when charged particles,emitted from the sun, arrive at the earth,and are accelerated in the vicinity of the the geomagneticpoles.auroral absorption Radio wave absorption by anaurora.auroral flutter Rapid fading of a signal at high orvery high frequencies, so-called because it oftenimparts a fluttering quality to the signal that iscaused by phase distortion and Doppler shiftwhen the waves are reflected from the aurora.auroral interference 1. Interference to highfrequencyradio propagation and also occasionallyto medium-frequency and low-frequencypropagation, caused by the activity of the aurora.2. Auroral flutter on a signal.auroral opening A condition in which radio communicationbecomes possible via AURORALPROPAGATION. It can occur when communicationbetween two points is normally impossible ata certain frequency. Auroral openings allow longdistancecommunication well into the very-highfrequency(VHF) spectrum.auroral propagation Reflection of radio signalsfrom aurora that occur during geomagneticstorms. Theoretically, auroral propagation is possiblewhen the aurora are active, between any twopoints on the earth’s surface from which the samepart of the aurora lie on a line of sight. This typeof propagation seldom occurs when one end of the

50 automatic chrominance control • automatic interceptgain of the chrominance bandpass amplifier byautomatically adjusting its bias.automatic circuit breaker Any device that opensa circuit automatically when the flow of currentbecomes excessive. The breaker generally resetsautomatically after a specified length of time, orafter power has been temporarily removed fromthe circuit.automatic coding The use of a computer to determinethe steps for solving a problem, before theactual program for the problem is written. Thiscan help software engineers develop long and/orcomplex computer programs.automatic contrast control A circuit that automaticallyadjusts the gain of the video IF and RFstages of a television (TV) receiver to preservegood picture contrast.automatic controller In servo systems, any of severalcircuits or devices that samples a variablesignal, compares it with a standard (reference)signal, and delivers a control or correction signalto an actuator.automatic crossover 1. Current limiting in apower supply. 2. A device that switches a circuitfrom one operating mode to another automaticallywhen conditions change in a predeterminedmanner.automatic current limiter A circuit or device forholding the output current of a power supply to asafe value during overload.automatic current regulator A circuit or devicethat holds the output current of a generator orpower supply to a predetermined value, in spite ofwide variations in load resistance.automatic cutout A device that shuts down a circuitor system when the safe limits of operationare exceeded. A circuit breaker is an example ofsuch a device, as is a thermostat in a power amplifier.automatic data processing Abbreviation, ADP.The use of computers and accessories for calculationsand tabulations using data gathered automaticallyby the system.automatic degausser A system for automaticallydemagnetizing the picture tube in a color television(TV) receiver.automatic dialing unit Abbreviated, ADU. A devicethat automatically generates dialing digits.Many telephone sets have these devices, some ofwhich can be programmed for several differenttelephone numbers, including country codes andarea codes.automatic dictionary A computer system componentthat substitutes codes for words andphrases in information retrieval systems. In language-translatingsystems, it provides wordfor-wordsubstitutions.automatic direction finder Abbreviated ADF. Aspecialized receiver/antenna combination for automaticallyshowing the direction from which asignal arrives.automatic error correction A technique of correctingtransmission errors using error-detectingand error-correcting codes and, usually, automaticretransmission.automatic exchange A transmission exchange inwhich interterminal communications are accomplishedwithout operators.automatic focusing A method of focusing a picturetube automatically, in which a resistor connectsthe focusing anode to the cathode; thus, noexternal focusing voltage is necessary.automatic frequency control Abbreviation, AFC.A system that keeps a circuit automatically tunedto a desired signal frequency. A detector (such asa discriminator) operated from the tuned circuitdelivers a dc output voltage only when the circuitis operating above or below the signal frequency;otherwise, it has zero dc output. The dc output,when present, alters the capacitance of a varactorin the tuned circuit to retune the stage to the desiredfrequency.automatic gain control Abbreviated AGC. A systemthat holds the output of a receiver or amplifiersubstantially constant despite input-signalamplitude fluctuations. A rectifier samples the acsignal output and delivers a dc signal proportionalto that output. The dc signal is filtered, andthe smoothed-out voltage is applied in correct polarityas bias to one or more preceding stages toreduce their gain. The stronger the signal enteringthe system, the greater the reduction in gain.As a result, weak signals are amplified muchmore than strong ones. Various forms of thisscheme are used in many types of amplifiers andcommunications systems.automatic gate bias A method of obtaining gatebias in a FET, where a resistor develops a voltagedrop because of the current flowing throughit. The resistor is usually placed in the sourcecircuit, raising the source above ground potential.automatic height control In a television (TV) receiver,a system that automatically maintains theheight of the picture, despite signal-amplitudefluctuations, power-line voltage changes, andgain variations.automatic intercept A telephone answering machine.It allows messages to be recorded when thesubscriber is not able to answer the telephone.

auxiliary equipment • avalanche breakdown 53auxiliary equipment 1. Also known as peripherals.An apparatus not directly governed by thecentral processing unit of a digital computer,such as a printer or personal robot. 2. Peripheralequipment in any system. 3. Backup equipment.auxiliary memory In a digital computer, a unitthat is supplementary to the main memory,which it augments.auxiliary receiver Also called standby receiver. Ina radio communications system, a receiver that isavailable for use if the main receiver fails.auxiliary relay 1. A standby relay. 2. A relaywhose operation supports that of another relay.3. A relay that is actuated by the operation of anotherrelay.auxiliary switch 1. A standby switch. 2. A switchwired in series or parallel with another switch. 3.A switch that is operated by another switch.available gain The ratio P o /P i , where P i is the availablepower at the input of a circuit and P o is theavailable power at the output.available line The percentage of the length of a facsimilescanning line that is usable for picture signals.available power The mean square of the opencircuitterminal voltage of a linear source dividedby four, times the resistive component of thesource impedance. The available power is themaximum power delivered to a load impedance,equal to the conjugate of the internal impedanceof the power source.available power gain In a power transistor, the ratioof available transistor output power to thepower available from the generator. It depends onthe generator resistance, but not on the transistorload resistance.available signal-to-noise ratio The ratio P s /P n ,where P s is the available signal power at a givenpoint in a system and P n is the available randomnoisepower at that point.available time 1. The time during which a computeris available and ready for immediate use. 2.The amount of time a computer is available to anindividual.avalanche The phenomenon in semiconductorsoperated at high reverse bias voltage, wherebycarriers acquire sufficient energy to produce newelectron-hole pairs as they collide with atoms.The action causes the reverse current to increasesharply.avalanche breakdown In a semiconductor P-Njunction, a condition that occurs when the reversebias voltage exceeds a certain value. If theelectric field in the vicinity of the junction becomesstrong enough, charge carriers are dislodgedfrom the atoms and the carriers (electronsand holes) flow freely across the P-N junction inthe opposite direction from normal. The mini-auxiliary transmitter Also called standby transmitter.In a radio communications system, atransmitter that is available for use if the maintransmitter fails.a/v Abbreviation of AUDIO-VISUAL.aV Abbreviation of attovolt.availability The proportion of time during whichan apparatus is operating correctly. It is usuallygiven as a percentage.available conversion gain The ratio of the inputpower to the output power of a transducer or converter.It is generally given in decibels.

54 avalanche breakdown • AX.25mum reverse-bias voltage required to cause thisphenomenon varies among different kinds ofdiodes. Some diodes are manufactured to haveprecise avalanche voltages. See ZENER DIODE.avalanche conduction In a semiconductor junction,the enhanced reverse-bias conductioncaused by a condition of AVALANCHE.avalanche current The high current that flowsthrough a semiconductor junction whenAVALANCHE occurs.avalanche diode See ZENER DIODE.avalanche impedance The reduced impedance ofa diode during avalanche.avalanche noise Electrical noise generated in ajunction diode operated at the point at whichavalanche just begins.avalanche transistor A transistor that operates ata high value of reverse-bias voltage, causing thepn junction between the emitter and base to conductbecause of avalanche breakdown.avalanche voltage In a semiconductor P-N junction,the minimum applied reverse-bias voltagethat produces AVALANCHE BREAKDOWN.AVC Abbreviation of automatic volume control.avdp Abbreviation for Avoirdupois, a weightmeasurementscheme that is used in Englishspeakingcountries and is based on the pound.average absolute pulse amplitude The average(disregarding algebraic sign) of the absolute amplitudesof a pulse, taken over the duration of thepulse.average brightness The average brilliance of atelevision (TV) picture, cathode-ray-tube (CRT)computer display, or oscilloscope image.average calculating operation The operating timeconsidered typical for a computer calculation(i.e., one that is longer than an addition andshorter than a multiplication); it is frequentlytaken as the average of nine additions and onemultiplication.average current Abbreviation, I avg . The averagevalue of alternating current flowing in a circuit.Taking polarity into account, this value is zero fora pure sine wave. For other waveforms, it canvary. When polarity is not considered, the sinewavevalue of I avg is equal to 0.637 times I pk , thepeak value of current; I avg = 0.637 I pk .average life See MEAN LIFE.average noise figure The ratio of the total noiseoutput from a circuit to the thermal noise outputat 290 degrees Kelvin. It is usually expressed indecibels, with the noise taken at all frequencies.average power The average value of power in an accircuit. In a resistive circuit, it is the square of theeffective (rms) current times the resistance; P avg =(I rms ) 2 R (for sine waves).average pulse amplitude Also called effectivepulse amplitude. The value obtained by integratingthe pulse amplitude, with respect to time,from the start of the pulse to its end, then dividingthis integral by the pulse duration.average rectified current Abbreviation, I avg . Theaverage value of rectifier output current before filtering.For a full-wave rectifier with a sine waveinput and a resistive load, I avg is equal to the maximumcurrent I m multiplied by 0.637.average rectified voltage Abbreviation, E avg . Theaverage value of rectifier output voltage before filtering.For a full-wave rectifier with a sine-waveinput and a resistive load, E avg is maximum voltageE m multiplied by 0.637.average value 1. The arithmetic mean of two or morequantities. 2. The geometric mean of two ormore quantities. 3. The harmonic mean of twoor more quantities. 4. In ac operation, the averagecurrent, voltage, or power.average voltage Abbreviation, E avg . The averagevalue of ac voltage in a circuit. Taking polarity intoaccount, this value is zero for a pure sine wave.For other waveforms, it can vary. When polarity isnot considered, the sine-wave value of E avg is equalto 0.637 times E pk , the peak value of voltage.avg Abbreviation of average.aviation channels Frequency channels assignedto the AVIATION SERVICES.Aviation services The radio-communication servicesused by aeronautical-mobile and radio navigationpersonnel.avigation Acronym for aviation navigation. Aircraftnavigation by means of electronic equipment.avionics Acronym for aviation electronics. The design,production, and application of electronic devicesand systems for use in aviation, navigation,and astronautics.Avogadro’s constant (Amedeo Avogadro, 1776–1856.) Symbol, NA. The number of molecules in akilogram-molecular weight of any substance; NAequals 6.025 × 10 26 (kg-mole) –1 .A voltage The filament voltage in a vacuum-tubecircuit.aW Abbreviation of attowatt.AWG Abbreviation of AMERICAN WIRE GAUGE.AX.25 A signal format used in some digital communicationssystems, notably amateur packet radio.

axial leads • azusa 55axial leads The centrally located leads emanatingfrom the ends of cylindrical components, such asresistors and diodes.axial ratio The ratio of the minor to major axes of awaveguide’s polarization ellipse.axis 1. A coordinate in a graphical presentation ordisplay (e.g., horizontal and vertical axes in arectangular coordinate system). 2. The real orimaginary straight line around which a body rotates,or the line that passes through the centerof a symmetrical arrangement (line of symmetry).axis of abscissas The horizontal axis (x-axis) of arectangular-coordinate graph or screen. CompareAXIS OF ORDINATES.axis of imaginaries The vertical axis of the complexplane in which rectangular vectors lie. CompareAXIS OF REALS.axis of ordinates The vertical (y-axis) of a rectangular-coordinategraph or screen. Compare AXISOF ABSCISSAS.axis of reals The horizontal axis of the complexplane in which rectangular vectors lie. CompareAXIS OF IMAGINARIES.Ayrton-Mather galvanometer shunt A stepadjustableuniversal shunt resistor for varyingthe sensitivity of a galvanometer. It has the virtueof keeping the galvanometer critically damped.The shunt is also useful in multirangemilliammeters, microammeters, and ammeters.The sensitive meter movement is never without ashunting resistor during range switching.azel display A plan-position display that incorporatestwo different radar traces on a singlecathode-ray tube (CRT), one giving bearing, theother elevation.azimuth Also called compass direction. Angularmeasurement in the horizontal plane, clockwisefrom north. It is important in radio and televisioncommunications, navigation, direction finding,land surveying, and radar.Ayrton-Perry winding A noninductive windingcomprising two inductors conducting current inopposite directions; the opposing flow cancels themagnetic field.azimuth alignment In a tape recorder, the alignmentof record and playback head gaps so thattheir centerlines are parallel.azimuth blanking In a radar system, blacking-outof the image as the antenna sweeps across aspecified range of azimuth angles. Effectivelyeliminates nuisance echoes from stationary, permanentobjects (such as tall buildings or communicationstowers).azimuth resolution In a radar system, the minimumazimuth separation of two targets whoserange (distance from the station) are equal that isrequired for the system to show two echoes, ratherthan one. It is generally measured in degrees.azusa An electronic tracking system, in which asingle station provides slant range and two directioncosines for a distant airborne object. This accuratelydefines the coordinates of the distantobject in three-dimensional space.

B 1. Symbol for SUSCEPTANCE. 2. Symbol forFLUX DENSITY. 3. Abbreviation of BATTERY. 4.Symbol for BORON. 5. Symbol for base of transistor(see BASE, 1). 6. Abbreviation of BASS. 7.Abbreviation of BEL. 8. Anode voltage or main operatingvoltage in any circuit (when used withsign). Also see B VOLTAGE.b 1. Symbol for SUSCEPTANCE. 2. Symbol forbase of transistor (see BASE, 1). 3. Abbreviationof BASS. 4. Symbol for BARN.B&S See AMERICAN WIRE GAUGE.B5-cut crystal A piezoelectric plate cut from aquartz crystal in such a way that the face of theplate is at an angle, with respect to the z-axis ofthe crystal. This type of crystal has good frequencystability under conditions of changingtemperature.BA Abbreviation of BATTERY. Also see B and BAT.Ba Symbol for BARIUM.babbit A relatively soft, tin-base alloy of variouscompositions. One composition contains 7.4%antimony, 3.7% copper, and 88.9% tin.babble Interference caused by crosstalk from anumber of channels.babble signal A jamming signal containing babblecomponents. See BABBLE and JAMMING.BABS Abbreviation of BLIND-APPROACH BEACONSYSTEM.baby monitor A short-range radio transmitter andreceiver that can be used to listen at a distance tothe sounds in an infant’s room. The transmittercontains a sensitive microphone, a whip antenna,and a power supply. The unit can be placed on atable or desk, or even on the floor near the baby’scrib. The receiver is similar to a handheld“walkie-talkie.” It is battery-powered and can becarried around. It has an inductively loaded, short“rubber duckie” antenna similar to the antennason cordless telephone sets. The receiver can pickup signals from the transmitter at distances of upto about 200 feet. The radio-frequency signalspass easily through walls, ceilings, and floors.back bias 1. A feedback signal (negative or positive).2. Reverse bias (also see BIAS). 3. A reversebias voltage, obtained from a voltage divider connectedbetween a voltage source and ground.InR1R2B−back bias, 3B+R1, R2providebiasOutCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

ackbone • back resistance 57backbone A form of transmission line with capacitiveconnections between the generator and theload.back conduction Conduction of current in the reversedirection, as across a semiconductor junctionthat is reverse-biased.back contact A contact that closes a circuit when arelay, switch, or jack is in its normal rest position.back current Symbol, I b . The normally small currentflowing through a reverse-biased pn semiconductorjunction. Also called reverse current andinverse current. Compare FORWARD CURRENT.back diode A semiconductor diode that is normallyback-biased (reverse-biased).back echo An echo resulting from the rear lobe ofan antenna radiation pattern.back emf See BACK VOLTAGE.Back-Goudsmit effect See ZEEMAN EFFECT.background 1. The context or supporting area of apicture (e.g., the background of a television picture).2. Background noise.background control In a color television receiver,a potentiometer used to set the dc level of thecolor signal at one input of the three-gun picturetube.background count Residual response of a radioactivitycounter in an environment as free aspracticable of radioactivity. This background iscaused largely by cosmic rays and inherent radioactivityof surrounding buildings and otherbodies.background job A low-priority, relatively longrunningcomputer program that can be interruptedso that a higher-priority program can berun.background noise Electrical noise inherent to aparticular circuit, system, or device that remainswhen no other signal is present.background processing In a computer, the runningof programs having low priority.background radiation Nuclear radiation from materialsin the environment. Also see BACK-GROUND COUNT.background response The response of a radiationdetector to background radiation.backing store In a computer, a device that storeslarge amounts of information. In most small computers,this is done via MAGNETIC DISK and/orMAGNETIC TAPE. A backing store can also be anoptical storage medium, such as CD-ROM (compactdisk, read-only memory).backlash 1. Slack or lag in action of moving parts.Example: delay between initial application of aforce (such as that required to turn a knob) andmovement of a part or device (e.g., a potentiometeror variable capacitor). 2. On a mechanicalanalog tuning dial, an arc within which slack orlag is discernible.backloaded horn A loudspeaker enclosure inwhich the front of the speaker cone feeds sounddirectly into the listening area, and the rear of thecone feeds sound into the same area through afolded horn.backloading In a cascaded series of amplifiers, thetendency of loading effects to be passed to earlierstages. A change in the output impedance of a finalamplifier circuit, for example, could also resultin a change in the output impedance of thedriver circuit, and perhaps even in a change inthe output impedance of the predriver.back lobe In the pattern of a directional antenna,the lobe directly opposite the major lobe, representingthe radiation or response in or from a direction180 degrees from that in which the gain isgreatest.backplate A flat electrode in a television (TV) cameratube that receives the stored-charge image viacapacitive coupling.back porch In a television (TV) horizontal syncpulse, the time interval between the end of therise of the blanking pedestal and the beginning ofthe rise of the sync pulse. That portion of the flattop of the blanking pedestal behind the syncpulse. Compare FRONT PORCH.back-porch effect In transistor operation, the continuationof collector-current flow for a short timeafter the input signal has fallen to zero.back-porch tilt The departure of the top edge of aback porch from true horizontal.back pressure sensor A device that detects andmeasures the torque that a motor is applying,and produces a signal whose amplitude is proportionalto the torque. This signal can be usedfor various purposes. In a robotic device, for example,the sensor output can be fed back to themotor control to limit the applied force.back resistance Symbol, R b . The resistance of a reverse-biasedpn semiconductor junction. Alsocalled REVERSE RESISTANCE.

58 back scatter • bailback scatter Scattering of a wave back toward aradio transmitter from points beyond the skipzone. This phenomenon is caused by ionosphericreflection. Compare FORWARD SCATTER.backstop A contact or barrier (such as a screw orpost) that serves to limit the BACKSWING of thearmature of a relay.backswing 1. The tendency of a pulse to overshoot,or reverse direction after completion. Backswingis measured in terms of the overshoot amplitudeas a percentage of the maximum amplitude of thepulse. 2. The extent to which a relay armaturemoves back from a contact when the relay contactsare open.back-to-back connection The connection ofdiodes or rectifiers in reverse parallel (i.e., the anodeof one to the cathode of the other) across asignal line to pass both half cycles of ac in certaincontrol circuits.back-to-back sawtooth A symmetrical sawtoothwave in which the rise slope is equal to the fallslope. Also called triangular wave and pyramidalwave.backup 1. An element, such as a circuit component,that is used to replace a main component,in case of main-component failure. 2. Any processor scheme that serves to maintain operationof a system in case of main-componentfailure. 3. A battery that maintains volatilememory data stored in one or more integratedcircuits. 4. A computer file, or set of files, storedin a nonvolatile medium, such as diskettes ormagnetic tape, to prevent catastrophic data lossin the event of hard-disk failure. 5. A battery oralternative power source that keeps an alarmsystem operational in the event of a utility powerfailure.backup battery 1. In a computer or microcomputer-controlledelectronic device, a source ofvoltage to preserve volatile memory data if thepower is removed. 2. A battery used for poweringa system in the event that the main power sourceshould fail.backup facility In an electrical or communicationssystem, a facility that is intended for use whenthe primary, or main, facility is not operational.back voltage 1. Voltage induced in an inductor bythe flow of current through the inductor, so calledbecause its polarity is opposite to that of the appliedvoltage. Also called counter emf. 2. A voltageused to obtain bucking action (e.g., the voltageused to zero the meter in an electronic voltmetercircuit). 3. Reverse voltage applied to a semiconductorjunction.backwall In a pot core, the plate or disk that connectsthe sleeve and center post to close the magneticcircuit.backward diode A semiconductor diode manufacturedin such a way that its high-current flow occurswhen the junction is reverse biased. Such adiode is also a negative-resistance device.backward-wave oscillator Abbreviation, BWO. Amicrowave oscillator tube similar to the travelingwavetube. Like the traveling-wave tube, the BWOcontains a helical transmission line. In the electronbeam, electron bunching results from interactionbetween the beam and the electromagneticfield, and reflection occurs at the collector. Thewave moves backward from collector to cathode,and oscillation is sustained because the backwardwave is in phase with the input. Output istaken from the cathode end of the helix.ElectrongunOutputbackward-wave oscillatorCollectorHelical lineback wave The oscillator signal present in an amplifier-keyed,continuous-wave (CW), Morse-codetransmitter. Normally, this signal is at the samefrequency as the transmitter output, but is notsufficiently strong to be radiated over the air.back-wave radiation The condition wherein a backwave is strong enough to be heard on a continuous-wave(CW) keyed signal at the receiving station.This results from ineffective amplifier keying.baffle A board on which a loudspeaker is mountedto separate acoustic radiation from the back ofthe cone from radiation emanating from the front.The baffle improves bass response by increasingthe wavelength (lowering the frequency) at whichphase cancellation occurs.baffle plate 1. See BAFFLE. 2. A metal platemounted in a waveguide to reduce the crosssectionalarea.bail A wire loop or chain that holds one member ofa two-member assembly to prevent loss (e.g., theshort chain holding the dust cap of a jack).

Bakelite • balanced low-pass filter 59Bakelite The trade name for a specialized plasticdielectric material. Its chemical composition isphenol-formaldehyde resin.baker An obsolete phonetic alphabet code word forletter B. BRAVO is commonly used instead.baking-out In the process of evacuating a system,the procedure of heating the system to a hightemperature to drive out gases occluded in theglass and metal parts.balance1. See BRIDGE. 2. To null a bridge or similarcircuit. 3. To equalize loads, voltages, or signalsbetween two circuits or components. 4. In ahigh-fidelity stereo sound system, a control or setof controls that adjusts the relative loudness ofthe left and right channels. 5. Alignment of a balancedmodulator for minimum carrier output amplitude.6. A condition in which two branches of acircuit have identical impedances, relative toground.balance coil 1. A type of autotransformer that enablesa three-wire ac circuit to be supplied from atwo-wire line. A series of taps around the center ofthe winding enables the circuit to be compensatedfor unequal loads. 2. See BALANCING COIL.balance control A variable component, such as apotentiometer or variable capacitor, that is usedto balance bridges, null circuits, or loudspeakers.balanced Having identical impedances, with respectto ground.balanced amplifier Any amplifier with twobranches that have identical impedances, withrespect to ground. Usually, the two branches arein phase opposition (180 degrees out of phase).balanced antenna An antenna system where twohalves are exact replicas of each other, geometricallyand electrically. Such an antenna normallymust either be fed with a balanced transmissionline or with a coaxial cable and balun.balanced antenna system A balanced antenna, fedwith a balanced transmission line, that has currentsof equal magnitude in each side. An example90°XmtrCenter-fedhorizontalradiatorbalanced antenna systemTwo-wirefeed lineis a half-wave dipole at uniform height above electricalground, fed at the center with parallel-wireline. It is important that the transmission lineruns away from the antenna at a right angle for atleast 1 ⁄4 wavelength, preferably 1 ⁄2 wavelength ormore, to prevent line imbalance caused by currentsinduced from the radiated field.balanced bridge Any four-leg bridge circuit inwhich all legs are identical in all electrical respects.balanced circuit 1. A circuit that has its electricalmidpoint grounded, as opposed to the singleendedcircuit, which has one side grounded. 2. Abridge circuit in the condition of null.balanced converter See BALUN.balanced currents Currents with the same value.In the two conductors of a balanced transmissionline, these currents are equal in amplitudeand opposite in phase at every point along theline.balanced delta A set of coils or generators in athree-phase system, connected so that the currentsin any two coils differ in phase by 120 degrees.balanced detector A symmetrical demodulator,such as a full-wave diode detector or a discriminator.balanced electronic voltmeter An electronic voltmetercircuit in which two matched transistorsare connected in a four-arm bridge arrangement.The drift in one half of the circuit opposes that inthe other half; the resulting drift of the zero pointis virtually eliminated.balanced filter A filter consisting of two identicalsections, one in each branch of a balanced system,such as a parallel-wire transmission line.balanced input An input circuit whose electricalmidpoint is grounded. Compare SINGLE-ENDEDINPUT.balanced input transformer An input transformerin which the center tap of the primary winding isgrounded.balanced line A pair of parallel wires that possessesa uniform characteristic impedance. Thetwo conductors are of the same material and haveidentical diameters. The distance between themis constant. In a balanced two-wire line, the currentsin the two conductors are of equal amplitudeand opposite phase.balanced lines In high-fidelity audio systems, acable that consists of two parallel conductorssurrounded by a single braid. The parallel wirescarry the audio-frequency (AF) signals, and thebraid is grounded for shielding.balanced loop antenna A loop antenna with agrounded electrical midpoint, determined by thejunction of two identical series-connected capacitorsshunting the loop.balanced low-pass filter A low-pass filter used ina balanced system or balanced transmissionline.

alun • bandstop 61usually providing a 1:1 or 1:4 impedance ratioand available in several different forms. It is socalled because it has an unbalanced input suitablefor coaxial transmission lines, and a balancedoutput suitable for dipole, Yagi, and quadantennas.banana jack The female half of a two-part quickconnectorcombination. Splicing of a circuit iscompleted by inserting a BANANA PLUG into thisjack.banana plug The male half of a two-part quickconnectorcombination, with sides usually composedof flat springs that ensure contact with thefemale BANANA JACK into which it is inserted.banana jack and plugband 1. A continuous range of radio or televisioncommunications frequencies or wavelengths,usually designated by the lowest and highest frequencies,or the approximate wavelength (e.g.,the 20-meter amateur radio band). 2. A set of discreteradio or television frequency channelswithin a specified range (e.g., the standard AMbroadcast band). 3. A range of wavelengths for infrared,visible, ultraviolet, X-ray, or gamma-rayenergy. 4. A range of energy levels. 5. A coloredstripe on a resistor or capacitor that forms part ofthe code that indicates component value and tolerance.band center 1. In a given radio or television communicationsband, the arithmetic mean of thelowest and highest frequencies. 2. In a givenband, the geometric mean of the longest andshortest wavelengths.band-elimination filter See BAND-REJECTIONFILTER.band gap In any atom, the difference in electron energybetween the conduction and valence bands.bandpass 1. The frequency limits between which aBANDPASS FILTER or BANDPASS AMPLIFIERtransmits ac energy with negligible loss. 2. Theability to allow passage of signals at a given frequencyor band of frequencies while blockingother signals. Compare BANDSTOP.bandpass amplifier An amplifier that is tuned topass only those frequencies between preset limits.bandpass coupling A coupling circuit with a flattoppedfrequency response so that a band of frequencies,rather than a single frequency, iscoupled into a succeeding circuit. Also see BAND-PASS, 1.bandpass filter Any resonant circuit, or combinationof resonant circuits, designed to discriminateagainst all frequencies except a specific frequencyf 0 , or a band of frequencies between two limitingfrequencies f 0 and f 1 . In a parallel inductancecapacitance(LC) circuit, the device exhibits highimpedance at the desired frequency or frequenciesand a low impedance at unwanted frequencies.In a series configuration, the filter has a lowimpedance at the desired frequency or frequenciesand a high impedance at unwanted frequencies.Compare BAND-REJECTION FILTER,HIGH-PASS FILTER, LOW-PASS FILTER.bandpass flatness The degree to which a bandpassdevice’s attenuation-versus-frequency curve is astraight line with zero slope within the passband.band pressure level The net acoustic pressure of asound source within a specified frequency range(band).band-rejection filter Also called a band-stop filter.Any resonant circuit, or combination of resonantcircuits designed to discriminate against a specificfrequency f 0 , or a band of frequencies betweentwo limiting frequencies f 0 and f 1 . In aparallel inductance-capacitance (LC) circuit, thedevice exhibits high impedance at the desired frequencies,and a low impedance at the unwantedfrequency or range of frequencies. In a series configuration,the filter has a low impedance at thedesired frequencies and a high impedance at theunwanted frequency or range of frequencies.Compare BANDPASS FILTER, HIGH-PASS FIL-TER, LOW-PASS FILTER, NOTCH FILTER.band selector Any switch or relay that facilitatesswitching the frequency of a radio transmitter, receiver,or transceiver among various bands.bandset capacitor In some older communicationsreceivers, a variable capacitor is used to presetthe tuning range in each band to correspond tograduations on the tuning dial. This capacitor isa trimmer or padder operated in conjunction withthe main tuning capacitor.bandspreading In some older communications receivers,the process of widening the tuning rangewithin a given frequency band to cover the entiredial. Otherwise, the band would occupy only aportion of the dial, and tuning would be difficult.It is usually accomplished with a BANDSPREADTUNING CONTROL whose range is preset via themain tuning control and/or a BANDSET CAPAC-ITOR.bandspread tuning control An analog adjustmentin some older communications receivers that allowscontinuous tuning over a desired band offrequencies. This control is separate from themain tuning control.bandstop 1. The frequency limits between which aBAND-REJECTION FILTER blocks, or greatlyattenuates, ac energy. 2. The ability to suppressor block signals of a given frequency or bandof frequencies, while allowing signals of otherfrequencies to pass with little or no attenuation.Compare BANDPASS.

62 bandstop filter • bar meterbandstop filter See BAND-REJECTION FILTER.band suppression 1. The property of blocking, orgreatly attenuating, signals within a specific frequencyband. 2. The frequency limits betweenwhich a device or circuit rejects or blocks ac energy,while passing energy at other frequencieswith negligible loss.band-suppression filter See BAND-REJECTIONFILTER.bandswitch A low-reactance selector switch (usuallyrotary) that facilitates changing the tuning range ofa radio receiver, transmitter or transceiver fromone band of frequencies to another.bandswitching In a receiver, transmitter, or testinstrument, the process of switching selfcontainedtuned circuits to change from one frequencyspectrum to another within the range ofthe device’s intended operation.bandwidth 1. For a communications or data signal,a measure of the amount of spectrum spacethe signal occupies. Usually, it is given as the differencebetween the frequencies at which the signalamplitude is nominally 3 dB down withrespect to the amplitude at the center frequency.These frequencies represent the half-powerpoints of the amplitude-versus-frequency function.In general, the bandwidth increases as thedata rate (in bits per second, baud, or words perminute) increases. 2. Also called NECESSARYBANDWIDTH. The minimum amount of spectrumspace normally required for effective transmissionand reception of a communications or datasignal. 3. See BANDPASS, 1.bank A collection of usually similar componentsused in conjunction with each other, usually in aparallel configuration. Some examples are resistorbank, lamp bank, and transformer bank.banked transformers Parallel-operated transformers.bankwound coil A coil wound in such a way thatmost of its turns are not side by side, thus reducingthe inherent distributed capacitance.bar 1. Abbreviation, b. The cgs unit of pressure, inwhich 1 b = 10 5 pascals per square centimeter. 2.A horizontal or vertical line produced on a television(TV) screen by a bar generator and used tocheck linearity. 3. A thick plate of piezoelectriccrystal. 4. A solid metal conductor, usually uninsulated,of any cross section. 5. A silicon ingotfrom which semiconductor devices can be fabricated.BAR Abbreviation of BUFFER ADDRESS REGIS-TER.bar code A printed pattern that contains data thatcan be recovered by laser scanning. It is commonlyused for the pricing and identification ofstore merchandise. It can also be used by an assemblyor maintenance robot as an aid to identifyingtools.bar-code reader A laser scanning device that recoversthe data from a tag that contains a BARCODE. The laser beam moves across the tag. Thebeam is reflected from the white regions betweenthe lines, but is absorbed by the dark lines themselves.This produces modulation of the reflectedbeam by the data contained in the tag.bare conductor A conductor with no insulating covering,a common example being bare copper wire.bar generator A special type of radio-frequencysignal generator that produces horizontal or verticalbars on the screen of a television receiver. Itis used in adjustment of horizontal and verticallinearity.bar graph A graphical presentation of data, inwhich numerical values are represented by horizontalbars of width that correspond to the values.This type of graph is nonstandard in thesense that the ordinate is horizontal, whereas it isusually vertical. Compare COLUMNAR GRAPH.bar-graph meter See BAR METER.bariumSymbol, Ba. An elemental metal of the alkaline-earthgroup. Atomic number, 56. Atomicweight, 137.36. It is present in some compoundsused as dielectrics (e.g., barium titanate).barium-strontium oxides The combined oxides ofbarium and strontium used as coatings ofvacuum-tube cathodes to increase electron emissionat relatively low temperatures.barium strontium titanate A compound of barium,strontium, oxygen, and titanium that isused as a ceramic dielectric material. It exhibitsferroelectric properties and is characterized by ahigh dielectric constant.barium titanate Formula, BaTi0 2 . A ceramic usedas the dielectric in ceramic capacitors. It exhibitshigh dielectric constant and some degree of ferroelectricity.Barkhausen effect The occurrence of minutejumps in the magnetization of a ferromagneticsubstance as the magnetic force is increased ordecreased over a continuous range.Barkhausen interference Interference that resultsfrom oscillation because of the BARK-HAUSENEFFECT.bar magnet A relatively long permanent magnet inthe shape of a bar with a rectangular or squarecross section.bar meter A digital meter that displays a quantity,such as signal strength, incrementally, usinga set of LEDs or LCDs arranged in a straightline. Its main advantage is that it has no movingparts, yet (unlike direct-readout digital meters)gives the viewer some impression of the way arapidly fluctuating quantity changes. Its chief

ar meter • baseband frequency response 63disadvantage is that it does not provide a preciseindication.barn Symbol, b. A non-SI unit of nuclear cross sectionequal to 100 square femtometers or 10 – 24square centimeters. This unit is approved ascompatible with SI (International System ofUnits).Barnett effect The development of a small amountof magnetization in a long iron cylinder that is rotatedrapidly about its longitudinal axis.barograph A recording barometer, using either adrum recorder (pen recorder) or a computer tostore the data as a function of atmospheric pressureversus time.barometer An instrument for measuring atmosphericpressure.barometer effect A relation that appears to existbetween the intensity of cosmic rays and the atmosphericpressure. It is an inverse relation; thatis, increasing pressure seems to correlate with reducedintensity of cosmic rays. It is said to be approximatelyto 1 or 2% per centimeter of mercury.barometric pressure The atmospheric pressure,usually given in inches of mercury. The averagebarometric pressure at the surface of the earth isjust under 30 inches of mercury.bar pattern A series of spaced lines or bars (horizontal,vertical, or both) produced on a televisionpicture screen by means of a BAR GENERATOR.It is useful in adjusting horizontal and verticallinearity of the picture.barrage array An antenna array in which a stringof collinear elements are vertically stacked. Theend quarter wavelength of each string is bent into meet the end quarter wavelength of the oppositeradiator to improve balance.barrage jamming The jamming of many frequencies,or an entire band, at the same time.barrell distortion Television picture distortionconsisting of horizontal and vertical bulging.barrier 1. The carrier-free space-charge region in asemiconductor pn junction. 2. An insulating partitionplaced between two conductors or terminalsto lengthen the dielectric path.barrier balance The state of near equilibrium in asemiconductor pn junction (after initial junctionforming), entailing a balance of majority and minoritycharge carrier currents.barrier capacitance 1. The capacitance in a bipolartransistor between the emitter and collector. Itvaries with changes in applied voltage, and alsowith the junction temperature. 2. The capacitanceacross any pn junction that is reverse-biased.barrier height The difference in voltage betweenopposite sides of a barrier in a semiconductormaterial.barrier layer See BARRIER, 1.barrier-layer cell A photovoltaic cell, such as thecopper oxide or selenium type, in which photonsstriking the barrier layer produce the potentialdifference.barrier potential The apparent internal dc potentialacross the barrier (see BARRIER, 1) in a pnjunction.barrier strip A terminal strip having a barrier (seeBARRIER, 2) between each pair of terminals.barrier stripbarrier voltage The voltage required for the initiationof current flow through a pn junction.Bartlett force See EXCHANGE FORCE.baryon A subatomic particle made up of threequarks.base 1. In a bipolar transistor, the intermediate regionbetween the emitter and collector, whichusually serves as the input or controlling elementof transistor operation. 2. A substance that dissociatesin water solution and forms hydroxyl(OH) ions. For example, sodium hydroxide. 3. Theconstant figure upon which logarithms are computed(10 for common logs, 2.71828 for naturallogs). 4. The radix of a number system (e.g., base10 for the decimal system, base 8 for the octalsystem, base 16 for the hexadecimal system, andbase 2 for the binary system). 5. A fixed nonportableradio communications installation.base address The number in a computer addressthat serves as the reference for subsequent addressnumbers.baseband The frequency band of the modulatingsignal in a communications, broadcast, or datatransmitter. For voice communications, this isgenerally the range of voice frequencies necessaryfor intelligible transmission. For high-fidelity musicbroadcasting, it is approximately the range ofhuman hearing. For fast-scan television, itranges up to several megahertz. It can be restrictedor expanded, depending on the nature ofthe transmitted signal. See BASEBAND FRE-QUENCY RESPONSE.baseband frequency response 1. The amplitudeversus-frequencycharacteristic of the audiofrequency(AF) or composite video section of atransmitter that defines the BASEBAND, or rangeof modulating frequencies. 2. The range of frequenciesover which a radio transmitter can bemodulated to convey information. For single sideband(SSB), it is approximately 300 Hz to 3 kHz;for high-fidelity, frequency-modulated (FM) music

64 baseband frequency response • BASICtransmission, it is about 10 Hz to 20 kHz or 30kHz; for fast-scan television, it consists of frequenciesup to several megahertz. This range isdetermined by bandpass and/or lowpass filtersin the AF or composite video section of the transmitter.base bias The steady dc voltage applied to the baseelectrode of a transistor to determine the operatingpoint along the transistor characteristiccurve.base-bulk resistance The resistance of the semiconductormaterial in the base layer of a bipolartransistor.base-charging capacitance In the commonemitterconnection of a bipolar transistor, the internalcapacitance of the base-emitter junction.base current Symbol, I B . Current flowing throughthe base electrode of a bipolar transistor. Also seeAC BASE CURRENT and DC BASE CURRENT.base electrode See BASE, 1. Also called base element.base element 1. Base electrode. 2. One of the basicmetals, such as iron or tin, that are not generallyconsidered precious (as opposed toNOBLE).base-e logarithm See NAPIERIAN LOGARITHM.base film The plastic substrate of a magneticrecording tape.base frequency 1. The frequency of the principal,or strongest, component in a complex signal orwaveform; also called basic frequency. 2. The frequencyof operation of a base-station transmitterwhen the receiver is tuned to a second channel.base-input circuit A common-collector circuit,common-emitter circuit, or emitter follower.base insulator A stout dielectric insulator, used tosupport a heavy conducting element and keep theconductor isolated from other possible conductorsor conductive paths.base line In visual alignment procedures involvingan oscilloscope and radio-frequency (RF) sweepgenerator, a zero-voltage reference line developedby the generator as a horizontal trace on the oscilloscopescreen.baseline stabilizer A clamping circuit that holdsthe reference voltage of a waveform to a predeterminedvalue. Also called DC RESTORER.base-loaded antenna A usually vertical antenna orradiating element, the electrical length of which isadjusted by means of a loading coil or tuned circuitin series with, and positioned at the bottomof, the antenna or radiator.base material In printed circuits, the dielectricmaterial used as a substrate for the metal pattern.Also called base medium.base notation The numbering or radix systemused in any application (as octal, decimal, binary,or hexadecimal).base number See BASE, 4.base pin One of the straight prong-like terminalson an electrical or electronic component; it isbase lineBaselineused to provide support for the device and to allowa physical connection between the socket terminal,into which it fits, and one of the internalelectrodes of the device.base plate The chassis plate upon which componentsare mounted before wiring.base potential See BASE VOLTAGE.base region See BASE, 1.base resistance Symbol, R B . Resistance associatedwith the base electrode of a bipolar transistor.Also see AC BASE RESISTANCE and DC BASERESISTANCE.base resistor The external resistor connected tothe base of a bipolar transistor. In the commonemittercircuit, the base resistor is analogous tothe gate resistor of a field-effect transistor (FET)circuit.base spreading resistance Symbol, r BB . In a bipolartransistor, the bulk-material resistance ofthe base region between the collector junctionand emitter junction.base station The head station or fixed home stationin a communication network.base-10 logarithm Abbreviation, log 10 . A logarithmbased on the decimal number 10. If log 10 (x) = y,then 10 y = x. Base-10 logarithms are commonlyused in engineering. Compare NAPIERIAN LOGA-RITHM.base voltage Symbol, V B . The voltage at the baseelectrode of a bipolar transistor. Also see ACBASE VOLTAGE and DC BASE VOLTAGE.BASIC Acronym for BEGINNER’S ALL-PURPOSESYMBOLIC INSTRUCTION CODE, a relativelyprimitive, but versatile and easy-to-learn computerlanguage developed at Dartmouth College.

asic frequency • battery 65basic frequency 1. The FUNDAMENTAL FRE-QUENCY of a signal, as opposed to one of its harmonics.2. See BASE FREQUENCY, 1.basic protection Devices and procedures essentialto minimize the risk of damage to electronicequipment, and/or injury or death to its operators,as a result of lightning. Hardware provisionsinclude a substantial earth ground, heavy-gaugegrounding wire, lightning arrestors for antennas,and transient suppressors for power connections.The safest procedure is to disconnect and groundall antennas, and unplug all equipment from utilityoutlets, during electrical storms and/or whenthe apparatus is not in use. Radio communicationsequipment with outdoor antennas, inparticular, should not be operated duringthunderstorms.basket The structure that supports the cone in anacoustic loudspeaker.basket-weave coil A type of single-layer inductorin which adjacent turns do not parallel eachother around the circumference, but zigzag oppositelyas a strand does in the woven pattern of abasket. This reduces distributed capacitance.bass Low audio frequencies (AF) corresponding tolow-frequency musical notes or sounds.bass boost 1. The special emphasis given to lowaudio frequencies (the bass notes) by selectivecircuits in audio systems. 2. The technique of increasingthe loudness of the bass, relative to thehigher audio frequencies, to render a more faithfulreproduction of sound at low volume levels.bass compensation See BASS BOOST, 2.bass control 1. A manually variable potentiometerfor adjusting bass boost of an amplifier or soundsystem. 2. The arrangement of components thatare required to achieve amplitude variation ofbass in an audio signal.bass port In a loudspeaker, a hole in the cabinetthat enhances the low-frequency (bass) soundoutput. Used in high-fidelity audio systems.bass-reflex enclosure A loudspeaker cabinet witha critically dimensioned duct or port that allowsback waves to be radiated in phase with frontwaves, thus averting unwanted acoustic phasecancellation.bass-reflex loudspeaker A loudspeaker mountedin a bass reflex enclosure. Also see ACOUSTICALPHASE INVERTER.bass-resonant frequency The low frequency atwhich a loudspeaker or its enclosure displaysresonant vibration.bass roll-off 1. The attenuation of the low-frequency(bass) component in a high-fidelity audiosignal. 2. A control that allows adjustable attenuationof the low-frequency component in a highfidelityaudio signal.bass suppression In speech transmission, the removalof all frequencies below about 300 Hz, onthe assumption that those frequencies contributelittle to intelligibility. This suppression permitsthe speech level to be increased without overmodulatinga transmitter. It also allows smaller audiotransformers to be used because transformercore size must increase as the frequency it passesdecreases.bassy In audio and high-fidelity applications, asound in which the low-frequency components,below about 500 Hz, are overly predominant.BAT Abbreviation of BATTERY.batch fabrication process The manufacture of devicesin a single batch from materials of uniformgrade. Particularly, the manufacture of a largenumber of semiconductor devices from one batchof semiconductor material by means of carefullycontrolled, identical processes.batch processing In digital-computer operations,the processing of quantities of similar informationduring a single run.bat-handle switch A toggle switch, the lever ofwhich is relatively long and thick, and is shapedlike a baseball bat.bat-handle switchbathtub capacitor A (usually oil-filled) capacitorhoused in a metal can that looks like a miniaturebathtub.bathyconductorgraph An instrument that is usedto measure the electrical conductivity of seawater.bathythermograph An instrument that plots agraph of temperature versus depth in a body ofwater, such as a lake or an ocean.batten Supporting bars or braces that hold a loudspeakerin place within its cabinet, and/or thathold the cabinet panels in place.battery Abbreviations, B, BA. BAT. A device consistingof two or more interconnected electrochemicalor photovoltaic cells that generate dcelectricity. The cells can be connected in series tosupply a desired voltage, in parallel to supply adesired current-delivering capability, or in seriesparallelto obtain a desired voltage and currentdeliveringcapability. Also see CELL, EDISONBATTERY, LEAD-ACID BATTERY, PHOTO-

66 battery • beaconVOLTAIC CELL, PRIMARY BATTERY, and STOR-AGE BATTERY.battery acid 1. A chemical acid, such as sulfuricacid, used as the electrolyte of a battery. 2. Colloquially,any cell or battery electrolyte, whetheracid, base, or salt.battery capacity The current-supplying capabilityof a battery, usually expressed in ampere-hours(Ah).battery cell See CELL, 1.battery charger 1. A specialized dc power supply,usually embodying a stepdown transformer, rectifier,and filter. It is used to charge a storage batteryfrom an ac power line. 2. A motor-generatorcombination used to charge a storage batteryfrom an ac power line. 3. A combination of solarcells, generators, or other voltaic transducers,that are used to charge a storage battery with dcobtained from a nonelectrical energy source.battery clip 1. A heavy-duty metallic clamp that isused for quick, temporary connection to a largecell terminal, such as that of a lead-acid storagebattery. 2. A small connector of the snap-fastenertype, used for quick connection to a small powersource, such as a transistor-radio battery.battery eliminator A specialized dc power supply,usually embodying a transformer, rectifier, andfilter, that permits battery-powered equipment tobe operated from an ac power line.battery holder 1. A case or container of any kindfor holding a cell or battery. 2. A shelf for holdinga cell or battery. 3. A small, metal bracket-typedevice for holding a cell or battery between twocontacts.battery life 1. The ampere-hour or watt-hour capacityof a battery. 2. The number of times that arechargeable electrochemical battery can be cycledbefore it becomes unusable. 3. The nominallength of time (e.g., hours, days, or weeks) that anelectrochemical battery will function effectively ina given application before it must be discarded orrecharged.battery memory See MEMORY DRAIN.battery receiver A usually portable radio or televisionreceiver operated from self-contained batteries.battery substitute See BATTERY ELIMINATOR.bat wing On a television (TV) or frequency-modulation(FM) broadcast receiving antenna, a metallicelement with a shape that resembles that of abat’s wing.baud A unit of communications processing speedin telegraphy and digital data communicationssystems. Often confused with bits per second(bps). Baud refers to the number of times per secondthat a signal changes state. The speed in bpsis generally higher than the speed in baud, sometimesby a factor of several times. Compare BITSPER SECOND.Baudot code A machine communications codethat uses five parallel binary digits of equallength, the interpretation of which depends onthe history of the previous transmission or an additionalcase bit.baud rate 1. A colloquial expression for data speedin BAUD. 2. Colloquial, and technically inaccurate,expression for data speed in BITS PER SEC-OND.Baume (Antione Baume, 1728–1804). Abbreviation,Be. Pertaining to the Baume scales for hydrometers.The two such scales are for liquids heavierthan water and for liquids lighter than water.bay One of several sections of a directional antennaarray.bayonet base The insertable portion of a plug-incomponent (e.g., a lamp) that has a projecting pinthat fits into a slot or keyway in the shell of thesocket into which the component is inserted.bayonet socket A socket with a suitably slottedshell for receiving the bayonet base of a plug-incomponent.bazookaA linear BALUN, in which a quarter wavelengthof metal sleeving surrounds a coaxialfeeder, and is shorted to the outer conductor ofthe feeder to form a shorted quarter-wave section.bb Abbreviation of BLACKBODY.BBC Abbreviation of British Broadcasting Corporation.BBM Abbreviation of BREAK BEFORE MAKE.b-box The index register of a computer.BC Abbreviation of BROADCAST.BCD Abbreviation of BINARY-CODED DECIMAL.BCFSK Abbreviation of BINARY CODE FRE-QUENCY-SHIFT KEYING.B channel One of the channels of a two-channelstereophonic system. Compare A CHANNEL.BCI Abbreviation of BROADCAST INTERFERENCE.BCL Amateur radio abbreviation of BROADCASTLISTENER.BCN Abbreviation of BEACON.BCO Abbreviation of BINARY-CODED OCTAL.BCST Abbreviation of BROADCAST.BDC Abbreviation of BINARY DECIMAL COUNTER.B display A radar display in which the target isrepresented by a bright spot on a rectangularcoordinatescreen. Compare A DISPLAY and JDISPLAY.Be Symbol for BERYLLIUM.Be Abbreviation of BAUME.beacon 1. A beam of radio waves, or a radio signal,that is used for navigation and/or direction finding.2. A transmitter that radiates a beam of radiowaves, or a radio signal, as an aid in navigationand/or direction finding. 3. A signal transmittedcontinuously on a specific frequency, to help radiooperators ascertain propagation conditions.4. A station or transmitter that generates and radiatesa signal to help radio operators determinepropagation conditions. 5. In robotics, a device orsystem that aids in navigation. For example, tricornerreflectors can be positioned in strategiclocations, and a mobile robot equipped with a

eacon • beam parametric amplifier 67scanning infrared laser. The robot controller determinesthe distance to any given reflector bymeasuring the time required for the laser beam toreturn. In this way, two mirrors can allow therobot to locate its position in two dimensions;three mirrors can facilitate position determinationin three-dimensional space.beacon direction finder A direction finder using asignal received from a beacon station.beacon receiver A receiver that is speciallyadapted for the reception of beacon signals (seeBEACON, 1 and 3).beacon station 1. A station broadcasting beaconsignals (see BEACON, 1 and 3) for direction finding,navigation, and/or determination of radiowavepropagation conditions. 2. Sometimes, aradar transmitting station.beacon transmitter A transmitter speciallyadapted for the transmission of beacon signals(see BEACON, 1 and 3).bead1. A small ferromagnetic ring that is used asa passive decoupling choke by slipping it over theinput power leads of a circuit or stage, or arounda coaxial transmission line. 2. A magnetic memoryelement in a ferrite-core matrix.beaded coax A low-loss, coaxial transmission line,in which the inner conductor is separated fromthe outer conductor by means of spaced dielectricbeads.beaded support A plastic or dielectric bead that isused to support the inner conductor of an airinsulatedtransmission line of coaxial construction.bead thermistor A thermistor consisting essentiallyof a small bead of temperature-sensitive resistancematerial into which two leads are inserted.beam 1. The more-or-less narrow pattern of radiationfrom a directional antenna. 2. A directionalantenna—especially a YAGI ANTENNA. 3. Thestream or cloud of electrons emitted by the cathodein an electron tube—especially a BEAMPOWER TUBE.beam alignment 1. The lining-up of a directionaltransmitting antenna with a directional receivingantenna for maximum signal transfer. 2. In abeam alignmenttelevision (TV) camera tube, the lining-up of theelectron beam so that it is perpendicular to thetarget. 3. In a cathode-ray tube, the positioning ofthe electron rays so that they converge properlyon the screen, regardless of the deflection path.beam angle In the radiation from an antenna, thedirection of most intense radiation, the side limitsof which are determined by the points at whichthe field strength drops to half the value in theprincipal direction.beam antenna 1. A multielement directional antenna,consisting of a half-wave driven dipole andone or more parasitic elements. See YAGI AN-TENNA. 2. Any directional antenna used fortransmitting and receiving radio-frequency (RF)signals.beam bender 1. In a television (TV) picture tube,the ion-trap magnet. 2. Deflection-plate correctiondevice or circuit.beam bending Deflection of an electron beam byelectric or magnetic fields.beam blanking See BLANK, 2.beam convergence The meeting, at a shadowmaskopening, of the three electron beams in athree-color television picture tube. See BEAMALIGNMENT, 3.beam coupling A method of producing an alternatingcurrent between two electrodes by passing adensity-modulated beam of electrons between theelectrodes. This, in effect, demodulates the electronbeam, recovering the information.beam crossover Either of the half-power pointsin the beam of a directional antenna, usually inthe horizontal plane. The reference point is consideredto be the direction of maximum radiation.beam current The current represented by the flowof electrons in the beam of a cathode-ray tube.beam cutoff In an oscilloscope or television picturetube, the complete interruption of the electronbeam, usually as a result of highly negative control-gridbias.beam deflector A deflection plate in an oscilloscopetube.beam efficiency In a cathode-ray tube, the ratio ofthe number of electrons generated by the gun tothe number reaching the screen. The efficiency ishigh in electromagnetic-deflection tubes andlower in electrostatic-deflection tubes.beam leadIn an integrated circuit, a relativelythick and strong lead that is deposited in contactwith portions of the thin-film circuit. It providesstouter connections than continuations of thethin film would provide.beam-lead isolation In an integrated circuit, reductionof distributed capacitance and other interactionthrough use of beam leads.beam modulation See INTENSITY MODULATION.beam parametric amplifier A PARAMETRIC AM-PLIFIER in which the variable-reactance componentis supplied by a modulated electron beam.

68 beam-positioning magnet • beat markerbeam-positioning magnet In a three-gun colortelevision picture tube, a permanent magnet thatis used to position one of the electron beams correctly,with respect to the other two.beam power tube A tetrode or pentode vacuumtube, in which special deflector plates concentratethe electrons into beams in their passage fromcathode to plate. The beam action greatly increasesplate current at a given plate voltage. It is used insome radio-frequency (RF) power amplifiers.beam-rider control system A missile-guidancesystem in which a control station sends a radiobeam to a missile. The beam is moved in such away that as the missile stays within the beam, ithits the target.beam-rider guidance 1. An aircraft landing guidancesystem, in which the aircraft follows a radiobeam in its glide path. 2. The circuitry in a guidedmissile using a beam-rider control system.beam splitter A device used to divide a light beam(as by a transparent mirror) into two components,one transmitted and the other reflected;hence, a BEAM-SPLITTING MIRROR.beam splitting In radar, a method of calculatingthe mean azimuth of a target from the azimuth atwhich the target is first revealed by one scan, andthe azimuth at which the target informationceases.beam-splitting mirror In an oscilloscope-camerasystem, a tilted, transparent mirror that allowsrays to pass horizontally from the oscilloscopescreen to the camera and to be reflected verticallyto the viewer’s eye.beamwidth of antenna The angular width of themain lobe of the pattern of radiation from a directionalantenna. Generally, it is measured be-Half-powerwidthtween the half-power points in the horizontalplane. Occasionally, it is measured in the verticalplane.bearing The direction of an object or point expressedin degrees within a 360° horizontal clockwiseboundary, with the center of the circleserving as the observation point.bearing resolution In radar operations, the minimumhorizontal separation of two targets, in degrees,that permits the individual targets to bedisplayed as two echoes, rather than one.beat Any one of the series of pulsations constitutinga beat note, which results from heterodyningone signal against another.beat frequency Either of two frequencies f C1 andf C2 resulting from the mixing of two signals of differentfrequencies f A and f B . Frequency f C1 is thesum of the two input frequencies; f C1 = f A + f B .Frequency f C2 is the difference; f C2 = f A – f B whenf A is the higher of the two input frequencies.beat-frequency oscillator Abbreviation, BFO. Anoscillator used to set up audible beat frequencieswith an incoming received signal and installedin the intermediate-frequency (IF) stagesof a superheterodyne communications receiver.For single-sideband (SSB) reception, the BFO isset at the frequency of the received suppressedcarrier. In continuous-wave (CW) Morse code reception,the BFO is set at a frequency that differsfrom that of the incoming signal by about400 to 1000 Hz. The resulting tone has an audiofrequency equal to the difference between theBFO frequency and the received signal carrierfrequency. For reception of frequency-shiftkeyed(FSK) signals, the BFO is set to such a frequencythat the resulting audio beat notes areappropriate for the mark and space inputs of aterminal unit or modem.IFamp.MixerAFamp.FrompreviousIF stageBFObeat-frequency oscillatorAudiooutputbeamwidth of antennabeating 1. Also called heterodyning. The combinationof signals of different frequencies resulting insum and difference frequencies. 2. The flutteringnoise heard when two audio tones, very close infrequency and very similar in amplitude, areemitted at the same time.beat marker In the visual (oscilloscopic) alignmentof a tuned circuit, a marker pip that results fromthe beat note between the sweep-generator signaland the signal from a marker oscillator.

eat note • Be0 69beat note The sum or difference frequency that resultsfrom the heterodyning of two signals or, undersome conditions, of more than two signals.beat-note reception 1. Reception in which a radio-frequencycarrier is made audible by heterodyningit with a beat-frequency oscillator (BFO) toproduce an audible beat note. 2. Superheterodynereception (see SUPERHETERODYNE CIR-CUIT).beat tone A beat note in which the frequency iswithin the range of hearing.beaver tail A flat or elongated radar beam, wide inthe azimuth plane. Primarily used to determinethe altitude of a target. The beam is moved upand down to find the target elevation.Becquerel effect A phenomenon in which a voltageis produced when radiant energy, such as infrared,visible light, ultraviolet, or X-rays, falls onone electrode in an electrolytic cell.bedspring A directional antenna consisting of abroadside array with a flat reflector and one ormore helical driven elements.beep A test or control signal, usually of single toneand short duration.beeper 1. A pocket- or hand-carried transceiver—especially one for maintaining two-way contactwith personnel who are away from their base. 2.An acoustic transducer that produces a beep inresponse to an input signal.beetle A urea formaldehyde plastic used as a dielectricmaterial and as a container material.bel Abbreviation, B. The basic logarithmic unit(named for Alexander Graham Bell) for expressinggain or loss ratios. One bel is equivalent to apower gain of 10. Also see DECIBEL.bell An electric alarm device consisting of a metallicgong that emits a ringing sound when it isstruck by an electrically vibrated clapper.Bellini-Tosi direction finder A direction finder inwhich the sensing element consists of two triangularvertical antennas crossed at right angles,the antennas being open at the top and accordinglynot acting as conventional coil antennas.bell-shaped curve A statistical curve (so calledfrom its characteristic shape) that exhibits a normaldistribution of data. Typically, the curve describesthe distribution of errors of measurementaround the real value.bell transformer A (usually inexpensive) stepdowntransformer that operates an electric bell or similaralarm or signaling device from the ac powerline.bell wire Insulated 18-gauge (AWG) solid copperwire, so called because of its principal early usein the wiring of electric-bell circuits.belt generator Also known as a Van de Graaff generator.A very-high-voltage electrostatic generator,a principal part of which is a fast-travelingendless belt of dielectric material. At the lowerend, charges of one sign are sprayed on the beltat 10 to 100 kV dc and are carried to the inside ofa hollow metal sphere at the upper end, wherethey are removed and spread to the surface of thesphere, which they raise to a potential up to severalmillion volts.benchmark A test standard to measure productperformance.benchmark routine A routine designed to evaluatecomputer software and/or hardware, producing agood indication of how well the software or hardwarewill perform in real-life situations. In particular,tests instructions per second andthroughput, thereby producing an indication ofthe overall computer power in applications, suchas word processing, database, spreadsheet,graphics, animation, and mathematical calculations.bench test An extensive checkout of a piece ofequipment in the test laboratory—either to findan intermittent problem, or to check for reliability.bend An angular shift in the lengthwise direction ofa waveguide.bending effect 1. The downward refraction of aradio wave by the ionosphere. 2. The lowatmosphereturning of a radio wave downward bytemperature discontinuity and atmospheric inversions.BenitoA continuous-wave method of measuringthe distance of an aircraft from the ground, involvingthe transmission of an audio-modulatedsignal from ground and the retransmission backto ground by the aircraft. The phase shift betweenthe two signals is proportional to the distance tothe aircraft.bent antenna An antenna that has its driven elementbent, usually near the ends and at right angles,to conserve space.bent gun A television picture tube neck arrangementhaving an electron gun that is slanted to directthe undesired ion beam toward a positiveelectrode, but which allows the electron beam topass to the screen. This prevents the ion beamfrom “burning” a permanent spot on the phosoporof the screen.Be0 Formula for beryllium oxide. Also see BERYL-LIA.CathodeControlgridIon trapmagnetFirst anodebent gunSecond anodeElectronbeam

70 berkelium • biased offberkelium Symbol, Bk. A radioactive elementalmetal produced artificially. Atomic number, 97.Atomic weight, 247.beryllia Formula, Be0. Beryllium oxide, used invarious forms as an insulator and structural element(as in resistor cores).beryllium Symbol, Be. An elemental metal. Atomicnumber, 4. Atomic weight, 9.01218. Beryllium ispresent in various dielectrics and alloys used inelectronic components.Bessel functions Sophisticated mathematicalfunctions for dealing with periodic electronic phenomenain which the waveform often displaysdecrement. Also called cylindrical functions.beta Symbol, β. The current gain of a commonemitterbipolar transistor stage. It is the ratio ofthe induced change of collector current to the appliedchange of base current: β = dIC/dIB.beta circuit The output-input feedback circuit inan amplifier.beta cutoff frequency The frequency at which thecurrent amplification of a bipolar transistor fallsto 70.7% of its low-frequency value.beta particles Minute radioactive subatomic bitsidentical to the electron or positron, and emittedby some radioactive materials. Also see BETARAYS.beta rays Rays emitted by the nuclei of radioactivesubstances, consisting of a stream of beta particles(i.e., electrons or positrons) that move at velocitiesup to 299.8 million meters per second.Compare ALPHA PARTICLE and GAMMA RAYS.beta-to-alpha conversion For a bipolar transistor,the conversion of current amplification expressedas beta (β) to current amplification expressed asalpha (α): α = β/(β + 1).betatron A particle accelerator in which injectedelectrons are given extreme velocity by being propelledin circular paths in a doughnut-shapedglass container. The term comes from the factthat high-speed electrons constitute BETA PAR-TICLES.beta videocassette recorder The earliest schemefor videocassette recording, developed by Sonycorporation in the 1970s. Compare VHS videocassetterecorder.beta zinc silicate phosphor Formula, (Zn0 +Si0 2 ):Mn. A phosphorescent substance used tocoat the screen of a cathode-ray tube. The fluorescenceis green-yellow.BeV Abbreviation of billion electronvolts. Also seeELECTRONVOLT, GEV, MEV, and MILLIONELECTRONVOLTS. This abbreviation has beensupplanted by the SI (International System ofUnits) abbreviation GeV, for GIGAELECTRON-VOLTS.bevatron An accelerator (see ACCELERATOR, 1)similar to the synchrotron, which acceleratesparticles to levels greater than 10 GeV.Beverage antenna (Harold H. Beverage.) A nonresonant,directional long-wire antenna, erected afew feet above ground and run in a straight linefor one to several wavelengths. It is generallyused for reception at low and medium frequencies,the best response is to vertically polarizedsignals arriving from one or both directions inline with the wire. It can be left unterminated forbidirectional response, or it can be terminated atits far end by a noninductive resistor of about 600ohms for a unidirectional response.beyond-the-horizon propagation See FORWARDSCATTER.bezel A faceplate for an electronic instrument,usually having a fitted rim and cutouts for knobs,switches, jacks, etc.BFO Abbreviation of BEAT-FREQUENCY OSCIL-LATOR.BG Abbreviation of BIRMINGHAM WIRE GAUGE.Also abbreviated BWG.B-H curve A plot showing the B and H properties ofa magnetic material. Magnetizing force H is plottedalong the horizontal axis, and flux density Bis plotted along the vertical axis.B-H loop See BOX-SHAPED LOOP.B-H meter Any instrument for displaying or evaluatingthe hysteresis loop of a magnetic material.bhp Abbreviation of brake horsepower.Bi Symbol for BISMUTH.bias 1. Any parameter of which the value is set to apredetermined level to establish a threshold oroperating point. Although it is common to thinkof bias currents and bias voltages, other parameters(e.g., capacitance, resistance, illumination,magnetic intensity, etc.) can serve as biases. 2. Ina high-fidelity audio system, a circuit in a taperecorder/player that optimizes performance for aparticular type of recording tape.bias current A steady, constant current that presetsthe operating threshold or operating pointof a circuit or device, such as a transistor,diode, or magnetic amplifier. Compare BIASVOLTAGE.bias current drift The ratio of a change in inputbias current to a change in ambient temperature,generally expressed in nanoamperes per degreeCelsius.bias distortion Distortion caused by operation of atube or transistor with incorrect bias so that theresponse of the device is nonlinear.biased diode A diode having a dc voltage applied ineither forward or reverse polarity. Current flowsreadily through the forward-biased diode; the reverse-biaseddiode appears as an open circuit.The biased diode is the basis of clippers, limiters,slicers, and similar circuits.biased offIn a circuit or device, the state of cutoffcaused by application of a control-electrode bias.Examples include collector-current cutoff (whenthe dc base bias of a bipolar transistor reaches acritical value), and drain-current cutoff (when thedc gate bias reaches a critical value in a fieldeffecttransistor).

iased search • bifilar electrometer 71PNReversebiasbiased diodesPNForwardbiasλ/4Feedbiased search A scheme that a mobile robot canuse to find its way to a destination or target, bydeliberately searching off to the side and thenhoming in as the approach progresses. It is socalled because the general nature of the initial error(bias) is known, although its exact extent neednot be known.bias oscillator In a magnetic recorder, an oscillatoroperated at a frequency in the 40-kHz to 100-kHz range to erase prerecorded material and biasthe system magnetically for linear recording.bias resistor A usually fixed resistor, such as thesource resistor in a field-effect-transistor (FET) circuitor the emitter resistor in a bipolar-transistorcircuit, across which a desired bias voltage is developedby current flowing through the resistor.bias set A control, such as a potentiometer or variableautotransformer, that facilitates manual adjustmentof the dc bias of a circuit.bias stabilization 1. The maintenance of a constantbias voltage, despite variations in loadimpedance or line voltage. It is usually accomplishedby means of automatic voltage regulation.2. The stabilization of transistor dc bias voltageby means of resistance networks or through theuse of barretters, diodes, or thermistors.bias supply 1. Batteries that provide bias voltageor current for bipolar or field-effect transistors. 2.A line-operated unit for supplying dc bias andconsisting of a transformer, rectifier, and highgradefilter.bias voltage A steady voltage that presets the operatingthreshold or operating point of a circuit ordevice, such as a transistor. Compare BIAS CUR-RENT.bias windings The dc control windings of a saturablereactor or magnetic amplifier.biconical antenna A form of broadband antenna,consisting of two conical sections joined at theapexes. The cones are at least 1 ⁄4 wavelength in diagonalheight. The vertex angles of the cones canvary, although the apex angle is usually the samein each cone. The vertex angle affects the feedpointimpedance. Such an antenna radiates, andresponds optimally to, signals with polarizationparallel to the axis of the cones.biconical horn antenna A double-horn microwaveantenna that radiates along relatively sharpfront and back beams.λ/4biconical antennabidecal base The 20-pin base of a cathode-raytube. Also see DIHEPTAL, DUODECAL, andMAGNAL.bidirectional Radiating or receiving (usuallyequally) from opposite directions (e.g., front-andbackradiation from an antenna or loudspeaker,or front-and-back pickup with an antenna or microphone).bidirectional antenna An antenna with a directionalpattern that consists of maximum lobes180 degrees apart.bidirectional bus In computers, a data path overwhich both input and output signals are routed.bidirectional bus driver In a microcomputer, asignal-driving device that permits direct connectionof a buffer-to-buffer arrangement on one end(the interface to I/O, memories, etc.) and data inputsand outputs on the other. This device permitsbidirectional signals to pass and providesdrive capability in both directions.bidirectional counter A counter that can countconsecutively up from a given number or downfrom that number. Also called UP-DOWNCOUNTER.bidirectional current A current that flows in bothdirections. Utility alternating current (ac) is acommon example.bidirectional loudspeaker A loudspeaker that deliverssound waves to the front and rear.bidirectional microphone A microphone thatpicks up sound waves equally well from the frontand rear.bidirectional transistor A symmetrical transistor(i.e., one in which the two main current-carryingelectrodes can be interchanged without influencingdevice performance). Some field-effect transistors(FETs) are of this type; the drain and thesource can be interchanged.bifilar electrometer An electrometer in which thesensitive element consists of two long platinizedquartzfibers. When an electric potential is ap-

72 bifilar electrometer • bimorphous cellplied, the fibers separate by a distance proportionalto the voltage.bifilar resistor A wirewound resistor with two oppositelywound filaments. The nature of the windingtends to cancel the inductance, making thedevice useful at a much higher frequency than anordinary wirewound resistor.bifilar transformer A transformer in which unitycoupling is approached by interwinding the primaryand secondary coils (i.e., the primary andsecondary turns are wound side by side and inthe same direction).bifilar winding 1. A method of winding a coil (suchas a resistor coil) in the shape of a coiled hairpinso that the magnetic field is self-canceling andthe inductance is minimized. 2. A method ofwinding transformers to minimize leakage reactance.R1R2R1C1R3R3C2R2R1R1C1L1L1bifilar windingbifurcated contact A forked contact whose partsact as two contacts in parallel for increased reliability.bilateral amplifier An amplifier that transmits orreceives in either direction equally well (i.e., theinput and output can be exchanged at will).bilateral antenna A bidirectional antenna, such asa loop antenna or a half-wave dipole.bilateral element A circuit element or component(as a capacitor, resistor, or inductor) that transmitsenergy equally well in either direction. CompareUNILATERAL ELEMENTS.bilateral network A network, usually passive andeither balanced or unbalanced, that has BILAT-ERAL SYMMETRY. Thus, the input and outputterminals can be exchanged without affecting theperformance of the network in any way.bilateral symmetry 1. Exhibiting symmetry, withrespect to a vertical line or plane. 2. For a network,having the property that if the input andoutput are reversed, the circuit behavior remainsprecisely the same. See BILATERAL NETWORK.3. For an amplitude-versus-frequency responsecurve, having the property that the right-handand left-hand halves are mirror images of eachother.billboard antenna A phased group of dipole antennasthat lie in one plane. A reflector might beused behind the entire array.bilobe pattern An antenna radiation pattern consistingof two major lobes in a given plane, usuallythe horizontal plane. Often the lobes exist inopposite directions relative to each other, as in abilateral networkhalf-wave dipole. But they can be at varying angles,as in a long-wire antenna.bimetal A union of two dissimilar metals—especiallythose having a different temperature coefficientof expansion. The two are usually weldedtogether over their entire surface.bimetallic element A strip or disk of bimetal.When the element is heated, it bends in the directionof the metal that has the lower temperaturecoefficient of expansion; when cooled, itunbends. Usually, an electrical contact is madeat one extreme or the other so that the elementcan serve as a thermostat.bimetallic switch A temperature-sensitive switchbased on a bimetallic element.bimetallic thermometer A thermometer based ona bimetallic element that is mechanically coupled(as through a lever and gear system) to a pointerthat moves over a temperature scale.bimetallic thermostat A thermostat in which abimetallic element closes or opens a pair ofswitch contacts.bimorphous cell A piezoelectric transducer thatconsists of two crystal plates, such as Rochellesalt, bound intimately face to face. In a crystalmicrophone, vibration of the transducer resultsin a voltage output; in a crystal headphone, an acsignal voltage impressed on the transducercauses vibratory mechanical motion.

BiMOS • binaural 73BiMOS A combination of bipolar and MOSFETtransistors in an integrated circuit. Thus, a typicalBiMOS device can have MOSFET input forhigh impedance and bipolar output for lowimpedance.binant electrometer An electrometer in which athin platinum vane (“the needle”) is suspendedwithin two halves of a metal pillbox-shaped container.The halves or binants are biased with a dcvoltage of 1 to 12 V, and the unknown voltage isapplied to the vane. It is also called DUANTELECTROMETER and HOFFMAN ELECTROME-TER.binary 1. Pertaining to the base-2 number system.Thus, binary arithmetic uses two digits: 0 and 1.2. Pertaining to two-element chemical compounds.binary arithmetic Mathematical operations performedusing only the digits 0 and 1.binary cell In a computer memory, an elementthat can display either of two stable states.binary chain A cascade of binary elements, suchas flip-flops, each unit of which affects the stablestate of the succeeding unit in sequence.binary channel Any channel whose use is limitedto two symbols.binary code A system of numbers representingquantities by combinations of 1 and 0; a binarynumbersystem.binary-coded decimal notation In digital computeroperations, a system of notation in whicheach digit of a decimal number is represented byits binary equivalent. Thus, the decimal number327 in BCD notation becomes 0011 0010 0111.(By contrast, in pure binary notation, 327 is101000111.)binary-coded octal notation A method of numberingin which each base-8 digit is representedby a binary number from 000 to 111.binary-controlled gate circuit A gate circuit controlledby a binary stage. An example is a gatingtransistor that receives its on/off pulses from aflip-flop.binary counter A counter circuit consisting of acascade of bistable stages. Each stage is a scaleof-twocounter because its output is on for everysecond input pulse. At any instant, the total binarycount in a multistage counter thus is shownby the on and off states of the various stages insequence.binary decoder A device or stage that accepts binarysignals on its input lines, and provides ausually exclusive output (representing a decimaldigit, for example).binary digit See BIT.binary number system The base-two system ofnotation. This system uses only two symbols, 0and 1, and accordingly is easily applied to twopositionswitches, relays, and flip-flops.binary preset switch In a binary counter or binarycontrol circuit, a selector switch that allows thecircuit to be preset to deliver an output pulse onlyafter a predetermined number of input pulses.binary relay See BISTABLE RELAY.binary scaler In its simplest form, a single twostagedevice, such as a flip-flop, which functionsas a divide-by-two counter, because one outputpulse results from every two input pulses.Higher-order scaling is obtained by cascadingstages.binary search A system of search entailing thesuccessive division of a set of items into two partsand the rejection of one of the two until all itemsof the sought-for kind are isolated.{{binary searchbinary signal Any signal that can attain either oftwo states. Such a signal is always a digital signal.binary-to-decimal conversion 1. The automaticconversion of a number represented by a series ofbinary pulses into the corresponding decimalnumber, which then is displayed by a readout device.2. The arithmetic operation of converting abinary number into a decimal number; this canbe done by noting the powers of 2 represented bythe various binary digits in a number, and thenadding the decimal values of these powers.binary word A binary numeral that has a particularmeaning, agreed upon by convention. For example,the letters A through Z can be representedby binary numbers 00001 through 11010; a wordcan be represented by several blocks of five digits.binaural Literally, two-eared. In sound recordingand reproduction, the transcription of a broadsound source using two microphones spaced atapproximately the distance between the ears on ahuman head, and played back using headphones

74 binaural • biofeedback monitorto re-create the stereo effect. The techniqueevolved into multichannel stereophonic reproduction.binaural machine hearing Also called stereo machinehearing. The ability of a machine, such as arobot, to sense the direction and distance to asource of sound, using two acoustic transducersand a computer to process their output signals.The machine determines the location of thesound source by comparing the relative amplitudeand phase of the signals from the two transducers.It functions according to the sameprinciple as human hearing, in which a personcan determine the general direction and distanceto a sound source by subconsciously comparingthe relative amplitude and phase of the soundsarriving at the left and right ears.binaural sound The equivalent of a listener hearinga concert through a pair of earholes; it takesearphones to reproduce the signal. If speakersare substituted for the earphones, the listenerhears monophonically, as if standing back severalfeet from the earholes.binder A material (such as lacquer) that acts as aholder and cohesive medium for the particles ofanother material. It is used in carbon resistors,ceramic dielectric bodies, powder cores, and resistiveand metallic paints.binding energy A property of the nucleus of anatom. The binding energy of a nucleus is equal tothe difference between the nuclear weight and thesum of the weights of the lighter particles makingup the nucleus. The nucleus is stable when thebinding energy is high.binding force Any one of the electrostatic forcesthat bind crystals together.binding post A screw-type terminal of variousstyles, often having a hole into which a wire or tipcan be inserted and gripped. It is used for temporaryindoor connections only.binding postbinistor A semiconductor switching device that exhibitstwo stable states and also negative resistance.binocular machine vision Also called stereoscopicmachine vision. The ability of a machine visionsystem to provide depth and perspective data.Uses two optical sensors spaced a fixed distanceapart. The left sensor sees a slightly different imagethan the right sensor. These two images arecombined and processed by a computer, allowingthe machine (such as a mobile robot) to determinethe distances to various objects in its environment.Functions on the same principle asstereoscopic human vision.bin picking In robotics, the selection of a particularobject from a container (bin) in which thereare many objects. Can be done using objectrecognition, bar coding, or passive transponders.It requires a sensor, operating in conjunctionwith a computer that processes the sensed dataand controls the movements of the robot.binomial An algebraic expression containing twoterms joined by a plus or minus sign. Examples:a 2 + b 2 , 3x 3 – 6x.binomial theorem The theorem, proven by IsaacNewton, permits a binomial to be raised to anydesired power without performing the multiplications.In electronics, power series are convenientfor expressing such expressions.biochemical cell A fuel-cell energy source inwhich electricity is generated chemically throughthe oxidation of biological substances. Also calledbiochemical fuel cell.biochip1. A natural, living organism with a physicalstructure that in some way resembles that ofan electronic integrated circuit (IC). 2. A theoreticalpossibility, according to some scientists, butnot yet a practical reality: An IC manufactured bya laboratory process that mimics the way inwhich nature builds living organisms. A form ofartificial life, harnessed for electronic and/orcomputing applications.bioelectricity 1. Electric currents in living tissues,generated by the organism and not applied by externalmeans. 2. The science or study of suchcurrents.bioelectrogenesis The study and application ofelectricity generated by living animals, includinghumans, in the powering and control of electronicdevices.bioelectronics Electronics in relation to the lifesciences—especially the electronic instrumentationof biological experiments.bioengineering 1. The engineering of equipment,such as electron microscopes, electroencephalographs,centrifuges, irradiators, etc., for studyand experimentation in the life sciences. 2. Theengineering of equipment, such as pacemakers,hearing aids, X-ray apparatus, shock-therapyunits, etc., for aid or support-of-life processes.biofeedback A technique in which changes in skintemperature and resistance are detected and displayedby an electronic device.biofeedback monitor A system that provides anindication of skin temperature and resistance toa user. Because skin temperature and resistanceare affected by emotions, such as fear, nervous-

iofeedback monitor • Birmingham wire gauge 75ness, anger, etc., these monitors might be ofvalue to people who wish to gain improved controlof their emotions, and thus perhaps minimize thephysiological effects of stress.biological robot Believed by some researchers tobe possible, but not yet a practical reality: A livingorganism created by biological cloning, whosebrain has been programmed exactly as a computeris programmed.biological shield An absorbent shield that blocksor attenuates ionizing radiation to protect personnelworking near radioactive materials.bioluminescence 1. The emission of light by a livingorganism. 2. The light itself so produced byliving organisms.biomechanism An electromechanical device thatsimulates the workings of some part of a livingbeing’s body. Examples are electromechanicalhands, arms, and legs. Such a device is often difficultto distinguish from its biological counterpartwhen obscured by clothing.biomechatronics A contraction of the words biology,mechanics and electronics. Research, developmentand manufacturing that encompassesaspects of all three fields. This is especially importantin robotics.biometrics Mathematics, and in particular, statisticsand probability, applied to biology.biometric security system An advanced intrusion-preventionsystem that measures biologicalcharacteristics of the people who are authorizedto enter a property. Such a machine can employvision systems, object recognition, and/or patternrecognition to check a person’s face. The machinemight use speech recognition to identifypeople by the waveforms of their voices. It mightrecord a hand print, a fingerprint, or an iris print,or a combination of all these things. A powerfulcomputer analyzes the data obtained by the sensorsand determines whether the person is authorizedto enter the premises.bionics The study, design, and application of microelectronicsystems that simulate the functionsof living organisms.biotelemetry The use of telemetry to collect datafrom living organisms or to direct their movement.biotelescanner An instrument that monitors bodyfunctions via radio, from a great distance.Biot/Savart law A principle of electromagnetismthat expresses the intensity of magnetic field H inthe vicinity of a long, straight wire carrying asteady current I. The basic formula is H = 2I/r,where H is in oersteds, I is in amperes, and r isthe distance in centimeters from the wire.bip Abbreviation of binary image processor.biphase half-wave rectifier An alternative termfor FULL-WAVE RECTIFIER; also, each leg of atwo-diode full-wave rectifier.BIPM Abbreviation of International Bureau ofWeights and Measures.bipolar The condition of possessing two pole sets. Ina conventional (non-FET) transistor, one pole setexists between the base and collector, and anotherpole set exists between the base and emitter.bipolar driving unit A magnetic headphone orloudspeaker in which both poles (north andsouth) of a magnet actuate a diaphragm or lever.bipolar operation See AUTOMATIC POLARITY.bipolar transistor A two-junction transistor whoseconstruction takes the form of a pnp or an npn“sandwich.” Such devices are current-operated,compared with field-effect transistors, which arevoltage-operated. The bipolar transistor (of whichthe familiar npn and pnp types are examples)uses both electron and hole conduction.biquinary code A variety of binary-coded-decimalnotation in which seven bits are used to representeach decimal digit. A number is written intwo groups of bits: a two-bit group followed by afive-bit group. The positional values are 5 and 0for the two-bit group, and 4, 3, 2, 1, and 0 for thefive-bit group.biquinary decade A decade counter that consistsof a binary stage, followed by a quinary stage.bird 1. Slang for orbiting SATELLITE. 2. Slang forguided missile.birdie 1. A spurious beat note in a superheterodynereceiver. So called because of the characteristicchirping sound it makes as the operatortunes by the frequency on which it occurs. 2. Aparasitic oscillation in a radio transmitter, alsocalled a spurious emission or spur.Birmingham wire gauge Abbreviation, BWG. Alsocalled Stubs gauge. A method of designating thevarious sizes of solid wire. BWG diameters aresomewhat larger than corresponding AMERICANWIRE GAUGE diameters for a given wire-sizedesignator.Birmingham Wire Gauge (BWG) DiametersBWG Millimeters Inches1 7.62 0.3002 7.21 0.2843 6.58 0.2594 6.05 0.2385 5.59 0.2206 5.16 0.2037 4.57 0.1808 4.19 0.1659 3.76 0.14810 3.40 0.13411 3.05 0.12012 2.77 0.10913 2.41 0.09514 2.11 0.08315 1.83 0.07216 1.65 0.06417 1.47 0.05818 1.25 0.04919 1.07 0.04220 0.889 0.035

76 bismuth • black boxbismuth Symbol, Bi. A metallic element. Atomicnumber, 83. Atomic weight, 209.bismuth flux meter A flux meter in which the sensorcontains a length of bismuth wire, which actsas a magnetoresistor.bismuth thermocouple A thermocouple that usesthe junction between bismuth and antimonywires. Used in thermocouple-type meters.bistable Having two stable states.bistable device Any device, such as a flip-flop, theoperation of which exhibits two stable states andwhich can be switched at will from one state tothe other.bistable multivibrator A multivibrator, the operationof which exhibits two stable states. Morecommonly known as a FLIP-FLOP. These circuitsare abundant in digital electronic equipment.Compare ASTABLE MULTIVIBRATOR andMONOSTABLE MULTIVIBRATOR.ResetSetbistable multivibratorbistable relay A relay that has two stable states:open and closed. Successive actuating pulsesopen and close the relay, two consecutive pulsesbeing required to return the relay to a given state.Also called binary relay, relay flip-flop, and electromechanicalflip-flop.bistatic radar A radar set in which the transmittingand receiving antennas are separate.bistate Having two states. Example: the performanceof a FLIP-FLOP.bit An acronym formed from the words binary digit.The smallest or elementary unit of data in digitalelectronics. Represented either by logic 0 (low) orlogic 1 (high). These states can be represented byany dichotomy, such as off/on, false/true, minus/plus,dark/bright, red/green, etc.BIT Abbreviation of built-in test.bit density The number of digital bits per unit areaor volume, as the number of bits per square centimeterof magnetic tape.BITE Abbreviation of built-in test equipment.bit rate The speed in BITS PER SECOND (bps) atwhich digital data bits are transmitted or handled.bit-slice processor A microprocessor whose wordor byte capacity is achieved through the use of in-Q−Qterrelated smaller capacity processors (e.g., a 16-bit unit derived from eight 2-bit “slices”).bits per second Abbreviation, bps. An expressionof digital data speed. Commonly used in computercommunications. This unit is often confusedwith, and improperly called, the baud.There is generally a difference between the speedof a signal in baud, and the speed of the same signalin bps. Compare BAUD.bitter pattern A pattern produced in a suspensionof ferromagnetic powder in the presence of an imperfectionin a magnet. The pattern appears as anirregularity that is easy to see.Bjerknes’ equation An expression for the total(primary plus secondary) decrement of a tunedcircuit, based on measurements of the tank currentat the resonant frequency and at a frequencynear resonance.BK 1. Radiotelegraph signal for BREAK. 2. Abbreviationof BREAK-IN.Bk Symbol for BERKELIUM.black-and-white Also called monochrome andgray-scale. Any system of image reproduction,transmission, or reception in which the image iscomposed of opaque elements (black) and whiteor bright areas, as in noncolor television reception.black area An area in which there is only an encryptedsignal.blackboard system A method via which computerscan recognize, and to some extent determinethe meaning of, spoken words and visual images.Incorporates machine vision and/or machinehearing in conjunction with artificial intelligence(AI). Incoming voices and/or images are digitizedand entered into a large-capacity random-accessmemory (RAM). The data is evaluated by sophisticatedsoftware to determine the most logical orprobable interpretations of the sounds and images.blackbody An ideal surface or object, that completelyabsorbs energy of any wavelength thatstrikes it. Such an object is a theoretically perfectradiator of energy at all wavelengths.blackbody radiation Electromagnetic radiationfrom a heated ideal BLACKBODY. This radiationis conceived as covering the entire ELECTRO-MAGNETIC FREQUENCY SPECTRUM. It can beexpressed graphically as a characteristic curvewith a peak at a wavelength that depends on theabsolute temperature of the object. As the absolutetemperature increases, the peak occurs atprogressively shorter wavelengths (higher frequencies).This enables radio astronomers to geta reasonably good idea of the temperatures of distantcelestial objects, such as planets.black box 1. Any “box” or “block” that can be includedin an analysis or synthesis based uponthe BLACK-BOX CONCEPT. 2. Any functionalunit (such as a module) whose operating characteristicsare known, and that can be inserted into

lack box • bleeder resistor 77a system in development or maintenance operations.3. Any subcircuit or stage that can be specifiedin total as required in a system, in terms ofits known or prescribed performance, but whoseinternal structure need not be known.black-box concept A technique for development ofequivalent circuits and of considering their operation.The “box” has a pair of input terminals anda pair of output terminals; one input terminal isoften common to one output terminal. The contentsof the box need not be known, but from theinput and output current and voltage relationships,its nature can be determined. Moreover,from the available input signal and desired outputsignal, the internal circuit of the box can bespecified. Integrated circuits (ICs) are oftentreated as black boxes by engineers designingcomplex electronic equipment.black compression Attenuation of the level of darkareas in a television picture.blacker than black The video-signal amplitude regionabove the level that just darkens the screen.Signal information (such as control pulses) inthis region are therefore not seen.black light 1. Ultraviolet radiation—especiallywhen used to cause visible fluorescence in certainmaterials. 2. A lamp that produces a principalportion of its radiation in the ultravioletregion, causing visible fluorescence of certainsubstances. Such lamps are used in some scientificexperiments, and also for creating special effectsat presentations or parties. It is hazardousto look directly at the output of such a lamp withunprotected eyes.blackout1. A complete interruption of ac utilitypower to numerous customers at the same time.2. A complete cessation of ionospheric radio-wavepropagation, such as might be caused by a solarflare. 3. Complete blanking of the screen of an oscilloscopeor picture tube.black reference In a television signal, the blankinglevel of pulses, beyond which the sync pulse is inthe blacker-than-black region.black reference level In a television signal, thevoltage threshold of the BLACK REFERENCE(i.e., its level above zero volts).black transmission A system of picture or facsimiletransmission in which the maximum copydarkness corresponds to the greatest amplitude(in an amplitude-modulated transmitter) or thelowest instantaneous frequency (in a frequencymodulatedtransmitter). Compare WHITETRANSMISSION.blank1. A piezoelectric plate cut from a quartzcrystal, but not yet finished to operate at a desiredfrequency. 2. To obscure or interrupt a signalor electron beam (usually momentarily), as inz-axis blanking in an oscilloscope. 3. A siliconwafer cut from a large slab, containing dopantsonly. 4. A magnetic diskette or tape on whichnothing is recorded. 5. An optical diskette onwhich nothing is recorded. 6. A location (such asa symbol or space) that is used to verify properdata character grouping and values.blanketing A form of radio interference accompaniedby severe degradation of reception, virtuallyunaffected by tuning, over a wide range of frequencies.An example is ac line noise caused byan arcing power transformer or electrical appliancein the vicinity of a receiving antenna. Ittends to occur most often at low, medium, andhigh frequencies.blanking Obscuring or momentary elimination of asignal (see BLANK, 2).blanking interval The short period during whichthe electron beam of a cathode-ray tube is cut offso that the beam can return to its start positionwithout creating a trace on the screen.blanking level The discrete, predetermined level(usually a threshold voltage) at which BLANKINGoccurs.blanking pedestal In the horizontal pulse of a televisionsignal, the lower portion between zero voltsand the blanking level.blanking pulse A pulse that produces momentaryblanking (see BLANK, 2).blanking time The time interval during which theelectron beam of a cathode-ray tube is interruptedby a blanking signal.blank tape 1. Magnetic tape that has never beensubjected to the recording process and that issubstantially free from noise. 2. Magnetic tapefrom which all preexisting information has beenerased.blasting 1. Severe overloading of a sound system,usually caused by setting the volume control ator near maximum and then applying a significantinput signal to the amplifier. Accompanied by distortion,in its worst form, it can cause damage tospeakers and/or headsets. 2. In a communicationsreceiver, the result of a strong signal comingin unexpectedly when the automatic gain control(AGC) has been switched off, and the audiofrequency(AF) and radio-frequency (RF) gain controlsare set high for reception of weak signals.bleederA resistor or group of resistors, used permanentlyto drain current from charged capacitors.It establishes the predetermined initial loadlevel for a power supply or signal source, and itserves as a safety device in high-voltage powersupplies.bleeder current The current normally flowingthrough a bleeder.bleeder divider A network of resistors, seriesstrungacross the output of a power supply or itsregulator. As a load resistor, the bleeder improvesregulation and protects against no-load voltagesurges. The resistor junctions allow various voltagesto be drawn from the supply.bleeder powerbleeder.bleeder resistorPower dissipated as heat in aSee BLEEDER.

78 bleeder temperature • blocking interference+Powersupply−+V 4+V 3+V 2+V 1Bloch functions Solutions of the Schrodingerwave equation for a single electron surroundedby an electric field. The field varies periodicallywith distance from the source.Bloch wall The transition layer between adjacentferromagnetic domains (see DOMAIN).block 1. A group of data words or digits. 2. A groupof memory storage spaces. 3. A circuit that operatesas an identifiable unit. 4. The symbol for acircuit, stage, unit, or device in a BLOCK DIA-GRAM.block diagram A simplified diagram of an electronicsystem, in which circuits, stages, units, ordevices are shown as two-dimensional boxes withthe internal wiring and detail circuitry omitted.This makes it possible to clearly show the interconnectionamong circuits, stages, units or devices.It also provides a concise rendition of theoverall functional concept of the system.CommonOscRFAmpdcbleeder dividerControlcircuitsPowersupplyModulatorbleeder temperature The operating temperaturein a bleeder. It is generally high because of powerdissipation in the form of heat.bleeding whites A flowing of the white areas of atelevision picture into the black areas; an overloadcondition.blemish See BURN.blind flight The flying of aircraft entirely by meansof instruments and electronic communications.blind landing Landing of an aircraft entirely bymeans of instruments and electronic commnications.blind zone 1. In radar operations, an area that givesno echoes. 2. Skip zone (see ZONE OF SILENCE).blip 1. The pulse-like figure on a radar scan, indicatingthe transmission or reflection (see A-SCANand J-SCAN). Also called PIP. 2. In visual alignmentof a tuned circuit using a sweep generatorand marker generator, the pulse or dot producedon the response curve by the marker signal. 3. Ashort, momentary signal pulse, such as a singleMorse dot.BLIP Abbreviation for background-limited infraredphotoconductor.blip-scan ratio The number of radar scans necessaryto show a visible blip, or echo, on a radarscreen.block diagram(of a radio transmitter)blocked impedance The input impedance of atransducer, whose output load is a theoreticallyinfinite impedance.blockette In a computer, the subdivision of a characterblock that is handled as a unit during datatransfer.blocking action Obstruction of circuit action, usuallyabrupt, through internal action or by theapplication of an external signal. Thus, theoperation of an amplifier can be blocked (outputreduced to zero) by an input signal or by excessivefeedback, either of which overloads theinput.blocking capacitor A capacitor inserted into a circuitto prevent the passage of direct current whileeasily passing alternating current.blocking choke Any inductor, such as a chokecoil, that is used to prevent the flow of an alternatingcurrent while allowing direct current topass with little resistance.blocking interference Radio interference from signalsstrong enough to reduce the receiver outputthrough blocking action.

looper 1. A radio receiver that is in oscillation,and is transmitting a signal that causes interferblockingoscillator • BNC 79B-minus Also called B-negative. The negative terminalof a B-power supply.BNC Abbreviation of bayonet Neill-Concelman. Atype of coaxial connector that can be quickly conblockingoscillator An oscillator that turns itselfoff after one or more cycles. It does this as a resultof an accumulation of negative charge on itsinput electrode (base of a bipolar transistor orgate of a field-effect transistor). The action isrepetitive. In the self-pulsing type of blocking oscillator,a series of pulses consisting of trains ofsine waves with intervening spaces is generated.In the single-swing type of blocking oscillator, theoutput consists of a series of single cycles withlong intervals between them.blocking oscillator synchronization 1. In theBLOCKING OSCILLATOR used in the vertical deflectioncircuit of a television receiver, the oscillatoris synchronized with vertical sync pulsesarriving in the video signal. 2. Synchronization ofthe repetition rate of any blocking oscillator witha suitable external control signal.blocking system In a telephone system, a methodof dealing with the condition of having more subscribersthan connection paths. Allocation ismade on a demand basis. If all channels are inuse, it is impossible to make new calls. This preventsexcessive degradation of the quality of existingconnections.block length The number of characters, bits, orwords that compose a defined unit word or charactergroup.block transfer The conveyance of a word or charactergrouping in a computer register to anotherregister or a peripheral device.blooming On a cathode-ray-tube (CRT) screen, anenlargement of the electron-beam spot, caused bypoor focusing. This results in poor imageresolution.ence. 2. A parasitic oscillation in a radio transmitter.3. In broadcasting, a statement in which aradio or television announcer makes an embarrassingerror or breach of etiquette.blow The opening of a fuse or circuit breaker as aresult of excessive current.blower A fan used to remove heat from electroniccircuits. These are often used in tube-type radiofrequency(RF) power amplifiers, where muchheat is generated, and in computers to cool themicroprocessor and surrounding components.blowout 1. An alternate term for BURNOUT. 2. Theforceful opening of a circuit breaker. 3. The extinguishingof an arc.blowout coil An electromagnet that provides a fieldto extinguish an arc.blowout magnet A permanent magnet that providesa field to extinguish an arc.blst Abbreviation of ballast.blue-beam magnet In a color television picturetubeassembly using three electron guns, a smallpermanent magnet to adjust the static convergenceof the beam for blue phosphor dots.blue box An accessory device (sometimes unlawfullyused) that generates tones that switch a telephonecircuit in the placing of calls.blue glow 1. In a neon lamp, a bluish light thatresults from high-voltage arcing. 2. The normalcolor of the gas discharge in an argon glowlamp. 3. The bluish glow between anode andcathode of a gassy vacuum tube. 4. The normalcolor of the discharge that fills a mercury-vaportube.blue gun The electron in a three-gun color picturetube, the beam from which strikes the blue phosphordots.blueprint1. A type of contact-print reproductionin which a sheet of sensitized paper is exposed toan image on a translucent or transparent film,under strong light, and is then developed andfixed. Although this process is still used to reproduceelectronic illustrations and typescripts, ithas been superseded largely by other (dry) processes.2. Loosely, any plan or design for the developmentof a system.blue restorer In a three-gun color television circuit,the dc restorer in the blue channel.blue ribbon program A computer program thathas been hand-prepared and debugged completelybefore its first computer run.blue video voltage The signal voltage presented tothe grid of the blue gun of a three-gun color picturetube.blurring 1. BLOOMING. 2. A defocusing of a televisionpicture or oscilloscope trace. 3. An obscuringof a signal by echoes or trailing (e.g., the slowdecrement of a Morse code signal element).

80 BNC • Boltzmann’s principleBNCnected and disconnected. It is commonly usedwith test equipment.B-negative Alternative expression for B-MINUS.BNL Abbreviation of Brookhaven NationalLaboratory.BO Abbreviation of beat oscillator. Also abbreviatedBFO.board 1. A panel containing patch jacks. 2. Aprinted circuit.boat A type of crucible in which a semiconductormaterial is melted and sometimes processed. Thematerial of which the boat is made (e.g., graphite)does not react with or contaminate the semiconductormaterial.bobbin 1. A usually nonmetallic spool on which acoil is wound. 2. The form onto which the voicecoil of a loudspeaker is wound.Bode plot A pair of curves plotted to the same frequencyaxis, one showing the gain of a network oramplifier and the other showing its phase shift.Phase and amplitude of active and passive networkscan be exhibited. Also called Bode curveand Bode diagram.body-antenna effect The tendency of the humanbody to act as a receiving antenna when a fingeris touched to the antenna input terminal of a receiveror when a hand (or the whole body) isbrought close enough to the circuit to provide capacitivecoupling.body capacitance Capacitance between the bodyof the operator (as one plate of an equivalent capacitor)and a piece of electronic equipment (asthe other plate). This phantom capacitance is oftenthe cause of detuning and of the injection ofinterfering signals and noise because the bodyacts as a pickup antenna.body electrode 1. An electrode attached to thehuman body (or to the body of a laboratory animal)to conduct body-generated currents to aninstrument, as in cardiography, electroencephalography,and myography. 2. An electrode attachedto the human body (or to the body of alaboratory animal) to conduct currents into thebody, as in shock therapy and skin-resistancemeasurement.body leakage Leakage of current through the bulkor body of a dielectric material, as opposed toSURFACE LEAKAGE.body temperature In a thermistor, a rating thatrepresents the temperature measured on thesurface of the device. It is any combination ofambient temperature, power dissipation, andoperation of the internal heater element (if thethermistor has one).bof Abbreviation of barium oxide ferrite.boffle A loudspeaker enclosure consisting ofstretched screens that are sound absorbing andelastic.bogie Also called bogey. 1. The exact value of aspecified characteristic. Thus, if resistance isgiven as 1 kΩ ±0.5%, the bogie value is 1 kΩ. 2.The average value (i.e., the ARITHMETIC MEAN).3. A false or unidentified echo on a radar screen.Bohr atom The concept of the nature of the atom,proposed by Niels Bohr in 1913 partly to explainwhy the electrons in the Rutherford atom do notfly off into space or fall into the nucleus. The Bohrtheory places the electrons in permissible orbitswhere they cannot radiate energy (see BOHR RA-DIUS). They can radiate or absorb energy, however,if they go to a lower orbit or to a higher orbit,respectively. Compare RUTHERFORD ATOM.bohrium Symbol, Bh. Also called unnilseptium(Uns). Atomic number, 107. The most commonisotope has atomic weight 262. Classified as atransition metal. It is human-made and is notknown to occur in nature.Bohr radius Symbol, a 0 . A physical constantwhose value is approximately 5.291772 × 10 –11meter.boiling point Abbreviation, bp. The temperature atwhich a liquid vaporizes. The boiling point of waterin air at a pressure of one atmosphere is100°C or 212°F.bolometer Any device that is essentially a small,nonrectifying, temperature-sensitive resistor thatcan be used for heat sensing, radio-frequencypower measurement, curve changing, demodulation,circuit protection, etc. Included in this categoryare the BARRETTER, the THERMISTOR, andthe wire-type FUSE.bolometer bridge A dc bridge in which a bolometeris one of the four arms. The bridge is balancedfirst with the bolometer cold. The bolometer thenis excited with a radio-frequency (RF) current,whereupon the resultant heating changes thebolometer resistance. The bridge is rebalanced forthe new resistance. The RF power driving thebolometer is determined according to a predeterminedfunction of bridge settings versus RF inputpower.Boltzmann constant Symbol, k. A figure that entersinto the calculation of thermionic emissionand of thermal noise factor. It represents the temperatureequivalent of work function, in electronvolts per Kelvin (eV/K) or joules per Kelvin (J/K).The values are approximately:k = 8.617 × 10 –5 eV/K = 1.38 × 10 –23 J/KBoltzmann’s principle A description of the statisticaldistribution of large numbers of tiny particlesunder the influence of a force, such as anelectric or magnetic field. When the system is in

Boltzmann’s principle • booster 81statistical equilibrium, the number of particles inany portion of the field is given by:N E = N–E/kT 0ewhere E is the potential energy of a particle in theobserved area, N 0 is the number of particles perunit volume in a part of the field where E is zero,k is the BOLTZMANN CONSTANT, T is the absolutetemperature of the system of particles, and eis approximately equal to 2.718.bombardment The usually forceful striking of atarget with rays or a stream of particles.bond 1. An area in which two or more items are securelyand intimately joined. 2. The attractiveforce that holds an atomic or subatomic particleor particle group together.bonded-barrier transistor A bipolar transistor inwhich the connection at the base region is alloyed.bonded negative-resistance diode A diode thatdisplays a negative-resistance characteristic overpart of its current curve. This results fromavalanche breakdown.bond energy In a molecule, the energy necessaryto break an atomic bond.bonding 1. The formation of bonds between adjacentatoms in a crystalline material, such as asemiconductor. See specifically COVALENTBINDING FORCES, IONIC BINDING FORCES,and METALLIC BINDING FORCES. 2. The securefastening together of conducting surfaces, as bysoldering or brazing, to produce a high-conductance,leak-free continuum.bond strength The minimum stress required toseparate a material from another to which it isbonded.bone-conduction transducer A device used inplace of the earphone in a hearing aid to conveysound energy to the bone structure of the head.Bongard problem A method of evaluating how wella machine vision system can differentiate amongpatterns. Similarities and differences are notedbetween objects in two sets of boxes. It was developedfor object-recognition systems, mainly foruse in intelligent robots.book capacitor A variable capacitor in which themetal plates are bonded along one edge and separatedfrom each other by means of mica sheets.The capacitance is varied by opening and closingthe assembly book fashion. It is used as a padderor trimmer.Boolean algebra A system of symbolic logic. Statementsare represented as symbols, usually variablessuch as x, y, and z. The logical AND operationis represented by multiplication; the logicalinclusive OR operation is represented by addition;the logical NOT operation is represented bya minus sign or a line over the element symbol.The system has rules, definitions and axioms viawhich theorems can be derived. Used by engineersin the design of digital electronic circuits.Boolean truth tableAND NOT ORx y xy x x + y___________________________________________________0 0 0 1 00 1 0 1 11 0 0 0 11 1 1 0 1Boolean function In mathematical logic, a functionthat makes use of BOOLEAN ALGEBRA.Boolean theoreams1. x + 0 = x (additive identity)2. x1 = x (multiplicative idenity)3. x + 1 = 14. x0 = 05. x + x = x6. xx = x7. (x’)’ = x (double negation)8. x + x’ = 19. x’x = 010. x + y = y + x (commutativity of addition)11. xy = yx (commutativity of multiplication)12. x + xy = x13. xy’ + y = x + y14. x + y + z = (x + y) + z = x + (y + z)(associativity of addition)15. xyz = (xy)z = x(yz) (associativity of multiplication)16. x(y + z) = xy + xz (distributivity)17. (x + w) (y + z) = xy + xz + wy + wz (distributivity)boom 1. A horizontal support for a microphone,enabling the microphone to be suspended over asound source, but out of the sight of a camera.2. A horizontal support for a small antenna that isundergoing tests or sampling the field of anotherantenna. 3. The supporting element in a Yagi,quad, or log-periodic antenna. It establishes thecenter of gravity and directional axis of the radiationpattern. The driven element(s) and parasiticelement(s) are attached, usually at rightangles.boost capacitor In the damper circuit of a televisionreceiver, the capacitor that is used to boostthe B-plus voltage. Also called booster capacitor.boost charge A high-current, short-interval chargeused to revitalize a storage battery quickly. Alsocalled booster charge.booster 1. Any device used to increase the amplitudeof a signal (e.g., as an amplifier or preamplifier)or of an energy source (e.g., to boost theoutput of a power supply). 2. A radio-frequencypreamplifier used ahead of a television receiver.

82 booster battery • bow-tie testbooster battery 1. A battery used to forward bias adiode detector into a favorable region of its conductioncurve, or to bias a bolometer into thesquare-law region of its response. 2. A batterysupplying power to a booster.booster gain The amplification (usually in terms ofvoltage gain) provided by a booster (see especiallyBOOSTER, 2).boot 1. The powering-up routine in a digital computer,in which the machine executes a series ofprograms to get itself ready for use. 2. Theresetting of a computer, by pressing certain keyboardkeys (e.g., CTRL-ALT-DEL), pressing a resetbutton, or by powering-down, waiting abouttwo minutes, and then powering-up again. 3. Toinstall a computer diskette and instruct the computerto execute one or more programs on thediskette. 4. A usually flexible protective nipple orjacket pulled over a cable or connector, so calledfrom its resemblance to a foot boot.boot loader A form of computer program that operateson the BOOTSTRAP ROUTINE.bootstrap A technique for making a device or processachieve a condition through its own actions;see BOOTSTRAP CIRCUIT, for example.bootstrap circuit A specialized form of followercircuit that presents very high input impedance.Its chief feature is the return of the control-elementresistor to a tap on the source or emitter resistor.The technique takes its name from thefigurative notion that such a circuit “lifts its inputimpedance by its own bootstraps.”Signal inputC1R1Vdc+ −R2R3C2Signal outputbootstrap circuit(with junction-type field-effect transistor)bootstrap routine 1. Also called bootstrap program.In a digital computer, and especially in apersonal computer, the routine that the machinefollows when first powered-up. See BOOT, 1.2. In a digital computer, a routine in which the firstfew instructions put in storage are later used tocomplete the routine, as supplemented by someoperator instruction. 3. A portion of a computerprogram that is used to establish an alternateversion of the program.borax-aluminum cell An electrolytic cell that consistsessentially of an aluminum electrode and alead electrode in a saturated solution of sodiumtetraborate (borax). After electroforming, such acell can be used either as a rectifier or as an electrolyticcapacitor.boric acid Formula, H 3 BO 3 . A compound used variouslyin electronics—especially as the electrolytein electrolytic capacitors.bornite Formula, Cu 5 FeS 4 . A natural mineral thatis a sulfide of copper and iron. Its crystallinestructure made it important in early semiconductordiodes (crystal detectors).boron Symbol, B. A metalloidal element. Atomicnumber, 5. Atomic weight, 10.82. It is used as adopant in semiconductor processing.bot 1. Abbreviation for beginning of tape. 2. Abbreviationof bottom.bottoming Excessive movement of the cone of aloudspeaker or the diaphragm of a headphone sothat the magnet or supporting structure is struckby the moving-coil piston assembly. It produces aclapping sound, particularly on bass (lowfrequency)audio peaks.bounce 1. The springback or vibration of the armatureof a relay on closure. 2. An abnormal,abrupt change in the brightness of the image in atelevision receiver or cathode-ray-tube (CRT)computer monitor.boundary 1. In a polycrystalline substance, thearea of contact between adjacent crystals. 2. Thearea of meeting of two regions (such as n and p)in a semiconductor.boundary defect A condition in which a piezoelectriccrystal has two regions, intersecting in aplane, with different polarizations.boundary effect In audio systems, a pheno-menonin which the proximity of an acoustic transducerto a flat surface enhances the pickup and/ortransmission of sound. Occurs because of reflectionof acoustic waves from the surface.bound charge The portion of the electric charge ona conductor that does not escape to ground whenthe conductor is grounded. This occurs becauseof induction from neighboring charge carriers.Compare FREE CHARGE.bound electron An electron held tightly in its orbitwithin an atom so that it is not ordinarily free todrift between atoms and contribute to electriccurrent flow.bow-tie antenna A center-fed antenna in whichthe two horizontal halves of the radiator are triangularplates that resemble a bow tie. A flat reflectorconsisting of closely spaced horizontalwires is mounted behind the triangles.bow-tie test An oscilloscope-display checkout of asingle-sideband (SSB) signal, in which the appearanceof the display indicates the signal quality.The transmitter output signal is fed to the

ow-tie test • brass pounder 83vertical deflection plates of the oscilloscope. Theexciter audio output is fed to the horizontal sweepinput of the scope.boxcars Long pulses with short separating spacesbetween them.box-shaped loop The characteristic square-loophysteresis curve (B-H loop) that result when asine wave of current is used to magnetize a sampleof magnetic material. In this plot, which coversall four quadrants, the horizontal axis (H)displays magnetizing force, and the vertical axis(B) displays magnetization. Also see HYSTERE-SIS.Boys radiomicrometer A detector for radiant energy.The device consists of a thermocouple and agalvanometer. When energy falls on the thermocouple,a voltage is produced, and this is measuredby the galvanometer.bp 1. Abbreviation of BOILING POINT. 2. Abbreviationof BANDPASS.bpi Abbreviation of bits per inch.B-plus Also called b-positive. 1. Symbol, B+. Thepositive dc voltage required for certain electrodesof vacuum tubes, transistors, etc. 2. The positiveterminal of a B power supply.B positive See B-PLUS.B power supply A name used sometimes for theunit that supplies high-voltage dc energy to avacuum tube plate or screen circuit.bps Abbreviation of BITS PER SECOND.Br Symbol for BROMINE.bracketing A troubleshooting routine characterizedby isolating progressively smaller areas in acircuit or chain of stages until the defective subcircuitor stage is located.Bradley detector A locked-oscillator circuit thatwas once used as an FM detector.braid 1. A woven network of fine metal wires usedfor grounding purposes. It is usually made of finecopper conductors. The increased surface-areato-volumeratio improves the conductivity, at radiofrequencies, over a single conductor that hasthe same cross-sectional area. Braid can betinned (saturated with solder) to retard corrosion.2. It is also called a shield. The outer conductor inprefabricated coaxial cable.braided wire A length of braid. Used for groundingor shielding purposes.brain waves Alternating or pulsating voltages thatare caused by electrical activity in the brain of ananimal or human being. The voltages can bepicked up by electrodes attached to the scalp,and amplified to be viewed on a cathode-ray-tube(CRT) screen, heard by headphones or speakers,or traced by an electroencephalograph.branch1. Any one of the separate paths of acircuit. With respect to the layout of its components,a branch can be series, parallel, seriesparallel,parallel-series, or any combination ofthese. It is also called a LEG. 2. See BRANCHCIRCUIT.branch circuit In electrical wiring, a group of outletsserved through a single cutout from a sourceof power-line ac voltage. The source can be a distributioncenter, subdistribution center, main, orsubmain. Interior lighting circuits are usuallybranch circuits because many lights are connectedto one circuit controlled by a single fuse orcircuit breaker.ServiceMaindistributioncenterFeederBranchSubdistribution centerSubfeederMainSubdistributioncenterSubmainLoadbranch circuit(enclosed in broken lines)SubfeederCutoutbranch current Current flowing through a branchof a circuit, whose magnitude, with respect to thetotal current of the circuit depends on the natureof the branch.branched In molecular polymers, the condition ofside chains being attached to the main chain.branched windings Forked windings of a polyphasetransformer.branching In robotics and artificial intelligence(AI), a set of routines or programs containingpoints at which a computer must select fromamong two or more alternatives. Such routinesare used in critical processes, such as the manufactureof precision equipment.branch point See JUNCTION POINT.branch voltage The voltage, or voltage drop,across a branch of a circuit.brass 1. An alloy of copper and zinc that is widelyused in electronics. Compared to annealed copper,this metal has four times the resistivity (or 1 ⁄4the conductivity), half the temperature coefficient,more than twice the tensile strength, and alower melting point (900°C). 2. A colloquialism foran old-fashioned, straight telegraph key.brass pounder 1. Colloquialism for telegraph operatoror radiotelegraph operator. 2. A radio ama-

84 brass pounder • brevity codeteur who handles large amounts of message traffic,particularly via Morse code. 3. A radio amateurproficient in Morse code operation.Braun electroscope An electroscope consisting essentiallyof a fixed metal vane to which a movableneedle is fastened at a pivot. The repulsion betweenthe two, when an electric charge is applied,causes the needle to move over a calibrated scale.bravo Phonetic representation of the letter B.brazing The joining of two metal (usually iron orsteel) parts together with a suitable melted copper-alloymetal. Compare SOLDERING.breadboard 1. A perforated board, a chassis, orany basic framework on which electronic componentscan be mounted and quickly wired for thepreliminary test of a circuit. It is so called becausethe first such foundation units of this sortactually were wooden breadboards. 2. Any preproductionelectronic prototype circuit. 3. To setup a circuit on a breadboard.breadboard model 1. The preliminary model of anelectronic device, often built on a breadboard (seeBREADBOARD, 1). 2. Loosely, any prototype.break 1. An open circuit. 2. To open a circuit. 3. Incommunications, a word indicating a desire totransmit on a wavelength already occupied by radiotraffic. 4. See BREAK-IN, 1.break-before-make contacts Contacts, especiallyin a rotary selector switch, that open one circuitbefore closing the next one.breakdown 1. Failure of a circuit or device, causedmainly by excessive voltage, current, or power. Asudden high current, however, does not alwaysindicate failure. 2. AVALANCHE BREAKDOWN.3. The separation of an electronics problem orproject into its constituent parts for an easiersolution.breakdown diode See ZENER DIODE.breakdown region The region, in a pn junction, inwhich avalanche breakdown occurs.breakdown strength See DIELECTRIC STRENGTH.breakdown voltage 1. The voltage at which currentsuddenly passes in destructive amountsthrough a dielectric. 2. The voltage at which a gassuddenly ionizes, as in a gas tube. 3. The voltageat which the reverse current of a semiconductorjunction suddenly rises to a high value (nondestructiveif the current is limited). SeeAVALANCHE BREAKDOWN.break-in 1. A technique of radio communication inwhich one station interrupts a transmission fromanother station, rather than waiting until the endof the latter’s transmission. 2. Also called fullbreak-in. In a radio communications transceiveror transmitter/receiver combination, extremelyrapid transmit/receive switching, approachingfull duplex communications. Every pause intransmission, even of only a few milliseconds,creates a “receive window” allowing receptionbetween spoken words or Morse code elements.3. BURN-IN.breaking current The momentary current thatflows when the contacts of a switch or relay arebroken.break-in keying A system of radiotelegraph keyingin which the receiver is in operation whenever thekey is open. See BREAK-IN, 2.break-in operation In radiotelegraph or singlesideband(SSB) communications, the practice ofinterrupting at any time to “talk back” to theother transmitting station. This operation ismade possible by high-speed transmit/receiveswitching. See BREAK-IN, 2.break-in relay An electromechanical or solid-staterelay that enables break-in operation. Largelysupplanted by solid-state switching devices.breakover point In a silicon-controlled rectifier,the source-voltage value at which the load currentis suddenly triggered to its steep climb. Alsocalled TRIGGERING POINT.breakover voltage In a silicon-controlled rectifierwith open gate circuit, the anode voltage at whichanode current is initiated.breakpoint A point in a computer program when,for the purpose of obtaining information for theprogram’s analysis, the sequence of operations isinterrupted by an operator or a monitor program.breakpoint frequencies The upper- and lowerfrequencypoints at which the gain-versusfrequencyresponse of an amplifier or networkdeparts from flatness.breakpoint instruction An instruction that stopsa computer.breakthrough 1. A new discovery, insight, or solutionto a problem that results in an advancementin the state of the art. 2. See PUNCHTHROUGH.3. See BREAKDOWN, 1. 4. See AVALANCHEBREAKDOWN.break time The time taken for a relay to drop outcompletely or a switch to open. Compare MAKETIME.breathing Slow, rhythmic pulsations of a quantity,such as current, voltage, brightness, beat note,etc.breezeway In a sync pulse in NTSC color television,the part of the back porch between the trailingedge of the pulse and the color burst.B-register An index register in a computer for storingwords that are used to change an instructionbefore it is executed by the program.Bremsstrahlung radiation The radiation emittedby a charged particle whose speed is altered whenit passes through the electric field in the vicinityof an atomic nucleus.brevity code A code not intended to conceal information,but to shorten the number of charactersin a message or data file. The Q SIGNALS are anexample of a brevity code used in communications.In computer data transfer and communications,brevity codes allow compression, speedingup the transfer rate and reducing the storagespace for a given amount of data.

Brewster angle • bridge-type meter 85Brewster angle From BREWSTER’S LAW, the polarizingangle at which the reflected and refractedrays of incident light are perpendicular to eachother.Brewster’s law (Sir David Brewster, 1781–1868).For any dielectric reflector, the relationship inwhich the refractive index is equal to the tangentof the polarizing angle.bridge 1. A network, usually consisting of fourbranches, connected so that an input signal canbe applied between two opposite points and theoutput taken between the other two oppositepoints. When the component values are in a certainratio, the voltage between the output pointsis zero, and the bridge is said to be balanced orset to null. 2. A circuit such as that described in(1) used for electrical measurements. 3. An audioor servo amplification system in which the load isdriven from two outputs having opposite polarity,neither of which are at ground potential. 4. Acommunications path between or among two ormore networks. This allows the subscribers inany network to obtain data from, or send data to,any other network, in effect creating a network ofnetworks.bridge balance control A potentiometer, variablecapacitor, or variable inductor that is used to adjusta bridge circuit to balance.bridge-connected amplifier 1. A dc amplifierstage in which the transistors and resistors areconnected in a four-arm bridge circuit, with respectto dc. When the bridge is initially balanced,all dc is eliminated in the output load. The inputsignal unbalances the bridge, which results in anamplified output signal in the load. 2. An amplifierpair having opposing outputs across which aload can be bridged to obtain twice the power outputof either amplifier alone.bridged differentiator See HALL NETWORK.bridge detector The output-indicating device(e.g., meter, oscilloscope, or headphones) thatindicates whether a bridge is balanced or unbalanced.Also called null detector or null indicator.bridged integrator A null network that consists ofa two-stage resistance-capacitance (RC) integratorcircuit bridged by a capacitor. This networkproduces a shallow null at a single frequency determinedby the R and C values in the integrator.Compare HALL NETWORK.bridged-tee attenuator An attenuator consistingof a tee section, between the input and output ofwhich is bridged a single-series arm.bridged-tee circuit Any circuit (of resistors, capacitors,inductors, or a combination of these)that consists of a tee section, bridged by a singleseriessection, from input to output.bridged-tee null network A bridged-tee circuit ofresistance (R) and capacitance (C), proportionedso that at some setting of the R and C values, theoutput of the circuit is zero.InputC1R1 R2 R3C2C 1 = C 2 = C 3R 1 = R 2 = R 3f null =1.7322πR 1 C 1bridged-tee oscillator A low-distortion oscillatorcircuit whose frequency is determined by abridged-tee null network inserted into the negative-feedbackpath of the circuit.bridge feedback A combination of current feedbackand voltage feedback around an amplifiercircuit. It is so called because, in the feedback circuit,the resistors and the output resistance ofthe amplifier form a four-arm bridge.bridge generator The power source (e.g., a batteryor oscillator) that supplies the signal to a BRIDGEused for electrical measurements.bridge indicator See BRIDGE DETECTOR.bridge oscillator See BRIDGE GENERATOR.bridge rectifier A full-wave rectifier circuit inwhich four rectifying diodes are connected in abridge configuration. Each half-cycle of ac inputis rectified by a pair of diodes in opposite quartersof the bridge and in series with each other. Thebridge does not require a transformer with acenter-tapped secondary, as does the FULL-WAVE, CENTER-TAP RECTIFIER circuit.bridge source See BRIDGE GENERATOR.bridge-type meter A frequency-sensitive bridge(such as the Wien bridge) that can be used tomeasure audio frequency. Because the bridgecan be balanced at only one frequency at a time,C3bridged integratorOutput

86 bridge-type meter • British Standard wire gaugeits adjustable arm can be calibrated to read thefrequency directly.bridge-type impedance meter An impedancemeasuringcircuit in which unknown impedanceZ is connected in series with a calibrated variableresistor R. An ac voltage is applied to the seriescircuit. The separate voltage drops across the resistorand impedance are measured successivelyas the value of R is varied. When the two voltagedrops are identical, Z equals R, and theimpedance can be read from a calibrated dial onthe variable-resistor control.bridge-type oscillator A resistance-capacitance(RC) tuned oscillator in which a Wien bridge isused as the frequency-determining circuit in thefeedback loop.bridge-type power meter 1. See BOLOMETERBRIDGE. 2. A four-arm bridge specially designedto operate at radio frequencies. At null, theimpedance of the unknown is read directly fromthe balancing dial or calculated from bridge constants.This instrument is used to measure theimpedance of circuit components, antennas, andtransmission lines.bridge-type SWR meter A four-arm bridge that isspecially designed to operate at radio frequencies.At null, the standing-wave ratio (SWR) is calculatedfrom the bridge resistance values or readfrom a direct-reading scale on the null-indicatingmeter.bridging amplifier An amplifier whose input impedanceis so high that it can be considered infinitefor practical purposes. Thus, the amplifiercan be connected across a load or line withoutsignificantly affecting the operation of the system.bridging coupler A voltage-dependent resistor thatpermits an occasionally used device (such as a bell)to be connected permanently across a regularlyused device (such as a telephone) without continuouslyshort-circuiting the latter. Thus, the bridgingcoupler ordinarily has very high resistance; butwhen the line voltage is momentarily raised, the resistancelowers and the occasionally used device isactuated (e.g., the bell rings).bridging gain The gain of a bridging amplifier expressedas the ratio (in decibels) of the power developedin the amplifier load to the power in theload to which the input terminals of the amplifierare connected.bridging loss The loss that results from the shuntingof a speaker, microphone, earphone, or othertransducer by a resistor, capacitor, or inductor.Generally, the loss is expressed as a power ratioin decibels.Briggsian logarithm (Henry Briggs, 1556-1631). Abase-10 logarithm, generally known as aCOMMON LOGARITHM. Compare NAPIERIANLOGARITHM.brightness SI unit, candela per square meter(cd/m 2 ); cgs unit, lambert (L). The quantity oflight, per unit area, emitted or reflected perpendicularto a light-emitting surface.brightness control 1. In a computer monitor, televisionreceiver, or oscilloscope, a potentiometerthat varies the negative bias voltage on the controlgrid of the cathode-ray tube (CRT). Thebrightness of the image is inversely proportionalto this negative bias voltage. 2. The control of thebrightness of an illuminated area.brilliance See BRIGHTNESS.brilliance control 1. The BRIGHTNESS CONTROLin a television receiver or computer monitor. 2.The brightness control in a cathode-ray oscilloscope.3. A control for adjusting the level of thetweeter output in a speaker system.British Standard wire gauge Abbreviation, NBSSWG. A classification of wire sizes sometimesused in England, Australia, and New Zealand.The higher the number, the thinner the wire. Thedesignator does not take into account any coatingson the wire, such as enamel, rubber, or plasticinsulation. In the United States, the Americanwire gauge is more often used. See AMERICANWIRE GAUGE.British Standard Wire Gauge (NBS SWG) DiametersNBS SWG Millimeters Inches1 7.62 0.3002 7.01 0.2763 6.40 0.2524 5.89 0.2325 5.38 0.2126 4.88 0.1927 4.47 0.1768 4.06 0.1609 3.66 0.14410 3.25 0.12811 2.95 0.11612 2.64 0.10413 2.34 0.09214 2.03 0.08015 1.83 0.07216 1.63 0.06417 1.42 0.05618 1.22 0.04819 1.02 0.04020 0.91 0.03621 0.81 0.03222 0.71 0.02823 0.61 0.02424 0.56 0.02225 0.51 0.02026 0.46 0.01827 0.42 0.016428 0.38 0.014829 0.345 0.013630 0.315 0.012431 0.295 0.011632 0.274 0.0108

British thermal unit • broad response 87NBS SWG Millimeters Inches33 0.254 0.010034 0.234 0.009235 0.213 0.008436 0.193 0.007637 0.173 0.006838 0.152 0.006039 0.132 0.005240 0.122 0.0048British thermal unit Abbreviation, Btu. Theamount of heat required to raise the temperature ofa pound of water by one degree Fahrenheit, in anambient environment of slightly greater than 39°F.broadband Also called wideband. Possessing acharacteristic wide bandwidth or range of operatingfrequencies. This term can be applied at audiofrequencies (AF) or radio frequencies (RF), and isfrequently used to describe the performance ofoscillators, amplifiers, antennas, and varioustypes of networks. The term can also be applied todescribe the nature of electromagnetic emissionsor noise. Examples are given in the following severaldefinitions. Compare NARROWBAND.broadband amplifier An amplifier that has verywide frequency response, such as 10 Hz to 10MHz. Examples are an instrument amplifier anda video amplifier.broadband antenna An antenna that operates satisfactorilyover a comparatively wide band of fre-Input+12 Vbroadband amplifierOutputquencies without requiring retuning at individualfrequencies. Examples are the log-periodic anddiscone antennas.broadband electrical noise Electrical noise that ispresent over a wide frequency spectrum (e.g., 3kHz to 30 MHz).broadband I-F An intermediate-frequency (IF) amplifieror amplifier chain. The wide frequency responseis important when an increased bandpassis preferred to high selectivity, as in high-fidelityradio tuners.broadband interference Interference, other thannoise, that is present over a wide band of frequencies.An example is over-the-horizon shortwaveradar, recognizable by its characteristic“woodpecker” sound in communications receiversat high frequencies.broadband Klystron A Klystron oscillator with abroadbanded tuned circuit.broadband tuning Receiver tuning characterizedby a selectivity curve having a pronounced flattop or broad nose that passes a wide band of frequencies.Also called broadband response.broadcast1. A radio-frequency transmission of anintelligence-bearing signal that is directed to numerousunspecified receiving stations. 2. Thetransmission or dissemination of signals to alarge, unspecified number of receiving stations.broadcast band Any band of frequencies allocatedfor broadcasting (see BROADCAST SERVICE, 1),but particularly the U.S. standard amplitudemodulation(AM) and frequency-modulation (FM)radio broadcast bands at 535 to 1605 kHz (AM)and 88 to 108 MHz (FM).broadcasting The dissemination of signals for receptionby the general public, not for communicationspurposes.broadcast interference Abbreviation, BCI. Interferenceto normal reception by broadcast receivers,usually arising from signals emitted byother stations.broadcast receiver A receiver intended primarilyto pick up standard broadcast stations. Also seeBROADCAST BAND.broadcast service 1. Any radio transmitting service(including television) that exists for the purposeof sending out electromagnetic signals forgeneral reception, rather than addressing them tospecific receiving stations. 2. The service providedby a station operating in the broadcast band.broadcast station Any station in the broadcastservice, but especially one assigned to operate inthe standard U.S. broadcast bands. Also calledbroadcasting station.broadcast transmitter A radio transmitter designedspecifically for, and operated in, thebroadcast service.broad response Slow deflection of an indicator,such as a meter, over a relatively wide range ofvalues of the input quantity.

88 broadside • bubble memorybroadside In a perpendicular direction; for example,broadside radiation from an antenna.broadside antenna See BROADSIDE ARRAY.broadside array Also called broadside antenna. Aphased group of antennas arranged so maximumradiation occurs in directions perpendicular tothe plane containing the driven elements. This requiresthat all of the antennas be fed in phase.The elements can be half-wave dipoles or fullwave,center-fed conductors. Full-wave elementshave a slight gain over half-wave elements. Athigh frequencies, this type of array is usuallyconstructed from two driven antennas. At veryhighand ultra-high frequencies there can be severaldriven antennas. The antennas can eachconsist of a single element, or they can be Yagis,loops, or other systems with individual directiveproperties. In general, the larger the number ofelements in the entire array, the greater the gainand directivity.PhasinglinesToTXbroadside arrayIn-phasedipolesMaximumradiationbroad tuning Tuning that is characterized bypronounced signal width, often resulting inadjacent-channel interference. A common causeof such impaired selectivity is low Q in the tunedcircuit(s).Broca galvanometer A device consisting of anastatic magnetic arrangement, with a coil enclosingcentral consequent poles. The device is characterizedby fast response and high sensitivity.bromine Symbol, Br. A nonmetallic element of thehalogen family. Atomic number, 35. Atomicweight, 79.90.bronze An alloy of copper and tin that has varioususes in electronics. Also see PHOSPHOR BRONZE.Brown and Sharpe gauge See AMERICAN WIREGAUGE.Brownian movement (Robert Brown, 1773 –1858).Random movement of microscopic particles—especially in solutions. It occurs because of colli-sions of molecules with the particles. Einsteinshowed, in his early work, a connection betweenthis movement and the Boltzmann constant.brownout A deliberate lowering of line voltage by apower company to reduce load demands. Minorevents of this type often pass unnoticed by theaverage consumer. More pronounced events produceobservable effects, such as shrinkage oftelevision and cathode-ray-tube (CRT) computerdisplayimages.Bruce antenna A vertical collinear array that consistsof several resonant sections connected byshort, rigid, parallel-conductor stubs. The currentsin the radiating sections are in phase. Maximumradiation and response occur broadside tothe antenna (omnidirectional in the horizontalplane). Polarization is vertical. The antennaproduces gain at low radiation and responseangles, and is commonly used in repeater installationsand fixed communications stations atvery-high frequencies (VHF) and ultra-high frequencies(UHF).brush A usually metal or carbon strip, blade, orblock, that slides in contact with another part, asin a motor commutator.brush discharge Also called Saint Elmo’s fire. Acloud of repelled ions around the tip of a pointedconductor charged to a high voltage. It often producesa visible glow in the air.brush holder The housing for a brush in a motor,generator, rheostat, slip-ring junction in a rotatingdata-transmission system, etc.brute force 1. The transmission of a signal of excessiveor unnecessary power. 2. An inefficientapproach to a problem, which might solve theproblem, but requires far more energy, effort, orcomputer memory/storage space than the minimumneeded to accomplish the same result.brute-force filter A pi-type lowpass dc powersupply filter, so called because of the extremelylarge inductances and capacitances that aregenerally used.brute supply An unregulated power supply.B-scope A cathode-ray tube (CRT), used in radar,that presents a B DISPLAY.B service A teletype communication system operatedby the Federal Aviation Administration(FAA).B-supply The dc power supply that provides anodeoperating voltages, such as plate and screen voltagesin a vacuum-tube radio-frequency (RF)power amplifier.BT-cut crystal A piezoelectric plate cut from aquartz crystal at an angle of rotation (relative tothe x-axis) of -49°. It has a zero temperature coefficientof frequency at approximately 25°C. Alsosee CRYSTAL AXES and CRYSTAL CUTS.Btu Abbreviation of BRITISH THERMAL UNIT.BuAer Abbreviation of Bureau of Aeronautics.bubble memory In digital-computer practice, aspecial type of static magnetic memory. The mag-

ubble memory • bulk effect 89netic material is divided into regions that aremagnetized in different directions. So called becausethe flux lines of the tiny magnetized regionsare shaped somewhat like, and move around afterthe fashion of, bubbles on the surface of aglass of soda.bubble shift register A shift register that uses amagnetic bubble (see BUBBLE MEMORY) thatcan be moved sequentially from electrode to electrodeon a wafer.bubbling See MOTORBOATING.bucket A computer memory or a designated locationin such a memory.buckingThe process of counteracting one quantity,such as a current or voltage, via series orparallel application of a similar quantity that hasopposite polarity (180 degrees out of phase).bucking circuit 1. A circuit used to obtain buckingaction. The simplest form is a battery and potentiometerthat supply a variable voltage ofpolarity opposite to that of the voltage to bebucked. A more sophisticated form is an ac transformer,the secondary of which is connected inseries and out of phase with the ac utility line. 2.The zero-set circuit in an electronic voltmeter.bucking coil A coil placed and positioned so thatits magnetic field partially or completely cancelsthe field of another coil. Troublesome hum fieldssometimes are neutralized with such a coil.bucking voltage See BACK VOLTAGE, 2.buckling The warping of storage-battery plates, usuallyresulting from excessive charge or discharge.buckshot In an amplitude-modulated (AM) or single-sideband(SSB) radio transmission, broadbandsignal splatter caused by excessive modulation,or detuned multiplier circuits.buffer1. An amplifier used principally to matchtwo dissimilar impedance points and isolate onestage from a succeeding one in a cascaded system,and thus to prevent undesirable interactionbetween the two. 2. In a digital computer, a storagesite used temporarily during data transfers tocompensate for differences in data flow rates. 3.In digital-computer operations, a follower stagethat is used to drive a number of gates withoutoverloading the preceding stage.UnbufferedinputTimebuffer, 2.Bufferedoutputbuffer amplifier See BUFFER, 1.buffer capacitor A high-voltage fixed capacitorthat is placed across a transformer secondary tosuppress voltage spikes and sharp waveforms—especially when the input is a square wave.buffer circuit 1. In a data system that uses a keyboard,an electronic circuit that allows the operatorto type ahead of the data output. 2. SeeBUFFER, 1, 2 and 3.buffered output An output (power, signal, etc.)that is delivered from the generating devicethrough an isolating stage, such as a buffer amplifier.This arrangement protects the device fromvariations in the external load. Compare UN-BUFFERED OUTPUT.buffer storage 1. A buffer that is used to interfacebetween data systems with different rates oftransmission. 2. See BUFFER, 2.bug 1. Slang for WIRETAP, 1. 2. Slang for circuitfault, 1. 3. A semiautomatic key that some radiotelegraphoperators use to send Morse code.bug key See BUG, 3.building-block technique The process of assemblingelectronic equipment by quickly connectingtogether already completed stages (in the form ofboxes or blocks) and supplying power and signalsto the setup. Also called modular technique andmodular construction.building-out circuit A short section of transmissionline shunting another line; it is used forimpedance matching. Also called building-outsection.buildup 1. The process whereby the voltage of a rotatinggenerator starts at a point that is determinedby the residual magnetism of the machine,and gradually increases to a voltage representingthe point at which the resistance line crosses themagnetization curve. 2. The (usually gradual) accumulationof a quantity (e.g., the buildup ofcharge in a capacitor).bulb A globe-like container having any of a numberof characteristic shapes from spherical to tubularand usually evacuated, for enclosing the elementsof an electron device, such as a vacuumtube, gas tube, photocell, or lamp.bulge 1. A nonlinear attenuation-versus-frequencycurve in a transmission line. 2. A localized nonlinearityin a function.bulk The body or mass of a semiconductor specimen,as opposed to junctions within the specimen.Current flows through a junction, but it canalso flow, more or less, through the mass of semiconductorwafer into which the junction has beenformed.bulk effect An effect, such as current, resistance,or resistivity, observed in the overall body of asample of material, as opposed to a region withinthe material or on its surface. Thus, a silicondiode can display junction resistance (i.e., resistanceoffered by a junction processed in a wafer ofsilicon), as well as bulk resistance (i.e., the effec-

90 bulk effect • burst generatortive resistance of all paths around the junction,through the mass of the wafer). Compare SUR-FACE EFFECT.bulk-erased tape Recording tape whose signalcontent has been removed via a bulk eraser.bulk-erase noise 1. The residual magnetic impulsesthat remain on a magnetic tape after it hasbeen bulk-erased. 2. Noise generated by bulkerasedtape when the latter passes through deenergizedrecord or erase heads in a tape machine.bulk eraser A type of power-line-frequency degausserthat erases an entire reel of magnetictape without requiring that the tape be unreeledand passed continuously under an erase head.This saves considerable time, but often leavessome BULK-ERASE NOISE on the tape. Alsocalled BULK DEGAUSSER.bulletin board In personal computing or amateurpacket communications, a system that allowssubscribers to leave messages for each other foraccess via a modem or terminal node controller.bulletin station A station intended for the transmissionof bulletins of interest to certain parties,such as military personnel or amateur radio operators.An example is W1AW in Newington, Connecticut,an amateur radio station that transmitsbulletins and code practice.buncher In a Klystron, a cavity resonator that containstwo grids mounted parallel to the electronstream. The electrostatic field of the grids alternatelyaccelerates and retards the electrons, velocity-modulatingthe stream into bunches.buncher grids In a Klystron, the closely spacedgrids that velocity-modulate the electron beaminto successive bunches.buncher resonator In a velocity-modulated tube,such as a Klystron, the input cavity resonator.buncher voltage The radio-frequency (RF) grid-togridvoltage in the buncher resonator of aKlystron.bunching The production of electron bunches in avelocity-modulated tube, such as a Klystron. Alsosee BUNCHER.bunch stranding A technique for combining severalthin wires into a single thick wire. Often usedin guy wires and electrical conductors to improvetensile strength and flexibility. At radio frequencies,bunch stranding also improves electricalconductivity by increasing the ratio of surfacearea to cross-sectional area. This minimizeslosses caused by skin effect.Bunet’s formula A formula for calculating the inductanceof a multilayer air-core coil that has adiameter less than three times the length:L = a 2 N 2 /(9a + 10l + 8.4c + 3.2cl/a)where N is the number of turns, a is the averagecoil radius, c is the winding thickness, and l is thelength of the coil.Bunsen cell A cell consisting of a zinc rod in a sulfuricacid solution contained in a porous pot,which is in a nitric acid solution. The zinc rodserves as the negative pole; the positive pole is apiece of hard carbon. The cell produces about 1.9volts and delivers relatively high current.See VOLTAGE BURDEN.burdenburn 1. A blemish on the screen of a cathode-raytube (CRT), caused by destruction of the phosphorthere. This results from prolonged focusingof an intense electron beam in one spot. 2. Ablemish on the screen of a television picture tube,usually resulting from ions that reach the screenwhen the ion trap is not working correctly.burn-inA long, thorough, carefully controlled preliminarytest of a component, device, or system,to stabilize its electrical characteristics aftermanufacture and to ensure that it will functionaccording to rated specifications. An importanttest for equipment whose reliability must beguaranteed, such as an emergency communicationstransceiver.burnout1. Failure of a conductor or componentcaused by overheating from excess current orvoltage. 2. The open-circuiting of a fuse. 3. Electricalfailure of any type.burstclBunet s formula1. The abrupt ionization of the gas in an ionizationchamber by cosmic rays. 2. An abrupt increasein the amplitude of a signal. Also, the typeof signal that results from burst action. 3. SeeCOLOR BURST.burst amplifier In a color-television receiver, theamplifier that separates the burst pulse from thevideo signals and amplifies the former. SeeCOLOR BURST.burst gate timing In a color-television receiver,the timing of the gating pulse with the input signalof the burst amplifier.burst generator A signal generator delivering aburst output (see BURST, 2) for testing varioustypes of equipment. Its output is intermediatebetween sine waves and square waves, and isconvenient for rapidly appraising the perfor-ad

urst generator • button microphone 91mance of such devices as amplifiers, filters, electronicswitches, transducers, and loudspeakers.burst transmission A short transmission at highspeed. This method of transmission saves time,but increases the necessary bandwidth of a signalby the same factor as the ratio of the highspeed to the original speed.bus 1. A main conductor in a circuit. A bus can behigh in the sense that its potential is above orbelow ground, or it can be low or at ground reference.2. In computer operations, a commongroup of paths over which input and output signalsare routed.bus driver A buffering device designed to increasethe driving capability of a microprocessor, whichitself might be capable of driving no more than asingle load.business machine Any piece of electronic or electromechanicalequipment used mainly, or entirely,for business purposes. Examples are photocopiers,facsimile (fax) machines, printers, and computers.busing The parallel interconnection of circuits.busy test A check conducted to find out whether ornot a certain telephone subscriber line is in use.busy tone Also called busy signal. An intermittenttone that indicates that the subscriber line beingcalled is in use.Butler oscillator An oscillator that consists of atwo-stage amplifier with a quartz crystal in thepositive-feedback path from output to input.butterfly capacitor A plate-type variable capacitorthat has two stator sections and a single rotorsection common to the two stators. External connectionsare made to the stators only. Thus, nowiping contact is required to the rotor, and thetroubles associated with such a contact areavoided. The butterfly capacitor is actually twovariable capacitors in series. The unit is so calledfrom the shape of its rotor.circuit. The ring supplies the inductance, and thebutterfly supplies the capacitance. It is alsocalled butterfly tank and butterfly resonator.Butterworth filter A high-pass, low-pass, bandpassor band-rejection filter, characterized by aflat passband (absence of passband ripple) andhigh attenuation at frequencies far removed fromthe passband.Butterworth function A mathematical functionthat is used in the design of a BUTTERWORTHFILTER.button 1. Usually, a small switch that is actuatedby finger pressure. It is also called pushbuttonand pushbutton switch. Sometimes, the term isapplied only to the insulated knob or pin which ispushed to operate the switch. 2. A tiny lump ofimpurity material, placed on the surface of asemiconductor wafer for alloying with the waferto form a junction. See ALLOY JUNCTION. 3. Thecarbon element(s) in a BUTTON MICROPHONE.button capacitor A button-shaped ceramic or silvered-micafixed capacitor. Because of its diskshape and mode of terminal connection, it offersvery low internal inductance.button microphone A microphone in which a button-shapedcarbon element is attached to a diaphragm,which is set into vibration by soundwaves. This motion causes the button resistanceto vary, modulating a direct current that passesDiaphragmCarbongranulesSingle buttonSoundwavesStator 1RotorOutputStator 2SoundwavesDouble buttonCarbonbuttonsOutputvoltagebutterfly capacitorDiaphragmbutterfly circuit A combination of a butterfly capacitorand a ring, of which the stator plates ofthe capacitor are an integral part. The resultingstructure is a compact variable-frequency tunedbutton microphone

92 button microphone • bytethrough the button. A single-button microphonehas only one button, whereas a double-buttonmicrophone has two—one mounted on each sideof the center of the diaphragm.buzz 1. A low-pitched rough sound with highfrequencycomponents, usually the result of electricalinterference from nonsinusoidal voltagesgenerated by neighboring equipment or devices.2. The waveform associated with such a sound.3. Fastening two conducting surfaces by a KEL-LIE BOND.buzzer A nonringing device used principally togenerate sound other than that achievable withsine waves. In an electromechanical vibratingreedbuzzer, the reed acts as an armature, whichis mounted close to the core of an electromagnet.At quiescence, the reed rests against a stationarycontact. When voltage is applied to the electromagnet,the reed is attracted to the core,moving away from the contact; but this breaksthe circuit, the magnetism ceases, and the reedsprings back to the contact. The action is repeatedcontinuously at a frequency that dependson the reed dimensions and its distance from thecore.BWO Abbreviation of BACKWARD-WAVE OSCIL-LATOR.BX Symbol and abbreviation for armored and insulatedflexible electrical cable.bypass A route (either intended or accidental)through which current easily flows around acomponent or circuit instead of through it.bypass capacitor A capacitor that is used to conductan alternating current around a componentor group of components. Often the ac is removedfrom an ac/dc signal, the dc being free to passthrough the bypassed component.ContactArmatureCoilCoreBatterybuzzerBV Abbreviation of BREAKDOWN VOLTAGE.B voltage The dc voltage required by certain electrodesof vacuum tubes and transistors. It especiallypertains to voltages required by the plateand screen of a vacuum tube, as opposed to thefilament voltage and control-grid voltage.bw 1. Abbreviation of bandwidth. 2. Abbreviationof black-and-white.BWA Abbreviation of backward-wave amplifier.BWG Abbreviation of BIRMINGHAM WIRE GAUGE.B-Y signal In a color television receiver, the colordifferencesignal which, when combined with aluminance (Y) signal, forms a blue primary signalfor the three-gun picture tube.byte In digital-computer and data-communicationsoperations, a unit of data consisting of eightcontiguous bits. In packet communications, theterm octet is often used.

C 1. Abbreviation of CAPACITANCE. 2. Symbol forCOLLECTOR of a transistor. 3. Symbol for CAR-BON. 4. Abbreviation of CELSIUS. 5. Symbol forCOULOMB. 6. Abbreviation of CALORIE.c 1. Abbreviation of CENTI. 2. Abbreviation ofCENTS. 3. Symbol for CAPACITANCE. 4. Symbolfor SPEED OF LIGHT in a vacuum.Ca Symbol for CALCIUM.cabinet An enclosure for a piece of apparatus. Itmight or might not incorporate electromagneticshielding.cable 1. A usually flexible (but sometimes rigid)medium, via which electrical power or signals aretransferred. Although the term is occasionally appliedto a single conductor, especially when it is abraid or weave of a number of wires, cable usuallymeans a bundle of separate, insulated wires orstrands of fiberoptic material. 2. CABLEGRAM.cable address A code word that specifies the recipientof a CABLEGRAM.cable assembly A special-purpose cable with connectors.cable attenuation Reduction of signal intensityalong a cable, usually expressed in decibels perfoot, hundred feet, mile, etc.cable capacitance Capacitance between conductorsin a cable or between conductors and theouter sheath of a cable. 2. Sometimes, capacitancebetween a cable and earth.cable clamp A support device for cable runs inequipment and systems.cable communications Telegraphy or telegraphyvia a (usually undersea) cable.cable connector A connector, such as a coaxial fitting,that joins cable circuits or connects a cableto a device.cabled wiring Insulated leads connecting circuitpoints; they are tied together with lacing cord orwith spaced fasteners.cablegram A (usually printed) message transmittedor received via undersea cable. CompareRADIOGRAM and TELEGRAM.cable loss See CABLE ATTENUATION.cable run The path taken by a cable.cable splice 1. An electrical attachment betweentwo sections of cable that has identical or similarconstruction, with or without the use of connectors.2. To electrically attach two sections ofcable that have identical or similar construction,with or without the use of connectors.cable tie A short piece of wire or plastic that holdswires or cables in a bundle.cable TV See COMMUNITY-ANTENNA TELEVI-SION.cache memory A short-term, high-speed, highcapacitycomputer memory. Similar to a scratchpador read-write memory.CAD Acronym for computer-aided design.CAD/CAM Acronym for computer-aided design andmanufacturing.cadmium Symbol, Cd. A metallic element. Atomicnumber, 48. Atomic weight, 112.41. Many electronicstructures are cadmium plated for protection.cadmium borate phosphor Formula, (CdO +B 2 O 3 ): Mn. A substance used as a phosphor coatingon the screen of cathode-ray tubes. The characteristicfluorescence is green-orange.cadmium cell Also called Weston standard cell.An electrochemical standard cell used as a referencevoltage source. Produces 1.0186 volt at20°C.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

94 cadmium plating • calibrated sweepcadmium plating The process of coating a conductoror component with cadmium to increase itsresistance to corrosion.cadmium selenide photocell A photoconductivecell in which cadmium selenide is the lightsensitivematerial.cadmium silicate phosphor Formula, (CdO +SiO 2 ). A substance used as a phosphor coating onthe screen of cathode-ray tubes; the characteristicfluorescence is orange-yellow.cadmium standard cell See STANDARD CELL.cadmium sulfide photocell A photoconductivecell in which cadmium sulfide is the lightsensitivematerial.cadmium tungstate phosphor Formula, CdO +WO 3 . A substance used as a phosphor coating onthe screen of cathode-ray tubes; the characteristicfluorescence is light blue.cage A completely shielded enclosure, such as ascreen room, which is covered with a groundedfine-mesh conductive screen on all sides.cage antenna An antenna, usually center-fed andbalanced, that consists of multiple parallel conductorsarranged in a cylindrical cage configuration.The cage results in a much broaderbandwidth than is the case with an antennamade up of a single conductor. Cage antennasare typically used at frequencies between about10 and 200 MHz.Feedcage antennaMultipleconductorsCAI Abbreviation for computer-assisted instruction.CAL An acronym for conversional algebraic language,a general-purpose problem-oriented computerprogramming language used in time-sharingsystems.calcium Symbol, Ca. A metallic element of thealkaline-earth group. Atomic number, 20. Atomicweight, 40.08.calcium phosphate phosphor Formula, Ca 3 (PO 4 ) 2 .A substance used as a phosphor coating on thescreen of long-persistence cathode-ray tubes; thecharacteristic fluorescence is white, as is thephosphorescence.calcium silicate phosphor Formula, (CaO +SiO 2 ): Mn. A substance used as a phosphor coat-ing on the screen of cathode-ray tubes; the characteristicfluorescence ranges from green toorange.calcium tungstate phosphor Formula, CaWO 4 . Asubstance used as a phosphor coating on thescreen of short-persistence cathode-ray tubes;the characteristic fluorescence is blue, as is thephosphorescence.calculate To perform the steps of an intricatemathematical operation. Compare COMPUTE.calculating punch A data-processing peripheralthat reads punched cards, makes calculations,and punches new data into those cards or newcards.calculator A machine that performs mathematicaloperations, especially arithmetic. Typically, thedevice is a small box with buttons and a miniaturenumeric display. Used only in mathematicalapplications. In contrast, a COMPUTER can beused for a much wider variety of jobs, such asword processing, graphics, and data-base. Manypersonal computers have calculator programs;the “buttons” are actuated by pointing and clickingwith a mouse.calculus1. The symbology and rules comprising asystem of logic, such as BOOLEAN ALGEBRA. 2.A branch of mathematical analysis concernedwith rates of change and accumulation. See DIF-FERENTIAL CALCULUS and INTEGRAL CALCU-LUS.calendar age The age of a piece of equipment, measuredsince the date of manufacture. Specified inyears, months, and days. The actual manufacturedate might alternatively be given.calendar time The time available in a working period[i.e., a 40-hour work week represents a calendartime of 120 hours (five days times 24 hoursper day)].calibrate To compare and bring into agreementwith a standard.calibrated measurement 1. A measurement madewith an instrument that has been calibrated witha standard reference source. 2. A measurementthat is corrected for instrument error.calibrated meter An analog or digital meter thathas been adjusted to agree as closely as possiblewith a reference source.calibrated scale 1. A scale whose graduationshave been carefully checked for accuracy (i.e.,they correspond to the true values of the quantitythat they represent). The scale is graduated toread directly in units of the quantity, such as milliamperes,kilohertz, volts, etc. 2. A scale withfixed, plain numeric graduations (e.g., 0 to 100)that do not directly indicate the magnitude of aquantity, but that can be converted to variousquantities via graphs, nomographs, tables, orcharts. See CALIBRATION CURVE.calibrated sweep In an oscilloscope, a sweep circuitcalibrated to indicate sweep frequency ortime at all control settings.

calibrated triggered sweep • CAN 95calibrated triggered sweep In an oscilloscope, atriggered sweep circuit calibrated in terms ofsweep time or frequency.calibration 1. Determining the accuracy withwhich an instrument indicates a quantity. 2. Determiningthe degree to which the response of acircuit or device corresponds to desired performance.3. Marking a scale to show actual valuesof a quantity in the form of a direct readout. Forexample, the scale of an analog meter might becalibrated in milliamperes (mA) from 0 to 50 in incrementsof 1 mA.calibration accuracy 1. A quantitative expressionof the agreement between the value of a quantity,as indicated by an instrument, and the truevalue. Usually expressed as the maximum percentageof the true value by which the indicatedvalue can be expected to deviate in either direction(e.g., ±0.5 percent). 2. The precision of a direct-readingmeter in terms of its full-scaledeflection (e.g., ±2.0 percent of full scale).calibration curve A graph showing the relation betweenthe actual values of a quantity and the settingor indication of an instrument or component.Usually plotted in rectangular coordinates.Frequency (MHz)1081061041021009896949290880 20 40 60 80 100Log scale readingcalibration curvecalibration marker A pip or blip, superimposed ona pattern displayed on a cathode-ray-tube (CRT)screen, to identify a point closely as to frequency,voltage, distance, or some similar term.calibrator A device used to perform a calibration(e.g., a signal generator).calibrator crystal A highly accurate and stablequartz crystal, used in an oscillator as a frequencystandard. An example is the 100-kHzcrystal oscillator and harmonic generator used insome communications receivers.californium Symbol, Cf. A radioactive element producedartificially. Atomic number, 98. Atomicweight, 251.call 1. In communications, a transmission by astation for the purpose of either alerting a particularreceiving station for which there is a mes-sage, or alerting all receiving stations to preparethem for a general broadcast message. 2. In acomputer program, a branch to a closed subroutine;also, to branch to such a subroutine.call direction code Abbreviation, CDC. In telegraphnetworks, a special code that, when transmittedto a terminal, causes the teleprinter to beautomatically switched on.calling sequence 1. Computer program instructionsneeded to establish the conditions for a call(see CALL, 2). 2. Subroutine instructions providinga link to the main program.call instruction A computer program instructionthat makes a program controller branch to a subroutine;it also locates and identifies the parametersneeded for the subroutine’s execution. Alsoknown as subroutine call.call letters Letters and/or numbers assigned to,and used to identify, licensed radio stations.calorie Abbreviation, cal or C. The amount of heatenergy, at a pressure of 1 atmosphere, that willraise the temperature of 1 gram of water by 1 degreeCelsius.calorimeter An instrument for measuring heat energy.By adaptation, a calorimeter can be used tomeasure radio-frequency (RF) power—especiallyat microwave frequencies (see CALORIMETRICPOWER METER).calorimeter system See CALORIMETRIC POWERMETER.calorimetric power meter A specialized form ofwattmeter, in which the power to be measured isdissipated in an oil or water bath that has aknown and fixed mass. The wattage is determinedindirectly, by measuring the extent towhich the temperature of the liquid increases in acertain amount of time.CAM 1. Abbreviation of computer-aided manufacturing.2. Abbreviation of content-addressedmemory.cambric Finely woven cotton or linen used for insulation.One type of spaghetti (conductor insulation),for example, is varnished cambric tubing.camera cable A multiwire cable that conducts thevideo signal from a television camera to controlequipment.camera chain In television, the camera and theequipment immediately associated with it, excludingthe transmitter and its peripherals.camera signal The output signal delivered by atelevision camera.camera tube Any video pickup tube, such as aniconoscope or orthicon, that converts light reflectedby a scene into a corresponding televisionsignal.Campbell bridge A circuit that is used for comparingmutual inductance with capacitance.camp-on In a telephone system, a method of engaginga line that is busy until it becomes availablefor use.CAN Abbreviation of CANCEL CHARACTER.

96 can • capacitive couplingcan 1. A metal enclosure or container roughly resemblinga tin can (though not necessarily cylindrical),used for shielding or potting components.2. Colloquial expression for HEADPHONE.Canada balsam A transparent cement derivedfrom the turpentine distilled from balsam firresin. It is useful in optical technology and in certainareas of electro-optics.Canadian Standards Association The Canadianequivalent of the National Bureau of Standards inthe United States. An agency that publishesagreed-on standards for industries.cancel character 1. IGNORE CHARACTER. 2. Acontrol character indicating that the associateddata is erroneous.cancellation The elimination of one quantity byanother, as when a voltage is reduced to zero byanother voltage of equal magnitude and oppositesign.candela Symbol, cd. The SI unit of luminous intensity;1 cd represents 1⁄60 of the radiating power ofone square centimeter of a perfect radiator at thetemperature of freezing platinum.candle Abbreviation, c. Also called internationalcandle. A unit of light intensity that is the value ofemission by the flame of a sperm-whale-oil candleburning at the rate of 7.776 grams per hour.candle power Abbreviation, cp. Luminous intensityin international candles: the luminous intensityresulting from the burning of asperm-whale-oil candle at 7.776 grams per hour.candoluminescence White light produced withoutextreme heat.cannibalization The deliberate use of parts fromoperational equipment to temporarily repair ormaintain other equipment. It is a last-resort,emergency measure.cap 1. Abbreviation of CAPACITANCE. 2. Abbreviationof CAPACITOR.capacimeter See CAPACITANCE METER.capacitance Symbol, C. Unit, farad. The propertyexhibited by two conductors separated by a dielectric,whereby an electric charge becomesstored between the conductors. Capacitance isthought of as analogous to mechanical elasticity.Also see FARAD.capacitance bridge A four-arm ac bridge for gaugingcapacitance against a standard capacitor. Inits simplest form, it has a standard capacitor inone arm and resistors in the other three.capacitance coupling The transfer of ac energybetween two circuits or devices by a capacitor orcapacitance effect. Also see COUPLING.capacitance diode See VARACTOR.capacitance divider An alternating-current voltagedivider that uses capacitors, rather than resistors.It is used in certain oscillators, such asthe Colpitts type.capacitance filter A filter consisting of only ahigh-capacitance capacitor. Because the capacitorcannot discharge instantaneously, it tends tomaintain its voltage and smooth out the ripples inthe voltage applied to it.capacitance-inductance bridge A combination acbridge that can be used for either capacitance orinductance measurement. Both capacitance andinductance can be measured in terms of a standardcapacitance; however, some of these bridgesuse standard inductors in the inductancemeasuringmode.capacitance meter A direct-reading meter formeasuring capacitance. In most available types, astable ac voltage is applied to the meter circuit, towhich an unknown capacitor is connected in series;meter deflection is roughly proportional tothe reactance of the capacitor. Also called MI-CROFARAD METER.capacitance ratio In a variable capacitor, the ratioof maximum to minimum capacitance.capacitance relay A relay circuit that operatesfrom a small change in its own capacitance. Itconsists of an RF oscillator whose tank capacitanceis very low. When a finger is brought nearthe circuit’s short pickup antenna, the attendantincrease in capacitance detunes the oscillator,activating the relay. Also called PROXIMITY RE-LAY and PROXIMITY SWITCH.capacitance-resistance bridge A combination acbridge that can be used for either capacitance orresistance measurement. The unknown resistanceis measured against a standard resistor;the unknown capacitance against a standard capacitor.capacitance sensor See CAPACITANCE TRANS-DUCER.capacitive amplifier See DIELECTRIC AMPLI-FIER.capacitive attenuator An ac attenuator whose elementsare capacitors in any desired combinationof fixed and/or variable units. The desired attenuationis afforded by the capacitance ratio.capacitive coupling A means of coupling betweencircuits that uses a series capacitor for directcurrentblocking. The signal passes through thecapacitor, but the blocking effect allows differentbias voltages to be applied to the two stages.+capacitive coupling

capacitive diaphragm • capacitive window 97capacitive diaphragm A metal plate deliberatelyplaced in a waveguide to introduce capacitive reactanceand, thereby, cancel an inductive reactance.capacitive-discharge ignition An electronic ignitionsystem for automotive engines. Providesnearly constant high voltage, regardless of enginespeed. A dc-to-dc step-up converter charges alarge capacitor (typically to 300 volts) when thedistributor breaker points are closed; when theyare open, the capacitor discharges through theignition coil, thereby generating an ignition pulseof several thousand volts.capacitive division Reduction of an ac voltage bya capacitive voltage divider.capacitive feedback Feeding energy back from theoutput to the input of an amplifier or oscillatorthrough a capacitor.capacitive-input filter A smoothing filter for acpower supplies, in which the element closest tothe rectifier is a capacitor, regardless of the componentsor circuits placed subsequently.capacitive load A load consisting of a capacitor ora predominantly capacitive circuit.capacitive loading In an antenna, the addition ofcapacitance in series with the element(s). Thisraises the resonant frequency for a radiator havinga given physical length. It can also serve to increasethe physical length required for a radiatorhaving a specified resonant frequency. CompareINDUCTIVE LOADING.capacitive post A protrusion inside a waveguidefor the purpose of introducing capacitive reactanceto cancel an inductive reactance.capacitive potentiometer See CAPACITIVE VOL-TAGE DIVIDER.capacitive pressure sensor A pressure sensorthat uses a radio-frequency oscillator and a pairof metal plates separated by dielectric foam. Thecircuit is designed so a change in the capacitancebetween the plates causes the oscillator frequencyto change. This change is sensed. A signalis sent to an analog-to-digital converter (ADC)and then to a microcomputer that calculates theextent of the pressure.capacitive proximity sensor A transducer used inmobile robots that detects the presence of certainkinds of objects. It consists of an oscillator whosefrequency is determined by an inductancecapacitance(LC) circuit to which a metal plateis connected. When a conducting or partially conductingobject comes near the plate, the mutualcapacitance changes the oscillator frequency.This change is detected and sent to the robotcontroller.capacitive reactance Symbol, X C . Unit, ohm. Thereactance exhibited by an ideal capacitor, consideredas a negative pure-imaginary quantity;X C = –j/(6.28fC), where f is the frequency inhertz, C is the capacitance in farads, and j is theunit imaginary number (the square root of –1).Alternatively, f can be specified in megahertzand C in microfarads. In a pure capacitive reactance,current leads voltage by 90 degrees. Alsosee CAPACITANCE, CAPACITOR, and REAC-TANCE.capacitive speaker See ELECTROSTATIC SPEAKER.capacitive transducer A transducer consisting essentiallyof a refined variable capacitor whosevalue is varied by a quantity under test, such aspressure, temperature, liquid level, etc.capacitive tuning Variable-capacitor tuning of acircuit.capacitive voltage divider A capacitive attenuatorusually consisting of two series-connected capacitorswhose values are such that an applied acvoltage is divided across them in the desired ratio.capacitive welding An electronic welding systemin which energy stored in a capacitor is dischargedthrough the joint to be welded. This developsthe heat necessary for the operation.capacitive window A pair of capacitive diaphragmsused in a waveguide to introduce capacitivereactance.

98 capacitor • carbon-button amplifiercapacitor A passive electronic-circuit componentconsisting of, in basic form, two metal electrodesor plates separated by a dielectric (insulator).capacitor amplifier See DIELECTRIC AMPLIFIER.capacitor antenna See CONDENSER ANTENNA.capacitor bank A network of capacitors connectedin combination, yielding a desired characteristic.capacitor braking The connection of a capacitor tothe winding of a motor after the removal of power,to speed up the process of braking.capacitor color code See COLOR CODE.capacitor decade See DECADE CAPACITOR.capacitor-discharge ignition CAPACITIVE-DISCHARGE IGNITION.capacitor filter In a direct-current power supply, afilter consisting simply of a capacitor connectedin parallel with the rectifier output.+Pulsatingdc input−+capacitor filter+Puredc outputcapacitor-input filter A filter whose input componentis a capacitor. The capacitor-input powersupplyfilter is distinguished by its relatively highdc output voltage, but somewhat poorer voltageregulation, compared with the CHOKE-INPUTFILTER.capacitor leakage Direct current flowing throughthe dielectric of a capacitor. In a good nonelectrolyticcapacitor, this current is normally lessthan 1 microampere. In an electrolytic capacitor,it can be up to several milliamperes, dependingon the capacitance and the applied voltage.capacitor loudspeaker See ELECTROSTATICSPEAKER.capacitor microphone See CONDENSER MICRO-PHONE.capacitor motor An ac motor that uses a capacitorin series with an auxiliary field winding forstarting purposes. Initially out-of-phase currentin the auxiliary field (starting winding) causes arotating field that turns the rotor. When the rotorreaches a safe speed, a centrifugal switch disconnectsthe capacitor and auxiliary field, andthe motor continues running as an inductionmotor.capacitor series resistance The ohmic loss ina capacitor. It results partly from conductorlosses, and partly from losses in the dielectricmaterial.capacitor substitution box An enclosed assortmentof selected-value capacitors arranged to beswitched one at a time to a pair of terminals. Introubleshooting and circuit development, any of−several useful fixed capacitance values can bethus obtained.capacitor voltage 1. The voltage at the terminalsof a capacitor. 2. The maximum voltage rating ofa capacitor.capacitor voltmeter See ELECTROSTATIC VOLT-METER.capacity 1. A measure of a cell’s or battery’s abilityto supply current during a given period. 2. CA-PACITANCE. 3. The number of bits or bytes acomputer storage device can hold. 4. The limits ofnumbers that a register can process.capacity lag In an automatic control system, a delaycaused by the storing of energy by the components.For example, in a heating system, capacitylag results from the time taken to heat the air orfluid after the thermostat turns on the heat.capillary electrometer A sensitive voltage indicator,consisting of a column of mercury in atransparent capillary tube, in which is suspendeda small drop of acid. When a voltage isapplied to both ends of the mercury column, theacid drop moves toward the low-potential end ofthe column over a distance proportional to thevoltage.capstan The driven spindle or shaft of a magnetictape recorder or transport.capture area The effective ability of a radio antennato pick up electromagnetic signals. The larger thecapture area, the greater the antenna gain.capture effect 1. In frequency-modulation (FM)radio receivers, the effect of domination by thestronger of two signals, or by the strongest of severalsignals, on the same frequency. 2. In anautomatic-frequency-control system, the tendencyof the receiver to move toward the strongest ofseveral signals near a given frequency. 3. In general,the tendency of one effect to totally predominateover other effects of lesser amplitude.capture ratio A measure of frequency-modulation(FM) tuner selectivity: The amplitude difference,in decibels, between unwanted signals and theone being tuned in.carbon Symbol, C. A nonmetallic element. Atomicnumber, 6. Atomic weight, 12.011. Carbon, besidesbeing an invaluable material in electronics,is an important constituent of organic compounds.carbon arc The arc between two electrified pencilsof carbon or, as in an arc converter, between acarbon pencil and a metal electrode.carbon brush A contact made of carbon or somemixture of carbon and another material, used inmotors, generators, variable auto-transformers,rheostats, and potentiometers.carbon-button amplifier An audio-frequencyamplifier having as the active component anearphone whose diaphragm is attached to a carbonmicrophone button. The input signal appliedto the earphone makes its diaphragmvibrate. The vibrating button modulates a local

carbon-button amplifier • cardistimulator 99direct current. Amplification results from thelarge ratio of modulated local current to inputsignalcurrent.carbon-composition resistor A non-inductive resistormade from a mixture of finely powderedcarbon with a non-conductive substance, usuallyphenolic. The resulting clay-like material ispressed into a cylindrical shape, and wire leadsare inserted in the ends. The resistance dependson the ratio of carbon to the non-conducting material,and on the physical distance between thewire leads. This type of resistor is useful from directcurrent to ultra-high radio frequencies. CompareFILM RESISTOR, WIREWOUND RESISTOR.carbon/disk rheostat A rheostat consisting of astack of carbon disks or washers, arranged sothat a controllable pressure can be exerted on thestack. As a knob is turned, a screw increases ordecreases the pressure, varying the total resistanceof the stack.carbon-film resistor A stable resistor whose resistanceelement is a film of carbon, vacuumdepositedon a substrate, such as a ceramic.carbonization The application of a coat of carbononto an electrode, either by electroplating or byany other means.carbon microphone A microphone that includesone or two carbon buttons. See BUTTON MICRO-PHONE.carbon-paper recorder A recorder in which asignal-actuated stylus writes, by impression only,through a sheet of carbon paper onto a plainsheet underneath. This eliminates the need for anink-carrying stylus.carbon-pile regulator A voltage regulator inwhich a stack of carbon disks or washers is inseries with the shunt field. The pile resistanceand field current depend on pressure applied tothe pile by a wafer spring acting through a movableiron armature. Voltage drops increase thepressure and voltage rises decrease the pressure,thus regulating the generator with whichit is associated.Arm+−CarbonpileShuntfield IronarmatureRheostatSpringcarbon-pile regulatorTo dc loadPotentialcoilcarbon-pile rheostat See CARBON-DISK RHEO-STAT.carbon recording 1. A record made with aCARBON-PAPER RECORDER. 2. The use of a carbon-paperrecorder in data acquisition, facsimile,communications, and similar applications.carbon resistor A resistor made from carbon,graphite, or some composition that contains carbon.carbon/silicon-carbide thermocouple A thermocouplethat is a junction between carbon and siliconcarbide.carbon transfer recording A method of facsimilereception in which the image is reproduced bycarbon particles sprayed on the paper, a processcontrolled by the received signal.carbon-zinc cell See ZINC-CARBON CELL.Carborundum Formula, SiC. Trade name for asynthetic silicon carbide used as a semiconductor,refractory, or abrasive. Also see SILICONCARBIDE.Carborundum crystal Trade name for a characteristicallysuperhard crystal of silicon carbide.Carborundum varistor A voltage-dependent resistormade from Carborundum.carcinotron A special kind of oscillator tube usedat ultra-high and microwave frequencies.card 1. A usually thin, rectangular board containinga PRINTED CIRCUIT, often equipped with anedge connector that makes it easy to install, remove,or replace. Common in electronic and computerequipment having modular construction. 2.The usually flat, thin insulating strip on which aresistor element is wound.cardiac monitor An electronic device that displaysor records electrical impulses from the heart formedical observation or diagnosis.cardiac pacemaker An electrical cardiac stimulatorthat causes the heart to beat at certain intervals.Used when the patient has heart diseasethat prevents the heart from regulating itself.cardiac stimulator An electronic device (sometimesimplanted in the subject) that supplieselectric pulses to stimulate heart action. Alsocalled DEFIBRILLATOR and PACEMAKER.card image In memory storage, the data containedon a single card.cardiogram ELECTROCARDIOGRAM.cardiograph ELECTROCARDIOGRAPH.cardioid diagram A polar response curve in theshape of a cardioid pattern.cardioid microphone A microphone with a (roughly)heart-shaped sound-field pickup pattern.cardioid pattern A radiation/response patternwith one sharp null in the direction opposite thesingle main lobe. The lobe is extremely broad. Intwo dimensions, the curve is shaped somewhatlike a “Valentine” heart.cardiotachometer A device that indicates thepulse rate.cardistimulator See CARDIAC STIMULATOR.

100 Carey-Foster bridge • carrier lineCarey-Foster bridge A special version of the slidewirebridge that is useful for measuring an unknownresistance, whose value is close to that ofa standard resistance.R XR1SlidewireS1S2Carey-Foster bridgeCarey-Foster mutual inductance bridge An acbridge that permits the measurement of mutualinductance in terms of a standard capacitor.R1CL1R3MDetGenR4R 2 = 0R2R3M = R 1 R 4 CR 3 = R 4 ( L 1 −1)MCarey-Foster mutual inductance bridgecarnauba wax A wax obtained from the Brazilianwax palm. Used as an electrical insulator, and asthe dielectric in some electrets.Carnot theorem In thermodynamics, the propositionthat in a reversible cycle, all available energyis converted into mechanical work. Also calledCarnot’s principle.carrier 1. See CARRIER WAVE. 2. See CHARGECARRIER.carrier amplifier See DIELECTRIC AMPLIFIER.carrier beating 1. The mixing of two radiofrequencycarriers that are separated by a smallamount of frequency, resulting in an audible tonein a receiver. 2. A heterodyne in a facsimile ortelevision signal, resulting in a pattern of crosshatches in the received image.carrier choke A radio-frequency (RF) choke, insertedin a line to block a carrier component.carrier chrominance signal For conveying colortelevision information, sidebands of a modulatedchrominance subcarrier.carrier color signal For conveying color informationin color television transmission, the sidebandsof a modulated chrominance subcarrier(plus the unsuppressed chrominance subcarrier)added to the monochrome signal.carrier concentration In a semiconductor material,the number of charge carriers per unit volume.carrier control 1. The modification, adjustment,or switching of a carrier wave. 2. Adjustment of acircuit or device by means of a carrier wave.carrier current The current component of a carrierwave, or the amplitude of that current. CompareCARRIER POWER and CARRIER VOLTAGE.carrier-current communication See WIREDWIRELESS.carrier-current control 1. Control of the currentcomponent in a carrier wave. 2. Remote controlby means of wired wireless.carrier-current receiver See WIRED-RADIO RE-CEIVER.carrier-current relay A radio-frequency (RF) relaycircuit, operated over a wire line by means of atransmitter.carrier-current transmitter See WIRED-RADIOTRANSMITTER.carrier deviation See CARRIER SWING.carrier dispersion In a semiconductor, the spreadingout of electrons and holes that leave the emittersimultaneously, but arrive at the collector atvarious times after following different paths.carrier frequency The center frequency of a CAR-RIER WAVE.carrier-frequency pulse A pulse that containsradio-frequency oscillation.carrier-frequency range The band of carrier frequenciesover which a transmitter or signal generatorcan operate.carrier injection The apparent emission (injection)of electrons or holes into a semiconductor when avoltage is applied to the junction.carrier leak 1. A point at which carrier-wave energyescapes a circuit or enclosure. 2. The residualcarrier voltage present in the output of acarrier-suppressing circuit.carrier level The amplitude of an unmodulatedcarrier wave.carrier lifetime In a semiconductor, the intervalbefore an injected current carrier (see CARRIERINJECTION) recombines with an opposite carrierand ceases to be mobile.carrier lineIn carrier-current systems (see WIREDWIRELESS), the line or cable conducting thecarrier-wave energy.

carrier mobility Symbol, µ. In a semiconductormaterial, the average drift velocity of electronsand holes per unit electrostatic field.carrier noise Modulation of a carrier when there isno input from the modulator itself; unwantedmodulation.carrier noise level The noise signal amplitude thatresults from unintentional fluctuations of an unmodulatedcarrier.carrier-on-light transmission A form of transmissionin which many different signals are sent simultaneouslyby modulating a beam of light atmultiple frequencies.carrier-on-microwave transmission A form oftransmission in which many different signals aresent simultaneously by modulating a microwavesignal at multiple lower frequencies.carrier-on-wire transmission A form of transmissionin which many different signals are sent atthe same time over a wire, by using radiofrequencycarriers. Also called CARRIER-CURRENTCOMMUNICATIONS or WIRED RADIO.carrier oscillator In a single-sideband receiver,the radio-frequency (RF) oscillator that suppliesthe missing CARRIER WAVE.carrier power The actual power represented by aradio-frequency (RF) carrier applied to an antenna,measured by either the direct or indirectmethod. The direct method involves determinationof power according to the formula P = I 2 R,where I is antenna current and R is antenna resistanceat the point of current measurement.The indirect method involves determination ofpower according to the formula P = EIF, where Eand I are antenna voltage and current, and F is afactor less than 1.0, whose value depends on thetype of modulation used.carrier power-output rating The power deliveredby an unmodulated transmitter or generator tothe normal load or its equivalent.carrier shift In an amplitude-modulated transmitteror generator, the undesired change of averagecarrier voltage during modulation.carrier-shift indicator An instrument for detectingcarrier shift. It usually contains only apickup coil, semiconductor diode, and dc milliammeterin series. Meter deflection is steadyuntil carrier shift is detected; then, the needlefluctuates.carrier signaling In wire telephony, the use ofcarrier-wave signals to operate such functions asdialing, ringing, busy signal, etc.carrier storage In a semiconductor device, the tendencyof mobile carriers to stay near a junctionfor a short time after the junction voltage hasbeen removed or reversed in polarity.carrier suppression The elimination of the carrierin an amplitude-modulated signal so that onlythe sideband energy remains.carrier swing In frequency-modulated or phasemodulatedtransmission, the total deviation (lowcarriermobility • carry system 101est to highest instantaneous frequency) of thecarrier wave.carrier system The transmission of many signalsover one circuit, accomplished by modulatingvarious different carriers at different frequencies.Different signals can use different modulationmethods.carrier telegraphy 1. Continuous-wave telegraphyby WIRED WIRELESS. 2. Wired-wireless telegraphyin which a radio-frequency carrier is modulatedby an audio-frequency keying wave.carrier telephony Telephone communication byWIRED WIRELESS.carrier terminal 1. At each end of a carrier-currentline or cable, the equipment for generating, modifying,or utilizing the carrier energy. 2. In a balancedmodulator, the point of carrier insertion.carrier-to-noise ratio The ratio of carrier amplitudeto noise-voltage amplitude.carrier transmission Transport of information bya carrier, as by an amplitude-modulated radiowave that carries the low-frequency informationas the AF modulation envelope and delivers it tothe demodulator at the receiving station.carrier-type dc amplifier A high-frequency ac amplifier,ahead of which is operated a generatorand transducer. A dc voltage applied to the transducermodulates the carrier supplied by the generator;the amplifier boosts the modulated wave,and the resultant output is rectified at a levelhigher than that of the dc input signal.carrier voltage The voltage component of a carrierwave; also, the amplitude of this component. CompareCARRIER CURRENT and CARRIER POWER.carrier wave A sine wave that is modulated toconvey information in wireless and cable communicationssystems. The lowest frequency normallyused for wireless signal transmission is 9kHz, corresponding to a wavelength of approximately33 km. The highest frequency is less welldefined; some systems make use of visible lightwaves, whose wavelengths are as short as approximately4 × 10 –7 m. For modulation to workeffectively, the carrier must have a frequency atleast 10 times the highest frequency of the modulatingsignal.carry 1. In adding a column of figures, the digitadded to the column at the left when the sum exceedsone less than the radix value. 2. In digitalcomputers and counters, a pulse that correspondsto the arithmetic operation in which a figureis carried to the next column in addition.carrying capacity The ability of a conductor, suchas copper wire, to carry current safely (expressedin maximum amperes).carry-complete signal In an arithmetic computationby a computer, an adder-produced signal indicatingthat the pertinent carries have beengenerated.carry system A communications system in whichseveral carries occupy one circuit.

102 carry time • cascaded amplifier100zCurrent (amperes)90807060504030201006 8 10 12 14 16 18 20 22Wire size (AWG)−5 −4 −3 −2 −1−4−5−1−2−354321125431 2 3 4 5−1−2−3−4−5Cartesian three-spaceyxcarrying capacity(of some AWG sizes of copper wire)carry time The time taken for a digital computer orcounter to perform a carry operation (See CARRY,2).Cartesian coordinate geometry Also called rectangularcoordinate geometry. In robotic systems, amovement scheme in two or three dimensions.The position of the robot arm is determined by linearcoordinates, relative to an origin point. Thesecoordinates are specified along linear axes—eachof which is perpendicular to the others at the origin.See CARTESIAN COORDINATES, CARTE-SIAN PLANE, and CARTESIAN THREE-SPACE.Cartesian coordinates Also called rectangular coordinates.A mathematical system that uniquelydefines the position of a point on a plane, in space,or in general, in an n-dimensional hyperspacewhen n is a whole number greater than 3. Thereare n axes for n dimensions, each axis intersectsall the others at a single point, called the origin.The axes are mutually perpendicular at this origin.The axes are scaled in units with the origin havingcoordinate values that are all equal to zero (usually).Positive values go along the axes in one direction;negative numbers go in the oppositedirection for each axis. Usually, the axes are graduatedin equal-sized units. The system gets itsname from the mathematician Rene Descartes.Cartesian plane A linear, two-dimensional coordinateplane commonly used for graphing equationsin one variable.Cartesian three-space A linear, three-dimensionalgraph-coordinate system used for renderingequations in one or two variables.Cartesian three-space graph A three-dimensionalgraph that shows an equation in one or two variables.Three-space graphs are often displayedmore clearly by means of computer graphics, inwhich the entire display can be rotated to showthe characteristics of the surface resulting from agiven equation or function.Cartesian n-space The coordinate space definedby a Cartesian system of n coordinates, where nis a whole number of 2 or greater.cartridge 1. The replaceable transducer assemblyof a microphone. 2. A magnetic-tape magazine.Also see TAPE CARTRIDGE. 3. A removable computermass-storage medium, containing a tape,magnetic diskette, or optical diskette. 4. An insulatingtube housing a fuse, semiconductor component,resistor, capacitor, or other part.cartridge fuse A fuse consisting of a fusible wireenclosed in a cartridge, having a ferrule at eachend for plug-in connection.cascadable Capable of, or designed for, being connectedin cascade with other similar or identicalcomponents.cascade 1. Components or stages connected andoperated in sequence, as in a three-stage amplifier.The components or stages are often but notnecessarily identical. 2. To form a cascade.cascade control 1. In an automatic control system,a controller whose setting is varied by theoutput of another controller. 2. An automaticcontrol system in which the control units are connectedin stages, so that one unit must operatebefore the next one can function.cascaded amplifier A multistage amplifier in whichthe stages are forward-coupled in succession.

cascaded carry • cathode 103cascaded carry In digital computer practice, a systemof performing the carry operation (seeCARRY) in which the n + 1 place receives a carrypulse only when the nth place has received carryinformation to generate the pulse.cascade thermoelectric device A thermoelectriccomponent or circuit that consists of several cascadedsensors (see CASCADE, 1).cascade voltage doubler A voltage-doubler circuit(see VOLTAGE DOUBLER) consisting of twodiode-capacitor combinations in cascade. Unlikethe conventional voltage-doubler circuit with twocapacitors in the output, the cascade voltage doublerhas one in the input and one in the output.cascode A high-gain, low-noise, high-inputimpedanceamplifier circuit, consisting of agrounded-emitter or grounded-source input stagecoupled directly to a grounded-base or groundedgateoutput stage.Incascode(field-effect transistorarrangement)Outcase temperature The temperature at a designatedpoint on the outside surface of a component’scase or housing.Cassegrain antenna A dish antenna that usesCASSEGRAIN FEED.Main dishFeedCassegrain antennaSemispherefocus reflectorCassegrain feed A dish-antenna feed system inwhich the feed point is located at the center of thedish itself. For transmission, the radio-frequencyenergy emerges from a waveguide and is directed toa small convex reflector at the focal point of thedish. The small reflector directs the signal back tothe dish, spreading the energy out to cover the entiresurface of the dish. The dish reflects the energyagain and collimates it in the desired direction ofpropagation. For reception, the process is reversed;the dish focuses the energy on the small reflector,which propagates it back to the feed point.cassette 1. A holder (magazine) of reels of magnetictape that is itself a mechanical subassembly,which can be easily inserted into andremoved from a tape deck. 2. A lightweight holderof photographic film or X-ray plates (before, during,and after exposure).castor oil A viscous insulating oil extracted fromcastor beans. Highly refined castor oil is used asan impregnant in some oil-filled capacitors. Dielectricconstant, 4.3 to 4.7. Dielectric strength,380 V/mil.CAT Abbreviation of COMPUTERIZED AXIAL TO-MOGRAPHY.catalysis The process whereby an agent, called acatalyst, enhances a chemical reaction withoutentering into the reaction. Catalysts are used inelectronics, for example, to promote the setting ofresins in potting and encapsulating operations.catalytic agent A substance that accomplishescatalysis.cataphoresis As caused by the influence of anelectrostatic field, the migration toward the cathodeof particles suspended in a liquid.catastrophic failure 1. Sudden, unexpected failureof a component or circuit. 2. Failure that canresult in the breakdown of an entire system. Alsocalled catastrophic breakdown.catcher In a Klystron, the second reentrant cavity.(See KLYSTRON.)catcher diode A diode that is connected to regulatethe voltage at the output of a power supply. Thecathode is connected to a source of reference voltage.If the anode, connected to the source to beregulated, becomes more positive than the cathode,the diode conducts and prevents the regulatedvoltage from rising more than 0.3 volt abovethe reference voltage (for germanium diodes) or 0.6volt above the reference voltage (for silicon diodes).catcher grids In a Klystron, the grids throughwhich the bunched electrons pass on their wayfrom the buncher to the collector. Catcher gridsabsorb energy from the bunched electrons andpresent it to the collector circuit.category In a computer system, a group of magneticdisk volumes containing information relatedby a common application.category storage A computer-file storage sectionthat contains a number of categories and used byan operating system.catenation See CONCATENATION.cathode 1. The negative electrode of a device (i.e.,the electrode from which electrons move when a

104 cathode • cavity lasercurrent passes through the device). 2. In an electrochemicalcell, the electrode that gains electrons.This is generally the positive electrode. 3.In a vacuum tube, the electron-emitting electrode(filament or indirectly heated cathode sleeve).cathode current Symbol I K . The current flowing inthe cathode circuit of a tube. Cathode current isthe total of grid, plate, screen, and suppressor currents,and can have an ac and a dc component.cathode dark current The electron emission fromthe photocathode of a camera tube when there isno illumination.cathode element In a vacuum tube, an indirectlyheated emitter of electrons. Also see CATHODE, 2.cathode emission 1. The giving up of electrons bythe cathode element of a device, such as a vacuumtube. Electrons can be emitted by either hotor cold cathodes, depending on the tube. 2. Collectively,electrons released by a cathode.cathode heating time The time required for thetemperature of a tube cathode to increase fromcold to its maximum specified operating temperatureafter the cathode current has been initiated.Also called cathode warmup time.cathode luminous sensitivity For a photomultipliertube, the cathode’s sensitivity to light. Thissensitivity figure is the ratio of photocathode currentto incident light flux.cathode-ray oscillograph An instrument that providesa permanent record, by photographic orother means, of the image on the screen of acathode-ray tube.cathode-ray oscilloscope See OSCILLOSCOPE.cathode rays Invisible rays emanating from thecathode element of an evacuated tube operatedwith a high voltage between the anode and cathode.Cathode rays (electrons) cause certain substances,PHOSPHORS, to glow upon striking them.cathode-ray scanning tube Any tube in which anelectron beam is deflected horizontally and verticallyto scan an area. These include oscilloscopetubes, some computer monitors, radar displays,and television camera tubes.cathode-ray tube 1. An evacuated tube containingan anode and cathode that generates cathodeGlass stem ShieldGlasshousingLowerdeflectingplatesUpperdeflectingplatesCathode Anode Streamofelectronscathode-ray tubeViewing screenrays when operated at high voltage. 2. An oscilloscopetube. 3. A picture tube.cathode terminal 1. In a diode (semiconductor ortube), the terminal to which a negative dc voltagemust be applied for forward-biasing the diode.Compare ANODE TERMINAL. 2. In a diode, theterminal at which a positive dc voltage appearswhen the diode acts as an ac rectifier. CompareANODE TERMINAL. 3. The terminal connectedinternally to the cathode element of device. 4. Ina vacuum tube, an indirectly heated electronemitter.cathode voltage Symbol, E K . The voltage betweenground (or B-minus) and the cathode of a tube; itcan have both ac and dc components.cathodic protection A method of preventing corrosivegalvanic action in underground metalpipes or the submerged hulls of ships. The part tobe protected is used as the cathode of a circuitthrough which a direct current is passed in thedirection opposite to that which caused the corrosion,thus counteracting it.cathodofluorescence Fluorescence resulting froma material’s exposure to cathode rays.cathodoluminescence In a vacuum chamber inwhich a metal target is bombarded with highvelocityelectrons (cathode rays), the emission ofradiation of a wavelength characteristic of themetal.cation A positive ion. Also see ION.CAT scanner The X-ray apparatus for COMPUT-ERIZED AXIAL TOMOGRAPHY.CATV Abbreviation of COMMUNITY-ANTENNATELEVISION (usually cable television).caustic soda electrolyte Symbol, NaOH. Sodiumhydroxide solution, as used in some secondarycells and experimental devices.cavitation The local formation of cavities in a fluidused in ultrasonic cleaning because of the reductionin pressure at those points.cavitation noise In an ultrasonic cleaner, thenoise resulting from the collapse of bubbles producedby cavitation.cavity A metallic chamber (can) in which energy isallowed to reflect, sometimes resulting in resonance.cavity filter A microwave (usually band rejection)filter consisting of a resonant cavity and associatedcoupling devices.cavity frequency meter See CAVITY WAVEME-TER.cavity impedance The impedance across a cavityat a particular frequency. At resonance, the cavityimpedance is purely resistive.cavity laser A laser that employs a resonant cavityfilled with gas, such as helium/neon or argon,and a pair of reflectors. Resonance occurs betweenthe reflectors, one of which is totally reflectiveand the other of which is approximately 95percent reflective. Output is from the partially reflectiveend of the device.

cavity magnetron • cell constant 105cavity magnetron A magnetron whose anode is aseries of resonant cavities.cavity oscillator An oscillator with a cavity-tunedcircuit.cavity radiation Energy radiated from a tiny holein an otherwise sealed chamber. The radiationoccurs at all electromagnetic wavelengths; thegreater the temperature within the chamber, thegreater the frequency at which the radiation hasits maximum amplitude.cavity resonance The phenomenon whereby ahollow cavity resonates; specifically, resonance insmall metal cavities at microwave frequencies.cavity resonator See RESONANT CAVITY.cavity wavemeter An absorption wavemeter whoseadjustable element is a tunable resonant cavityinto which radio-frequency (RF) energy is injectedthrough a waveguide or coaxial cable. Such an instrumentis useful at microwave frequencies.CB Abbreviation of CITIZENS BAND.Cb Symbol for COLUMBIUM.C B Symbol for BASE CAPACITANCE of a transistor.C band The band of radio frequencies between 3.9and 6.2 GHz.C C Symbol for collector capacitance of a transistor.cc 1. Alternative abbreviation of cubic centimeter.The International Organization for Standardizationrecommends cm 3 . 2. Abbreviation ofCOTTON-COVERED.CCA Abbreviation of CURRENT-CONTROLLEDAMPLIFIER.CCD Abbreviation of CHARGE-COUPLED DEVICE.CCIS Abbreviation of COMMON-CHANNEL INTER-FACE SIGNALING.CCIR Abbreviation of Comite Consultatif Internationaldes Radiocommunications (International RadioConsultative Committee).CCIT Abbreviation of Comite Consultatif InternationalTelegrafique (International Telegraph ConsultativeCommittee).CCITT Abbreviation of Comite Consultatif InternationalTelegrafique et Telephonique (InternationalTelegraph and Telephone Consultative Committee).CCS 1. Abbreviation of CONTINUOUS COMMER-CIAL SERVICE. 2. Abbreviation of commonchannelsignaling.CCTV Abbreviation of CLOSED-CIRCUIT TELEVI-SION.CCTV monitor A video monitor that receives a signalfrom a CCTV transmitter.CCTV signal The picture signal in a CCTV system.It can be either a modulated radio-frequency signalor a composite video signal.ccw Abbreviation of COUNTERCLOCKWISE.CD Abbreviation of COMPACT DISK.Cd Symbol for CADMIUM.cd Abbreviation of CANDELA.CD-4 A method of obtaining quadraphonic reproductionon a phonograph disk using modulatedcarriers with frequencies above the human hearingrange.CDI Abbreviation of CAPACITOR-DISCHARGE IG-NITION.C display A radar display showing the target as adot whose coordinates represent the bearing (horizontal)and angle of elevation (vertical). CompareA DISPLAY, J DISPLAY, and K DISPLAY.cd/m 2 Candelas per square meter, the SI unit ofluminance.CD-ROM Abbreviation of COMPACT-DISK READ-ONLY MEMORY.Ce Symbol for CERIUM.C e Symbol for EMITTER CAPACITANCE of a transistor.ceiling 1. The maximum possible power outputfrom a transmitter. 2. The maximum possiblecurrent or voltage that a circuit can deliver. 3. Inaviation, the level of the cloud base.ceilometer An instrument for measuring ceiling(cloud height).cel In animated graphics, an individual image orframe.cell 1. A single (basic) unit for producing dc electricityby electrochemical or photovoltaic action,as in a battery or a solar panel. Also see PRIMARYCELL, STANDARD CELL, STORAGE CELL. 2. Anaddressable, one-word-capacity storage elementin a computer memory. 3. The geographic regioncovered by a specified repeater in a cellular communicationsnetwork. See CELLULAR COMMU-NICATIONS. 4. An electrostatic charge dipole inthe atmosphere, usually occurring in or nearthunderstorms. 5. A thunderstorm.cell constant The surface area of the electrodes ina cell divided by the distance between them. Thebasic linear units must be the same: for example,square centimeters for surface area and centimetersfor distance.

106 cell counter • center-tapped filamentcell counter A bioelectronic instrument used tocount blood cells and other minute particles.cell reversal A condition that can occur in somerechargeable electrochemical cells and batteries,such as nickel-cadmium batteries. It most oftenresults from neglecting to recharge the cell or batterywhen it has become fully discharged.cell-type enclosure A room designed to preventthe entrance or escape of radio-frequency (RF)electromagnetic fields, characterized by doublewalledcopper-mesh shielding.cellular coil A coil having a crisscross (usuallymultilayer) winding. Examples: lattice-woundcoil, honeycomb coil, basket-weave coil.cellular communications A radio, telephone, ortelevision communications network that makesuse of numerous fixed repeaters. Subscribers usemobile or portable transceivers that are alwayswithin range of at least one repeater. The mostcommon form is known as cellular telephone orcellular mobile radio telephone.celluloid A thermoplastic dielectric material that isa blend of cellulose nitrate and camphor. Dielectricconstant, 4 to 7. Dielectric strength, 250 to780 V/mil.cellulose acetate A plastic dielectric material usedas a substrate for magnetic tapes, photographicfilm, and similar applications. Dielectric constant,6 to 8. Dielectric strength, 300 V to 1kV/mil. Also see ACETATE.cellulose acetate base See ACETATE BASE.cellulose acetate butyrate A thermoplastic dielectricmaterial that is an acetic and butyric acid esterof cellulose.cellulose acetate tape See ACETATE TAPE.cellulose nitrate The nitric acid ester of cellulose,a plastic insulating material.cellulose propionate A thermoplastic molding materialthat is a propionic acid ester of cellulose.Celsius scale A temperature scale in which 0 degreesis the freezing point of water, and 100 degreesthe boiling point of water. Also calledCENTIGRADE SCALE. Compare ABSOLUTESCALE, and FAHRENHEIT SCALE.cent An audio-frequency interval of 0.01 (1⁄100) ofa half step. A half step is the frequency differencebetween two immediately adjacent keys ona piano.center channel In high-fidelity stereo, a phantomsound source that appears to exist midway betweenthe left and right speakers or earpieces.The effect is caused by identical, or nearly identical,signals in the left and right channels.center-fed antenna An antenna in which the feedersare connected to the center of the radiator.center feed 1. Attaching a feeder or transmissionline to the center of the radiator of an antenna. 2.Connection of signal-input terminals to the centerof a coil. 3. Descriptive of paper tape whosefeed holes are aligned with character hole centers.Compare ADVANCE FEED TAPE.center frequency 1. The frequency, in a communicationsreceiver, that is midway between thelower and upper 3-dB-down amplitude points.2. The average frequency of a modulated carrier.3. The carrier frequency of a modulated signal,whether or not the carrier is suppressed.MaxAmplitudeMinLowersidebandsLowerFrequencyUppersidebandscenter frequency, 3.Center(suppressedcarrier)Highercentering control In an oscilloscope circuit, a potentiometerused to position the image on thescreen (particularly in the center). Separate controlsare provided for horizontal and vertical centering.center loading In an inductively loaded antenna,placement of the loading coil(s) at or near a pointor points midway between the feed point and theend(s) of the radiating element.center of beam 1. In a directional antenna system,the direction, denoted by a straight ray, wherethe signal strength or response is the greatest. 2.In a beam of visible light, the geometric center ofthe spot produced when the beam strikes a surfaceperpendicular to the beam. 3. In a beam ofvisible light, the axis within the beam where theintensity is greatest.center of channel The frequency that is midwaybetween the lowest and highest frequency componentsof a communications channel.center of radiation The point from which the energyradiated by an object appears to arrive.center tap A connection made to the centermostturn of a coil or to the center-value point of a resistor,filament, or capacitor pair.center-tapped coil See CENTER-TAPPED WIND-ING.center-tapped filament A tube or lamp filamentthat has a tap at its center.

center-tapped inductor • ceramic-to-metal seal 107center-tapped inductor An inductor that has atap at half the total number of turns (the physicalcenter of the winding).center-tapped potentiometer A potentiometerthat has a tap at half the total resistance of theresistance element.center-tapped resistor A fixed resistor that has atap at half the total resistance.center-tapped transformer A transformer thathas one or more center-tapped windings.center-tapped winding A winding that has a tapat half the total number of turns (the physicalcenter of the winding).center-tapped windingcenter tracking frequency In three-frequencyalignment (tracking) of a circuit, the frequencybetween the upper and lower frequency limits(alignment or tracking points of the circuit).center-zero meter A meter that has its zero pointat the center of the scale (e.g., a dc galvanometer).centi- Abbreviation, c. Prefix meaning hundredth(s)(10 –2 ).centigrade scale See CELSIUS SCALE.centimeter Abbreviation, cm. A unit of lengthequal to 10 -2 meter, or 0.3937 inch.centimeter-gram-second system Abbreviation,cgs. A system of units, now seldom used, inwhich the centimeter is the fundamental unit oflength, the gram is the fundamental unit ofmass, and the mean solar second is the fundamentalunit of time. Electrical units in the cgssystem fall into two categories: electrostatic andelectromagnetic. The names of cgs electrostaticunits have the prefix stat- (e.g., STATAMPERE,STATVOLT, etc.). Cgs electromagnetic unitshave the prefix ab- (e.g., ABAMPERE, ABVOLT,etc.).centimetric waves See MICROWAVES.centipoise A cgs measure of the dynamic viscosityof liquids. Equal to 10 –2 poise.central office In telephone systems, a switchingnetwork at which numerous circuits or subscriberlines converge.central processing unit Abbreviation, CPU. In a digitalcomputer, the section containing the arithmeticand logic unit (ALU), control circuits, and internalmemory circuits. Also called central processor.Central Radio Propagation Laboratory A governmentlaboratory that studies radio propagationand collects, correlates, and analyzes datafor predicting propagation conditions. The organizationalso studies methods of measuringpropagation.centrifugation potential An electric potential thatoccurs in a colloidal solution when the solution iscentrifuged.centrifugal switch A switch actuated by rotationalmotion (e.g., the automatic disconnection switchin a capacitor motor).centripetal force The force that draws the mass ofa rotating body toward the axis of rotation.ceramal See CERMET.ceramet seal See CERAMIC-TO-METAL SEAL.ceramic-based microcircuit A tiny circuit printedor deposited on a ceramic substrate.ceramic capacitor A component made with sheetsof metal stacked alternately with wafers of ceramic.This material, like mica, has low loss, andtherefore allows for high efficiency. For low valuesof capacitance, only one layer of ceramic isneeded, and two metal plates can be glued to adisk of porcelain, one on each side. Alternatively,a tube or cylinder of ceramic can be employed,and metal ink applied to the inside and outside ofthe tube. These capacitors have values rangingfrom a few picofarads to about 0.5 µF. Their voltageratings are comparable to those of paper capacitors.Compare ELECTROLYTIC CAPACITOR,MICA CAPACITOR, PAPER CAPACITOR, PLAS-TIC-FILM CAPACITOR, TANTALUM CAPACITOR.ceramic dielectric 1. A ceramic used as a dielectricin capacitors. Examples: barium titanate,barium strontium titanate, and titanium dioxide.Ceramic dielectrics provide high dielectric constant.2. A ceramic used as an insulator. Examples:isolantite, porcelain, and steatite.ceramic filter A resonant filter similar to a crystalfilter, but using a piezoelectric ceramic material.ceramic magnet A permanent magnet made of amagnetic ceramic material, such as mixtures ofbarium oxide and iron oxide.ceramic microphone A microphone that uses aCERAMIC PIEZOELEMENT to convert soundwaves into electrical impulses.ceramic piezoelement A component that uses apiezoelectric ceramic material. Examples: ceramicfilter, ceramic microphone, ceramic phono pickup,ceramic transducer, and electrostrictive transducer.Also called PIEZOELECTRIC CERAMIC.ceramic resistor A carborundum resistor whosevalue is voltage-dependent. It usually displays anegative temperature coefficient of resistance(but a positive coefficient is available) and a negativevoltage coefficient of resistance.ceramics 1. Clay-based materials used as dielectricsand insulators in electronics. Examples:barium titanate, titanium dioxide, porcelain,isolantite, and steatite. 2. The science and art ofusing and developing ceramics.ceramic-to-metal seal A bond in which ceramicand metal bodies are joined, for example, thebonding of a metal lead to a ceramic disk,through which it passes to provide a leak-proofseal. Also called ceramet seal.

108 ceramic transducer • change recordceramic transducer A transducer that uses a CE-RAMIC PIEZOELEMENT to translate such parametersas pressure and vibration into electricalpulses.ceramic tube A high-temperature vacuum tubethat uses a ceramic material, instead of glass, asthe envelope; the tube offers low losses at highfrequencies.Cerenkov radiation Light emanating from a transparentmaterial that is traversed by charged particles,whose speed is higher than the speed oflight through the material.InternalreflectingmirrorAtomicradiationVisiblelightsensorTransparentmaterialCerenkov radiationCerenkov rebatron device An apparatus for generatingradio-frequency energy by passing anelectron beam through a piece of dielectric havinga small aperture.ceresin wax A yellow or white wax obtained by refiningozocerite. Used as an insulant and sealantagainst moisture. Dielectric constant, 2.5 to 2.6.cerium Symbol, Ce. A metallic element of the rareearthgroup. Atomic number, 58. Atomic weight,140.13.cerium metals A group of metals belonging tothe rare-earth group: cerium, lanthanum,neodymium, praseodymium, promethium, andsamarium.cermet An alloy of a ceramic, such as titaniumcarbide, and nickel, a metal. A thin film of cermetis used as a resistive element in some microcircuits.Cermet is an acronym for ceramic metal.certified tape A magnetic recording tape that hasbeen thoroughly checked and found to have noflaws.cesium Symbol, Cs. A metallic element of the alkali-metalgroup. Atomic number, 55. Atomicweight, 132.91. The oscillations of this element’satoms have been used as atomic time standards.The element is used in some phototubes as thelight-sensitive material, and in some arc lamps.cesium-vapor lamp A low-voltage arc lamp usedas an infrared source.Cf Symbol for CALIFORNIUM.cgs Abbreviation of CENTIMETER-GRAM-SECOND.chad The punched-out particle(s) constituting refusefrom paper-tape punching.chadded tape Punched paper tape in which thechad is left partially attached to the tape’spunched holes.chadless tape Punched paper tape without CHAD.chafe 1. An area that has been abraded by rubbingor scraping. 2. To produce a chafe.chaff Strips of metal foil used to create radar interferenceor ambiguity in locating a target by multiplereflections of the beam. Also called MIRROR.chain broadcasting Simultaneous transmissionsfrom a number of broadcast transmitters connectedtogether in a network by wire line, coaxialcable, or microwave link.chain calculation As performed by a calculator, acalculation that can be entered as it would normallybe written (i.e., without the need for regroupingoperands).chain printer In the readout channel of a digitalcomputer, a high-speed printer carrying printer’stype on a revolving chain.chain radar system A number of radar stationsalong a missile-flight path that are connected in acommunications or control network.chain reaction A reaction (as in nuclear fission)that is self-sustaining or self-repeating. Unlesscontrolled from outside, such a reaction runs todestruction.chain switch A switch that is actuated by pulling alight metal chain. Successive pulls turn theswitch alternatively on and off.ChainCordchain switchchange dump In computer operation (especially indebugging), the display of the names of locationsthat have changed following a specific event.change file See TRANSACTION FILE.change of control In a sequence of computerrecords being processed, a logical break that initiatesa predetermined action, after which processingcontinues.changer In a high-fidelity disk player, a device thatallows several disks to be played, one after theother, without the need for manually exchangingthe disks.change record A computer record that changes informationin a related master record. Also calledtransaction record.

change tape • character density 109change tape See TRANSACTION TAPE.channel 1. A frequency (or band of frequencies) assignedto a radio or television station. 2. See KEY-WAY. 3. A subcircuit in a large system [e.g., theradio-frequency (RF) channel of a receiver, thevertical-amplifier channel of an oscilloscope, or themodulator channel of a radio transmitter]. 4. Theend-to-end electrical path through the semiconductorbody in a field-effect transistor. 5. One ofthe independent audio circuits in a stereo soundsystem (e.g., the left channel or the right channel).channel analyzer A (usually multiband) continuouslytunable instrument, similar to a tuned radioreceiver, used in troubleshooting radiocommunications circuits by substituting a perfectchannel for one that is out of order.channel balance The state in which the apparentamplitude of two or more channels is identical.channel bank In a transmission system, the terminalequipment used for the purpose of multiplexingthe individual channels.channel capacity The fullest extent to which achannel can accommodate the information (frequencies,bits, words, etc.) to be passed through it.channel designator A name, number, or abbreviationgiven to a channel in a communications system.channel effect The possible current flow through ahigh impedance between the collector and emitterin a bipolar transistor.channel frequency The CENTER FREQUENCY ofa communications channel.channeling Multiplex transmission in which separatecarriers within a sufficiently wide frequencyband are used for simultaneous transmission.channelizing The subdivision of a relatively widefrequency band into a number of separate subbands.channel reliability 1. The proportion of time, usuallyexpressed as a percentage, that a communicationschannel is useful for its intended purpose.2. The relative ease with which communicationscan be carried out over a particular channel.channel reversal In stereo reproduction, interchangingthe left and right channels.channel-reversing switch In a stereo system, aswitch that allows channel reversal without theneed for reorienting speaker cables or connectors.channel sampling rate The rate at which individualchannels are sampled. For example, in theelectronic switching of an oscilloscope, the numberof times per second each input-signal channelis switched to the instrument.channel selector A switch or relay used to put anyof a series of channels into functional status in asystem.channel separation 1. The spacing between communicationschannels, expressed in kilohertz. 2.In stereo reproduction, the degree to which theinformation on one channel is separate from theother; usually expressed in decibels.MaxAmplitudeMinLowerChannelseparationf 1 f 2 f 3FrequencyHigherchannel separation, 1.channel slot On a carrier modulated by numeroussignals, the position or frequency of a specificmodulating signal.channel shift The interchange of communicationschannels (e.g., the shift from a calling frequencyto a working frequency).channel strip A fixed-channel amplifier for a televisionreceiver.channel time slot In a frame of transmitted information,such as a television picture, a time intervaldesignated to a channel for the transmissionof a character signal or other information.channel-to-channel connection A device, such asa channel adapter, used to transfer data rapidlybetween any two channels of two digital computers,at the data speed of the slower channel.channel-utilization index An indication of the extentto which channel capacity is used. For agiven channel, the index is the ratio of informationrate to channel capacity, each expressed inunits per second.channel wave An acoustic wave that travelswithin a region or layer of a substance because ofa physical difference between that layer and thesurrounding material. An example of a channelwave is the propagation of sound over a still lake.channel width In a frequency channel, the differencef 2 – f 1 , where f 1 is the lower-frequency limitand f 2 is the upper-frequency limit of the channel.chapter A self-contained computer program section.character 1. One of the symbols in a code. 2. Incomputer operations, a digit, letter, or symbolused alone or in some combination to express information,data, or instructions.character code In a communications or computersystem, the combination of elements (e.g., bits)representing characters.character crowding A reduction of the time intervalbetween successive characters—especiallythose read from tape.character density The number of characters thatcan be stored in a given length or surface area of

110 character density • charge carriera medium. On a magnetic tape, it might be specifiedin characters per millimeter; on a magneticdisk, it might be specified in characters persquare millimeter.character emitter A coded-pulse generator in adigital computer.character generator A device that converts codedinformation into readable alphanumeric characters.characteristic 1. A quantity that characterizes(typifies) the operation of a device or circuit. Examplesare emitter current, output power, andfrequency deviation. 2. In floating point notation,the exponent.characteristic curve A curve showing the relationshipbetween an independent variable and a dependentvariable, with respect to the parameter(s)for a device or circuit. Example: the collector voltage-collectorcurrent characteristic curve of atransistor.characteristic distortion 1. In a digital signal,pulse distortion caused by the effects of the previouspulse or pulses. 2. Distortion in the characteristiccurve of a component or device.characteristic frequency The frequency peculiarto a given channel, service, or response.characteristic impedance Symbol, Z 0 . 1. Theoretically,the impedance that would be simulatedby a given two-conductor or coaxial line of uniformconstruction, if that line were of infinitelength. This value is determined by the materialsused for the two conductors, the dielectric usedto insulate the two conductors, the diameters ofthe conductors, and the spacing between them.2. In practice, for a transmission line or waveguideterminated with a load that produces nostanding waves on the line, the ratio of radio-frequency(RF) voltage to RF current. This ratio isthe same at all points along the length of a perfectlymatched line, and depends on the physicalconstruction of the line. Coaxial lines typicallyhave Z 0 between 50 and 100 ohms. Twinlead isavailable with 75-ohm and 300-ohm Z 0 values.Open-wire line has Z 0 between 300 and 600ohms, depending on the spacing between theconductors, and also on the type of dielectric (insulatingmaterial) employed to keep the spacingconstant between the conductors. 3. Experimentally,the value of impedance that, if it terminatesa transmission line or waveguide, results in noreflected power from the load end of line. This isalways a pure resistance; that is, it contains noreactance.characteristic overflow In floating-point arithmetic,the condition that occurs when a characteristicexceeds the upper limit specified by aprogram or computer.characteristic spread The range of values overwhich a characteristic extends. For example, if anamplifier’s output ranges from 15 W to 25 W, itscharacteristic spread is 10 W.characteristic underflow In floating-point arithmetic,the condition that occurs when a characteristicexceeds the lower limit specified by aprogram or computer.character modifier In address modification, aconstant (compare VARIABLE) that refers to aspecific character’s location in memory.character-oriented A computer in which characterlocations, rather than words, can be addressed.character printer A computer output device thatprints matter in the manner of a conventionaltypewriter.character reader Also called an optical scanner. Ina digital computer, an input device that can readprinting and script directly.character recognition The reading of a written orprinted character by a computer, including itsidentification and encoding.character sensing The detection of characters bya computer input device. This can be done galvanically,electrostatically, magnetically, or optically.character set The set of characters in a completelanguage, or in a communications system.character signal The set of elements or bits representinga character in a digital transmission system.The signal can also represent the quantizingvalue of a sample.characters per minute An expression of the speedof transmission of a digital signal. The number ofcharacters (on average) transmitted in a period ofone minute. In Morse code (CW) transmission,this is generally taken as the number of times theword paris plus the subsequent space, multipliedby six (five letters and one space following), canbe sent in one minute.characters per second An expression of the speedof transmission of a digital signal. The number ofcharacters (on average) transmitted in a period ofone second.character string A one-dimensional character array[i.e., a list of characters that, when printed ordisplayed, would appear in a row or column, butnot both (as in a matrix)].character subset A classification of characterswithin a set.Charactron A cathode-ray readout tube that displaysletters, numbers, and symbols on itsscreen. More commonly called a monitor.charcoal tube In a system for producing a highvacuum, a trap containing activated charcoal,which is heated to dull red, then cooled by liquidair to absorb gases.charge1. A quantity of electricity associated with aspace, particle, or body. 2. To electrify a space,particle, or body (i.e., to give an electric charge).3. To store electricity, as in a storage battery orcapacitor. Compare DISCHARGE.charge carrier 1. An ELECTRON whose movementconstitutes a flow of electric current. 2. An elec-

charge carrier • checking program 111tron deficiency (HOLE) whose movement constitutesa flow of electric current. 3. Any particle,such as a charged atom (ION), PROTON, ALPHAPARTICLE, or BETA PARTICLE, whose movementconstitutes a flow of electric current.charge-coupled device Abbreviation, CCD. Aform of analog-to-digital converter that generatesa digital signal output representing an analogimage input. The transfer of stored charges providesthe method of operation. Used in machinevision systems and in numerous scientific applications.charge density The degree of charge or currentcarrierconcentration in a region.charged particle 1. See CHARGE CARRIER. 2. SeeION.charged voltage 1. The voltage across a fullycharged capacitor. 2. The terminal voltage of afully charged storage cell.charge holding See CHARGE RETENTION.charge of electron The negative electric chargecarried by a single electron. Approximately equalto 1.602 × 10 –19 coulombs.charger 1. See BATTERY CHARGER. 2. Any deviceor circuit that charges a capacitor.charge retention 1. The holding of an electriccharge by a cell or battery when no current is beingdrawn from it. 2. A measure of the ability of acell or battery to maintain an electric chargewhen no current is drawn from it. Often specifiedin terms of shelf life. 3. The holding of a charge bya capacitor.charge-storage tube A cathode-ray tube that holdsa display of information on its screen until the operatorremoves it by pressing an erase button.charge-to-mass The ratio of the electric charge tothe mass of a subatomic particle.charge-to-mass ratio of electron The ratio of thecharge (e) of the electron to the mass (m e ) of theelectron, in coulombs per kilogram (C/kg). For anelectron at rest, e/m e is approximately equal to1.602 × 10 –19 C divided by 9.11 × 10 –31 kg = 1.76× 10 11 C/kg.charge transfer 1. The switching of an electriccharge from one capacitor to another. 2. The captureof an electron by a positive ion from a neutralatom of the same kind, resulting in the ion becominga neutral atom, and the previously neutralatom becoming a positive ion.charge transfer device A semiconductor in whichan electric charge is moved from location to location.Applications include delay lines, video signalprocessing, and signal storage.charging 1. The process of storing electrical energyin a capacitor. 2. The process of storing electrochemicalenergy in a storage cell or battery.charging current 1. The current flowing into a capacitor.2. The current flowing into a previouslydischarged storage cell.charging rate 1. The rate at which charging currentflows into a storage cell or battery, expressedin amperes or milliamperes. For most cells andbatteries, the rate is greatest initially, when thecell or battery is depleted or nearly depleted; therate decreases as the cell or battery becomescharged. 2. The instantaneous rate at whichcharging current flows into a capacitor or capacitance-resistancecircuit, expressed in amperes,milliamperes, or microamperes.charged voltage 1. The voltage across a fullycharged capacitor. 2. The terminal voltage of afully charged storage cell.Charlie Phonetic alphabet code word for the letter C.chassis A (usually metal) foundation on whichcomponents are mounted and wired.chassis ground A ground connection made to themetal chassis on which the components of a circuitare mounted. When several ground connectionsare made to a single point on the chassis, aCOMMON GROUND results.chatter 1. A rapidly repetitive signal, caused by interruptionor variation of a current (usually interference).2. Extraneous vibration, as of thearmature in a relay.chatter time The interval between the instant thatcontacts close (for example, in a relay) and the instantat which chatter ends.cheater cord An extension cord used to conductpower to a piece of equipment (especially a televisionreceiver) by temporarily bypassing the safetyswitch or interlock. Use of such a cord presents apotentially fatal shock hazard to personnel using,or working on, the equipment.Chebyshev filter Also spelled Tschebyscheff orTschebysheff. A form of inductance-capacitance(LC) lowpass, highpass, bandpass, or bandrejectionfilter, characterized by an attenuationversus-frequencycurve with ripple in thepassband.check1. A test generally made to verify condition,performance, state, or calculations; specifically, incomputer operations, it applies to operands or results.2. The usually abrupt halting of an action.check bit A binary CHECK DIGIT.check character In a group of characters, onewhose value depends on the other characters,which it checks when the group is stored ortransferred.check digit Also called check number. In computeroperations, a number added to a group of digits,forming a code that identifies entities in the system(including personnel) and can be used forverification. The check digit is the remainderwhen the number code (for example, 459) is dividedby a fixed number (for example, 5); in thiscase, the check digit (the remainder of 459/5) is4, and the amended code number is 4594.check indicator An indication, made via a videodisplay, that something has been shown to be invalidaccording to a check.checking program Also called checking routine.For debugging purposes, a diagnostic computer

112 checking program • chirpprogram capable of detecting errors in anotherprogram.checkout A test routine that ascertains whether ornot a circuit or system is functioning according tospecifications.checkout routine A routine used by programmersto debug programs.checkpoint A point in a digital-computer programat which sufficient information has been stored toallow restarting the computation from that point.checkpoint dump The process of recording detailsof a computer program run. This process mightbe necessary in the event of a system failure thatrequires reconstruction of a program or programs.checkpointing The writing of a computer programin such a manner that, during a program run, informationis frequently dumped as insuranceagainst possible loss in the event of a system failure.check problem A presolved problem used to checkthe operation of a digital computer or program.check register In some digital computers, a registerin which transferred information is stored sothat it can be checked against the same informationas it is received a second time.check routine A special program designed to ascertainif a program or computer is operating correctly.Also see CHECK PROBLEM.checksum Used as part of a summation check, asum derived from the digits of a number. For example,the checksum of 23,335 is 16. Also calledHASH TOTAL.check symbol For a specific data item, a digit ordigits obtained by performing an arithmeticcheck on the item, which it then accompaniesthrough processing stages for the purpose ofchecking it.check total See CONTROL TOTAL.check word A check symbol in the form of a wordadded to, and containing data from, a block ofrecords.chelate Pertaining to cyclic molecular structure inwhich several atoms in a ring hold a centralmetallic ion in a COORDINATION COMPLEX.chemical deposition The coating of a surface witha substance resulting from chemical reduction ofa solution. In mirror making, for example,formaldehyde reduces a solution of silver nitrate,and deposits metallic silver on the surface of polishedglass. Also see CHEMICALLY DEPOSITEDPRINTED CIRCUIT and CHEMICAL REDUCTION.chemical detector See ELECTROLYTIC DETEC-TOR.chemical effect An alteration in the chemicalmakeup of a substance or solution, resultingfrom the passage of an electric current through it.Examples include electrolysis, electroplating, andthe reduction of ores.chemical energy Energy that is stored in thechemical bonds of a material or solution. An exampleis the stored energy in terms of watt hoursin an electrolytic cell.chemical load An arrangement of a chemical materialor device for the passage of electricitythrough it. Examples: electroplater, electrolyticcell for the production of hydrogen gas, and storagebattery.chemically deposited printed circuit A printedcircuit in which the pattern of metal lines and areasare chemically deposited on a substrate.chemically pure Abbreviation, CP. Free from impurities.chemical rectifier See ELECTROLYTIC CELL.chemical reduction The process of making achemical compound (usually in solution) into ametal, by removing the nonmetallic componentfrom the compound. For example, when copperoxide is heated in the presence of hydrogen (a reductingagent), the oxygen (the nonmetallic component)is driven out, and copper (along withsome water) remains.chemical resistor See ELECTROLYTIC RESIS-TOR.chemical switch See ELECTROCHEMICALSWITCH.CHIL Abbreviation for current-hogging injectionlogic. A form of bipolar digital logic technology.chip 1. An INTEGRATED CIRCUIT. 2. A small slab,wafer, or die of dielectric or semiconductor material,on which a subminiature component or circuitis formed or deposited.chip capacitor A subminiature capacitor formedon a chip.chip resistor A subminiature resistor formed on achip.chip tray A chad receptacle located at a card or papertape punching site.Chireix-Mesny antenna A high-frequency (HF)beam antenna, in which each dipole section constitutesone side of a diamond. Cophased horizontaland vertical components of current flow ineach of the diagonals, and radiation is broadsideto the plane of the driven element.MaximumradiationFeedlineChireix-Mesny antennachirp A rapid change in the frequency of a continuous-waveMorse-code signal. The chirp usuallyoccurs at the beginning of each dot or dash, and

chirp • chopper power supply 113can go up or down in frequency. Chirp occurs becauseof a change in the output impedance of anoscillator as it is keyed. Modern code transmittersdo not exhibit significant chirp.chirp modulation A form of modulation in whichthe frequency of a signal is deliberately changedin a systematic way. Used in some radar systems.chirp radar A radar system that uses CHIRP MOD-ULATION.Chladni’s plates Conducting plates that are usedto evaluate the nature of a vibration in a solid material.The plates are clamped to the material, andsand is sprinkled on the surface. This producespatterns that indicate the nature of the vibrations.chlorinated diphenyl A synthetic organic substanceused as an impregnant in some oil-filledcapacitors.chlorinated naphthalene See HALOWAX.chlorine Symbol, Cl. A gaseous element of thehalogen family. Atomic number, 17. Atomicweight, 35.453.choke1. To restrict or curtail passage of a particularcurrent or frequency by means of a discretecomponent, such as a choke coil. 2. See CHOKECOIL.choke air gap A fractional-inch opening in the ironcore of a filter choke, usually filled with wood orplastic. The gap prevents saturation of the corewhen the choke coil carries maximum rated directcurrent.choke coil 1. A large-value inductor that providesa high impedance to alternating current (ac),while offering virtually no opposition to directcurrent (dc). 2. In radio-frequency (RF) applications,an inductor that provides a highimpedance to RF signals while showing lowimpedance for audio-frequency (AF) signals anddirect currents (dc).choke-coupled modulation An amplitudemodulation(AM) scheme, in which the modulatoris coupled to the radio-frequency (RF) amplifierthrough a shared iron-core choke coil.choke flange At the end of a waveguide, a flange inwhich a groove forms a CHOKE JOINT.choke-input filter A filter whose input componentis an inductor (choke). The choke-input powersupplyfilter is distinguished by its superiorvoltage regulation, compared with theCAPACITOR-INPUT FILTER.choke joint A joint connecting two waveguide sectionsand permitting efficient energy transferwithout requiring electrical contact with the insidewall of the waveguide.chopped dc See INTERRUPTED DC.chopped mode In a single-gun cathode-ray-tube(CRT) oscilloscope, a technique for sequentiallydisplaying several signals that are not referencedto the oscilloscope sweep.chopped signal An ac or dc signal that is periodicallyinterrupted, as by means of a CHOPPER.+Pulsatingdc input−FilterchokeFiltercapacitorSmootheddc outputchopper A device or circuit that interrupts a directcurrent (dc) at some predetermined rate. Ideally,such a device is characterized by distinct on andoff operation.chopper amplifier A circuit that amplifies the outputof a CHOPPER. Used in conjunction with aCHOPPER CONVERTER in dc amplification.chopper converter A device that interrupts a directcurrent (dc), and changes it to a pulsating,rectangular-wave current or voltage that can behandled by a stable ac amplifier and rectified tosupply amplified dc.chopper power supply Also called power inverter.A circuit that delivers high-voltage ac from a dcsource. The input is typically 12 volts dc, and theoutput is usually 117 volts rms ac. These devicesfacilitate the use of small appliances such ascomputers, television sets, and communicationsradios in portable and mobile environments. Theoutput of a low-cost power inverter is generallynot a good sine wave. More sophisticated invertersproduce good sine waves and have a frequencyclose to 60 Hz.+choke-input filter+−

114 chopper stabilization • chrominance modulatorchopper stabilization 1. Stabilization of directcurrent(dc) amplification by using a CHOPPERCONVERTER ahead of a stable ac amplifier, andrectifying the amplifier output. 2. In a regulatedpower supply, use of a CHOPPER AMPLIFIER atthe control-circuit input to improve regulation.chopper-stabilized amplifier See CHOPPER AMP-LIFIER and CHOPPER STABILIZATION, 1.chopper transistor A transistor that providesrapid and repeated on/off switching of direct current(dc), in the manner of an electromechanicalinterrupter. See CHOPPER.chopping frequency The frequency at which achopper interrupts a signal.chord 1. A harmonious mixture of musical tones ofvarious frequencies. 2. A straight line that joinstwo points on a curve (such as an arc of a circle).3. The width of an airfoil.chord organ An electronic organ that will sound amusical chord when a key is pressed (seeCHORD, 1).choreographer program A computer programsimilar to one originally written by Charles Lechtof Lecht Sciences, Inc. The computer operatorgives commands that cause a human form, portrayedon the display screen, to make variousmovements. Used in animated computer graphics.chorus Signals at very low radio frequencies(VLF), natural in origin, that sweep upward infrequency. Believed to result from lightninggeneratedelectromagnetic fields that circulate inthe magnetosphere (earth’s magnetic field). Theterm is derived from the sound the signals makein high-gain audio-frequency (AF) amplifiers connecteddirectly to VLF receiving antennas.Christiansen antenna A radio-telescope antennafor obtaining high resolution. Two straight arraysare placed at an angle, intersecting approximatelyat their centers. The resulting interferencepattern has extremely narrow lobes.Christmas tree A tree-like pattern on the screen ofa television receiver, caused by loss of horizontalsynchronization.chroma The quality of a color: hue and saturation.chroma circuit In color television, one of severalcircuits whose ultimate purpose is to produce acolor component on the screen.chroma-clear raster In color television reception,the clear raster resulting from a white video signal,or from operation of the chroma circuits ofthe receiver (as if they were receiving a whitetransmission). Also called white raster.chroma control In a color television receiver, arheostat or potentiometer that permits adjustmentof color saturation through variation of thechrominance-signal amplitude before demodulation.chromatic fidelity See COLOR FIDELITY.chromaticity 1. The state of being chromatic (seeCHROMA). 2. A quantitative assessment of acolor in terms of dominant or complementarywavelength and purity.chromaticity coordinate For a color sample, theratio of any one of the three tristimulus values(primary colors) to the sum of the three.chromaticity diagram A rectangular-coordinategraph in which one of the three CHROMATICITYCOORDINATES of a three-color system is plottedagainst another coordinate.chromaticity flicker Flicker caused entirely bychromaticity fluctuation (see CHROMATICITY, 2).chromel A nickel-chromium alloy with some ironcontent, used in thermocouples.chromel-alumel junction A thermocouple thatuses wires of the alloys chromel and alumel.chromel-constantan thermocouple A thermocoupleconsisting of a junction between wires orstrips of chromel and constantan. Typical outputis 6.3 mV at 100°C.chrome plating The process of coating a metalwith chromium. Generally protects against corrosion.chrome recording tape Also called chrome tape orchromium tape. Tape that is manufactured fromthe compound chromium dioxide. Noted for itsability to faithfully record and reproduce music.chrominance In color television, the difference betweena reproduced color and a standard referencecolor of the same luminous intensity.chrominance amplifier In a color television circuit,the amplifier separating the chrominancesignal from the total video signal.chrominance cancellation On a black-and-whitepicture tube screen, cancellation of the fluctuationsin brightness caused by a chrominance signal.chrominance-carrier reference In color television,a continuous signal at the frequency of thechrominance subcarrier; it is in fixed phasewith the color burst and provides modulationor demodulation phase reference for carrierchrominancesignals.chrominance channel In color television, a circuitdevoted exclusively to the color function, as opposedto audio and general control channels.chrominance component In the NTSC color televisionsystems, either of the components (I-signalor Q-signal) of the complete chrominance signal.chrominance demodulator In a color televisionreceiver, a demodulator that extracts videofrequencychrominance components from thechrominance signal, and a sine wave from thechrominance subcarrier oscillator.chrominance gain control A rheostat or potentiometerin the red, green, and blue matrix channelsof a color television receiver, used to adjustthe primary-signal amplitudes.chrominance modulator In a color televisiontransmitter, a device that generates the chrominancesignal from the I and Q components andthe chrominance subcarrier.

chrominance primary • circuit diagram 115chrominance primary One of the transmissionprimaries (red, green, and blue) upon which thechrominance of a color depends.chrominance signal The signal component incolor television that represents the hues and saturationlevels of the colors in the picture.chrominance subcarrier In color television, the3579.545-kHz signal that serves as a carrier forthe I- and Q-signals.chrominance-subcarrier oscillator In a color televisionreceiver, a crystal-controlled oscillator thatgenerates the subcarrier signal (see CHROMI-NANCE SUBCARRIER).chrominance video signals Output signals fromthe red, green, and blue channels of a color televisioncamera or receiver matrix.chromium Symbol, Cr. A metallic element. Atomicnumber, 24. Atomic weight, 51.996. Commonlyused as a plating for metals to improve resistanceto corrosion.chronistor An elapsed-time indicator in whichcurrent, flowing during a given time interval,electroplates an electrode. The duration of theinterval is determined from the amount of deposit.chronograph 1. An instrument that provides anaccurate time base along the horizontal axis of itspermanent record. 2. Stopwatch.chronometer A precision clock. Electronic chronometersoften use a highly accurate and stablecrystal oscillator, followed by a string of multivibratorsto reduce the crystal frequency to an audiofrequency (such as 1 kHz) that drives theclock motor.chronoscope An instrument for precisely measuringsmall time intervals.CHU Call letters of the Canadian time-signal stationwhose primary frequency is 7.335 MHz.Ci Symbol for INPUT CAPACITANCE.CIE Abbreviation for International Commission onIllumination.cinching In a reel of magnetic tape, the slipping oftape as force is applied.cinematograph See KINEMATOGRAPH.cipher A code used for the purpose of preventinginterception of a message by third parties.circ 1. Abbreviation of circuit. 2. Abbreviation ofcircular.circle graph Also called a pie graph. A representationaldevice consisting of a disk subdividedinto various triangular areas (radiating from thecenter of the circle), which are proportional torepresented quantities.circle of confusion A circular image of a pointsource of light, resulting from an aberration in anoptical system.circle of declination The graduated circular scaleof a declinometer.circlotron amplifier A high-powered microwaveamplifier of the one-port, cross-field, nonlineartype using a magnetron.circuit 1. A closed path through which currentflows from a generator, through various components,and back to the generator. (An electroniccircuit is often a combination of interconnectedsubcircuits.) 2. The wiring diagram of an electronicdevice or system.circuit analysis The careful determination of thenature and behavior of a circuit and its variousparts. It can be theoretical, practical, or both.Compare CIRCUIT SYNTHESIS.circuit analyzer See CIRCUIT TESTER.circuit board A panel, plate, or card on which electroniccomponents are mounted and interconnectedto provide a functional unit.circuit breaker A resettable fuse-like device that isdesigned to protect a circuit against overloading.In a typical circuit breaker, the winding of anelectromagnet is connected in series with the loadcircuit and with the switch contact points. Excessivecurrent through the magnet winding causesthe switch to be opened.SpringsPower supplyArmaturecircuit breakerLoad circuitin series with coilcircuit capacitance The total capacitance(lumped, distributed, and stray) present in a circuit.circuit capacity 1. The ability of a circuit to handlea quantity (such as current, voltage, frequency,power, etc.) safely and efficiently. 2. Themaximum value of some parameter at which acircuit can function safely and efficiently (e.g., acircuit capacity of 50 A). 3. The number of channelsthat can be accommodated simultaneouslyby a circuit.circuit component 1. Any of the electronic devicesor parts (capacitors, resistors, transistors, etc.)that are connected through wiring to form a circuit.2. An electrical quantity required for, orarising from, circuit operation. Examples: inputvoltage, feedback current, stray capacitance, andcircuit noise.circuit diagram A drawing in which symbols andlines represent the components and wiring ofan electronic circuit. Also called CIRCUIT

116 circuit diagram • circular magnetic waveSCHEMATIC, SCHEMATIC DIAGRAM, andWIRING DIAGRAM.circuit dropout A momentary interruption of circuitoperation, often caused by a break in the circuit.circuit efficiency A quantitative measure of theeffectiveness of circuit operation, customarily expressedas the ratio of the useful output power tothe total input power.circuit element See CIRCUIT COMPONENT, 1.circuit engineer An electronics engineer who specializesin circuit analysis, circuit synthesis, orboth.circuit fault 1. Malfunction of a circuit. 2. An errorin circuit wiring.circuit hole A perforation within the conductivearea of a printed-circuit board, for the insertionand connection of a pigtail, terminal, etc., or forconnecting the conductors on one side of theboard with those on the other.circuit loading Intentionally or unintentionallydrawing power from a circuit.circuit noise 1. Electrical noise generated by a circuitin the absence of an applied signal. 2. In wiretelephony, electrical noise as opposed to acousticnoise.circuit noise level The ratio of circuit-noise amplitudeto reference-noise amplitude, expressed indecibels above the reference amplitude.circuit-noise meter A meter that measures the intensityof the noise generated within a circuit.circuit parameter See CIRCUIT COMPONENT, 2.circuit protection Automatic safeguarding of acircuit from damage from overload, excessivedrive, heat, vibration, etc. Protection is affordedby various devices and subcircuits, ranging fromthe common fuse to sophisticated limiters andbreakers.circuit reliability A quantitative indication of theability of a circuit to provide dependable operationas specified. See MEAN TIME BEFORE FAIL-URE and MEAN TIME BETWEEN FAILURES.circuitry 1. Collectively, electronic and electricalcircuits. 2. A detailed plan of a circuit and itssubcircuits. 3. Collectively, the components of acircuit.circuit schematic See CIRCUIT DIAGRAM.circuit simplification 1. In circuit analysis, thereduction of a complex circuit to its simplest representationto minimize labor and to promoteclarity. Thus, through application of Kirchhoff’slaws, a complicated circuit could theoretically bereduced to a single generator in series with a singleimpedance. 2. In circuit synthesis, the arrangementof a circuit so as to provide desiredperformance with the fewest components andleast-complex wiring.circuit switching In telephony, a method of connectionin which a single circuit is maintained betweentwo subscribers for the entire duration ofthe call. The signal path does not change. Theconnection is maintained even during periods ofsilence (no data transmitted by either subscriber).Compare PACKET SWITCHING.circuit synthesis The development of a circuit underthe guidance of theoretical or practical knowledgeof basic electronics principles andcomponent parameters. Compare CIRCUITANALYSIS.circuit tester An instrument for checking the performanceof electronic circuits. Often consists ofa specialized continuity tester, but occasionally itincludes a dynamic performance tester.circuit tracking The alignment and/or pretuningof circuits for identical or optimum response. Itapplies especially to cascaded circuits, whosevariable elements, such as tuned inductancecapacitance(LC) networks, must follow eachother in step when ganged together.circular angle The angle described by a radius vectoras it rotates counterclockwise around a circle.circular antenna A half-wave horizontally polarizedantenna, whose driven element is a rigidconductor bent into a circle with a break oppositethe feed point. Also called halo antenna. Used primarilyat very-high frequencies (VHF).circular electric wave An electromagnetic wavewith circular electric lines of flux. An example isthe field in the immediate vicinity of a CIRCULARANTENNA.Loopcarrying accircular electric waveElectric linesof fluxcircular functions Trigonometric functions of theangle described by a vector rotating counterclockwisearound a circle. Also see COSINE,COSECANT, COTANGENT, SECANT, SINE, andTANGENT.circular magnet See RING MAGNET.circular magnetic wave An electromagnetic wavein which the magnetic lines of flux are circular.An example is the field in the immediate vicinityof a straight-conductor antenna.

circular mil • class-A amplifier 117Conductorcarrying accircular magnetic waveMagnetic linesof fluxcircular mil A unit of cross-sectional area equivalentto 0.785 millionths of a square inch, or thearea of a circle having a diameter of 0.001 inch.Generally, the circular mil is used to specify thecross-sectional area of a conductor, such as wire.circular mil foot A unit of volume in which thelength is 1 foot and the cross-sectional area is 1circular mil.circular polarization A form of electromagneticwavepolarization in which the orientation of theelectric flux rotates continuously and uniformlyas the wave propagates through space. Circularpolarization can occur in either a clockwise orcounterclockwise sense.circular radian The angle enclosed by two radii ofa unit circle and subtended by a unit arc. Equalto about 57.296 angular degrees.circular scan A radar scan in which the electronbeamspot describes a circle centered around thetransmitting antenna.circular sweep In an oscilloscope, a sweep obtainedwhen the horizontal and vertical sinusoidaldeflecting voltages have the sameamplitude and frequency, but are out of phase by90 degrees (1 ⁄4 cycle).circular trace An oscilloscope pattern consistingof a circle obtained with a circular sweep of theelectron beam.circular waveguide A waveguide with a circularcross section.circulating register In a digital computer, a registerin which digits are taken from locations at oneend and returned to those at the other end.circulating tank current The alternating currentthat oscillates between the capacitor and inductorwithin a tank circuit.circulator A multi-terminal coupler in which microwaveenergy is transmitted in a particular directionfrom one terminal to the next.circumvention In a security or alarm system, theevasion of detection. Can be done by physicallyavoiding regions of coverage, or by defeating thesystem electronically.cis A prefix meaning “on this side of.” For example,the cislunar field is the field on this side of themoon.Citizen Band Abbreviation, CB. A band of radiofrequencies allocated for two-way communicationbetween private citizens (apart from amateur andcommercial services).Citizens Radio Service Two-way radio communicationin a CITIZEN BAND. In the United States,the FCC licenses users of this service without requiringthem to take an examination.C/kg Abbreviation of coulombs per kilogram, theunit for electron charge-to-mass ratio.C/kmol Abbreviation of coulombs per kilomole, theunit for the Faraday constant.ckt Abbreviation of CIRCUIT.Cl Symbol for CHLORINE.cl Abbreviation of CENTILITER.cladding The bonding of one metal to another tominimize or prevent corrosion. A common exampleis copper-clad steel wire, ideal for use inradio-frequency antenna systems. The copperprovides excellent conduction, and the steel provideshigh tensile strength with a minimum ofwire stretching.clamper A device that restricts a wave to a predetermineddc level. Also called DC RESTORER.clamping 1. Fixing the operation of a device at adefinite dc level. Also see CLAMPER. 2. In television,establishing a fixed level for the picture signalat the start of each scanning line.clamping circuit See CLAMPER.clamping diode A diode used to fix the voltagelevel of a signal at a particular reference point.clapper In a bell, the ball or hammer that strikesthe bell; in an electric bell, it is affixed to the vibratingarmature.Clapp-Gouriet oscillator A Colpitts oscillator inwhich a capacitor is connected in series with theinductor. The circuit offers high frequency stabilityin the presence of input and output capacitancevariations.Clapp oscillator A series-tuned hybrid Colpitts oscillator,having a tuning capacitor in series withthe inductor, rather than in parallel with the inductor.The circuit allows the use of a smallertuning capacitor, resulting in improved stability.Clark cell See ZINC STANDARD CELL.class-A amplifier An amplifier whose bias is set atapproximately the midpoint of the characteristiccurve. Output electrode current flows during the

118 class-A amplifier • click methodFreq.adj. {Clapp oscillatorcomplete ac driving-voltage cycle. The input signalnever drives the device into the nonlinear portionof the characteristic curve.class-AB amplifier Either a CLASS-AB 1 AMPLI-FIER or a CLASS-AB 2 AMPLIFIER.class-AB 1 amplifier An amplifier whose bias is adjustedto a level between that of a class-A amplifierand that of a class-AB 2 amplifier. Outputelectrode current flows during the entire ac driving-voltagecycle. The input signal drives thedevice into the nonlinear portion of thecharacteristic curve during part of the cycle.class-AB 2 amplifier An amplifier whose bias is adjustedto a level between that of a class-AB 1 amplifierand that of a class-B amplifier. Outputelectrode current flows during more than 50 percent,but less than 100 percent, of the input signalcycle.class-AB modulator A modulator whose outputstage is a class-AB 1 or class-AB 2 amplifier.class-A modulator A circuit for obtaining amplitude-modulatedsignals; essentially a class-A amplifierwith two inputs, one for the carrier and theother for the modulating signal.class-A operation The operation of a transistor,field-effect transistor, or vacuum tube, in whichthe collector, drain, or plate current flows duringthe entire signal cycle.class-B amplifier An amplifier whose bias is adjustedto operate at the cutoff point in the characteristiccurve. Output current flows duringapproximately 50 percent of the input signal cycle.Efficiency is higher than that of a class-A amplifier.class-B modulator A push-pull modulator whoseoutput stage is a class-B amplifier.class-B operation The operation of a transistor,field-effect transistor, or vacuum tube, in whichthe collector, drain, or plate current flows for approximatelyhalf the signal cycle.+Outclass-C amplifier An amplifier whose input-electrodebias is adjusted for operation at a pointconsiderably beyond cutoff. Output current flowsduring less than half of the input signal cycle.Such an amplifier requires comparatively highdriving power, but is capable of excellent efficiency.Commonly used in continuous-wave(CW), amplitude-modulated (AM), and frequencymodulated(FM) radio transmitters.class-C operation The operation of a transistor,field-effect transistor, or vacuum tube, in whichthe collector, drain, or plate current flows for significantlyless than half the signal cycle.class-D telephone A telephone restricted to use byemergency services, such as fire departmentsand guard alarm installations.classical electron radius Abbreviated r e . Thequantity expressed as e 2 /(m e c 2 ), where e is theelectron’s charge in electrostatic units, m e is itsrest mass, and c is the speed of light. The valuer e is equal to approximately 2.82 × 10 –13 cm or2.82 × 10 –15 m.clean room A room for the assembly or testing ofcritical electronic equipment. The term is derivedfrom the extraordinary steps taken to removedust and other contaminating agents. The personnelwear carefully cleaned garments (or disposableclothing), gloves, caps, and masks; insome situations, they are required to walk betweenceiling and floor ducts of a vacuum systemupon entering the room.cleanup process In the process of electron tubeevacuation, a technique used to remove residualand occluded gases from the vacuum apparatusand from the device being evacuated.clear 1. In computer operations, to restore aswitching element (e.g., a flip-flop) or a memoryelement to its standard (e.g., zero) state. 2. Incomputer practice, an asynchronous input.clearance The distance between two live terminals,or between one live terminal and ground.clear band In optical character recognition, thepart of a document that must remain unprinted.clear channel 1. A channel in the standard amplitude-modulation(AM) broadcast band that is designatedto only one station within the area coveredby the signal from that station. 2. In televisionbroadcasting, a channel for which there are no restrictionson the nature of the programming.clear memory A function in a calculator or smallcomputer that erases the contents of the memory.clear raster The raster on the screen of a televisionpicture tube in the absence of a signal, noise, orfaulty beam deflection.cleavage In a crystalline substance, the quality ofsplitting along definite planes. Also, a fragmentresulting from such a cleft.click filter See KEY-CLICK FILTER.click method An emergency technique for renderingan electric current audibly detectable, by

click method • closed-circuit security system 119making and breaking the circuit carrying the currentto a headset or earphone. A single click resultsfrom each make and each break. Also seeTIKKER.click suppressor See KEY-CLICK FILTER.climate chamber A test chamber that provides accuratelycontrolled temperature, humidity, and/orbarometric pressure, for evaluating the performanceof electronic components and circuits. Alsocalled ENVIRONMENTAL TEST CHAMBER.climatometer An instrument incorporating a hygrometerand bimetallic thermometer, whose dialpointers intersect to indicate comfort zones (besttemperature-to-humidity ratio).clinometerAn electromechanical device that measuresthe steepness of a slope. When the device islevel (horizontal), the output voltage is zero. If thedevice is tipped in one direction, a negative voltageis produced; if it is tipped in the other direction,a positive voltage is produced. The outputvoltage is proportional to the angle at which thedevice is tipped. Used in mobile robots.clip A pinch-type connector whose jaws are normallyheld closed by a spring.clipclipped-noise modulation Modulation of a jammingsignal through clipping action to increasethe sideband energy and resulting interference.clipper A circuit whose output voltage is fixed at avalue for all input voltages higher than a predeterminedvalue. Clippers can flat-top the positive,negative, or both positive and negative peaks ofan input voltage.clipper amplifier An amplifier operated so that thepositive, negative, or both positive and negativepeaks are clipped in the output signal. The clippingaction results from feeding a regular symmetricwaveform into an amplifier so that onnegative excursion extremes, the stage is cut off;on positive excursion extremes, the amplifier isdriven into saturation.clipper limiter A device that delivers an output signalwhose amplitude range corresponds to inputsignalvoltages between two predetermined limits.It can be used as a noise limiter with an element orelements that clip all pulses whose amplitudes aregreater than the signal being processed.clipping 1. Leveling off (flat-topping) a signal peakat a predetermined level. Also see CLIPPER. 2. Inaudio practice, the loss of syllables or words becauseof cutoff periods in the operation of the circuit(usually caused by overdriving a stage).clock In a digital computer or controller, the deviceor circuit that supplies timing pulses to pace theoperation of the system.clocked flip-flops A master-slave arrangement ofdirect-coupled flip-flops. Information entered intothe master unit when the input-trigger pulse amplitudeis high is transferred to the slave unitwhen the amplitude is low.clock frequency In a digital computer or control,the reciprocal of the period of a single cycle, expressedin terms of the number of cycles occurringin one second of time (hertz, kilohertz, ormegahertz).clock generator A test-signal generator that suppliesa chain of pulses identical to those suppliedby the clock of a digital computer.clock module A complete plug-in or wire-in digitalunit whose readout indicates time of day orelapsed time. Connected to a suitable power supply,it serves as either a clock or timer.clock pulse A time-base pulse supplied by theclock of a digital computer, expressed as a periodwhose reciprocal is frequency.clock rate See CLOCK FREQUENCY.clock track On a magnetic tape or disk for datastorage, a track containing read or write control(clock) pulses.clockwise Abbreviation, cw. Rotation in a righthanddirection around a circle, starting at thetop. Compare COUNTERCLOCKWISE.clockwise-polarized wave An elliptically polarizedelectromagnetic wave whose electric-intensityvector rotates clockwise, as observed from thepoint of propagation. Compare COUNTER-CLOCKWISE-POLARIZED WAVE.clone A machine manufactured by a relatively unknowncompany that performs all the same functions,in basically the same way, as anothermachine manufactured by a well-known, majorcorporation. The term is used especially in referenceto computers and computer peripherals. If adevice is compatible with a certain computer,then clones of that device are generally compatiblewith that computer. Also, the device is likelyto be compatible with all clones of the computer.close coupling Also called tight coupling. In atransformer, the placement of the primary andsecondary coils as close together as possible formaximum energy transfer. Compare LOOSECOUPLING.closed capacitance The value of a variable capacitorwhose rotor plates are completely meshed withthe stator plates. Compare OPEN CAPACITANCE.closed circuit A continuous unbroken circuit (i.e.,one in which current can flow without interruption).Compare OPEN CIRCUIT.closed-circuit cell A primary cell, such as theearly gravity cell, designed for heavy and polarization-freeservice.closed-circuit communication Communicationbetween units only within a defined, hard-wiredsystem, not extending to other units or systems.closed-circuit security system An electronic securityor alarm system, consisting of subsystems

120 closed-circuit security system • CMRinterconnected so that a disturbance anywhere inthe circuit will result in an alarm signal pinpointingthe location of the disturbance.closed-circuit signaling Signaling accomplishedby raising or lowering the level of a signaling currentflowing continuously in a circuit.closed-circuit television Abbreviation, CCTV. Ausually in-plant television system, in which atransmitter feeds one or more receivers through acable.closed core A magnetic core generally constructedin an “O” or “D” configuration to confine the magneticpath to the core material. Compare OPENCORE.closed-core choke A choke coil wound on aCLOSED CORE. Also called CLOSED-CORE IN-DUCTOR.closed-core chokeclosed-core transformera CLOSED CORE.PrimaryLaminated coreclosed-core transformerA transformer wound onSecondaryclosed loop 1. The feedback path in a self-regulatingcontrol system. An oscillator, for example, is aclosed-loop amplifier. 2. A loop within a programthat would continue indefinitely, except for an externalexit command.closed-loop bandwidth The frequency at whichthe gain of a closed-loop circuit (see CLOSEDLOOP, 1) drops 3 decibels from the direct-currentor midband value.closed-loop control system A control system inwhich self regulation is obtained by means of afeedback path (see CLOSED LOOP). An exampleis a voltage regulator, in which a rise in outputvoltage is fed back to the input. This changes theinput voltage and reduces the output voltage toits correct value. Compare OPEN-LOOP CON-TROL SYSTEM.closed-loop input impedance The input impedanceof an amplifier that has feedback.closed-loop output impedance The output impedanceof an amplifier that has feedback.closed-loop voltage gain The voltage gain of anamplifier that has feedback.closed magnetic circuit A magnetic circuit inwhich the flux is uninterrupted, as in a ferromagneticcore, which has no air gap. Also seeCLOSED CORE.closed subroutine In a digital computer program,a subroutine that can be accessed and left bybranch instructions, such as GOSUB and RE-TURN in the high-level language BASIC.close-spaced array A beam antenna in which theelements (radiator, director, and reflector) arespaced less than a quarter-wavelength apart.close-talk microphone A microphone that mustbe placed close to the mouth. Such a microphoneis less susceptible to background noises than anordinary microphone, and is useful in environmentswhere the ambient noise level is high.closing rating A specification for closure conditionsin a relay, including duty cycle and contactlife (total guaranteed closures before contactfailure).closure 1. The act of closing or being closed (e.g.,switch closure or relay closure). 2. Circuit completion(i.e., the elimination of all discontinuities).cloud The mass of electrons constituting the spacecharge in a vacuum tube.cloverleaf antenna An omnidirectional transmittingantenna in which numerous horizontal,four-element radiators (stacked vertically, a quarter-wavelengthapart) are arranged in the shapeof a four-leaf clover.C/L ratio See LC RATIO.clutter Extraneous echoes that interfere with theimage on a radar display.clutter gating In radar operations, a switchingprocess that causes the normal video to be displayedin regions free of clutter, and the video indicatingtarget movement to be displayed only incluttered areas.Cm Symbol for CURIUM.cm Abbreviation of CENTIMETER.c.m. Abbreviation of CIRCULAR MIL.cm 2 Abbreviation of square centimeter.cm 3 Abbreviation of cubic centimeter.C max Abbreviation of maximum capacitance.C meter See CAPACITANCE METER.C min Abbreviation of minimum capacitance.CML Abbreviation of CURRENT-MODE LOGIC.CMOS Abbreviation of COMPLEMENTARY METAL-OXIDE SEMICONDUCTOR.CMR See COMMON-MODE REJECTION.

CMRR • coaxial capacitor 121CMRR See COMMON-MODE REJECTION RATIO.CMV See COMMON-MODE VOLTAGE.C network A circuit with three impedances connectedin series, the free leads being connected toa pair of terminals and the two internal junctions,to another pair of terminals.Co Symbol for COBALT.C o Symbol for OUTPUT CAPACITANCE.coalesce In computer operations, to create one filefrom several.coarse adjustment Adjustment of a quantity inlarge increments. Compare FINE ADJUSTMENT.coarse-chrominance primary See Q SIGNAL.coastal bending A change in the horizontal directionof a line-of-sight radio wave when it crosses acoastline.coast station In the Maritime Mobile Radio Service,a land station that communicates with shipboardstations.coating 1. The application of a substance to anothersubstance by means of electroplating, electrophoresis,or similar process, for the purpose ofprotecting the material, isolating it from the environment,or improving the conductivity of anelectrical connection to some other object. 2. Themagnetic material on a recording tape. 3. In acomputer system, the magnetic material on amagnetic diskette or hard disk.coating thickness On magnetic tape or magneticdisks, the depth of the magnetic coating appliedto the base.coax Abbreviation of COAXIAL CABLE or COAXIALLINE.coaxial antenna A half-wave vertical antenna thatis center-fed by coaxial cable. The cable runs upwardthrough a 1⁄4-wave section of tubing thatcomposes the lower half of the antenna. Theouter conductor of the cable is connected to thistubing through a shorting disk at the top. The innerconductor of the cable is connected to a 1 ⁄4-wave vertical radiator that is insulated from, andthat extends upward from the top of, the lowersection.coaxial cable An unbalanced cable consisting oftwo concentric conductors: an inner wire and anouter, braided sleeve. The inner and outer conductorsare separated by a dielectric, usuallysolid or foamed polyethylene. The outer conductoris generally grounded while the inner conductorcarries the signals. This cable is used incommunity-antenna television (CATV) networks,and as a transmission line connecting antennasto radio transmitters, receivers, and transceiversat low, medium, high, and very-high frequencies.It is also used in some high-fidelity sound systems—especiallyto connect microphones, compact-discplayers, tape players, tuners, andspeakers to audio amplifiers.coaxial cable(From left to right: insulating jacket,woven outer conductor, low-loss insulatingsleeve, inner conductor.)Characteristics ofprefabricated coaxial transmission lines.Characteristicimpedance, Velocity Outside PicofaradsType (ohms) factor dia. (in.) per footRG-8/U 52 0.66 0.41 29.5RG-9/U 51 0.66 0.42 30.0RG-11/U 75 0.66 0.41 20.6RG-17/U 52 0.66 0.87 29.5RG-58/U 54 0.66 0.20 28.5RG-59/U 73 0.66 0.24 21.0RG-174/U 50 0.66 0.10 30.8hard line 50 0.81 0.50 25.0( 1 /2-inch) 75 0.81 0.50 16.7hard line 50 0.81 0.75 25.0( 3 /4-inch) 75 0.81 0.75 16.7coaxial capacitor 1. A somewhat uncommon, buthighly effective, capacitor that uses two telescopingsections of tubing. It works because there is acertain effective surface area between the innerand the outer tubing sections. A sleeve of plasticdielectric is placed between the sections of tubing.This allows the capacitance to be adjusted bysliding the inner section in or out of the outer section.Coaxial capacitors are especially useful inantenna systems for tuning and/or impedancematching. Their values are generally from a few

122 coaxial capacitor • codepicofarads up to about 100 pF. 2. A short lengthof coaxial cable that is used as a capacitor ratherthan a transmission line because of the inherentcapacitance between its center conductor andbraid. See COAXIAL CABLE.coaxial cavity A cavity consisting of a cylindricalmetal chamber housing a central rod. The cavitycan be tuned to resonance by means of a piston.coaxial connector A device used to splice coaxialline or to connect a coaxial line to a transmitter,receiver, or other piece of apparatus.Femalecoaxial connectorMalecoaxial diode A semiconductor diode housed in acylindrical metal shell acting as one contact, andprovided with a recessed, concentrically mountedend pin, which serves as the other contact.coaxial driver See COAXIAL SPEAKER.coaxial filter 1. A filter that uses a coaxial cable asa tuned circuit. 2. A filter designed to be used ina coaxial transmission line.coaxial jack A female receptacle or connector,whose concentric terminals have the same spacingas a male coaxial-cable connector designed tofit it.coaxial line A signal transmission line consistingof COAXIAL CABLE.coaxial-line frequency meter A microwave absorptionwavemeter (see WAVEMETER) with inputand output receptacles for insertion into acoaxial line.coaxial-line oscillator See CONCENTRIC-LINEOSCILLATOR.coaxial loudspeaker See COAXIAL SPEAKER.coaxial plug A male connector whose concentricterminals have the same spacing as a femalecoaxial cable connector designed to fit it.coaxial receptacle A coaxial connector, such as acoaxial jack or plug. Receptacles are installed inequipment, whereas plugs are usually attachedto the end of coaxial cables.coaxial relay A relay designed to connect and disconnect,or to interchange, coaxial cables in atransmission line without disturbing the characteristicimpedance of the line.coaxial speaker Also called coaxial driver and coaxialloudspeaker. A large low-frequency speakerand a small high-frequency speaker mountedconcentrically, the smaller within the larger.When used with a crossover network, this arrangementprovides fairly good wide-range audiofrequencyresponse, and saves physical space,compared with the use of separate speakers.coaxial stub 1. A length of coaxial cable acting asa branch to another coaxial cable. Commonlyused for impedance matching. 2. A length ofcoaxial cable, usually cut to 1 ⁄4 or 1 ⁄ 2 wavelength,and connected across a coaxial transmissionline to act as a WAVETRAP. Commonly usedto reject strong interfering signals.coaxial switch A switch designed to connect anddisconnect, or to interchange, coaxial cables in atransmission line without disturbing the characteristicimpedance of the line.coaxial tank A tank circuit consisting of a rodwithin a cylinder. The tank is usually tuned by asmall variable capacitor connected between therod and cylinder at one end of the combination.Generally used at ultra-high frequencies (UHF).coaxial-tank oscillator A stable, self-excited oscillatorthat uses a COAXIAL TANK. Also seeCONCENTRIC-LINE OSCILLATOR.coaxial transistor A transistor in which a semiconductorwafer is mounted centrally in a metalcylinder (the base connection) and is contactedon opposite faces by the emitter and collectorwhiskers, which are axially mounted.coaxial transmission line A transmission linethat is a COAXIAL CABLE.coaxial wavemeter A type of absorption wavemeterin which the tunable element is a section ofcoaxial line (i.e., a metal cylinder surrounding ametal rod). An internal short-circuiting disk ismoved along the cylinder to connect its inner wallto selected points along the rod’s length, therebyvarying the resonant frequency. The instrumentis useful at microwave frequencies.cobalt Symbol, Co. A metallic element. Atomicnumber, 27. Atomic weight, 58.94.cochannel interference Interference between similarsignals transmitted on the same channel.Cockcroft-Walton accelerator A proton acceleratorin which nuclei of hydrogen atoms are givenhigh velocity through a straight tube by a high dcvoltage.codanAny of several muting (SQUELCH) systems.In particular, a squelch circuit that suppressesnoise in a sensitive receiver equipped with automaticgain control (AGC). The receiver is quietuntil a carrier of predetermined strength is received.The name is an acronym for carrieroperateddevice antinoise.codan lamp A lamp that alerts a radio operatorthat a signal of satisfactory strength is being received.Also see CODAN.code 1. A set of symbols for communications (e.g.,the Morse code of radiotelegraphy and wire telegraphyin which dots and dashes correspond to

code • coherence 123letters, numbers, and marks of punctuation). 2.In a computer program, symbolically representedinstructions. 3. ENCODE.codec In encoding and decoding equipment, acoder/decoder, usually in a single package andoperating at 8 kHz for an input signal with apassband of 3100 Hz (300 to 3400 Hz).code character 1. The representation of characterin a particular code form. 2. A sequence of dotsand dashes in the Morse code.code conversion The translation of a coded signalfrom one form of code to another.coded decimal digit A number expressed in binaryform (computer code), that is, in terms of zerosand ones only.code-directing characters Characters added to amessage to indicate how and where it is going.coded program See PROGRAM.coded signal 1. A wire- or radiotelegraph signal inwhich secrecy is achieved by using letters in ciphergroups, instead of straight language. 2.SCRAMBLED SIGNAL.coded stop See PROGRAMMED HALT.code elements The smallest identifiable parts thatcompose a digital code. For example, in computercode, the elements are ones and zeroes (high andlow logic states); in Morse code, they are dots anddashes.code holes In a punched card or tape, holes representingdata.code line A written computer program instruction.code machine Any one of several devices forrecording or reproducing code signals.code position The part of a data medium (e.g.,card row) reserved for data.code-practice oscillator A simple keyed audio oscillatorintended for practicing Morse code.coder 1. In computer operations, a person whoprepares instructions from flow charts and proceduresdevised by a programmer. 2. A device thatdelivers coded signals.code receiver A radiotelegraph receiver.code ringing A method of ringing a telephone subscriberin a predetermined manner to convey acertain message.code segment The instruction part of computerstorage associated with a process. CompareDATA SEGMENT and DUMP SEGMENT.code set The collection of codes representing all ofthe characters in a language.code speed See KEYING SPEED.code transmitter 1. A radiotelegraph transmitter.2. A tape-operated keyer for wire telegraphy or radiotelegraphy.code word See PHONETIC ALPHABET CODEWORD.coding 1. Performing the service of a CODER. 2.Writing instructions for a digital computer; a partof programming.coding check A pencil-and-paper verification of aroutine’s validity.coding sheet A form on which program instructionsare written prior to input.codiphase radar A radar system that uses beamforming, signal processing, and a phased-arrayantenna.codistor A voltage-regulating semiconductor device.coefficient 1. A factor in an indicated product.Thus, in 4y, 4 is the coefficient of y. 2. A parameterthat indicates a specific characteristic ofsome component or device (e.g., COEFFICIENTOF COUPLING or COEFFICIENT OF REFLEC-TION).coefficient of coupling Symbol k. The ratio of MU-TUAL INDUCTANCE between two inductors tothe maximum possible (theoretical) value of mutualinductance. This ratio is always greater thanor equal to 0 (no coupling between inductors),and less than or equal to 1 (perfect coupling betweeninductors).coefficient of current detection See CURRENT-DETECTION COEFFICIENT.coefficient of reflection A measure of the amountof electromagnetic field reflected in a transmissionline from the load feed point. The coefficientof reflection is equal to the square root of the reflectedpower divided by the forward power.coercive force The demagnetizing force requiredto remove residual magnetism from a material.coercivity See COERCIVE FORCE.cogging Nonuniform rotation of a motor armature.The velocity increases as an armature coil entersthe magnetic field and decreases as it leaves thefield.coherence In electromagnetic radiation, a conditionin which all the wavefronts are in phase. Thisresults in high energy concentration, and makespossible the long-distance transmission of infrared,visible light, and ultraviolet, because therays are almost perfectly parallel. It also makespossible the extreme radiation intensity characteristicof some LASER devices.AmplitudeSame frequencysame phasecoherenceTimeTimeTime

124 coherent bundle • cold resistancecoherent bundle A bundle of optical fibers, suchthat the individual fibers are in the same relativepositions at either end of the bundle.coherent carrier A carrier that agrees in frequencyand phase with a reference signal.coherent electroluminescent device See LASERDIODE.coherent light Visible light in which the phase relationshipbetween successive waves is such thatthe beam consists of parallel rays that provide ahigh concentration of energy. Also see LASER.coherent-light radar See COLIDAR.coherent oscillator In a radar system, an oscillatorthat provides a COHERENT REFERENCE.coherent-pulse operation Pulse operation characterizedby a fixed phase relationship betweenpulses.coherent radiation Radiation characterized byCOHERENCE.coherent reference A stable reference frequencywith which other signals are phase locked for coherence.coherent transponder A transponder in which thefrequency and phase of the input and output signalshave a fixed relationship.coil A long conductor or group of conductors woundinto a tight helical package, often in several layerson a cylindrical form. This takes advantage of theresulting concentration of magnetic flux, maximizingthe inductance that can be obtained in a componentof limited physical size. Further increasesin inductance can be realized by the use of ferromagneticcore materials. See also INDUCTOR.coil antenna See LOOP ANTENNA.coil checker An alternating-current (ac) meter orsimple bridge for checking inductors. Such instrumentsusually only indicate inductance values,but some list readings of resistance orapproximate inductor Q factor.coil dissipation The power wasted in a coil asheat. Generally, this dissipation or loss is proportionalto the resistance of the coil, and to thesquare of the current passing through the coil.coil form The insulating support around which anair-core coil is wound.coil loading The insertion of one or more inductorsinto a transmission line or antenna element, forthe purpose of impedance matching, alteration ofthe resonant frequency, or both.coil magnification factor The Q factor of an inductor.Generally given by the ratio X L /R L , whereX L is the inductive reactance of the coil in ohms,and R L is the resistance of the coil in ohms.coil neutralization See INDUCTIVE NEUTRALIZA-TION.coil resistance The resistance of a coil (inductor),as distinct from its reactance. It is almost entirelythe result of ohmic loss in the wire from whichthe coil is manufactured.coilshield A metal can designed to provide efficientelectrostatic and electromagnetic shielding of acoil, preventing unwanted inductive coupling toother components.coincidence The simultaneous occurrence of twoor more signals. Compare ANTICOINCIDENCE.coincidence amplifier An amplifier that deliversan output signal only when two or more input signalsoccur simultaneously.coincidence circuit See AND CIRCUIT.coincidence counter A circuit or device, such as agate, that delivers an output pulse only when twoor more input pulses occur simultaneously; theoutput pulses go to a device that counts them.coincidence detector See AND CIRCUIT.coincidence gate See AND GATE.coincident-current selection Selection of a magneticcore (in a core memory or similar device) byapplying two or more currents simultaneously.coin shooting Searching for coins and similarsmall, buried metallic objects using a METAL LO-CATOR.coke A porous material obtained from the destructivedistillation of coal. It is valued for theproduction of carbon components for electronics,such as dry-cell electrodes and motorbrushes.cold 1. Pertaining to an electrical circuit, component,or terminal that is at ground potential. 2. Aterm denoting a bad solder joint. 3. Pertaining toan unheated electrode or element. See COLDCATHODE.cold alignment The alignment of a tracking system(especially of its tuned circuits) when the systemis not in operation, as when transistor poweris off. Also called QUIET ALIGNMENT.cold cathode 1. In an electron tube, a cathode thatemits electrons without being heated. 2. A cathodeelectrode operated at a temperature belowambient temperature.cold chamber An enclosure in which electronicequipment can be tested at selected, precise lowtemperatures. Compare OVEN.cold flow The (usually gradual) change in the dimensionsof a material, such as plastic in amolded part.cold junction In a thermocouple system, an auxiliarythermocouple connected in series with thehot thermocouple, and immersed in ice or operatedat ambient temperature.cold light Light produced without significant heat,as from the ionization of a gas by a high voltage(as in neon bulbs and fluorescent lamps), or byelectroluminescence, bioluminescence, cathodoluminescence,or a similar phenomenon.cold pressure welding Welding sometimes used inthe fabrication of electronic equipment, in whichthe metal parts to be joined are pressed togethertightly to the point of deformation, whereuponthey become welded.cold resistance The resistance of an unheatedelectronic component. Compare HOT RESIS-TANCE.

cold rolling • collector voltage 125cold rolling A method of manufacturing an inductorcore so that the magnetic grains are all arrangedlengthwise.cold solder joint A solder joint in which insufficientheat has been applied, resulting in a badconnection.cold spot 1. An area of a circuit or componentwhose temperature is ordinarily lower than thatof the surrounding area. 2. A node of current orvoltage. Compare HOT SPOT.cold weld A welded joint produced by means ofCOLD PRESSURE WELDING.colidar An optical radar system using unmodulated,coherent (laser-produced) light. The term isan acronym for coherent light detection andranging.collate In data processing, to produce an orderedset from two or more similarly ordered sets (aspunched cards).collator In a punched-card system, a device thatcollates (see COLLATE) punched cards.collector 1. In a bipolar transistor, the electrodetoward which emitted current carriers travel. 2.In a Klystron, the final electrode toward whichelectrons migrate after passing through thebuncher and catcher. 3. In an iconoscope, acylindrical electrode around the circumference ofthe tube, which gathers and conducts away theelectrons released by the mosaic. 4. The final (target)electrode in a backward-wave or travelingwavetube. 5. A computer program segment thatcollates compiled segments so that they can beloaded into the computer.collector capacitance 1. Symbol, C C . The capacitanceof the collector junction in a bipolar transistor.2. The capacitance of the collectorelectrode in a Klystron, iconoscope, backwardwavetube, or traveling-wave tube.collector current 1. Symbol, I C . The current flowingin the collector circuit of a bipolar transistor.Also see AC COLLECTOR CURRENT and DCCOLLECTOR CURRENT. 2. Current flowing inthe collector circuit of a Klystron, iconoscope,backward-wave tube, or traveling-wave tube.collector-current cutoff See COLLECTOR CUT-OFF.collector cutoff In a bipolar transistor, the conditionin which the collector current is cut off (i.e.,reduced to the residual value). Also see CUTOFFCURRENT.collector cutoff current See CUTOFF CURRENT.collector-diffusion isolation A method of makingintegrated circuits that contain bipolartransistors. Provides electrical separation ofthe transistors in a semiconductor integratedcircuit.collector dissipation Symbol, P C . In a bipolartransistor, the power dissipation of the collectorelectrode. The collector dc power dissipation isthe product of collector current and collector voltage:P C = V C I C .collector efficiency In a bipolar transistor circuit,the ratio of ac power output to dc collector-powerinput.collector family For a bipolar transistor, a groupof collector current versus collector voltagecurves. Each is plotted for a particular value ofbase current (common-emitter circuit) or emittercurrent (common-base circuit).I C}Variousvaluesofbasevoltageorcurrent(E B orI B )Collector currentCollector voltagecollector familycollector junction In a bipolar transistor, thejunction between collector and base layers.collector mesh In a cathode-ray storage tube, aflat, fine wire screen that attracts and conductsaway the secondary electrons knocked out of thestorage mesh by the electron beam.collector multiplication In a bipolar transistor,an increase in the number of electrons at the collectorelectrode, caused by a momentary alterationof the charge density of the collectorjunction by injected carriers reaching the junction.collector resistance In a bipolar transistor, the internalresistance of the collector junction. See ACCOLLECTOR RESISTANCE and DC COLLECTORRESISTANCE.collector ring 1. A rotating, brush-contacted ringelectrode connected to one end of a coil in an acgenerator. 2. A similar ring which, with a brush,serves as a connection to a rotating element, as ina signal-gathering system. 3. The collector electrodein an iconoscope.collector transition capacitance The capacitancebetween the collector and base of a bipolar transistorunder normal operating conditions. Thiscapacitance has a limiting effect on the operatingfrequency of a bipolar device.collector voltage Symbol, V C . In a bipolar transistor,the voltage on the collector electrode. See ACE C

126 collector voltage • color fringingCOLLECTOR VOLTAGE and DC COLLECTORVOLTAGE.collimated rays Electromagnetic waves made parallelor nearly parallel. This can be done bymeans of a reflector, a lens, or a laser.collimation 1. The process of rendering electromagneticrays parallel. 2. Adjustment of the lineof sight of an instrument, such as a level or transit.collimation equipment Optical-alignment equipment.collimator A device for producing parallel rays oflight or other radiation. In electronics, the mostcommon example is a dish antenna.collinear antenna A broadside directional antennaconsisting of two or more half-wave radiators;the current is kept in phase in each section byquarter-wave stubs between each radiating section.The radiators are stacked end to end horizontallyor vertically. Also called FRANKLIN ANTENNA.Collins coupler A single-section, pi-filter circuit,used to match a radio transmitter to a wide rangeof antenna impedances. Also called pi coupler andCollins network.collodion A viscous solution of pyroxylin and asolvent (such as acetone, alcohol, or ether) sometimesused as a binding agent for coils and othercomponents.cologarithm Abbreviation, colog. The logarithm ofthe reciprocal of a number; colog x = log (1/x) =log x –1 = –log x.color A perceived characteristic, and a direct function,of visible-light wavelength. Seen by the humaneye as a spectrum of hues, ranging from redat the longest visible wavelengths, through orange,yellow, green, blue, indigo, and finally violetat the shortest visible wavelengths. See HUE.coloration In audio applications, a blending ofsounds as a result of mixing among componentsat different frequencies. Sometimes this is donedeliberately; in other instances, it is undesirable.color balance In a color television receiver, adjustmentof the beam intensities of the individualguns of a three-gun picture tube. Compensatesfor the difference in light emissivity of the red,green, and blue phosphors on the tube screen.color bar-dot generator A radio-frequency (RF)signal generator that produces a bar or dot patternon the screen of a color television picturetube. Used for testing and alignment.color-bar pattern A color television test pattern ofvertical bars—each of a different color.color breakup A transient separation of a colortelevision picture into its red, green, and bluecomponents, as a result of a sudden disturbanceof viewing conditions (blinking of eyes, moving ofhead, intermittent blocking of screen, etc.).color burst As a phase reference for the 3.579545-MHz oscillator in a color television receiver, approximatelynine cycles of the chrominancesubcarrier added to the back porch of the horizontalblanking pedestal in the composite colorsignal.color carrier See CHROMINANCE SUBCARRIER.colorcast A color television broadcast.color code 1. A system that uses colored stripes ordots to mark the nominal values and other characteristicson capacitors, resistors, and othercomponents. 2. A code that represents the variousfrequencies being used by radio-control modelersin competition, and used on flags attachedto transmitters, for example, as a safeguardagainst jamming.color coder See COLOR ENCODER.color contamination In a color television system,faulty color reproduction resulting from incompleteseparation of the red, green, and blue channels.color-coordinate transformation In a color televisionsystem, the computation (performed electricallyin the system) of the tristimulus (primary)values with reference to one set of primaries, fromthe same colors derived from another set of primaries.color depth An expression for the extent to whichan image can accurately render color. Generallyexpressed in bits or in number of colors. Somesystems can reproduce millions of different colors.color-difference signal Designated B-Y, G-Y, andR-Y. The signal resulting from reducing the amplitudeof a color signal by an amount equal tothe luminance-signal amplitude. Also see B-YSIGNAL, G-Y SIGNAL, and R-Y SIGNAL.color dot 1. A phosphor spot on the screen of acolor television picture tube. 2. One of the spotsstamped on a capacitor, indicating the capacitance,voltage, and tolerance (see COLOR CODE,1). 3. A spot stamped on a resistor, indicating thenumber of zeros to be added to the value indicatedby the color bands.color edging In a color television picture, an aberrationconsisting of false color at the boundariesbetween areas of different color.color encoder In a color television transmitter, thecircuit or channel in which the camera signalsand the chrominance subcarrier are combinedinto the color-picture signal.color equation A mathematical means of determiningthe resultant color obtained by addingprimary colors in various proportions.color fidelity The faithfulness with which a colortelevision system, lens, or film reproduces thecolors of a scene.color filter A transparent plate or film that transmitslight of a desired color, and eliminates or attenuatesall other colors.color flicker In a color television system, image instabilitythat occurs when the luminance andchromaticity both fluctuate.color fringing In a color television picture, falsecolor around objects, sometimes causing them toappear separated into different colors.

color generator • color spectrum 127color generator A special radio-frequency (RF) signalgenerator to adjust or troubleshoot a colortelevision receiver. The color signals it deliversare identical to those produced by a broadcaststation.color graphics Computer graphics displayed incolor on a cathode-ray tube (CRT) or liquidcrystaldisplay (LCD).colorimeter A device used to quantitatively measurethe color intensity of a sample relative to astandard.colorimetric A characteristic of visible light, representingthe wavelength concentration. Refers tothe perceived color of a light beam.colorimetry The science and art of color measurement.color killer In a color television receiver, a circuitthat, in the absence of a color signal, delivers anegative bias to cut off the bandpass amplifier.color match In photometry, the condition in whichcolor agreement exists between the halves of anarea. Also see COLOR MATCHING.color matching The art of selecting colors that areidentical in hue, saturation, and brilliance. Thiscan be done with the unaided eye or with the helpof an instrument.color media Substances that transmit essentiallyone color of visible light while blocking other colors.color meter A photoelectric instrument for measuringcolor values, and comparing and matchingcolors.color mixture An additive combination of two ormore colors. Thus, red + yellow = orange, blue +red = violet, red + blue + green = white, etc.color oscillator The oscillator in a color televisionreceiver that coordinates the color response. Thisoscillator is operated at 3.579545 MHz, to withinplus or minus 10 Hz.color palette In a color video image, the total numberof possible colors that can be displayed.color phase In color television, the phase differencebetween an I or Q chrominance primary signaland the chrominance carrier reference.color-phase diagram In color television, a quadrantdiagram showing (for each of the three primaryand complementary colors) the difference inphase between the color-burst signal and thechrominance signal, as well as the peak amplitudeof the chrominance signal. Also shown arethe peak amplitude and polarity of both in-phaseand quadrature components required for thechrominance signals. For color TV receiver adjustment,the color-phase diagram is displayed,in effect, by a VECTORSCOPE when a suitablesignal from a color generator is applied to the receiver.color picture signal 1. In color television and/orcomputer graphics, an electrical signal containingcomponents corresponding to the hue, saturation,and brilliance of a fixed or changing visualimage. 2. In color television, the combination ofchrominance and luminance signals minusblanking and sync signals.color picture tube A specialized type of cathoderaytube (CRT), used in color television receiversand computer displays. Three different imagesare produced: one in red, one in blue, and one ingreen. The three monochrome images are combinedto form a complete color image.color primaries 1. Also called additive primaries orprimary colors. In color television, the hues red(R), green (G), and blue (B). When these colors aremixed in various ratios, any visual color can result.2. Also called subtractive primaries or primarypigments. In color printing, the huesmagenta (M), cyan (C), and yellow (Y). Theseroughly correspond to red (R), blue (B) and yellow(Y). Sometimes black (K) is also included. Whenthese pigments are mixed in various ratios, anyvisual pigment can result.color purity The ratio of wanted to unwanted componentsin a color. In a pure color, there are nocomponents other than those required to producethe color. Color, in this context, includes white,black, and all shades of gray.color-purity magnet A permanent magnet on theneck of a color television picture tube, used tohelp ensure color purity by maintaining properdisplacement of the electron beam.color registration In color television reception, theprecise superimposition of red, green, and blue sothat the composite is free from COLOR EDGING.color rendering index A mathematical expressiondefining the effect of the color of a light source onan object. For example, in red light, a blue objectappears nearly black.color sampling rate The number of times per secondthat each primary color is sampled in a colortelevision receiver.color saturation A measure of the purity of a hue.The extent to which a hue is without a white component;100% saturation indicates a completeabsence of white.color sensing In machine vision systems, the abilityto distinguish between light of different wavelengths.Usually done with red, green and bluecolor filters and three separate cameras.color sensitivity 1. The degree of which a photosensitivedevice, such as a photocell or cameratube, responds to various colors of light. 2. Thedegree to which photographic film responds tovarious colors of light.color signal See COLOR PICTURE SIGNAL.color spectrum The band of electromagnetic energycontaining visible light; it extends from red(at the longest wavelengths) to violet (at the shortest).Commonly measured in nanometers (nm),where 1 nm = 10 –9 m. Also expressed inAngstroms, where 1 Angstrom = 10 –10 m = 0.1nm. In order of decreasing wavelength, the colorsare red at 750 to 700 nm (7500 to 7000

128 color spectrum • coma lobesToultraviolet,Xrays,Gamma raysVioletIndigoBlueGreenYellowOrangeRed0.40.50.60.7Toinfared,radio wavesWavelength, µmas violet, blue, green, yellow, orange, and red, inorder of increasing intensity.Colpitts oscillator A radio-frequency (RF) oscillatorthat uses a single, untapped inductor. A combinationof two fixed capacitors in series isconnected in parallel with the inductor. The feedbackis controlled by the ratio of capacitances. Apermeability-tuned coil or a roller inductor can beused to obtain variable-frequency operation. Stabilityis enhanced when the output of the oscillatoris taken from the emitter or source portion ofthe circuit. To prevent the output signal from beingshort-circuited to ground, an RF choke is connectedin series with the emitter or source.Compare HARTLEY OSCILLATOR.color spectrumAngstroms), orange, yellow, green, blue, indigo,and violet at 410 to 390 nm (4100 to 3900Angstroms).color subcarrier A modulated monochrome signalwhose sidebands convey color information.color-sync signal See COLOR BURST.color system Also called RGB color model. A meansof representing a color in terms of mathematicalcoordinates. This can be done in three dimensionsbecause there are three COLOR PRI-MARIES. Each color primary is represented by anaxis. Any COMPOSITE COLOR can be representedby a unique vector. The relative amount ofeach color primary is given by the length of thecomposite-color vector components along eachaxis.color television Television in which the pictureapproximates natural color. It operates on the basisof mixing three primary colors (red, blue, andgreen) of phosphors on the picture tube screen.color television receiver A television receiver designedto reproduce color pictures.color television signal The signal transmitted bya color television transmitter, containing all of theinformation needed to reproduce a complete, fullcolor,moving image.color transmission The television transmission ofa picture in color.color triad On the screen of a color picture tube,one of the color cells, each of which contains oneof the three phosphor dots: red, green, and blue.color triangle A triangle that can be inscribed on achromaticity diagram to reveal the chromaticityrange resulting from adding the three color primaries.color TV signal The complete signal (video, color,and sync components) required for transmitting apicture in color.color weather radar A computer-enhanced radarrendition of weather patterns, usually showingvarious intensities of precipitation as differentcolors. Commonly, areas of precipitation show upColpitts oscillatorcolumbium Symbol, Cb. The former name of themetallic element niobium. Atomic number, 41.Atomic weight, 92.9064.column See CARD COLUMN.columnar graph A graphical presentation of data,in which the ordinates are represented by verticalcolumns whose height depends on the value.Commonly used in presentation graphics, but lesscommon in analytical graphics.column binary Binary number representation onpunched cards, wherein consecutive digits correspondto consecutive column punching positions.column speaker An acoustic speaker with a longcabinet, so that a large column of air is used forresonating or reinforcing purposes. This type ofspeaker radiates over a wide azimuth angle, whileproviding a narrow beam in the elevation plane.column split On a punched card machine, the devicefor reading, as two separate characters orcodes, two parts of a single column.COM 1. Abbreviation for communications port.2. Abbreviation for computer output on microfilm.coma An aberration that causes the beam spot onthe screen of a cathode-ray tube to resemble acomet.coma lobes An aberration in the radiation or responsepattern of a dish antenna that occurswhen the radiating element is not exactly at thefocal point of the reflector. When the directional

coma lobes • commercial data processing 129pattern is altered by moving the driven element,rather than turning the entire antenna, theselobes appear.comb amplifier An arrangement of several sharplytuned bandpass amplifiers whose inputs are connectedin parallel and whose outputs are separate;the amplifiers separate various frequenciesfrom a multifrequency input signal. The name isderived from the comb-like appearance of the responsepattern of various output peaks displayedalong a frequency-base axis.comb filter A selective device that passes severalnarrow bands of frequencies within a larger band,while rejecting frequencies in between the narrowbands. So called because its frequency-responsecurve resembles the teeth of a comb when observedon a spectrum analyzer. Also see COMBAMPLIFIER.AmplitudeFrequencycomb filter responsecomb generator 1. A signal generator that providesoutputs at evenly spaced frequencies. Socalled because, on a spectrum analyzer, its outputlooks like the teeth of a comb. 2. A transmitterwith many spurious signals at its output.combination 1. A functional, usually stationary,installation consisting of two or more pieces ofequipment. Examples: transmitter/receiver combination,motor/generator combination, andtuner/amplifier combination. 2. In mathematics,a selection of several factors from a group, withoutregard to order. Thus, from the group ABC,the three possible combinations are AB, AC, andBC. Compare PERMUTATION.combinational circuit Two or more basic logic circuits,combined in such a way that the outputstate depends entirely on the input states.combination bridge A bridge that affords two ormore classes of measurement, usually selectableby means of a function switch. Examples:capacitance-inductance bridge, and capacitanceresistancebridge.combination cable A cable that has conductorsgrouped in pairs, threes, quads, or similar arrangements.combination feedback See CURRENT-VOLTAGEFEEDBACK.combination microphone Two or more microphonescombined into one unit.combination speaker Two or more loudspeakerscombined into one (e.g., a COAXIAL SPEAKER).combination tone An acoustic tone resulting fromthe combination of two other acoustic tones. Ifthe original tones have frequencies f 1 and f 2(where f 1 is higher than f 2 ), then the first-ordercombination frequencies are f 1 + f 2 and f 1 – f 2 .Higher-order combination tones can result frommixing among the original tones and the firstordercombination tones.combinatorial logic A form of digital logic, inwhich the output states depend on the inputstates, but on no other factor.combined head See READ-WRITE HEAD.combined reactance The net reactance (X) in acircuit, obtained by vectorially adding the inductivereactance (X L ) and the capacitive reactance(X C ).combiner A circuit or device for mixing various signalsto form a new signal. Also see MIXER.combiner circuit In a color television camera, thecircuit that combines the chroma and luminancewith the sync.comeback A spurious response in a bandpass orband-rejection filter, at a frequency well above orbelow the passband or stopband.command 1. In computer operations, the group ofselected pulses or other signals that cause thecomputer to execute a step in its program. 2. Instruction.command chain Part of a computer operation carriedout independently as a series of input/output instructions.command control In automation, electronic control,and computer operations, the performanceof functions in response to a transmitted signal.command destruct signal A signal for instigatingthe destruction of a missile in flight.command guidance system A system in which aguided missile and its target are both tracked byradar.command language A computer language madeup of command operators.command link In a command guidance system,the section that transmits missile-steering commands.command network A radio communications networkin which the chain of command is rigorouslydefined and followed.command reference The current or voltage towhich a feedback signal is referenced in a controlsystem or servomechanism.comment A statement written into a computerprogram for a documentation, rather than implementation(e.g., to describe the purpose of a stepor subroutine).comment field A record or file in which instructionsor explanations are given.commercial data processing A commercial(rather than industrial, scientific, or personal) applicationof data processing.

130 commercial-level security • common-mode input capacitancecommercial-level security See LEVEL-2 SECU-RITY.commercial killer A usually remote-controlled,electronic relay for disabling a radio or televisionreceiver during advertisements.commercial language A computer programminglanguage for commercial applications (payroll, forexample).common 1. Grounded. 2. Pertaining to a connectionshared by several different points in a circuitor system. 3. See COMMON GROUND.common area A computer storage area usable byseveral programs or segments within a program.common-base circuit A bipolar transistor circuitin which the transistor base is the common (orgrounded) electrode. Also called grounded-basecircuit.common battery 1. A battery shared by two ormore different circuits or pieces of equipment. 2.In wire telephony, a central office battery thatsupplies the entire system.common-battery office In wire telephony, a centraloffice that provides a common battery.common business-oriented language See COBOL.common-capacitor coupling The process of couplingone tuned circuit to another by means of acapacitor that is common to both circuits.InputL1C1C3C2(Commoncapacitor)L2common-capacitor couplingOutputcommon-carrier fixed station A fixed radio stationthat provides public service.common-cathode circuit A tube circuit in whichthe cathode is the common (or grounded) electrode.Also called grounded-cathode circuit.common-channel interference Radio interferenceresulting from two stations transmitting on thesame channel. It is characterized principally bybeat-note (heterodyne whistle) generation, andsuppression or capture of the weaker signal bythe stronger one.common-collector circuit A bipolar-transistorcircuit in which the collector is the common (orgrounded) electrode. Also called grounded-collectorcircuit and EMITTER FOLLOWER.common communications carrier A communicationscompany authorized by the licensing agencyto furnish public communications.common-component coupling See COMMON-CAPACITOR COUPLING, COMMON-INDUCTORCOUPLING, and COMMON-RESISTOR COU-PLING.common-drain circuit A field-effect transistor circuitin which the drain terminal is the common(or grounded) electrode. Also called groundeddraincircuit and SOURCE FOLLOWER.common-emitter circuit A bipolar transistor circuitin which the emitter is the common (orgrounded) electrode. Also called grounded-emittercircuit.common-gate circuit A field-effect transistor circuitin which the gate is the common (or grounded)electrode. Also called grounded-gate circuit.common-grid circuit A tube circuit in which thecontrol grid is the common (or grounded) electrode.Also called grounded-grid circuit.common ground A single ground-point connectionshared by several portions of a circuit.common impedance A single impedance sharedby parts of a circuit. Because currents from thevarious parts flow through this impedance simultaneously,coupling (desired or undesired) canoccur between them.common-impedance coupling See COMMON-CAPACITOR COUPLING, COMMON-INDUCTORCOUPLING, and COMMON-RESISTOR COU-PLING.common-inductor coupling The process of couplingone tuned circuit to another by means of aninductor that is common to both circuits.InputL1C1C2L2(Commoninductor)L3common-inductor couplingOutputcommon language A language recognized by allthe equipment in a data processing system.common logarithm Abbreviation, log 10 . Alsocalled base-10 logarithm. A logarithm in whichthe base number is 10. Also see LOGARITHM.common mode Pertaining to signals or signalcomponents that are identical in amplitude andduration.common-mode characteristics In an operationalamplifier, characteristics denoting amplifier performancewhen a common signal is applied to invertingand noninverting inputs.common-mode gain The voltage gain of a differentialamplifier with a common-mode input.common-mode impedance input The impedancebetween ground and one of the inputs of a differentialamplifier. Compare COMMON-MODE IN-PUT IMPEDANCE.common-mode input capacitance In a differentialamplifier, the internal capacitance of thecommon-mode input circuit.

common-mode input circuit • commutating capacitor 131common-mode input circuit In a differential amplifier,the input circuit between ground and theinputs connected together.common-mode input impedance In a differentialamplifier, the open-loop impedance betweenground and the inputs connected together. CompareCOMMON-MODE IMPEDANCE INPUT.common-mode input signal A signal applied tothe common-mode input circuit of a differentialamplifier (i.e., to both inputs connected together).Compare COMMON-MODE SIGNAL.common-mode input voltage In a differential amplifier,the maximum voltage that can be appliedsafely between ground and the inputs connectedtogether.common-mode interference A form of interferencethat occurs across the terminals of agrounded system.common-mode rejection The extent to which adifferential amplifier will reject a signal presentedsimultaneously to both inputs in phase,or of two signals identical in amplitude, frequency,and phase applied separately to the twoinputs. Also see COMMON-MODE REJECTIONRATIO.common-mode rejection ratio In a differentialamplifier, the extent to which the amplifier cancelsundesired signals. It is the ratio of the differentialgain to the common-mode gain. Also seeCOMMON-MODE REJECTION.common-mode signal The algebraic average oftwo signals applied simultaneously to the twoends of a balanced circuit, such as a differentialamplifier. Compare COMMON-MODE INPUT SIG-NAL.common-mode voltage The part of the input thatis common to both inputs of a differential amplifiercircuit. It is quantitatively defined as thearithmetic mean of the voltages at the inputs.common-mode voltage gain See COMMON-MODE GAIN.common-mode voltage range The range limitedby the maximum nonsaturating input voltagethat can be applied to both inputs of an operationalamplifier.common pool An assigned memory store, utilizedby two or more circuits or systems.common-resistor coupling The process of couplingone circuit to another by means of a resistorthat is common to both circuits.InputL1C1C2R1(Commonresistor)common-resistor couplingL2Outputcommon-source circuit A field-effect transistorcircuit in which the source terminal is thecommon (or grounded) electrode. Also calledgrounded-source circuit.common-user channels Communication channelsopen to all licensees in a particular service.communication band A band of frequencieswhose use is authorized expressly for communications,rather than for other services (such asbroadcasting, education, remote control, etc.).communication channel 1. In radio or wire service,a (usually auxiliary) channel for direct exchangeof information between units of theservice (e.g., a “talking circuit” between a broadcaststudio and the transmitter house). 2. A datatransmission channel between two points (e.g., aremote terminal and a central computer system).communication link 1. Collectively, the equipmentproviding a communication channel betweentwo transmitters. 2. Data terminalequipment.communication protocol The specifications of adigital signal, including the speed in bits per second(bps) or bauds, the code type, the bit duration,the mark-to-space ratio, etc.communications The science and art of using anddeveloping electronic equipment and processesfor the transmission and reception of information.communications common carrier An organizationlicensed to provide public communicationservices.communications network An organization oftransmitting and receiving stations for the reliableexchange of intelligence. Also called net.communications receiver A general-coverage ormultiband radio receiver, designed primarily forlistening to amateur, weather, or other nonbroadcaststations. Compare BROADCAST RE-CEIVER.communications satellites Satellites in earth orbitthat provide propagation paths (e.g., by reflectionor retransmission) for radio waves betweenterrestrial transmitters and receivers. Also seeACTIVE COMMUNICATIONS SATELLITE andPASSIVE COMMUNICATIONS SATELLITE.community-antenna television Abbreviation,CATV. A system in which an advantageously locatedreceiving station receives television signals,amplifies them if necessary, and distributes themin the community served by the system. Commonlycalled cable TV.commutating capacitor 1. In a flip-flop circuit, acapacitor connected in parallel with the crosscouplingresistor to accelerate the transition fromone stable state to the other. Also called speedupcapacitor. 2. A capacitor connected in parallel betweensilicon-controlled rectifier (SCR) stages tomomentarily reverse the current going throughthe SCR, thereby causing the SCR to go into thecutoff condition.

132 commutation • compasscommutation 1. In a direct-current (dc) generator,periodic reversal of the current in the armaturecoils as the coils alternately pass the north andsouth poles of the magnetic field. When the endsof each coil are connected to opposite bars of thecommutator, the electrical polarity at the commutatorbrushes remains constant. 2. In a thyratronor silicon-controlled rectifier (SCR) circuit,momentarily reversing the polarity to cut the deviceoff.commutator 1. In a direct-current (dc) motor,generator, or rotating selector, an arrangementof parallel metal bars or strips on a rotatingdrum. As the drum turns, the bars contact oneor more brushes that are in sliding contact withthe commutator. 2. An electronic circuit thatswitches a single input sequentially to a series ofoutput terminals, or switches a number of inputssequentially to a single pair of output terminals.commutator ripple The pulsating voltage superimposedon the direct-current (dc) voltage deliveredby an unfiltered dc generator.compact disc Abbreviation, CD. A digital, highdensityoptical disc, used in high-fidelity stereosound systems. Also used to store computer data.The information is encoded as tiny pits on thesurface of the disc, and is recovered by a laser, asensor and a digital-to-analog (D/A) converter.These disks have largely superseded magnetictapes, and have rendered long-playing vinyl disksand turntables obsolete. See also COMPACT-DISK READ-ONLY MEMORY.compact-disk read-only memory Abbreviation,CD-ROM. A digital COMPACT DISC used for thelong-term storage of computer data and/or softwareprograms. Usually the same size as a highfidelitystereo disk, it can hold over 600megabytes of data. Although data can be readfrom the disk, it cannot be overwritten.compander Term for compressor/expander. In thetransmission and reception of audio-frequency(AF) intelligence, a system that uses an amplitudecompressor at the transmitter and an amplitudeexpander at the receiver. The compressor reducesthe dynamic range before transmission, and theexpander restores it after reception. Provides improvedsignal-to-noise ratio under marginal communicationsconditions. Also increases the ratioof average power to peak power. See COMPAND-ING.companding A process in which a signal is compressedat the transmitting end of a circuit andexpanded at the receiving end, yielding a signallike the original at the receiver output. Signalsare more efficiently transmitted when they arecompressed because the average power increases,relative to the peak power. This improvesthe average signal-to-noise ratio for weak signals.See COMPANDER.companding law The mathematical function usedfor companding. It is an output-amplitude versusinput-amplitude function for the compression atthe transmitter, and the inverse of this functionfor the expansion at the receiver.companion keyboard An auxiliary keyboard connectedto a regular keyboard and operated remotely.companionship machine A computer or robotwith sufficient machine intelligence to provide entertainmentand mental stimulation for humans.comparator 1. An integrated circuit (IC) with twoinputs, called A and B. The device compares thevoltages that appear at these inputs. If the inputvoltage at A is significantly greater than the inputvoltage at B, the output is about +5 V. If the inputvoltage at A is not greater than the inputvoltage at B, the output voltage is about +2 V.These ICs are used to actuate, or trigger, otherdevices such as relays and electronic switchingcircuits. 2. In general, any circuit that comparessome characteristic of two input signals and producesan output that depends on the relationshipbetween the inputs. 3. An instrument forchecking the condition of a component by comparingit directly with an identical component ofknown quality has a scale reading in percentagedeviation, or simply “GO/NO-GO.” Examples: capacitorcomparator, resistor comparator, coilcomparator.compare In computer operations, a relational testperformed on two quantities to determine theirrelative magnitude, including an indication of thetest result and, sometimes, the taking of action.Example: the process and acton resulting fromexecution of the statement “IF A > B THEN GO TOLINE 250.”comparison 1. An expression of the relationship betweentwo voltages, currents, phase angles, componentvalues, or other quantities in an electricalor electronic circuit or system. 2. An examinationof different data bits or items, which results in aconclusion about some aspect of their relationship.comparison bridge A bridge designed especiallyfor the quick comparison of components (e.g., thecomparison of resistors with a standard resistor,inductors with a standard inductor, and capacitorswith a standard capacitor).comparison measurement A measurement inwhich a quantity or component is compared witha known, similar quantity or component value,rather than having the measurement displayeddirectly by a meter. Examples: bridge measurements,potentiometric measurements, and frequencymatching.compass 1. Any of several instruments for determiningdirection on the earth’s surface [e.g., magnetic(mariner’s) compass and gyrocompass]. 2. Aradio direction finder. 3. An instrument for drawingcircles.

compatibility • compensation theorem 133compatibility 1. A desirable condition in whichdevices or systems can function efficiently together,without any modification of equipment. 2.In computer operations, a desirable condition inwhich different computers can run the same software,without any modification of hardware orsoftware.compatible color television A color-televisionsystem whose transmissions can be received inblack and white by any ordinary monochromaticreceiver.compatible integrated circuit A hybrid integratedcircuit (IC) that has an active element inside theintegrated structure and a passive element depositedon its insulated outer surface.compensated amplifier A wideband amplifierwhose frequency range is extended by specialcomponents and circuit modifications. Also seeCOMPENSATING CAPACITOR and COMPENSAT-ING COIL.compensated diode detector A diode detector inwhich a positive dc voltage from the automaticgain-control(AGC) rectifier is applied to the diodeanode. The voltage is always proportional to thesignal carrier. The arrangement allows the diodeto handle a heavily modulated AM signal withoutproducing excessive distortion.compensated-impurity resistor A resistor consistingof a diffused semiconductor material towhich are added controlled amounts of n- or p-type dopants (impurities).compensated-loop direction finder A directionfinder whose loop antenna is complemented byanother antenna for polarization-error compensation.compensated semiconductor A doped semiconductormaterial in which the acceptor impuritycancels the effects of the donor impurity.compensated volume control A combination volume-tonecontrol that provides bass boost at lowvolume levels to compensate for the ear’s deficiencyat low frequencies.compensating capacitor 1. A capacitor that has atemperature coefficient of capacitance numericallyequal to, but having the opposite sign from, that ofanother capacitor in a tank or other circuit. Whenthe capacitors are connected in parallel, a temperature-inducedvalue change in the main capacitoris balanced by an equal and opposite change inthe compensating capacitor; the net capacitance ofthe circuit does not change. This greatly reducesfrequency drift. 2. In a video amplifier, a large capacitanceconnected between ground and a tap onthe collector or drain resistor to boost lowfrequencyresponse. Compare COMPENSATIONCOIL. 3. A usually low-capacitance capacitor ofknown temperature coefficient, operated in combinationwith a main capacitor to reduce capacitance/temperaturedrift of the latter to zero or tosome desired positive or negative value.compensating diode A junction diode used totemperature-stabilize a transistor circuit. It isusually forward-biased in the base-bias networkof the transistor.compensating filter 1. A selective filter used forthe purpose of eliminating some irregularity inthe frequency distribution of received energy. 2. Afilter used to change the wavelength distributionof electromagnetic energy.compensating resistor 1. A low-value resistorof known temperature coefficient, connected inseries with a main resistor to reduce theresistance/temperature drift to zero, or to somedesired positive or negative value. 2. See TRIM-MER RESISTOR.MainCompcompensating capacitor, 1.MainCompcompensating resistor, 1.compensation Adjusting a quantity, manually orautomatically, to obtain precise values, or tocounteract undesired variations. Example: temperaturecompensation of electronic components.For illustration, see COMPENSATING CAPACI-TOR, 1.compensation coil In a video amplifier, an inductorconnected in series with the collector or drainresistor, or in the coupling path between stages,or both, to boost high-frequency response.compensation filter See COMPENSATING CA-PACITOR, 2.compensation signal A signal recorded on a tapetrack containing computer data, to ensure thatthe tape plays back at exactly the correct speed atall times.compensation theorem An impedance (Z ) in anetwork can be replaced by a generator having

134 compensation theorem • complementary wavezero internal impedance, and whose generatedvoltage equals the instantaneous potential differenceproduced across Z by the current flowingthrough it. Compare MAXIMUM POWERTRANSFER THEOREM, NORTON’S THEOREM,RECIPROCITY THEOREM, SUPERPOSITIONTHEOREM, and THEVENIN’S THEOREM.compensator A device or circuit that facilitates theadjustment of a quantity, manually or automatically,to obtain precise values, or to counteractundesired variations.compilation time The period during which a programis compiled, as distinct from RUN TIME.compile 1. To unify computer subroutines into anall-encompassing program. 2. To gather informationor data together into a single file or fileset.compilerIn computer operations, a program thatchanges a HIGH-LEVEL LANGUAGE, such asBASIC, C, C++, COBOL, or FORTRAN, into MA-CHINE LANGUAGE. A compiler must be writtenespecially for the high-level language being used.compiler language Any computer language thatserves as an interface between the operator andthe computer.compiler program A program that converts compilerlanguage into machine language.compiling routine In digital computer operation, aroutine permitting the computer itself to constructa program to solve a problem.complement 1. The difference between a numberand the radix (modulus or base) of the numbersystem. For example, the complement of 7 isequal to 3 (because 10 – 7 = 3) in the decimal(radix-10) number system. 2. Also called onescomplement. In computer operations, a representationof the negative value of a binary number.All the available digits are set to 1, and thenthe number in question is subtracted. For example,the complement of 101 is equal to 010(because 111 – 101 – 010); the complement of1001 is equal to 0110 (because 1111 – 1001 =0110).complementary A Boolean operation whose resultis the same as that of another operation, but withthe opposite sign; thus, OR and NOR operationsare complementary.complementary colors 1. In the additive colorsystem, two colors that produce light gray orwhite when combined. 2. In the subtractivecolor system, two pigments that produce darkgray or black when combined. 3. Colors or pigmentsthat are opposite each other on the colorwheel.complementary constant-current logic A form ofbipolar logic with high operating speed and highcomponent density.complementary metal-oxide semiconductorAlso sometimes called complementary metal-oxidesilicon. Acronym, CMOS (pronounced “seamoss”).A digital integrated-circuit (IC) technology, inwhich logic gates are formed by n-channel/p-channel pairs of metal-oxide-semiconductorfield-effect transistors (MOSFETs) fabricated on asubstrate. Noted for high speed and low currentdrain.complementary operator The logical negation(NOT) operation.complementary pushpull circuit See COMPLE-MENTARY-SYMMETRY CIRCUIT.complementary rectifier In the output circuit of amagnetic amplifier, nonsaturating half-wave rectifierelements.complementary silicon-controlled rectifier Asilicon-controlled rectifier that has polarityopposite from the usual silicon-controlled rectifier.complementary-symmetry circuit A bipolartransistorcircuit that uses an npn and pnp transistor.The transistors conduct during oppositehalf-cycles of the input signal, the result beingthat push-pull output is provided with a singleendedinput; no phase-splitting input circuit isrequired. The complementary-symmetry circuitoffers very low output impedance, permitting aloudspeaker voice coil (or other low-impedanceload) to be operated directly without a couplingtransformer.Incomplementary-symmetry circuitcomplementary tracking A control system inwhich several secondary (slave) devices are controlledby a primary (master) device.complementary transistors A transistor pair ofopposite polarity operated in a complementarysymmetrycircuit or its equivalent.complementary wave An electromagnetic wave ina transmission line that occurs as a result of reflection.Any impedance discontinuity will resultin complementary waves.+++−

complementer • component 135complementer A logic circuit that provides an outputpulse when there is no input pulse, and viceversa. Also called INVERTER and NOT CIRCUIT.complement number In a base-n number system,for a given positive integer p less than n, the positiveinteger m such that m + p = n. For example, inthe decimal (base-10) system, the complement of 4is 6, the complement of 7 is 3, and the complementof 9 is 1. In the hexadecimal (base-16) numbersystem, the complement of 4 is 12, the complementof 7 is 9, and the complement of 9 is 7.complement-number handling A computer systemin which the operations are carried out viathe complements of the input numbers.complement-setting technique A process of determiningthe number of pulses required to completethe switching of a counter circuit when it isstarted at some state higher than full zero. Thenumber of pulses required for completion is equalto the number that represents the starting state’scomplement.complete carry In digital computer operation, asystem permitting all carries to generate carries.complete circuit See CONTINUOUS CIRCUIT.complete modulation Modulation to the maximumextent possible while maintaining acceptablecircuit or system operation.complete operation In computer operations, thecondition in which the machine rigorously followsprogram instructions.complete routine A vendor-supplied computerprogram that is usable without modification.complex function 1. A mathematical function of acomplex-number variable. 2. An integrated circuit(IC) containing two or more subcircuits thatperform an operation more complicated that ofany one of the circuits alone.complex notation Notation taking into considerationboth the real-number and imaginary-numbercomponents of a quantity. Thus, impedance(Z ) is a complex quantity that includes a resistive(real) component (R) and a reactive (imaginary)component ( jX). See COMPLEX NUMBER andCOMPLEX OPERATOR.complex number A number expressed in complexnotation (e.g., a + jb, where a and b are real numbersand j is the COMPLEX OPERATOR). Canalso be expressed as a point or a vector in an AR-GAND DIAGRAM.complex operator The unit imaginary number,represented as j by engineers and as i by mathematicians.This number is defined mathematicallyas the positive square root of –1.complex parallel permeability An expression ofthe permeability of an inductor core under actualoperating conditions, assuming zero loss in theconductors of the coil winding. A parallel combinationof reactance and resistance.complex periodic wave A periodic wave composedof a sine-wave fundamental and certain harmonicsin specific proportions.complex permeability An expression of inductorcorepermeability, obtained from the mathematicalratio of the magnitudes of the vectorsrepresenting the induction and electromagneticfield strength within the core.complex plane A Cartesian coordinate systemwith real numbers on the horizontal axis andimaginary numbers on the vertical axis. Used forvectorial representation of complex numbers. SeeARGAND DIAGRAM.complex quantity A quantity containing both realand imaginary components. Example: Impedance(Z ) is a complex combination of resistanceR (a real component) and reactance jX (animaginary component): Z = R + jX.complex radar target A radar target that is largeenough in theory to be detected by radar, but, becauseof its geometry, cannot be detected. This effectis the result of phase combinations of signalcomponents reflected from various surfaces onthe target.complex series permeability An expression ofcomplex permeability of an inductor core underactual operating conditions, assuming zero lossin the conductors of the coil winding. A seriescombination of reactance and resistance.complex steady-state vibration Periodic vibrationwith more than one sine-wave component.complex tone An audio tone made up of morethan one sine-wave component.complex variable A variable having real and imaginaryparts.complex waveform The shape of a COMPLEXPERIODIC WAVE. It is the resultant of the individualsine-wave components (i.e., of the fundamentaland the harmonics).complex-wave generator A signal generatorwhose output signal is any of several selectablewaveforms and frequencies (or repetition rates).Also see FUNCTION GENERATOR.compliance 1. The ease with which a material canbe flexed or bent, an important characteristic oftransducers (such as loudspeakers). Expressedin cm/dyne, compliance is the reciprocal of stiffness,and is the acoustical or mechanical equivalentof capacitance. 2. A measure of the outputimpedance of a switched-current signal source.Generally given as maximum current for a certainchange in the voltage.compliance range The voltage range required tomaintain a constant current throughout a loadresistancerange.compliance voltage The range over which the outputvoltage of a constant-current power supplymust swing in order to maintain a steady currentin a varying load.compliance-voltage range The output voltagerange of a constant-current power supply.component 1. A device or part used in a circuit toobtain some desired electrical action [e.g., a resistor(passive component) or an integrated circuit

136 component • compress(active component)]. Also see ACTIVE COMPO-NENT and PASSIVE COMPONENT. 2. An attributeinherent in a device, circuit, orperformance (e.g., the REACTIVE COMPONENTof an inductor). 3. A specified quantity or term(e.g., the WATTLESS COMPONENT of ac power).4. A piece of equipment in a high-fidelity soundsystem.component density The number of components(see COMPONENT, 1) in an electronic assembly ofa given physical volume.component failure rate 1. The percentage ofcomponents, out of a specified group, that canbe expected to fail within a specified length oftime. 2. The frequency with which a given component,in a certain application, can be expectedto fail.component layout The mechanical arrangementof components (see COMPONENT, 1) in an electronicassembly.component stress The electrical or mechanicalstrain to which a component is subjected. In general,the greater the stress, the higher the componentfailure rate.composite cable A cable containing other cables ofdifferent types.composite circuit A circuit handling telegraphyand telephony simultaneously without causingmutual interference.composite color A color that is not one of theCOLOR PRIMARIES, but instead, consists of acombination of the three color primaries.composite color signal The complete color televisionsignal, including all picture, color, and controlcomponents.composite conductor A set of wires connected inparallel. The wires are often, but not necessarily,of identical size and constitution.composite current A current having both alternating-current(ac) and direct-current (dc) components;an alternating current superimposed ona direct current. Also called fluctuating current.composite curve A curve or pair of curves showingtwo modes of operation, as of biased and unbiasedconditions.composite filter A filter consisting of more thanone section. The sections might be, but often arenot, identical.composite video signal The television picture signalcontaining picture information and syncpulses.composite-video-signal distortion Distortion ofthe composite video signal as evidenced by overshooting,ringing, and sync-pulse shortening.composite voltage A voltage having both alternating-current(ac) and direct-current (dc) components;an ac voltage superimposed on a dcvoltage. Also called fluctuating voltage.composite wave filter Two or more wave filters(not necessarily of the same type) operated in cascade.composition resistor A resistor made from a mixtureof materials, usually finely powdered carbonand a binder.compound A substance in which the atoms of twoor more elements have united chemically to forma molecule. For example, an atom of cadmium(Cd) and one of sulfur (S) combine to form amolecule of cadmium sulfide (CdS).compound connection A direct connection of twotransistors, the amplified output of the first beingfurther amplified by the second. The connectionprovides extremely high current gain. Also calledDARLINGTON PAIR.compound generator A generator that has bothseries and shunt fields. Also called compoundwoundgenerator.compound horn A horn reflector used for transmissionof microwave energy. The faces of thehorn approach four geometric plane surfaces asthe distance from the center increases.compound modulation A system of successivemodulation, the modulated wave from one stepbecoming the modulating wave in the next. Alsocalled multiple modulation.DatainAmpMod#1Osc#1Mod#2Osc#2compound modulationPAMod#3Osc#3compound motor An electric motor having bothseries and shunt fields. Also called compoundwoundmotor.compound transistor Two or more transistors directlycoupled in the same envelope for increasedamplification. Also see COMPOUND CONNEC-TION.compound-wound generator See COMPOUNDGENERATOR.compound-wound motor See COMPOUND MO-TOR.compress 1. In communications, to reduce or minimizethe bandwidth of a signal. 2. In communications,the processing of a signal to increaselow-level components and thereby raise the averagepower level relative to the peak power level. 3.In computer operations, to reduce or minimizethe number of bits in a digital signal or file, while

compress • computer graphics 137still retaining all the essential information. CompareEXPAND.compressed-air capacitor A high voltage airdielectriccapacitor enclosed in a case in whichthe air pressure is held at several atmospheres.The device exploits the dielectric strength of compressedair, which is higher than that of air atnormal pressure.compressed-air speaker A speaker that uses anairtight chamber to enhance the acoustic reproductionat certain frequencies.compression 1. In communications, the reductionor minimization of signal bandwidth. 2. In communications,the processing of a signal to increaselow-level components and thereby raisethe average power level relative to the peak powerlevel. Usually, a logarithmic function. 3. In computeroperations, the reduction or minimizationof the number of bits in a digital signal or file,while still retaining all the essential information.Compare EXPANSION.compression ratio In a system using COMPRES-SION, the ratio A 1 /A 2 , where A 1 is the gain (ortransmission) at a reference-signal level and A 2 isthe gain (or transmission) at a specified highersignal level.compression wave A wave disturbance that travelsvia longitudinal motion of particles in amedium. Sound waves through air are the mostcommon example.compressor A circuit or device that limits the amplitudeof its output signal to a predeterminedvalue, despite wide variations in input signal amplitude.compressor driver unit A loudspeaker that worksinto an air space connected by a throat to a horn,rather than by driving a diaphragm.Compton diffusion An effect that occurs when aphoton and electron collide. Some of the energyfrom the photon is transferred to the electron. Ona large scale, such collisions result in diffusion ofelectromagnetic waves.Compton effect The increase in wavelength (decreasein frequency) of X-rays scattered by theelectrons of lighter atoms bombarded with theX-rays.Compton shift See COMPTON EFFECT.compute To perform a mathematical operation bymeans of a relatively simple process. Thus, a digitalcomputer solves intricate problems usingsimple arithmetic steps. Compare CALCULATE.computer A device or machine for performingmathematical operations on data, and producingthe results as information or control signals.There are numerous types, the most common beingthe digital computer.computer-aided design Abbreviation, CAD. Theuse of computers in conceiving, developing, andperfecting new products.computer-aided manufacturing Abbreviation,CAM. The use of automated manufacturing systems,such as assembly lines, that are partially ortotally controlled by computers.computer antibody Also called vaccine. A smallsubprogram designed to eliminate viruses fromcomputer systems.computer-assisted instruction Abbreviation, CAI.The use of computers as teaching and trainingaids.computer code See MACHINE LANGUAGE.computer consciousness The degree to which amachine can be considered aware of its own existence.Until recently, this idea was consideredridiculous. But as microprocessor power continuesto grow, some researchers now consider itworth thinking about.computer-controlled catalytic converter A microprocessor-controlledsystem for automaticallysupervising gaseous emissions exhausted by amotor vehicle. An oxygen sensor monitors the exhauststream, and the associated electronic systemadjusts the air-to-fuel ratio of the carburetorto reduce smog-producing pollutants in the exhaust.computer diode A semiconductor diode havinglow capacitance and fast RECOVERY TIME, thussuiting it to rapid switching in computer circuitsand to very-high-frequency applications.computer engineer A person skilled in the theoryand application of computers, related equipment,and associated mathematics.computer file See FILE.computer game See VIDEO GAME.computer graphics 1. The use of computers toassist in drawing and drafting, and in the processingof video images such as photographs.2. Broadly, any computer-generated or computerprocessedimage.

138 computer instruction • condenser microphonecomputer instruction See INSTRUCTION.computer interfacing apparatus The equipmentused to connect a computer to other systems,and to peripherals.computerized axial tomography Abbreviation,CAT. A multiple X-ray system that enables theobserver to obtain cross-sectional images of theinternal organs of the body.computer map A blueprint, used in conjunctionwith machine vision, sonar, radar or beacons,that a mobile robot can use as a navigational aid.One or more such blueprints are stored in therobot controller’s main memory.computer music 1. Music that is composed by acomputer. 2. See MUSICAL INSTRUMENT DIGI-TAL INTERFACE.computer program See PROGRAM.computer programmer A person skilled in devisingand/or writing the routines that a digitalcomputer uses to solve problems or process data.computer storage tube A cathode-ray tube inwhich the electron beam scans and stores informationin thousands of memory cells on a target.A cell “remembers” by acquiring and holding anelectrostatic charge when it is struck by the beamfrom the writing gun. Information taken is readout of a cell by a second beam from the readinggun.computer system A central processor and its associatedonline and offline peripherals, such as amonitor, modem, printer, optical scanner, magneticdisk drives, CD-ROM drive, and tapebackup.computer technician A professional skilled inbuilding, repairing, and maintaining computers,and who, occasionally, designs them. Usuallyworks under the supervision of a computer engineer.computer terminal 1. A teleprinter or video displayunit and keyboard, used by human operator(s)of a computer. 2. An interface between acomputer and its human operator(s).computer/TV interface A device or circuit for deliveringthe output of a digital computer to a standardtelevision receiver so that the latter canserve as a GRAPHIC TERMINAL.computer virus A deliberately created and disseminatedsubprogram or piece of programming code,that electronically spreads through computersystems and hinders operation. Usually divertsthe computer(s) from intended functions; sometimescauses a catastrophic malfunction. Oftenexists undetected, being transferred from onecomputer to another by means of diskettes orsoftware.computer word See WORD.computing amplifier See OPERATIONAL AMPLI-FIER.computing machine See COMPUTER.concatenation 1. A method of speed control for a3-phase motor in which two induction motors areoperated with their shafts coupled together. Thestator of the first motor is connected to the 3-phase supply, and the slip rings of this motor areconnected to the field of the second motor. Theslip rings of the second motor are connected tothe three ganged sections of a Y-rheostat used foradjusting the speed. 2. Arrangement of a set intoa series.concentrated-arc lamp A brilliant low-voltagelamp, containing nonvaporizing electrodes in aninert-gas atmosphere. An arc across the electrodescreates the light source.concentrated winding A coil winding that has alarge number of turns in a small space.concentration cell An electrolytic cell in whichtwo electrodes are immersed in solutions of thesame compound but having different combinations.The voltage is usually very small, 0.1 volt orless.concentration gradient Between points in a semiconductor,the difference in electron or hole concentration.concentric cable See COAXIAL CABLE.concentric capacitor A fixed or variable capacitorwhose plates are concentric cylinders. Also calledconcentric-plate capacitor.concentric jack See COAXIAL JACK.concentric line See COAXIAL LINE.concentric-line oscillator A stable, self-excitedoscillator whose frequency-determining tank consistsprincipally of a section of concentric (coaxial)line. Used primarily at ultra-high frequencies(UHF).concentric plug See COAXIAL PLUG.concentric receptacle See COAXIAL RECEPTA-CLE.concentric tank See COAXIAL TANK.concentric-wound coil A combination of two ormore coils wound on top of, and insulated from,each other.conceptual modeling A technique for solvingproblems by devising a mathematical modelbased on the results of an experiment; experimentsperformed on the model are used to verifyits validity.concurrent conversion In computer operations,running conversion and conventional programstogether. Also see CONVERSION PROGRAM.concurrent processing See MULTIPROGRAM-MING.condenser 1. An obsolete term for CAPACITOR. 2.A mirror or lens for concentrating light (on an object,for example). 3. Something that condenses agas or vapor. 4. See CONDENSER MICRO-PHONE.condenser antenna A two-wire horizontal antennasystem in which the radiator is a wire situatedabove a counterpoise.condenser microphone Also called capacitor microphone.A microphone in which a tightlystretched metal diaphragm forms one plate of an

condenser microphone • conductor 139air capacitor, and a closely situated metal plugforms the other plate. A dc bias voltage is appliedto the arrangement. Impinging sound wavescause the diaphragm to vibrate, varying the capacitanceand causing the output current to fluctuateaccordingly.condensing routine In computer operations, aprogram that compresses data. See COMPRES-SION, 3.condensite A plastic insulating material whosebase is phenol formaldehyde resin.conditional Pertaining to a quantity or phenomenonthat depends on some external factor,and is therefore subject to change.conditional branch A point in a computer programwhere a relational test is performed, andthe statement line in which the test is made is leftso that an out-of-sequence instruction can be implemented.Such a branch might be made, for example,following a statement, such as “IF Z = YTHEN GO TO LINE 380.”conditional branch instruction The instructionin a computer program that causes a CONDI-TIONAL BRANCH.conditional implication operation A Boolean operationin which the result of operand values Xand Y are such that the output is high only if inputX is high and input Y is low. Also called inclusionor if-then operation.conditional jump See CONDITIONAL BRANCH.conditional stop instruction In a computer program,an instruction that can cause a halt in therun, as dictated by some specified condition.conditional transfer See CONDITIONAL BRANCH.condition code A set of constraints for a computerprogram; sets limits on what can be done with thecomputer under certain circumstances.conditioning 1. The process of making equipmentcompatible for use with other equipment. Generallyinvolves some design or installation changes.2. Interfacing.Condor1/2 -WaveradiatorCounterpoisecondenser antennaFeed lineA continuous-wave navigational systemthat produces a cathode-ray-tube display for automaticallydetermining the bearing and distancefrom a ground station.conductance Symbol, G. Unit, siemens. The abilityof a circuit, conductor, or device to conduct electricity.Conductance in siemens is the reciprocalof resistance: G = 1/R, where R is the resistancein ohms.conducted heat Heat transferred by conductionthrough a material substance, as opposed to convectionand radiation. A heatsink conducts dissipatedenergy away from a transistor, whereuponconvection and radiation allow heat to escapefrom the sink.conduction 1. The propagation of energy througha medium, depending on the medium for itstravel. 2. The transfer of electrons through a wire.3. The transfer of holes through a P-type semiconductormaterial. 4. Heat transfer through amaterial object (see CONDUCTED HEAT).conduction angle See ANGLE OF CONDUCTION.conduction band In the arrangement of energylevels within an atom, the band in which a freeelectron can exist; it is above the valence band inwhich electrons are bound to the atom. In ametallic atom, conduction and valence bandsoverlap; but in semiconductors and insulators,they are separated by an energy gap.conduction current 1. The electromagnetic-fieldflow that occurs in the direction of propagation. Ameasure of the ease with which the field is propagated.2. Current in a wire or other conductor.conduction-current modulation In a microwavetube, cyclic variations in the conduction current;also, the method of producing such modulation.conduction electron See FREE ELECTRON.conduction error In a temperature-acutatedtransducer, error caused by conduction of heatbetween the sensor and the mounting.conduction field An energy field that exists in thevicinity of an electric current.conductive coating A conducting layer applied tothe glass envelope of a cathode-ray tube, such asan oscilloscope tube or picture tube.conductive coupling See DIRECT COUPLING.conductive material See CONDUCTOR.conductive pattern The pattern of conductivelines and areas in a printed circuit.conductivity Unit, S/m (siemens per meter). Anexpression of conductance per unit length of amaterial; the reciprocal of resistivity.conductivity meter A device for measuring electricalconductivity. Generally, such a device iscalibrated in siemens.conductivity modulation In a semiconductor, thevariation in conductivity that results from a variationof charge-carrier density.conductivity-modulation transistor A transistorin which the bulk resistivity of the semiconductormaterial is modulated by minority carriers.conductor 1. A material that allows charge carriers(usually electrons) to move with ease amongatoms. Examples are metals, electrolytes, andionized gases. Substances vary widely in theirsuitability as conductors; the conductivity ofcommercial copper, for example, is almost twicethat of aluminum. Compare INSULATOR. 2. Anindividual conducting wire in a cable, insulatedor uninsulated.

140 conduit • conic sectionsconduit A hollow tube, made of plastic or metal,through which wires, cables, and other transmissionmedia are fed.cone The conical diaphragm of a (usually dynamic)loudspeaker.cone antenna An antenna in which the radiator isa sheet-metal cone or a conical arrangement ofrods or wires.Conelrad An early amplitude-modulation (AM)broadcast protocol, intended for use in the eventof a nuclear war. Now replaced by the EMER-GENCY BROADCAST SYSTEM.cone marker A UHF marker beacon whose conicalenergy lobe radiates vertically from a radio-rangebeacon station. Aircraft in flight use such markersto accurately locate the beacon station.cone of protection The zone surrounding a lightningrod, in which the chances of a lightningstrike are greatly reduced. The cone has an apexangle of 45°, relative to the rod. Objects entirelywithin this cone are unlikely to be struck (althoughit is still possible).Approximateprotectedregion45°45°Lightningrodcone of protectioncone of silence A small zero-signal zone directlyover a low-frequency radio-range beacon. Thezone is the product of the combined directiveproperties of the beacon transmitting antennaand the antenna on an aircraft.cone speaker A loudspeaker having a soundproducingcone (diaphragm) made of speciallytreated paper or other material, as opposed to aloudspeaker having a flat diaphragm.confetti On a color TV screen, color spots causedby chrominance-amplifier noise.confidence The probability that a predicted resultwill occur.confidence factor Confidence, expressed either asa fraction (between 0 and 1) or as a percentage.confidence interval The range over which a parametercan vary so that a given confidence factoris maintained.confidence level See CONFIDENCE FACTOR.confidence limitations The maximum and minimumpoints of a confidence interval. Outside theconfidence-limitation points, the confidence factordrops below the required minimum.configuration 1. The characteristic arrangementof components in an electronic assembly, or ofthe equipment symbols in the corresponding circuitdiagram. 2. Computer system.configuration state In a computer system, an expressionof the availability status of a device for agiven application. A configured-in device is available;a configured-out device is available, but isrestricted to certain users; a configured-off deviceis unavailable.configuration table Within a computer’s operatingsystem, a table that provides the configurationstate for various system units.configured-in See CONFIGURATION STATE.configured-off See CONFIGURATION STATE.configured-out See CONFIGURATION STATE.conformance The degree to which a quantity orvariable corresponds to a standard or to expectations.conformance error The extent (usually expressedas a percentage) to which conformance is lacking.conical antenna See CONE ANTENNA.conical horn A horn (antenna, loudspeaker, orsound pickup) having the general shape of acone: the cross-sectional area varies directly asthe square of the horn’s axial length.conical monopole antenna An unbalanced broadbandantenna that derives its name from itsshape. It is usually constructed from wire andmust be operated against a good radio-frequency(RF) ground.conical monopole antennaAntennaconductorMastCrossbracesFeed pointconical scanning In radar transmission, a methodof scanning in which the beam describes a cone,at the apex of which is the antenna.conic sections The geometric plane figures thatresult from the intersection of a cone with a

conic sections • constant-current source 141plane. These figures are the circle, the ellipse, theparabola, and the hyperbola.conjugate For a given complex number A + jB, thequantity A – jB. When complex conjugates aremultiplied together, the result is A 2 + B 2 .conjugate branches In a network, two branches ofsuch a nature that a signal in one has no effect onthe other.conjugate bridge A bridge in which the detectorand generator occupy positions opposite to thosein a conventional bridge of the same general type.conjugate impedance For a given complex impedance,R + jX, where R is the resistive componentand jX is the reactive component, theimpedance: R – jX. The resistance is identical; thereactance is of equal magnitude, but oppositesign (capacitive as opposed to inductive, or viceversa).conjunction The logical AND operation.connect To provide an electrical path between twopoints.connection The point at which two conductors arephysically joined.connective An operation symbol written betweenoperands.connector 1. A device that provides electrical connection.2. A fixture (either male or female) attachedto a cable or chassis for quickly makingand breaking one or more circuits. 3. A symbolthat connects points on a flowchart.conoscope A device that uses focused polarizedlight to examine crystals (as in checking the opticalaxis of a quartz crystal).consequent poles The poles of an equivalent singlemagnet that is formed when two magnets arealigned with their two identical poles together.Thus, when the two north poles are placed together,the consequent poles are a south pole ateach end and a north pole at the center.conservation of energy 1. The preservation ofthe potential for work by a given quantity of energy—evenwhen it undergoes a change in formwithin a system. 2. The law of conservation ofenergy, which states that energy can be neithercreated nor destroyed, but only changed inform.console 1. The main station or position for thecontrol of electronic and/or computer equipment.2. The equipment at a fixed location. 3. An equipment-containingcabinet that stands on the floor.4. Equipment permitting communication with acomputer. Also called dumb terminal.consonance 1. Harmony between audio tones. 2.Acoustical or electrical resonance between bodiesor circuits that are not physically connected.constant 1. A quantity whose value remainsfixed, such as the speed of light in a vacuum.Compare VARIABLE. 2. The value of a componentspecified for use in a particular electroniccircuit. 3. An electronic component, particularlya capacitance or inductance. 4. In a computerprogram, data items that remain unchanged foreach run.constant-amplitude recording In sound recording,the technique of holding the maximum amplitudeof the signal steady as the frequencychanges.constantan An alloy of copper and nickel used insome thermocouples and standard resistors.constantan-platinum thermocouple A thermocouplethat uses the junction between constantanand platinum wires, which is contained inthermocouple-type meters.constant area As allocated by a computer program,an area of memory that holds constants.constant bandwidth In a broadband tuned circuit,bandwidth that does not change with frequency.constant current A current that undergoes nochange in value as it flows through a changing resistance.Compare CONSTANT VOLTAGE.constant-current characteristic A condition inwhich the current through a circuit remains constant—evenif the voltage across the circuit increasesor decreases.constant-current curve A graph in which the dependentvariable is an electric current that levelsoff at, or approaches, a specific maximum. An exampleis the collector-current versus collectorvoltagecurve for a bipolar transistor.Max.Collector current00Collector voltageconstant-current curveConstantcurrentregion+10 Vconstant-current drive Driving power obtainedfrom a constant-current source.constant-current modulation See CHOKE-COUPLED MODULATION.constant-current power supply See CONSTANT-CURRENT SOURCE.constant-current sink See CURRENT SINK.constant-current source A power supply whosecurrent remains steady during variations inload resistance. Also called constant-currentsupply and current-regulated supply. CompareCONSTANT-VOLTAGE SOURCE.

142 constant-current supply • contactor noiseconstant-current supply See CONSTANT-CURRENT SOURCE.constant-current transformer A transformer suppliedfrom a constant-voltage source that automaticallydelivers a constant current to a varyingsecondary load.constant-k filter Also called a Zobel filter. A filtersection in which Z 1 Z 2 equals k 2 at all frequencies,where Z 1 is the impedance of the series elementand Z 2 is the impedance of the shunt element.constant-power dissipation line A line connectingpoints on a family of current-voltage characteristiccurves, the points corresponding to themaximum power that can safely be dissipated bythe device to which the curves apply.constant-resistance network A circuit of resistorsthat, when terminated in a resistance load, presentsa constant resistance to a driving sourceunder various conditions of operation.constant-speed motor 1. Also called a shunt motor.A motor whose speed varies little, or not at all,with variations in the armature current. 2. A motorthat runs at an unvarying speed through theaction of associated automatic electronic controlcircuitry.constant voltage A voltage that does not changeas the load resistance varies. Compare CON-STANT CURRENT.constant-voltage, constant-current supply Acombination current-regulated and voltageregulatedpower supply; delivers constant currentto low load resistances and constant voltageto high load resistances.constant-voltage drive Driving power obtainedfrom a CONSTANT-VOLTAGE SOURCE.constant-voltage source A power supply whoseoutput voltage remains steady during variationsin load current. Also called constant-voltage supplyand voltage-regulated supply.constant-voltage transformer A special transformerused to reduce variations in power-linevoltage. A capacitor in the device causes a windingto resonate at the line frequency (e.g., 60 Hz). Thistends to maintain a more constant current thanwould be the case in an ordinary transformer.construct A source (user’s) computer programstatement that, when implemented, produces apredetermined effect.consumer reliability risk 1. The chance a consumertakes when buying a component or pieceof equipment that has not been subjected toquality-assurance/quality-control (QA/QC) testing.2. An expression of the failure rate for a consumeritem.contact 1. A conducting body (such as a button,disk, or blade) that serves to close an electric circuitwhen pressed against another conductor.Example: switch contact and spring contact. 2.The state of being touched together, as when twoconductors are brought into contact to close acircuit.contact arc The arc that initially occurs whencurrent-carrying contacts are separated.contact area 1. The face of an electrical contact.2. The common area shared by two conductors inmutual contact.contact bounce The springing apart or vibration ofcontacts upon making or breaking.contact chatter The abnormal vibration of matingcontacts, caused by contact bounce or by an extraneousalternating current.contact-closure input The input circuit of a device,such as a control-system amplifier, that isactuated by the closing of switching contacts.Compare CONTACT-OPEN INPUT.contact combination The set of contacts on aswitch or electronic relay.contact detector A rectifier or demodulator, composedof two dissimilar materials in contact witheach other. Semiconductor diodes are of this generaltype. Some contact-detector action can beobtained with two dissimilar fine wires (such ascopper and iron) by touching their tips lightly together.contact EMF Short for contact electromotive force;also called contact potential. A low direct-current(dc) voltage that is sometimes generated by thecontact of two dissimilar materials.contact follow The tendency of relay contacts tofollow the actuating signals.contact force 1. The force with which relay contactsclose with a given amount of coil current. 2.The force with which a pair of relay contacts areheld together when current flows through thecoil. 3. In a mercury-wetted relay, the force exertedby the mercury on the contacts as the relaycloses.contact gap The distance between contacts whenthey are open.contact load 1. The power dissipated by a loadthat is connected to a power supply through aclosed set of contacts. 2. The current passingthrough a set of closed contacts.contact microphone A microphone placed in directcontact with a vibrating surface for pickup.Actuated by the vibration of a solid, rather thanby the movement of air molecules.contact miss 1. The improper alignment of contactsin a switch or relay. 2. The condition of relaycontacts not lining up properly.contact modulator An electromechanical CHOP-PER.contact-open input The input circuit of a device,such as a control-system amplifier, that is actuatedby the opening of switching contacts. CompareCONTACT-CLOSURE INPUT.contactor A switch used for frequent opening orclosing of a circuit. An example is a relay contactorused for keying a transmitter.contactor noise 1. Electrical noise that is theproduct of make-and-break contact action orfluctuations in conduction when the contacts are

contactor noise • Continuous Commercial Service 143MovablemagnetFixed coilOutputDiaphragmcontact microphoneObject carryingsound disturbanceclosed. 2. Sounds coming directly from contactsthat are opening and closing.contact potential The small direct-current (dc)voltage that results from the bombardment of anelectrode by electrons, when the electrode has noexternal voltage applied to it.contact pressure The pressure that holds contactstogether.contact protector A component (such as a diode,capacitor, resistor, or combination of these) thatserves to suppress contact arcing.contact rating The maximum current, voltage,and/or power specified for a given set of contacts.contact rectifier A rectifier consisting of two dissimilarmaterials in direct contact. Examples:copper and copper oxide, magnesium and coppersulfide, selenium and aluminum, and germaniumand indium.contact resistance The resistance of the closedcontacts of switches, relays, and other similar devices.Normally, this is a very small resistance.contact separation See CONTACT GAP.contact strip See TERMINAL STRIP.contact switch An electromechanical switch thatuses contacts to make and break a circuit, ascompared with an electronic switch that usessemiconductor devices.contact travel The distance over which a relay orswitch contact must move to close a circuit.contact wetting The use of mercury (a conductingliquid) to improve the action of a relay contact orcontacts.contact wipe A sliding motion between closed contacts.Helps to establish a good connection and tokeep the contact surfaces clean.container file See CONTROLLING FILE.contaminated material 1. A semiconductor materialcontaining some undesired substance. 2. Amaterial unintentionally made radioactive.contamination 1. The presence of an impurity in asubstance. 2. The addition of a radioactive materialto a substance. 3. In a coaxial cable, the tendencyfor the jacket material to bleed through theouter braid into the dielectric, resulting in increasedloss.content-addressed storage In a computer, memory-or data-storage locations identified by content(see CONTENTS), instead of by address. Alsocalled associative storage.contention The result of interference among morethan one transmitting station on the same communicationschannel.contents 1. The data in a computer randomaccessmemory (RAM). 2. The data in a specificstorage location, such as on a hard disk, diskette,or CD-ROM.context 1. The environment in which a word isused in a natural language (such as English,Spanish, or Russian). Important in speechrecognition and speech synthesis. 2. The environmentin which a string of characters, composinga data unit or word, is used in acomputer program.Continental code A version of the Morse codeused internationally in radiotelegraphy. Alsocalled International Morse code and general servicecode. Compare AMERICAN MORSE CODE.continuity A condition of being uninterrupted—especially pertaining to current flowing in anelectrical or electronic circuit.continuity test A test of the completeness of anelectrical path. Ideally, the only concern iswhether the circuit is open or closed, but sometimescircuit resistance is also of interest.continuity tester A device (such as an ohmmeter,battery and buzzer, and battery and lamp) withwhich a continuity test can be made.continuity writer The person who prepares copyfor a radio or television broadcaster.continuous carrier A medium (such as a radiofrequencywave) that will convey information (aswhen the carrier is modulated) with no disruptionof the medium itself.continuous circuit An uninterrupted circuit.Continuous Commercial Service Abbreviation,CCS. A category in which safe operating parametersare listed for electronic components andcommunications equipment operated over long,uninterrupted periods. Compare INTERMITTENTCOMMERCIAL AND AMATEUR SERVICE.

144 continuous duty • contrastCharacter SymbolA • –B– •••C– • – •D– ••E•F••– •G––•H••••I••J • –––K – • –L• – • •M ––N– •O –––P• ––•Q ––• –R• – •S• • •T –U • • –V • • • –W • ––X – • • –Y – • ––Z––• •0 –––––1 • ––––2 • • –––3 • • • ––4 • • • • –5 • • • • •6 – • • • •7 ––• • •8 –––• •9 ––––•Period • – • – • –Comma ––• • ––Query• • ––• •Slash– • • – •Dash – • • • • –Break (pause) – • • • –Semicolon– • – • – •Colon–––• • •Continental code+continuity testerTest probecontinuous duty The requirement of a device tosustain a 100-percent duty cycle for a prolongedperiod of time.continuous-duty rating A maximum current, voltage,or power rating for equipment operated forextended periods at a 100-percent duty cycle.continuous load A load that requires a continuousfeed for a prolonged period of time.continuous memory See NONVOLATILE MEM-ORY.continuous-path motion In robotics, machinemovement that occurs in a smooth fashion,rather than in discrete steps. Allows precise positioningof a mechanical arm or gripper.continuous power The maximum sine-wave powerthat an amplifier can deliver for 30 seconds.continuous recorder An instrument that providesan uninterrupted recording.continuous recording A record made on a continuoussheet or tape, instead of on separate sheetsor tapes. An example is a continuous-playingtape used for repeated public announcements.continuous spectrum 1. The range of all electromagneticfrequencies between a specified lowerlimit f 1 and a specified upper limit f 2 . 2. A rangeof electromagnetic frequencies that exhibits similarbehavior between its lower and upper limits.continuous stationery Also called fanfold paper.The pack of paper a line printer uses. It consistsof sheets connected by perforated or tear-offedges, folded in accordion fashion. It usually hastear-off perforated strips along either side to facilitatefeed through the printer mechanism.continuous variable A variable that can attain anyvalue within a specific range of values. An exampleis a frequency within the 75- to 80-meter amateurradio band, from 3.5 to 4.0 MHz.continuous wave Abbreviation, CW. 1. A periodicwave, such as a radio-frequency (RF) carrier, thatis not interrupted at any point between its normalstart and termination, and that is unmodulated.2. An RF carrier that is interrupted digitally witha keying device according to some code (such asMorse), for the purpose of conveying information.continuous-wave laser See CW LASER.continuous-wave radar See CW RADAR.contour A control on an audio reproduction systemthat increases the base and treble amplitudesat low levels to compensate for the ear’snatural losses in these ranges. Alternatively, thiscontrol can attenuate signals in the 3-kHz region,where the human ear is most sensitive.contours of equal loudness See AUDIBILITYCURVES.CONTRAN A computer language that requires nocompiler, or translating, interface between theoperator and the machine. The programming isdone in a language similar to machine language.contrast 1. In a video image, the degree to whichadjacent areas of a picture are differentiated. Insufficientcontrast makes for a “flat” picture; ex-

control circuit 1. A circuit in which one signal orprocess is made to control another signal or procontrast• controlling file 145maxOutput levelminlowBassMidrangeFrequencycontourTreblehighcessive contrast, a “hard” picture. 2. In opticalcharacter recognition, the degree to which a characteris distinguishable from its background.contrast control A potentiometer for adjusting thegain of the video in a television receiver or cathode-ray-tube(CRT) computer display and, accordingly,the image contrast.contrast range In an image or pattern, the brightnessrange from the lightest to the darkest parts.contrast ratio In a video image, the ratio of maximumto minimum luminance.control 1. An adjustable component, such as arheostat, potentiometer, variable capacitor, orvariable inductor, that allows some quantity to bevaried at will. 2. A test or experiment conductedsimultaneously with another similar test conductedunder conditions lacking the factor underconsideration. Thus, if 100 resistors coated witha special varnish are tested at 120°F, 100 identicalunvarnished resistors could be tested (as acontrol) under the same conditions; in this way,the effect of the varnish would be ascertainable.3. As a computer function, understanding andimplementing instructions or carrying out tasks,according to specific conditions.control ampere-turns The ampere-turns of thecontrol winding in a magnetic amplifier.control block A storage block for control informationin a computer.control bus In a digital computer, the electricalconductors linking the central-processing-unit(CPU) control register to the memory circuits.control card A card that provides control informationfor a computer.control character A character (bit group) used tostart the control of a peripheral.control characteristic A representation (such as acollector-current versus collector-voltage curve)depicting the extent to which the value of onequantity affects or controls the value of another.cess. 2. In a digital computer, a circuit that handlesand interprets instructions and commands,particularly in the arithmetic and logic unit(ALU).control computer A computer that receives signalsconcerning the parameters in some process,and responds with signals that control those parameters.control counter See CONTROL REGISTER.control data 1. In a computer record having a key,information used to put the records in some sequence.2. Information affecting a routine’s selectionor modification.control electrode An electrode to which an inputsignal can be applied to control an output signal.Common examples are the base of a bipolar transistor,the gate of a field-effect transistor, and theinputs of a logic gate.control field 1. In direct-current generators of theamplifying type, an auxiliary field winding usedfor feedback and regulation, in contrast to theself-excited field winding (which is the conventionalfield winding of the generator). 2. A computerrecord field containing control data.control flux In an amplidyne, magnetic flux generatedby current flowing through the control winding.control grid See GRID, 1.control-grid bias The negative dc voltage appliedbetween ground and the control grid of a vacuumtube to establish the operating point.control language Within the operating system of acomputer, the command set that the operator orprogrammer uses to control the running of a programor the operation of peripherals. Also calledjob control language or system control language.control language interpreter See CONTROL LAN-GUAGE and INTERPRETER.controlled avalanche diode Also called avalanchediode or Zener diode. A diode that has a welldefinedavalanche voltage. Used primarily forvoltage regulation in power supplies.controlled-carrier modulation See QUIESCENTCARRIER OPERATION.controlled-carrier transmission See QUIESCENTCARRIER OPERATION.controlled rectifier A rectifier whose dc outputcan be varied by adjusting the voltage or phase ofa signal applied to the control element. SeeSILICON-CONTROLLED RECTIFIER.controller1. The control signal of an electroniccontrol (or servo), system. 2. A device, such as aspecialized variable resistor, used to adjust currentor voltage. 3. A computer that oversees andcontrols the operation of a robot or fleet of robots.controller function The control of the movementsof a servo system.controlling file A computer storage area encompassingseveral complete magnetic disk cylinders;its size can be changed to accommodate anumber of files.

146 control loop • convergence magnetcontrol loop See CONTROL TAPE.control mark See TAPE MARK.control panel 1. An accessible surface on which aremounted switches, buttons, potentiometers, meters,digital indicators, monitoring devices, andother apparatus essential to regulating and supervisingan electronic system. 2. The console that acomputer operator or programmer uses to communicatewith the central processing unit (CPU).control plate The metallic plate or disk that servesas the antenna of a CAPACITANCE RELAY orTOUCHPLATE RELAY.control program A program that arranges computer-operationprograms in a certain order. Putsinformation in the computer memory for lateruse.control rectifier A semiconductor diode device,used for the purpose of switching large currents.A small control signal can provide switching ofhigh-power devices.control register In a computer, the register thatstores the address of the next instruction in theprogram being run.control sequence The order in which instructionsare executed in a digital computer.control stack In a computer system, a unit ofhardware having storage locations and used toperform arithmetic, assist in allocating memoryto programs, and to control internal processes.control statement In a programming language, aninstruction that causes some action to be taken,as specified by a condition; it is also applicable tosource program statements that affect the compiler’soperation without modifying the machinecode.control tape Punched paper or plastic tape in theform of a closed loop and used to control printingdevices. Also called control loop.control total For a file or record group, a total derivedduring an operation; it is used to verify thatall the records have been processed similarly.control transfer The situation in which the controlunit of a digital computer leaves the main sequenceof instructions and takes its next instructionfrom an out-of-sequence address.control transfer instruction See BRANCH IN-STRUCTION.control-voltage winding In a servomotor, thewinding that receives a varying voltage of a phasedifferent from that applied to the fixed-voltagewindings.control winding In a magnetic amplifier, the windingthat conducts the control-signal current.control word A word (a bit group) stored in a computermemory and used for a control function.convection The flow of a gas or liquid that results inthe transfer of heat from one location to another.convection cooling The removal of excess heatfrom a component, such as a power vacuum tubeor transistor, via upward movement of surroundingair that has been heated by the component.TransistorAir currentsAir currentsconvectioncoolingHeatsinkconvection current 1. The motion of current carriersor a charge across the surface of a conductoror dielectric. 2. Air currents rising above aheat source or heated body.convective discharge The continuous highvoltagecurrent discharge across a spark gap.convectron A device that indicates the angle, withrespect to the vertical, based on convection coolingof a straight wire. The temperature differenceis greatest when the angle is 0 degrees (the wire isvertical); the temperature difference decreases asthe angle increases, reaching a minimum at 90degrees (when the wire is horizontal).convenience outlet 1. In North America, a walloutlet providing a nominal 117 volts alternatingcurrent (ac) at 60 Hz for common household appliances.2. An outlet in a laboratory that providespower for a certain application.conventional current The notion that currentflows from the positive pole to the negative pole inan electric circuit. This representation is usedmost often by physicists. Electron flow is oppositeto conventional current flow; positively chargedparticles, such as holes, move in the same directionas the conventional current.convergence 1. The eventual meeting of values orbodies at some point (sometimes at infinity, as incertain mathematical series). 2. The intersectionpoint of the beams from separate electron guns ina cathode-ray tube (CRT).convergence coil One of a pair of coils used in acolor television receiver to produce dynamic beamconvergence (see CONVERGENCE, 2).convergence control In a color television receiver,a potentiometer in the high-voltage circuit for convergenceadjustment (see CONVERGENCE, 2).convergence electrode An electrode that providesan electrostatic field for converging electronbeams. Compare CONVERGENCE MAGNET.convergence frequency The frequency of the lastmember of a spectrum series.convergence magnet An assembly that provides amagnetic field to converge electron beams. CompareCONVERGENCE ELECTRODE.

convergence phase control • coordinates 147convergence phase control In a three-gun colorpicture tube, a variable resistor or variable inductorused to adjust the phase of the dynamic convergencevoltage.convergence plane 1. In a color picture tube, theplane in which the red, green, and blue beams allfocus. 2. In a cathode-ray tube, the plane inwhich the electron beam reaches its sharpest focus.convergent series A mathematical series that approachesa specific, finite numerical value as thenumber of terms increases. Thus, the series 0.3 +0.03 + 0.003 + . . . approaches a limiting value of1⁄3. Compare DIVERGENT SERIES and INFINITESERIES.converging lens A lens having a real focus for parallelrays; generally a convex lens.conversational compiler In computer operations,a compiler that, using the CONVERSATIONALMODE of operation, shows the programmerwhether or not each statement entered into thecomputer is valid, and whether or not to proceedwith the next instruction.conversational mode High-level computer operationor programming, in which the computergives responses to the operator’s input.conversion 1. The deliberate mixing of radiofrequency(RF) signals to produce signals at thesum and/or difference frequencies. 2. The processof changing direct current (dc) to alternatingcurrent (ac). 3. The process of changing low-voltagedc to high-voltage dc. 4. The changing of acomputer file to another format and, possibly,transferring it to a different storage medium (e.g.,from tape to internal memory). 5. The processingof a program or file written for one computer orapplication into a form suitable for another computeror application.conversion efficiency In a converter (see CON-VERTER, 1), the ratio of output-signal amplitudeto input-signal amplitude. For example, ina superheterodyne converter, a large intermediate-frequency(IF) output for a low radiofrequency(RF) input indicates high conversionefficiency.conversion equipment In a computer system, anoffline device for transferring data from onemedium to another [e.g., a disk-to-tape converter(tape drive)]. Also called CONVERTER.conversion exciter An exciter for transmitters, inwhich an output signal of a desired frequency isobtained by beating the output of a variablefrequencyself-excited oscillator with the outputof a fixed-frequency oscillator (such as a crystaloscillator).conversion gain Amplification as a byproduct ofconversion. See CONVERSION EFFICIENCY.conversion loss Conversion gain of less than 1.conversion program In computer operations, aprogram for data conversion (see CONVERSION,4 and 5).conversion rate Also called sampling rate. Thenumber of samples per second taken by anANALOG-TO-DIGITAL CONVERTER.conversion time In digital computer operation,the time required for the machine to read out allthe digits in a coded word.conversion transconductance See CONVERSIONEFFICIENCY.convert 1. To perform frequency conversion (seeCONVERSION, 1). 2. To perform voltage conversion(see CONVERSION, 2 and 3). 3. In computeroperations, to change information from one numberbase to another. 4. To perform data conversion(see CONVERSION, 4 and 5).converter 1. A heterodyne mixer in which two inputsignals of different frequency are mixed toyield a third (output) signal of yet a different frequency.2. A machine for converting direct current(dc) to alternating current (ac) (e.g., achopper converter). 3. A transistor circuit for convertinga low-voltage dc to higher-voltage dc. 4.Conversion equipment. 5. A circuit or device thatchanges analog data to digital data or vice versa.converter amplifier See CHOPPER AMPLIFIER.converter stage A circuit used principally to mixtwo signals (such as a received signal and localoscillatorsignal in a superheterodyne receiver),and deliver the resultant signal.convexo-concave Pertaining to a lens having aconvex face of greater curvature than its concaveface.coolant A liquid (often water or oil) used to removeheat from an electronic component.Coolidge X-ray tube An X-ray tube containing aheated filament (with focusing shield) and aslanting tungsten target embedded in a heavycopper anode.cooling Maintenance of the operating temperatureof an electronic component or system at a safelevel. Common devices for cooling are heatsinks,circulating or forced air, and circulating liquid.coordinate bond A covalent bond that consists ofa pair of electrons supplied by only one of theatoms joined by the bond.Coordinated Universal Time Abbreviation, UTC.Astronomical time at the Greenwich meridian(zero degrees longitude). The UTC day begins at0000 hours and ends at 2400 hours. Based onthe mean, or average, synodic (sun-based) rotationalperiod of the earth. The earth is slightly behindUTC near June 1, and is slightly ahead nearOctober 1.coordinate digitizer A device or circuit that encodesa coordinate graph into digital signals forstorage or transmission.coordinate of chromaticity See CHROMATICITYCOORDINATE.coordinates A set of axes with points that can beuniquely defined or located on a line, in a plane,or in space. See CARTESIAN COORDINATES andPOLAR COORDINATES.

148 coordinate system • cordless modemcoordinate system A mathematical means ofuniquely defining or locating a point on a line, ina plane, or in space. The most common coordinatesare CARTESIAN COORDINATES (alsocalled rectangular coordinates), consisting ofnumbered lines intersecting at right angles.642−6 −4 −2 2 4 6−2−4−6ycoordinate system(Cartesian)coordination complex An ion or compound havinga central (usually metallic) ion combined bycoordinate bonds with a definite number of surroundinggroups, ions, or molecules.coplanar array A set of antennas that lie in thesame plane, and are fed by a common transmissionline.copper Symbol, Cu. A metallic element. Atomicnumber, 29. Atomic weight, 63.546. An excellentconductor of electricity and heat, commonly usedin the manufacture of wires and cables.copper-clad wire Iron or steel wire plated withcopper.copper-constantan thermocouple A thermocoupleconsisting of a junction between wires orstrips of copper and constantan. Typical outputis 4.24 mV at 100°C.copper loss Power (I 2 R) loss in copper wires, cables,and/or coils.copper-oxide diode A small diode in which thesemiconductor material is copper oxide. Suchdiodes, widely used before the ready availabilityof selenium and silicon, are still occasionallyfound in meter-rectifier service.copper-oxide modulator An amplitude modulatorwhose action is derived from the nonlinear conductioncharacteristic of copper-oxide diodes.copper-oxide photocell A photoelectric cell inwhich the light-sensitive material is copper oxide.copper-oxide rectifier A rectifier in which thesemiconductor material is copper oxide. Rectifiersof this type are suitable for low-voltage ser-xvice; they were widely used before the advent ofgermanium, silicon, and selenium rectifiers.copper pyrites See CHALCOPYRITE.copper-sulfide rectifier A rectifier in which theunilateral junction is between copper-sulfide andmagnesium elements. Like the copper-oxide rectifier,the copper-sulfide unit was once widelyused in low-voltage applications.copy 1. Also called hard copy. Printed or writtentext. 2. In communications, a qualitative expressionof the extent to which received data is intelligible(e.g., a radio operator’s signal report, “Youare solid (perfect) copy.”). 3. To duplicate data ina storage system, the original being in anothersystem, or in a different location in the samesystem. 4. An exact duplicate of data in anyform.copying telegraph A descriptive term for a facsimilesystem.Corbino disk A variable resistor consisting of asemiconductor disk capable of exhibiting theCORBINO EFFECT. The disk is inserted into anadjustable magnetic field, which serves as thecontrol medium.Corbino effect A phenomenon similar to the HALLEFFECT, in which a current flows around a diskcarrying a radial current when the disk is insertedinto a magnetic field whose lines of flux areperpendicular to the disk. Compare HALL EF-FECT.Semiconductordisk+MagneticfieldCorbino effectCurrentflowcord 1. A length of flexible, insulated cable, usuallyhaving two or three conductors. 2. Tough, insulatingstring (e.g., dial cord or lacing cord).cordless 1. Descriptive of a plug without a flexiblecord. 2. Pertaining to radio-frequency (RF) or infraredshort-range links for communications andcontrol (e.g., a cordless telephone set).cordless keyboard A computer keyboard that employsan infrared (IR), very-high frequency (VHF),or ultra-high-frequency (UHF) transmitter and receiver.Commonly used with so-called Web TVsystems and in presentations using a display projectionsystem. Operates according to the sameelectronic scheme as a CORDLESS MOUSE.cordless modem See WIRELESS MODEM, 3.−

cordless mouse • corner reflector 149cordless mouse A hand-controlled computermouse that employs an infrared (IR), a very-highfrequency (VHF), or an ultra-high-frequency(UHF) transmitter and receiver. The transmitteris inside the device, and the receiver is containedeither inside the computer main unit, or in asmall box attached to the computer main unit bya cord. The box can be placed somewhere out ofthe way; for example, at the back of the desk.Then the mouse can be moved around freely. Thislink is effective at distances of up to 20 or 30 feet.cordwood A type of construction in which electroniccomponents are sandwiched perpendicularlybetween layers of components. So calledbecause it looks somewhat like stacked cordwood.cordwood module A module containing discretecomponents mounted perpendicularly betweentwo parallel printed circuits.core1. The body or form on which a coil or transformeris wound. Can be made of ferromagneticor dielectric material. The properties depend onthe application. 2. CORE MEMORY.core dump Dumping core memory content to anoutput peripheral. Also see DUMP.coreless induction heater An induction heater inwhich the body to be heated receives energy directlyfrom the field of the energizing coil (there isno intervening core). Compare CORE-TYPE IN-DUCTION HEATER.core loss Loss of energy in a magnetic core, causedby eddy currents and hysteresis in the core material.core memory An older memory technology, consistingof a series of small ringshaped magneticcores, into or out of which data can be written orread by changing the magnetization of the cores.core planeA usually flat assembly of special magneticcores, through which pass associatedcurrent-conducting wires to provide a COREMEMORY.core saturation The condition in which a core ofmagnetic material accommodates the maximumnumber of magnetic lines characteristic of thatmaterial. Increasing the magnetizing force producesno additional magnetization.core shift register A shift register that uses specialmagnetic cores as bistable components. SeeCORE MEMORY.core storage A high-speed magnetic core storageunit. Also see CORE MEMORY and CORE PLANE.core transformer A transformer whose coils arewound around a ferromagnetic core.core wrapping The placing of an insulating layerover an inductor or transformer core. This minimizesthe chances of short-circuiting between thewindings and the core material.core-type induction heater An induction heaterin which the body to be heated is magneticallylinked, by a core, to the energizing coil. CompareCORELESS INDUCTION HEATER.corner 1. An abrupt turn in the axis of a waveguide.2. The line, and the region in the vicinitythereof, at which two intersecting plane surfacesmeet (e.g., the reflector screen of a CORNER-REFLECTION ANTENNA). The plane surfaces areusually perpendicular to each other. 3. The point,and the region in the vicinity thereof, at whichthree intersecting plane surfaces meet. Generally,the plane surfaces are mutually perpendicular. 4.The passband frequency limit(s) of a bandpass,band-rejection, high-pass, or low-pass filter. 5. Asharp bend in the attenuation-versus-frequencycurve of a bandpass, band-rejection, high-pass,or low-pass filter, depicting the limit(s) of thepassband.corner diffraction 1. The bending of sound wavesaround a corner. 2. The bending of radiofrequency(RF) energy around an object, when thewavelength is great, compared with the size of theobject.corner effect A rounding off of the frequency responseof a filter at the corner(s) [i.e., at thelimit(s) of the passband].corner frequency See CORNER, 4.corner reflection The reflection of a beam of light(or of microwave energy or other short-wavelengthenergy) from a corner reflector, so thebeam leaves the reflector in exactly the oppositedirection from which it approaches. See CORNERREFLECTOR, 2.corner-reflection antenna A directional antennaconsisting of a dipole radiator situated at theapex formed by two nonparallel, flat reflectingsheets or a single folded sheet. See CORNER RE-FLECTOR, 1.corner reflector 1. An antenna with a half-wavedriven element and a reflector made of wire mesh,screen, or sheet metal that resembles an openfolder. The flare angle of the reflecting element isabout 90 degrees. The antenna is used at ultra-

150 corner reflector • corrosion-resistantcorner reflector, 2high and microwave frequencies for television receptionand satellite communications. Sometimesseveral half-wave dipoles are fed in phaseand arranged along a common line with a single,elongated reflector. 2. Also called tricorner reflector.A set of three flat metal surfaces or screens,attached together in a manner identical to theway two walls meet the floor or ceiling in a room.Such a device, if it is at least several wavelengthsacross, returns electromagnetic energy in exactlythe same direction from which it arrives. Devicesof this type are used as radar dummy targets andin optical and infrared (IR) wireless rangingsystems.corona A luminous discharge in the space surroundinga high-voltage conductor; caused byionization of the air. The discharge constitutes aloss of energy.corona effect The production of a luminous discharge,especially at the end of a pointed terminal,when the voltage gradient reaches a criticalvalue.corona failure A form of high-voltage failure, resultingfrom the erosion of an object (such as anelectrical insulator) by corona.corona loss Loss caused by energy dissipationthrough a corona. It occurs as a result of theemission of electrons from the surface of electricalconductors at high potentials, and dependson the curvature of the conductor surface, withmost emission occurring from sharp points andthe least from surfaces with a large radius of curvature.It is often accompanied by a blue glowand a crackling or hissing sound.corona resistance The length of time that an insulatingmaterial can withstand a specified level offield-intensified ionization before completelybreaking down.corona shield A shield surrounding a high-voltagepoint to prevent corona by redistributing the electricflux.corona starting voltage The minimum voltage betweentwo electrodes, or on a single electrode infree space, at which corona occurs.corona voltmeter A voltmeter used to measure thepeak value of a voltage in terms of corona discharge.It consists of a metal tube in which a centralwire is mounted, the parts being connected tothe voltage source. The air density in the tube isvaried until corona occurs.corpuscle A tiny particle. It was the name given tothe ELECTRON by some early experimenters andtheorists.correction 1. The addition of a factor that providesgreater accuracy in a measurement. 2. A changein the calibration of an instrument to increase theaccuracy.correction factor A percentage, or numerical factor,added to or subtracted from a reading to providea greater degree of accuracy. Often used withinstruments known to be inaccurate by a certainamount.corrective feedback Feedback that is used to correct(bring to a prescribed level) a quantity constitutingthe input to a system.corrective maintenance The repair of a circuit orsystem after it has malfunctioned or brokendown.corrective network A network that improves theperformance of the circuit into which it is inserted.corrective stub A combination tuning-matchingstub used in some antenna systems. It matchesthe resistive component of the antenna impedanceto the characteristic impedance of a feedline, and also eliminates any reactance thatmight be present at the antenna feed point.correed relay A sealed reed relay used as a highspeedswitching device in communications equipment.correlation A statistical expression or measure ofthe degree to which two sets of data are related.Can be given qualitatively (high-positive, lowpositive,zero, low-negative, or high-negative) orquantitatively (as a number between –1 and 1).Does not necessarily imply causation.correlation detector A detector that compares asignal of interest with a standard signal at everypoint, delivering an output that is proportional tothe correspondence between the two signals.correlation distance The smallest distance betweentwo antennas that results in fading of signals underconditions of tropospheric propagation. It isused at very-high frequencies (VHF) and above, todetermine the maximum range over which communicationscan be carried out reliably.correlation tracking A method of target trackingin which phase relationships are used to determinepositions.correspondence The ability of a binocular machinevision system to tell when both of its opticalsensors are processing an image from the sameobject; also, the ability of the system to keep bothsensors tracking the same object.corrosion-resistant Pertaining to materials thatare treated to be immune to corrosion by the elements.Such substances are preferable for use inmarine or tropical environments, where corrosionis especially severe.

corruption • counterpoise 151corruption The altering of data or a code as a resultof a program error or machine fault.COS Abbreviation of COMPLEMENTARY-SYMME-TRY CIRCUIT.cosecant Abbreviation, csc. A trigonometric function;csc q = c/a, where c is the hypotenuse of aright triangle and a is the side opposite q. Thecosecant is the reciprocal of sine: csc q = 1/sin q.cosecant-squared antenna A radar antenna thatradiates a COSECANT-SQUARED BEAM.cosecant-squared beam A radar beam whose intensityvaries directly with the square of the cosecantof the angle of elevation.cosech Abbreviation of HYPERBOLIC COSECANT.Also abbreviated as csch.cosh Abbreviation of HYPERBOLIC COSINE.cosine Abbreviation, cos. A trigonometric function;cos q = b/c, where b is the side adjacent to q andc is the hypotenuse of the right triangle.cosine law The brightness in any direction from aperfectly diffusing surface is proportional to thecosine of the angle between the direction vectorand a vector perpendicular to the surface.cosine wave A periodic wave that follows the cosineof the phase angle. It has a shape identicalwith a SINE WAVE, but differs by 90 degrees ofphase.cosine yoke A magnetic-deflection yoke that hasnonuniform windings for improved focus at theedges of a television picture. Also called anastigmaticyoke and full-focus yoke.cosmic noise Radio noise produced by signalsfrom extraterrestrial space.cosmic rays Extremely penetrating rays consistingof streams of atomic nuclei entering the earth’satmosphere from outer space.COS/MOS IC An integrated circuit (IC), such as anoperational amplifier, utilizing metal-oxide-semiconductor(MOS) field-effect transistors in a complementary-symmetry(COS) arrangement.cost analysis In a commercial or industrial organization,ascertaining the expense associated witha service, process, or job.cot Abbreviation of COTANGENT.cotangent Abbreviation, cot. A trigonometric function;cot q = b/a, where a is the side adjacent to qand b is the side opposite q (in a right triangle).Cotangent is the reciprocal of tangent: cot q =1/tan q.coth Abbreviation of HYPERBOLIC COTANGENT.Cotton-Mouton effect See KERR MAGNETO-OPTICAL EFFECT.Cottrell process Dust precipitated by high voltage.Dust in the air is made to flow through agrounded metal chamber that contains a wiremaintained at high voltage. The dust particles becomecharged and adhere to the chamber walls,from which they are later collected.coul-cell A coulometer of the electrolytic-cell type.coulomb (Charles Augustin Coulomb, 1736–1806). Abbreviation, C. The unit of electricalcharge quantity, equal to the charge contained in6.24 × 10 18 electrons. A current of one ampere(1 A) represents 1 coulomb per second (C/s).Coulomb’s law The force between two electricallycharged objects is directly proportional to theproduct of the charge quantities in coulombs,and inversely proportional to the square of thedistance between the charge centers. This force isan attraction for opposite charges, and a repulsionfor similar charges.coulometer An instrument that measures electricalcharge quantity in coulombs. A typical versionkeeps a cumulative count of coulombs (ampereseconds)by integrating current, with respect totime. Also called coulombmeter.Coulter counter See CELL COUNTER.count 1. The number of pulses tallied by a countingsystem in a given period of time. 2. A singleresponse by a radioactivity counter. 3. A record ofthe number of times an instruction or subroutinein a computer program is executed (by increasingthe value of a variable by one, as stated in a FOR-NEXT loop, for example).countdown A decreasing count of time units remainingbefore an event or operation occursshowing time elapsed and time remaining.counter 1. A circuit, such as a cascade of flipflops,that tracks the number of pulses applied toit and usually displays the total number ofpulses. 2. A mechanism, such as an electromechanicalindicator, that tracks the number of impulsesapplied to it and displays the total. 3. Anelectronic switching circuit, such as a flip-flop orstepping circuit, that responds to sequential inputpulses applied to it, giving one output pulseafter receiving a certain number of input pulses.counter- Prefix meaning “opposite to” or “contraryto.” Examples: counter EMF, counterclockwise.counterclockwise Abbreviation, ccw. Pertaining torotational motion in a sense opposite that of atypical analog clock. Movement is to the left at thetop of the rotational circle, and to the right at thebottom of the circle. Compare CLOCKWISE.counterclockwise-polarized wave An ellipticallypolarized electromagnetic wave whose electricintensityvector rotates counterclockwise as observedfrom the point of propagation. CompareCLOCKWISE-POLARIZED WAVE.counter efficiency The sensitivity of a radiationcounter or scintillation counter to incident X-raysor gamma rays.counterelectromotive cell A cell used to counteracta direct-current voltage.counter EMF See BACK VOLTAGE and KICK-BACK.counter-meter A radioactivity instrument, such asa Geiger counter, that indicates the number of radioactiveparticles per unit time.counterpoise A means of obtaining a radiofrequency(RF) ground by using a grid of wires ortubing in a plane parallel to the earth’s surface or

152 counterpoise • CPUto average terrain. The radius of the grid is usuallyat least 0.25 wavelength, but might besmaller if the feed-point impedance of the antennais very high.counterpoise ground system A counterpoise witha radius such that resonance is obtained with aquarter-wavelength antenna operated at a heightof more than 0.25 wavelength above actualground. Usually such a system consists of threeor four radials measuring 0.25 wavelength each,and extending outward from the base of the antennanearly parallel to the average terrain.AntennaelementRadialscounterpoiseground systemFeedlineRadialscounter tube A tube, such as the Geiger-Meullertube, in which a penetrating radioactive particleionizes a gas and produces an output pulse.counter voltage See BACK VOLTAGE and KICK-BACK.counting-type frequency meter A direct-readinganalog or digital frequency meter that indicatesthe number of pulses (or cycles) per second appliedto it.count-remaining technique See COMPLEMENT-SETTING TECHNIQUE.couple Two dissimilar metals in contact with eachother or immersed in an electrolyte.coupled circuits Circuits between which energy istransferred electrostatically, electromagnetically,by some combination of the two, or by direct connection.coupled impedance The impedance that a circuit“sees” when it is coupled to another circuit. Thus,when the secondary of a transformer is terminatedwith an impedance, the primary “sees” acombination of that impedance and its own.coupler A device for transferring energy betweentwo circuits and using capacitive coupling, directcoupling, inductive coupling, or some combinationof these.coupling 1. Also called electrostatic coupling or capacitivecoupling. The linking of two circuits or de-vices by electric flux. 2. Also called magnetic couplingor inductive coupling. The linking of two circuitsor devices by magnetic flux. 3. Also calleddirect coupling. The linking of two circuits or devicesby direct connection. 4. Also called resistivecoupling. The linking of two circuits or devicesthrough a resistance. 5. Also called optical coupling.The linking of two circuits or devicesthrough an optoisolator.coupling aperture A hole in a waveguide that isused to transmit energy to the waveguide, or receivingenergy from outside the waveguide.coupling capacitor A capacitor used to conduct acenergy from one circuit to another. Also see CA-PACITIVE COUPLING.coupling coefficient See COEFFICIENT OF COU-PLING.coupling diode A semiconductor diode connectedbetween the stages of a direct-coupled amplifier.When the diode is connected in the correct polarity,it acts as a high resistance between stageswhen there is no signal, and does not pass thehigh dc operating voltage from one stage to thenext. When a signal is present, the diode resistancedecreases, and the signal gets through.coupling efficiency A measure of the effectivenessof a coupling system (i.e., the degree to which itdelivers an undistorted signal of correct amplitudeand phase).coupling loop 1. A single turn of a coupling transformer.2. A small loop inserted into a waveguideto introduce microwave energy.coupling probe A usually short, straight wire orpin protruding into a waveguide to electrostaticallyintroduce microwave energy into the waveguide.It acts like a miniature whip antenna.coupling transformer A transformer used primarilyto transfer alternating-current (ac) energyelectromagnetically into or out of a circuit.covalent binding forces In a crystal, the bindingforces resulting from the sharing of valence electronsby neighboring atoms.covalent bonding The binding together of theatoms of a material as a result of shared electronsor holes.coverage 1. The area within which a broadcast orcommunication station can be reliably heard. 2.The shielding effectiveness of a coaxial cable.coversed sine Abbreviation, covers. The trigonometricfunctional equivalent of the versed sine ofthe complement of an angle [i.e., the differencebetween the sine of an angle and unity (1)]. Thus,covers q = 1 – sin q.CP Abbreviation of chemically pure.cp 1. Abbreviation of CANDLE POWER. 2. Abbreviationof central processor.cps 1. Abbreviation of CYCLES PER SECOND. Cyclesper second, to denote ac frequency, has beensupplanted by HERTZ. 2. Abbreviation of charactersper second.CPU Abbreviation of CENTRAL PROCESSING UNIT.

CQ • critical field 153CQ A general call signal used in radio communication,especially by amateur stations, to invite aresponse from any station that hears it.Cr Symbol for CHROMIUM.cracked-carbon resistor A high-stability resistorin which the resistance material is particulatecarbon.cracker A hacker with malicious intent (also seeHACKER). Such a person attempts to gain accessto computer systems or databases in order tosteal something or inflict damage. Examples includetheft, erasure, or mutilation of data; fraudulentdebiting of bank accounts; alteration ofcredit information; and identity theft.cradle guard See GUARD WIRE.cradlephone A telephone set in which the microphoneand earphone are mounted on oppositeends of a handle. This handle, called the receiver,rests on the crossmember of a stand connected toa base containing the dial and ringing circuits.Also called French phone, French telephone, andhandset.crash 1. A condition in which a computer or networkserver becomes inoperative because of asoftware or memory-management problem. 2. Ina computer hard disk or diskette drive, contact ofthe read/write head with the surface of a disk orplatter. Usually, it is the result of excessive physicalvibration or shock.crate A foundation unit into which modules areplugged to establish a circuit.crawl 1. See CREEPING COMPONENT. 2. Thecredits (names of staff and their contribution tocontent) superimposed and moving on a televisionpicture at the end of a program.crazing The formation of tiny cracks in materials,particularly in such dielectrics as plastic and ceramic.creep See COLD FLOW.creepage Current leakage across the surface of adielectric.creeping component A quantity, such as current,voltage, or frequency, that slowly changes invalue with time.crest factor See AMPLITUDE FACTOR.crest value The maximum amplitude of a compositecurrent or voltage.crest voltmeter A peak-reading (or sometimespeak-responsive) voltmeter.crippled mode The mode of operation for a computeror other hardware in which some of thecomponents are inoperable. Compare GRACE-FUL DEGRADATION.crisscross neutralization See CROSS-CON-NECTED NEUTRALIZATION.crisscross rectifier circuit A conventional bridgerectifier circuit configured in such a way that twoof the diodes are connected in crisscross fashionbetween the input and output terminals.critical angle 1. In radio communications, an angleof departure that a transmitted electromag-netic field subtends, with respect to the horizonat the transmitting (TX) point, below which theionosphere will reliably return the signal to theearth, and above which the ionosphere will notreliably return the signal. This angle (shown bythe double arc marked X in the drawing) dependson the frequency of the transmitted electromagneticwave, and also on ionospheric conditions. 2.For an electromagnetic wave or ray approachinga boundary at which the index of refractionabruptly decreases, the minimum angle of incidence(relative to a line perpendicular to a planetangent to the boundary) at which the energy istotally reflected.TXXEarth’s surfacecritical angle, 1Ionized layercritical characteristic A parameter that has a disproportionateeffect on other variables. A smallchange in this characteristic can result in a largechange in the operating conditions of a circuit orsystem.critical component A component or part that isespecially important in the operation of a circuitor system.critical coupling The value of coupling at whichmaximum power transfer occurs. Increasing theextent of coupling beyond the critical value decreasespower transfer.critical damping The value of damping that yieldsthe fastest transient response without overshoot.critical dimension The cross-sectional size of awaveguide that determines its minimum usablefrequency.critical failure A component or circuit failure thatresults in shutdown of a system, or a malfunctionthat results in improper operation.critical field The smallest magnetic-field intensityin a magnetron that keeps an electron, emittedfrom the cathode, from reaching the anode.

154 critical frequency • cross modulationcritical frequency For a particular layer of theionosphere, the high frequency at which a verticallypropagated wave is no longer reflected backto the earth.critical inductance In a choke-input powersupplyfilter, the minimum inductance that willmaintain a steady value of average load current.critical potential The potential difference requiredfor an electron to excite or ionize an atom withwhich it collides.critical voltage The voltage at which a gas ionizes.critical wavelength The wavelength that correspondsto CRITICAL FREQUENCY.CRO Abbreviation of cathode-ray oscilloscope.Crookes dark space In a glow-discharge tube, thenarrow dark space next to the cathode. Also seeCROOKES TUBE.Crookes tube A glow-discharge tube containing ananode, cathode, and a small amount of gas underlow pressure.cross antenna An antenna in which two (usuallyequal-length) horizontal radiators cross eachother at right angles and are connected togetherto a feeder at their point of intersection. It takesits name from its horizontal-cross shape.cross assembler A program used with one computerto translate instructions for another computer.crossband operation 1. Communications in whichtwo frequency bands are used. Station X, for example,might transmit on frequency f A in band Aand receive on frequency f B in band B; station Ywould then transmit on f B and receive on f A . 2. Insatellite communications, the use of two frequencybands to facilitate full-duplex operationand to allow the satellite transponder to effectivelyfunction. The transponder receives signalsfrom the earth within a specific frequency band,and converts this entire band of signals to a set ofsignals that occupies an equal amount of spectrumspace on another frequency band. The convertedsignals are then retransmitted back toearth.crossbar switch A three-dimensional array ofswitch contacts in which a magnetic selectorchooses individual contacts, according to theircoordinates in the matrix.cross bearings A method of radionavigation, inwhich directional readings are taken from a receivingstation (such as a ship or aircraft) for twofixed transmitting stations whose locations areknown. Lines are drawn on a map from the transmittingstations, in directions 180 degrees oppositethe bearings obtained from the receivingstation. The intersection point of these lines is thelocation of the receiving station.cross beat A spurious frequency arising fromCROSS MODULATION.cross-check To compare the result of a calculationor computer routine with the result obtained by adifferent method.cross color In the chrominance channel of a colortelevision receiver, crosstalk interference causedby monochrome signals.cross-connected neutralization Neutralization ofa push-pull amplifier by feedback through twocapacitors—each connected from the output circuitof one transistor to the input circuit of theother.cross-coupled multivibrator A multivibrator circuitin which feedback is provided by a couplingcapacitor between the output of the second stageand the input of the first stage; the stages areforward-coupled by a capacitor of the same value.cross coupling 1. The state of being cross-coupled(see, for example, CROSS-COUPLED MULTIVI-BRATOR). 2. Undesired coupling between two circuits.cross current A current that flows in the oppositedirection from some other current.crossed-pointer indicator 1. Also called crossedneedlemeter. A combination of two analog meteringinstruments in one case. Each needle has itsown independently calibrated scale. A third scalecorresponds to the intersection point of the needles.Commonly used in directional wattmetersthat simultaneously show forward power, reflectedpower, and standing-wave ratio (SWR). 2.A two-pointer meter used in aircraft to show theposition of the aircraft, relative to the glide path.crossed-wire thermoelement Two wires or stripsof dissimilar metals joined or twisted at a pointthat constitutes a thermoelectric junction. Inusual operation, a high-frequency current ispassed through one wire, and a proportionaldirect-current (dc) voltage, generated by thermoelectricaction, appears at the other wire.cross flux The magnetic flux component that isperpendicular to the flux produced by field magnets.cross-hair pattern A television test pattern consistingof a single vertical line and a single horizontalline, which form a simple cross. Thepattern resembles the cross hairs of an optical instrument.crosshatch generator A modulated radiofrequency(RF) signal generator that produces acrosshatch pattern on a picture-tube screen.crosshatch pattern A grid of horizontal and verticallines produced on a picture-tube screen by across-hatch generator. It is used in checking horizontaland vertical linearity.cross modulation 1. A type of radio-frequency interference(RFI) between two strong stations thatare close in frequency. The desired carrier is modulatedby the interfering signal. 2. The productionof signals by rectifier junctions in pipes andwiring near a radio receiver. These objects pickup waves and deliver energy at a different frequency,which finds its way into the receiver. Alsocalled external cross modulation. 3. The interactionbetween signals of different frequency when

cross modulation • cryotron 155they magnetize a core of nonlinear magnetic material.Also see CROSSTALK.cross-modulation factor An expression of theamount of cross modulation (or crosstalk) presentin a particular instance. It is equal to M 1 /M 2 ,where M 1 is the modulation percentage that amodulated wave produces in a superimposed unmodulatedwave, and M 2 is the modulation percentageof the modulated wave.cross-neutralized circuit See CROSS-CON-NECTED NEUTRALIZATION.crossover 1. In a circuit diagram, a point at whichlines representing wires intersect, but are notconnected. 2. In a characteristic curve, point atwhich the plot crosses an axis or operating point.3. See CROSSOVER NETWORK.crossover distortion Distortion of a characteristicat a crossover point (see CROSSOVER, 2); for example,a bend in the curve where the plot of awaveform passes through zero.crossover frequency The frequency at which acrossover network delivers equal power to the twocircuits it supplies.crossover network Following final amplification ina sound-reproduction system, an outboard filtercircuit that facilitates delivery of the low and highaudio frequency (AF) components to the correctspeakers.crossover point See CROSSOVER, 2.crossover S-curve The S-shaped image obtainedon an oscilloscope screen during sweep-generatoralignment of a frequency-modulation (FM) detector.In correct alignment, the exact center of theS-curve (the crossover point) coincides with thezero point on the screen.cross product Also called vector product. For vectorsA and B having lengths A and B, respectively,and subtending an angle θ relative to each other,the cross product A × B points in a direction perpendicularto the plane containing both A and B.The length of A × B is equal to AB sin θ.zAyθA × BBcross productxcross-sectional area 1. The surface area of a faceof a conductor after cutting through it at a rightangle. Specified in square inches, square millimeters,or circular mils. 2. The total of the crosssectionalareas of all the wires in a strandedconductor.cross-sectional testing In quality assurance andquality control (QA/QC), a method of checking alarge lot of units or components. Instead of testingevery device, a fraction of the devices istested. The sampling is taken uniformly from thegroup (e.g., every fifth unit).crosstalk Undesired transfer of signals between oramong telephone lines, data lines, or systemcomponents. In computer operations, this effectplaces a practical limit on the lengths of paralleldata cables.crosstalk coupling Undesired coupling betweencircuits, caused by crosstalk.crosstalk factor See CROSS-MODULATION FAC-TOR.crosstalk level The amplitude of crosstalk, usuallyexpressed in decibels above a reference level.crosstalk loss Loss of energy caused by crosstalk.crowbar An action producing a high overload on acircuit protection device.crowfoot 1. A pattern formed by the cracking orcrazing of solid plastics of solidified encapsulatingcompounds, so called from its resemblance toa bird’s footprint. 2. In a gravity battery cell, thezinc electrode, so called from its resemblance to abird’s foot.CRT Abbreviation of CATHODE-RAY TUBE.crud 1. Broadband electrical noise, originating insideand/or outside a system. 2. Undesired signalsthat interfere with a desired signal.cryogenic device A device that exhibits uniqueelectrical characteristics (such as superconductivity)at extremely low temperatures.cryogenic motor A motor designed for operationat extremely low temperatures.cryoelectronics The study of the behavior of electronicdevices, circuits, and systems at extremelylow temperatures.cryogenics The branch of physics dealing with thebehavior of matter at temperatures approachingabsolute zero. Also concerned with methods ofobtaining such temperatures in controlled environments.cryosar A semiconductor switch utilizing lowtemperatureavalanche breakdown.cryoscope An instrument used to determine freezingpoint.cryostat A chamber for maintaining a very lowtemperature for cryogenic operations. Also seeCRYOGENICS.cryotron A switching device consisting essentiallyof a straight tantalum wire, around which asingle-layer control coil is wound. The magneticfield generated by control current flowing throughthe coil causes the tantalum wire to become

156 cryotron • crystal loudspeakersuperconductive at a temperature of approximately4.4 degrees K.cryotronics Low-temperature electronics, concernedwith such phenomena as superconductivity.The term is an acronym from cryogenics andelectronics. Also see CRYOGENICS.cryptanalysis The breaking of ciphers.crypto- A prefix added to words, that implies encodingfor the purpose of changing or hiding themeaning of a message or signal.cryptography The creating and writing of ciphers.cryptology The art and science of creating, writing,unscrambling, and breaking ciphers.crystal 1. A material distinguished by the arrangementof its atoms into a redundant pattern calleda lattice that presents, in fragments of varioussizes, a characteristic polyhedral shape. Commonshapes include cubes, parallelepipeds, andhexagonal prisms. 2. A fragment of material asdefined in (1). 3. A plate or bar cut from a piece ofpiezoelectric material.crystal amplifier 1. A semiconductor diode circuitusing carrier storage. Transistor action and, accordingly,pulse amplification is obtained by alternatelymaking one electrode of the diode anemitter or collector. 2. Archaic term for TRANSIS-TOR.crystal audio receiver An audio radar receiver,consisting of a crystal detector and audio-amplifierstages.crystal axes The imaginary lines traversing a piezoelectriccrystal, along which (or perpendicularto which) plates are cut for oscillators, resonators,or transducers.crystal calibrator A crystal oscillator used togenerate harmonic checkpoints for frequencycalibration. Common fundamental calibratorfrequencies are 100 kHz and 1 MHz.crystal capacitor See VARACTOR.crystal control The control of the operating frequencyof a circuit by means of a piezoelectriccrystal.crystal-controlled receiver A superheterodyneradio receiver whose local oscillator is crystalcontrolled.crystal-controlled transmitter A radio transmitterwhose master oscillator is crystal controlled.crystal counter A device for counting the frequencyof subatomic particles, based on theirability to change the conductivity of a crystal. Theparticles can be photons, electrons, protons, neutrons,or the nuclei of atoms.crystal current Current flowing through a crystal;specifically, the radio-frequency (RF) currentflowing through a quartz plate in a crystalcontrolledoscillator.crystal cuts The classification of piezoelectricplates according to the angle at which they werecut from a quartz crystal. Common cut designationsare AT, BT, CT, DT, X, Y, and Z. Variouscuts afford such complementary factors as fre-X cut35°Z axis(center of crystal)quency, temperature, and thickness. Also seeCRYSTAL AXES.crystal detector A rudimentary form of semiconductordiode consisting of a mounted lump ofmineral (the crystal) in contact with a springywire (“cat’s whisker”). The point of the wire ismoved to various points of contact on the crystalsurface until the most-sensitive rectifying spot isfound.crystal diffraction The tendency of electromagneticwaves to be scattered when passing througha crystal material.crystal diode Archaic term for SEMICONDUCTORDIODE. Also see GALLIUM-ARSENIDE DIODE;GERMANIUM DIODE; JUNCTION DIODE; LASERDIODE; POINT-CONTACT DIODE; SELENIUMDIODE; SIGNAL DIODE; SILICON DIODE.crystal earphone An earphone in which the transduceris a piezoelectric crystal. Electrical impulsesapplied to the crystal vary its shape andcause a vibration that is transmitted to a diaphragm;this in turn produces correspondingsound waves.crystal filter See CRYSTAL RESONATOR.crystal headphone See CRYSTAL EARPHONE.crystal holder A fixture specially designed to holda piezoelectric crystal; it ensures minimum distortionof crystal dimensions and minimum residualcapacitance, inductance, and resistance.crystal imperfection A flaw in the lattice structureof a crystal.crystal lattice The orderly, redundant pattern ofatoms and molecules within a crystalline material;it is a characteristic of a given material.crystal-lattice filter A crystal resonator in whichpiezoelectric crystals are used to give a desiredshape to the filter response curve.crystalline material A material exhibiting thecharacteristic properties of a crystal (see CRYS-TAL, 1).crystallogram An X-ray photograph or otherrecord of crystal structure.crystallography The science dealing with crystalsand their properties (see CRYSTAL, 1).crystal loudspeaker A loudspeaker whose transduceris a piezoelectric crystal. Electrical impulsesapplied to the crystal vary its shape andXYcrystal cutsY cutAT cut

crystal loudspeaker • crystal tester 157cause vibrations that are transmitted to a diaphragmor cone, which produces correspondingsound waves.crystal meter A rectifier-type ac meter using asemiconductor diode in series with a dc milliammeteror microammeter.crystal microphone A microphone whose transduceris a natural or synthetic piezoelectriccrystal. Sound waves striking the crystal (directlyor via a diaphragm) vary its shape, makingit produce an audio-frequency (AF) outputvoltage.CrystalElectrodesDiaphragmSoundwavesSoundwavesOutputvoltageCrystalcrystal pulling 1. The extraction of a single crystalfrom a molten mass of crystalline material. Singlecrystals are used for high-quality semiconductordevices. Also see CZOCHRALSKI METHOD, SIN-GLE CRYSTAL, and SINGLE-CRYSTAL MATE-RIAL. 2. The use of an inductor or capacitor in acrystal-controlled radio-frequency (RF) oscillatorcircuit to allow adjustment of the frequency overa small range.crystal receiver See CRYSTAL SET.crystal rectifier 1. A semiconductor diode usedfor the purpose of rectifying alternating current(dc), usually in a power supply.crystal resistor A temperature-sensitive resistormade from silicon, and exhibiting a positive temperaturecoefficient of resistance.crystal resonator A highly selective resonant circuitin which the center frequency is the resonantfrequency of a piezoelectric quartz-crystal plate.crystal sensor See CRYSTAL TRANSDUCER.crystal set A simple radio receiver that uses atuned circuit, semiconductor-diode detector, andearphones.ElectrodesOutputvoltagecrystal microphonescrystal mixer A mixer (converter) circuit utilizingthe nonlinearity of a semiconductor diode to mixsignals.crystal operation 1. The characteristics of a piezoelectriccrystal in a particular circuit. 2. Crystalfrequency control.crystal oscillator An oscillator whose operatingfrequency is determined by the dimensions of anoscillating piezoelectric quartz-crystal plate.Compare SELF-EXCITED OSCILLATOR.crystal oven A constant-temperature chamber forstabilizing the frequency of a quartz crystal bymaintaining its operating temperature at a fixedpoint.crystal photocell A photoelectric cell in which thelight-sensitive material is a crystalline substance,such as germanium, selenium, silicon, etc.crystal pickup A phonograph pickup whose transduceris a natural or synthetic piezoelectric crystal.The crystal is attached (either directly orthrough a mechanical linkage) to a stylus, whosemovement in the disk groove varies the shape ofthe crystal. The resultant vibration generates acorresponding audio-frequency (AF) output voltageacross the crystal.crystal probe A radio-frequency (RF) probe, whoserectifying element is a semiconductor diode.crystal setcrystal slab See QUARTZ BAR.crystal socket 1. A low-capacitance, low-losssocket for a piezoelectric crystal. 2. A socket for asemiconductor diode.crystal tester 1. An oscillator used to check quartzcrystals. Most such units check only the crystal’sability to oscillate; more elaborate ones also checkcrystal current, frequency, temperature coefficient,activity, filter action, etc. 2. An instrumentfor checking the electrical characteristics of semiconductordiodes. 3. An instrument for checkingthe performance of piezoelectric ceramics.

158 crystal tetrode • current antinodecrystal tetrode A transistor having four elements:emitter, collector, and two bases.crystal transducer A transducer using a piezoelectriccrystal as the sensitive element. Examples:crystal earphone, crystal loudspeaker,crystal microphone, and crystal pickup.crystal triode See TRANSISTOR.Cs Symbol for CESIUM.CS Abbreviation of COMPLEMENTARY SYMME-TRY. Also COS.C S 1. Symbol for standard capacitance. 2. Symbolfor source capacitance.csc Abbreviation of COSECANT.C scan See C DISPLAY.csch Abbreviation of HYPERBOLIC COSECANT.C scope A cathode-ray tube used in radar to providea C DISPLAY.CT-cut crystal A piezoelectric plate cut from aquartz crystal at an angle of rotation around theX-axis of +38°. Such a plate has a zero temperaturecoefficient of frequency at 25°C. Also seeCRYSTAL AXES and CRYSTAL CUTS.CTL Abbreviation of complementary-transistorlogic.Cu Symbol for COPPER.cube 1. A regular polyhedron with six identicalsquare faces and eight vertices. At each vertex,three edges converge at mutual right angles. 2.The third power of a number; thus the cube of nis written n 3 .cube tap An electrical adapter, in which a set ofmale prongs and three sets of female contacts areon the sides of a molded cube. Allows three appliancesto be used with a single electrical socket.To walloutletcube tapToappliancescubical antenna An antenna in which the elementsform the outline of a geometric cube orrectangular prism. The most common example isthe QUAD ANTENNA.cubical quad antenna See QUAD ANTENNA.cubic equation A polynomial equation of the thirddegree. Its general form is ax 3 + bx 2 + cx + d = 0.cue A condition or signal that alerts an operator,circuit or system to act in a specific manner.cue circuit A device for transmitting cues used inprogram control.cueing receiver 1. A (usually miniature) radio receiverused to pick up cues. Example: a receivercarried by a technician, actor, or lecturer. 2. A receiveror other pickup circuit that receives a cuingpulse, which it uses to set another circuit.cu ft Abbreviation of cubic foot or cubic feet.cu in Abbreviation of cubic inch or cubic inches.cumulative error In a sum or other final value, thetotal error that has accumulated from the individualerrors in the terms. Also called systematicerror.cup core A coil core that also forms a magneticshield around the coil.cuprous-oxide rectifier See COPPER-OXIDERECTIFIER.cur Abbreviation of CURRENT.curie Abbreviation Ci. A unit of radioactivity; 1curie is the amount of radiation from (or in equilibriumwith) 1 gram of radium. Also equivalent to3.7 × 10 10 atomic breakdowns per second.Curie point 1. The temperature above which a ferromagneticmaterial loses its magnetism or becomesparamagnetic. 2. The temperature atwhich the ferroelectric properties of a substancedisappear.curie temperature As a magnetized substance isheated, the lowest temperature at which magnetizationis lost. It is generally measured in degreesCelsius or degrees Kelvin. For iron, this temperatureis 760 degrees Celsius; for nickel, it is 356degrees Celsius.Curie’s law For a paramagnetic substance, the ratioof the magnetization to the magnetizing forceis inversely proportional to the absolute temperature.Curie-Weiss law Above the Curie point, the susceptibilityof a paramagnetic material varies inverselyas the excess of temperature above theCurie point increases. This law is invalid for applicationsat or below the Curie point.curium Symbol, Cm. A radioactive metallic elementproduced artificially. Atomic number, 96.Atomic weight, 247.current Symbol, I or i. The movement of chargecarriers, such as electrons, holes, or ions. Alsosee AMPERE.current amplification 1. An electronic processin which the instantaneous, average, or peakmagnitude of a current is increased. 2. The extentto which a current increases in a circuit;the ratio (always greater than one) of outputcurrent to input current, I out /I in . Also called currentgain.current amplifier An amplifier operated primarilyto increase a signal current. Compare POWERAMPLIFIER and VOLTAGE AMPLIFIER.current antinode See CURRENT LOOP.

current attenuation • current relay 159current attenuation 1. The reduction of currentamplitude along a line. 2. The extent to which acurrent decreases in a line or circuit; the ratio (alwaysless than one) of output current to inputcurrent, I out /I in .current balance An instrument for determiningthe size of the ampere. This is done by measuringthe force between two current-carrying conductors.current-balance switch A switch or relay, operatedby the existence of a difference between twocurrents.current-carrying capacity The maximum current(usually expressed in amperes) that a conductoror device can safely conduct.current coil The series coil in a nonelectronicwattmeter. Compare POTENTIAL COIL.current-controlled amplifier Abbreviation, CCA.An amplifier in which gain is controlled by meansof a current applied to a control-input terminal.current density The current (usually expressed inamperes per square centimeter) passing througha cross-sectional area of a conductor.current drain 1. The current supplied to a load bya generator or generator-equivalent. 2. The currentrequired by a device for its operation; also,the current taken by the device during standbyperiods.current echo Reflected current in a transmissionline that is not terminated in an impedance exactlymatching its characteristic impedance.current-fed antenna An antenna in which thetransmission line is attached to the radiator at acurrent loop (voltage node). Compare VOLTAGE-FED ANTENNA.current feed 1. The delivery of power to a device orcircuit at a point where current dominates. CompareVOLTAGE FEED. 2. In an antenna, feedingit at a current maximum.Current feedCurrentcurrent feedback 1. A feedback signal consistingof current fed from the output to the input circuitof an amplifier. 2. A system or circuit for obtainingcurrent feedback.current-feedback pair A two-stage, direct-coupledtransistor amplifier having direct-current shuntseriesfeedback.current flow Charge carriers passing through asolid, liquid, gas, or vacuum. Also see CURRENTand CURRENT DENSITY.current gain See CURRENT AMPLIFICATION.current hogging 1. An undesirable condition thatsometimes takes place when two or more transistorsare operated in parallel. One device tends todo all the work, taking all the current. The resultcan be destruction of that device. 2. The tendencyof one component in a group of identical parallelconnectedcomponents to dissipate most of thepower.current-hogging injection logic Acronym, CHIL.A form of bipolar digital logic, similar to currenthogginglogic but having the greater density characteristicof injection logic.current instruction register A register in whichare held instructions ready for execution by aprogram controller.current lag A circuit condition in which currentvariations are delayed by up to 180 degrees ofphase relative to voltage variations. CompareCURRENT LEAD.current lead A circuit condition in which currentvariations occur earlier than voltage variations byup to 180 degrees of phase. Compare CURRENTLAG.current limiting The controlling of current so thatit does not exceed a desired value.current-limiting resistor A series resistor insertedinto a circuit to limit the current to a prescribedvalue.current loop A point on a transmission line or antennaradiator at which the current reaches a localmaximum. Compare CURRENT NODE.current meter A usually direct-reading instrument,such as an ammeter, milliammeter, or microammeter,used to measure current strength.Also see ELECTRONIC CURRENT METER.current-meter operation The operation of a voltmeteras a current meter by connecting it to respondto the voltage drop across a resistor thatcarries the current of interest.current-mode logic In computer operations, transistorlogic in which the transistors operate in theunsaturated mode.current node A point on a transmission line or antennaradiator at which the current reaches a localminimum. Compare CURRENT LOOP.current noise Electrical noise produced by currentflowing through a resistor.current probe A transformer usually having asnap-around, one-turn coil that picks up energyfrom a conductor and couples it into an alternating-currentammeter.current rating 1. A specified value of operatingcurrent. 2. See CURRENT-CARRYING CAPACITY.current-regulated supply See CONSTANT-CURRENT SOURCE.current regulation The stabilization of current ata predetermined level or value.current regulator See BARRETTER.current relay A relay actuated by specific values ofpickup and dropout current.

160 current saturation • cutoff frequencycurrent saturation In the operation of a device(such as a transistor, saturable reactor, or magneticamplifier), the leveling off of current at avalue beyond which no further increase occurs—even though an input parameter is further increased.current sense amplifier An amplifier used to increasethe sensitivity of, or to decrease the loadingof, a current-sensing component.current sensing Sampling a current (e.g., whenthe voltage drop across a series resistor is used asa proportional indication of the current flowingthrough the resistor).current-sensing resistor A low-value resistor insertedinto a circuit primarily for current sensing.current sensitivity In a current meter or galvanometer,current (in amperes or fractionsthereof) per scale division.current-sheet inductance Symbol, L S . The lowfrequencyinductance of a single-layer coil, calculatedwith the formula L S = (0.10028 a 2 N 2 )/s,where L S is in microhenrys, a is the coil radius ininches, N is the total number of turns, and s isthe coil length in inches.current shunt 1. A resistor connected in parallelwith a voltmeter to convert it into an ammeter. 2.A resistor connected in parallel with the input ofa voltage amplifier to make the response of theamplifier proportional to input-signal current.current sink A circuit or device through which aconstant current can be maintained.current-sinking logic A form of bipolar digitallogic. Current flows from one stage to the input ofthe stage immediately before.current-squared meter An ammeter or milliammeterwhose deflection is proportional to thesquare of the current.current-stability factor In a common-base connectedbipolar transistor, the ratio dI E /dI C , whereI E is the emitter current and I C is the collectorcurrent.current strength The magnitude of electric current(see CURRENT) (i.e., the number of carriersflowing past a given point per unit time, expressedin coulombs per second or in amperes).current transformer 1. A transformer used to increaseor decrease current flow. A primary-tosecondarystep-up turns ratio reduces thecurrent; a primary-to-secondary step-down turnsratio increases the current. 2. A particular transformer(as in 1) used to change the range of an alternating-currentmilliammeter or ammeter.current vector In a vector diagram, a line with anarrowhead (vector) showing the magnitude andphase of a current. Compare VOLTAGE VEC-TOR.current-voltage feedback In an amplifier or oscillator,the process of applying some of the outputcurrent and voltage to the input. This feedbackmight be in phase (positive) or out of phase (negative),with respect to the input.cursor 1. A marker that indicates the positionwhere a character can be entered in a video alphanumericdisplay. Commonly used in computersand word processors. 2. The sweeping line ona radar display. 3. The movable marker on a sliderule.curve trace 1. A device that supplies a specialvariable test voltage to a component or circuit undertest, at the same time supplying a sweep voltageto an oscilloscope. The component’s outputvoltage is also presented to the oscilloscope. As aresult, the response curve of the component appearson the oscilloscope screen. 2. A device thatproduces a permanent record (photographic orgraphic) of an electrical phenomenon. Also calledOSCILLOGRAPH or RECORDER.curvilinear trace A trace made on paper withcurved vertical lines. The lines are curved tomatch the arc through which the recording penswings.cut-in angle In a semiconductor rectifier circuit, aphase angle slightly greater than zero degrees, atwhich current conduction begins. Compare CUT-OUT ANGLE.Cutler antenna A parabolic-dish antenna, inwhich the driven element consists of a waveguidethat has two apertures on opposite sides ofa resonant cavity.Cutler feed An aircraft antenna feed system inwhich radio-frequency (RF) energy is fed to the reflectorby a resonant cavity at the end of a waveguide.Cutler tone control A dual resistance-capacitance(RC) filter circuit of the general bridged-tee variety.Variation of the series leg provides adjustabletreble boost; variation of the shunt leg providesadjustable bass boost.cutoff 1. The process of reducing some operatingparameter, such as collector current, to zero byadjusting the bias at the input electrode. 2. Thepoint on the characteristic curve of an amplifyingdevice, at which the output current drops to zerounder no-signal conditions. 3. The lowestfrequency at which a waveguide will efficientlyfunction. 4. The frequency or frequencies correspondingto the point or points in a filterresponse, at which the attenuation is threedecibels greater than the lowest attenuation withinthe passband. See also CUTOFF FREQUENCY.cutoff attenuator A variable, nondissipating attenuatorconsisting of a variable length of waveguideused at a frequency below cutoff.cutoff bias In a transistor or vacuum-tube circuit,the value of control-electrode bias that producesoutput current cutoff.cutoff current Symbol, I co . In a transistor, thesmall collector current that flows when the emittercurrent is zero (common-base circuit) or whenthe base current is zero (common-emitter circuit).cutoff frequency 1. Symbol, f co . The high frequencyat which the current-amplification factor

cutoff frequency • cyclic variations 161of a transistor drops to 70.7% of its 1-kHz value.2. In a filter, amplifier, or transmission line, thefrequency point(s) at which transmission loss orfilter rejection begins. It is generally specified asthe half-power point(s), or the point(s) at whichthe attenuation is three decibels, relative tothe lowest attenuation. Examples: the highfrequencycutoff of an amplifier and the upperand lower cutoff points of a bandpass filter.cutoff limiting Output-peak clipping that resultsfrom overdrive in an amplifying device. CompareSATURATION LIMITING.cutoff potential See CUTOFF BIAS.cutoff voltage See CUTOFF BIAS.cutoff wavelength 1. The wavelength correspondingto cutoff frequency. 2. For a waveguide, theratio of the velocity of electromagnetic waves infree space (3 × 10 8 meters per second) to the cutofffrequency of the waveguide in Hz. The result isthus expressed in meters.cutout1. A device, such as a circuit breaker, thatautomatically disconnects a circuit, usually toprevent overload, but occasionally to prevent underload.2. Emergency switch. 3. Fuse.cut-out angle In a semiconductor rectifier circuit,a phase angle slightly less than 180 degrees atwhich current conduction ceases. Compare CUT-IN ANGLE.cutout base A fuse block.cut rate 1. The speed at which a cutter movesacross the surface of a blank vinyl disk during therecording process. 2. The number of cut lines perinch in a vinyl disk recording.CW 1. Abbreviation of CONTINUOUS WAVE. 2. Abbreviationof CLOCKWISE.CW filter In a communications receiver, a highlyselective filter in the intermediate-frequency (IF)or audio-frequency (AF) stage. The bandwidth istypically 200 Hz to 500 Hz; some audio filterscan be set for bandwidths as low as about 50Hz.CW laser A laser that emits energy in an uninterruptedstream, rather than in pulses.CW monitor See KEYING MONITOR.CW oscillator 1. In a radio receiver, a variablefrequencyoscillator that heterodynes a radiotelegraphsignal in the intermediate-frequency (IF)amplifier chain, to make audible the continuouswavedits and dahs. 2. Sometimes, an externalvariable-frequency radio-frequency (RF) oscillator,whose output beats against the actual carrierof a continuous-wave radiotelegraph signal, makingit audible as dits and dahs. 3. An unmodulated,unkeyed oscillator.CW radar A radar system in which radio-frequency(RF) energy is transmitted continuously.CW reference signal A sinusoidal radiofrequency(RF) signal, used to control the conductiontime of a synchronous demodulator incolor television.C xSymbol for UNKNOWN CAPACITANCE.cyan Blue-green, one of the three primary pigments.cyber- A prefix that indicates relevance to, or involvementwith, computers, computer systems,and electronic control systems.cybernetics The study of control system theory interms of the relationship between animal andmachine behavior.Cyber Sapiens An expression for a computer orrobot with artificial intelligence (AI) on the forefrontof current technology.cyberspace 1. Alternative expression for INFOR-MATION SUPERHIGHWAY. 2. Alternative expressionfor VIRTUAL REALITY.cyborg Acronym of the words cybernetic and organism.1. A human being with at least one artificialbody part, such as a prosthesis (artificiallimb). 2. A human being who is largely composedof robotic body parts.cycle 1. Abbreviation, c. One complete, 360-degreerevolution of the current or voltage vector in analternating-current (ac) wave. An ac frequency of1 cycle per second is 1 Hz (see HERTZ). 2. A completesequence of operations.cycle counter A device that totals the number ofcycles of a phenomenon repeated during a givenperiod.cycle index The number of times that a particularcycle has been, or must be, iterated in a computerprogram.cycle index counter A variable that indicates howoften a cycle of computer program instructionshas been executed. In a program, for example,this can be accomplished by increasing, throughinstruction, the value of a location’s content everytime a loop operation is performed.cycle life The total number of charge-discharge cyclesa rechargeable cell or battery can tolerate beforebecoming useless.cycle reset To change the value of a cycle count(making it zero or some other value).cycle shift See CYCLIC SHIFT.cycles per second Abbreviation, cps. Archaic termfor HERTZ.cycle time Pertaining to an operation, the durationof a complete cycle.cycle timer A timer that switches a circuit or deviceon and off, according to a predetermined cycle.Also called programmed timer.cyclic code See GRAY CODE.cyclic memory In computer operations, a memorywhose locations can only be accessed points in acycle, as of a magnetic diskette.cyclic shift The moving of data out of one end of astorage register and reentering it character-bycharacteror bit-by-bit at the other end in a closedloop (e.g., 87654 cyclically shifted one place tothe right becomes 48765).cyclic variations Periodic changes in the featuresof the ionosphere, occurring on a daily, seasonal,or sunspot-related basis. These changes are fairlypredictable.

162 cycling • Czochralski methodcycling The tendency of a parameter to oscillateback and forth between two different values.cyclogram A method of showing the relationshipbetween two signals on an oscilloscope. The twosignals must have a fixed phase relationship.cyclotron A type of particle accelerator. An appliedelectromagnetic field, acting together with an intenseapplied magnetic field, cause charged subatomicparticles to travel with increasing velocityin a spiral path between two semicircular metalboxes called dees. When the particles go fastenough in the correct path, they are expelled andstrike a target in their path.Path ofacceleratedparticlescylindrical contour The most common curvatureof the face of a magnetic tape recording head; it isa section of a cylinder having a constant radius of0.5 inch to 1 inch.cylindrical coordinate geometry A scheme forrobot-arm movement. There are three coordinates,called reach, angle, and elevation. It allowsprecise positioning of a robot end effector within aregion consisting of two concentric cylinders andall the volume in between.cylindrical coordinates A method of locating apoint in three-space in which height, distance,and angle are used to uniquely define points.h axisDee 1Dee 2P = (h, r,θ)DeflectorTargetHotcathodeh rθcylindrical coordinatesθ = 0axiscyclotroncyclotron frequency The angular frequency of acharged particle in a cyclotron. The cyclotron frequencydepends on the number of times per secondthe magnetic field of the device is reversed.cyclotron radiation An electromagnetic field producedby the circular movement of charged particlesin a fluctuating magnetic field.cylinder In computer operations, the combinationof equal-radius tracks on the platters of a harddisk.cylinder magnet A permanent magnet in theshape of a cylinder.cylindrical capacitor See CONCENTRIC CAPACI-TOR.cylindrical magnet See CYLINDER MAGNET.cylindrical wave An electromagnetic wave whosefield surfaces are nearly perfect cylinders.cylindrical waveguide A waveguide resembling around pipe.cylindrical winding A method of coil winding inwhich the wire is formed into a helix. There mightbe only one layer, or there might be several layers.The length of the coil is greater than the diameter.Also called a linear winding.Czochralski method A technique for obtaining arelatively large single crystal from a substance,such as the semiconductors germanium and silicon.The method consists essentially of dipping aseed crystal into a molten mass of the same substance,then slowly withdrawing it while rotating it.

D 1. Symbol for DEUTERIUM. 2. Symbol for ELEC-TRIC DISPLACEMENT. 3. Symbol for ELECTRICFLUX DENSITY. 4. Symbol for DISSIPATIONFACTOR. 5. Symbol for drain (see DRAIN, 3). 6.Abbreviation of DISSIPATION. 7. Symbol for determinant.8. Symbol for DIFFUSION CONSTANT.d 1. Abbreviation of DECI. 2. Symbol for DIFFER-ENTIAL. 3. Symbol for distance. 4. Symbol forDENSITY. 5. Symbol for drain (see DRAIN, 3). 6.Abbreviation of DISSIPATION. 7. Abbreviation ofday. 8. Abbreviation of DEGREE. 9. Abbreviationof diameter. 10. Abbreviation of DRIVE.D/A Abbreviation of DIGITAL-TO-ANALOG. SeeDIGITAL-TO-ANALOG CONVERSION.dA 1. Symbol for DIFFERENTIAL OF AREA. 2.Symbol for differential of amplification. 3. Seldomusedabbreviation of deciampere.da Abbreviation of DEKA.DAC Abbreviation of DIGITAL-TO-ANALOG CON-VERTER.DACI Abbreviation of direct adjacent-channel interference.DAGC Abbreviation of DELAYED AUTOMATICGAIN CONTROL.daisy chain A method of transferring a signal in acomputer from one stage to the next.daisy wheel A form of printing device consistingof a disk having several dozen radial spokes,each of which has a character molded on itsface. The disk rotates to the proper position inthe printing process, and a hammer strikes thespoke to press the molding against the ribbonand paper.DAM Abbreviation of data-addressed memory.Damon effect The change that the susceptibility offerrite undergoes under the influence of high RFpower.damped galvanometer A galvanometer with a provisionfor overswing limiting or oscillation prevention.damped loudspeaker A loudspeaker in which undesirableexcursions are prevented by damping inthe associated amplifier or speaker circuit.damped meter 1. A meter with a provision foroverswing limiting or oscillation prevention. 2. Ameter that is protected during transport by ashorting bus between the two meter terminals.damped natural frequency 1. The frequency atwhich a damped system having one degree offreedom will oscillate after momentary applicationof a transient force. 2. In the presence ofdamping, the rate at which a sensing element oscillatesfreely.damped oscillations Oscillations in which the amplitudeof each peak is lower than that of the precedingone; the oscillation eventually dies out (theamplitude becomes zero). Compare CONTINU-OUS WAVE.damped speaker See DAMPED LOUDSPEAKER.damped wave A wave whose successive peaks decreasein amplitude (i.e., it decays), eventuallyreaching an amplitude of zero. Compare CONTIN-UOUS WAVE and UNDAMPED WAVE.damped-wave decay See DECREMENT, 1.dampen To cause the amplitude of a signal todecay.damper See DAMPING DIODE.damper diode See DAMPING DIODE.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

164 damper winding • data-acquisition systemAmplitudedamped waveTimedamper winding A special short-circuited motorwinding that opposes pulsation or rotation of themagnetic field.damping 1. See DAMPING ACTION. 2. In a loudspeaker,sound-absorbent material used to minimizeresonant effects within the enclosure.damping action 1. Quenching action. 2. The preventionof overswing, dither, or flutter in a meteror loudspeaker (see DAMPED GALVANOMETER,DAMPED LOUDSPEAKER, DAMPED METER). 3.The prevention of oscillation or ringing in a circuit.4. Inhibition of the vibration of an acoustictransducer to prevent ringing and other unwantedeffects.damping coefficient A figure expressing the ratioof the damping in a system to critical damping.damping diode A diode used to prevent oscillationin an electric circuit (e.g., the diode that preventsringing in the power supply of a television receiver).Also called damper.damping factor 1. Symbol, a. For a coil of inductanceL and RF resistance R in a damped-wavecircuit, the value R/2L, where L is in henrys andR in ohms. 2. Abbreviation, F o . For a torque motor,the ratio of the stall torque to the no-load rotationalspeed.damping magnet A permanent magnet so situated,with respect to a moving conductor, disk, orplate, that the resulting field opposes the movement.damping ratio See DAMPING COEFFICIENT.damping resistance 1. The value of shunt resistancerequired to prevent ringing in a coil. 2. Thevalue of resistance required for critical dampingof a galvanometer.damping resistor 1. A shunt across a coil to preventringing. 2. A resistor used to provide criticaldamping of a galvanometer.Daniell cell A nonpolarizing primary wet cell withzinc (negative) and copper (positive) electrodes.The zinc plate is in a porous cup containing aweak zinc-sulfate solution with a little sulfuricacid; the cup is in a jar filled with a saturated copper-sulfatesolution in which the copper electrodeis immersed. Typical voltage for the cell is 1.1 V.daraf The unit of ELASTANCE. Elastance in darafsis the reciprocal of capacitance in farads.dark conduction The flow of dark current in aphotoconductive or glow-discharge device.dark current The usually tiny current flowingthrough a darkened photoconductive cell, phototransistor,or glow-discharge device.dark discharge The occurrence of a discharge in agas, without the production of visible light.dark-spot signal A spurious signal generated bysome camera tubes, arising from secondaryemissioneffects.dark-trace tube An oscilloscope tube on whosewhite screen a long-persistence magenta image istraced by the electron beam. Illuminating thescreen with bright light intensifies the image.Darlington amplifier A high-gain amplifier thatuses a COMPOUND CONNECTION of two bipolartransistors.Darlington pair See COMPOUND CONNECTION.D’Arsonval current A large, low-voltage, highfrequencycurrent at one time thought to betherapeutic.D’Arsonval meter A electromechanical analog meter,in which a coil turns on jeweled pivots betweenthe poles of a strong magnet and againstthe force of spiral springs. A pointer is attached tothe coil. The pointer moves over a calibrated scale.D’Arsonval movement The mechanism of aD’Arsonval meter.DART Abbreviation of data analysis recording tape.dart leader A flow of electrons along a path traveledby a lightning stroke, preceding a secondstroke. The dart leader, if any, occurs a few millisecondsafter the first stroke. Several strokescould occur, each preceded by a dart leader,within less than 1 second.dash The longer of the two characters (DOT andDASH) of the telegraph code. The duration of thedash is three times longer than that of a dot.dashpot A delayed-action device in which themovement of a piston is slowed by air or a liquidin a closed cylinder.dashpot relay A time-delay relay assembly inwhich the delay is obtained with a DASHPOT.DAT 1. Abbreviation of DIGITAL AUDIO TAPE. 2.Abbreviation of diffused-alloy transistor.data1. A collection of digital bits (binary digits)with informational content (e.g., a computer file,a digital image, or a digital sound recording). 2.General expression for information, especially inencoded or written form.data acquisition The reception and gathering ofdata (see DATA COLLECTION and DATA SYS-TEM, 1).data-acquisition system A computer or dumb terminalused to gather data from one or more externalpoints.

data analysis display unit • data processor 165data analysis display unit A video display peripheralfor online data analysis.data area A computer memory area that holds dataonly (i.e., one that does not contain program instructions).data bank A data file stored in a direct-access storagedevice, which can be drawn from by manysystem users through remote terminals.database 1. A computer file containing often-usedinformation (e.g., names and addresses, or electronicpart numbers). 2. A popular form of computersoftware that allows users to create,maintain, and modify information.data block A set of data bits, comprising an identifiableitem.data bus A conductor or medium over which digitaldata is transmitted from one place to anotherwithin a computer.data carrier storage A medium of data storageoutside of a computer (e.g., a magnetic disk).data code A set of abbreviations or codes for datacharacters or words.data collection The pickup of signals representingtest data and their transmission to a computer,data processor, or recorder. Also see DATA SYS-TEM, 1.datacom Acronym for DATA COMMUNICATION.data communication The transmission and receptionof data signals between or among pointsin a system.data communication terminal A computer peripheralproviding an input and output link to acentral computer system, and that can be usedoffline for other functions.data compression 1. The process of reducing thesize of a data file by eliminating redundancies. 2.The process of minimizing the length of a datatransmission by eliminating redundancies. 3.The process of reducing the bandwidth of a datatransmission. 4. The process of reducing the dynamicamplitude range of a data transmission.data control The automatic control of incomingand outgoing data in a data processing system.data conversion The process of changing datafrom one form to another, e.g., from analog to digital(A/D), digital to analog (D/A), parallel to serial,or serial to parallel.data converter 1. A circuit or device for performingDATA CONVERSION. 2. An analog-to-digital(A/D) converter. 3. A digital-to-analog (D/A) converter.4. A parallel-to-serial converter. 5. Aserial-to-parallel converter.data description The description of a unit of data,as included in a computer source program.data display A device, such as a cathode-ray tube(CRT) or liquid-crystal display (LCD), that presentsdata for visual examination. CompareDATA PRINTOUT.data element 1. A component of a data signal (e.g.,a number, letter, symbol, or the equivalent electricalpulses). 2. A device or circuit for acquiringor processing data. 3. A unit of data (e.g., a fieldin a file).data-flow diagram A block diagram showing themovement of data through a data-processing system.data format The form of data in a record or file(e.g., character format or numerical format).data gathering See DATA COLLECTION.data-handling capacity 1. The amount of datathat can be stored in a memory circuit. 2. Theamount of data that can be transmitted over acertain medium. 3. The rate at which data can betransferred under certain conditions.data-handling system A system that gathers,routes, transmits, or receives data, but does notnecessarily process it.data item A logical element (character, byte, or bit)describing a characteristic of a record used by asystem for which there is a specific application.data level Descriptive, through a programminglanguage, of the relative weight of logical elements(data items) in a computer record. Alsocalled data hierarchy.data link The portion of a computer system thatgathers data and, if necessary, converts it to aform acceptable by a computer.data matrix Variables and their possible valuesstored as a series of columns and rows of valuesin a computer memory.data name An operand specified in a computersource program.data pickup 1. A transducer that collects data signalsfrom a source; it converts nonelectrical datainto corresponding electrical signals and deliversits output to a data processing system. 2. Dataacquisition.data playback The reproduction of data signalsstored by some method of data recording.data plotter See X-Y PLOTTER.data printout 1. A device that prints a record ofdata or the results of a computation. 2. A permanentprinted record, usually of a calculation orcomputation—especially the printed output of acomputer peripheral device.data processing Work performed on acquireddata, as in solving problems, making comparisons,classifying material, organizing files. Usuallydone by a computer.data-processing equipment A digital computerand the peripheral equipment needed to collate,store, analyze, and reduce data.data-processing machine A computer or systemused to collate, store, analyze, and reduce data,as opposed to a computer or system used primarilyto solve problems or perform routine tasks.Also called data processor.data-processing system An electronic system forautomatic data processing. It can be based onanalog and/or digital techniques.data processor See DATA-PROCESSING MA-CHINE.

166 data receiver • daylight lampToothercomputersTotelephoneToradiotransceiverMonitorModem Computer PrinterSoftwaredata-processing systemdata receiver At a particular point in a dataprocessingsystem, a circuit or device forreceiving data from a data transmitter.data reception Receiving data signals from somepoint within or outside a data-processing system.data-reception system A data receiver and its associatedequipment.data record A computer-processed record containinga data unit.data recorder A machine for storing data acquiredin the form of electrical signals (see DATARECORDING).data recording 1. The preservation of data signalsby some process, such as magnetic-disk encoding,optical-disk encoding, or tape recording, forfuture use or as a backup. 2. A record of data signals,as on magnetic tape.data reduction The summarization of a mass ofelectronically gathered data.data-reduction system A system used to minimizethe amount of data necessary to convey given information.data representation Values and data as describedby numerals, symbols, and letters (e.g., computerprogram instructions).data segment As related to a particular computerprocess, a subunit of allocated storage containingdata only.data selector/multiplexer A digital circuit thathas several or many input signals, and feeds oneof them onto a common line.data set A device that connects a data processor toa telegraph or telephone line.data signal 1. A signal (such as one of binary bitcombinations) that can represent data as numbers,letters, or symbols. 2. A signal current orvoltage proportional to some sampled quantity,and that can be used to actuate indicating instrumentsduring tests or measurements.data statement A computer source program statementidentifying a data item and specifying itsformat.data storage The preservation of data, particularlycomputer files, for long periods of time in nonvolatileform (no source of power is required toensure that the data remains intact).data storage media Hardware that preserves data,particularly computer files, for long periods oftime in nonvolatile form (no source of power is requiredto ensure that the data remains intact).Common media include magnetic disks, magnetictape, and optical disks.data synchronizer A device used to synchronizedata transmission within a computing or processingsystem.data system 1. An arrangement for collecting,recording, and routing data in the form of electricalsignals. 2. An arrangement for processingdata (i.e., for correlating, computing, routing,storing, etc.).data terminal A remote input/output device connectedto a central computer.data throughput In a computer system, theamount of data per unit time (bytes, kilobytes,megabytes, gigabytes, or terabytes per second orminute) that can be transferred from one place toanother.data transducer In tests and measurements, atransducer that converts a monitored phenomenoninto electrical quantities that can beused for computer analysis or calculations.data transmission Sending data signals from apickup point or processing stage to another pointwithin a data-processing system; also, sendingsuch signals to points outside the system.data-transmission system A data transmitter andits associated equipment.data transmission utilization measure The ratioof the useful data output of a data-transmissionsystem to the total data input.data transmitter A circuit or device for sendingdata from point to point within or outside of adata-processing system.data unit Characters in a group that are related ina way that makes them a meaningful whole (e.g.,a text word, or an object such as a circle in vectorgraphics).data value A measure of the amount of informationcontained in a certain number of data bits.The greater the ratio of the actual information tothe number of bits, the higher the data value.data words In digital computer operations, words(bit groups) representing data, rather than programinstructions.DAVC Abbreviation of DELAYED AUTOMATICVOLUME CONTROL.David Phonetic alphabet code word for letter D.daylight effect The modification of transmissionpaths during the day because of ionization of theupper atmosphere by solar radiation.daylight lamp An incandescent lamp whose filamentis housed in a blue glass bulb, which absorbssome red radiation and transmits most of

daylight lamp • dc converter 167the green, blue, and violet. So called because thespectral output resembles that of typical daylight.daylight range The distance over which signalsfrom a given transmitter are consistently receivedduring the day.DB 1. Abbreviation of DIFFUSED BASE of a transistor.2. Abbreviation of DOUBLE BREAK (relay).dB 1. Abbreviation of DECIBEL or decibels. 2.Symbol for differential of susceptance.dBa Abbreviation of ADJUSTED DECIBELS.dBc Abbreviation of decibels referred to the carrier.DBD Abbreviation of double-base diode.dBd The power gain of an antenna in the directionof maximum radiation, compared to the radiationin the favored direction of a half-wave dipole infree space receiving the same amount of power.Expressed in decibels.dBi The power gain of an antenna in the directionof maximum radiation, compared to the radiationfrom a theoretical isotropic antenna in free spacereceiving the same amount of power. Expressedin decibels.dBj The level of an RF signal, in decibels, relative to1 millivolt.dBk Abbreviation of DECIBELS REFERRED TO 1KILOWATT.DBM Abbreviation of database management.dBm Abbreviation of DECIBELS REFERRED TO 1MILLIWATT.dBm0 Signal level in dBm, referred to a zero-transmissionlevel.dBm0p Noise in dBm0, measured with set phosphometricweighting.dB meter A usually high-impedance ac voltmeterwith a scale reading directly in decibels.dBmp The level in dBm, measured with phosphometricweighting. Generally equal to dBm –2.5,for a noise level that is flat within the communicationsaudio range.dBmr Decibels measured with respect to zerotransmission level.dBmV Abbreviation of DECIBELS REFERRED TO1 MILLIVOLT.dBrap Abbreviation of DECIBELS ABOVE REFER-ENCE ACOUSTIC POWER (10 –6 W).dBrn Abbreviation for decibels above referencenoise. A level of 0 dBrn is defined as noise powerof 10 –9 W (1 nanowatt).dBrnc Noise power in dBrn for a circuit with messageweighting c.dBrnc0 Noise in dBrnc measured with respect tozero transmission level.dBV Abbreviation of DECIBELS REFERRED TO 1VOLT.dBW Abbreviation of DECIBELS REFERRED TO 1WATT.dBx Abbreviation of DECIBELS ABOVE REFER-ENCE COUPLING.dC Symbol for differential of capacitance.dc 1. Abbreviation of DIRECT CURRENT. 2. Abbreviationof direct-coupled.dc-ac converter A circuit that converts a dc inputvoltage into an ac output voltage, with or withoutstep-up or step-down. Also called INVERTER.dc alpha The current amplification factor (ALPHA)of a common-base transistor stage for a dc input(emitter) signal. Compare DC BETA.dc amplifier 1. A direct-coupled amplifier. 2. Anamplifier for boosting direct-current signals.dc balance 1. Adjustment of a circuit or device fordc stability or dc null. 2. Adjustment of a circuitfor dc stability during gain changes. 3. A potentiometeror other variable component used to stabilizeor null a dc circuit.dc bar See DC BUS.dc base current Symbol, I B(dc) . The static directcurrent in the base element of a bipolar transistor.dc base resistance Symbol, R B(dc) . The static dc resistanceof a bipolar transistor’s base element;R B(dc) = V B /I B .dc base voltage Symbol, V B(dc) . The static dc voltageat the base element of a bipolar transistor.dc beta The current amplification factor (BETA) ofa common-emitter-connected transistor for a dcinput (base) signal. Compare DC ALPHA.dc block A coaxial section that has a capacitancein series with the inner or outer conductor, orboth, to block dc while passing RF. Compare DCSHORT.dc bus A supply conductor carrying direct currentonly.dcc Abbreviation of double cotton covered (wire).dc cathode current Symbol, I K(dc) . The static directcurrent in the cathode element of an electrontube.dc cathode resistance Symbol, R K(dc) . The static dcresistance of the cathode path of an electrontube.dc cathode voltage Symbol, V K(dc) . The static dcvoltage at the cathode of an electron tube.dc circuit breaker A circuit breaker operated bydirect-current overload or underload, dependingon its design and application.dc collector current Symbol, I C(dc) . The static directcurrent in the collector element of a bipolartransistor.dc collector resistance Symbol, R C(dc) . The staticdc resistance of a bipolar transistor’s collector element;R C(dc) = V C /I C .dc collector voltage Symbol, V C(dc) . The static dcvoltage at the collector element of a bipolar transistor.dc component In a complex wave (i.e., one containingboth ac and dc), the current componenthaving an unchanging polarity. The dc componentconstitutes the mean (average) value aroundwhich the ac component alternates, pulsates, orfluctuates.dc converter A dynamoelectric machine for convertinglow-voltage dc into higher-voltage dc. It isessentially a low-voltage dc motor coupled me-

168 dc converter • dc plate resistanceAmplitude+−dc componentdc componentTimechanically to a higher-voltage dc generator. CompareDC INVERTER.dc coupling See DIRECT COUPLING.dc drain current Symbol, I D(dc) . The static directcurrent in the drain element of a field-effect transistor.dc drain resistance Symbol, R D(dc) . The static dcresistance of an FET’s drain element; R D(dc) =V D /I D .dc drain voltage Symbol, V D(dc) . The static dc voltageat the drain element of a field-effect transistor.dc dump In digital computer operation, removingdc power from a computer, which would eradicatematerial stored in a volatile memory.dc emitter current Symbol, I E(dc) . The static directcurrent in the emitter element of a bipolar transistor.dc emitter resistance Symbol, R E(dc) . The static dcresistance of a bipolar transistor’s emitter element;R E(dc) = V E /I E .dc emitter voltage Symbol, V E(dc) . The static dcvoltage at the emitter element of a bipolar transistor.dc equipment Apparatus designed expressly foroperation from a dc power supply. Compare ACEQUIPMENT and AC/DC.dc erase head In a magnetic recorder, a head suppliedwith a dc current for the purpose of removingdata.dc error voltage In a television receiver, the dcoutput of the phase detector, which is used tocontrol the frequency of the horizontal oscillator.dc gate current Symbol, I G(dc) . The very small staticdirect current in the gate element of a field-effecttransistor.dc gate resistance Symbol, R G(dc) . The very high,static dc resistance of an FET’s gate element;R G(dc) = V G /I G .dc gate voltage Symbol, V G(dc) . The static dc voltageat the gate element of a field-effect transistor.dc generator 1. A rotating machine (dynamo) forproducing direct current. Also see DYNAMO-ELECTRIC MACHINERY. 2. Generically, a devicethat produces direct current: batteries, photocells,thermocouples, etc.dc generator amplifier A special type of generatorthat provides power amplification. The input signalenergizes the field winding of a constantspeedmachine; because the output voltage isproportional to field flux and armature speed, ahigh output voltage is obtained. Also see AMPLI-DYNE.dc grid bias Steady dc control-grid voltage used toset the operating point of an electron tube.dc grid current Symbol, I G(dc) . The static direct currentin the control-grid element of an electron tube.dc grid resistance Symbol, R G(dc) . The static dc resistancein the control-grid element of an electrontube; R G(dc) = V G /I G .dc grid voltage Symbol, V G(dc) . The static dc voltageat the control grid of an electron tube.dc inserter In a television transmitter, a stage thatadds the dc pedestal (blanking) level to the videosignal.dc inverter An electrical, electronic, or mechanicaldevice that converts dc to ac. Also called IN-VERTER.dcl Abbreviation of dynamic load characteristic.dc leakage The unintended flow of direct current.dc leakage current 1. The direct current that normallypasses through a correctly polarized electrolyticcapacitor operated at its rated dc workingvoltage. 2. The zero-signal reverse current in asemiconductor pn junction.DCM Abbreviation of DIGITAL CAPACITANCE ME-TER.D/CMOS Combination of DMOS and CMOS on amonolithic chip.dc motor A motor that operates from direct currentonly.dc noise Noise heard during the playback of magnetictape that was recorded while direct currentwas in the record head.dc noise margin In a digital or switching circuit,the difference V o – V i , where V o is the outputvoltagelevel of a driver gate and V i is the inputthreshold voltage of a driven gate.dc operating point For a bipolar transistor, fieldeffecttransistor, or vacuum tube, the static, zerosignaldc voltage and current levels.dc overcurrent relay A relay or relay circuit actuatedby dc coil current rising above a specifiedlevel. Compare DC UNDERCURRENT RELAY.dc overvoltage relay A relay or relay circuit actuatedas a result of the dc coil voltage rising abovea specified level. Compare DC UNDERVOLTAGERELAY.dc patch bay A patch bay in which the dc circuitsof a system are terminated.dc picture transmission In television, transmissionof the dc component of the video signal; thiscomponent corresponds to the average illuminationof the scene.dc plate current Symbol, I P(dc) . The static directcurrent in the plate element of an electron tube.dc plate resistance Symbol, R P(dc) . The static dc resistanceof the internal plate-cathode path of anelectron tube; R P(dc) = V P /I P .

dc plate voltage • dead band 169dc plate voltage Symbol, V P(dc) . The static dc voltageat the plate electrode of an electron tube.dc positioning Alignment of the spot on the screenof an oscilloscope tube, by means of adjustable dcvoltages applied to the horizontal and vertical deflectingplates.dc power Symbol, P dc . Unit, watt. The power in adc circuit; P dc = EI, where E is in volts and I is inamperes. Compare AC POWER. Also see POWER.dc power supply A power unit that supplies directcurrent only. Examples: battery, transformer/rectifier/filter circuit, dc generator, and photovoltaiccell. Compare AC POWER SUPPLY.dc relay A relay having a simple coil and core systemfor closure by direct current, which can berectified ac.dc resistance Resistance offered to direct current,as opposed to in-phase ac resistance.dc resistivity The resistivity of a sample of materialmeasured using a pure dc voltage underspecified conditions (physical dimensions, temperature,etc.).dc restoration The reinsertion of the dc componentinto a signal from which the component hasbeen extracted through a capacitor or transformer.dc restorer A circuit that reinserts the average dccomponent of a signal after the component hasbeen lost because the signal passed through a capacitoror transformer.DCS Abbreviation of DORSAL COLUMN STIMULA-TOR.dc shift A shift in the DC OPERATING POINT.dc short A coaxial fitting providing a dc path betweenthe center and outer conductors, whilepermitting radio-frequency (RF) current to floweasily through the coaxial section. Compare DCBLOCK.dc signaling A signaling procedure that uses directcurrent as the medium (e.g., simple wire telegraphyor telephony).dc source 1. DC GENERATOR. 2. A live circuitpoint from which one or more direct currents canbe taken.dc source current Symbol, I S(dc) . The static directcurrent in the source element of a field-effecttransistor.dc source resistance Symbol, R S(dc) . The static dcresistance of an FET’s source element.dc source voltage Symbol, V S(dc) . The static dcvoltage at the source element of a field-effecttransistor.DCTL Abbreviation of DIRECT-COUPLED TRAN-SISTOR LOGIC.dc-to-dc inverter See DC INVERTER.dc transducer 1. A transducer that depends on directcurrent for its operation (i.e., it has a dcpower supply whose output is modulated by thesensed phenomenon). 2. A transducer that convertsa direct current into some other form of energy,such as heat, pressure, or sound.dc transformer A dc-to-dc converter providingvoltage step-up. The applied dc is usually firstconverted to ac, which is then stepped up by atransformer. The higher-voltage ac is then rectifiedto produce a high dc output voltage.+In−Chopper Rectifier Filterdc transformer+Out−dc transmission 1. Sending dc power from a generatingpoint to a point of use. 2. In televisiontransmission, the retention of the dc componentin the video signal.dc tuning voltage The capacitance-varying dcvoltage applied to a varactor in an inductancecapacitance(LC) tuned circuit.dcu Abbreviation of decimal counting unit.dc undercurrent relay A relay or relay circuit thatis actuated as a result of the dc coil current droppingbelow a specified level. Compare DC OVER-CURRENT RELAY.dc undervoltage relay A relay or relay circuit thatis actuated as a result of the dc voltage droppingbelow a specified level. Compare DC OVERVOLT-AGE RELAY.dcv Abbreviation of DC VOLTS or DC VOLTAGE.dc voltage Abbreviation, dcv. A voltage that doesnot change in polarity, an example being the voltagedelivered by a battery or dc generator. Alsosee VOLTAGE.dc working voltage Abbreviation, dcwv. The rateddc voltage at which a component can be operatedcontinuously with safety and reliability.dc working volts Abbreviation, dcwv. The actualvalue, expressed in volts, of a DC WORKINGVOLTAGE.dcwv Abbreviation of DC WORKING VOLTAGE.dD Symbol for differential of electric displacement.DDA Abbreviation of digital differential analyzer.DDD Abbreviation of DIRECT DISTANCE DIALING(telephone).D display See D SCOPE.DE Abbreviation of decision element.dE Symbol for differential of voltage.deac In frequency-modulation (FM) receivers, a deviceused for deemphasis. The name is short fordeaccentuator.deactuating pressure For an electrical contact,the pressure at which contact is made or brokenas the pressure reaches the level of activation.dead 1. Unelectrified. 2. Lacking electromagneticsignals or fields. 3. Electrically or mechanicallyinoperative.dead band 1. A radio-frequency band on which nosignals are heard. 2. A range of values for whichan applied control quantity (e.g., current or voltage)has no effect on the response of a circuit.

170 deadbeat • decade capacitordeadbeat The state wherein a moving body (suchas the pointer of a meter or the voice coil of aloudspeaker) comes to rest without overswing oroscillation.deadbeat galvanometer See DEADBEAT INSTRU-MENT.deadbeat instrument A meter or recorder that ishighly damped to ensure that overswing or oscillationdoes not occur.deadbeat meter See DEADBEAT INSTRUMENT.dead break An unreliable contact of a relay,caused by insufficient pressure.dead circuit A circuit that is electrically disabled.dead end The unused end of a tapped coil (i.e., theturns between the end of the coil and the lastturn used).dead-end tower A supporting tower for an antennaor transmission line that can withstand stressescaused by loading or pulling.dead file A computer file that is not in use, but isbeing kept in a record.dead front panel A metal panel that, for safety anddesensitization, is completely insulated from voltage-bearingcomponents mounted on it; it is oftengrounded.dead interval See DEAD TIME.dead line A deenergized line or conductor.dead period See DEAD TIME.dead room An anechoic room in which acoustictests and studies are made.dead short A short circuit with extremely low (virtuallyno) resistance from dc into the radiofrequencyspectrum.dead space See DEAD BAND.dead spot 1. An area in which radio waves from aparticular station are not received. 2. On avacuum-tube cathode (directly or indirectlyheated), a spot from which no electrons areemitted.dead stretch The tendency of insulating materialsto permanently retain their approximate dimensionsafter having been stretched.dead time 1. DOWN TIME. 2. An interval duringwhich there is no response to an actuating signal.3. In a computer system, an interval between relatedevents that is allocated to prevent interferencebetween the events.dead volume In a pressure transducer, the zerostimulusvolume of the pressure port cavity.dead zone See ZONE OF SILENCE.debatable time Computer time that cannot beplaced in any other category.debounced switch A switch in sensitive computeror control systems that has circuitry for eliminatingthe electrical effects of bounce (see BOUNCE,1).de Broglie waves Electromagnetic waves that arebelieved to be associated with moving particles(such as electrons, protons, and neutrons).debug 1. To eliminate errors in, and maximize theefficiency of, a computer program or group of programs.2. To optimize the design and constructionof electronic equipment.debugging A process by which engineers eliminatethe flaws in a circuit, machine, or computer program.debugging aid routine A computer program usedto test other programs.debugging period The time interval following completionof a software design, a hardware interconnection,or the manufacture of a piece ofelectronic equipment, during which errors andimperfections are sought and corrected.debunching In a velocity-modulated tube, such asa Klystron, a beamspreading space-charge effectthat destroys electron bunching.Debye length The maximum distance between anelectron and a positive ion over which the electronis influenced by the field of the ion.Debye shielding distance See DEBYE LENGTH.deca- A prefix that indicates multiplication by 10.decade 1. A frequency band whose upper limit is 10times the lower limit. Example: 20 Hz to 200 Hz. 2.A set of 10 switched or selectable components inwhich the total value is 10 times that of individualvalues. Example: a decade capacitor. Also calledDECADE BOX. 3. A group, sometimes a unit of access,of 10 computer storage locations.decade amplifier An amplifier or preamplifierwhose gain can be adjusted in increments of 10(×1, ×10, ×100, etc.).decade box A group of components that providesvalues in 10 equal steps selected by a switch orjacks. For compactness, the components and theassociated hardware are enclosed in a box or can.See, for example, DECADE CAPACITOR.decade capacitor A composite capacitor whosevalue is variable in 10 equal steps. For example,the values might be set at 100 picofarads (pF),200 pF, 300 pF, etc., up to 1000 pF. CompareDECADE INDUCTOR and DECADE RESISTOR.0 1 2 3 4 5 6 7 8 91234 5decade box6789

decade counter • decimal code 171decade counter A counter (see COUNTER, 1, 2) inwhich the numeric display is divided intosections, each having a value 10 times that of thenext and displaying a digit from zero to nine.decade inductor An inductor whose value is variablein 10 equal steps. Compare DECADE CA-PACITOR and DECADE RESISTOR.decade resistor A resistor whose value is variablein 10 equal increments. Compare DECADE CA-PACITOR and DECADE INDUCTOR.decade scaler A scale-of-10 electronic counter(i.e., a circuit delivering one output pulse for eachgroup of 10 input pulses).decametric waves Waves in the 10- to 100-meterband (30 to 3 MHz).decay 1. The decrease in the value of a quantity,e.g., current decay in a resistance-capacitancecircuit. 2. The gradual, natural loss of radioactivityby a substance.decay characteristics 1. The decay of a parameter;usually an exponential function. 2. The persistencetime in a storage oscilloscope.decay curve A curve, usually logarithmic, representingthe function of quantity versus time for asignal decrement, the decrement of radioactivity,or other natural process.decay rateA quantitative expression for the rapiditywith which a quantity decreases. Generallylisted in decibels per second (dB/s) or decibelsper millisecond (dB/ms).decay time The time required for pulse amplitudeto fall from 90% to 10% of the peak value. Alsocalled FALL TIME.Decca A 70- to 130-kHz CW radio navigation system(British).decelerated electron A high-speed electron that isabruptly decelerated upon striking a target, causingX-rays to be emitted.decelerating electrode A charged electrode thatslows the electrons in an electron beam.deceleration Acceleration that results in a decreasein speed.deceleration time 1. The time taken by magnetictape to stop moving after the last recording orplayback has finished. 2. The time taken by amechanical data storage medium, such asa hard disk, to come to rest after completionof a read or write operation, or on poweringdown.decentralized data processing Data processing inwhich the computing equipment is distributedamong managerial subgroups.deception A method of producing misleadingechoes in enemy radar.deception device A radar device, or radar-associateddevice, for deception.deci- Abbreviation, d. A prefix meaning one-tenth(10 –1 ). Examples: DECIBEL, DECIMETER.decibel Abbreviation, dB. A practical unit of relativegain. In terms of power, the relative gain indecibels is equal to:Gain (dB) = 10 log 10 (P out /P in ),where P out is the output power and P in is the inputpower. For voltage, if the input and outputimpedances are the same, the gain in decibels isgiven by:Gain (dB) = 20 log 10 (V out /V in ),where V out is the output voltage and V in is the inputvoltage. For current, if the input and outputimpedances are the same, the gain in decibels isgiven by:Gain (dB) = 20 log 10 (I out /I in ),where I out is the output current and I in is the inputcurrent. Losses are indicated by negative dB gainvalues.decibels above reference acoustic power Abbreviation,dBrap. The ratio of a given acousticpower level to a lower reference acoustic powerlevel, specified in decibels.decibels above reference noise Abbreviation,dBrn. The ratio of the noise level at a selectedpoint in a circuit to a lower reference noise level,in decibels.decibels referred to 1 millivolt Abbreviation,dBmV. The relative voltage level of a signal whencompared with a 1-mV signal measured at thesame terminals.decibels referred to 1 milliwatt Abbreviation,dBm. The ratio, in decibels, of an applied powerlevel to the power level of 1 mW.decibels referred to 1 volt Abbreviation, dBV. Theratio, in decibels, of a given voltage to 1 V, expressedin decibels.decibels referred to 1 watt Abbreviation, dBW.The ratio of a given power level to the power levelof 1 W, expressed in decibels.decider See DECISION ELEMENT.decigram A unit of mass equal to 0.1 gram.deciliter A unit of volume equal to 0.1 liter, or 10 –4cubic meter.decilog A unit equal to 0.1 times the common logarithmof a ratio.decimal 1. Pertaining to the base-10 number system(see DECIMAL NUMBER SYSTEM). 2. Abase-10 numerical fraction, represented by figuresto the right of the radix point (decimal point),and arranged serially according to negativepowers of 10. Examples: 0.12 = 1.2 × 10 –1 ,0.00135 = 1.35 × 10 –3 .decimal attenuator An attenuator circuit whoseresistances are chosen for attenuation in decimalsteps. Thus, one section provides attenuationin steps of 0.1 times the applied voltage,another in steps of 0.01 times the applied voltage,another in steps of 0.001 times the appliedvoltage, etc.decimal code A method of defining numbers, inwhich each place has a value of ten times that immediatelyto the right.

172 decimal-coded digit • decommutationdecimal-coded digit 1. A numeral from 0 to 9. 2.A numeral in the DECIMAL NUMBER SYSTEM.3. A binary representation of a decimal valuefrom 0 to 9.decimal digit A numeral from 0 to 9.decimal equivalent The decimal number equal toa given fraction (e.g., the decimal equivalent of21⁄64 is 0.3281).decimal fraction See DECIMAL, 2.decimal notation See DECIMAL NUMBER SYS-TEM.decimal number system The familiar base-10 orradix-10 number system, in which the digits 0through 9 represent values according to their position,relative to the decimal point (also calledthe radix point). Positions to the left of the pointrepresent successive positive powers of 10, andthose to the right represent successive negativepowers of 10.decimal point The radix point in a decimal number.It serves to separate the integral part fromthe fractional part of the number.decimeter waves See MICROWAVES.decimetric waves Electromagnetic waves havinglengths ranging from 0.1 meter to 1 meter (3000MHz to 300 MHz). Also known as ultrahigh frequency(UHF).decineper A natural-logarithmic unit equal to 0.1neper.decipher See DECODING, 3.decision 1. A choice based on the evaluation andcomparison of data, and the identification of aspecified objective. 2. In digital computer operations,the automatic selection of the next step ina sequence, on the basis of data being comparedby a relational test.decision box A block on a computer flowchart indicatingthe point at which a decision (see DECI-SION, 2) must be made as to which of severalbranches the program will take.decision elements See LOGIC CIRCUITS.decision instruction A computer programinstruction to compare the values of operandsand take an appropriate action, as per the BASICinstruction “IF A = B THEN GO TO (line number).”decision procedure In decision theory, a series ofcalculations made to optimize the speed or efficiencyof a process, or to minimize risk, failure,cost, etc.decision theory A statistical discipline concernedwith identifying and evaluating choices and alternatives,and determining the best sequence ofsteps to take in reaching an objective.decision tree In decision theory, a diagram showingalternative choices, so called from its resemblanceto a tree with branches.decision value A value that defines the boundarybetween two intervals in the encoding process.deck 1. See TAPE DECK. 2. A pack of punchedcards in a computer file.declarative macroinstruction As part of an assemblylanguage, instructions to the compiler todo something or record a condition without affectingthe object program.declarative statement A computer source programinstruction specifying the size, format, andkind of data elements and variables in a programfor a compiler.declination 1. The angle representing the deviationof magnetic north from true north; it is theangle subtended by a freely turning magneticneedle and the meridian. Compare INCLINATION.2. Celestial latitude.MagneticnorthTruenorth θ = DeclinationθCompass needledeclination, 1declinometer An instrument for measuring declination.decode 1. To unscramble a coded message. 2. Indigital computer operations, to deliver a specificoutput from character-coded inputs. 3. In a multiplexsystem, the separation of the subcarrierfrom the main carrier.decoder A circuit or device for performing DECOD-ING.decoder/demultiplexer A circuit that places aninput signal on a selected output line.decoder/driver An integrated circuit containing adecoder and driver.decoding 1. In computer and data-processing operations,DIGITAL-TO-ANALOG CONVERSION.2. The conversion to English of a message receivedin a code. 3. Translating a message from asecret code (i.e., deciphering a message). 4. Theautomatic conversion of a signal into the appropriateswitching action (as the enabling of atransmitter or receiver by a tone in a selectivecalling system).decoding circuit A circuit intended for the purposeof translating a code into ordinary language.decollator An offline computer device for separatingthe parts of output continuous stationerysets. Also see CONTINUOUS STATIONERY.decommutation The extraction of a signal componentfrom the composite signal, resulting fromcommutation.

decommutator • definite-purpose component 173decommutator A circuit or device for performingdecommutation, including demodulators, demultiplexers,and signal separators.decoupler A device that isolates two circuits sothat a minimal amount of coupling exists betweenthem.decoupling The elimination or effective minimizationof coupling effects, as in decoupling amplifierstages to prevent interaction through a commonpower-supply lead.decoupling capacitor 1. A capacitor that providesa low-impedance path to ground to preventundesired stray coupling among the circuits in asystem. 2. The capacitive member of a resistancecapacitance(RC) decoupling filter.decoupling filter A resistance-capacitance (RC) filter,usually inserted into a common dc line in amultistage amplifier to prevent interstage feedbackcoupling through the common impedance ofthe line.decoupling network One or more decoupling filters.decoupling resistor The resistive member of a resistance-capacitance(RC) decoupling filter.decoy In radar, an object that provides misleadingreflections. Also see CHAFF.decreasing function A function whose curve has anegative slope at all points in the domain.decrement 1. Also called logarithmic decrement.The rate at which a damped wave dies down. Thedecrement value is the natural (base-e) logarithmof the ratio of two successive peaks of the samepolarity. 2. A quantity used to lessen the value ofa variable. 3. To lower the value (of a register, forexample) by a single increment.decremeter An instrument for measuring the decrementof a radio wave.decremeter capacitor A variable capacitor for usein a decremeter. The rotor plates are shaped sothat equal angular rotations correspond to thesame decrement at all settings. Thus, the percentageof capacitance change for a given angle of rotationis constant throughout the capacitance range.decryption The conversion of an encrypted signalfrom a cipher into plain text, graphics, or othercommonly recognizable form. Also see CIPHER.Compare ENCRYPTION.decryption key An algorithm, or a set of algorithms,that converts an encrypted signal from a cipherinto plain text, graphics, or other commonly recognizableform. Each cipher has its own uniquealgorithm or set of algorithms for this purpose.The signal cannot be decrypted unless all thecomponents of the key are present.dedicated Assigned exclusively to a certain purpose[e.g., a dedicated facsimile (fax) line].deductive logic A form of symbolic logic used todemonstrate that a certain conclusion will alwaysfollow, given a certain set of circumstances. Thelogic of digital circuits is deductive. Compare IN-DUCTIVE LOGIC.dee In a cyclotron, one of the D-shaped chambersin and between which particles accelerate in aspiral path to high velocity.dee line In a cyclotron, a support for the dee, withwhich it forms a resonant circuit.deemphasis In frequency modulation, the introductionof a low-pass characteristic (responsefalls as modulating frequency increases) to complementthe rising response of preemphasis. Alsocalled postemphasis or postequalization. ComparePREEMPHASIS.deemphasis amplifier An amplifier used to removethe high-frequency preemphasis applied tosignals prior to broadcasting, multiplexing, taperecording, or telemetering. Also see DEEMPHA-SIS and PREEMPHASIS.deemphasis circuit A low-pass filter that providesdeemphasis in an FM receiver.deemphasis network See DEEMPHASIS CIRCUIT.deenergize To take a circuit or device out of operation(i.e., to remove its power or signal excitation).deep cycle Pertaining to a rechargeable cell or batterythat can operate until it is almost completelydischarged. It generally has a high ampere-hourcapacity.deep-diffused junction A pn junction made by diffusingthe impurity material deep in the semiconductorwafer. Compare SHALLOW-DIFFUSEDJUNCTION.deep discharge The nearly complete discharge of acell or battery; usually done prior to recharging.deep-space net A radar system intended for constantmonitoring of spacecraft.defeating 1. The disabling or circumvention of analarm or security system, leaving the protectedproperty vulnerable to intrusion. 2. The dangerous,and potentially lethal, disabling of a safetydevice in an electrical or electronic system.defect 1. Absence of an electron (hence, presenceof a hole) in the lattice of a semiconductor crystal.2. An abnormality of design, construction, or performanceof an electronic circuit or device. 3. In acomputer system, a hardware or software faultthat could be the eventual cause of a failure. 4. Aflaw in a crystalline substance.defect conduction In a semiconductor material,conduction via holes.deferred addressing Indirect addressing in whicha preset counter makes several references to finda desired address.deferred entry An entry into a computer subroutine,delayed because of a delay in the exit from acontrol program.deferred exit An exit from a computer subroutine,delayed because of a particular command.defibrillation Use of a CARDIAC STIMULATOR tohalt fibrillation of the heart, as caused by electricshock.defibrillator See CARDIAC STIMULATOR.definite-purpose component A component designedfor a specific use, rather than for a wide

174 definite-purpose component • degenerate parametric amplifierrange of possible applications (e.g., a video detectordiode, as opposed to a general-purpose diode).Compare GENERAL-PURPOSE COMPONENT.definition 1. Clarity of a video image (i.e., one havinggood contrast and faithful tones). 2. Good intelligibilityof reproduced sounds.deflecting coil One of a set of external coils carryingsawtooth currents, which provide electromagneticdeflection of the cathode-ray beam inpicture tubes, camera tubes, radar display tubes,sonar display tubes, and some oscilloscopes. Alsocalled deflection coil.deflecting electrode An electrode, such as a deflectingplate, used to alter the direction an electronbeam. Also called deflection electrode.deflecting plate In a cathode-ray tube, a plate thatattracts or repels the electron beam, causing thespot to move horizontally or vertically on thescreen. Also called deflection plate.ElectrongunDeflectingplates+−deflecting plateScreenPath ofelectrondeflecting torque The torque required to move thepointer of a meter, or the pen or mirror of arecorder.deflection 1. In a cathode-ray tube, movement ofthe electron beam by electric or magnetic fields.2. Movement of the pointer of a meter or the penor mirror of a recorder by an applied current orvoltage.deflection factor Symbol, G. The reciprocal of DE-FLECTION SENSITIVITY.deflection plane In a cathode-ray tube, the planeperpendicular to the axis of the tube. This planecontains the electromagnetic and/or electrostaticlines of flux that result in deflection of the electronbeam.deflection coil See DEFLECTING COIL.deflection electrode See DEFLECTING ELEC-TRODE.deflection plate See DEFLECTING PLATE.deflection polarity In a cathode-ray tube, the polarityof the voltage applied to a particular deflectingplate to move the electron beam in aparticular direction.deflection sensitivity Symbol, S. A quantitativemeasure of the extent to which the input voltagewill displace the electron beam on the screen ofan electrostatic cathode-ray tube. Expressed involts per centimeter (V/cm) or volts per inch(V/in).deflection voltage The potential difference betweenthe deflection plates of an electrostaticcathode-ray tube. It is used to control the directionof the electron beam striking the phosphorscreen.deflection yoke An assembly of deflection coils inpicture and camera tubes, and in some magneticallydeflected oscilloscope tubes. The usual combinationis two series-connected horizontaldeflection coils and two series-connected verticaldeflection coils.deflector1. A beam-forming plate in a beampowertube. 2. A deflection plate in a cathode-raytube. 3. A deflection coil or yoke in a picture tube,camera tube, or magnetic-deflection oscilloscopetube. 4. A mechanical attachment for improvingthe angle of radiation of a loudspeaker by spreadingthe higher-frequency waves.defocusing Blurring of the image on the screen ofa cathode-ray tube, caused by spreading of theelectron beam.deformation potential The voltage generatedwhen a crystal lattice is subjected to pressure. Anexample is the voltage produced by a crystal microphonewhen acoustic waves strike the crystal.defruiting The elimination of non-synchronizedechoes in a radar system.deg Abbreviation of DEGREE.degassing During the evacuation of a vacuum tubeor similar device, the removal of gas, includingthat which has bonded to the glass and metalparts.degauss See DEMAGNETIZE.degausser 1. A circuit that performs DEGAUSS-ING. 2. A device for bulk erasing magnetic tape;also called a bulk tape eraser.degaussing 1. The demagnetization of an object; inparticular, the removal of all residual magnetism.2. The erasure of data from a magnetic ormagneto-optical data-storage medium.degaussing circuit In a color television receiver, acircuit including a thermistor, voltage-dependentresistor, and coil for automatically demagnetizingthe picture tube when the receiver is switched on.degaussing coil A coil carrying an alternating current;the resulting magnetic field demagnetizesobjects that have become accidentally magnetized.degeneracy In microwave practice, the appearanceof a single resonant frequency for two or moremodes in a resonator.degenerate modes In microwave operations, a setof modes with the same resonant frequency orpropagation constant.degenerate parametric amplifier An invertingparametric amplifier, in which the two signals areof the same frequency, which is half the pumpfrequency.

degenerate semiconductor • deka- 175degenerate semiconductor A semiconductor thatbehaves like a metal over a wide range of temperatures.degeneration In an amplifier, the technique offeeding a portion of the output back to the inputout of phase with the input signal, to improve fidelityat the expense of gain. Also called negativefeedback or inverse feedback. Compare REGEN-ERATION.degenerative resistor An unbypassed emitter resistorin a common-emitter bipolar-transistorcircuit, or an unbypassed source resistor in acommon-source field-effect transistor circuit.Signal current flowing through the resistorproduces negative feedback current (degeneration),which reduces the gain of the stage, butincreases the linearity of the transfer characteristic.Indegenerative resistor+DegenerativeresistorOutdegradation 1. Gradual deterioration in the conditionor performance of a circuit or device. 2. In acomputer system, compromised performancecaused by component failure.degradation failure Failure occurring at the terminalpoint of degradation.degraded operation See DEGRADATION.degreaser See ULTRASONIC CLEANING TANK.degree 1. A unit of circular angular measurementequal to 1 /360 of the circumference of a circle. Alsocalled GEOMETRIC DEGREE. 2. A unit oftemperature measurement. See DEGREEABSOLUTE, DEGREE CELSIUS, DEGREE CENTI-GRADE, DEGREE FAHRENHEIT, and DEGREEREAUMUR.degree absolute Symbol, K. The unit of temperatureon the absolute scale. Also see ABSOLUTESCALE.degree Celsius Symbol, °C. The unit of temperatureon the CELSIUS SCALE.degree centigrade Symbol, °C. The unit of temperatureon the centigrade scale (now called CEL-SIUS SCALE).degree Fahrenheit Symbol, °F. The unit of temperatureon the FAHRENHEIT SCALE.degree of current rectification For a rectifier, theratio of the average direct output current to theroot-mean-square (rms) alternating input current.degree of voltage rectification For a rectifier, theratio of the average direct-current (dc) outputvoltage to the root-mean-square (rms) alternating-current(ac) input voltage.degree Reaumur Symbol, °R. The unit of temperatureon the REAUMUR SCALE.degrees of freedom 1. The ways in which a pointcan move or a system can change. In threedimensionalspace, a rigid body has six degrees offreedom: motion in three linear directions, androtation around three linear axes extendingthrough its center. 2. The ways in which a robotarm can move, including linear motion and rotationalmotion.degrees of rotation A measure of the extent towhich a robot joint, or a set of robot joints, can beturned. Some reference axis is always used; anglesare specified in degrees, relative to that axis.degrees-to-radians conversion The conversion ofangles in degrees to angles in radians. To changedegrees to radians, multiply degrees by 0.01745.Compare RADIANS-TO-DEGREES CONVER-SION.deion circuit breaker A circuit breaker in whichthe arc occurring when the contacts open isquickly extinguished by an external magnetic device.deionization The conversion of an ionized substance,such as a gas, to a neutral (non-ionized)state. The process changes the ions into unchargedatoms.deionization potential The voltage at which anionized substance becomes deionized; for example,the voltage at which a glow discharge is extinguishedwhen the gas ions become neutralatoms at that voltage. Also called extinction potential.deionization time The time required for an ionizedgas to become neutral after the removal of theionizing voltage.deionization voltage See DEIONIZATION POTEN-TIAL.deionize To restore to an electrically neutral condition(i.e., to convert ions to neutral atoms, as inthe deionization of the gas when the discharge ina glow tube is extinguished).deka- A prefix meaning ten(s) (e.g., DEKAMETER).

delay timer • demodulator 177delay timer 1. A timer that starts or stops an operationafter a prescribed length of time. 2. A delayrelay or switch.delay unit In a radar system, a circuit for delayingpulses.delete 1. To erase or blank out a signal. 2. Theelimination from a computer file of a record orrecord group. 3. To remove a computer programfrom memory or storage.deletion record In the master file of a digital computer,a new record that causes existing ones tobe deleted.delimiter In digital computer operations, a characterlimiting a sequence of characters of which it isnot itself a member.Dellinger effect The sudden disappearance of aradio signal as a result of an abrupt increase inatmospheric ionization caused by a solar eruption.deliquescent material A material that absorbsenough moisture from the air to get wet. For example;calcium chloride, a deliquescent material,is often used to keep electronic equipment dry.Compare HYGROSCOPIC MATERIAL.delta circuit A three-phase electrical circuit withno common ground.delta connection A triangular connection of coilsor load devices in a three-phase system, so calledfrom its resemblance to the Greek letter delta.Compare WYE-CONNECTION.delta-matched antenna See WYE-MATCHED IM-PEDANCE ANTENNA.delta-matched impedance antenna See WYE-MATCHED IMPEDANCE ANTENNA.delta matching transformer In a WYE-MATCHEDIMPEDANCE ANTENNA, the fanned-out (roughlydelta-shaped) portion of the two-wire feeder at itspoint of connection to the radiator. It matches theimpedance of the feeder to that of the radiator.AntennaradiatorMatchingtransformerParallel-wirefeed linedelta-matching transformerdelta modulation The conversion of an analog signalinto a digital pulse train that can be decodedto yield the original analog signal.delta network See DELTA CONNECTION.delta pulse-code modulation In wire or radiocommunications, the conversion of an audio signalinto a digital pulse train.delta quantity An increment (i.e., the differencebetween two values of a variable).delta rays The emission of secondary electrons asa result of radioactivity.delta-sigma modulation A method of analog-todigitalconversion. The output is a pulse densityfunction of the input. The input can be obtainedby low-pass filtering of the output.delta tune Also called receiver incremental tuning(RIT). In high-frequency (HF) communicationstransceivers, a control that allows the receiverfrequency to be adjusted up to several kilohertzhigher or lower than the transmitter frequency.delta waves Brain waves having a frequency lessthan 9 Hz. Also see ELECTROENCEPHALO-GRAPH and ELECTROENCEPHALOGRAM.Deluc’s pile See DRY PILE.dem Abbreviation of DEMODULATOR.demagnetization curve The portion of a magnetichysteresis curve, showing reduction of demagnetization.demagnetization effect The phenomenon inwhich uncompensated magnetic poles at the surfacecause a reduction of the magnetic field insidea sample of a material.demagnetize To remove magnetism from an object,either temporarily or permanently.demagnetizer See DEGAUSSER.demagnetizing current The half-cycle of an alternatingcurrent (or polarity of a direct current)flowing through a coil wound on a permanentmagnet (as in a headphone, permanent-magnetloudspeaker, or polarized relay), that reduces themagnetic field.demagnetizing force 1. A magnetic force whosedirection reduces the residual induction of amagnetized material. 2. An effect that reduces themagnetism of a permanent magnet, such as hightemperature or a physical blow.demand factor In the use of electric power, the ratioof the consumer’s maximum demand to theactual power consumed.demand processing Descriptive of a system thatprocesses data as it is available, without storingit.demarcation strip An interface between a terminalunit and a carrier line.Dember effect The appearance of a voltage betweenregions in a semiconductor when one ofthe regions is illuminated.demodulation The process of retrieving the information(modulation) from a modulated carrier. Inreceivers and certain test instruments, this processis called DETECTION.demodulator 1. A circuit that recovers the informationfrom a modulated analog or digital signal.In radio communications, such a device isusually called a DETECTOR. 2. In computercommunications, a device that performsANALOG-TO-DIGITAL CONVERSION of incomingonline signals.

178 demand read (write) • depth of dischargedemand read (write) Inputting or outputting datablocks to or from a central processor, as neededfor processing.demodulator probe A diode probe that removesthe modulation envelope from an applied amplitude-modulatedsignal, and presents the envelopeto a voltmeter or oscilloscope.demonstrator A device used to show and teach theway in which a component, circuit, or system operates.DeMorgan’s theorem A rule of sequential or digitallogic. It states that the negation of (A AND B),for any two statements A AND B, is equivalent toNOT A OR NOT B. Also, the negation of (A OR B)is equivalent, logically, to NOT A AND NOT B.demultiplexer A circuit or device that separatesthe components of a multiplexed signal transmittedover a channel.demultiplexing circuit See DEMULTIPLEXER.denary band A band in which the highest frequencyis 10 times the lowest frequency.dendrite 1. The branching (tree-like) structureformed by some materials, such as semiconductors,as they crystallize. 2. The branching portionof a nerve cell; hence, the corresponding circuitelement in the electronic model of such a cell.dendritic growth 1. Dendrite (see DENDRITE, 1).2. The process of growing long, flat semiconductorcrystals.dendron See DENDRITE, 2.dens Abbreviation of DENSITY.dense binary code A binary representation system,in which any possible combination of charactersis assigned some correspondent.densitometer An instrument for measuring thedensity of a body.density 1. Mass per unit volume of a material. 2.Concentration of charge carriers or of lines offlux. 3. The number of items per unit volume,area, distance, or time.density modulation Modulation of the density,with respect to time, of electrons in an electronbeam.Electron beam(Least) (Most) (Least) (Most) (Least)density modulationdensity of electrons The concentration of electrons(i.e., the number per unit volume, area, distance,or time).density packing A figure indicating the quantity ofbits per inch or per centimeter, stored on a magnetictape.dependent equations Equations that are alikeand have an infinite number of solutions. CompareINDEPENDENT EQUATIONS and INCON-SISTENT EQUATIONS.dependent linearity Linearity (especially in its deviationfrom an ideal slope) as a dependent variable.dependent variable A changing quantity whosevalue at any instant is governed by the value atthat instant of another changing quantity (the independentvariable). Compare INDEPENDENTVARIABLE.depletion-enhancement-mode MOSFET A metaloxide-semiconductorfield-effect transistor (MOS-FET) designed for zero gate-bias voltage. An acgate signal voltage drives the MOSFET alternatelyinto the depletion mode (negative signal halfcycle)and enhancement mode (positive signalhalf-cycle). Compare DEPLETION-TYPE MOSFETand ENHANCEMENT-TYPE MOSFET.depletion field-effect transistor A field-effecttransistor whose operation is based on the controlof depletion layer width.depletion layer See BARRIER, 1.depletion-layer capacitance See JUNCTION CA-PACITANCE.depletion-layer rectification Rectification providedby a semiconductor junction.depletion-layer transistor A transistor whose actiondepends on modulation of current carriers ina space-charge region (depletion layer).depletion mode Operation characteristic of theDEPLETION-TYPE MOSFET.depletion region See BARRIER, 1.depletion-type MOSFET A metal-oxide-semiconductorfield-effect transistor (MOSFET) in whichthe channel directly under the gate electrode isnarrowed by a negative gate voltage (in an n-channel device) or by a positive gate voltage (in ap-channel device).depolarization 1. In a primary cell, the removal ofthe agents that have caused polarization. 2. Theaddition of a polarization-inhibiting substance tothe electrolyte of a primary cell.depolarizer A substance that retards polarizationin an electrochemical cell. An example is themanganese dioxide used in dry cells.depolarizing agent See DEPOLARIZER.deposition The application of a layer of one substance(usually a metal) to the surface of another(the substrate), as in evaporation, sputtering,electroplating, silk-screening, etc.depth finder See ACOUSTIC DEPTH FINDER.depth indicator 1. A sounding instrument for determiningthe depth of a body of water. 2. On anACOUSTIC DEPTH FINDER, the meter that indicatesthe depth of water.depth of cut On a phonograph disk, the depth ofthe recorded groove.depth of discharge Abbreviation, DOD. In a rechargeablecell or battery, a measure of the extent

depth of discharge • designation 179to which discharging has occurred. It is generallyspecified as a percentage. For example, if theDOD of a 10-ampere-hour (10-AH) battery is 80percent, then 8 AH have been used up, and 2 AHremain before recharging will be necessary.depth of heating In dielectric heating, the depth ofheat penetration in the sample when both electrodesare applied to one of its faces.depth of modulation The degree to which a carrierwave is modulated.depth of penetration The extent to which a skineffectcurrent penetrates the surface of a conductor.depth sounder See ACOUSTIC DEPTH FINDER.de-Q 1. To reduce the Q of a component or tunedcircuit. 2. To inhibit laser action during aninterval when an ion population excess ispumped up.derating To reduce an operating parameter (e.g.,current, voltage, power) as another factor (suchas temperature) increases, to ensure efficient, reliable,and safe operation.derating curve A graph that shows the extent towhich a quantity (such as allowable power dissipation)must be reduced as another quantity(such as temperature) increases.derating factor The amount by which a current,power, or voltage must be decreased to ensuresafe and efficient operation of a circuit or devicein a given environment (temperature, altitude,humidity, etc.). Also see DERATING and DERAT-ING CURVE.derivative1. A mathematical expression indicatingthe rate at which a function changes, withrespect to the independent variable. SeeDERIVATIVE FUNCTION. 2. The slope of a linetangent to a curve at a given point. 3. The outputsignal of a DIFFERENTIATOR, relative to theinput signal.derivative action In a control system, an actionproducing a corrective signal proportional to thedydx =(Positive)ydydx =derivativedydx = 0(Negative)xrate of change (derivative) of the controlledvariable.derivative control A method of automatic control,actuated according to the number of errors persecond.derivative function For a mathematical functionf (x), the function f '(x) = df (x)/dx, over the domainof f. For any specific point x 0 in the domain of f,the value of f '(x 0 ) is equal to the slope of a linetangent to f at the point (x 0 , f (x 0 )).derived center channel The sum or difference ofthe left and right channels in a stereophonic system.Dershem electrometer A variation of the quadrantelectrometer. In the Dershem instrument, theneedle (to which a small mirror is attached) rotateswithin slots cut in the quadrant plates and,therefore, can never accidentally touch theplates.descending node For a satellite orbiting the earthor another planet, any point at which the groundtrackcrosses the equator as it moves from thenorthern hemisphere into the southern hemisphere.This node generally changes for each succeedingorbit, because the earth or planet rotatesunderneath the orbit of the satellite. CompareASCENDING NODE.descending pass For a specific point on the earth’ssurface, the time during which an artificial communicationssatellite is accessible when its latitudeis moving southward. The duration ofaccessibility depends on the altitude of the satelliteand on how close its groundtrack comes tothe earth-based point. Compare ASCENDINGPASS.description A data element that is part of a recordand is used to identify it.desensitization 1. The process of making a circuitor device less responsive to small values of aquantity. 2. Also called desensing. In a communicationsreceiver, an unwanted, often intermittentreduction in front-end gain, caused by an extremelystrong local signal.desensitize 1. To reduce the sensitivity of a receiver.2. To reduce the gain of an amplifier. 3. Toreduce the small-quantity response of an instrument.desiccant A compound, such as cobalt chloride,used for the purpose of keeping enclosed itemsdry.design 1. A unique, planned arrangement of electroniccomponents in a circuit, in accordancewith good engineering practice, to achieve a desiredend result. 2. A unique layout of componentsor controls, in accordance with goodengineering practice, esthetics, and (often) ergonomics.3. Invention. 4. Plan. 5. To produce adesign, as defined in 1, 2, 3, or 4.designation Within a computer record, coded informationidentifying the record so that it can behandled accordingly.

180 design-center rating • detector blockingdesign-center rating A specified parameter that, ifnot exceeded, should provide acceptable averageperformance for the greatest number of the componentsso rated.design compatibility The degree to which a transmitterand receiver are designed for the rejectionof unwanted electromagnetic noise.design engineer An engineer who is skilled in thecreation of new designs and in the comparativeanalysis of designs.design-maximum rating See MAXIMUM RATING.design-proof test A performance test made on anewly completed circuit or device to determinethe suitability of the design.Desk-Fax A facsimile transceiver that can beplaced on a desktop, used for wire or radio transmissionand reception of still images.desk microphone A microphone equipped with astand that sits on a table or desktop. It allows theoperator to use both hands for equipment adjustment,taking notes, etc.desktop computer A personal computer designedfor nonportable use, usually equipped with abuilt-in hard disk, one or more diskette drives, aCD-ROM drive, and a fax/modem. It generallyuses an external cathode-ray-tube display,printer, and keyboard. The power supply is intendedfor use with 117-volt utility circuits.desolder To unsolder joints, usually with a specialtool that protects delicate parts and removesmelted solder by suction.destaticization A chemical process used to minimizethe retention of electrostatic charges by certainsubstances.CD-ROMdriveDiskettedrive #1HarddiskMicroprocessorandmemoryToexternalsdesktop computer(main unit only)Tophone lineFax/ModemDiskettedrive #2destination 1. The point in a system to which asignal of any sort is directed. 2. In communications,a receiving station.destination file A computer file that receives dataoutput during a specific program run.destination register In a digital computer, a registerinto which data is entered.Destriau effect Light emission resulting from theaction of an alternating electric field on phosphorsembedded in a dielectric.destructive addition A computer logic operationin which the sum of two operands appears inthe memory location occupied by one of theoperands.destructive breakdown A breakdown in which theeffects are irreversible (e.g., permanent damage toa dielectric by excessive applied voltage).destructive interference Interference resultingfrom the addition of two waves that have thesame frequency, but opposite phase.destructive read In a computer or calculator, thecondition in which reading the answer erases thedata (as from a location) used in the calculation.destructive test A test that unavoidably destroysthe test sample. Compare NONDESTRUCTIVETEST.DETAB A COBOL-based computer programminglanguage permitting the programmer to presentproblems as decision tables.detail constant Pertaining to a video signal, theratio V H /V L , where V H is the amplitude of highfrequencycomponents, and V L is the amplitude ofthe low-frequency reference component.detected error In a computer system, an errorthat is identified, but remains uncorrected untilfinal output is available.detection 1. See DEMODULATION. 2. The sensingof a change in the operating parameters of a circuitor system.detection range In security applications, the radiuswithin which transducers or sensors can beexpected to reliably operate. This radius varies,depending on the environment, the sensitivity ofthe receiving circuits and transducers, and thestrength of the transmitted signal (if any).detectophone A device for eavesdropping on aconversation. The device can use a tape recorderor a tiny radio transmitter.detector 1. In radio communications, a device orcircuit that extracts the information from a modulatedcarrier. Also sometimes called a demodulator.2. A device that senses a signal or conditionand indicates its presence.detector balanced bias In a radar system, bias obtainedfrom a controlling circuit and used to reduceor eliminate clutter.detector bias Steady dc voltage applied to a detectorto set its operating point.detector blocking In a regenerative receiver, aphenomenon in which a strong signal tends topull the detector oscillator into phase with itself,

deviation ratio In a frequency-modulated (FM)signal, the ratio between the highest modulatingfrequency and the maximum carrier deviation.deviation sensitivity For a frequency-modulation(FM) receiver, the smallest deviation that will prodetectorblocking • diagnosis 181thereby causing the detector to oscillate at thesignal frequency.detector circuit A demodulator circuit (i.e., oneused to recover the intelligence from a modulatedcarrier).detector probe See DEMODULATOR PROBE.detector pull-in See DETECTOR BLOCKING.detector stage In a receiver or instrument, theseparate stage that contains the detector circuit.Some systems, such as a superheterodyne receiver,have more than one detector. Also seeFIRST DETECTOR and SECOND DETECTOR.detent A mechanical stop used on a rotary switchto hold the switch pole securely in each selectedposition.detune 1. To adjust a circuit to some frequencyother than its resonant frequency. 2. To set thefrequency of a receiver or transmitter to somepoint other than the frequency normally used. 3.To stagger-tune a receiver intermediate-frequencysystem.detuningTuning to a point above or below the frequencyto which a device or system is normally(or initially) adjusted (usually the resonant frequencyof the device).detuning stub A device used for the purpose ofcoupling a feed line to an antenna, while chokingoff currents induced on the feed line as a result ofthe near-field radiation of the antenna.deupdating Producing an earlier form of a computerfile by substituting older records for currentones.deuterium Symbol, D, d, H 2 , or 2 H. Also calledheavy hydrogen. The hydrogen isotope having anucleus consisting of one proton and one neutron.deuterium oxide Symbol, D 2 O. Also called heavywater. This compound has wide use in nuclearreactors.deuteron The nucleus of a deuterium atom.deuton See DEUTERON.deutron See DEUTERON.deviation 1. In a frequency-modulated (FM) radiosignal, the instantaneous amount of carrier frequencyshift away from the unmodulated frequency.It is usually expressed in kilohertz;directly proportional to the amplitude of the modulatingsignal, up to a certain maximum that dependson the bandwidth allowed. 2. Themaximum instantaneous carrier frequency shiftin a FM signal. 3. The extent or amount by whicha quantity drifts from its proper value.deviation distortion In a frequency-modulation(FM) receiver, distortion resulting chiefly fromdiscriminator nonlinearity and restricted bandwidth.duce a specified audio output power. Expressedin kilohertz, or as a percentage of rated deviationof the receiver, measured with the receiver set formaximum gain.device 1. A simple or complex discrete electroniccomponent. 2. A subsystem used as a unit, andregarded as a single component.device complexity The number of components inan integrated circuit.device independence A characteristic of a computer,that allows operation independent of thetypes of input/output devices used.dew point For a gas containing water vapor(typically air), the highest temperature at whichthe vapor condenses as the gas is cooled. The dewpoint depends on the amount of vapor in the gas.dew-point recorder An instrument for determiningand recording the temperature at which watervapor in the air condenses to a liquid.DF Abbreviation of DIRECTION FINDER.DF antenna An antenna that is mechanically rotatableor has an electrically rotatable responsepattern for use with a direction finder.DF antenna system Two or more DF antennas arrangedfor maximum directivity and maneuverability,together with associated feeders andcouplers.D flip-flop A delayed flip-flop. The state of the inputdetermines the state of the output during thefollowing pulse, rather than during the currentpulse.dg Abbreviation of decigram.dia Abbreviation of diameter.diacInstantaneous deviation (kHz)A two-terminal, bilateral, three-layer semiconductordevice that exhibits negative resistance.When the applied voltage exceeds a critical value,the device conducts.diagnosis+6+4+20−2−4−6Deviation= 5 kHz +−deviationTime1. Determination of the cause and locationof a hardware malfunction. 2. In computeroperations, determination of the cause of a systemoperation error.

182 diagnostic routine • diamond latticediagnostic routine 1. An efficient sequence of diagnostictests for rapid, foolproof trouble-shootingof electronic hardware. 2. A computersoftware package intended for debuggingprograms, or for finding the cause of a hardwareor operating-system malfunction. Also calleddiagnostic, diagnostic program, or diagnosticutility.diagnostic test 1. A test made primarily toascertain the cause of dysfunction in electronicequipment. Compare PERFORMANCE TEST. 2.To apply a diagnostic routine to hardware faults,or to implement one to prevent such a fault.diagnotor In digital computer operations, a troubleshootingroutine combining both diagnosisand editing.diagram A (usually line) drawing depicting a circuit,assembly, or organization. See, for example,BLOCK DIAGRAM and CIRCUIT DIAGRAM.dial 1. A graduated scale, arranged horizontally,vertically, in a circle, or over an arc. Used to showthe distance through which a variable component(such as a potentiometer, variable capacitor, orswitch) has been adjusted. A pointer can moveover the scale, or the scale can be moved past astationary pointer. 2. The graduated face of a meter.3. In a telephone system, to press the keys oractuate the tones that establish contact with anothersubscriber.dial cable A flexible cable or belt conveying motionon the shaft of an adjustable component (such asa potentiometer or variable capacitor) to a dial.dial-calibrated attenuator A variable attenuatorwith a dial reading directly in decibels.dial-calibrated capacitor A variable capacitorwith a dial reading directly in picofarads.dial-calibrated inductor A variable inductor witha dial reading directly in microhenrys.dial-calibrated potentiometer A potentiometerwith a dial reading directly in output volts,percentage of input voltage, number of turns(when resistance is a linear function), or otherquantity.dial-calibrated resistor A variable resistor with adial reading directly in ohms, kilohms, ormegohms.dial-calibrated rheostat See DIAL-CALIBRATEDRESISTOR.dial cord A form of dial cable. Cord usually designatesa fabric string, whereas a cable is a flexible,braided wire.dial knob The knob used to turn a dial under apointer, or to turn a pointer over a dial scale.dial lamp See DIAL LIGHT.dial light A small lamp sometimes used to illuminatea dial. Can also serve as a pilot light.dial lock A small mechanism used to lock a dial ata particular setting to prevent further turning.dialer See AUTOMATIC DIALING UNIT.dialing key In a telephone system, a dial that useskeys, rather than a rotary dial.dial jack In a telephone system, a set of jacks thatfacilitates interconnections between dial cordsand external lines.dial light A lamp or light-emitting diode placed inthe dial mechanism of a radio receiver, transmitter,or transceiver. Allows the dial to be read indim light or in darkness.dialog equalizer In sound transmission and recording,a high-pass filter that reduces lowfrequencyresponse during dialog and extremecloseups.dial pulse An interruption of the direct current in atelephone system when the dial contacts of thecalling telephone open. The number of such interruptionscorresponds to the digit dialed.dial scale The graduated portion of a dial.dial system 1. See DIAL TELEPHONE SYSTEM.2. The arrangement of dials and knobs that facilitatesadjustment of electronic equipment.dial telephone A telephone set in which a numberedrotatable disk is used to produce the switchinterruptions that cause generation of the transmittedmultidigit telephone numbers.dial telephone system The complete automaticcircuit, including central-office facilities, for dialtelephone operation.dial tone In a telephone system, a constant hum orwhine heard before dialing, indicating that thesystem is operational.dial-up In a telephone system, the calling of onesubscriber by another, using a dial system.diam Abbreviation of diameter.diamagnetic Pertaining to a material having magneticpermeability less than unity.diamagnetism The state of having magnetic permeabilityless than unity. A material with this propertyreduces the flux density of a magnetic field,relative to the flux density in air or in free space.diamond antenna Also called rhombic antenna.A nonresonant wideband directional antennawhose horizontal wire elements are arranged inthe shape of a diamond (rhombus). The arrangementis fed at one corner, the opposite corner beingterminated with a noninductive resistor.diamond lattice The orderly internal arrangementof atoms in a redundant pattern in crystallinematerials, such as germanium or silicon.FeedLinexxxxAll sides x are equalx ≥ 1 λdiamond antenna≈ 600 ΩMaximumradiation

diamond stylus • dielectric constant 183diamond stylus A phonograph “needle” having asits point a small, ground diamond.diapason 1. Either of the two principal stops (openand closed) of an electronic organ that cover theentire range of the instrument. When one is used,a note played is automatically sounded in severaloctaves. 2. Tuning fork.diaphony See DISSONANCE.diaphragm A usually thin metal or dielectric diskused as the vibrating member in headphones,loudspeakers, and microphones, and as the pressure-sensitiveelement in some sensors andbarometers.diaphragm gauge A sensitive gas pressure gaugeusing a thin metal diaphragm stretched flat. Incrementsof pressure move the diaphragm,relative to a nearby electrode, varying thecapacitance between the two.diathermic Pertaining to a substance that efficientlytransfers heat or infrared energy.diathermotherapy The use of diathermy in thetreatment of various physiological disorders.diathermy 1. In medicine and physical therapy,the production of heat in subcutaneous (belowthe skin) tissues by means of high-frequency radiowaves. 2. A radio-frequency (RF) power oscillatorand associated equipment used to produceheat in subcutaneous tissues.diathermy interference Radio-frequency interference(RFI) resulting from the operation ofunshielded and/or unfiltered diathermy equipment.diathermy machine See DIATHERMY, 2.diatomic Having two atoms (e.g., a DIATOMICMOLECULE).diatomic molecule A molecule (such as that ofoxygen) composed of two atoms. Compare MON-ATOMIC MOLECULE.dibble A mathematical function in which a number(usually an integer) is doubled, and then one isadded to the result. Thus, dibble n = 2n + 1.dibit A combination of two binary digits (bits). Thefour possible dibits are 00, 01, 10, and 11.dice Plural of DIE, 1, 3.dichotomizing search Also called binary search.In digital computer operations, locating an itemin a table of items that are arranged by key valuesin serial order. The required key is compared witha key halfway through the table; according to thisrelational test, half of the table is accepted andagain divided for comparison, etc. until the keysmatch and the item is found.dichotomy Characterized by the usually repetitivebranching into two sets, groups, or factions.dichroism Also called dichromatism. 1. The propertyof a crystal showing different colors,depending on which axis corresponds to the lineof sight. 2. The property of a solid taking on differentcolors as the thickness of the transmittinglayer changes. 3. The property of a liquid changingcolor, according to solution concentration.dichromate cell An electrolytic cell consisting ofelectrodes of carbon and zinc. The zinc electrodeis immersed in a diluted solution of sulfuric acid,and the carbon electrode in a solution of potassiumdichromate.dicing The cutting of a semiconductor melt, crystalwafer, or other material into dice (see DIE).dictionary A table of specifications for the size andformat of computer file operands, and datanames for field and file types.die 1. A small wafer of useful electrical material,such as a semiconductor or a precision resistorchip. 2. A casting designed to mold molten metalinto a specific configuration until the metal hardens.3. Any small object of roughly cubical proportions.4. To lose power or energy completely,usually unintentionally. 5. In a computer program,to produce unpredicted and useless resultsfollowing an initial run.die bonding The bonding of dice or chips to a substrate.die casting Making a casting by forcing moltenmetal (such as an aluminum alloy, lead, tin, orzinc) under high pressure into a die or mold.dielectric A material that is a nonconductor ofelectricity; especially, a substance that facilitatesthe storage of energy in the form of an electricfield. Such materials are commonly used in capacitorsand transmission lines.dielectric absorption The ability of certain dielectricmaterials to retain some of their electriccharge—even after being momentarily shortcircuited.Capacitors with this property must beshorted out continuously for a certain length oftime before the dielectric has completely discharged.dielectric amplifier A voltage amplifier circuit inwhich the active component is a capacitor havinga nonlinear dielectric. A signal voltage applied tothe capacitor varies the capacitance, thus varyingthe current. The modulated current flowsthrough a load resistor, developing an outputsignalvoltage higher than the input-signal voltage.dielectric antenna An antenna in which some orall of the radiating element is made of a dielectricmaterial, such as polystyrene. Primarily used atmicrowave frequencies.dielectric breakdown Sudden, destructive conductionthrough a dielectric when the appliedvoltage exceeds a critical value.dielectric breakdown voltage The voltage atwhich DIELECTRIC BREAKDOWN occurs in aninsulating material. Varies, depending on theparticular dielectric substance.dielectric capacity See DIELECTRIC CONSTANT.dielectric constant Symbol, k. For a dielectric material,the ratio of the capacitance of a two-platecapacitor using the dielectric material, to the capacitanceof the equivalent capacitor with dry airas a dielectric. Also called inductivity and specificinductive capacity.

184 dielectric current • dielectric wiredielectric current 1. Current flowing over the surfaceof a dielectric material in response to a varyingelectric field. 2. Current flowing through adielectric as a result of its finite insulation resistance.dielectric dissipation For a dielectric material inwhich an electric field exists, the ratio of the lost(dissipated) electrical energy to the recoverableelectrical energy.dielectric dissipation factor The cotangent of thedielectric phase angle, also equal to the reciprocalof the Q factor.dielectric fatigue In some dielectric materialssubjected to a constant voltage, the deteriorationof dielectric properties with time.dielectric guide A waveguide made from a solid dielectric,such as polystyrene.dielectric heater A high-frequency power generatorused for DIELECTRIC HEATING.dielectric heating The heating and forming of adielectric material, such as a plastic, by temporarilymaking the material the dielectric of atwo-plate capacitor. This capacitor is connectedto the output of a high-power radio-frequency(RF) generator. Losses in the dielectric cause itsheating. Compare INDUCTION HEATING.dielectric hysteresis See DIELECTRIC ABSORP-TION.dielectric isolation In a monolithic integrated circuit(IC), the isolation of circuit elements fromeach other by a dielectric film, as opposed to isolationby reverse-biased pn junctions.dielectric lens A molded piece of dielectric materialused to focus microwaves. Its operation isanalogous to that of an optical lens.MicrowaveBeamDielectricmaterialdielectric lensdielectric loss For a dielectric material subjectedto a changing electric field, the rate of transformationof electric energy into heat.dielectric loss angle Ninety degrees minus the DI-ELECTRIC PHASE ANGLE.dielectric loss factor For a dielectric material, theproduct of the dielectric constant and the tangentof the dielectric loss angle.dielectric loss index See DIELECTRIC LOSS FAC-TOR.dielectric matching plate A dielectric plate usedin some waveguides for impedance matching.dielectric mirror A reflector containing a numberof layers of dielectric material. Its action dependson electromagnetic energy being partially reflectedfrom the interfaces between materialshaving unequal indexes of refraction.dielectric phase angle For a dielectric material,the angular phase difference between a sinusoidalvoltage applied to the material and thecomponent of the resultant current having thesame period as that of the voltage.dielectric phase difference See DIELECTRICLOSS ANGLE.dielectric polarization The effect characterized bythe slight displacement of the positive charge ineach atom of a dielectric material, with respect tothe negative charge, under the influence of anelectric field.dielectric power factor The cosine of the dielectricphase angle, or the sine of the dielectric loss angle.dielectric puncture voltage See DIELECTRICBREAKDOWN VOLTAGE.dielectric rating The breakdown voltage, andsometimes the power factor, of the dielectric materialused in a device, such as a relay, motor, orswitch.dielectric ratings Electrical characteristics of a dielectricmaterial: breakdown voltage, power factor,dielectric constant, etc.dielectric resistance See INSULATION RESIS-TANCE.dielectric rigidity See DIELECTRIC STRENGTH.dielectric-rod antenna A unidirectional antennathat uses a dielectric substance to obtain powergain.dielectric soak See DIELECTRIC ABSORPTION.dielectric strain The distorted internal state of adielectric, caused by the influence of an electricfield. Also called DIELECTRIC STRESS.dielectric strength The highest voltage a dielectriccan withstand before DIELECTRIC BREAKDOWNoccurs. Usually expressed in volts or kilovolts permil of material thickness.dielectric stress The distortion of electron orbitsin the atoms of a dielectric material subjected toan electric field.dielectric susceptibility For a polarized dielectric,the ratio of polarization to electric intensity.dielectric tests Laboratory experiments performedto determine the dielectric characteristics of asubstance—especially the dielectric constant andthe dielectric breakdown voltage.dielectric waveguide See DIELECTRIC GUIDE.dielectric wedge A wedge-shaped dielectric slugplaced inside a waveguide for impedance matching.dielectric wire A small dielectric waveguide thatacts as a wire to carry signals between points in acircuit.

Dietzhold network • differential input 185Dietzhold network A four-terminal, shunt m-derivedcircuit used in some wideband amplifiers.Dietzhold peaking In some wideband amplifiers,frequency compensation obtained with a shuntm-derived network (see DIETZHOLD NETWORK).difference amplifier See DIFFERENTIAL AMPLI-FIER.difference channel In a stereophonic amplifier, anaudio channel that handles the difference betweensignals in the right channel and those inthe left channel.difference detector A detector whose output is thedifference between two simultaneous input signals.difference frequency A signal frequency producedby mixing or heterodyning of signals at two otherfrequencies. If the lower input signal frequency isf 1 and the higher input signal frequency is f 2 ,then the difference frequency f d is equal to f 2 – f 1 .difference of potential The absolute value of thealgebraic difference of voltages at two points ofdifferent electrical potential. Thus, the differenceof potential between a +5-V point and a –5-Vpoint is +5 – (–5) V = 10 V. Also see POTENTIALDIFFERENCE.difference quantity See INCREMENT.difference signal 1. The resultant signal obtainedby subtracting, at every instant for at least onefull cycle, the amplitudes of two signals. 2. Thedifference of the left- and right-channel outputsin a stereo system.differential 1. A device, consisting of a gear system,that adds or subtracts angular motions anddelivers the result. 2. A gear system in which themotion of a shaft is transferred to two othershafts aligned with each other and perpendicularto the first shaft. 3. One of two coils arranged toproduce opposite polarities at a point in a circuit.4. Pertaining to a difference between two signalsor quantities.differential amplifier A circuit, usually an operationalamplifier, that amplifies the voltage differencebetween two input signals. Theinstantaneous output voltage is equal to someconstant multiple of the difference between theinstantaneous input voltages.differential analyzer An analog computer thatsolves differential equations using integrators.differential angle For a mercury switch, the anglebetween operation and release positions.differential capacitor A dual variable capacitorwith two identical stator sections, and a single rotorsection that turns into one stator section andout of the other. The capacitance of one sectiondecreases while that of the other increases.differential coil See DIFFERENTIAL, 3.differential comparator A linear integrated circuit(IC) that delivers an output proportional to thedifference between two input signals.differential compound dc generator A compound-wounddc generator in which the magne-End viewRotordifferential capacitorStator AStator Btomotive force of the series field opposes that ofthe shunt (main) field.differential compound dc motor A compoundwounddc motor in which the magnetomotiveforce of the series field coil opposes that of theshunt (main) field coil.differential cooling Reducing temperature at differentpoints on a surface at different rates.differential delay The difference d max – d min acrossa frequency band, where d max is the maximumfrequency delay and d min is the minimum frequencydelay.differential discriminator A device that passespulses, whose amplitudes are between two predeterminedvalues above or below zero.differential distortion In an automatic-gaincontrolcircuit, distortion from effects that causeshunting of the diode load resistor.differential flutter Fluctuations in the speed of amagnetic tape that are nonuniform in differentparts of the tape.differential gain In a differential amplifier, the averagegain of the two sections of the amplifier.Compare DIFFERENTIAL UNBALANCE.differential gain control A circuit or device forsetting the gain of a radio receiver in terms of ananticipated change in signal strength, to reducethe receiver output signal differential.differential galvanometer A galvanometer inwhich currents in two similar coils neutralizeeach other; thus, there is zero deflection when thecurrents are equal.differential gap The smallest range of values thata controlled variable must take to change a threepositioncontroller’s output from on to off, or viceversa.differential heating Increase of temperature atdifferent points on a surface at different rates.differential impedance See DIFFERENTIAL-INPUT IMPEDANCE.differential induction coil An induction coil havingtwo differentially wound primary coils.differential input In a differential amplifier, thecircuit between input terminals 1 and 2, as opposedto the circuit between input 1 or input 2and ground.

186 differential-input amplifier • differential-wound fielddifferential-input amplifier A differential amplifierwhose output is proportional to the differencebetween two input signals—each applied betweenan input terminal and common ground.differential-input capacitance In a differentialamplifier, the capacitance between the input terminals.differential-input impedance In a differential amplifier,the impedance between the input terminals.differential-input measurement For a differentialamplifier, a floating measurement made betweenthe input terminals.differential-input rating In an operational amplifier,the greatest difference signal that can beplaced between the inputs while allowing properoperation.differential-input resistance In a differential amplifier,the resistance between the input terminals.differential-input voltage In a differential amplifier,the signal voltage presented to the floatinginput terminals.differential-input voltage range In a differentialamplifier, the range of signal voltages that can beapplied between the differential input terminalswithout overdriving the amplifier.differential input-voltage rating The maximumdifferential-input voltage that can be appliedsafely to a differential amplifier.differential instrument A galvanometer or othermeter in which deflection results from the differentialeffect of currents flowing in opposite directionsthrough two identical coils. Also seeDIFFERENTIAL GALVANOMETER.differential keying A system of break-in keying, inwhich the oscillator stage of a transmitter containinga keyed amplifier is disabled when the keyis open to prevent interference with the receiverat the keying station, and is enabled when thekey is closed.differential-mode gain In an operational amplifier,the ratio, in decibels, between the outputvoltage and the differential input voltage.differential-mode input In an operational amplifierin differential mode, the difference betweenthe two input signal voltages.differential-mode signal In a balanced threeterminalcircuit, such as the input of a differentialamplifier, a signal applied between thefloating (ungrounded) input terminals.differential multiplexer An analog multiplexerthat selects both the high and low portion of theinput signal.differential nonlinearity Incremental error froman ideal analog output difference when the inputis changed by a certain value. Generally expressedas a fraction of full-scale output.differential permeability The derivative of normalinduction, with respect to magnetizing force.differential phase In a television system testedwith a low-level, high-frequency sine-wave signal(f 1 ) superimposed on a low-frequency, sine-wavesignal (f 2 ), the difference in phase shift of f 1throughout the system for two specified levels off 2 .differential phase-shift keying Keying of a carrierby varying the carrier phase.differential pressure The difference in pressurebetween two points.differential-pressure transducer A transducerthat delivers an output proportional to the differencebetween two sensed actuating pressures.differential protective relay A differential relaythat operates to protect equipment or personnelwhen the difference between the two actuatingquantities reaches a prescribed level.differential receiver A synchro differential that receivesthe electrical output of two synchro transmitters.The receiver can subtract one inputvoltage from the other.differential relay A relay actuated by the differencebetween two currents or voltages.differential selsyn A selsyn in which the positionassumed by the rotor is proportional to the sumof rotor and stator field values.differential stage See DIFFERENTIAL AMPLIFIER.differential synchro See DIFFERENTIAL RE-CEIVER and DIFFERENTIAL TRANSMITTER.differential transducer A dual-input, single-outputsensor, such as a pressure transducer, thatis actuated by two sensed quantities and deliversan output proportional to their difference.differential transformer A variable inductancetransformer having a (usually cylindrical) corethat is moved in and out to provide adjustablecoupling between the interwound primary andsecondary windings. This permits adjustment ofthe amplitude and phase of the transformer outputvoltage, with respect to the input voltage.differential transmitter A synchro differentialconnected to a synchro transmitter. In a synchroreceiver supplied by this combination, the changein rotor position is the algebraic difference betweenthe transmitter-rotor position and the differential-rotorposition.differential unbalance For a differential amplifier,the average difference in gain between the twoamplifier sections. Compare DIFFERENTIALGAIN.differential voltage 1. The voltage difference betweenthe input signals to a differential device. 2.The breakdown voltage minus the operating voltagefor a lamp.differential voltage gain 1. The ratio, in decibels,between the differential output and differential inputvoltages of an amplifier. 2. The instantaneousratio, in decibels, between the rate of change ofthe output signal voltage and the rate of change ofthe input signal voltage in an amplifier.differential-wound field In a motor or generator, afield winding having series and shunt coils whosefields are opposing.

differentiate • diffused sound 187differentiate 1. To produce an output signal, theinstantaneous amplitude of which is proportionalto the instantaneous rate of change of the inputamplitude. 2. To determine the derivative of amathematical function.differentiating circuit See DIFFERENTIATINGNETWORK.differentiating network A four-terminal resistance-capacitance(RC) network whose outputvoltage is the derivative of the input voltage, withrespect to time. Compare INTEGRATING NET-WORK.differentiation 1. The processing of an input signalto create an output signal whose voltagewaveform represents the derivative, with respectto time, of the input voltage waveform. 2. The processof computing a mathematical derivative.differentiator 1. See DIFFERENTIATING NET-WORK. 2. An operational amplifier whose outputwaveform is the mathematical derivative of theinput waveform.E iCRA Vdifferentiator, 2E o = −RC (dE i /dt)diffracted wave A wave or ray of energy undergoingDIFFRACTION.diffraction 1. Interference of one part of an energybeam with another part when the beam is deflectedalong two or more paths having differentlengths. When this happens with visible light,dark and light bands or colored bands appear.This effect is responsible for the rainbow-like appearanceof light reflected from the surface of acompact disc. 2. The bending of electromagneticwaves around an object. This effect explains whyradio signals can propagate around large obstructions,such as buildings and hills. The effectbecomes more pronounced as the wavelength increases(the frequency decreases). 3. The bendingof acoustic waves around an object. This effectexplains why sound propagates around large obstructions,such as buildings. The effect becomesmore pronounced as the wavelength increases(the frequency decreases).diffraction grating A transparent plate containingthousands of parallel lines or grooves spaced extremelyclose together. Light passing through theslits between the lines produces a rainbow spectrumas a result of DIFFRACTION.diffraction spectrum 1. The spectrum producedin visible light by a diffraction grating. 2. The dis-tribution of energy at various frequencies, producedby diffraction of electromagnetic waves. 3.The distribution of energy at various frequencies,produced by diffraction of acoustic waves.diffractometer An instrument for measuring thediffraction of radiation, such as light or X-rays.diffuse 1. To produce or cause DIFFUSION. 2. Energythat is diffused.diffused-alloy transistor See DRIFT-FIELD TRAN-SISTOR.diffused-base transistor A bipolar transistor inwhich the base region has been diffused into thesemiconductor wafer. Also see DIFFUSED JUNC-TION.diffused device A semiconductor device in whichthe junction is produced by diffusion (see DIFFU-SION, 1). Examples: DIFFUSED-BASE TRANSIS-TOR, DIFFUSED DIODE, DIFFUSED-JUNCTIONRECTIFIER, and DIFFUSED-MESA TRANSIS-TOR.diffused diode A semiconductor diode having adiffused junction.diffused-emitter-and-base transistor A transistorin which n and p materials both have been diffusedinto the semiconductor wafer to provideemitter and base junctions. Also see DIFFUSION,1 and DIFFUSED TRANSISTOR.diffused junction In a semiconductor device, a pnjunction formed by diffusing a gas into a semiconductorat a high temperature that is below themelting point of the semiconductor. Typically, agas containing an n-type impurity is diffused intop-type semiconductor material. Compare ALLOYJUNCTION.diffused-junction rectifier A semiconductor rectifierusing a diffused junction.diffused-junction transistor See DIFFUSED-BASE TRANSISTOR, DIFFUSED-MESA TRAN-SISTOR, and DIFFUSED TRANSISTOR.diffused-layer resistor In an integrated circuit, aresistor produced by diffusing a suitable materialinto the substrate.diffused-mesa transistor A transistor whose baseis a n-type layer diffused into a p-type wafer (theremaining p-type material serving as the collector);its emitter is a small p-type area diffusedinto or alloyed with the n-layer. Unwanted diffusedportions are etched away, leaving the transistorin a mesa shape.diffused planar transistor A diffused transistor inwhich emitter, base, and collector electrodes areexposed at the face of the wafer, which has an oxidelayer to forestall leakage between surface electrodes.diffused resistor See DIFFUSED-LAYER RESIS-TOR.diffused sound 1. Sound distributed so that itsenergy flux is the same at all points. 2. Soundwhose source is difficult to locate or seems toshift, as that heard from out-of-phase stereochannels.

188 diffused transistor • digital comparatordiffused transistor A transistor in which one orboth electrodes are created by diffusion. See DIF-FUSED JUNCTION.diffused-junction transistor See DIFFUSED-BASE TRANSISTOR, DIFFUSED-MESA TRAN-SISTOR, and DIFFUSED TRANSISTOR.diffusion 1. In the fabrication of semiconductordevices, the slow, controlled introduction of a materialinto the semiconductor, for example, thehigh-temperature diffusion of a n-type impurity(from a gas containing it) into a p-type wafer toform a diode. 2. The random velocity and movementof current carriers in a semiconductor, resultingfrom a high-density gradient. 3. Thecharacteristic spreading of light reflected from arough surface or transmitted through a translucentmaterial. 4. The spreading-out of soundwaves, for example when reflected from acousticbaffles. 5. The migration of atoms from one substanceto another, as in the spreading of one gasthroughout another.IncidentraysTranslucentmaterialdiffusion, 3Transmittedraysdiffusion bonding A method of joining differentsubstances by diffusing atoms of one into theother. This technique is employed in the manufactureof certain semiconductor diodes, transistors,and other devices.diffusion capacitance The current-dependent capacitanceof a forward-biased semiconductorjunction.diffusion current Current resulting from the diffusionof carriers within a substance (see DIFFU-SION, 2).diffusion length In a semiconductor junction, thedistance a current carrier travels to the junctionduring carrier life.diffusion process 1. The technique of processingsemiconductor devices by diffusion (see DIFFU-SION, 1). 2. Producing a high vacuum by meansof diffusion (see DIFFUSION PUMP).diffusion pump A pump for fast, efficient creationof a high vacuum in electron tubes and similardevices. In one form, the pump, in conjunctionwith a force pump, uses mercury vapor as thepumped medium. Gas molecules evacuated fromthe device diffuse into a chamber, where condensingmercury vapor traps and carries themoff.diffusion theory The notion that, in a homogeneousmedium, current density is directlyproportional to the gradient of particle fluxdensity.diffusion transistor A transistor whose operationis based principally on the diffusion of currentcarriers (see DIFFUSION, 2).diffusor In acoustics, a device or structure deliberatelyinstalled to spread sound waves throughouta region.dig-in angle A stylus angle of 90 degrees, relativeto the surface of a phonograph disc. CompareDRAG ANGLE.DIGIRALT Acronym for digital radar altimetry. Asystem that utilizes digital techniques to enhancethe accuracy of an altimeter using radar.digit A single symbol in a numbering system (e.g.,0 through 9 in the decimal system, or 0 or 1 inthe binary system), whose value depends on itsposition in a group and on the radix of the particularsystem used.digital 1. Pertaining to components, circuits, orsystems that use signals having an integral numberof discrete levels or values, rather than signals,whose levels or values vary over acontinuous range. 2. Pertaining to a numericreadout or display. 3. See BINARY, 1.digital annunciator An annunciator that gives analphanumeric digital display of information, aswell as sounding an alarm.digital audio tape Abbreviation, DAT. A magnetictape intended for recording digitally encoded audiodata. Used in some high-fidelity applications,and also for computer data storage.digital barometer An electronic barometer providinga digital readout.digital capacitance meter Abbreviation DCM. Ameter with a digital readout for measuring capacitancevalues.digital cellular See PERSONAL COMMUNICA-TIONS SERVICE.digital circuit A circuit affording a dual-stateswitching operation (i.e., on or off, high or low,etc.). Also called binary circuit.digital communications Radio or wire communicationsusing a dual-state mechanism (on/off,positive/negative, or modulated/unmodulated)to represent information.digital comparator A comparator that presentstwo digital values, one for each of the quantitiesbeing compared.

digital computer • digital representation 189digital computer A high-speed, electronic machinefor performing mathematical operations,file management, machine control, or other “intelligent”functions, and whose basic internaloperations (data storage, comparing, and computation)are based on semiconductor devices assumingone of two states (on or off, high or low).Compare ANALOG COMPUTER.digital data Information represented and processedin the form of combinations of digits (0and 1, in the binary system).digital-data cable A cable designed to conducthigh-speed digital pulses with minimal distortionand loss.digital data-handling system A system that accepts,sorts, modifies, classifies, or records digitaldata, displaying the final result or passing thedata to a computer.digital delay circuit A device that stores digitizedaudio data, and releases it after a specified delay.digital device 1. A digital integrated circuit (IC). 2.Any circuit or system that operates by digitalmeans.digital differential analyzer Abbreviation, DDA. Adigital computer that can perform integration usingspecialized circuitry.digital display A presentation of information (suchas the answer to a problem) in the form of actualdigits, as opposed to one in the form of, for example,a meter deflection. See, for example, DIGI-TAL-TYPE METER.digital divider In a computer, a device that can divide(i.e., provide a quotient and remainder usingdividend and divisor signals).digital electrometer An electrometer that has adigital current or voltage indicator.digital electronics The branch of electronics concernedwith components, circuits, and systemsthat use signals having an integral number of discretelevels or values, as opposed to signalswhose levels or values vary over a continuousrange. Compare ANALOG ELECTRONICS.digital frequency meter A direct-reading frequencymeter using high-speed electronic switchingcircuits and a digital readout. Suchinstruments read frequency from less than 1 Hzto many gigahertz.digital HIC A hybrid integrated circuit (HIC) designedfor digital applications. Also see DIGITALINTEGRATED CIRCUIT.digital IC See DIGITAL INTEGRATED CIRCUIT.digital incremental plotter A device that candraw, according to signals received from a computer,graphs depicting solutions to problems.digital information See DIGITAL DATA.digital information display See DIGITAL DIS-PLAY.digital integrated circuit An integrated circuit(IC) intended for binary operations, such asswitching, gating, etc. Compare LINEAR INTE-GRATED CIRCUIT.digital integrator A device that can perform integration,in which increments in input variables,and an output variable, are represented by digitalsignals.digital logic A form of Boolean algebra, consistingof negation, conjunction, and disjunction, inwhich the binary digit 1 has the value “true” and0 the value “false” (in positive logic) or vice versa(in negative logic). Digital logic is the basis bywhich all digital devices function.digital-logic module 1. A circuit that performsdigital operations. 2. A logic gate.digital meter A meter that produces a readout indiscrete blocks or directly as numerals. The first,more primitive and less precise type, is known as aBAR METER. The second, more sophisticated typecan resolve to several significant digits and oftenincludes a fixed or floating radix point. Thisscheme eliminates the need for personnel to interpolatethe reading on a scale. There is little chancefor error on the part of the technician or engineer,because the readout is straightforward. Anotheradvantage is the fact that there are no movingparts to wear out or be damaged by physical shock.Compare ANALOG METER.digital multimeter Abbreviation, DMM. Avoltohm-milliammeter producing a digital readoutof measured values.digital multiplex 1. The combination of several ormany digital signals into a single digital signal. 2.Also called digital demultiplex. The reverse processfrom that defined in 1, in which the originalsignals are obtained from the combination signal.3. Communication using the techniques definedin 1 and 2.digital multiplex equipment Equipment that accomplishesdigital multiplexing or the reverseprocess, digital demultiplexing.digital multiplier In a digital computer, a devicethat produces a product signal from multiplierand multiplicand signals.digital output An output signal of digital pulsesrepresenting a number equal or proportional tothe value of a corresponding input signal.digital panel meter A numeric-readout meter whoserelatively small size allows mounting on a panel.digital phase shifter A phase shifter actuated by adigital control signal.digital photometer An electronic photometer providinga digital readout of illumination values.digital power meter An electronic wattmeter providinga digital readout of measured power.digital readout An indicating device that displaysa sequence of numerals that represent a measuredvalue.digital recording A system for tape-recordinghigh-fidelity sound. The audio is converted fromanalog to binary digital form, and the binary digits(bits) are recorded on magnetic tape.digital representation The use of digital signals torepresent information as characters or numbers.

190 digital rotary transducer • digit delay elementdigital rotary transducer A device that delivers adigital output signal proportional to the rotationof a shaft.Digital Satellite System Abbreviation, DSS. Tradename for a satellite television (TV) system developedby RCA. The analog signal is changed intodigital pulses at the transmitting station viaanalog-to-digital (A/D) conversion. The digitalsignal is amplified and uplinked to a geostationarysatellite. The satellite has a transponder thatreceives the signal, converts it to a different frequency,and downlinks it back to the earth. Thedownlink is picked up by a portable dish that canbe placed on a balcony or patio, on a rooftop, orin a window. A tuner selects the channel that thesubscriber wants to watch. The digital signal isamplified. If necessary, digital signal processing(DSP) can be used to improve the quality of receptionunder marginal conditions. The digitalsignal is changed back into analog form, suitablefor viewing on a conventional TV set, via digitalto-analog(D/A) conversion.digital signal A signal having an integral numberof discrete levels or values, as opposed to a signalwhose levels or values vary over a continuousrange.10digital signalTimedigital signal processing Abbreviation, DSP. Amethod of signal enhancement that operates byeliminating confusion between digital states. Thisimproves dynamic range and frequency response,reduces the number of errors, and virtually eliminatesnoise. It is used extensively in digital communicationand recording, often in conjunctionwith analog-to-digital (A/D) and digital-to-analog(D/A) conversion to enhance the quality of analogsignals and recordings.digital sound Sound recording and reproductionaccomplished with digital, rather than analog,signals. Advantages include wideband frequencyresponse, superior dynamic range, and relativeimmunity to noise.digital speech communications A system of voicecommunications, in which the analog voice signalis encoded into digital pulses at the transmitter,and decoded at the receiver.digital subtractor In a computer, a device that producesan output signal whose value is equal to thedifference of the values of two input signals.digital switching Routing operations carried outon digital signals to establish communicationslinks between specified system users.digital television 1. A television system in whichthe picture information is encoded into digitalform at the transmitter, and decoded at the receiver.2. A form of television picture transmissionthat functions according to picture motion,rather than absolute brightness.digital temperature indicator See DIGITALTHERMOMETER.digital thermometer An electronic thermometerthat provides a digital readout of temperature.digital-to-analog conversion The conversion of adigital quantity into an analog representation,such as shown by a performance curve. CompareANALOG-TO-DIGITAL CONVERSION.digital-to-analog converter A circuit or devicethat performs DIGITAL-TO-ANALOG CONVER-SION.digital transmission 1. A method of signaltransmission in which the modulation occursin defined increments, rather than over a continuousrange. 2. A message that is sent in digitalform.digital-type meter An indicating instrument inwhich a row of numeral indicators displays avalue. Compare ANALOG-TYPE METER.digital voltmeter Abbreviation, DVM. An electronicvoltmeter having a direct numerical readout,rather than an analog display.digital wattmeter See DIGITAL POWER METER.digital compression In digital computer operation,the process of representing data with aneconomy of characters to reduce file size.digit current In digital computer operations, thecurrent associated with writing or reading a digitinto or out of a memory cell.digit delay element A logic element (gate) whoseoutput signal lags the input signal by one digitperiod.

digit filter • diode-capacitor memory cell 191digit filter A device for detecting designations. SeeDESIGNATION.digitize 1. To express the results of an analogmeasurement in digital units. 2. To convert ananalog signal into corresponding digital pulses.digitizer See ANALOG-TO-DIGITAL CONVERTER.digit period In a digital circuit or system, the timeinterval between the start of one digital pulse andthe start of the next pulse.digit place See DIGIT POSITION.digit plane In a matrix-type computer memory, theplane within a three-dimensional array of memorystorage elements representing a DIGIT POSI-TION.digit position The ordinal position of a digit in anumeral, the first position being occupied by theleast-significant digit (e.g., 7 is in the third positionin the numeral 756).digit pulse A pulse that energizes magnetic corememory elements representing a digit position inseveral words.digitron A display in which all of the characters liein a single, flat plane.digit time The duration of a digit signal in a seriesof signals.digit time slot In digital communications, the intervalof time assigned to one bit or one digit.digit-transfer bus In a digital computer, a mainline (of conductors) that transfers informationamong various registers; it does not handle controlsignals.diheptal CRT base The 14-pin base of a cathoderaytube. Also see BIDECAL, DUODECAL, andMAGNAL.DIIC Abbreviation for dielectric-isolated integratedcircuit. Several separate integrated-circuit wafersare contained in a single package, and kept electricallyinsulated by layers of dielectric.dilatometer An instrument used to measure expansion.dimension 1. Any measurable quantity, such asdistance, time, temperature, humidity, etc. 2. Anaxis in the three-dimensional Cartesian coordinatesystem. 3. An independent variable in afunction of one or more variables.dimensional analysis A mathematical procedurewhereby an equation involving quantities withdifferent units is verified as being dimensionallycorrect. The original variables are replaced withfundamental quantities, such as resistance (R),current (I ), length or displacement (d ), and time(t), applicable to electrical systems. The equationis dimensionally correct if it can be shown thatthe left and right sides of the equation are identical.dimensional ratio In magnetism, the ratio of thelongest diameter of an elongated ellipsoid of revolutionto the shortest.dimensional stability Nonvariance or little variancein the shape and size of a medium (such asfilm) during the processing of that material.dimensionless quantity A quantity that is merelya real number. Example: logarithm, exponent,numerical ratio, etc. In contrast are physicalquantities: 3 volts, 5000 hertz, 10 amperes, etc.diminished radix complement See COMPLE-MENT.dimmer An electronic device used for controllingthe brightness of incandescent lamps. Using amplifiedcontrol, the device enables high-wattagelamp loads to be smoothly adjusted via a smallrheostat or potentiometer. A photoelectric-typedimmer automatically controls lamps in accordancewith the amount of daylight.dimmer curve The function of a light-dimmer voltageoutput as a function of setting on a linearscale.DIN Abbreviation for Deutsche Industrie Normenausschuss.A German association that setsstandards for the manufacture and performanceof electrical and electronic equipment, as well asother devices.D indicator In radar operations, an indicator combiningtype B and C indicators (see B DISPLAYand C DISPLAY).Dingley induction-type landing system An aircraftlanding system that provides lateral andvertical guidance; instead of radio, it uses themagnetic field surrounding two horizontal cableslaid on or under either side of the runway.diode A two-element device containing an anodeand a cathode, and providing unidirectional conduction.The many types are used in such devicesas rectifiers, detectors, peak clippers, mixers,modulators, amplifiers, oscillators, and test instruments.diode action 1. The characteristic behavior of adiode (i.e., rectification and unidirectional conduction).2. Two-electrode rectification or unidirectionalconductivity in any device other than adiode (e.g., asymmetrical conductivity betweenthe collector and base of a transistor).diode amplifier 1. A parametric amplifier employinga varactor. 2. An amplifier utilizing holestorageeffects in a semiconductor diode. 3. Anegative-resistance amplifier using a tunnel diode.diode array A combination of several diodes in asingle housing.diode assembly See DIODE ARRAY.diode bias A steady direct-current (dc) voltage appliedto a diode to establish its operating point.diode capacitance The capacitance existing at thep-n junction of a semiconductor diode when thejunction is reverse-biased. The capacitance generallyvaries, depending on the reverse-bias voltage.diode capacitor 1. A capacitor normally operatedwith a diode. 2. A voltage-variable capacitor utilizingthe junction capacitance of a semiconductordiode (e.g., a varactor).diode-capacitor memory cell A high-value capacitorin series with a high-back-resistance semi-

192 diode-capacitor memory cell • diode peak detectorconductor diode. A data pulse forward-biases thediode and charges the capacitor, which remainscharged, thus holding the data bit, because of thelong time constant of the high capacitance andthe high back resistance of the diode.diode characteristic The current-versus-voltagecurve for a diode.diode checker An instrument for testing semiconductordiodes. There are two forms: A staticchecker, which measures forward and reversecurrent; and a dynamic checker (see DYNAMICDIODE TESTER), which displays the entire dioderesponse curve on an oscilloscope screen.diode chopper A chopper using an alternately biaseddiode as the switching element.diode clipper A clipper using one or more diodes.A single biased diode will limit the positive or negativepeak of an applied alternating-current (ac)voltage, depending on diode polarity and bias.Two biased diodes with opposing polarity will clipboth peaks. Also see LIMITER.Inputdiode clipperOutputdiode converter See DIODE MIXER.diode current The forward or reverse current flowingthrough a diode.diode current meter A direct-current (dc) milliammeteror microammeter with a semiconductor-dioderectifier that allows the measurement ofalternating current (ac).diode curve changer A diode or network of diodesused to make a linear current-voltage curve acquiresome nonlinear shape.diode demodulator See DEMODULATOR PROBEand DIODE DETECTOR.diode detector A detector circuit in which a diodedemodulates a signal. The diode, a simple device,provides linear response at high signal amplitudes,but affords no amplification.diode feedback rectifier 1. In a rectified-carrier,negative-feedback system for an amplitudemodulated(AM) transmitter, the diode thatrectifies the modulated carrier and provides theaudio envelope for use as negative-feedbackvoltage. This voltage is applied to the speechamplifier/modulator channel to reduce distortion,noise, and hum, at the same time providingautomatic modulation control. 2. The diode thatrectifies a part of the signal at the output of anaudio amplifier and provides a proportionaldirect-current (dc) voltage for use as bias in anautomatic-gain-control (AGC) circuit.diode field-strength meter A simple meter formeasuring the intensity of a radio-frequency(RF) electromagnetic field. It consists of a shortwhip antenna, an inductance-capacitance (LC)tuned circuit, a diode detector, and a directcurrent(dc) microammeter. The deflection of themeter is roughly proportional to the RF signalvoltage.diode gate A passive switching circuit of biaseddiodes. Also see AND CIRCUIT and OR CIRCUIT.diode impedance The vector sum (resultant) of theresistive and reactive components of a diode. In asemiconductor diode, the inductive component ofreactance is almost entirely the inductance ofleads and electrodes, whereas the capacitive componentof reactance is the shunting capacitancebetween leads and electrodes, plus the voltagevariablecapacitance of the pn junction. Theresistive component is almost entirely the voltage-variableresistance of the pn junction.diode isolation A means of insulating an integrated-circuitchip from its substrate. The chip issurrounded by a pn junction that is reversebiased.This prevents conduction between thechip and the substrate.diode lamp See LASER DIODE.diode laser See LASER DIODE.diode light source See LASER DIODE.diode limiter See DIODE CLIPPER.diode load 1. The current drawn from a diode actingas a rectifier or demodulator. 2. The output(load) resistor into which a diode operates.diode load resistance The required value for adiode load resistor.diode load resistor A resistor usually connected tothe output of a diode rectifier or diode detector.diode logic Digital circuitry, such as AND and ORcircuits, using diodes as the principal components.diode matrix In some digital devices, a grid ofwires, the intersections of some being interconnectedthrough diodes, whose polarities determinecircuit operation. A series of AND circuits isprovided by this arrangement, which acts as ahigh-speed rotary switch when it is supplied withinput pulses.diode mixer A frequency converter that operatesvia the nonlinearity of semiconductor diodes.diode noise limiter A noise limiter circuit havingone or more biased diodes.diode oscillator An oscillator based on the negativeresistance or breakdown characteristics ofcertain diodes, such as high-reverse-biased germaniumdiodes, tunnel diodes, Gunn diodes, andfour-layer diodes. It is generally used at microwavefrequencies.diode pack A device containing more than onediode. An example is the full-wave bridge-rectifierintegrated circuit.diode peak detector A diode detector whose loadresistance is high at modulation frequencies; thevoltage across the resistance is proportional tothe peak amplitude of the modulated signal.

diode peak voltmeter • diplex reception 193Regulated+voltageGunndiodediode oscillator, 1ResonantcavityRFCdiode peak voltmeter A diode-type alternatingcurrent(ac) voltmeter, in which the deflection ofthe direct-current (dc) milliammeter or microammeteris proportional to the peak value of the appliedac voltage.diode probe A test probe containing a diode usedas either a rectifier or demodulator.diode recovery time The interval during which relativelyhigh current continues to flow after thevoltage across a semiconductor junction has beenabruptly switched from forward to reverse. Recoverytime is attributable to DIODE STORAGE.diode rectification Conversion of alternating current(ac) to pulsating direct current (dc) by diodeaction.diode rectifier 1. A diode device that converts alternatingcurrent (ac) to pulsating direct current(dc) in a power supply. 2. A small-signal diode devicethat converts ac to dc in the automatic-gaincontrol(AGC) circuit of a superheterodynereceiver. Also called AGC rectifier.diode resistor 1. A resistor usually operated witha diode. 2. A voltage-variable resistor utilizing the(usually forward) resistance of a semiconductordiode.diode storage The charge carriers (electrons andholes) remaining within a pn junction for a shorttime after forward bias has been either removedor switched to reverse polarity.diode storage time See DIODE RECOVERY TIME.diode switch See DIODE GATE.diode sync separator A diode used in a televisionreceiver circuit to separate and deliver the syncpulses from the composite video signal.diode temperature stabilization 1. Keeping thetemperature of a diode at a constant level. 2. Usingthe temperature-resistance characteristic of aforward-biased semiconductor diode to stabilize acircuit (such as a transistor amplifier stage) (i.e.,to prevent variations caused by temperaturechanges).diode tester See DIODE CHECKER.diode transistor 1. See UNIJUNCTION TRANSIS-TOR. 2. A semiconductor diode whose operationsimulates that of a transistor by means of pulsedoperation that alternately makes the single junctionan emitter or collector. 3. A transistor connectedto operate solely as a diode.diode-transistor logic Abbreviation, DTL. Logiccircuitry in which a diode is the logic element anda transistor acts as an inverting amplifier.diode-type meter A rectifier-type alternatingcurrent(ac) meter consisting of a semiconductordiode(s) and a direct-current (dc) milliammeter ormicroammeter. The diode rectifies the ac input,the resulting dc deflecting the meter.diode varactor A conventional semiconductordiode or rectifier used as a makeshift varactor(voltage-variable capacitor).diode variable resistor See DIODE VARISTOR.diode varistor A conventional diode used as amakeshift varistor (voltage-variable resistor).diode voltage reference See ZENER VOLTAGEREFERENCE.diode voltage regulator See ZENER VOLTAGEREGULATOR.DIP Abbreviation of DUAL IN-LINE PACKAGE.dip 1. A distinct decrease in the value of a varyingquantity, followed by an increase [e.g., the suddendrop, followed by a rise, in collector currentwhen a bipolar-transistor radio-frequency (RF)power amplifier is tuned through resonance]. 2.Also called magnetic inclination. The slanting of acompass needle, resulting from the orientation ofthe geomagnetic lines of flux, with respect to theearth’s surface. It varies, depending on magneticlatitude.dip adapter An external accessory that allows a radio-frequency(RF) signal generator to be used asa DIP METER.dip coating 1. Applying a protective coat of insulatingmaterial to a conductor or component bydipping it into the liquid material, then drainingand drying it. Compare SPRAY COATING. 2. Thecoat applied in this way.dip encapsulation Embedding a component or circuitin a protective block of insulating material(such as a plastic) while the material is in a liquidstate, and then allowing the material to harden inambient air or in an oven.dip impregnation Saturating a component or material(such as absorbent film) with a substance(such as oil or wax) by dipping or vacuum forcing.diplexer A coupler that permits two or more transmittersto operate simultaneously into a singleantenna.diplex operation 1. Simultaneous transmission orreception of two signals using a single antenna.2. Simultaneous transmission or reception of twosignals on a single carrier.diplex reception The reception of signals whiletransmitting with the same antenna.

194 diplex transmission • direct-conversion receiverdiplex transmission The transmission of signalswhile receiving with the same antenna.dip meter A tunable radio-frequency (RF) instrumentthat, by means of a sharp dip of an indicatingmeter, indicates resonance with an externalcircuit under test. Specific names are derivedfrom the active component used: grid-dip meter,gate-dip meter, etc.dip needle See INCLINOMETER.dipolar Also, bipolar. Possessing two poles (usuallyelectric or magnetic).dipolarization See DEPOLARIZATION.dipole 1. A pair of electrically opposite chargepoles separated by a specific distance. 2. A pair ofmagnetically opposite poles separated by a specificdistance. 3. See DIPOLE ANTENNA. 4. SeeFOLDED DIPOLE.dipole antenna Also called dipole and doublet. Ahalf-wavelength radiator fed at the center with atwo-wire or coaxial transmission line. Each “leg”of the antenna is one-quarter wavelength long.Such an antenna can be oriented horizontally orvertically, or at a slant. The radiating element isusually straight. For a straight wire radiator,properly insulated at the ends and placed wellaway from obstructions, the length L ft (in feet) ata design frequency f (in megahertz) is approximatelyL ft = 467/fThe length L m (in meters) is close toL m = 143/fBecause of its simplicity, this antenna is popularamong shortwave listeners and radio amateurs,especially at frequencies below 10 MHz. A fullsizeantenna of this type has a feed-pointimpedance of approximately 73 ohms, purely resistive.Compare FOLDED DIPOLE.λ/4 λ/4Feedlinedipole antennadipole disk feed A method of coupling radio-frequencyenergy to a disk-shaped antenna. The energyis applied to a dipole located adjacent to thedisk.dipole feed A method of coupling radio-frequencyenergy to an antenna by means of a half-wavedipole. The dipole is directly fed by the transmissionline, and the dipole radiates energy to therest of the system.dip oscillator The oscillator that provides the signalfor a DIP METER.dipotassium tartrate Abbreviation, DKT. An organicpiezoelectric material.dipped component A discrete electronic componentthat has been given a protective coating bydipping into a suitable material (such as oil, varnish,or wax) and draining off the surplus.dipper Collective term for resonance-type instruments,such as a DIP METER or DIP ADAPTER.dipper interrupter A cyclic switching device inwhich a contact pin is part of a revolving wheelpartially immersed in mercury.dipping 1. The application of a protective coatingor impregnant to a component by immersing it ina suitable material. Also see DIP COATING, DIPENCAPSULATION, and DIP IMPREGNATION. 2.In a resonant (tuned) amplifier circuit, the adjustmentof the resonant circuit for minimumcurrent through the amplifying device.dipping needle See INCLINOMETER.dip soldering 1. Soldering leads or terminals bydipping them into molten solder and then removingexcess solder. 2. Tinning printed-circuit patternsby dipping the boards into molten solder orplacing them in contact with the surface of a solderbath. 3. Soldering leads in printed circuits bythe methods defined in (2).DIP switch A switch (or group of miniatureswitches) mounted in a dual-inline package (DIP)for easy insertion into an integrated-circuitsocket or printed-circuit board.direct-access storage device A computer memoryin which data access time is unaffected by thedata location. Also called random-access memorydevice.direct-acting recorder See GRAPHIC RECORDER.direct-acting recording instrument SeeGRAPHIC RECORDER.direct address The actual address of a computerstorage location (i.e., the one designated by machinecode 0. Also called absolute address or realaddress.direct capacitance The capacitance between twopoints in a circuit, as opposed to the capacitancebetween either point and other objects (includingground).direct allocation In digital computer operations,to specify the necessary memory locations andperipherals for a particular program when it iswritten.direct coding Computer programming in machinelanguage.direct control Control of one machine by another,for example, the control of a computerized mobilerobot by a central computer system.direct-conversion receiver A heterodyne receiverin which the incoming radio-frequency (RF) signal

direct-conversion receiver • direct ground 195Ant.RF amp.MixerLocalosc.direct-conversion receiverAF amp.Speaker orheadsetis amplified, then mixed with the RF output of atunable local oscillator, producing an audiofrequency(AF) beat note. The AF is amplified;audio filtering can be added. Although the directconversionreceiver somewhat resembles thesuperheterodyne type, it has no intermediatefrequency(IF) chain, and does not normallyprovide single-signal reception. Also see ZERO-BEAT RECEPTION.direct-coupled amplifier An amplifier in whichthe output circuit of one stage is wired directly tothe input circuit of the following stage (i.e., thereis no intervening capacitor or transformer). Suchan amplifier can handle alternating-current (ac)or direct-current (dc) signals, and has wide frequencyresponse.direct-coupled transistor logic Abbreviation,DCTL. In digital computer and switching circuits,a logic system using only direct-coupled transistorstages.direct coupling Direct connection of one circuitpoint to another for signal transmission (i.e.,without intermediate capacitors or transformers).Because coupling devices aren’t used, direct couplingprovides transmission of direct current (dc),as well as alternating current (ac).direct current 1. Abbreviation, dc. A current thatalways flows in the same direction (i.e., the polaritynever reverses). The current might be constant,as from a battery or a regulated powersupply; it might be pulsating, as from an unfilteredrectifier. 2. Pertaining to current that alwaysflows in the same direction. 3. Descriptiveof a voltage, resistance, or other parameter underconditions in which there is a usually constantcurrent that always flows in the samedirection.direct-current amplifier An amplifier for boostingdirect-current (dc) signals, as opposed to dc voltagesignals.direct-current bar See DC BAR.direct-current beta See DC BETA.direct-current block See DC BLOCK.direct-current bus See DC BUS.direct-current circuit breaker See DC CIRCUITBREAKER.direct-current component See DC COMPONENT.direct-current converter See DC CONVERTER.direct-current coupling See DC COUPLING.direct-current dump See DC DUMP.direct-current equipment See DC EQUIPMENT.direct-current erase head See DC ERASE HEAD.direct-current generator See DC GENERATOR.direct-current inverter See DC INVERTER.direct-current leakage See DC LEAKAGE.direct-current motor See DC MOTOR.direct-current noise See DC NOISE.direct-current power See DC POWER.direct-current relay See DC RELAY.direct-current resistance See DC RESISTANCE.direct-current shift See DC SHIFT.direct-current short See DC SHORT.direct-current signaling See DC SIGNALING.direct-current source See DC SOURCE.direct-current transducer See DC TRANSDUCER.direct-current transformer See DC TRANS-FORMER.direct-current transmission See DC TRANSMIS-SION.direct digital control In a digital computer, multiplexingor time sharing among a number of controlledloops.direct display unit A cathode-ray-tube (CRT) peripheralthat displays data recalled from memory.direct-distance dialing A form of telephone servicethat allows dialing of long-distance numberswithout involving a human operator.direct drive 1. Pertaining to electromechanical accessoriesfor electronic equipment. 2. The transmissionof power directly from a source (such asa motor) to a driven device without intermediategears, belts, or clutches.direct-drive robot A robot that uses the minimumpossible number of gears and other drive systems.direct-drive torque motor In a positioning orspeed-control system, a servoactuator connecteddirectly to the driven load.direct-drive tuning A tuning or adjusting mechanismin which the shaft of the variable component(such as a potentiometer or variablecapacitor) is turned directly by a knob (i.e., withoutgearing, dial cable, or similar linkage).directed number A number having direction aswell as magnitude; a vector quantity.direct electromotive force A direct-current (dc)voltage that does not fluctuate or pulsate.direct emf See DIRECT ELECTROMOTIVE FORCE.direct ground 1. A ground connection made by theshortest practicable route. Compare INDIRECTGROUND. 2. An earth ground.

196 direct induced current • directional wattmeter+j4+j2j0−j2−j4jx4 + j4directed numberdirect induced current A transient current inducedin the same direction as the induction currentwhen it is interrupted.directing antenna See DIRECTIONAL ANTENNA.direct-input circuit A circuit, especially an amplifier,whose input is wired directly to the inputelectrode of the active device (i.e., without a couplingcapacitor or transformer).direct-insert subroutine In digital computer operations,a subroutine directly inserted into a largerinstruction sequence. It must be rewritten at everypoint it is needed.direct instruction A computer program instructionthat indicates the location of an operand inmemory.directional 1. Depending on direction or orientation.2. Having a concentration in an identifiabledirection. 3. Pertaining to a transducer in whichradiation, or sensitivity, is concentrated in certaindirections at the expense of radiation or sensitivityin other directions.directional antenna An antenna that transmitsand receives signals more effectively in some directionsthan in others. Also called beam, beamantenna, and directive antenna.directional array 1. A directional antenna havinga set of elements assembled in such a way thattheir combined action shapes the radiation into aunidirectional pattern. 2. A group of antennasspaced and phased to produce unidirectional radiationand reception patterns.directional beam 1. An antenna whose radiationor reception pattern strongly favors a specific direction.2. The radiation or reception pattern ofsuch an antenna.directional characteristic The precise directionalproperties of an antenna or transducer.directional CQ In amateur radio, a transmissionthat invites replies only from stations in a certaindirection or in a particular city, state, orcountry.R5 − j2directional coupler A microwave device that couplesan external system to waves travelingthrough the coupler in one direction.directional diode A high-back-resistance semiconductordiode inserted into a direct-current(dc) signal circuit or control circuit. Permits unidirectionalcurrent flow.directional filter In carrier-current transmission,a filter that halves the frequency band, one halfbeing for transmission in one direction, and theother half being for transmission in the oppositedirection.directional gain Symbol, k S . The ratio of the powerthat would be radiated by a loudspeaker if thefree-space axial sound pressure were constantover a sphere, to the actual radiated power. Usuallyexpressed in decibels.directional homing A scheme for locating thesource of a radio signal. An effort is made to keepthe bearing of the target or guiding station constant.Therefore, the search path is as direct (asnearly a straight line) as practicable.directional horn See DIRECTIVE HORN.directional hydrophone A hydrophone whose responsepattern strongly favors one direction.directional lobe In the spatial response pattern ofa device, such as an antenna or loudspeaker, aportion showing emphasized response in a givendirection.directional microphone A microphone thatstrongly favors sound emanating from in front ofit.directional pattern See DIRECTIVITY PATTERN.directional phase shifter A phase-shifting circuitin which the characteristics are different in onedirection, as compared with the other direction.directional power relay A relay that is actuatedwhen the monitored power reaches a prescribedlevel in a given direction.directional relay See POLARIZED RELAY.directional response For any form of transducer,a radiation or sensitivity pattern that is concentratedin certain directions.directional separation filter See DIRECTIONALFILTER.directional transducer A device that senses oremits some effect to an extent that depends onthe direction from which the effect comes. Directionaleffects are often, but not always, accompaniedby gain in the favored direction(s).Examples: directional microphone, directionalspeaker, and directional antenna.directional variation of radio waves Changes inthe field strength of radio waves, depending onthe direction. There are various causes, includingantenna directivity, ground characteristics, ionosphericfactors, weather conditions, and the presenceof obstructing objects.directional wattmeter A device that can measureradio transmitter output power and can also givean indication of how well an antenna is matched

directional wattmeter • directivity index 197to a transmission line. Such meters fall into twocategories. One type has a single scale, calibratedin watts, and sometimes also in milliwatts or kilowatts(switch selectable). The meter reads eitherforward power or reflected power, depending onthe position of a switch or rotatable internal element.Another type has two needles in a singleenclosure, with a different calibrated scale foreach needle. Both of these scales are graduatedin watts, and sometimes also in milliwatts or kilowatts.One needle/scale indicates forward powerand the other needle/scale indicates reflectedpower. There is a third scale, calibrated for thepoint where the two needles cross. This scale indicatesthe standing-wave ratio (SWR). See alsoCROSSED-POINTER INDICATOR.direction angle In radar operations, the angle betweenthe center of the antenna baseline and aline going to the target.direction finder A receiver specially adapted toshow the direction from which a signal is received,thus revealing the direction of the receiverwith respect to the transmitting station, and viceversa. In its simplest form, it is a receiver with aloop antenna that is rotatable over a map or compasscard. For increased accuracy, checks aremade with signals from two transmitting stations;the exact location of the receiver is pinpointedby triangulation.direction finding The taking of bearings by meansof a direction finder.direction of lay In a multiconductor cable, the lateraldirection of winding of the topmost conductorsas they recede from the observer; calledRcvrxBearingySeaLandBearingxdirection findingRcvryPosition ofvessel sendingdistress signalleft-hand lay or right-hand lay. If the cable isviewed from either end, left-hand lay is equivalentto conductors that rotate clockwise as they recedefrom the viewer; right-hand lay is equivalentto conductors that rotate counterclockwise asthey recede from the viewer.direction of polarization The direction of the electrostaticfield in a linearly polarized wave.direction of propagation The direction in whichenergy moves from a transmitter, or betweenequivalent points in a sector of space under consideration.direction rectifier In a control system, a rectifierwhose direct-current (dc) output voltage has amagnitude and polarity dependent on the magnitudeand phase of an alternating-current (ac) selsynerror voltage.direction resolution 1. The smallest difference inazimuth that a direction-finding device can detect.2. The smallest angular separation betweentwo targets that allows a radar set to show twoseparate echoes rather than a single echo.directiveIn a computer source program, a statementdirecting the compiler in translating theprogram into machine language without beingtranslated itself. Also called control statement.directive antenna An antenna designed for bestpropagation or reception in one (often steerable)horizontal direction. Also called beam antennaand directional antenna.directive gain For a directional antenna, a ratingequal to 12.566(Pr/Pt), where Pr is the radiatedpower per steradian in a given direction and Pt isthe total radiated power.directive horn A microwave antenna having theshape of a (usually rectangular) horn.directivity 1. In an antenna, a directional response.2. The degree to which the radiation orsensitivity of a transducer is concentrated in certaindirections. 3. The angle between the halfpowerpoints of a directive antenna in theazimuth plane. 4. In an antenna system, the ratio,in decibels, between the power in the favoreddirection and the power in the exact opposite direction;also called front-to-back ratio. 5. The forwardpower gain of an antenna, with respect to adipole in free space. 6. The forward power gain ofan antenna, with respect to an isotropic radiatorin free space.directivity diagram A graph of the radiation/response pattern of a beam antenna or otherdirectional device, usually in a horizontal orvertical plane. Also see DIRECTIVITY PATTERN.directivity factor 1. A measure of the directivity ofan antenna or transducer. 2. In acoustics, the ratio,in decibels, between the gain in the maximumdirection and the gain in the minimum direction,for a transducer, such as a speaker or microphone.directivity index 1. For an acoustic-emittingtransducer, the ratio, in decibels, of E 1 to E 2 ,

198 directivity index • directrixwhere E 1 is the average intensity over an entiresphere surrounding the transducer, and E 2 is theintensity on the acoustic axis. 2. For an acousticpickup transducer, the ratio, in decibels, of E 1 toE 2 , where E 1 is the average response over an entiresphere surrounding the transducer, and E 2 isthe response on the acoustic axis.directivity of antenna For a beam antenna, theratio E max /E avg , where E max is the maximum fieldintensity at a selected distance from the antennaand E avg is the average field intensity at the samedistance.directivity of directional coupler The ratio, indecibels, of P 1 to P 2 , where P 1 is the power at theforward wave-sampling terminals (measured witha forward wave in the transmission line) and P 2 isthe power at the terminals when the wave is reversedin direction.directivity pattern The calculated or measured radiationor response pattern (transmission or reception)of an antenna, microphone, loudspeaker,or similar device, with particular attention to thedirectional features of the pattern.directivity signal A spurious output signal resultingfrom finite directivity in a coupler.direct light Light rays traveling directly from asource to a receptor or target without reflection.directly grounded Connected to earth or to thelowest-potential point in a circuit, without any interveningresistance or reactance.directly heated cathode A vacuum-tube filament.It is so called because, when heated, it becomesthe cathode of the tube (i.e., the emitter of electrons).directly heated thermistor A thermistor whosetemperature changes with the surrounding temperature,and also as a result of power dissipationin the device itself. Compare INDIRECTLYHEATED THERMISTOR.directly heated thermocouple A meter thermocoupleheated directly by signal currents passingthrough it. Compare INDIRECTLY HEATEDTHERMOCOUPLE.direct measurement Immediate measurement ofa quantity, rather than determining the value ofthe quantity through adjustments of a measuringdevice (e.g., measuring capacitance with a capacitancemeter, rather than with a bridge). CompareINDIRECT MEASUREMENT.direct memory access Abbreviation, DMA. Thetransfer of data from a computer memory to someother location, without the intervention of thecentral processing unit (CPU).direct numerical control In a computer or datasystem, the capability for distributing informationamong numerically controlled machineswhenever desired.directorIn a multielement directional antenna, anelement that is usually mounted in front of theradiator element, and that is phased and spacedto direct the radiation forward. The director functionsin conjunction with the reflector element,which is usually mounted behind the radiator.directory See DICTIONARY.direct pickup The broadcasting, especially in television,of events at the same time as they occur(e.g., without recording/reproduction).direct piezoelectricity The production of a piezoelectricvoltage by mechanically stressing a suitablecrystal.direct playback In audio or video recording, thereproduction of a recording without additionalprocessing (e.g., the playing of an originalrecorded tape, rather than a tape that has beenmass produced).direct-point repeater A relay-operated telegraphrepeater. The received signals actuate the relay,which switches the second line.direct-radiator loudspeaker A loudspeaker whosecone or diaphragm is directly coupled to the air.direct ray An electromagnetic ray (wave) thatreaches a receiver without reflection or refraction,and without encountering obstructions.direct recording 1. A record produced by agraphic recorder. 2. The technique of producingsuch a record.direct-recording instrument A device, such as agraphic recorder, that directly produces a permanentrecord (such as an inked trace) of the variationsof a quantity.direct resistance coupling A form of coupling inwhich the output of the first amplifying device isconnected through a resistor directly to the inputof the second device. The resistance value canvary; sometimes the connection is a short circuit.directrix A fixed line to which a curve is referred(e.g., the axis of a parabola).+direct resistance coupling

direct scanning • discrete capacitor 199direct scanning In television, the sequential viewingof parts of a scene by the camera—eventhough the entire scene is continuously illuminated.direct serial file organization A technique of organizingfiles stored in a direct access device, inwhich a record can be chosen by number andamended where it is without altering other membersof the file.direct sound wave A sound wave arriving directlyfrom its source—especially a wave within an enclosurethat is not affected by reflection.direct substitution 1. An exact component replacement.2. Installing an exact component replacement.direct synthesizer A device for producing random,rapidly changing frequencies for security purposes.A reference oscillator provides a comparisonfrequency; the output frequency is arational-number multiple of this reference frequency.direct voltage See DC VOLTAGE.direct wave A wave that travels from a transmitterto a receiver without being reflected by the ionosphereor the ground. Compare SKYWAVE.direct Wiedemann effect Twisting force (torque)in a wire carrying current in a longitudinal magneticfield. Occurs because of interaction betweenthe longitudinal field and the circular magneticfield around the wire.direct-wire circuit A communications or controlline of wires connecting a transmitter (or controlpoint) and a receiver (or controlled point) withoutan intermediary, such as a switchboard.direct-writing recorder See GRAPHIC RE-CORDER.direct-writing telegraph 1. See PRINTING TELE-GRAPH. 2. See TELAUTOGRAPH.dis- A prefix meaning “deprived of.” For the formationof electronic terms, the prefix must be distinguishedfrom un-, meaning “not.” For example, adischarged body is one that was charged, but hasbeen emptied of its charge. An uncharged body isone that ordinarily or presently is not charged.disable 1. To deliberately render a circuit, device,or system inoperative. 2. In digital computeroperations, to defeat a software or hardwarefunction.disc See DISK.disc engraving 1. Recording sound by cutting agroove in a record disc. 2. The groove resultingfrom such a process.discharge The emptying or draining of electricityfrom a source, such as a battery or capacitor. Theterm also denotes a sudden, heavy flow of current,as in DISRUPTIVE DISCHARGE. CompareCHARGE.discharge current 1. Current flowing out of a capacitor.2. Current flowing out of a cell—especiallya storage cell. Compare CHARGINGCURRENT.discharge key See DISCHARGE SWITCH.discharge lamp A gas-filled tube or globe in whichlight is produced by ionization of the gas betweenelectrodes. Familiar examples are the neon bulband fluorescent tube.discharge phenomena The effects associated withelectrical discharges in gases, such as luminousglow.discharge potential See IONIZATION POTENTIAL.discharger 1. A short-circuiting tool for dischargingcapacitors. 2. A spark gap or other device forautomatically discharging an overcharged capacitor.discharge rate 1. The current that can be suppliedby an electrochemical cell or battery reliably duringits discharging cycle. Usually expressed inmilliamperes or amperes. 2. An expression of thespeed with which a battery is being discharged ata specific point in time. It is usually specified inamperes or milliamperes.discharge switch A switch for connecting acharged capacitor to a resistor or other load,through which the capacitor discharges. In somecircuits, when the switch is in its resting position,it connects the capacitor to the charging source.discharge voltage See IONIZATION POTENTIAL.discharging 1. The conversion of chemical energyto electrical energy by an electrochemical cell orbattery. 2. The release of stored electrical energyfrom a capacitor, or from a network containingcapacitors.discharging tongs See DISCHARGER, 1.discone antenna An antenna consisting of a horizontalmetal or wire-mesh disk above a metal orwire-mesh cone. The antenna has an omnidirectionalradiation pattern in the horizontal plane,and provides a good match to a coaxial transmissionline over a frequency range of several octaves.Commonly used at very-high frequencies(VHF) and ultra-high frequencies (UHF).disconnect 1. To separate leads or connections,thereby interrupting a circuit. 2. A type of connectorwhose halves can be pulled apart to opena cable or other circuit quickly. 3. To open aswitch or relay.disconnector See DISCONNECT, 2 and DISCON-NECT SWITCH.disconnect signal A signal sent over a telephoneline, ending the connection.disconnect switch A switch whose main functionis to open a circuit quickly (either manually orautomatically) in the event of an overload.discontinuity 1. A break in a conductor. 2. Apoint at which the impedance in a transmissionline abruptly changes.discontinuous wave trains See DAMPED WAVES.discrete 1. Complete and self-contained, as opposedto a part of something else. 2. Composed ofindividual, separate members.discrete capacitor Capacitance that is entirelyself-contained, rather than being electrically dis-

200 discrete capacitor • disk capacitortributed. Also called LUMPED CAPACITOR. CompareDISTRIBUTED CAPACITANCE.discrete circuit A circuit comprised of discretecomponents, such as resistors, capacitors,diodes, and transistors, not fabricated into an integratedcircuit.discrete component A self-contained device thatoffers one particular electrical property in lumpedform (i.e., concentrated at one place in a circuit,rather than being distributed). A discrete componentis built especially to have a specific electricalproperty, and exists independently, not in combinationwith other components. Examples: diskcapacitor, toroidal inductor, and carbon-compositionresistor. Compare DISTRIBUTED COMPO-NENT.discrete device Any component or device that operatesas a self-contained unit.discrete element A discrete device that forms partof a larger system.discrete inductor An inductive component that isentirely self-contained, rather than being electricallyspread out. Also called lumped inductor.Compare DISTRIBUTED INDUCTANCE.discrete information source A source of data containinga finite number of individual elements,rather than a continuously variable parameter.discrete part See DISCRETE COMPONENT.discrete resistor A resistive component that is entirelyself-contained, rather than being electricallyspread out. Also called lumped resistor.Compare DISTRIBUTED RESISTANCE.discrete sampling Sampling of individual bits orcharacters, one or more at a time.discrete thin-film component A discrete componentproduced by the thin-film process (e.g., thinfilmcapacitor, thin-film potentiometer, etc.).discretionary wiring A method of interconnectingthe components and circuits on a semiconductorwafer for optimum performance. This requires aseparate analysis and wiring pattern for everychip.discrimination 1. Sharp distinction between electricalquantities of different value. 2. The detectionof a frequency-modulated (FM) signal (i.e., the deliveryof an audio signal corresponding to the frequencyor phase variations in the FM carrier).discriminator A second detector for frequencymodulated(FM) signals, in which two diodes areoperated from the center-tapped secondary of aspecial intermediate-frequency (IF) transformer.The circuit is balanced for zero output when theinstantaneous received signal frequency is at theunmodulated carrier frequency; the circuit deliversoutput when the instantaneous receivedsignal frequency swings above or below theunmodulated carrier frequency. Also see FOS-TER-SEELEY DISCRIMINATOR and TRAVIS DIS-CRIMINATOR.discriminator transformer The special inputtransformer in a DISCRIMINATOR.FromlimiterC2C1T1C3D1D2discriminator tuner A device that tunes a discriminatorto a selected subcarrier.discriminator tuning device See DISCRIMINA-TOR TUNER.dish See DISH ANTENNA.dish antenna A transmitting and/or receiving antennaconsisting of a driven element and a largereflector. The reflector has the shape of a shallow,circular section of a paraboloid or sphere. Thefeed point is at the focus of the reflector. This antenna,noted for its high directivity and gain, isused mainly at ultra-high and microwave frequenciesfor communications and satellite television.Large antennas of this type are used insome radio telescopes.dish-type construction A type of panel-and-chassisconstruction in which the chassis is fastenedvertically to the back of the panel.disintegration 1. The destructive breakdown of amaterial. 2. The stripping of a vacuum-tube cathodeof its emissive coating (see DISINTEGRATIONVOLTAGE). 3. The decay of a radioactive material.disintegration voltage The anode voltage at whichthe cathode of a gas tube begins to be stripped ofits electron-emitting material. For safety and reasonabletube life, the anode working voltage mustbe between the ionization and disintegration values.disintegrator An ultrasonic device for reducingcrystals or particles to fine suspensions.disjunction The logical inclusive-OR operation.disk 1. A flat, circular plate (e.g., rectifier disk). 2.See DISKETTE. 3. See HARD DISK. 4. See COM-PACT DISC. 5. See CD-ROM. 6. A phonographrecord or the equivalent unrecorded blank.disk capacitor A fixed (usually two-plate) capacitorconsisting of a disk of dielectric material onwhose faces are deposited metal-film plates.R1R2discriminatordisk capacitorR3C5C6C4To AFamp

disk coil • display loss 201disk coil See DISK WINDING.disk dynamo A rudimentary direct-current (dc)generator, in which a copper disk rotates betweenthe poles of a permanent magnet. The outer edgeof the disk becomes positively charged; the centerof the disk becomes negatively charged.disketteA magnetic recording disk used for microcomputerdata storage. Housed in a square, flatcase. In personal computing, there are two sizes:5.25 inches square and 3.5 inches square. The5.25-inch version is flexible and is sometimescalled a floppy disk.disk files An information-storage system in whichdata are recorded on rotating magnetic disks.disk generator 1. See DISK DYNAMO. 2. A disktypeelectrostatic generator.disk memory A common misnomer for DISKSTORAGE.Disk Operating System Abbreviation, DOS. Any ofseveral command-driven operating systems commonlyused in IBM-compatible personal computers.disk pack In disk files, a set of disks that can behandled as a single unit.disk recorder A device for recording (and usuallyalso playing back) sound or other signals onrecord disks.disk recording 1. Recording sound or other signalson disks. 2. A disk resulting from such arecording. See DISK.disk rectifier A semiconductor rectifier (such ascopper-oxide, selenium, magnesium-coppersulfide,or germanium type) in which the activematerial is deposited on a metal disk.disk resistor A resistor consisting of a resistivematerial deposited on a metal disk; or a disk ofresistive material. In the latter, electrodes areplated on the faces of the disk, one or more ofwhich are held between clips or screws for connections.disk storage In digital computer systems, an onlineor offline data storage scheme, in which informationis recorded on the magnetic coating ofa rotating disk or set of disks. See DISKETTE,and HARD DISK.disk system A sound-motion-picture system usingaudio disks synchronized with the film.disk thermistor A thermistor having the generalshape of a disk.disk-type storage See DISK STORAGE.disk varistor A varistor having the general shapeof a disk.disk winding An armature or coil winding that isflat, rather than cylindrical. Also called disk coil,pancake coil, and spiral coil.dislocation A crystal region in which the arrangementof atoms does not have the perfect latticestructure of the crystal.dispersion 1. The property of a material thatcauses energy at different wavelengths to passthrough it at different speeds. 2. The separationof a wave into its various component frequencies(as when white light is broken up into the colorspectrum by a prism). 3. The scattering of a microwavebeam when it strikes an obstruction. 4.The scattering of sound or ultrasound as it emanatesfrom an acoustic transducer. 5. A suspensionof finely divided particles within anothersubstance.dispersive medium A medium that disperses awave passing through it.displacement 1. A change in the position of apoint, particle, figure, or body. 2. The vector representinga change in the position of a point, particle,figure, or body. 3. Movement of a memberthrough a specified distance.displacement current 1. An alternating currentproportional to the rate of change of an electricfield, and existing in addition to usual conductioncurrent. 2. The current flowing into a capacitorimmediately after application of a voltage. Thiscurrent continues to flow, although continuallydiminishing in value, until the capacitor becomesfully charged.displacement of porches In a television signal,the amplitude difference between the front porchand back porch of a horizontal sync pulse.displacement of vectors Vector rotation througha specified number of angular degrees or radians.displacement transducer A transducer in whichmovement (displacement) of a rod, armature,core, reed, or other object converts mechanicalenergy into proportionate electrical energy.display1. Visually observable presentation of information,such as data entered into a computer,an answer to a problem solved by a computer, thevalue of a measured quantity, or a graph of afunction. 2. The screen in a computer system orterminal that visually portrays text and graphicaldata. In laptop, notebook, and portable computers,this is usually a liquid-crystal display (LCD);in desktop computers and terminals, it is usuallya cathode-ray tube (CRT ). 3. To portray informationin a visual manner (e.g., as text, numerals,symbols, or graphic images).display blanking See DISPLAY INHIBIT.display console In a computer system, a peripheralthat is used to access and display data beingprocessed or stored; often, it is a unit with acathode-ray tube (CRT), keyboard, and light pen.display control An interface device between a centralprocessor and several visual display units(terminals).display dimming See DISPLAY INHIBIT.display inhibit In a digital meter, the blanking ordimming of the display when the instrument isnot being used. It is used to conserve battery energy.display loss The ratio P 1 /P 2 , where P 1 is the minimuminput-signal power that can be detected byan ideal output device at the output of a receiver,and P 2 is the minimum input-signal power value

202 display loss • distance-double lawseen by an operator using an output device withthe same receiver. Also called visibility factor.display mode 1. A particular method of presentinga display. For example, a character display on avideo unit might consist of bright characters on adark background, or dark characters on a lightbackground. 2. An operating mode for a particulardevice, in which a display is used.display module A self-contained unit with circuitryand readouts for indicating a numericalcount.display primaries Also called primary colors. In acolor television receiver, the colors red, green,and blue. When mixed correctly, these three colorscan produce any visible hue.display-storage tube A special cathode-ray tube inwhich patterns and other information can bestored for later viewing. The tube has two electronguns: a writing gun and a reading (viewing) gun.display unit A device that presents information forvisual reading. Included are analog and digitalmeters, cathode-ray tubes, data printers, graphicrecorders, etc. Also see DISPLAY CONSOLE.display visibility The ease with which a displaycan be read by an operator.display window 1. In a panoramic display, thewidth of the presented frequency band in hertz.2. The panel opening through which the indicationof a display unit appears.displayed part That portion of a number displayedin the readout of a calculator or computer. Theremight be digits that are not displayed, but whichthe machine might take into considerationwhen making calculations. For example, in a10-digit calculator display, the number245.789378214895 would be displayed as245.7893782. Depending on the calculator design,the machine might truncate (disregard) theundisplayed digits (14895), or take the undisplayeddigits into account when making calculations.disposable component A circuit component ormachine part that is so inexpensive that it ismore cost-effective to discard it than to repair itwhen it fails.disruptive discharge Sudden, heavy current flowthrough a dielectric material when it fails completelyunder electric stress.dissector A transducer that samples an illuminatedimage point by point.dissector tube A camera tube using a flat photocathode,upon which the image is focused by thelens system. Electromagnetic deflection fromexternal coils provides scanning. Electrons passsequentially from the image cathode to a scanningtube at the opposite end of the camera tube.Also called Farnsworth dissector tube and orthiconoscope.dissipation 1. The consumption of power, oftenwithout contributing to a useful end, and usuallyaccompanied by the generation of heat. 2. In anObjectamplifier, the difference between the collector,drain, or plate input power and the usable outputpower.dissipation constant For a thermistor, the ratio ofthe change in power dissipation to a correspondingchange in body temperature.dissipation factor 1. For a dielectric material, thetangent of the dielectric loss angle. Also calledloss tangent. 2. Symbol, D. For an impedance(such as a capacitor), the ratio of resistance to reactance;D = R/X. It is the reciprocal of the figureof merit (Q).dissipation line A resistive section of transmissionline, used for dissipating power at a certainimpedance. Two parallel lengths of resistancewire are terminated by a large, noninductive resistorthat has a value equal to the characteristicimpedance of the line.dissipatorOpticsAnodedissector tubeApertureImagedcInputOutputdcInputPhotocathode1. A device used primarily to consumepower (i.e., a power sink). 2. A device for removingheat generated by a device’s operation (e.g., aheatsink attached to a power transistor).dissociation The condition that characterizes electrolytes(certain acids, bases, or salts in water solution)in which the molecules of the materialbreak up into positive and negative ions.dissonance The unpleasant effect (especially inmusic) produced by nonharmonious combinationsof sounds.dissymmetrical network A network having unequalinput and output image impedances.dissymmetrical transducer A transducer havingunequal input and output image impedances.distance-double law A theoretical rule for determiningthe rate at which sound intensity decreasesas distance increases. Under idealconditions, when the distance from a soundsource is doubled, the sound pressure is reducedto one-fourth of its original level, a reductionof 6 decibels. This is analogous to theinverse-square law for visible light and other radiantenergy.

distance mark • distributed component 203distortion tolerance The maximum amount ofdistortion that can be present in a signal withoutmaking it useless. This varies over wide limits.The maximum harmonic distortion that might beacceptable in a high-fidelity sound system couldbe less than 0.1% total, whereas in some applicationsof ac power, 10% would be acceptable.distress frequency A radio frequency on which anemergency signal is transmitted. Ships at sea andaircraft over the sea use 500 kHz (by internationalagreement). In Citizen Band communications,channel 9 has been set aside for emergencyuse.distress signal A signal indicating that trouble existsat the transmitting station and imploring aidfrom the recipient. The international radiotelegraphdistress signal is the three-letter combinationSOS; the international radiotelephonedistress signal is the word mayday, the phoneticequivalent of the French m’aidez (help me).distributed Existing over a measurable interval,area, or volume; not concentrated in a singleplace or places.distributed amplifier A wideband, untuned amplifierwhose active devices are spaced (distributed)along parallel, artificial delay linesconsisting of coils that act in combination withthe input and output capacitances of the activedevices. Adding active devices to the lineup increasesthe gain. Commonly used as preamplifiersfor television receivers.distributed capacitance Symbol, C d . Capacitancethat is dispersed throughout a component or system,rather than being lumped in one place. Anexample is the distributed capacitance of a coil.distributed component An electrical property thatis spread throughout a circuit or device, ratherthan being concentrated at one point, as in a discretecomponent. For example, DISTRIBUTEDCAPACITANCE and DISTRUBUTED INDUC-TANCE are spread along the length of a transmissionline. Another example is the DISTRIBUTEDRESISTANCE of a wire coil. Distributed compodistancemark On a radar screen, a mark indicatingthe distance from the radar set to the target.distance measurement Also called ranging. Amethod or system that allows a robot to navigatein its environment. It also allows a central computerto track the locations of robots under itscontrol. Can use radar, sonar, visible light, or infrared.distance-measuring equipment In radionavigation,a system that measures the distance of theinterrogator to a transponder beacon in terms ofthe transmission time to and from the beacon.distance protection The use of a protective devicewithin a specified electrical distance along a circuit.distance relay In circuit protection, a relay thatoperates to remove power when a fault occurswithin a predetermined distance along the circuit.distance resolution 1. Qualitatively, the ability ofa ranging system to differentiate between two objectsor beacons that are almost, but not quite,the same distance away. See RANGING. 2.Quantitatively, the minimum radial separation ofobjects or beacons necessary for a rangingsystem to tell them apart. 3. For two targetshaving the same azimuth bearing, the minimumdifference in range for which a radar displayrenders them as distinct blips.distant control See REMOTE CONTROL.distorted-drive multiplier A frequency multiplierwhose excitation signal is a peaked wave that hasbeen predistorted to decrease the angle of flow inthe device, thus increasing its efficiency.distorted nonsinusoidal wave A nonsinusoidalwave whose ideal shape (square, rectangular,sawtooth, etc.) has been altered.distorted sine wave A wave that is approximatelyof sinusoidal shape (i.e., it is not an exact plot of asine wave because of the presence of harmonics).distortion 1. Deformation of a signal waveform. 2.The additional deformation of a signal exhibitinga less-than-ideal waveshape when it passesthrough a circuit. Some distortion originateswithin the signal generator itself; other forms resultfrom circuits and devices transmitting thesignal. 3. Any degradation in the quality of ahigh-fidelity audio signal. 4. See TOTAL HAR-MONIC DISTORTION.distortionless 1. Having no distortion. 2. Having apropagation velocity that does not depend on frequency.distortion meter An instrument for measuringharmonic distortion. It consists of a highly selectiveband-rejection filter (notch filter) that removesthe fundamental frequency of the signalunder test, and a sensitive voltmeter that can beswitched between the filter input and the filteroutput. The distortion percentage is determinedfrom the ratio between filter-output and filterinputvoltages.InputNotchfilterdistortion meterVoltmeter

204 distributed component • diversity gainnents are often unintended, but they can be useful.Compare DISCRETE COMPONENT andLUMPED COMPONENT.distributed constant See DISTRIBUTED COMPO-NENT.distributed-constant delay line A delay linewhose capacitance and inductance are distributedthroughout the line. Compare LUMPED-CONSTANT DELAY LINE.distributed inductance Symbol, L d . Inductancethat is dispersed throughout a system or component,rather than being lumped in one place,such as in a coil (e.g., the inductance of an antennaor capacitor).distributed network 1. A network in which electricalproperties (such as resistance, inductance,and capacitance) are distributed over a measurableinterval, area, or volume. 2. A networkwhose characteristics do not depend on frequencywithin a given range.distributed-parameter network A network composedof distributed components, rather thanlumped components.distributed pole In a motor or generator, a polehaving a DISTRIBUTED WINDING.distributed resistance Symbol, R d . Resistancethat is dispersed throughout a component or circuit,rather than being lumped in one place, suchas in a resistor. An example is the high-frequencyresistance of an antenna system.distributed-shell transformer A transformer havingtwo complete closed cores that are perpendicularto each other.distributed winding In a motor or generator, awinding that is placed in several slots (ratherthan in one slot) under a pole piece.distributing amplifier An amplifier having a singleinput and two or more outputs that are isolatedfrom each other; it distributes signals to variouspoints.distributing cable 1. In cable television, the cableconnecting the receiver to the transmission cable.2. In power service, the cable running between afeeder and a consumer’s house.distribution 1. The selective delivery of a quantity(e.g., power distribution). 2. In statistical analysis,the number of times particular values of avariable appear. Also called frequency distribution.distribution amplifier A low-output-impedancepower amplifier that distributes a radio, television,or audio signal to a number of receivers orspeakers.distribution cable See DISTRIBUTING CABLE.distribution center 1. The central point fromwhich a signal is routed to various points of use.2. In electric power operations, the point at whichgeneration, conversion, and control equipment isoperated to route power to points of use.distribution factor For a polyphase alternator, thefactor by which the total voltage V T can be determinedin terms of the coil voltage V C and thenumber of coils n: V T = nV C . Distribution factork d = (sin(sd/2))/(s × sin(d/2)), where s is thenumber of slots per phase per pole, and d is theangle between adjacent slots.distribution function In statistical analysis, thefunction F(x) expressing the probability that Ftakes on a value equal to or less than x.distribution switchboard 1. A switchboardthrough which signals can be routed to or amongvarious points. 2. A switchboard for routing electricpower to points of use.distribution transformer A step-down transformerused to supply low-voltage alternatingcurrent(ac) utility power to one or moreconsumers from a high-voltage line.distributor1. See COMMUTATOR. 2. A switchingdevice consisting of a rotating blade and a numberof contacts arranged in a circle. Accomplishessequential switching of a voltage to a number ofpoints in a circuit. A common example is the distributorin the ignition system of an automotiveengine.disturbance An undesired variation in, or interferencewith, an electrical or physical quantity.disturbed-one output In digital computers, theone output of a magnetic cell that has receivedonly a partial write pulse train because it was lastwritten into. Compare UNDISTURBED-ONEOUTPUT.disturbed-zero output In digital computers, thezero output of a magnetic cell that has receivedonly a partial write pulse train since it was lastread from. Compare UNDISTURBED-ZERO OUT-PUT.dither1. Vibrate; quiver. 2. The condition of vibrationor quivering (e.g., the dither of a meterpointer). 3. To blend pixels in a digitized image toobtain various shades and colors.divergence1. The tendency of a collimated beamof energy to spread out. 2. The extent to which acollimated beam of energy spreads out, generallymeasured in seconds of arc, minutes of arc, angulardegrees, or angular radians.divergence loss Loss of transmitted sound energy,resulting from spreading.diverging lens A lens having a virtual focus forparallel rays; generally a concave lens.diversity 1. The property of consisting of two ormore independent components or media. 2. SeeDIVERSITY RECEPTION. 3. See DIVERSITYTRANSMISSION.diversity factor 1. A measure of the degree towhich a system exhibits unity among its constituents.2. The sum of the requirements of eachconstituent of a system, divided by the total requirementof the system.diversity gain 1. Signal gain achieved by usingtwo or more receiving antennas. 2. Signal gainachieved by using two or more transmitting antennas.

diversity reception • DNL 205diversity reception Also called dual-diversity reception.A method of minimizing the effects of fadingin ionospheric communication at highfrequencies (HF). Accomplished using two receiverswhose antennas are 5 to 10 wavelengthsapart. Each receiver, tuned to the same signal,feeds a common audio amplifier. The timing ofthe fading is different at the two antennas becauseof phasing effects. The composite signal,therefore, fades less than either of the componentsignals. Some diversity systems use three or moreantennas and receivers to reduce the effects offading even further; this is sometimes calledmultiple-diversity reception.RFstagesMixer andlocaloscillatorIFstagesSeconddetector5 to 10wavelengthsAudioamplifierOutputdiversity receptionSeconddetectorRFstagesMixer andlocaloscillatorIFstagesdiversity transmission Also called dual-diversitytransmission or multiple-diversity transmission. Ascheme similar to DIVERSITY RECEPTION, exceptapplied at the transmitting end of a communicationcircuit. The signals from two or moretransmitters, at identical frequencies, are fed toantennas spaced several wavelengths apart.diverter-pole generator A well-regulated directcurrent(dc) generator, whose shunt winding is onthe main field pole, the series winding being on adiverter pole whose flux opposes that of the mainpole.divide-by-seven circuit A three-stage binary circuithaving feedback from stage three to stageone. Stage three is switched on by the fourth inputpulse; at that time, the feedback pulseswitches on stage one, simulating one inputpulse and reducing the usual counting capacityfrom eight to seven.divide-by-two circuit A circuit that delivers oneoutput pulse for each two successive input pulses(i.e., a flip-flop).Input4 7 7C5 5divide-by-seven circuitdivided-carrier modulation Modulation obtainedby adding two identical frequency carriers thatare 90 degrees out of phase.divided circuit A parallel circuit.divided equipment A system of modular electroniccomponents interconnected with cables. Asimple example is a radio receiver having an externalpower supply and external loudspeaker.divider 1. See VOLTAGE DIVIDER. 2. See FRE-QUENCY DIVIDER. 3. See PULSE-COUNT DI-VIDER. 4. A computing circuit or device forperforming mathematical division.divider probe A test probe that divides an appliedsignal voltage by some factor (such as 2, 5, or 10)to place it within the range of the instrument withwhich the probe is used.dividing network See CROSSOVER NETWORK.division 1. Separating a quantity into a number ofequal parts, as indicated by the divisor. 2. Voltagedivision (see VOLTAGE DIVIDER). 3. Frequencydivision (see FREQUENCY DIVIDER). 4.Pulse-count division (see PULSE-COUNT DI-VIDER).division of vectors 1. The quotient of two rectangularvectors determined by the principle of rationalizationin algebra (i.e., by multiplying thenumerator and denominator of the indicated divisionby the conjugate of the denominator, simplifying,and performing the division). 2. To find thequotient of two polar vectors: the quotient of theirmoduli and the difference of their arguments.dj Abbreviation of diffused junction.DKT Abbreviation of dipotassium tartrate.D layer A layer of the ionosphere that is below theE layer; its altitude is approximately 60 kilometers.dm Abbreviation of decimeter.DMA Abbreviation of DIRECT MEMORY ACCESSand direct memory addressing.DME Abbreviation of DISTANCE-MEASURINGEQUIPMENT.DMM Abbreviation of DIGITAL MULTIMETER.DMOS Abbreviation for double-diffused metal-oxidesemiconductor, a type of field-effect transistorthat exhibits extremely low capacitance and lowsource-drain resistance when conducting.DNL See DIFFERENTIAL NONLINEARITY.R67Output

206 DNS • donut patternDNS Abbreviation of Doppler navigation system.doctor To use unconventional (sometimes substandard)methods in fixing a circuit or device orin correcting a bad design.document 1. In digital computer operations, especiallyin file maintenance, a form that provides informationpertinent to a transaction. Also seeTRANSACTION. 2. To perform documentation (seeDOCUMENTATION, 2). 3. A computer text file.documentation 1. Paperwork explaining the scopeof programs and how they can be optimized. 2. Annotatinga computer program at critical points duringits writing (e.g., so that the purpose of varioussegments are understood). A measure of good programming,documentation becomes especiallyvaluable for program modification or debugging.document reader An electronic device that readsprinted cards, usually for data entry into a computer.dog 1. A malfunctioning circuit or device. 2. Thecause of a circuit or device malfunction.doghouse An enclosure for antenna loading inductorsand other resonating components, placed atthe base of a vertical broadcasting tower.dog whistle See ULTRASONIC WHISTLE.Doherty amplifier A highly efficient linear radiofrequency(RF) amplifier in which a carrier tube anda peak tube operate jointly, both receiving amplitude-modulatedRF excitation. During unmodulatedintervals, the carrier tube supplies carrierpower to the load, while the peak tube, biased tocutoff, idles. On positive modulation peaks, thepeak tube supplies output power that combineswith that of the carrier tube, the increase in powercorresponding to the condition of full modulation ofthe carrier. On negative modulation peaks, thepeak tube does not supply power, and the outputof the carrier tube is reduced to zero.Dolby An electronic method of improving the audioreproduction quality of magnetic-tape systems.The gain is increased for low-level sounds duringthe recording process. During playback, the gainof the low-level sounds is reduced back to its originallevel.Dolby A A Dolby system with four frequencyranges, operated independently. It is used mostlyby recording professionals.Dolby B A modified form of Dolby A, with only oneband of noise-reducing circuitry. It is used primarilyby hobbyists.Dolezalek electrometer See QUADRANT ELEC-TROMETER.dolly 1. A low, wheeled frame or platform for transportingelectronic equipment. 2. A tool withwhich one end of a rivet is held while the head ishammered out of the other end.DOM Abbreviation of DIGITAL OHMMETER.domain 1. A region of unidirectional magnetizationin a magnetic material. 2. A region of unidirectionalpolarization in a ferroelectric material. 3. Aregion in which a variable is confined.domestic electronics Also called consumer electronics.The branch of electronics concerned withappliances, automatic controls, protective devices,entertainment systems, communicationsdevices, and other equipment for the home.domestic induction heater A household cookingutensil heated by currents induced in it. A primarycoil (connected to the power line) is imbeddedin the utensil, which acts as a short-circuitedsecondary coil.dome tweeter A speaker designed for highfrequency(treble), high-fidelity audio, and oftenfunctional at frequencies considerably above thelimit of the human hearing. Characterized by aconvex diaphragm. Usually part of an assemblyincluding a woofer and midrange speaker.dominant In statistical analysis, the nature of anyquantity that imposes its effects even in the presenceof other quantities.dominant mode In a waveguide, the propagationmode exhibiting the lowest cutoff frequency.dominant wave In a waveguide, the wave havingthe lowest cutoff frequency.dominant wavelength For visible light of a givenhue, the wavelength at which the emitted energyis the greatest.donor An electron-rich impurity added to a semiconductorto make it into an n-type material. Socalled because it donates its excess electrons.Compare ACCEPTOR.donor atom An atom having an excess electron.When a substance having such atoms is added toan intrinsic semiconductor, the extra electron isdonated, making the semiconductor into an n-type material.donor impurity A substance whose atoms haveexcess electrons, and that donates electrons tothe atomic structure of the semiconductor crystalto which it is added. Donor elements make semiconductorsinto n-type materials. Also seeDONOR ATOM. Compare ACCEPTOR IMPURITY.do-nothing instruction A computer program instructionthat causes no action to be taken. Can beused to provide space for future program updating,or to fill out a block of instructions, as needed by acompiler. Also called dummy instruction.don’t-care state In a logic function or gate, an inputdigit whose state (high or low) does not affectthe output.donut capacitor A flat, ring-shaped capacitor.donut coil See TOROIDAL COIL.donut crystal A relatively large, zero-temperaturecoefficientpiezoelectric quartz crystal cut in theform of a torus with the y-axis passing throughthe center of rotation.donut magnet See RING MAGNET.donut pattern The three-dimensional radiofrequency(RF) radiation/response pattern of afree-space straight antenna element measuring1 ⁄2 wavelength, neglecting the effects of groundand nearby objects.

doohickey • dot 207doohickey A usually unnamed device—especiallyone used to achieve some significant modificationof circuit performance.doorknob capacitor A high-voltage fixed capacitor,so called from its round package, whichsomewhat resembles a doorknob.doorknob tube A special UHF vacuum tube, socalled from its characteristic shape. The uniquedesign provides short electron-transit time andlow interelectrode capacitance. Largely replacedin recent years by semiconductor devices.dopant An impurity added in controlled amountsto a semiconductor to make it an n-type or p-typematerial. Also see ACCEPTOR and DONOR.dope To add impurities to a semiconductor material.Doping allows the manufacture of n-type orp-type semiconductors with varying degrees ofconductivity. In general, the greater the extent ofdoping, the higher the conductivity.doped junction In a semiconductor device, a junctionproduced by adding a dopant to the semiconductormelt.doping Adding a dopant to a semiconductor to alterthe way it conducts current.doping agent See DOPANT.doping compensation Opposite doping (i.e., addinga donor impurity to p-type semiconductormaterial or adding an acceptor impurity to n-typesemiconductor material).doping gas A gas diffused into a semiconductormaterial to dope it. For example, phosphoruspentoxide gas can be used to create an n-type regionin a p-type silicon chip.doping level The relative concentration of impurityadded to a semiconductor material to obtain acertain resistivity and polarity. The greater thedoping level, the lower the resistivity.Doppler broadening In a spectrum, the spreadingout or blurring of a spectral line caused byDOPPLER EFFECT, in turn resulting from motionof molecules, atoms, or other particles in themedium.Doppler cabinet A loudspeaker enclosure withwhich a vibrato effect is achieved by rotating orreciprocating either the loudspeaker or a baffleboard; the length of the sound path is alteredcyclically.Doppler effect A change in the frequency of a wavethat occurs when the source and observer are inrelative motion. The frequency of the wave increases(the wavelength shortens) as the sourceand observer approach each other; the frequencydecreases (the wavelength becomes greater) asthe source and observer recede from each other.This effect is often observed with sound waves, aswhen the pitch of an automobile horn seems torise as the car approaches and to fall as the carpasses. The effect is also observable in electromagneticradiation at all wavelengths. It affectssatellite communication and space communication.Doppler enclosure See DOPPLER CABINET.Doppler radar A radar that uses the change in carrierfrequency of the signal returned by a movingtarget (approaching or receding) to measure itsvelocity. Used by law enforcement officers to determinethe speed of moving vehicles. Also usedby meteorologists to evaluate air circulation patternsin thunderstorms, and to determine windspeeds in hurricanes and tornadoes.Doppler ranging See DORAN.Doppler shift The extent to which the frequency orwavelength of a signal changes because ofDOPPLER EFFECT. Can be measured in Hertz(for frequency) or in meters (for wavelength). Inastronomy, the shift is also measured as displacementof absorption or emission lines in aninfrared, visible, or ultraviolet spectrum.Doppler’s principle See DOPPLER EFFECT.doran A continuous-wave trajectory-measuringsystem utilizing Doppler shift (see DOPPLER EF-FECT). The name is a contraction of doppler ranging.dorsal column stimulator Abbreviation, DCS. Amachine that generates radio-frequency energythat is applied to human tissues for the temporaryrelief of pain.dosage meter See DOSIMETER.dose The total quantity of radiation received uponexposure to nuclear radiation or X-rays.dosimeter An instrument for measuring theamount of exposure to nuclear radiation orX-rays.dot 1. The shorter of the two characters (dot anddash) of the telegraph code. The dot, a shortsound, mark, or perforation, is one-third the

208 dot • double bufferinglength (duration) of a dash. Compare DASH. 2.One of the small spots of red, green, or blue phosphoron the screen of a color-television picturetube or cathode-ray-tube (CRT) computer display.3. A small spot of material alloyed with asemiconductor to form an alloy junction. 4. Thejunction of two lines on a schematic diagram,representing a wired connection; also calledsolder dot.dot AND Externally connected circuits or functionswhose combined outputs result in an AND function.Compare DOT OR.dot-and-dash telegraphy Telegraphy (wire or radio)by means of dot and dash characters.dot cycle One period of an alternation between twosignaling conditions, each of which is of unit duration(e.g., a unit mark followed by a unit space).dot encapsulation A method of packaging cylindricalcomponents by pressing them into theholes of perforated disks; interconnections aremade, to complete a circuit, on each face of thedisks.dot generator A special radio-frequency (RF) signalgenerator used to produce a pattern of red,green, and blue dots on the screen of a color televisionreceiver.dot matrix A rectangular array of spaces, some ofwhich are filled in to form alphanumeric andpunctuation characters.dot matrixdot-matrix display A display that shows charactersin dot-matrix form.dot-matrix printer A computer output peripheralthat prints characters and images on paper as afine grid of dots. A print head, containing severalpins, presses the ribbon against the paper as itmoves laterally across each line. Can be used toprint text and/or graphics.dot movement pattern The movement of the red,green, and blue dots on the screen of a color televisionpicture tube as the red, green, and bluemagnets and the lateral magnet are adjusted forconvergence of the dots at the center. The bluedots move horizontally or vertically; the red andgreen dots, diagonally.dot OR Externally connected circuits or functionswhose combined outputs result in an OR function.Compare DOT AND.dot pattern In color television testing with a dotgenerator, dots of color (a red group, green group,and blue group) produced on the screen. Withoverall beam convergence, the three groups blendto produce white.dot-sequential system The color television systemin which the image is reproduced by means of primary-colordots (red, green, blue) sequentially activatedon the screen of the picture tube.Compare FIELD-SEQUENTIAL SYSTEM andLINE-SEQUENTIAL SYSTEM.double-amplitude-modulation multiplier A modulatingsystem in which a carrier is amplitudemodulatedfirst by one signal and then by a secondsignal. The resulting signal is fed to adetector, the output of which contains the productof the two modulating signals.double-anode diode A semiconductor diode havingtwo anodes and a common cathode.double armature An armature (such as that of adynamotor or a two-voltage generator) that hastwo separate windings on a single core, and hastwo separate commutators.double-balanced mixer See BALANCED MIXER.double-balanced modulator See BALANCEDMODULATOR.double-base diode See UNIJUNCTION TRANSIS-TOR.double-base junction transistor A junction transistorhaving the usual emitter, base, and collectorelectrodes, plus two base connections, one oneither side of the base region. The additional baseconnection acts as a fourth electrode to which acontrol voltage is applied. Also called tetrode transistor.double-beam CRT See DUAL-BEAM OSCILLO-SCOPE.double-beam oscilloscope See DUAL-BEAM OS-CILLOSCOPE.double-bounce calibration In radar operations, acalibration technique for determining zero-beaterror. Round-trip echoes are observed, the correctrange being the difference between the twoechoes.double-bounce signal A signal that is received afterhaving been reflected twice.double-break contacts The member of a set ofcontacts that is normally closed on two others.Compare DOUBLE-MAKE CONTACTS.double-break switch A switch that opens a previouslyclosed circuit at two points simultaneouslyon closing. Compare DOUBLE-MAKE SWITCH.double bridge See KELVIN DOUBLE BRIDGE.double buffering In the input/output operation ofa computer peripheral, the use of two memory areasfor temporary storage.

double-coil direction finder A radio directionfinder (RDF) using an antenna that consists oftwo identical, perpendicular coils. The directivityof the antenna is the resultant of the directivity ofthe individual coils.double conversion 1. Two complete frequencyconversions in a superheterodyne system. For example,the incoming signal might be converted toa 9-MHz first intermediate frequency (first IF); ata later stage, this signal might be converted to a455-kHz second IF. The high first IF widely sepadouble-buttonmicrophone • double-extended Zepp antenna 209double-button microphone A carbon microphonehaving two buttons mounted on each side of thecenter of a stretched diaphragm, and connectedin push-pull. Also see BUTTON MICROPHONE.double-channel duplex Two-way communicationover two independent channels. One stationtransmits on one channel, and the other stationtransmits on the other channel. The result is conversation-modecommunications, in which oneoperator can interrupt the other at any time; bothreceivers are always operational.double-channel simplex A system of communicationin which two channels are used. One stationtransmits on one channel, and the other stationtransmits on the other channel. Interruption isnot possible because whenever either operatortransmits, the station receiver is muted.double-checkerboard pattern In a magnetic corememory, the maximum noise that appears whenhalf of the half-selected cores are in the one stateand the others are in the zero state. Also calledworst-case noise pattern.double circuit tuning A circuit whose output andinput are tuned separately. Such tuning providesincreased selectivity when the input and outputare resonant at the same frequency, and decreasedselectivity when they are tuned to different frequencies.Also see DOUBLE-TUNED AMPLIFIER.double clocking A phenomenon that occurs insome digital circuits when the input pulse isnonuniform, and appears as two pulses to the device.The device is thus actuated at twice the desiredfrequency.In1stmix.1stIFAmp.2ndmix.2ndIFOutrates the signal from the image; the low second IFallows superior selectivity to be achieved at a reasonablecost. Also called dual conversion. 2. Pertainingto a superheterodyne receiver with twointermediate frequencies.double-conversion receiver Also called doubleconversionsuperheterodyne. A superheterodynereceiver using DOUBLE CONVERSION to achieveoptimum selectivity and image rejection.double-current generator 1. A dynamo-type generatorsupplying both alternating current (ac) and directcurrent (dc) from one armature winding. 2. Arotary converter operating on dc and delivering ac.double-diamond antenna A broadband antennaconsisting of two rhomboid plates, one attachedto each side of the feeder.double-diffused epitaxial mesa transistor A transistorin which a thin mesa crystal is overlaid onanother mesa crystal. Also called epitaxial-growthmesa transistor.double-diffused transistor See DIFFUSED-EMITTER-AND-BASE TRANSISTOR.double diode See DUODIODE.double-diode limiter A limiter in which two diodesare connected back to back in parallel, to limitboth peaks of an alternating-current (ac) signal.double-doped transistor See GROWN-JUNCTIONTRANSISTOR.double edit In audio tape recording, to make twochanges in a given span of the tape. For example,a producer might dislike the wording of a certainsentence, and re-record the sentence. Then,changing his or her mind, the producer mightrecord the original sentence back over the rerecordedsentence. These changes increase therisk of audible irregularities appearing in the finalrecording.double emitter follower See COMPOUND CON-NECTION.double-ended amplifier See PUSH-PULL AMPLI-FIER and DOUBLE-ENDED CIRCUIT.double-ended circuit A symmetrical circuit (i.e.,one having identical halves, each operating on ahalf-cycle of the input signal). Example: a pushpullamplifier.double-extended Zepp antenna A horizontal,collinear, center-fed antenna, in which each sectionmeasures 0.65 wavelength. This antennagives increased gain over that of the Zepp anddouble Zepp (see DOUBLE ZEPP ANTENNA).0.65λ/2Radiator0.65λ/2Osc.Osc.Feederdouble conversiondouble-extended Zepp antenna

210 double-hump resonance curve • double-sideband systemdouble-hump resonance curve A resonant responsethat is flattened by double tuning; itexhibits two resonance peaks. Also see DOUBLE-TUNED AMPLIFIER.double-hump wave See DOUBLE-PULSE WAVE.double image Two overlapping television pictures,one usually fainter than the other. Caused by thesignal arriving over two different paths (one possiblyattributable to reflection of the wave) and,hence, at different instants in time. The fainterimage is called a GHOST.double insulation The use of two layers of insulationon a conductor, made of different materials.double ionization Ionization resulting from anelectron colliding with an ion. In a gas, for example,a neutral atom might collide with an electron,which can knock an electron out of the atom. Theatom then becomes a positive ion; it might in turnbe bombarded by an electron, releasing still anotherelectron.double-junction photosensitive semiconductorSee PHOTOTRANSISTOR.double layer See HELMHOLTZ DOUBLE LAYER.double local oscillator A mixer system in which alocal oscillator generates two accurate radiofrequency(RF) signals separated by a few hundredhertz. The difference frequency is used as areference in some applications.double-make contacts A set of normally open contactsof which one closes against two otherssimultaneously. Compare DOUBLE-BREAKCONTACTS.double-make switch A switch that closes a previouslyopen circuit at two points simultaneously.Compare DOUBLE-BREAK SWITCH.double moding In microwave operations, theabrupt changing of frequency at irregular intervals.double modulation Using a modulated carrier tomodulate another carrier of a different frequency.double-play tape A thin magnetic recording tapethat has approximately twice the playing time ofthe usual tape. Although the playing time islonger, double-play tape is more subject to jammingand stretching than standard-thicknessrecording tape.double-pole Having two poles or switchable circuits(e.g., a double-pole switch).double-pole, double-throw switch or relay Abbreviation,DPDT. A switch or relay having twocontacts that can be closed simultaneously inone of two directions, to close or open two circuits.double precision The use of two computer wordsto represent a single number to gain precision.double-pole, single-throw switch or relay Abbreviation,DPST. A switch or relay having two contactsthat can be closed in only one direction, tosimultaneously close or open two circuits.double precision hardware Within a computer,arithmetic units permitting the use of doubleprecisionoperands, sometimes also accommodatingfloating-point arithmetic.double-precision number In digital computer operations,a number represented by two words forgreater precision.double pulse reading Pertaining to a magneticcore in a computer memory, recording bits as twostates held simultaneously by one core havingtwo areas that can be magnetized with alternatepolarities. For example, positive-negative couldrepresent zero, and negative-positive could representone.double-pulse wave An alternating-current (ac)wave having two successive positive peaks followedby two successive negative peaks withineach cycle. The output voltage of a varistor bridgehas such a waveshape for an ac input.double-pulsing station A loran station that transmitsat two pulse rates upon receiving two pairsof pulses.double pumping A method of obtaining increasedpeak output power from a laser by pumping it fora comparatively long interval and then immediatelypumping it for a short interval.doubler 1. A circuit or device for multiplying a frequencyby two (see FREQUENCY DOUBLER). 2.A circuit or device for multiplying a voltage by two(see VOLTAGE DOUBLER).double probe A test probe that multiplies an appliedsignal voltage by two, so it can be handledmore effectively by the instrument with which theprobe is used.double punching In perforating a punched card,putting two holes in one column; it is an error if itoccurs in a field of a card that is part of a record.double rail A form of logic system in which twolines are used, with three possible states. Theoutput can be high, low, or undecided.double response 1. Two-point response, as thatassociated with tuning a receiver to a signal andthen to its image. 2. See DOUBLE-HUMP RESO-NANCE CURVE.double screen A cathode-ray tube having a twolayerscreen on which there is an additional,long-persistence coating of a different color.double shield Two independent electromagneticshields for a circuit enclosure or cable. Theshielding structures are concentric, and can beconnected together at a single point (the commonpoint).double sideband Abbreviation, DSB. In a modulatedsignal, the presence of both sidebands.double-sideband suppressed carrier Abbreviation,DSSC. A transmission technique in which bothsideband products of modulation are transmittedand the carrier is suppressed. Compare LOWERSIDEBAND, SUPPRESSED CARRIER, UPPERSIDEBAND, and SUPPRESSED CARRIER.double-sideband system A modulation or demodulationsystem utilizing both sidebands, with orwithout the carrier.

double-sideband transmitter • double Zepp antenna 211Outer shieldDielectricInner shieldDielectricCenterconductorJacketdouble shielddouble-sideband transmitter A modulated transmitterusing a double-sideband system.double signal In reception, the property of havinga signal on either side of the carrier frequency, asin a direct-conversion receiver. The two signalsrepresent the sum and difference of the local oscillatorsignal and the actual received signal.Because the two signals convey identicalinformation, the phenomenon is wasteful of receivedspectrum, and degrading to receiver selectivityand sensitivity.double-signal receiver A receiver, such as a direct-conversiontype, in which the signals occurin replicated form on either side of the local oscillatorsignal. Compare SINGLE SIGNAL.double-spot tuning In a superheterodyne receiver,tuning in the same signal at two different placeson the dial, a condition caused by image response.double squirrel-cage induction motor A polyphaseinduction motor having a double squirrelcagerotor. The rotor slots contain two bars, anupper bar having low reactance (being near theair gap) and high resistance, and a lower bar havinghigh reactance and low resistance. This motorhas low starting current, high starting torque,and a full-load slip of less than 5%.double-stream amplifier A traveling-wave tube inwhich microwave amplification results from theinteraction of two electron beams of different averagevelocity.double-stub tuner Two stubs (see STUB) connectedin parallel with a transmission line andusually spaced 0.375 wavelength (135 electricaldegrees) apart; it is used as an impedancematcher.double superheterodyne See DOUBLE-CONVER-SION SUPERHETERODYNE.double superheterodyne reception See DOUBLE-CONVERSION SUPERHETERODYNE.double-surface transistor See COAXIAL TRAN-SISTOR.doublet See DIPOLE ANTENNA.double-throw Operating in opposite directions asselected (e.g., a double-throw relay or switch).double-throw circuit breaker A circuit breaker thatcloses in both its pull-in and dropout positions.double-throw switch or relay A switch or relayhaving two ganged poles.double-trace recorder See DOUBLE-TRACK RE-CORDER, 2.double tracing Displaying two signals simultaneouslyon the screen of an oscilloscope throughthe use of an electronic switch.double-track recorder 1. A tape recorder whosehead is positioned so that separate recordingscan be made as two tracks on the tape. 2. Agraphic recorder that produces two separate paralleltracings.doublet trigger A two-pulse, constant-spaced triggersignal used for coding.double-tuned amplifier An amplifier whose inputand output circuits are both tuned.double-tuned circuit A circuit, such as an amplifieror filter, using separate input and output tuning.Also see DOUBLE CIRCUIT TUNING andDOUBLE-TUNED AMPLIFIER.InputL1Input tuning: L2 and C1L2 C1 C2 L3double-tuned circuitL4 OutputOutput tuning: L3 and C2double-tuned detector A form of frequencymodulation(FM) discriminator with two resonantcircuits. One is tuned slightly higher than thechannel center frequency, and the other is tunedan equal amount below the center.double-vee antenna A broadband, modified dipoleantenna resembling two vees in line. Also seeVEE ANTENNA.double-winding generator A dynamo-type generatorhaving separate armature windings for supplyingtwo voltages, either of which can be direct(dc voltage) or alternating (ac voltage).double-wye rectifier A heavy-load circuit using sixrectifier diodes, each conducting for 120 degreesof the cycle. An interphase winding is used. Thecircuit is equivalent to two three-phase, half-waverectifiers connected in parallel.double-Y rectifier See DOUBLE-WYE RECTIFIER.double Zepp antenna A usually horizontal,straight, center-fed, full-wavelength antenna.

212 double Zepp antenna • dressAlso called two half waves in phase. Its name wasderived because it is, in fact, two Zepp antennasforming a collinear array.doubling 1. Producing the second harmonic of asignal. 2. In communication, unintentional simultaneoustransmission by both operators, resultingin missed information. 3. In a speaker,distortion resulting in large amounts of secondharmonicoutput.doubly balanced modulator See BALANCEDMODULATOR.doughnut capacitor See DONUT CAPACITOR.doughnut coil See TOROIDAL COIL.doughnut crystal See DONUT CRYSTAL.doughnut magnet See RING MAGNET.down convert In superheterodyne conversion, toheterodyne a signal to an intermediate frequencylower than the signal frequency. Compare UPCONVERT.down lead See LEAD-IN.downlink The signal sent down from an activecommunications satellite to the earth, usually ona different frequency than the signal sent up. SeeUPLINK.downlink beamwidth The angle subtended betweenthe half-power points of the downlink signalfrom an active communications satellite.downlink frequency The frequency of the downlinksignal from an active communications satellite.Usually, the downlink signals occupy acertain band of frequencies, anywhere from severalkilohertz to several megahertz wide.downlink power 1. The output power of the downlinktransmitter in an active communicationssatellite. 2. The effective radiated power (ERP) ofthe downlink signal from an active communicationssatellite.down time A period of time during which electronicequipment is completely inoperative (forany reason).downturn A usually sudden dip in a performancecurve. Compare UPTURN.downward modulation Modulation in which theaverage carrier component decreases duringmodulation. Example: amplitude modulation of atransmitter in which the antenna current decreasesduring modulation. Compare UPWARDMODULATION.DP Abbreviation of DATA PROCESSING.DPDT Abbreviation of double-pole, double-throw(switch or relay).DPM 1. Abbreviation of digital power meter. 2. Abbreviationof DIGITAL PANEL METER. 3. Abbreviationof disintegrations per minute.DPS Abbreviaton of disintegrations per second.DPST Abbreviation of double-pole, single-throw(switch or relay).dr Abbreviation of dram.drag 1. A retarding force, caused by friction, actingon a moving body in contact with another movingor stationary body or medium. 2. A retardingforce introduced by an applied magnetic or electricfield.drag angle In disk recording, an angle of less than90° between the stylus and the disk. The acuteangle causes the stylus to drag instead of diggingin.drag cupA cup of nonmagnetic metal (usually copperor aluminum) that, when rotated in a magneticfield, acquires a voltage proportional to thespeed of rotation. The device is often used as abrake.drag-cup motor A servomotor whose shaft has acopper or aluminum drag cup that rotates in thefield of a two-phase stator. Eddy currents set upin the cup by the field winding produce torque;braking action, direction control, and speed controlare obtainable by means of associated electronics.drag magnet In a motor-type meter, a brakingmagnet (i.e., one used to reduce speed througheddy-current effects). Also called retarding magnet.drain1. The current or power drawn from a signalor power source. 2. A load that absorbs currentor power. 3. The electrode in a field-effect transistor(FET) from which the output is usually taken;equivalent to the collector of a bipolar transistor.drainage equipment Devices and systems for protectingcircuits against transients generated bycircuit breakers and similar safety devices.drain-coupled multivibrator An oscillator thatuses two field-effect transistors (FETs) in the circuitequivalent of a collector-coupled bipolartransistormultivibrator. The drain of one stage iscapacitance-coupled to the gate of the otherstage.R1C1Q1R2+ dcR3C2R4Q2drain-coupled multivibratorC3OutD-region A low region of the ionosphere beneaththe E-region, whose ionization varies with the inclinationof the sun. The greatest ionization is atmidday; the layer disappears at night.dress The (usually experimental) arrangement ofleads for optimum circuit operation (minimum

1. To excite (i.e., to supply with input-signalcurrent, power, or voltage) (see DRIVING CUR-RENT, DRIVING POWER, and DRIVING VOLTdress• driver element 213capacitance, best suppression of oscillation, minimumpickup, etc.).dressed contact A contact having a permanentlyattached locking spring member.drift 1. Within a conductor or semiconductor, thecontrolled, directed movement of charge carriersresulting from an applied electric field. 2. A usuallygradual and undesirable change in a quantity,such as current, as a result of a disturbingfactor, such as temperature or age.drift current In a semiconductor, the current resultingfrom a flow of charge carriers in the presenceof an electric field. The charge carriers areelectrons in n-type material and holes in p-typematerial.drift field The inherent internal electric field of aDRIFT-FIELD TRANSISTOR.drift-field transistor An alloy-junction, bipolar,radio-frequency (RF) transistor for which the impurityconcentration is graded from high on theemitter side of the base wafer to low on the collectorside. This creates an internal drift field thataccelerates current carriers and raises the upperfrequency limit of the transistor.drift-matched components Active or passivecomponents that have been closely matched interms of the drift of one or more parameters, withrespect to time, temperature, etc.drift mobility For current carriers in a semiconductor,the average drift velocity per unit electricfield.drift space 1. In a vacuum tube, a space that isnearly free of alternating-current (ac) fields fromthe outside, and in which the repositioning ofelectrons is governed by the space-charge forcesand the velocity distribution of the electrons. 2.In a Klystron, the space between buncher andcatcher cavities in which there is no field.drift speed The average velocity of charge carriersmoving through a medium.drift transistor See DRIFT-FIELD TRANSISTOR.drift velocity The net velocity of a charged particle(electron, hole, or ion) in the direction of the fieldapplied to the conducting medium.drift voltage The usually gradual change in voltageresulting from such causes as internal heating.Also called voltage drift.drip loop In a transmission line for an antenna orpower service, a loop near the point of entry to thebuilding for the purpose of allowing condensationor rain water to drip off.drip-proof motor A motor with ventilating aperturesarranged so that moisture and particlescannot enter the machine.drip-tight enclosure A housing designed to prevententry of rain, snow, and dust; it also preventsaccidental contact with the enclosedapparatus or machinery.driveAGE). 2. Input-signal excitation (see DRIVINGCURRENT, DRIVING POWER, and DRIVINGVOLTAGE). 3. A device that moves a recordingmedium (e.g., tape drive and diskette drive). 4.The transmission of mechanical energy from oneplace to another (e.g., motor drive).drive array A set of two or more hard-disk drives ina computer system. They function together tominimize the possibility of data loss. Such a systemcan also increase the amount of fast-accessdata storage.drive belt A continuous belt used to transmit mechanicalenergy from a driving pulley to a drivenpulley.drive circuit 1. A circuit used to provide the excitationto a motor. 2. An amplifier that suppliesdrive to a more powerful amplifier.drive control In a television receiver, the potentiometerused to adjust the ratio of horizontalpulse amplitude to the level of the linear portionof the sawtooth scanning-current wave.driven element In a multielement antenna, an elementto which electromagnetic energy is fed directly,as opposed to a PARASITIC ELEMENT,which is excited by a nearby radiator element.driven-element directive antenna A multielementdirectional antenna whose elements aredriven from the feed line (i.e., no element is parasitic).Compare PARASITIC-ELEMENT DIREC-TIVE ANTENNA.driven multivibrator A multivibrator whose operationor frequency is controlled by an externalsynchronizing or triggering voltage. CompareFREE-RUNNING MULTIVIBRATOR.driven single sweep A single oscilloscope sweepthat is initiated by the signal under observation.drive pattern A pattern of interference in a facsimilesystem that is caused by improper synchronizationof the recording spot.driven sweep An oscilloscope sweep that is initiatedby the signal under observation.drive pin A pin used to prevent a record from slippingon the rotating turntable of a recorder or reproducer.It is similar to, and located near, thecenter pin of the turntable.drive pulse In digital computer operations, a pulsethat magnetizes a cell in a memory bank.driver 1. A device that supplies a useful amount ofsignal energy to another device to ensure itsproper operation (e.g., a current driver for a magnetic-corememory, an oscillator driving a loudspeaker).2. A power amplifier stage that suppliessignal power to a higher-powered amplifier stage.3. In a digital computer, a stage that increasesthe output current or power of another stage(e.g., a clock driver). 4. The cone and magnet of adynamic speaker.driver element In a multielement directive antenna,the element excited directly by the feeder,the other elements (directors and reflectors) beingparasitic.

214 driver impedance • dropsondedriver impedance 1. The output impedance of adriver stage. 2. The impedance “seen” from thedriven stage of an amplifier, through the drivertransformer, to the driver stage. It is the vectorsum of driver reactance and resistance.driver inductance In an amplifier’s driver transformer,the inductance, as “seen” looking throughthe transformer from the driven stage into thedriver stage.driver resistance In an amplifier’s driver transformer,the resistance “seen” looking through thetransformer from the driven stage into the driverstage.driver stage An amplifier stage whose chief purposeis to supply excitation (input-signal current,power, or voltage) to the next stage. Also seeDRIVER.driver transformer The transformer that couples adriver stage to a driven stage. Example: the interstagetransformer inserted between the collectorof a single-ended driver transistor and the twobases of a push-pull power-output stage in anaudio amplifier.driving current In a power amplifier, the inputsignal current required to produce a givenamount of output power.driving-point admittance The reciprocal ofDRIVING-POINT IMPEDANCE.driving-point impedance The input impedance ofa network.driving power In a power amplifier, the input signalpower required to produce a given amount ofoutput power.drive wire The wire forming the coil around thetoroidal cell in a magnetic core memory; suppliespulses that magnetize the cell.driving-range potential In cathodic protection,the difference of potential between the anode and(protected) cathode.driving signal 1. Drive (see DRIVE, 2). 2. In television,time-scanning signals (line-frequency pulsesand field-frequency pulses) at the pickup location.driving spring In a stepping relay, the spring thatmoves the wiper blades.driving voltage In a power amplifier, the input signalvoltage required to produce a given amount ofoutput power.DRO Abbreviation of DIGITAL READOUT.drone A pilotless radio-controlled aircraft withouta human pilot.drone cone An undriven loudspeaker cone that ismounted in a bass-reflex enclosure with otherspeakers. Also called PASSIVE RADIATOR.droop 1. A dip in the graph of a function. 2. In apulse train, the decrease in mean amplitude (inpercent of maximum amplitude) at a given instantafter attainment of maximum amplitude.drooping radials In a ground-plane antenna, radialsthat slope downward to provide a transmission-lineimpedance match. The slope angleApprox. 135°drooping radialsRadiatorRadials(grounded)depends on the characteristic impedance of theline; typically, the angle is between 45 degreesand 70 degrees, relative to horizontal.drop 1. In wire communications, the line connectinga telephone cable to a subscriber’s building.2. See VOLTAGE DROP.drop bar A device that automatically grounds orshort-circuits a capacitor when the door of a protectiveenclosure is opened.drop cable See DISTRIBUTING CABLE, 1.drop channel In a communications system utilizingseveral channels, a channel that is not used.drop-in The unintentional creation of bits when amagnetic storage device is being read from orwritten into. Compare DROP-OUT, 4.drop indicator In a signaling system, such as anannunciator, a hinged flap that drops into viewwhen the signaling device is actuated.drop-out 1. The opening of a relay or circuitbreaker. 2. In digital computer operations, variationin signal level of the reproduced taperecordeddata. Such variation can result in errorsin data reproduction. 3. In the production ofmonolithic circuits, a special image placed at adesired point on the photomask. 4. Digit lossduring a read or write operation involving a magneticstorage device.dropout current See DROPOUT VALUE.dropout power See DROPOUT VALUE.dropout value The level of current, power, or voltageat which a device, such as a circuit breaker orrelay, is released.dropout voltage See DROPOUT VALUE.dropping resistor A series resistor providing avoltage reduction equal to the voltage drop acrossitself. For example, a 1000-ohm resistor in serieswith a 45-V battery, and carrying a current of 10mA, will provide a voltage reduction equal to 10 V(IR = 0.01 × 1000 = 10 V), thus dropping the 45 Vto 35 V.drop relay In a telephone system, a relay that isactivated by the ringing signal. The relay is usedto switch on a buzzer, light, or other device.drop repeater A repeater intended for a terminationof a communications circuit in a telephonesystem.dropsonde A parachute-supported radiosondedropped from a high-flying aircraft.

drop-tracks • dry flashover voltage 215drop-tracks The tracks of radioactive particles madevisible by moisture in an ionization chamber.drop wire A wire that runs from a building to apole (for line extension) or to a cable terminal (forcable extension).drum 1. A rotating cylinder coated with a magneticmaterial on which digital information can berecorded in the form of tiny magnetized spots.These spots are read as the drum rotates underpickup heads, or erased when the stored informationis no longer needed. 2. In some graphicrecorders, facsimile receivers, etc., a rotatingcylinder carrying the recording sheet.drum capacitor See CONCENTRIC CAPACITOR.drum controller The device that regulates the recordingprocess on a drum memory.drum mark On a track of a magnetic drum, a characterthat signifies the end of a character group.drum memory In digital computers, a memorybased on a magnetic drum (see DRUM, 1). Theyhave been largely replaced in recent years by electronicrandom-access memory, in the form of integratedcircuits (ICs) and/or PCMCIA standardadapter cards.drum parity The degree of accuracy in a drumrecording/reproducing system.drum programmer A device for sequencing operations.Its heart is a rotating drum, around whosesurface contacts or points can be placed to actuateor terminate operations at selected times.drum receiver A facsimile receiver using recordingpaper or photographic film wound around a revolvingdrum.drum recorder A graphic recorder in which therecord sheet is wound around a rotating drum.Rotatingdrumdrum recorderArmature withmarkerMeterdeviceInputdrum resistor A resistor consisting of a hollowcylinder of resistive material. Such a resistor canbe cooled by circulating air or liquid through thecylinder.drum speed The speed, usually measured in revolutionsper minute (rpm), of the rotating drum ina graphic recorder, facsimile transmitter, or facsimilereceiver.drum storage The storage of data as magneticimpulses on a cylindrical, or drum-shaped,medium. Largely supplanted in recent years bymagnetic disks, optical disks, and magnetictapes.drum switch A sequential switch whose contactsare pins or teeth placed at points around the outsideof a revolving drum.drum transmitter A facsimile transmitter in whichthe sheet bearing the material to be transmittedis wound around a revolving drum.drum-type controller A motor-driven drum switcharranged to time various operations through sequentialswitching.drum varistor A varistor that is a hollow cylinderof nonlinear resistance material. This varistorcan be cooled by circulating air or liquid throughit.drum winding In a motor or generator, an armaturewhose conductors are on the outer face ofthe core, the two branches of a turn lying underadjacent poles of opposite polarity.drunkometer An instrument for testing the extentof alcoholic intoxication. It electronically measuresblood alcohol content through analysis ofthe subject’s breath.dry In an electric cell, a term used to describe anelectrolyte that is semiliquid or solid.dry battery A battery of dry cells.dry cell 1. A Leclanche primary cell in which thepositive electrode is carbon, the negative electrodeis zinc, and the electrolyte is a gel of ammoniumchloride and additives. Also see CELL andPRIMARY CELL. 2. A cell whose electrolyte is agel or paste.dry circuit A circuit in which the maximum voltageis 50 mV and the maximum current 200 mA.dry-contact rectifier See DRY-DISK RECTIFIER.dry contacts Contacts that neither make norbreak a circuit.dry-disk rectifier A solid-state rectifier, such as acopper-oxide, magnesium-copper-sulfide, or seleniumtype, that consists of a metal disk coatedwith a semiconductor material. The name wasoriginally used to distinguish this rectifier fromthe wet electrolytic rectifier.dry electrolytic capacitor An electrolytic capacitorwhose electrolyte is a paste or solid. CompareWET ELECTROLYTIC CAPACITOR.dry flashover voltage The breakdown voltage betweenelectrodes in dry air when all insulation isclean and dry.

216 dry pile • dual-cone speakerdry pile A voltaic pile containing numerous diskssilvered or tinned on one face and covered withmanganese dioxide on the other.dry reed A metal contact, generally used as a relayor switch, that moves toward or away from anotherfixed contact under the influence of a magneticfield.dry-reed relay See DRY-REED SWITCH.dry-reed switch A switch consisting of two thin,metallic strips (reeds) hermetically sealed in aglass tube. The tube is surrounded by a coil ofwire. When a current flows in the coil, a magneticfield affects the reeds. In the normally open dryreedswitch, the magnetic field causes the reedsto come together and close the circuit. In the normallyclosed dry-reed switch, the magnetic fieldcauses the reeds to separate, opening the circuit.Compare MERCURY-WETTED REED RELAY.dry run 1. The preliminary operation of equipmentfor testing and appraisal. Such a procedure precedesputting the equipment into regular service.2. A step-by-step, paper-and-pencil “run” of acomputer program before it is machine-implemented.dry shelf life The life of a battery cell stored withoutits electrolyte.dry-transfer process A method of transferringprinted-circuit patterns and panel labels fromsheets by rubbing them onto the substrate orpanel.dry-type forced-air-cooled transformer A DRY-TYPE TRANSFORMER that is cooled by convectionof air circulated by a blower or fan. Thisincreases the amount of power that the transformercan safely handle.dry-type self-cooled transformer A DRY-TYPETRANSFORMER that is cooled by natural air circulation(convection), without the use of a bloweror fan.dry-type transformer A transformer that, ratherthan being immersed in oil, is cooled entirely bythe circulation of air.DSB Abbreviation of DOUBLE SIDEBAND.DSBSC Abbreviation of DOUBLE-SIDEBAND SUP-PRESSED CARRIER. Also abbreviated DSSC.dsc Abbreviation of double silk covered (wire).D scope A radar whose display resembles that of aC scope, the difference being that blip heightgives an approximation of the distance.D service A Federal Aviation Agency service providingradio broadcasts of weather data, noticesto aircraft personnel, and other advisory messages.D-shell connector A multi-pin connector (eithermale or female) with a characteristic shape thatensures proper pin placement. Commonly usedfor computer ports, and for connections of peripheralsto electronic equipment.dsp Abbreviation of double silver plated.DSR Abbreviation of DYNAMIC SPATIAL RECON-STRUCTOR.DSS Abbreviation of direct station selection (telephone).DSSC Abbreviation of DOUBLE-SIDEBAND SUP-PRESSED CARRIER. Also abbreviated DSBSC.DT Abbreviation of DATA TRANSMISSION.DTA Abbreviation of differential thermoanalysis.DT-cut crystal A piezoelectric plate cut from a quartzcrystal at an angle of rotation about the z-axis of–53 degrees. It has a zero temperature coefficient offrequency at approximately 30 degrees Celsius.Also see CRYSTAL AXES and CRYSTAL CUTS.DTL Abbreviation of DIODE-TRANSISTOR LOGIC.DTn Abbreviation of DOUBLE TINNED.DTS 1. Abbreviation of DATA-TRANSMISSION SYS-TEM. 2. Abbreviation of digital telemetry system.DU Abbreviation of DUTY CYCLE.dual 1. Pertaining to a combination of two componentssuch as diodes, transistors, etc., in a singlehousing. The components are often carefullymatched. Compare QUAD. 2. Pertaining to a deviceor circuit that behaves in a manner analogousto that of another operating with componentand parameter counterparts. Thus, a current amplifiercan be the dual of a voltage amplifier;a series-resonant circuit, the dual of a parallelresonantcircuit; or a field-effect transistor, thedual of a bipolar transistor.dual-beam CRT A cathode-ray tube having twoseparate electron guns, for use in a dual-beamoscilloscope.dual-beam oscilloscope Also called dual-trace oscilloscope.An oscilloscope having two electronguns and deflection systems; it can display twophenomena on the screen simultaneously forcomparison.dual capacitor 1. Two fixed capacitors combinedin a single housing, sometimes sharing a commoncapacitor plate. 2. A two-section, gangedvariable capacitor.dual-channel amplifier An amplifier having twoseparate, independent channels (e.g., a stereohigh-fidelity audio amplifier).dual-cone speaker A speaker designed for a widerange of audio frequencies. One cone responds tothe bass (low) and midrange audio frequencies,and a smaller cone responds to the treble (high)audio frequencies.

dual diode • Duant electrometer 217dual diode A discrete component consisting of twodiodes in one package.dual-diversity receiver A receiver or receiver systemfor DIVERSITY RECEPTION.dual-diversity reception See DIVERSITY RECEP-TION.dual-emitter transistor A low-level silicon pnpchopper transistor of the planar passivated epitaxialtype; it has two emitter electrodes.dual-frequency calibrator A secondary frequencystandard providing two fundamental test frequencies(e.g., 100 kHz and 1 MHz).dual-frequency induction heater An inductionheater whose work coils carry energy of two differentfrequencies. The coils heat the work eithersimultaneously or successively.dual gate1. A digital integrated circuit (IC) consistingof two logic gate units. 2. Pertaining to afield-effect transistor (FET) with two gates or gateelectrode connections.dual-gate FET A field-effect transistor with twogate (input) electrodes.dual-gate MOSFET A metal-oxide-semiconductorfield-effect transistor (MOSFET) with two gate (input)electrodes.dual-inline package Abbreviation, DIP. A flat,molded integrated-circuit (IC) package having terminalpins along both long edges.dual-inline packageCasePinsduality 1. The condition of being dual (see DUAL).This can be an aid in the design of certain circuitsrequiring complementary parameters, e.g., current-operatedcircuit analogs of voltage-operatedcircuits. 2. See DUALITY OF NATURE.duality of nature 1. Any of various situations inwhich a phenomenon exhibits two distinct anddifferent natures. A commonly cited example isthe dual model of light. In some instances, visiblelight behaves like a barrage of particles, but inother environments it appears to be a wave effect.Another example is the dual model of electro-static energy, behaving as point charges in somescenarios and as force fields in other situations.2. The tendency of a set of principles to be duplicatedin sense by predictable analogies, as betweeninductance and capacitance, electrostaticsand magnetics, etc.dual local oscillator See DOUBLE LOCAL OSCIL-LATOR.dual meter A meter having two meter movementsand scales in a single case; the arrangement permitssimultaneous monitoring of two quantities.dual modulation The modulation of a single carrieror subcarrier by two different types of modulation—eachcarrying different information.dual network A network that is the dual of anothernetwork having complementary parameters. Forexample, a common-emitter, current-sensitive,bipolar-transistor circuit is the dual of a common-source,voltage-sensitive, field-effect-transistor(FET) circuit. Also see DUALITY.dual operation In digital logic, the operation resultingfrom inverting all of the digits. Every 1 isreplaced with a 0, and vice versa.dual-output power supply A power supply withtwo outputs. Often, one output is positive and theother is negative. In some cases, one output consistsof alternating current (ac) and the other consistsof direct current (dc).dual pickup In disk reproduction, a pickup havingtwo styli, one for large-groove records and one forfine-groove records.dual potentiometer A ganged assembly of two potentiometers.The resistance values might ormight not be the same.dual preset counter A preset counter that will setalternately to two different numbers.dual rail See DOUBLE RAIL.dual resistor See DUAL POTENTIOMETER andDUAL RHEOSTAT.dual rheostat A ganged assembly of two rheostats.The resistance values might or might notbe the same.dual stereo amplifier 1. A two-channel audio amplifierfor stereophonic audio applications. 2. Atwo-channel linear integrated circuit (IC) forstereophonic audio applications.dual-system loudspeaker See TWO-WAYSPEAKER.dual trace In a cathode-ray oscilloscope, the use oftwo separate electron beams, which can show twodifferent signals simultaneously on a singlescreen.dual-trace recorder See DOUBLE-TRACK RE-CORDER, 2.dual-track recorder See DOUBLE-TRACK RE-CORDER.dual recording In digital computer operations, updatingtwo sets of master files simultaneously.dual use The use of a communications system fortwo modes of data transfer at the same time.Duant electrometer See BINANT ELECTROMETER.

218 duct • dump checkChannel 1Channel 2dual traceduct 1. A narrow propagation path, sometimestraveled by microwaves, created by unusual atmosphericconditions. 2. A pipe or channel for cablesand wires.dubbing The adding of sound to a recorded magnetictape, record disk, or film (e.g., replacing thesound track of a film in one language with that ofanother language).dubnium Symbol, Db. Also clalled unnilpentium(Unp) and hahnium (Ha). Atomic number, 105.The most common isotope has atomic weight262. Classified as a transition metal. It has ahalf-life on the order of a few seconds to a fewtenths of a second (depending on the isotope), ishuman-made, and is not known to occur in nature.duct 1. A narrow propagation path, sometimestraveled by microwaves, created by unusual atmosphericconditions. 2. A pipe or channel for cablesand wires. 3. An opening, vent, or otherairway used for various purposes, such as coolingand acoustic wave transmission.ducted port An opening in a speaker cabinet thathas an airway (duct) extending several inchesinto the cabinet. It improves the quality of soundfrom a speaker system by equalizing the air pressureinside and outside the cabinet. Also providesresonant audio effects at frequencies that dependon the dimensions of the duct.duct effect see TROPOSPHERIC DUCTING.ductilimeter An instrument used for measuringthe ductility of metals.ducting The confinement of a radio wave to a duct(see DUCT, 1) between two layers of the atmosphereor between an atmospheric layer and theearth.Duddell arc A carbon copper arc circuit that producesaudible continuous waves. Consists of aseries inductance-capacitance (LC) circuit shuntingan electric arc.Duerdoth’s multiple feedback system In an amplifier,feedback through several paths to improveresponse over that afforded by single-path feedback.In a simple application of multiple feedback,a single external loop is augmented withunbypassed emitter resistors in the amplifierstages.Duerdoth’s stability margin A feedback-amplifierstability margin equal to a 6-dB increase in gainat low and high frequencies over beta values between0.3 and somewhat less than 2. For higherbeta values, Duerdoth adopts an angular margin(for example, 15°); below β = 0.3, no danger of instabilityis present.dummy 1. A nonoperative model of a piece ofequipment, usually assembled with dummy components(see DUMMY COMPONENT, 1) for thepurpose of developing a layout. 2. DUMMY AN-TENNA, DUMMY COMPONENT, or DUMMYLOAD. 3. Part of a computer program that, ratherthan being useful for the problem at hand, onlyserves to satisfy some other format or logic requirement.dummy antenna 1. A nonradiating device thatserves as a load for a transmitter (i.e., it takes theplace of the regular antenna during tests and adjustmentsof the transmitter). 2. A devicecontaining a network of discrete inductive,capacitive, and resistive elements, inserted betweena radio-frequency signal generator and receiverto simulate a standard antenna.dummy component 1. A nonoperative componentused in developing a layout or package. 2.A nonoperative component fraudulently includedin a piece of equipment (e.g., an unwiredtransistor in a receiver circuit, a common occurrenceduring the early days of the transistor,when a 10-transistor radio brought more moneythan an 8-transistor radio, without regard to thecircuit itself).dummy instruction In a computer, a commandthat serves no operational purpose, other than tofill a format requirement.dummy load 1. A load device, usually consisting ofresistance without reactance, used to terminate apower generator or power amplifier during adjustmentsand tests. The load resistance is equalto the output impedance of the generator or amplifier.2. See DUMMY ANTENNA.dummy resistor A power-type resistor used as adummy load.dump 1. In digital-computer operations, to transfer,completely or partially, the contents of memoryinto a peripheral. 2. To switch off all power toa computer, deliberately or accidentally, therebylosing what is in the volatile memory.dump and restart During a halt in a computerprogram run, to backtrack to the last dump pointand use the data there to resume the run. Alsosee DUMP POINT.dump check In digital-computer operations, thechecking of all digits being transferred (seeDUMP, 1) to prevent errors when they are retransferred.

dumping • dust cover 219dumping To transfer the output at various stagesin a computer program run to an external storagemedium, so it will be available (in case of a failure)for the program’s resumption from a pointother than at the beginning.dump point In writing a computer program, a pointat which instructions are given to transfer dataprocessed thus far to a storage medium that wouldbe unaffected by a software or hardware failure.Also see DUMP AND RESTART and DUMPING.dumping resistor 1. See BLEEDER. 2. A resistorhaving the minimum resistance permissible in agiven situation. Used to discharge a capacitor, itacts to provide an alternative path to a potentiallydestructive short circuit.duo Any pair of matched components, usually in asingle package.duodecal CRT base The 12-pin base of a cathoderaytube. Also see BIDECAL, DIHEPTAL, andMAGNAL.duodecal socket A 12-pin tube socket. Also seeDUODECAL CRT BASE.duodecimal 1. Having 12 possibilities, states,choices, etc. 2. Pertaining to the DUODECIMALNUMBER SYSTEM. 3. A number or numeral inthe DUODECIMAL NUMBER SYSTEM.duodecimal number system A system of numberingin which the radix, also called the base ormodulus, is 12. The system uses the digits 0through 9, plus two other characters (usually Aand B) to represent 10 and 11. Thus, countingproceeds as 0, 1, 2, . . . , 9, A, B, 10, 11, 12, . . . , 19,1A, 1B, 20, 21, 22, etc. At one time, some peopleseriously proposed that this system replace theDECIMAL NUMBER SYSTEM for general use.duodiode See DUAL DIODE.duolateral coil A multilayer, lattice-wound coil(see UNIVERSAL WINDING) in which the turns insuccessive layers are staggered slightly. Alsocalled honeycomb coil.duopole A two-pole all-pass device.duplex 1. A mode of communication in which twochannels are used so that either operator in aconversation can interrupt the other at any time.2. The transmission of two messages over a singlecircuit, at the same time.duplex artificial line In wire telephony, a balancingnetwork that simulates the impedance of theactual line and the remote terminal equipment; itprevents an outgoing transmission from interferingwith the local receiver.duplex cable A cable consisting of a twisted pair ofinsulated stranded-wire conductors.duplex channel A channel used for wire or radioDUPLEX OPERATION.duplex communication See DUPLEX OPERA-TION.duplex diode See DUAL DIODE.duplexer In radar operations, a device operated bythe transmitted pulse to automatically switch theantenna from the receiver to the transmitter.duplexing assembly In a radar system, a devicethat automatically makes the receiver unresponsiveto the outgoing transmitted signal while allowingincoming signals to reach the receivereasily. Also see TRANSMIT-RECEIVE SWITCH.duplex computer system An installation of twocomputer systems, one standing by to take overin case the other fails.duplex operation The simultaneous operation of atransmitter and receiver at a single location. Thisbecomes possible (without mutual interference)through the use of two sufficiently separated carrierfrequencies.duplex system A system composed of two identicalequipment sets—either of which will perform theintended function while the other stands by.duplication check In digital-computer operations,the checking of an operation by doing it twice, usingdifferent methods in each case, to ensure theaccuracy of results.duplication house A professional person or companywho makes high-quality copies of taperecordings (either audio or video). Charges vary,depending on the type and length of the recording.duplicate To transfer data from one storage locationto another. Compare DUMP, 1.dural See DURALUMIN.duralumin An alloy of aluminum, copper, magnesium,manganese, and silicon. It offers strengthwith minimal weight.duration control A potentiometer or variable capacitorfor adjusting the duration of a pulse.duration time The period during which a pulse issustained (i.e., the interval between turn-on andturn-off time).AmplitudeDurationtimeduration timeTimeduring cycle The interval during which a timer isin operation.durometer An instrument for measuring the hardnessof a material.dust collector See DUST PRECIPITATOR.dust core A magnetic core for radio-frequency coilsconsisting of very minute particles of iron or analloy, such as Permalloy.dust cover A removable, usually plastic cover forelectronic and computer equipment, to protecthardware during periods of nonuse.

220 dust-ignition-proof motor • dynamic debuggingdust-ignition-proof motor A motor whose housingcompletely prevents the entry of dust, virtuallyeliminating the danger of fine dust sparkinginside the machine.dust precipitator An electrostatic device for removingdust, lint, and other particles from theair. It consists essentially of a pair of screens orwires through which the air passes; a potential ofseveral thousand volts is maintained betweenthem. The particles acquire a charge, then stickto the oppositely charged screen.Dutch metal A copper-zinc alloy.duty cycle 1. The proportion or percentage oftime during which a device, circuit, or system isoperating or handling power. For example, whena radiotelegraph transmitter is keyed on and offto send Morse code, the duty cycle is approximately50 percent; with frequency-shift keying,the duty cycle is 100 percent. 2. The conditionsunder which an electrochemical cell or batteryis used. In particular, the proportion or percentageof time during which current is drawn fromthe cell or battery for the purpose of operatingan electrical or electronic circuit, device, orsystem.duty cyclometer A direct-reading instrument formeasuring duty cycle.duty factor 1. The ratio P avg /P pk , where P avg is theaverage power in a system and P pk is the peakpower. 2. The product of the duration and therepetition rate of regularly recurring pulses comprisinga carrier.duty ratio See DUTY FACTOR, 1.DVM Abbreviation of DIGITAL VOLTMETER.DVOM Abbreviation of DIGITAL VOLT-OHM-MILLIAMMETER.dwell meter An instrument that shows the period(or angle) during which contacts remain closed.dwell switching Switching action in which thecontacts are held closed (or a circuit kept on) forspecified periods, as opposed to MOMENTARYSWITCHING.dwell tachometer A combination dwell meter/tachometer for automobile engine testing and adjustment.The dwell meter allows observation andadjustment of the ignition point cam angle; thetachometer shows the motor speed in revolutionsper minute (rpm).DX 1. Radiotelegraph abbreviation meaning longdistance or foreign country. 2. A communicationor broadcast station located far away and/or in aforeign country. 3. Abbreviation of DUPLEX.DXer An amateur radio operator who prefers tocommunicate with stations far away and/or inforeign countries.Dy Symbol for DYSPROSIUM.dyadic operation A binary operation (i.e., one usingtwo operands).dyn Abbreviation of DYNE.dyna- A prefix (combined form) meaning power(e.g., dynamometer and dynatron).dynamic acceleration Acceleration whose magnitudeand direction are constantly changing.dynamic allocation In multiprogramming, a systemin which a monitor program assigns peripheralsand areas of memory to a program.dynamic analogy A mathematical similarity betweenor among various phenomena involving themotion of particles.dynamic base current See AC BASE CURRENT.dynamic base resistance See AC BASE RESIS-TANCE.dynamic base voltage See AC BASE VOLTAGE.dynamic behavior 1. The behavior of a component,device, or system when signals are applied, asopposed to static behavior under no-signal conditions.2. The behavior of a device or system involvingthe motion of particles over a period of time.dynamic braking A technique for stopping a motorquickly using a resistor (the dynamic braking resistance)connected across the spinning armature.The resistor dissipates the energy generatedby the motor, producing a damping action thatresults in braking.dynamic characteristic The performance characteristicof a device or circuit under alternatingcurrent(ac) operating conditions, as opposed tothe static characteristic, when only direct current(dc) flows.dynamic check 1. A test made under actual operatingconditions of a device or circuit. 2. A testmade with an alternating-current (ac) applied signal,rather than with direct-current (dc) quantities.dynamic collector current See AC COLLECTORCURRENT.dynamic collector resistance See AC COLLEC-TOR RESISTANCE.dynamic collector voltage See AC COLLECTORVOLTAGE.dynamic contact resistance In relay or switchcontacts, variation in the electrical resistance ofthe closed contacts because of variations in contactpressure.dynamic convergence In a color picture tube, themeeting of the three beams at the aperture maskduring scanning.dynamic current amplification Abbreviation,DCA. An expression of gain in a bipolar transistor.Specified as the ratio of the difference in collectorcurrent I C to the difference in base current I BDCA = dI C /dI BGeometrically, the dynamic current amplificationat a given bias point is the slope of a line tangentto the I C -versus-I B curve at that point.dynamic curve A characteristic curve that accountsfor the presence of resistance in serieswith the device to which the curve applies.dynamic debugging Any debugging operation performedon a computer system during a normalspeedprogram run.

dynamic decay • dynamic range 221dynamic decay Decay resulting from such factorsas ion charging in a storage tube.dynamic demonstrator A teaching aid consistingof a board displaying an electronic circuit, behindwhich is mounted the actual circuit. Various circuitcomponents (especially adjustable ones) aremounted on the front of the board, in clear viewat places where their circuit symbols appear. Pinjacks at important test points in the circuit allowconnection of a meter, signal generator, and oscilloscopeleads for testing or demonstrating thecircuit.dynamic deviation The difference between idealoutput and actual output of a circuit or device operatingwith a reference input that changes at aconstant rate and is free of transients.dynamic diode tester An instrument that displaysthe response curve (or family of curves) of a diodeon a calibrated oscilloscope screen. The horizontalaxis of the screen indicates voltage, the verticalaxis shows current, and zeros for bothquantities are at center screen. Also see DY-NAMIC RECTIFIER TESTER.dynamic drain current See AC DRAIN CURRENT.dynamic drain resistance See AC DRAIN RESIS-TANCE.dynamic drain voltage See AC DRAIN VOLTAGE.dynamic dump A dump that occurs during a programrun. See DUMPING.dynamic electric field An electric field whose intensityis constantly changing, either periodicallyor in a complex way.dynamic emitter current See AC EMITTER CUR-RENT.dynamic emitter resistance See AC EMITTERRESISTANCE.dynamic emitter voltage See AC EMITTER VOL-TAGE.dynamic equilibrium 1. The state of balance betweenconstantly varying quantities. 2. The tendencyof two current-carrying circuits to maintainat a maximum the magnetic flux linking them.dynamic error In a periodic signal delivered by atransducer, an error resulting from the restricteddynamic response of the device.dynamic flip-flop A flip-flop (bistable multivibrator)that is kept on by recirculating an alternating-current(ac) signal. The device can beswitched on or off by a single pulse. CompareSTATIC FLIP-FLOP.dynamic focus Compensation for defocusing,caused by the electron beam sweeping in an arcacross a flat color picture-tube screen; themethod uses an alternating-current (ac) focusing-electrodevoltage.dynamic gate voltage See AC GATE VOLTAGE.dynamic impedance The impedance of a device(such as a transistor or diode) when it is operatingwith an applied alternating-current (ac) signal,as opposed to its static resistance with onlydirect current (dc) applied.dynamic limiter A limiter, such as is used in frequency-modulation(FM) receivers, that maintainsthe output-signal level, despite appreciableexcursions of input-signal amplitude.dynamic loudspeaker See DYNAMIC SPEAKER.dynamic magnetic field A magnetic field whoseintensity is constantly changing, either periodicallyor in a complex way.dynamic memory A usually random-access datastorage method in which the memory cells mustbe electrically refreshed periodically to avoid theloss of held data.dynamic microphone A microphone in which asmall coil attached to a vibrating diaphragm orcone moves in a uniform magnetic field to generatethe output signal.CoilMagnetOutputDiaphragmSound wavesdynamic microphonedynamic mutual conductance See DYNAMICTRANSCONDUCTANCE.dynamic noise suppressor A noise limiter consistingof an audio filter whose bandwidth is directlyproportional to signal strength (i.e., it is variedautomatically by signal amplitude).dynamic operating line A curve displaying thecontrol function of a device. For example, thecollector-current-versus-base-current curve of abipolar transistor is drawn between the limits ofsaturation and cutoff.dynamic output impedance The output impedanceof a power supply, as “seen” by the load.dynamic pickup A phonograph pickup whose styluscauses a small coil to vibrate in the field of apermanent magnet. Works on the same principleas the DYNAMIC MICROPHONE.dynamic printout A printout that occurs as a singlefunction, actuated by one command, andcompleting itself in one operation.dynamic problem checking A method of checkingthe solution obtained by an analog computer, tosee that it makes sense (is not absurd).dynamic programming A method of problemsolving in which continual checks are made toensure accuracy or conformance to a certain setof rules.dynamic range 1. In high-fidelity audio, the ratioof the loudest sound to the faintest sound thatcan be reproduced without significant distortion

222 dynamic range • dynatronor noise. It is usually expressed in decibels. 2. Ina communications receiver, a measure of theability to receive both weak and strong signalswithout excessive noise, distortion, desensitizationor other undesirable effects. It is expressedin various ways, typically in decibels. 3. The ratiobetween the loudest and faintest sounds, or betweenthe strongest and weakest signals, encounteredin a given environment or situation. It isusually expressed in decibels.dynamic rectifier tester An instrument that displaysthe response curve of a rectifier on a calibratedoscilloscope screen. During the test, therectifier receives an alternating-current (ac)voltage with a low positive peak and high negativepeak, both corresponding to the rated forwardand reverse voltages (respectively) of therectifier. The horizontal axis of the screen indicatesvoltage, the vertical axis indicates current,and zeros for both quantities are at centerscreen.dynamic regulation In an automatically regulatedsystem, such as a voltage-regulated power supply,the transient response of the system. Dynamicregulation is determined from maximumovershoot and recovery time when the load or linevalue is suddenly changed.dynamic regulator A circuit or device providingdynamic regulation.dynamic reproducer 1. See DYNAMIC MICRO-PHONE. 2. See DYNAMIC PICKUP. 3. See DY-NAMIC SPEAKER.dynamic resistance See DYNAMIC IMPEDANCE.dynamic run See DYNAMIC CHECK, 1. See alsoDYNAMIC DEBUGGING.dynamics The study of bodies, charges, fields,forces, or pulses in motion. Compare STATICS.dynamic sequential control In digital computeroperation, the computer’s changing the sequenceof instructions during a run.dynamic source current See AC SOURCE CUR-RENT.dynamic source resistance See AC SOURCE RE-SISTANCE.dynamic source voltage See AC SOURCE VOLT-AGE.dynamic spatial reconstructor Abbreviation,DSR. An advanced x-ray machine, developed atthe Mayo Clinic, that displays organs in threedimensionalviews in motion, and allows them tobe electronically dissected without actuallyoperating on the patient.dynamic speaker A loudspeaker in which a smallcoil (voice coil), attached to a diaphragm or coneand carrying an audio-frequency signal current,moves back and forth in a permanent magneticfield and, accordingly, causes the diaphragm orcone to vibrate (emit sound). Compare MAG-NETIC SPEAKER.dynamic stability A measure of the ability of arobot to maintain its balance while in motion.dynamic stop As caused by a computer programinstruction, a loop indicating the presence of anerror.dynamic storage See DYNAMIC MEMORY.dynamic subroutine A form of computer subroutinethat allows the derivation of other subroutinesin various forms.dynamic test See DYNAMIC CHECK.dynamic transconductance Transconductancedetermined from alternating-current (ac) signalparameters, rather than from direct-current (dc)parameters.dynamic transducer A coil-and-magnet devicethat converts mechanical vibration into electriccurrents, or vice versa. Common examples includemost microphones, headphones, and loudspeakers.dynamic transfer characteristic An input-outputcharacteristic determined, with respect to theload of a transfer device. Also see DYNAMICCHARACTERISTIC.dynamic transistor tester 1. An instrument forchecking the alternating-current (ac) gain of atransistor, rather than its direct-current (dc)beta. 2. An instrument for determining the conditionof a transistor from its performance in a simpleoscillator circuit. 3. An instrument thatdisplays a transistor response curve, or a familyof such curves, on a calibrated oscilloscopescreen. Also see DYNAMIC DIODE TESTER andDYNAMIC RECTIFIER TESTER.dynamo A mechanical generator of electricity; typicallya rotating machine.dynamoelectric machinery Rotating electric machinery.Examples: amplidynes, generators, dynamotors,rotary converters.dynamometer 1. See ELECTRODYNAMOMETER.2. A device for mechanically measuring the outputpower of a motor.dynamometer ammeter See ELECTRODYNA-MOMETER.dynamometer voltmeter See ELECTRODYNA-MOMETER.dynamophone A dynamometer (see DYNAMO-METER, 2) that uses two telephone circuits tomeasure the twist of a shaft.dynamostatic machine A machine driven by alternating-current(ac) or direct-current (dc) powerfor the generation of static electricity.dynamotor A (usually small) self-containedmotor-generator. The motor and generatorportions are enclosed in a common housing,giving the machine the appearance of a simplemotor.dynaquad A pnpn four-layer semiconductor devicewith three terminals, similar to the siliconcontrolledrectifier or thyristor.dynatron A form of vacuum tube that displays anegative-resistance characteristic, resulting inoscillation at ultra-high and microwave frequencies.

dynatron frequency meter • dysprosium 223dynatron frequency meter A heterodyne-type frequencymeter using a dynatron oscillator.dyne Abbreviation, d. A unit of force. One dyne(10 –5 newton) is the force that will give a mass of1 gram an acceleration of 1 centimeter per secondper second. Compare NEWTON.dyne-centimeter See ERG.dyne-five In the Giorgi mks system, a unit of forceequal to 1 newton.dyne per square centimeter Abbreviation, d/cm 2 .A unit of pressure equal to 0.1 pascal (9.869 ×10 -7 atmosphere).dyne-seven A unit of force equal to 10 7 dynes.dynistor A semiconductor diode that continues toconduct after the forward voltage is reduced belowthe normal threshold point. To stop the conduction,a reverse voltage must be applied, orvoltage must be entirely removed from the device.It is used in switching applications.dynode In a photomultiplier tube, any of severalslanting electrodes that receives a beam of electronsgenerated by the light-sensitive cathodeand reflects it, along with secondary electrons.This amplifies the beam; the process is repeatedseveral times. Thus, the emission from theVisiblelight−ElectronbeamPhotocathodeDynodesdynodeDynodesLoad+Anodecathode is greatly amplified when it reaches theplate.dysprosium Symbol, Dy. An element of the rareearthgroup. Atomic number, 66. Atomic weight,162.50. Dysprosium is a highly magnetic substance.

E 1. Symbol for VOLTAGE. 2. Symbol for ELEC-TRIC FIELD STRENGTH. 3. Abbreviation ofEMITTER. 4. Symbol for prefix EXA. 5. Symbolfor ENERGY.e 1. Symbol for VOLTAGE. 2. Abbreviation ofEMITTER. 3. Symbol for ELECTRON CHARGE. 4.Symbol for the natural logarithm base (approximatelyequal to 2.71828). 5. Symbol for ECCEN-TRICITY. 6. Abbreviation of ERG.EAM Abbreviation of electronic accounting machine.E and M terminals The output and input leads insome signaling systems. Also called E and Mleads.early early sound Sound propagated throughsolids and/or liquids that reaches a pickup device(such as a microphone) before the soundpropagated through the air. In general, soundwaves travel faster as the medium becomes moredense.early-failure period The period immediately aftermanufacture of a device, during which the failurerate (caused by defects in equipment or workmanship)is high.early-warning radar Abbreviation, EWR. A radarsystem that produces immediate warning whenenemy aircraft enter the monitored area.earphone 1. Headphone (usually a single unit).2. Telephone receiver. 3. A miniature acoustictransducer that is small enough to be insertedinto the ear.earpiece See EARPHONE, 3.earth 1. The ground. 2. An electrical connection tothe earth (see GROUND CONNECTION, 2). 3. Inspace communications, the planet Earth.earth connection See GROUND CONNECTION, 2.earth currents 1. Electric currents induced in theearth by current flowing through underground orunderwater cables. 2. Electric currents flowingthrough the earth between ground connections ofelectrical equipment.earth ground 1. A common connection to an electrodeburied in the earth so that good conductivityis maintained between the common circuitpoint and the earth itself. 2. A rod driven into thesurface of the earth for use as a common circuitconnection.earth inductor A magnetometer consisting of acoil that is rotated in the earth’s magnetic field. Itdelivers an alternating-current (ac) voltage proportionalto the field strength. Also called generatingmagnetometer.earth-moon-earth See MOONBOUNCE.earth resonance A resonant effect at extremely lowfrequencies, caused by reflection of currentswithin the earth. Resonant currents have beentested as a means of communicating with submarinesworldwide.earth’s magnetic field Also called geomagneticfield. The natural magnetic field whose lines of fluxextend from north to south. The earth’s magneticpoles, also called the geomagnetic poles, do not exactlycoincide with the geographic poles. The fieldsomewhat resembles that of a bar magnet.Eastern Standard Time Abbreviation, EST. Localmean time at the 75th meridian west of Greenwich.east-west effect The phenomenon in which thenumber of cosmic rays approaching earth nearthe equator from the west is greater than thatfrom the east by 10 percent.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

E avg • echo 225Symbol for AVERAGE VOLTAGE.Symbol for BATTERY VOLTAGE.E bend In a waveguide, a smooth change in the directionof the axis, which remains parallel to thedirection of polarization.EBI Abbreviation of EQUIVALENT BACKGROUNDINPUT.ebiconductivity Conductivity resulting from electronbombardment.ebonite Hard rubber used as an insulant. Dielectricconstant: 2.8. Dielectric strength: 30 to 110kV/mm.EBR Abbreviation of ELECTRON-BEAM RECORD-ING.EBS Abbreviation of ELECTRON-BOMBARDEDSEMICONDUCTOR.E avgE bMagnetic poleEarthMagnetic poleearth’s magnetic fieldFlux linesEBS amplifier An amplifying device using an electron-bombardedsemiconductor. The electronbeam is modulated by the input signal, and themodulated resistance of the semiconductor targetmodulates a relatively heavy current to providean amplified output. Current gains on the orderof 2000 are possible.ec Abbreviation of ENAMEL-COVERED (in referenceto wire).eccentric circle See ECCENTRIC GROOVE.eccentric groove On a phonograph record, an offcentergroove in which the stylus rides at the endof the recording, where it causes the tone arm totrip the record-changing mechanism.eccentricity 1. The condition of being off center,intentionally or not. It is often a consideration inthe behavior of dials, potentiometers, and servomechanisms.2. On a phonograph record, thecondition in which the spiral recording grooveand the center hole of the disk are not concentric.3. A quantitative expression for the extent towhich an ellipse is elongated.eccentricity of orbit The extent to which the orbitor path of a satellite differs from a circle. Acircular orbit has eccentricity zero. As the orbitbecomes elliptical and deviates more and morefrom a perfect circle, the eccentricity increases.When the eccentricity reaches 1, the object takesa parabolic path through space. If the eccentricityexceeds 1, the path is a hyperbola.ECCM Abbreviation of ELECTRONIC COUNTER-COUNTERMEASURES.ECDC Abbreviation of electrochemical diffused collector.ECG Abbreviation of electrocardiogram. (Also,EKG.)ECG telemetry Use of a radio telemetering systemto monitor the heart function of a person from adistance.echelon 1. A level of calibration accuracy, thehighest echelon being the national standard forthe particular measurement involved. 2. A level ofmaintenance in which lower ordinal numbers referto less-critical tasks, and higher ordinal numbersrefer to tasks requiring progressively higherskills and technological expertise.echelon grating A diffraction grating with extremelyhigh resolution. Generally useful onlyover a small range of wavelengths.echo 1. A signal that is reflected back to the pointof origin. 2. A reflected or delayed signal componentthat arrives at a given point behind the maincomponent. 3. A radar blip, indicating an objector thundershower. 4. Reflection of the signal on atelephone line, caused by improper impedancematching, or by overload of the system by toomany subscribers attempting to use the systemat the same time. 5. In audio systems, a circuitthat causes sounds to repeat one or more times,at intervals ranging from a fraction of a second toseveral seconds. 6. The effect produced by a circuit,as defined in 5.XLong path (echo)EarthShort pathYechoIonosphere

226 echo area • eddy-current lossecho area The area of a target that will return aradar signal as an echo.echo attenuation In a bidirectional wirecommunicationcircuit equipped with repeatersor multiplexers, the attenuation of echo currentsset up by conventional operation.echo box A resonant-cavity device used to test aradar set. Part of the transmitted energy entersthe box, which retransmits it to the receiver. Thesignal reaching the receiver is a slowly decayingtransient whose intensity eventually falls belowthe level that can be displayed on the screen; thetime required to reach this level indicates radarperformance.echo chamber A reverberation chamber, electronicrecording device, or room for acoustic tests or forsimulating sonic delays.echo check In data communication, a means ofchecking the accuracy of received data by sendingit back to the transmitting station for comparisonwith the original data.echo depth sounder See ACOUSTIC DEPTHSOUNDER.echo eliminator 1. A device that quiets a navigationalinstrument after receipt of a pulse, to preventreception of a subsequent, delayed pulse. 2.In a two-way telephone circuit, a voice-operateddevice that suppresses echo currents caused byconversation currents going in the opposite direction.echoencephalograph An ultrasonic medical instrumentthat allows viewing of internal organs.Used for diagnostic purposes in certain situations,instead of the X-ray machine.echogram In acoustics, a graph of the sounddecrement in an enclosure. Time is plotted onthe horizontal axis; signal amplitude is plottedon the vertical axis. An intense pulse is transmittedfrom a speaker; a microphone picks up theechoes and sends them to a pen recorder or microprocessor.echo intensifier A device used at a radar target toboost the intensity of reflected energy.echo interference Radio interference resultingfrom a reflected signal arriving slightly later thanthe direct signal.echo matching In an echo-splitting radar system,the trial-and-error orientation of the antenna tofind the direction from which the pulse indicationsare identical.echo ranging An ultrasonic method of determiningthe bearing and distance of an underwater object.echo send In an audio mixer, an output for deliveringsignals to external systems, such as anecho box (see ECHO, 5). It can also provide anauxiliary output for a second set of speakers, atape recorder, etc.echo sounder See ACOUSTIC DEPTH SOUNDER.echo splitting Separating a radar echo into twoparts so that a double indication appears on theradar screen.echo suppression In a telephone circuit, a devicethat chokes off reflected waves, thereby minimizingaudible echo.echo suppressor See ECHO ELIMINATOR.echo talk Echo in a telephone system that resultsin distracting interference.echo wave A reflected wave, such as a radio wavereflected alternately between earth’s surface andthe ionosphere.ECL Abbreviation of EMITTER-COUPLED LOGIC.eclipse effect A decrease in the critical frequencyof the E and F1 layers of the ionosphere during asolar eclipse.ecliptic orbit Any orbit that lies in the same planeas the orbit of the earth around the sun (the eclipticplane). The ecliptic plane is slanted about23.5° from the plane of the earth’s equator.ECM Abbreviation of ELECTRONIC COUNTER-MEASURES.ECO Abbreviation of ELECTRON-COUPLED OS-CILLATOR.econometer An instrument for continuously monitoringthe amount of carbon dioxide in (factory)flue gases.E core A transformer or transducer core having theshape of an E. Coils can be wound on one, two, orall three of the crosspieces.E coreECPD Abbreviation of Engineer’s Council for ProfessionalDevelopment.ECTL Abbreviation of emitter-coupled transistor logic.EDD Abbreviation of ENVELOPE-DELAY DISTOR-TION.eddy current A circulating current induced in aconducting material by a varying magnetic field,often parasitic in nature. Such a current can, forexample, flow in the iron core of a transformer.eddy-current device A brake, coupling, clutch,drag cup, drive unit, or similar device whose operationis based on the generation of torque, pull,or opposition by the action of eddy currents.eddy-current heating Heating caused by eddycurrentloss in a material.eddy-current loss Power loss resulting from eddycurrents induced in nearby structures by an

eddy-current loss • effective acoustic center 227electromagnetic field. Eddy currents in the core ofa transformer give rise to such loss.edge connector A terminal block with a number ofcontacts, attached to the edge of a printed-circuitboard for easy plugging into a foundation circuit.edge control In the manufacture of paper, arobotic system for maintaining the width of asheet by sensing the edges and correcting themachine accordingly. Transducers that sense thepassing edges deliver output signals proportionalto variations from standard width.edge detection The ability of a machine vision systemto locate and follow boundaries. Used extensivelyin mobile robots.edge effect The extension of electric lines of fluxbetween the outer edges of capacitor plates. Thisportion of the interplate field contributes a smallamount of capacitance. Because the lines of fluxare not confined to the space between plates, theycan cause capacitive coupling with externalbodies.Positive plate of capacitorNegative plate of capacitoredge effectEdgelinesedge-punched card In digital computer operations,a punched card whose edge is perforated ina narrow column, the center being used for writtenannotation.edgewise meter A meter having a curved horizontalscale; this arrangement allows mounting theinstrument edgewise in a panel.edgewise-wound coil A coil made of a flat metalstrip cut in the shape of a coil spring. The designallows the use of clips to vary the inductance, butthis advantage is often offset by the coil’s highdistributed capacitance.edging In a color television picture, extraneouscolor of a different hue than the objects aroundwhose edges it appears.Edison base A threaded base on light bulbs, conetypeheaters, and some pilot lamps.Edison battery A group of Edison cells connectedin series, parallel, or both, and contained in a singlepackage with two electrodes.Edison cell A secondary (storage) cell in which theactive positive plate material consists of nickelhydroxide held in steel tubes assembled into asteel grid; the active negative plate material ispowdered iron oxide mixed with cadmium; theelectrolyte is potassium hydroxide. The open-circuit voltage of the cell is typically 1.2 V at fullcharge.Edison distribution system A three-wire, 110- to250-volt direct-current (dc) power-distributionsystem.Edison effect Thermionic emission of negativelycharged particles (electrons) from a hot filamentsealed in an evacuated bulb; they are attracted bya cold, positively charged metal plate in the bulb.E display A radar display in which the horizontalcoordinate indicates distance, and the vertical coordinateindicates elevation.edit 1. In tape recording, the modifying of therecorded material by deleting (cutting out or erasing),adding (splicing or overrecording), or changingthe sequence of the material by physically ormagnetically altering the tape. 2. In digital computeroperations, to make data ready for processing.edit decision list In the editing of a digital audio/videopresentation, a record of every change(cut and paste). The list is automatically made bythe computer and stored on disk for later referenceif needed.editing 1. Alteration of a magnetic-tape recordingby means of splicing. 2. Alteration of data storedin memory, either by adding information, removinginformation, changing information, or (usually)a combination of these operations.EDL Abbreviation of EDIT DECISION LIST.EDM Abbreviation of ELECTRICAL-DISCHARGEMACHINING.EDP Abbreviation of electronic data processing.EDPC Abbreviation of ELECTRONIC DATA-PROCESSING CENTER.EDPM Abbreviation of ELECTRONIC DATA-PROCESSING MACHINE.EDPS Abbreviation of ELECTRONIC DATA-PROCESSING SYSTEM.EDT 1. Abbreviation of ethylene diamine tartrate (asynthetic piezoelectric material). 2. Abbreviationof Eastern Daylight Time.EDU Abbreviation of electronic display unit.educational robot A robot that can be programmedfor the purpose of teaching its users something.Popular as an educational toy for children.EDVAC Acronym for Electronic Discrete VariableAutomatic Computer, a development of the Universityof Pennsylvania.EE Abbreviation of ELECTRICAL ENGINEER orELECTRONICS ENGINEER.E eff Symbol for EFFECTIVE VOLTAGE.EEG Abbreviation of ELECTROENCEPHALO-GRAM.EEPROM Abbreviation of ELECTRICALLYERASABLE PROGRAMMABLE READ-ONLYMEMORY. See PROM and ROM.EES Abbreviation of EARLY EARLY SOUND.effective acoustic center The apparent point ofpropagation of spherically divergent sound wavesradiated by an acoustic generator.

228 effective actuation time • effective phase angleeffective actuation time The total actuation timeof a relay (i.e., the sum of the initial actuationtime and subsequent intervals of contactchatter).effective address The address a computer uses inimplementing an instruction (i.e., one not necessarilycoinciding with the address given in the instruction).effective ampere An effective current of 1 ampere.Also see EFFECTIVE CURRENT.effective antenna length See ELECTRICALLENGTH.effective antenna resistance The radiation resistanceof an antenna, as measured at the inputpoint.effective bandwidth The bandwidth of an idealbandpass filter, which, at a reference frequency,has the same transfer ratio as an actual bandpassfilter under consideration; it also has thesame current and voltage characteristics.AmplitudeEffectivebandwidthf oFrequencyeffective bandwidthTheoreticalrectangularresponseActualfilterresponseeffective capacitance The actual capacitance betweentwo points in a circuit resulting from thecombination of inherent, lumped, and stray capacitances.effective conductivity Conductivity measured betweenthe parallel faces of a unit cube of a material.effective confusion area In a radar system, anarea in which interference makes it impossible tosee whether a target is present.effective current Symbol, I eff . The root-meansquare(rms) value of alternating current (seeEFFECTIVE VALUE). For a sinusoidal current,I eff = 0.707I max , where I max is the maximum valueof the current. Also called rms current.effective cutoff See EFFECTIVE CUTOFF FRE-QUENCY.effective cutoff frequency For a filter or similardevice operated between specified impedances,the frequency at which insertion loss is higherthan the loss at a specified reference frequency inthe passband.effective field intensity The root-mean-square(rms) value of the field-strength voltage, averagedfor all points at a horizontal distance of one milefrom a transmitting antenna.effective height The height of an antenna in termsof its performance as a transmitter or receiver ofelectromagnetic energy.effective input capacitance The actual operativecapacitance present at the input terminals of acircuit or device, caused by the shunt capacitanceof the terminals themselves and the netcapacitance of the circuit connected to theterminals.effective internal resistance In an electrochemicalcell or battery, a resistance that originateswithin the electrolyte and electrodes. This resistanceis low when the current drain is low; it risesas the current drain increases. It limits the maximumcurrent that the cell or battery can deliver.effective isolation The condition of componentsor circuits being so well isolated or shielded thatno significant direct coupling, capacitive coupling,or inductive coupling exists between them.effective instruction The machine-language versionof an instruction given in a computer program,as produced by resident software.effectively bonded The condition afforded by anextremely low-resistance union between two conductingsurfaces that are solidly fastened together.effectively grounded The condition of being connectedto earth or to the low-potential end of acircuit by means of an extremely low-resistanceconnection.effective parallel capacitance Inherent capacitancethat manifests itself in parallel with two circuitpoints in combination with any lumpedcapacitance.effective parallel resistance 1. The leakage resistancethat manifests itself in parallel with adielectric (e.g., the leakage resistance of acapacitor). 2. Parallel-resistance effects causedby stray shunt-resistance components.effective percentage of modulation For a complexwaveform, an expression of the equivalentpercentage of modulation by a pure sine wave.Given a certain proportion of power in the sidebandswith modulation by a complex signal, theeffective percentage of modulation is that percentagewhich, when the modulating signal is sinusoidal,results in the same proportion of powerin the sidebands.effective phase angle In alternating-current (ac)circuits, the phase angle, with respect to waveformsfor current and voltage. When both waveformsare sinusoidal, the effective phase angle is

effective phase angle • eight-level code 229the actual phase angle. But when harmonics arepresent in current or voltage, the angles differ,the difference being greater in capacitive circuitsthan in inductive circuits.effective radiated power Abbreviation, ERP orP ER . 1. A measure of the performance of a wirelesstransmitting antenna. Suppose a test antenna,A T , is set up and the field strength in its favoreddirection at a frequency f is measured at a distanced in free space. Let the field strength thusmeasured be F watts per square meter. SupposeA T is replaced with an isotropic radiator, A I , andthe field strength at the same frequency f is measuredat the same distance d in free space. Letthe radio-frequency (RF) power at the feed pointof the isotropic radiator A I be varied until the fieldstrength is F, the same as it was with the test antennaA T . Let this RF power be symbolized P.Then P is defined as the effective radiated power(ERP or P ER ) of the test antenna, A T . 2. The figuredefined as in (1), measured in some directionother than the favored direction of a test antenna.effective resistance 1. In a coupled circuit, thesum of the actual resistance of the circuit and thereflected resistance of the load. 2. See EFFEC-TIVE ANTENNA RESISTANCE.effective series inductance Inherent (distributed)inductance acting in series with other componentsin a circuit. The inherent inductance ofthe wire in a wirewound resistor, for example,manifests itself in series with the resistance of thedevice.effective series resistance Inherent (distributed)resistance acting in series with other componentsin a circuit. Thus, the inherent resistance of thewire in a coil appears in series with the inductanceof the coil. Likewise, a capacitor has an effectiveseries resistance because of the resistanceof the leads, plates, and connections.effective shunt capacitance See EFFECTIVEPARALLEL CAPACITANCE.effective shunt resistance See EFFECTIVE PAR-ALLEL RESISTANCE.effective sound pressure The root-mean-square(rms) value of instantaneous sound pressure atone point in a sound cycle.effective speed of transmission In telegraphy(wire or radio) and in electronic data transmission,the transmission speed (characters perminute, bits per second, etc.) that can be reliablymaintained for a given period.effective thermal resistance The effective temperaturerise (in degrees per watt of dissipation)of a semiconductor junction above an externalreference temperature that is at equilibrium.effective time For a computer, the time duringwhich useful work is performed.effective transmission speed See EFFECTIVESPEED OF TRANSMISSION.effective value The root-mean-square (rms) valueof an alternating-current (ac) quantity. Theeffective value an alternating current produces ina pure resistance has the same heating effect asthe equivalent direct current. See also ROOTMEAN SQUARE.effective volt An effective potential of one rootmean-square(rms) volt. Also see EFFECTIVEVOLTAGE.effective voltage Symbol, E eff . The root-meansquarevalue of alternating-current (ac) voltage(see EFFECTIVE VALUE). For a sinusoidal voltage,E eff = 0.707E max , where E max is the maximumvalue of the voltage. Also called rms voltage.effective wavelength Wavelength in terms of measuredfrequency and effective propagation velocity.effects processor In audio systems, a circuit thatproduces various sound effects via digital signalprocessing.efficiency 1. The ratio of useful power or energyoutput to total power or energy input to a deviceor system. 2. The proportion of applied audiofrequency(AF) power that a loudspeaker convertsinto acoustic energy. 3. See ELECTRICAL EFFI-CIENCY.efficiency modulation A system of amplitudemodulation in which the efficiency of a radiofrequency(RF) power amplifier is varied at an audio-frequency(AF) rate.efficiency of rectification For a rectifier, the ratioof the direct-current (dc) output voltage to thepeak value of alternating-current (ac) input voltage.For percent efficiency, the ratio is multipliedby 100.efflorescence The giving up of water by a substanceupon exposure to air. Some materials usedin electronics exhibit this property. Common efflorescentcompounds are hydrated ferrous carbonate,ferrous sulfate, and sodium carbonate.efflorescent material A material exhibiting efflorescence.Compare DELIQUESCENT MATERIAL.E field 1. An electric field. 2. the electric-field componentof an electromagnetic wave.EFL Abbreviation of emitter-follower logic.E g Symbol for GENERATOR VOLTAGE.EHD Abbreviation of electrohydrodynamic(s).EHF Abbreviation of EXTREMELY HIGH FRE-QUENCY.EHP Abbreviation of effective horsepower.E-H tee A waveguide junction in which E- andH-plane tee junctions intersect the main waveguideat the same point. Also see WAVEGUIDETEE.E-H tunerAn impedance-transforming E-H teewith two arms that are terminated in tunableplungers for critical adjustments. See WAVE-GUIDE PLUNGER.EHV Abbreviation of extra-high voltage.E i Symbol for INPUT VOLTAGE.EIA Abbreviation of Electronics Industries Association.eight-level code A code, such as the AmericanStandard Code for Information Interchange (ASCII),

230 eight-level code • electret microphonein which each character is represented by eightbits.E indicator A radar elevation display, in which thehorizontal scale shows range and the verticalscale shows elevation.Einstein equation The equation depicting theinterconversion of mass and energy; E = mc 2 ,where E is energy (ergs), m is mass (grams), and cis the speed of light in a vacuum (centimeters persecond).einsteinium Symbol, Es. A radioactive elementproduced artificially. Atomic number, 99. Atomicweight, 252.Einstein/Dehaas effect The tendency for an ironor steel cylinder to become magnetized as it rotates.Einstein shift The decrease in frequency and lossof energy experienced by quanta acted upon bygravitation.Einthoven string galvanometer A simple galvanometerin which a silvered glass filament carryingcurrent is mounted in a magnetic field setup by either a permanent magnet or an electromagnet.The current causes the filament to be deflectedthrough a distance proportional to currentstrength, the deflection being observed through amicroscope.EIT Abbreviation of engineer-in-training.either-or operation The logical inclusive-OR operation.EJC Abbreviation of Engineers’ Joint Council.eka-aluminum See GALLIUM.eka-silicon See GERMANIUM.EKG Abbreviation of ELECTROCARDIOGRAM.(Also, ECG.)EKG telemetry See ECG TELEMETRY.EL Abbreviation of ELECTROLUMINESCENCE.elapsed time 1. In data-processing and computeroperations, what appears to be the duration of aprocess, compared with actual processing time,as measured by internal clocks, for example.2. The accumulated time, usually expressed inhours, minutes, and seconds, that an operationtakes or a machine runs.elapsed-time meter An instrument that indicatesthe time an electronic device or system has beenin operation. Most such meters are based on electricclockwork that runs only while the system isin operation, holding the count during shutdownperiods. Also see ELECTROLYTIC ELAPSED-TIME METER.elastance Unit, daraf. The opposition of a capacitorto being charged. It is the reciprocal of capacitance.elastic collision A collision between two chargedparticles in which neither loses energy—eventhough they are deflected from their normal paths.elasticity 1. The ability of a body to return to itsoriginal shape after being deformed. SeeYOUNG’S MODULUS. 2. See ELASTIVITY.elastic limit The maximum stress that can betolerated by a material without being permanentlydeformed.elastic wave A wave in an elastic medium, such asair or water; thus, a wave that is mechanicallyproduced.CompressionTravelelastic waveselastivity 1. Specific elastance (i.e., the elastancein darafs per cubic unit of a dielectric). 2. The ratioof electric stress to displacement.elastomer A compressible, conducting substanceused in pressure sensing. In one arrangement, anarray of electrodes is connected to each side of apad of the material. When pressure appears atsome point, the material compresses, loweringthe resistance in the pressure zone. A microprocessordetermines the location and extent of thepressure.E layer A layer in the ionosphere that is 50 to 90miles above the surface of the earth, and is notedfor returning radio waves at high and very-highfrequencies.elbow bend A 90-degree bend in a waveguide.ELD Abbreviation of edge-lighted display.electra A radio-navigational system in whichequal-intensity signal zones (usually 24) are provided.electralloy A nonmagnetic alloy used in the manufactureof radio hardware, such as chassis.electre See ELECTRUM.electrepeter A device used to change the directionof an electric current.electret A device whose heart is a dielectric disk orslab that is permanently polarized electrically,and so possesses a permanent electric field. Theelectrical equivalent of the permanent magnet.Certain waxes, ceramics, and plastics acquirepermanent polarization after they have beenheated, then cooled slowly in an intense electricfield.electret microphone Also called electret capacitormicrophone. A microphone in which soundwaves cause an electret to vibrate and generate

electret microphone • electrical engineer 231audio-frequency (AF) output current. An internalpower supply (such as a battery) suppliesthe necessary voltage.electric 1. Pertaining to electricity and its variousmanifestations. 2. See ELECTROSTATIC.electric absorption See DIELECTRIC ABSORP-TION.electric accounting machine A self-containeddata-processing machine that is neither a computernor a computer peripheral.electrical-acoustical transducer A transducer,such as a headphone, sonic applicator, or buzzer,that converts electrical energy into sound energy.Compare ACOUSTICAL-ELECTRICAL TRANS-DUCER.electrical angle The angle assumed at any instantby the rotating vector representing an alternatingcurrent or voltage. A complete cycle is dividedinto 360 electrical degrees. Thus, for an alternating-current(ac) sine wave, the angle is 0 degreesfor zero and positive-going, 90 degrees for positivemaximum, 180 degrees for zero and negativegoing,and 270 degrees for negative maximum.−Amplitudey+−electrical angleθ +Rate ofxchangeelectrical attraction The attraction between twooppositely charged bodies or particles. CompareELECTRICAL REPULSION.electrical axis In a quartz crystal, the axis throughopposite corners of the hexagonal cross section.The various electrical axes are x, x’, and x” (or x-x, x’-x’, and x”-x”). The electrical axis is perpendicularto the mechanical axis, which runsthrough the crystal’s length. Also see CRYSTALAXES and X-AXIS, 2.electrical bail An action in which a special switchchanges contact position and locks itself in thatposition after a station has been actuated, at thesame time releasing a previously actuated station.electrical bandspread In a tuned circuit, bandspreadobtained by changing values of inductanceor capacitance, rather than by mechanicalgearing.electrical bias A current maintained in a relay coil(sometimes an auxiliary coil) to keep the relaypartially closed, thus sensitizing it. Compare ME-CHANICAL BIAS.electrical boresight In radar operations, thetracking axis, as determined by an electrical test,such as one involving a sharp null or sharp peakresponse.electrical center The point at which an adjustablecomponent (variable resistor, variable inductor,etc.) has exactly half its total value. This pointdoes not always coincide with the physical center.electrical conductance See CONDUCTANCE.electrical conduction The flow of charge carriersthrough a material. The degree of conduction isindicated by the material’s value of conductance.electrical conductivity See CONDUCTIVITY.electrical coupling The coupling of two or morecircuits or elements by means of electric-field effects.electrical degree 1. In a periodic waveform, thelength of time corresponding to 1 ⁄360 of the time forcompletion of one cycle. 2. In space, that distancerepresenting 1 ⁄360 of the wavelength in themedium through which electromagnetic energytravels.electrical discharge The flow of current out of avoltage reservoir, such as a battery or capacitor.electrical discharge in gases The phenomenon ofelectric conduction (current) by a gas, caused bysudden breakdown as a result of gas ionization.The discharge is often accompanied by light, as inthe red glow of a neon bulb.electrical-discharge machining A method of machiningmetals in which the metal is vaporized byan arc formed between an electrode and the metalworkpiece (anode). In this way, metal is removedin tiny bits from the surface of the workpiece.electrical distance Distance in terms of the timerequired for an electromagnetic wave to travel betweentwo points in a particular medium.electrical drainage The diversion of electric currentsaway from underground pipes to preventcorrosion by electrolysis.electrical efficiency The ratio of the output of anelectrical or electronic device to the total input. Itcan be expressed as a decimal or percentage. Forexample, for a bipolar transistor amplifier, thepercent efficiency is equal to 100(P out /P in ), whereP in is the collector input in volt-amperes, and P outis the output power in watts.electrical elasticity See CAPACITANCE.electrical element See ELEMENT, 2.electrical energy Energy in the form of electricity(see ELECTRICITY, 1). The term is often used inplace of ELECTRICITY.electrical engineer Abbreviation, EE. A trainedprofessional skilled in applying physics and mathematicsto electricity, and in the theory and applicationof basic engineering and related subjects.Of particular interest to the EE are the generation

232 electrical engineer • electrical transducerand distribution of electrical energy and the designand application of electromechanical devices.Compare ELECTRONICS ENGINEER.electrical erosion In electrical contacts, the loss ofmetal as a result of the evaporation or transfer ofmetal during switching.electrical filter A bandpass, band-rejection, highpass,or low-pass filter that operates by electricalmeans. Examples: Butterworth filter and Chebyshevfilter.electrical forming See ELECTROFORM, 1.electrical gearing In an electromechanical system,such as a servo, the condition in which anoutput shaft is electrically rotated at a speed differentfrom that of an input shaft.electrical glass High-temperature insulating materialsmade from glass fibers.electrical inertia See INDUCTANCE.electrical initiation 1. Starting an action (electricalor nonelectrical) by means of an electrical signal.2. Using an enabling pulse.electrical instrument A device for measuring anelectrical quantity (such as voltage, current, orpower).electrical interlock Also called an interlock switchor door-interlock switch. A door- or lid-operatedswitch connected in series with the power switchof a piece of equipment. The interlock causespower to be removed from internal circuits wheneverthe door is opened, the lid lifted, or the caseremoved. This minimizes the chance for electricshock to occur to service personnel.electrical length The length, in wavelengths, of anantenna or transmission line. The electricallength usually differs from the actual length becauseof ground-capacitance effects, end effects,and the speed of electromagnetic waves in conductorsand/or dielectrics.electrical load A device connected to a source ofelectricity (generator, amplifier, network, etc.) fora useful purpose (heat, work, etc.).electrically connected Connected via direct path,such as through a wire, resistance, inductance,or capacitance.electrically erasable PROM A programmableread-only memory (PROM) that can be erased byan electrical signal, rather than by exposure toultraviolet light. Also see PROM and ROM.electrically variable capacitor See VOLTAGE-VARIABLE CAPACITOR.electrically variable inductor An inductor whosevalue varies inversely with the amount of directcurrent that is caused to flow through it orthrough an auxiliary winding on the same core.electrically variable resistor See VOLTAGE-DEPENDENT RESISTOR.electrical nature of matter The general behaviorof matter as a complex interplay of waves andparticles. Also see ELECTRON THEORY OF MAT-TER, WAVE MECHANICS, and WAVE THEORYOF MATTER.electrical network A circuit containing two ormore components (including generators andloads), usually arranged in some pattern.electrical noise Extraneous currents and/or voltagesthat interfere with desired electrical quantities.Compare ACOUSTIC NOISE.electrical polarity The distinct difference observablein electrification, designated positive (orplus) and negative (or minus). Negative electrificationis generally characterized by a surplus ofelectrons; positive electrification is characterizedby a deficiency of electrons.electrical quantity 1. See COULOMB and QUAN-TITY, 3. 2. An electrical unit (e.g., AMPERE,OHM, VOLT, and WATT).electrical repulsion The mutual repulsion of bodiesor particles having similar electric charges.Two positively charged objects will repel eachother, as will two negatively charged objects.electrical reset An electromechanical device forresetting a relay that ordinarily remains in theposition resulting from actuation.electrical resistance The in-phase currentretardingeffect that all conductors exhibit tosome extent. Also see RESISTANCE.electrical resistivity See RESISTIVITY.electrical resolver A synchro whose rotor has twoperpendicular windings in addition to anotherwinding.electrical scan A method of changing the orientationof the major lobe of an antenna. The antennais kept physically stationary, but the phase/amplitude relationships of the signals applied todifferent driven elements are varied.electrical sheet Sheet iron or steel used for motorlaminations.electrical system 1. The overall configuration ofelectrical elements for a set of apparatus. 2. Thewiring system that supplies power to a set of devices.3. One of several methods of quantizingelectrical properties, such as METER-KILOGRAM-SECOND (mks), CENTIMETER-GRAM-SECOND(cgs) electromagnetic, cgs electrostatic, and theINTERNATIONAL SYSTEM OF UNITS (SI).electrical taste See GALVANIC TASTE.electrical technology The theory and practicalapplication of electricity. Taught as a subengineeringmajor, usually in two-year colleges thataward the degree of Associate in Arts (AA) or Associatein Science (AS).electrical time constant For a torque motor, theratio of armature inductance to effective armatureresistance. Compare MECHANICAL TIMECONSTANT.electrical transcription 1. A phonograph recordmade electrically, as opposed to one made mechanically.2. A radio program in which such arecord is played. 3. Any direct mechanical or electricalrecording of an audio signal.electrical transducer 1. A transducer that convertsa nonelectrical phenomenon into a proportional

electrical transducer • electric column 233current, voltage, or frequency. 2. A transducerthat converts electricity in one form to electricity inanother [e.g., a transducer actuated by directcurrent(dc) voltage, delivering an alternatingcurrent(ac) output, whose frequency isproportional to the dc input voltage].electrical twinning A defect in which two quartzcrystals intergrow in such a way that the electricalsense of their axes becomes reversed. CompareOPTICAL TWINNING.electrical unit A standard for measuring an electricalquantity (e.g., ampere, ohm, volt, watt,siemens, etc.).electrical wavelength The distance between onepoint in an electromagnetic wave cycle and thenext identical point. This is usually expressed asthe separation between points where the instantaneousamplitude of the electric field is zero andincreasing positively. This quantity depends onthe velocity factor, ν, of the medium through, oralong, which the field propagates. The electricalwavelength also depends on the frequency, f, ofthe energy. In a transmission line with a velocityfactor ν (given as a fraction rather than as a percentage),the electrical wavelength λ is given byElectricalfield intensityλ = 3.00 × 10 8 ν / fwhere s is in meters, ν is in meters per second,and f is in hertz. Often, this formula is modifiedfor values of f expressed in megahertz (Mhz)rather than in hertz. The equation in this casebecomesλ = 300 ν / fThe wavelength of a signal in a radio-frequency(RF) transmission line is always less than thewavelength of the same signal in free space.+−λelectrical wavelengthDirectionofpropagationelectrical zero 1. A zero-output or minimumoutputpoint resulting from the adjustment of abridge or other zero-set circuit. 2. In a meterwhose pointer is mechanically set to some pointabove or below the zero on the scale, the zero settingobtained when the meter is deflected to scalezero by a current or voltage. 3. For a synchro, theposition at which the amplitudes and time phaseof the outputs are defined.electric and magnetic double refraction SeeKERR ELECTRO-OPTICAL EFFECT and KERRMAGNETO-OPTICAL EFFECT.electric arc A sustained luminous discharge in thespace between two electrodes. Compare ELEC-TRIC SPARK.electric aura See ELECTRIC WIND.electric balance See BRIDGE, 1 and 2.electric bell See BELL.electric brazing A method of brazing in whichelectric current generates the required heat.electric breakdown 1. The usually sudden ionizationof a gas by an electric field and the accompanyingheavy current flow through the gas. 2. The(destructive) puncture of a dielectric by the strainproduced by high voltage. Also see DIELECTRICSTRENGTH. 3. The usually nondestructive,abrupt increase in semiconductor junction currentat a high reverse voltage. See, for example,AVALANCHE BREAKDOWN.electric breakdown voltage 1. The voltage atwhich avalanche effect occurs. 2. Dielectricstrength.electric breeze See ELECTRIC WIND.electric buzzer See BUZZER. Compare ELEC-TRONIC BUZZER.electric calculator An electrically driven machinefor performing mathematical operations. Its electromechanicalnature distinguishes it from theelectronic calculator, which features no movingparts, other than keys. Also see CALCULATOR.electric catfish A fish native to tropical and northernAfrica, capable of delivering a strong electricshock.electric cell See CELL, 1.electric chair An electrode-bearing chair used insome states for administering the death penaltyvia high-voltage electricity. See ELECTROCU-TION.electric charge Potential energy as the electrificationof a body or component. For a capacitance ofC farads charged to a potential of E volts, thecharge Q, in coulombs, is equal to the productCE. Also see ENERGY STORED IN CAPACITOR.electric chronograph An instrument for accuratelyrecording time intervals.electric chronometer A precision electric or electronictimepiece. Also see ELECTRIC CLOCK andELECTRONIC CLOCK.electric circuit A network of interconnected componentsand devices, often including a source ofelectric power. Current flowing through a circuitis acted on by components, which produce specificdesired effects.electric clock A clock driven by electric current.Electric clocks fall into two categories: thosedriven by synchronous alternating-current (ac)motors, and those driven by stepping mechanismsthat usually operate from direct current(dc).electric column See VOLTAIC PILE.

234 electric conduction • electric generatorelectric conduction The flow of current carriersthrough a conductor.electric constant Also called permitivity of vacuum.The fixed electrical permitivity of free space,the value of which is 8.8542 × 10 –12 farad permeter.electric contact See CONTACT, 1, 2.electric controller An adjustable device for modifyingthe operating voltage or power of a componentor system. Compare ELECTRONICCONTROLLER.electric cooling 1. Cooling via PELTIER EFFECT.2. See ELECTROSTATIC COOLING. 3. Forced-aircooling (of equipment) by electric blowers or fans.electric current The phenomenon wherein chargecarriers move in a directed manner through amaterial or vacuum. In most electrical conductors,current results from movement of electrons.In a semiconductor material, electric current canresult from the movement of holes, as well aselectrons; the proportion of holes to electrons dependson the nature of the semiconductor. In agas or electrolyte, current consists of a flow ofions. In certain situations, electric currents canresult from the movement of positrons, protons,anti-protons, alpha particles, and various atomicnuclei.electric current density See CURRENT DENSITY.electric delay line See DELAY LINE.electric density See ELECTRIC SPACE DENSITYand ELECTRIC SURFACE DENSITY.electric dipole A pair of equal charges having oppositepolarity and separated by a fixed distance.electric discharge See ELECTRICAL DISCHARGE.electric-discharge lamp See DISCHARGE LAMP.electric disintegration See ELECTRIC DISPER-SION.electric dispersion In a colloidal suspension, dispersionaccomplished by passing an electric currentthrough the material.electric displacement The movement of a body orparticle in response to an electric current or field.electric double refraction See KERR ELECTRO-OPTICAL EFFECT.electric dust precipitator See DUST PRECIPITA-TOR.electric eel An eel (fish) capable of delivering a disablingshock on contact.electric elasticity See ELASTIVITY, 1, 2.electric endosmosis See ELECTRO-OSMOSIS.electric eye A sensing device that uses a radiantenergy beam to detect objects. It generally uses alaser diode as the beam source, and a photoelectriccell, phototransistor, or photovoltaic cell asthe beam detector. The output is used to controlsome external machine or system.electric fence A wire fence through which an electriccurrent is passed. Anyone touching the fencewill receive a shock. It is used in some prisons,and also by cattle ranchers to keep people or animalscontained.electric fidelity The frequency response of a circuitor device.electric field The space surrounding an electriccharge or charged body, in which electric energyacts (electric lines of flux fill the space).electric field intensity See ELECTROSTATICFIELD INTENSITY.electric field strength 1. Symbol, E. In an electromagneticwave, the amplitude of the electric componentof the field, expressed in volts per meter.2. Dielectric strength.electric-field vector See ELECTRIC-FIELDSTRENGTH, 1.electric filter See ELECTRIC WAVE FILTER.electric fish Fish capable of generating intense electricshocks (e.g., electric catfish and electric eel).electric flux See ELECTROSTATIC FLUX.electric flux density Symbol, D. In an electricfield, the number of lines of flux per unit area,usually expressed in coulombs per square meter.electric flux lines The direction of the electric fieldin the vicinity of a charged object. The field is denotedby means of “lines of flux” or “lines offorce,” with each line representing a designatedelectric field intensity. The closer together thelines, the more intense the field in a given region.electric focusing See ELECTROSTATIC FOCUS-ING.electric force The force exerted by an electricallycharged particle or an electric field.electric forces The forces exerted by electriccharges or electric fields. Also see UNIT ELEC-TROSTATIC CHARGE.electric furnace An electrically heated chamber(sometimes heated by an electric arc) used in orereduction, carbide manufacture, and other hightemperatureprocesses.electric generator A device for producing electricity.Thus, many different devices, such as bat-

electric generator • electric residue 235+ −Fluxlineselectric flux linesFluxlinesteries, dynamos, oscillators, solar cells, and thermocouples,are classed as generators.electric glow The light (usually pale blue) that occasionallyaccompanies an electric discharge inair.electric guitar A guitar whose acoustic vibrationsare converted by a transducer to an electrical signalfor amplification.electric hygrometer An instrument for measuringhumidity in terms of the moisture-sensitive resistanceof a sensor. A relatively simple directcurrent(dc) circuit is used. CompareELECTRONIC HYGROMETER.electric hysteresis See ELECTROSTATIC HYS-TERESIS.electrician A professional person who installs andservices electrical equipment and wiring.electric image For solving certain problems involvingelectricity, an array of electrical pointsforming an image of certain other electricalpoints.electricity 1. Phenomena resulting from the existenceof stationary or moving electric charge carriers,such as electrons, holes, and ions. 2. Abranch of physics concerned with phenomena resultingfrom the existence of stationary or movingcharge carriers. 3. Electrical energy or power. 4.The voltage existing at utility outlets. In the NorthAmerica, this is nominally an alternating-current(ac) voltage of 117 or 234 V at 60 Hz.electric lamp An electric-powered device used primarilyas a source of light. Common types arearc, incandescent, and fluorescent.electric light 1. Visible light produced by means ofelectricity. 2. Electric lamp.electric lines of flux Lines of flux associated withan electric charge and constituting the charge’selectric field.electric machine A mechanical device for generatingstatic electricity. See, for example, ELEC-TROSTATIC GENERATOR, VAN DE GRAAFF GEN-ERATOR, and WIMSHURST MACHINE.electric meter 1. An instrument such as an ammeter,voltmeter, or wattmeter, used to indicatean electrical quantity (usually directly). 2. SeeKILOWATT-HOUR METER.electric mirror See ELECTRON MIRROR.electric moment In an electric field of unit intensity,the maximum torque exerted on an electricdipole.electric motor A machine that converts electricalenergy into mechanical work. The familiar form isa machine in which an armature rotates betweenthe poles of a field magnet, mechanical energy beingproduced at the armature’s revolving shaft.electric needle A needle electrode carrying highfrequencycurrent; it is used in surgery to cut tissueand sear it immediately to prevent bleeding.electric network See ELECTRICAL NETWORK.electric organ See ELECTRONIC ORGAN.electric oscillations The alternate flow of electriccharges in opposite directions, occurring at a definedfrequency or frequencies.electric osmosis See ELECTRO-OSMOSIS.electric piano See ELECTRONIC PIANO.electric polarization 1. The orientation of fluxlines in an electric field. 2. The orientation of theelectric field component in an electromagneticfield.electric potential See ELECTROSTATIC POTEN-TIAL.electric power Symbol, P. Unit, watt. The rate atwhich electrical energy is used. Power is energyper unit time; in the context of electricity, it is expressedas the product of current and voltage. Interms of heat losses, it is often expressed as I 2 R(current in amperes squared, multiplied by resistancein ohms).electric precipitator See DUST PRECIPITATOR.electric probe A pin or rod inserted into an electrostaticfield to sample it, or into an electromagneticfield to sample its electric component. See,for example, WAVEGUIDE PROBE. CompareMAGNETIC PROBE.electric radiation 1. The radiation of energy bymeans of electric waves. 2. The energy so radiated.electric recording Inkless recording on paper bydirect use of an electric current. The two principaltypes are: (1) A current-carrying stylus burnsaway (in a fine line) the metallic coating of therecording paper, exposing the dark underlyinglayer. (2) A stylus delivers current that producesa line by means of electrolysis in a special paper(see ELECTROLYTIC RECORDER). CompareELECTROSTATIC PRINTER.electric reset See ELECTRICAL RESET.electric residue A residual electric charge, such asmight remain on a capacitor after it has been incompletelydischarged.

236 electric rings • electroballisticselectric rings Colored rings formed on a plate bythe electrolytic deposition of substances, such ascopper and some peroxides.electric screen See ELECTROSTATIC SCREEN.electric shield See ELECTROSTATIC SCREEN.electric shock A physiological reaction caused bythe passage of electric current through living tissue.When slight, it is characterized by tinglingsensations and involuntary contractions of themuscles; a severe shock can cause paralysis, unconsciousness,heart fibrillation, and/or burns. Ifheart fibrillation occurs or if burns are severe,death can result.electric spark A momentary, luminous dischargeof electricity in the space between two electrodes.Compare ARC, 1.electric steel Steel that has been processed in anelectric furnace.electric strain See DIELECTRIC STRAIN.electric strain gauge A device for detecting thestrain that a certain stress produces in a body.Typically, such a gauge consists of one or morefine insulated wires cemented to the surface undertest. As the surface becomes strained, thewire stretches, undergoing a change in electricalresistance that is proportional to the change instrain.electric strength See DIELECTRIC STRENGTH.electric stress See DIELECTRIC STRESS.electric stroboscope See ELECTRONIC STROBO-SCOPE.electric surface density The ratio of the electriccharge on a surface to the area of the surface.Compare ELECTRIC VOLUME DENSITY.electric tachometer See ELECTRONIC TACHO-METER.electric telemeter A device that sends metereddata over a wire transmission line to a remotepoint for monitoring.electric thermometer See ELECTRONIC THER-MOMETER.electric transcription See ELECTRICAL TRAN-SCRIPTION.electric transducer A transducer that responds tonon-electric energy, then delivers a proportionalelectric current or voltage to another circuit.electric tuning A means of adjusting the frequencyof a receiver, transmitter, transceiver, oroscillator, without the use of mechanical devices.An example is the use of a varactor diode, whosecapacitance varies with voltage.electric utilities The power companies that supplyelectric current for industrial and consumeruse.electric vane A small demonstration device consistingof a rotor having several spokes terminatingin points. The rotor is mounted on a pivotbearing and, when it is connected to a source ofhigh voltage, spins from the force of electricityescaping from the points into the surroundingair.VariabletuningvoltageVaractorelectric tuningTuned circuitToosc.electric vector In an electromagnetic field, thevector representing the electric component. It isperpendicular to the magnetic vector.electric volume density The ratio of the electriccharge in a space to the volume of the space.Compare ELECTRIC SURFACE DENSITY.electric watch A small timepiece driven by a tiny,self-contained electrochemical cell that drives anelectrical escapement or other stepping mechanism.Compare ELECTRONIC WATCH.electric wave See ELECTROMAGNETIC WAVES.electric-wave filter A circuit or device for separatingsignals of one frequency from those of otherfrequencies.electric whirl See ELECTRIC VANE.electric wind 1. Air currents set up by electronsescaping from the sharp point of a high-voltageelectrode. 2. The outward-rushing plasma (solarwind) ejected by the sun and traveling throughspace.electrification 1. Generating an electric charge ina body, as in charging a glass rod by rubbing itwith a silk cloth. 2. Providing electric service (e.g.,RURAL ELECTRIFICATION). 3. The conversion ofa system from purely mechanical to electrical orelectromechanical.electroacoustic Pertaining to devices and systemsthat exhibit both electrical and acoustic effects.For example, speakers and microphones are electroacousticdevices.electroacoustic device A device that transfers energyby converting it from electrical to acousticform or vice-versa.electroacoustic transducer A transducer thatconverts sound vibrations into electrical pulsationsor, conversely, one that converts electricityinto sound.electroanalysis Chemical analysis performed byelectrolytic methods.electroanesthesia Anesthesia produced by anelectric current going through some part of thebody.electroballistics A branch of physics concernedwith the electrical or electronic measurement ofthe velocities and trajectories of projectiles.

electrobath • electrode efficiency 237electrobath A solution in which ELECTRO-PHORESIS or ELECTROPLATING is done.electrobiology Biology concerned with electricalphenomena in living organisms.electrobioscopy The examination of a body for viabilityby inducing muscular contractions withan electrical impulse.electrocapillarity The production of capillary effectsby means of electricity. See, for example,CAPILLARY ELECTROMETER.electrocardiogram Abbreviation, ECG or EKG. Arecord made by an electrocardiograph of thechanges in potential caused by the heartbeat;used as a diagnostic aid.electrocardiograph An instrument that recordschanges in electrical potential caused by theheartbeat.electrocardiophonograph A medical instrumentthat detects and records the impulses of theheart.electrocatalysis Catalytic action produced byelectricity (see CATALYSIS).electrocautery 1. In medicine, a cauterizing instrumentconsisting essentially of a platinumwire (at the tip of an insulated probe) that isheated by an electric current. Also see ELECTRICNEEDLE. 2. Cauterizing with an electrocautery.electrochemical deterioration An electrochemicalreaction that results in the permanent or temporaryfailure of a device.electrochemical diffused-collector transistor Ahigh-current pnp transistor in which metal hasreplaced the etched-away mass of p material,providing a built-in heatsink.electrochemical equivalent In electrolysis or electroplating,a constant (Z ) for the metal in plates.For a given metal, Z is the mass (in grams) of themetal deposited by 1 coulomb of electricity.electrochemical junction transistor See SUR-FACE-BARRIER TRANSISTOR.electrochemical measurements 1. Measurementsmade on chemical substances with electrical instrumentsto determine such factors as conductivity,pH, dielectric strength, dielectric constant,etc. 2. Measurements of electrical or electronicphenomena in terms of electrochemical response(e.g., current drain in terms of weight of platedmetal, or voltage in terms of gas breakdown).electrochemical polarization The disabling of aprimary cell caused by gas products depositedaround or on one of the electrodes.electrochemical recording See ELECTRIC RE-CORDING.electrochemical reduction Extracting a metalfrom a compound by means of electrolysis.electrochemical series See ELECTROMOTIVESERIES.electrochemical switch A static, ionic alternating-current(ac) switch consisting of an anode,cathode, and a control electrode, all immersed inan electrolyte. A positive control-electrode voltageswitches the device on, initiating ion current fromanode to cathode through the liquid.electrochemical transducer A transducer thatconverts chemical changes into electrical quantities,or vice versa. Examples: soil-acidity probeand electrolytic elapsed-time meter.electrochemistry The branch of chemistry, overlappingwith physics, concerned with chemicalaction arising from the effect of electricity on substances,and electrical effects produced by chemicalaction.electrochromic display A display that operates bymeans of electric fields, which control the lighttransmissionand light-reflection characteristicsin different regions of the material.electrochronometer A precision electric or electronicclock. Also see ELECTRIC CLOCK andELECTRONIC CLOCK.electrocoagulation Use of a high-frequency alternatingcurrent to solidify tissue, as in arrestingbleeding.electrocorticogram See ELECTROENCEPHALO-GRAM.electroculture Acceleration or modification ofplant growth through the application of electricityto plants, seeds, or soil.electrocution 1. Death resulting from electricshock. 2. An electric shock inflicted for the purposeof causing death (e.g., in an ELECTRIC CHAIR).electrode A body, point, or terminal in a device orcircuit that delivers electricity, or to which electricityis applied. A positive electrode is usuallyan ANODE; a negative electrode is usually aCATHODE.electrode admittance The admittance encounteredby current flowing through an electrode; theproperty is entirely that of the electrode and is thereciprocal of ELECTRODE IMPEDANCE. Consistsof a real-number component (ELECTRODECONDUCTANCE) and an imaginary-numbercomponent that is 90 degrees out of phase(ELECTRODE SUSCEPTANCE).electrode capacitance The capacitance betweenan electrode and a reference body, such asground or another electrode.electrode characteristic The mathematical functionor graph of electrode current versus electrodevoltage.electrode conductance The conductance encounteredby current flowing through an electrode; theproperty is entirely that of the electrode and is thereciprocal of ELECTRODE RESISTANCE.electrode current Current entering or leaving anelectrode.electrode dark current See DARK CURRENT.electrode dissipation The power lost in the formof heat in an electrode.electrode drop Voltage drop resulting from ELEC-TRODE RESISTANCE.electrode efficiency In an electrolytic cell, the ratioof the yield of metal deposited to the maximum

238 electrode efficiency • electrokineticspossible theoretical yield. This value ranges between0 and 1 (0 percent and 100 percent).electrode impedance The impedance encounteredby alternating current flowing through an electrode;the property is entirely that of the electrodeand is the reciprocal of ELECTRODE ADMIT-TANCE. Consists of a real-number component(ELECTRODE RESISTANCE) and an imaginarynumbercomponent that is 90 degrees out ofphase (ELECTRODE REACTANCE).electrodeless discharge Discharge in a gas tubethat is not directly connected to a power source.A familiar example is the glow of a neon lamp heldin a strong radio-frequency (RF) electromagneticfield.electrodeposit 1. To deposit a substance by electricalaction. Also see ELECTROPHORESIS andELECTROPLATING. 2. A deposit that is formedon an electrode by electrophoresis or electroplating.electrodeposition The electrical application of alayer of one material (such as a metal) on the surfaceof another (the substrate) (e.g., electroplating,evaporation, and sputtering).electrode potential See ELECTRODE VOLTAGE.electrode reactance The imaginary-number componentof ELECTRODE IMPEDANCE.electrode resistance The resistance encounteredby current flowing through an electrode; theproperty is entirely that of the electrode and is thereciprocal of ELECTRODE CONDUCTANCE.electrodermography A method of monitoringthe functions of the human body by measuringthe resistance between two electrodes placed onthe surface of the skin.electrode susceptance The imaginary-numbercomponent of ELECTRODE ADMITTANCE.electrode voltage The voltage between an electrodeand a reference point, such as ground oranother electrode.electrodiagnosis 1. The diagnosis of a disease ordisorder through the use of electromedical instruments.2. Troubleshooting the electrical portionof electromechanical equipment.electrodialysis See ELECTRO-OSMOSIS.electrodissolution Dissolving a constituent substanceof an immersed electrode by means ofelectrolysis.electrodynamic Pertaining to electricity in motion(i.e., current flow and its accompanying electricand magnetic fields).electrodynamic braking Stopping a tape-deckmotor quickly by applying a braking voltage. Inthis method, direct braking current flows throughthe shaded-pole alternating-current (ac) reelmotor.electrodynamic instrument See ELECTRODY-NAMOMETER.electrodynamic loudspeaker See DYNAMICSPEAKER.electrodynamics The branch of physics concernedwith moving electric charge carriers,such as electrons, holes, and ions. Also concernedwith the interaction of electrical and mechanicalphenomena. Important in the designand manufacture of devices, such as motors andgenerators.electrodynamic speaker See DYNAMIC SPEAKER.electrodynamism See ELECTRODYNAMICS.electrodynamometer An indicating meter whosemovable coil rotates between two stationary coils.All three coils are connected in series, and themagnetic fields of the two stationary coils are additive.This meter produces a positive indicationfor alternating current (ac), as well as for directcurrent (dc). Can be adapted for use as an ammeter,voltmeter, or wattmeter.electroencephalogram Abbreviation, EEG. Arecord made by an ELECTROENCEPHALO-GRAPH, showing changes in electric potential resultingfrom bioelectric action in the brain. Therecord is used as a diagnostic aid.electroencephalograph An instrument that producesa record of voltage changes resulting fromthe brain’s bioelectricity.electroencephaloscope A type of oscilloscopeused to pick up, amplify, and display changes inpotential caused by the brain’s bioelectric action.electroextraction Extracting a substance from amixture (e.g., a metal from an ore) by an electricalprocess, such as electrolysis.electroform 1. To precondition a material or device(e.g., a semiconductor junction) by passing acurrent through it for a specified period. 2. Toform articles by electrodepositing material on amold or core.electrogalvanized Electroplated with zinc.electrogastrogram A recording of the electrical impulsesand other functions of the stomach, formedical diagnostic purposes.electrograph 1. A picture transmitting or receivingdevice (see FACSIMILE RECEIVER and FACSIM-ILE TRANSMITTER). 2. A device used for the electrolyticetching or transfer of designs.electrographic recording A method of producinga visible pattern or record, using electrodes tocreate discharge through an insulating material.electrographite Synthetic graphite prepared byheating carbon in an electric furnace.electrojet A region of high current concentrationin the sky near bright auroral displays or alongthe magnetic equator.electrokinetic energy The energy of electriccharge carriers in motion; a form of kinetic energy.The current in a wire (a flow of electrons) isa common manifestation of this form of energy.Compare ELECTROSTATIC ENERGY.electrokinetics A branch of electricity concernedwith (1) the behavior of moving charged particles(such as ions and molecules) and bodies in

electrokinetics • electrolytic elapsed-time meter 239motion, and (2) the generation of static chargesby moving liquids or solids in contact with eachother.electroless process Plating a metal from asolution of one of its salts without using electricity.electroluminescence The ability of certain phosphorsto emit light continuously when an alternating-current(ac) voltage is applied to them.electroluminescent cell A device for generatinglight by electroluminescence. It consists of a luminescent-phosphorlayer and two transparentmetal films. An alternating-current (ac) voltageapplied between the films causes the phosphor toglow through the transparent metal.Glass plateTransparentmetal coatGlass plateLight raysPhosphorPhosphorTo acvoltageelectrolytic capacitor A component that is manufacturedby rolling up aluminum foil stripsseparated by paper saturated with electrolyte.When a polarized voltage is applied, the aluminumoxidizes. The oxide layer forms the dielectricfor the capacitor. The layer is extremelythin, producing high capacitance per unit volume.This type of capacitor must be connectedwith the proper polarity in a circuit. The componentcan have values up to thousands of microfarads,and some units can handle thousands ofvolts. They are used in audio circuits and inpower supplies. Compare CERAMIC CAPACI-TOR, MICA CAPACITOR, PAPER CAPACITOR,PLASTIC-FILM CAPACITOR, TANTALUMCAPACITOR.Aluminumcan+−Spiral-woundaluminum foilelectrolytic capacitorElectrolytepasteelectroluminescent cellClearconductiveelectrodeselectroluminescent lamp A lamp using one ormore electroluminescent panels.electroluminescent panel A panel that forms acomplete electroluminescent cell. It delivers lowintensityvisible light when an alternatingcurrent(ac) voltage is applied to it. Available invarious sizes and shapes.electrolysis 1. The action whereby a current passingthrough a conductive solution (electrolyte)produces a chemical change in the solution andthe electrodes. 2. An electrical method of destroyinghair roots.electrolyte A substance that ionizes in solution.Electrolytes conduct electricity; in batteries, theyare instrumental in producing electricity bychemical action.electrolytic 1. Containing an electrolyte substance.2. See ELECTROLYTIC CAPACITOR.electrolytic cell An electrochemical device containingan electrolyte and at least two electrodes.Included in this category are voltaiccells, electrolytic capacitors, and electrolytic resistors.electrolytic conduction Electric current flowingthrough an electrolyte, an action characterized by(1) positive electrolyte ions migrating to thenegative electrode, where they acquire electrons;(2) negative ions migrating to the positive electrode,where they lose electrons; and (3) currentflow in the external circuit, which consists of conventionalelectron flow (current in the electrolyteis a movement of ions).electrolytic conductivity Conductance of an electrolyte.It is the conductance of a cube of the electrolyte,measuring one centimeter along eachedge, at a specified temperature.electrolytic corrosion Corrosion caused by an appliedvoltage, or that is accelerated by the voltage.Compare GALVANIC CORROSION.electrolytic current meter See VOLTAMMETER.electrolytic dissociation See DISSOCIATION.electrolytic elapsed-time meter An instrumentthat indicates the time that equipment has beenin operation in terms of the amount of metal

240 electrolytic elapsed-time meter • electromagnetic energy conversionelectroplated on the cathode of an electrolyticcell by energy consumed during the period.electrolytic gas A gas produced by electrolysis.Examples are hydrogen (H) and oxygen (O), generatedin a ratio of two to one, by the electrolysisof water (H 2 O).electrolytic iron Very pure iron obtained by electrolyticrefining.electrolytic polarization In electrolysis, the tendencyfor the products to recombine. In an electrolyticcell, this effect interferes with theperformance of the cell, reducing the voltage.electrolytic potential The difference of potentialthat appears between a metal electrode in anelectrolyte and the electrolyte immediatelysurrounding it. Also see ELECTROMOTIVESERIES.electrolytic recorder A data recorder that uses apaper impregnated with a chemical that turnsdark when an electric current passes through thepaper from the point of a stylus.electrolytic rectifier A rectifier consisting of analuminum electrode and a lead or carbon electrodein a solution of borax or sodium bicarbonate,or in a solution of ammonium citrate,ammonium phosphate, and potassium citrate.Also called chemical rectifier.electrolytic refining Extracting or purifying metalsby electrolysis.electrolytic resistor An emergency resistor madeby immersing two wire leads in an electrolyte; theweaker the solution, the higher the resistance.electrolytic switch See ELECTROCHEMICALSWITCH.electrolyze To subject something to electrolyticaction.electrolyzer A cell used in the production of variousmaterials by electrolysis. See, for example,ELECTROCHEMICAL REDUCTION and ELEC-TROLYTIC REFINING.electromagnet 1. A coil of insulated wire woundaround an iron or steel cylinder, intended for useas a magnet. When current flows through thecoil, a magnetic field develops, in effect renderingthe cylinder a strong bar magnet. 2. Any devicethat exhibits magnetism only while an electriccurrent flows through it.electromagnetic Exhibiting both electric andmagnetic properties (e.g., an electromagneticwave).electromagnetic attraction 1. The attraction ofiron or steel to an electromagnet. 2. The attractionof an electromagnetic pole to the oppositepole of another electromagnet. A unit pole attractsanother unit pole 1 centimeter away with aforce of 1 dyne or 10 -5 newton. Compare ELEC-TROMAGNETIC REPULSION.electromagnetic communication 1. Any form ofcommunication using a combination of electricand magnetic phenomena. Examples includewire telegraphy, wire telephony, radiotelegraphy,radiotelephony, facsimile, and television. 2. Electroniccommunication via electromagnetic fields(i.e., radio communication).electromagnetic compatibility 1. The ability of aset of electronic devices to work together withoutbeing adversely affected by each other’s electromagneticfields. 2. In radio communication, therelative immunity of a device or devices to the effectsof electromagnetic fields.electromagnetic complex A system that produceselectromagnetic radiation.electromagnetic component 1. The magneticcomponent of an electromagnetic wave, which isperpendicular to the electrostatic component,and can be thought of as the wave’s currentcomponent. 2. A device operated by electromagnetism,such as a coil-type relay or a currentoperatedfield magnet.electromagnetic consonance An effect that takesplace when two antenna elements, both havingidentical or nearly identical resonant frequencies,are in close proximity. If one antenna is fed withenergy at its resonant frequency, currents will beinduced in the other antenna, and it, too, will radiate.Parasitic arrays, such as the Yagi antennaand the quad antenna, operate on this principle.See RESONANCE.electromagnetic constant 1. Symbol, c. The propagationspeed of electromagnetic waves in a vacuum,approximately equal to 299,792 kilometersper second or 186,282 miles per second. Alsocalled SPEED OF LIGHT and VELOCITY OFLIGHT. 2. The propagation speed of electromagneticwaves in a particular medium. Equal to vc,where v is the VELOCITY FACTOR of themedium, and c is the speed of electromagneticwaves in a vacuum (299,792 kilometers per secondor 186,282 miles per second).electromagnetic coupling See INDUCTIVE COU-PLING.electromagnetic crack detector An instrumentthat uses electromagnetic fields to find cracks iniron or steel.electromagnetic CRT A cathode-ray tube usingelectromagnetic deflection.electromagnetic cylinder See SOLENOID.electromagnetic deflection In a television picturetube and some oscilloscopes, deflection of theelectron beam by the magnetic fields of externalhorizontal- and vertical-deflection coils. CompareELECTROSTATIC DEFLECTION.electromagnetic deflection coil See DEFLEC-TION COILS.electromagnetic delay line See DELAY LINE.electromagnetic energy Energy in the form ofelectric and magnetic fields. A radio wave travelingthrough space, for example, has electric andmagnetic components, between which energy oscillates.electromagnetic energy conversion The conversionof electrical energy into mechanical work

electromagnetic energy conversion • electromagnetic microphone 241and vice versa, through the intermediary of anelectromagnetic field.electromagnetic environment A region in whichelectric and magnetic fields are present.electromagnetic field A combination of alternatingelectric and magnetic fields. The electric linesof flux are perpendicular to the magnetic lines offlux at every point in space. The field propagatesin a direction perpendicular to both the electricand magnetic lines of flux. The frequency of oscillationcan range from a fraction of one Hz to manyquadrillions of Hz. In order from longest wavelength(lowest frequency) to shortest wavelength(highest frequency), effects of this type include radiowaves, infrared, visible light, ultraviolet,X rays, and gamma rays.Control gridCathodeCross section offocusing coilLines of force bendelectron streamsinward so that theyconverge at thescreenBeamelectromagnetic focusingWavelength(meters)ScreenMagneticfieldElectric field10 −1610 −1410 −12 Gamma rays10 −10 X rays10 −8 Ultraviolet rays10 −6 Infrared10 −4 Microwaves10 −2 FM broadcast short waves1 AM broadcast10 210 410 6 60 Hz alternating current10 8Directionof propagationelectromagnetic fieldelectromagnetic flux The magnetic field surroundinga coil or conductor carrying an electriccurrent.electromagnetic focusing In a television picturetube, electron-beam focusing obtained by varyingthe direct current flowing through an externalfocusing coil.electromagnetic force The force that causes aconductor to be displaced from its position in amagnetic field when it conducts current.electromagnetic frequency spectrum The frequencyrange of electromagnetic fields includingradio waves, infrared, visible light, ultraviolet,X rays, and gamma rays. Ranges from a fractionof one Hz to many quadrillions of Hz.electromagnetic horn radiator A horn used to radiatemicrowave energy. Also see HORN AN-TENNA.electromagnetic induction Inducing a voltage ina circuit or conductor by causing alternatingcurrent to flow in another nearby circuit or con-electromagnetic frequency spectrumductor. Compare ELECTROSTATIC INDUC-TION.electromagnetic inertia The tendency for the currentin a circuit to lag the voltage at high frequencies.electromagnetic interference Abbreviation, EMI.A phenomenon in which electronic devices upseteach other’s operation. Computers, television receivers,telephone sets, high-fidelity soundequipment, and certain medical devices canmalfunction because of strong radio-frequencyfields such as those from a nearby broadcasttransmitter. The EMI is usually the result ofimproper or ineffective shielding in the affecteddevice or system.electromagnetic lens A coil or coil system whosemagnetic field causes an electron beam passingthrough it to converge or diverge as a light beamdoes in passing through an optical lens. CompareELECTROSTATIC LENS. Also see ELECTROMAG-NETIC FOCUSING.electromagnetic mass The mass that a movingelectric charge is thought to possess.electromagnetic microphone A microphone inwhich sound energy is converted into proportionateelectrical energy by electromagnetism. Common

242 electromagnetic microphone • electromagnetizerexamples are the dynamic microphone and velocitymicrophone.electromagnetic mirror A reflector of electromagneticwaves (e.g., antenna elements, ionosphericlayers, buildings, and hills).electromagnetic momentum The momentum of amoving electric charge, comparable to that ofmatter in motion. Electromagnetic momentum isthe product of electromagnetic mass and chargevelocity.electromagnetic oscillograph 1. An electromechanicaldata recorder for tracing the waveformor variations of a signal. 2. See ELECTROME-CHANICAL OSCILLOSCOPE.electromagnetic oscilloscope 1. An oscilloscopeusing electromagnetic deflection. 2. See ELEC-TROMECHANICAL OSCILLOSCOPE.electromagnetic pump A device used for movingconducting or semiconducting fluids. When acurrent is passed through the fluid, a force is exertedon the molecules of the fluid because of themagnetic field set up by the current.electromagnetic pulse Abbreviation, EMP. 1. Abroadband electromagnetic field emitted in ashort, intense burst from a lightning stroke ornuclear explosion. This field can disrupt the operationof, and (in some cases) cause damage to,electrical and electronic apparatus. 2. In electromagneticinduction, the displacement of an electronin a conductor by the magnetic field.electromagnetic radiation The propagation ofelectromagnetic fields through space; it normallyoccurs at approximately 299,792 kilometers persecond or 186,282 miles per second.electromagnetic reaction The reaction betweenmagnetic fields. Also see ELECTROMAGNETICATTRACTION and ELECTROMAGNETIC REPUL-SION.electromagnetic reconnaissance In military applications,the use of electromagnetic apparatusto detect potential enemy activity in a certain geographicregion.electromagnetic relay See ELECTROMECHANI-CAL RELAY.electromagnetic repulsion The repulsion of a poleof an electromagnet by the pole of another electromagnet(north pole opposing north pole, southopposing south). Compare ELECTROMAGNETICATTRACTION.electromagnetics A branch of physics concernedwith the theory and application of electromagnetism.electromagnetic screen See ELECTROMAG-NETIC SHIELD.electromagnetic shield 1. A partition, can, or boxmade of magnetic material (iron, steel, or specialalloy) enclosing a magnetic component. Themagnetic flux generated by the component is confinedby the shield, thus preventing interferencewith external components. Likewise, externalmagnetic fields are prevented from reaching thecomponent. 2. A grounded partition, metal sheet,wire braid, or other barrier that prevents electromagneticfields from passing through. Commonlyused in electronic equipment to prevent ELEC-TROMAGNETIC INTERFERENCE. Also used inCOAXIAL CABLE to confine electromagneticfields to the transmission line.electromagnetic shielding The use of an ELEC-TROMAGNETIC SHIELD to prevent undesired interactionamong electrical and electronic devicesand systems.electromagnetic spectrum See ELECTROMAG-NETIC FREQUENCY SPECTRUM and ELECTRO-MAGNETIC WAVELENGTH SPECTRUM.electromagnetic switch 1. A switch actuated bymagnetism produced by control current flowingthrough a coil wound on an iron core. 2. SeeELECTROMECHANICAL RELAY.electromagnetic theory of light The theory thatlight consists of electromagnetic waves that aresimilar to radio waves, but of shorter wavelength.electromagnetic tube A cathode-ray tube usingelectromagnetic deflection (e.g., a television picturetube).electromagnetic unit Abbreviation, emu. A unitof measure in the electromagnetic system ofCENTIMETER-GRAM-SECOND (cgs) units.electromagnetic vibrator See INTERRUPTER.electromagnetic wavelength spectrum Thewavelength range of electromagnetic fields, includingradio waves, infrared, visible light, ultraviolet,X rays, and gamma rays. It ranges frommany kilometers to a tiny fraction of one millimeter.electromagnetic-wave polarization The orientationof the electric flux lines in an electromagnetic(EM) field, especially a field propagating throughspace. The polarization is generally parallel withthe active element of a radio transmitting or receivingantenna. Thus, a vertical antenna radiatesand receives fields with vertical polarization,and a horizontal antenna radiates and receivesfields having horizontal polarization. Some antennasradiate and receive an EM field whose polarizationcontinually and rapidly rotates. This iselliptical polarization. If the rate of rotation is constant,it is circular polarization.electromagnetic waves Waves produced in a conductoror in space by the acceleration or oscillationof electric charge carriers. Such waves havean electric and a magnetic component acting atright angles to each other. The waves propagateat right angles to both the electric and magneticflux lines.electromagnetism 1. Magnetism resulting fromthe movement of electric charge carriers (e.g., themagnetic field surrounding a coil of wire carryingan electric current). 2. See ELECTROMAGNET-ICS.electromagnetizer A magnetizer using continuousdirect current (dc) as the magnetic-field source.

electromechanical • electromigration 243electromechanical Descriptive of any device thatconverts energy from electrical to mechanicalform or vice-versa. Examples are the motor andthe generator.electromechanical amplifier An amplifier thatconverts an electrical input signal into mechanicalmotion (vibratory or rotary), which it thenconverts back into an electrical output signal ofhigher current, voltage, or power.electromechanical chopper A vibrator-type interrupterused primarily to chop direct current, convertingit into a square-wave signal, whoseamplitude is proportional to current strength.Also see CHOPPER.electromechanical counter A device that indicatesthe number of pulses that have been appliedto it. Typically, it has a series of dials—eachcapable of displaying the numerals 0 to 9 in sequence,one for each decade in the count. The dialsare geared together, the train being operatedby the stepping action of an electromagnetic escapement.Compare ELECTRONIC COUNTER.electromechanical energy The energy stored byan inductor or capacitor in an electromechanicaldevice.electromechanical filter See ULTRASONIC FIL-TER, 1.electromechanical flip-flop See BISTABLE RELAY.electromechanical frequency meter A usually direct-readinginstrument for measuring frequencyin the lower and middle portions of the audiospectrum. It works via the mechanical motion resultingfrom the applied signal. The two varietiesare the movable-iron type and the reed type.electromechanical modulator See CHOPPER.electromechanical oscillator An oscillator consistingof an electromechanical amplifier providedwith regenerative feedback.electromechanical oscilloscope A galvanometertypeinstrument for displaying a varying or alternatingcurrent or voltage. The signal is applied toa meter movement having a movable coil, whichswings or vibrates in response to the signal. Atiny mirror cemented to the coil reflects a beam oflight to a rotating mirror that sweeps the beamacross a translucent screen on which the image isproduced.electromechanical recorder An instrument inwhich a pen or stylus is moved on a sheet of paperby the varying signal current or voltage beingrecorded.electromechanical rectifier A rectifier in which amoving part, such as a vibrating reed or rotatingcommutator-slip-ring unit, is driven by alternatingcurrent (ac) to close the circuit during positiveor negative ac half-cycles, thus rectifying the ac.Compare ELECTROLYTIC RECTIFIER and ELEC-TRONIC RECTIFIER.electromechanical relay An electromagneticswitch consisting of a multiturn coil wound on aniron core near an armature with a movable endcontact. When control current flows through thecoil, it becomes magnetized and attracts the armature,closing the movable contact against astationary one.SwitchedterminalsActuatingcurrentelectromechanical relayMovable contactFixed contactIron-core coil(electromagnetic)electromechanical timer A device for automaticallytiming a process or an observed event. Mostsuch timers are based on an accurate clock (electricor spring driven) that opens or closescontacts at predetermined instants. CompareELECTRONIC TIMER.electromechanical transducer A transducer thattranslates mechanical signals directly into electricalones or vice versa, without the intermediaryof active devices, such as transistors or integratedcircuits.electromechanical valve A usually poppet-typevalve for gases or liquids. The valve is operated byelectromagnetic action and is often aided by anelectronic (servo) circuit.electromechanics The theory and application ofelectromechanical devices.electromedical engineering The branch of electronicsengineering concerned with the theory,design, and application of electronic equipmentfor medical diagnosis or treatment.electromedical equipment Electrical or electronicequipment used in medical diagnosis or treatment.electromerism Ionization in gases.electrometallurgy The branch of metallurgy concernedwith the use of electricity (especially inelectrolysis) to separate or purify metals or to furnishheat for metallurgical processes.electrometer A specially designed, highly sensitiveelectronic voltmeter used to measure extremelylow voltages and, indirectly, extremely low currents.It is sometimes used as a galvanometer.electrometer amplifier A stable low-noise amplifierfor increasing the sensitivity of an electrometer.electrometry The science of electrical measurements.electromigration The movement of atoms in asubstance from one place to another, because ofinteraction between electrons and ions in thepresence of electric currents. This effect cancause the eventual deterioration of certain semiconductordevices.

244 electromotion • electron gunelectromotion Motion produced by electriccharges or electrons.electromotive force Abbreviation, emf. Electricalpressure, the potential that causes charge carriersto move through a substance or circuit. SeeVOLTAGE.electromotive series A list of metals arranged accordingto the potential between the surface ofthe metals and an electrolyte into which they areimmersed. Some metals acquire a positive potential(with respect to hydrogen, for which the potentialis zero) and others, a negative potential.electromotor A generator or motor, dependingupon the context in which the term is used.electromyogram The record produced by anELECTROMYOGRAPH.electromyograph An instrument for detecting,measuring, and analyzing the weak electricalcurrents generated by muscular activity.electromyography The monitoring and analysis ofthe electrical activity of human muscles.electron The subatomic particle that carries theunit negative charge of electricity. The electronhas a mass of 9.109 × 10 –31 kilogram and carriesa charge of 1.602 × 10 –19 coulomb.electron acceleration See ELECTRON MOTION, 2.electronarcosis Loss of consciousness caused bypassing a weak current through the brain. Usefulin treating certain mental disorders, the processis somewhat similar to ELECTROSHOCK.electron attachment The bonding of an electronto a neutral atom to form a negative ion. Also seeANION and ION.electron avalanche See AVALANCHE and ELEC-TRON MULTIPLICATION.electron band 1. An emission line in the spectrumof an element or compound, caused by the movementof electrons from higher to lower energy levelswithin the atoms. 2. An absorption line in thespectrum of an element or compound, caused bythe movement of electrons from lower to higherenergy levels within the atoms.electron beam See ELECTRON STREAM, 1.electron-beam bender Any element that causesintentional deflection of the electron stream in acathode-ray tube.electron-beam focusing Reducing the size of thespot produced by the electron beam in a cathoderaytube or television picture tube. This is accomplishedby adjusting the direct-current (dc) biasvoltage on a focusing electrode.electron-beam generator 1. See ELECTRON GUN.2. A tube, such as a Klystron, in which velocitymodulation of the electron beam generates extremelyhigh radio frequencies.electron-beam instrument An instrument, suchas an oscilloscope, based on a cathode-ray tube.electron-beam machining Welding or shapingmaterials by controlled electron beams.electron-beam magnetometer A magnetometer inwhich the magnetic field under measurementdeflects the electron beam in a cathode-ray tubeover a distance that is proportional to field intensity.electron-beam recording In digital computer operations,a technique whereby the output of acomputer is recorded on microfilm by an electronbeam.electron-beam scanning tube A tube in which anelectron beam strikes a sensitized screen to producea spot of light, which is deflected electricallyor magnetically across a screen. Examples are oscilloscopetubes, storage tubes, and televisionpicture tubes.electron-beam tube Electron tubes (such asbeam-power tubes, klystrons, oscilloscope tubes,and television picture tubes), in which an electronbeam is generated and controlled.electron-beam welding A method of welding inwhich an electron beam is focused on the workpieceto heat it.electron-bombarded semiconductor A semiconductorwafer, plate, or junction that is acted onby an electron beam; it alters the resistance of thesemiconductor to control the current in an externalcircuit.electron-bombarded semiconductor amplifierSee EBS AMPLIFIER.electron bunching See BUNCHING.electron charge See ELEMENTARY CHARGE.electron cloud A mass of free electrons.electron diffraction Diffraction that occurs whena beam of electrons passes through a crystal material.Fast-moving electrons have wavelike properties;the wavelength depends on the speed ofthe particles. This effect can also occur withbeams of other particles, such as neutrons, protons,or alpha particles.electron drift 1. The movement of an electronfrom atom to atom in a conductor, as caused bythe influence of an applied voltage. 2. In a semiconductor,directed electron movement. Also seeDRIFT, 1.electronegative Having negative electrification orpolarity (see ELECTRICAL POLARITY). CompareELECTROPOSITIVE.electron emission The emission of electrons intosurrounding space by a material. Depending onthe material, this effect can be initiated by applicationof heat, light, torsion, electron impact, ahigh-voltage field, and other actions.electron flow See ELECTRON DRIFT.electron g-factor A physical constant that expressesthe ratio of electron magnetic moment tothe Bohr magneton, and equal to approximately1.00116. Also called free-electron g-factor.electron-gas binding forces See METALLIC BIND-ING FORCES.electron-gas bonding See BONDING, 1 andMETALLIC BINDING FORCES.electron gun A composite electrode for generatingan electron beam (see ELECTRON STREAM, 1) in

electron gun • electronic counter 245a vacuum. In a cathode-ray tube, the gun comprisesa heated cathode, control electrode, acceleratingelectrodes, and a focusing electrode.electron-hole pair In a semiconductor, an electronand a related hole. Each electron in the conductionband has a counterpart in the valence band,a vacancy (hole) left by the electron’s moving tothe conduction band.HoleNucleusElectronelectron-hole pairValence bandConductionbandelectronic 1. Descriptive of any component, device,or system that functions, according to theprinciples of ELECTRONICS. 2. Pertaining toelectrons.electronic adder A circuit (such as an operationalamplifier) for performing arithmetic addition. Insuch a circuit, the output-signal amplitude is thesum of the input-signal amplitudes. Also seeADDER and ANALOG ADDER.electronic aid An electronic device or circuit thatcontributes to the operation of a nonelectronicdevice or system; a pH meter, for example, is anelectronic aid to chemistry.electronics aide See ELECTRONICS TECHNICIAN.electronic attenuator An attenuator in which thevariable resistor is the output section of an activedevice, such as a transistor. Varying the directcurrent(dc) bias of the input section varies theresistance of the output section.electronic autopilot A servo system for detectingand automatically correcting an aircraft’s flightpath.electronic balance An electronic scale, which usesa sensitive current-measuring device in conjunctionwith a movable tension device.electronic brain 1. A high-end computer. 2. Arobot controller. 3. A system that possesses oruses artificial intelligence (AI).electronic breadboard 1. A thin, usually nonmetallicboard or card having prepunched holesfor the quick assembly of electronic circuits fortest and evaluation. 2. Any circuit prototype thatis manually wired during the experimental phaseof product development.electronic bug 1. A semiautomatic telegraph keythat produces dots via an oscillating mechanicalarm. The operator produces dashes manually.2. A telegraph keying device that automaticallygenerates dots and dashes. Also see ELECTRONICKEY, 1. 3. An undetermined source of problemsor improper operation in an electronic circuit.electronic buzzer 1. A mechanical buzzer drivenby a direct-current (dc) amplifier. 2. An oscillatorcircuit that produces a sound similar to that of amechanical buzzer.electronic calculating punch A machine thatpunches on a card the result of calculations ithas performed on data it has read from anotherpunched card.electronic calculator A fully electronic machinefor performing mathematical calculations. Thesimplest machines perform basic arithmetic;more sophisticated ones can do operations withtrigonometric, logarithmic, hyperbolic, and otherscientific functions. Basic machines are availablein department stores for about five dollars. It isusually powered via a small cell or battery, or bya small photovoltaic panel.electronic camouflage The use of electronics by atarget craft to minimize or prevent the reflectionof radar echoes.electronic carillon An electronic system that producessounds resembling those of a bell carillon.electronic chime See ELECTRONIC CARILLON.electronic circuit An electric circuit containingactive electronic components, such as transistorsand integrated circuits, as opposed to a circuitcontaining only passive electrical components(such as resistors, switches, heating elements,etc.).electronic clock 1. An electric clock whose motoris driven by a constant-frequency oscillator (crystalor tuning fork type), followed by multivibratorsand amplifiers. 2. Any electronic timing circuitthat produces pulses at predetermined intervalsfor the purpose of regulating the operation ofother circuits, subsystems, or assemblies.electronic commutator See COMMUTATOR, 2.electronic conduction A flow of electric currentresulting from the movement of electrons amongatoms in a conductor.electronic control 1. The science of automaticallycontrolling machines and devices by means ofelectronic circuits. 2. A circuit or device that providesautomatic electronic control.electronic controller A controller (see CON-TROLLER, 2) having no moving parts. For automaticoperation, such a device often contains acircuit that senses control signals, comparesthem with a signal standard, and automaticallyadjusts the output control power accordingly.electronic counter A fully electronic circuit thatindicates the number of pulses that have been

246 electronic counter • electronic heatingapplied to it (see COUNTER, 1). Unlike the electromechanicalcounter, the electronic counterhas no moving parts and is therefore capable ofextremely high-speed, noiseless operation.electronic counter-countermeasures Abbreviation,ECCM. Military procedures for interferingwith a foe’s electronic countermeasures.electronic countermeasures Abbreviation, ECM.Interference with enemy radio and radar emissionsby electronic means. Also see JAMMING.electronic coupling Coupling via electronic effectsor devices.electronic crowbar A switch that prevents destructivecurrents from flowing through the componentsof a circuit.electronic current meter A current meter thatuses an amplifier ahead of an analog or digital indicatorto provide increased sensitivity.+Input−dc mAelectronic current meter+12 Velectronic data processing Abbreviation, EDP.See DATA PROCESSING and ELECTRONIC IN-FORMATION PROCESSING.electronic data-processing center Abbreviation,EDPC. An installation of electronic equipmentand accessories for processing and storing data,usually in digital form. Also see DATA PROCESS-ING and ELECTRONIC INFORMATION PRO-CESSING.electronic data-processing machine Abbreviation,EDPM. A device, such as an electronic computer,used in the automatic processing of data,usually in digital form.electronic data-processing system 1. A uniquearrangement of machines for processing data. 2.The sequence of steps in, and the underlying rationalefor, the processing of data by automatedequipment.electronic deception See DECEPTION and DE-CEPTION DEVICE.electronic differential analyzer See ANALOGDIFFERENTIATOR, DIGITAL DIFFERENTIAL AN-ALYZER, and DIFFERENTIAL ANALYZER.electronic differentiator A circuit that performsmathematical differentiation. Also see DIFFER-ENTIATOR, 2.electronic divider 1. An electronic device for performingarithmetic division. In a digital computer,such a divider can be a sequence of flip-flops,each of which produces a single output for everytwo input pulses. In an analog computer, the outputsignal amplitude is equal to the quotient oftwo input-signal amplitudes. 2. See FREQUENCYDIVIDER. 3. A voltage divider using active components,rather than resistors.electronic dust precipitator See DUST PRECIPI-TATOR.electronic efficiency A quantitative expression forthe effectiveness of an electron beam as amedium of power transmission. The electronic efficiency,in percent, is equal to 100P out /P in , whereP out is the (output) power delivered by the beam,and P in is the (input) power supplied to the beam.electronic equivalent of gravity In equations forthe acceleration, velocity, and distance traveledfor an electron, the factor equal to eF/m, where eis the electron charge, F is the potential gradientof field, and m is the electron mass. Also seeELECTRON MOTION, 2.electronic flash 1. A device containing a circuitthat uses an electronic flash tube as a lightsource for photography or other purposes. Alsocalled photoflash. 2. A bright momentary lightburst produced by the equipment described in 1,above.electronic flash tube A tube used to produce brilliantbursts of light in photoflash units, stroboscopes,and laser exciters. A flash tube usuallycontains xenon gas, which is fired by a highvoltagepulse.electronic frequency meter 1. An instrumentthat gives direct readings of frequency in hertz,kilohertz, or megahertz on an analog scale or as adigital readout. 2. Any device that indicates theoperating frequency of another device, directly orindirectly, when used for such purpose.electronic frequency synthesizer An instrumentthat supplies a number of selectable frequenciesderived from one or more internally generatedfixed frequencies.electronic gas A collection of free electrons whosebehavior resembles that of a gas.electronic gate 1. A logic gate that operates byelectronic means. 2. A security system, consistingof a mechanical gate controlled electronically.Similar to an electronic garage door.electronic guitar See ELECTRIC GUITAR.electronic heating The production of heat in anobject via high-frequency energy. The two principalmethods are dielectric heating and inductionheating.

electronic hygrometer • electronic power supply 247electronic hygrometer An electrical device formeasuring relative humidity, whose sensitivityand stability have been increased by the additionof active amplifying devices.electronician See ELECTRONICS TECHNICIAN.electronic induction See ELECTROSTATIC IN-DUCTION.Electronic Industries Association Abbreviation,EIA. An American association of electronic manufacturersand engineers. It sets standards, disseminatesinformation, provides industrygovernmentliaison, and maintains public relationsfor the industry.electronic information processing The use ofelectronic equipment (especially digital computersand attendant devices) to perform mathematicaloperations on data entered into the system inthe form of electrical signals. Also see DATA PRO-CESSING.electronic instrument An instrument whose circuituses active devices for increased sensitivityover that of the electrical counterpart, and forminimum loading of a device under test. CompareELECTRICAL INSTRUMENT.electronic integrator A active device (such as anoperational amplifier) for performing mathematicalintegration. Also see INTEGRATOR, 2.electronic intelligence 1. Information exchangedby electronic means. Examples: radio messages,radar information, and computer data. 2. Thefaculties of reasoning and decision making, asapparently simulated by a high-level computer.electronic interference The malfunctioning of adevice because of nearby currents, voltages, orelectromagnetic fields.electronic inverter An electronic device for convertingdirect current (dc) to alternating current(ac). Typically, an inverter is a transistorizedsquare-wave oscillator inductively coupled to acoutput terminals. The dc to be inverted energizesthe transistors, which perform the switchingfunction at the rate determined by the componentsof the circuit. Also see INVERTER, 1.+dc Input−OscillatorAmplifierelectronic inverteracInputelectronic jamming The deliberate transmissionof electromagnetic energy for the purpose of interferingwith the operation of a device or devices.electronic key 1. For telegraphy (radio or wire), anelectronic circuit that generates a continuousstring of accurately spaced and timed Morse codedots or dashes, depending on its lever’s position(right or left). 2. For telegraphy (radio or wire), akeyboard that produces perfectly timed Morsecode output that corresponds to the operator’styped input. 3. An electronic device for openingan electronic lock.electronic keyer See ELECTRONIC KEY, 1.electronic lock A lock that will open only after applicationof a special coded sequence of signals.electronic mail Also called e-mail. A communicationssystem that allows people to leave digitaltext messages for each other. It is popular amongusers of personal computers. Operates throughthe telephone lines using terminal emulationsoftware and a modem. It can also be used viaamateur radio packet communications.electronic microammeter See FET CURRENTMETER and TRANSISTOR CURRENT METER.electronic microvoltmeter See MICROVOLT-METER.electronic milliammeter See FET CURRENT ME-TER and TRANSISTOR CURRENT METER.electronic millivoltmeter A millivoltmeter thatuses an amplifier ahead of an analog or digital indicatorto provide high input impedance and increasedsensitivity.electronic multimeter A voltohm-milliammeterthat uses active amplifying devices. Also seeELECTRONIC INSTRUMENT.electronic multiplier A device, such as a Hall generator,whose output is equal (or proportional) tothe product of two inputs (i.e., it can performarithmetic multiplication).electronic music 1. Music produced by a combinationof electronic oscillator, amplifier, andloudspeaker. A number of successful instrumentshave been developed. See, for example,ELECTRONIC CARILLON, ELECTRONIC ORGAN,ELECTRONIC PIANO, and THEREMIN. 2. Theelectronically amplified sounds of conventionalmusical instruments.electronic organ A musical instrument with a keyboardsimilar to that of a conventional organ, inwhich tones produced by oscillators or electricallydriven reeds are processed and amplified fordelivery to a system of loudspeakers.electronic packaging See ENCAPSULATION.electronic part A lowest replaceable unit, or component,in an electronic circuit.electronic phase meter An electronic instrumentfor measuring phase difference. Direct readings,in degrees of lead or lag, are visible on an analogscale or as a digital readout.electronic photoflash A transistorized light-intensitymeter. Also see ELECTRONIC INSTRUMENT.electronic piano A musical instrument having thekeyboard of a conventional piano and providedwith electronic amplification.electronic power supply A power supply usingtransistors or integrated circuits for stabilizationand output control.

248 electronic precipitator • electronic watchelectronic precipitator See DUST PRECIPITATOR.electronic product Any commercially manufacturedelectronic device, intended for purchase bythe public, by industry, or by government.electronic profilometer An electronic instrumentfor measuring surface roughness.electronic ratchet A stair-step circuit or other arrangementfunctioning in the manner of anequivalent electromechanical stepping switch.Also see COMMUTATOR.electronic reconnaissance In military applications,the use of electronic systems to locate enemyinstallations (such as radio stations,guided-missile sites, and radar bases).electronic rectifier A rectifier that uses active devicesto change alternating current (ac) to directcurrent (dc).electronic regulator A voltage regulator that usesactive electronic circuits, as opposed to a reactortypeor electromechanical device. See, for example,VOLTAGE REGULATOR.electronic relay 1. A switching circuit that usesone or more transistors, and performs the relayfunction without moving parts. 2. An electroniccomponent designed to switch when gating signalsare applied (e.g., triac, diac, or siliconcontrolledrectifier).electronic resistor 1. The effective internal collector-emitterresistance of a common-emitter bipolar-transistorstage. 2. The effective internaldrain-source resistance of a field-effect transistor(FET) stage.electronics The branch of physics concerned withthe behavior and application of electric chargecarriers in components, devices and systems thataccomplish amplification, oscillation, signal processing,and/or switching.electronics engineer A trained professionalskilled in the physics and mathematics of electronics,and in the theory and application of basicengineering and related subjects. CompareELECTRICAL ENGINEER.electronics service person An electronics technicianskilled in repairing and maintaining electronicequipment. Also called electronics servicetechnician.electronic shutter See KERR CELL.electronics technician A professional skilled inbuilding, testing, repairing, or maintaining electronicequipment.electronics technology The theory and practicalapplication of electronics. Taught as a subengineeringmajor, usually in two-year junior collegesor technical institutes, awarding the degree of associatein arts (AA) or associate in science (AS).electronic stethoscope A stethoscope employinga miniature microphone, amplifier, and earphones.The amplifier gain is continuously controllable,and its bandwidth often selectable foremphasizing particular heart sounds and otherbody noises.electronic stimulator A device for applying controlledelectrical pulses to the body to stimulatemuscles or nerves during diagnosis or therapy.electronic stroboscope A stroboscope that uses arate-calibrated oscillator, rather than a mechanicalcontactor to generate pulses that strobe the lamp.electronic subtracter An electronic circuit for performingarithmetic subtraction.electronic surge A sudden, large increase in thecurrent in a conductor. Can be caused by an electromagneticpulse; can also occur when utilitypower is restored following a blackout.electronic switch 1. A nonmechanical device,such as a flip-flop or gate, whose characteristicon-off operation can be used to make and breakan electric circuit. Compare CONTACT SWITCH.2. A device using electronic gating and sequencingcircuits to present several signals alternatelyto the single input of an oscilloscope, allowing simultaneousviewing of the signals.electronic tachometer An instrument for measuringangular velocity, usually in revolutions perminute (rpm). Ideally, the response is independentof sensor voltage amplitude, showing onlythe number of pulses per unit time reaching themeter circuit.electronic thermal conductivity The thermalconductivitycomponent, resulting from thetransfer of heat by electrons and holes.electronic thermometer An instrument for measuringtemperature as a result of variations in atemperature-sensitive component, such as a resistor,thermocouple, or thermistor.electronic timer An electronic circuit or device forautomatically timing a process or observed event.Most are based on the time constant of a stableresistance-capacitance (RC) circuit. CompareELECTROMECHANICAL TIMER.electronic tube See ELECTRON TUBE.electronic tuning Variation of the resonant frequencyof a device or circuit by changing the biasvoltage or current of a controlling electronic component.electronic voltmeter A voltmeter that uses electronicamplification ahead of the indicating meterto provide high input impedance and increasedsensitivity. Also see FET VOLTMETER and TRAN-SISTOR VOLTMETER.electronic voltohmmeter A voltohmmeter thatuses electronic amplification ahead of the indicatingmeter to provide high input impedanceand increased sensitivity.electronic typewriter A typewriter with a microcomputerthat provides features, such as buffering,automatic repeat, erase memory, andparagraph/page memory.electronic warfare The use of electronic systemsfor military purposes, including interfering withan enemy’s use of similar systems.electronic watch 1. A watch whose movement isa tiny, high-frequency, alternating-current (ac)

electronic watch • electron stream 249motor driven by a stable oscillator. 2. Any miniaturetimepiece incorporating solid-state circuitry,but especially one using a digital readout.electronic wattmeter A wattmeter in which anamplifier is used for increased sensitivity.electronic waveform synthesizer A signal generatorthat delivers an alternating or pulsating signalwhose waveform can be tailored by means ofadjustable circuit components.electron lens A device that focuses an electronbeam in a manner similar to the focusing of lightrays by a glass lens. Also see ELECTROSTATICLENS, ELECTROMAGNETIC LENS, and WAVE-GUIDE LENS.electron magnetic moment The energy per unitflux density available in an electron. Approximatelyequal to 9.2848 × 10 –24 joule per tesla.electron mass See MASS OF ELECTRON AT REST.electron microscope A microscope in which thesource of illumination is an electron beam focusedby electromagnetic lenses. It allows muchgreater magnification than is possible with opticalmicroscopes.ImageElectron gunObject+dcMagnetic lensMagnetic lensImageMagnetic lensFluorescentscreenelectron microscopeelectron mirror A reflector of electrons—especiallya dynode element in a photomultiplier tube orelectron-multiplier tube.electron motion 1. The movement of electrons ina conductor, semiconductor, or space, as theresult of electric or magnetic attraction orrepulsion. 2. The movement of an electron as acharged mass. In an electric field, this movementsimulates that of a free-falling body in a gravitationalfield.electron multiplication 1. In a gas discharge, theproduction of additional electrons as a resultof collisions between electrons, atoms, andmolecules. 2. The increased production of electronsin a semiconductor when avalanche occurs.electron-multiplier tube 1. A vacuum tube utilizinga sequence of secondary emissions for increasedcurrent amplification. Electrons from thecathode strike a positively biased dynode with aforce that dislodges secondary electrons, which,upon joining those first emitted, are reflected to asecond positive dynode that contributes moresecondary electrons, reflecting the total to a thirdpositive dynode, etc. The last dynode in the chainreflects the enhanced beam to an anode collectorthat passes the high current to an external circuit.2. See PHOTOMULTIPLIER TUBE.electronography Printing by means of the electrostatictransfer of ink from a printing plate acrossa gap to an impression cylinder.electron optics See ELECTRO-OPTICS.electron orbits See ELECTRON SHELLS.electron oscillator A device in which oscillation isobtained by causing electrons to move in an oscillatorypath, to travel in bunches, etc. Examples:klystron, magnetron, and traveling-wavetube.electron pair Two electrons from adjacent atoms,which sometimes share the same orbits, but alwaysproduce a bond between two adjacentatoms.electron-pair bond The bond between an electronpair.electron physics The physics of electronics, usuallyfrom a highly theoretical viewpoint.electron-proton magnetic moment ratio A physicalconstant whose value is approximately equalto 658.211, derived from the division of the magneticmoment of the electron by that of the proton.electron recoil The recoil of an electron from aphoton it has collided with.electron rest mass See MASS OF ELECTRON ATREST.electron scanning Deflection of an electron beam.See, for example, ELECTROSTATIC DEFLEC-TION and ELECTROMAGNETIC DEFLECTION.electron shells The spheres, concentric with thenucleus of an atom, that represent the mediandistances from the nucleus around which electronsmigrate.electron spin The rotation of an electron (i.e.,around its axis). This motion is independent ofthe electron’s movement around the nucleus ofan atom.electron stream 1. The beam of electrons generatedby the electron gun in a cathode-ray tube.

250 electron stream • electrophorus2. The electrons moving between the cathode andplate in an electron tube.electron-stream instrument See ELECTRON-BEAM INSTRUMENT.electron-stream meter An oscilloscope (or cathode-raytube alone) used as a device for makingmeasurements.electron-stream transmission efficiency The ratioof the current through a positive electrode tothe current impinging on it. In a tube, for example,some electrons are absorbed by the plate,and others are reflected.electron telescope A telescope using a combinationof a glass lens, photocathode, and electrostaticfocusing. Light from the object is focusedon the photocathode by the lens, the electronsemitted being focused electrostatically on a phosphorescentviewing screen.electron transit time The time required for an electronto travel a given distance. For a vacuum tube,the upper frequency limit of operation is governedby the time required for an electron to reach theplate after leaving the cathode. Transit time isusually stated in fractions of a microsecond.electron tube An evacuated or gas-filled chamberin which electrons are emitted (usually by a hotcathode) and controlled (usually by a voltage appliedto a grid electrode).electron unit See ELEMENTARY CHARGE.electron velocity The velocity acquired by an electronthat moves between two points having agiven potential difference. Also see ELECTRONMOTION, 2.electronvolt Abbreviation, eV. The energy acquiredby a unit charge moving through a potentialdifference of one volt; it is equal toapproximately 1.6022 × 10 –19 joule.electron-wave tube A tube, such as a klystron ortraveling-wave tube, in which electrons travelingat different velocities interact with each other,modulating the electron stream.electro-oculogram A recording of the voltage thatis found between the anterior and posterior partsof the eyeball.electro-optical transistor A phototransistor orpair of phototransistors in a single package. Usedin electronic circuits to sense changes in lightlevels.electro-optical valve See KERR CELL.electro-optic radar A form of radar that makesuse of visual apparatus for locating a target.electro-optics The branch of electronics dealingwith related electrical and optical phenomena:photoelectricity, light generation, laser technology,light amplification, etc. It is also concernedwith electronic phenomena that are analogous tooptical phenomena, such as electronic focusing,reflection, refraction, diffraction, etc. Also calledelectron optics and optoelectronics.electro-osmosis Causing liquids to flow by applyingan electric field across the walls of a porousplug. The force exerted by the field on ions in theliquid causes it to flow.electropad The skin-contacting electrode of anelectrocardiograph.electropathy See ELECTROTHERAPY.electrophilic Pertaining to the tendency to seekelectrons.electrophobia An irrational fear of electricity, apsychological condition sometimes exhibited byvictims of serious electric shock.electrophonic effect Sound heard by a personwhen an alternating current is passed throughsome part of the body.electrophoresis The movement of dielectric particlesthrough a liquid in which they are suspended,produced by the electric field betweenelectrodes immersed in the suspension.electrophoresis equipment 1. Any device intendedfor the purpose of depositing a dielectricmaterial onto a metal by means of electrophoresis.2. Any equipment in which electrophoresisoccurs.electrophoresis scanner A device that senses themovement of charged particles caused by electrophoresiseffects.electrophoretic deposition A type of deposition inwhich a low-voltage direct current passingthrough a colloidal suspension of dielectric polymerparticles deposits them as a coating on ametallic body (the anode in the process). It canprovide a better coating than one obtained withspray painting or dipping.Anode partto be coatedSuspended particles+ −electrophoretic depositionCathodeelectrophorus A simple device used to demonstrateelectrostatic generation and induction. Itconsists of a smooth metal plate at the end of aninsulating handle and an accompanying cake ofresin or hard rubber. The cake is rubbed withcat’s fur, making it negatively charged. The metalplate is touched to the charged cake; by induction,it acquires a bound positive charge on theface that touched the cake and a free negativecharge on the opposite face. When the plate islifted and its top face touched momentarily withthe finger or grounded, the negative charge leaks

electrophorus • electrostatic field 251off, often with a sharp spark, but the positivecharge remains.electrophotographic process See XEROGRAPHY.electrophotography The production of photographsby means of electricity. See XEROGRAPHY.electrophotometer A light-intensity meter using aphotoelectric sensor and a meter, but usually notincorporating an amplifier. Compare ELEC-TRONIC PHOTOMETER.electrophrenic respiration A system of inducingrespiration in which one or both of the phrenicnerves (i.e., of the diaphragm) are stimulatedelectrically to produce contractions of the diaphragmmuscles.electrophysiology 1. The study of electrical processesin the human body. 2. The study of howelectrical impulses affect, and are produced by,body organs.electroplaques In electric fish, small voltagegeneratingcells that are connected in seriesparallelnetworks.electroplate 1. To cause one metallic substance toadhere to the surface of another through the effectsof electrolysis. 2. A metal plating depositedvia electrolysis.electroplating Depositing one metal on the surfaceof another by electrolytic action.electropolar Having electrical polarity (either positiveor negative).electropolishing An electrolytic method ofsmoothing a rough metal surface. The workpieceto be polished becomes the anode of an electrolyticcell in which electrolytic action dissolvestiny surface irregularities.electropositive Having positive electrification orpolarity. Compare ELECTRONEGATIVE.electropotential series See ELECTROMOTIVESERIES.electropsychrometer An electronic instrument forhumidity measurements.electroreduction In electrolysis, reduction of thecathode electrode.electrorefining The refining of metals by means ofelectrolysis.electroretinograph An instrument used to measurethe electrical response of the human retinato light.electroretinography The process of detecting andmeasuring electrical impulses from the retina.electroscope An instrument for detecting electriccharges and fields. The common type uses a pairof gold-leaf strips hung from the end of a metalrod in a glass tube or jar. When the exposed endof the rod is brought near a charged object, theleaves repel each other and spread apart.electrosection The use of an arc-generating devicefor making surgical incisions.electrosensitive recording See ELECTRIC RE-CORDING.electroshock 1. The system of creating a controlledelectric shock in the brain as a treatmentfor certain mental disorders. 2. The electric shockused in the therapy described in 1.electrospinograph An instrument that senses andrecords electrical impulses from the spinal cord.electrostatic Pertaining to stationary electriccharges and fields, and their application.electrostatic actuator A device for measuring thesensitivity of a microphone. Electrostatic chargesproduce forces on the diaphragm of the microphone,and the resulting output is recorded.electrostatic amplifier See DIELECTRIC AMPLI-FIER.electrostatic charge See ELECTRIC CHARGE.electrostatic component The electric componentof an electromagnetic wave. It is perpendicular tothe magnetic component and can be thought ofas the wave’s voltage component.electrostatic constant See ELECTRIC CON-STANT.electrostatic convergence See ELECTROSTATICFOCUSING.electrostatic cooling Accelerated cooling of a bodythrough the application of an intense electrostaticfield. The body must be in a free convectionstate, a corona discharge must be present, andthe field must not be uniform.electrostatic copier A document-copying apparatusthat uses electrostatic effects to reproduceprinted material.electrostatic coupling See CAPACITANCE COU-PLING.electrostatic deflection In a cathode-ray tube,deflection of the electron beam by the electrostaticfields between pairs of internal horizontaland vertical deflecting plates. It is primarily usedin laboratory oscilloscopes. Compare ELECTRO-MAGNETIC DEFLECTION.+150 V−150 Velectrostatic deflectionElectronstreamLines offluxelectrostatic electrometer See KELVIN ABSO-LUTE ELECTROMETER.electrostatic electrophotography See XEROG-RAPHY.electrostatic energy The potential energy containedin an electrostatic field (e.g., the energy ina charged capacitor). Compare ELECTROKI-NETIC ENERGY.electrostatic field A stationary electric field.

252 electrostatic field intensity • electrostatic stresselectrostatic field intensity An expression of thestrength of an electrostatic field. Usually expressedin volts per meter, millivolts per meter, ormicrovolts per meter.electrostatic flux The flux existing around anelectric charge or a charged body.electrostatic focusing In a cathode-ray tube, electron-beamfocusing achieved by varying the dcbias voltage on a focusing electrode. CompareELECTROMAGNETIC FOCUSING.electrostatic galvanometer A galvanometer operatingon the principle of the electrostatic voltmeter.electrostatic generator A device for producinghigh-voltage electric charges; e.g., a Van deGraaff generator.electrostatic headphone A device similar to anelectrostatic speaker, but held against the headfor private listening. Incoming audio signalscause attraction and repulsion among chargedplates, resulting in acoustic vibration.electrostatic hysteresis The tendency of some dielectrics(especially ferroelectric materials) to saturateand retain a portion of their polarizationwhen an alternating electric field to which theyare exposed reverses polarity. This causes thecharge to lag behind the charging force.electrostatic induction The charge acquired by abody inserted into an electric field. CompareELECTROMAGNETIC INDUCTION.electrostatic instrument See ELECTROSTATICVOLTMETER.electrostatic lens An assembly of deflecting platesor cylinders, whose electric field causes an electronbeam to converge or diverge in much thesame way as a visible light beam passing throughan optical lens. Compare ELECTROMAGNETICLENS.electrostatic loudspeaker See ELECTROSTATICSPEAKER.electrostatic memory A memory unit in which aninformation bit is stored as an electric charge.electrostatic memory tube A cathode-ray tube inwhich information bits are stored in capacitivecells swept by the scanning electron beam.electrostatic microphone See CAPACITOR MI-CROPHONE.electrostatic phase shifter See PHASE-SHIFTINGCAPACITOR.electrostatic potential In an electric field, the potentialenergy represented by the voltage betweenthe two elements creating the field, or betweenany two points within the field.electrostatic precipitator See DUST PRECIPITA-TOR.electrostatic printer A computer output peripheralin which the printing medium, a fine dust, isfused by heat onto paper that has been chargedaccording to the data being represented.electrostatic process 1. Any process that useselectrostatic action. 2. A method of photographyin which visual images are converted to electrostaticimages.electrostatic recording A method of recordingthat employs a signal-controlled electric field.electrostatic relay A high-input-impedance relayconsisting of two polarity-controlled contacts; oppositecharges on the contacts close the relay,and like charges open it.electrostatics The branch of electricity concernedwith electrical charges at rest. Compare ELEC-TRODYNAMICS and ELECTROKINETICS.electrostatic screen A shield against electric fluxconsisting of a number of straight, narrowly separatedrods or wires joined at only one end. Theshield has little effect on magnetic flux. Alsocalled Faraday shield.electrostatic separator A device for separatingfine particles from a mixture by exposing the mixtureto an intense electrostatic field.electrostatic series A list of materials arranged inthis sequence: any one of them becomes positivelyelectrified when rubbed with another lowerin the list, or negatively electrified when rubbedwith another higher in the list. Compare ELEC-TROMOTIVE SERIES.electrostatic shield Any metallic enclosure designedto confine an electric field.electrostatic speaker A loudspeaker whose vibratingdiaphragm is one of two plates in a largeair-dielectric capacitor, the other being a closelysituated metal plate (or plug). An audio voltageapplied to the plates causes them to vibrate. Alsocalled capacitive loudspeaker and capacitor loudspeaker.electrostatic sprayer An equipment for spraypainting in which fine droplets of paint are attractedby an electrostatic field to the surface tobe coated.electrostatic storage See ELECTROSTATIC MEM-ORY.electrostatic stress 1. Stress in the vicinity of acharged body or particle. 2. See DIELECTRICSTRESS.

electrostatic transducer • element 253electrostatic transducer See CAPACITANCETRANSDUCER.electrostatic tube of flux The space between electriclines of flux going through adjacent points onthe boundary of a given area in an electric field.electrostatic tweeter A small electrostaticspeaker for reproducing high-frequency sounds.Compare WOOFER.electrostatic unit Abbreviation, esu. A unit ofmeasure in the electrostatic system of cgs units.Also see CENTIMETER-GRAM-SECOND. CompareELECTROMAGNETIC UNIT.electrostatic vector See ELECTRIC VECTOR.electrostatic voltmeter An indicating meterwhose movement consists of a stationary metalplate near a rotating metal plate. A voltage appliedto the plates charges them, and the attractionbetween them causes the movable memberto rotate against the torque of a returning springover an arc proportional to the voltage.CalibratedscaleMovablevaneSpringbearingelectrostatic voltmeterFixedvaneInputelectrostatography See XEROGRAPHY.electrosteel See ELECTRIC STEEL.electrostenolysis The deposition of certain metalsfrom a solution in capillary tubes when an electriccurrent passes through the solution.electrostimulation Electrical excitation of nervesfor the relief of pain.electrostriction In certain materials, the physicalcontraction that occurs when a voltage is applied.Compare MAGNETOSTRICTION.electrostrictive ceramic A ceramic exhibitingELECTROSTRICTION when voltage is applied.electrostrictive relay A relay in which the movablecontact is carried by a bar of electrostrictivematerial, such as barium titanate. A control voltagedeforms the material, causing the contacts toclose.electrosurgery Surgery, sometimes bloodless,achieved with diathermy-like equipment. SeeDIATHERMY, 2.electrosynthesis Chemical synthesis produced bymeans of electric currents or fields.electrotape Also called electronic tape measure.Any device that measures distance by electronicmeans, such as radar or sonar.electrotechnology See ELECTRICAL TECHNOL-OGY and ELECTRONICS TECHNOLOGY.electrotellurograph An instrument for measuringground currents.electrotherapeutics See ELECTROTHERAPY.electrotherapy The treatment of disorders or diseasesby electrically induced heat—especially byDIATHERMY.electrothermal 1. Pertaining to electrically generatedheat. 2. Pertaining to a combination of electricityand heat.electrothermal device A device whose operationdepends on the heat generated by an electric current(e.g., a bolometer, hot-wire ammeter, thermocouple,or varistor).electrothermal expansion element A thermostaticelement, such as a bimetallic strip, whoseexpansion is used in heat-sensitive switches.electrothermal instrument A hot-wire or thermocouple-typemeter.electrothermal recorder See ELECTRIC RE-CORDING, 1 and THERMAL RECORDER.electrothermic See ELECTROTHERMAL.electrothermics The study and application of theheating effects of electricity in conductors andjunctions.electrotitration In chemistry, the completion oftitration, as indicated by an electrical measurement,such as of the resistance of the solution beingtitrated.electrotonic Pertaining to ELECTROTONUS.electrotonus Modification of a nerve’s sensitivityby passing a constant current through it.electro-ultrafiltration In physical chemistry, filteringa colloidal suspension by electro-osmosis.electrovalence 1. The number of charges acquiredby an atom gaining electrons. 2. The number ofcharges forfeited by an atom losing electrons. 3.Valence resulting from electron transfer betweenatoms and the resulting creation of ions.electrovalency See ELECTROVALENCE.electrovalent bond See IONIC BOND.electrowin To recover (win) a metal from a solutionof its salts by means of electrolysis.electrum A natural alloy of gold and silver.element 1. See ELECTRODE. 2. A circuit componentintended for a specific purpose. 3. A specificpart of an antenna array (e.g., drivenelement or parasitic element). 4. A fundamental,unique substance whose atoms are of only onekind (examples: aluminum, carbon, silicon, andsulfur). There are more than 100 elements, someman-made. Elements combine to form compounds.5. A circuit, such as an AND gate, thatcan be taken as a unit because it performsa special function. 6. In digital computer

254 element • ELSIEoperations, a subunit of a category that cannotbe further categorized [e.g., a bit (word element)or a record (file element)].elemental area In a facsimile or television picture,a scanning line segment as long as the line’swidth.elemental charge See ELEMENTARY CHARGE.elemental semiconductor A semiconductor containingone undoped chemical element.elementary charge Symbol, e. Also called unitelectric charge. The electric charge of a singleelectron or proton. This charge is approximatelyequal to 1.6022 × 10 –19 coulomb.elementary particle 1. A minute charged or unchargedparticle within the atom (i.e., electron,proton, neutron, quark, etc.). 2. In theory, a subatomicparticle that cannot be broken down intosmaller particles.element error rate In communications or datatransfer, the ratio n i /n t , where n i is the number ofelements received incorrectly and n t is the numberof elements transmitted.element spacing 1. The spacing between radiator,director, and reflector elements in a directionalantenna. 2. The spacing between the internalelectrodes of a vacuum tube.elevation Angular position (in degrees) of a pointabove the horizontal.elevation-position indicator A type of radar displaysimultaneously indicating the elevation of,and the line-of-sight distance to, the target.elevator control 1. An electronic system for automaticallystopping an elevator and opening thedoors. Various safety functions are included, anexample being the reopening of a closing doorwhen a passenger steps into the car. 2. In an aircraft,the mechanical, electronic, or electromechanicaldevices or circuits involved in actuationof the elevators.ELF Abbreviation for EXTREMELY LOW FRE-QUENCY.eliminator 1. A device or circuit acting as a surrogatefor an inconvenient or undesirable component(e.g., battery eliminator). 2. A device forremoving or minimizing an undesirable signal orquantity (e.g., harmonic eliminator); interferenceeliminator.ell A coaxial fitting that is a right-angle line sectionwith a coaxial connector at each end. It takes itsname from its L shape.ellipse A geometric figure having the Cartesianplaneformula (x – x 0 ) 2 /a 2 + (y – y 0 ) 2 /b 2 = 1, wherea and b are constants, and x o and y 0 representthe center point.elliptical filter See ELLIPTIC FILTER.elliptical function See ELLIPTIC FUNCTION.elliptical load line For any amplifier with an outputtransformer, a load line in the shape of an ellipse,obtained when the load connected to theoutput element is reactive, rather than purely resistive.elliptically polarized wave An electromagneticwave in which the rotation of the electricintensityvector at one point describes an ellipse.elliptical orbit A satellite orbit that is not a perfectcircle. In theory, all satellites deviate slightly fromperfectly circular orbits. Sometimes a satellite isdeliberately put into an orbit that is greatly elongated.The closer the satellite is to the earth, thefaster it moves.elliptical polarization Polarization characterizedby elliptical rotation of the wave vector at a givenpoint.elliptical stylus In a phonograph (turntable) system,a stylus with a characteristic ellipsoidalshape.elliptic filter A band-pass, band-stop, high-pass,or low-pass inductance-capacitance (LC) filter,designed according to an ELLIPTIC FUNCTION.Characterized by a steep attentuation-versusfrequencycutoff response with ripple in both thepassband and the stopband.elliptic function A function, similar to theChebyshev and Butterworth functions, used inthe design of certain selective filters. The ellipticfunction results in a better filter magnitude responsethan the Chebyshev or Butterworthfunctions in some applications. See ELLIPTICFILTER.elongationA form of modulation distortion resultingfrom multipath propagation. Some of thepaths result in greater propagation delay thanother paths; this causes the modulation envelopeto spread out. The higher the modulating frequency,the greater the effect.ELSEy oyellipseA word used in a BASIC computer programthat provides an instruction based on a relationaltest and, in this respect, is related to IF-THEN,ON-GOTO, etc. It specifies the operation to bedone if the conditions given in the same programline don’t occur.ELSIE Abbreviation of electronic letter-sorting andindicator equipment.x oaxb

EM • emissivity 255EM 1. Abbreviation of EFFICIENCY MODULATION.2. Abbreviation of ELECTROMAGNETIC(S). 3. Abbreviationof electromagnetic iron. 4. Abbreviationof ELECTROMAGNETIZER. 5. Abbreviation ofELECTRON MICROSCOPE. 6. Abbreviation of EX-POSURE METER. 7. Abbreviation of electromotive.E m 1. Symbol for MAXIMUM VOLTAGE. 2. Symbolfor MAXIMUM JUNCTION FIELD.emanation 1. Emission of electrons. 2. Emissionof radioactive particles or ionizing radiation. 3.Emission of electromagnetic energy.E max Symbol for MAXIMUM VOLTAGE.embedded path A means of guiding a mobile robotalong a specific route. One common scheme usesa buried, current-carrying wire that produces amagnetic field. The robot can sense and followthis field. Colored paints and tapes can also beused in conjunction with machine vision systems.Compare EDGE DETECTION.embedded training The inclusion of training/tutorial programs in computerized equipmentthat assist users in the operation of the equipment.embedding See ENCAPSULATION.embossed-foil printed circuit A printed circuitmade by pressing the pattern from metal foil intothe insulating substrate and then removing thesurplus foil.embossed-groove recording 1. A phonographrecord into which grooves are embossed, ratherthan scribed. 2. Recording sound by embossinggrooves on record disks.embossing stylus The rounded-tip stylus used tomake an embossed-groove recording.EMC Abbreviation of ELECTROMAGNETIC COM-PATIBILITY.EME Abbreviation of earth-moon-earth. See MOON-BOUNCE.e/m e The ratio of the elementary electron charge toits mass: 1.7588 × 10 11 coulombs per kilogram.Also see CHARGE-MASS RATIO.Emergency Broadcast System In the UnitedStates, a general plan for dissemanating informationvia broadcast stations in the event of a nationalemergency.emergency channel A communication channel allocatedfor emergency service.emergency communication Radio or other electronictransmission and reception of urgent messages(e.g., distress signals, storm warnings,etc.).emergency equipment 1. Apparatus kept instandby status for immediate operation whenregularly used equipment fails. 2. Equipment, especiallyvehicular, for use in emergency situations.Examples are ambulances, fire-fightingtrucks and equipment, etc.emergency power supply An alternating-current(ac) or direct-current (dc) power unit kept instandby status for immediate use when the regularpower supply fails.emergency service A communications service devotedexclusively to emergency communication.EMF, emf Abbreviation of ELECTROMOTIVEFORCE.emf standard See STANDARD CELL.EMG 1. Abbreviation of ELECTROMYOGRAM. 2.Abbreviation of ELECTROMYOGRAPH.EMI Abbreviation of ELECTROMAGNETIC INTER-FERENCE.E microscope See ELECTRON MICROSCOPE.emission 1. The ejection of particles, especiallyelectrons, from a material. 2. Waves radiatedfrom any source (as from a transmitting antennaor from an amplifier stage). 3. The emanation ofradiant, electromagnetic, acoustical, electrical, ormagnetic energy.emission code A system of abbreviating the varioustypes of radio emission. See EMISSION MODE.emission frequency 1. In communications, thecarrier frequency of the transmitted signal as it isradiated from the antenna or fed into a transmissionline. 2. The actual frequency or frequencyrange of a signal as it is transmitted or radiated.This might be the carrier frequency. 3. The frequencyof energy in an emission band or bands ina spectrum.emission lines In a spectrum, radiation intensitypeaks that appear as bright lines in a visible display.In a radio-frequency spectrum, the emissionlines occur as sharp peaks in radiated energy atspecific wavelengths.emission mode Any of various official classificationsof radio communication emission types.Emissions are designated according to the modulationmethod used (e.g., continuous waves,amplitude modulation, single-sideband withsuppressed carrier, frequency modulation, pulsemodulation, etc.).emission power 1. The rate at which energy is radiatedfrom an object. 2. In radio communication,the transmitter output power.emission spectrum The radiation spectrum of asubstance that emits energy (e.g., the light spectrumof an incandescent metal).emission types See EMISSION MODE.emission velocity The initial velocity of an electronas it leaves an emitting surface.emission wavelength 1. In communications, thecarrier wavelength of the transmitted signal as itis radiated from the antenna or fed into a transmissionline. 2. The actual wavelength or wavelengthrange of a signal as it is transmitted orradiated. This might or might not be the carrierwavelength. 3. The wavelength of energy in anemission band or bands in a spectrum.emissive power The rate at which a surface emitsenergy of all wavelengths in all directions, perunit area of radiating surface, regardless of temperature.emissivity For a radiating source, the ratioW 1 /W 2 , where W 1 is the energy emitted by the

256 emissivity • empirical designsource at a particular temperature, and W 2 is theenergy emitted by a blackbody (i.e., a theoreticallyperfect radiator) at the same temperature.emittance For an energy-radiating source, the radiatedpower per unit area of radiating surface.emitted electron An electron that has left an atomof a material and has escaped into surroundingspace or entered a neighboring material.emitter 1. A body that discharges particles orwaves (see EMISSION). 2. In a semiconductor device,the area, region, or element from which currentcarriers are injected into the device. In atransistor symbol, the emitter is that electrodeshown with an arrowhead.emitter-base junction In a bipolar transistor, theboundary between base and emitter regions.emitter bias Emitter current or voltage maintainedto set the operating point of a bipolar transistor.emitter bulk resistance The portion of the resistanceof the semiconductor material in a transistorthat affects emitter resistance.emitter-coupled logic A bipolar form of digitallogic, abbreviated ECL.emitter-coupled multivibrator A two-transistormultivibrator circuit in which the emitters sharea common resistor.emitter-coupled phase inverter A transistorphase inverter in which the out-of-phase componentis taken from the collector and the in-phasecomponent from the emitter resistor (of the sametransistor). Another transistor is often used toamplify the in-phase component so that both outputsare equal in magnitude.Input+dcemitter-coupled phase inverterOutputOutputemitter current Symbol, I E . The current in theemitter electrode of a bipolar transistor.emitter degeneration In a transistor amplifier,current degeneration obtained by use of an unbypassedemitter resistor. The arrangement resultsin virtually distortion-free amplification at a sacrificein voltage gain.emitter follower A transistor circuit in which theinput signal is applied to the base, and the outputsignal is taken from the emitter resistor. Gain isalways less than unity; output impedance is low.Input+dcemitter followerOutputemitter-input circuit See COMMON-BASE CIR-CUIT.emitter junction See EMITTER-BASE JUNCTION.emitter resistance Symbol, R E . 1. The resistanceof the emitter electrode in a bipolar transistor. 2.External resistance connected to a transistor’semitter terminal.emitter stabilization In a common-emitter transistorstage, an emitter resistor that stabilizes thecircuit against temperature variations.emitter-to-base junction See EMITTER-BASEJUNCTION.emitter voltage Symbol, V E . The voltage at theemitter electrode of a bipolar transistor.EMP, emp 1. Abbreviation of ELECTROMAGNETICPULSE. 2. Abbreviation of electromagnetic power.emphasis Modification of the amplitude-versusfrequencyoutput or response of an audio circuit,for the purpose of optimizing signal intelligibility.emphasizer An audio-frequency device with a speciallytailored response, intended to maximize intelligibilityof a voice.Empire cloth Varnished cambric used as an insulatingsheet or tape.empirical Observable; derived from experimentation.empirical curve A curve plotted from data acquiredfrom observations, tests, and calculations,rather than from mathematical laws or other theory.empirical design The design of electronic circuitsby cut-and-try methods and, to some extent,

empirical design • end feed 257through intuition arising from experience (i.e.,practical as opposed to theoretical design).empirical probability Probability estimated fromexperience and observations. This method is oftenused in quality-control and reliability procedures.empty medium A computer storage medium, suchas a magnetic tape or disk, that is ready to acceptdata (i.e., rather than being completely blank, itcontains the signals necessary for processing theto-be-added data).EMU, emu Abbreviation of ELECTROMAGNETICUNIT(S).emulator In computer engineering, a sophisticateddevice that substitutes for a similar device orstage in the computer, and thereby provides a basisfor experimenting and troubleshooting withoutdisturbing the equivalent part of the computer.E n Symbol for voltage remaining at null.enable To initiate the operation of a circuit or deviceby applying a pulse or trigger signal.enable pulse 1. A pulse that initiates the operationof a circuit or device. 2. A binary pulse that augmentsa write pulse to make a magnetic corechange state.enabling gate A digital device that regulates thelength of a pulse for specialized use.enameled wire Wire that is insulated by a thincoat of baked enamel. Commonly used in coilwinding because the thin enamel allows for amaximum number of turns in a given volume fora given wire gauge.encapsulant A material, such as potting resin,used to embed (encapsulate) a component, circuit,or device.encapsulated circuit A component, circuit, or deviceembedded in plastic or wax (see ENCAPSU-LATION).encapsulated component An electronic part thatis embedded in plastic or wax (see ENCAPSULA-TION).encapsulating material See ENCAPSULANT.encapsulation The embedding of a circuit or componentin a solid mass of plastic or wax. The moldor container remains as part of the assembly afterthe plastic or wax has solidified. Protectsagainst the environment, and/or against the effectsof physical vibration. Compare POTTING.encephalogram See ELECTROENCEPHALO-GRAM.encephalograph See ELECTROENCEPHALO-GRAPH.enciphered facsimile Facsimile communicationsthat have been rearranged or scrambled at thetransmitting location so that it cannot be interceptedby a third party. A deciphering device isneeded at the receiver end of the circuit.enclosure 1. A cabinet, case, or other housing forelectronic equipment, such as a receiver, transmitter,or test instrument. 2. A specially designedhousing for a loudspeaker.encode 1. To convert signals or data into a desired(usually digital) form. Also called CODE. 2. Toequip a transmitter with a tone-producing device(encoder). 3. To develop and apply an encodingsystem to a group of transceivers or transmittersof a communications network.encoder 1. An analog-to-digital or digital-to-analogconverter. 2. An electromechanical device fortranslating the angular position of a rotatingshaft into a corresponding series of digital pulses.Also see SHAFT-ANGLE ENCODER. 3. A devicefor encoding data (see ENCODE). 4. A machinewith a keyboard for printing characters that canbe read by optical character recognition (OCR)equipment. 5. A tone generator used as a receiverenabler in the transmitters of a communicationsnetwork.encoding 1. The translation, either by a machineor by a human operator, of a spoken or writtenlanguage into digital code. 2. Any function performedby an ENCODER.encryption The conversion of a signal from plaintext, graphics, or other commonly recognizableform into a cipher. See also CIPHER. CompareDECRYPTION.end-around carry In a computer, a carry producedin the most significant position, causing a carryinto the least-significant position.end-around shift In digital-computer operations,the transfer of characters from one end of a registerto the other end. Also called LOGICAL SHIFT.end bell 1. The part of a motor housing that supportsthe bearing and protects internal rotatingparts. 2. A clamping part fastened to the back ofa plug or receptacle. 3. Either of the two frames ofa transformer that contains the mounting lugs.end bracket See END BELL, 2.end cell A cell intended for series operation in conjunctionwith a storage battery. As the voltage ofthe battery drops, the end cell can be added intothe circuit.end effect 1. In a tapped coil, losses because of inducedcurrents flowing in the inductance anddistributed capacitance of the unused end of thecoil. 2. EDGE EFFECT in a capacitor. 3. An effectivecapacitance at the ends of an antenna, resultingfrom air discharge. This lowers theresonant frequency slightly below that predictedby theory. The effect is exaggerated by the proximityof objects, such as trees and buildings, orwhen an antenna is placed close to the earth.end effector The device or tool connected to theend of a robot arm (e.g., a gripper, screwdriver,drill, or soldering iron).end-fed antenna An antenna whose lead-in orfeeders are attached to an end of the radiator.end feed A method of feeding electromagneticfields to an antenna by connecting the transmissionline to the end. Ordinarily, the antenna mustbe a multiple of 0.5 wavelength long for end feedto be effective.

258 end-fire antenna • end pointend-fire antenna See END-FIRE ARRAY.end-fire array Also called end-fire antenna. Aphased antenna in which the greatest radiation/responsetakes place off one or both ends.The array consists of two or more parallel drivenelements, all of which lie in a single plane. A typicalsystem might consist of two half-wavedipoles, fed 90 degrees out of phase and spacedone-quarter wavelength apart in free space. Thisproduces a unidirectional directivity pattern. Twoelements might be driven in phase and spaced1 wavelength apart, producing a bidirectionalpattern. These systems show some power gain, intheir favored directions, compared to a singlehalf-wave dipole. The larger the number of elements,with optimum phasing and spacing, thegreater the gain.end-fire directivity In a directive antenna, beaminga signal along the plane of the antenna (i.e.,off its ends).end instrument A device capable of converting intelligenceinto electrical signals or vice versa, andthat needs to be connected to only one terminal ofa loop.end item A final, completed product or component.endless loop Also called infinite loop. A computerprogramming bug that causes the machine to goin an indefinite, and often useless, logical circle.For example, suppose that at line 180, the computerencounters the command GOTO 250,meaning “Go to line 250,” but line 250 gives thecommand GOTO 180. Once the computer gets toline 180, it enters a loop in which nothing is accomplished,and from which the only escape isintervention by the operator (e.g., terminating theprogram).end mark In digital-computer operations, a signalor code indicating the close of an informationunit.endodyne reception See ZERO-BEAT RECEP-TION.end-of-charge voltage For a rechargeable cell orbattery, the voltage at full charge (i.e., just afterdisconnection of the charging apparatus and beforeuse).end-of-data mark A code or character signalingthat all the data in a computer storage mediumhas been read or used.end-of-discharge voltage For a rechargeable cellor battery, the voltage at the termination of a dischargingcycle, immediately before the unit istaken out of use and the charging apparatus isconnected.end-of-field mark In computer operations, a “flag”code that signals when the end of a field has beenreached.end-of-file mark In computer operations, a codeinstruction that signals when the last record in afile has been read.end-of-line unit The last device or circuit in achain.end-of-message character A character or codesignaling the end of a message.end-of-run The end of a computer program or programrun, as indicated by the program.end-of-tape mark A physical marker at the end ofa magnetic tape (e.g., something that can besensed by methods other than that used to readthe tape).end-of-tape routine A computer program thathandles the processing needed after the lastrecord on a reel of magnetic tape has beenreached.end-on armature A relay armature that moves inthe direction of the core’s axis.end-on directional antenna See END-FIRE AN-TENNA and END-FIRE ARRAY.endoradiograph An X-ray picture, derived or enhancedby the introduction of substances into thebody.endoradiosonde A tiny pill-enclosed transducerand radio transmitter for sensing physiologicalconditions in the stomach and intestines; ittransmits corresponding signals to instrumentsoutside.endothermic reaction A chemical reaction producingcold (i.e., one in which kinetic energy islost). Compare EXOTHERMIC REACTION.end-plate magnetron A magnetron whose oscillationintensity is increased by a positive and a negativeend plate, the electric field between themcauses the electrons to move axially while spinning.end point 1. For a precision potentiometer, theshaft position between the last and first positionsof measurement. 2. The point at which theuseful life of a device can be considered spent.3. The point at which a time interval or operationalsequence ends. 4. The end-point voltageof a primary or Edison storage cell. 5. For a

end point • energy-level diagram 259MagnetMagnetNegativeelectrodeElectron pathElectron pathPlateend-plate magnetronPlateMagnetCathodePositiveelectrodeCathodeMagnetlead-acid storage cell, the specific-gravity valueof the electrolyte at which the cell is consideredin need of recharging (nominally 1.150 to1.175).end-point control A form of quality control inwhich the end item is checked for defects.end-point sensitivity A means of expressing thesensitivity of a meter or other indicating device:the ratio, in decibels, between the input signalrequired to produce a full-scale or maximumreading and the smallest detectable input signal.end-point voltage The voltage of a battery or cellterminal when the device is no longer useful.end resistance In a rheostat or potentiometer, theresistance between the wiper and the end terminalwhen the wiper is set to the end point of thedevice.end-resistance offset In a potentiometer, the resistancebetween the wiper and an end terminalwhen they are in contact.end-scale deflection See END-SCALE VALUE.end-scale value For an indicating meter, the electricalquantity indicated at the last graduation onthe scale.end section Either the input or output section of amultisection filter.end setting 1. The fully clockwise or fully counterclockwisesetting of a rotatable control. 2. Theminimum or maximum setting of a control.end shield In a magnetron, a shield that confinesthe space charge to the interaction space.end spaces The cavities at either end of the anodeblock in a multicavity magnetron tube; they terminateall the anode-block cavity resonators.end use The intended application of a circuit or device.energize To apply operating power and input signalsto a circuit or device.energized The condition of a circuit or device thatis powered or excited.energy Symbol, W. Common units: joule, watthour,and kilowatt-hour. 1. The capacity for doingwork. Some common forms of energy areelectrical, mechanical, and chemical. Also seeCONSERVATION OF ENERGY, KINETIC EN-ERGY, and POTENTIAL ENERGY. 2. The workperformed by electric power. The unit used byutility companies is the kilowatt-hour (kWh),equal to the product Pt, where P is power in kilowattsand t is the period (hours) during which thepower is used.energy-band diagram A diagram depicting the variousenergy levels within the atom of a conductor,semiconductor, or insulator.energy barrier The natural potential gradientacross a semiconductor junction. In the absenceof an applied voltage, the gradient, not measurablefrom the outside, prevents total interactionbetween the n- and p-type materials.energy cell 1. A usually small primary or secondarycell—especially the kind used in hearingaids and electronic watches. 2. A capacitivetypedirect-current (dc) source (see ENERGY-STORAGE DEVICE, 2).energy consumption 1. The conversion of energyfrom one form to another by a component, circuit,system, or machine, in the process of performingsome useful task. 2. The amount of energy involvedin the process defined in 1.energy conversion The transformation of energyfrom one form to another. See also CONSERVA-TION OF ENERGY and ENERGY TRANSFORMA-TION.energy-conversion device A component, circuit,system, or machine that changes energy from oneform to another. See also CONSERVATION OFENERGY.energy density 1. For an energy-producing cell,such as an electrochemical cell, the ratio of availableenergy to cell mass. It is expressed in joulesper gram or in watt-hours per kilogram. 2. Foran energy-producing cell, the ratio of availableenergy to cell volume. Expressed in joules per cubiccentimeter or in watt-hours per cubic centimeter.energy gap In the energy-level diagram for a semiconductoror insulator, the region between valenceand conduction bands representing theminimum energy required to make the electronpass from the valence to the conduction band(i.e., to become a current carrier). Also called forbiddenenergy band.energy level A constant-energy state, such as oneof the energy levels of an electron in an atom.energy-level diagram 1. A diagram showing theenergy levels (in electronvolts) of electrons in thevarious shells of an atom. 2. A diagram showingvariations in power that correspond to variationsin current in a channel.

260 energy loss • entladungsstrahlenenergy loss In any system, the energy that is unavoidablylost (i.e., it is not converted into usefulwork). Also see ENTROPY and POWER LOSS.energy of a charge The energy level of an electrostaticcharge. It is QV/2 ergs, where Q is thequantity of electricity in coulombs, and V is thepotential in volts.energy product An expression of the effectivenessof a permanent magnet. The magnetic flux densityis multiplied by the magnetic field strength toobtain the energy product, specified in gaussoersteds.energy redistribution A mathematical process fordetermining the effective duration of an irregularpulse. The instantaneous power output of the irregularpulse is integrated from the start to theend of the pulse. Then, a rectangular pulse isconstructed having the same peak power and thesame total energy content (area under the powercurve). The length of this rectangular pulse isconsidered to be the effective duration of the irregularpulse.Max.Instantaneous power0Equivalent rectangularpulse (same start time)Timeenergy redistributionIrregularpulseenergy state The condition of an electron, as expressedby its position and velocity, with respectto the position and velocity of other electrons.energy-storage capacitor A usually high-value capacitorused primarily to store the charge used tofire a lamp (as in a photoflash unit), create aspark discharge (as in electronic ignition), or performsome similar function.energy-storage device 1. See CAPACITOR. 2. Asmall, electrochemical component offering veryhigh capacitance (e.g., several farads) and lowleakage current (less than 1 pA). It has a numberof applications, including long-interval timing,power-supply filtering, and energy-cell service. Itsactive ingredients are compressed powders.energy stored in capacitor The electrical energyin the field between the plates of a charged capacitor.In this instance, energy W = CE 2 /2,where W is the energy in joules, C is the capacitancein farads, and E is the voltage in volts.energy stored in inductor The magnetic energy inthe field surrounding an inductor carrying current.In this instance, energy W = LI 2 /2, where Wis the energy in joules, L is the inductance in henrys,and I is the current in amperes.energy transformation The conversion of oneform of energy into another, as with a transducer.engine analyzer An instrument for checking theperformance of an automobile engine. In additionto measuring voltage and resistance throughout acar’s electrical system, the instrument measuresengine speed, cam dwell angle, and other factors.engineer 1. A person who designs machines, circuits,and other devices. 2. A person who developsmethods of utilizing machines, circuits, orother devices more efficiently, or for new applications.3. To design or implement an apparatus.engineering The science of applying scientific lawsto technical problems and designing practical devices.Also see ELECTRICAL ENGINEER andELECTRONICS ENGINEER.enhanced-carrier demodulation A method ofreducing distortion in the demodulation ofamplitude-modulated (AM) signals. A properlyphased and synchronized local carrier is added tothe signal in the demodulator.enhancement mode Operation characteristic ofan ENHANCEMENT-TYPE MOSFET.enhancement-type MOSFET A metal-oxide semiconductorfield-effect transistor (MOSFET) inwhich the channel directly under the gate electrodeis widened (enhanced) by a negative gatevoltage in the n-channel unit or by a positivegate voltage in the p-channel unit. CompareDEPLETION-TYPE MOSFET.ENIAC An electronic computer developed at theUniversity of Pennsylvania. The name is anacronym for Electronic Numerical Integrator AndCalculator.ENIC Abbreviation of voltage negative-impedanceconverter.enrichment In a mixture of different isotopes of agiven element, the increase in the relative concentrationof one particular isotope.ensemble 1. A collection of devices that functionstogether as a complete unit. 2. In music recording,the ability of all the musicians to hear each otherduring the session. 3. A set of random mathematicalfunctions, all starting at the same point.ENSI Abbreviation of EQUIVALENT-NOISE-SIDE-BAND INPUT.entladungsstrahlen Ultraviolet radiation emittedby electric arcs. At atmospheric pressure, thewavelength is approximately 40 to 90 nanometers,

entladungsstrahlen • epitaxial deposition 261depending on the arc length. The term is derivedfrom the German word for discharge rays.entrainment Providing a path for gases to escapefrom an electrochemical cell or battery.entrance delay In security applications, a delaythat allows authorized people time to leave theprotected area after activating the alarm system,or to deactivate the system after entering the protectedarea. The delay is approximately 30 to 45seconds.entropy 1. In all closed physical systems, the measureof energy wasted. According to the secondlaw of thermodynamics, for example, suppliedheat can never be converted entirely into work.2. In communications, the amount of informationin a message, defined as the base-10 logarithm ofthe number of equivalent messages that can exist.3. A natural process in which the energy inthe universe tends to become more uniformly distributedwith the passage of time.entropy coding A form of digital encoding thatminimizes redundancy, thereby increasing theamount of data in a given amount of memory orstorage space.entry 1. A unit of computer input or output information.2. A data item in a table or list. 3. A computersource program statement. 4. In a computerprogram, the address of the first instruction.entry condition A condition that must be specifiedbefore a computer program is run (e.g., establishingoperand values).entry-level system 1. The least-sophisticatedcomputer that will perform the things that a userrequires. 2. A simple electronic or computer system(e.g., an amateur radio transciever or personalcomputer, intended for ease of operation,and from which the user expects to upgrade to amore powerful system at a later date).entry point In a computer program, the first instructionto be implemented, or a point duringthe run when data can be entered.envelope 1. On a graph, the imaginary line joiningsuccessive signal peaks. In the graph for an amplitude-modulatedsignal, the line reproduces themodulating wave. 2. The enclosure of a transistoror integrated circuit. 3. The glass shell of a vacuumtube.envelope delay In a tuned amplifier, time delay introducedin the envelope of a modulated signal byvarying the phase of the envelope with the modulatingfrequency. This delay varies directly withthe amount by which the sidebands shift, with respectto the carrier frequency.enveloped file A computer file with labels permittingit to be handled by a computer of a type differentfrom that used to make the file.environmental conditions See ENVIRONMENTALFACTORS.environmental factors Aspects of the space immediatelysurrounding and sometimes influencingelectronic equipment. Examples: altitude,dust, light, moisture, noise, pressure, shock,temperature, and vibration.environmentally sealed Sealed against the effectsof adverse environmental factors.environmental test chamber See CLIMATECHAMBER.E o 1. Symbol for OUTPUT VOLTAGE. 2. Symbol forzero reference voltage.EOF Abbreviation of end of file.EOL Abbreviation of end of line.EOLM Abbreviation of electro-optical light modulator.EOR Abbreviation of END OF (program) RUN.EOS Abbreviation of electro-optical system(s).EOT Abbreviation of end of tape.EOTS Abbreviation of electro-optical tracking system.E P 1. Symbol for PLATE VOLTAGE. 2. Symbol forPEAK VOLTAGE.EP Abbreviation for EXTENDED PLAY.ephemeris time Time measured with respect tothe orbit of the earth around the sun. Initiated inthe year 1900 AD.epipolar navigation A scheme for position sensingand navigation that uses an artificially intelligentvision system. Allows calculation of position andvelocity, based on changes in the visualized direction,size, and shape of an object whose actuallocation, size, and shape are precisely known. Itis used in some mobile robots.episcotister A mechanical light beam modulator.The device consists of a series of rotating diskshaving transparent and opaque sections that alternatelyinterrupt and pass the light beam at anaudio-frequency rate.ModulatedlightepiscotisterLightStationary diskRotatingdiskepitaxial Pertaining to, or having the property of,EPITAXY.epitaxial deposition The tendency of certain materialsto grow on a semiconductor substrate undercertain conditions.

262 epitaxial device • equation solverepitaxial device A semiconductor device built bymeans of EPITAXIAL GROWTH.epitaxial film A film of single-crystal semiconductormaterial deposited onto a single-crystal semiconductorsubstrate.epitaxial growth Growing monocrystalline siliconon a silicon wafer by precipitating silicon from agas in which the wafer is placed. Epitaxy is securedbetween the precipitate and the wafer.epitaxial layer A semiconductor layer exhibitingepitaxy. Also see EPITAXIAL GROWTH.epitaxial mesa transistor See DOUBLE-DIFFUSED EPITAXIAL MESA TRANSISTOR.epitaxial planar transistor A planar transistorhaving an epitaxially grown collector on a lowresistivitysubstrate, and a diffused base andemitter.epitaxial process See EPITAXIAL GROWTH PRO-CESS.epitaxial transistor A transistor in which an epitaxiallayer (into which a base region later is diffusedand an emitter region alloyed) is grown onthe face of a semiconductor wafer, which servesas the collector. Also see DOUBLE-DIFFUSEDEPITAXIAL MESA TRANSISTOR.epitaxy The condition in which atoms in a thinfilm of single-crystal semiconductor materialgrown on the surface of the same kind of wafercontinue their characteristic alignment. Also seeEPITAXIAL GROWTH.E plane The plane of an antenna containing theelectric field.E plane bend See E BEND.E-plane tee junction A waveguide junction whosestructure changes in the plane of the electricfield.epoxy resin A synthetic resin used to encapsulateelectronic equipment, or as a cement. Epoxyresins are based on ethylene oxide or its derivatives.EPROM Abbreviation of erasable programmableread-only memory.EPU 1. Abbreviation of electronic power unit. 2. Abbreviationof emergency power unit.Eq 1. Abbreviation of equation. 2. Abbreviation ofEQUALIZER or EQUALIZATION.equal alternations Positive and negative halfcyclesof a wave that have identical shape andamplitude.equal-energy source A light source that has a constantemission rate (energy per unit wavelength).equal-energy white The color of light emitted by asource radiating equally the wavelengths of thevisible-light spectrum.equal heterodyne In a beat-frequency system, thecondition in which the outputs of the two heterodyningoscillators are identical.equality circuit A logic circuit that, when twonumbers are put into it, outputs logic 1 if thenumbers are equal, and logic 0 if the numbers arenot equal.equalization 1. The use of an EQUALIZER to makethe frequency response of a line, amplifier, or otherdevice uniform over a given frequency range.2. The use of an EQUALIZER to modify the frequencyresponse of a line, amplifier, or other device.equalizer A circuit or device, such as a compensatedattenuator, that allows the user to tailor thefrequency response of a line, amplifier, or otherdevice. Sometimes used in sophisticated high-fidelitystereo amplifier systems, to obtain a desiredbass/midrange/treble frequency output.equalizer circuit breaker A form of circuit breakerthat trips in the event of unbalance in an electricalsystem.equalizing current A current that flows in the circuitof two compound generators connected inparallel.equalizing network A circuit used to equalize aline.equalizing pulses In a television signal waveform,several pulses (preceding and following the verticalsync pulse and having a repetition rate of twice thepower-line frequency) that start the vertical retraceat the correct instant for good interlace.equal-loudness curves See AUDIBILITY CURVES.equal vectors Vectors having the same magnitudeand the same direction. They do not necessarilyoriginate at the same point. Compare IDENTICALVECTORS.equal vectorsXXZY= Y = Zequation solver A (usually analog) computer forsolving linear simultaneous equations or for determiningthe roots of polynomials.

equatorial orbit • equivalent inductance 263equatorial orbit A satellite orbit that lies in theplane of the earth’s equator.equiphase surface Any surface in a wave, overwhich the field vectors at a particular instanthave either 0° or 180° phase difference.equiphase zone The space region in which two radionavigationsignals show no phase difference.equipment 1. Collectively, apparatus or componentsdesignated for a specific purpose (e.g., radioequipment). 2. A functional electronic unit,such as a test instrument, receiver, or memoryunit.equipment chain A system consisting of seriesconnectedcircuits or devices.equipment ground An electrical ground connectionintended to reduce the chances of electricshock. An equipment ground does not necessarilyconstitute a good radio-frequency ground; itserves only to eliminate potential differencesamong the individual units in a system.equipment life The period during which electronicequipment functions according to specifications;it is terminated at an END POINT.equipment test A usually preliminary, qualifyingtest of electronic equipment.equipotential Having a potential difference of zero;being at the same voltage level.equipotential line Between two charged plates,the locus (an imaginary line) of points having thesame potential, with respect to the plates.equipotential surface A surface on which allpoints have the same electrical potential.equisignal Pertaining to signals having equal intensity.equisignal localizer See TONE LOCALIZER.equisignal radio-range beacon For aircraft guidance,a radio-range beacon that transmits twodistinct signals that are received by aircraft withequal intensity only in certain directions.equisignal surface The “surface” around a transmittingantenna formed by points of equal fieldintensity.equisignal zone The region in which two radionavigationsignals have identical amplitude.equivalence The condition existing when one networkcan be substituted for another without disturbingcurrents, impedances, and voltages atthe terminals.equivalent absorbing power See EQUIVALENTSTOPPING POWER.equivalent absorption Unit, sabin. The rate atwhich a surface absorbs sound energy.equivalent binary digits For a given decimal numberor specific character, the corresponding binarydigits (bits).equivalent bit rate The number of binary digits(bits) that can be sent in a given unit of time,such as one second, in a digital communicationssystem.equivalent capacitance The value of a singlelumped capacitance, that would cause the sameaction as the capacitance distributed throughouta circuit.equivalent circuit A circuit that has the sameoverall current, impedance, phase, and voltagerelationships as a more-complicated counterpartthat it usually replaces for analysis.equivalent component density For a circuit inwhich discrete components are not used or arenot evident, the volume of that circuit divided bythe number of discrete components that would berequired if the circuit used them.equivalent conductivity The conductivity of a solutionthat contains 1 gram equivalent of the solutein the space between electrodes 1 centimeterapart.equivalent dark-input current For a photoelectricdevice, the illumination required for an outputcurrent equal to the DARK CURRENT of the device.equivalent decrement The value of decrement ina damped wave that would result in the sameamount of interference at a receiver as the interferencecaused by the sidebands of an amplitudemodulatedsignal.equivalent delay line A comparatively simple network,such as a resistance-capacitance (RC) circuit,that will provide the attenuation and phasecharacteristics of an ideal delay line.equivalent delta In a three-phase system, a deltaconnectedcircuit that is equivalent to a givenwye-connected circuit, from the standpoint ofimpedance and phase. Also see DELTA CONNEC-TION and WYE CONNECTION. Compare EQUIV-ALENT WYE and WYE-EQUIVALENT CIRCUIT.equivalent differential input capacitance For adifferential amplifier, the equivalent input capacitance(see EQUIVALENT CAPACITANCE) at oneinput (inverting or noninverting) when the oppositeinput is grounded.equivalent differential input impedance For adifferential amplifier, the equivalent inputimpedance at one input (inverting or noninverting)when the other input is grounded.equivalent differential input resistance For adifferential amplifier, the equivalent input resistanceat one input (inverting or noninverting)when the other input is grounded.equivalent equations Two equations for an unknownthat have the same root.equivalent four-wire system A two-wire line overwhich full-duplex operation is obtained by use offrequency division.equivalent height See VIRTUAL HEIGHT.equivalent impedance 1. The value of a singlelumped impedance that would cause the sameaction as the impedance distributed throughout acircuit. 2. An impedance that draws current ofthe same strength and phase as that drawn by animpedance it replaces.equivalent inductance The value of a singlelumped inductance that would cause the same

264 equivalent inductance • equivalent wyeaction as the inductance distributed throughouta circuit.equivalent input offset current For a differentialamplifier, the difference between currents flowinginto the inverting and noninverting inputs whenthe output voltage is zero.equivalent input offset voltage For a differentialamplifier, the input voltage required to reduce theoutput voltage to zero.equivalent input wideband noise voltage For adifferential amplifier, the ratio V o /G v , where V o isthe root-mean-square (rms) output-noise voltage,and G v is the direct-current (dc) voltage gain.equivalent length of antenna 1. The electricallength of an antenna, as measured in degrees orwavelengths. 2. The free-space length of an antenna.3. The length d (in feet) of a quarter-waveresonant antenna at a specific frequency f (inmegahertz), given by the formula d = 234/f. 4.The length d (in feet) of a half-wave resonant antennaat a specific frequency f (in megahertz),given by the formula d = 468/f.equivalent length of electric dipole The distance,measured in a straight line, separating the pointsthat represent the charge centers of an electricdipole.equivalent length of feed line The electricallength of a feed line as measured in degrees orwavelengths. Generally, this is equal to 1/v timesthe line length in free-space wavelengths, where vis the VELOCITY FACTOR of the line, expressedas a fraction between 0 and 1.equivalent length of magnet The distance separatingthe poles of a magnet. In a bar magnet,these poles are not exactly at the ends. The actualequivalent length is about 83% of the length ofthe bar magnet.FluxNSFluxEquivalentlengthequivalent length of magnetequivalent loudness The actual intensity, in decibels,of a given sound whose apparent loudnesschanges with frequency.equivalent network A network that can replace amore-complex network for analysis purposes.equivalent noise input The value of modulated luminousflux that, when applied to a photoelectricdevice, produces a root-mean-square (rms) outputcurrent equal to the device’s rms noise current.equivalent-noise-sideband input Abbreviation,ENSI. A specification for receiver noise characteristics.Numerically, ENSI = 0.3E s (P n /P s ) 1 ⁄ 2, whereE s is the voltage of an unmodulated radiofrequency(RF) carrier applied to the receiver, P nis the resulting noise-output power of the receiver(measured with an rms meter), and P s is thenoise-output power measured with the RF signal30% amplitude modulated at 400 Hz with a 400-Hz bandpass filter inserted between the receiveroutput terminals and the meter.equivalent noise temperature For a componenthaving resistance, the temperature (degrees absolute)at which a theoretically perfect resistorhaving the resistance of the component wouldgenerate the same noise the component generatesat room temperature.equivalent optics The analogy between certain opticallenses and prisms and the electrostatic deflectionof an electron beam. Thus, when theupper deflecting plate in an electrostatic deflectionsystem is made negative and the lower plateis positive, the beam is deflected downward, likehorizontal light rays bent by a prism. When bothplates are made equally negative, the beam convergesto a point, as light rays do when they passthrough a double convex lens. When both platesare made equally positive, the beam spreads out,as do light rays passing through a double concavelens.equivalent permeability The permeability of acomponent made of certain materials, comparedwith that of a component having the same reluctance,shape, and size, but made of different materials.equivalent reactance The value of a single lumpedreactance that would cause the same action asthe reactance distributed throughout a circuit.equivalent resistance The value of a single lumpedresistance that would cause the same action asthe resistance distributed throughout a circuit.equivalent series and parallel circuits Series andparallel circuits in which current, voltage, phase,and frequency relationships are identical. Any seriescircuit can be transformed into an equivalentparallel circuit.equivalent series resistance The equivalent resistanceacting in series with circuit components.equivalent sine wave A sine wave of the same frequencyand effective voltage as a given wave.equivalent stopping power For a material in thepath of radioactive particles, the thickness of thematerial that produces the same energy loss asthat produced by one centimeter of air.equivalent time The effective duration of somephenomenon, such as a pulse.equivalent volt See ELECTRONVOLT.equivalent wye In a three-phase system, a wyeconnectedcircuit that is equivalent to a givendelta-connected circuit from a standpoint ofimpedance and phase. Also see DELTA

equivalent wye • error correction 265CONNECTION, EQUIVALENT DELTA, WYE CON-NECTION, and WYE-EQUIVALENT CIRCUIT.equivalent Y See EQUIVALENT WYE.equivocation A condition in which the meaning ofdata depends on certain parameters.ER Abbreviation of ECHO RANGING.Er Symbol for ERBIUM.E r Symbol for voltage drop across a resistance.erasable storage In computer operations, anystorage medium holding information that can beerased.erasable PROM A programmable read-only memory(PROM) from which the data can be removed,usually by exposure to ultraviolet light. Also seePROM.erase To obliterate or remove a signal, especially arecorded one, as in the erasure of recorded materialfrom a magnetic tape or the data from a computerdisk.erase button A pushbutton that actuates the circuitsupplying a signal that erases stored material(as the display on a storage oscilloscope).erase current In an electromagnetic erase head,the current flowing through the coil of the head.In most instances, it is a high-frequency current(usually the regular bias current), but it can be aslow as 60 Hz, as long as the speaker does not respondto what remains of it on the tape after erasure.erase head In a tape recorder, a head used to eraserecorded material from tape. It can contain a permanentmagnet (see ERASE MAGNET) or an electromagnetwhose coil carries erase current.MagnetictapeacErasesignalTape movementerase headMagneticheaderase magnet In a tape recorder, a magnet used toerase recorded material from tape. Because thestrength of the magnet is greater than that of themagnetized areas on the tape, erasure is complete(the tape left demagnetized).erase oscillator In a tape recorder, a highfrequency(typically 30 to 80 kHz) oscillator thatsupplies erase current.eraser See BULK ERASER.erase signal A signal that causes recorded materialto be erased (see ERASE and ERASE CURRENT).erasing speed The rate at which successive storageelements are erased, as in a charge-storagetube.erasure 1. In tape-recording and digital-computeroperations, the process of erasing a recorded signal(see ERASE). 2. An erasure accomplished bythe process described in 1, above.erbium Symbol, Er. A metallic element of the rareearthgroup. Atomic number, 68. Atomic weight,167.26.E region See E LAYER.e register In a computer, a register used in doubleprecisioncalculations.E r -E y signal In color television, the resultant signalthat is the difference between the original full-redand E y signals.ERG Abbreviation of ELECTRORETINOGRAPHY.erg Abbreviation, e. A unit of work. It is the workdone by a force of one dyne (10 –5 newton) actingthrough a distance of one centimeter.ergograph An instrument used to measure andrecord work done by muscles.ergometer An instrument for measuring energyconsumed or work accomplished.ergon See ERG.E rms Symbol for ROOT-MEAN-SQUARE VOLTAGE.ERP Abbreviation of EFFECTIVE RADIATEDPOWER.error 1. In calculations and measurements, thedifference between a true value and an observedor calculated value. 2. In electronic circuits, especiallythose of automatic control systems, thedifference between a required (or reference signal)level and the actual signal level. 3. In communications,a discrepancy between the transmitteddata and the received data.error accumulation The adding-up of maximumpossible error when measurements are repeatedlymade. Generally, the maximum plus-orminuserror per measurement is multiplied bythe number of measurements.error amplifier An amplifier for boosting error currentor voltage.error-checking code An error-correcting or errordetectingcode.error-correcting code An error-detecting codethat, in addition to the function indicated by itsname, indicates the correct code.error-correcting telegraph A digital communicationssystem in which an improbable or incorrectcharacter is not accepted. In the event that sucha character is received, the receiver instructs thetransmitter to send that character again.error correction 1. The restoration of mutilated,corrupted, or missing data in a digital system,

266 error correction • ETespecially in magnetic data storage media, such astapes and disks. 2. In digital communications, anyscheme in which the receiver (destination) automaticallyeliminates (to the greatest possible extent)errors in data from a transmitter (source). Forexample, the destination can instruct the sourceto repeat questionable characters or words.error-correction routine In computer operations,a series of programmed instructions to detect andcorrect errors in files. A common example is aspell-checking program for word-processed documentfiles.error current An error signal that is a feedbackcurrent for automatically correcting a system.error curve A bell-shaped curve that describes thedistribution of errors in measurement around atrue value.error-detecting code In computer operations, acharacter-coding system that ensures that an impossiblecombination (forbidden characters) willbe generated by an error (for error detection).error-detecting routine A computer program thatdetects errors by checking the validity of data.error detection and feedback In computer operations,a system in which an error (sensed by anerror-detecting code) automatically generates arequest to repeat the suspect signal.error detector A sensor that responds to an errorsignal by delivering a signal proportional to theerror.error diagnostics As performed by a compiler, detectingand indicating the presence of errors insource language statements.error interrupt A computer program halt causedby a software or hardware error and accompaniedby a display of what has happened.error list As produced by a compiler, a list ofsource language statement faults.error message During a computer program run, astatement (displayed on a peripheral) of what isin error.error of measurement The positive or negative differencebetween the value of an actual measurementand the true (or most probable) value.error range For a data item, the range of valuesover which it will cause an error.error rate In data transmission, the ratio of errorstransmitted to the data transmitted.error-rate damping Damping that involves addingto an error signal another signal that is proportionalin rate of change.error ratio 1. In a received message, the number ofincorrect characters divided by the total numberof characters. Can be represented as a fractionbetween 0 and 1 or as a percentage by multiplyingthe fraction by 100. 2. A measure of distortionfor digital signal communications. The number ofinaccurately received bits divided by the totalnumber of received bits.error routine A computer program segment that isinput when an error is detected so that anappropriate action is taken (correct the error, repeatthe process, etc.).error-sensing circuit A circuit that samples theoutput current or voltage of a power supply, amplifier,or control system, compares this outputwith a standard value, and delivers a feedback(correction) signal whose amplitude is proportionalto the difference (error).error signal In a servo system, an output signalwhose value is proportional to the difference betweenthe actual operating quantity of the systemand a standard reference quantity. The signal isfed back to the input of the system for automaticcorrection.error tape In data processing, a record tape designedand used for storing errors for subsequentstudy.error voltage An error signal that is a feedbackvoltage for automatically correcting a system.Es Symbol for EINSTEINIUM.Esaki diode See TUNNEL DIODE.E scope See E DISPLAY.escape character In computer operations, a characterindicating that the next character belongsin a new group.escapement A (usually oscillating) mechanical orelectromechanical device that stores energy (oftenin a spiral spring) on one swing, and returns thatenergy on the next swing. Such a mechanism advancesa shaft progressively in a clock or watch,and in some control equipment.escape velocity 1. The minimum velocity (about25,000 miles per hour or seven miles per second)required for a space vehicle to completely escapethe gravitational field of the earth. 2. The minimumvelocity required for a space vehicle to completelyescape the gravitational field of a planet orstar. 3. The minimum velocity required for anelectron to escape the electrical influence of anatomic nucleus.escutcheon A usually decorative plate thatframes an opening or covers a panel in a piece ofequipment (e.g., the escutcheon of a radio tuningdial).ESD Abbreviation of ENERGY-STORAGE DEVICE.ESG Abbreviation of electronic sweep generator.Esnault-Pelterie formula A formula for approximatelycalculating the inductance of a singlelayersolenoidal coil:L = 0.1008(a 2 n 2 )/(s + 0.92a)where L is the coil inductance in microhenrys, ais the radius of the coil in inches, s is the lengthof the coil in inches, and n is the number of turnsin the winding. The formula is accurate to 0.1percent for all values of 2a/s between 0.2 and1.5.ESS Abbreviation of electronic switching system.EST Abbreviation of EASTERN STANDARD TIME.esu Abbreviation of ELECTROSTATIC UNIT(S).ET Abbreviation of EPHEMERIS TIME.

ETC • even-line field 267ETC Abbreviation of electronic temperature control.etchant Any substance such as cupric chloride,ferrous chloride, or hydrochloric acid, used inetching.etched circuit A circuit produced by etching themetallic coating of a substrate to provide the requiredpattern of conductors and terminals towhich discrete components are soldered.etched circuitetch factor The ratio of the depth to the width ofan etched track in an etched circuit.etching 1. Chemically eating away a metal to forma desired pattern, such as an etched circuit. 2.Thinning a quartz-crystal plate by slowly erodingone or both of its faces with hydrofluoric acid tofine-tune the resonant frequency.ET-cut crystal A piezoelectric plate cut from aquartz crystal at an angle of +66°, with respect tothe z-axis. Also see CRYSTAL AXES and CRYS-TAL CUTS.ether 1. Also called luminiferous ether. A nonviscousfluid once thought to fill space, conveywaves (radio, light, etc.), and sustain fields. 2. Avolatile liquid occasionally used in electronics asa solvent [e.g., ethyl oxide (C 2 H 5 ) 2 O].ether drift The postulated motion between a materialbody and the ether (see ETHER, 1). The conceptwas checked by Michelson and Morley, whofailed to find that the earth moves relative to theether. This eventually led to scientific rejection ofthe so-called ether theory of the propagation oflight.ethical slave A machine, especially a smart robot,that is treated in the manner of a slave, based onthe notion that a machine cannot have “feelings.”Some researchers fear that the use of ethicalslaves could lead to technological nightmares. Forexample, robots might be used as soldiers in a maraudingoffensive army; the commanders could rationalizethat there is nothing immoral about thewar because there is no loss of life on their side.E transformer A differential transformer whoseprimary is wound on the center leg of an E core,the secondaries being wound on the outer legs.Ettinghausen effect A phenomenon somewhatlike the HALL EFFECT. It occurs when a metalstrip, carrying current longitudinally, is placedinto a magnetic field perpendicular to the plane ofthe strip: corresponding points on opposite edgesof the strip exhibit different temperatures.Eu Symbol for EUROPIUM.eudiometer 1. An instrument for measuring theamount of oxygen in the air. 2. An instrument foranalyzing gases.eureka 1. See CONSTANTAN. 2. The groundtransponder beacon in the British rebeccaeurekaradar navigational system (see REBECCA-EUREKA SYSTEM).europium Symbol, Eu. An element of the rareearthgroup. Atomic number, 63. Atomic weight,151.96.eutectic 1. A form of reaction in which mixed liquidssolidify when cooled. 2. The solid substanceresulting from a reaction as defined in 1.eutectic alloy A metallic alloy with a specific meltingpoint, made via eutectic process.eutectic bond A connection between two dissimilarmetals, facilitated by a third metal alloyed, viaeutectic process, to the adjoining faces.eV Symbol for ELECTRONVOLT.evacuation The removal of air or other gases froma tube or chamber, specifically, the envelope of avacuum tube that houses the internal elements.evaporation 1. A technique for electrically depositinga film of a selected metal on a metallic or nonmetallicsurface. A filament of the metal to bedeposited is heated by an electric current in avacuum chamber, which makes filament particlestravel to the (nearby) object to be coated,where they condense as a film. In an alternatemethod, a piece of the metal to be deposited islaid on or wrapped around a filament of someother metal. 2. Electron emission by a hot cathode.evaporation theory The theory that electrons willacquire sufficient escape velocity to leave a materialwhen the energy acquired by (or imparted to)the electron exceeds the work function of the material.Also see WORK FUNCTION.E vector The vector that represents the electriccomponent of an electromagnetic wave.even-even nucleus An atomic nucleus containingan even number of protons and an even numberof neutrons. An example is the alpha particle, orhelium nucleus, which contains two protons andtwo neutrons.even harmonic In a complex waveform, an evennumberedmultiple of the fundamental frequency.Compare ODD HARMONIC.even line In a television picture, an evennumberedmember of the 262.5 horizontal linesscanned by the spot in developing the even-linefield. Compare ODD LINE.even-line field On a television screen, the completefield obtained when the spot has traced all

268 even-line field • excited statethe even-numbered lines. Compare ODD-LINEFIELD.even parity check A check to verify the presence ofan even number of ones or zeros in a group of bits.event An occurrence that affects the state of acomputer file.event counter Any device that measures the numberof specified events taking place within a certaininterval of time.evolution Extracting a root of a number (e.g.,square root, cube root, etc.).E wave In microwave operations, the transversemagnetic (TM) wave. Also see WAVEGUIDEMODES.EWR Abbreviation of EARLY-WARNING RADAR.EWS Abbreviation of early-warning system.E X 1. Symbol for voltage drop across a reactance.2. Symbol for EXCITATION ENERGY.exa- Symbol, E. A prefix meaning 10 18 (InternationalSystem of Units).exalted-carrier reception In radio reception, overcomingthe effects of selective fading by maintainingthe carrier at a high amplitude. This isaccomplished before demodulation by removingthe carrier from an amplitude-modulated or phasemodulatedsignal, amplifying it, and reinserting itat a higher amplitude with the sidebands.exc 1. Abbreviation of EXCITER. 2. Abbreviation ofEXCITATION.except gate A logic gate that delivers an outputpulse when an input pulse is present at one ormore of a set of input terminals, and absent fromone or more of another set of input terminals.Also called exclusive-OR element.excess charge The amount of overcharge for astorage battery.excess conduction In a semiconductor, currentconduction by excess electrons.excess electron 1. An electron that, when introducedinto an atom, results in a negative ion. 2.An electron resulting from the addition of a donorimpurity to a semiconductor substance.excess meter A meter that integrates the amountof power in excess of some predetermined level.excess minority carriers The number of minoritycarriers in excess of the normal equilibrium numberin a semiconductor material.excess modified index of refraction Symbol, M.For waves transmitted through a refractingmedium, a modified index of refraction greaterthan unity.excess noise Electrical noise caused by current ina semiconductor material.excess sound pressure Unit, dyne/cm 2 . In amedium conducting sound waves, the quantityP i – P s , where P i is total instantaneous pressure ata given point in the medium, and P s is static pressurein the absence of the sound waves.excess-three code A computer code derived frombinary notation by adding binary three (i.e.,0011) to each four-bit group. Thus, decimal sevenis 1010 in the code (it is 0111 in binary). Unlikethe binary representation for zero, the excessthreerepresentation (0011) contains two ones, afeature that distinguishes actual zero from a machinefault.exchange 1. To reverse the contents of two memorybanks. For example, if the memory banks arecalled A and B, an exchange is the placing of thecontents of memory A into memory B, and theplacing of the contents of memory B into memoryA. The original contents are removed. 2. A twowaysequence of data transmissions. 3. A designatedlocation in a telephone circuit.exchange line A telephone line.exciplex In a laser, a method of adjusting the colorby means of chemical reactions in organic dyes.excitant The electrolyte in a voltaic cell.excitation 1. Supplying input-signal driving current,driving power, or driving voltage. 2. Inputsignaldriving current, driving power, or drivingvoltage.excitation anode In a mercury-pool tube, an auxiliaryanode whose operation maintains the cathodespot when no output current is being drawnfrom the tube.excitation current 1. Input-electrode current inan excited transistor amplifier. 2. Grid current inan excited vacuum-tube amplifier. 3. Currentflowing in the circuit of the excitation anode of amercury-pool tube. 4. Current flowing in the excitercircuit of an alternator. 5. Shunt-field currentin a motor.excitation energy 1. Symbol, E X . In artificialtransmutation, the energy of a nucleus when protonsof less than maximum energy have beenemitted from the atom. 2. Electrical energy requiredby a transducer.excitation purity In color television, complete saturationof a hue (i.e., there is no contaminationby other colors, and the saturated hue is distributeduniformly).excitation voltage 1. The signal voltage thatachieves, or is required for, excitation (see EXCI-TATION, 1). 2. The value of driving voltage.excitator An electrical discharger.excited atom An atom in which one or moreelectrons have been pushed out of their normalorbits into higher ones by energy applied from theoutside.excited-field speaker A dynamic speaker in whichthe magnetic field is provided, not by a permanentmagnet, but by direct current flowingthrough a large coil of wire wound around thespeaker core. The coil usually acts as a filterchoke in the power supply of the attendant amplifieror receiver.excited state In artificial transmutation, the stateof the nucleus when protons of less-than-maximumenergy have been emitted from the atom.The energy of the protons, in this instance, isgreater than the ground state.

exciter • expandable 269exciter 1. An amplifier or oscillator (or a system ofsuch units) that supplies the input (driving) signalto the output amplifier in a radio transmitteror similar device. 2. A small direct-current (dc)generator that supplies direct current to the fieldwinding of an alternating-current (ac) generator.3. See INDUCTION COIL.exciter lamp 1. A concentrated-filament, highintensityincandescent lamp used in soundon-filmrecording and reproduction and in sometypes of electromechanical television. 2. In afacsimile transmitter, the lamp illuminating whatis being scanned.exciter relay In an electromechanical generator,the relay that activates the direct-current (dc)field excitation during machine startup.exciter response 1. A change in the exciter voltageof a motor when the field-circuit resistancechanges. 2. A change in the operating conditionsof a radio frequency exciter, as a result of achange in the impedance at the input of the finalamplifier.exciter unit See EXCITER.exciting current 1. The output current producedby the exciter of a generator (see EXCITER, 2). 2.The field current of a dynamo-type generator. 3.Primary current in an unloaded transformer.exciting power 1. The output power produced byan exciter. 2. The input-signal power required forfull output from a power amplifier. Also calledDRIVING POWER.exciting voltage 1. Input-signal voltage. 2. Theinput-signal-voltage amplitude required for fullrated output from a power amplifier. Also calledDRIVING VOLTAGE. 3. The output voltage producedby an exciter.exciton In a semiconductor or dielectric, a boundelectron-hole pair.excitron A mercury-pool rectifier whose arc isinitiated mechanically (e.g., by means of amagnetic plunger in the tube).exclusion principle The rule that only one particleof a particular kind can occupy a given quantumstate at one time.exclusive-NOR A logic function where the outputis 1 if both inputs are 1 or both are 0 (same). Theoutput is 0 if one input is 0 and the other is 1 (different).Compare EXCLUSIVE OR.exclusive-OR A logic function in which the outputis 1 when the two inputs are different, and is 0when the two inputs are the same.excursion 1. A change in the value of a quantity ina given direction. 2. In an oscillatory system, abody’s moving away from the point of equilibriumor mean position.execution A computer’s performance of the operationsrequired by an instruction.execution time The length of time required for acomputer to complete a designated operation.executive routine In computer operations, a programthat controls and processes other routines.ABA B C00110 01 10 11 0exclusive-ORAlso called monitor program. Compare MONITORSYSTEM.exhaust analyzer An instrument for examiningthe exhaust fumes of an internal combustion engine,to measure the presence of noxious materialsand to evaluate air-to-fuel ratio andcombustion efficiency.exhaustion See EVACUATION.exit 1. In computer operations, the last instructionin a program or program segment, often taking asubroutine back to the main program. 2. To leavea computer application, routine or subroutine.exoskeleton A robot that resembles a suit of armor,and that greatly magnifies the force of physicalmovements. A human operator occupies theinterior. Thus, for example, the operator mightuse the machine to throw a football 2500 yards,or to run 50 miles an hour, or to smash throughwalls. Primarily a tool of science fiction writers,this machine is within the scope of currentrobotic technology.exosphere The extreme outer layer of the earth’satmosphere.exothermic Pertaining to a chemical or electrochemicalreaction in which heat is given off. CompareENDOTHERMIC.exothermic reaction In a chemical reaction, theproduction of positive reaction energy (i.e., kineticenergy is gained). Compare ENDOTHERMICREACTION.exp 1. Symbol for EXPONENTIAL. 2. Abbreviationof EXPERIMENT(AL).expand 1. In communications, to increase thebandwidth of a signal, restoring it to normalbandwidth after it has been compressed. 2. Incommunications, to increase the dynamic rangeof a signal. 3. In computer operations, to restorea file to full or normal size after it has been compressed.4. To widen the scale of a meter. 5. Towiden (or magnify a portion of) the trace of an oscilloscopebeam. Compare COMPRESS.expandable Capable of being built up into largercircuits or systems.C

270 expandable gate • exponential hornexpandable gate In digital logic, a gate that can beprovided with an unlimited number of input linesby electrical interconnection with other gates.expanded memory In personal computer systems,memory beyond the basic 640 kilobytes (640 kb),up to one megabyte (1 MB). This memory residesin integrated circuits (ICs) in the computer, and isnormally volatile (i.e., it is not retained whenpower is removed). Compare EXTENDED MEM-ORY.expanded-scale meter A meter having a scale designedto display a narrow range of values. Sucha meter used for monitoring the 117-V power linemight have a scale reading 100 to 140 V, insteadof a conventional scale beginning at zero.expanded sweep 1. In an oscilloscope, speedingup the deflection of the beam during a selectedportion of the trace. 2. The circuit for the actiondescribed in 1.expander A circuit for increasing the dynamicrange over which a signal or quantity can vary. Atypical example is the volume expander, a devicethat greatly increases the amplitude of strong signalswhile weakening, or having no effect on, signalsof low amplitude.expansion 1. In communications, the process ofincreasing the bandwidth of a signal, restoring itto normal bandwidth after it has been compressed.2. In communications, a process inwhich stronger components are amplified morethan weak ones, restoring a signal to its normaldynamic range after it has been compressed.3. In computer operations, the restoration of a fileto full or normal size after it has been compressed.4. The widening of a meter scale. 5. The wideningor magnification of an oscilloscope trace. CompareCOMPRESS.expansion chamber A cloud chamber for viewingthe paths of radioactive particles. It consists of aclosed glass cylinder containing humid air and apiston. An electrostatic field is applied throughthe cylinder, the piston is pulled quickly, and thevolume of the chamber expands. The temperatureinside falls below the dew point, a cloud isformed, and droplets of water condense on ions,making their paths visible for observation or photographythrough the cylinder walls.expansion ratio In communications, the inverse ofCOMPRESSION RATIO.expansion time For an expansion chamber, theinterval during which expansion occurs. Theinterval is kept short to ensure that the temperaturewill drop low enough for vapor condensation,and to minimize the possibility ofcontinuing gas motion distorting the track of aparticle.expectation In probability theory, the middlevalue (average or mean) of a random variable.expendable A component or system that, for economy,is best discarded instead of repaired when itfails. Also called DISPOSABLE COMPONENT.experiment One or a series of carefully plannedtests carried out under controlled conditions toobtain data or to check performance.experimental chassis See ELECTRONIC CHASSIS.experimental model A prototype of an electroniccircuit or device, produced solely for operationaltests or as a model against which theory and designcan be checked.experimental service A special, nonamateur radioservice intended for on-the-air testing of newmethods and equipment.experimental station A station specially licensedto operate on specific frequencies in the experimentalservice.expert system Also called rule-based system. Aform of artificial intelligence (AI) that allows acomputer or smart robot to act as a highly talentedspecialist in a specific field. An example isthe use of a computer to help a physician diagnosea complex disease. A smart robot might beused as a surgical assistant.exploring coil A pickup coil for sensing a signal ormagnetic field. Sometimes called a sniffer.exploring electrode 1. A sampling electrode sealedin a discharge tube for measuring ionization atthe point of insertion. 2. Broadly, a test probe.explosion-proof device A device that is housedand operated so that its sparking, heating, orproduction of radiant energy will not cause materialsin the environment to explode.exponent A number written as a superscript indicatingthe power to which another number (calledthe base) is to be raised. For example, 2 2 is thesquare (second power) of 2; x 3 is the cube (thirdpower) of x.exponential 1. A base (such as the natural numbere) modified by an exponent. 2. Related to achange in value as determined by an exponent.Thus, using increments for x in the equation y =e x produces an exponential curve.exponential curve A curve based on powers of anumber (such as for y = e x ). Also see EXPONEN-TIAL, EXPONENTIAL DECREASE, and EXPO-NENTIAL INCREASE.exponential damping Damping action describedby an exponential curve.exponential decay See EXPONENTIAL DE-CREASE.exponential decrease The continuous reductionin the value of a quantity, according to the equationy = e -x , which depicts the natural decaycurve.exponential function A function, such as f (x) = e x ,that varies exponentially. See, for example, EX-PONENTIAL DECAY, EXPONENTIAL GROWTH,and EXPONENTIAL SERIES.exponential horn A horn of circular or rectangularcross section, whose cross-sectional area S at anypoint x feet along its axis is given by the formulaS = S 0 e mx , where S 0 is the cross-sectional area atthe throat, e is the natural logarithm base

exponential horn • external damping device 271(approximately 2.71828), and m is the horn flaringconstant.exponential increase The continuous increase ofa quantity, according to the equation y = e x ,which depicts the natural growth curve.exponential line A transmission line whose characteristicimpedance varies exponentially with itselectrical length.exponential quantity A quantity involving an exponential(e.g., 3e x ).exponential series A mathematical series basedon exponential expressions. Example: e x = 1 + x +(x 2 /2!) + (x 3 /3!) + (x 4 /4!) + . . .exponential sweep In cathode-ray-tube (CRT) devices,such as oscilloscopes, a beam sweep thatstarts fast and slows exponentially.exponential transmission line See EXPONEN-TIAL LINE.exponential waveform Any waveform in which therate of change in the amplitude is directly or inverselyproportional to the instantaneous amplitude.The absolute value of the derivative of sucha waveform is equal to the absolute value of theinstantaneous amplitude, multiplied by a constantthat depends on the amplitude units.exposure 1. The total amount of radiation receivedin a given area, or by a given sample, or by a person,over a specified length of time. 2. The extentto which a photographic film has been darkenedor otherwise modified by visible light, infrared, ultraviolet,or X rays.exposure meter 1. A usually simple instrumentfor measuring light intensity—especially for photographicpurposes. A common form consists of aself-generating photocell connected to a directcurrentmicroammeter. 2. A device that indicatesthe amount of ionizing radiation that has been receivedover a given period of time.PhotovoltaiccellSensitivityexposure meterMeterexpression control A volume control in an electronicorgan.extended double Zepp antenna See DOUBLE-EXTENDED ZEPP ANTENNA.extended memory In personal computer systems,memory beyond the first megabyte (1 MB). Thereis no limit in theory to the extent of this memory,although it is limited by current technology. Usedin high-level programs—especially those involvinggraphical applications, artificial intelligence,or intensive calculations. Resides in integratedcircuits (ICs) in the computer, and is normallyvolatile (i.e., it is not retained when power is removed).Compare EXPANDED MEMORY.extended octaves Audio-frequency tones above orbelow the normal range of an electronic musicalinstrument. Special circuits must be added tomake the extended octaves available.extended play Pertaining to a recorded phonographdisc that provides a longer playing timethan conventional discs of the same size andrecording speed.extender A substance added to an encapsulant tomake it go further.extensimeter See EXTENSOMETER.extension cable A flexible, low-capacitance (usuallyconcentric) cable for connecting part of onecircuit to part of another. Extension cables areavailable with a variety of end connectors.extension cord A flexible power cord having amale plug on one end and female receptacle onthe other.extension loudspeaker An auxiliary loudspeakerserving areas in which the main speakers can’t beadequately heard.extensometer An instrument used to measuresmall amounts of expansion, contraction, or deformation.exterior label On a diskette or tape cartridge usedfor computer data storage, a written identificationon the housing or cartridge, as opposed to the label,which is recorded on the diskette or tape itself.external armature In a dynamo-type machine, anarmature that rotates around the outside of thefield magnets, as opposed to the usual (inside) arrangement.external capacitor A high-value capacitor connectedexternally to an oscillator or sweep generatorto lower its frequency.external circuit A circuit or subcircuit connectedand external to a main equipment.external controls 1. Control devices that are connectedto, but operated away from, a main circuit.2. Manual or screwdriver-adjusted controlsthat are mounted on the panel of an equipment,as opposed to those mounted in the case or behindthe panel.external critical damping resistance The value ofexternal resistance that must be connected to agalvanometer or other meter to produce criticaldamping.external damping device A resistor or shortcircuitingbar connected temporarily between theterminals of a meter to keep its movement immobileduring transportation.

272 external feedback • extremeexternal feedback Negative or positive feedbackthrough a separate path outside of and aroundthe main circuit. Example: negative feedbackthrough a resistance-capacitance (RC) path betweenthe output terminals and the input terminalsof an amplifier.Externalfeedbackexternal feedbackexternal impedance Load impedance (i.e., animpedance connected to the output terminals of agenerator or amplifier).external load See EXTERNAL IMPEDANCE.external loudspeaker See EXTERNAL SPEAKER.externally caused chatter In a relay, contactchatter caused by mechanical vibration outsideof the relay.externally caused failure Failure of a circuit orcomponent resulting from unfavorable environmentalfactors.external memory In computer operations, a memoryunit outside of the computer mainframe.external power supply A power supply unit situatedapart from the powered equipment. Suchseparation is helpful in eliminating the disturbingeffects of heat, hum, and vibration associatedwith internal power units.external Q For a microwave tube, the quantity1/(1/Q 1 + 1/Q 2 ), where Q 1 is the loaded Q and Q 2is the unloaded Q.external S-meter A signal-strength meter connectedto a receiver, but not installed in its panel.external speaker A loudspeaker that doesn’t sharean enclosure with an amplifier, receiver, or otherdevice that drives it. Such isolation is helpful ineliminating the undesirable effects of vibrationand acoustic feedback.external storage In computer operations, storagemedia (such as magnetic diskettes or tapes) thatare outside of the computer.extinction potential See DEIONIZATION POTEN-TIAL.extinction voltage See DEIONIZATION POTEN-TIAL.Extra-class license An amateur-radio license thatconveys all available amateur operating privilegesin the United States. The highest class of amateurlicense.extract 1. To remove a signal or quantity fromsome product containing it, or from its source.Examples: extracting a fifth harmonic from acomplex signal, extracting the direct-current (dc)component from a signal containing both alternatingcurrent (ac) and dc. 2. To derive a factor(e.g., to extract a root). 3. To separate certainclasses of information from an aggregate of information.extract instruction In computer operations, theinstruction to generate a new word by the serialarrangement of designated segments of specifiedwords.extractor 1. A circuit or device for removing a signal(or a signal component) from another circuitor device. A demodulator probe, for example, extractsthe modulation from a modulated signal.2. A device for removing used active devices froma circuit board. Such extractors can also employheat to desolder, as well as remove the devices.extraneous component A usually undesired inherenteffect that results from the physicalnature of a component or device. Examples:distributed capacitance of a coil, internal inductanceof a capacitor.extraneous emission Undesired emission from atransmitter (e.g., excessive harmonics).extraneous response The unintended response ofa circuit or device (e.g., image response in a superheterodynecommunications receiver).extraneous root In the solution of an equation derivedfrom another equation, one or more rootsthat satisfy the derived equation but not the originalone.extraneous signal A superfluous and potentiallyinterference-causing signal.extranuclear Outside the nucleus of an atom.extraordinary ray Of the two rays resulting fromthe double refraction of electromagnetic waves,the one that does not follow the usual laws of refraction.Also see X WAVE.extraordinary wave See X WAVE.extrapolar 1. Outside of electrical or magneticpoles. 2. Not between electrical or magnetic poles.extrapolation Estimation of values beyond therange of available data. An example is the extensionof a curve beyond its final plotted point to determinea value for a variable. There is alwayssome margin for error, which increases as theprocess is extended further and further beyondthe range of actual data values. Commonly doneby computers (e.g., prediction of the probablepath of a hurricane 12, 24, 36, and 48 hours inadvance).extrared See INFRARED.extraviolet See ULTRAVIOLET.extreme 1. The lowest or highest value of a

extreme • E zone 273quantity. 2. The lowest or highest point of the dependentvariable in the range of a function. 3. Anunusual value for a parameter (e.g., temperatureextreme and pressure extreme).extremely high frequency Abbreviation, EHF. Afrequency near the upper limit of the radio-frequencyspectrum—especially one in the 30- to300-GHz band.extremely low frequency 1. Abbreviation, ELF.Pertaining to a signal or current within the audiofrequency(AF) range, but not used for audio applications.2. Electromagnetic emissions from acathode-ray tube (CRT), resulting from the currentsin the deflecting coils and/or electronbeam. 3. The 60-Hz electromagnetic field generatedby utility power lines and wiring.extrinsic base-resistance/collector-capacitanceproduct Units: seconds, milliseconds, and microseconds.For a bipolar transistor, the productR B C C , where R B is the base resistance and C C isthe collector capacitance. This product is a timeconstant that determines the high-frequency operatinglimit of the transistor.extrinsic conductance For a material, the conductanceresulting from impurities or such externalfactors as environmental conditions.extrinsic properties For a semiconductor material,properties resulting from doping (e.g., alteredresistivity or majority/minority carrier differentiation).Also see EXTRINSIC SEMICONDUCTOR.extrinsic semiconductor A semiconductor material,such as germanium or silicon, to which acontrolled amount of a suitable impurity materialhas been added to give the semiconductor a desiredresistivity and polarity. Compare INTRINSICSEMICONDUCTOR.extrinsic transconductance Symbol, g m . For abipolar transistor, the first derivative of collectorcurrent, with respect to base-emitter voltage. It isthe ratio of a small change in collector current(dI C ) to the small change in base-emitter voltage(dV BE ) that produced it, collector voltage beingconstant; g m = dI C /dV BE .extrusion The process of forming a material suchas metal or plastic, by forcing it through dies.Many pieces of electronic hardware are mass producedin this manner. Examples are insulatingrods and tubes, metal cans, and metal tubing.eye-in-hand system In robotics, a scheme thatuses a vision system, servo, and microprocessorto precisely manipulate an END EFFECTOR, suchas a robot gripper (“hand”). A camera (the “eye”) iscontained in the end effector itself, and is designedto work at close range (i.e., approximatelyone meter down to a fraction of a millimeter).eyelet connection A connection made by fasteningconductors together with an eyelet or by solderingleads or pigtails to an eyelet.eyepiece A small lens system for viewing an oscilloscopescreen through a camera setup.E Z Symbol for voltage drop across an impedance.E zone A portion of the earth including most of theeastern hemisphere. When propagation forecastsare made, this region is one of three longitudezones specifie

F 1. Symbol for FORCE. 2. Symbol for FLUORINE.3. Abbreviation of FAHRENHEIT. 4. Abbreviationof FARAD. 5. Abbreviation of FERMI. 6. Symbolfor FOCAL LENGTH. 7. Symbol for FUSE.8. Symbol for FARADAY CONSTANT.f 1. Abbreviation of FEMTO. 2. Symbol for FRE-QUENCY. 3. Symbol for FUNCTION.F 0 Symbol for DAMPING FACTOR.F1 layer The lower part of the ionosphere’s F RE-GION. Also called F1 region.F2 layer The upper part of the ionosphere’s F RE-GION. Also called F2 region.fA Abbreviation of FEMTOAMPERE.fabrication tolerance The amount of variationthat can be tolerated in the manufacture of components.Fabry-Perot interferometer A resonant cavity, oftenused with lasers, that has mirrors at eachend; the interferometer produces the opticalequivalent of standing waves.face 1. A flat crystal surface whose orientation canbe expressed as its position relative to otherfaces. 2. The viewer’s side of a screen. 3. Thescale part of a meter.face material In a tape recorder, the plastic usedto coat the face of a head.face-parallel cut See Y-CUT CRYSTAL.face-perpendicular cut See X-CUT CRYSTAL.face side The side of pressure-sensitive insulatingtape that is coated with adhesive.facom A radionavigation system that operates bymeans of phase comparison at low frequencies.Effective over long distances and under poor conditions.facsimile Also called fax. The transmission and reception,through the medium of radio or by wire,of permanent pictures, writing, and other graphicmaterial.facsimile receiver The complete device or systemthat selects, amplifies, and demodulates a picturesignal received up from the air, wires, or cable,and uses the elements of this signal to reproducethe picture. Also see FACSIMILE.facsimile recorder The machine that puts a transmittedfacsimile image on paper.facsimile transmitter The complete device or systemthat generates signals depicting graphic material(pictures, writing, printing, etc.) and sendsthem to a distant point via cable, wire lines, or radiofor subsequent reproduction. Also see FAC-SIMILE.factor1. A data element that is an operand in anarithmetic operation. 2. To find the two or morenumbers whose product is the number being factored.3. One of two or more numbers whoseproduct is the number being factored.factorialSymbol, !. For an integer n, the product ofall positive integers up to and including n. Thus,5! = 1 × 2 × 3 × 4 × 5 = 120. The term n! is read “nfactorial.”factor of merit See FIGURE OF MERIT.factor of safety See SAFETY FACTOR.fade in To gradually increase an audio or video signal—especiallyfor recording.fade out 1. To gradually decrease an audio or videosignal—especially for recording. 2. The completedisappearance of a radio communications signal.See FADING.fader1. In sound amplification systems, an attenuatorcircuit that enables the operator to fade outone signal and fade in another. Ordinarily, afader does not provide mixing action. 2. In an au-Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

fader • fan-out 275tomotive high-fidelity sound system, a controlthat adjusts the volume of the front speaker setand rear speaker set. Usually, this is a singleknob; increasing the front volume decreases therear volume, and vice-versa.fading 1. Repeated increases and decreases of radiocommunications signal amplitude at the receptionpoint. Fading of a radio wave results frommultiple propagation paths from transmitter toreceiver, causing the received waves to arrive inconstantly varying phase relationships. 2. In acell or battery power supply, a gradual loss ofpower-delivering capability that occurs duringthe discharge cycle.TXEarthfadingIonizedlayerRXcent to 10 percent of its peak amplitude. CompareRISE TIME.false add A logic add (i.e., addition without carries).false alarm 1. Improper operation of an electronicsecurity system, resulting in actuation of thedevice when no breach of security has occurred.2. In radar, the presence of a false echo thatcauses the attendant circuits or personnel to actas though an enemy target is present.false error A condition in which a computer systemerroneously signals the existence of an error.false precision See MISLEADING PRECISION.false retrieval The incorrect specification of criteriafor information to be selected for retrieval sothat an unwanted item of data is selected. Alsocalled false drop.family Any group of components, circuits, ratings,or characteristics, classed together because ofsome common or analogous feature or application.Examples: IC family, family of curves, andfamily of equations.family of curves A group of curves plotted on thesame axes, that depict the performance of a circuitor device at several levels of a third parameter (e.g.,curves showing transistor collector current vs. collectorvoltage for several levels of base current).Collectorcurrent,milliamps8_6 _4 _2 _0 ____0 51015Collector voltage, voltsfactory automation The use of robotic devices, tothe greatest extent possible, as laborers in manufacturingplants.Fahnestock clip A flat, sheet-metal spring clip forholding a wire (usually in a temporary breadboardsetup).Fahrenheit scale A temperature scale on whichthe freezing point of water is 32 degrees, and theboiling point of water is 212 degrees. CompareABSOLUTE SCALE and CELSIUS SCALE.failsafe Pertaining to devices or circuits that, uponfailure, cause no damage or serious malfunction.failsoft In a computer, a system in which operationis maintained—even in the event of partial failure.Efficiency is reduced but the computer doesnot completely shut down.failure The condition wherein a circuit, system, ordevice is not operating correctly.failure analysis 1. The process of determining thefailure rate for a component, system, or device.2. The process of determining the cause of afailure.failure mode The particular way in which a failureof equipment or a method occurs.failure unit A unit of machine or device failure:one failure per billion (10 9 ) hours of operation.fall-in The time when synchronous speed is attainedin a synchronous motor.falling characteristic A NEGATIVE RESISTANCEcharacteristic.fall time 1. Decay time. 2. The time required forthe amplitude of a pulse to decrease from 90 perfamilyof curvesBasecurrent,microamps15010050250_fan antenna See DOUBLE-V ANTENNA.fan-in 1. A number of inputs entering a commoninput terminal. 2. In digital computer operations,the number of inputs that can be accommodatedby a logic circuit. Compare FAN-OUT.fan-in circuit A circuit having a number of inputlines entering a common input point. Also seeFAN-IN, 1.fan-out 1. One common output terminal feeding anumber of output lines. 2. In digital computer

276 fan-out • fatigueoperations, the number of outputs that can be fedby a logic circuit. Compare FAN-IN.fan-out circuit A circuit in which a number of outputlines leave a common output terminal. Alsosee FANOUT, 1.fantasy robot A robot as portrayed in science fictionor fantasy. Such robots are usually, but notalways, androids (that is, they have humanoidform). Some fictional robot characteristics arelater realized. Science fiction can even give roboticistsideas for future designs.farad (Michael Faraday, 1791–1867) Abbreviation,F. The basic unit of capacitance. A capacitor hasa capacitance of 1 F when a charge of 1 volt persecond across the capacitor produces a current of1 ampere through it.faraday An electrical quantity approximately equalto 9.65 × 10 4 coulombs; it is the quantity of electricityrequired in electrolysis to free 1 gramatomic weight of a univalent element. The equivalent,and preferred, unit is the COULOMB. Alsocalled Faraday constant.Faraday cage See ELECTROSTATIC SCREEN.Faraday constant See FARADAY.Faraday cylinder A cylindrical metal shield placedaround electrical equipment or circuits to preventelectromagnetic fields from affecting the equipmentor circuits.Faraday rotation 1. A change in the polarization ofan electromagnetic wave as it passes through amedium. 2. Constant and random fluctuations inthe polarization of radio signals as they passthrough the earth’s ionosphere. This phenomenonaffects signals having linear polarization at frequencieswell below 10 GHz. It has little or no effecton circularly polarized signals, or on signals atfrequencies above 10 GHz. It can be a problemwith some satellite communications links.Faraday effect See MAGNETO-OPTICAL ROTA-TION.Faraday’s disk dynamo See DISK DYNAMO.Faraday shield See ELECTROSTATIC SCREEN.Faraday’s law The voltage induced in a conductormoving in a magnetic field is proportional to therate at which the conductor cuts the magneticlines of flux.Faraday’s laws of electrolysis 1. In electrolysis,the mass of a substance liberated from solution isproportional to the strength and duration of thecurrent. 2. For different substances liberated bythe same current in a certain time, the massesare proportional to the electrochemical equivalentsof the substances. Also see ELECTRO-CHEMICAL EQUIVALENT; ELECTROLYSIS, 1;and ELECTROLYTE.faradic current The lopsided alternating currentproduced by an induction coil.faradmeter An alternate term for MICROFARADMETER.far field 1. The region beyond the near field of anantenna (see NEAR FIELD, 1). 2. The region beyondthe near field of a loudspeaker (see NEARFIELD, 2).far infrared Also called far IR. The lower-frequencyportion of the infrared (IR) spectrum.farming robot A robot that performs labor in anagricultural setting. Examples: fruit-pickingrobot, field-watering robot, cow-milking robot.Such machines are usually overseen by a centralcomputer, via which the farmer can monitor andcontrol the robots’ actions.far zone See FAR FIELD, 1, 2.fast access storage In a computer memory, thesection from which information can be mostquickly accessed, depending on the relative speedof other system devices.fast-break, fast-make relay A relay that opensand closes rapidly.fast-break, slow-make relay A relay that opensrapidly and closes slowly.fast charge The rapid charging of a rechargeablecell or battery, particularly of a nickel-cadmium(NICAD) or nickel-metal-hydride (NiMH) device.fast diode See COMPUTER DIODE.fast drift The rapid change of a quantity or setting,usually in one direction. Compare SLOW DRIFT.fast-food robot A robot that prepares and/orserves items in a fast-food establishment.Robots have not yet gained wide acceptance inthis setting, mainly because of technical difficultiesand prohibitive cost. Another problem isthat some customers are put off or intimidatedby robots.fast-forward Abbreviation, FF or FFWD. In a taperecorder, a mechanism for running the tapethrough the machine rapidly.fast groove The informationless groove betweentracks on a disk recording.fast-make/fast-break relay A relay that closesand opens rapidly.fast-make, slow-break relay A relay that closesrapidly and opens slowly.fast-forward playback In a videotape recorder, theplaying back of the tape at faster than real-lifespeed. It allows the viewer to move quickly aheadin a program, and also to watch the images so asto know when to resume normal replay.fast-reverse playback In a videotape recorder, theplaying back of the tape rapidly backwards. It allowsthe viewer to move quickly back in a program,and also to watch the images so as to knowwhen to resume normal replay.fast time constant 1. The property of respondingquickly to changes in input parameters. 2. Inradar, a method of defeating attempts at jammingby modification of the receiving circuitry.fathometer See ACOUSTIC DEPTH FINDER.fathom 1. To measure the depth of a body of water,as in the use of sonar for this purpose. 2. A unitof length (distance) equal to six feet.fatigue 1. The degradation of the performance ofcircuits or materials with time. 2. The tendency of

fatigue • feedback factor 277bodies and materials to weaken, deform, or fractureunder repeated strain.fault 1. A defective point or region in a circuit ordevice. 2. A failure in a circuit or device.fault current 1. A momentary current surge. 2. Aleakage current.fault finder A troubleshooting instrument or device(e.g., a multimeter).fault resilience 1. A design scheme for an electronicor computer device or system so that if acomponent or circuit fails, the system will continueto operate, although perhaps at reduced efficiency.The operator is notified of the problem sothat it can be repaired with minimal downtime. 2.In a computer system, the property of being asnearly sabotage-proof as possible.fault tolerance Total redundancy in an electronicor computer system so that if a component or circuitfails, the system will continue to function atfull efficiency. Every component has a backupthat automatically takes over in case of failure.The operator is notified of the problem, so the defectivepart or circuit can be replaced while itsbackup keeps the circuit working continuously at100-percent capacity.Faure plate A storage battery plate consisting of alead grid containing a chemical electrolytic paste.fax Abbreviation of FACSIMILE.fc Abbreviation of FOOT-CANDLE.f c Abbreviation of CARRIER FREQUENCY.FCC See FEDERAL COMMUNICATIONS COMMIS-SION.f co Abbreviation of CUTOFF FREQUENCY.F connector A type of antenna feedline connectionespecially common on television receivers andvideocassette recorders.F display See F SCAN.FDM Abbreviation of frequency-division multiplex.FE Abbreviation of FERROELECTRIC. See FERRO-ELECTRICITY.Fe Symbol for IRON.feasibility study The procedures for evaluatingthe potential gains in applying a computer systemto a job or to an organization’s process, or inmodifying or replacing an existing system.FEB Abbreviation of FUNCTIONAL ELECTRONICBLOCK.Federal Communications Commission Abbreviation,FCC. Established in 1934, the U.S. Governmentagency that regulates electronic communications.The FCC succeeded the Federal RadioCommission (FRC), which was established in1927; the FRC succeeded the Radio Division ofthe Bureau of Navigation in the Department ofCommerce, whose jurisdiction over radio beganin 1912.feed 1. To supply power or a signal to a circuit ordevice. 2. The method of supplying such a signalor power. See, for example, PARALLEL FEED andSERIES FEED. 3. To cause data to be enteredinto a computer for processing.feedback 1. The transmission of current or voltagefrom the output of a circuit or device back to theinput, where it interacts with the input signal tomodify operation of the device. Feedback is positivewhen it is in phase with the input, and is negativewhen it is out of phase. 2. To input theresult at one point in a series of operations to anotherpoint; the method allows a system to monitorits actions and make necessary corrections.InputFeedback(negative)feedback, 1.+12 VOutputfeedback amplifier 1. An amplifier whose performance(especially frequency response) is modifiedby means of positive, negative or bothpositive and negative feedback. 2. An amplifierplaced in the feedback path of another circuit toincrease the amplitude of feedback.feedback attenuation 1. In an operationalamplifiercircuit, the attenuation in the voltagefrom output to input. 2. In an audio-frequency orradio-frequency amplifier circuit, the reduction offeedback by electronic means.feedback bridge A bridge circuit in the feedbackchannel of an amplifier or oscillator.feedback capacitance 1. A capacitance throughwhich feedback current is coupled from the outputto the input of a circuit or system. 2. The interelectrodecapacitance of a vacuum tube.feedback control 1. The variable component (potentiometeror variable capacitor) used to adjustthe level of feedback current or voltage. 2. Thecontrol of circuit performance by means of feedback.feedback cutter A device used for the purpose ofcutting grooves in phonograph disks. Feedback isused to provide a flat frequency response.feedback factor For a feedback amplifier, thequantity 1 – bA, where A is the open-loop gain ofthe amplifier and b is the FEEDBACK RATIO.

278 feedback input current • feedthrough terminalfeedback input current In a feedback network,the current drawn by the feedback input. Thiscurrent affects the design parameters of a network.feedback loop The part of a circuit that providescontrolled feedback in an operational-amplifiercircuit.feedback oscillator A circuit in which oscillationis obtained by feeding a portion of the output ofan active amplifying device back to the input circuitby inductive coupling. Also called tickler oscillator.feedback path A path over which feedback, eitherpositive or negative, can occur in a circuit. Thefeedback can be intentionally produced, or it canbe undesirable.feedback percentage Symbol, n. In a feedback circuit,the percentage of output voltage that is fedback; n = 100V f /V o , where V f is the feedback voltageand V o is the open-loop output voltage. CompareFEEDBACK RATIO.feedback ratio For a feedback system, the ratioV f /V o , where V f is the voltage that is fed backand V o is the open-loop output voltage of thesystem.feedback rectifier See DIODE FEEDBACK RECTI-FIER.feedback regulator In a controlled-feedback circuit,the device that determines the amount offeedback.feedback resistance 1. The internal base resistanceof a point-contact transistor. 2. The resistancein a feedback loop.feedback transfer function The transfer functionof a feedback loop exclusively.feedback winding A special winding on a magneticamplifier or saturable reactor, for the introductionof feedback currents.feeder 1. A conductor or set of conductors thatcarries electric power from one point to another.2. The transmission line connecting a transmitterto an antenna.feeder cable 1. A communication cable running ina primary route from a central station (or in a secondaryroute from a main feeder cable) as ameans of making connections to distribution cables.2. In a cable television system, the cablecarrying transmission from the head end to thetrunk amplifier. Also called TRUNK CABLE.feeder loss Loss of energy resulting from resistancein, or radiation from, feeder lines.feeding In character recognition, a system inwhich documents go into the transport of a characterreader at a steady, specified rate.feed pitch The distance between feed holes.feed reel The tape supply reel of a tape recorder.feedthrough 1. The usually undesirable transmissionof a signal through a circuit without beingprocessed by the circuit, because of unavoidablecapacitive coupling, for example. 2. Contractionof FEEDTHROUGH COMPONENT.feedthrough capacitor A capacitor whose designis like that of a feedthrough terminal; it ismounted in a hole in a chassis. The center screwor wire is the “high” terminal of the capacitor, towhich connections can be made above or belowthe chassis. The body of the device is the “low”terminal of the capacitor; it is soldered to thechassis or secured with a nut.NutsInsulatingmaterialChassis wallMetal flangefeedthrough capacitorPanel orchassisfeedthrough insulatorCenterconductorfeedthrough component A passive device permanentlyinstalled in a panel or plate (e.g., aFEEDTHROUGH CAPACITOR or FEED-THROUGH INSULATOR).feedthrough insulator An insulator mountedtightly in a hole in a wall or chassis, and providedwith a center hole for a lead.ThreadedshaftNutsfeedthrough terminal A terminal mounted tightlyin a hole in a chassis or wall; it consists of ascrew going through a feedthrough insulator.Connections can be made to either end of thescrew.

FE-EL • ferrite limiter 279FE-EL Abbreviation of ferroelectric-electroluminescent.feeler 1. A wire or blade contact (e.g., a finger thatsenses holes in a punched card). 2. The wire portionof a point-contact diode.Felici mutual-inductance balance An inductivenull circuit for determining mutual inductance(M x ) in terms of a standard mutual inductance(M s ). The secondary coils of two mutual-inductancecircuits are connected in phase opposition.The standard mutual inductor, which is variable,is adjusted for null. At null, M x = M s .GeneratorM xPrimary Secondary NulldetectorSecondaryPrimaryM sFelici mutual-inductance balancefemale plug A plug whose contacts are separatedby a recess into which the prongs of a matingmale plug are inserted. Compare HERMA-PHRODITE PLUG and MALE PLUG.femto- Abbreviation, f. A prefix meaning quadrillionth(10 –15 ).femtoampere Abbreviation, fA. A unit of extremelylow current; 1 fA equals 10 –15 A.femtofarad Abbreviation, fF. A unit of extremelylow capacitance; 1 fF equals 10 –15 F.femtovolt Abbreviation, fV. A unit of extremely lowvoltage; 1 fV equals 10 –15 V.fence A system or string of early warning radarstations.Fermat’s principle The principle that the path of aray of radiant energy between two points in anymedium is the shortest distance between thosepoints in that medium. This path is also the pathof least propagation time. This might not necessarilybe a straight line. On a flat plane, the pathof least time between any two points is always astraight line, assuming constant velocity of propagation.However, on a sphere, the path of leasttime between two points is represented by a greatcircle.fermi Abbreviation, F. An extremely small unit oflength and wavelength, equal to one quadrillionth(10 –15 ) of a meter.Fermi-Dirac distribution function The probabilitythat an electron will be in a certain quantumstate under conditions of thermal equilbrium.This is determined as the probability that theelectron will be in a given energy band at a particularinstant of time.fermium Symbol, Fm. A radioactive metallic elementthat is artificially produced. Atomic number,100. Atomic weight, 257.ferpic Acronym for ferroelectric ceramic picture device.An image-storing device containing a photoconductivefilm, transparent electrodes, and aferroelectric ceramic, in layers.ferreed A form of magnetic switching device, similarto a reed relay, that maintains its position indefinitelywithout the need for a continuouscurrent.ferret A vehicle or craft equipped for determiningthe locations of enemy radar transmitters.ferri- A prefix used to denote magnetic properties.ferric oxide Formula, Fe 2 O 3 . A red oxide of ironused to coat magnetic recording tape.ferristor A high-frequency magnetic amplifier usinga ferroresonant circuit.ferrite A high-resistance magnetic material consistingprincipally of ferric oxide and one or moreother metals. After being powdered and sintered,ferrites exhibit low eddy-current loss at high frequenciesand make ideal core material for inductorsand switching elements. Also used intelevision deflection yokes and in miniature antennas.Also see FERROSPINELS.ferrite antenna See FERRITE-ROD ANTENNA.ferrite bead 1. A magnetic storage device in theform of a bead of ferrite powder fused onto thesignal conductors of a memory matrix. 2. A tinyring of ferrite that can be slipped over a wire orcable to choke off radio-frequency (RF) currents.Ferritebeadferrite beadCableferrite core A coil or switching-element core madefrom a ferrite; specifically, in a core memory, asmall magnetic toroid that can retain its polaritywhen charged by a pulse.ferrite core memory A magnetic memory in whichferrite cores are interconnected by a network ofinput and output wires.ferrite isolator A microwave device that permitsenergy to pass with negligible loss in one directionthrough a waveguide or coaxial line, while absorbingenergy passing in the opposite direction.ferrite limiter A device used in the antenna circuitor front end of a receiver, to prevent overloadwhile maintaining a linear response. Used mostlyat ultra-high and microwave frequencies.

280 ferrite loopstick • fetchferrite loopstick See FERRITE-ROD ANTENNA.ferrite memory A static memory using ferritecores. See CORE MEMORY.ferrite-rod antenna Also called loopstick antenna.A small antenna that can be used for wireless receptionat frequencies below approximately20 MHz. This antenna consists of a coil woundon a solenoidal, high-permeability, powderedironcore, usually less than 20 centimeters (cm)long and 1 cm in diameter. A series or parallelcapacitor, in conjunction with the coil forms atuned circuit. The operating frequency is determinedby the resonant frequency of the inductance-capacitance(LC) combination. Responseis maximum off the sides of the coil, and a sharpnull occurs off the ends. This antenna has narrowbandwidth. The null can be oriented to minimizesystem response to undesired local signalsor humanmade noise. Compare SMALL LOOPANTENNA.ferrite switch A device that regulates the flow ofpower through a waveguide. The electric-fieldvector is rotated, resulting in a high degree of attenuationwhen actuated, but little or no attenuationwhen not activated.ferroelectric 1. Producing ferroelectricity. 2. A ferroelectricmaterial.ferroelectric amplifier See DIELECTRIC AMPLI-FIER.ferroelectric capacitor A capacitor in which a ferroelectricmaterial is the dielectric.ferroelectric cell See FERROELECTRIC CAPACI-TOR.ferroelectric crystal A crystal of ferroelectric material.ferroelectric flip-flop A flip-flop based on the hysteresisof a ferroelectric capacitor. Compare FER-RORESONANT FLIP-FLOP.ferroelectricity Electric polarization in certaincrystalline materials. The effect is analogous tothe magnetization of a ferromagnetic material bya magnetic field.ferroelectric-luminescent Pertaining to a ferroelectriccell that emits light.ferroelectric material A nonlinear dielectric materialcapable of producing ferroelectricity. Examples:barium titanate, barium strontium titanate,potassium dihydrogen phosphate, guanadinealuminum sulfate hexahydrate (GASH), Rochellesalt, and triglycene sulfate.ferromagnetic 1. Pertaining to a substance thatconducts a magnetic field with relative ease. 2.Pertaining to a material in which a magnetic-fieldchange causes a voltage, which in turn results ina measurable current flow.ferromagnetic-core inductor A coil of wire designedto introduce inductive reactance into a circuitor system, wound around a core consisting offerromagnetic material that greatly increases theinductance for a given number of turns. Withproper design and choice of core material, the Qfactor (selectivity attainable) can be extremelyhigh. The core confines much of the magneticflux within itself. When the coil current exceedsa certain level, core saturation occurs, and furtherincreases in the current will not produce a correspondingincrease in magnetic flux. This decreasesthe effective inductance, and reduces theefficiency because power is dissipated as heat inthe core.ferromagnetic material A substance that concentratesmagnetic lines of flux relative to their concentrationin free space. Iron, powdered iron, andferrite are common examples.ferromagnetic resonance The point at which thepermeability of a magnetic material peaks at amicrowave frequency.ferromagnetic spinels Highly permeable and resistiveceramic-like materials. The low eddycurrentlosses and high permeability of thesematerials suit them for use as cores in radiofrequency(RF) transformers and inductors. Alsosee FERRITE.ferromagnetic tape Magnetic tape used for windingclosed transformer cores.ferrometer An instrument for testing hysteresisand permeability in steel and iron.Ferron detector See IRON-PYRITES DETECTOR.ferroresonant circuit An inductance-capacitance(LC) circuit in which the coil is a saturable reactor.Because of coil nonlinearity, the circuit is resonantat only one value of alternating-current (ac)voltage, and exhibits both negative resistanceand bistable operation.ferroresonant counter A digital counter using ferroresonantflip-flops, rather than semiconductordevices.ferroresonant flip-flop A flip-flop using one or twoferroresonant circuits instead of semiconductordevices. See BISTABLE MULTIVIBRATOR. CompareFERROELECTRIC FLIP-FLOP.ferroresonant shift register A shift register usingferroresonant circuits instead of semiconductordevices.ferrosoferric oxide See MAGNETITE.ferrospinels See FERROMAGNETIC SPINELS.ferrous Pertaining to a substance that containsiron and is magnetizable.Ferroxcube A nonmetallic ferromagnetic materialhaving high permeability and resistivity, and aCurie point near room temperature. These characteristicsmake the material suitable for thecores of radio-frequency (RF) inductors andtransformers, and for high-frequency magneticshields.Fessenden oscillator In underwater communications,a transmitter of acoustic waves.FET Abbreviation of FIELD-EFFECT TRANSISTOR.fetch An operation in a computer run in which thelocation of the next instruction is taken frommemory and changed if necessary; it then goes tothe control register.

FET current meter • field coil 281FET current meter An ammeter, milliammeter, ormicroammeter having a self-contained amplifierthat uses field-effect transistors. Also see ELEC-TRONIC CURRENT METER.FET op-amp 1. An operational amplifier composedof field-effect transistors and associated components.2. An operational amplifier having a fieldeffecttransistor in its input stage.FET voltmeter A voltmeter using a field-effecttransistor amplifier for high-impedance input.Also see ELECTRONIC VOLTMETER.fiberoptics 1. Also called optical fibers. Extrudedmaterials, such as certain plastic filaments, thatprovide paths for light. 2. The science of developingand using communications systems that useoptical fibers to transfer data.FiberReflectionpointReflectionpointLightbeamfiberopticsFET VOM A volt-ohm-milliammeter (VOM) using afield-effect transistor amplifier for increased sensitivityand high input impedance.FF Abbreviation of FLIP-FLOP.fF Abbreviation of FEMTOFARAD.FFI Abbreviation of FUEL-FLOW INDICATOR.fhp Abbreviation of FRACTIONAL HORSEPOWER.fiber 1. A tough, vulcanized insulating material.Dielectric constant, 2.5 to 5. Dielectric strength,2 kV/mm. 2. A thin thread of a material. 3. Alsocalled optical fiber. A light-conductive transparentfilament; see FIBEROPTICS, 1.fiber electrometer An instrument for measuringsmall quantities of electricity. It consists of athin thread, such as one of plasticized quartz,hanging freely between two knife-edged metalpieces that are charged by the electricity beingmeasured. The charge draws the fiber away fromits position of rest. The movement can be observedwith a microscope. A special form of thisinstrument, using two fibers, is the bifilar electrometer.fiber needle A soft phonograph needle made froma fiber. It produces less disk wear than otherstyli, but is short-lived.fiber metallurgy A process in which metallic fibersor filaments are grown.fiberoptic bundle A cable of optical fibers. SeeFIBEROPTICS, 1.fiberoptic coupling Also called optical coupling. Amethod of coupling in which a light-conductingfiber is placed between a light (signal) source anda photoreceptor. Also see FIBEROPTICS, 1, 2.fiberoptic scrambler A fiberscope in which a centersection of fibers in the core is deliberately disorientedbefore the bundle is encapsulated; whencut, one half can decode the image encoded bythe other half. See FIBERSCOPE.fiberscope A flexible bundle of optical fibers havinga lens at each end; it is used to view areas thatare otherwise inaccessible to view.fiber stylus See FIBER NEEDLE.fibre Alternate (Brit.) spelling of FIBER.fibrillation Dangerous, irregular beating of theheart that often follows electric shock. Also seeCARDIAC STIMULATOR and DEFIBRILLATION.fidelity The degree to which a circuit or devicetransmits a signal without distorting it. Pertainsespecially to acoustic devices and stereo audioequipment.field 1. A volume of space in which a force is operative.See, for example, ELECTRIC FIELD andMAGNETIC FIELD. 2. Half of a video image, consistingeither of all the even-numbered lines, orall the odd-numbered lines. 3. A computer recordsubdivision containing an information unit (e.g.,a bank account record might have deposits as afield).field circuit breaker A circuit breaker designed tocontrol the field excitation of a motor or other device.field coil 1. The winding on the field pole of a motoror generator. 2. The winding on the pole of anelectrodynamic speaker. 3. The main coil of a relay.4. The fixed coil in an electrodynamometer.

282 Field Day • filField Day In amateur radio, an annual contestsponsored by the American Radio Relay League(ARRL) to simulate emergency communicationconditions. It occurs during the last full weekendin June.field direction The direction in which an electricfield or magnetic field exerts its force.field effect The phenomenon in which the flow ofcurrent carriers in a solid substance is controlledby an external electric field. A useful applicationis the FIELD-EFFECT TRANSISTOR (FET).field-effect tetrode Also called dual-gate FET. Afield-effect transistor (FET) in which the gate electrodeis split into two parts, each connected to aseparate external lead. The reverse bias betweenthe channel and either gate lead affects the conductivitythrough the device.field-effect transistor Abbreviation, FET. A monolithicsemiconductor amplifying device in whicha high-impedance GATE electrode controls theflow of current carriers through a thin bar of silicon(rarely, germanium) called the CHANNEL.Ohmic connections made to the ends of the channelconstitute SOURCE and DRAIN electrodes.Also see JUNCTION FIELD-EFFECT TRAN-SISTOR, METAL-OXIDE SEMICONDUCTORFIELD-EFFECT TRANSISTOR, and CHANNELJUNCTION FIELD-EFFECT TRANSISTOR.field-effect varistor A nonlinear dual-terminalsemiconductor device capable of maintaining avalue of current for a range of voltages.field-emission microscope An instrument for examiningthe atomic structure of high-meltingpointmetals; it magnifies more than 2 milliontimes. The metal to be examined is made into aneedle that is subjected to 5 to 30 kV; electronsemitted by the tip of the needle form an image ona fluorescent screen.field forcing A method of controlling a motor bychanging the magnetic field in the windings.field frequency In television, the product of framefrequency and fields per frame (in the UnitedStates, 60 per second).field intensity 1. The strength of an electric ormagnetic field. 2. The strength of an electromagneticfield, usually expressed in microvolts permeter or millivolts per meter.field-intensity meter See FIELD-STRENGTH ME-TER.field ionization The tendency for atoms to be ionizedin a gas by a high-intensity electric field. Theionization occurs mostly near the poles of theelectric field.field-ion microscope A high-resolution field-emissionmicroscope that uses helium ions instead ofelectrons. The ions are repelled by the tip of themetal needle under observation, forming an imageon a fluorescent screen. Also see FIELD-EMISSION MICROSCOPE.field length Record field size in applicable units,usually bytes, characters, or words.field magnet 1. The permanent magnet in a dynamicspeaker. 2. A similar magnet in an earphone,generator, microphone, motor, phonopickup, transducer, etc.field pickup 1. A probe or sensor for insertion intoan electric or magnetic field. 2. An on-location radioor television program (i.e., one coming fromoutside the studio). Also called remote or NEMO.field resistor A resistive component consisting ofan insulated form with a thin layer of conductivematerial.field rheostat The rheostat whose setting determinesthe amount of current flow through thefield coil of a motor or generator.field scan A form of television scanning in whichthe lines are scanned alternately.field-sequential system A color-television systemin which the image is reproduced by means of primarycolor fields (red, green, and blue) flashed sequentiallyon the screen of the picture tube.Compare DOT-SEQUENTIAL SYSTEM and LINE-SEQUENTIAL SYSTEM.field strength See FIELD INTENSITY.field-strength meter An instrument for measuringthe radio-frequency (RF) voltage of a signalreaching a chosen location. The instrument consistsessentially of a radio detector equipped witha portable antenna and an output meter.µAfield-strength meterfield telephone A rugged, portable telephone systemfor outdoor use.field test A test of equipment under actual operatingconditions (i.e., outside the laboratory or factory).field winding See FIELD COIL, 1, 2.fig. Abbreviation of figure (usually in reference toan illustration).figure-8 pattern 1. A bidirectional antenna patternwhose cross section, in a specified plane, resemblesthe numeral 8. 2. A Lissajous figureresembling the numeral 8.figure of merit 1. For a capacitor, inductor, ortuned circuit, the ratio of reactance to resistance.Also called Q factor or Q. 2. For a magnetic amplifier,the ratio of power amplification to controltime constant. 3. For a transistor, the gain-bandwidthfactor.fil Abbreviation of FILAMENT.

filament • filler 283filament In a vacuum tube or incandescent lamp,the thin wire heated by electric current; it emitselectrons, light, and heat. The filament is thecathode in a filament-type tube, but serves onlyto heat indirectly the cathode sleeve in an indirectlyheated tube.filament battery See A BATTERY.filament choke A radio-frequency (RF) choke operatedin the filament lead of an electron tube.Such chokes are necessary in filament-type tubesin RF power amplifiers.filament circuit The circuit carrying filament current.filament coil See FILAMENT WINDING.filament current Symbol, I F . The current flowingthrough the filament of a vacuum tube.filament emission Electrons emitted directly bythe filament in an electron tube (thermionic emission)or the amount of such emission.filament hum A hum signal caused by voltage inducedin a circuit by the alternating-current (ac)-operated filaments (heaters) of tubes or by thefilament wiring.filament lag The time delay in the heating andcooling of an ac tube or lamp filament as filament-currentchanges polarity.filament power supply A source of power, usuallyalternating-current, for heating the filament of avacuum tube or tubes.filament resistance 1. The resistance of the filamentin an electron tube or incandescentlamp. 2. The resistance of an external droppingresistor in the filament circuit of a tube orlamp.filament transformer A step-down transformerthat supplies power exclusively to the filament(heater) of an electron tube.filament-type bolometer A BOLOMETER inwhich the sensitive element is a wire filament.Examples: barretter, incandescent lamp, andwire fuse.filament voltage Symbol, V F . The voltage acrossthe filament of an electron tube.filament winding In a power transformer, the coilthat supplies heating power to the filament of avacuum tube. Also called FILAMENT COIL.file An organized collection of records related by acommon format, data source, or application.file conversion Converting data files from oneform to another, often for the purpose of makingthem compatible with other computers.file gap An area of a data medium that signifies theend of a file; it can also mark the start of anotherfile.file identification A code that identifies a file.file label File identification in which the firstrecord in the file is a set of characters unique tothe file; it conveys such information about (for example,a tape file as a description of content, generationnumber, reel number, date of writing,etc.). Also called HEADER LABEL.file layout How the contents of a file are organized;usually defined by the system or specified by aprogram.file maintenance To delete, add, or correct recordsin a file. Unlike updating, which is done to reflectchanges in events recorded in the file, maintenanceensures that the contents of the file are accuraterecords of the necessary data.file management A method of storing and recallingdata from computer storage media, such asmagnetic disks.filename In a computer file label, the alphanumericcharacter set that identifies and describesthe file. It generally consists of one to eight characters,often including an extension of one tothree characters. In some computer operatingsystems, filenames can be much longer (e.g., upto 32 characters). See FILENAME EXTENSION.filename extension A group of one, two, or threecharacters following the main body of a FILE-NAME, and separated from it by a period (.). Itgenerally denotes the application or purpose ofthe file. The extension .BAK, for example, denotesa backup file; .TXT denotes a text file; .BMP denotesa bit-mapped graphics file.file organization The way words, bits, or recordsare physically arranged in the storage medium fora file, possibly including the method of access (serial,alphabetical, random, etc.).file-oriented programming Computer programmingthat uses a general file and record-controlprogram to simplify I/O coding.file-oriented system A system having file storageas its basis.file print A hard copy (printout) of the contents ofa file.file processing The operations associated withmaking and using files.file protection Preventing the possibility of writingover data files before they are made available foruse. It is usually done by having a program checkfile labels.file reconstitution Restoring a partially or completelydamaged file by updating a previous generationof the file using a file of interim transactions.file recovery Following the interruption of file processingbecause of system failure, the procedurefor reestablishing the file’s condition as necessaryfor the resumption of processing without losingaccuracy.file section Part of a file in certain consecutive locationson a storage medium.file security Protective and security measures(e.g., the issuance of clearances, status markers,etc.) as they relate to computer files.file set A collection of interrelated files stored consecutivelyin a magnetic disk volume (package).fill The percentage of lines in a cable that are actuallyin use at a given time.filler A nonessential data part used, for example,to bring a record to a standard size.

284 film • filter stopbandfilm See THIN-FILM MEMORY.film capacitor A capacitor in which the electrodesare plated or deposited on the faces of a thin filmof plastic or other dielectric material.film chain A system designed for the transmissionof movies over a television system. This requiressynchronization of the movie frame rate with thetelevision scanning rate.film frame A single picture on a strip of motionpicture film.film-frame blanking interval The interval duringwhich a film frame is blanked out as motionpicturefilm moves through a camera, projector,or pickup. The blanking action allows a frame tomove into position without blurring the image asseen by viewers.film integrated circuit A monolithic circuit whoseelements are films formed on an insulating substrate.film pickup A photocell, photodiode, or phototransistorcircuit used to pick up recordings from thesound track of motion-picture film.film reader A device for converting data on filminto digital form for a computer.film recorder An apparatus that records data as asound pattern on film. Compare FILM REPRO-DUCER.film reproducer An apparatus that plays backdata recorded on photographic film. CompareFILM RECORDER.film resistor Also called carbon-film resistor ormetal-film resistor. An electronic component consistingof a mixture of ceramic, carbon, and/ormetal, applied to a cylindrical form in a thin layerto obtain a desired value of resistance. The cylindricalform is made of an insulating substance,such as porcelain. The film can be deposited onthis form by various methods, and the value tailoredas desired. Metal-film units can be made tohave nearly exact values. Film type resistors usuallyhave low to medium-high resistance. A majoradvantage of film-type resistors is that they, likecarbon-composition units, do not have much inductanceor capacitance. A disadvantage, insome applications, is that they cannot handle asmuch power as the more massive carbon-compositionunits, or as wirewound types. CompareCARBON-COMPOSITION RESISTOR, WIRE-WOUND RESISTOR.film scanning The conversion of a movie into aform suitable for transmission by television.film speed 1. The speed at which motion-picturefilm moves intermittently through a camera, projector,or pickup, measured in feet or frames persecond. 2. A measure of film’s light sensitivity,given as an ASA (American Standards Association)or DIN (European) number; in either system,the higher the number, the greater the light sensitivity.filter 1. A circuit or device that passes alternatingcurrents at some frequencies while attenuating orblocking currents at other frequencies. Examples:BANDPASS FILTER, BAND-REJECTIONFILTER, HIGH-PASS FILTER, and LOW-PASSFILTER. 2. An inductance-capacitance (LC) orresistance-capacitance (RC) circuit for removingthe ripple from the output of a power-supply rectifier.3. A transparent disk with special opticalproperties placed in front of a camera lens for aspecial photographic effect. 4. A character patternedto control the elimination or selection ofcharacters in another pattern. 5. A device or programthat separates information, according tocertain specifications or characteristics. 6. A machineword that specifies the elements to betreated in another machine word; also calledMASK.filter attenuation In a selective filter, the power,current, or voltage loss, in decibels, that occurswithin the passband.filter attenuation band In a selective filter, thefrequency band(s) outside the passband; that is,the frequency range over which signals are significantlyattenuated.filter bank In audio applications, a set of bandpassfilters, each of which covers a specific portionof the audio-frequency (AF) spectrum. Thereis some (minimal) overlap between the passbandsof the filters, so an AF signal of a specific frequencywill always pass through at least one ofthe filters, but will never pass through more thantwo of the filters.filter capacitor A capacitor that provides capacitivereactance in a wave filter or power-supply filterwhile also blocking direct current.filter center A place where information is modifiedfor transmission to aircraft pilots. Such informationcan include weather data, course changes, orother instructions.filter choke An inductor that provides inductivereactance in a wave filter or power-supply filterwhile affording relatively easy conduction of directcurrent.filter crystal A piezoelectric crystal used in aCRYSTAL RESONATOR.filter cutoff The frequency or frequencies at whichthe transmission figure of a filter is below itsmaximum value by a prescribed amount, usually3 dB, representing the half-power point(s).filter discrimination The amount of fluctuation inthe insertion loss of a bandpass, band-rejection,high-pass, or low-pass selective filter. The fluctuationis measured at various points in the filterpassband.filter inductor See FILTER CHOKE.filter passband The frequency range over which aselective filter passes signals with minimum attenuation.filter reactor See FILTER CHOKE.filter slot In a waveguide, a slot that acts as achoke to suppress undesirable modes.filter stopband See FILTER ATTENUATION BAND.

filter transmission band • firing angle 285filter transmission band See FILTER PASSBAND.fin 1. A metal disk or plate attached to a componentfor the purpose of radiating heat. 2. A projectionin an irregular heatsink.final amplifier Also called output amplifier orpower amplifier. In a wireless transmitter, theamplifier that boosts the signal power to the levelto be emitted over the airwaves. The input isprovided by the driver; the output is connected tothe system, to a transverter, or to a network cablepower amplifier. In some transmitters, theoutput amplifier requires no tuning; in others,adjustment of the output circuitry is necessary toobtain proper coupling to the antenna system. Ina single-sideband (SSB) or amplitude-modulated(AM) transmitter, all amplifiers following themodulator must be linear. In transmitters intendedfor use only in digital modes or for frequencymodulation (FM), power amplifiers neednot be linear.final result A result displayed at the end of a dataprocessing operation. Compare INTERMEDIATERESULT.finder The switch or group of relays that selectsthe path for a call going through a telephoneswitching system. Also called LINE FINDER.fine adjustment Adjustment of a quantity in smallincrements or as a smooth, continuous variation.Compare COARSE ADJUSTMENT.fine-chrominance primary See I SIGNAL.fine frequency control A variable component,such as a potentiometer or variable capacitor,that permits a signal or response frequency to bevaried over a small increment; it is often used inconjunction with a coarse frequency control.Finecontrol10pFCoarsecontrol365pFfine frequency controlToosc.fine-groove record See MICROGROOVE REC-ORD.fine index In computer operations, a secondary,supplemental index used with a main, or gross,index when the latter does not adequately detailthe differences between the items being indexed.fine-motion planning The scheme used by arobotic end effector (“hand”) to get in exactly thecorrect position. It uses machine vision, tactilesensors, pressure sensors, or high-precision displacementtransducers.finger See FEELER, 1.finger plethysmograph A device that senses andrecords the resistance through the human fingerduring various parts of the heart cycle.finger rules See FLEMING’S LEFT-HAND RULE,FLEMING’S RIGHT-HAND RULE, and RIGHT-HAND RULE FOR WIRE.finish lead The lead attached to the last turn of acoil. Also called outside lead. Compare STARTLEAD.finished blank The end product in the crystal manufacturingprocess, often including electrodes.finishing The careful handwork and testing involvedin bringing a crystal blank to a conditionthat is acceptable as finished, according to specifications.finishing rate The rate of charging a battery, asthe battery approaches a full charge. Generally,the finishing rate is less than the normal chargingrate.finite Pertaining to that which has defined limits.finite sample space In statistics, a sample spacehaving definite limits.finite series A mathematical series having a limitednumber of terms. Example: 1 + 0.1 + 0.01 +0.001, a finite series containing four terms andwhose sum is equal to 1.111.finned surface The irregular surface of a heatsink.The ratio of surface area to volume is greater thanwith a flat surface; this increases the cooling effectivenessof the heatsink.fins Metal vanes radiating from components thatdissipate large amounts of power as heat.FIR Abbreviation of FAR INFRARED.fire A transition from non-conduction to conductionin an ionizing switching device.fire control The aiming and firing of guns automaticallyvia radar and associated electronic systems.firefighter robot A robotic device or system intendedto protect lives and property from fire.Such a robot can be simple, such as an automaticsprinkler system actuated via heat sensorsand/or smoke detectors. More sophisticated systemsmight use autonomous or remotely controlledandroids that perform the same functionsas human firefighters.Fire Underwriter’s regulations See NATIONALELECTRIC CODE.firing The pulse that initiates conduction in anionization switching device.firing angle 1. For a magnetic amplifier, the angulardistance through which the input-voltagevector rotates before the core is driven intosaturation. 2. For a silicon-controlled rectifier(SCR), the point, as an angle (in degrees orradians), along the control voltage half-cycle atwhich the SCR fires.

286 firing circuit • fixed-frequency oscillatorfiring circuit Any circuit, such as a phase shifter,that permits adjustment of the firing angle of asilicon-controlled rectifier (SCR) or similar device,or which delivers the required pulse or other signalto initiate firing.firmware 1. Programs (software) in nonvolatilecomputer memory [e.g., in a read-only memory(ROM), that can only be changed by replacementwith an alternate unit]. 2. Unalterable internalinterconnections that determine what a computingdevice or system can do. Also called MICRO-PROGRAM.first detector In a superheterodyne circuit, thesignal frequency detector. Compare SECOND DE-TECTOR.first filter capacitor The input capacitor in a capacitor-inputpower-supply filter.first Fresnel region A portion of a directionaltransmitted electromagnetic ray, shaped generallylike a paraboloid with the apex at the transmitterand the axis in the direction oftransmission. Any point in the first Fresnel zoneis in such a position that the sum of the lengthsof the paths from the point to the receiver, andthe point to the transmitter, is no greater than0.5 wavelength more than the distance from thetransmitter to receiver.first harmonic The fundamental frequency in acomplex waveform from which multiples are generated.first-in/first-out Acronym, FIFO. A read-writememory commonly used as a buffer to smoothout the flow of data bits in a digital system. Theoutput bits are in the same order (sequence) asthe input bits. If a data bit x goes into the FIFObefore data bit y, then x will always emerge fromthe FIFO before y. Compare PUSHDOWN STACK.first-in/last-out See PUSHDOWN STACK.first law of thermodynamics Quantities of heatcan be converted into mechanical work, and viceversa. Also see MECHANICAL EQUIVALENT OFHEAT.first level address See ABSOLUTE ADDRESS.first selector The selector that responds to thefirst-digit dial pulses when a telephone number iscalled.fishbone antenna An untuned, wideband directionalantenna of the general end-fire type. Consistsof a number of collector antennas, eachcapacitively coupled to the resistor-terminatedtransmission line in collinear pairs. It is socalled from its resemblance to the skeleton of afish.fishpaper A chemically treated, vulcanized-fiberpaper used for electrical insulation.fish pole A microphone boom that can be held inthe hand.fist In radiotelegraphy and wire telegraphy, an operator’smanual sending style.fitting A device intended to mechanically fasten awire or cable in place.TerminatingresistorCollector antennasTransmission linefishbone antennaTo receiverfive-element code A five-impulse telegraph codethat describes a character (e.g., Baudot, whichalso includes start and stop elements).five-layer device A semiconductor device containingfour pn junctions. Examples: diac and triac.five-level code A teletype code that utilizes five binaryelements to define a character.fix 1. In direction finding, the point at which twolines of direction intersect. 2. In electronics maintenance,to repair successfully. 3. To subject anin-process circuit board to a solution or othermedium to stop a photographic action permanently.Also, the solution in which such photosensitivematerials can be immersed to haltdevelopment.fixed bias Bias voltage or current supplied from afixed external source (such as a battery or powersupply) independent of the operation of the biaseddevice. Compare AUTOMATIC BIAS.fixed block length Blocks of data having a fixednumber of words or characters, as required becauseof hardware limitations or a program instruction.Compare VARIABLE BLOCK LENGTH.fixed capacitor A nonadjustable capacitor (i.e.,one having a single unalterable value).fixed component Any component (e.g., a capacitor,inductor, or resistor that has one unalterablevalue).fixed contact The stationary contact in a relay orswitch. Compare MOVABLE CONTACT.fixed-crystal detector A simple crystal detector inwhich the point of the contact wire is permanentlyplaced in contact with a sensitive spot onthe surface of the crystal.fixed field Fields in records organized so thatthose containing similar information in eachrecord are the same length and in the same relativeposition in the record. Compare VARIABLEFIELD.fixed form coding The coding of source languagesso that each part of the instruction is in a fixedfield.fixed-frequency amplifier An amplifier that ispretuned to operate on one frequency, or in a relativelynarrow band of frequencies.fixed-frequency oscillator An oscillator that ispreset to operate on one frequency. Such an os-

fixed-frequency oscillator • flange 287cillator can be self-excited or controlled (crystal,fork, magnetostriction, etc.).fixed-frequency receiver A receiver that is pretunedto receive signals of one frequency.fixed-frequency transmitter A transmitter that ispretuned to radiate signals of one frequency.Such a transmitter can contain a self-excited orcrystal-controlled oscillator.fixed inductor A nonadjustable inductor (i.e., onehaving an unalterable value of inductance).fixed-length record A record in which word orcharacter size is constant. Compare VARIABLELENGTH RECORD.fixed logic Applicable to computers or peripheralswhose logic can only be altered internally bychanging connections.fixed memory A nonvolatile readout computermemory that can only be altered mechanically.fixed placement file A file that has been allocateda fixed location in storage.fixed-point system A notation system in which asingle set of digits represents a number, and theradix point (in the decimal system, the decimalpoint) can only be placed in one position for thevalue being expressed. Also see FLOATING-POINT CALCULATION.fixed resistor A nonadjustable resistor (i.e., onehaving an unalterable value of resistance).fixed-sequence robot A robot that performs onetask or set of tasks, making exactly the samemovements every time. The sequence is programmedin the robot controller via firmware.Many assembly robots and toy robots are of thistype. Compare FLEXIBLE AUTOMATION.fixed station A radio station operating from a stationarypoint; one that is not mobile.fixed-step potentiometer A potentiometer whoseoutput is varied in one or more discrete steps byfixed-resistor sections. Also see POTENTIOME-TER.fixed wireless 1. A cellular communications networkin which some, or all, of the end users are atfixed locations. This is increasingly popular as analternative to conventional hard-wired telephoneand Internet access. 2. The use of wireless equipment,such as cell phones and wirelessmodem–equippedcomputers, at fixed (ratherthan mobile or portable) locations.fixed word length Applicable to the organization ofinformation in storage in which each computerword stored has a fixed number of characters orbits.fixture A piece of hardware used in equipment setups(e.g., microwave couplers, joints, sections,etc.).fL Abbreviation of FOOT-LAMBERT.flag 1. A piece of information added to a data itemthat gives information about the data item. 2. Abit added to a character or word to delineate afield boundary. 3. An indication that an operationis complete and need not be done by the program.4. An indicator identifying the members of mixedsets. 5. A character that signals the presence ofsome condition (e.g., an error flag indicates that adata item caused an error).flag event A program condition that causes a flagto be set.flag line An input pulse to a microprocessor thatdepends on specific external instructions. Indicatesa certain condition or change of state.flagpole antenna 1. Any of several vertical UHF orVHF antennas consisting of a radiator mountedatop a coaxial pipe or cable (see, for example,COAXIAL ANTENNA). It takes its name from itsresemblance to a flagpole. 2. A vertical antennaformed by shunt-feeding a pole already in existence,such as a flagpole. This can be done toconceal the antenna.Coaxialfeed lineWhip to coaxcenter conductorCenterinsulatorPipe to coaxouter conductorBaseinsulatorflagpole antenna, 1flag terminal A form of terminal that does not requiresoldering for electrical contact. A protruding“flag” is crimped around the conductor.flame alarm A (usually photoelectric or thermoelectric)device or circuit for detecting a flame andactuating an alarm.flame control A (usually photoelectric or thermoelectric)device or circuit for sensing and automaticallycontrolling the height of a flame, suchas a gas pilot.flame-failure control A FLAME CONTROL that automaticallycuts off the fuel if the flame goes out.flame microphone A microphone in which twoelectrodes in a flame undergo a change in electricalresistance when the flame is influenced bysound waves, thus modulating current passingbetween the electrodes.flange 1. A flat, protruding edge used for fasteninga connector or plug to the chassis of a piece ofequipment. 2. In a waveguide, a coupling used forconnection to another section of waveguide, or toa horn or other external device.

288 flange focus • flatteningflange focus The focal length of a lens, based onthe distance from the mounting flange to the focalplane.flanging In sound systems, a means of obtainingspecial effects using a COMB FILTER. Creates an“extraterrestrial,” digitized sound. Commonlyused by rock music bands.flanking Modification of the response of a selectivefilter, resulting from the parallel connection oftwo or more similar filters.flap See DROP INDICATOR.flap attenuator A waveguide attenuator consistingof a sheet of resistance material inserted transverselyinto the waveguide through a slot.flare 1. The hyperbolic cross section of a horn antennaor loudspeaker. 2. A transient or stationarybright area with (usually) a central pip on thescreen of an otherwise blank oscilloscope or televisionpicture tube.flare angle The gradual change in a waveguide’sdiameter over its length.flare factor The angle at which the faces of a hornspeaker are curved or turned outward.flaring constant Symbol, m. A number expressingthe degree of flare (see FLARE, 1) in a hornantenna or loudspeaker. The value of m is equalto 0.6931/d, where d is the distance along theaxis required for the cross-sectional area A ofthe horn to double. If d is given in feet (ft), for example,then A is in units of square feet (ft 2 ) andm is in units of reciprocal feet (1/ft). If d is incentimeters (cm), then A is in units of squarecentimeters (cm 2 ) and m is in units of reciprocalcentimeters (1/cm).flash 1. A photographic camera flash. 2. To vaporizea metal (such as magnesium) in an electrontube being evacuated, to absorb gases. 3.Flashover.flash arc In a vacuum tube, a sudden high-currentarc between cathode and plate at high plate voltages;it can short-circuit the plate power supply.flashback voltage The maximum inverse voltagethat causes the gas in a tube to ionize.flash delay A device that automatically postponesthe operation of a FLASHTUBE until a predeterminedinstant, such as the moment when a movingobject arrives at a particular point before acamera.flasher An electrical or electronic device or circuitthat flashes a light or a series of lights sequentially.flasher LED A light-emitting diode (LED) that,when connected to a low-voltage direct-current(dc) source, emits light that flashes at a basic rateof a few pulses per second.flashlamp 1. See FLASHTUBE. 2. A small portablelight operated from self-contained cells; a flashlightor lantern.flashlight See FLASHLAMP, 2.flash memory High-capacity, nonvolatile randomaccessmemory, used in some computers in placeof an electromechanical hard drive. This type ofmemory allows a computer to store, access, andrun large data files or programs much faster thanis possible with a conventional hard drive. Seealso NONVOLATILE MEMORY, RANDOM-ACCESS MEMORY.flashover The sudden discharge of electrical energybetween electrodes or conductors, often accompaniedby light; it is usually the result ofexcessive voltage.flashover voltage 1. The peak voltage at whichFLASHOVER occurs. 2. The voltage at which disruptivedischarge occurs between electrodes andacross the surface of an insulating material.flash plating Electroplating in which a thin layer isdeposited quickly.flash test Insulation testing by applying a higherthan-normalvoltage for a short time.flashtube A straight or coiled glass tube filled withgas and provided with electrodes. When a highvoltage is applied to the electrodes, the tube emitsa brilliant flash of light.flat cableAlso called ribbon cable. A cable whoseflexible conductors are molded side by side in aflexible, flat ribbon of plastic (such as polyethylene).flat-compounded generator A compound-woundgenerator whose windings are proportioned so thatthe full-load and no-load voltages are identical.flat fading Fading of a radio signal that occurs independentlyof frequency; all frequency componentsof the signal fade to the same extent at thesame time.flat file A computer file containing unfolded documents.flat frequency response Relatively equal responseto all fixed-point frequencies within a given spectrum,exhibited by an amplifier or other circuitthat must transmit a band of frequencies.flat line A transmission line in which there are nostanding waves, or for which the standing-waveratio is very low.flat pack An integrated circuit package consistingof a square or rectangular flat housing, with pinsprojecting straight outward from the edges.flat response A response characteristic in whichthe dependent variable is substantially constantover a specified range of values of the independentvariable. For example, in amplifier operation,an output signal whose componentfundamental frequencies and their harmonics arein the same proportion as those of the input signalbeing amplified.flat-ribbon line A transmission line (feeder) consistingof two flexible conductors molded in a flexible,flat ribbon of plastic, such as polyethylene.Also called twinlead.flatteningThe leveling-off or blunting of a normallypeaked or curved response, often caused bysignal saturation within a circuit. Sine-wave clippingis an example.

flat top • flight telerobotic servicer 289flat top 1. The horizontal radiating portion of anantenna. 2. See FLAT-TOP ANTENNA. 3. Of anamplifier, to distort by clipping of the positivehalf-cycles.flat-top antenna An antenna having a horizontalwire or wires at the top to lower the resonant frequencyand increase the bandwidth.flat-top beam A bidirectional, end-fire antennaconsisting of two close-spaced dipoles center-fedout of phase. Also see KRAUS ANTENNA.flat-topping The positive-peak clipping of a modulationenvelope that occurs when an amplifier isoverdriven or when a signal is overmodulated.This is in contrast to deliberate clipping. Flattoppingresults in “splatter” and is, therefore, anundesirable characteristic in an amplitudemodulatedsignal.flat-top response The ability to uniformly transmitfrequencies in a given band.flat transmission line 1. A transmission line that isfree of standing waves. Also see MATCHEDTRANSMISSION LINE. 2. See FLAT-RIBBON LINE.flaw An irregularity in a substance that can resultin problems, such as mechanical failure or poorequipment performance.flaw detector An instrument that uses ultrasonicwaves to detect internal flaws in metal. The wavesare reflected by flaws.F layer See F REGION.fLb Abbreviation of FOOT-LAMBERT.Fleming/Kennelly law Under conditions at ornear magnetic saturation in a ferromagnetic substance,the reluctivity is directly proportional tothe intensity of the magnetic field.Fleming’s generator rule See FLEMING’S RIGHT-HAND RULE.Fleming’s left-hand rule A simple way of indicatingcertain relationships in the behavior of electricgenerators and motors. If the thumb, indexfinger, and middle finger of the left hand are positionedso that they are at right angles to eachother, the thumb will point in the direction offorce or motion when the index finger is pointedin the direction of flux; the middle finger points inthe direction of current flow. Compare FLEM-ING’S RIGHT-HAND RULE.Fleming’s motor rule See FLEMING’S LEFT-HAND RULE.Fleming’s right-hand rule A simple way of indicatingcertain relationships in the behavior ofelectric generators and motors. If the thumb, indexfinger, and middle finger of the right hand arepositioned so that they are at right angles to eachother, the middle finger points in the direction ofan induced voltage, the thumb in the direction ofthe motion of a conductor, and the index finger inthe direction of the magnetic field. CompareFLEMING’S LEFT-HAND RULE.Fletcher-Munson curves A set of curves depictingthe uneven frequency response of human hearing.Also called AUDIBILITY CURVES.flexible automation The ability of a robot or systemto do various different tasks. Changing fromone task to another is simply a matter of changingsoftware. Compare FIXED-SEQUENCEROBOT.flexible collodion A viscous solution of pyroxylin(cellulose nitrates) used sometimes as a binderfor coils.flexible contact A contact made from flat, metalspring stock; it is usually bent or curved. Alsocalled spring contact.flexible coupling A device for joining two shaftsand conveying rotary motion from one to theother; it is elastic, so the shafts need not be exactlyaligned with each other.flexible flat cable See FLAT CABLE.flexible manufacturing system A roboticizedmanufacturing plant that can turn out a varietyof different products. One or more central computersoversee the operation of the facility. Suchfactories are commonly used in the production ofelectronic devices (such as printed circuits, calculators,and portable radios).flexible resistor An insulated, wirewound resistorthat can be bent, coiled, or knotted.flexible shaft A control shaft that can be bentsomewhat while still allowing easy adjustment.flex life A measure of how much bending a conductoror other flexible object can take withoutbreaking.flexode A diode that is flexible in that its junctioncan be changed (i.e., reversed without reversingits leads, its resistance being variable from theforward- to backward-resistance value).flicker 1. A tendency for a video image to appear,disappear, and reappear, or to increase and decreasein intensity frequently. 2. The effect createdby such action (as in a flickering light).flicker frequency The number of times the screenillumination flashes on and off in the projection ofa motion picture. It is 48 per second (twice theframe rate) in conventional movie projectors; foreach frame, the screen is blanked once when theframe is pulled into position and once again duringprojection of the frame.flight control Electronic monitoring and control ofan aircraft in flight.flight path The course planned for an aircraft’sflight.flight-path computer A computer that controlsthe course of an aircraft in flight, from takeoff tolanding.flight-path deviation The departure of an aircraftin flight from the course in the flight plan. Alsosee FLIGHT PATH.flight-path-deviation meter An instrument thatprovides a visual indication of the departure of anaircraft in flight from the course in the flight plan.flight telerobotic servicer A remotely controlledrobot used to maintain and repair space vehiclesand satellites. The machine can be controlled by

290 flight telerobotic servicer • floating-point systema computer program or by a human operator. Themost-sophisticated machines can use TELEOP-ERATION and/or TELEPRESENCE so that a humancan perform dangerous work without beingplaced at personal risk.flight test 1. To test airborne electronic equipmentin actual flight. 2. Any test made as in 1.Flinders bar In a magnetic compass, a metal barthat corrects for the vertical component (inclination)of the earth’s magnetic field. The bar mustbe designed differently in different geographic locations,because the inclination varies from placeto place. Inclination is greatest near the geomagneticpoles, and is zero at the geomagnetic equator.flint glass A hard, bright, lead glass. Dielectricconstant, 7 to 9.9. Dielectric strength, 30 to 150kV/mm. Also see GLASS.flip chip A monolithic semiconductor device (suchas a diode, transistor, or integrated circuit), inwhich bead-like terminals are provided on oneface of the chip for bonding.flip-chip bonding A scheme for making connectionsbetween a semiconductor chip and aheader, in which leads are not run between chipand header. Instead, bead-like projections areelectrodeposited as terminals around one face ofthe chip, which is then registered with the headerterminals and bonded to them.flip-flop 1. See BISTABLE MULTIVIBRATOR. 2. Atwo-position relay that locks in alternate positionsupon receiving successive actuating pulses.flip-flop key In a video display, a key that, whenpressed, allows viewing of one half of the screenand then the other.flip-flop memory A bistable computer memorythat stores bits of data as flip-flop states.flip-flop relay See BISTABLE RELAY.float charging The constant charging of a storagebattery, keeping the battery at or near the fullycharged state at all times.floated battery A storage battery connected inparallel with a generator, which supplies theload; the battery, always completely charged,helps during high-current demands.floating 1. To float a storage battery; see FLOAT. 2.An ungrounded device or circuit that is not connectedto a source of voltage. 3. Not loaded ordriven. 4. Not fixed in position. 5. A dedicatedground connection that remains isolated from thecommon circuit ground.floating address See RELATIVE ADDRESS.floating charge See TRICKLE CHARGE.floating control 1. A potentiometer, such as again control, installed with its shaft insulatedfrom ground and, accordingly, subject to bodycapacitanceeffects. 2. A type of automatic controlin which the rate of final control element movementdepends on the amount that the controlledvariable deviates from a prescribed value.floating ground See FLOATING, 5.floating input An ungrounded input circuit.floating-input measurement See DIFFERENTIAL-INPUT MEASUREMENT.floating instrument An instrument whose signalterminals are above ground.floating I/O port An input/output (I/O) terminalthat is not loaded or being driven.floating junction A junction (in a semiconductordevice, for example), that has no net current flowingthrough it.floating neutral A circuit with a variable commonvoltage reference.floating paraphase inverter A dual-transistoradaptation of the paraphase inverter. The secondstage receives its input signal from a tap on theload resistor of the first stage and provides theadditional phase shift that is required.InputSDDSfloating paraphase inverterOutput 1CommonOutput 2floating-point calculation An electronic calculationusing a floating point number [i.e., a numberwhose value is represented by two sets of digits, afixed-point part (see FIXED-POINT SYSTEM) anda radix (base number) with an exponent]. Importantin the operation of microprocessors, especiallyin computer systems.floating-point number A number expressed in thefloating-point system.floating-point package Computer-vendor softwarethat enables that computer to perform floating-pointcalculations.floating-point system A system of notation inwhich a number n is represented by two sets ofnumbers: a fixed-point part (see FIXED-POINTSYSTEM) a, the radix (base number) r, and an exponentb as follows: n = a × r b . For example, in thefloating-point system, 623 can be written 6.23 ×10 2 . Floating-point numbers can be stored economically(in terms of memory) and in magnitudesthat might otherwise be beyond thecapacity of the computer to operate upon withrelatively consistent accuracy. Compare FIXED-POINT SYSTEM.

floating probe • fluorescent materials 291floating probe A test electrode (wire or plate) insertedin a discharge tube at a desired point tosample the potential gradient, but which acquiresa misleading negative charge, with respect to thegas cloud, because electrons (traveling fasterthan the positive ions) tend to accumulate on theprobe.floating zero A control system in which the referencepoint is easily moved.floating zone In a semiconductor ingot undergoingpurification, a molten zone in which impuritiesfloat. The material in the zone is melted by theradio-frequency (RF) field of an external heatingcoil, which is passed along the ingot to move themolten zone to one end, picking up impuritiesalong the way and concentrating them at the endthat is later sawed off.float switch A switch operated by a float, such asin a sump pump.flocking 1. Particulate felt used on phonographturntables to protect disks from being scratched.2. To coat with flocking.flood gun In a storage (image-holding) oscilloscope,the electron gun that sprays the storagetarget with low-velocity electrons and makes theimage visible on the viewing screen. The gun ismounted next to one pair of deflection plates.Compare WRITING GUN.floor stand A support for a microphone, consistingof a heavy base that rests on the floor, and an adjustable,vertical boom that allows the microphoneto be set at various heights.floppy disk A flexible magnetic disk used inrecording, as in computer and data system storage.It usually refers to a 5.25-inch diskette.flow 1. The movement of current carriers underthe influence of an electric field. 2. See ANGLEOF CONDUCTION. 3. A series of interrelatedevents in a time sequence.flow angle See ANGLE OF CONDUCTION.flowchart 1. A diagram depicting the logic steps ina digital-computer program. 2. A diagram showingthe flow of material through a sequence ofprocesses.flow direction The method of delineating antecedentand successor events on a flowchart;usually arrows and flowlines connecting theevents in the way a page is read (top to bottom,left to right).flowed-wax disk A form of recording disk, in whichwax is melted onto a plastic or metal base. Thegrooves are cut in the wax layer.flowline A line showing flow direction on aflowchart.flowmeter An instrument for measuring liquidflow rate.flow relay A relay that is actuated by a predeterminedrate of fluid flow.fluctuating current See COMPOSITE CURRENT.fluctuating voltage See COMPOSITE VOLTAGE.fluid absorption See LIQUID ABSORPTION.fluid analogy The comparison of electric currentflow to the movement of a simple fluid. Also seeWATER ANALOGY.fluid capacitor See WATER CAPACITOR.fluid computer A digital computer that uses fluidlogic elements (i.e., one that contains no electroniccircuits or moving parts).fluid damping Use of a viscous fluid to damp a mechanicalmember’s movement.fluid-flow alarm An electronic circuit that actuatesan alarm when fluid flowing through pipes or otherchannels changes from a predetermined rate.fluid-flow control A servo system that automaticallymaintains or adjusts liquid flow throughpipes or other channels.fluid-flow gauge See FLUID-FLOW METER.fluid-flow indicator See FLUID-FLOW METER.fluid-flow meter An instrument that indicatesfluid flow rate through pipes or other channels.fluid-flow switch In a fluid-cooled system, aswitch that actuates an alarm when the fluidslows or stops.fluidics 1. A form of digital logic in which circuitsoperate by means of fluid flow. 2. A branch ofphysics concerned with the behavior of fluids;more commonly called fluid dynamics.fluid-level control A servo system that automaticallymaintains the level of a fluid in a tank.fluid-level gauge An electronic system that providesdirect readings of the level of a fluid in a tank.fluid-level indicator See FLUID-LEVEL GAUGE.fluid logic Logic operations carried out by varyingthe flow and pressure of a gas or liquid in a circuitof channels. Also see FLUID COMPUTER.fluid ounce (U.S.) Abbreviation, fl. oz. A unit of volumeequal to 2.957 × 10 –5 cubic meters, or0.02957 liter. A quart is 32 ounces; a gallon is128 ounces.fluid-pressure alarm An electronic circuit that actuatesan alarm when fluid pressure rises or fallsbeyond set limits.fluid-pressure control A servo system that automaticallymaintains or adjusts fluid pressure inpipes or other channels.fluid-pressure gauge See FLUID-PRESSURE ME-TER.fluid-pressure indicator See FLUID-PRESSUREMETER.fluid-pressure meter An instrument that indicatesthe pressure of a fluid in a pipe or other channel.fluid valve See ELECTROMECHANICAL VALVE.fluorescence The property of some materials toglow when excited by a stimulus, such as ultraviolet,X rays, or an electron beam. ComparePHOSPHORESCENCE.fluorescent lamp See FLUORESCENT TUBE.fluorescent materials Materials that glow whenirradiated, but cease to glow when the source ofexcitation is removed. An example is the phosphorcoating on the screen of a cathode-ray tube(CRT).

292 fluorescent screen • flyback timefluorescent screen A transparent or translucentplate (such as the end of a cathode-ray tube orfluoroscope) coated with phosphors that glowwhen struck by an electron beam, or by highenergyelectromagnetic radiation, such as ultravioletor X rays.fluorescent tube A mercury-vapor glow lamp distinguishedby having a glass tube whose innerwall is coated with a phosphor that emits lightwhen excited by the ultraviolet glow discharge inthe vapor.fluorescent X rays X rays reradiated by the atomsof a material that has absorbed X radiation. Duringinitial exposure, energy absorbed from the radiationraises the energy level of electrons in theatoms; when the electrons return to their normalenergy levels, they reradiate some of the absorbedenergy.fluorine Symbol, F. A gaseous element of the halogenfamily. Atomic number, 9. Atomic weight,18.998.fluoroscope A device used for viewing the internalstructures of objects. A screen coated with materialthat fluoresces when exposed to X rays ismounted in one end of a light-tight viewing hood.When an object is placed between the screen andan X-ray tube, an image is produced on thescreen. In medical applications, this device hasbeen supplanted by methods that do not use ionizingradiation; nuclear magnetic resonance imaging(NMRI) is one example.fluoroscopy The art of using a fluoroscope in theinspection of materials and parts or in medicalexaminations.flush A form of mounting in which there is little orno protrusion from the panel surface.flutter 1. In a high-frequency superheterodyne receiver,a rapid fluctuation in signal strength,caused by tuning and detuning of the oscillatorstage. This usually results from poor directcurrent(dc) power-supply regulation. 2. Repetitive,rapid fluctuations in the output of a soundreproducer. Also see WOW. 3. An echo effectsometimes observed in rooms or auditoriums ofpoor acoustic design.flutter bridge A bridge-type instrument for measuringflutter in constant-speed machines, suchas sound recording and reproducing devices.flutter rate The frequency of flutter, in cycles persecond (Hertz).flux 1. Theoretical lines of force that extend in alldirections from an electric charge (electric flux)or from a magnetic pole (magnetic flux). 2. Amaterial that makes metals more amenable tobeing joined by soldering. 3. The number ofphotons that pass through a surface for a giventime.flux density Symbol, B. Unit, tesla. The degree ofconcentration of magnetic lines of force. One teslarepresents a flux density of one volt-second persquare meter (V•s/m 2 ).fluxgate A device that controls the azimuth bearingof a directional system by means of interactionwith the geomagnetic field.fluxgate magnetometer A magnetic compass forrobot guidance. Uses coils to sense changes in artificiallygenerated reference fields. Output fromthe sensors is sent to a computer that calculatesthe robot’s position, based on the orientation andintensity of the lines of flux in the reference fields.flux graph A device that graphically records the intensityof a magnetic field around a permanentmagnet or electromagnet, or around an inductorcarrying a current.flux leakage See MAGNETIC LEAKAGE.flux lines The theoretical lines of force in an electricor magnetic field.flux linkage The passage of lines of force set up byone component through another component, soas to enclose most of the penetrated component’svolume.Influx linkageOutFluxlinesfluxmeter An instrument for measuring magneticflux density. Also called gaussmeter.flux refraction The tendency for magnetic lines offlux to change direction at the boundary betweensubstances having different permeability. Fluxrefraction resembles refraction of electromagneticradiation in or at a boundary between substanceshaving different indices of refraction.flyback 1. The abrupt drop or reversal of a currentor voltage that was previously increasing (e.g., therapid fall of a sawtooth wave). Also see KICK-BACK. 2. The duration of the drop of a current orvoltage that was previously increasing, for a sawtoothor similar wave. 3. In an oscilloscope or picturetube, the rapid return of the beam to itsstarting position.flyback checker An apparatus that senses thepresence of short or open circuits in motors,transformers, and generators, by measuring theamount of flyback (kickback).flyback power supply See KICKBACK POWERSUPPLY.flyback time The time taken for the electron beamin an oscilloscope tube, picture tube, or cameratube to return to its starting point after it hasreached the point of maximum deflection.

flyback transformer • focal length 293flyback transformer In a television receiver circuit,the horizontal output transformer. The unit supplieshorizontal scanning voltage and kickbackvoltage, which is rectified to produce the highvoltagedirect-current (dc) anode potential. Alsosee FLYBACK and KICKBACK POWER SUPPLY.flying eyeball An undersea exploration robot consistingof a television camera, illumination lamps,and thrusters (such as jets or propellers). A cable,which also serves as a tether, sends data to a humanoperator, and allows the operator to controlthe movements of the robot. In some cases, thetether/cable can be replaced by an infrared orvisible-light laser data link.flying-spot tube A tube, such as a camera tube, inwhich a rapidly deflected spot of light scans animage on a transparent screen; the spot is projectedthrough the picture to a photomultiplier.fly’s-eye lens A lens consisting of hundreds ofmuch smaller lenses. Used in microelectronic circuitfabrication to produce many images of thesame circuit.flywheel effect 1. In an inductance-capacitance(LC) tank circuit, the completion of a partial inputwave cycle at the resonant frequency, resultingfrom the storage and release of energy. This providesa nearly perfect sine-wave output for class-AB, class-B, and class-C radio-frequency (RF)power amplifiers. 2. In an LC tank circuit, the actionin which energy continues to oscillate betweenthe capacitor and inductor after an inputsignal has been removed. The oscillation stopswhen the tank-circuit finally loses the energy absorbed.The lower the inherent resistance of thecircuit, the longer the decrement (decay time).AmplitudeInput waveformFilled in byflywheel effectflywheel effect, 1.Timeflywheel synchronization A form of televisionscanning synchronization used when the receivedsignal is very weak. The synchronizationsignals from the transmitter are sensed by the receiver,which then produces its own local pulsesbased on the rate of received pulses.flywheel tuning A tuning dial mechanism inwhich the control shaft has a flywheel for thesmoother tuning action afforded by the addedmomentum.Fm Symbol for FERMIUM.FM Abbreviation of FREQUENCY MODULATION.f m Abbreviation of MODULATION FREQUENCY.FM-AM Pertaining to equipment that will operatewith either amplitude-modulated or frequencymodulatedsignals.FM-AM multiplier A method of frequency multiplicationusing both amplitude and frequency modulationof a carrier wave.FM broadcast band The 88- to 108-MHz frequencyband, within which channels spaced 200 kHzapart occupy positions from 88.1 to 107.9 MHz.FM detector See DISCRIMINATOR, RATIO DE-TECTOR, and SLOPE DETECTOR.FM-FM Frequency modulation by one or more FMsubcarriers.FM limiter In a frequency-modulation circuit, astage which holds the amplitude of the FM signalto a constant value. The limiter can be active(e.g., an amplifier-limiter transistor) or passive(e.g., a diode clipper).FM multiplex See MULTIPLEX ADAPTER.FM noise Unintentional modulation of a frequency-modulatedtransmitter, resulting fromnoise in the audio-input stages.FM-PM A system of modulation in which a carrieris phase modulated by frequency-modulated subcarriers.FM radar A radar system in which the signal is frequencymodulated; the distance to the target ismeasured in terms of the beat note betweentransmitted and reflected waves.FM repeater A two-way radio system composedof a simultaneously operating receiver andtransmitter, the latter of which retransmits(usually on a different frequency) all signalspicked up by the receiver. The system is usuallytower- or hilltop-mounted, and is used to extendthe range of two-way units in a communicationsnetwork.FM stereo The use of multiplex methods to transmitand receive stereophonic programs in an FMchannel. Also see MULTIPLEX ADAPTER.FM tuner A compact radio receiver that handlesfrequency-modulated (FM) signals, and deliversits low-amplitude audio output to a high-fidelitysystem. Compare AM TUNER and AM-FMTUNER.focal length Symbol, F. The distance from the centerof a lens or dish antenna to the principal focus.Also see PRINCIPAL FOCUS.

294 focus • folded patternfocus 1. The point at which rays converge. Also seePRINCIPAL FOCUS. 2. To bring rays to a point ofconvergence.focus coil See FOCUSING COIL.focus control In an oscilloscope or television circuit,the potentiometer that controls the voltageon the focusing electrode of the cathode-ray tubeand, accordingly, the sharpness of the image.focus grid 1. The focusing electrode in an electrostaticcathode-ray tube. 2. The focusing electrodein an oscilloscope tube.focusing Bringing a ray of particles or energy to acommon point. This can be done using lenses,deflecting coils, deflecting plates, or reflecting devices.Focusing can be done with acoustic waves,electromagnetic waves, and theoretically with anykind of disturbance propagated through anymedium.focusing anode See FOCUSING ELECTRODE.focusing coil An external coil used to focus anelectron beam in a cathode-ray tube. Also seeELECTROMAGNETIC FOCUSING.focusing electrode The internal electrode (grid orring) used to focus the electron beam in a cathode-raytube. Also called focus electrode. Also seeELECTROSTATIC FOCUSING and FOCUS GRID,1, 2.focusing magnet A permanent magnet assemblyfor focusing the electron beam in a cathode-raytube.foil 1. The thin conductive strips on a printedcircuitboard. 2. Also known as tape. Thin metalsupplied in strips, intended for use in certain securitysystems. It can be installed in closed loopsat potential points of entry.foil capacitor A capacitor whose plates are sheetsor strips of metal foil separated by a dielectricfilm.foil coil See FOIL-WOUND COIL.foil conductor A conductor that is a strip of metalfoil, rather than wire. Also see FOIL PATTERN.foil electroscope See LEAF ELECTROSCOPE.foil pattern The pattern of thin metal circuit pathsthat constitute the “wiring” of a printed circuit.Also see ETCHED CIRCUIT and PRINTED CIR-CUIT.foil-wound coil A coil wound with metal foil (usuallyaluminum or copper) instead of wire. Suchcoils substantially reduce the weight of largetransformers and filter chokes.foldback 1. See FOLDBACK CURRENT LIMITING.2. In audio recording, the routing of sound (via anaudio mixer) to some other destination in additionto the recording medium. Example: playingan electronic organ while singing, recording thearrangement on tape, and also listening to it (organand voice) in a headset.foldback current limiting In a power supply, amethod of automatically reducing the output currentto a safe level when the load current exceedsthe maximum recommended value. This actionprotects both the power supply and the poweredequipment.folded dipole A half-wavelength, center-fed antennaconstructed of two parallel wires with theirends connected together. It has the same lengthas a simple dipole antenna, but the feed-pointimpedance is four times that of the ordinarydipole. Instead of approximately 73 ohms, thefolded dipole presents a resistive impedance ofabout 300 ohms. This makes the folded antennadesirable for use with high-impedance, parallelwiretransmission lines. It also can be used toobtain a good match with 75-ohm coaxial cablewhen four antennas are connected in phase, orwith 50-ohm coaxial cable when six antennasare connected in phase. Compare DIPOLEANTENNA.1/2 λfolded dipolefolded pattern300-Ω Feederfolded horn A loudspeaker having a horn whoseflare is divided into several zigzagging chambers;that is, the horn is, in effect, folded to squeeze arequired length into a small cabinet.folded-horn enclosure See LABYRINTH SPEAKER.folded pattern An oscilloscope image having anelongated time axis obtained by successive horizontalsweeps—each placed slightly lower on the

folded pattern • fork oscillator 295screen than the preceding one. The foldedpatterntechnique provides a time axis severaltimes longer than the screen width.folding frequency In a system where sampling ismade at uniform frequency increments, the frequencycorresponding to half the sampling rate inhertz.foldover Distortion characterized by the horizontalor vertical overlapping of a television picture.follower A single-stage, active circuit characterizedby zero phase reversal, and voltage gain less thanunity. The emitter follower is also called a common-collectorcircuit; the source follower is alsoknown as a common-drain circuit. Characterizedby moderate to high input impedance, and lowoutput impedance over a wide band of frequencies.follower drive In a servo system, the drive thatmechanically follows the master drive.following blacks In a television picture, the effectin which a moving white object has a black borderfollowing it.following whites In a TV picture, the effect inwhich a moving dark object has a white borderfollowing it.follow-up motor See SERVOMOTOR.font The physical shape and size of the letters andnumbers in an alphanumeric system.font reticle In optical character recognition, anoverlay reference pattern of lines used to checkthe size and configuration of an input character,the size of punctuation marks, and spacing betweenlines and characters.food-service robot Any robot that is used for thepurpose of packaging, preparing, and/or servingfood.foot Abbreviation, ft. A unit of linear measure inthe English system equal to 0.3048 meter.foot-candle Abbreviation, fc. A unit of illuminance;1 fc is the amount of direct light emitted by 1 candela(see CANDLEPOWER) that falls on 1 squarefoot of a surface on which every point is 1 footaway from the source. In the International Systemof Units, the unit is lux (lumens per squaremeter). Compare METER-CANDLE.foot-candle meter A light meter whose scale readsdirectly in foot-candles.foot-lambert Abbreviation, fL. A unit of luminance;the average brightness of a surface thatemits or reflects 1 lumen per square foot. TheStandard International (S.I.) unit is the candelaper square meter (cd/m 2 ); 1 fL = 3.426 cd/m 2 .foot-poundAbbreviation, ft-lb. In the English system,a unit of energy equal to 1 pound displacedthrough 1 foot in the direction of the exertingforce. The Standard International (S.I.) unit is thejoule (j); 1 ft-lb = 1.356 j.foot-pound-second system See FPS SYSTEM OFUNITS.foot switch A switch operated by the foot, generallyused for the purpose of turning a playback orrecording system on and off. Often used for takingdictation.forbidden band See ENERGY GAP.forbidden character code An error-finding codeusing forbidden characters: combinations of prohibitedbits. Also called forbidden combination.forbidden energy band See ENERGY GAP.force 1. Symbol, F. Units: newton, dyne, poundal.The agency or influence that accomplishes work.2. An operator interjection made during a programrun that causes the computer to execute abranch instruction; it is usually necessary whena condition responsible for halting a programmust be bypassed.forced coding Programming that minimizes thetime required to retrieve information from storage.Also called minimum latency programming orminimum access programming.forced oscillations Oscillations in a circuit, such asin an inductance-capacitance (LC) tank, that resultfrom continuously applied alternating-current(ac) excitation. Compare FREE OSCILLATIONS.foreground job A relatively high-priority, shortrunningprogram that is carried out by interruptinga low priority, long-running program.Compare BACKGROUND JOB.force pump In a multistage vacuum system, thefirst pump that reduces the pressure considerablybelow atmospheric pressure. Also see DIF-FUSION PUMP and VACUUM PUMP.force summing device A transducer element thatis physically moved by a force being transduced.foreshortened addressing In control computers,the mixing of available storage by using simplifiedaddressing instructions.fork oscillator An audio-frequency oscillator controlledby a tuning fork. The dimensions of thefork determine its vibration frequency and, accordingly,the frequency of the oscillator.Tuningforkfork oscillatorB+B−AF output

296 form • forward voltage dropform 1. The core or frame upon which an inductoris wound. 2. A vessel, such as a mold, used in theshaping stage of a manufacturing process.formaldehyde Formula, HCHO. A colorless, pungentgas that is a constituent of many well-knownplastic insulating materials (see PHENOLFORM-ALDEHYDE PLASTICS).formant 1. The audio-frequency range in whichthe sound of a spoken syllable is concentrated. 2.Any general group of audio frequencies.formant filter In an electronic organ, an audio filterthat changes the waveshape of a tone so thatthe tone will have the desired characteristics.format 1. The form in which data is presented(e.g., the arrangement of characters, fields,words, totals, etc.). 2. To prepare a computer diskor tape so that it will accept data.form factor 1. The SHAPE FACTOR for a filter ortuned circuit. 2. For a half-cycle of an alternating-current(ac) quantity, the ratio of the rootmean-square(rms) value to the average value.form feed 1. A mechanical system that positionspaper being supplied to a line printer. 2. The FFcharacter that initiates advancement of printoutpaper in a printer. 3. The advancement of printoutpaper in a printer.form feed character In a control loop, a character(symbol, FF) used on printing devices for controllingform feed.forming See ELECTROFORM, 1.form stop An automatic device that stops a printerwhen the paper runs out.FORTH A high-level computer programming languageused in certain robots, automated factories,medical electronic devices, and electronicgames. It was originally developed in the 1970s tofacilitate computer control of equipment in astronomicalobservatories.FORTRAN A high-level computer programminglanguage developed in the 1950s, and still usedin some scientific and mathematical applications.It is not especially useful for the control of electronicor mechanical devices.fortuitous conductor A medium that creates anunwanted electrical path.fortuitous distortion Waveform distortion that resultsfrom causes other than characteristic effectsor bias effects.forward AGC Automatic gain control provided byspecial transistors whose transconductance decreaseswith increasing emitter current, and viceversa. Compare REVERSE AGC.forward-backward counter A counter that runsforward to perform addition and backward to performsubtraction.forward bias Forward voltage or current in a transistoror semiconductor diode.forward-blocking state For a silicon-controlledrectifier, the off state, during which the forwardbias is so much less than the forward breakovervoltage that only small off-state current flows.forward breakover voltage 1. For a semiconductorpn junction, the smallest forward voltage atwhich appreciable conduction occurs. This isabout 0.3 V for germanium and 0.6 V for silicon.2. For a silicon-controlled rectifier, the forwardvoltage value at which the device abruptlyswitches on.forward characteristic The current-voltage responseof a semiconductor junction that is biasedin the forward (high-conduction) direction. CompareREVERSE CHARACTERISTIC.forward compatibility standards Standards developedto make programs for one computer systemusable for additional or replacement equipment.forward conduction The increased current conductionthrough a pn junction that is forward biased.Compare REVERSE CONDUCTION.forward current Symbol, I f . The increase in currentflow through a pn junction that is forward biased.Compare REVERSE CURRENT.forward current-transfer ratio The current gain ofa bipolar transistor (alpha for the common-baseconnection and beta for the common-emitter connection).forward power 1. In a transmission line, the powerleaving the generating source, as measured by adirectional wattmeter at that location. 2. Thepower arriving at the load at the terminating endof a transmission line.forward propagation by ionospheric scatter SeeFORWARD SCATTER.forward propagation by tropospheric scatter Abbreviation,FPTS. A method of transmitting partof a radio signal beyond the horizon using thescattering effect of the troposphere. Also see FOR-WARD SCATTER and TROPOSPHERE.forward resistance Symbol, R f . The resistance of aforward-biased pn junction. Also see FORWARDBIAS. Compare REVERSE RESISTANCE.forward-reverse ratio See FRONT-TO-BACK RA-TIO.forward scatter Also called forward propagation byionospheric scatter. The scattering of a radio wavein the normal direction of propagation to pointsbeyond the skip zone. The phenomenon occursbecause of waves returned from regions in theionosphere. Compare BACK SCATTER.forward transconductance Symbol, g fs . For acommon-source-connected FET, the ratio of adrain-current differential to the differential ofgate-to-source voltage that produces it; g fs =1000(dI D /dV GS ), where g fs is in microsiemens, I D isthe drain current in milliamperes, and V GS is thegate-to-source voltage in volts.forward voltage Symbol, E f or V f . Voltage whosepolarity causes maximum current to flow througha pn junction. Compare REVERSE VOLTAGE.forward voltage drop The voltage across a semiconductorjunction that is biased in the forward(high-conduction) direction. Compare REVERSEVOLTAGE DROP.

FOSDIC • fps system of units 297FOSDIC Acronym for film optical scanning devicesfor input to computer.Foster-Seeley discriminator A discriminator circuitin which the diodes are operated from asingle-tuned, center-tapped secondary of the inputtransformer. The center tap is also capacitivelycoupled to the top of the transformer’s primarycoil. Compare TRAVIS DISCRIMINATOR.FromlimiterC1E pB+T1C2E1E2C3R2A+−R3Foster-Seeley discriminatorAudiooutputC4Foucault currents See EDDY CURRENTS.four-address instruction A computer instructionin which the address is comprised of four addresses:two for operands, one for the result ofthe operation, and one for the upcoming instruction.four-channel sound system Also called quadraphonicsound system. A high-fidelity, stereophonicsound reproduction system, in whichthere are four channels, rather than the usualtwo. The channels are generally designated leftfront, left rear, right front, and right rear. Thefour-channel system is an enhancement of twochannelstereo.four-dimensional continuum 1. In relativistictheory, the space-time continuum. There arethree spatial dimensions and one time dimension.A point in the continuum can be uniquelydefined by three space coordinates and one timecoordinate. 2. Any continuum that requires fourand only four coordinates to uniquely determinethe position of a point.Fourier analysis Use of the FOURIER SERIES toevaluate the components of a complex wave, or todefine a complex wave in terms of its components.Fourier series An infinite mathematical series thatshows any periodic function to be a combinationof sine terms and cosine terms. Any complexwave (e.g., a square wave) consists of fundamentaland harmonic sine-wave components. In simplifiedform, the series is:f(x) = A 0 /2 + A 1 cos x + B 1 sin x + A 2 cos 2x + B 2sin 2x + A 3 cos 3x + B 3 sin 3x + . . .In general, the more terms to which the series iscalculated, the better the approximation of acomplex waveform.C5four-layer diode A dual-terminal npnp device thatis usable as a bistable switch, sawtooth or pulsegenerator, memory device, etc.four-layer transistor A transistor in which thewafer or block has four processed regions; however,the device might have only three terminals.Some examples are the silicon-controlled rectifier,silicon-controlled switch, and thyristor.four-level laser A laser identical to the three-levellaser, except for the addition of one excited state.four-phase system A two-phase system in whichthe center taps of the coils are interconnected.Also called QUARTER-PHASE SYSTEM.four-terminal network A network having two inputterminals and two output terminals. One inputterminal can be internally connected to oneoutput terminal (as when a common ground ispresent), but this is not mandatory.four-space 1. A mathematical space in which fourcoordinates (w,x,y,z) are necessary to uniquelydefine a point. 2. Three-dimensional space withthe addition of time as a fourth dimension; coordinatesare, for example, (x,y,z) for space and t fortime.four-space coordinates 1. A system of coordinatesfor uniquely determining points in four-space.Such a system can be Euclidean or non-Euclidean, as with space of any number ofdimensions. 2. The set of numbers that defines aparticular point uniquely in four-space; for example,P = (3,–15,0,–7).four-sphere The set of all points equidistant from agiven point P in four-space. Formula is w 2 + x 2 +y 2 + z 2 = r 2 , where r is the radius and the coordinatesare (w,x,y,z) in the Euclidean, Cartesian system.four-track recording A tape recording in whichfour channels are recorded in two adjacent trackson the tape. Usually, tracks number 1 and 3 arein the forward direction, and tracks number 2and 4 are in the reverse direction.four-track tape A magnetic tape with four parallelsound paths.four-wire wye system A three-phase system inwhich three wires supply the respective phases, afourth being the neutral conductor.F p Symbol for POWER-LOSS FACTOR.fp Abbreviation of FREEZING POINT.FPC Abbreviation of Federal Power Commission.FPI Abbreviation of FUEL-PRESSURE INDICATOR.FPIS Abbreviation of forward propagation by ionosphericscatter. See FORWARD SCATTER.fpm Abbreviation of feet per minute.fps 1. Abbreviation of feet per second. 2. Abbreviationof frames per second. 3. Abbreviation of footpound-second(fps), a chiefly British system ofunits.fps system of units The British system of units ofmeasurement that uses the foot for length, thepound for mass, and the second for time. CompareCENTIMETER-GRAM-SECOND and INTER-NATIONAL SYSTEM OF UNITS.

298 FPTS • Fraunhofer regionFPTS Abbreviation of FORWARD PROPAGATIONBY TROPOSPHERIC SCATTER.Fr Symbol for FRANCIUM.fr Abbreviation of FRANKLINE.fractional exponent An exponent indicating that anumber is to be raised to a fractional power (e.g.,10 4/3 ). The numerator of the exponent indicatesthe power to which the base number must beraised; the denominator of the exponent indicatesthe root that must be taken of the result. Thus,na/b is equal to the bth root of na.fractional gain Amplification less than unity. Anotable example is the transfer function of asource follower or emitter follower.fractional horsepower Any power rating lowerthan one horsepower (1 hp). Also see HORSE-POWER.fractional uncertainty See RELATIVE UNCER-TAINTY.frame 1. A single, complete video image, scannedin 1 ⁄30 second in conventional television receivers.2. A single motion-picture (film) image. 3. Inpacket communications, a fundamental unit ofdata. The three types are called information (I)frame, supervisory (S) frame, and unnumbered (U)frame. 4. One of a recurring cycle of pulses. 5. Inpulse-code modulation (PCM), a cyclic wordgroup including a sync signal. 6. A complete commutatorcycle. 7. A digital representation of a setof objects, useful in robotics and artificial intelligence(AI).frame alignment The condition in which the receiver,or receiving apparatus, is in correct alignmentwith the signal to be received. In television,for example, this results in true rendition of thepicture. Incorrect frame alignment (misalignment)might result in the picture being split withthe top and bottom interposed. For other types ofsignals, misalignment would result in garbled reception.frame-alignment signal In television, a transmittedsignal that is used to ensure that frame alignmentoccurs in the receiver. It is a form ofsynchronizing pulse.frame-alignment time slot In a transmitted televisionframe, an interval of time that is used forthe purpose of transmitting a frame-alignmentsignal. There might or might not be other signalinformation transmitted during this time interval.frame frequency The number of frames of a motion-picturefilm that come into position per unitof time in a camera, projector, or pickup.frame of reference Geometric relationships usedto describe the location of a body in space.frame rate See FRAME FREQUENCY.frame-repetition rate See FRAME FREQUENCY.frame roll Momentary vertical roll in a televisionpicture.frame synchronizing signal 1. In pulse amplitudemodulation (PAM), a coded pulse indicating initiationof a commutation frame. 2. In pulse-codemodulation (PCM), a signal used to identify an informationframe.framing 1. Synchronization of the vertical componentof a video signal so that the top and bottomof the transmitted and received pictures line up.2. The process of lining up the top and bottom ofa movie picture. 3. Alignment of the characters ina digital alphanumeric transmission.francium Symbol, Fr. A radioactive metal elementof the alkali-metal group. Produced artificiallythrough radioactive disintegration. Atomic number,87. Atomic weight, 223.Frankenstein scenario A theme often depicted inscience fiction, in which intelligent machinesseize power from their human creators. With therapid advance of technology, especially inrobotics and artificial intelligence (AI), some people,including a few educated researchers, believethis scenario is within the realm of possibility.Most scientists think it is highly improbable.Franklin antenna A vertical collinear array thatproduces omnidirectional gain because of phasingamong the individual components.frankline (Benjamin Franklin, 1706–1790) Abbreviation,fr. A name that has been suggested forthe unit of electric charge; 1 fr is the charge thatexerts a force of 1 dyne on an equal charge at adistance of 1 centimeter in a vacuum.Franklin oscillator A dual-terminal, audio/radiofrequency(AF/RF) oscillator circuit. Consists of aB−B+Franklin oscillatorOutputtwo-stage, resistance-capacitance (RC) coupledamplifier, with a tuned inductance-capacitance(LC) tank in the input gate circuit, and with capacitivefeedback from the second drain to thetank.Fraunhofer region The area surrounding a radiatingantenna, throughout which the energy ap-

Fraunhofer region • frequency band 299pears to come from a single point located near theactual antenna.free air resonance For a speaker, the resonant frequencyor frequencies exhibited when the deviceis not mounted in a cabinet.free carrier A free electron or, in a semiconductormaterial, the equivalent hole. Also see ELEC-TRON and HOLE.free charge The portion of a charge on a conductorthat, being unaffected by a neighboring charge,will escape to ground when the conductor isgrounded. Compare BOUND CHARGE.free electron 1. An electron situated in one of theouter orbits of an atom, held loosely by the nucleus.Because free electrons can easily escapethe attraction of atomic nuclei, they will driftamong atoms if the material is subjected to anelectric potential. The result is electric current.Also see ELECTRON and BOUND ELECTRON. 2.An electron that is not associated with any atomicnucleus.free field Data organized in a storage medium insuch a way that a data item or field can be anywherein the medium. Compare FIXED FIELD.free impedance For a transducer, the inputimpedance produced by a perfectly shortcircuitedload.free magnetic pole A magnetic pole that is so wellisolated from its opposing pole that it experienceslittle or no influence from the latter.free magnetism A theoretical medium or fluid towhich magnetic effects are conventionally given.The sum of free magnetism in any given object isalways zero. Within any small part of the field, thefree magnetism is thought of as flux lines. Thistheoretical medium can be any nonmagnetic material.free net In radio communications, a network inwhich stations are free to communicate withother stations in the net without constant supervisionby the net control station. Such communicationis carried out on a frequencyslightly above or below that of the net’s formaloperation.free oscillations Oscillations in a circuit, such asan inductance-capacitance (LC) tank, that continueafter excitation has been removed. Also seeFLYWHEEL EFFECT. Compare FORCED OSCIL-LATIONS.free path In a gas tube, the path taken by an electronas it collides with atoms. Also see MEANFREE PATH.free-power supply 1. A simple tuned radio-frequency(RF) detector diode, used to rectify a radiosignal and supply small amounts of direct currentfor the operation of low-powered transistorcircuits. 2. See SOLAR BATTERY.free reel The supply reel of a magnetic-taperecorder.free-running frequency The frequency at which asynchronized generator, such as a multivibratoror self-excited oscillator, will operate when thesynchronizing voltage is removed.free-running multivibrator See ASTABLE MULTI-VIBRATOR and UNCONTROLLED MULTIVIBRA-TOR.free space Empty space; a theoretical ideal.free-space loss Radio transmission loss disregardingvariable factors (a theoretical condition).free-space pattern The ideal directivity pattern ofan antenna that is situated many wavelengthsabove ground. In use, this pattern is modified byreflections from ground.free speed The angular velocity of an unloadedmotor.free-standing display In a computer system, a remotedisplay unit for prompting peripheral operators.freezing point Abbreviation, fp. The temperatureat which a liquid starts becoming a solid at normalpressure. Compare MELTING POINT.F region Also called F layer. A region of the ionospherewith an altitude at night of approximately175 miles. In daytime, the region splits into thelower F1 region and the higher F2 region. Thislayer is primarily responsible for long-distancepropagation of radio waves at high frequencies(3 MHz to 30 MHz). At times it returns waves atfrequencies as high as about 70 MHz.Fremodyne detector A frequency-modulation(FM) detector that is essentially a conventionalamplitude-modulation (AM) circuit detuned toone side of resonance (slope-tuned) to demodulatea frequency-modulated signal. Also seeSLOPE DETECTOR.French phone See CRADLEPHONE.freqmeter Contraction of FREQUENCY METER.frequency Symbol, f. The rate at which a phenomenonis repeated. The basic unit of frequencyis the Hertz (Hz), which represents onecomplete cycle per second. Common units encounteredin electronics are the kilohertz (kHz),megahertz (MHz), and gigahertz (GHz), where1 kHz = 10 3 Hz, 1 MHz = 10 6 Hz, and 1 GHz = 10 9Hz. Occasionally, the terahertz (THz) is used;1 THz = 10 12 Hz.frequency-agile radar A radar system in which thetransmitter frequency is shifted in a predeterminedpattern for the purpose of avoiding detection.A frequency-agile radar system, with acomplex frequency control program, is very difficultto jam.frequency allocation 1. The assignment of frequenciesto radio and allied services by the licensingauthority (in the United States, theFederal Communications Commission). 2. A specificassignment of a frequency or a band of frequencies.Also see RADIO SPECTRUM.frequency band A given range of frequencies, usuallyspecified for some application (e.g., the bandallocated for standard radio broadcast service).Also see BAND.

300 frequency bias • frequency driftfrequency bias An intentional change in the frequencyof a transmitted signal.frequency bridge 1. Any alternating-currentbridge, such as the Wien bridge or resonancebridge, that can be nulled at only one frequencyfor a given set of bridge-arm values. 2. Any alternating-currentbridge that is used to measureunknown frequencies.frequency calibrator A device, such as a crystal oscillator,that provides a signal of precise frequencywith which other signals can be compared. Alsosee SECONDARY FREQUENCY STANDARD.frequency changer 1. A superheterodyne converter(see CONVERTER). 2. A motor-generator inwhich the output voltage has the same value asthe input voltage, but is of a different frequency.3. See FREQUENCY-MULTIPLYING TRANS-FORMER. 4. See FREQUENCY MULTIPLIER.frequency-change signaling See FREQUENCY-SHIFT KEYING.frequency channel A relatively narrow segment ofa frequency band allocated to a station in a particularservice. The bandwidth of the channel dependson the type of modulation used, the type ofdata to be transmitted, and the speed or fidelity ofthe data to be transmitted.frequency comparator A device, such as an oscilloscopeor zero-beat indicator, used to check onefrequency against another. Also see FREQUENCYCOMPARISON.frequency comparison The observation of a currentor voltage of one frequency for similarities inthat of another frequency. Comparisons (as infrequency matching) can be made by audiomeans, by visual means, or both. Common instrumentsused are oscilloscopes, beat-note detectors,and beat-note meters.frequency-compensated attenuator An attenuator,such as one in an electronic voltmeter orwideband oscilloscope, that has been modified bythe addition of capacitors or inductors to achievereasonably flat response over a wide range of frequencies.frequency compensation The modification of acircuit, such as an amplifier or attenuator, by theaddition of capacitors or inductors to tailor its responseat specified frequencies.frequency control 1. An adjustable component(potentiometer, variable capacitor, or variable inductor)with which the frequency or frequency responseof a circuit is adjusted. 2. A device, suchas a quartz crystal or tuning fork, that automaticallysets the frequency of an oscillator.frequency conversion The process of changing asignal from one frequency to another, usuallywithout altering the signal bandwidth. In somecases, a signal is turned “upside down” by thisprocess [e.g., an upper-sideband (USB) signalmight be changed to a lower-sideband (LSB) signal].Generally accomplished by means of aMIXER.frequency converter 1. An active or passive devicefor changing the frequency of a signal. 2. Themixer in a superheterodyne circuit.frequency correction Manual or automatic resettingof a deviated frequency to its original value.frequency counter An instrument that counts signalcycles or pulses over a standard time base (afrequency measurement). Often used to accuratelymeasure the frequencies of radio or televisionsignals; in this application, it is a precisionFREQUENCY METER.frequency cutoff See CUTOFF FREQUENCY.frequency detector See FREMODYNE DETEC-TOR.frequency deviation 1. The degree to which a frequencychanges from a prescribed value. Thus, ifthe frequency of a 1000-Hz oscillator drifts between990 and 1010 Hz, the deviation is ±10 Hz.2. In a frequency-modulated (FM) signal, theamount of instantaneous frequency shift aboveand below the unmodulated carrier frequency.frequency-deviation meter In frequency-modulation(FM) communications operations, a meterthat gives a direct reading of frequency deviationresulting from a modulating signal. It uses eithera tuned circuit or a frequency comparator.frequency difference 1. In a superheterodyne circuit,the difference between the signal frequencyand the oscillator frequency. 2. In any beatfrequencyoperation, the quantity f 2 – f 1 , where f 2is the higher frequency and f 1 is the lowerfrequency. Compare FREQUENCY SUM.frequency discriminator See DISCRIMINATOR.frequency distortion A form of distortion in whichthe amplification of some frequencies is differentfrom that of others.frequency distribution See DISTRIBUTION, 2.frequency diversity The transmission and receptionof signals at two or more frequencies for thepurpose of reducing the effects of fading. It is generallyused in long-distance, high-frequency circuits.frequency divider A circuit or device whose outputfrequency is a fraction of the input frequency.Compare FREQUENCY MULTIPLIER.frequency-dividing network See CROSSOVERNETWORK.frequency-division multiplex A form of multiplesignalparallel transmission in which a single carrieris modulated by two or more signalssimultaneously.frequency doubler A circuit that multiplies an inputfrequency by two. If a doubler’s input circuitis tuned to frequency f, then its output circuit isgenerally tuned to 2f. Frequency doubling is performedby various nonlinear devices, includingtransistors, varactors, and biased diodes.frequency drift An undesired, usually gradual,change in the frequency of a signal from its intendedfrequency or channel; expressed in hertzor kilohertz.

frequency function • frequency response 301InTunedto2ffrequency doublerTunedto2fOutfrequency function See PROBABILITY DENSITYFUNCTION.frequency indicator 1. A device that indicateswhen a phase or frequency is common to two alternatingcurrents. 2. The display or dial thatshows the operating frequency of a radio receiveror transmitter. 3. See FREQUENCY ME-TER.frequency keying See FREQUENCY-SHIFT KEY-ING.frequency meter An instrument for measuring thefrequency of an alternating current. The severaldifferent types are used in different applications.Also see AUDIO FREQUENCY METER, FRE-QUENCY COUNTER, POWER-FREQUENCY ME-TER, and WAVEMETER.frequency-modulated radar See FM RADAR.frequency modulation Abbreviation, FM. Amethod of conveying intelligence in wireless communicationsand broadcasting. The amplitude ofthe carrier remains constant, and the instantaneousfrequency varies. One scheme for obtainingthis type of modulation is to apply themodulating signal to a varactor in an oscillator.Another method is to modulate the phase of theoscillator signal. This causes small fluctuationsin the frequency as well, because any instantaneousphase change shows up as an instantaneousfrequency change (and vice versa). Alsosee AMPLITUDE MODULATION, PHASE MODU-LATION, SINGLE SIDEBAND.frequency modulation deviation 1. In frequencymodulation (FM), the largest difference betweenthe instantaneous signal frequency and the unmodulatedcarrier frequency. 2. The maximumbandwidth of an FM signal at its audio modulationamplitude peak.frequency modulator 1. A circuit or device thatmodulates the frequency of an oscillator. 2. Themodulator section of an FM transmitter.frequency monitor A device used (often continuously)to check the frequency of a signal (e.g., afrequency-deviation meter used in radio broad-cast stations or a frequency meter used in electric-generatingstations).frequency multiplier A circuit or device whose outputfrequency is a multiple of the input frequency.See, for example, FREQUENCY DOUBLER.frequency-multiplying amplifier See MULTI-PLIER AMPLIFIER.frequency-multiplying transformer A magneticamplifier that generates harmonics of the supplyfrequency. The effect results from the nonlinearityof the transformer core material.frequency offset 1. The difference between an actualfrequency and the desired frequency. 2. In acommunications transceiver, the difference betweenthe receiver frequency and the transmitterfrequency. In some modes, such as single-sideband(SSB), the offset is normally zero. In othermodes, notably continuous-wave (CW) Morsecode, the offset is normally several hundred Hz.3. See FREQUENCY SPLIT, 1.frequency overlap 1. A common band of frequenciesbetween two adjacent channels in a communicationssystem. 2. A common frequency regionbetween two assigned bands. 3. A condition inwhich parts of the sidebands of two signals occupythe same range of frequencies.frequency pulling A change in the frequency of acircuit, especially of a self-excited oscillator, resultingfrom the detuning effects of an externalcircuit, device, or condition (such as body capacitanceor a change in the temperature).frequency pushing An effect in which a currentchange in a source oscillator causes a shift insource frequency.frequency quadrupler See QUADRUPLER, 2.frequency quintupler See QUINTUPLER, 2.frequency range 1. A communication system’s frequencytransmission limits, beyond which thepower output is attenuated below a specifiedamount. 2. The frequency band or bands withinwhich a radio transmitter, receiver, or transceiveris designed to operate.frequency ratio counter See FREQUENCY RATIOMETER.frequency ratio meter A meter that indicates theratio between two frequencies, and is useful inthe quick identification of harmonics.frequency record A phonograph test disk containingrecordings of various frequencies at specifiedamplitudes.frequency rejection The elimination, usually by afilter, of a single frequency (or narrow band of frequencies)from a mixture of frequencies. CompareFREQUENCY TRANSMISSION.frequency relay A frequency-sensitive relay (seeSELECTIVE RELAY, 1).frequency response A performance characteristicthat describes the operation of a device or circuitover a specified range of signal frequencies (e.g.,the gain-versus-frequency characteristic of anamplifier).

302 frequency-response recorder • frequency-variation methodfrequency-response recorder A graphic recorderthat automatically plots a frequency-responsecurve for a device under test.frequency run A test, or test sequence, that determinesthe loss characteristics of a circuit as afunction of the operating frequency.frequency scanning 1. A controlled fluctuation ofthe transmitter frequency in a frequency-agileradar or communications system. 2. In a programmable,digital communications receiver ortransceiver, a form of simultaneous digital monitoringof two or more channels. 3. The frequencyresponsechange in a spectrum analyzer.frequency scaler See SCALER.frequency-selection sensor A sensor that passesor rejects phenomena at certain frequencies whileignoring those at other frequencies.frequency-selective relay See SELECTIVE RE-LAY, 1.frequency-sensitive bridge A bridge, such as theWien bridge or resonance bridge, that can be balancedat only one frequency for a given set ofbridge-arm values.frequency separator In a television receiver, thecircuit that separates horizontal- and verticalscanningsync pulses.frequency-shift keying Abbreviation, FSK. Amethod of digital signal transmission. The logic 1(high or mark) pulses are sent at a specific carrierfrequency, and the logic 0 (low or space) pulsesare transmitted at another frequency slightlyhigher or lower than the logic 1 pulses. This isthe most primitive form of frequency modulation(FM). The difference between the mark and spacefrequencies is called the shift, and is usuallybetween 100 and 1000 Hz. CompareAUDIOFREQUENCY-SHIFT KEYING.frequency-shift radar See DOPPLER RADAR.frequency span The difference f 2 – f 1 , where f 1 isthe lowest frequency in a given range of frequenciesand f 2 is the highest frequency. CompareFREQUENCY SPREAD.frequency spectrum All electromagnetic radiation,from longest to shortest wavelengths, withina set of specified limits.frequency split 1. The difference between the receiverfrequency and the transmitter frequency ina communications repeater. 2. See FREQUENCYOFFSET, 2.frequency spotting The setting-up of signals atreference frequencies (usually harmonics of astandard-frequency oscillator), and their use inidentifying unknown frequencies. Also see FRE-QUENCY CALIBRATOR.frequency spread The ratio f 2 /f 1 , where f 1 is thelowest frequency in a given range of frequenciesand f 2 is the highest frequency. Compare FRE-QUENCY SPAN.frequency stability The degree to which a frequencyremains constant during variations intemperature, current, voltage, and similar factors.It is specified in Hertz (Hz), kilohertz (kHz),or megahertz (MHz), or in parts per million perunit of the variable parameter.frequency standard A signal source of a precisefrequency, against which other signal sourcescan be calibrated. See specifically PRIMARY FRE-QUENCY STANDARD and SECONDARY FRE-QUENCY STANDARD.frequency sum In a beat-frequency system, thequantity f 1 + f 2 , where f 1 is the lower frequencyand f 2 is the higher frequency. Compare FRE-QUENCY DIFFERENCE, 2.frequency swing See FREQUENCY DEVIATION, 1,2.frequency synthesizer A generator of signals at aprecise frequency or set of frequencies, generallyadjustable in discrete frequency steps. It is usedfor test or communications purposes. The signalsare derived from a single-frequency source, usuallya crystal oscillator. Also see SIGNAL SYN-THESIZER.frequency tolerance The acceptable amount bywhich a frequency can vary from its intendedvalue. The tolerance can be specified as a percentageof the stated frequency, a certain numberof parts per million, or a certain number of hertz(Hz), kilohertz (kHz), or megahertz (MHz). Example:3.675000 MHz ±10 Hz.frequency-to-voltage converter A device or circuitthat delivers an output voltage that is proportionalto the input frequency.frequency translation 1. The conversion of agiven frequency band from one part of the electromagneticspectrum to another, without changingthe actual separation of channels or theoverall width of the band. 2. See FREQUENCYCONVERSION.frequency transmission The passage of a frequencyor band of frequencies from a mixture offrequencies through a filter or other circuit. CompareFREQUENCY REJECTION.frequency tripler See TRIPLER, 2.frequency-variation method A method of determiningthe figure of merit (Q) of a tuned circuit byvarying the frequency of the applied test voltage

front contact The movable contact of a relay.front end 1. The first radio-frequency (RF) amplifierstage in a radio or television receiver. 2. The confrequency-variationmethod • ft 303from resonance (f r ) to a high point (f 2 ) and a lowpoint (f 1 ). At the high and low points, the circuitvoltage is 0.707 times the voltage at resonance.The figure of merit then is calculated from the formulaQ = f r /(f 2 – f 1 ).frequency-voltage converter See FREQUENCY-TO-VOLTAGE CONVERTER.frequency-wavelength conversion See WAVE-LENGTH-PERIOD-FREQUENCY RELATIONSHIPS.fresnel (A.J. Fresnel, 1788–1827) A unit of frequencyequal to 10 12 Hz. Also called terahertz andabbreviated THz.fresnel lens A usually square plastic sheet withprogressively thicker concentric areas; its effect issimilar to that of an automotive headlight lens.Fresnel number A measure of the relative effects ofdiffraction in an optical lens. The Fresnel numberis equal to the radius of the lens divided by theproduct of the light wavelength and the lens focallength, all measured in the same units.Fresnel region For a radio-frequency transmittingantenna, the zone between the antenna and theFRAUNHOFER REGION. The size of the Fresnelregion depends on the wavelength of the radiatedenergy.frictionThe resistance to mechanical motion whenone material is rubbed against another. Frictionwas one of the earliest sources of human-madeelectricity (see FRICTIONAL ELECTRICITY andELECTRIC MACHINE). Electrical resistance, opposingthe flow of current, is analogous to friction.frictional electricity Static electricity generatedby rubbing one material against another.frictional electric machine See ELECTRIC MA-CHINE.frictional error The change in parameters of aphonograph pickup, resulting from friction withthe disk surface.frictional loss A decrease or impairment in the efficiencywith which energy is converted into usefulwork, caused by friction between movingparts.fringe area The region in which a signal falls to theminimum field strength necessary for satisfactorycommunication.fringe howl In a regenerative detector, a howlingsound that occurs when the transistor first beginsto oscillate, obscuring the signal. The term isused because the circuit is operated at the fringeof oscillation.fringing See EDGE EFFECT.Fritch Trade name (American Telephone & TelegraphCo.) for frequency-selective switch.fritting A condition in which electrical contact corrosioncreates a small hole, through whichmolten contact material passes to form a conductivebridge.verter portion of a superheterodyne communicationsreceiver (i.e., the RF amplifier, first detector,and local oscillator). Compare REAR END.front layer photocell See RECTIFIER PHOTO-CELL.front porch In a television horizontal sync pulse,the interval between the end of the sync pulseand the fall of the blanking pedestal. CompareBACK PORCH.front projection In big-screen video, a scheme inwhich the images from a set of bright cathode-raytubes (CRTs) are projected onto a reflectivescreen, in a manner similar to the way the film isprojected in a movie theater.front-surface mirror Also called first-surface mirror.A mirror that has its reflective material on thefront, instead of on the back.front-to-back ratio Abbreviation, f/b. An expressionof the ability of a unidirectional antennato concentrate its radiation or response inits favored direction. This specification is nearlyalways given in decibels (dB). The field strengthin the favored direction is compared with thefield strength exactly opposite the favored directionat the same distance from the antenna infree space, at the same frequency, and with thesame power applied to the antenna feed point.Measurements can be made with a calibratedfield-strength meter. Compare FRONT-TO-SIDE RATIO.front-to-side ratio Abbreviation, f/s. An expressionof the directivity of a unidirectional or bidirectionalantenna system. This specification isnearly always given in decibels (dB). The fieldstrength in the favored direction(s) is comparedwith the field strength at right angles to the favoreddirection(s) at the same distance from theantenna in free space, at the same frequency, andwith the same power applied to the antenna feedpoint. Measurements can be made with a calibratedfield-strength meter. Compare FRONT-TO-BACK RATIO.frost alarmA device or circuit that responds to thepresence of frost and actuates an alarm. Suchalarms are sensitive to temperature, moisture, orboth.FRUGAL Acronym for FORTRAN rules used as ageneral applications language.FRUSA Acronym for flexible rolled-up solar array,such as the type used in spacecraft and communicationssatellites.F scan In radar operations, a display in which acentral blip represents the target at which theantenna is pointed; horizontal and verticaldisplacement of the blip indicate correspondinghorizontal and vertical aiming errors.FSK Abbreviation of FREQUENCY-SHIFT KEYING.FSM Abbreviation of FIELD-STRENGTH METER.FS meter See FIELD-STRENGTH METER.FSR Abbreviation of feedback shift register.ft Abbreviation of foot or feet.

304 FT-cut crystal • full-scale sensitivityFT-cut crystal A piezoelectric plate cut from aquartz crystal at an angle of +57°, with respect tothe z-axis. Also see CRYSTAL AXES and CRYS-TAL CUTS.ft-Lb Abbreviation of FOOT-LAMBERT.ft-lb Abbreviation of FOOT-POUND.Fuchs antenna A simple antenna consisting of asingle-wire radiator without feeder or transmissionline, connected directly to the transmitter. Itis usually an odd multiple of 0.25 wavelengthlong. When a good radio-frequency (RF) ground isused, this antenna can be effective at high frequencies,although part of its radiated field is ofteninside the transmitter building.TXFuchs antennaRadiatingelement:odd multipleof λ/4fuel alarm A sensing circuit that actuates analarm when the fuel in a tank or reservoir falls toa prescribed level.fuel cell A generator that produces electricity directlyfrom a reaction between fuel substances,such as hydrogen and oxygen.fuel-flow alarm An electronic circuit that actuatesan alarm when fuel flow changes from a prescribedvalue.fuel-flow control A servo system that automaticallymaintains or corrects the flow rate of a fuel.fuel-flow gauge See FUEL-FLOW METER.fuel-flow indicator See FUEL-FLOW METER.fuel-flow meter An instrument for measuring fuelflow rate.fuel-flow switch A switch that is actuated by fuelflowing in pipes or other channels.fuel gauge An instrument consisting of a transducerthat senses the level of liquid fuel in a tankand delivers a proportional output current orvoltage, and an electric meter whose needle is deflectedin proportion to the current or voltageand, therefore, to the fuel level. Alternatively, themeter can be a direct-readout digital device,showing the number of gallons remaining in thetank, and/or the extent to which the tank is full(fraction or percentage).fuel meter See FUEL GAUGE.fuel-pressure indicator An instrument for measuringfuel pressure in pipes or other channels.fuel-pressure meter See FUEL-PRESSURE INDI-CATOR.full adder In a digital computer, an adder circuitthat can handle the carry signal, as well as the binaryelements that are to be added. Also seeADDER and CARRY. Compare HALF ADDER.full bridge A bridge-rectifier circuit in which eachof the four arms contains a diode. By comparison,the three-quarter bridge contains a resistor inone arm; the half bridge, resistors in two arms;and the quarter bridge, resistors in three arms.full-duplex system In data communications, asystem that transmits data in both directions simultaneouslyand continuously. Compare HALF-DUPLEX SYSTEM.full-focus yoke See COSINE YOKE.fullhouse A multichannel radio-control modelplane system that allows the use of a realisticcomplement of working control surfaces.full-load current The output current from asource when the load is maximum (that is, theload resistance is minimum).full-load power The power drawn from a sourcewhen the load is maximum (that is, the load resistanceis minimum).full-load voltage The output voltage of a sourcewhen full power is drawn [i.e., when the load ismaximum (that is, the load resistance is minimum)].full-load wattage See FULL-LOAD POWER.full-power frequency response The highest frequencyat which a signal can fluctuate at full voltage(peak-to-peak) without causing distortion ofmore than a certain specified amount.full-range speaker See MONORANGE SPEAKER.full scale 1. The operating range of an instrument.2. In an analog meter, the quantity indicated bymaximum deflection of the needle (usually at theextreme right-hand end of the calibrated scale).3. Transducer output as a function of highest allowableinput stimulus.full-scale current Symbol, I FS . In a digital-toanalogconverter, the maximum current that canoccur at the output.full-scale error For an electrical indicating instrument,the rated full-scale input signal minus theactual input signal that causes a full-scale deflection.Thus, the predictable error in an instrument,expressed as a percentage of the full-scale reading.full-scale frequency Generally expressed in Hertz(Hz) or kilohertz (kHz). The maximum frequencyat which a voltage-to-frequency converter can operatewhile remaining within its specifications.full-scale sensitivity The current, voltage, orpower required to deflect a meter mechanism tofull scale.

full-scale symmetry • function generator 305full-scale symmetry Expressed in microamperes(mA). The mathematical difference between thefull-scale current outputs in a complementaryoutputdigital-to-analog converter.full track A recording track covering the full widthof a magnetic tape.full-track head A tape-recorder head having a gapthat covers the full width of the tape.full-track recording Usually applicable to quarterinchor narrower magnetic recording tape, a onetrackrecording made by a head that magnetizesessentially the entire width of the tape.full-wave bridge rectifier See BRIDGE RECTI-FIER.full-wave, center-tap rectifier A circuit in whichthe center-tapped secondary winding of a transformeroperates two rectifier diodes, each on analternate half-cycle of secondary voltage. The frequencyof the ripple in the direct-current (dc) outputis equal to twice the alternating-current (ac)input frequency. Compare BRIDGE RECTIFIER.acinfull-wave, center-tap rectifier+Pulsatingdc outfull-wave detector A detector circuit using twodiodes in a full-wave, center-tap rectifier configuration.full-wave doubler See FULL-WAVE VOLTAGEDOUBLER.full wavelength Symbol, λ. The distance that correspondsto 360 degrees of phase as an electromagnetic(EM) field is propagated. In free space, itis related to the frequency by a simple equation:L ft = 984/fwhere L ft represents λ in feet, and f represents thefrequency in megahertz. If λ is expressed in meters,then the formula is:L m = 300/fWhere L m represents the displacement in meters.In general, if ν is the velocity factor (expressed asa ratio) in a given medium, then:L ft = 984ν/fandL m = 300ν/fCompare HALF WAVELENGTH, QUARTERWAVELENGTH.full-wave loop antenna A loop antenna with a circumferenceof one wavelength, fed at a break. Theloop can be circular, square, triangular, or occa-sionally some odd shape. The most efficient configurationis the circular loop. Maximum radiationoccurs perpendicular to the plane of the loop.full-wave rectifier A rectifier that delivers a halfcycleof pulsating direct-current (dc) outputvoltage for each half-cycle of applied alternatingcurrent(ac) voltage. The successive outputhalf-cycles have the same polarity. See, specifically,BRIDGE RECTIFIER and FULL-WAVE, CENTER-TAP RECTIFIER. CompareHALF-WAVE RECTIFIER.full-wave vibrator 1. In a vibrator-type power supply,an interrupter that closes contacts on bothends of its swing, thus causing direct current (dc)to flow through the transformer in alternate directions.2. A vibrator-type rectifier that closes inboth directions.full-wave voltage doubler A voltage-doubler circuitwhose direct-current (dc) output has a rippleof twice the alternating-current (ac) supply frequency.Compare HALF-WAVE VOLTAGE DOU-BLER.function 1. A mapping between two sets of quantitiesor points A and B, such that: (1) For each y inB, there exists at least one corresponding x in A;and (2) For each x in A, there exists exactly one yin B. In this case y is said to be a function of x;this can be written as y = f(x). The set A is calledthe domain of f; the set B is called the range of f.2. A mathematical expression, using symbols, relatingvariables (e.g., the expression x - y = z is afunction of variables x, y, and z). 3. The behaviorand application for which a device or system isdesigned. 4. Part of a computer instruction specifyingthe operation to be done.functional blocks Combinations of substances orcomponents that perform specific tasks in anelectronic circuit. An example is a tuned circuit,containing inductive reactance, capacitive reactance,and resistance.functional character See CONTROL CHARACTER.functional design Design specifications encompassinga description of how system elements willinterrelate, and what their logic design will be.functional diagram FUNCTIONAL DESIGN representedin graphic form; that is, as an illustrationor set of illustrations.functional electronic block Abbreviation, FEB. Acomplete integrated circuit. See INTEGRATEDCIRCUIT.functional end (FE) point In a system operatingfrom a battery power supply, the lowest voltage atwhich the equipment will properly operate. As abattery discharges, the voltage decreases; whenthe voltage drops to the FE point, the batterymust be replaced or recharged.functional test A performance test of a device orcircuit, to see that it behaves as intended in theenvironment in which it is to be used.function generator 1. A signal generator whoseoutput is any of several selectable waveforms

306 function generator • fV(e.g., sine, square, triangular, step-pulse) and frequencies(or repetition rates). 2. An analog computercircuit that produces a variable based on amathematical function and one or more inputvariables.function key 1. In digital communications, a keyboardkey used to control the form in which amessage will be received. 2. On a computer keyboard,any of 12 keys (usually designated F1through F12) that activates special functions.The precise action of a given key depends on theprogram being run.function polling A polling technique in which adisabled device signals its condition and specifiesthe remedy.function switch In a multifunction instrument,such as a voltohm-milliammeter, the switch thatpermits selection of the various functions.function table 1. A table of mathematical functionvalues. 2. Hardware or software that translatesone representation of information into another.3. A routine that allows a computer to use thevalues of independent variables to determine thevalue of a dependent variable.fundamental Contraction of FUNDAMENTAL FRE-QUENCY.fundamental component The FUNDAMENTALFREQUENCY of a complex wave.fundamental frequency 1. The lowest frequencyin a complex wave containing harmonic energy.2. In a radio or television transmitter, the intendedfrequency of operation. 3. In acousticsand audio applications, the predominant pitch ofa musical tone.fundamental group A set of trunk lines in a telephonesystem, through which zone centers areinterconnected.fundamental mode See DOMINANT MODE.fundamental suppression Removal of the fundamentalfrequency from a complex wave, leavingonly the harmonics, as in the operation of a nullnetwork adjusted to the fundamental frequency.fundamental units Base units of an absolute systemof units. Example: the meter (m), the kilogram(kg), and the second (s) in the mks system.fundamental wavelength The wavelength thatcorresponds to the FUNDAMENTAL FREQUENCYof a wave or signal.fuse A safety device consisting of a wire of lowmelting-pointmetal. When current passingthrough the wire exceeds a prescribed (safe) level,the resulting heat melts the wire and opens thecircuit, protecting equipment from damage. SeePROXIMITY FUSE.fuse box A set of electrical fuses, usually enclosedin a metal box.fused junction In a semiconductor, a junction producedby alloying metals to the semiconductormaterial.fused junction See ALLOY JUNCTION.fuse resistor See FUSIBLE RESISTOR.fuse wire The low-melting-point wire used infuses. See FUSE.fusible resistor A low-value resistor that alsoserves as a fuse in certain appliances, such astelevision receivers.fusing current The specified current level at whicha wire of a given diameter and material compositionwill melt.fusion 1. In acoustics, pertaining to delayed orreflected waves that arrive within approximately1⁄25 of a second of the direct wave. So called becausethe human ear/brain “fuses” (blends)sounds together when they are separated byless than about 1 ⁄25 second. If the delay is longer,the ear/brain usually perceives an echo instead.2. In a nuclear reaction, the uniting oftwo atomic nuclei, accompanied by the releaseof energy.future labels In a computer system, program instructionlabels that refer to locations not designatedas absolute addresses by a compiler orassembler.futuristA person who tries to anticipate or predict,based on current technology and trends, whatwill be accomplished in a given field in the nextseveral years or decades.fuzz A form of deliberate distortion in the waveformproduced by an electric guitar.fuzzbox A circuit that distorts the waveform producedby an electric guitar, for the purpose of creatingvarious musical sound effects.fuzz buster Slang for a specialized mobile radio receiver,used by drivers of vehicles to signal thepresence of law-enforcement radar equipment.fV Abbreviation of femtovolt.

G 1. Symbol for CONDUCTANCE. 2. Abbreviationof GIGA-. 3. Symbol for DEFLECTION FACTOR.4. Symbol for PERVEANCE. 5. Symbol for GRAV-ITATIONAL CONSTANT. 6. Symbol for GENERA-TOR. 7. Symbol for GATE. 8. Abbreviation forGAUSS.g 1. Symbol for CONDUCTANCE. 2. Abbreviationof GRAM. 3. Subscript for GATE. 4. Subscript forGENERATOR. 5. Symbol for GRAVITY.GA Radiotelegraph abbreviation of “Go ahead.”G/A Abbreviation of ground-to-air.Ga Symbol for GALLIUM.GaAs 1. Formula for gallium arsenide. 2. Pertainingto semiconductor devices based on galliumarsenide.GA coil A special form of coil, wound with extraspace among the turns to reduce the distributedcapacitance.gadget 1. A device or component. 2. A superfluousor makeshift device.gadolinium Symbol, Gd. A metallic element of therare-earth group. Atomic number, 64. Atomicweight, 157.25.gage See GAUGE.gain The extent to which a component, circuit, device,or system increases current, voltage, orpower. Applicable especially to active devices,such as transistors and integrated circuits (ICs),and to amplifiers and filters that use them. Alsoused to express the directional properties of someantenna systems. Usually specified in decibels(dB). See AMPLIFICATION, CURRENT AMPLIFI-CATION, DECIBEL, VOLTAGE AMPLIFICATION,and POWER AMPLIFICATION.gain bandwidth product Symbol, f T . The frequencyat which the gain of a bipolar transistor isequal to 1 (no amplification or loss) in thecommon-emitter configuration. The f T representsan absolute upper limit for the frequency atwhich a bipolar transistor will works as anamplifier. Any attempt to design an amplifierusing a bipolar transistor at a frequency higherthan its f T will inevitably fail. Compare ALPHACUTOFF FREQUENCY.gain control 1. To adjust the gain of an amplifier.2. A potentiometer used to adjust amplifier gain.Input+gain control+GainadjustmentOutputgain function A function between two currents orvoltages in a circuit with gain.gain-level linearity The quantitative measure ofthe extent to which the gain of a device dependson the signal level. The level is found by compar-Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

308 gain-level linearity • gamma raysing the output to the input level over a range ofinput signal levels.gain reduction The drop in gain of an amplifier athigh- and low-frequency extremes.gain sensitivity control See DIFFERENTIAL GAINCONTROL.gain stability The degree to which the gain of asystem remains constant during changes in relatedfactors, such as temperature, supply power,and loading.gain temperature coefficient The extent to whichthe full-scale current varies over a certain temperaturerange, expressed in parts per million perdegree Celsius (ppm/°C).galactic noise Radio noise propagated from theplane of our galaxy, and especially from the center,located in the direction of the constellationSagittarius. It is of significance in space communicationsand radio astronomy.galena Formula, PbS. Natural lead sulfide, whichin nature takes the form of bluish-gray, cubicalcrystals.gallium Symbol, Ga. Atomic number, 31. Atomicweight, 69.72. One of the constituents of thesemiconductor compound GALLIUM ARSENIDE.gallium arsenide Formula, GaAs. A compound ofgallium and arsenic, used as a semiconductormaterial. It is noted for its low-noise characteristics.gallium-arsenide diode A diode in which the semiconductormaterial is processed gallium arsenide.gallium-arsenide varactor A low-noise, microwavevaractor in which the semiconductor materialis gallium arsenide.gallium-phosphide diode A light-emitting diode inwhich the semiconductor material is processedgallium phosphide.galloping ghost A form of radio-control system inwhich the elevation and rudder can be moved tothe desired extent.Galton whistle A device for producing highfrequencyacoustic waves (ultrasound), similar toa common dog whistle.galvanic cell Generic term for any electrochemicalprimary voltaic cell.galvanic corrosion Corrosion that occurs on oneof two dissimilar metals when they are immersedin an electrolyte. Caused by battery action betweenthem. Compare ELECTROLYTIC CORRO-SION.galvanic couple See VOLTAIC COUPLE.galvanic current A very small direct current suchas that produced by dissimilar metals in acid orby nervous reaction in living tissue.galvanic pile See VOLTAIC PILE.galvanic series A list of metals and alloys arrangedin order of the most to least likely to oxidize in agiven environment.galvanic skin response Abbreviation, GSR. Thevariations in electrical resistance of the (usuallyhuman) skin. This phenomenon is a useful indicatorin physiology, psychology, and criminology.galvanic taste A sharp, metallic taste experiencedwhen a small electric current is passed throughthe tip of the tongue.galvanism (After Luigi Galvani, 1737–1798) Theproduction of an electric current by chemical action,as in a battery.galvanize To coat steel with zinc to forestall corrosion.galvanometer A sensitive, bi-directional currentmeter. Used in various electrical tests—especiallyas a null indicator in bridge operation. Also seeMICROAMMETER.galvanometer constant The number by which agalvanometer reading must be multiplied in orderto obtain the current in microamperes, milliamperes,or amperes.galvanometer recorder A graphic recorder inwhich a mirror in a movable-coil galvanometer reflectsa beam of light to a passing strip of photographicfilm.galvanometer shunt A resistor placed in parallelwith a galvanometer to decrease its sensitivity.Also see SHUNT RESISTOR.galvanometry The use of galvanometers to determinethe intensity and direction of electric currents.galvanoplastics The science of ELECTROPHO-RESIS and ELECTROPLATING.galvanoscope An instrument for detecting andshowing the direction of very weak electric currents.galvanotherapy The use of electric currents toproduce heat in the body of a human or animal.gamma ferric oxide A form of coating used in formulationof magnetic recording tape.gamma match A linear transformer for matchingan unbalanced (usually coaxial) feed line to a balanced(usually half-wave) antenna. The outerconductor of the cable is connected to the centerof the radiator, and an extension of the centerconductor runs for a short distance parallel to theradiator, making a right-angle bend before connectingto the radiator.Coaxialfeed linegamma matchRadiatorMatchingsectiongamma rays High-energy, ionizing radiation emittedby radioactive substances; similar to X rays,but of a shorter wavelength.

gamma section • gaseous voltage regulator 309gamma section See GAMMA MATCH.gang To mechanically couple components (pots,switches, etc.) for operation by a single knob.gang capacitor A variable capacitor consisting ofsections mounted on the same shaft for simultaneousvariation. It is usually specified by thenumber of sections (e.g., four-gang capacitor).Compare GANGED CAPACITORS.ganged capacitors Separate variable capacitorsmechanically connected together (e.g., by belt orgear drive) for simultaneous variation. CompareGANG CAPACITOR.ganged potentiometers Separate potentiometersmechanically connected together (e.g., by belt orgear drive) for simultaneous variation. CompareGANG POTENTIOMETER.ganged rheostats See GANGED POTENTIOME-TERS.ganged switches Separate switches mechanicallyconnected together for simultaneous operation.Compare MULTISWITCH.ganged tuning Simultaneous tuning of separatecircuits by means of ganged capacitors or gangedpotentiometers.gang potentiometer A potentiometer consistingof sections mounted on the same shaft for simultaneousvariation. Usually specified accordingto the number of sections (e.g., dualpotentiometer).gang printer In digital computer and data processingoperations, an electromechanical printer capableof printing an entire line at one time.gang punch 1. To punch identical or nonvaryinginformation into the cards of a group. 2. A machinefor this operation.gang rheostat See GANG POTENTIOMETER.gang switch See MULTISWITCH.Gantt chart A chart of activity versus time used inindustry as an aid in making decisions regardingthe allocation of resources for specific activities[e.g., as applied to PERT (project evaluation andreview techniques)].gap 1. A space between electrodes or magneticpoles. 2. A device consisting essentially of separatedelectrodes (e.g., spark gap). 3. A relativelynarrow space cut in iron cores to provide a breakin a magnetic circuit. Also see SLOT, 1. 4. Theopening between the opposite poles of a taperecorder or playback head.gap arrester A lightning arrester consisting of anumber of metal cylinders separated by air gaps.gap coding A system in which silent periods are inserted,according to a specific timing code, into atransmission.gap depth In a magnetic recording head, the depthof the gap (taken perpendicular to the face). CompareGAP WIDTH.gap digit A digit that contributes no intelligence tothe word in which it appears (e.g., a parity bit).gap energy The energy represented by the forbiddengap in electron energy levels (e.g., betweenthe M-valence band and the N-conduction bandin a material).gap filling Modification of an antenna for thepurpose of eliminating nulls in the directionalpattern.gap insulation See SLOT INSULATION, 1, 2.gap loss In a reproducing head, the loss that occursbecause of the GAP DEPTH.gap-type protector A spark gap used to protectequipment from high-voltage transients.gap voltmeter See NEEDLE GAP and SPHEREGAP.gap width In a magnetic recording head, the widthof the gap (taken parallel with the face). CompareGAP DEPTH.garbage 1. In digital computer operations, a colloquialismfor useless or incorrect data. 2. Colloquialismfor unreadable signals or severeintermodulation in a radio communications circuit.3. Colloquialism for an unsound theory.garble 1. Garbled matter. 2. Also called scramble.To purposely render communications or data unintelligibleto everyone, except the intended recipient(s).See SCRAMBLER CIRCUIT.garbled matter Confused communications ordata, usually resulting from distortion in a circuitor system. Also called GARBLE.garbler See SCRAMBLER CIRCUIT.garnet maser A maser that uses natural or syntheticgarnet as the stimulated material. Also seeYTTRIUM-IRON-GARNET.gas One of the states of matter, characterized bymolecules that are widely separated and are incontinual, relatively rapid motion. Because it is afluid, a gas will readily conform to a container ofany shape. Gases can readily be compressed andliquefied. Compare LIQUID, PLASMA, and SOLID.gas amplification In a radiation-counting device,the ratio, in decibels, of the charge collected tothe charge produced in the gas.gas breakdown The ionization of a gas by means ofhigh voltage. The intensity of the electric field preventsrecombination of ions. Collisions amongatoms cause further ionization. Thus, the gas becomesa good conductor of current.gas cell A cell whose operation depends on gas absorptionby the electrodes.gas cleanup Loss of pressure in a gas-filled tube,eventually leading to failure. Caused by gas ionsforming compounds with metal parts or with theglass envelope.gas detector A device for sensing presence of variousgases in the air—especially toxic or explosivegases (such as chlorine, hydrogen, or methane).gaseous conduction The conduction of an electriccurrent through an ionized gas.gaseous phototube A PHOTOTUBE containing asmall amount of a gas suitable for ionic conduction.gaseous voltage regulator A gas-filled diodeacross which the voltage drop is substantially

310 gaseous voltage regulator • gated amplifierconstant during the gas discharge and which accordinglydelivers a constant output voltage.gas-filled cable A sealed cable filled with an inertgas that serves as a low-loss dielectric and moisturebarrier.gas-filled counter tube A radiation counter tubecontaining a gas that ionizes when irradiated. SeeGEIGER-MUELLER TUBE.gas-filled lamp 1. An incandescent lamp filledwith a gas, such as nitrogen, for improved performance.2. Discharge lamp.gas-filled tube An enclosure filled with gas that issubjected to an electric potential, intended toproduce specific effects, such as light emission orvoltage regulation.gas-flow alarm An electronic circuit that actuatesan alarm when the flow of gas through a pipechanges from a predetermined rate.gas-flow control A servo system for automaticallymaintaining or adjusting the flow of gas throughpipes.gas-flow gauge See GAS-FLOW METER.gas-flow indicator See GAS-FLOW METER.gas-flow meter An instrument that indicates therate of gas flow through a pipe, in terms of volumeper unit time (e.g., cubic feet per minute).gas-flow switch In a gas-circulating system, aswitch that actuates an alarm when the gas flowrate changes.gas focusing In a cathode-ray tube, a technique bywhich a gas is used for the purpose of focusing anelectron beam. The ionization of the gas causesthe electron beam to be made more narrow.GASH Acronym for guanidine aluminum sulfatehexahydrate, an organic crystalline material usedas the dielectric in certain ferroelectric capacitorsand ferroelectric memory elements.gas laser A LASER that uses a gas or mixture ofgases (instead of a solid rod) as the stimulatedmedium. Some of the gases used are argon, carbondioxide, helium, krypton, and neon.gas maser A MASER in which the stimulated materialis a gas, such as ammonia.gas multiplication See GAS AMPLIFICATION.gas noise Electrical noise resulting from the undirectedmotion of gas molecules in a gas-filled tube.gas-pressure alarm An electronic circuit that actuatesan alarm when gas pressure rises or falls.gas-pressure control A servo system for automaticallymaintaining or adjusting gas pressure inpipes or other channels.gas-pressure gauge See GAS-PRESSURE METER.gas-pressure indicator See GAS-PRESSURE ME-TER.gas-pressure meter An instrument that indicatesgas pressure in a pipe or container, but provides nomeans for automatically correcting the pressure.gas ratio For a gas-filled tube, the ratio I i /E i , where I iis the ion current and E i is the ionization potential.gas sensor Any element, such as the filament in ahot-filament gas detector, that responds to thepresence of a gas in the environment and activatesthe detector or alarm circuit.gassing 1. The generation of gas by a storage battery,especially while it is being charged. 2. Thegeneration of gas during electrolysis.gas sniffer See GAS DETECTOR.gaston A device intended for the purpose of modulatingan aircraft signal, making the signal difficultto jam. The signal is randomly modulated bynoise from the device.gas tube See GAS-FILLED TUBE.gas-tube lightning arrester A lightning arrester,consisting of a special gas diode. The tube has virtuallyinfinite resistance at low voltages, but providesa low-resistance path to ground when thehigh voltage of a lightning stroke ionizes the gas.gas-tube oscillator A relaxation oscillator using atwo-element gas tube, such as a neon lamp, asthe breakdown device.B+RCgas-tube oscillatorSawtoothoutputgas valve See ELECTROMECHANICAL VALVE.gas X-ray tube An X-ray tube in which the positiveions of a gas bombard the cathode, which emitselectrons.gate 1. A device or circuit that has no output untilit is triggered into operation by one or more enablingsignals, or until an input signal exceeds apredetermined threshold amplitude. 2. The input(control) electrode of a field-effect transistor orthyristor device (e.g., silicon-controlled rectifier).3. A signal that triggers the passage of other signalsthrough a circuit.gate array Basic gates arranged in a pattern on achip; the gates can be interconnected duringmanufacture to form a unit that performs whateverfunction is needed.gate circuit 1. An electronic switching circuit (seeGATE, 1). 2. The circuit associated with the gateelectrode of a field-effect transistor.gate-controlled switch A device similar to a siliconcontrolledrectifier or thyristor. A negative current,applied to the gate, switches the device off.gate current Symbol, I G . Current flowing in thegate (control) circuit of a semiconductor device.The current is finite in thyristors, but is almostzero in some types of field-effect transistors.gated amplifier An amplifier whose input is effectivelyswitched on and off by gating signals.

gated buffer • Gauss’ theorem 311gated buffer A low-voltage, high-current driver,used for differentiation in a multivibrator circuit.gated flip-flop A flip-flop in which it is impossiblefor both outputs to be low simultaneously.gate-dip meter A dip meter using a field-effecttransistoroscillator with the indicating microammeterin the gate circuit.gate-dip oscillator See GATE-DIP METER.gated multivibrator A rectangular-wave generatorthat produces a gate voltage when triggered.gate-drain voltage Symbol, V GD . In a field-effecttransistor, the maximum voltage permitted betweenthe gate and drain electrodes.gated sweep 1. In radar, a sweep whose initiationand duration are closely controlled to eliminateechoes in the image. 2. A circuit providing the actiondescribed in 1.gate electrode See GATE, 2.gate impedance 1. The impedance of the gate electrodeof a field-effect transistor with respect to theother electrode, which serves as the return. 2.The impedance of the gate winding of a magneticamplifier.gate leakage current See GATE REVERSE CUR-RENT.gate nontrigger voltage Symbol, V Gnt . For a thyristor,the direct-current (dc) voltage applied betweenthe gate and the cathode, above which thedevice fails to maintain its rated blocking voltage.gate power dissipation Symbol, P G . In a siliconcontrolled rectifier, the power consumed by thegate-cathode path.gate-protected MOSFET A metal-oxide-semiconductorfield-effect transistor in which the gateelectrode is protected from accidental burnout viabuilt-in Zener diodes, connected back-to-back.gate pulse 1. A pulse applied to the gate electrodeto actuate a gate-controlled semiconductor device.2. An actuating pulse in a gate circuit.gate recovery time Symbol, t Gr . For a siliconcontrolledrectifier, an extension of the reverserecovery time: the interval following application ofthe reverse voltage required before the forwardblocking voltage can be reapplied and thenblocked by the device.gate reverse current Symbol, I GSS . In a field-effecttransistor, reverse current in the gate-source circuit.Also called gate leakage current.gate signal 1. The input or control signal appliedto the gate electrode of a semiconductor device. 2.An actuating signal in a gate circuit.gate-source breakdown voltage Symbol, BV GSS .The voltage at which the gate junction of a junctionfield-effect transistor (JFET) entersavalanche.gate-source pinchoff voltage Symbol, V P . In afield-effect transistor, the gate-source voltage atwhich the conduction channel just closes.gate-source voltage Symbol, V GS . In a field-effecttransistor, the direct-current (dc) voltage betweenthe gate and source electrodes.gate terminal 1. The terminal connected to thegate semiconductor in a field-effect transistor.2. The terminal, or terminals, connected to theinput or inputs of a digital-logic network.gate trigger current In a gate-controlled semiconductorswitch, the current flowing in the gate circuitwhen the device is being switched on by agate trigger voltage.gate trigger voltage In a gate-controlled semiconductorswitch, the trigger voltage required to actuatethe device.gate turn-off current In a gate-controlled semiconductorswitch, the low value of gate current thatflows when the device is being switched off. Turnoffcurrent varies with collector (anode) current.gate turn-off voltage In a gate-controlled semiconductorswitch, the low value of gate voltagethat causes the device to switch off.gate voltage 1. The voltage applied to the gateelectrode of a field-effect transistor. See GATE-SOURCE VOLTAGE. 2. The instantaneous gatecathodevoltage in a silicon-controlled rectifier. 3.The voltage across the gate winding of a magneticamplifier.gate winding In a magnetic amplifier, a windingthat produces gating action.gating 1. The process of using one signal to switchanother (or part of another) on or off for a desiredinterval. 2. Selecting a part of a wave for observationor for control purposes.gauge 1. Any device, such as a METER, used forthe purpose of measuring the magnitude of aquantity. 2. Wire data and measurements (seeWIRE GAUGE, 1, 2, 3). 3. Sheet metal thickness(e.g., 10 gauge).Gauss (Karl F. Gauss, 1777–1855) Unit of magneticflux density, equivalent to one line of flux persquare centimeter. The SI (preferred) unit of magneticflux density is the TESLA (webers persquare meter); 1 gauss equals 10 –4 teslas (symbol,T). Also see FLUX DENSITY.Gaussian curve See BELL-SHAPED CURVE.Gaussian distribution In statistics, the symmetricaldistribution described by a bell-shaped curve.Also called NORMAL DISTRIBUTION.Gaussian function A mathematical function usedin the design of lowpass filters. The Gaussian responseis characterized by low band-edge selectivity,high transition bandwidth, negligible stepresponse overshoot, and low step-response delaytime.Gaussian noise Electrical noise whose amplitudeversus-frequencycharacteristic is described bythe GAUSSIAN DISTRIBUTION.Gaussian waveform A waveform that results in minimalside lobes in a pulse-compression system.gaussmeter See FLUXMETER.Gauss’ theorem Across any closed surface withinan electric field, the total flux is approximatelyequal to 12.566 times the enclosed quantity ofelectric charge.

312 gauze resistor • general class licenseProbabilityGeiger counter A radioactivity rate-counting instrumentbased on the GEIGER-MUELLERTUBE. Pulses from the tube drive a transistor,which, in turn, drives a meter or digital counter toindicate the count.Trigger 8 rangeParameterMedianG-MtubeDetectorvoltagesupplyMeterGaussian distributiongauze resistor See WOVEN RESISTOR.GAVRS Abbreviation of gyrocompass attitude verticalreference system.GCA Abbreviation of GROUND-CONTROLLEDAPPROACH.GCI Abbreviation of GROUND-CONTROLLEDINTERCEPTION.GCM Abbreviation of gyrocompass module. SeeGYROCOMPASS.GCT Abbreviation of GREENWICH CIVIL TIME.Gd Symbol for GADOLINIUM.G display See G SCAN.GDO 1. Abbreviation of GRID-DIP OSCILLATOR.2. Abbreviation of GATE-DIP OSCILLATOR.Ge Symbol for GERMANIUM.gear 1. Collectively, electronic equipment. 2. Atoothed wheel commonly used in mechanical devices.gearmotor An electric motor with a gear train forspeed changing.gear-wheel pattern A pattern produced on an oscilloscopeby intensity-modulating a circulartrace. A signal of unknown frequency f x is appliedto the intensity-modulation (z-axis) input. Thesignal produces corrugations in the trace. If thereare n corrugations around the trace, and if thetrace itself completes f s revolutions per second,then the unknown frequency f x , in Hz, is equal tonf s . Compare SPOT-WHEEL PATTERN.f x = nf sgear-wheel patternGeiger counterGeiger-Mueller counter See GEIGER COUNTER.Geiger-Mueller region For a GEIGER-MUELLERTUBE, the range of voltages within which the outputpulse amplitude is constant, regardless ofionizing radiation intensity.Geiger-Mueller threshold The lowest voltage inthe Geiger-Mueller region.Geiger-Mueller tube A gas-filled radiation detector/countertube consisting of a straight wire asan anode, surrounded by a cylindrical cathode.The tube is biased by high voltage. Radiation penetratingthe tube ionizes the gas; each ionizingevent causes an output pulse.Geiger point counter See POINT COUNTER.Geiger region See GEIGER-MUELLER REGION.Geiger threshold See GEIGER-MUELLER THRES-HOLD.Geissler tube A simple gas-filled glow-dischargetube with metal electrodes sealed in each end.When a sufficiently high voltage is applied betweenthe electrodes, the highly rarefied gas ionizesand glows with the color associated with theparticular gas used.gel A substance equivalent to colloidal solution inthe solid phase (e.g., silica gel).gel battery A rechargeable electrochemical BAT-TERY designed for use with portable electronicand computer equipment. Noted for its ability todeliver high current for short periods, when necessary,and also to deliver moderate current continuouslythroughout its discharge cycle.gen Abbreviation of GENERATOR.genemotor Contraction of generator/motor, a(usually battery-driven) dynamotor that has separatemotor and generator windings on the samearmature core.general class license An amateur-radio licensethat conveys some privileges in the highfrequencybands, and all operating privileges inthe very-high-frequency region and above. An examinationof moderate difficulty is required.

General Packet Radio Service • geometric progression 313General Packet Radio Service A form of packetradio especially designed for mobile use. Subscriberspay for the volume of data they send andreceive, rather than for the time they spend accessingthe network. This optimizes the efficiencyof the network, both from an engineering standpointand a financial standpoint. See PACKETCOMMUNICATIONS.general-purpose bridge See UNIVERSAL BRIDGE.general-purpose component A component designedor used for a wide range of applications.For example, a general-purpose germaniumdiode is useful as a detector, mixer, limiter, clipper,meter rectifier, automatic-gain-control (AGC)rectifier, and curve changer.general-purpose computer A computer that canbe used in a number of applications for which itwas not specifically designed.general-purpose diode A small-signal semiconductordiode that is useful for a variety of applications,such as detection, light-dutyrectification, limiting, logic switching, etc.general-purpose function generator A nonspecializedfunction generator that is capable of generatinga variety of different waveforms.general-purpose program A program for the solutionof a class of problems or for a specific problem,according to certain parametric values. Alsocalled general routine.general-purpose relay Any relay that can be usedin various situations, such as for switching alternatingor direct currents.general-purpose tester An instrument, such as avoltohm-milliammeter, that offers several test capabilities.general-purpose transistor A transistor that canbe used in several applications, such as audioamplification, detection, and oscillation.general service code See CONTINENTAL CODE.generate 1. To produce a signal or carrier wave.2. To convert some non-electrical form of energy(usually mechanical) into electrical energy.3. To develop subroutines from parameters appliedto skeletal coding. 4. To use a programgenerator to produce a specialized version of ageneral-purpose program.generated address An address developed by programinstructions for later use by that program.generated noise 1. Electrical noise caused by batteryaction (i.e., between dissimilar metals) in acomponent, such as in a potentiometer. 2. Electricalnoise caused by small output variations ofgenerating devices (rotating machines, vibrators,etc.). Also called generator noise.generating magnetometer See EARTH INDUC-TOR.generating station An electric power station.generating voltmeter An instrument based on arapidly spinning variable capacitor. A directcurrent(dc) voltage applied to the capacitor isconverted into an alternating current (ac) by thevarying capacitance; the ac is proportional to thevoltage.generation 1. The production of a signal or carrierwave. 2. The conversion of some non-electricalform of energy (usually mechanical) into electricalenergy. 3. The number of recording steps betweena master recording and a copy. 4. A copy ofdata in any form (e.g., tape recording, disk file,and photocopy).generation number A number that identifies theage of a file; it is included in the file label on thedisk or tape containing the file.generator 1. Symbol, G. Any signal source. 2. Arotating machine for producing electricity. 3. Anelectronic device for converting direct current intoalternating current of a specific frequency andwaveshape. 4. In computer operation, a routine(akin to a compiler) that will produce a programto perform a specific version of some general operationby implementing skeletal coding, accordingto specific parameters (e.g., sort generator).generator efficiency The ratio of consumed powerto delivered power in a generator. It is usually expressedas a percentage.generator noise Electrical noise caused by a rotatinggenerator. Also see GENERATED NOISE, 2.generator-type microphone A microphone thatproduces an output voltage without the need fora supply voltage. Examples: ceramic, crystal, dynamic,electret, and velocity types.generator-type transducer A transducer that convertsmechanical motion into an electrical signalof a proportional voltage. In such a transducer, anarmature or conductor moves in a magnetic field.generic A form of software collection. Severalspecialized software packages can be derivedfrom the generic collection, for use in differentsystems.geodesic 1. On a surface, the shortest path betweentwo points. 2. The shortest path between two geographicallocations, measured over the surface ofthe earth. Also called geodetic and great circle.geodesy The branch of applied mathematics concernedwith the precise dimensions of the earth.geodetic system The application of a computer toseismographic studies for the purpose of reducingdrilling and mining costs.geomagnetic field See EARTH’S MAGNETICFIELD.geomagnetism The earth’s magnetism. Also seeEARTH’S MAGNETIC FIELD.geometric capacitance The ratio of the freecharge of a capacitor to the voltage across itsterminals.geometric mean The nth root of the product of nquantities.geometric progression A mathematical sequencein which each term after the first is obtained bymultiplying the preceding one by a constantquantity (e.g., 1, 2, 4, 8, 16, 32, 64, . . .). Alsocalled geometric sequence.

314 geometric symmetry • GIGOgeometric symmetry In a bandpass or bandrejectionfilter, a condition in which the responseis identical on either side of the center frequency.Also called mirror-image symmetry.LowerLowerAmplitudeFrequencyAmplitudeMin. Max. Min.Max.Frequencygeometric symmetryHigherHighergeorge box In an intermediate-frequency amplifier,a device used to reject jamming signals. Any jammingsignal with an amplitude lower than a certainminimum is rejected.geostationary orbit An orbit in which a satelliterevolves around the earth exactly once a day, so itremains over the same place on the earth all thetime. The altitude must be 22,300 miles, and theorbit must lie in the plane of the earth’s equator.geostationary satellite A satellite in GEOSTA-TIONARY ORBIT. It is always in the same spotin the sky from any given observing point. Ageostationary satellite provides coverage overabout 40 percent of the earth, and is commonlyused for communications and weather-observationpurposes.germanium Symbol, Ge. A metalloidal element.Atomic number, 32. Atomic weight, 72.59. Usedin semiconductor diodes, photocells, rectifiers,and transistors.germanium diode A diode in which the semiconductormaterial is specially processed germanium.germanium dioxide Formula, GeO 2 . A gray orwhite powder obtainable from various sources; itis reduced in an atmosphere of hydrogen or heliumto yield germanium, a semiconductor material.germanium junction diode A germanium diodethat contains a pn junction.germanium photocell A photoconductive cell consistingof a reverse-biased germanium pointcontactdiode or germanium junction diode.germanium point contact The contact between apointed metal wire and a germanium wafer, as ina point-contact diode or point-contact transistor.germanium rectifier A power rectifier that containsa germanium pn junction.germanium transistor A transistor in whichgermanium is the semiconductor material. Sucha transistor has lower internal resistance andgreater temperature drift than a silicon transistor.German silver A copper-nickel-zinc alloy used insome resistance wires. Also called NICKEL SIL-VER.GEV Abbreviation of ground effect vehicle.GeV Abbreviation of GIGAELECTRONVOLT.gfi Abbreviation of GROUND-FAULT INTER-RUPTER.g-force See GRAVITY, 2.g FS Symbol for FORWARD TRANSCONDUCTANCE.G/G Abbreviation of GROUND-TO-GROUND.ghost In television reception, a slightly displacedimage appearing on the screen simultaneouslywith its twin (the false member of a double image).ghost signal Any signal (such as an undesired reflection)that produces a ghost.GHz Abbreviation of GIGAHERTZ.G i Symbol for INPUT CONDUCTANCE.Gibson girl A portable radio transmitter, powered byan integral crank-operated generator, introducedduring World War II for pilots forced down at sea.giga- Abbreviation, G. 1. A prefix meaning billion(10 9 ). 2. In digital data applications, a prefixmeaning 2 30 .gigabit A unit of digital data, equal to 2 30 bits or1024 megabits. Also see BIT and MEGABIT.gigabyte A unit of digital data, equal to 2 30 bytes or1024 megabytes. Also see BYTE and MEGABYTE.gigacycle See GIGAHERTZ.gigaelectronvolt Abbreviation, GeV. A large unit ofvoltage; 1 GeV equals 10 9 eV. Also see BEV,ELECTRONVOLT, MEV, and MILLION ELEC-TRON VOLTS.gigahertz Abbreviation, GHz. A unit of ultra-highfrequency; 1 GHz equals 1,000,000,000 Hz = 10 9Hz.gigaohm A unit of extremely high resistance, reactance,or impedance, equal to 1,000,000,000ohms = 10 9 ohms.GIGO Abbreviation of garbage in = garbage out, anexpression signifying that incorrect or improper

GIGO • glucinium 315input to a computer will produce meaninglessoutput.gilbert (William Gilbert, 1540–1603) A unit of magnetomotiveforce, equal to 1.26 times the numberof ampere-turns. The SI (preferred) unit of magnetomotiveforce is the ampere (symbol, A); 1gilbert = 0.796 A.gilbert per centimeter See OERSTED.gimbal A suspension device whose orientation canbe changed without affecting the attitude of thebody being suspended.gimmick 1. Colloquialism for any unnamed device.Also see GADGET. 2. Colloquialism for anytricky manipulation or design. 3. A low-value capacitormade by twisting two short pieces of insulatedwire together.gimp Colloquialism for the tinsel and cloth conductorused in some earphone cords.Giorgi system The meter-kilogram-second (mks)system of units.GJD Abbreviation of GERMANIUM JUNCTIONDIODE.glass A hard, brittle, amorphous, and usuallytransparent substance that is largely silicon dioxide.Glass has a multitude of uses in electronics,and there are several kinds, each having differentelectrical properties. The dielectric constantranges from about 4 to 10; the dielectric strengthranges from about 20 to 300 kilovolts per millimeter.glass arm A stiffness of the wrist or forearm, somewhatresembling writer’s cramp, sometimes experiencedby radiotelegraph operators or wiretelegraph operators after prolonged use of a handkey.glass bulb The glass enclosure of electron tubesand incandescent lamps.glass capacitor A capacitor that uses thin glass asthe dielectric, and usually has plates consistingof metal electroplated or electrodeposited on oppositefaces of the glass. Also see MOLDEDGLASS CAPACITOR.glass diode A semiconductor diode molded in glass.glass electrode A probe used with a pH meter; itconsists of a thin-walled glass tube containingpotassium chloride and mercurous chloride. Alsosee CALOMEL ELECTRODE.glass envelope See GLASS BULB.glassivation A procedure for encapsulating semiconductordevices in glass or other dielectric material.glass-metal seal See GLASS-TO-METAL SEAL.glass plate capacitor See GLASS CAPACITOR.glass shell See GLASS BULB.glass-to-metal seal A bond between glass andmetal in electronic devices, such as vacuum tubes,feedthrough terminals, and glass capacitors.glass tube A vacuum tube whose elements arehoused in an evacuated glass envelope.glide path The guidance beam used by aircraftmaking instrument landings.RunwayTransmitterGlide-pathbeamglide-path transmitterPlaneglide-path transmitter A radio-frequency transmitterthat produces a guidance beam for aircraftlanding purposes. The aircraft follows the beamtoward the runway.glide slope See GLIDE PATH.G line A microwave conductor consisting of around wire coated with a dielectric.glitch 1. In a television image, a narrow, horizontalinterference bar that moves vertically. 2. A veryshort and unwanted high-amplitude transientthat recurs irregularly in an electronic system.glitter 1. In radar, an echo or set of echoes thatfluctuates rapidly in intensity because of motionin the target. 2. A system in which moving devicesare used to confuse enemy radar systems.gloss factor For a reflecting surface, the ratio of reflectedlight in a selected direction to reflectedlight in all directions.glossmeter An instrument for determining GLOSSFACTOR.glow discharge The luminous electrical dischargeresulting from the passage of current throughionized gas in a partially evacuated tube. Thecolor of the glow is characteristic of the particulargas used.glow-discharge microphone A device that producesaudio-frequency currents from the actionof sound waves in a glow-discharge tube.glow-discharge tube A partially evacuated tubethat contains two or more electrodes. The rarefiedgas in the tube glows when a sufficient voltage isapplied to the electrodes. See DISCHARGE LAMP,FLUORESCENT TUBE, and NEON BULB.glow lamp See DISCHARGE LAMP.glow modulator tube A gas tube whose luminousoutput can be modulated by an audio input signal.glow potential The voltage at which glow dischargejust begins in a gas-filled tube.glow switch In fluorescent light circuits, an electrontube containing two bimetal strips that makemutual contact when heated by the glow discharge.glow tube See DISCHARGE LAMP, FLUORES-CENT TUBE, GLOW MODULATOR TUBE, NEONBULB, and STROBOTRON.glow voltage See BREAKDOWN VOLTAGE, 2.glucinium See BERYLLIUM.

316 gluon • Graffitigluon A subatomic particle that is believed to bindquarks together (coined by Prof. Murray Gell-Mann of California Institute of Technology).GM Abbreviation of Geiger-Mueller (see, for example,GEIGER-MUELLER TUBE).gm Abbreviation of gram. Also abbreviated g.g m Symbol for TRANSCONDUCTANCE.g-m Abbreviation of GRAM-METER.gm-cal Abbreviation of GRAM-CALORIE.gm-cm Abbreviation of GRAM-CENTIMETER.G-M counter See GEIGER COUNTER.GMT Abbreviation of GREENWICH MEAN TIME.G/M tube See GEIGER-MUELLER TUBE.gnd Abbreviation of GROUND.g o Symbol for OUTPUT CONDUCTANCE.gold Symbol, Au. A precious metallic element.Atomic number, 79. Atomic weight, 196.967.Electrical contacts that must have low radiofrequencyresistance, and that must berelatively immune to corrosion, are often platedwith gold.gold-bonded diode A germanium point-contactdiode having a fine gold wire whose point isbonded to the germanium wafer. Its principal featuresare high forward current and almost constant,low reverse current.gold doping The diffusion of gold into the base andcollector regions of a diffused-mesa transistor; itshortens carrier storage time.golden ratio A set of proportions used in the designof some speaker cabinets. The width (W) is 5 ⁄8of the height (H); the depth (D) is 5 ⁄8 of the width.These correspond to a ratio H : W : D = 1.000 :0.625 : 0.391. These proportions are thought bysome acoustics engineers to result in the bestpossible sound quality.gold-leaf electroscope See ELECTROSCOPE.Goldschmidt alternator An early dynamo for generatingradio-frequency power. The highfrequencyenergy was not generated directly bythe machine, but by resonant circuits andfrequency-multiplying interaction betweencomponents.Golf Standard phonetic alphabet code word for theletter G.goniometer 1. Generically, any radio directionfinder. 2. An inductive coupler having a secondarycoil rotated by a dial calibrated to read azimuth.The coupler, when used with a suitableantenna system, comprises a direction finder.3. A device for electrically varying the directionalpattern of an antenna.go-no test A test that indicates only acceptance orrejection of a device. No diagnosis is made.GOTO In computers and programmable calculators,an instruction that, followed by a suitablelabel, directs the program to that label.goto circuit In a digital-logic circuit, a device thatsenses the direction of electric current.goto pair A pair of diodes connected in reverse seriesused in digital-logic circuits.governor 1. A device that prevents a motor or enginefrom running faster than a certain speed.2. Any device that limits a circuit parameter.g parameters Conductance parameters obtainedfor the equivalent-pi model of a transistor: g BE ,g GC , g CE , and g m .gpc Abbreviation of GERMANIUM POINT CONTACT.GPI Abbreviation of GROUND-POSITION INDICA-TOR.GPRS Abbreviation for GENERAL PACKET RADIOSERVICE.gr Abbreviation of grain(s).graceful degradation A computer programmingtechnique used to prevent debilitating breakdownby operating the system—even though severalsubsystems have malfunctioned; also known ascrippled mode.grad A unit of angular measurement equal to 0.9degree.graded-base transistor See DIFFUSED-BASETRANSISTOR.graded filter A power-supply filter that suppliesdirect-current output at various points in the filtersequence. Thus, the points in the poweredequipment that can tolerate the least ripple areconnected to the filter output, and those that cantolerate appreciable ripple are connected to thefilter input; fairly critical points are connected toan intermediate position in the filter, such as atthe junction of two chokes.+−−Out OutA+B+−graded filterOutC−graded-junction transistor A grown-junctiontransistor in which the temperature of the meltand the rate at which the crystal is pulled from itare closely controlled as the n and p layers areformed.gradient The rate at which a variable quantity increasesor decreases. See, for example, VOLTAGEGRADIENT.gradient microphone A microphone whose outputvaries with sound pressure. Also see PRESSUREMICROPHONE.Graetz bridge A full bridge rectifier (i.e., one havinga diode in each arm).Graffiti 1. Trade name for a specialized written alphabetused for entering data into a handheldcomputer using a stylus. 2. The entry of data into

Graffiti • graphic panel 317a handheld computer using a stylus. See HAND-HELD COMPUTER.grain boundary In a polycrystalline solid, a boundarybetween single crystalline regions.gram 1. Abbreviation, g. A unit of mass andweight, equal to 0.001 kilogram or 0.0353 ounce.2. A suffix meaning something drawn (written), orrecorded, as in radiogram or electrocardiogram.gram atom See GRAM ATOMIC WEIGHT.gram atomic weight Also called gram-equivalent.The quantity of an element with a mass in gramsthat is equal to the atomic weight of the element.For example, copper has an atomic weight of63.546; therefore, one gram atomic weight of copperhas a mass of 63.546 grams.gram-calorie Abbreviation, gm-cal. The amount ofheat required to raise the temperature of onegram of water by one degree Celsius.gram-centimeter Abbreviation, gm-cm. The workdone by a force of one gram exerted over a distanceof one centimeter. Also see JOULE.gram-equivalent See GRAM ATOMIC WEIGHT.grammar 1. The sequence of words and/or abbreviationsin a communication or part of a communication.2. The sequence of codes and/orcommands in a high-level computer programminglanguage.gramme armature See GRAMME RING.Gramme ring A type of armature for a motor orgenerator, consisting of an iron ring onto which iswound a coil of wire, each turn being connectedto a commutator bar.gram-meter Abbreviation, g-m. A unit of workequal to a force of one gram exerted over a distanceof one meter. Compare JOULE.gram-molecular weight See MOL.gram molecule See MOL.gramophone Archaic term for phonograph.grandfather cycle A backup scheme in a magneticreproduction system. The original records are retainedfor a period of time so that new copies ofhigh precision can be made in case of loss.grandfather file An original copy of a file on a magneticdisk or tape, retained as a source for reconstructionas needed. Usually, three generations ofa file (grandfather, father, and son) are kept, eachidentified by a generation number. Sometimesthe terms grandparent, parent, and child are usedinstead. See GENERATION NUMBER.grand synthesizer A hypothetical child with amind perfectly attuned to artificial intelligence(AI), who grows up to revolutionize the whole industry;a “grand master of AI.”granular carbon Carbon in the form of fine granules,used in the button of a carbon microphone.granularity 1. In a digital device, the smallest incrementthat can be differentiated. 2. The limit ofdetail in a reproduction system.granule One of many narrow frequency subbands,the combination of which composes a completesignal. Each subband carries its own specific data.graph 1. A presentation of data, particularly a depictionof the manner in which one variable or setof variables changes, with respect to another.Can be in the form of discrete points, curves,bars, columns, pie-shaped slices, etc. 2. A curveor set of curves in a coordinate system.graphical analysis The solution of problemsthrough the use of graphic devices, such as vectordiagrams, load lines, Nyquist plots, topologicalflow diagrams, etc.graphical harmonic analysis See SCHEDULEMETHOD.graphical user interface Acronym, GUI (pronounced“gooey”). An operating system or softwarethat makes it easy for lay people to use acomputer. Commands are given by makingchoices from among items displayed on thescreen. Popular versions use symbols, calledicons, along with a pointing device, such as amouse or trackball.graphic documentation Records of data in theform of graphs, charts, tables, diagrams, etc.graphic equalizer A device for tailoring the amplitude-versus-frequencyresponse of a high-fidelityaudio system. Consists of a splitter, several audiofilters, and a mixer. The gain of each filter is adjustablevia a slide potentiometer. The potentiometersare arranged on the front panel in sucha way that their relative positions show the approximateshape of the response curve.SplitterInput30-Hz filter100-Hz filter300-Hz filter900-Hz filter2.5-kHz filter7-kHz filter18-kHz filtergraphic equalizerAudiocombinerOutputgraphic instrument See GRAPHIC RECORDER.graphic-level recorder An instrument that makesa permanent recording of signal amplitude as afunction of some independent variable (such astime, frequency, or direction).graphic panel In process control, a panel of illuminatedlights or dials that display the status of aprocess.

318 graphic recorder • gray tingraphic recorder An instrument in which a signaldrivenpen or stylus makes a permanent record ofa quantity on graph paper. The paper passes at acontrolled speed beneath the pen.graphics1. Diagrams, charts, photos, tables, orsimilar, often symbolic, artwork used to conveyinformation. 2. The video display in a computersystem. 3. Computer software designed specificallyto create and edit illustrations.graphic solution 1. A method of depicting the solution(s)to a problem or equation by means ofgraphs. 2. The process of solving problems orequations with the aid of graphs.graphic terminal A display or plotter that providesvisual output of a computer run.graphite A soft form of carbon used in resistors,attenuators, contacts, brushes, vacuum-tubeplates, cathode-ray tube coatings, etc.graphite-line resistor An emergency, makeshiftresistor consisting of a pencil line drawn on apiece of paper. The heavier the line for a givenwidth and length, the lower its resistance.graphophone Archaic term for phonograph.grasping planning A scheme that a robot arm andgripper use to get hold of a particular object. Itcan use a vision system, a bar-code reader, tactilesensing, and/or proximity sensing. The robotcontroller (computer) must be programmed torecognize the input from these devices, and toseek out the object.grass The background noise (noise floor) on thedisplay of a spectrum analyzer; it also appears oncertain types of radar displays.grasshopper fuse A special type of spring-operatedfuse. When it burns out, it actuates an alarm thatalerts personnel of a possible circuit or systemmalfunction.graticule Calibrated gridwork, as on the face of anoscilloscope or spectrum-analyzer screen.grating A set of parallel, closely spaced, equidistantconductors or bars. When an electromagneticfield that has a wavelength comparable tothe conductor spacing passes through the planecontaining the conductors, diffraction occurs,producing an interference pattern. An adaptationof this device, called a DIFFRACTION GRATING,is used to separate visible light into its constituentspectral colors.grating reflector A metal antenna reflector consistingof numerous parallel, straight, closelyspaced conductors. When the conductor spacingis much smaller than the wavelength, the set behaveslike a solid sheet of metal.Gratz rectifier A form of full-wave rectifier circuitin a three-phase, alternating-current system.gravitational constant Symbol, g. The accelerationproduced by the attraction of a unit mass atunit distance; g = 6.673 × 10 –11 N•m 2 /kg 2 .gravitational wave See GRAVITY WAVE.gravity 1. The universal force of attraction betweenmaterial bodies—especially that force evidencedby the earth’s drawing of bodies toward its center,causing them to have weight. 2. Abbreviation, g.The rate at which a free-falling mass acceleratesin a vacuum at the earth’s surface; equal to 9.802meters per second per second (m/s 2 ). 3. The rateat which a free-falling mass accelerates in a vacuumin the vicinity, or at the surface, of an astronomicalobject, such as a planet or star.gravity cell An electrochemical cell in which thepositive electrode is made of copper and the negativeelectrode is made of zinc. The copper electrodeis placed at the bottom of a jar, and the zincelectrode is placed at the top. The jar is half filledwith copper sulfate solution, and then filled withzinc sulfate solution. The solutions remain separatebecause copper sulfate has a higher specificgravity than zinc sulfate.gravity wave A disturbance in a gravitational field,such as might be caused by a collapsing star.These waves might emanate from black holes orrapidly spinning neutron stars.gray body A radiating body exhibiting constantspectral emissivity at all wavelengths. That is, theemitted energy is the same at all wavelengths andall frequencies.Gray code A computer code in which the expressionsrepresenting sequential numbers differ inonly one bit.gray scale A reference scale for use in black-andwhitetelevision and video display images, consistingof several defined levels of brightness withneutral color.Gray scale:hypothetical 16-shade binary codes.PercentCode Relative shade brightness0000 Black 0.000001 6.670010 Very dark gray 13.330011 20.000100 Dark gray 26.670101 33.330110 Medium-dark gray 40.000111 46.671000 Medium gray 53.331001 60.001010 Medium-light gray 66.671011 73.331100 Light gray 80.001101 86.671110 Off-white 93.331111 White 100.00gray tin A form of tin that exhibits some propertiesof a semiconductor at temperatures below 18 degreesCelsius.

greatest lower bound • grid resistor 319greatest lower bound The largest value of a parameterthat can be obtained without changingsome characteristic of a circuit, program, or system.Greek alphabet The 24-letter alphabet of theGreek language. Virtually all of letters are used assymbols in electronics and related sciences.Green Book A specialized format for compact-diskread-only memory (CD-ROM) computer data storagemedia, developed by Sony and Philips. Requiresthe use of a Compact Disk-Interactive (CD-I)player for data retrieval. See also CD-ROM, OR-ANGE BOOK, RED BOOK, and YELLOW BOOK.green gun The electron gun in a color cathode-raytube whose correctly adjusted beam strikes onlythe green phosphors on the screen.green video voltage In a three-gun color cathoderay-tubecircuit, the green-signal voltage, whichactuates the green gun.Greenwich Civil Time Abbreviation, GCT. Meantime counted from mean midnight at Greenwich,England, the location of zero meridian.Greenwich Mean Time Abbreviation, GMT. Meansolar time at zero degrees longitude, also calledthe Greenwich meridian because it passesthrough Greenwich, England. In recent years,GMT has been supplanted by COORDINATEDUNIVERSAL TIME (UTC) as the basis of standardtime throughout the world.grid 1. The prime control electrode in a vacuumtube. Usually, it is a coil or mesh, but it can haveother forms. Also called control grid. 2. Any electrodein a vacuum tube placed between the cathodeand the anode (plate) (e.g., screen grid andsuppressor grid). 3. Two sets of straight, uniformlyspaced, parallel conducting wires or rods,one set perpendicular to the other. The conductorsare electrically connected at all crossingpoints. Used as an electrostatic or electromagneticshield, or as a reflector of electromagneticwaves. 4. Two sets of uniformly spaced parallellines, one set perpendicular to the other, used asa system of coordinates or as a basis for physicalmeasurements.grid capacitor 1. A capacitor in series with the gridof a vacuum tube, used for blocking purposes.2. A bypass capacitor in a grounded-grid tubetype amplifier. 3. The capacitor in the grid tankcircuit of a tube type oscillator or amplifier.grid-cathode capacitance Symbol, CGK. The internalcapacitance between the control grid andcathode of an electron tube. Also called INPUTCAPACITANCE.grid characteristic The grid-current-versus-gridvoltageperformance curve for a vacuum tube.grid circuit The external circuit associated withthe control grid of a vacuum tube.grid current Symbol, I G . Current flowing betweenthe control grid and cathode in a vacuum tube.grid cylinder The metal cylinder that acts as acontrol grid in a cathode-ray tube.grid-dip meter 1. A dip meter that contains a vacuum-tubeoscillator; the indicating microammeteris in the grid circuit. 2. Loosely, any frequencysensitivewavemeter that indicates resonance by amarked dip in input (base, grid, and gate) current.grid-dip oscillator See GRID-DIP METER.grid dissipation 1. The amount of power given upas heat in the grid circuit of a vacuum-tube amplifier.2. The maximum amount of power that atube can safely dissipate as heat in the grid.grid drive See GRID EXCITATION.grid-driving power The signal power required bythe control grid of a power tube.grid emission Electron or ion emission by the controlgrid of a vacuum tube.grid excitation Signal voltage or power applied tothe control grid in a vacuum-tube amplifier circuit.grid impedance Symbol, Z G . The internal impedanceof the grid-cathode path in a vacuum tube.grid input impedance The impedance of the gridinput section of a vacuum-tube circuit. It is acomplex combination of grid impedance and theimpedance of input-circuit components.gridistor A special form of field-effect transistorwith several channels.grid-limiter resistor A resistor connected in serieswith the grid of a tube to limit grid current duringthe positive half-cycle of grid-signal voltage.grid limiting The cutting off of plate current in avacuum tube, with consequent limiting action, bymeans of a high, negative grid voltage developedby overdriving the grid.grid loading effect The tendency of the internalgrid-cathode path of a vacuum tube to load atuned circuit—especially when the grid drawscurrent.grid locking A vacuum-tube fault in which the gridpotential has become permanently positive becauseof excessive grid electron emission.grid mesh The mechanical structure of a grid (e.g.,gauze or a metal screen).grid neutralization See GRID-NEUTRALIZED AM-PLIFIER.grid-neutralized amplifier A neutralized radiofrequencypower amplifier in which the neutralizingcapacitor is connected from the plate of thetube to the free end of a center-tapped grid-tankcoil.grid north In the grid system of navigation, the directionmost nearly corresponding to geographicnorth.grid-plate capacitance See PLATE-GRID CAPA-CITANCE.grid pool tube A gas-discharge tube in which thecathode is a pool of mercury.grid power loss Driving-power loss in the gridinputcircuit of a power amplifier.grid resistor A high-value resistor connected betweenthe control grid and ground in a vacuumtubeamplifier circuit.

320 grid return • ground conduitgrid return The circuit path through which thecontrol grid of a vacuum tube is returned toground or to the negative grid bias supply.grid-separation circuit A vacuum-tube circuitin which the control grid is grounded. SeeCOMMON-GRID CIRCUIT.grid swing The peak-to-peak variation of a gridexcitation signal.grid tank A resonant inductance-capacitance circuitoperating in the control-grid circuit of a vacuumtube. Compare PLATE TANK.grid tank capacitance The capacitance requiredto tune a GRID TANK to resonance.grid tank inductance The inductance of the coilin a GRID TANK.grid tank voltage The alternating-current (ac)voltage developed across the grid tank of a vacuum-tubecircuit.grid tuning Tuning of a vacuum-tube circuit byvarying the capacitance, inductance, or both inthe GRID TANK.grid voltage 1. Symbol, V G . The direct-current(dc) bias voltage applied to the control grid of avacuum tube. 2. Symbol, V G(ac) . The voltage ofthe radio-frequency (RF) or audio-frequency (AF)signal in the grid circuit.grille A covering for an acoustic speaker, usedprimarily to protect the speaker cone, but alsofor esthetic appeal.grille cloth A durable fabric often used forspeaker grilles in high-fidelity sound systems. Ittransmits sound at all audio frequencies, butprotects the speaker(s) and provides an attractivephysical appearance.gripper See ROBOT GRIPPER.grommet An elastic washer inserted through ahole in a chassis to prevent accidental groundingof a conductor or to reduce wear on a cord orcable exiting the chassis.groove 1. See KEYWAY. 2. The fine, spiral linecut into a phonograph disc when it is manufactured.groove angle On a phonograph disk, the anglebetween the walls of the unmodulated groove.DisksurfaceDiskmotion:toward observerθgroove angleθ = Groove angle(usually 90°)groove speed In a phonograph recording or reproducingsystem, the speed of the cutter or needle,with respect to the disc. The speed is greatestnear the outer edge of the disk, and least near thecenter.gross content The overall amount of data containedin a message. It can be expressed in bits,bytes, words, or other units.gross index One of a pair of indexes, used to give areference in the fine index, a supplement; bothindexes are used to locate computer records instorage.gross-motion planning The method(s) that a robotuses to navigate in a general area without runninginto objects, knocking things over, fallingdown stairs, or losing its balance. It is often performedusing a COMPUTER MAP of the work environment.ground 1. The earth in relation to electricity andmagnetism. 2. An electrical connection to theearth. 3. The return point in a circuit. 4. A shortcircuitto the earth or to a circuit return point.5. A short-circuit to the metal chassis, case, orpanel of a piece of equipment.ground absorption The absorption (and resultingloss) of radio-frequency electromagnetic energyby the earth.ground bus A conductor connected to an earthground, and to which devices in a system are individuallyconnected. The common ground points(e.g., chassis) of the individual devices are not directlyconnected to each other, so ground loopsare avoided. This scheme minimizes the probabilityof ELECTROMAGNETIC INTERFERENCE toor from the system. Compare GROUND LOOP.A B CBusground busground clamp A device that provides a mechanicaland electrical bond between a conductor and aground rod or pipe. It is generally capable of passinga large amount of current.ground clutter 1. In a surface-based radar system,echoes from nearby buildings, hills, andother objects, producing blips or blobs near thecenter of the screen. 2. In radar operations, an interferencepattern on the screen, caused by accidentalgrounding in the system.ground conductivity The ease with which theearth will carry electrical current. Saltwater hasthe best conductivity; dark, moist soil and freshwater (because of the mineral content) rate fromfair to good. Sandy soil has the poorest groundconductivity.ground conduit A pipe housing one or moreground leads.

ground connection • ground-mounted vertical antenna 321ground connection 1. A low-resistance connectionto the earth. 2. The common point, such as achassis, to which zero-potential terminals of circuitcomponents are connected.ground constants The conductivity and dielectricconstant of the earth for a particular kind of terrainand soil at a given location. Affects the behaviorof radio antenna systems and electricalutility systems. Usually, high conductivity (lowresistance) and low dielectric constant are desirablecharacteristics.ground-controlled approach Abbreviation, GCA.In air navigation, a ground radar system that providesinformation for radio-directed aircraft approaches.ground-controlled interception Abbreviation,GCI. A ground radar system by which an aircraftcan be directed to intercept enemy aircraft.ground current 1. A direct electric current flowinginto the earth from an electrical or electronic device,or into a device from the earth. 2. An alternatingcurrent flowing between the earth and adevice. 3. An electric current flowing through theearth between two points. 4. A current flowing inthe normal ground (low-potential) line of a circuit.ground detector A device that indicates whetheror not a given circuit point is at direct-currentground.grounded antenna See MARCONI ANTENNA.grounded-base circuit See COMMON-BASE CIR-CUIT.grounded-cathode circuit See COMMON-CATHODE CIRCUIT.grounded-collector circuit See COMMON-COLLECTOR CIRCUIT.grounded-drain circuit See COMMON-DRAINCIRCUIT.grounded-emitter circuit See COMMON-EMITTER CIRCUIT.grounded-gate circuit See COMMON-GATE CIR-CUIT.grounded-grid circuit See COMMON-GRID CIR-CUIT.grounded outlet An outlet with a receptacle havinga ground contact that can be connected toequipment-grounding conductors.grounded-source circuit See COMMON-SOURCECIRCUIT.grounded system A set of electrical conductors ora transmission line in which one conductor is deliberatelygrounded.ground effect 1. Modification or distortion of theideal free-space directivity pattern of an antennaby reflections from, and absorption by, the earth.2. Effects of the earth on radio-wave propagation(e.g., the production of a reflected wave and a surfacewave, neither of which can exist if the earthis not part of the signal path). 3. Effects on antennabehavior, such as modification of theimpedance and resonant frequency, caused bythe proximity of the earth.ground efficiency In an antenna system, the qualityof the ground circuit. For some antenna systems,such as a balanced dipole at great height,this is not a consideration. Ideal ground efficiency(100%) results in zero ground loss.ground environment 1. See GROUND CON-STANTS. 2. The ground characteristics in thevicinity of an unbalanced antenna workingagainst ground. 3. In aviation, the set of groundbasedinstallations.ground fault 1. Loss of a ground connection. 2. Ashort-circuit to ground.ground-fault interrupter Abbreviation, GFI. Afast-acting electronic circuit breaker that opensthe power-line circuit breaker to prevent electricshock or equipment damage when the path ofcurrent flow is through the earth.grounding electrode A device, such as a groundplate or ground rod, that facilitates lowresistanceconnections to the earth.grounding plate A metal plate connected to theearth, on which a person stands to dischargestatic electricity from the body.grounding rod See GROUND ROD.ground insulation Electrical insulation used betweenadjacent energized and grounded parts,such as transformer windings and metal cores.ground level See GROUND STATE.ground loop A closed current path resulting fromimproper grounding of the components in a system.A loop is formed when two devices are connectedto each other, and also to separate earthgrounds or to a single earth ground via conductorsof appreciable length. The loops can act as antennas,increasing the likelihood of ELECTROMAG-NETIC INTERFERENCE to or from the system. Theuse of a single GROUND BUS is preferred.A B CLoopground loopLoopground mat A grid or network of conductors, connectedto earth ground, for the purpose of improvingthe earth conductivity.ground-mounted vertical antenna A vertical radiatormounted at the earth’s surface or at the surfaceof a body of water, and fed with coaxial cable.The radiator can be any physical length, but it istuned to resonance at the operating frequency.

322 ground-mounted vertical antenna • groundtrackThe center conductor of the cable is connected tothe base of the radiator, and the shield is connectedto a ground system. Radial wires, usuallyburied just below the surface, minimize losses.The antenna can be made resonant on severalfrequencies by inserting multiple loading coils ortraps in the radiator. The chief advantages of thisantenna are unobtrusiveness and ease of installation.The main problems are marginal efficiencyand susceptibility to human-made electromagneticnoise. See also RADIAL, 1. CompareGROUND-PLANE ANTENNA.ground noise 1. Electrical noise that results froma faulty ground connection. 2. Background noise.3. In wire circuits, such as a telephone system,electrical noise that results from fluctuations inground current.ground plane 1. A metal plate or a system of horizontalrods or wires mounted high on a mast, atthe base of a vertical antenna, to provide a radiofrequencyground at a point several wavelengthsabove the surface of the earth. Also see GROUND-PLANE ANTENNA. 2. In noise and interferencetests, a sheet metal structure used to simulatethe skin of an aircraft or missile. 3. On a circuitboard, a thin metallic sheet, usually bound to theunderside, that serves as a common ground andRF shield.ground-plane antenna A vertical radiator operatedagainst a system of quarter-wave radials,elevated at least a quarter wavelength above theearth’s surface and fed with coaxial cable.The center conductor of the cable is connectedto the base of the radiator, and the shield is connectedto three or four quarter-wave radials thatrun outward from the base of the radiator. Atshorter wavelengths, a disk or cone can replacethe radials. The chief advantages of this antennaare simplicity and high efficiency. Themain problem is susceptibility to human-madeelectromagnetic noise. See also RADIAL,1. Compare GROUND-MOUNTED VERTICALANTENNA.ground plate A metal plate buried in the earth toprovide a low-resistance ground connection.ground-position indicator Abbreviation, GPI. Acomputer system that gives a continuous indicationof an aircraft’s position in terms of heading,elapsed time, and speed, with respect to the surface.This provides a more useful indication of theaircraft position than an air-speed indicator becauseit is not affected by high-altitude winds.ground potential See ZERO POTENTIAL, 3.ground protection The use of a GROUND-FAULTINTERRUPTER.ground-reflected wave A radio wave componentthat results from ground reflection.ground reflection The reflection of a radio wave bythe earth.ground resistance The direct-current resistance ofa connection to the earth, or the resistance betweentwo points through the earth. The magnitudeof the resistance depends on several factors:composition of the soil, amount of moisture, soilelectrolytic action, and the area of contact withthe earth.ground return 1. The point or path used to returna circuit to ground for completion. 2. In radar,echoes returned from the earth’s surface (includingreflections from objects on it).ground-return circuit A circuit, such as a singlewiretelephone line, in which earth ground formsone leg of the circuit. Compare METALLIC CIR-CUIT.ground rod A strong metal rod driven deep into theearth as a point of ground connection.ground speed The speed of an aircraft or missile,relative to the surface of the earth.ground state The least-energy level of all possiblestates in a system.ground support equipment Electronic surfacebasedapparatus upon which the functioning of aweapons system is dependent.ground switch A switch for grounding an outsideantenna during idle periods. Also called lightningswitch. Ideally, antennas should be disconnectedfrom equipment, as well as grounded, when notin use.ground-to-air communication Radio or radartransmission from a land station to an aircraft inflight.ground-to-ground 1. Pertaining to communicationsbetween land-based stations. 2. Pertainingto missiles intended for use between points onthe surface of the earth.ground-to-ground communication Communicationsbetween land-based stations.groundtrack For an earth-orbiting satellite, thepath followed by the point on the earth’s surfacefrom which the spacecraft appears directly overhead.For most satellites, this path shifts towardthe west for each succeeding orbit, because theearth rotates eastward underneath the satellite.For geostationary satellites, the point never

groundtrack • G-string antenna 323changes position on the surface. For satellites inequatorial orbits, the track follows the equator.ground wave In wireless communications andbroadcasting, an electromagnetic (EM) wave thatconsists of three distinct components: the directwave (also called the line-of-sight wave), the reflectedwave, and the surface wave. The directwave is significant only when the transmitting andreceiving antennas are connected by a line throughfree space without obstructions. The reflectedwave, after returning from the earth’s surface or ahuman made structure, combines with the directwave (if any) at the receiving antenna. The surfacewave travels in electrical contact with the earth.This occurs only with vertically polarized EM fieldsat frequencies below about 15 MHz. Below about300 kHz, the surface wave propagates for hundredsor even thousands of miles. Sometimes thesurface wave is called the ground wave.ground wire A conductor between an equipmentand a ground connection, either for circuit completionor for safety.group 1. A series of computer storage locationscontaining a specific record or records. 2. Thedata in these locations. 3. A record set having acommon key value in a sorted file.group busy In a telephone system, an audio signalindicating that all of the lines in a group are inuse.group code In digital communications, an errordetectingcode used to verify a character grouptransferred between terminals.group delay In a modulated signal, a delay in thetransmission of data.grouped-frequency operation In a two-wire communicationssystem, the grouping of directionalsignals into certain frequency bands.grouped records A set of data records in which thekey of one record identifies the entire set.grouping 1. The arrangement of data into blocksor sets. 2. On a phonograph disc, the insertion ofgaps in the arrangement of grooves. 3. Any periodicirregularity in the spacing of a data transmission.4. The bunching of grooves on a discrecording. 5. In a facsimile system, occasionalspacing errors between recorded lines. 6. A massof data arranged into groups, according to commoncharacteristics.group mark 1. In telegraphy, an indicator that signalsthe end of a data unit. 2. A character indicatingthe end of a character group; usually, it isa logical record that is addressed and processedas a unit.group velocity The velocity at which a group ofwaves or a pulse is propagated.Grove cell A closed-circuit primary cell in whichthe positive electrode, platinum, is immersed innitric acid; the negative electrode, zinc, is immersedin sulfuric acid. The nitric acid is held ina porous cup, surrounded by a larger jar of sulfuricacid.growler 1. An electromechanical troubleshootingdevice that indicates the location of short circuitsand grounds (especially in electric motors) byemitting a growling or rumbling sound. 2. Anytester that provides an audible signal, which indicateselectrical continuity.grown-diffused transistor A transistor that ismade by first growing the emitter and collectorregions as a crystal, into which the base region islater diffused while the crystal is being pulled.grown diode A semiconductor diode created bygrowing a layer of p-type material into n-type material(or vice versa) as the single-crystal materialis being pulled from the melt.grown junction A pn junction produced by addingimpurities in various amounts to a crystal while itis being pulled from molten semiconductor material.grown-junction diode See GROWN DIODE.grown-junction photocell A grown-junction diodeused as a photoconductive cell.grown-junction transistor A transistor made byadding n-type and p-type impurities successivelyto a crystal in its molten state, then slicingthe resulting npn formations from the finishedcrystal.G-scanA rectangular radar display consisting of alaterally centered blip that “grows wings” as a targetapproaches. Horizontal and vertical displacementof the blip indicate horizontal and verticalaiming errors.TransmittinghornCoaxialcableZinc(−)Platinum(+)NitricacidSulfuricacidGrove cellG scope See G SCAN.GSR Abbreviation of GALVANIC SKIN RESPONSE.G-string antenna In microwave operations, a communicationspath provided by a dielectric-coatedwire that behaves like an extremely low-losscoaxial line with its outer conductor removed toinfinity. A horn at each end matches the line tothe transmitter and receiver. The term comesWireG-string antennaPorous cupSolidcontainerReceivinghornCoaxialcable

324 G-string antenna • Gunnplexerfrom the first initial of Dr. George Groubau, inventorof the device, and the stringy appearanceof the wire.GTO Abbreviation of GOTO.guard band A narrow unoccupied band of frequenciesat the upper and lower limits of an assignedchannel; its purpose is to prevent adjacentchannelinterference by ensuring adequateseparation between channels.guard circle On a phonograph disk, an innergroove that prevents collision of the pickup withthe spindle at the center of the disc.guard circuit An auxiliary circuit added to analternating-current bridge to compensate for theeffects of stray capacitance in the bridge arms.One of its several forms is the WAGNERGROUND.guarded input An input-terminal arrangement inwhich one terminal, maintained at the proper potential,shields the entire input-terminal combination.guardingA method of short-circuiting a leakagecurrent to ground. On a printed-circuit board,guarding is usually accomplished by the use of alarge conducting foil surface near critical components.guard relay A relay that ensures that only onelinefinder will be connected to a line circuit whenother line relays are in operation.guard ring A metal ring (or other configuration)surrounding, but separate from, a charged bodyor terminal, for the purpose of evenly distributingthe electric charge over the latter’s surface.guard shield A shield that encloses the input circuitof an amplifier or instrument.guard terminal In a GUARDED INPUT, the terminalthat shields the combination.guard wire A grounded wire that is intended tocatch and ground a broken high-voltage line.Gudden-Pohl effect The tendency of an ultravioletirradiated phosphor to glow momentarily whensubjected to an electric field.GUI Acronym for GRAPHICAL USER INTERFACE.Can be spelled out or pronounced “gooey.”guidance Electronic control of the path or courseof a robot, missile, or other vehicle.guidance system The complete electromechanicalsystem for control of a robot, missile, or other vehicle.It consists of hardware and software. Thehardware includes beacons, sensors, drive systems,rockets, etc. The software interprets datafrom, and transmits commands to, the hardware.The nature of the hardware and software dependon the application.guidance tape In a guided missile, a magnetic tapecontaining computer instructions for steering themissile in a designated course.guide See WAVEGUIDE.guide connector See WAVEGUIDE CONNECTOR.guided missile A missile whose progress to a targetis controlled electronically by signals from acontrol station or by sensing equipment aboardthe missile.guided propagation A form of radio-wave propagationin which air masses of different temperaturesor humidity levels cause refraction and/or reflectionof electromagnetic waves, guiding signalsover long distances with very little attenuation.Commonly observed at very-high and ultra-highfrequencies.guide elbow See WAVEGUIDE ELBOW.guide flange See WAVEGUIDE FLANGE.guide gasket See WAVEGUIDE GASKET.guide junction See WAVEGUIDE JUNCTION.guide load See WAVEGUIDE LOAD.guide slot See KEYWAY.guide wavelength See WAVEGUIDE WAVE-LENGTH.Guillemin effect The tendency for a strip of ferromagneticmaterial to become straight in a strongmagnetic field. This is a form of MAGNETO-STRICTION.Guillemin line In radar operations, a specialpulse-forming network for controlling modulationpulse duration.guillotine capacitor A variable capacitor in whicha sliding (instead of rotary) plate moves betweentwo stator plates. Its name results from its resemblanceto the infamous beheading apparatus.gulp Several bytes of digital information.gun See ELECTRON GUN.Gunn diode A semiconductor diode that can operateas an oscillator in the ultra-high-frequency(UHF) and microwave parts of the radio spectrum.Oscillation takes place as a result of a negative-resistanceeffect in which, within a certainrange of applied voltages, the current decreasesas the voltage increases. The device is not particularlyefficient. Only a small fraction of the inputpower results in useful signal output. The frequencyand oscillation stability are sensitive tochanges in temperature and bias voltage. SeeGUNN EFFECT, NEGATIVE RESISTANCE.Gunn effect A semiconductor phenomenon namedafter J. Gunn of International Business Machines(IBM) who first observed and studied it in the1960s. In certain types of diodes having a negative-resistancecharacteristic, oscillation occurswhen the applied voltage is within a certainrange. See GUNN DIODE, NEGATIVE RESIS-TANCE.Gunn-effect circuit Any circuit exploiting theGunn effect, especially a GUNN OSCILLATOR.Gunn oscillator A discrete semiconductor microwaveoscillator using a GUNN DIODE.Gunnplexer A microwave transmitter consisting ofa Gunn-diode oscillator connected to a horn antenna.Usually, the entire device is a compact,self-contained unit. The output power is low.When the device is placed at the focal point of alarge dish antenna with the horn pointing towardthe dish reflector (conventional dish feed), consid-

Gunnplexer • G-Y signal 325erable transmission range is possible. Used primarilyby experimenters, and in wireless communicationslinks. See GUNN DIODE.gutta percha A hard, rubberlike, organic insulatingmaterial. Dielectric constant, 3.3 to 4.9. Dielectricstrength, 203 to 508 kV/in.guyed tower In radio communications or in microwavelinks, a structure that is supported byone or more sets of guy wires to add strength andto prevent collapse.guying The support of a radio communications ormicrowave-link tower by the use of one or moresets of guy wires.guy insulator Also called egg insulator. An insulatordesigned to electrically break a guy wire whilemaintaining its ability to support a structure.Such an insulator has two slots with holes placedat right angles, in such a position that the wirewill not separate even if the insulator breaks. Thestress exerted on the insulator is compression,and the insulating material is stronger under thistype of stress than under tension (pulling).guy insulatorguy wire A bracing wire for antenna masts or towers.gyrator An active (usually cascaded-transistor) deviceexhibiting nonreciprocal phase shift. It provides,among other functions, the simulation ofinductance using capacitors.gyro Contraction of GYROSCOPE.gyro- A prefix meaning “pertaining to gyroscopes,”“containing a gyroscope,” or “behaving like a gyroscope.”gyrocompass A type of compass in which a spinninggyroscope, acted upon by the earth’s rotation,causes the device to point to true north.Compare MAGNETIC COMPASS.gyrofrequency The natural frequency of rotationof charged particles around the earth’s magneticlines of flux.gyromagnetic Pertaining to the magnetic propertiesof rotating electric charges (e.g., the effect ofelectrons spinning inside an atom).gyromagnetic effect The tendency of a rotatingbody to become magnetized because of the magneticfield of the earth.gyropilot See AUTOPILOT.gyroscope A device that consists of a spinningwheel mounted in a gimbal. The shaft of thewheel will point in one direction, despite themovement of the earth beneath it.gyrostat See GYROSCOPE.G-Y signal In a color-television circuit, the signalrepresenting primary green (G) minus luminance(Y). A primary green signal is obtained when theG-Y signal is combined with the luminance (Y)signal. Compare B-Y SIGNAL and R-Y SIGNAL.

H 1. Symbol for magnetic field strength. 2. Symbolfor MAGNETIZING FORCE. 3. Symbol for HYDRO-GEN. 4. Symbol for UNIT FUNCTION. 5. Abbreviationof HORIZONTAL. (Also, hor and horiz.)6. Symbol for HENRY. 7. Symbol for HARMONIC.h 1. Abbreviation of prefix HECTO-. 2. Symbol forthe PLANCK CONSTANT. 3. Abbreviation of HOUR.Haas effect See FUSION, 1.hack In computer networking, to access, andsometimes to change, sensitive data without authorization.hacker A person knowledgeable in computer networkingwho uses his or her expertise to access,and sometimes alter, sensitive data. This is illegaland can sometimes be destructive. The intent, israrely malicious, however, the activity is viewedas a challenge. Compare CRACKER.HACKER program A computer program developedby Gerry Sussman as an early experiment withartificial intelligence (AI), to see how the machinewould deal with complex decision-making problems.hadron A subatomic particle consisting of quarks.hafnium Symbol, Hf. A metallic element. Atomicnumber, 72. Atomic weight, 178.49. Readilyemits electrons.hahnium See DUBNIUM.hailer 1. A marine microphone-amplifier-speakersystem for calling to other boats or personsashore. 2. A comparable system for land vehicles,such as police cars. Also see MEGAPHONE, 1.hair See HAIRLINE.hair hygrometer A device for measuring relativehumidity, in which a stretched hair is themoisture-sensitive element.hairline A fine line used as an index or a graticulemarker in a precision instrument.hairpin coil A quarter-turn coil, so called from itsresemblance to a hairpin.hairpin coupling coil A hairpin coil used as a lowimpedanceprimary or secondary coil for input oroutput coupling.hairpin match A form of impedance-matching networkused at the feed point of a half-wave dipoleantenna. A short length of open-wire transmissionline, short-circuited at the far end, is connectedin parallel with the antenna at the feedpoint.hairpin pickup A short, doubled length of wirethat acts as a pickup coil at very-high and ultrahighfrequencies.hairspring A fine, usually spiral spring—especiallythe one in a movable-coil meter or the oneconnected to the balance wheel of a watch orclock.hair-trigger Pertaining to extreme sensitivity of response,such as the tendency of a switching deviceto change state when excited by a weakpulse.hair wire 1. An extremely thin wire filament in alamp or bolometer. 2. Very small gauge wire (e.g.,#44).hal Abbreviation of HALOGEN.half-add The sum of two binary digits, in which thecarry operation is omitted. Thus 0 + 0 = 0, 0 + 1 =1, 1 + 0 = 1, and 1 + 1 = 0.half-adder In digital systems, an adder circuit thatcan handle the two binary bits that are to beadded, but that cannot accommodate a carry signal.Compare FULL ADDER.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

half-bridge • half-wavelength 327XInputYacInputhalf-adderCarry outputhalf-bridgeSum outputhalf-bridge A bridge rectifier that has diodes in twoarms and resistors in the other two.half-cell A voltaic cell consisting of a single electrodeimmersed in an electrolyte and having adefinite difference of potential; it is, in effect, halfof a primary cell. Also see HELMHOLTZ DOUBLELAYER.half-cycle Half of a complete alternation (i.e., 180degrees of phase).half-cycle magnetizer A magnetizer using halfcyclesof rectified alternating current as the magnetic-fieldsource.half-duplex channel A communications channelin a HALF-DUPLEX SYSTEM.half-duplex system In data communications, asystem that transmits data in both directions,but not simultaneously. Compare FULL-DUPLEXSYSTEM.half-lattice crystal filter A band-pass crystalfiltercircuit using two piezoelectric crystalsin a four-arm bridge. Also see CRYSTAL RES-ONATOR.half-nut In a facsimile receiver, a device thatguides the lead screw.half-power point In a response curve or directionalpattern, such as for a selective filter or aunidirectional antenna, the points on each side ofmaximum at which the power is 3 dB below thepeak value.+dcOutput−half-power width In a directional antenna system,an expression of beamwidth. It is usually listed asthe horizontal-plane angle, in degrees, betweenthe half-power points in the main lobe of the directivepattern.half-step 1. In audio engineering, the frequencyinterval between two sounds, whose ratio is1.06:1. 2. The difference in pitch between thenotes produced by two adjacent keys on apiano.half tap A bridging circuit or device that can shuntanother circuit with the least electrical disturbance.half-track recorder A magnetic tape recorder thatapplies signals to both halves of a tape with ahead that covers only half the tape’s width ineach of two directions. Also called dual-trackrecorder.half-track tape Magnetic tape recorded by aHALF-TRACK RECORDER.half-wave Half of a complete wave (i.e., a completerise and fall in one direction). Its graphic representationis similar in appearance to that for ahalf-cycle.half-wave antenna An antenna whose radiatormeasures an electrical half wavelength from endto end. Such a radiator is about 5 percent lessthan a free-space half-wavelength long, becauseof capacitive effects and the velocity factor of theconductor.half-wave chopper A chopper that closes a circuitduring only half the switching signal cycle.half-wave dipole A center-fed antenna whose radiatormeasures 0.5 electrical wavelength from endto end. Also see DIPOLE ANTENNA.half-wave doubler See HALF-WAVE VOLTAGEDOUBLER.half-wave feeder See HALF-WAVE TRANSMIS-SION LINE.half-wavelength Symbol λ/2. The distance thatcorresponds to 180 degrees of phase as an electromagnetic(EM) field is propagated in freespace, it is related to the frequency by a simpleequation:L ft = 492/fwhere L ft represents λ/2 in feet, and f representsthe frequency in megahertz. If λ/2 is expressed inmeters, then the formula is:L m = 150/fwhere L m represents the displacement in meters.In general, if ν is the velocity factor (expressed asa ratio) in a given medium, then:L ft = 492ν/fandL m = 150ν/fCompare FULL WAVELENGTH, QUARTERWAVELENGTH.

328 half-wave loop antenna • Hall fieldhalf-wave loop antenna A loop antenna having acircumference of 0.5 wavelength with a break oppositethe feed point. It is, in effect, a HALF-WAVEDIPOLE bent into a circle or square (although anysymmetrical configuration can be used). The circleis the most efficient configuration.Gaphalf-wave vibrator A vibrator (see INTERRUPTER)whose reed operates against only one stationarycontact. Compare FULL-WAVE VIBRATOR.half-wave voltage doubler A voltage-doubler circuitwhose direct-current (dc) output has a ripplefrequency equal to that of the alternating-current(ac) supply. Although its output is harder to filterthan that of a full-wave doubler, this circuit hasthe advantage of a common ground. CompareFULL-WAVE VOLTAGE DOUBLER.λ/4λ/4C1100 V− +D2100 Vac+−D1C2200 Vdchalf-wave loop antennahalf-wave radiator An antenna consisting of a single,usually straight, active element that measuresan electrical half wavelength from end toend. It is therefore a resonant element. A simplehalf-wavelength (λ/2) conductor with a highlength-to-diameter ratio measures approximately95 percent of λ/2 in free space. The element can bemuch shorter than free-space λ/2 yet remain λ/2-resonant if inductance is inserted in series withthe radiator. The element can be much longerthan free-space λ/2 yet remain λ/2-resonant if distributedcapacitances are inserted in series withthe radiator.half-wave rectification The conversion of alternatingcurrent (ac) to direct current (dc) duringhalf of each ac cycle. Also see HALF-WAVE REC-TIFIER.half-wave rectifier A rectifier that delivers a halfcycleof direct-current (dc) output for every otherhalf-cycle of applied alternating-current (ac) voltage.Because the successive dc half-cycles are180 degrees apart, they have the same polarity.Compare FULL-WAVE RECTIFIER.half-wave transmission line A transmission linemeasuring 0.5 electrical wavelength at the transmissionfrequency. The physical length is somewhatless than a free-space half wavelengthbecause of the VELOCITY FACTOR of the line.half-wave voltage doublerhalide A compound of a HALOGEN. Examples:sodium iodide, used as a scintillating crystal; ammoniumchloride, used as the electrolyte in a drycell.halide crystal A halogen-compound crystal, suchas mercuric iodide and sodium iodide, useful indetecting radioactivity.Hall coefficient For a current-carrying conductor,the constant relationship between the Hall(transverse electric) field and the magnetic fluxdensity.Hall constant For a current-carrying conductor,the constant of proportionality k given by theequation k = e/(im), where e is the transverseelectric field (Hall field), i is the current density,and m is the magnetic field strength.Hall effect A phenomenon observed in thin stripsof metal and in some semiconductors. When astrip carrying current longitudinally is placed in amagnetic field that is perpendicular to the strip’splane, a voltage appears between opposite edgesof the strip that, although feeble, will force a currentthrough an external circuit. The voltage ispositive in some metals (such as zinc) and negativein others (such as gold). Also see ETTING-HAUSEN EFFECT, NERNST EFFECT, andRIGHT-LEDUC EFFECT.Hall-effect modulator A device that uses the HALLEFFECT to modulate a signal, or to mix two signals.Hall-effect multiplier A device based upon theHall generator and used in analog mathematicaloperations, such as multiplication and the extractionof roots.Hall field The transverse electric field of a conductorcarrying current in a magnetic field.

Hall generator • handoff 329Hall generator A semiconductor device exhibitingthe HALL EFFECT. It is a thin wafer or film of indiumantimonide or indium arsenide with leadson opposite edges.MHall currentMagnetic fieldperpendicularto ohmiccontactOhmiccontactControl currentHall generatorHall-effectelementControlelectrodeHall mobility For a conductor or semiconductor,the product of conductivity and the HALL CON-STANT.Hall network A resistance-capacitance null circuitwhose general configuration is two cascadedhigh-pass tee-sections bridged by a high resistance.The circuit can be tuned with one potentiometer.InputR1C1 C2 C3R2R3Hall networkOutputHallwacks effect The phenomenon (observed byHallwacks in 1888) in which ultraviolet lightfalling on a polished zinc plate causes a negativelycharged electroscope to which it is connectedto discharge.hallucination In complex computers and artificiallyintelligent systems, the generation or appearanceof data for no apparent reason.halo See AFTERGLOW and PERSISTENCE.halo antenna A horizontally polarized antenna,consisting of a circular half-wave dipole whoseends are capacitance loaded. Commonly used atvery high frequencies (VHF).halogen Abbreviation, hal. A group of five very activenonmetallic elements whose similar chemicalproperties put them in group VIIA of the periodictable; they are astatine, bromine, chlorine, fluorine,and iodine.Halowax A chlorinated naphthalene wax used asan impregnant for paper capacitors. Dielectricconstant, 3.4 to 5.5. Resistivity, 10 13 to 10 14 ohmcm.halt A stop during the execution of a computerprogram run, often resulting from a HALT IN-STRUCTION.halt instruction An instruction in a computer programthat causes a break in the program’s execution,as by BASIC’s STOP command, for example.ham Colloquialism for AMATEUR RADIO operator.ham radio See AMATEUR RADIO.Hamilton’s principle Also called the principle ofleast action. Motion tends to occur in such away that the integral of the product of kinetic energyand elapsed time is minimal.hammer 1. The striking member in a WHEELPRINTER. 2. The clapper in an electric bell orgong.hammer-and-wheel See WHEEL PRINTER.Hamming code An error-correction code used insome digital communications circuits.hand capacitance Also called body capacitance.Capacitive coupling effects between a circuit andthe human body (e.g., as evidenced between anoperator’s hand and a device having extremelyhigh impedance and poor grounding and/orshielding).hand generator An electric generator operated byturning a hand crank.handheld computer Also called personal digitalassistant (PDA) or palmtop computer. The namesPalmPilot and Palm are proprietary (Palm Computing,Inc.) and refer to specific families of handheldcomputers, although they might somedaybecome generic and refer to handheld computersin general. A battery-powered portable computer,smaller than a notebook computer, and usedfor simple tasks such as note-taking andrecord keeping. Some units incorporate wirelessmodems for connection to the Internet. Others includepaging, wireless fax, videoconferencing capability,remote-control capability, and otherfeatures. Many units can recognize a specializedform of handwriting so users can enter data witha penlike device called a stylus.Handie-Talkie Abbreviation, HT. Tradename for aportable transceiver small enough to be held inthe hand during operation.hand key Also called brass pounder. An oldfashioned,hand-operated telegraph key, operatedby manual downward pressure.handoff In cellular communications networks, thechangeover of reception from, and transmission

330 handoff • hard-wire telemetryto, a mobile or portable set from one repeater toanother as the subscriber moves from one cellinto another. When the subscriber is movingrapidly—for example, driving along a freeway,such transfers occur relatively often. When asubscriber is moving slowly, for example, walkingalong a trail, such transfers occur rarely. When asubscriber is in a fixed location, such transfersdo not normally occur.hand-operated device A device manipulated directlyand manually by the operator’s hand(s).Also called manual device.hand receiver 1. A single earphone that must beheld against the ear. 2. A telephone receiver.hand rules See FLEMING’S LEFT-HAND RULE,FLEMING’S RIGHT-HAND RULE, and RIGHT-HAND RULE FOR WIRE.handset See CRADLEPHONE.handshaking 1. A controlled, periodic exchange ofsynchronizing pulses between a digital transmitterand receiver. 2. In a digital communicationssystem, a method of error correction. The receiverdetects nonstandard or improbable character sequences,and instructs the transmitter to repeatthem for double-checking.hand-type pointer In an electric meter, a spearlikepointer (resembling the hand of a clock), asopposed to a knife-edged pointer.hand-wired Pertaining to electronic equipmentwired by hand, rather than being assembled onprinted-circuit boards. This form of constructionis rarely seen nowadays, except in some radiofrequencypower amplifiers.hang AGCAn automatic-gain-control (AGC) circuitwhose action is sustained for a brief interval afteran actuating signal has passed, an advantage insome applications. Also called fast-attack/slowreleaseAGC.hangover In sound operations, the blurring orsmearing of low-frequency (bass) notes by apoorly damped or poorly mounted loudspeaker.hangup 1. In phonograph operation, the state inwhich the same material is played repetitiously(i.e., the stylus does not move toward the spindle).2. In digital-computer operations, an unexpectedbreak during a program run as a result ofsoftware or hardware failure. Sometimes calledUNEXPECTED HALT.H antennahard copySee LAZY-H ANTENNA.1. In digital computer operations, areadable document (printout) of material beingtranslated to a form understood by a computer.2. Generally, written or typed documents, as opposedto data on other media, such as diskettes,tapes, CD-ROM, etc.hard disk An electromechanical data storage mediumcommonly used in personal computers.Consists of several rigid disks, called platters,coated with ferromagnetic material.hard-drawn wire High-tensile-strength unannealedwire.hard dump See HARDWARE DUMP.hard magnetic material High-retentivity magneticmaterial. Also see RETENTIVITY.hardness 1. The property that causes a material toresist penetration, deformation, scratches, etc. 2.The penetrative ability of ultraviolet rays, X rays,or other ionizing radiation. Generally, the radiationhardness increases as the wavelength decreases,and as the photon or particle energyincreases.hardness tester A device for measuring the hardnessof a solid in terms of the force required topenetrate its surface. Also see HARDNESS, 1.hard radiation In general, any radiation with highpenetrating power. Usually, this term is used inreference to short-wavelength (high-energy) ultravioletrays or X rays.hard solder Solder that melts at a comparativelyhigh temperature. Compare SOFT SOLDER.hard vacuum A nearly perfect vacuum, that is, amedium essentially devoid of atomic or subatomicparticles.hardware 1. Collectively, electronic circuit componentsand associated fittings and attachments. 2.In a computer system, the electronic and electromechanicalcomponents (e.g., integrated circuits,keyboards, and disk drives) associated withoperation. Compare SOFTWARE.hardware availability ratio A figure depicting theavailability of a computer system to do productivework; as a percentage, it is given by the formula:A = 100(ta – td)/ta,where A is the availability ratio, ta is the operationaltime, and td is the downtime over a specifiedtime period.hardware check A check on data being transferredwithin a computer, as done by hardware (e.g., aparity check).hardware cloth A finely woven wire screen sometimesused in place of a metal plate for an antennaelement, an antenna reflector, or a shieldedenclosure. Especially useful when free-air circulationis required.hardware dump During a computer program run,data sent to a storage device for later evaluation;it occurs at the time of a failure. Also called AU-TOMATIC HARDWARE DUMP.hardware engineer A person who designs and perfectsthe actual electronic circuitry in a system.The hardware engineer is not involved with theprogramming of the system.hardware recovery A computer system’s ability(through software or hardware) to recover from afailure (i.e., to proceed from the point of failure).hardware serviceability ratio See HARDWAREAVAILABILITY RATIO.hardwire 1. To construct a circuit for direct-currentconductivity. 2. A circuit exhibiting direct-currentconductivity over a complete, closed path.hard-wire telemetry See WIRE-LINK TELEMETRY.

hard wiring • harmonic-distortion percentage 331hard wiring 1. In computer systems, functions orprograms built directly into the machine hardware.In order to alter such functions or programs,the system wiring and/or componentsmust be physically changed. 2. A system interconnectedentirely by wires and cables, and usingno free-space links, such as radio or infrared.hard X rays High-frequency (shortwave) X rays.Such radiation has high penetrating power. CompareSOFT X RAYS.harmonic 1. Symbol, H. In a complex sound or signalwave, a component whose frequency is a multipleof the FUNDAMENTAL FREQUENCY by awhole-number factor of 2 or more. 2. Pertainingto whole-number multiples of the FUNDAMEN-TAL FREQUENCY of a sound or signal, as definedin 1.Amplitude AmplitudeThirdharmonicwaveFundamental waveFundamental pipSecond harmonic waveASecondharmonicpipFrequencyBThirdharmonicpipFourthharmonicwaveFourthharmonicpipharmonic: waves (A)and spectrum-analyzer display (B)Timeharmonic accentuation Increasing the amplitudeof harmonic components in a complex wave usingfilters, amplifiers, or special modes of operation.harmonic accentuator A circuit or device, such asa harmonic amplifier or bandpass filter, for emphasizingsignal harmonics.harmonically related bands In communications,frequency bands arranged so that the frequenciesin one band are harmonics of the frequencies inanother band. An example of bands that are preciselyrelated in this way are 4.1 to 4.3 MHz and8.2 to 8.6 MHz. Various amateur radio bands areharmonically related to some extent, such as 40meters (7.0 to 7.3 MHz) and 20 meters (14.0 to14.35 MHz).harmonic amplifier An amplifier, such as oneused with a frequency standard, used to increasethe amplitude of weak harmonics. Also see HAR-MONIC ACCENTUATION.harmonic analysis 1. The evaluation of the harmoniccontent of a complex wave. See, for example,HARMONIC WAVE ANALYZER; SCHEDULEMETHOD, 2; SPECTRUM ANALYZER; and WAVEANALYZER. 2. See FOURIER ANALYSIS.harmonic analyzer See HARMONIC WAVE ANA-LYZER, SPECTRUM ANALYZER, and WAVE ANA-LYZER.harmonic antenna An antenna operated at a harmonicof the lowest frequency at which it is resonant.For example, a half-wave dipole cut for 7.0MHz, but used for transmitting and receiving at21.0 MHz, is functioning at the third harmonic.harmonic attenuation Reduction of the amplitudeof harmonic components in a complex wave usingfilters, tuned amplifiers, or special modes of operation.harmonic attenuator A circuit, device, or methodof operation (such as a filter, tuned amplifier,special biasing, or special bypassing) for reducingthe amplitude of harmonics.harmonic component See HARMONIC.harmonic composition See HARMONIC DISTRI-BUTION.harmonic content The amount of harmonicenergy present in a complex wave. Also seeHARMONIC-DISTORTION PERCENTAGE andHARMONIC RATIO.harmonic-cut crystal Also called overtone crystal.A quartz crystal that, when operated in theproper circuit, oscillates at a harmonic of the(fundamental) frequency dictated by its thickness.harmonic detector A detector tuned to respond toa harmonic of a signal.harmonic distortion 1. The generation of harmonicsby the circuit or device by which the signalis processed. 2. The deformation of theoriginal signal that results from the action describedin 1. 3. The disproportionate reproductionof a signal’s harmonic components.harmonic distortion meter See DISTORTION ME-TER.harmonic-distortion percentage In a signal containingharmonics, the harmonic energy as a percentageof the total signal energy (fundamentalplus all harmonics). Also called total harmonicdistortion (THD).

332 harmonic distribution • hassiumharmonic distribution For a given signal, the variousfrequencies and amplitudes of its harmonics,specified within a certain range of frequencies.harmonic elimination The complete removal ofone or more harmonics from a complex wave usinga filter or special mode of operation.harmonic eliminator A circuit or device, such as aband-suppression filter, for removing harmonics.harmonic filter 1. A bandpass filter for transmittingone or more harmonics of a complex inputwave. 2. A band-suppression filter for removingone or more harmonics of a complex input wave.harmonic frequency 1. In a complex wave, thefrequency of a component that is a multiple ofthe FUNDAMENTAL FREQUENCY by a wholenumberfactor of two or more. 2. A frequency thatis a whole-number (two or more) multiple of anotherfrequency to which it is referred. CompareNONHARMONIC FREQUENCY.harmonic generator 1. An oscillator operated sothat it generates strong harmonics of the fundamentalfrequency. 2. See FREQUENCY MULTI-PLIER. 3. See HARMONIC AMPLIFIER.harmonic intensification See HARMONIC AC-CENTUATION.harmonic intensifier See HARMONIC ACCENTU-ATOR.harmonic interference Interference resultingfrom the harmonics of radio or test signals.harmonic motion Periodic motion typified by aswinging pendulum and illustrated by the plot ofa sine wave.harmonic oscillator A crystal oscillator whoseoutput frequency is a harmonic of the crystal frequency.harmonic percentage See HARMONIC-DISTOR-TION PERCENTAGE.harmonic producer 1. An oscillator that uses atuning fork to establish the fundamental frequency.The output can be an odd or even harmonicof this frequency. 2. See FREQUENCYMULTIPLIER. 3. A nonlinear circuit used in a calibratorto generate markers at integral multiplesof the fundamental frequency.harmonic ratio 1. In a complex wave, the ratio ofharmonic energy to total signal energy (fundamentalplus all harmonics). 2. In a complex wave,the ratio of harmonic energy to fundamentalfrequencyenergy.harmonic reducer See HARMONIC ATTENUATOR.harmonic reduction See HARMONIC ATTENUA-TION.harmonic resonance Resonance of an antenna ora circuit at a whole multiple of the applied signalfrequency.harmonic ringing In wire telephony, the use ofalternating-current signal harmonics for selectiveringing.harmonic series of tones A set of audio-frequencytones in which the frequencies can be specified byf, 2f, 3f, 4f, and so on.harmonic suppression See HARMONIC ELIMINA-TION.harmonic suppressor See HARMONIC ELIMINA-TOR.harmonic tolerance The harmonic content permissiblein a given system.harmonic totalizer An instrument for measuringtotal harmonic distortion. See, for example, DIS-TORTION METER.harmonizer A circuit that changes the frequencyof an audio signal, or produces an output at severalaudio frequencies from an input having onlyone audio frequency. Used in sound recording forspecial effects.harness A tied bundle of wires or cables for wiringelectronic equipment.harp antenna A vertical antenna consisting of anumber of wires that fan out from point to pointalong a horizontal supporting wire.hartley A unit of digital information equivalent to3.32 bits. Used in certain computer applications.Hartley oscillator A radio-frequency (RF) oscillatorthat uses a single inductor with a tap on thewindings to provide the feedback. The amount offeedback is controlled by the position of the coiltap. A variable capacitor in parallel with the inductordetermines the oscillating frequency andallows for frequency adjustment. The circuit usesabout 25 percent of its output power to producefeedback. The other 75 percent of the power canbe delivered to external circuits or devices. CompareCOLPITTS OSCILLATOR.Hartley oscillatorhash 1. Electrical noise, especially wideband noisewith a characteristic hissing sound in a radio receiver.2. Undesirable or purposefully meaninglessinformation, as used in a hash total (checksum).hash filter A radio-frequency filter for eliminatingHASH noise in a radio receiver.hassium Symbol, Hs. Also called unniloctium(Uno). Atomic number, 108. The most commonisotope has atomic weight 265. Classified as atransition metal. It is human-made and notknown to occur in nature.

hat • head room 333hat 1. Also called capacitance hat. A small disk orset of wires attached to the end(s) of an antennaradiator, lowering the resonant frequency and increasingthe usable bandwidth. 2. A procedurefor randomizing data.hash total See CHECKSUM.hatchdot pattern A television test pattern consistingof a crosshatch pattern with dots around itsouter edges and one dot at its center.hatted code A form of code in which randomizationis used to maximize the difficulty of breakingthe code.Hay bridge An alternating-current bridge for measuringthe inductance and Q of an inductor interms of resistance, frequency, and a standardcapacitance.L xR xR1InductancebalanceR2R3detHay bridgeC sQ Balancehaywire Loose, disorderly, or apparently carelesswiring.haz Abbreviation of HAZARD.hazard Abbreviation, haz. A dangerous or potentiallydangerous circuit, device, material, method,situation, or system (e.g., electric-shock hazard).H beacon A form of homing beacon with an omnidirectionalradiation pattern and a radiofrequencyoutput of between 50 W and 2 kW.H bend See H-PLANE BEND.HCD Abbreviation of hard-copy device.HCM Abbreviation of HALF-CYCLE MAGNETIZER.HDB-3 code Abbreviation of HIGH-DENSITYBIPOLAR-3 CODE.HDF Abbreviation of HIGH-FREQUENCY DIREC-TION FINDER.HDTV Abbreviation of HIGH-DEFINITION TELEVI-SION.H-display See H-SCAN.He Symbol for HELIUM.head 1. The top or operating portion of a device(e.g., microphone head or dynamic-speakerhead). 2. In magnetic recording and reproduction,the magnetic device (transducer) that deliversor picks up recorded impulses. 3. In a harddisk or diskette drive, a transducer that deliversand picks up recorded data.head alignment 1. Positioning the cone of a dynamicspeaker so that the voice coil moves freely(i.e., without rubbing against the core). 2. Positioninga magnetic-recorder head so that a properrelationship to the moving tape is maintained.head amplifier A self-contained amplifier or preamplifierin the head of a microphone or soundon-filmpickup.head degausser A device used for the purpose ofdemagnetizing the head of a tape recorder. Unwantedmagnetization can build up because ofdirect-current components in the driving signal.head demagnetizer See HEAD DEGAUSSER.head end In a television network or system, the locationfrom which signals are sent to subscribers.header 1. A (usually glass) disk or wafer throughwhich one or more leads pass and to which theyare fully sealed. Can be used as the terminal baseof an enclosed plug-in unit, such as a miniaturecoil, filter, or similar components. Also seeGLASS-TO-METAL SEAL. 2. A data set placed beforeother sets as a means of identifying themand, possibly, including control data pertinent tothe sets so identified.header capacitance Capacitance between oramong the leads in a header (see HEADER, 1).header label A header recorded on a magnetic tapefile (see HEADER, 2).head gap 1. In computer disk or tape drives, thedistance between the head and the magneticmedium. 2. In audio operations, the spacing betweentape-unit head electrodes; also called gapwidth.heading The direction taken by a vehicle with referenceto some point (such as a radio beacon,true north, or magnetic north).headlight In radar operations, a small rotating antenna.headphone A small acoustic transducer wornagainst the ear for listening to music without disturbingothers, or for monitoring live or recordedmaterial without being disturbed by noise in theenvironment. Also see RECEIVER, 2.headphone amplifier An audio-frequency amplifierdesigned and operated primarily to supply asignal to headphones.headphone receiver A portable radio receiver,usually for AM and/or FM broadcast, consistingof a pair of headphones or a headset with the radiobuilt into it.head room 1. In a high-fidelity sound system, theextent, measured in decibels, to which an amplifiercan be operated beyond the zero point on itsvolume-unit (VU) meter without causing objectionabledistortion on sound peaks. 2. In taperecording, the region between the maximumrecording level specified by the manufacturer ofthe equipment, and the amplitude at which tapeoverload occurs. It is specified in decibels.

334 headset • heat therapyheadset An assembly consisting of one or two earphones,a headband, and a flexible cord. Also seeHEADPHONE and RECEIVER, 2.head stack In magnetic recording, an assembly oftwo or more heads for multitrack service. Also seeHEAD, 2.head station See BASE STATION.head-to-tape contact In magnetic-tape recordingor playback, physical contact between the tapeand the head.hearing aid A miniature audio-frequency devicethat amplifies sound for people with impairedhearing. It consists of a microphone, a high-gainamplifier, and an earphone or bone-conductiontransducer.hearing-aid battery A physically small battery designedfor use with hearing aids. Such a batteryis usually of the lithium type, or some other typethat has long life under conditions of low currentdrain.hearing loss A measure of hearing impairment.Generally expressed as the ratio, in decibels, ofan individual’s threshold of hearing to the normalthreshold of hearing. Also see AUDIOLOGIST,AUDIOMETER, and AUDIOMETRIST.heart fibrillation A condition in which the heartmuscle twitches at random, rather than pumpingblood normally. This can be caused by an electricshock through the heart of 100 mA to 300 mA. Ifnormal heart function is not restored, death willfollow.heart pattern See CARDIOID PATTERN.heart telemetry See ECG TELEMETRY.heat A form of energy transferred by conduction,convection, or radiation between two bodies havingdifferent temperatures. The amount of heat isexpressed in degrees, British thermal units, calories,joules, or kelvins.heat aging 1. The degeneration of a substance, aggravatedby high temperatures. 2. A test thatindicates the immunity of a substance todegeneration because of high temperatures.heat coil A device that disconnects a circuit whenthe temperature reaches a certain minimumlevel.heat detector A sensor of heat. See, for example,BOLOMETER, INFRARED DETECTOR, MICRO-RADIOMETER, RADIOMETER, THERMISTOR,THERMOCOUPLE, and THERMOPILE.heated-pen recorder See THERMAL RECORDER.heated-stylus recorder See THERMAL RE-CORDER.heated-wire flowmeter See HOT-WIRE FLOWME-TER.heated-wire sensor A hot wire used to discriminatebetween substances, according to how theyaffect its heating. See, for example, GAS DETEC-TOR (also usable as a vacuum gauge), HOT-WIREANEMOMETER, and HOT-WIRE MICROPHONE.heat engine A machine that converts heat energyinto mechanical energy.heater 1. The filament of an indirectly heated vacuumtube. 2. The filament in an indirectly heatedthermistor.heater-voltage coefficient The amount of frequencychange per volt of fluctuation in the filamentvoltage of a Klystron.heat exchanger A device or system that removesheat from a hot body and transfers it to anotherbody or to the surrounding air.heat-eye tube An infrared-sensitive device usedfor the purpose of locating objects in visible darkness.The tube consists of a cathode-ray devicethat is sensitive to infrared radiation.heat gradient The temperature difference betweentwo points on a body, divided by the distance betweenthe two points.heating depth See DEPTH OF HEATING.heating effect The production of heat (power loss)by electric current flowing in a conductor.heating element 1. See HEATER. 2. The resistanceelement (such as a strip or coil) that generatesheat in an electric-heating device.heat loss 1. Heat emitted by conduction, convection,or radiation from a body at a relatively hightemperature. 2. Power loss as a result of the heatingeffect of an electric current.heat of fusion The amount of heat required to melta unit mass of a solid that has reached its meltingpoint.heat of radioactivity Heat generated during theprocess of radioactive disintegration.heat of reaction In a chemical or electrochemicalreaction, the heat (in calories) absorbed or released.heat of vaporization The amount of heat requiredto convert 1 gram of a liquid to a vapor withoutraising its temperature.heat radiator See HEATSINK.heat rays See INFRARED RAYS.heat remover 1. See HEATSINK. 2. A forced-air orforced-liquid cooling system.heat-resistant glass See PYREX.heat-sensitive resistor See THERMISTOR.heat-sensitive switch A make-and-break device,such as a thermostat, that is actuated by achange in temperature.heat-shrink tubing An insulated flexible sleevingmade from a plastic that shrinks permanently fora tight fit when heated; it is commonly used at thejoint between a cable and connector.heatsink A heat exchanger in the form of a heavy,metallic mounting base or a set of radiating fins.It conducts heat away from such devices aspower transistors, heavy-duty resistors, or powertubes, and dissipates the heat into the surroundingenvironment via convection and radiation.heatsink resistance The opposition offered by aheatsink to the flow of heat.heat therapy 1. The use of radio-frequency heatingfor therapeutic purposes. Also see DIATHERMY. 2.The use of infrared rays for therapeutic purposes.

heat transfer • helical antenna 335RadiationConvectionHeatsinkHeat-generatingcomponentsheatsinkRadiationChassisheat transfer The movement of heat from onepoint to another by absorption, conduction, convection,or radiation.heatronic Pertaining to the heating of a dielectricmaterial subjected to a high voltage.heat unit 1. See BRITISH THERMAL UNIT. 2. SeeCALORIE. 3. See KELVIN.heat waves See INFRARED RAYS.heat writer See THERMAL RECORDER.Heaviside-Campbell bridge A form of mutualinductancebridge. Mutual inductance is determinedwithout regard to the operating frequency.Heaviside layer See KENNELLY-HEAVISIDELAYER.heavy hydrogen An isotope of hydrogen. The termis applied to deuterium, whose nucleus consistsof one proton and one neutron, and also to tritium,whose nucleus consists of one proton andtwo neutrons.heavy metal A metal having a specific gravity of5.0 or higher. Examples: iron (7.85 to 7.88), lead(11.3), nickel (8.6 to 8.9), mercury (13.6), platinum(21.4).heavy water Formula, D 2 O. Water in which deuterium(HEAVY HYDROGEN), rather than ordinaryhydrogen has combined with oxygen.hecto- Abbreviation, h. A prefix meaning hundred(s),(i.e., 10 2 ).hectometric wave An electromagnetic field whosewavelength is on the order of hundreds of meters(i.e., at least 100 meters, but less than 1000 meters).The frequency ranges from 300 kHz to 3MHz.hectowatt Abbreviation, hW. A unit of power equalto 100 watts. Seldom used; power in this range isusually expressed in terms of the WATT or theKILOWATT.heelpiece A part of an electronic relay that providesmechanical support for the armature.Hefner candle A unit of luminous intensity equalto 0.9 candela; the standard (German) is theHEFNER LAMP.Hefner lamp A standard light source whose luminousintensity is 0.9 candela. It burns amyl acetate(banana oil) and its flame has been thestandard of the HEFNER CANDLE, a unit of luminousintensity devised in Germany. Also seeCANDLE POWER and LUMINOUS INTENSITY.height control In a television receiver circuit, thepotentiometer or rheostat that controls the verticaldimension of the picture by varying the amplitudeof vertical scanning pulses.height finder An altitude-measuring radar system.height-position indicator Abbreviation, HPI. Aradar displaying the height of a target, its angularelevation, and the slant range.Heil oscillator An oscillator based on a specialtube consisting of a heated cathode, first anode,metal cylinder, and second anode. Electronsemitted by the cathode pass through a hole in thefirst anode and become a beam, which passesthrough the cylinder and strikes the second anode(collector). Electron bunching in the cylindercauses energy to be transferred to a tank circuitbetween the cylinder and anodes.CathodeAnode 1−dc Input+CylinderHeil oscillatorElectronbeamAnode 2RF outputHeisenberg uncertainty principle See UNCER-TAINTY PRINCIPLE.hekto- See HECTO-.heliacal cycle See SUNSPOT CYCLE.helical antenna A spring-shaped antenna mountedperpendicular to a flat metal-plate reflector, an arrangementthat produces circularly polarizedwaves in a narrow beam. It is used primarily atultra-high and microwave radio frequencies.

336 helical-beam antenna • Herschel-Quincke tubehelical-beam antenna See HELICAL ANTENNA.helical line The helix in a backward-wave oscillatoror traveling-wave tube.helical potentiometer A potentiometer whose resistanceelement is a wire wound into a coil ofseveral turns. The slider moves over the wire (orthe larger coil) from one end to the other as theslider or coil is turned through several completerevolutions. Also called MULTITURN POTEN-TIOMETER.helical scanning Radar scanning by an antennathat moves vertically as it moves horizontally,producing a spiral motion to the radiated beam.helical sweep See SPIRAL SWEEP, 1, 2.helical transmission line See HELICAL LINE.helicone An antenna used at ultra-high and microwavefrequencies, consisting of a helical radiatorwithin a cone-shaped reflector.helix recorder An information recorder using aspiral method of scanning. The recordingmedium is usually drum-shaped.Helmholtz coil A device consisting of two crossedfieldprimary windings in which an inductivelycoupled secondary winding rotates. The primarywindings carry currents that differ in phase by 90degrees. Rotating the secondary coil provides 360degrees of continuously variable phase shift.InputV 2H S2 H2V 2OutputSignalheliconeFeed pointHelixReflectingconehelionics The science of converting solar heat intoelectrical energy. The term is an acronym fromhelio- (pertaining to the sun) and electronics.heliostat 1. A servo-controlled motor-driven devicethat drives a mirror to keep sunlighttrained upon a specific target. 2. By extension,any similar device to keep a solar cell pointed tothe sun.helitron A form of oscillator used at ultra-high andmicrowave frequencies. The output frequency isvariable over a wide range.helium Symbol, He. A gaseous element. Atomicnumber, 2. Atomic weight, 4.0026.helium group The six inert gases in group 0 of theperiodic table: argon, helium, krypton, neon,xenon, and radon.helium-neon laser A laser in which the lasing substanceis a mixture of helium and neon. Producesa characteristic brilliant red visible output. Alsosee HELIUM and NEON.helix 1. A single-layer coil. 2. That which is coilshaped(i.e., spiral in configuration). 3. See HELI-CAL ANTENNA. 4. See HELICAL LINE.helix line See HELICAL LINE.Helmholtz coilHelmholtz double layer An intermolecular layerbetween a metal and an electrolyte in which it isimmersed. It is formed when the adhesive force betweenthe metal and electrolyte decreases the surfacetension of the metal, causing positive ions tomigrate from the metal into the liquid. The metal,charged negatively, and the electrolyte, chargedpositively, form a capacitor whose dielectric is theHelmholtz layer.Helmholtz resonator An acoustic (sound) chamberwhose geometry, in combination with the sizeof a small opening, results in resonance at a specificfrequency.HEM Abbreviation of hybrid electromagnetic (see, forexample, HYBRID ELECTROMAGNETIC WAVE).hemimorphic Pertaining to an object with endsthat have unlike faces.He-Ne laser See HELIUM-NEON LASER.henry Symbol, H. The standard unit of inductance.It is the inductance exhibited by a closed circuitin which one volt is produced by a current changinguniformly at one ampere per second. This is alarge unit of inductance; more common units arethe MILLIHENRY and the MICROHENRY.hermaphroditic plug A plug that has the prongs ofa male plug and the recessed contacts of a femaleplug. Compare FEMALE PLUG and MALE PLUG.hermetically sealed Constructed in manufactureso as to be permanently closed against the entryof air or other gases, dust, and moisture.hermetic seal A permanent, air-tight seal that effectivelyprevents corrosion from elements in theoutside environment.herringbone pattern A pattern of interference in atelevision picture, so named because of its resemblanceto the skeleton of a fish.Herschel-Quincke tube An acoustic device thatdemonstrates sound interference. The device has

Herschel-Quincke tube • heterodyne wave analyzer 337two hollow cylinders, one of which can be adjustedin length. At the far end of the apparatus,the cylinders are joined together. The resultantamplitude depends on the difference in length betweenthe cylinders. Sound wavelengths can bemeasured using this apparatus.hertz Abbreviation, Hz. The standard unit of frequency(of periodic phenomena, such as alternatingor pulsating currents); 1 Hz = 1 cycle persecond. One Hz is an extremely small unit of frequency;more common units are the KILOHERTZ,the MEGAHERTZ, and the GIGAHERTZ.Hertz antenna An ungrounded halfwave antennafed by a transmission line attached to one end orto the center of the radiator. See, for example,CENTER-FED ANTENNA and END-FED AN-TENNA. Compare MARCONI ANTENNA.Hertz effect Ionization of a gas, produced by intenseultraviolet radiation.Hertzian antenna See HERTZ ANTENNA.Hertzian oscillator See HERTZ OSCILLATOR.Hertzian radiation Radiation of electromagnetic(radio) waves.Hertzian waves Electromagnetic waves in the radiospectrum, with wavelengths longer than thoseof infrared, visible light, ultraviolet, X rays, orgamma rays.Hertz oscillator A damped-wave generator of oscillations,used by Hertz in his demonstration ofradio waves in 1888 (verifying the earlier predictionby James Clerk Maxwell). The oscillator containsa spark gap supplied by an induction coil,attendant coils, capacitors (in the prototype, Leydenjars), and two large metal plates.MetalplateSpark gapFrom secondaryof induction coilHertz oscillatorMetalplateHertz vector A single vector that specifies the electromagneticfield (electric and magnetic components)of a radio wave.hesitation As distinct from a halt, a brief break ina computer program run during which internaloperations are occurring, such as data transfer toa peripheral.heterochromatic Consisting of different frequencies,wavelengths, or colors. Compare MONO-CHROMATIC.heterodyne 1. To beat one alternating-current signalagainst another to produce one or more beatfrequencysignals. Also see BEAT FREQUENCYand BEAT NOTE. 2. The whistle produced whentwo signals very close in frequency are mixed in aradio receiver. 3. To combine radio signals in amixer, the purpose of which is to produce a sumor difference signal for further processing.heterodyne detection 1. Signal detection by beatingthe incoming signal against one produced bya local oscillator. In this way, an unmodulatedsignal is made audible (the beat note is an audiofrequency). 2. Signal detection by a superheterodynecircuit.heterodyne detector 1. A detector that makes aradio-frequency (RF) signal audible by beating itagainst the RF signal of a local oscillator, theproduct being an audio-frequency (AF) beat note.2. The FIRST DETECTOR or SECOND DETEC-TOR in a SUPERHETERODYNE CIRCUIT. 3. Acombination linear detector and local RF oscillatorused to detect and measure the frequencyof test signals. Also see HETERODYNE FRE-QUENCY METER.heterodyne eliminator See WHISTLE FILTER.heterodyne filter See WHISTLE FILTER.heterodyne frequency The frequency of the signalobtained by beating one signal against another.heterodyne frequency meter A frequencymeasuringdevice that contains a variablefrequencyoscillator (VFO), a mixer, and anindicator such as an analog meter. The oscillatorfrequency is adjusted until zero beat is reachedwith the signal source. This condition is shown bya dip in the meter indication. An audio amplifiercan be coupled to the output of the device insteadof a meter; in this case the heterodyne appears asan audible tone whose frequency drops to zerowhen the oscillator frequency is equal to thesignal frequency being measured.heterodyne method See HETERODYNE, 1.heterodyne oscillator A signal generator whoseoutput is the beat product of outputs from two internaloscillators. The output frequency can be eitherthe sum or the difference of the oscillatorfrequencies, as selected by output filtering ortuning. See BEAT-FREQUENCY OSCILLATOR.heterodyne reception Radio reception (especiallyin telegraphy) by means of the beat-note process.Also see HETERODYNE DETECTION, 1 and HET-ERODYNE DETECTOR, 1.heterodyne repeater A REPEATER in which thereceived signals are converted to another frequencybefore transmission.heterodyne-type frequency meter See HETERO-DYNE FREQUENCY METER.heterodyne wave analyzer A type of audiofrequency(AF) wave analyzer. The input signal isheterodyned in a balanced modulator with thesignal from an internal tunable oscillator. One ofthe resulting sidebands is passed through a

338 heterodyne wave analyzer • high-efficiency linear amplifiersharp bandpass filter, whose output actuates analternating-current (ac) voltmeter. The internaloscillator is tuned slowly so that different componentsof the balanced-modulator output sidebandpass successively through the filter. Theamplitude-versus-frequency function of the inputsignal is determined by noting the meter readingsas the internal oscillator is tuned.heterodyne wavemeter See HETERODYNE FRE-QUENCY METER.heterodyne whistle See HETERODYNE, 2.heterogeneous Pertaining to a group of objects ordevices that have differing characteristics.heterogeneous radiation Any broadband form ofradiation. In particular, broadbanded radiowaves, infrared radiation, visible light, ultraviolet,X rays, or gamma rays.heterolysis The HYDROLYSIS of a compound intotwo oppositely charged ions.heteropolar generator An electric generator inwhich the active conductors move through magneticfields, first in one direction, then in theother direction. This is done by means of rotationin a nonuniform magnetic field. Most generatorsin common use are of this kind.heuristic knowledge In artificial intelligence (AI), aform of machine knowledge in which a computerlearns from its mistakes. As a complex program isrepeatedly run over a period of time, the numberof errors per run approaches zero.heuristic program In artificial intelligence (AI), aprogram with which the computer solves a problemby trial and error, often learning in the processso that mistakes will not be repeated onsubsequent runs.Heusler’s alloys Ferromagnetic alloys that containone or more non-magnetic metals (such as aluminum,copper, or manganese).hexadecimal number system An alphanumeric,base-16 system of number notation used in somecomputers. The system uses the usual digits plusthe letters A through F to represent the numbers10 through 15 (each place can only hold one symbol).hex inverter A collection of six digital inverters, orNOT gates, contained within one package, usuallyan integrated circuit.Hf Symbol for HAFNIUM.HF Abbreviation of HIGH FREQUENCY.Hg Symbol for MERCURY.HH beacon In radionavigation, a nondirectionalhoming beacon.hi 1. Contraction of HIGH. 2. Radiotelegraph symbolfor a laugh, often verbalized by radio amateurs.HIC Abbreviation of HYBRID INTEGRATED CIR-CUIT.HIDM Abbreviation of HIGH-INFORMATIONDELTA MODULATION.hierarchical password protection Also calledmultilevel password protection. A security featurethat prevents unauthorized use of a computer,network, or database. The password levels allowusers various degrees of control over the host machine.hi-fi 1. Contraction of HIGH-FIDELITY. 2. In videorecording, the addition of sound having high fidelity.high 1. Pertaining to a circuit point or condition atsome potential above ground. 2. The logical digit1. 3. The condition of having relatively large magnitude(e.g., HIGH FREQUENCY and HIGH VOLT-AGE). 4. Pertaining to the upper portion of arange, as in HIGH BAND or HIGH FREQUENCY.5. Characterized by greater-than-normal responseor performance, as in HIGH Q or HIGH FI-DELITY.high band 1. The higher or highest frequency bandused in communications, testing, or processing,when several bands are available. 2. The veryhigh-frequency(VHF) television channels 7through 13. 3. The communications frequencyrange from about 144 MHz to about 170 MHz.high boost In sound recording and reproduction,the emphasis of high frequencies in an operatingspectrum. Also called HIGH-FREQUENCY COM-PENSATION.high-C circuit A tuned circuit having high capacitanceand low inductance at a given frequency.Such a circuit is characterized by high selectivityand low voltage. Compare HIGH-L CIRCUIT. Alsosee LC RATIO.high contrast In an image, a limited range of grayvalues between black and white, or a similar conditionin a color image (overbright whites, littleshadow detail). Also see CONTRAST.high definition In facsimile or television, a conditionof minute detail so that the original scene isfaithfully reproduced.high-definition television Abbreviation, HDTV. Amethod of getting enhanced detail into a television(TV) picture and for obtaining better audioquality, compared with standard analog TV.There are several different schemes. The most noticeablefeature is the crispness of the picture.This is vividly apparent in big-screen installations,which have traditionally suffered from imageblurring. A standard TV picture has 525 linesper frame, but HDTV systems can have morethan twice that number. Another important differenceis that HDTV is digital; this minimizessusceptibility to interference. Interlacing is usedin some systems.high-density bipolar-3 code A communications ordigital code in which two logic highs (ones) canoccur in sequence, without the need for an interveninglogic low (zero) to separate them.high-efficiency linear amplifier A LINEAR AM-PLIFIER with higher operating efficiency than isobtainable with conventional class-B linear amplifiers.Efficiencies on the order of 60% at 100%modulation are possible.

high-energy materials • high order 339high-energy materials See HARD MAGNETIC MA-TERIALS.high-energy particle 1. A SUBATOMIC PARTICLEthat has been given high velocity by a particle accelerator.2. High-speed subatomic particlesemitted by the sun during a solar flare, or arrivingfrom outer space.high-energy physics The discipline dealing withthe characteristics, properties, and applicationsof HIGH-ENERGY PARTICLES.higher-order language See HIGH-LEVEL LAN-GUAGE.high fidelity Abbreviation, hi-fi. Pertaining to anaudio-frequency system that is very faithful tothe signal it is processing (i.e., one characterizedby extremely low distortion and wide frequencyresponse).high frequency Abbreviation, HF. Pertaining tofrequencies in the 3- to 30-MHz band (wavelengthsfrom 10 to 100 meters). Also see RADIOSPECTRUM.high-frequency alternator A dynamo for generatingradio-frequency energy.high-frequency bias In a tape recorder, a highfrequencysinusoidal signal superimposed on thesignal being recorded, for improving linearity anddynamic range.high-frequency compensation See HIGH BOOST.high-frequency converter See SHORTWAVECONVERTER.high-frequency crystal See HARMONIC CRYS-TAL.high-frequency direction finder Abbreviation,HDF. A direction finder operated at high radio frequencies(i.e., between about 3 MHz and 30 MHz).high-frequency heating Electronic heating of materialsby high-frequency energy. See, for example,DIELECTRIC HEATING and INDUCTIONHEATING.high-frequency resistance See RADIO-FRE-QUENCY RESISTANCE.high-frequency speaker See TWEETER.high-frequency trimmer 1. In older highfrequencycommunications receivers, a low-valuevariable capacitor operated in parallel with a usuallyfront-panel tuning capacitor to set the highfrequencyend of the tuning range. See, forexample, OSCILLATOR TRIMMER. 2. A smallvariable capacitor used in conjunction with alarger tuning capacitor, the function of which isto permit precision tuning of the larger device.high-impedance-state output current Pertainingto tests that ensure that an integrated circuit willnot overload a bus line.high-impedance voltmeter A voltmeter having aninput impedance of at least several megohms.high-information delta modulation A compandedform of delta modulation, operating atcomparatively low sample rate.high-L circuit A tuned circuit having high inductanceand low capacitance at a given frequency.Such a circuit is characterized by low selectivityand high voltage. Compare HIGH-C CIRCUIT.Also see LC RATIO.high-level audio signal An audio-frequency signalthat has been preamplified (e.g., the output of acompact-disc player). Compare LOW-LEVEL AU-DIO SIGNAL.high-level input current 1. Pertaining to the testingof intertransistor leakage in an integrated circuit(IC) having multiple emitter inputs. 2. Thecurrent into an IC input at minimum high-levelvoltage.high-level language Also called higher-order language.A computer programming language inwhich the operator is easily able to communicatewith the machine. It generally serves as an interfacebetween a human programmer and the MA-CHINE LANGUAGE. Examples are BASIC, C,C++, COBOL, and FORTRAN.high-level modulation In an amplitude-modulatedtransmitter, introduction of the audio at thefinal stage of radio-frequency amplification, permitting100% modulation of the full-power signal.Osc Amp FinalampMixedAudioamphigh-level modulationAudiopoweramphigh-level output current 1. Pertaining to thetesting of drive capability and fanout of an integratedcircuit (IC). 2. The current flowing from anIC output when in the high state.high-level recovery Hardware recovery using datanot involved in the failure, such as that on a magneticstorage medium. Also see HARDWARE RE-COVERY.highlight 1. A bright area in a television picture. 2.In computer data processing, the defining or setting-offof a block of data (such as text), with theintention of relocating, editing, or deleting it.high-noise-immunity logic Abbreviation, HNIL. Aform of bipolar digital logic designed for minimalsensitivity to noise. Also known as high-thresholdlogic (HTL).high order Descriptive of the relationship betweenbits or digits in a word or number. Of two digits,

340 high order • hissthe one holding the higher place value is the highorderdigit (e.g., 2 is the high-order digit in 25).high-pass filter A combination of capacitance, inductance,and/or resistance, intended to producelarge amounts of attenuation below a certain frequencyand little or no attenuation above that frequency.The frequency at which the transitionoccurs is called cutoff. At cutoff, the power attenuationis 3 dB with respect to the minimum attenuation.At frequencies above cutoff, the powerattenuation is less than 3 dB. At frequencies belowcutoff, the power attenuation is more than3 dB. The simplest circuit consists of a parallelinductor or a series capacitor. The inductancecapacitance(LC) circuit has a combination of parallelinductors and series capacitors. In theresistance-capacitance (RC) circuit, resistors aresubstituted for the inductors. Compare BAND-PASS FILTER, BAND-REJECTION FILTER, LOW-PASS FILTER.InCL L LChigh-pass filterOuthigh-pass-filter method A method of measuringthe total harmonic distortion (THD) percentageusing a high-pass filter to separate the harmonicsfrom the fundamental. The output voltage V o ofthe filter is compared with the input voltage V i ;then THD = 100V o /V i .high-performance Pertaining to apparatus designedfor continuous operation with maximum reliability.high-performance navigation system AcronymHIPERNAS. An electromechanical guidance systemthat is purely inertial and self-compensating.high-potential test A high-voltage test of insulation,in which the applied voltage is continuouslyincreased until the breakdown point of the dielectricis reached.high-power rectifier A rectifier designed for highvoltage,high-current operation.high Q For a component or circuit, a high value forthe ratio X/R (reactance to resistance). This is arelative term because a particular numericalvalue of Q, considered high in one situation,might be regarded as low under other circumstances.Also see FIGURE OF MERIT.high-resistance joint In the wiring of electronicequipment, a joint or connection between conductorsthat is poorly made, thereby introducinga high resistance between the parts.high-resistance voltmeter A voltmeter having aninput resistance of at least several megohms.high-speed carry In computer operation, a carryinto a column causing a carry out, circumventingthe usual intermediate adding circuit.high-speed diode See COMPUTER DIODE.high-speed flip-flop A flip-flop having shortswitch-on and switch-off time.high-speed oscilloscope An oscilloscope with excellenthigh-frequency and unit-function response. Itcan reproduce high-speed pulses faithfully.high-speed relay A relay with a short make orshort break interval.high-speed transistor See SWITCHING TRANSIS-TOR.high tension Pertaining to utility power-transmissionlines on which there are very high voltages,typically 100 kilovolts (100 kV) or more.high-tension line A power-transmission line carryinga very high voltage. It is generally used forthe transfer of electric power over long distances.high-threshold logic See HIGH-NOISE-IMMUNITYLOGIC.high voltage 1. A voltage considerably higher thanthose ordinarily encountered in a particular application.The term is comparative; a few hundredvolts might be considered high in one situation,but low in another. 2. In a cathode-ray tube, thevoltage that accelerates the beam electrons. 3. Ina television receiver, the picture-tube anode voltage.4. In a vacuum-tube power amplifier, theplate supply voltage.high-voltage probe A very-high-resistance probefor measuring high voltages with a low-rangevoltmeter.highway A path over which multiple signals arepropagated using time-division multiplexing.HILAC Acronym for heavy-ion linear accelerator.hill-and-dale recording See VERTICAL RECORD-ING.hinged-iron instrument An alternating-currentmeter whose input transformer core is hinged intwo parts. By means of a thumb trigger, the corecan be opened, then closed around the currentcarryingconductor that induces magnetism in thecore; a secondary coil delivers current to the meter.Also called clamp ammeter or clamp voltmeter.HIPERNAS Acronym for HIGH-PERFORMANCENAVIGATION SYSTEM.hipernick A high-permeability alloy of iron andnickel.hipot Contraction of high potential. See HIGH-POTENTIAL TEST.hiss 1. A high-pitched sound rich in sibilants (s,sh, and z sounds) produced by random highfrequencyfluctuations in current. 2. The characteristic,high-pitched background noise (as in 1)accompanying super-regeneration. 3. Internallygenerated noise in a communications receiver,amplified by the audio-frequency stages and appearingat the speaker or headphones.

hiss filter • hole injector 341hiss filter See HASH FILTER.hit 1. The occurrence of a lightning stroke at a specificpoint on the ground. Also called direct hit. 2.The coincidence of two pulses.H lines Magnetic lines of flux.HLL Abbreviation of HIGH-LEVEL LANGUAGE.H network A network of five impedances: two connectedin series between the upper input andoutput terminals, two between the lower inputand output terminals, and one shunted betweenthe junctions of the series-connected impedances.Also called H pad, balanced tee network,and balanced tee pad.InH networkOutHo Symbol for HOLMIUM.hobby robot A robot intended for amusement and,sometimes, for education. Such robots often takehumanoid form. Some are programmable, andcan give demonstrations, play musical instruments,and do other complex routines.hockey-stick lead On a capacitor, resistor, orother component, a pigtail lead that is given asingle crimp for easy insertion into a printedcircuitboard.hodoscope An instrument consisting essentially ofclosely spaced ion counters, for studying the pathof an ionizing particle.Hoffmann electrometer See BINANT ELECTRO-METER.hog horn A form of horn antenna used in microwaveapplications. It is generally used in thefeed system of a dish antenna. The horn openingpoints in the direction of the feed waveguide.hold 1. To retain data in a storage device after thedata has been duplicated in another location ordevice. 2. A momentary halt of an operation orprocess. 3. In a television receiver, a control thatstabilizes the vertical or horizontal synchronization.hold circuit 1. See HOLDING CIRCUIT. 2. In atelevision receiver, the circuit associated with thehold control(s). Also see HORIZONTAL-HOLDCONTROL and VERTICAL-HOLD CONTROL.hold control See HORIZONTAL-HOLD CONTROLand VERTICAL-HOLD CONTROL.hold current Symbol, I h . The minimum currentthat will keep a normally open relay closed or anormally closed relay open.hold electrode In a mercury switch, the electrodethat is in permanent contact with the mercury.holding beam In an electrostatic cathode-ray storagetube, the electron beam that generates replacementcharges for those that were stored onthe dielectric surface and then lost.holding circuit In an electromechanical relay, aseparate circuit that, when energized, keeps therelay actuated.holding coil In an electromechanical relay, the extracoil that is associated with the holding circuit.holding current 1. Current in the holding coil of arelay. 2. In a gas tube, the minimum current requiredto maintain ionization.holding gun In an electrostatic cathode-ray storagetube, the electron gun that generates theholding beam.hold mode A condition in which the output state ofa digital-logic circuit remains unchanged whilethe input signals are removed.hold-off voltage The highest voltage that can beapplied to a flashtube without causing it to fire.holdover The flow of current through the ionizedpath created by an electric arc.hold time 1. The time permitted for a weld toharden in resistance welding. 2. In digital communications,the time for which a signal is maintainedat a certain input after changing state atanother specified input.hole 1. In a semiconductor atom, the vacancy resultingfrom the loss of an electron. When anelectron is lost, so is its negative charge, leavingan equivalent net positive charge. This charge,like that of an electron, can move as a currentcarrier. 2. The punched-out portion of a chassisor panel, through which wires can be passed orcomponents mounted.hole conduction In a semiconductor material,electrical conduction as a result of HOLE CUR-RENT.hole current In a semiconductor material, theelectrical current resulting from the movementof positive charge carriers (holes). Also seeHOLE.hole density The degree of concentration of holesin a semiconductor. Also see HOLE.hole-electron pair In a semiconductor, a hole anda related electron. Each electron in the conductionband has a counterpart in the valence band,a vacancy (HOLE) left by the movement of theelectron to the conduction band.hole injection The creation of mobile holes in asemiconductor by applying an electric charge.Also see HOLE.hole injector 1. The emitter electrode of a bipolarpnp transistor. 2. The metal whisker of a pointcontactdiode having an n-type wafer. 3. Theplayer of a forward-biased junction diode.

342 hole mobility • horizonhole mobility The ease with which a hole moveswithin a semiconductor. Also see CARRIER MO-BILITY.hole storage See CARRIER STORAGE.hole storage factor In a bipolar transistor biasedto saturation, the amount of storage chargecaused by excess base current.hole trap In a semiconductor, an impurity that cancancel holes by releasing electrons to fill them.hollow coil A coreless inductor.hollow conductor Tubing used as a low-loss conductorat radio frequencies.hollow core A core that is not solid throughout—especially one that has a central mounting hole.holmium Symbol, Ho. A metallic element of therare-earth group. Atomic number, 67. Atomicweight, 164.93. Forms highly magnetic compounds.holocamera A camera for making holograms. Alsosee HOLOGRAM, 1 and HOLOGRAPHY.hologram 1. A wavefront recording made on photographicfilm by the process of HOLOGRAPHY.By changing the frequency of the light transmitted,various magnifications of the image can beobtained. Produces a true three-dimensional image.2. A visible, three-dimensional display projectedin the air or underwater by means oflasers. They are often used at outdoor music concertsand other events.holography A method of producing a wavefrontrecording of an object illuminated by laser light.The result, an interference pattern, appearsmeaningless when viewed in ordinary diffuselight. But when a point source of illumination isused, especially a laser, an image appears that isconvincingly three-dimensional.homeostasis The condition of being in static equilibrium.home station See BASE STATION.homing 1. Guidance by means of an electronicbeacon. The vehicle maintains a course towardthe beacon. 2. Guidance by means of some formof emission from a target object. The emissioncan be acoustic or electromagnetic energy.homing antenna A direction-finding antenna—especially one on a mobile vehicle.homing beacon A station radiating a beam for usein direction finding by mobile vehicles.homing device A receiving device mounted on amobile vehicle, and that continuously indicatesthe direction of a selected transmitting stationthat is the vehicle’s destination.homing relay A stepping relay that returns to itsstarting position after each switching sequence.Also see STEPPING SWITCH.homing station See HOMING BEACON.homodyne reception See ZERO-BEAT RECEP-TION.homogeneous 1. Uniform in structure; similar atall points or locations. 2. Consisting of manyidentical elements.homogous field A field whose lines of flux in oneplane pass through a single point.homolysis The decomposition of a compound intoa pair of neutral atoms or radicals.homomorphism A one-to-one correspondence betweenthe elements of two sets.homopolar Pertaining to the union of atoms of thesame polarity; nonionic.homopolar generator A direct-current (dc) generatorwhose poles have the same polarity, with respectto the armature. Thus, no commutator isnecessary.homopolar magnet A magnet whose pole piecesare concentric.homunculus In artificial intelligence (AI), a computeror robot that exhibits characteristics of aliving being; especially, an ANDROID.honeycomb coil A multilayer coil having a UNI-VERSAL WINDING.honeycomb winding See UNIVERSAL WINDING.honker Also called midrange speaker. A loudspeakerthat favors the middle audio frequencies.Compare TWEETER and WOOFER.hood A light shield for a cathode-ray tube; it allowsthe screen to be viewed with a minimum of interferencefrom room light.Hooke’s law Strain is proportional to the stressthat produces it, as long as the ELASTIC LIMIT isnot exceeded.hook switch A switch that closes a circuit when aheadset or handset is lifted from the resting position.The common telephone receiver uses such aswitch.hook transistor A four-layer pnpn semiconductordevice, in which the outer p and n layersserve as emitter and collector, the inner n layerbeing the base. This places a p layer betweenthe base and collector, resulting in a transistorthat provides high alpha as a result of carriermultiplication by the additional junction in thecollector layer.hookup See SCHEMATIC DIAGRAM.hookup wire Flexible, insulated wire used in thewiring of some electrical and electronic devices.hoop antenna See CAGE ANTENNA.hoot stop During a computer program run, a loopmade evident by a sound signal.hop In long-distance radio communications, thetransmission of a wave and its subsequent returnto the earth from the ionosphere; it is of importancemainly at low, medium, and high frequencies.hor Abbreviation of HORIZONTAL. (Also, H andhoriz.)horiz Occasional abbreviation of HORIZONTAL.The usual form is hor; another alternate is H.horizon 1. For a specific location, the circle on thecelestial sphere midway between the zenith (thepoint directly overhead) and the nadir (the pointdirectly underfoot). 2. Also called visual horizon.The set of points, as viewed from a particular

horizon • horizontal flowcharting 343location, where the sky and the earth appear tomeet (i.e., the last visible part of the earth’s surfacefrom a given observation point). 3. Alsocalled radio horizon. The set of points, from a particularlocation at a given radio frequency, representingthe maximum communications range viathe ground wave under normal conditions. Alsosee ARTIFICIAL HORIZON.horizontal 1. Pertaining to objects or effects in aplane perpendicular to a line connecting thezenith (the point directly overhead) and the nadir(the point directly underfoot). 2. Pertaining tothat which is parallel to an assumed flat surface.3. Pertaining to width deflection on a cathode-raytube.horizontal AFC In a television receiver circuit, automaticfrequency control (AFC) of the horizontalsweep. It keeps the receiver’s horizontal scanningin step with that of the camera at the transmittingstation.horizontal amplification Gain provided by thehorizontal channel of a device, such as an oscilloscope,cathode-ray electrocardiograph, ortelevision receiver. Compare VERTICALAMPLIFICATION.horizontal amplifier A circuit or device that providesHORIZONTAL AMPLIFICATION. CompareVERTICAL AMPLIFIER.horizontal angle of radiation For an antenna, thedirection of maximum radiation in the horizontalplane (see HORIZONTAL, 1), provided as an azimuthangle measured clockwise from geographicnorth.horizontal angle of deviation In a communicationscircuit, the angular difference, in degrees,between the compass direction from which a receivedsignal arrives, and the great-circle pathconnecting the receiving station with the transmittingstation.horizontal axis The axis that is parallel to an assumedhorizontal surface (of the earth, for example)or the one so represented in a diagram. Alsosee X-AXIS.horizontal beamwidth In a directional antennasystem, the angle, measured in the horizontalplane, between the half-power points in the majorlobe.horizontal blanking See HORIZONTAL RETRACEBLANKING.horizontal-blanking pulse In a television signal,the rectangular pedestal-shaped pulse that occursbetween the active horizontal lines toachieve horizontal retrace blanking. CompareVERTICAL-BLANKING PULSE.horizontal centering control See CENTERINGCONTROL.horizontal channel The system of amplifiers, controls,and terminations that constitute the path ofthe horizontal signal in an equipment, such as anoscilloscope or graphic recorder. Compare VER-TICAL CHANNEL.270°Beamwidth0°180°horizontal beamwidth90°horizontal-convergence control In a color televisionreceiver, the variable component for adjustingthe horizontal dynamic convergence voltage.horizontal coordinates See CARTESIAN COORDI-NATES.horizontal deflection In a cathode-ray tube, thelateral movement of the electron beam on thescreen. Compare VERTICAL DEFLECTION.horizontal deflection coils The pair of coils thatproduces the magnetic field to horizontally deflectthe electron beam in an electromagnetic cathoderaytube. Also see DEFLECTION COIL.horizontal-deflection electrodes See HORIZON-TAL DEFLECTION COILS and HORIZONTAL DE-FLECTION PLATES.horizontal deflection plates In an electrostaticcathode-ray tube (typical of laboratory oscilloscopesand some early television picture tubes), apair of plates that produces an electric field tohorizontally deflect the electron beam. CompareVERTICAL DEFLECTION PLATES.horizontal directivity The radiation or receptionpattern of a directional antenna in the horizontalplane.horizontal-drive control See DRIVE CONTROL.horizontal dynamic convergence During thescanning of a horizontal line in a color picturetube, convergence of the electron beams at theaperture mask. Compare VERTICAL DYNAMICCONVERGENCE.horizontal field strength The field strength of signalspassing through an antenna in a horizontalplane. Compare VERTICAL FIELD STRENGTH.horizontal-field-strength diagram A plot of horizontalfield strength, usually in polar form. CompareVERTICAL-FIELD-STRENGTH DIAGRAM.horizontal flowcharting Flowcharting the movementof documents or files, rather than the databits themselves, through a digital system.

344 horizontal frequency • horizontal synchronizationhorizontal frequency In television circuits, thehorizontal scanning frequency [i.e., the frequencyat which the horizontal lines are traced (generally15.750 kHz)].horizontal frequency response The gain-vsfrequencycharacteristic of the horizontal channelof an oscilloscope or graphic recorder. CompareVERTICAL FREQUENCY RESPONSE.horizontal gain At a specified frequency, the overallamplification of the horizontal channel of anoscilloscope or graphic recorder. Compare VER-TICAL GAIN.horizontal-gain control A control, such as a potentiometer,for adjusting horizontal gain. CompareVERTICAL-GAIN CONTROL.horizontal-hold control In a television receiver,the control for adjusting the horizontal oscillatorfrequency to prevent horizontal tearing ofthe picture. Compare VERTICAL-HOLD CON-TROL.horizontal hum bars Dark, horizontal interferentialbars in a television picture, caused by HUMinterference.horizontal linearity The precision of gain and deflectionin the horizontal channel of an oscilloscope,graphic recorder, or television receiver. Alinear picture is a faithful (undistorted) reproductionof the original image. Compare VERTICALLINEARITY.horizontal-linearity control In an oscilloscope ortelevision receiver, the control with which horizontallinearity is adjusted. Compare VERTICAL-LINEARITY CONTROL.horizontal line frequency See HORIZONTAL FRE-QUENCY.horizontal lock See HORIZONTAL-HOLD CON-TROL.horizontally polarized wave An electromagneticwave whose electric lines of flux are parallel to theplane of the horizon. Compare VERTICALLY PO-LARIZED WAVE.horizontal multivibrator In a television receiver, a15.750-kHz multivibrator that generates the horizontalsweep signal.horizontal oscillator In a TV receiver, the oscillator(usually a multivibrator) that generates thehorizontal sweep signal. Compare VERTICAL OS-CILLATOR.horizontal output stage In a television receiver,an output amplifier following the horizontal oscillator.Compare VERTICAL OUTPUT STAGE.horizontal output transformer In a television receiver,the output transformer in the horizontaloscillator-outputamplifier section. Also calledFLYBACK TRANSFORMER.horizontal polarization Pertaining to an electromagneticwave whose electric lines of flux arehorizontal. In general, when the radiating elementof an antenna is horizontal, the electriclines of flux in the transmitted waves are horizontal,and the antenna is most sensitive to in-coming signals whose electric lines of flux arehorizontal. Compare VERTICAL POLARIZA-TION.horizontal positioning control See CENTERINGCONTROL.horizontal quantity The quantity measured alongthe X-axis of a graph represented by the horizontaldeflection of an oscilloscope beam. CompareVERTICAL QUANTITY.horizontal recording See LATERAL RECORDING.horizontal repetition rate See HORIZONTALFREQUENCY.horizontal resolution In a television picture, thenumber of picture elements (pixels) that can bediscerned in a horizontal scanning line. CompareVERTICAL RESOLUTION.horizontal retrace In a cathode-ray device, suchas an oscilloscope or television receiver, the rapidreturn of the electron beam to its starting pointafter completing a horizontal sweep of the screen.Compare VERTICAL RETRACE.horizontal retrace blanking In oscilloscopes andtelevision receivers, the automatic cutoff of theelectron beam during a horizontal retrace period,preventing an extraneous line on the screen duringthe period. Compare VERTICAL RETRACEBLANKING.horizontal scanning 1. The lateral sweeping of theelectron beam in a cathode-ray tube. 2. The samplingof x-axis values in a repetitive or nonrepetitivesweep of that axis.horizontal scanning frequency See HORIZONTALFREQUENCY.horizontal sensitivity The signal voltage requiredat the input of a horizontal channel for full horizontaldeflection. Also see HORIZONTAL GAIN.Compare VERTICAL SENSITIVITY.horizontal signal A signal serving as a horizontalquantity. Compare VERTICAL SIGNAL.horizontal sweep 1. In a cathode-ray tube, thehorizontal movement of the spot on the screen; inparticular, the movement from left to right, duringwhich a line of the image is formed on thescreen. 2. The circuit that produces horizontalsweep.horizontal sweep frequency The frequency atwhich horizontal sweep occurs; in a television receiver,it is generally 15.750 kHz. Also called horizontalsweep rate. Compare VERTICAL SWEEPFREQUENCY.horizontal sweep rate See HORIZONTAL SWEEPFREQUENCY.horizontal-sync discriminator In a television receiver,a circuit that compares horizontal syncpulsephase with the phase of the signal from thehorizontal sweep oscillator.horizontal synchronization In a television receiver,synchronization of the horizontal componentof scanning with that of the transmittingcamera. Also see HORIZONTAL SYNC PULSE.Compare VERTICAL SYNCHRONIZATION.

horizontal sync pulse • hot line 345horizontal sync pulse In a video signal, the pulsethat synchronizes the horizontal scanning componentin a television receiver with that of thecamera; it also triggers horizontal retrace andblanking. Also see BACK PORCH. Compare VER-TICAL SYNC PULSE.horizontal wave See HORIZONTALLY POLARIZEDWAVE.horizontal-width control See WIDTH CONTROL,1, 2.horn A radiating device that is essentially a cylindricalor rectangular pipe, whose surface flaresfrom a narrow entry to a wide exit. See, for example,HORN ANTENNA, HORN SPEAKER, andMEGAPHONE.horn antenna An antenna used for transmissionand reception of signals at microwave frequencies.There are several configurations; most havea square or rectangular cross section. The antennaprovides a unidirectional radiation andresponse pattern, with the favored directioncoincident with the opening of the horn. The feedline consists of a waveguide that joins the antennaat the narrowest point (throat) of the horn.This type of device is used alone in microwavetransmitters known as Gunnplexers. The deviceworks well in the feed systems of large dish antennas;the horn is pointed toward the center ofthe dish, in the opposite direction from the favoreddirection of the dish. See also DISH AN-TENNA, GUNNPLEXER.horn cutoff frequency The lowest frequency atwhich an exponential horn will function properly.Maximumsignalhorn antennaCouplingtowaveguidehorn loading In a sound-transmission system, aform of propagation that makes use of a hornshapedspeaker.horn mouth The wider (radiating) end of a hornantenna or speaker. Compare HORN THROAT.horn radiator See HORN ANTENNA.horn speaker A loudspeaker using a horn in conjunctionwith an acoustic transducer. It generallyproduces sound of low fidelity, and is intended foruse in marginal environments, such as outdoorpublic-address (PA) systems.horn throat The narrower (input) end of a horn antennaor speaker. Compare HORN MOUTH.horsepower Abbreviation, hp. A unit of powerequal to 746 watts. It is generally used to expressmechanical power delivered by engines and electricmotors.horsepower-hour Abbreviation, hp-hr. A unit ofenergy or work represented by the equivalent ofone horsepower delivered for a period of onehour; equal to 746 watt-hours.horseshoe coil See HAIRPIN COIL and HAIRPINCOUPLING COIL.horseshoe magnet A (usually permanent) magnethaving the shape of a horseshoe or a U and arectangular cross section.host A programmable computer that gathers andstores the information from all of the data-entryterminals in a system.HOT 1. Abbreviation of HORIZONTAL OUTPUTTRANSFORMER. 2. Abbreviation of HORIZON-TAL OUTPUT TUBE.hot 1. Pertaining to an object from which heat energyis transferred to the environment by radiation,convection, and/or conduction. 2. Chargedto an electrical potential, either positive or negative,with respect to common ground. 3. Pertainingto a conductor that carries a highradio-frequency (RF) current or voltage.hot carrier In a semiconductor, a charge carrier(electron or hole) whose energy is higher thanthat of majority carriers normally encountered inthe same material.hot-carrier diode A semiconductor diode having ametal base that receives HOT CARRIERS from asemiconductor layer. The unit has a fast switchingspeed because there are virtually no minoritycarriers—either injected or stored.Hotel Phonetic alphabet code word for the letter H.hot-filament gas detector A gas detector in whichthe sensor is a heated filament acting as one armof a Wheatstone bridge circuit. The bridge, previouslybalanced, becomes unbalanced when gasimpinges upon the filament and changes its resistance.hot junction The heated junction in a two-junctionthermocouple circuit. Compare COLD JUNCTION.hot line 1. An energized wire, transmission line, orbusbar. 2. A private communications channel(wire or radio) kept in constant readiness for instantuse between persons of high authority.

346 hot-pen recorder • H scopehot-pen recorder See THERMAL RECORDER.hot plate A metal device, usually heated by meansof electricity, used for the purpose of conductingcertain experiments.hot resistance The resistance of a component duringits operation (i.e., after it has been heated byambient temperature or internal power dissipation).Compare COLD RESISTANCE.hot spark A brilliant flash seen when a capacitordischarges through a spark gap in a vacuum.hot spot 1. In a circuit or component, an areawhose temperature is ordinarily higher thanthat of the surrounding area. 2. A local currentor voltage maximum on an antenna or transmissionline. 3. In communications operations, ageographic location in which reception ismarkedly better than in other nearby places orfrom which the transmitted signal appears to bestronger.hot-strip ammeter A current meter similar to thehot-wire meter, except that it has a heated metallicstrip instead of a heated wire.hot-stylus recorder See THERMAL RECORDER.hot-tip writing The use of a heated-tip stylus ingraphic recording. Also see THERMAL RE-CORDER.hot-wire ammeter See HOT-WIRE METER.hot-wire anemometer An electrical anemometerwhose indication is based on the cooling effect ofthe wind on a heated filament.hot-wire flowmeter An instrument for determiningthe rate of flow of a gas in a pipe or otherchannel. The circuit is similar to that of the gasdetector and hot-wire anemometer.hot-wire gasmeter See GAS DETECTOR.hot-wire instrument See HOT-WIRE METER.hot-wire meter A meter in which current heats awire, stretching it so that it moves a pointeracross a scale over a distance proportional to themagnitude of the current.hot-wire microphone A microphone in whichsound waves vary the temperature of a heatedwire and, accordingly, its electrical resistance.hot-wire relay A time-delay relay in which actuatingcurrent heats a wire, causing it to expand,eventually opening or closing the contacts. Alsosee DELAY RELAY.hot-wire sensor See HEATED-WIRE SENSOR.hot-wire transducer See HOT-WIRE MICRO-PHONE.hour Abbreviation, h; (sometimes, hr). A unit oftime measure equal to 60 minutes or 3600 seconds.Compare MINUTE, 1 and SECOND, 1. Alsosee TIME.housekeeping In digital-computer operations, thepart of a program that attends to chores (e.g., settingvariables to zero), rather than being involvedin making computations for a solution.howl A discordant sound produced in headphonesor a loudspeaker, usually as a result of acousticor electrical feedback.howler 1. An audio-frequency alarm device. 2. Asound-emitting test device (see GROWLER, 1,2).howl repeater A form of electric feedback inwhich a hum or howl occurs because of oscillation.The term is used to describe an oscillatingconduction in a wire-communications-systemrepeater.hp Abbreviation of HORSEPOWER.h-p Abbreviation of HIGH PRESSURE.H pad See H NETWORK.h parameters Parameters of the four-terminal networkequivalent of a transistor. They are hybridparameters (thus, h) because of their appearancein mesh and nodal equations. The basic h parametersare h 11 , input resistance with output shortcircuited;h 12 , reverse voltage ratio with inputopen-circuited; h 21 , forward current gain withoutput short-circuited; and h 22 , output conductancewith input open-circuited.h particle A positive hydrogen ion or proton obtainedby bombarding a hydrogen atom with alphaparticles or high-velocity positive ions.HPF Abbreviation of highest probable frequency.hp-hr Abbreviation of HORSEPOWER-HOUR.HPI Abbreviation of HEIGHT-POSITION INDICA-TOR.H plane The plane of the magnetic field of an antenna,or the magnetic component of an electromagneticfield. Compare E PLANE.H-plane bend In a waveguide, a smooth change inthe direction of the axis perpendicular to the directionof polarization.H-plane tee junction A waveguide tee junction,whose structure changes in the magnetic-fieldplane. Also see WAVEGUIDE JUNCTION andWAVEGUIDE TEE.hr Abbreviation of HOUR. (Also, h.)H scan A radar display in which the target is representedby two close blips, approximating a line,whose shape is proportional to the sine of the target’sangle of elevation.H scope See H SCAN.

HSM • Huygens’ principle 347HSM Abbreviation of high-speed memory.HTL Abbreviation of HIGH-THRESHOLD LOGIC.hub The hole in the center of a magnetic tape reel.hue The quality of having a particular visiblecolor; an attribute that depends on the wavelength(s)of light emitted or reflected. Thus, electromagneticenergy at a wavelength of 700nanometers (nm) has a red hue; energy at awavelength of 400 nm has a violet hue. CompareSATURATION, 2.hue control Also called tint control. In a color televisionreceiver, a control that allows adjustmentof the color wavelength, but does not affect thesaturation (intensity).hum 1. Alternating current having a frequency of 60Hz. 2. Residual ripple in the output of a power supply,having a frequency of 60 Hz or 120 Hz, dependingon the type of rectifier circuit used. 3. Anelectromagnetic field of long wavelength, usuallyoriginating from utility lines and having a primaryfrequency of 60 Hz. 4. The effects of low-frequencyelectromagnetic fields or currents, such as movinghorizontal bars on a television screen. 5. An acousticdisturbance of long wavelength (low pitch).human engineering 1. Also called user-friendliness.The extent to which an electronic or electromechanicaldevice or system is easy tooperate. 2. The branch of engineering devoted tointerfacing human beings with the machines andinstruments they operate. Both a science and anart, the discipline is concerned with the safestand most efficient design, arrangement, and operationof equipment.human interface The interface between a sophisticatedelectronic device and a human operator.human-made interference Also called artificial interference.Electromagnetic interference to radioand television receiving systems or to data terminals,originating from artificial sources (such asradio transmitters, certain electrical appliances,and internal-combustion engines). Of the numerousdifferent forms, some affect only a narrowband of frequencies or set of frequencies, andothers affect a wide band of frequencies.humanoid robot A robot that bears structural resemblanceto a human being (e.g., has arms, ahead, and perhaps legs). In its most advancedform, such a robot is an ANDROID.hum-balance potentiometer A potentiometerconnected across an alternating-current powersupply, with its slider grounded. At a certain setting,hum interference is nulled.hum bars See HORIZONTAL HUM BARS.hum bucking The reduction of hum interferenceby introducing an alternating-current voltage ofthe same frequency and amplitude as the hum,but opposite in phase.hum-bucking coil An auxiliary coil used in conjunctionwith the field and voice coils of an electrodynamicspeaker. Reduces hum interferencevia HUM BUCKING.hum field The magnetic field surrounding a conductorcarrying hum-frequency alternating current.humidity The amount of moisture in the air. Alsosee ABSOLUTE HUMIDITY and RELATIVE HU-MIDITY.humidity meter See ELECTRIC HYGROMETERand ELECTRONIC HYGROMETER.humidity sensor A pickup whose resistance or capacitancevaries proportionally with ambient humidity.hum interference Electrical interference resultingfrom HUM in any of its various electrical forms(see HUM, 1–4).hum loop A ground loop that results in undesiredhum in the output of an amplifier.hummer A nonelectronic audio oscillator similar tothe fork oscillator, but using a thick, metal reed,instead of a tuning fork. A carbon microphonebutton attached to the reed provides the feedbackpath necessary for sustained oscillation.ReedCarbonmicrophonebuttonhummerAF outputhum modulation Undesirable modulation of a radiosignal or audio amplifier output signal byHUM interference.hump 1. Either the positive or the negative halfcycleof a sine wave; that is, either the portionfrom 0 degrees to 180 degrees, or the portion from180 degrees to 360 degrees. 2. A curve whosegraph is a multiple of the sine function, andwhose domain is restricted to a half-cycle (0 to180 degrees or 180 to 360 degrees). See, for example,DOUBLE-HUMP RESONANCE CURVEand DOUBLE-HUMP WAVE.hunting An undesirable condition in which anelectrical or electromechanical system oscillatesback and forth, relative to some mean mode ofoperation (“hunts” for the mode), sometimeseventually settling down at the mode. It can occurin a servo system because of overcompensation,lack of hysteresis, or both.Huygens’ principle The observation that an advancingwave is the resultant of secondary waves

348 Huygens’ principle • hygrometerthat arise from points in the medium that havealready been passed.HV Abbreviation of HIGH VOLTAGE.H vector A vector representing the magnetic fieldof an electromagnetic wave. Compare E VECTOR.hW Abbreviation of HECTOWATT.H-wave mode In a waveguide, a mode of transmissionin which the electric lines of flux are at rightangles to the direction of the waveguide. Alsocalled transverse-electric (TE) mode.hy Occasional abbreviation of HENRY. The SI abbreviationand symbol, H, is preferred.hybrid Descriptive of a device that is an offspringof other devices or a product of dissimilar technologies(but using elements of each). See,for example, HYBRID JUNCTION and HYBRIDCOIL.hybrid active circuit An active circuit (such as anamplifier, oscillator, or switch) using a combinationof two dissimilar active devices (e.g., transistorsand vacuum tubes).hybrid coil A special type of bridging transformerused in wire telephony to prevent self-oscillationin a repeater amplifier that operates in both directions.hybrid computer A computer system incorporatingmore than one major computer technology.Examples: analog/digital and digital/neuralnetwork.hybrid electromagnetic wave Abbreviation, HEMwave. An electromagnetic wave whose electricfieldand magnetic-field vectors are both in the directionof propagation.hybrid IC See HYBRID INTEGRATED CIRCUIT.hybrid integrated circuit Abbreviation, HIC. Anintegrated circuit embodying both integrated andmicrominiature discrete components (i.e., onecombining both monolithic and thin-film construction).hybrid junction 1. See MAGIC TEE. 2. A fourterminaldevice, such as a resistor circuit, specialtransformer, or waveguide assembly, in which asignal applied to one pair of terminals divides andappears at only the two adjacent terminals.hybrid microcircuit A microcircuit containing diffusedor thin-film elements interconnected withseparate chip elements.hybrid parameters See H PARAMETERS.hybrid ring A hybrid waveguide junction (see HY-BRID JUNCTION, 2) consisting essentially of areentrant line with four side arms. Used as anequal power divider.hybrid-tee See HYBRID JUNCTION, 1.hybrid thin-film circuit A microcircuit in whichsemiconductor devices and discrete componentsare attached to passive components and conductorsthat have been electrodeposited on a substrate.hybrid transformer See HYBRID COIL.hydroacoustic Pertaining to the sound of fluids,especially water, under pressure.hydroacoustic transducer A transducer that convertsenergy from the high-pressure flow of a fluidinto acoustic energy.hydrodynamic pressure The pressure of a fluid inmotion. Compare HYDROSTATIC PRESSURE.hydroelectric Pertaining to the production of electricityby water power, as by a generator turnedby water turbines.hydroelectric machine A device for generatingelectricity from high-pressure steam escapingfrom a series of jets.hydroelectric power See WATER POWER.hydrogen Symbol, H. A gaseous element. Atomicnumber, 1. Atomic weight, 1.00794. Used inmaking semiconductor materials, it is the lightestand most abundant element in the universe.Compare DEUTERIUM and TRITIUM.hydrogen atmosphere The nonoxidizing atmospherein which semiconductor materials aremelted and processed, and in which semiconductorcrystals are grown. Occasionally, helium isused instead of hydrogen.hydrogen atom A single atom of the element hydrogen,consisting of one electron and one proton.hydrogen-ion concentration See pH.hydrogen lamp A glow-discharge lamp that produceslight by means of the ionization of rarefiedhydrogen gas. Visible light is emitted at discretewavelengths.hydrokinetic Pertaining to fluids in motion or theforces behind such motion.hydrolysis The process whereby chemical substancesbecome ionized in water solution, producingelectrolytes.hydromagnetics See MAGNETOHYDRODYNAM-ICS.hydromagnetic wave In a fluid, a wave in whichthe energy is propagated via magnetic and dynamicmodes.hydrometer An instrument for measuring the specificgravity of liquids.hydrophone An underwater sound-to-electricitytransducer (microphone).hydropower See WATER POWER.hydrostatic pressure The pressure of a fluid atrest. Compare HYDRODYNAMIC PRESSURE.hygristor A resistor, the resistance of which dependson humidity. A common application is inthe measurement of relative atmospheric humidity.hygrogram A graphic rendition of atmospheric humidityversus time, made by a HYGROGRAPH.hygrograph A device that produces a graphicrecording of atmospheric humidity as a functionof time. Consists essentially of a HYGROMETERconnected to a permanent data-storage device,such as a computer or pen recorder.hygrometer An instrument for measuring humidity.Also see ELECTRIC HYGROMETER, ELECTRONICHYGROMETER, and HAIR HYGROMETER.

hygroscopic material • hyperpolarization 349hygroscopic material A material that absorbsmoisture from the air, but not enough to get wet(e.g., lime and silk). Compare DELIQUESCENTMATERIAL.hygrostat A humidity-sensitive relay or switchingcircuit.hygrothermograph A graphic recorder indicatinghumidity and temperature on the same chart,both as functions of time.hyperacoustical zone In the upper atmosphere, aregion in which the distance between airmolecules is comparable to the wavelengths ofaudible sound. As the altitude increases withinthis zone, the upper-frequency limit of effectivesound propagation decreases. At altitudes abovethis zone, no audible sound can be propagated.hyperbola A conic-section curve satisfying theequation:(x – x 0 ) 2 /a 2 – (y – y 0 ) 2 /b 2 = 1where x and y are the independent and dependentvariables, x 0 and y 0 are the coordinates ofthe center, a is half the length of the major axis,and b is half the length of the minor axis.PlaneDoublecone(x 0, y 0 ) yhyperbolaxConeaxishyperbolic angle An angle subtended by a sectorof a hyperbola in a manner analogous to that inwhich a circular angle is subtended by an arc of acircle.hyperbolic-cosine horn See CATENOIDAL HORN.hyperbolic error 1. In an interferometer, a miscalculationin the direction of arrival of a signal. Thesignal from one antenna in the system can be as-sumed to be in phase with the signal from anotherantenna, when actually the two componentsdiffer by an integral number of wholewavelengths. 2. The angular error, in degrees,minutes, or seconds of arc, resulting from a miscalculationof phase in an interferometer.hyperbolic face contour See HYPERBOLIC GRIND.hyperbolic functions The nonperiodic functions ofa hyperbolic angle. Hyperbolic functions are relatedto the hyperbola in the same manner thatcommon trigonometric functions are related tothe circle. Hyperbolic functions are useful in calculationsinvolving traveling waves on transmissionlines, attenuator design, and wave-filterdesign.hyperbolic grind The shape (approximately hyperbolic)to which the face of a magnetic recordinghead is ground. It provides optimum contact withthe tape and ensures good high-frequency response.hyperbolic horn A horn antenna whose crosssectionalarea is a hyperbolic function of thedistance along the axis.hyperbolic logarithm See NAPIERIAN LOGA-RITHM.hyperbolic navigation A radionavigation systemin which the operator of an aircraft or boat determinesposition by comparison of two received signals.The two transmitters radiate signals fromknown positions and with known timing characteristics.The time delay from each transmitter isdetermined, resulting in two hyperbolic curves ona map. The point of intersection of the curves isthe location of the aircraft or ship.hyperbolic radian A unit of measure derived froma hyperbolic angle. A hyperbolic radian is the hyperbolicangle that encloses an area of 0.5 whenthe distance along the x-axis to the hyperbola isunity. Also see HYPERBOLIC ANGLE. CompareCIRCULAR RADIAN.hyperbolic trigonometry The branch of mathematicsdealing with the theory and application ofhyperbolic angles and their functions.hypercardioid microphone A unidirectional microphonewith exceptional sensitivity in front,and minimal responsiveness from the sides andrear.hypercardioid pattern A directional CARDIOIDPATTERN with accentuated responsiveness oremission in the favored direction (front), andgreatly suppressed responsiveness or emission inother directions (sides and rear).hyperfocal distance The shortest distance towhich a lens can be focused without degradingdefinition at infinity.hyperfrequency waves See MICROWAVES.hypernik See HIPERNICK.hyperon Any one of various particles having amass greater than that of a neutron or proton.hyperpolarization The production of an increasedvoltage across a biological membrane.

350 hypersonic • hysteresis errorhypersonicPertaining to speeds of at least fivetimes that of sound. In air at normal atmosphericpressure, such speeds are more than approximately1700 meters, or 5600 feet, per second.hypersonic speed Any speed greater than fivetimes the speed of sound in a given medium.hypersyn motor A high-efficiency, high-powerfactorsynchronous motor combining the advantagesof the direct-current-excited synchronousmotor (stiffness), the hysteresis motor (synchronizingtorque), and the induction motor (highstarting torque).hypervelocity Velocity in excess of 3 kilometersper second.hypotenuse The side of a right triangle opposite tothe right angle.Hypotenusecausing magnetization to lag behind the magnetizingforce. 2. A similar electrostatic action in aferroelectric dielectric material. 3. In a servosystem, the condition in which a variable quantitylags the effect or stimulus that causes it tochange. The plot for this is a double-line HYS-TERESIS CURVE.hysteresis brake A brake whose retarding actioncomes from hysteresis in a permanent-magnetmotor.hysteresis clutch A magnetic clutch whose outputtorque (for synchronous drive or continuous slip)comes from hysteresis in a permanent-magnetmotor.hysteresis coefficient In a sample of iron whosevolume is one cubic centimeter, the energy inergs dissipated during one cycle of magnetization.Also called coefficient of hysteresis.hysteresiscope An oscilloscope that is speciallydesigned to display the hysteresis curve of a material.Compare HYSTERESIGRAPH.hysteresis curve A response curve depicting hysteresisin a magnetic material, a dielectric, or aservo system. A graph of the extent to which avariable quantity lags the effect or stimulus thatcauses it to change (e.g., a curve showing the effectof response delay in a thermostatically controlledheating/cooling system).OnOff90°Hypotenusehypothesis An idea, concept, or system that seemstrue or workable, but must be subjected to logicalanalysis and/or practical testing to prove its validity.hypsometer An altimeter in which a thermistor(connected to a battery and current meter) is immersedin a boiling liquid. Because the liquid’sboiling point is proportional to altitude, it affectsthe resistance of the thermistor and, hence, thedeflection of the meter.hysteresigram The hysteresis-curve record producedby a HYSTERESIGRAPH.hysteresigraph A graphic recorder that displays orrecords the hysteresis curve for a material. Alsosee HYSTERESISCOPE.hysteresimeter See HYSTERESIS METER.hysteresis 1. The tendency of a magnetic materialto saturate and retain some of its magnetismafter the alternating magnetic field towhich it is subjected reverses polarity, thusHeatingOff| | |65 70 75Temperature, Fahrenheithysteresis curveCoolinghysteresis cycle A complete hysteresis curve.hysteresis distortion Signal distortion in ironcorecomponents, such as coupling transformers,resulting from hysteresis in the iron.hysteresis error In a meter, a difference in indicationsfor increasing and decreasing current, aneffect caused by hysteresis in iron meter parts.On

hysteresis heater • Hz 351hysteresis heater An induction heater in whichheating results from hysteresis loss in the load.hysteresis loop See HYSTERESIS CURVE.hysteresis loss Power loss caused by hysteresis ina magnetic material exposed to an alternatingmagnetic field, or in a dielectric material exposedto an alternating electric field. It is characterizedby the generation of heat.hysteresis meter An instrument that determinesthe hysteresis loss in a ferromagnetic material interms of the torque produced when the materialis rotated in a magnetic field, or vice versa.hysteresis motor A synchronous motor that doesnot require direct-current excitation, and doesnot have salient poles. It is started by means ofhysteresis losses that the rotating magnetic fieldcauses in the secondary.hysteretic constant For a ferromagnetic material,hysteresis loss in ergs per cubic centimeter ofmaterial per cycle of magnetization.hysteretic loss See HYSTERESIS LOSS.hystoroscope A device used to determine the magneticcharacteristics of a material.Hz Abbreviation of HERTZ.

I 1. Symbol for CURRENT. 2. Symbol for INTRIN-SIC SEMICONDUCTOR. 3. Symbol for LUMI-NOUS INTENSITY. 4. Symbol for IODINE.i 1. Symbol for the unit imaginary number, thesquare root of -1. (Also, j.) 2. Subscript for IN-STANTANEOUS VALUE. 3. Symbol for INTRINSICSEMICONDUCTOR. 4. Symbol for ANGLE OF IN-CIDENCE. 5. Symbol for INSTANTANEOUS CUR-RENT. (Also, I i .) 6. Symbol for a unit vector parallelto the x-axis. 7. Symbol for INCIDENT RAY.I ac Symbol for the ac component of a COMPOSITECURRENT.I AF Symbol for AUDIO-FREQUENCY CURRENT.IAGC Abbreviation of INSTANTANEOUS AUTO-MATIC GAIN CONTROL.IAVC Abbreviation of INSTANTANEOUS AUTO-MATIC VOLUME CONTROL.I B 1. Symbol for plate power-supply current. 2. Occasionalsymbol for plate current (usually, I P ).IBM Abbreviation for International Business MachinesCorporation.IC 1. Abbreviation of INTEGRATED CIRCUIT. 2.Abbreviation of INTERNAL CONNECTION.I C 1. Symbol for transistor COLLECTOR CUR-RENT. 2. Occasional symbol for grid current (usually,I G ).ICAD Abbreviation of integrated control and display.ICAS Abbreviation of INTERMITTENT COMMER-CIAL AND AMATEUR SERVICE.I CBO Symbol for the static reverse collector (leakage)current in a common-base connected transistorwith an open-circuited emitter.ICBS Abbreviation of interconnected business system.I CEO Symbol for the static reverse collector (leakage)current in a common-emitter-connected transistorwith an open-circuited base.ice loading 1. In an antenna, power-line system,or other structure, the additional stress causedby accumulation of ice. 2. The weight or thicknessof ice a structure can safely withstand.ice-removal circuit A high-voltage, low-frequencypower supply used to heat certain antennas tomelt ice that accumulates on them.ICET Abbreviation of Institute for the Certification ofEngineering Technicians (National Society of ProfessionalEngineers).ICME Abbreviation of International Conference onMedical Electronics.I co Symbol for the collector cutoff current (staticleakage current) of a bipolar transistor (see CUT-OFF CURRENT).icon In a graphical computer interface, a symbolthat aids the user in recognizing a selection thatcan be made.iconoscope A camera tube in which an electronbeam scans a photomosaic on which the image isfocused. The light-sensitive droplets of the mosaicform tiny capacitors with the insulated,metallic backplate of the mosaic, each capacitorbecoming charged by the light of the picture. Asthe electron beam scans the mosaic, each capacitordischarges as the beam strikes it, deliveringan output pulse proportional to the light intensityat that spot in the picture.IC tester An instrument for checking the operationof an integrated circuit.ICW Abbreviation of INTERRUPTED CONTINUOUSWAVE.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

ID • IEC 353ObjectDeflecting coilsCollector plateOptical imageElectron guniconoscopePhotocathodeOutputID Abbreviation of INSIDE DIAMETER.IDA Abbreviation of integrodifferential analyzer.I dc Symbol for the dc component of a COMPOSITECURRENT.ideal Pertaining to a circuit, device, material, ormanner of operation that is assumed to conformto the theoretical best-case example; it is notusually realized in real life. Thus, an ideal reactancehas no inherent resistance.ideal capacitor A capacitor having zero dielectricloss and a constant value of capacitance at allalternating-current frequencies.ideal component A theoretical component that isassumed to be 100-percent efficient and to haveno extraneous properties. Compare PRACTICALCOMPONENT.ideal crystal A piezoelectric crystal that acts as atheoretically perfect tuned circuit, that is, anideal capacitor and inductor.ideal inductor An inductor having zero loss and aconstant value of inductance at all alternatingcurrentfrequencies.I demodulator In a color-television receiver circuit,a demodulator that receives the chrominanceand 3.58-MHz oscillator signals anddelivers a video output corresponding to color inthe picture.identical vectors Equal vectors that have thesame initial point or point of application.identification 1. In radar operations, the (oftenautomatic) determination of the target’s identity.See, for example, IDENTIFICATION, FRIEND ORFOE. 2. In digital computer operations, a symbolor set of symbols within a label identifying a unitof data or its location.identification beacon 1. A beacon used for the determinationof a particular geographic location.2. An automatically transmitted station-identificationsignal or code, usually superimposed onthe regular transmission in the form of a subcarrieror subaudible signal.identification division The division (one of four)in a COBOL program that describes and identifiesthe program being compiled.identification, friend or foe Abbreviation, IFF. Atechnique in which a radar station transmits aninterrogating signal and the station questionedreplies automatically with a suitable pulse orother signal if it is aboard a friendly aircraft orvessel. If it is aboard an enemy vehicle, the stationgives no reply or sends an unsatisfactoryone.identifier A data file identification label in an input/outputdevice, or a label that identifies a specificstorage location.identity element A logic element that, upon receiptof two input signals, provides an outputthat is logic 1 (high) only if the input signals areboth logic 1 (high) or logic 0 (low).idiochromatic Possessing the photoelectric propertiesof a true crystal.I display See I SCAN.idle channel noise A measurement of widebandnoise. The total energy at an output of an integratedcircuit or other communications stagewith that output grounded (idle).idle character A digital character that conveys noinformation, but helps maintain synchronizationbetween the transmitter and receiver. Sometimescalled a blank.idler wheel In a phonograph or magnetic taperecorder, an auxiliary, rubber-coated wheel thattransfers rotary motion from the motor pulley tothe platter or the rim of the capstan flywheel.idle time The period during which data processingequipment, although operable, is not in use.idling Standby equipment operation, as when vacuum-tubefilaments in a radio-frequency poweramplifier are kept hot—even when the amplifier isnot actually being used to transmit a signal.idling current The current flowing in a device duringa standby period, as opposed to operatingcurrent. Also called STANDBY CURRENT.idling frequency In a parametric amplifier, the differencebetween the signal frequency and pumpfrequency.idling power See STANDBY POWER.idling voltage The voltage required by or measuredin a device that is in standby mode.I D(off) Symbol for drain cutoff current in a field-effecttransistor.IDOT Abbreviation of instrumentation online transcriber.IDP 1. Abbreviation of INDUSTRIAL DATA PRO-CESSING. 2. Abbreviation of INTEGRATED DATAPROCESSING. 3. Abbreviation of INTERMODU-LATION-DISTORTION PERCENTAGE.I DSS Symbol for DRAIN CURRENT AT ZERO GATEVOLTAGE in a field-effect transistor.I E Symbol for EMITTER CURRENT.IEC Abbreviation of integrated electronic component.

354 IEE • illuminated pushbuttonIEE Abbreviation of Institution of Electrical Engineers(British).IEEE Abbreviation of Institute of Electrical and ElectronicsEngineers.IES Abbreviation of Illuminating Engineering Society.IF Abbreviation of INTERMEDIATE FREQUENCY.IF amplifier See INTERMEDIATE-FREQUENCYAMPLIFIER.I FB In an integrated circuit, current limit feedbackor feedback current.IF channel See INTERMEDIATE-FREQUENCYCHANNEL.IF converter The converter (first detector-oscillator)section of a superheterodyne radio receiver.IFF Abbreviation of IDENTIFICATION, FRIEND ORFOE.IF gain 1. The amplification provided by the intermediate-frequency(IF) channel of a superheterodynereceiver, usually specified in decibels. 2. Acontrol that allows adjustment of the amplificationin the IF channel of a superheterodyne radioreceiver.IF interference See INTERMEDIATE-FREQUEN-CY INTERFERENCE.IFIPS Abbreviation of International Federation ofInformation Processing Societies.IF selectivity See INTERMEDIATE-FREQUENCYSELECTIVITY.IF strip A (sometimes removable) circuit sectioncontaining a complete intermediate-frequencychannel.IF/THEN/ELSE In computer systems and artificialintelligence, a two-way choice that is made duringthe execution of a program. For example, infinding the absolute value of a number, the logicproceeds as follows: “IF x < 0, THEN multiply x by-1; otherwise (ELSE) leave it alone.”IF transformer See INTERMEDIATE-FREQUEN-CY TRANSFORMER.I G Symbol for GATE CURRENT.I G Symbol for GRID CURRENT.IGFET Abbreviation of INSULATED-GATE FIELD-EFFECT TRANSISTOR.ignition coil A small open-core transformer havinga high step-up turns ratio for converting6- or 12-volt battery potential to the high voltageneeded in an automotive ignition system.ignition interference Electrical noise generatedby the ignition system of an internal combustionengine.ignition potential 1. The minimum voltageneeded to cause electrical discharge in an internalcombustion engine. 2. See BREAKDOWNVOLTAGE, 1, 2.ignition reserve The extra voltage provided by thestarter, as compared with the voltage actuallyneeded for ignition of an internal-combustion engine.ignition system An electrical or electronic systemthat supplies the high voltage in an automotiveengine. See, for example, CAPACITOR-DISCHARGE IGNITION SYSTEM.ignition voltage See IGNITION POTENTIAL.ignitron A form of rectifier tube that contains ionizedmercury. It is used with some extremelyhigh-voltage power supplies.Iron anodesShieldsSteel tankWater jacketMercury cathode−ac supply+ignitrondc loadignore character 1. A character used as a signal toinhibit an action. 2. A digital character that is ignoredby the system.I GSS Symbol for GATE REVERSE CURRENT in afield-effect transistor.IGY Abbreviation for INTERNATIONAL GEOPHYSI-CAL YEAR.I H 1. Symbol for HOLD CURRENT. 2. Symbol forHOLDING CURRENT.IHF Abbreviation of INHIBIT FLIP-FLOP.IHFM Abbreviation for Institute of High FidelityManufacturers.ihp Abbreviation of INDICATED HORSEPOWER.ihp-hr Abbreviation of INDICATED HORSE-POWER-HOURS.I i 1. Symbol for INPUT CURRENT. 2. Symbol for IN-STANTANEOUS CURRENT (also, i).I K Symbol for CATHODE CURRENT.I L Symbol for current in an inductor.I 2 L Abbreviation of INTEGRATED INJECTIONLOGIC. (Also IIL.)illegal character 1. A character or bit group that is,according to some standard, invalid. 2. A bit groupthat represents a symbol in a character set.illuminance The amount of luminous flux receivedper unit surface area, measured in lux (lumensper square meter).illuminant-C In color television, the referencewhite that closely resembles average daylight.illuminated pushbutton See LIGHTED PUSH-BUTTON.

illuminated switch • image transfer constant 355illuminated switch See LIGHTED SWITCH.illumination 1. Visible light. 2. The condition ofbeing irradiated by visible light. 3. The intensityof visible light irradiating an object or region.illumination control A photoelectric circuit thatautomatically regulates electric lights, accordingto the amount of daylight.illuminometer A device for measuring the intensityof visible light, or, less often, infrared orultraviolet. In its simplest form, the meterconsists of a photovoltaic cell, a potentiometer foradjusting the sensitivity, and a microammeter.More sophisticated devices include direct-currentamplification.ILS Abbreviation of INSTRUMENT LANDING SYS-TEM.IM Abbreviation of INTERMODULATION.I m 1. Abbreviation of maximum current. (Also, I max ).2. Abbreviation of meter current.image 1. In a superheterodyne circuit, a spuriousresponse whose frequency differs from that of thedesired signal by twice the intermediate frequency.2. A picture on the screen of a televisionreceiver or computer display. 3. A pattern on thescreen of an oscilloscope tube. 4. A picture on themosaic of a television camera tube. 5. A duplicateof a computer storage area that is in another partof storage or on another medium.image admittance The reciprocal of IMAGE IM-PEDANCE.image antenna An imaginary “mirror” antennabelow the effective radio-frequency (RF) groundsurface, at a depth equal to the height of thetrue radiating antenna above effective RFground.image attenuation constant The real-numberpart of the IMAGE TRANSFER CONSTANT. Alsosee IMAGE PHASE CONSTANT.image compression Any of various methods bywhich the number of bytes in a digital image canbe reduced, without significant degradation ofimage quality. The two most common methodsare JPEG (Joint Photographic Experts Group) imagecompression and fractal image compression.Other schemes include MPEG (Moving Picture ExpertsGroup) image compression and Indeo, developedby Intel Corporation. Fractal imagecompression can provide a compression factor ofas much as 100:1 without significant degradationof image quality.image converter 1. A device that changes an invisibleimage into a visible image. Examples includethe snooperscope, an infrared-to-visibleconverter, and photographic apparatus for infrared,ultraviolet, and X-ray wavelengths. 2. Atube that operates as an image converter.image dissector See DISSECTOR TUBE.image effect The effect of reflection of electromagneticwaves from the ground. An IMAGE AN-TENNA appears to radiate from a point beneaththe effective RF ground plane. The depth of theimage antenna below the effective RF groundplane is equal to the height of the actual antennaabove the effective RF ground plane.image frequency The frequency of the image responsein a superheterodyne radio receiver. SeeIMAGE, 1.image impedance The property of a network inwhich the load impedance is “seen,” looking intothe output terminals with the generator connectedto the opposite end, and the generatorimpedance is “seen,” looking into the input terminalswith a load connected to the oppositeend.image intensification An increase of the brightnessof the display on a cathode-ray tube.image intensifier A device that increases thebrightness of the spot produced when a beam ofelectrons or X rays hits a fluorescent screen.image interference A type of interference that canoccur in superheterodyne circuits. It occurs whenthere is a sufficiently strong signal on the IMAGEFREQUENCY.image orthicon See ORTHICON.image phase constant The imaginary-numberpart of the IMAGE TRANSFER CONSTANT. Alsosee IMAGE ATTENUATION CONSTANT.image potential The potential energy of a chargedparticle at a given distance from a metal surface.The metal surface acts in a way similar to a mirror;a reflected image of the object, having equalcharge but opposite polarity, is formed on theother side of the surface.image ratio See SIGNAL-TO-IMAGE RATIO.image rejection In a superheterodyne radio receiver,the suppression or elimination of IMAGEINTERFERENCE by means of a selective circuit,such as a radio-frequency preamplifier.image response In a superheterodyne receiver, anundesired response to signals removed from thedesired frequency by twice the intermediate frequency.image transfer constant A number depicting thetransfer of power by an impedance network. Ithas the same value, regardless of the direction oftransmission through the network. Also see IM-AGE ATTENUATION CONSTANT and IMAGEPHASE CONSTANT.

356 imaginary axis • impedance-matching networkimaginary axis In a vector diagram of compleximpedance, the axis of the imaginary-numbercomponent (jX).imaginary number A real-number multiple of thepositive square root of -1. Engineers depict thepositive square root of -1 by the lowercase letter j;mathematicians use the lowercase letter i. Engineerswrite imaginary numbers in the form jX,and mathematicians write Xi, where X is a realnumber.imaginary-number component The imaginarynumberpart of a COMPLEX NUMBER.I max Abbreviation of maximum current.IM distortion meter INTERMODULATION ME-TER.IM distortion percentage See INTERMODULA-TION-DISTORTION PERCENTAGE.I min Abbreviation of minimum current.imitation The transmission of false signals forpurposes of deception. For example, duringwartime, the signals from an enemy station mightbe recorded and retransmitted.immediate access 1. The ability of a computer tostore and retrieve data in a minimal amount oftime. 2. Computer storage that can be accessedin a minimal amount of time.immediate address An instruction address that isused as data by that instruction.IM meter See INTERMODULATION METER.immitance Impedance or admittance; a contractionof IMPEDANCE and ADMITTANCE. Example:a negative-immitance circuit.immortal knowledge Knowledge that can be keptindefinitely in the form of detailed computer datafiles. Some scientists and sociologists believe thatthis will eventually have a profound effect on theway that future generations view history.impact excitation See SHOCK EXCITATION.impact strength 1. The ability of a component ormaterial to withstand mechanical shock loading.2. The work required to fracture the material undershock loading.IMPATT diode Acronym for impact avalanche transittime diode. A microwave semiconductor (siliconor gallium arsenide) diode exhibiting negativeresistance resulting from the combined effects ofcharge-carrier transit time and impact avalanchebreakdown. It is used as an oscillator or amplifier.IMPATT oscillator A microwave oscillator thatuses an IMPATT DIODE.impedance Symbol, Z. Unit, ohm. The total oppositionoffered by a circuit or device to the flow of alternatingcurrent. It is the vector sum ofRESISTANCE and REACTANCE. This is a COM-PLEX NUMBER whose real-number component isresistance R, and whose imaginary-number componentis reactance jX; mathematically, Z = R + jX.impedance angle The angle between the resistanceand impedance vectors in an IMPEDANCETRIANGLE.impedance arm The network branch that containsone or more impedances, as opposed to an armthat contains only resistance or (predominantly,reactance). Also called impedance leg.impedance branch See IMPEDANCE ARM.impedance bridge 1. An alternating-current (ac)bridge (commonly operated at 1 kHz) used tomeasure resistance, inductance, capacitance,and resistive components associated with inductorsand capacitors, from which impedance canbe calculated. 2. Sometimes, an ac half-bridgecircuit in which an unknown impedance is comparedwith a known resistance. 3. A radiofrequencybridge circuit whose balancing elementreads impedance directly in ohms.impedance bump A discontinuity in the characteristicimpedance of a radio-frequency transmissionline. It is often caused by the use of impropersplicing techniques.impedance coil See CHOKE COIL.impedance converter See IMPEDANCE TRANS-FORMER.impedance-coupled amplifier An amplifier usingcapacitor/coil combinations for interstage andoutput load coupling.impedance drop In an alternating-current circuit,the complex sum of the resistance drop and reactancedrop.impedance ground A ground connection in whichthe impedance at the operating frequency is determinedby a network of resistors, capacitors,and/or inductors.impedance leg See IMPEDANCE ARM.impedance magnetometer A device that is usedfor measuring small local variations in the intensityof the earth’s magnetic field. A small changein the intensity of the magnetic field will cause achange in impedance of a nickel-iron wire havinghigh permeability.impedance match The condition (for maximumpower transfer) when the transmitting impedanceequals the receiving impedance, or when asuitable transformer is inserted between differentimpedances for matching purposes. Also seeIMPEDANCE MATCHING.impedance matching 1. The adjustment or modificationof two impedances so that they are identical,that is, the two resistive components areequal, and the two reactive components areequal. 2. The insertion of a suitable transformeror network between circuits having differentimpedances, for the purpose of optimizing powertransfer.impedance-matching network A network of discretecomponents, often adjustable, that is usedto match a circuit having a certain impedance toa circuit having a different impedance. Anexample is the inductive-capacitive (LC) coupler,also called a transmatch, commonly usedto match a radio transmitter to an antennasystem.

impedance-matching transformer • impulse ratio 357impedance-matching transformer See IMPED-ANCE TRANSFORMER.impedance meter See Z METER.impedance plethysmograph An electronic deviceused to measure changes in the chemical contentof body cells.impedance poles See POLES OF IMPEDANCE.impedance ratio The quotient of two impedancesthat are related in some situation, such asimpedance match or impedance mismatch. Theimpedance ratio of a transformer is equal to thesquare of the turns ratio.impedance transformer 1. A transformer for convertingan impedance to a different value. Theturns ratio is equal to the square root of theimpedance ratio. 2. An emitter follower or sourcefollower circuit, used primarily to match a highimpedance to a lower impedance. 3. A shortcircuitedtransmission-line section used to matchor convert impedances at radio frequencies.Z p Primary Secondary Z sT = N pri /N secimpedance transformerimpedance triangle A triangular vector diagram inwhich the impedance vector is the hypotenuse,and the reactance and resistance vectors are theperpendicular sides.−R+X LZRX+Rimperfection A fault in the lattice of a crystal. Alsosee CRYSTAL LATTICE.implementation 1. Putting a system into operationand evaluating its performance. 2. Doingall that is necessary to install a device or system.implosion The inward collapse of an evacuatedchamber, such as the envelope of a cathode-raytube. It is the opposite of explosion, an outwardbursting.impregnant A substance for the IMPREGNATIONof electronic components. Examples: waxes, oils,liquid plastics, and varnish.impregnation The process of filling the spaceswithin a material or structure with an insulatingcompound. Various electronic components, suchas capacitors, inductors, transformers, transistors,and diodes, are impregnated for protectionand stability.impressed voltage The voltage applied or presentedto a circuit or device.impulse 1. A signal of extremely short duration(e.g., a noise burst). 2. A brief, unidirectionalsurge in voltage (usually) or current.impulse excitation Driving a tank circuit with asingle pulse, then allowing it to oscillate at itsown frequency until another driving pulse arrives.impulse frequency In a digital telephone, thenumber of pulse periods per second, correspondingto a dialed digit, generated by the pulsesprings.impulse generator See MARX GENERATOR.impulse noise Electrical noise from short-durationpulses, such as those produced by an automotiveignition system.impulse ratio The ratio V p /V s , where V p is thebreakdown (or flashover or sparkover) voltagecaused by an impulse, and V s is the correspondingvoltage at the crest of the power-frequencycycle.−X cimpedance triangleimpedance vector In a vector diagram, the resultant(vector) representing the combined reactanceand resistance vectors. Also see IMPEDANCETRIANGLE.impedance zeros See ZEROS OF IMPEDANCE.imperative macroinstruction A MACROIN-STRUCTION used to create object (machine language)program instructions.imperative statement A source language programinstruction that is converted into object program(machine language) instructions.

358 impulse relay • inclusive-ORimpulse relay A relay that is able to close or opencompletely when driven by a short pulse.impulse speed The switching rate of a telephonedialing device as it transmits pulses.impulse timer A synchronous-motor-driventimer whose cams can control many circuits; itcan advance by a number of specified increments,as controlled by an integral steppingmechanism.impulse transmission A method of transmissionin which defined impulses are used to denotechanges in signal content or format.impurity A substance added to an intrinsic semiconductorto alter its electrical properties.impurity atom In a processed semiconductor material,an atom of an IMPURITY material that produceseither n- or p-type properties to theintrinsic semiconductor.impurity density In the manufacturing process ofa semiconductor material, the amount of impurityadded to the original semiconductor.impurity ion In a crystal, an ion in a space betweenatoms, or one taking the place of an atom.impurity level 1. The energy existing in a semiconductormaterial as a result of doping (the additionof an impurity). 2. See IMPURITYDENSITY.impurity material See IMPURITY.IN Abbreviation for INTELLIGENT NETWORK.In Symbol for INDIUM.I n Symbol for the nth value of current in a series ofvalues.in 1. Abbreviation of INPUT. 2. Abbreviation ofINCH.inaccuracy 1. The state or condition of instrumenterror. 2. The difference between the actualvalue of a parameter and the value indicated byan instrument. 3. The percentage of instrumenterror.inactive leg Within a transducer, an electricalcomponent whose characteristic remains unchangedwhen the stimulus (quantity beingtransduced) is applied; specifically, a Wheatstonebridge element in a transducer.inactive lines In a conventional television picture,blanked lines that do not contribute to the visiblepart of the image. Approximately half of theselines are at the top of the screen; the other halfare at the bottom.inactive time The period during which a radioactivitycounter is insensitive to ionizing agents.incandescence The state of glowing from intenseheat, as when a metal becomes white hot from anelectric current flowing through it.incandescent lamp A filament-type lamp. The filamentbecomes so hot when an electric currentpasses through it that it glows brilliantly.inch Abbreviation, in. A unit of linear measure inthe English system; 1 in. = 2.54 centimeters =0.0254 meter.inching See JOGGING.inch-pound Abbreviation, in-lb. A unit of workequal to a force of 1 pound exerted over a distanceof 1 inch. Compare FOOT-POUND.incident 1. A failure in a computer system requiringthe intervention of an operator in removing orrevising the job involved. 2. Pertaining to a ray orrays of energy striking a surface or boundary, orencountering a device (such as an antenna orphotovoltaic cell).incidental AM Undesired amplitude modulation ina frequency-modulated signal. Compare INCI-DENTAL FM.incident field intensity The field strength of anelectromagnetic field as it arrives at a receivingantenna.incidental FM Undesired frequency modulation inan amplitude-modulated signal. Compare INCI-DENTAL AM.incidental time Computer time devoted to otherthan program runs or program development.incident light The light that strikes or enters analtering device or medium. See INCIDENT RAY.incident power In a transmission line, the powerthat reaches the end of the line. Compare RE-FLECTED POWER.incident ray The ray that strikes the surface of areflecting, refracting, or absorbing body. CompareREFLECTED RAY and REFRACTED RAY.incident wave 1. A wave propagated to the ionosphere.Compare REFLECTED WAVE and RE-FRACTED WAVE. Also see IONOSPHERE andIONOSPHERIC PROPAGATION. 2. A wave thatencounters a change (in density, for example) in apropagation medium or the transition point betweenmedia.in-circuit tester An instrument that permits thechecking of components (especially transistors)without removing them from the circuit in whichthey are wired.inclination 1. At a given geographic location, theangle between the earth’s magnetic lines of fluxand the horizon. This angle ranges from 0 degreesat the geomagnetic equator to 90 degrees at thegeomagnetic poles. Compare DECLINATION, 1. 2.The angle between the plane of a satellite orbitand the plane containing the equator of the earth,planet, or star around which the satellite revolves.Generally measured as the angle at whichthe satellite crosses the equator while passingfrom the southern hemisphere to the northernhemisphere. This angle is between 0 and 90 degreesfor satellites in non-retrograde orbits, andbetween 90 and 180 degrees for satellites in retrogradeorbits.inclinometer An instrument for measuring INCLI-NATION. One form consists of a magnetic needlemounted so that it can swing inside a verticallymounted circular scale.inclusive-OR Also called OR operation. A logicaloperation between two operands, the result ofwhich depends on rules for combining bits in

inclusive-OR • indexing 359each position within the operands: an output of 1results if one or both of the bits have a value of 1;zero only if both are zero. Compare EXCLUSIVE-OR.incoherent light Electromagnetic radiation in thevisible spectrum in which the waves are notaligned (not in phase) and can be of more thanone wavelength.incoherent radiation Electromagnetic radiation inwhich the waves are not aligned (not in phase)and can be of more than one frequency or wavelength.incoming inspection The examination of equipmentand materials as they enter a factory or laboratory,for the purpose of identifying damaged orfaulty units.incoming line A line that enters a device, facility,or stage. Compare OUTGOING LINE.Incompleteness Theorem A mathematical theoremof significance in artificial intelligence. Forany consistent set of axioms (postulates), thereare always more true statements than provablestatements.incomplete program Also called incomplete routine.A computer program of generalized stepsthat must be augmented with specific requirementsto be implemented for a given operation.inconsistency Contradictory computer statements,as detected by the program.inconsistent equations A set of equations thathave no common solution.Increductor A specialized radio-frequency magneticamplifier or saturable reactor.increment 1. The difference between two successivevalues of a variable. 2. A small change in aquantity, such as mass, distance, or time. 3. Aquantity to be added to another quantity. 4. Thedifference in value between adjacent hash markson a meter scale.01234 5 6dc VoltsIncrement = 0.5 Vincrement, 4incremental computer A computer that operateson changes in variables. Example: differential analyzer.incremental digital recorder A magnetic taperecorder that moves the tape across the recordhead in increments.78910incremental display A device that converts digitaldata into a form for display (characters; graphs).incremental inductance The inductance exhibitedby an inductor, such as an iron-core choke,carrying a direct current.incremental permeability The permeability exhibitedby a material when an alternating-currentmagnetizing force is superimposed upon a directcurrent.incremental plotter A device that, by direction ofa computer program, provides the results of aprogram run in the form of curves or points on acurve, along with annotational characters.incremental representation For incrementalcomputers, a method of representing variables interms of changes in the variables.incremental sensitivity The smallest change in aquantity under measurement that can be detectedby the instrument used.ind 1. Abbreviation of indicator. 2. Abbreviation ofINDUCTANCE (more commonly, L). 3. Abbreviationof INDUCTOR (More commonly, L).indefinite integral See INTEGRAL, 1.Indeo Also called Digital Video Interactive (DVI). Amethod of IMAGE COMPRESSION developed byIntel Corporation.independent equations A set of equations havingone common solution.independent events In probability and statistics,the case where the occurrence of one event hasno effect on the occurrence of another.independent failure A circuit failure whose directcause is not related to malfunctions elsewhere inthe system.independent mode In tracking supplies, an optionalmethod of operation in which the separateunits are adjustable independently of each other.Compare TRACKING MODE.independent variable A changing quantity whosevalue at any instant is not governed by the valueof any other quantity. Compare DEPENDENTVARIABLE.index 1. A reference line, hair, or point (e.g., a fileindex). 2. In mathematics, an exponent. 3. A ratioof one quantity to another, as index of refraction.4. In a computer memory, a table of references ina key sequence; it can be addressed to find theaddresses of other data items. 5. A number thatis used to select a specific item within an array ofitems in memory.index counter Also called tape counter. In a magnetictape recorder, a (usually electromechanical)counting device that the operator can refer to inorder to find material on the tape.indexed address During or preceding the executionof a computer program instruction, an addressthat is modified by the content of an index register.indexing 1. An information retrieval techniqueused with files on a direct-access storage mediumor on tables in memory. 2. To modify an instructionusing an index word.

360 index of modulation • indiumindex of modulation In frequency modulation, theratio of carrier frequency deviation to modulatingfrequency.index of refraction Symbol, n. The ratio v 1 /v 2 ,where v 1 is the speed of energy propagation inthe first medium through which the energypasses, and v 2 is the speed in the secondmedium.index register Abbreviation, XR. In digital computeroperations, a register holding a modifierthat allows data to be directly addressed (eachprogram refers to an index register when addressingstorage locations). Also called MODI-FIER REGISTER.index word A word (bit group) containing a modifierthat will be added to a basic instruction whenit is executed during a program run.India mica High-grade mica mined in India. Its excellentdielectric properties make it useful for capacitorstacks, high-Q radio-frequency circuits,and other critical applications.indicated horsepower Abbreviation, ihp. Horsepowercalculated from data or ratings, as opposedto measured horsepower.indicated horsepower-hours Abbreviation, ihphr.Horsepower-hours based on calculation of indicatedhorsepower.indicating fuse A fuse that provides some signal(such as a protruding pin) to show that it hasblown.indicating instrument An instrument, such as ameter, that provides direct readings of a measuredquantity, as opposed to an instrument,such as a bridge, that must be manipulated andwhose operation must often be followed by calculations.indicating lamp A lamp that is marked or coded sothat when it is on or off it conveys information.indicator 1. Meter (see METER, 1). 2. See MONI-TOR. 3. See ANNUNCIATOR. 4. In a computer, adevice that can be set by a specific condition (e.g.,by a negative result or error indicator).indicator probe A test probe having a built-in meter.indicial response Symbol, I(T). The sum of thetransient and steady-state responses to a unitfunction.indirect addressing In computer programming,a technique in which the address in an instructionrefers to a different location containing anotheraddress, that can specify yet anotheraddress or an operand. Also called multilevel addressing.indirect coupling Collectively, capacitive and inductivecoupling, as opposed to direct coupling.indirect ground An unintentional ground connection(e.g., accidental grounding of part of a circuit)or one obtained through a roundabout path.Compare DIRECT GROUND.indirect light Light that has been reflected fromone or more surfaces. Compare DIRECT LIGHT.indirectly controlled Influenced by a directly controlledparameter, but not itself directly controlled.indirectly grounded Connected to earth or to thelowest-potential point in a system inadvertentlyor through a roundabout path (e.g., by meansof an indirect ground). Compare DIRECTLYGROUNDED.indirectly heated cathode An electron-tube cathodeconsisting of a cylindrical or rectangularsleeve coated with a substance that is a rich emitterof electrons; it is heated by a filament insidethe cylinder.indirectly heated thermistor A thermistor whosetemperature is changed by a built-in heater (filament)operated by the control current.indirectly heated thermocouple A meter thermocoupleheated by a small heater (filament)through which the signal current passes.indirect material A semiconductor substance inwhich electrons move from the conductionband to the valence band in discrete jumps orsteps.indirect measurement The measurement of aquantity by comparing it with a similar quantity,using an instrument that requires adjustment ormanipulation (rather than a simple meter). Forexample, resistance can be measured with abridge, instead of an ohmmeter. Compare DI-RECT MEASUREMENT.indirect piezoelectricity In a piezoelectric crystal,the application of a voltage for the purpose of producinga strain on the crystal. A piezoelectricbuzzer operates on this principle.indirect scanning A method of video scanning, inwhich a fast-moving spot of light scans the film oran object and is passed through the film (or reflectedby the object) to a photocell.indirect wave 1. In communications, a wave thatarrives at a receiver after having traveled via refraction,reflection, or both. 2. A radio wave propagatedvia the ionosphere. 3. A wave reflectedfrom some object, such as the moon or a meteortrail. 4. A wave received from a satellite, originatingfrom a distant earth station.indium Symbol, In. A metallic element. Atomicnumber, 49. Atomic weight, 114.82. Used as adopant in semiconductor processing.TXIonized layerindirect waveRX

indoor antenna • induction modulator 361indoor antenna An antenna erected and operatedin a building, but kept away from other objects asmuch as possible.indoor radiation Electromagnetic radiation fromthe part of an antenna feeder or lead-in that is insidethe transmitter building.indoor transformer A power service transformerthat, for protection against the elements, is installedinside the building it serves.induced Brought about by the influence of a magneticor electric field.induced charge An electric charge produced in abody by the electric field surrounding anothercharge.induced current An alternating current establishedin one circuit by the alternating magneticfield of another circuit. Also see INDUCTION.induced EMF See INDUCED VOLTAGE.induced failure A form of component failure thatoccurs because of operation beyond the normalspecifications.induced voltage An alternating voltage set upacross one circuit (especially a coil) by the alternatingmagnetic field of another circuit. Also seeINDUCTION.inductance Symbol, L. Unit, henry. In a conductor,device, or circuit, the inertial property(caused by an induced reverse voltage) that opposesthe flow of current when a voltage is applied;it opposes a change in current that hasbeen established. Also see HENRY, INDUCTION,and MUTUAL INDUCTANCE.inductance bridge An alternating-current bridgefor measuring inductance in terms of a standardinductance or a standard capacitance. See, forexample, HAY BRIDGE, MAXWELL BRIDGE, andOWEN BRIDGE.inductance-capacitance Abbreviation, LC. 1. Acombination of inductance and capacitance in acircuit, such as a filter, a parallel-resonant circuit,or a series-resonant circuit. 2. Pertaining toa device for measuring inductance and capacitance(e.g., LC bridge and LC meter).inductance-capacitance bridge An alternatingcurrentbridge for measuring inductance and capacitanceonly.inductance-capacitance filter A filter composedof inductors and capacitors. Also called LC filter.inductance-capacitance meter A direct-readingmeter for measuring inductance and capacitance.inductance-capacitance-resistance Abbreviation,LCR. 1. A combination of inductance, capacitance,and resistance in a circuit, such as a basictuned circuit. The resistive component representsloss in the inductor and capacitor. 2. Pertainingto a device for measuring inductance, capacitance,and resistance (e.g., LCR bridge and LCRmeter).inductance-capacitance-resistance bridge SeeIMPEDANCE BRIDGE.inductance coil See INDUCTOR.inductance filter A filter using only an inductor,usually a coil of wire.inductance-resistance time constant The timeconstant t (see ELECTRICAL TIME CONSTANT) ofa circuit containing, ideally, only inductance andresistance. Mathematically, t = LR, where t is inseconds, L is the inductance in henrys, and R isthe resistance in ohms. Also called LR time constant.inductance standard A highly accurate, stable inductorused in precision measurements. Also seePRIMARY STANDARD and SECONDARY STAN-DARD.induction 1. The ability of an alternating, pulsating,or otherwise changing current flowing in onecircuit to set up a current in a nearby circuit. Thecircuits need not be physically connected, butneed only be linked by magnetic lines of flux. Alsosee SELF-INDUCTION. 2. The phenomenonwhereby a body becomes electrically charged bythe field surrounding a nearby charged body.Also see ELECTRIC CHARGE.induction coil A special high-voltage step-uptransformer having an open core and a vibratorinterrupterin series with the primary winding,which carries direct current from a battery. Thecurrent is broken up into short pulses by the interrupter,and a high alternating-current voltageis generated in the secondary winding.induction compass A compass whose indicationsdepend on current induced in a coil revolving inthe earth’s magnetic field. Compare GYROCOM-PASS and MAGNETIC COMPASS.induction factor The ratio of total current to nonproductivecurrent in an alternating-current circuit.induction field The portion of an electromagneticfield that returns to a radiator, such as a coil, asopposed to the RADIATION FIELD.induction frequency converter A mechanical deviceused for converting a signal at a fixed frequencyto a signal at another fixed frequency.induction furnace A furnace in which highfrequencymagnetic fields induce currents inmetal ores, causing the ore to become hot enoughto melt.induction heater A high-power, radio-frequencygenerator designed especially for induction heating.induction heating The heating of metallic worksamples by placing them in (but insulated from) aWORK COIL carrying current from a high-powerradio-frequency generator. The workpiece is heatedby radio-frequency currents induced in it as a resultof the intense alternating magnetic field withinthe coil. Compare DIELECTRIC HEATING.induction loss Loss of energy from a currentcarryingconductor because of inductive couplingto a nearby conductor.induction modulator See ELECTROMECHANI-CAL MODULATOR.

362 induction motor • inductive transducerinduction motor An electric motor in which thestator’s rotating magnetic field makes the rotorrevolve.induction speaker An acoustic loudspeaker inwhich an audio-frequency current is passedthrough a diaphragm or coil located in a constantmagnetic field. This results in movement of thediaphragm or coil.induction transducer See INDUCTIVE TRANS-DUCER.induction-type landing system See DINGLEYINDUCTION-TYPE LANDING SYSTEM.induction welding Welding in which the heatingcurrent flowing in the workpieces is induced byan electromagnetic field.inductive capacitor A wound capacitor in whichthe inductance of the roll is controlled and specified.Such a capacitor is useful in compact filtersand in single-frequency bypassing, where the reactivecomponents are supplied by the capacitor.Compare NONINDUCTIVE CAPACITOR.Metal caseSpirally woundplatesinductive capacitorDielectricinductive circuit 1. A circuit in which inductancepredominates. 2. A (theoretical) circuit containinginductance only.inductive coupling The transfer of energy betweentwo inductors (or inductive devices) by a linkingelectromagnetic field. Also see COEFFICIENT OFCOUPLING, COUPLING, INDUCTION, and MU-TUAL INDUCTANCE.inductive feedback See MAGNETIC FEEDBACK.inductive heater See INDUCTION HEATER.inductive heating See INDUCTION HEATING.inductive kick See BACK VOLTAGE and KICK-BACK.inductive load A load device that approaches apure inductive reactance (e.g., loudspeaker andelectric motor).inductive loading In an antenna, the addition ofinductance in series with the element(s). This reducesthe resonant frequency for a radiator havinga given physical length. It can also serve toreduce the physical length required for a radiatorhaving a specified resonant frequency. CompareCAPACITIVE LOADING.inductive logic A form of reasoning that demonstratesthat a certain conclusion is highly probable,given a certain set of circumstances. This isof interest to researchers in artificial intelligence(AI). Compare DEDUCTIVE LOGIC.inductive microphone A microphone in whichsound waves vibrate a conductor or coil in astrong magnetic field, producing a correspondingalternating-current output by the resulting induction.Example: dynamic microphone.induction neutralization Neutralization of a vacuum-tuberadio-frequency power amplifier, vianegative feedback from the output to the inputthrough coupling coils.inductive reactance Symbol, X L. Unit, ohm. Thereactance exhibited by an ideal inductor, consideredas a positive imaginary-number quantity; X L= j6.28f L , where X L is in ohms, f is the frequencyin Hertz, L is the inductance in henrys, and j isthe unit imaginary number (the square root of–1). Alternatively, f can be specified in megahertz,and L in microhenries. In a pure inductive reactance,current lags 90 degrees behind voltage.Also see INDUCTANCE, INDUCTION, INDUCTOR,and REACTANCE.inductive switching Switching operations in a circuitcontaining an inductor. Switching time isinfluenced by the INDUCTANCE-RESISTANCETIME CONSTANT of the inductor; overall operationis affected by the back voltage generated bythe inductor.inductive transducer A transducer in which thesensed phenomenon causes a change in inductance(or reluctance), which, in turn, causes aproportional change in output current, voltage,frequency, or bridge balance. Compare CAPACI-TIVE TRANSDUCER, CRYSTAL TRANSDUCER,MAGNETIC TRANSDUCER, and RESISTIVETRANSDUCER.

inductive trimmer • inertial guidance 363Reactance (ohms)Reactance (ohms)600040002000L = 100 µH00 2 4 6 8 10600400200Frequency (MHz)f = 1 MHz00 20 40 60 80 100Inductance (µH)inductive reactanceinductive trimmer See TRIMMER INDUCTOR.inductive tuning Also called permeability tuning.In a radio receiver, transmitter or transceiver, theadjustment of frequency by changing the inductanceof a coil having a movable core.inductivity See DIELECTRIC CONSTANT.inductometer An instrument for measuring inductancein terms of the resonant frequency of anINDUCTANCE-CAPACITANCE (LC) circuit, inwhich L is the unknown inductance and C is calibrationcapacitance.inductor A coil of wire wound according to variousdesigns, with or without a core of ferromagneticmaterial, to concentrate the magnetic flux resultingfrom current flowing in the wire. The coiling ofthe wire and/or the addition of a ferromagneticcore increases the self-inductance compared withthat of a straight wire having the same length.Also see INDUCTANCE; INDUCTION, 1; andSELF-INDUCTANCE, 1.inductor alternator See ALTERNATOR.inductor amplifier See MAGNETIC AMPLIFIER.inductor decade See DECADE INDUCTOR.inductor microphone See INDUCTIVE MICRO-PHONE.inductors in parallel See PARALLEL INDUCTORS.inductors in parallel-series See PARALLEL-SERIES INDUCTORS.inductors in series See SERIES INDUCTORS.inductors in series-parallel See SERIES-PARAL-LEL INDUCTORS.inductor substitution box An enclosed assortmentof common-value inductors that can beswitched, one at a time, to a pair of terminals. Introubleshooting and circuit development, any ofseveral useful fixed inductances can be thus obtained.industrial data processing Abbreviation, IDP. Theapplication of digital computers and associatedequipment to industrial problems, through theclassification, sorting, storing, and manipulationof information.industrial electronics The branch of electronicsconcerned with manufacturing processes andtheir control, and with the operation and safeguardingof factories.industrial instrumentation 1. Supplementing anindustrial process with electrical and electronicmeasuring instruments. 2. The instruments usedfor the purpose defined in 1.industrial television Abbreviation, ITV. A usuallyclosed-circuit television (CCTV) system, used asan adjunct to a manufacturing process, or as ameans of communication or surveillance withinan industrial plant.industrial robot A robotic device used in industrialapplications (e.g., mining, construction,manufacturing, or laboratory work).industrial tube An (often heavy-duty) highly reliablevacuum tube designed expressly for industrialservice, such as high-power radio ortelevision broadcasting.ineffective time The period during which an otherwiseoperational computer is not being used effectivelybecause of delays or idle time.inelastic collision A collision between chargedparticles in which one gains energy and the otherloses energy.inert gas A gas that does not readily react withother elements. Inert gases include argon, helium,krypton, neon, and xenon. Such gases are oftenused in hermetically sealed devices to retard corrosion.inertance See ACOUSTIC INDUCTANCE.inertia The tendency of a body at rest to remain atrest unless acted on by an outside force. Also, thetendency for a body in motion to maintain thatmotion unless acted on by an outside force. CompareMOMENTUM.inertia in electric circuit The condition in a circuitcontaining inductance, in which a currentchange lags behind a voltage change (analogousto mechanical inertia; see INERTIA).inertial guidance A system that automaticallyguides missiles and satellites in a desired trajectorywithout the need for continuous control bysignals from a station.

364 inertia relay • information superhighwayinertia relay A time-delay relay whose operation isslowed by the addition of weights or other attachments.inertia switch A switch that can sense a disturbanceof its inertia.inference engine A circuit that gives instructionsto a computer or robot, by applying programmedrules to commands issued by a human operator.Comprises the functional portion of an EXPERTSYSTEM.infinite Pertaining to a quantity or region that hasno defined limits.infinite baffle A loudspeaker baffle having noopenings for the passage of sound from the frontto the back of the speaker cone.infinite-impedance detector A detector that offersthe very high input impedance of a gatesourcecircuit and the large-signal capabilities ofa diode detector. Audio-frequency output is takenacross the source resistor, which is bypassed forradio-frequency signals. There is no drain resistor.Drain current increases with the input signalfrom a very low value at zero signal level.RF inputL1L2C1C2−BR1C3infinite-impedance detectorR3AFoutputR2+Binfinite line See INFINITE TRANSMISSION LINE.infinite regress A reasoning pattern (either humanor machine-based) that is fallacious becauseit defines or explains something in terms of itself.infinite sample space In statistics, a samplespace having no definite limits.infinite series A mathematical series in which thenumber of terms is limitless. For example, 1 ⁄6 = 0.1+ 0.06 + 0.006 + 0.0006 + . . .infinitesimal 1. A quantity, such as a differential,that approaches zero as the limit. 2. Pertaining toa quantity whose magnitude is extremely small ornegligible. 3. Pertaining to an extremely smallchange in a quantity or measured value.infinite transmission line A theoretical transmissionline with normal characteristics, but extendingaway from the signal generator or receiver fora limitless distance.C4infinity Symbol, ∞. A quantity that is unlimited induration or dimension. A quantity that increaseswithout limit is sometimes said to “approach infinity.”infix notation A system of logical operation notationwherein operands are separated by operators,thus, A & B, where the ampersand meansAND. Compare PREFIX NOTATION.Infobahn See INFORMATION SUPERHIGHWAY.infobond On a printed circuit board, a form ofwiring on the side opposite the components. Thewiring is used in place of the foil normally onsuch a circuit board.information 1. Collectively, data or communications,excluding the symbols or signals used todescribe, present, or store them. 2. The result ofdata processing (i.e., that which is derived fromthe compilation, analysis, and distillation ofdata).information bits In an encoded signal, data charactersor digits that can be treated to give information(excluding control characters).information center A storage bank designed foruse by many different subscribers, via computer.information channel A channel through whichdata and associated signals are transmitted andreceived.information feedback system In message transmission,a control system in which intelligencereceived at a terminal is returned to the sendingunit for automatic verification.information gate A device or circuit that opensand closes an information channel.“information processor” species Anything thatuses data to derive conclusions, to produce otherdata, or to take specific actions, and whose functioningcan be explained entirely on the basis ofdata-processing operations. This includes computersand smart robots. Many (but not all) scientistsbelieve that animals are also included;some believe that human beings qualify as well.information retrieval In digital computer anddata-processing operations, the categorizing andstorage of information and the automatic recall ofspecific file items. Also see ACCESS TIME.information separator An indicator that separatesitems of information or fields in a (usuallyvariable-length) record.information storage In digital computer and dataprocessing operations, holding information inmemory pending retrieval.information superhighway 1. General expressionfor a worldwide network consisting of computers(personal, educational, industrial, and government)interconnected by telephone lines. 2. SeeINTERNET. 3. A massive, evolving, somewhatcontroversial data communication network linkingcomputers, television, and telephone systems.It uses high-speed, high-volume data links.Communication technologies include fiberoptics,radio-frequency repeaters, microwaves, geosta-

information superhighway • inherited error 365tionary satellites, and low-earth-orbit (LEO) satellitesystems.information word A character group representingstored information and managed, as a unit, byhardware or software.infra- Prefix meaning below or lower than (e.g., IN-FRARED).infrablack region In a composite video signal, theblacker-than-black region (see BLACKER THANBLACK).infradyne receiver A superheterodyne receiver inwhich the intermediate frequency is the sum ofthe signal and oscillator frequencies, rather thantheir (usual) difference.infrared Pertaining to electromagnetic energy in aband whose wavelength is longer than that of visiblelight, but shorter than that of microwave energy.infrared communication Communication by keyingor modulating infrared rays.infrared counter-countermeasure A military tacticin which action is taken against an enemy infraredcountermeasure.infrared countermeasure A military tactic usingcountermeasure methods to cripple enemy infraredequipment.infrared detector A device that senses the presenceof infrared energy. Some such detectors arebolometers, radiometers, radiomicrometers, andphotocells.infrared-emitting diode Abbreviation, IRED. Asemiconductor diode, such as the galliumarsenidetype, that emits infrared rays when acurrent passes through the p-n junction in theforward direction.infrared guidance A navigation and reconnaissancesystem using infrared rays.infrared homing The method whereby a guidedmissile uses infrared rays to guide it to its target.infrared light See INFRARED RAYS.infrared motion detector See MOTION DETEC-TOR and INFRARED.infrared photography Photography in which thescene is illuminated with infrared light or emitsinfrared rays, and the film is infrared sensitive.infrared radiation See INFRARED RAYS.infrared rays Radiation at frequencies in the IN-FRARED region. Also (somewhat mistakenly)called heat rays.infrared remote control 1. The use of an infraredlink, usually over short line-of-sight distances,for the purpose of controlling the operation ofelectronic equipment. A common example is thelocal remote control of a television receiver orhigh-fidelity system. 2. A small box, containingbuttons, a transmitter and an infrared-emittingdiode (IRED), used for local remote control of devices,such as television receivers and highfidelitysound systems.infrared spectrum The region of the electromagneticspectrum in which INFRARED radiation isfound. This band lies between the microwave radiospectrum and the visible-light spectrum.infrared therapy The use of infrared rays byphysicians and other practitioners to treat certaindisorders.infrared waves Electromagnetic waves whoselengths are greater than those of visible lightwaves, but less than those of microwaves.infrared window Any portion of the infrared spectrumin which energy is easily transmittedthrough the lower atmosphere of the earth.infrasonic Pertaining to acoustic disturbanceswhose frequencies are below the range of humanhearing (less than about 20 Hz).infrasonic intrusion detector A system that detectsthe presence of extremely low-frequencyacoustic disturbances, and sends a signal to analarm. Such INFRASONIC waves can be causedby various actions such as walking on a woodenfloor, opening or closing a door, etc.infrasonics The branch of physics dealing with IN-FRASONIC phenomena.infrasound Acoustic disturbances in the air,whose frequencies are lower than about 20 Hz,and whose wavelengths are longer than about 55feet (17 meters).inharmonic distortion Distortion in which the frequenciesof extraneous components are not harmonicallyrelated to the fundamental frequency.It is sometimes experienced when a tone-burstsignal is applied to a loudspeaker.Max.AmplitudeMin.0 1 2 3Frequency, kHzFundamentalinharmonic distortioninherent component A (usually extraneous) propertypossessed by a device because of its internalpeculiarities. Thus, an inductor has inherent capacitance;a capacitor has inherent inductance.inherited error In an extended calculation, an errorcarried through from one of the earlier steps.

366 inhibit • in-plant systeminhibit 1. In digital computer and logic operations,to prevent an action or block the input of data bymeans of a pulse. 2. To delay an action or process.inhibit gate A pulse-actuated gate circuit that actsas an INHIBITOR.inhibitor 1. A device or circuit that produces apulse or signal that prevents an action, or thatblocks data input. 2. An additive, such as an organicliquid, that delays the hardening of a mixture,such as an encapsulating compound.inhibit pulse In a computer, a drive pulse that preventsother pulses from changing the direction ofmagnetization in the cells of a magnetic corememory.inhibit signal In digital computer and logic operations,the signal that causes an INHIBIT action.initial drain 1. The current supplied by a battery orcell at its rated voltage. 2. The current deliveredby a rechargeable battery or cell when it is put touse immediately after receiving a full charge.initial failure The first failure occurring in the operationof a circuit or device.initial instructions A resident computer routineused to aid program loading. Also called initial order.initial ionizing event In the operation of a radioactivitycounter, the first event that starts thechain of similar events constituting the count.initialization A computer program instructionthat sets the value of a variable to zero.initial permeability Permeability in the low magnetizationregion of a material.initial time delay Abbreviation, ITD. In acoustics,the elapsed time between the instant the directsound wave is first heard, and the instant thefirst echoes (reflected sound waves) arrive.initiate See TRIGGER.injection 1. Introducing a signal into a circuit ordevice. 2. Introducing charge carriers (electronsor holes) into a semiconductor.injector 1. An element or electrode for INJECTION.2. A device or circuit that injects a signal into anotherdevice or circuit.injector electrode See INJECTOR, 1.ink bleed In the printing of matter for optical characterrecognition, ink flow around the characters,often making them unrecognizable to the reader.inkjet galvanometer A galvanometer whose movementcontrols the pressure of a jet of ink for makinga recording on a paper chart. Also seeLIQUID-JET OSCILLOGRAPH.inkjet printer A printer commonly used with personalcomputers, in which images are created byjets of ink sprayed directly onto the paper. Notedfor low operating noise level, high image resolution,and excellent color-reproduction capability.ink-mist recorder A graphic recorder in which theline is traced by a mist of ink.ink recorder A graphic recorder using a pen-andinkstylus.ink squeeze-out In the printing of matter for opticalcharacter recognition, the squeezing of inkfrom a character’s center.ink-vapor recorder See INK-MIST RECORDER.in-lb Abbreviation of INCH-POUND.inlead The part of an electrode that passes throughthe external shell or case of a component.inline procedure The main portion of a COBOLcomputer program, responsible for the primaryoperations.inline processing The action peculiar to a systemthat processes data almost immediately upon receipt(i.e., one that need not be capable of storinga lot of unprocessed data).inline readout In digital computer operations, areadout device that displays digits side-by-sidehorizontally.inline subroutine A subroutine that must be writteneach time it is needed, as compared with onethat can be accessed by a program branch.inline tuning Tuning of all the stages of a channel,such as an intermediate-frequency amplifier, tothe same frequency.inner conductor The inner wire or rod of a coaxialcable or coaxial tank. It generally carries the signal,and is isolated from the surrounding environmentby the grounded OUTER CONDUCTOR.inorganic Consisting of materials other than carboncompounds; therefore, it is not related to livingthings.inorganic electrolyte Any electrolyte that is completelyinorganic: containing no compounds ofcarbon.in phase The condition in which alternating or pulsatingwaves or wave phenomena are in step witheach other at all points. Compare OUT-OF-PHASE.in phasein-phase carrier See I-PHASE CARRIER.in-phase current Resistive current in an ac circuit(i.e., current in phase with voltage). CompareQUADRATURE CURRENT.in-phase feedback Feedback in phase with a mainsignal. Also called POSITIVE FEEDBACK and RE-GENERATION.in-phase voltage A voltage that is in phase withanother (reference) voltage.in-plant system An automatic data communicationssystem within a specific building or complex.

input • input/output module 367input 1. Energy or information delivered or transferredto a circuit or device. 2. The terminals of adevice or circuit to which energy or information isapplied. 3. To deliver or transfer energy or informationto a circuit or device (as to input datafrom a computer peripheral to memory).input admittance Symbol, Y i . The internal admittanceof a circuit or device, as “seen” from the inputterminals; the reciprocal of input impedance.Compare OUTPUT ADMITTANCE.input area In a computer memory, an area setaside for data input from a source other than aprogram.input bias current The input bias required by anoperational amplifier.input capacitance Symbol, C i . 1. The internal capacitanceof a circuit or device, as “seen” from theinput terminals. Compare OUTPUT CAPACI-TANCE. 2. The grid-cathode capacitance of a vacuumtube.input capacitor 1. In a capacitance-coupled circuit,the input coupling capacitor. Compare OUT-PUT CAPACITOR. 2. The first capacitor in acapacitor-input filter (i.e., that capacitor electricallynearest the rectifier output electrode).input choke The first choke in a choke-input filter(i.e., that choke electrically nearest the rectifieroutput electrode, when no preceding capacitor isused).input circuit The circuit or subcircuit constitutingthe input section of a network or device. CompareOUTPUT CIRCUIT.input clamp current The current from an inputwhen the input is in a state below ground potential.A test for the input clamp diode.input conductance Symbol, G i . The internal conductanceof a circuit or device, as “seen” from theinput terminals; it is the reciprocal of INPUT RE-SISTANCE. Compare OUTPUT CONDUCTANCE.input coupling capacitor See INPUT CAPACITOR,1.input coupling transformer See INPUT TRANS-FORMER.input current Symbol, I i . 1. The current deliveredto a circuit or device. 2. Current flowing in the inputleg or electrode of a circuit or device.input device 1. A device, such as an input transformer,that couples energy or information to acircuit or device. Compare OUTPUT DEVICE. 2. Adevice through which another device receivesdata.input equipment Collectively, input devices usedwith a computer.input error voltage In an operational amplifier,the error voltage at the input terminals when afeedback loop operates around the amplifier.input extender A diode network that provides increasedfan-in for a logic circuit. Also see FAN-IN,1.input gap In a velocity-modulated tube, the gap inwhich the electron stream is initially modulated.input guarding A method of eliminating stray couplingamong inputs in an integrated circuit. Ashield is provided at the input; it is driven to followalong with the input voltage. This ensures lowloss and minimum errors resulting from unwantedcoupling.input impedance Symbol, Z i . The internal impedanceof a circuit or device, as “seen” from theinput terminals. Compare OUTPUT IMPEDANCE.input limited The processing time limitation imposedby an input unit on the speed of a programrun.input noise current At the input of an integratedcircuit, the root-mean-square (rms) or peak-topeak(pk-pk) noise current existing within a specifiedrange of frequencies.input noise current density The noise current,usually expressed as a root-mean-square (rms)value, in a band 1 Hz wide around a given frequency.input noise voltage At the input of an integratedcircuit, the root-mean-square (rms) or peak-topeak(pk-pk) noise voltage existing within a specifiedrange of frequencies.input noise voltage density The noise voltage, usuallyexpressed as a root-mean-square (rms) value,in a band 1 Hz wide around a given frequency.input offset current In an operational amplifier,the difference between the currents going to theinput terminals when the output is zero.input offset voltage In an operational amplifier,the potential that has to be applied between theinput terminals for a zero output voltage.input/output Abbreviation, I/O. 1. Data transmittedto, or received from, a computer. 2. A terminalthrough which data is transmitted to, or receivedfrom, a device.input/output bound A condition affecting a systemin which the time consumed by input andoutput operations is greater than that requiredfor other processes.input/output buffer A computer memory areaspecifically reserved for the receipt of data comingfrom or going to a peripheral.input/output control The part of a computer systemthat coordinates activity between a centralprocessor and peripherals.input/output equipment 1. In digital computeroperations, devices for entering information intothe computer or for reading information from it.Examples: keyboard, mouse, display, and opticalscanner. 2. In robotics and artificial intelligence,a data link between a controller and one or morerobots, and/or between or among two or morecontrollers.input/output isolation Arrangement or operationof a circuit or device so that there is no directpath between input and output terminals aroundthe circuit or device. Also see ISOLATION.input/output module See INPUT/OUTPUTEQUIPMENT.

368 input/output routine • insect robotinput/output routine A routine for simplifying theprogramming of standard input/output equipmentoperations.input/output switching The allocation of morethan one channel to peripherals for communicationswith a central processor.input/output voltage differential At a given loadcurrent, the potential difference that is necessaryfor an integrated circuit to operate according toits output voltage specifications.input power Symbol, P i . 1. The power presented tothe input terminals of a circuit or device. Alsocalled POWER INPUT. Compare OUTPUTPOWER. 2. The operating power of a circuit or device(i.e., the power-supply requirement).input protection In an integrated circuit, ameans of preventing damage to the device fromexcessive voltage at the input, such as transientspikes or the result of malfunctioning of someother circuit.input record 1. A computer record of immediateinterest that is ready for processing. 2. During acomputer program run, a record read into memoryfrom an input device.input recorder A device that makes a permanentrecord of the signals or data input to a circuit orsystem.input register In a computer, a register that receivesdata from a peripheral relatively slowly andthen passes it on to a central processor at a fasterspeed as a sequence of informational units. Alsosee REGISTER.input resistance Symbol, R i . The internal resistanceof a circuit or device, as “seen” from the inputterminals. Compare OUTPUT RESISTANCE.input resonator In a velocity/modulated tube, theresonator in which electron bunching occurs.input routine A computer program section thatmanages data transferal between an externalstorage medium and a memory input area.input section 1. See INPUT ROUTINE. 2. See IN-PUT AREA.input sensitivity 1. The level of input-signal amplitudethat will result in a certain signal-to-noiseratio at the output of a device. The specified signal-to-noiseratio is usually 10 or 20 dB. 2. Thelevel of input signal in a frequency-modulated device,required to produce a specified amount ofnoise quieting. The specified level of noise quietingis usually 20 dB. Alternatively, 12-dB SINAD(ratio of signal to the level of noise and distortion)can be specified. 3. The minimum level of inputvoltage required to actuate a logic gate.input signal The signal (current, voltage, andpower) presented to the input terminals of a circuitor device for processing.input tank In a double-tuned stage of a transmitteror power generator, the tank circuit in whichthe input signal is resonated. This is generallythe base or gate circuit. Compare OUTPUTTANK.InputTankinput tankOutputinput terminals Terminals (usually a pair) associatedwith the input section of a circuit or device.Compare OUTPUT TERMINALS.input transformer The transformer that deliverssignal voltage or power to the input circuit of anetwork or device. Compare OUTPUT TRANS-FORMER.input uncertainty The combination of all parametersthat result in adverse behavior in an operationalamplifier.input unit In a digital computer, the device or circuitthat receives information from peripherals.input voltage 1. Symbol, E i or V i . The voltage presentedto a circuit or device. Compare OUTPUTVOLTAGE, 1. 2. The voltage across the input legor electrode of a circuit or device. Compare OUT-PUT VOLTAGE, 2.input-voltage drift For an integrated circuit (IC),the time- and temperature-dependent change inoutput voltage divided by the IC’s open-loop voltagegain.input-voltage offset For a differential amplifier,the input signal voltage at the differential inputthat results in zero output voltage.input-voltage range The range, in volts, overwhich the input voltage can fluctuate in an integratedcircuit so that the common-mode rejectionratio (CMRR) specifications are not exceeded.input winding The signal winding of a magneticamplifier.inquiry A programmed request for informationfrom storage in a computer.inquiry display terminal A video display/keyboardterminal used to make an inquiry to a computersystem, and display the response.inquiry station A terminal from which an inquirycan be sent to a central computer.inrush The initial surge of current that occurswhen voltage is first applied to the primary windingof a transformer with no load connected.inscribe To convert data to a form on a documentthat is readable by a character-recognition device,as through the use of magnetic ink, for example.insect robot A member of a fleet of robots, all ofwhich are under the control of a single computer.+

insect robot • instantaneous speech power 369The term arises because the system functionslike an anthill or beehive, in which the individualmachines are “stupid,” but the system as a wholeis “smart.” Such robots often have six legs, likeinsects. Compare AUTONOMOUS ROBOT.insert A (usually metallic) bushing that can bemolded into a plastic part (or pressed into it aftermolding is completed) to provide a bearing sleeveor threaded hole.insert core A ferromagnetic core whose positioncan be adjusted to vary the inductance of the coilsurrounding it.insert edit 1. In magnetic tape recording, a sectionof tape on which new audio is recorded over existingaudio. 2. The process of recording new audioover existing audio in a defined interval on amagnetic tape.insertion gain In a circuit or system, the gain resultingfrom the amplifier inserted into the system;it is usually expressed in decibels. CompareINSERTION LOSS.insertion loss Loss of energy or gain by placingcertain devices or subcircuits (filters, impedancematchers, etc.) in a circuit. It is usually expressedin decibels. Also see INSERTION RESISTANCE.insertion phase shift The difference in phase producedby a circuit installed in an electrical transmissionline.insertion resistance The resistance of a componentor instrument that is introduced intoa circuit. Thus, the internal resistance of amicroammeter becomes an insertion resistancein the circuit in which the meter is connected forcurrent measurement.inside antenna See INDOOR ANTENNA.inside diameter Abbreviation, ID. The innermostdiameter of a body or figure having two concentricdiameters. Compare OUTSIDE DIAMETER.inside lead See START LEAD.inside radiation See INDOOR RADIATION.inside spider A voice-coil centering device within aloudspeaker.inst 1. Abbreviation of INSTRUMENT or INSTRU-MENTATION. 2. Abbreviation of INSTANT.instability Inconsistency in the operation of a circuitor device, in the parameters of a device, or inan electrical quantity. It can be attributed to anumber of causes, including temperature, loading,age, humidity, negative resistance, and radioactivity.installation tape number An identification numbergiven to a reel of magnetic tape by the processingfacility.instant Abbreviation, inst. The point in time atwhich an event occurs, or at which a quantityreaches a particular value.instantaneous Occurring at a specified moment,or instant, of time.instantaneous amplitude The amplitude, specifiedin amperes, volts, or watts, of a signal, specifiedat a particular moment in time.Amplitudet 1(Instant)t 2(Instant)instantaneous amplitudeTimeinstantaneous automatic gain control Abbreviation,IAGC. An automatic gain control whose operationalmost immediately follows a change insignal amplitude.instantaneous automatic volume control Abbreviation,IAVC. An instantaneous automatic gaincontrol system for the immediate control of volumein receivers and audio-frequency amplifiers.instantaneous companding A form of compandingthat operates according to the instantaneousamplitude of the input signal.instantaneous contacts Timer contacts that openor close almost immediately upon application ofthe control signal.instantaneous current Symbol, i or I i . The value ofan alternating or fluctuating current at a particularinstant in the cycle.instantaneous disc A phonograph disc that can beplayed back immediately after being recorded.instantaneous frequency The frequency of a signalat a particular moment in time. The instantaneousfrequency changes in frequencymodulatedor phase-modulated signals.instantaneous power 1. In a single-sideband, suppressed-carriersignal, the power at a specified instantin time. It varies between zero and the peakenvelope power (PEP). 2. The output power of anaudio amplifier at a specified instant in time.instantaneous power output The rate of powerdelivery to a load at a given instant.instantaneous relay A relay, such as a fully electronictype (having no moving parts), that showsvirtually no delay in its operation.instantaneous sample A measurement obtainedby INSTANTANEOUS SAMPLING.instantaneous sampling The measurement ofwave or signal amplitude at a specific moment intime. See, for example, INSTANTANEOUS CUR-RENT and INSTANTANEOUS VOLTAGE.instantaneous speech power In the output of anaudio amplifier, the instantaneous value of powerin a speech wave, as opposed to that in a sinewave. Also see INSTANTANEOUS VALUE andSPEECH POWER, 1.

370 instantaneous value • instrument transformerinstantaneous value The magnitude of a fluctuatingvalue at a selected instant in time. See,for example, INSTANTANEOUS CURRENT,INSTANTANEOUS POWER, INSTANTANEOUSSPEECH POWER, and INSTANTANEOUS VOLT-AGE. Compare AVERAGE VALUE, and EFFEC-TIVE VALUE.instantaneous voltage Symbol, e or E i . The valueof an alternating or fluctuating voltage at a particularinstant in the cycle.instant loop In electronic security applications, acircuit that actuates an alarm without delaywhen an intrusion is detected.instruction In digital computer operations, a set ofbits defining an operation. Consists of an operationcode specifying the operation to be performed,one or more operands or their addresses,and one or more modifiers or their addresses (tomodify the operand or its address).instruction address In a computer memory, theaddress of a location containing an instruction.instruction address register Also called programcounter. A register that holds instruction addressesso that the retrieval of the instructionsfrom memory can be controlled during a programrun.instruction code Also called INSTRUCTION SET.The symbols and characters that compose thesyntax of a computer programming language.instruction format In a computer’s basic machinecode, the part that specifies how characters ordigits are used to represent the codes within themachine’s instruction set.instruction modification In a computer instruction,a change in the instruction code that makesthe computer do a different operation when theroutine containing the code is encountered again.instruction register A register in a computer containingthe address of the current instruction.Also called CONTROL REGISTER (abbreviation,CR).instruction set 1. The range of commands thatform a programming language. 2. See INSTRUC-TION CODE.instruction storage A memory circuit that storescomputer instructions or programs.instruction time The time required for a controlunit to analyze and implement a computer programinstruction.instruction word In digital computer programming,a word containing the instruction code(type of operation to be performed) and the addresspart (location of the associated data in storage).instrument A device for measuring electricalquantities or the performance of electronic equipment.A meter provides a direct indication; otherdevices, such as a bridge, must be adjusted, themeasured quantities being determined from oneor more adjustments (sometimes augmented withcalculations).instrumental error See INSTRUMENT ERROR.instrument amplifier Also called INSTRUMENTA-TION AMPLIFIER. A high-gain, wideband amplifierthat increases the sensitivity of aninstrument (such as an oscilloscope, meter, orgraphic recorder).instrument-approach system See INSTRUMENTLANDING SYSTEM.instrumentation Planning and providing instrumentsand instrument systems for the collectionand, sometimes, storage and analysis of data.instrumentation amplifier 1. A form of integrated-circuitvoltage amplifier designed for highlinearity, high input impedance, and highcommon-mode rejection. It is intended for usewith electronic instruments. 2. See INSTRUMENTAMPLIFIER.instrument chopper A refined chopper for convertinga direct-current (dc) signal to alternatingcurrent (ac) for an ac instrument, such as a voltmeteror recorder.instrument error Discrepancy in measured quantitiesresulting from inaccuracy of the instrumentused, insertion resistance, environmental factors,operator error, etc.instrument flight Also called blind flight. Aircraftflight guided by navigational instruments andsignals alone. Required when visibility is extremelypoor.instrument fuse A fast-acting, low-current fuseused to protect a sensitive instrument, such as agalvanometer, milliammeter, and/or microammeter.instrument lamp A light or lamp that illuminatesthe face of an instrument to facilitate viewing inthe dark.instrument landing Also called blind landing. Aircraftlanding guided entirely by instruments. Requiredwhen visibility is poor and when landing isimperative at a given location at a given time.instrument landing station The radio or radarstation in a blind-landing system (see INSTRU-MENT LANDING SYSTEM).instrument landing system Abbreviation, ILS.The complete instrument and signal system (onthe ground or in aircraft) required for an INSTRU-MENT LANDING.instrument multiplier See MULTIPLIER PROBE,1.instrument preamplifier An external, sensitiveamplifier for an instrument that has an internalinput amplifier. Also see INSTRUMENT AMPLI-FIER.instrument relay See METER RELAY.instrument resistance See METER RESISTANCE.instrument shunt A resistance connected in parallelwith a current-measuring instrument, usedto increase the range of currents that can be measured.instrument transformer A transformer used tochange the range of an alternating-current meter.

instrument transformer • Integrated Services Digital Network 371instrument shuntFor ammeters, it is called a current transformer;for voltmeters, it is called a potential transformer.insulant A nonconducting material, used to preventthe flow of electric current between or amongpoints. See INSULATOR, 1.insulated Isolated from conductors by an INSU-LANT.insulated-gate field-effect transistor Abbreviation,IGFET. See METAL-OXIDE SILICON FET.insulated resistor A resistor around which ismolded a nonconducting material, such as vitreousenamel or a plastic.insulating tape Electrical insulation in the form ofa thin, usually adhesive, strip of fabric, paper, orplastic.insulation 1. A coating of dielectric material thatprevents a short circuit between a conductor andthe surrounding environment. 2. The applicationof a dielectric coating to an electrical conductor.3. Electrical separation between or among differentcomponents, circuits, or systems.insulation breakdown Current leakage through,and rupture of, an insulating material because ofhigh-voltage stress.insulation ratings Collectively, the dielectric constant,dielectric strength, power factor, and resistivityof an insulating material. Sometimes includedare such physical properties as rupturestrength, melting point, etc.insulation resistance The very high resistance exhibitedby a good insulating material. It is expressedin megohms (or higher units of resistance)for a sample of material of stated volume or area.insulation system Collectively, the materialsneeded to insulate a given electronic device.insulator 1. A material that, ideally, conducts noelectricity; it can, therefore, be used for isolationand protection of energized circuits and components(also see DIELECTRIC). Actually, no insulatoris perfectly nonconductive (see, for example,INSULATION RESISTANCE). 2. A molded piece ofsolid insulating material, used to electrically isolateconductors—especially in antenna systemsand power transmission lines. 3. Any body madefrom an insulating material.insulator arcover A sudden arc, or flow of current,over the surface of an insulator, because of excessivevoltage.integer A positive or negative whole number, asopposed to a fraction or mixed number.integral 1. Also called indefinite integral and antiderivative.For given mathematical function f,function g, whose derivative is equal to f. 2. Alsocalled definite integral. The area under a curve ofa function, between two vertical lines defined bytwo specific points in the domain of the function.3. The part of a number to the left of the radixpoint. 4. Pertaining to integers (positive or negativewhole numbers) or quantities that can berepresented by integers.integral action In automatic control operations, acontrol action delivering a corrective signal proportionalto the time that the controlled quantityhas differed from a desired value.integral contact In a relay or switch, a contactthat carries current to be switched.integral-horsepower motor A motor rated at onehorsepower.integral multiple A whole multiple of a number.Thus, a harmonic is an integral multiple of fundamentalfrequency f: 2f, 3f, 4f, etc.integral number See INTEGER.integrate 1. To perform the function of mathematicalor electrical INTEGRATION. 2. To construct acircuit on a piece of semiconductor material.integrated Constructed on a single piece of material,such as a semiconductor wafer.integrated amplifier An audio-frequency (AF) amplifierhaving a preamplifier, intermediate amplifier,and output amplifier on a single chassis.integrated capacitor In an integrated circuit, afixed capacitor in which one plate is a layer of materialdiffused into the substrate, the dielectric isa thin-oxide film grown on top of the first layer,and the other plate is a metal layer deposited ontop of the oxide film.integrated circuit Abbreviation, IC. A circuitwhose components and connecting “wires” aremade by processing distinct areas of a chip ofsemiconductor material, such as silicon. Classifiedaccording to construction (e.g., monolithic IC,thin-film IC, hybrid IC).integrated data processing Abbreviation, IDP.The detailed electronic classification, sorting,storage, and mathematical processing of datawithin a coordinated system of equipment, usuallyat one location.integrated electronics The branch of electronicsthat is concerned with the design and fabricationof integrated circuits.integrated resistor See DIFFUSED-LAYER RESIS-TOR.Integrated Services Digital Network Abbreviation,ISDN. A communications network or connectionintended primarily for Internet accessvia telephone lines. Allows significantly higherdata speed than is possible with a conventionalanalog connection. In addition, it is possible touse a digital system, such as a computer, onlinesimultaneously with an analog voice conversation.

372 integrating circuit • interactive photovoltaic systemintegrating circuit See INTEGRATING NETWORK.integrating galvanometer A device for measuringthe change in electric flux produced in a coil in anelectric field. Even very slow changes can be measured.integrating meter An instrument whose indicationis a summation (usually) of an electricalquantity that is time-dependent (e.g., amperehourmeter and watt-hour meter).integrating motor An electric motor that followsthe integral of the input signal. The angle of rotationof the motor shaft is equal to the integral ofthe input waveform.integrating network A four-terminal networkwhose output voltage is proportional to the timeintegral of the input voltage. It can be a passiveresistance-capacitance (RC) circuit or it can usean operational amplifier. Compare DIFFERENTI-ATING NETWORK.InputInput−+integrating networksOutputOutputintegrating photometer A photometer whosereading is the average candlepower at all anglesin one plane.integration 1. The process of determining amathematical function when its derivative isgiven. 2. The processing of a signal by an INTE-GRATOR circuit. 3. Collectively, the processesby which an INTEGRATED CIRCUIT is manufactured.integrator 1. See INTEGRATING NETWORK. 2. Adevice having an output variable whose value isproportional to the integral of one variable, withrespect to another, or is proportional to the integralof an input variable, with respect to elapsedtime.intelligence 1. Meaningful data that modulates acarrier [e.g., the voice or music in a frequencymodulated(FM) radio signal, or the image in atelevision signal]. 2. Also called machine intelligence.The quality of a system or device, especiallya computer, that allows it to “learn” (i.e., tobetter its capability by repeatedly operating on agiven problem).intelligence bandwidth 1. The bandwidth necessaryto convey a specified amount of data withina certain period of time. 2. The total bandwidth ofone complete signal channel in a communicationsor broadcast system.intelligence signal 1. A signal that conveys dataor information. 2. The modulating waveform in acommunications or broadcast transmission.intelligent network Abbreviation, IN. 1. In general,any advanced and sophisticated communicationsnetwork, particularly a broadband digitalnetwork. 2. A network designed to readily accommodatenew technologies and services, such asvideoconferencing, interactive television, or remotecontrol.intelligent terminal A computer terminal (e.g., aninput/output video display/keyboard unit) thatthrough its circuitry (i.e., by use of a microprocessor)has some data-processing ability.intelligibility tests Tests that measure the coherenceof electronically reproduced speech.intensification of image See IMAGE INTENSIFI-CATION.intensifying ring In some electrostatic cathoderaytubes, an internal metal ring serving as an extraanode to accelerate the beam and, thus,brighten the image.intensity The degree or extent of a phenomenon(such as amplitude, brightness, loudness, power,force, etc.).intensity control In an oscilloscope circuit, thepotentiometer that adjusts the direct-currentvoltage on the control electrode of the cathoderaytube and, accordingly, the brightness of theimage. Also called BRIGHTNESS CONTROL andBRILLIANCE CONTROL.intensity level 1. A measure of sound magnitude,expressed in decibels, with respect to a value ofone microwatt per square centimeter (10 -6W/cm 2 ) at sea level in the atmosphere. 2. The settingof the brightness control in a cathode-raytubedevice.intensity modulation 1. Modulation of electronbeamintensity in a cathode-ray tube. Also calledz-axis modulation. 2. Sometimes, the video-signalmodulation in a television image.intensity-modulation amplifier The z-axis amplifierin an oscilloscope. Also see INTENSITY MOD-ULATION.interaction The (sometimes mutual) influence ofone circuit or device on the behavior of another,as in induction.interactive display A computer display devicewith which its operator can supply data to thecomputer in response to what is displayed. Example:touch screen.interactive graphics A computer graphics systemusing a cathode-ray tube to draw or modify threedimensionalrepresentations.interactive photovoltaic system A solar-powerplant that operates in conjunction with the utility

interactive photovoltaic system • interference stub 373companies. Energy is sold to the companies duringtimes of daylight and minimum usage, and isbought back from the companies at night or duringtimes of heavy usage. The principal advantageof this system is that the user can keep usingelectricity (by buying it all from the utilities) if thesolar-energy system breaks down. But such asystem does not provide the independence fromutility companies that some users desire. CompareSTAND-ALONE PHOTOVOLTAIC SYSTEM.interactive program A computer program inwhich the machine and its operator engage intwo-way communication. Most personal computingsoftware is of this type, in contrast to programsthat carry out all their functions withoutoperator intervention (other than initialization).interactive television Television provided to consumers,in which viewers can transmit data, aswell as receive it. For example, a survey might beconducted in which viewers are polled and sendin their responses. Another example: productsmight be ordered while viewing an advertisement.interactive mode See CONVERSATIONAL MODE.interbase resistance The internal resistance betweenthe bases of a unijunction transistor.interblock A part of a computer program or ahardware device that will prevent interference betweenparts of a computer system.interblock space 1. On a magnetic tape, the spacebetween recordings, caused by starting and stoppingthe tape. 2. On magnetic tape used as acomputer storage medium, the interval betweenrecorded blocks.intercarrier receiver A television (TV) receiver circuitin which video, sound, and sync componentsof the composite TV signal are amplifiedtogether in the radio-frequency (RF), intermediate-frequency(IF), and video IF stages; then theyare separated in the video detector and video amplifierstages. Compare SPLIT-SOUND RE-CEIVER.intercept receiver In military service, a search receivertuned over a wide band of frequencies to locateand evaluate enemy signals.interchangeability The ability of one componentto substitute directly for another component ofthe same kind. Example: capacitor interchangeability,transistor interchangeability. Also see RE-PLACEMENT.intercharacter space The three-unit interval betweenletter symbols in telegraphy. Compare IN-TERWORD SPACE.intercom A comparatively simple two-way telephoneor low-power radio system for use on thepremises of a home or business.intercommunicator See INTERCOM.interconnection 1. A mutual connection of separatecircuits. 2. The interconnection of two ormore separate power-generating systems.interdigital contacts A pair of contacts with “fingers”that are plated, printed, or deposited on thesurface of a resistor material or semiconductorsubstrate. The fingers of each contact are interconnectedat one end, the fingers of one contactbeing interleaved with those of the other.interdigital tube A magnetron having a cathodesurrounded by anode segments that are alternatelyinterconnected at opposite ends in themanner of INTERDIGITAL CONTACTS.interelectrode capacitance Capacitance betweenor among electrodes—especially between theplate and control grid of a vacuum tube.interelement capacitance Internal pn-junctioncapacitance in a semiconductor device, such as adiode or transistor.interface 1. The circuitry that interconnects andprovides compatibility between a central processorand peripherals in a computer system. 2. Collectively,the hardware and software that allows acomputer to interact with its operator. 3. To providean efficient pathway for data between two devicesor systems. 4. The meeting of surfaces orregions in a material. 5. The surface of a bodythat mates with another body similar or identicalto it.interface resistance See CATHODE INTERFACE.interface routine A computer program routinethat links one system to another.interfacial connection A connection that runsthrough a printed-circuit board and joins circuitjoints on opposite faces of the board.interference 1. In communications, degradationof reception caused by noise or undesired signals.2. The interaction of acoustic or electromagneticwaves from more than one source, especiallywhen they are of the same frequency, producing acharacteristic INTERFERENCE PATTERN of highamplitudeand low-amplitude regions.interference attenuator A device or mode of operationthat reduces the amplitude of interference.interference eliminator A filter, wavetrap, or similardevice that removes interfering signals ornoise. Also see INTERFERENCE.interference filter See INTERFERENCE ELIMINA-TOR.interference pattern A regular pattern of highamplitudeand low-amplitude regions, lobes, orbands, produced when waves of identical frequencyfrom two or more sources combine invarying phase. Such patterns can be observedwith sound, radio waves, infrared, visible light,ultraviolet, X rays, and gamma rays. The phenomenonis of interest in acoustic engineering,the design of radio antenna systems, and inphysics (particularly optics).interference stub A length of twin-lead feeder cutto appropriate length, connected to the antennainputterminals of a television receiver, andshort-circuited at the opposite end. A stub of thecorrect length resonates at the frequency of an interferingsignal and, acting as a wavetrap, keepsit out of the receiver. Also see STUB.

374 interference trap • intermittent commercial and amateur serviceinterference trap A wavetrap that suppresses interferingsignals at the rejection frequency of thetrap.interferometer 1. A radio telescope having two antennasspaced at a distance of many wavelengths,providing much greater resolution than asingle antenna. Pioneered by M. Ryle of Englandand J.L. Pawsey of Australia. 2. Any device thatdisplays an INTERFERENCE PATTERN for testingor experimental purposes.interfix A method used in information-retrievalsystems that eliminates ambiguity in the responsesto inquiries by describing the relationshipbetween keywords in a record.Interframe A method of digital IMAGE COMPRES-SION developed by MPEG (Moving Picture ExpertsGroup). It operates by eliminating redundantdata from between image frames. Compare IN-TRAFRAME.interharmonic beats Beat notes produced by variouscombinations of the harmonics of a signal.interim storage See TEMPORARY STORAGE.interior label On a magnetic tape used as a computer-storagemedium, a label recorded at the beginningof the tape. Compare EXTERIOR LABEL.interior protection 1. In electronic security applications,a set of sensors contained entirely withinthe region to be protected. 2. The installation andoperation of a security system whose sensors areall within the region to be protected.interlace A form of data storage in which portionsof the data are stored in alternate locations in thetape or disk.interlaced field A video image field produced byINTERLACED SCANNING.interlaced scanning In the display of a video image,the alternate presentation of the even- andodd-line fields. This process increases the obtainableimage resolution for a given refresh rate, butcan result in “jerkiness” of the image when rapidmotion is portrayed.interlace factor A number expressing the extentto which two fields are interlaced. Also see IN-TERLACED SCANNING.interleaving In multiprogramming, the inclusionin a program of segments of another program sothat both can be effectively executed simultaneously.interlock switch See ELECTRICAL INTERLOCK.intermediate amplifier See BUFFER.intermediate frequency Abbreviation, IF. In a superheterodynecircuit, the frequency of the signalthat results from beating the incoming signalwith the signal produced by the local oscillator.intermediate-frequency amplifier In a superheterodynecircuit, the fixed-frequency amplifierthat boosts the intermediate-frequency signal.Also see INTERMEDIATE FREQUENCY.intermediate-frequency channel Usually, the intermediate-frequencyamplifier in a superheterodynecircuit, but sometimes including the secondInputTunedto IF+Tunedto IFintermediate-frequency amplifierdetector, automatic gain control (AGC), and oscillatorstages.intermediate-frequency converter See IF CON-VERTER.intermediate-frequency interference Interferencefrom signals at the intermediate frequencyof a receiver or instrument.intermediate-frequency selectivity The selectivityof an intermediate-frequency (IF) channelalone, usually determined by the characteristicsof the bandpass filter(s) in the IF channel.intermediate-frequency transformer A couplingtransformer designed for use in an intermediatefrequencyamplifier.intermediate-puck drive In a tape recorder, aspeed-reducing drive system in which an intermediatewheel conveys motion from the motorshaft to the rim of the flywheel.intermediate puck wheel See IDLER WHEEL.intermediate repeater In wire telephony, a repeaterinserted into a line or trunk at some pointother than the end.intermediate result Obtained during a programrun or the execution of a subroutine, a result thatis used again as an operand in deriving the finalresult.intermediate section Any of the internal sectionsof a multisection filter. Thus, the middle sectionof a three-section filter.intermediate storage In a computer system, astorage medium for temporarily holding totals orworking figures. Also called WORK AREA.intermediate subcarrier A modulated or unmodulatedsubcarrier that modulates either a carrier oranother intermediate subcarrier.intermittent 1. Pertaining to a circuit fault, suchas an open or short circuit, that occurs some ofthe time, but not all the time. 2. See INTER-MITTENT CONDITION. 3. Pertaining to a phenomenonthat is observed some of the time, butnot all the time; sporadic. 4. Pertaining to a DUTYCYCLE greater than zero, but less than 100 percent;usually between 25 and 50 percent.intermittent commercial and amateur serviceAbbreviation, ICAS. Operation of equipment,such as radio transmitters, for short, irregular+Output

intermittent commercial and amateur service • international farad 375periods, as in amateur (hobbyist) activity or infrequentcommercial service. ICAS ratings arehigher than continuous commercial service (CCS)ratings. Compare CONTINUOUS COMMERCIALSERVICE.intermittent condition A defect in a circuit or devicethat causes erratic and unreliable operation.The cause of such a problem is often difficult todetermine.intermittent dc See INTERMITTENT DIRECTCURRENT.intermittent direct current A regularly pulsedunidirectional current. Also called PULSATINGDIRECT CURRENT.intermittent duty A DUTY CYCLE of less than100 percent, but greater than zero. Generally, anoperating duty cycle of 25 to 50 percent.intermittent-duty rating The dissipation orpower rating of a component, circuit, or system,under conditions of intermittent use, usually a25-percent to 50-percent DUTY CYCLE.intermittent operation Operation characterizedby often long nonoperating intervals. Intermittentoperation is often random, whereas on-off operationtends to be regular.intermittent signal An interrupted signal resultingfrom the intermittent operation of a circuit ordevice.intermodulation Abbreviation, IM. 1. The (usuallyundesired) modulation of one signal by another,caused by nonlinear processing of the signals. 2.The heterodyning of components in the sidebandsproduced by an amplitude-modulated (AM)or single-sideband (SSB) transmitter.intermodulation distortion Abbreviation, IMD. 1.Distortion products in the output of an amplitude-modulated(AM) or single-sideband (SSB)transmitter, caused by heterodyning of componentsin the sidebands. 2. Distortion products inthe output of an audio amplifier, caused by heterodyningof the fundamental components. 3.The extent to which distortion as defined in 1occurs. See INTERMODULATION-DISTORTIONPERCENTAGE.intermodulation-distortion meter See INTER-MODULATION METER.intermodulation-distortion percentage Abbreviation,IDP. The degree to which a low-frequencytest signal modulates a higher-frequency test signalwhen both are applied simultaneously (in aprescribed amplitude ratio) to a device under test;IDP = 100(b – a)/a, where a is the peak-to-peakamplitude of the unmodulated high-frequencywave and b is the peak-to-peak amplitude of themodulated high-frequency wave.intermodulation meter An instrument for measuringpercentage of intermodulation distortion(IMD). The instrument combines a dual-frequencysignal generator, filter circuits, and percent-ofmodulationmeter. Also see INTERMODULATION-DISTORTION PERCENTAGE.intermodulation noise Electrical noise producedin one channel by signals in another; it is causedby INTERMODULATION.internal absorptance The ratio of flux absorbed ina substance to the flux leaving at the entry surfaceof the substance. It does not include energyreflected at the entry surface.internal amplification In a radioactivity countertube, current enhancement resulting from cumulativeionization initiated by an ionizing particle.internal arithmetic In a digital computer, arithmeticoperations performed in the computer, asopposed to those performed by peripherals.internal impedance The impedance in a device, asopposed to that added from the outside. CompareINTERNAL RESISTANCE.internal input impedance The impedance in a circuitor device, as “seen” from the input terminals.Compare INTERNAL OUTPUT IMPEDANCE.internal input resistance The resistance in a circuitor device, as “seen” from the input terminals.Compare INTERNAL OUTPUT RESISTANCE.internal noise Electrical noise generated within acircuit, as opposed to that picked up from outside.Such noise comes from transistors, diodes,integrated circuits, resistors, and any other componentthrough which current flows.internal output impedance The impedance in acircuit or device, as “seen” from the output terminals.Compare INTERNAL INPUT IMPEDANCE.internal output resistance The resistance in a circuitor device, as “seen” from the output terminals.Compare INTERNAL INPUT RESISTANCE.internal resistance 1. The resistance of a device,as opposed to added resistance. See, for example,METER RESISTANCE. 2. In a cell or battery, theequivalent resistance, resulting from imperfectconductivity of the electrolyte and electrodes,which limits the maximum deliverable current.internal thermal shutdown In an integrated circuit,the junction temperature at which thermalshutdown occurs. It is generally indicated in degreesCelsius (°C).internal transmittance The ratio of flux reachingthe exit surface of a material to the flux leavingthe entry surface. Reflection is not taken into account.The sum of internal transmittance and IN-TERNAL ABSORPTANCE is always equal to 1.international broadcast station A shortwavebroadcast station transmitting programs for internationalreception between 6 and 26.6 MHz.international callsign The call letters of a station,assigned within a country, according to themethod of arrangement (identifying letters, or lettersand numerals) prescribed by the InternationalTelecommunication Union.international candle See CANDLE.international coulomb A unit of electrical quantity,equal to 0.99985 absolute coulomb.international farad A unit of capacitance, equal to0.99952 absolute farad.

376 international henry • interpreterinternational henry A unit of inductance, equal to1.00018 absolute henry.international joule A unit of energy, equal to1.00018 absolute joule.International Morse Code See CONTINENTALCODE.international ohm A unit of electrical resistance,equal to 1.000495 absolute ohm. The other internationalunits are derived from this value.International Radio Consultative CommitteeAbbreviation, CCIR (Comite Consultatif InternationalRadiodiffusion). An international organizationreporting to the InternationalTelecommunication Union, and studying technicaloperations and tariffs of radio and television.International Steam Table calorie A unit of heatenergy equal to 4.1868 joules.International System of Units Abbreviation, SI(Systeme International d’Unites). The system ofunits of measurement established in 1960 underthe Treaty of the Meter. The base units are as follows.–METER (m), length: 1,650,763.73 times thewavelength of the light emitted in a vacuum ofkrypton 86–KILOGRAM (kg), mass: the mass of the protypekilogram kept at Sevres, France–SECOND (s), time: the duration of9,192,631,770 periods of the radiation that correspondsto the transition between the two hyperfinelevels of the ground state of cesium 133–KELVIN (K), thermodynamic temperature: 1 ⁄273.16the thermodynamic temperature of the triplepoint of water–AMPERE (A), electric current: the current that,flowing through two infinitely long parallel wiresin a vacuum and separated by 1 meter, producesa force of 2 × 10 –7 newton per meter oflength between the wires–CANDELA (cd), luminous intensity: the luminousintensity of 1 ⁄600,000 square meter of perfectlyradiating surface at the temperature of freezingplatinumInternational Telecommunication Union Abbreviation,ITU. An international, nongovernmentalorganization devoted to standardizing worldwidecommunications practices and procedures.International Telegraph and Telephone ConsultativeCommittee See CCITT.International Telegraph Consultative CommitteeSee CCIT.international units A system of electrical units,based on the resistance through a specifiedquantity and configuration of the element mercury.The INTERNATIONAL OHM forms the basisfor the international system of units.international volt A unit of electrical potential,equal to 1.00033 absolute volt.international watt A unit of power, equal to1.00018 absolute watt.Internet A worldwide, interconnected system ofcomputer networks. Originated in the late 1960sas ARPAnet (Advanced Research Projects Agencynetwork). Still used extensively by educators andscientists, but gaining popularity amongpersonal-computer users. Sometimes calledthe INFORMATION SUPERHIGHWAY.interphone An intercom aboard a mobile vehicle.interpolation Finding a value that falls betweentwo values listed in a table, indicated by a dial,plotted on a graph, derived by estimate, or givenby intermediate calculation. For example, if a linearvariable capacitor has a value of 100 pF whenits dial is set to 10, and 140 pF when the dial isset to 20, then the capacitance when the dialreads 15 (midway between 10 and 20) can be assumedto be 120 pF (midway between 100 pF and140 pF). When functions are not linear, interpolationis usually not exact.EstimatedpointACBDEinterpolationFA—F:known pointsinterpolation meter See INTERPOLATION-TYPEINSTRUMENT.interpolation oscillator A frequency-measuringsignal generator with a built-in crystal oscillator,whose harmonics provide calibration points onthe tuning dial. The dial provides a continuousindication of generator frequencies between crystal-harmonicpoints. Also see INTERPOLATION-TYPE INSTRUMENT.interpolation-type instrument An instrument,such as a meter or signal generator, that is usedto transfer an accurate quantity point from astandard to another instrument and to provide arange of values between such points. A secondarystandard is sometimes used as an interpolationtypeinstrument (see, for example, INTERPOLA-TION OSCILLATOR).interpole motor A direct-current motor with smallauxiliary poles (interpoles) between its main fieldpoles. The interpoles reduce sparking at the commutator.interpreter A computer program that can convertinstructions given in a high-level language (BA-SIC, for example) into the machine language that

interpreter • intrinsic conduction 377a computer uses; if it is not resident in the computer’snonvolatile memory, it must be loadedeach time the machine is activated.interrecord gap See INTERBLOCK SPACE.interrupt A break in a computer program, as whena background job is interrupted so that a foregroundjob can be run. Also see BACKGROUNDJOB and FOREGROUND JOB.interrupted commercial and amateur serviceSee INTERMITTENT COMMERCIAL AND AMA-TEUR SERVICE.interrupted continuous wave Abbreviation, ICW.A continuous wave that is interrupted at regularintervals, as in the chopping of a wave at a regularrate. Compare CONTINUOUS WAVE (CW) andMODULATED CONTINUOUS WAVE (MCW).interrupted dc A direct current or voltage that isperiodically started and stopped by switching orchopping.interrupter contacts Auxiliary contacts operateddirectly by the armature of a stepping switch.interruption frequency See QUENCHING FRE-QUENCY.interruption-frequency oscillator See QUENCHOSCILLATOR.interrupt signal The signal that causes a break(INTERRUPT) in a computer program.intersatellite communication 1. Communicationbetween or among satellites. 2. Communicationbetween two earth-based stations, usingtwo or more satellites. 3. Communication betweenan earth-based station and a satellitebasedstation, using at least one intermediaterelaying satellite.SatellitesEarthintersatellite communicationintersecting storage ring A device for producinggreat amounts of energy. It is similar to a vacuumtube. High-speed subatomic particles are fed to aring-shaped evacuated structure in opposite directions.The two particle beams collide at variouspoints, yielding high energy.intersection The logical AND operation.interstage capacitor A coupling capacitor usedbetween two circuit stages.interstage coupling The transfer of a signal betweentwo circuit stages, such as those of an amplifier.Common forms of interstage couplinginclude direct coupling, capacitive coupling, transformercoupling, diode coupling, and optoisolatorcoupling.interstage diode A semiconductor coupling diodeused between two circuit stages.interstage transformer A coupling transformerused between two circuit stages. It provides direct-currentisolation, and also can match purelyresistive impedances.intersymbol interference In a digital communicationssignal, a condition in which a given symboloverlaps with one or more other symbols (eitherimmediately preceding it or immediately followingit), upsetting the ability of the receiver to deciphersignals in certain time intervals. The phenomenonis sometimes a problem in time-divisionmultiplexing—especially at data speeds near themaximum for the system.intersystem A power-generating network of interconnectedseparate systems.intersystem communications Communicationsbetween computer systems, either through directlinking of central processors, or by mutual use ofperipherals and input/output channels.intertie See INTERCONNECTION, 2.interval 1. The amount of separation between successivepoints, events, or quantities. 2. The continuousrange of values between two definedpoints. 3. A specific period of time, with definedbeginning and ending points.intervalometer A timing device for operatingequipment over a precisely defined time interval.interval timer A device that provides power to anequipment for a precise interval upon applicationof a simple initiating signal or action. See also IN-TERVALOMETER.interword space The seven-unit interval betweenwords or code groups in telegraphy. Compare IN-TERCHARACTER SPACE.intoxication tester See DRUNKOMETER.intracoding The coding of data using only datathat it contains.Intrafax Western Union’s private facsimile system.Intraframe A method of digital IMAGE COMPRES-SION developed by MPEG (Moving Picture ExpertsGroup) and JPEG (Joint Photographic ExpertsGroup). It operates by eliminating redundant datawithin image frames. Compare INTERFRAME.intrinsic-barrier diode See PIN DIODE.intrinsic-barrier transistor A bipolar transistorwith a layer of intrinsic semiconductor betweenone of its pn junctions.intrinsic concentration The number of minoritycarriers exceeding the normal equilibrium numberin a semiconductor.intrinsic conduction The flow of electron/holepairs in an intrinsic semiconductor subjected toan electric field.

378 intrinsic flux • inverse voltageintrinsic flux A quantity equal to the product ofthe intrinsic flux density and the cross-sectionalarea in a magnet.intrinsic flux density The increased flux densityof a magnet in its actual environment, as comparedwith the flux density resulting from thesame magnetizing force in a perfect vacuum.intrinsic mobility Electron mobility in an intrinsicsemiconductor. Also see CARRIER MOBILITY andMOBILITY.intrinsic Q The value of the Q, also known as theFIGURE OF MERIT, for an unloaded circuit. Thisvalue is generally higher than the value when aload is connected to the circuit.intrinsic semiconductor A semiconductor whosecharacteristics are identical to those of a purecrystal of the material. In this condition, thesemiconductor is nearly an insulator. Example:highly purified germanium or silicon before n- orp-type impurities have been added. Compare EX-TRINSIC SEMICONDUCTOR.intrusion alarm A set of electronic sensors and associatedcircuitry composing a system that detectsand warns of the presence of unauthorizedpersonnel within a specific region.intrusion sensor A sensitive pickup (such as aphotocell, ultrasonic detector, or capacitivetransducer) that responds to a nearby body bydelivering an actuating signal to an intrusionalarm.INV Abbreviation of INVERTER.inv Abbreviation of INVERSE.Invar A nickel-steel alloy (36% nickel) having a lowtemperature coefficient of linear expansion (1ppm/°C). Invar is used in electronic equipmentwhere mechanical distortion resulting from temperaturechanges must be negligible, and in magnetostrictivecircuits (see MAGNETOSTRICTION).inverse 1. Opposite in nature (e.g., an INVERSECHARACTERISTIC). 2. Of opposite sign (e.g., anegative current or voltage). 3. An operation ofopposite kind; thus, subtraction is the inverse ofaddition, and division is the inverse of multiplication.inverse beta The beta of a transistor operated withthe emitter and collector interchanged.inverse bias See REVERSE BIAS.inverse characteristics The characteristics of abipolar transistor when operated with the emitterand collector reversed.inverse conduction See REVERSE CONDUC-TION.inverse cube law A principle relating the intensityof an effect to the reciprocal of the cube of the distancefrom the source. The magnetic field arounda solenoidal coil of wire obeys this principle.inverse current See REVERSE CURRENT.inverse-distance law The inverse-square law appliedto the propagation of radio waves, assumingthat the waves do not encounter obstacles.inverse feedback See DEGENERATION.inverse fourth-power law A rule of propagation forcertain complex forms of energy: I = k/d 4 , where Iis the intensity of the field, d is the distance fromthe source, and k is a constant.inverse impedances Impedances (Z 1 and Z 2 ) thatare the reciprocal of another impedance (Z 3 ), satisfyingthe relationship Z 1 Z 2 = (Z 3 ) 2 . Also calledRECIPROCAL IMPEDANCES.inverse leakage The flow of a small static reversecurrent in semiconductor devices.inverse-parallel circuit See BACK-TO-BACK CIR-CUIT and BACK-TO-BACK CONNECTION.inverse peak voltage See PEAK INVERSE VOLT-AGE.inverse piezoelectric effect Mechanical movementin a piezoelectric material, caused by applicationof voltage.inverse resistance See REVERSE RESISTANCE.inverse resonance See PARALLEL RESONANCE.inverse-square law The energy or power intensityof a phenomenon is inversely proportional to thesquare of the distance from the source. This isoften applied to quantitative reasoning aboutradiant energy, electromagnetic energy, andacoustic energy. Thus, if the distance doubles,the energy or power drops to 1 ⁄4 its previousvalue.inverse trigonometric function An angle expressedin terms of a given trigonometric function,followed by the exponent -1 or preceded by“arc” (sin -1 is the equivalent of arcsin).inverse voltage 1. The negative voltage at the anodeof a rectifier during the negative half-cycle ofalternating-current (ac) input. 2. The voltageacross a power-supply filter capacitor during the

inverse voltage • invister 379negative half-cycle of ac input. 3. Semiconductorjunctionreverse voltage.inverse Wiedeman effect See DIRECT WIEDE-MAN EFFECT.inversion 1. A reversal of the normal vertical temperaturegradient of the atmosphere, often resultingin long-distance tropospheric radio-wavepropagation. 2. Speech scrambling (see SCRAM-BLER CIRCUIT). 3. Phase inversion (see PHASEINVERTER). 4. Changing direct current into alternatingcurrent, often increasing the voltage(see INVERTER, 1).inverted amplifier A push-pull, grounded-gate,field-effect-transistor (FET) amplifier.Dinverter, 1InputSOutputInputOutputSRFCIn01Out10D+inverted amplifierinverted-L antenna An antenna having a horizontalradiator and a vertical feeder or lead-in attachedto one end of the radiator. The entirearrangement resembles an upside-down L. Theoverall length is generally 1 ⁄4 to 1 ⁄2 wavelength.inverted speech See SCRAMBLED SPEECH.inverter 1. Also called power inverter. A device thatconverts direct current (dc) into alternating current(ac), often of a much higher voltage (e.g., 12Vdc into 117 Vac). 2. A logic circuit that providesan output pulse that is a negation of the inputpulse. Also called a COMPLEMENTER or a NOTCIRCUIT. 3. See PHASE INVERTER.inverting adder An analog adder circuit that isprovided with an amplifier for a 180° phaseshift.inverting amplifier An amplifier providing a 180°phase shift between input and output.inverting connection Connection to the invertinginput terminals of a differential amplifier or operationalamplifier. Also see INVERTING INPUT.Compare NONINVERTING INPUT.inverting input In a differential amplifier or operationalamplifier, the input circuit that produces aphase reversal between the input and output.Compare NONINVERTING INPUT.inverter, 2inverting transponder In a communicationssatellite, a transponder in which the downlinkband is “upside-down” in frequency relative to theuplink band. That is, the highest downlink frequencycorresponds to the lowest uplink frequency,and the lowest downlink frequencycorresponds to the highest uplink frequency.Compare NONINVERTING TRANSPONDER. Seealso DOWNLINK, TRANSPONDER, UPLINK.invisible failure In a computer system, a hardwareor software failure whose effect on the system isunnoticeable in a given application. A failure thatis invisible in one application might be vividly apparentin some other application.invister A unipolar semiconductor material, capableof operation at very high frequencies.

380 involution • ionization timeinvolution Raising a number to a power: squaring,cubing, etc. Compare EVOLUTION.inward-outward dialing Also called direct dialing.In a telephone system, a method of dialing inwhich calls can be made to and from branch exchanges,without operator assistance.I/O Abbreviation of input/output (see INPUT/OUTPUT EQUIPMENT).Io Symbol for OUTPUT CURRENT.iodine Symbol, I. A nonmetallic element of thehalogen family. Atomic number, 53. Atomicweight, 126.905. Also see HALOGEN.ion A charged atom [i.e., one that has gained oneor more electrons (a negative ion, or anion) or lostone or more electrons (a positive ion, or cation)].ion burn A spot burned on the screen of a cathoderaytube by negative ions from the cathode strikinga single point on the faceplate with highintensity for long periods.ion concentration 1. The number of ions, expressedas a percentage or as a number per unitvolume, in a substance. 2. Ionization density inthe atmosphere.ion exchange resins Granular resins that containacid or base groups, and that trade ions withsalts in solutions. The resins play a part in thepurification of water for various industrial processes.ionic binding forces In a crystal, the bindingforces that occur when valence electrons of oneatom are joined to those of a neighboring atomwhose outer shell they fill.ionic bond In a solid, a bond between atoms,formed as a result of the attraction between oppositelycharged atoms (ions).ionic conduction Conduction, as in a gas or electrolyte,by ion migration (positive to the cathode,negative to the anode).ionic crystal A crystal whose lattice is held togetherby the electric forces between ions. Alsosee IONIC BINDING FORCES and IONIC BOND.ionic current Current caused by ion movement ina gas or liquid. Also see ION, IONIZATION, andIONIC CONDUCTION.ionic semiconductor A semiconductor in whichthe carrier is an ion, as opposed to an electron orhole.ionic switch See ELECTROCHEMICAL SWITCH.ionization 1. The loss or gain of one or more electronsby an atom. Also see ANION, CATION, andION. 2. The formation or existence of significantnumbers of ions in a gas, liquid, or solid (e.g., ionizationof the upper atmosphere).ionization arc The electrical discharge resultingfrom the ionization of a material because of highvoltage.ionization chamber An enclosure containing a gasand a pair of electrodes between which a highvoltage is applied. Radiation, such as X rays orradioactive particles, passing through the walls ofthe chamber ionize the gas, creating an ionizationcurrent that is proportional to the intensity of theradiation.ionization current 1. Current in an ionized gas(such as air). 2. Current flowing in an electrolyte.3. Current in an ionization chamber, Geiger-Mueller tube, or similar gaseous device. 4. In agas tube, current flowing after the ignition potentialhas been reached. 5. Negative grid current resultingfrom gassiness in a vacuum tube.ionization density The extent to which ionizationexists in an ionized layer of the atmosphere. Thehigher the ionization density, the greater the effecton radio waves—especially at frequencies belowabout 150 MHz.ionization gauge A form of vacuum tube that canbe used to measure the hardness of a vacuum. Itconsists of a cathode, an anode (plate), and a positivelycharged grid. Plate current flows as a resultof ionization of the atoms within the tube.The more nearly perfect the vacuum, the lowerthe plate current.To recorderand measuringcircuitsGridCathodeAnodeElectronsionization gaugeTo vacuum systemGas ionsElectronsionization potential The voltage at which a substance(especially a gas) ionizes. Also called (for agas) ignition potential (see BREAKDOWN VOLT-AGE).ionization pressure In an ionized gas, the pressureincrease resulting from the ionization, ascompared with the same volume and mass of gaswhen not ionized.ionization resistance See CORONA RESISTANCE.ionization smoke detector A device that sensesthe presence of smoke or other particles as a resultof changes in the IONIZATION CURRENTthrough the air. When the ionization current suddenlychanges, a signal is sent to an alarm circuit.ionization time The interval, usually measured inmicroseconds or milliseconds, between the instantthat an ionizing potential is applied to agas, and the instant at which the gas begins toionize. Compare DEIONIZATION TIME.dc

ionization trail • I RF 381ionization trail The ionized path of a meteor as itpasses through the upper atmosphere.ionize To cause the electrons in a substance,particularly a gas, to move freely from atom toatom.ionized gas A gas whose atoms, under the influenceof a strong electric field or IONIZING RADIA-TION, have become positive or negative ions.ionized layer See KENNELLY-HEAVISIDE LAYER.ionized liquid See ELECTROLYTE.ionizing radiation 1. Any high-energy electromagneticradiation that causes ionization in a gasthrough which the field passes. Examples: ultraviolet,X rays, and gamma rays. 2. High-speedatomic nuclei (e.g., protons or alpha particles).ion migration The movement of ions through asolid, liquid, or gas because of the influence of anelectric field.ionosphere 1. Any of several ionized regions atspecific altitudes above the earth’s surface.These layers cause absorption and refraction ofelectromagnetic (EM) fields at some radio frequencies.The D layer exists at an altitude ofabout 30 miles (50 km) and is ordinarily presentonly on the daylight side of the planet. This layerdoes not contribute to, and in fact sometimeshinders, wireless communications. The E layer,about 50 miles (80 km) above the surface, alsoexists mainly during the day, but nighttime ionizationis sometimes observed. The E layer canfacilitate medium-range radio communication atcertain frequencies. The uppermost regions arethe F1 and F2 layers. The F1 layer, normally presentonly on the daylight side of the earth, formsat about 125 miles (200 km) altitude; the F2 layerexists at about 180 miles (300 km) more or lessaround the clock. Sometimes the distinction betweenthe F1 and F2 layers is ignored, and theyare spoken of together as the F layer.ionospheric disturbance See IONOSPHERICSTORM.ionospheric forecasting Predicting ionosphericconditions. Radio propagation data is derivedfrom such predictions.ionospheric layers The respective layers of theionosphere: D layer (at an altitude of about 30 mior 50 km), E layer (at an altitude of about 50 mior 80 km), the F1 layer (at an altitude of about125 mi or 200 km), and the F2 layer (at an altitudeof about 180 mi or 300 km). The F1 layer isgenerally present only in the daytime.ionospheric propagation Propagation of radiowaves by means of reflection or refraction by theionosphere. Also see HOP; INCIDENT WAVE;IONOSPHERE; MULTIHOP PROPAGATION; RE-FLECTED WAVE, 1; REFRACTED WAVE; andSKYWAVE.ionospheric storm Turbulence in the ionosphere,usually accompanied by a magnetic storm andcaused by high-speed particles emitted from aneruption on the sun.ion sensorA device whose operation is based onthe detection of ions and the delivery of a proportionatevoltage. Examples are the Geiger counter,halogen gas leak detector, mass spectrometer,and vacuum gauge.ion spot See ION BURN.ion trap See BENT-GUN CRT.ion-trap magnet An external (usually double)magnet used with a television picture tube to deflectthe ion beam away from the screen. This preventsION BURN.I/O port That part of a computer providing, via aconnector, a point through which data can enterfrom, or exit to, peripheral equipment.I P 1. Abbreviation of PLATE CURRENT. 2. Abbreviationof PEAK CURRENT.I-phase carrier In color television, a carrier separatedby 57 degrees from the color subcarrier.I-picture A video image that is coded using onlydata that it contains.ipm Abbreviation of INCHES PER MINUTE.ips Abbreviation of INCHES PER SECOND.IR 1. The product of current and resistance (see,for example, IR DROP). 2. Abbreviation of INSU-LATION RESISTANCE. 3. Abbreviation of IN-FRARED.I r Symbol for IRIDIUM.I r Symbol for CURRENT in a resistor.IRAC Abbreviation for Interdepartment Radio AdvisoryCommittee (a federal government group inthe United States).IR diode See INFRARED DIODE.IR drop The voltage drop (E) across a resistance (R)when there is a current (I) through the resistor;according to Ohm’s law, E = IR.IRE Abbreviation for Institute of Radio Engineers,the predecessor of the IEEE (Institute of Electricaland Electronics Engineers).IRED Abbreviation for INFRARED-EMITTINGDIODE.I RFSymbol for RADIO-FREQUENCY CURRENT.

382 iridescence • I sEnclosureiridescence A sparkling, colorful appearance in amaterial, resulting from refraction, internal reflection,and interference in light waves passingthrough the substance. It is especially noticeablein quartz and certain gems.iridium Symbol, Ir. A metallic element of the platinumgroup. Atomic number, 77. Atomic weight,192.22.iron Symbol, Fe. A ferromagnetic, metallic element.Atomic number, 26. Atomic weight,55.847. Iron (and its special form, steel) is widelyused in magnetic circuits.iron/constantan thermocouple A thermocoupleconsisting of a junction between wires or strips ofIRON and CONSTANTAN.iron core A transformer or choke core made fromiron or steel. The core is usually laminated to reduceeddy-current loss.iron-core coil An inductor having an iron or steelcore, usually laminated to reduce eddy-currentloss.iron-core IF transformer An intermediate-frequencytransformer having a core of powderediron, a form of iron that has the advantage of highpermeability while greatly minimizing eddy currents.iron-core transformer A transformer whose coilsare wound on a core of laminated iron or steel.iron loss Power lost in the iron cores of transformers,inductors, and electrical machinery as a resultof eddy currents and hysteresis.iron magnet A permanent magnet consisting ofmagnetized iron or a mixture of iron and nickel.iron oxide A compound of iron and oxygen, whosemost familiar form is common rust. The severalvariants have characteristics that depend on thenumber of iron and oxygen atoms in the ironoxidemolecule. See, for example, MAGNETITEand RED OXIDE OF IRON.iron pyrites Formula, FeS 2 . Natural iron sulfidethat occurs as bright yellow crystals in its naturalstate.iron-vane meter An alternating-current meterwhose movable element, a soft iron vane, carriesthe pointer and pivots near a similar, stationaryvane. The vanes are mounted in a multiturn coilof wire. The current flows through the coil, the resultingmagnetic field magnetizing the vanes.Because the magnetic poles of the vanes areidentical, they repel each other; the movable vaneis deflected (against the torque of returningsprings) over an arc proportional to the current,carrying the pointer over the scale.irradiance The amount of radiant flux impingingon a unit surface area; it is generally specified inwatts per square meter (W/m 2 ).irradiation 1. Exposure of a device to radioactivityor X rays. 2. The total radiant power density thatis incident upon a receiving surface.irrational number A number that cannot be expressedas the quotient of two integers. Its deci-NeedleBearingwithspringMovable vaneiron-vane meterInputwith coilFixedvanemal expansion is nonterminating and nonrepeating.irregularity 1. The condition of being nonuniform,or rapidly fluctuating, rather than constant. 2. Adeparture from normal operating conditions. 3.Nonuniformity in a surface. 4. Nonuniform distributionof matter. 5. Nonuniform distribution ofdata.irregular wave A wave disturbance, or the plot ofsuch a disturbance versus time, that has a complex,periodic, repeating nature.IR viewer A device that allows observation of imagesat infrared wavelengths. See SNIPERSCOPEand SNOOPERSCOPE.I s 1. Symbol for source current in a field-effecttransistor. 2. Symbol for screen current in a vacuumtube.

ISDN • isoplanar 383ISDN Abbreviation for INTEGRATED SERVICESDIGITAL NETWORK.ISCAN Abbreviation of inertialess steerable communicationsantenna.I-scan A radar display in which the target is shownas a complete circle, whose radius is proportionalto the distance to the target.I-signal With the Z-signal, one of the two signalsthat modulates the chrominance subcarrier incolor television. The I-signal results from mixinga B-Y signal (with -0.27 polarity) and an R-Y signal(with +0.74 polarity).Isinglass Thinly laminated mica.ISO Abbreviation for International Standards Organization.ISO 9660 A standard format for producing CD-ROM (COMPACT DISK READ-ONLY MEMORY)mass storage media for use with computers. It isa part of the YELLOW BOOK scheme.isobar 1. An atom whose nucleus has the sameweight as that of another atom but differs inatomic number. 2. On a weather map, a line connectingpoints of equal pressure. Also see BAR, 1.isochromal phenomena 1. Effects occurring at regulartime intervals. 2. Effects of equal duration.isochromatic Also orthochromatic. 1. The qualityof having or producing natural visible-light hues.2. Color sensitivity excluding a response to red.isochronal See ISOCHRONE.isochrone On a map, a line connecting points ofconstant time difference in radio-signal reception.It is useful in radiolocation and radionavigation.isochronous Having identical resonant frequenciesor wavelengths.isoclinic line See ACLINIC LINE.isodose Pertaining to points receiving identicaldosage of radiation.isodynamic line On a map of the geomagnetic field(the earth’s magnetic field), a line connectingpoints of equal flux density.isoelectric Having a potential difference of zero.isoelectronic Having the same number of electrons.isogonal 1. See ISOGONIC LINE. 2. Having uniformmagnetic declination at all points.isogonic line On a map of the geomagnetic field(the earth’s magnetic field), a line connectingpoints of equal magnetic declination.isolantite An insulating ceramic. Dielectric constant,6.1.isolated 1. Electrically insulated. 2. Separated insuch a way that interaction does not take place.isolated input 1. An ungrounded input. 2. An inputcircuit with a blocking capacitor to preventthe passage of direct current.isolated location In a computer, a storage locationthat is hardware-protected from being addressedby a user’s program.isolating amplifier See BUFFER, 1.isolating capacitor A series capacitor inserted in acircuit to pass an alternating-current signal whileblocking direct current. Also called a BLOCKINGCAPACITOR.isolating diode A diode used (because of its unidirectionalconduction) to pass signals in one direction,but block them in the other direction.isolating resistor A high-value resistor connectedin series with the input circuit of a voltmeter oroscilloscope to protect the instrument from straypickup. In most voltmeters, this resistor is builtinto the probe.isolating transformer A power transformer, usuallyhaving a 1:1 turns ratio, for isolating equipmentfrom direct connection to the power line.Hot117 VacGndNeutisolating transformerToequipmentisolation The arrangement or operation of a circuitso that signals in one portion are not transferredto (nor affect) another portion.isolation amplifier See ISOLATING AMPLIFIER.isolation capacitor See ISOLATING CAPACITOR.isolation diode 1. In an integrated circuit, a reverse-biaseddiode that is formed in the substrateto prevent cross-coupling and grounds. 2. SeeISOLATING DIODE.isolation resistor See ISOLATING RESISTOR.isolation transformer See ISOLATING TRANS-FORMER.isolator See OPTOELECTRONIC COUPLER.isolith A form of monolithic integrated circuit, inwhich the semiconductor is removed in certainplaces for the purpose of isolating different partsof the circuit.isomagnetic Having equal magnetic intensity.isomer A material that has the same atomic numberor chemical formula as some other substance,but, because of a difference in the atomic structure,is an entirely different substance. An exampleis carbon; it can be either graphite (by far themore common form) or diamond.isophote On a graph of visible-light intensity, acurve joining points of equal brightness.isoplanar An integrated-circuit configuration inwhich insulating barriers or metal oxides are fabricatedamong the bipolar elements.

384 isothermal process • -izeisothermal process A physical or chemical processin which there is no temperature change asother factors vary. Compare ENDOTHERMIC RE-ACTION and EXOTHERMIC REACTION.isotope An atom having the same number of protonsas another atom, thereby composing thesame chemical element, but having a differentnumber of neutrons. Thus, deuterium is an isotopeof hydrogen. Some isotopes are radioactive[e.g., carbon 14 (an isotope of the more-commoncarbon 12)]. The two extra neutrons in carbon 14make it less stable than carbon 12.isotropic antenna A theoretically ideal antennathat transmits and/or receives electromagneticfields equally well, and with 100-percent efficiency,in all directions in three-dimensional freespace.isotropic radiator A theoretically ideal radiatingelement that transmits electromagnetic fieldsequally well, and with 100-percent efficiency, inall directions in three-dimensional free space.I sup Symbol for suppressor current.I(t) Symbol for INDICIAL RESPONSE.ITD Abbreviation for INITIAL TIME DELAY.item 1. Component. 2. Any one of a number ofsimilar or identical components, circuits, or systems.iteration Repeating a series of arithmetic operationsto arrive at a solution to a problem. Computersare commonly programmed to do thisthousands, millions, or billions of times. Such aprogram must include a statement of acceptableaccuracy so that it knows when to leave the iterationloop.iterative impedance In a network consisting ofidentical, cascaded sections, the input impedanceof a section to which the output impedanceof the preceding section is made equal.iterative routine A program or subroutine thatprovides a solution to a problem by iteration.iterative transfer constant Symbol, P. A propertyof ITERATIVE IMPEDANCE networks. If I i is thenetwork input current and I o is the network outputcurrent, then P = log e (I o /I i ).ITU Abbreviation for International TelecommunicationUnion.ITV 1. Abbreviation of INDUSTRIAL TELEVISION.2. Abbreviation for INTERACTIVE TELEVISION.I-type semiconductor See INTRINSIC SEMICON-DUCTOR.I X Symbol for current in a reactance.I Y Symbol for current in an admittance.I Z Symbol for current in an impedance.-ize A suffix used, with some liberty, to formverbs from nouns. In electronics, this commonlyrefers to procedures or processes (e.g., to AN-ODIZE, ELECTROCIZE, PLASTICIZE, or TRAN-SISTORIZE).

J 1. Abbreviation for JOULE. 2. Symbol for JACKor CONNECTOR. 3. Symbol for EMISSIVEPOWER.j (j operator) The square root of –1; an imaginarynumber (usually denoted i in mathematics). Assignedto reactance values depicted on the verticalaxis of the resistance-reactance (RX) plane inimpedance vector diagrams, and whose currentsare 90 degrees out of phase with the current inthe resistive part of an alternating-current circuit.jack A receptacle for a plug. A plug (a male connector)is inserted into a jack (a female connector) tocomplete a circuit or removed from it to break acircuit.jacking outer case or wrapper on a component, suchas a capacitor. 3. A shield can or shield box. 4. Aheat-radiating or water-conducting enclosureused in cooling a power vacuum tube.jack panel A (usually metallic) panel in which anumber of jacks are mounted, usually in someorder or sequence as denoted by labels.jack box A (usually metallic) box or can used tohold, shield, or protect a jack or group of jacks.jacket 1. The outer covering on a cable, as opposedto the insulation or dielectric separating the individualconductors within the cable. 2. An insulatjackpaneljackscrew In a two-piece connector, a screw formating or separating the halves of the connector.Jacob’s law A principle concerning the behavior ofmotors. An electric motor develops maximumpower when E i = 2E bk , where E i is the applied voltageand E bk is the back voltage.JAES Abbreviation for Journal of the Audio EngineeringSociety.jaff Colloquial term for radar jamming that combineselectronic and chaff techniques.jag Distortion caused by temporary loss of synchronizationbetween the scanner and recorder ina facsimile system.jam input 1. A means of setting a logic line to thedesired condition by directly applying the desiredhigh or low voltage. 2. A voltage applied to a logicline to force it high or low.jammer 1. A radio transmitter or station used forthe purpose of JAMMING communications be-Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

386 jammer • job streamtween or among other stations. 2. A radio operatorwho engages in the practice of deliberatelyJAMMING communications between or amongother stations.jamming The deliberate use of countermeasures,such as malicious transmission of interfering signals,to obstruct communications.jamming effectiveness The extent to which JAM-MING is able to disrupt a service. It can be expressedquantitatively as the ratio of jammingsignal voltage to jammed signal voltage. It canalso be determined according to the percentage ofdata that is effectively obliterated.JAN Abbreviation of JOINT ARMY-NAVY.janet A system for point-to-point communicationvia meteor-trail forward scatter. It is generallyused at very high frequencies (VHF).Jansky noise Wideband, high-frequency electromagneticnoise generated by objects in interstellarand intergalactic space.J antenna An end-fed half-wave antenna having aquarter-wave, parallel-wire matching section. Theentire antenna, when oriented vertically, resemblesthe letter J.CoaxiallineJ antennaRadiatorλ/2Matchingsectionλ/4Janus antenna array (from Janus, an ancient Romangod.) A Doppler-navigation antenna arrayradiating forward and backward beams.jar 1. (From Leyden jar) An obsolete unit of capacitanceequal to 1/900 microfarad. 2. The containerfor the elements of a storage cell.JASA Abbreviation for Journal of the Acoustical Societyof America.J-carrier system In carrier-current (wired/wireless)telephony, a broadband system that provides12 telephone channels at frequencies up to140 kHz.JCET Abbreviation of Joint Council on EducationalTelevision.JCL Abbreviation of job control language.J-display A radar display having a circular timebase. The transmitted pulse and reflected (target)pulse are spaced around the circumference; distancescan be measured circumferentially betweenthem.JEDEC Acronym for Joint Electron Device EngineeringCouncil.jerk The rate of change of acceleration; the thirdderivative of displacement.JETEC Acronym for Joint Electron Tube EngineeringCouncil.jewel bearing A low-friction bearing used in electricmeters and other sensitive devices. It takesits name from a jewel pivot (such as a sapphire) inthe groove of which rides the pointed end of a rotatingshaft. Also called jeweled bearing or jewel.jezebel A passive sonobuoy used in military applications.It detects enemy submarine noises, andtransmits them by radio to a monitoring station.JFET Abbreviation of junction field-effect transistor.JHG Abbreviation of JOULE HEAT GRADIENT.jig A device constructed especially for the purposeof holding an equipment or circuit board duringits repair.jitter A (usually small and rapid) fluctuation in aphenomenon, such as a quantity or wave, becauseof noise, mechanical vibration, interferingsignals, or similar internal or external disturbances.It is used especially in reference tocathode-ray-tube (CRT) displays.J/K Abbreviation for joule(s) per Kelvin, the SI unitof entropy; also the unit for the Boltzmann constant.J-K flip-flop A transistor-resistor flip-flop stageproducing an output signal even when both inputsare in the logic 1 state (high). It is so calledbecause its input terminals are labeled J and K.J/(kg•K) Abbreviation for joule(s) per kilogramKelvin, the SI unit of specific heat capacity.job A unit of computer work, usually consisting ofseveral program runs.job control language An operating system languageused to describe the control requirementsfor jobs within the system.job control program A program that uses controllanguage statements and implements them as instructionscontrolling a job in an operating system.job control, stacked See SEQUENTIAL-STACKEDJOB CONTROL.job flow control To control the order of jobs beingprocessed by a computer to make the most efficientuse of peripherals and central processortime—either manually or by an operating system.job library A series of related sets of data that willbe loaded for a given job.job-oriented terminal A terminal that producesdata in computer-ready form.job statement A control statement identifying thebeginning of a series of job control statements fora job.job step The execution of a computer program accordingto a job control statement; several jobsteps can be specified by a job.job stream In a processing system, a group of consecutivelyrun jobs.

jogging • J rule 387jogging Rapid, repetitive switching of power to amotor to advance its shaft by small amounts.Also called inching.Johnson counter See RING COUNTER.Johnson curve A spectral curve (important in appraisingsolar cell performance) for air mass zero(i.e., for conditions beyond the earth’s atmosphere).Johnson-Lark-Horowitz effect The resistivitygained by a metal or degenerate semiconductor(one in which conduction is nearly equal to thatof a simple metal) because of electron scatteringby impurity atoms.Johnson noise See THERMAL NOISE.Johnson-Q feed system See Q-ANTENNA.join Also called disjunction. The logical inclusive-OR operation.joined actuator A form of multiple circuit breakerin which the opening of one circuit results in theopening of all circuits.joint See JUNCTION, 1.joint circuit A communications circuit shared bytwo or more services.joint communications Communication facilitiesbeing used by more than one service of the samecountry.joint denial The logical NOR (NOT-OR) operation.joint-force sensor A feedback servo device that preventsa robot joint from exerting excessive force. Itworks by detecting the mechanical resistance therobot arm encounters. If the resistance becomestoo great, the joint force is reduced or removed.jolt 1. Colloquialism for KILOVOLT. 2. Colloquialismfor ELECTRIC SHOCK. 3. Colloquialism forTRANSIENT. 4. Colloquialism for a lightning discharge.Joly transformer A frequency-tripling transformerwhose frequency-multiplying action depends onthe nonlinearity of the magnetic induction curveof the core material.Jones plug A special form of polarized receptaclehaving numerous contacts.joule Abbreviation, J. The SI unit of work. Onejoule is the work performed when the point of applicationof one newton is moved one meter in thedirection of the applied force. Also see NEWTON.Joule calorimeter A heat-measuring device thatoperates electrically.Joule constant See MECHANICAL EQUIVALENTOF HEAT.Joule effect 1. The heat resulting from currentflowing through a resistance. 2. See MAGNE-TOSTRICTION.joule heat See JOULE EFFECT, 1.joule heat gradient The rate of change in the temperatureof a resistive object through which acurrent flows.joule meter An integrating wattmeter producingreadings in joules.Joule’s law The rate at which heat is produced bycurrent flowing in a constant-resistance circuit isproportional to the square of the current.journal A file of messages within an operating system,providing information for restarts and historicalanalysis of system functioning.joystick A two- or three-dimensional potentiometerwith a movable lever, allowing control of a parameter,according to the position of the lever inthe up/down and left/right directions. It is oftenused in computer games for the purpose of manipulatingimages on a screen. In some suchdevices, the lever can be rotated clockwise orcounterclockwise to obtain additional functions.joystickJones plugj operator See J.Josephson effect The phenomenon, predicted byBrian Josephson, wherein a current flows acrossthe gap between the tips of two superconductorsbrought close together; a high-frequency wave isgenerated.Joshi effect The phenomenon whereby current ina gas changes as the result of irradiation by light.JPEG Abbreviation of Joint Photographic ExpertsGroup.JPEG image compression An image-compressionscheme that eliminates redundancies, greatly reducingthe necessary digital storage space. Theprocess is fast enough to allow animated graphicsat moderate speed.JPL Abbreviation of Jet Propulsion Laboratory.J-pole antenna See J ANTENNA.J rule During transitions of orbital electrons fromhigher to lower energy states (accompanied bythe emission of photons), changes in the innerquantum number can only be by a factor of 0 or+1, or –1.

388 J scan • juxtaposed imagesJ scan See J DISPLAY.J scope A radar device that produces a J DISPLAY.JSR Abbreviation of jump to subroutine.JTAC Abbreviation of Joint Technical AdvisoryCommittee.judder In facsimile transmission, distortion causedby movements of the transmission or receptionequipment.juice Colloquialism for electric voltage or current.jukebox An automatic phonograph (usually foundin public places) that contains a large assortmentof records.Juliet Phonetic representation for the letter J,used in voice communications.jump 1. To purposely provide a short circuitaround some component or circuit. 2. Also calledbranch. In digital computer operations, a programminginstruction specifying the memory locationof the next instruction and directing thecomputer to it.jump, conditional See CONDITIONAL BRANCH.jump, unconditional See UNCONDITIONALBRANCH INSTRUCTION.jumper A short piece of wire (usually flexible, insulated,and equipped with clips) for jumping acomponent or circuit. See JUMP, 1.jump instruction See BRANCH INSTRUCTION.junction 1. A joint (connection) between two conductors.2. The region of contact between semiconductormaterials of opposite type (e.g., pn junction).3. A waveguide fitting used to attach a branchwaveguide to a main waveguide at an angle.junction barrier See DEPLETION REGION.junction battery A nuclear battery in which a siliconpn junction is irradiated by strontium 90.junction box A (usually metal) protective box orcan into which several conductors are brought togetherand connected.junction capacitance In a semiconductor pn junction,the internal capacitance across the junction;it is of special interest when the junction is reverse-biased.Also called barrier capacitance.junction capacitor See VOLTAGE-VARIABLE CA-PACITOR.junction diode A semiconductor diode created byjoining an n-type region and p-type region as awafer of semiconductor material, such as germaniumor silicon.junction field-effect transistor Abbreviation,JFET. A field-effect transistor in which the gateelectrode consists of a pn junction.junction filter A combination of separate low- andhigh-pass filters having a common input, butseparate outputs. The filter is used to separatetwo frequency bands and transmit them to differentcircuits.junction laser See LASER DIODE.junction light source See LIGHT-EMITTINGDIODE.junction loss 1. The loss that occurs in a telephonecircuit at connecting points. 2. Loss in asemiconductor pn junction. 3. Loss occurring atan electrical connection because of poor bonding.junction photocell A photoconductive or photovoltaiccell that is essentially a light-sensitiveJUNCTION DIODE.junction point 1. A point at which two or moreconductors, components, or circuits join in anelectrical connection. 2. The point in a computerroutine at which one of several choices is made.junction rectifier A semiconductor rectifier thatis, in effect, a heavy-duty junction diode, or theequivalent of several heavy-duty junction diodesin combination.junction station A microwave relay station joiningone or more microwave radio legs to the mainroute or through route.junction transistor A transistor in which the emitterand collector consists of junctions (see JUNC-TION, 2) between p and n semiconductor regions.Compare POINT-CONTACT TRANSISTOR.junctor In a crossbar system, a circuit that bridgesframes of a switching unit and terminates in aswitching device on each frame.Jungian-world theory The theory that societieskeep repeating the same mistakes, generation aftergeneration. Of interest to some researchers inartificial intelligence. It has been suggested thatsupercomputers might help find solutions to recurringsocial problems.justification 1. The alignment of text along the leftmargin, the right margin, or both margins. 2. Amethod of altering the speed of a digital signal sothat it can be received by equipment designed fora different data speed. The rate of speed is lowerafter this process is applied. Also called pulsestuffing.justify 1. To adjust the printing of words foraligned left and/or right margins. 2. In computeroperations, to shift an item in a register so thatthe most- or least-significant digit is at the correspondingend of the register.just-operate value The current or voltage level atwhich a relay or similar device just closes. Alsocalled just-close value.just-release value The current or voltage level atwhich a relay or similar device just opens. Alsocalled just-open value.just scale A musical scale of three consecutive triads,the highest note of each being the lowestnote of the next. Each triad has the ratio 4:5:6 or10:12:15.jute Tar-saturated fiber, such as hemp, used as aprotective covering for cable.jute-protected cable A cable whose outer coveringis a wrapping of JUTE or similar material.juxtaposed elements Components placed ormounted side by side.juxtaposed images Images (e.g., those on thescreen of a dual-beam cathode-ray tube) that areclose to each other for simultaneous viewing, butdo not overlap at any point.

K 1. General symbol for CONSTANT. 2. Symbol forPOTASSIUM. 3. Symbol for KELVIN. 4. Radiotelegraphsymbol for go ahead or over. 5. Symbol forCATHODE. 6. Symbol for KILOBYTE. 7. Abbreviationof KILOHM (k is preferred). 8. Abbreviationof KILO-.k 1. Abbreviation of KILO-. 2. Symbol for theBOLTZMANN CONSTANT. 3. General symbol fora mathematical constant. 4. Symbol for DIELEC-TRIC CONSTANT. 5. Abbreviation for KILOHM.kA Abbreviation of KILOAMPERE.Karnaugh map A logic chart showing switchingfunctionrelationships and used in computerlogic analysis to determine quickly the simplestform of logic circuit for a given function. The Karnaughmap is sometimes regarded as a tabularform of the Venn diagram.Kansas City standard A frequency-shift modulationstandard for a computer/tape-recorder interface.Also called byte standard.KB 1. Abbreviation of KEYBOARD. 2. Abbreviationof KILOBYTE.K band The 18- to 27-GHz band of frequencies,pertaining to their use in radar applications.kcal Abbreviation of KILOCALORIE.K carrier system A four-wire carrier-current telephonesystem using frequencies up to 60 kHzand providing 12 channels.kCi Abbreviation of KILOCURIE.kcs Abbreviation of kilocharacter per second (1000characters per second).K display See K SCAN.KDP Abbreviation of POTASSIUM DIHYDROGENPHOSPHATE, a ferrolelectric material.keeper A small iron bar placed across the poles ofa permanent magnet to forestall demagnetization.K electron In certain atoms, one of the electronswhose orbit is nearest the nucleus.Kel-f Abbreviation of polymonochlorotrifluorethylene,a high-temperature insulating material.Kellie bond 1. The junction of two mated electricallyconductive surfaces that are held togetherby an adhesive that exhibits negligible resistancethermally and electrically when set. 2. To make athermally conductive joint, as from a heatsink toa chassis or component.kelvin (Lord Kelvin, 1824–1907) Symbol, K. The SIunit of thermodynamic temperature; 1 K =1/273.16, the thermodynamic temperature of thetriple point of water.Kelvin absolute electrometer An electrostaticvoltmeter consisting of a movable metal plate (orplates) and a stationary metal plate (or plates)ac or dcinputSpiralspringsStationaryplatesMovableplateKelvin absolute electrometerPointerCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

390 Kelvin absolute electrometer • keyboard keyerbetween which voltage is applied. The movableplate(s) is displaced over a distance that is proportionalto the potential, against the torque of areturn spring.Kelvin balance An apparatus for measuring currentin terms of magnetic pull. A coil is attachedto each end of the beam of a balance, and coilsride directly above two stationary coils. Currentflows through all coils, making one pair attractiveand the other repellent, thus unbalancing thebeam. Balance is restored by sliding a weightwhose position along a graduated scale indicatesthe current strength.Kelvin contacts Electrical contacts designed toeliminate the effect of lead resistance on the accuracyof measurement. Two leads run to each testpoint, one lead carrying the test signal and theother leading directly to the measuring instrument.Kelvin double bridge A special bridge for measuringvery low resistance (0.1 ohm or less). The arrangementof the bridge reduces the effects ofcontact resistance that causes significant errorwhen such low resistances are connected to conventionalresistance bridges.R xR 1 R 2MR 3 R 4R sKelvin double bridgeWhen R 1 /R 2 = R 3 /R 4 ,R x = (R 1 /R 2 )R sKelvin replenisher A static generator consisting oftwo pairs of concentric, rotating semicircularconductors connected to brushes. The machinecan be regarded as a rotating electric doubler.Kelvin scale See ABSOLUTE SCALE.Kelvin temperature scale See ABSOLUTE SCALE.Kelvin voltmeter An electrostatic voltmeter inwhich an assembly of figure-8-shaped metalplates rotates between the plates of a stationaryassembly when a voltage is applied between theassemblies. The length of the arc of rotation isproportional to the electrostatic attraction and,thus, to the applied voltage.Kendall effect Distortion in a facsimile recordcaused by unwanted modulation produced by acarrier signal.Kennelly-Heaviside layer (A.E. Kennelly, 1861–1939; Oliver Heaviside, 1850–1925) An earlyname for ionized regions in the upper atmosphere.These regions reflect and refract radiowaves at certain frequencies. There are severallayers at various altitudes. Also see IONO-SPHERE and IONOSPHERIC LAYERS.keraunograph A meteorological instrument for detectingdistant electrical storms. In its simplestform, it consists of a galvanometer connected inseries with an antenna and ground.keraunophone A radio-receiving KERAUNO-GRAPH.kernel Inside an electrical conductor, a line alongwhich the magnetic field strength is zero. Generally,this line is near the center of the conductor.Kerr cell A nitrobenzene-filled cell that makes useof the KERR ELECTRO-OPTICAL EFFECT. It canfunction as an electric light shutter or control.Kerr electro-optical effect The tendency of certaindielectric materials to become doublerefractingin an electric field.Kerr magneto-optical effect The tendency ofglass and some other solids and liquids to becomedouble-refracting in a magnetic field.Kerst induction accelerator See BETATRON.keV Abbreviation of KILOELECTRONVOLT.Kew magnetometer A special magnetometer usedto measure the intensity of the earth’s magneticfield, and also the magnetic declination at a givenpoint on the earth’s surface. The device is designedfor very high accuracy, using magnifyinglenses.key1. See DECRYPTION KEY. 2. A projection orpin that guides the insertion of a plug-in componentinto a holder or socket. 3. A digit or digitsused to locate or identify a computer record (butnot necessarily part of the record). 4. A specializedhand-operated switch, used to make andbreak a circuit repetitively to form the dot anddash signals of Morse code telegraphy. Primarilyof historical interest. Used by some amateur radiooperators for hobby purposes. 5. Slang forprincipal or main.keyboardAn array of lettered or numbered, lowtorquepush buttons, used to enter informationinto a computer, telegraph, teletypewriter, or automaticcontrol system.keyboard computer A digital computer in whichthe input device is an electrical keyboard of thetypewriter or calculator type.keyboard entry The operation of a keyboard to enterinformation into a computer for processing.keyboard keyer A device for automatically sendingMorse code using a typewriter-like keyboard,rather than a paddle or straight key. Each key onthe keyboard, when pressed, produces the completecharacter and a space following it. Most keyboardkeyers have buffers to allow typing wellahead of the code being sent, with insertion of allthe correct spaces. The speed range is usually

keyboard keyer • keying speed 391from about 5 words per minute (wpm) to 60 or 70wpm, although some keyboard keyers are programmedfor speeds over 100 wpm.keyboard lockout A keyboard interlock in a datatransmission circuit that prevents data from beingtransmitted while the transmitter of anotherstation on the same circuit is operating.keyboard send-receive unit A teletypewriter lackingan automatic input device.key cabinet In a telephone system, a facility thatshows a subscriber which lines are busy andwhich lines are open.key chirpA chirping sound in a received signal, resultingfrom slight frequency shift when a radiotelegraphtransmitter is keyed. It does notoccur with a well-designed transmitter.key-click filter An inductance-capacitance (LC) orresistance-capacitance (RC) filter for smoothing akeying wave to eliminate KEY CLICKS. It functionsby optimizing the rise and decay times ofthe keyed waveform.key clicksExcessive bandwidth of a radiotelegraphsignal that can result when a keyed signalhas rise and decay times that are too rapid. Producescharacteristic clicking or popping sounds,with resulting interference, in receivers tuned tofrequencies near that of the transmitted signal. AKEY-CLICK FILTER can eliminate this.AmplitudeNo clickproducedkey clicksClickproducedTimekeyed AGC A controlled automatic gain control(AGC) system in a television receiver circuit. TheAGC acts when the horizontal sync pulse appears;it is inactive between pulses. This preventsunwanted actuation of the AGC by noise transientsand picture-signal elements.keyed clamp A clamping circuit that uses a controlsignal to determine the clamping time.keyed interval In a transmission system that iskeyed periodically, an interval beginning with achange in state and having a duration of theshortest time between changes in state.keyed rainbow generator For testing of colortelevisionreceivers, a signal generator thatproduces a rainbow color pattern on the screen(i.e., a set of 10 vertical color bars representingthe spectrum, with blank bars in between). Thepattern results from gating the 3.56-MHz oscillatorin the receiver at a frequency of 189 kHz.keyer An automatic device for keying a radiotelegraphtransmitter or wire telegraph circuit. Thekeyer can operate from perforated tape, an embosseddisk, magnetic tape, or other similarrecording.keyer adaptor A modulated-signal detector thatproduces a direct-current signal having an amplitudesympathetic with the modulation; it providesthe keying signal for a frequency-shiftexciter in radio facsimile transmission.key escrow A controversial system in which thegovernment is provided with certain componentsof decryption keys to all communications ciphers,according to laws that would allow the governmentto eavesdrop on private communications ortransactions after getting a court order. The keycomponents are held in a secure place, that is, in“escrow,” unless and until the necessary court orderis obtained. See DECRYPTION KEY.keying 1. The modulation of a carrier by switchingit on and off. It is commonly used in radiotelegraphy.2. The modulation of a carrier by switchingits frequency between two defined values. It isalso called FREQUENCY-SHIFT KEYING (FSK)and it is used in data transmission. 3. The modulationof a carrier with an audio tone that isswitched on and off. The carrier can be modulatedvia amplitude modulation (AM), frequencymodulation (FM), pulse modulation, or any otherform that will convey the audio tone. It is occasionallyused in radiotelegraphy at very-high frequencies(VHF) and above. Also called audiokeying. 4. The modulation of a carrier with an audiotone whose frequency is switched betweentwo defined values. The carrier can be modulatedvia amplitude modulation (AM), frequency modulation(FM), pulse modulation, or any other formthat will convey the audio tone. It is commonlyused in data transmission at VHF and above.Also called AUDIO FREQUENCY-SHIFT KEYING(AFSK).keying chirp A rapid change in the frequency of acontinuous-wave signal, occurring at the beginningof each code element. In the receiver, the resultingsound is a chirp.keying error rate In data transmission, the ratioof incorrectly keyed signals to the total number ofsignals keyed.keying filter See KEY-CLICK FILTER.keying frequency 1. In audio-keyed radiotelegraphy,the audio frequency (tone) of the dot anddash signals (as opposed to the carrier frequency).2. In radiotelegraphy, the transmissionspeed (see KEYING SPEED). 3. The number oftimes per second that a black-line signal occurswhile an object is scanned in a facsimile system.keying monitor A simple detector used by an operatorto listen to the keying of a radiotelegraphtransmitter.keying speed The speed (in words per minute) of atelegraph or radio-telegraph transmission.

392 keying transients • kilogram-caloriekeying transients 1. Transients arising from thekeying of a radiotelegraph transmitter or wiretelegraph circuit. 2. Transients that arise fromthe repetitive making and breaking of any circuit.keyless ringing In a telephone system, ringingthat begins as soon as the calling plug is put inthe appropriate jack on the jack panel.key pulse In telephone operations, a signaling systemin which the desired numbers are entered bypressing corresponding pushbuttons or keys.key punch A keyboard-operated machine forrecording information by perforating a tape orcards.keyshelf A shelf that supports manually operatedtelephone switchboard keys.key station The master (control) station in a communicationsor control network.keystoning A form of video image distortion inwhich the top of the picture is wider than the bottom,or vice versa. Thus, the image area is shapedlike a trapezoid, rather than a rectangle.TVpicturekeystoningkey switch 1. A lockable switch that is operated byinserting and turning a key in it. 2. A switch havinga long handle that transmits motion to themechanism through a cam. 3. See KEY, 1. 4.The separate short-circuiting switch sometimesmounted on the base of a telegraph key (see KEY,1). 5. A switch that actuates the keys of an electronicorgan.key-to-disk unit A keyboard-to-magnetic-diskdata-processing unit.keyway A groove or slot into which a mating keyslides to position a plug-in component (see KEY,2).keyword In information retrieval systems, the significantword in the title describing a document(e.g., in the title “A Primer on French Cuisine,”the word cuisine would be the keyword, the othershaving no singular significance).kg Abbreviation of KILOGRAM.kgC Abbreviation of KILOGRAM-CALORIE.kgm Abbreviation of KILOGRAM-METER.kg/m 3 Symbol for KILOGRAMS PER CUBIC ME-TER, the SI unit of density.K-H layer See KENNELLY-HEAVISIDE LAYER.kHz Abbreviation of KILOHERTZ.kick 1. To place into sudden operation, as by thequick, forcible closure of a switch or the rapid applicationof an enabling pulse. 2. See TRIGGER.3. Colloquialism for an abrupt, momentary electricshock.kickback 1. The counter EMF that appears acrossan inductor when current is interrupted. 2. SeeFLYBACK.kickback power supply A high-voltage power supplyusing the flyback principle. See FLYBACK.kidney joint A waveguide coupling used in radar.The joint is flexible, or can consist of an air gap,to allow rotation of the antenna.Kikuchi lines A characteristic spectral patternproduced by the electrons scattered when anelectron beam strikes a crystal.killer 1. A pulse or other signal used to disable acircuit temporarily (e.g., a blanking pulse). 2. Inpersonal computing, an application of such importancethat it alone serves as the motivation forsomeone to purchase or upgrade a system. Commonexamples are word processing and onlinecommunications.killer circuit 1. A circuit that disables somefunction of a system, such as the audio in atelevision receiver. 2. The blanking circuit in aradar receiver. 3. A circuit that prevents responsesto side-lobe signals in a repeater ortransponder.Kilo Pronunciation, KEY-low. Phonetic alphabetcode word for the letter K.kilo- Abbreviation, K or k. 1. A prefix meaningthousand(s). 2. In digital data applications, a prefixmeaning 2 10 (1024).kiloampere Abbreviation, kA. A unit of currentequal to 1000 amperes.kilobit A unit of digital data equal to 2 10 (1024)bits. Also see BIT.kilobyte Abbreviation, K or KB. A unit of digitaldata equal to 2 10 (1024) bytes. Also see BYTE.kilocalorie Abbreviation, kcal. A large unit of heat;1 kcal equals 1000 calories. See CALORIE.kilocurie Abbreviation, kCi. A large unit of radioactivityequal to 3.71 × 10 13 disintegrationsper second; 1 kCi equals 1000 curies. Also seeCURIE, MEGACURIE, MICROCURIE, and MILLI-CURIE.kilocycle See KILOHERTZ.kiloelectronvolt Abbreviation, keV. A large unit ofelectrical energy equal to 1000 electronvolts. SeeELECTRONVOLT.kilogauss A large unit of magnetic flux density;1 kilogauss equals 1000 gauss or 0.1 tesla.kilogram Abbreviation, kg. The SI base unit ofmass; it is equal to 1000 grams.kilogram-calorie The heat required to raise 1 kilogramof water 1°C.

kilogram-meter • kite-supported antenna 393kilogram-meter Abbreviation, kgm. A unit of mechanicalenergy (work); 1 kgm is the energy requiredto raise a mass of 1 kilogram vertically bya distance of 1 meter (equal to 7.2334 footpounds).Also see JOULE.kilohertz Abbreviation, kHz. A unit of frequency;1 kHz equals 1000 Hz.kilohm Symbol, kΩ. A unit of high resistance, reactance,or impedance; 1 kΩ equals 1000 ohms.kilojoule Abbreviation, kJ. A unit of energy orwork; 1 kJ equals 1000 joules. See JOULE.kilolumen Abbreviation, klm. A unit of luminousflux equal to 1000 lumens. See LUMEN.kilomega- See GIGA-.kilomegahertz See GIGAHERTZ.kilometer Abbreviation, km. A large metric unit oflinear measure; 1 km equals 1000 meters (3280.8feet).kilo-oersted Abbreviation, kOe. A unit of magneticfield strength; 1 kOe equals 1000 oersteds. SeeOERSTED.kiloroentgen Abbreviation, kr. A large unit of radioactiveradiation; 1 kr equals 1000 roentgens.See ROENTGEN.kilorutherford Abbreviation, krd. A large unit of radioactivityequal to 10 9 disintegrations per second.kilovar A compound term coined from kilo- andVAR (the abbreviation of volt-amperes reactive). Itis equal to a reactive power of 1000 watts.kilovar-hour A large unit of reactive electrical energy,equivalent to 1000 reactive watts manifestedfor a period of one hour.kilovolt Abbreviation, kV. A unit of high voltage;1 kV equals 1000 V.kilovolt-ampere Abbreviation, kVA. A unit of highpower that gives the TRUE POWER in a directcurrentcircuit and the APPARENT POWER in analternating-current circuit; 1 kVA equals 1000 W.Also see DC POWER.kilovolt-ampere reactive See KILOVAR.kilovoltmeter A voltmeter designed to measurethousands of volts (kilovolts).kilowatt Abbreviation, kW. A unit of high power;1 kW equals 1000 watts. Also see WATT.kilowatt-hour Abbreviation, kWh. A common unitof electrical energy; 1 kWh equals 1000 watthours, or the equivalent of 1000 watts dissipatedfor a period of one hour. Also see ENERGY,KILOWATT-HOUR, POWER, WATT-HOUR, andWATT-SECOND.kilowatt-hour meter A motorized meter forrecording (electrical) power consumption in kilowatt-hours.Also see KILOWATT-HOUR.kinematograph A motion picture camera. Alsocalled CINEMATOGRAPH and KINETOGRAPH.kine 1. See KINESCOPE, 1. 2. See KINESCOPERECORDING.kinescope 1. The picture tube in a television receiver.2. See KINESCOPE RECORDING.kinescope recorder A film or tape apparatus forrecording television pictures.kinescope recording A motion-picture or videotapemade from the screen (or taken from the circuit)of a television picture tube.kinetic energy The energy associated with particles,bodies, or electric charge carriers in motion.kinetograph See KINEMATOGRAPH.kinetoscope A motion-picture projector.kiosk A computer and peripherals set up for thepurpose of multimedia use by the general public.It generally uses a touch screen for inputting dataand must be ruggedly constructed to toleraterough treatment.Kirchhoff’s first law The sum of the currents flowingout of a point in a direct-current circuitequals the sum of the currents flowing into thatpoint.Kirchhoff’s laws (Gustav Robert Kirchhoff, 1824–1887) Two laws of electric circuits that accountfor the behavior of certain networks. See KIRCH-HOFF’S FIRST LAW and KIRCHHOFF’S SECONDLAW.First law: I 1 + I 2 + I 3 = I 4 + I 5I 4 I 5xI 1 I 2 I 3Second law: V 1 + V 2 + V 3 + V 4 = V 5V 1 V 2V 3 V 4V 5Kirchhoff’s lawsKirchhoff’s second law The algebraic sum of allthe voltage drops around a direct-current circuit(including supply voltages) is always equal tozero.kit A selection of components, associated equipment,supplies (such as wire and hardware), andinstructions for constructing a piece of electronicequipment.kite-supported antenna A longwire antenna thatuses a kite as a support for the far (nonstation)end. A tether is used to reduce the chance thatthe kite will fly away with wire attached. It wasused by Marconi in early experiments with radio.Radio amateurs and shortwave listeners sometimesuse this scheme at low and medium

394 kite-supported antenna • Kramer systemfrequencies. It is a dangerous antenna because ofelectrostatic buildup, a tendency to attract lightning,the possibility of its breaking loose, and therisk that it might contact utility lines.kJ Abbreviation of KILOJOULE.k-line programming A method by which an artificiallyintelligent robot can learn as it does a job,so it will have an easier time doing the same jobin the future. The robot controller actually learnsfrom the robot’s mistakes.Klipsch horn A loudspeaker that includes a foldedlow-frequency horn housed in a corner enclosure.klm Abbreviation of KILOLUMEN.kludge 1. A crude, useless, or grossly inefficientmachine or process. 2. A hastily contrived prototypeof a circuit or device, put together for thepurpose of testing a concept, but not intended asa representative of a production unit.klydonograph A device that photographicallyrecords the voltage gradient in the presence of anelectric field.klystron A microwave tube whose operation isbased on the velocity modulation of an electronbeam by buncher and cavity reentrant cavities.Coupling loopHeaterBuncherGridCathodeTerminalsInput OutputFeedback pathklystronMetalDrift spaceCatcherCollectorGlassklystron amplifier A microwave amplifier using aklystron.klystron harmonic generator A frequencymultiplyingpower amplifier using a klystron. It isused at microwave radio frequencies.klystron oscillator A klystron operated as a selfexcitedmicrowave oscillator.klystron repeater A microwave amplifier in whicha klystron inserted in a waveguide boosts the amplitudeof an incoming signal.km Abbreviation of KILOMETER.knee 1. A sharp bend in a response curve for a device,usually indicating the onset of conduction,saturation, cutoff, pinchoff, or limiting action. Itapplies especially to semiconductor diodes andtransistors. 2. The characteristics of a devicewhen it is operated at a point in the vicinity of asharp bend in its response curve.knee noise Electrical noise generated by rapidlyrepeating current fluctuations at the knee in aZener diode.knife-edge diffraction The lessening of atmosphericsignal attenuation when the signalpasses over a sharp obstacle and is diffracted.knife switch A switch composed of one or more flatblades roughly resembling knife blades, whichare slid firmly between the jaws of pinching contactsto close a circuit.knob1. A (usually round and insulated) finger dialfor adjusting a variable electronic component,such as a potentiometer, variable capacitor, orrotary switch. 2. A solid round insulator usuallyhaving a low diameter to height ratio. 3. A smallball- or rod-shaped electrode or protuberance.knocker A fire-control radar subassembly of synchronizingand triggering circuits.knockout An area in a metal box or chassis that iseasily removed by tapping or knocking to providean opening.knot A unit of speed, corresponding to 1 nauticalmile per hour. A speed of 1 knot is about 1.15statute miles per hour; a speed of 1 statute mileper hour is about 0.868 knots. It is used bymariners for specifying speeds at sea, and alsooccasionally by meteorologists in specifying windspeeds.knowledge The data in a computer and in massstoragemedia, accumulated over time and capableof being put to practical use.kOe Abbreviation of KILO-OERSTED.Kolster decremeter An absorption wavemeterwith a movable scale; it permits measurement ofthe decrement of a radio wave.Kooman antenna A unidirectional antenna consistingof stacked, full-wave, center-fed driven elements,and a reflecting screen.Korner Killer Trade name for an acoustically absorbentobject that reduces sound echoes thatcan occur in enclosed rooms. The name resultsbecause the device works best when placed in acorner (where two walls meet).Kovar An alloy of cobalt, iron, and nickel. It is usedmostly in glass-to-metal seals because it hascharacteristics of both kinds of material.Kozanowski oscillator A positive-grid vacuumtubeUHF oscillator circuit using two tubeshaving cylindrical elements, and a pair ofparallel-wire tanks.Kr Symbol for KRYPTON.kr Abbreviation of KILOROENTGEN.K radiation X rays emitted from an atom when anelectron becomes a K electron.kraft paper Strong brown paper used for insulationand as the dielectric of paper capacitors.Kramer system A system of three-phase motorcontrol providing constant horsepower, andhaving a direct-current (dc) motor coupled to theshaft of a wound-rotor three-phase induction motor.The dc supply for the motor also supplies arotary converter. The speed-control rheostat isconnected in series with the field of the motor andthe dc power supply.

Kraus antenna • kWh 395+−ARFC1RFC2RFC3RFC4V 1V 2C1C2Plate wireCathode wireB+Cathode wirePlate wireKozanowski oscillatorC−RFC5Kraus antenna A bidirectional, flat-top beam antennaconsisting of a pair of closely spaceddipoles. Several such sections can be connectedin series by crisscrossing the wires at voltageloops.krd Abbreviation of KILORUTHERFORD.Kryptol A mixture of clay, graphite, and siliconcarbide. It is used in electric heater elements becauseof its low resistance and high meltingpoint.krypton Symbol, Kr. An inert, gaseous element.Atomic number, 36. Atomic weight, 83.80. Kryp-ton is present in trace amounts in the earth’s atmosphere.K scan In radar operations, a modified A-scanused in aiming antennas in which two pips aredisplayed; their relative amplitudes indicate theantenna-aiming error.K series A series of spectral lines for the shortestwavelengths of radiation from the innermost electronshell of a radiating atom.KSR Abbreviation of keyboard send-receive unit.Ku band A band of microwave frequencies betweenapproximately 12 and 18 GHz.Kundt’s law The index of refraction of a mediumdoes not change continuously with wavelength inthe absorption bands.Kundt tube A device used to measure the speed ofsound in gases under various conditions. Suspendedparticles in the gas form standing wavesthat can be easily seen. Knowing the frequency ofthe disturbance and the distance between nodesof the standing waves, the speed can be determined.The pressure and density of the gas, aswell as temperature and humidity, affect thespeed.kurchatovium See RUTHERFORDIUM.kV Abbreviation of KILOVOLT.kVA Abbreviation of KILOVOLT-AMPERE.kVAR Abbreviation of REACTIVE KILOVOLT-AMPERE.kVARh Abbreviation of KILOVAR-HOUR.kW Abbreviation of KILOWATT.kWh Abbreviation of KILOWATT-HOUR.

L 1. Symbol for INDUCTANCE. 2. Symbol forMEAN LIFE. 3. Abbreviation of LOW. 4. Resemblingthe capital letter L in physical shape.5. Symbol for LAPLACE TRANSFORM.l 1. Symbol for LENGTH. 2. Abbreviation of LITER.3. Subscript for LOW. 4. Abbreviation of LUMEN;also abbreviated lm (preferred) and lum.La Symbol for LANTHANUM.label 1. A symbolic group of characters that identifiesan area of memory, an item of data, a file, ora record. 2. A name assigned to a source programinstruction step to identify the step as a codingentry point, or to make the step usable as a referencepoint for entry to the routine or subroutinein which it appears.label group A collection of labels, usually of thesame type, held in an operating system.label identifier Within a label, a character setused to name the kind of item labeled.label record A record identifying a file recordedon a magnetic storage medium (e.g., magnetictape).label set A collection of labels having a common labelidentifier.labile oscillator A frequency-controlled local oscillator.laboratory conditions The environmental, mechanical,and electrical parameters characteristicof controlled conditions. Actual operating conditionscan be much different.laboratory-grade instrument An instrument havingthe high accuracy and stability that suit it toprecision measurements in a laboratory. Alsocalled PRECISION INSTRUMENT. CompareSERVICE-TYPE INSTRUMENT.laboratory power supply A regulated directcurrentsource whose adjustable output is lessthan 10 kV at no more than 500 W.laboratory standard See PRIMARY STANDARDand SECONDARY STANDARD.labyrinth speaker A loudspeaker whose enclosure(a wooden cubicle) includes a folded pipe oracoustic transmission line (behind the speaker);the inner walls are lined with a sound-absorbentmaterial. When the pipe, which is open-ended, ishalf as long as the wavelength of the frequencybeing reproduced, the sound emerging from theopen end is in phase with that radiated by thefront of the speaker and, therefore, reinforces it.laced wiring Circuit wiring in which wires or cablesrun parallel in bundles that are tied togetherwith LACING CORD.lacing cord Strong, sometimes waxed cord used totie together wires running parallel in a bundle.Also see LACED WIRING.lacquer disk See CELLULOSE-NITRATE DISK.lacquer-film capacitor A fixed capacitor with aplastic film dielectric; the film is applied as liquidlacquer to the metal foil.lacquer master A master recording made on aCELLULOSE-NITRATE DISK.lacquer original See LACQUER MASTER.ladar Abbreviation of LASER DOPPLER RADAR.Also abbreviated lopplar.ladder attenuator See LADDER-TYPE ATTENUA-TOR.ladder filter A form of delay line or filter. It generallyconsists of series and parallel impedances,either in a balanced or unbalanced form.ladder line See AIR-INSULATED LINE.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

ladder network • lamp driver 397ladder network A network consisting of several Lsections in cascade. See L SECTION, 1, 2, 3.ladder-type attenuator An attenuator consistingof a ladder network equipped with a switchingcircuit for selecting the output at various sections.Inputladder-type attenuatorOutputLAFOT Coded weather broadcasts aired every sixhours by the U.S. Weather Bureau through marineradiotelephone broadcasting stations for theGreat Lakes region.lag In computations relating the phase of alternating-currentsignals, the extent to which onequantity follows another in time (e.g., the currentlags the voltage by 90 degrees in a pure inductivereactance). Compare LEAD.lagged-demand meter A meter with a built-in timedelay.lagging current Current that follows voltage (intime). Also see LAG.lagging load A load in which current lags behindvoltage (i.e., an inductive load). Compare LEAD-ING LOAD.lag network A phase-shifting circuit containingseries-resistance and shunt-capacitance arms. Itproduces a lagging phase shift. Compare LEADNETWORK.lambda wave An electromagnetic disturbance thattravels along the surface of an object. An exampleis the surface wave characteristic of lowfrequencypropagation.lambert Symbol, L. The centimeter-gram-second(cgs) unit of luminance, equal to the brightness ofan ideal diffusing surface that radiates or reflectslight at 1 lumen per square centimeter. The SI(preferred) unit of luminance is the candela persquare meter (cd/m 2 ); 1 lambert equals 10 4cd/m 2 . Also see CANDELA.Lambert’s law of illumination The illuminationof a surface by a point light source is inverselyproportional to the square of the distance betweenthe surface and the source. If the surfaceis not perpendicular to the rays, the illuminationis proportional to the cosine of the angle of incidence.laminated armature An armature for a motor orgenerator, made of stacked laminations.laminated contact A switch contact consisting ofa number of laminations—each contacting a conductingcounterpart.laminated core A core for a transformer, choke, relay,or similar device, made of stacked laminations.laminated disk A layered recording disk.laminated pole A pole within a motor, generator,relay, electromagnet, or similar device, made ofstacked laminations.lamination 1. A relatively thin sheet of metal cutto a required shape to be stacked with other similarsheets to form a laminated core or pole. 2. Arelatively thin sheet of plastic that is bonded togetherand heat-formed with other similar sheetsto produce a sheet or piece of desired thicknessand strength.lamp A device for converting electrical energy intovisible light. The term includes a number of devices(e.g., arc lamp, fluorescent tube, incandescentlamp, mercury-vapor lamp, and neonbulb).lamp-bank resistor A makeshift heavy-duty resistorconsisting of several incandescent lampsarranged so that they can be switched in variousseries, parallel, and series-parallel combinationsto vary the resistance provided by thefilaments.lampblack Carbon obtained from soot depositedby a smoky flame. The substance is used as thebasic material for some resistors.lamp cord A two-wire insulated cord, used withlow-wattage alternating-current appliances at117 volts. The wire is usually stranded copperequivalent to American Wire Gauge (AWG) #16.lamp dimmer See DIMMER.lamp driver A usually single-stage circuit for amplifyinga small pulse to drive an indicator lamp.

398 lamp extractor • Laplace transformlamp extractor A special tool used to insert or extractminiature lamps for electronic equipment.lamp jack A receptacle with a spring release thatholds a small incandescent bulb. The bulb is removedand replaced by pushing and twisting.lamp jacklamp-type expander A volume expander in whichthe tungsten filament in an incandescent lampserves as the nonlinear resistor.lamp-type readout For counters, calculators, anddigital meters, a readout device in which eachdigit is indicated by a lamp.LAN Abbreviation of LOCAL AREA NETWORK.land 1. The flat, reflective surface between pits ona compact disc (CD). Compare PIT, 1. 2. The thinvinyl wall between grooves on a phonographrecord. 3. A bonding point in a microcircuit. 4.Pertaining to earthbound communications stations.Land camera See POLAROID CAMERA.landing beacon The aircraft landing-beam transmitter.Also see LANDING BEAM.landing beam A highly directional airport radiosignal beamed upward to guide aircraft landingduring conditions of poor visibility.landline A telephone or telegraph circuit completedwith wires.landmark beacon Any beacon that is not an airwayor airport beacon.land mobile service Two-way radio service betweena base station and mobile land vehicles, oramong mobile land vehicles.land mobile station A radio station aboard a mobile,earthbound vehicle.land return Ground reflection of radar signalsback to the transmitter.land station A fixed ground station.Langevin ion An electrically charged particle, suchas a grain of dust or droplet of water, resultingfrom the accumulation of ions.Langmuir dark space In a luminous gas discharge,the dark region around a negativelycharged probe inserted into the positive column.Compare CROOKES’ DARK SPACE.Langmuir’s law See CHILD’S LAW.language In digital-computer operations, any oneof the detailed systems for representing data, instructions,and procedures through the use ofsymbols and symbol sequences. See MACHINELANGUAGE, ASSEMBLY LANGUAGE, COBOL,FORTRAN, and BASIC.language laboratory An electronic contribution tothe teaching and learning of languages. It consistsof recordings in a language being studiedand all the equipment associated with recording,playback, and monitoring. Students listen to thespeech of experts in the language record, listento, and later erase their own utterances in thelanguage.language translation 1. The conversion of statementsin one computer language to equivalentstatements in another. 2. The conversion of onewritten natural language into another (e.g., Frenchto Russian) by means of a computer program.language translator 1. An assembly program,compiler, or other routine used for translation betweencomputer languages. 2. A high-level programthat allows a computer to translate onewritten natural language into another (e.g., Chineseto Italian).L antenna See INVERTED-L ANTENNA.lantern battery A moderate-sized electrochemicalbattery usually rated at 6 volts. Derives its namefrom its original use as a power source for portablelamps. One type has spring contacts on the top.Another type has thumbscrew terminals. The nonrechargeablebattery consists of 4 zinc–carbonor alkaline cells in series. Some varieties arerechargeable, consisting of nickel–cadmium (NiCd)or nickel–metal-hydride (NiMH) cells. This type ofbattery can provide enough energy to operate alow-power radio transceiver. Two units connectedin series, or four units in series-parallel, make a12-volt battery that can power a small portableCitizen Band (CB) or amateur radio station.lanthanum Symbol, La. An elemental metal of therare-earth group. Atomic number, 57. Atomicweight, 138.906.lanyard A wire or cable used to quickly pull apartthe halves of a quick-disconnect connector.lap A device used for grinding piezoelectric crystalsfor resonance at a desired frequency.lap dissolve The simultaneous fading out of onetelevised scene while another is fading in so thatone is apparently dissolving into the next. It isalso applicable to motion pictures.lapel microphone A small microphone that isclipped to a lapel of a user’s jacket or coat.lap joint An overlapping splice of two conductors.Laplace transform Symbol, L. An operator that reducesthe work of solving certain differentialequations by permitting them to be handled bysimpler algebraic methods.

lapping • laser diode 399lapping Fine-tuning quartz crystal plates by movingthem over a flat plate coated with a liquidabrasive.laptop computer See NOTEBOOK COMPUTER.lap winding In a motor or generator armature, awinding in which the opposite ends of each coilare connected to the adjoining segments of thecommutator.lap wrap 1. A form of asbestos cloth wire insulation.2. A method of wrapping with electrical tape,in which there is considerable overlap among theturns of the tape.large calorie See KILOGRAM-CALORIE.large loop antenna A single-turn open or closedloop, usually having a circumference of 0.5 wavelengthor 1 wavelength. With a half-wavelengthopen or closed loop, maximum radiation occursin the plane of the loop. A full-wavelength closedloop exhibits maximum radiation and responsealong the axis. This type of antenna can be usedfor wireless transmitting and receiving applications.Either the open or the closed halfwavelengthloop exhibits a slight power lossrelative to a dipole, but the full-wavelength loopshows a small gain over a dipole in its favoreddirections. Compare SMALL LOOP ANTENNA.large-scale integration Abbreviation, LSI. The inclusionof more than 100 transistors, performingvarious individual, but interrelated circuit functions,on a single integrated-circuit chip.large signal A relatively high-amplitude signal thattraverses so large a part of the operating characteristicof a device that nonlinear portions of thecharacteristic are usually encountered. CompareSMALL SIGNAL.large-signal analysis The rigorous study of circuitsand devices that process large signals.large-signal component 1. A coefficient or parametersuch as amplification, transconductance, ordynamic resistance, measured under conditionsof large-signal operation. Also see LARGE SIGNALand LARGE-SIGNAL EQUIVALENT CIRCUIT. 2. Adevice designed for operation at high signallevels.large-signal equivalent circuit For a given transistorcircuit, the equivalent circuit at high signallevels (i.e., at amplitudes approaching saturationand cutoff levels). Also see EQUIVALENT CIR-CUIT.large-signal operation The use of a circuit or deviceat signal levels sufficiently high so that nonlinearportions of the characteristic are usuallyencountered. Compare SMALL-SIGNAL OPERA-TION.large-signal transistor See POWER TRANSISTOR.large-signal voltage gain In an integrated-circuitamplifier, the voltage gain under open-loop conditions,determined as the difference in the outputvoltage divided by the difference in the input voltage.It is usually specified in volts per millivolt orvolts per microvolt.Larmor orbit The path followed by a charged particlein a constant magnetic field. Because of interactionbetween the external field and the fieldgenerated by the particle, the charged particletravels in a circular path.laryngaphone See THROAT MICROPHONE.LASCR Abbreviation of LIGHT-ACTIVATED SILI-CON-CONTROLLED RECTIFIER.LASCS Abbreviation of LIGHT-ACTIVATED SILI-CON-CONTROLLED SWITCH.lase To emit coherent electromagnetic energy inthe visible-light spectrum. See LASER.laser Acronym for light amplification by stimulatedemission of radiation. A device that produces coherentradiation in the visible-light range, that is,between 750 and 390 nanometers (one nanometeris 10 -9 meter). Some devices that produce coherentradiation in the infrared, ultraviolet, orX-ray parts of the spectrum are also referred to aslasers. Lasers can be either continuous or pulsed,and are characterized by coherent, monochromaticemissions. The peak intensity ranges froma few microwatts to many megawatts.LaserbeamRuby rodFlashtubePower supplylaserSilveredendlaser beam The radiation from a laser—especiallyif the divergence is very low, that is, the rays arealmost perfectly parallel, resulting in minimal divergence.laser-beam communication A form of coherentinfrared or optical communication in which alaser beam is the link between transmitting andreceiving stations. Also see LASER, LASERDIODE, and LIGHT-BEAM COMMUNICATION.laser capacitor An energy-storage capacitor usedto discharge-fire the exciter lamp of a laser. Alsosee LASER.laser cavity An optical-resonant cavity that resultsin the emission of coherent light.laser cutting A method of using a laser for severingmaterials.laser diode A special form of semiconductor lightemittingdiode (LED), usually of the galliumarsenidetype, that emits coherent light when avoltage is applied to its terminals. Also see LASER.

400 laser disk • laue diagramOutput+EndmirrorSubstrate andheatsink−laser diodeP-typematerialN-typemateriallaser disk A method of reproducing sound inwhich a laser is used to recover the sound from acompact disk.laser Doppler radar Acronyms, ladar or lopplar. Aform of Doppler radar using the light beam of alaser instead of radio waves.laser eye surgery A method of repairing the retinaof the eye without cutting the eyeball, using laserbeams to push loose retina tissue back intoplace.laser gun A colloquial term for a weapon thatmakes use of a laser as a device of destruction.laser optical videodisc system A system in whicha low-powered laser reads audio and video informationfrom a videodisc and delivers it to a televisionreceiver.laser ranger A radar-like device using intense light(instead of microwaves).laser show A three-dimensional, midair displayhaving motion, made by using lasers in variouscombinations.laser surgery The application of a laser inmedicine for the purpose of assisting in, or actuallyperforming, operations on human subjects.laser welding Welding (especially of tiny pieces)with the heat produced by a laser beam.lasing The emission of coherent electromagneticenergy in the visible-light spectrum. See LASER.lat Abbreviation of LATITUDE.latch 1. A feedback loop in a symmetrical digitalcircuit, such as a flip-flop, used to maintain agiven state. 2. A simple logic-circuit storage elementthat consists of two gates as a unit. 3. Tomaintain a closed (energized) state in a pair of relaycontacts after initial energization from a singleelectrical pulse. See LATCHING RELAY.latching current In a thyristor, the minimumvalue of anode current (slightly higher than theholding current) that will sustain conduction immediatelyafter switch-on.latching relay An electromechanical or fully electronicrelay that locks into whichever mode it isenergized for (on or off).latch-on relay See LOCKING RELAY.latchup In a transistor switching circuit, the abnormalcondition in which the collector voltageremains at its switched-on level after the transistoris switched to cutoff from saturation.latch voltage The input voltage at which a flip-flopchanges states.late contacts Relay contacts that are operated followingthe movement of other contacts during therelay’s operation.latency 1. The time taken by a digital computer todeliver information from its memory. 2. In a serialstorage system, the access time less the wordtime.latent image 1. In a storage tube, a stored imagethat is not yet visible. 2. An image stored in the mosaicof an iconoscope. 3. The image that will appearwhen photographic film or paper is developed.lateral chromatic aberration An aberration affectingthe sharpness of off-axis color televisionimages.lateral compliance In phonograph reproduction,the ease with which the stylus can move laterallyas it follows the groove. Also see COMPLIANCEand LATERAL RECORDING.lateral-correction magnet In a color picture tube,a magnet operated with a set of pole pieces attachedto the focus element of the blue gun; itcontrols horizontal positioning of the blue beamfor convergence.lateral magnet See LATERAL-CORRECTIONMAGNET.lateral recording A disc recording in which thegroove undulates from side to side. CompareVERTICAL RECORDING.latitude Abbreviation, lat. Angular distance measuredaround the earth’s circumference to thenorth and south from the equator. CompareLONGITUDE.latitude effect The tendency of the earth’s magneticfield to decrease the number of chargedsubatomic particles that reach the surface of theearth near the equator, as compared with thenumber reaching the surface at other latitudes.Latour alternator See BETHENOD ALTERNATOR.lattice 1. The orderly internal pattern (matrix) ofatoms in a crystal. Also see CRYSTAL LATTICE.2. A symmetrical arrangement of components ina network (such as an attenuator, a filter, or abridge circuit).lattice filter A lattice network having reactance inits arms that makes it a selective circuit.lattice network See LATTICE, 2.lattice section See LATTICE, 2.lattice structure See LATTICE, 1.lattice winding See UNIVERSAL WINDING.laue diagram A pattern of spots on a photographicplate produced by the scattering of high energyradiation as it falls on a thin crystal. This patternis used to determine the nature of the crystalmaterial.

launching • LC 401InputZZZlattice filterOutputlaunching The energy transference from a cableinto a waveguide.lavalier microphone A small microphone that canbe hung from the user’s neck on a cord or chain.law 1. A general, verifiable statement that describesthe behavior of entities or the relationships betweenphenomena or concepts. The product of inductivereasoning that follows many observationsand controlled experiments (e.g., first law ofthermodynamics, inverse-square law, Kirchhoff’slaws, and Ohm’s law. 2. The nature of the changeof a dependent variable, particularly as depictedby a response curve (e.g., square law).LAWEB Civilian weather bulletins issued every sixhours from ship and shore positions along theGreat Lakes during the sailing season.lawn mower 1. A facsimile term for a helix recordingmechanism. 2. A radar receiver preamplifier.law of a curve See LAW, 2.law of averages In probability and statistics, aprinciple stating that for a large sampling ofevents, the numerical probability value will bemore closely approached than when the samplingis small. Compare LAW OF LARGE NUMBERS.law of charges Different electric charges attracteach other, and similar charges repel each other.law of electric charges See LAW OF CHARGES.law of electromagnetic induction See LENZ’SLAW.law of electrostatic attraction See COULOMB’SLAWS.law of electrostatic repulsion See COULOMB’SLAWS.law of first wavefront In acoustics, a rule statingthat the perceived direction from which a soundarrives is determined by the first wavefront thatreaches the listener’s ears.law of induction See FARADAY’S LAW.law of inverse squares See INVERSE-SQUARELAW.law of large numbers In probability and statistics,a principle stating that with a large sample, thesample average will approximate the populationaverage. It is often erroneously called LAW OFAVERAGES.law of magnetism Different magnetic poles attracteach other, and similar magnetic poles repel eachother.Zlaw of natural decay See EXPONENTIAL DE-CREASE.law of natural growth See EXPONENTIAL IN-CREASE.law of normal distribution Gauss’ law of the frequencydistribution of a repetitive function, describingthe probability of deviations from themean.law of octals Chemical activity occurs between twoatoms lacking eight valence electrons, and continuesuntil the requirement of eight electrons issatisfied for all but the first orbit, where only twoelectrons are required. Of interest in the study ofsemiconductors.law of radiation See QUANTUM THEORY.law of reflection For a ray of energy striking asmooth reflective surface, the angle of reflectionis equal to the angle of incidence, with respect toa plane tangent to the surface at the point of incidence.Lawrence accelerator See CYCLOTRON.lawrencium Symbol, Lr (occasionally Lw). A shortlivedradioactive element produced artificiallyfrom californium. Atomic number, 103. Atomicweight, about 260.lay See DIRECTION OF LAY.layer 1. A complete coil winding consisting of turnslaid side by side (not on top of each other). 2. In asemiconductor device, a region having uniqueelectrical properties (e.g., n layer). 3. A regionof the ionosphere. See IONOSPHERIC LAYERS.4. The tape on a reel or in a cassette, encompassingone complete turn (rotation). 5. In general, asingle stratum of a stratified medium.layer-to-layer transfer In a roll of magnetic tape,unwanted transfer of data between adjacentturns on the reel. If severe, this transfer cancause drop-in or drop-out in a computer. In audioapplications, it can sometimes be heard as a delayedecho or a faint sound occurring just prior tothe actual recorded sound.layer winding A coil winding in which the turnsare arranged in two or more concentric layers.layerwound coil An inductor wound in layers, oneon top of the other. Also see LAYER, 1. CompareSINGLE-LAYER COIL.layout The arrangement of components on a chassis,printed circuit board, or panel.lazy-H antenna An antenna consisting of two verticallystacked collinear elements, producing bothhorizontal and vertical directivity.Lb Abbreviation of LAMBERT; also, L (preferred).lb Abbreviation of POUND.L band A radio-frequency band extending from 390MHz to 1.55 GHz. For subdivisions of this band,see L C BAND, L F BAND, L K BAND, L L BAND, L PBAND, L S BAND, L T BAND, L X BAND, L Y BAND,and L Z BAND.LC 1. Abbreviation of LIQUID CRYSTAL; also abbreviatedlix. 2. Abbreviation of INDUCTANCE-CAPACITANCE. 3. Symbol for LC CONSTANT.

402 L carrier • lead frameL carrier In a telephone system, a carrier having afrequency between approximately 68 kHz and 10MHz. It can be used in wire-transmission or radiolinks.L C band A section of the L BAND extending from465 MHz to 510 MHz.LC bridge See INDUCTANCE-CAPACITANCEBRIDGE.LC constant Abbreviation, LC. The product of theinductance and capacitance required for resonanceat a given frequency.LCD Abbreviation of LIQUID-CRYSTAL DISPLAY.LC filter See INDUCTANCE-CAPACITANCE FIL-TER.L circuit See L NETWORK.LC meter See INDUCTANCE-CAPACITANCE ME-TER.LCR See INDUCTANCE-CAPACITANCE-RESIS-TANCE.LC ratio In a tuned circuit, the ratio of inductanceto capacitance.LCR bridge See IMPEDANCE BRIDGE, 1.L d Symbol for DISTRIBUTED INDUCTANCE.LDF See LOW-FREQUENCY DIRECTION FINDER.L display Also called L scan. A radar display inwhich the target appears as two horizontaltraces, one extending from a vertical timebase tothe right, the other to the left.lead Pronunciation, leed. 1. A conductor (usuallya wire) leading to or emerging from a terminal orelectrode. 2. In computations relating phase, theextent to which one quantity precedes another(e.g., current leads voltage by 90 degrees in apure capacitance). Compare LAG.lead Pronunciation, led. Symbol, Pb. A heavymetallic element. Atomic number, 82. Atomicweight, 207.2. It can be used as a shield againstatomic radiation, and has various applications inelectronics (e.g., as electrodes in batteries and asa component of solder). See LEAD-ACID BAT-TERY, FUSE, and SOLDER.lead–acid battery A set of two or more lead–acidcells connected in series, usually housed in acommon enclosure. Some batteries of this type,notably automotive batteries, are made from setsof lead–acid cells having a free-flowing liquid acid.Other cells have a semisolid “paste” electrolyte.These batteries are popular in consumer electronicdevices that require a moderate amount ofcurrent. They are also used in uninterruptiblepower supplies (UPSs) for personal computers.See LEAD–ACID CELL.lead–acid cell A rechargeable electrochemical cellhaving an electrolyte of sulfuric acid. The electrodesare lead (negative) and lead dioxide (positive).Produces about 1.5 volts under no-loadconditions when fully charged. A large cell of thistype can store several tens of ampere-hours.Smaller units have less capacity but more versatility.Their main advantage is reasonable cost,considering that they can be charged and dischargedmany times.StrapPositiveplateSlotted rubberseparatorWoodseparatorTerminalBottom ofpositive plateFiller cap and ventSealing compoundCoverRubbercontainerNegativeplateBottomofnegativeplateSupportsSediment spaceslead-acid celllead cell 1. A lead-acid cell. 2. A lead-sulfide photocell;see LEAD SULFIDE, 1.lead dress See DRESS.leader 1. The blank section at the beginning of amagnetic tape. It is usually made of plastic. 2. Arecord, preceding a group of records, that identifiesthe group and provides other data pertinentto the group. 3. In a lightning stroke, the initialmovement of electrons or positive ions, creatingthe ionized path that allows discharge.lead frame The metal frame holding the leadsof a circuit package (DIP) in place beforeencapsulation.

lead-in • least-significant digit 403lead-in The wire connecting an antenna to a receiveror transmitter.leading current Current that precedes voltage intime. Also see LEAD.leading edge The rising edge of a pulse; compareTRAILING EDGE.leading ghost A twin television image to the left ofthe original on the screen.leading load A load in which current leads voltage(i.e., a capacitive load).lead-in groove Around the outer edge of a phonographrecord, a blank spiral groove that leads thestylus into the first groove of the recording. CompareLEAD-OUT GROOVE.leading whites In a television picture, an abnormalcondition in which the leading (left) edge of ablack object has a white border.leading-zero suppression In a digital meter, theblanking out of all zeros to the left of the decimalpoint.lead-in spiral See LEAD-IN GROOVE.lead-in tube A tube of insulating material, such asplastic or ceramic, used to conduct an antennalead-in through a wall.lead-in wire 1. A single wire, used as a feed line fora shortwave receiving antenna. 2. The feed linefor a television receiving antenna. 3. A feed linefor a transmitting antenna.lead network A phase-shift circuit containing seriescapacitance and shunt resistance; it produces aleading phase shift. Compare LAG NETWORK.lead-out groove Around the inner edge of a phonographrecord, a blank spiral groove leading intothe eccentric or locked groove.lead-over groove On a phonograph record containingseveral recorded tracks, a blank groovethat conducts the stylus from the end of onerecording to the beginning of the next.lead screw 1. A threaded rod that guides the cutteracross the surface of a disc during its recording.2. In facsimile transmission, a threaded shaftthat moves the drum or scanning mechanismlengthwise.lead sulfate Formula, PbSO 4 . An insulating compoundformed in a LEAD-ACID CELL by thechemical action between the lead in the platesand the sulfuric-acid electrolyte. If the sulfate isnot broken down during charging of the cell, itwill eventually ruin the cell.lead sulfide Formula, PbS. A compound of leadand sulfur used as the light-sensitive material insome photoconductive cells.lead zirconate titanate A synthetic piezoelectricmaterial.leaf electroscope An electroscope using a pair ofgold leaves or a single gold leaf and a solid strip ofmetal.leak 1. The loss of energy through a stray path notintended for conduction. 2. A point from whichenergy is lost through a stray path not intendedfor conduction.leakage 1. The small current that flows through anelectrical insulator. 2. The electromagnetic fieldthat is radiated or received by a feed line thatshould theoretically have 100-percent shielding.leakage current The zero-signal current flowingacross a reverse-biased semiconductor junction.leakage flux Collectively, magnetic lines of fluxaround a transformer that do not link the primaryand secondary coils.leakage inductance Self-inductance caused byLEAKAGE FLUX. Leakage inductance is effectivelyin series with the primary or secondarywinding of a transformer.leakage resistance 1. In an imperfect insulator,the ohmic resistance, calculated by dividing thevoltage across the insulator by the current flowingthrough the insulator. 2. The quotient ofvoltage and current in a reverse-biased semiconductorjunction.leakage radiation Radiation from parts of a system,as compared with that from the true radiator.leakage reactance Inductive reactance caused byleakage inductance in the primary or secondarycircuit of a transformer.leakance The conductance of an insulating material,measured in siemens. It is equal to the reciprocalof the leakage resistance in ohms.leaky 1. Descriptive of a capacitor in which the dielectricmaterial is not a perfect insulator. 2. Descriptiveof imperfect shielding in a coaxialtransmission line. 3. Descriptive of a waveguidewith imperfect shielding.leaky dielectric See LEAKY INSULATOR.leaky insulator An insulator that conducts significantcurrent at a specified (test) voltage.leaky waveguide A waveguide that has imperfectshielding, allowing some electromagnetic field toescape.leapfrogging In radar, a phasing process thateliminates false echoes resulting from the signalsof other radar sets.leapfrog test A test performed on different locationsby a computer program in memory; it movesto another memory area to continue tests onother locations.learning The ability of an artificially intelligent machineto improve or expand its knowledge withtime. This can occur as a result of accumulationof information; it can also occur in systems thattrack their errors to avoid repeating them.leased line A communications circuit reserved exclusivelyfor a specific user.least-significant bit Abbreviation, LSB. The digitwith the lowest place value in a binary number.least-significant character Abbreviation, LSC. Inpositional notation, the extreme right-hand characterin a group of significant characters. SeePOSITIONAL NOTATION.least-significant digit Abbreviation, LSD. Thedigit in a number that is at the extreme right (i.e.,the one having the lowest place value).

404 least upper bound • level-0 securityleast upper bound The smallest value of a parameterthat can be obtained without changing somecharacteristic of a circuit, program or system.Lecher frame A sturdy assemblage of LECHERWIRES.InputcouplinglinkfromRFsourceStandoffinsulatorShort-circuitingsliderPointerLecher frameDiodedcMilliammeterPickupinkBaseScaleLecher lines See LECHER WIRES.Lecher oscillator A self-excited radio-frequencyoscillator using Lecher wires in place of an inductance-capacitance(LC) tank circuit. Also seeLINE-TYPE OSCILLATOR.Lecher wires A circuit segment consisting of twoparallel wires or rods joined by a coupling loop onone end, the other end being open. A shortcircuitingbar is moved along the wires to vary theeffective length of the circuit. Radio-frequency energyis inductively coupled into the systemthrough the loop, and the bar is slid along to variousresponse points, as indicated by a meter orlamp coupled to the wires. The frequency can bedetermined by measuring the distance betweenadjacent response points. It is used at very-highfrequencies (VHF), ultra-high frequencies (UHF),and microwave frequencies. Also called Lecherframe and Lecher lines.Leclanche cell See DRY CELL, 1.LED See LIGHT-EMITTING DIODE.LED phototransistor isolator An optoelectronicisolator in which the light source is a lightemittingdiode and the light-sensitive componentis a phototransistor.LEDE Abbreviation for LIVE END/DEAD END.LEF See LIGHT-EMITTING FILM.left-hand lay See DIRECTION OF LAY.left-hand motor rule See FLEMING’S LEFT-HANDRULE.left-hand polarized wave See COUNTERCLOCK-WISE-POLARIZED WAVE.left-hand taper Potentiometer or rheostat taper inwhich most of the resistance is in the counterclockwisehalf of rotation as viewed from thefront. Compare RIGHT-HAND TAPER.left justified An item of data that occupies consecutivelocations in storage, starting at the lefthandend of its area; empty locations mightappear consecutively at the right-hand end if theitem needs fewer positions than have been provided.left shift A shift operation in which the digits of aword are displaced to the left; the effect is multiplicationin an arithmetic shift.leg 1. Any one of the distinct branches of a circuitor network; also called ARM or BRANCH. 2. In acomputer program, a path in a routine or subroutine.L electron In certain atoms, an electron whose orbitis outside of, and nearest to, the orbit of the Kelectrons.Lenard rays See CATHODE RAYS.length 1. The number of bits or characters in arecord, word, or other data unit. 2. The endto-enddimension of a device, circuit, line, etc.3. The start-to-finish duration of a time interval.length to fault In cable or line measurements fromthe home station, the distance (i.e., the cable orline length) to the point at which a fault, such asa short circuit or ground, is located.lens 1. A usually circular piece of transparent materialwith one or both surfaces curved in crosssection, used (through its refractive properties) tofocus or spread rays that pass through it. Lensesfor visible light must be transparent, but thosefor other radiation, such as radio waves, need nottransmit light. Also see ANTENNA LENS. 2. In acathode-ray tube, one or more high-voltage electrodesfor focusing an electron beam to a finepoint on the screen.lens antenna See ANTENNA LENS.lens disk A NIPKOW DISK having a lens in eachhole.lens speed The light-transmitting ability of a lens,given as an f-stop number: the lens’ focal lengthdivided by its diameter.lens turret A multiple-lens mount on a camerathat can be rotated for quick lens interchange.LEO Acronym for LOW EARTH ORBIT.LEO satellite system A set of several dozen lowearth orbit (LEO) satellites in polar orbits spacedstrategically around the globe such that, for anypoint on the earth, there is always at least onesatellite in range. The satellites can relay messagesthroughout the fleet. Any two points on thesurface are always able to make contact throughthe satellites.Lepel discharger See QUENCHED SPARK GAP.letter-identification word See PHONETIC ALPHA-BET CODE WORD.letters patent See PATENT.letters shift In a text communications terminal, acontrol character that causes all of the followingcharacters to occur in the lower case. This can bean automatic or a manual control character.let-through current The current conducted by acircuit breaker during a short-circuit.level-0 security In communications, the completelack of security measures. Anyone can listen inon a conversation at any time, provided they are

level-0 security • life 405willing to spend the money and/or time to obtainthe necessary equipment. Examples are amateur(“ham”) radio and Citizens’ Band (CB) voice communications.level-1 security Also called wire-equivalent security.In communications, the implementation ofsecurity measures such that the circuit is protectedto the extent of a typical hard-wired link.The encryption is anticipated to be unbreakablefor at least 12 months, and preferably for24 months or more. The technology is updatedat least every 12 months, and preferably every6 months.level-2 security Also called commercial-level security.In communications, the implementation ofsecurity measures such that the circuit isdeemed safe for ordinary commercial transactions.The encryption is anticipated to be of sucha nature that engineers believe it would take ahacker at least 10 years, and preferably 20 yearsor more, to break the cipher. The technologyshould be updated at least every 10 years, butpreferably every 3 to 5 years, and more often ifpossible.level-3 security Also called mil-spec security. Incommunications, the implementation of securityinvolving the most sophisticated forms of encryptionand personnel restriction that a governmentcan muster.level 1. The amplitude at which a device is functioningor at which a phenomenon occurs (e.g.,collector-current level, or received signal level).2. The minimum amplitude at which a phenomenonoccurs; also called threshold amplitude. 3.A functional plateau or echelon.level clipper See CLIPPER.level compensator 1. An automatic gain control(AGC) that effectively reduces amplitude variationsin a received signal. 2. An automatic gaincontrol in telegraph receiving equipment.level control 1. The adjustment of amplitude orthreshold. 2. A potentiometer or other variablecomponent for adjusting the amplitude or thresholdof a quantity.level indicator See VOLUME INDICATOR.level translator Any circuit or device that altersthe voltage levels of input signals. An example isa converter that changes positive-logic signals tonegative-logic signals.level-triggered flip-flop A flip-flop that respondsto voltage level, rather than to the frequency of aninput signal.lever switch 1. A switch designed for rapid makingand breaking of a circuit. 2. A radiotelegraph key.Lewis antenna A form of antenna used at ultrahighand microwave frequencies. It resembles ahorn antenna.Leyden bottle See LEYDEN JAR.Leyden jar [Leyden, Holland (also Leiden), site ofthe invention in 1745 by Peiter van Musschenbroek,1692–1761.] The first practical capacitor.In modern form, it is a glass jar covered insideand out with metal foil and has a rod topped by ametal ball that touches the inner foil. It is stillused occasionally in classrooms for demonstratingstatic electricity. The Leyden jar was coinventedby van Musschenbroek and inventedindependently by E. G. von Kleist of Pomerania,among others.Inner,electrodemetalplateLeyden jarInsulatingcoverGlassChainOuter metalplateLeyden phial See LEYDEN JAR.Leyden vial See LEYDEN JAR.LF Abbreviation of LOW FREQUENCY.L F band A section of the L BAND extending from1.35 to 1.45 GHz.L fitting See ELL.LHD Abbreviation of LOAD/HAUL/DUMP.Li Symbol for LITHIUM.librarian program A computer program controllinga LIBRARY.library In digital-computer and data-processingoperations, the permanent storage of data or instructions.Also called permanent mass storage.libration fading In earth-moon-earth (EME) communications,also known as moonbounce, rapidand deep fading, accompanied by phase modulation,that takes place because the moon does notalways show the earth exactly the same portion ofits surface. The moon “wobbles” slightly back andforth on its axis. This causes changes in the relativephases of signals reflected from the topographicfeatures (mountains, in particular) on thelunar surface.licrystal An acronym from liquid and crystal. SeeLIQUID CRYSTAL.lidar See LIGHT DETECTION AND RANGING.lie detector See POLYGRAPH.life 1. The duration of useful service (or of operationbefore failure) of electronic equipment. 2. Fora non-rechargeable cell or battery, the length oftime it will last in a given application before itmust be discarded and replaced. 3. In roboticsand artificial intelligence (AI), a general term thatrefers to qualitative similarities between machinesand animate creatures, including humanbeings.

406 life test • light-induced electricitylife test An assessment of the life of electronicequipment—either by means of full-time testruns or accelerated time tests.lifetime See CARRIER LIFETIME.lifter A device in a magnetic tape recorder thatremoves the tape from the recording and playbackheads under fast-forward and rewind conditions.light Visible electromagnetic radiation occurring inthe wavelength band of about 750 nanometers(red light) to 390 nanometers (violet light). Includedsometimes in the category of light are infraredand ultraviolet rays.light-activated silicon-controlled rectifier Abbreviation,LASCR. A silicon-controlled rectifierthat functions both as a photosensor and a heavydutybistable electronic switch, allowing high currentsto be switched by means of a light beam.light-activated silicon-controlled switch Abbreviation,LASCS. A pnpn device that acts simultaneouslyas photocell and electronic switch.light adaption 1. The process whereby the eye adjustsitself to an increase or decrease in illumination.2. Similar action in photoelectric devices.3. The length of time required for the eye to adjustitself to an increase or decrease in illumination.light amplifier A solid-state amplifier using an inputelectroluminescent cell and an output photocell,or some similar pair of components. Thedevice is essentially an optoelectronic couplerwith gain.light-beam communication A system of communicationin which a beam of light between transmittingand receiving stations is modulated orinterrupted to convey intelligence. A laser is commonlyused because it has minimal beam divergence,allowing maximum communication range.light-beam meter An electric meter using aLIGHT-BEAM POINTER.light-beam pointer A slender beam of light that replacesthe pointer in a moving-coil meter. Thelight comes from a small incandescent lamp andis reflected by a mirror attached to the coil; whenthe coil moves, a spot of light moves over the scaleof the meter.light-beam receiver The receiver in a LIGHT-BEAM COMMUNICATION system.light-beam recorder A graphic recorder using alight-beam pointer. In this device, a small spot oflight traces a pattern on moving photographicfilm, which is subsequently developed to producea permanent record.light-beam transmitter The transmitter in aLIGHT-BEAM COMMUNICATION system.light cable A cable, consisting of numerous thinoptical fibers, through which light can be transmittedfor communication or control purposes.See, for example, LIGHT-WAVE TELEPHONY.light chopper A device that modulates a lightbeam by interrupting it repetitively.TerminalModulatedlightbeamPhotocellModemTelescope(for focusing light beam)Modemlight-beam communicationTerminalLaserlight detection and ranging Acronym, lidar. Anavigation and surveillance system in which laserlight scans in a manner similar to that of RADAR.light dimmer See DIMMER.lighted pushbutton See LIGHTED SWITCH.lighted switch A pushbutton switch containing apilot light that glows to show when the switch ison. Also called illuminated switch.light-emitting diode Abbreviation, LED. A semiconductordevice that emits visible light when forwardbiased. Also see LASER DIODE.light-emitting film A thin phosphor film thatbecomes luminescent when a high-frequencyvoltage is applied across its surface. Also seeELECTROLUMINESCENCE and ELECTROLUMI-NESCENT CELL.light flasher An electronic circuit or simple automaticflasher switch for flashing a lamp at regularintervals.light flicker See LOAD FLICKER.light flux See LUMINOUS FLUX.light hood See HOOD.light-induced electricity See PHOTOELECTRIC-ITY.

light load • light sensor 407light load A load that is a fraction of the usualvalue for a given application. That is, its resistanceor impedance is several times higher thannormal.light meter An electronic instrument for measuringthe intensity of light. It generally consists ofa photodiode, a battery, and a direct-current microammeterconnected in series. A directcurrentamplifier can be used to increase thesensitivity.light microsecond A unit of electrical distance;the distance that light, or any electromagneticdisturbance, travels in free space in 1 microsecond.Approximately equal to 300 meters.light modulation Variation of the instantaneousbrightness of a visible light beam in synchronizationwith the instantaneous amplitude of a modulatingsignal. Also see LIGHT MODULATOR.light modulator A device with which a beam oflight can be modulated by an electrical signal.light negative Pertaining to negative photoconductivity,the decrease in conductivity of a photosensitivematerial under illumination. CompareLIGHT POSITIVE.lightning The discharge that occurs between positiveand negative poles in the atmosphere. Commonin and near areas where heavy rainfall isoccurring. It also can occur in snow storms, insand storms, and over erupting volcanoes. Generally,the negative pole is in a cloud and the positivepole is at the surface of the earth, resultingin a flow of electrons from cloud to ground. Somelightning occurs as a flow of electrons fromground to cloud, or between two clouds. Suchdischarges sometimes attain current levels ofmore than 1,000,000 amperes.lightning arrester A device that bypasses highvoltagepulses from most nearby lightning dischargesto the earth, helping to protect electronicequipment connected to an outdoor antenna orpower line. Is not a total guarantee of protection,however.lightning conductor 1. A system for protectingbuildings from lightning strikes. A common systemincludes a lightning rod, heavy conductor,and ground rod. The ground rod is placed at leastsix feet from the base of a building and is at leasteight feet long. 2. The conductor between thelightning rod and ground rod in a system, as definedin 1.lightning detector See KERAUNOGRAPH andKERAUNOPHONE.lightning rod A protective device mounted on theoutside of structures, consisting of a pointed,grounded metal rod that will conduct a lightningdischarge to earth.lightning strike A direct hit of an object by a lightningstroke. It usually causes extensive damageto electrical and electronic equipment throughwhich the discharge passes.LightningrodCone ofprotection 45° 45°lightning rodlightning stroke The discharge that occurs withlightning. The peak current is typically severaltens of thousands of amperes, but in some casescan exceed 1,000,000 amperes. A stroke can consistof one discharge or several individual dischargesin rapid succession.lightning switch See GROUND SWITCH.light-operated relay See PHOTOELECTRIC RE-LAY.light-operated switch A PHOTOELECTRIC RE-LAY, or a switch operated by such a relay.light pen A probe containing a tiny photosensor inits tip. The tip of the light pen is touched to thescreen of a cathode-ray tube to sense the beamwhen it passes the spot of contact. It is used asan input device in some computers and terminals.light pipe 1. An OPTICAL FIBER. 2. A cable consistingof numerous optical fibers in a bundle.See FIBEROPTICS, 1.light positive Pertaining to positive photoconductivity,when the conductivity of a photosensitivematerial increases under illumination. CompareLIGHT NEGATIVE.light quantum See PHOTON.light ray A thin beam of light. Theoretically, a rayemerges from a point source (i.e., it has no width).light receiver See LIGHT-BEAM RECEIVER.light relay A photoelectric device that operates arelay, according to fluctuations in the intensity ofa light beam.light-sensitive cathode Also called photocathode.A cathode that emits electrons when exposed tolight.light-sensitive diode A semiconductor diode usableas a photoconductive cell. Such diodes areavailable as both junction and point-contacttypes.light-sensitive material A photoconductive orphotoemissive substance.light-sensitive resistor See PHOTOCONDUCTIVECELL.light sensor 1. A light-sensitive device, such asa photocell, photodiode, phototransistor, or

408 light sensor • linear algebraphototube. 2. A light-sensitive substance, suchas cesium, selenium, silicon, cadmium selenide,or lead sulfide.light source Any generator of light. Under someconditions, the source is regarded as a point.light spectrum See ELECTROMAGNETIC THE-ORY OF LIGHT.light-spot scanner Also called flying-spot scanner.A television camera using (as a source of illumination)a spot of light that scans what is to betelevised.light transmitter See LIGHT-BEAM TRANSMIT-TER.light valve 1. An electromechanical device forvarying the intensity of light passing through itsadjustable aperture. 2. See KERR CELL.light-wave telephony Telephone communicationby means of modulated-light transmission, usuallythrough an OPTICAL FIBER.light-year Abbreviation, lt-yr. Pertaining to astronomy,a unit of distance equal to the distance traveledby light in one year in a vacuum: 9.460 55 ×10 15 meters (5.878 × 10 12 miles).likelihood In probability and statistics, the chancethat an event will occur or that an outcome willbe realized. Also see PROBABILITY, 1, 2.lim Abbreviation of LIMIT.Lima Pronunciation, LEE-ma. Phonetic alphabetword for the letter L.limen A unit that has been proposed as the minimumaudible change in frequency that can be detectedby at least half of a group of listeners.limit1. The lowest or highest frequency in a band.2. In mathematics, a fixed value that a variableapproaches. 3. The upper and lower extremes inany performance range or value range.limit bridge A bridge used to check a component(e.g., resistance, capacitance, or inductance) interms of the tolerance limits, rather than thenominal (named) value, of that component. Alsosee BRIDGE, 2.limited integrator A circuit that integrates two inputsignals until the corresponding output signalexceeds a certain limit.limited stability A characteristic of a circuit orsystem, allowing proper operation only if the inputsignal and applied voltages are within certainmaximum and minimum limits.limiter A device or circuit whose output-signal amplituderemains at some predetermined level, despitewide variations in input-signal amplitude.limiting The restriction of the maximum peak amplitudeof a signal to a designated level.limiting amplifier An amplifier that automaticallyholds the output-signal level to a prescribed value.limiting current In electrolysis, the highest currentthat conducts under certain conditions ofion concentration. This current depends on theelectrolyte material, the concentration of the electrolytein solution, the electrode substance, andthe size of the electrolytic cell.LimitedamplitudelimitingPeak amplitudelimiting error The anticipated maximum value ofthe absolute error in a computation.limiting resistor See CURRENT-LIMITING RESIS-TOR.limiting resolution As a measure of video imageresolution, the maximum number of lines for pictureheight that can be discriminated on a testchart.limit switch A switch that is actuated when amonitored quantity (e.g., current, voltage, or illumination)reaches the limit of its range.line 1. A wire, cable, or waveguide, along whichelectrical or electromagnetic energy travels fromone defined place to another. 2. One lengthwisepath in which a force, such as electricity or magnetism,is evidenced. Such a line of flux has theoreticallyzero width.line advance 1. The physical separation betweenthe centers of adjacent scanning lines in a televisionsystem. 2. Line feed in a text data transmissionsystem.line amplifier An amplifier in a telephone line orsimilar channel, or one feeding such a line fromthe input end.linear 1. In a straight line. 2. In the manner of astraight line. Thus, linear response is indicatedwhen one quantity varies directly with another;the graph of this response is a straight line (i.e.,one of constant slope). 3. The characteristic of asignal that is a replica of another (e.g., an amplifieroutput signal of the same waveform as that ofthe input signal).linear absorption coefficient A number expressingthe extent to which the intensity of an X-raybeam is reduced per centimeter of the materialthrough which it passes.linear accelerator A device in which subatomicparticles are accelerated in a straight linethrough a long tube. This action is in contrastwith that occurring in a circular accelerator, suchas a CYCLOTRON.linear algebra A branch of mathematics that dealswith the solving of linear equations or sets of linearequations.

linear amplifier • linear scale 409linear amplifier 1. An amplifier for which a linearrelationship exists between input and output parameters(e.g., a high-fidelity audio amplifier).2. A class-AB radio-frequency power amplifier thatdoes not distort the envelope of an amplitudemodulated(AM) or single-sideband (SSB) signal.It is commonly used by amateur radio operators.linear array A directional antenna having equallyspaced, in-line elements.linear circuit 1. A circuit whose output is a faithfulreproduction of the input. See LINEAR AMPLI-FIER, 1 and LINEAR DETECTOR. 2. A circuitwhose performance is linear. See LINEAR RE-SPONSE, 1.linear decrement In a damped wave, a constantdecrease in amplitude with time, as opposed to adecrease that is a logarithmic or otherwise nonlinearfunction of time. Compare DECREMENT.linear detector A detector whose output/input relationshipis linear. Also see LINEAR, 2, 3; LIN-EAR CIRCUIT, 1; and LINEAR RESPONSE, 1, 2,3.linear differential transformer A device that convertsthe physical position of an object into anoutput voltage or current. The voltage or currentis directly proportional to the displacement.linear distortion Amplitude distortion in whichthe output and input signal envelopes are disproportionate(in the absence of spurious frequencies).linear equation See FIRST-DEGREE EQUATION.linear function 1. In Cartesian two-space, a functionof the form y = mx + b, where the coordinatesare (x,y), the slope is m (any real number) and b isthe point on the y axis at which the graph crossesthe axis. 2. Any function in any number of dimensionswhose graph appears as a straight linein the Cartesian system of coordinates.ylinear functionlinear IC See LINEAR INTEGRATED CIRCUIT.linear integrated circuit An integrated circuit designedfor analog operations (such as signalxamplification, oscillation, nondigital regulation,analog instrumentation, and similar applications).Compare DIGITAL INTEGRATED CIRCUIT.linearity 1. The degree to which performance orresponse approaches the condition of being linear,expressed in percent or parts per million.Also see LINEAR AMPLIFIER, 1; LINEAR CIR-CUIT, 1, 2; LINEAR OSCILLATOR, 1; LINEAR RE-SPONSE, 1, 2, 3; and LINEAR TAPER. 2. In acathode-ray-tube image, absence of compressionor stretching of any portion of the image; that is,an undistorted reproduction.linearity control In a cathode-ray-tube display,the potentiometer used to correct image linearity.See LINEARITY, 2.linearity error 1. The difference between a theoreticallylinear function and the actual function,as observed under experimental conditions.2. The degree of nonlinearity in an amplifier thatis supposed to be linear.linear modulation 1. Modulation in which theinstantaneous amplitude of the input signal isdirectly proportional to the instantaneous amplitudeof the output signal. 2. Modulation in whichthe instantaneous amplitude of the input signalis inversely proportional to the instantaneousamplitude of the output signal. 3. Modulation inwhich the instantaneous amplitude of the inputsignal is directly proportional to the frequency orphase deviation of the output signal.linear motor A motor in which the stator and rotorare parallel and straight.linear oscillator 1. An oscillator whose alternating-currentoutput amplitude varies linearly withits direct-current input. 2. A line-type oscillator.linear programming A method of determining theoptimum value for a certain set of linear equations.Generally, this is done by finding the pointon a plane in space closest to some point not onthe plane.linear quantizing A method of quantizing in whichall of the intervals are of equal size or duration.An example is a linear analog-to-digital convertercircuit.linear reflex detector See INFINITE-IMPEDANCEDETECTOR.linear response 1. A response in which the valueof the dependent variable is equal or directly proportionalto the value of the independent variable.Thus, the graph of the response function is astraight line over the range of normal operatingvalues. Compare LOGARITHMIC RESPONSE, 1and SQUARE-LAW RESPONSE. 2. A type of responsein which a quantity (such as current)varies directly with another quantity (such asvoltage). Compare LOGARITHMIC RESPONSE, 2.3. Low-distortion response. Also see HIGH FI-DELITY.linear scale A scale in which all of the divisionsrepresent the same differential and are equallyspaced. On a linear scale, a given difference

410 linear scale • line filter109876543210linear scale10987654always has the same physical length, no matterwhere on the scale it appears. For example, theinterval between 3 and 4 on a linear scale is thesame as any interval between x and x + 1, wherex is any real value on the scale.linear sweep In a television or oscilloscope circuit,the scanning of the electron beam across thescreen at a constant speed. Also see LINEAR, 1;LINEAR RESPONSE, 1; and LINEARITY, 2.linear taper In a potentiometer or rheostat, resistancevariation that is directly proportional toshaft rotation. Thus, half the total resistance correspondsto movement of the shaft over half thearc of full rotation. Compare LOG TAPER. Alsosee TAPER.linear time base For an oscilloscope, the base providedby sweeping the electron beam horizontallyat a uniform rate. Also see LINEAR SWEEP.linear track On a video tape, the track that containsaudio information that accompanies thevideo data. It was so named because it is a single,straight track, in contrast to the video tracks,which are angled.linear tracking In a turntable system, a designscheme in which the lateral movement of the stylus,as the disc is played, occurs in a straight line,rather than in an arc.linear transformer A radio-frequency transformerconsisting of a section of transmission line.linear variable differential transformer Abbreviation,LVDT. A differential transformer exhibitinglinear response. Also see LINEAR RESPONSE, 1,2.InputLinearCoupling linkλ/4linear transformer321NonlinearOutputline balance The degree of electrical similarity betweentransmission line conductors, or between aconductor and ground.line-balance converter A device used to isolatethe outer conductor at the end of a coaxial linefrom ground.line characteristic distortion Fluctuations in theduration of received signal impulses in text datacommunications, caused by changing currenttransitions in the wire circuit.line circuit The telephone system relay equipmentassociated with stations connected to a switchboard.line code A code between the digits in processingequipment and the pulses representing the digitsin a line transmission.line conditioning In data communications, themodification of private or leased lines by addingcompensating reactances to reduce amplitudevariations or phase delays over a band of frequencies.line contact stylus A needle used to reproducestereo high-fidelity sound from vinyl discs. It hasa characteristic oblate ellipsoidal shape.line coordinate A symbol identifying a specific rowof cells in a matrix; a specific cell can be locatedwith an additional column coordinate.line cord A flexible two- or three-wire insulated cableconnecting equipment to the power line bymeans of a plug that mates to a standard electricaloutlet.line current 1. Current flowing from a power lineinto equipment. 2. Current flowing in a transmissionline. 3. Current flowing into a parallelresonantcircuit.line diffuser A circuit that creates minor verticaloscillations of the spot on a television screen,making the individual scanning lines less noticeable.line driver An integrated circuit capable of transmittinglogic signals through long lines.line drop The voltage drop along a line supplyingpower to a device.line equalizer See EQUALIZER.line fault A discontinuity in a transmission line,resulting in signal loss at the receiving end of acircuit.line feed In a text data transmission system, themovement of the paper, platen, or cursor to allowfor printing or displaying an additional line oftext.line filter1. A circuit that can be inserted in theutility power cord of an appliance, device, or systemfor transient suppression and the minimizationof electromagnetic interference (EMI). Thefilter employs series inductors, parallel capacitors,and in some cases, a clamping device. Installedbetween a radio transmitter and theutility lines, such a filter can choke off radiofrequency(RF) current and help keep utilitywiring from acting as an antenna. Installed in the

line filter • linkage 411power cords of home entertainment equipment,such as stereo audio amplifiers, line filters cankeep RF from entering the apparatus throughthe power supply. 2. A circuit containing parallelcapacitors and/or series inductors, installedin a twisted-pair telephone line to reduce oreliminate the effects of EMI and transients in atelephone set.linefinder A switching device that finds one of agroup of calling telephone lines and connects it toa trunk, connector, or selector.line frequency 1. The frequency of power-line voltagein the United States, 60 Hz. 2. The rate atwhich the horizontal lines are traced in a videoimage. Also see HORIZONTAL FREQUENCY.line group 1. A group of signals sent by wire transmission.2. The frequency spectrum occupied bya group of signals sent by wireless transmission.line leakage Resistance between insulators of twowires in a telephone line loop.line loss The sum of energy losses in a transmissionline.lineman A technician who works mainly with telephoneor telegraph lines.line matching transformer A device that providesan impedance match in an audio circuit, and alsocan adapt balanced to unbalanced audio transmissionlines (or vice versa).line noise1. Electrical noise (as received by a radio)arising from fluctuations of current or voltagein a power line. 2. Noise in a data transmissionline.line of flux1. A line (usually curved) depicting thepoints of equal-intensity field strength in thevicinity of an electric charge or a charged body.Also see FLUX. 2. A line depicting the points ofequal-intensity field strength in the vicinity of amagnetic pole or a magnetized body. Also seeFLUX.line-of-sight communication Radio communicationsbetween points located so that a straightline between them does not pass through theearth, or through any major obstructions. Alsosee LINE-OF-SIGHT DISTANCE.line-of-sight distance The maximum distanceover which an ultra-high-frequency (UHF) or microwavesignal can be directly transmitted alongthe surface of the earth. It is slightly more thanthe maximum optical line-of-sight distance.line oscillator See LINE-TYPE OSCILLATOR.line plug The plug terminating a line cord. Also seeMALE PLUG.line printer A machine that prints the results of acomputer run, line by line.line radio See WIRED RADIO.line regulation Automatic stabilization of powerlinevoltage.line-sequential system The color television systemin which the image is reproduced by meansof primary color lines (red, green, and blue) sequentiallybeamed across the screen of the picturetube. Compare DOT-SEQUENTIAL SYSTEMand FIELD-SEQUENTIAL SYSTEM.lines of cleavage See CLEAVAGE.lines oscillator See LINE-TYPE OSCILLATOR.line supervision In electronic security systems, amethod of monitoring circuit characteristics todetect possible tampering.line switch 1. The main power-line switch to a system.2. Within a piece of electronic equipment,the switch that opens and closes the circuit to theincoming power line.line-type amplifier A radio-frequency amplifier inwhich the tuned circuits are transmission linesconsisting of parallel wires, rods, or tubing, or ofcoaxial cable sections.line-type oscillator A radio-frequency oscillator inwhich the tuned circuits are transmission linesconsisting of parallel wires, rods, or tubing, or ofcoaxial cable sections.line unit In a wire data transmission system, theterminal unit, or device that converts the text signalsinto electrical impulses and vice versa.line voltage 1. The voltage between the conductorsin a power line. 2. The voltage between the conductorsof a transmission line.line-voltage drop See LINE DROP.line-voltage monitor See POWER-LINE MONI-TOR.linguistics The study of languages, includingstructure, symbology, and phonetics.link 1. The small coupling coil used in link coupling.2. A communication path between two radiofacilities for the purpose of extending therange of one, as between a remote pickup pointand a broadcast transmitter. 3. A data connectionbetween two different computers. 4. The actor process of creating a signal path or data connection,as defined in 1, 2, or 3. 5. In a digitalcomputer, a branch instruction, or an address insuch an instruction, used to leave a subroutine toreturn to some point in the main program.linkageCoupling between separated conductors ordevices through the medium of electric or magneticlines of flux.

412 link circuit • liquid-pressure alarmlink circuit A closed-loop coupling circuit havingtwo coils of a few turns of wire; each coil is placednear one of the circuits to be coupled.link coupling Low-impedance coupling via a small(usually one-turn) input or output coil fed by atwisted pair or a coaxial line.Back glassand polarizerSealed-influidInputC1 L1 L2 C2OutputFront glassandpolarizerlink couplinglinked subroutine A subroutine, entered by abranch instruction from a main routine, that executesa branch instruction returning control tothe main routine.link fuse A fuse consisting of an exposed length offuse wire.link neutralization Neutralization achieved byout-of-phase current fed back via link couplingfrom the output to the input of an amplifier. Alsocalled INDUCTIVE NEUTRALIZATION.lin-log receiver A radar receiver whose amplituderesponse is linear for small signals, but logarithmicfor large ones.lip microphone A small microphone operatedclose to or in contact with the lips.liquid A state of matter characterized by a level ofmolecular motion intermediate between that ofgases and solids; liquids have the ability (likegases) to take the shape of a container and are onlyslightly compressible. Compare GAS, PLASMA,and SOLID. Also see STATE OF MATTER.liquid absorption For a solid material, such as dielectric,the ratio of the weight of liquid absorbedby the material to the weight of the material.liquid capacitor See WATER CAPACITOR.liquid cell See ELECTROLYTIC CELL.liquid conductor See ELECTROLYTE.liquid cooling Use of circulating water, oil, orother fluid to remove heat from components orequipment, such as microprocessors or poweramplifiers.liquid crystal A liquid exhibiting some of the characteristicsof a crystal. Also see NEMATIC CRYS-TAL and SMECTIC CRYSTAL.liquid-crystal display Abbreviation, LCD. A flatpaneldisplay noted for its thin profile, lightweight, and low power consumption. The simplestdevices are used in calculators, meters,wristwatches, and radios. More sophisticateddisplays are used in computers and portablevideo units. This type of display can operate at amuch lower voltage than a cathode-ray tube(CRT). This makes it ideal for portable electronicsystems in which batteries are used. Olderdisplays of this type can be difficult to read fromcertain viewing angles. This situation hasliquid-crystal displayimproved in recent years with the advent ofactive-matrix, also known as thin-film-transistor(TFT), displays.liquid-filled transformer A transformer filled witha protective liquid insulator, such as oil.liquid-flow alarm An electronic circuit that actuatesan alarm when the flow of a liquid through pipes orother channels changes from a desired rate.liquid-flow control A servo system that automaticallymaintains or corrects the rate of liquid flowthrough pipes or other channels.liquid-flow gauge See LIQUID-FLOW METER.liquid-flow indicator See LIQUID-FLOW METER.liquid-flow meter An instrument that indicatesthe rate at which a liquid moves through pipes orother channels.liquid-flow switch In a liquid-cooled system, aswitch that actuates an alarm when the liquidslows or stops.liquid-jet oscillograph A graphic recorder usingan ink-jet galvanometer to trace the pattern on apaper chart.liquid laser A laser in which the active material isa liquid.liquid-level alarm An electronic device that actuatesvisual or audio signal devices when the surfaceof a liquid inside a tank rises or falls to apredetermined level.liquid-level control A servo system that automaticallymaintains the liquid in a tank at a predeterminedlevel.liquid-level gauge An electronic system that providesdirect readings of the level of a liquid in atank.liquid-level indicator See LIQUID-LEVEL GAUGE.liquid-level meter See LIQUID-LEVEL GAUGE.liquid load See WATER LOAD.liquid-pressure alarm An electronic circuit thatactuates an alarm when the pressure of a liquidchanges.

liquid-pressure control • lm-hr 413liquid-pressure control A servo system that automaticallymaintains or corrects liquid pressure inpipes or other channels.liquid-pressure gauge See LIQUID-PRESSUREMETER.liquid-pressure indicator See LIQUID-PRESSUREMETER.liquid-pressure meter An instrument that providesdirect readings of liquid pressure in a pipeor other channel.liquid-pressure switch A switch that actuates anexternal circuit or device when the pressure of aliquid changes.liquid rheostat See WATER RHEOSTAT.liquid valve See ELECTROMECHANICAL VALVE.liser An oscillator that produces an extremely puremicrowave carrier signal.LISP A digital-computer language written in theform of lists. A program can be directly interpretedas data, and vice versa. The entire languageis derived from a few basic functions.Programs are easy to debug. It is used in artificialintelligence (AI) research. Also see LANGUAGE.Lissajous figure Any one of several curves resultingfrom the combination of two harmonically relatedsine waves. These figures are familiar inelectronics; they are obtained when signals areapplied simultaneously to both axes of an oscilloscope.It is also called Lissajous pattern.list1. To print serially the records in a file or inmemory. 2. To print (instruct a computer to display)every item of input data in a program. 3. Aone-dimensional array of numbers.listener fatigue Physiological symptoms, such asheadaches, caused by prolonged listening to certainsounds (e.g., a pure sine wave or poorly reproducedmusic).listening angle In stereo sound reproduction, theangle between the speakers, with respect to thelistener. This angle can vary from zero to 180 degrees.Larger angles result in increased apparentchannel separation.listening test The subjective evaluation of audioequipment by listeners.liter Abbreviation, l. A metric unit of volume equalto 1.0567 U.S. liquid quarts or 0.908 U.S. dryquart. A liter is the volume of 1 kilogram of waterat 4¯C and under a pressure of 1 pascal.literal operands It is usually applicable to sourcelanguage instructions, operands that specify thevalue of a constant, rather than an address of alocation in which the constant is stored.lithium Symbol, Li. An element of the alkali-metalgroup, and the lightest elemental metal. Atomicnumber, 3. Atomic weight, 6.941.lithium battery See LITHIUM CELL.lithium cell A type of electrochemical cell with exceptionalenergy-to-mass ratio and long shelf life.There are several variations in the chemicalmakeup; they all contain lithium, a light, highlyreactive metal. These units can be manufacturedLeftchannelspeakerto supply 1.5 to 3.5 volts, depending on the particularchemistry used. These cells can last foryears in very-low-current applications such asmemory backup.Litzendraht wire See LITZ WIRE.Litz wire A woven wire having a number of copperstrands, each separately enameled to insulate itfrom the others. The wire is woven so that innerstrands come to the surface at regular intervals.It is noted for its low losses at radio frequencies.live 1. Electrically activated (i.e., sustaining voltageor current). 2. Being broadcast as it occurs.3. Acoustically reflective, as in a LIVE ROOM(contrasted with one that is acoustically absorbent).live end 1. In a recording or broadcasting studio,the part of the room in which the acoustic concentrationis greatest. 2. In a utility circuit, thewire or terminal that carries 117 volts alternatingcurrent (the ungrounded end).live end/dead end Pertaining to a room that isacoustically reflective (live) at one end, andacoustically absorbent (dead) at the other end.live roomStereosystemListeninganglelistening angleListenerRightchannelspeakerA room with little or no acoustically absorbentmaterial in its ceiling, walls, and floor,with the result that echoes and reverberation arepronounced. Compare DEAD ROOM.lix Abbreviation of LIQUID CRYSTAL.L K band A section of the L BAND that extends from1.150 to 1.350 GHz.L L band A section of the L BAND that extends from510 to 725 MHz.LLL Abbreviation of LOW-LEVEL LOGIC.lm Preferred abbreviation of LUMEN.lm/ft 2 Abbreviation of lumens per square foot. Alsosee LUMEN.lm-hr Abbreviation of LUMEN-HOUR.

414 lm/m 2 • loading disklm/m 2 Abbreviation of lumens per square meter.Also see LUMEN and LUX.lm/W Abbreviation of lumens per watt, a unit of luminosity.Also see LUMEN.ln Representation of the natural (base-e) logarithmfunction (see NAPIERIAN LOGARITHM). Alsowritten loge.L network An impedance-matching circuit, filter,or attenuator whose schematic representation resemblesan inverted letter L.LO Abbreviation of LOCAL OSCILLATOR.lo Abbreviation of low, usually as a prefix or subscript.Also abbreviated L.load 1. Also called electrical load. A device or circuitthat is operated by the electrical power output ofanother device or circuit. Examples: speaker, lightbulb, power amplifier, antenna system. 2. Alsocalled mechanical load. The mechanical poweroutput demanded of a machine—especially a motor.3. To fill an internal computer storage with informationfrom an external storage [e.g., from amagnetic disk to a computer’s random accessmemory (RAM)]. 4. To add inductors and/or capacitorsto an antenna system to alter the characteristicsof the system—especially the resonantfrequency. 5. To adjust the output circuit of aradio-frequency power amplifier for optimumenergy transfer to the antenna system.load-and-go Automatic coding in which a user’s(source) program is translated automatically intomachine language and stored.load capacitance 1. The capacitance present in anelectrical load (see LOAD, 1). 2. A capacitanceused as an electrical load.load capacity 1. In pulse-code modulation, thelevel at which a sine-wave signal has peaks coincidingwith the plus/minus virtual decision valuesof the encoder. 2. The maximum number ofsignals that a medium or line can carry withoutserious degradation of reception.load circuit 1. The circuit that forms the load, orpower-consuming portion, of a system. 2. A circuitthat facilitates transfer of power to a load.load coil See WORK COIL.load current The current flowing in a load. SeeLOAD.load division A method of connecting two or morepower sources to a single load, for optimumpower transfer.loaded antenna An antenna incorporating aLOADING COIL and/or LOADING DISK to increaseits electrical (effective) length. See LOAD-ING COIL and LOADING DISK.loaded line A transmission line in which inductorsor capacitors are inserted at appropriate points toalter the characteristics of the line.load end The end of a transmission line to which aradiator or receiver is connected.load flicker Fluctuations in the brightness oflamps, caused by intermittent loading of thepower line by other devices.Coaxialfeedlineloaded antennaShortened radiatorLoading coilRadialsystemload/haul/dump Abbreviation, LHD. A remotecontrolledor computer-controlled robot used inmining and construction work. Under the directionof a human operator or a computer, it loads,hauls, and dumps materials (hence its name). Itcan use various navigation methods, includingbeacons, computer maps, position sensors, andvision systems.load impedance Symbol, Z L . The impedance presentedby a load connected to a generator or othersource.loading 1. The matching of source impedance toload impedance, usually by means of the introductionof an inductance or capacitance into theload itself. 2. Any form of impedance matching.3. The addition of inductance and/or capacitanceto an antenna system to alter the characteristicsof the system—especially the resonant frequency.4. The modification of the acoustic impedance ofa loudspeaker.loading coil An inductor inserted in a circuit to increaseits total inductance or to provide somespecial effect, such as canceling capacitive reactance.See LOADED ANTENNA and PUPIN COIL.loading disk Also called capacitance hat. A metaldisk mounted atop a vertical antenna to increaseits effective length and thereby lower its resonantfrequency. It also increases the bandwidth of thesystem.

loading factor • local side 415loading factor The ratio of source impedance toload impedance before the introduction of loadingcircuits.loading inductance 1. The inductance present ina load. 2. An inductance used as a load.loading routine Also called loading program. Aroutine permanently in memory; it allows a programto be loaded into memory from an externalstorage medium.load life The longevity of a device in terms of thenumber of hours it can withstand its full powerrating.load line In a group of voltage-current (EI) curves,a line connecting points of equal resistance (E/I)that are equal to a particular value of load resistance(impedance).load power The power dissipated in a load.load regulation Automatic stabilization of load resistance(impedance) at a constant value.load resistance 1. The resistance present in aload. 2. A resistance used as load.load stabilizer A device for holding load current orload voltage to a constant value.loadstone Alternate spelling of LODESTONE.load termination The load connected to the outputof a circuit or device as the terminal elementin a circuit or system.load voltage The voltage developed across a load.load-voltage stabilization Automatic regulation ofload voltage.load wattage See LOAD POWER.lobe In the directivity pattern of a transducer, a figure,such as a circle or ellipse enclosing an areaof intensified response. Applicable especially toantennas.80 90 80707060 30 605025502040401530302020109°101050030°5101010202015303020404025505060 30 60707080 90 80lobe (pattern ofhorizontal half-wave antenna)lobing 1. In a transmitting or receiving antenna,the effect of ground reflection, resulting in phasereinforcement (lobes) at some elevation anglesand phase opposition (nulls) at other angles.2. The pattern of secondary maxima in theradiation response of a directional antenna.local action Electrolysis between separate areas ofa single electrode immersed in an electrolyte. Theaction is caused by impurities at different spotsin the electrode metal, causing one spot to act asan anode and the other as a cathode, thereby creatinga small battery cell.local alarm In security applications, a visibleand/or audible alarm that can be seen and/orheard easily throughout the protected zone.local area network Abbreviation, LAN. A group ofcomputers and/or terminals that are linked togetherwithin a relatively small geographic area,such as a college campus. Interconnections areusually made via cable. There are several differentconfigurations, called topologies.local battery In wire telephony, a battery installedon the subscriber’s premises.local broadcast station A standard broadcast stationlicensed in the local service. See LOCALCHANNEL and LOCAL STATION.local channel A channel in the standard amplitude-modulation(AM) broadcast band, intendedto serve only the area near the station. Transmitterpower and operating time are restricted toprevent long-distance propagation.local control The control of a radio transmitterfrom the site (in contrast to remote control).local feature focus In robotic systems, the use ofonly a small portion of the available image data toperform a function. The robot computer recognizesand acts on the data it needs, disregardingthe rest.local feedback Feedback within a circuit stage.localizer A radionavigation transmitter whose signalguides aircraft to the centerline of a runway.local oscillator Abbreviation, LO. In a wirelesstransmitter, one of the oscillators that contributesto the signal that is ultimately modulated andtransmitted. The LO output is mixed with the outputof a variable-frequency oscillator (VFO). TheLO frequency can be switchable at increments ofseveral hundred kilohertz (500 kHz and 1000 kHzare typical), facilitating band changes when mixedwith the VFO output. In some transmitters, theLO can operate at a single, fixed frequency if theVFO tunes over an exceptionally wide range.local program A program that originates at thesame single broadcast station from which it istransmitted.local reception The reception of signals from localstations. Compare LONG-DISTANCE COMMUNI-CATIONS.local side The group of circuits and componentsassociated with a communications terminal at agiven location.

416 local station • logarithmic voltmeterlocal station A station situated within the samegeneral area as the receiver, as opposed to a distantstation.local system library A computer program librarycontaining standard software associated with aspecific system.local transmission The sending of signals to receiversin the same general locality as the transmitter,as opposed to long-distance transmission.local trunk In a telephone system, the interconnectingline between local and long-distancelines.location In digital computer operation, a memoryposition (often a register) specified by an addressand usually described in terms of the basic storageunit a particular system uses (e.g., a characteris a location in a character-oriented machine).location counter A register in the control sectionof a computer containing the address of the instructionbeing executed.locked groove A continuous blank groove aroundthe inside of a phonograph record. When the discis done playing, this groove keeps the stylus fromrunning into the label or sliding across the disc.locked oscillator 1. A fixed-frequency oscillator,such as a crystal-controlled oscillator. 2. SeeBRADLEY DETECTOR.lock-in A state of synchronism, as when a selfexcitedoscillator is synchronized (locked-in) witha standard-frequency generator.lock-in amplifier A detector that makes use of abalanced amplifier. The output is the differencebetween the collector or drain currents of the twodevices.locking circuit See HOLDING CIRCUIT.locking relay See LATCHING RELAY.lock-in relay See LATCHING RELAY.lock-out 1. To prevent a hardware unit or routinefrom being activated (e.g., when there would be aconflict between operations using the same areasof memory). 2. A safeguard against an attempt torefer to a routine in use.lock-up relay An electromagnetic relay that can belocked in the actuated state nonmechanically(i.e., by means of an electromagnet or permanentmagnet).locus The set of all points located by stated conditions(e.g., the locus of secondary points that areall equidistant from a primary point is a sphere).lodestone A natural magnet; a form of the mineralmagnetite. Also spelled loadstone.log 1. Abbreviation of LOGARITHM. 2. A continuousrecord of communications kept by a station,or a record of the operation of an equipment.log 10 Abbreviation of common logarithm (base-10logarithm). Also called Briggsian logarithm.logarithm Abbreviation, log. The power y to whicha fixed number a, called the base, must be raisedto equal a given number x. Suppose x = a y , wherea, x, and y are real numbers. Then, log a x = y. Themost common logarithmic bases are 10 and thetranscendental number e, approximately equalto 2.71828. See COMMON LOGARITHM andNAPIERIAN LOGARITHM.logarithmic amplifier An amplifier whose outputsignalamplitude is proportional to the logarithmof the input-signal amplitude.logarithmic curve A graphical representation of alogarithmic function, having the form y = k log a x,where k is a nonzero real-number constant, anda is a positive real number (the logarithmic base).logarithmic decrement See DECREMENT.logarithmic graph Also called log-log graph. Agraph in which the x and y axes are both incrementedlogarithmically. Compare SEMILOG-ARITHMIC GRAPH.logarithmic horn A horn whose diameter variesdirectly, according to the logarithm of the displacementalong the axis. See HORN.logarithmic mean See GEOMETRIC MEAN.logarithmic meter A current meter or voltmeterwhose deflection is proportional to the logarithmof the quantity under measurement. The incrementson the scale of such an instrument arecloser together in the upper portion.logarithmic rate of decay See EXPONENTIAL DE-CREASE.logarithmic rate of growth See EXPONENTIALINCREASE.logarithmic response 1. Response in which thevalue of a dependent variable is at every pointproportional to the logarithm of the independentvariable. 2. A type of response in which a quantity(such as current) varies directly with the logarithmof another quantity (such as voltage).logarithmic scale A graduated scale in which thecoordinates are positioned, according to the logarithmof the actual distance from the origin.logarithmic voltmeter See LOGARITHMICMETER.Linear012Logarithmic123461020304060100logarithmic scale

log e • logic probe 417log e Abbreviation of logarithm to the base e (theNAPIERIAN LOGARITHM). Also written ln.logic 1. In digital circuits, the mathematics dealingwith the truth or falsity of statements (representedby variables) and their combinations. Alsosee SYMBOLIC LOGIC. Generally, “truth” is representedby the binary digit 1, and “falsity” is representedby the binary digit 0. 2. Collectively, theswitching circuits and associated hardware forimplementing digital functions (see 1), such asAND, NAND, NOR, OR, etc.logical decision During a computer program run,a choice between alternatives based on specifiedconditions. For example, one alternative path in aroutine might be selected because an intermediateresult was negative.logical diagram A schematic diagram showing theinterconnection between gates of a logic circuit.logical equivalence The condition in which twological statements have identical truth value forall possible combinations of truth value of theirconstituents.logical file A data set composing one or severallogical records.logical implication For logical statements x and y,the condition that y is true whenever x is true: Ifx, then y.logical operation 1. An operation using logical operators:AND, NOR, OR, and NAND. 2. A processingoperation in which arithmetic is not involved(e.g., a shift).logical operator A word or symbol representing alogic function operating on one or more operands.Examples: NOT, OR, AND, NOR, and NAND.logical shift A shift operation in which digits in aword are moved to the left or right in circular fashion;digits displaced at one end of the word are returnedat the other. Also called CYCLIC SHIFT.logic array In logic circuits, a redundant arrangementof identical components in a single package.logic circuit In digital systems, a gating or switchingcircuit that performs such logical operationsas AND, NAND, NOR, OR, and XOR. It can usediodes, transistors, charge-coupled devices, tunneldiodes, thyristors, ferroelectric elements, magnetic-coreelements, or a combination of these. Itusually consists of diodes and transistors fabricatedonto an integrated-circuit (IC) chip.AND NOT OREX-OR NAND NORlogic circuits(or gates)logic comparison An operation in which two operandsare compared for equal value.logic connectives Words connecting operands in alogic statement; the truth or falsity of the statementscan be determined from their content andthe connectives’ meanings.logic diagram 1. A graphic representation of alogic function (e.g., AND, NAND, NOR, OR, andXOR). 2. The design of a device or system representedby graphic symbols for logic elements andtheir relationships.ABCANDNOTORA B C AB + C −00001111001100110101010110101011logic diagram and truth tableOutputlogic diode See COMPUTER DIODE.logic flowchart The logical steps in a program orsubroutine represented by a set of symbols.logic function An expression for an operation involvingone or a combination of logic operators.logic gate See LOGIC CIRCUIT.logic input current In an integrated circuit, theinput current to the logic gate at a certain voltagevalue.logic input levels The range of voltages over whichthe logic trip level occurs, from low to high or highto low. It is usually expressed in volts for the lowstate and the high state; for example, low is –1 to+2 volts, high is +4 to +6 volts.logic instruction A command to execute a logicalfunction.logic level 1. One of the two logic states 0 or 1 (onor off, high or low). 2. Of the two logic states, thatwhich represents the “true” condition. 3. The voltageamplitude of digital signals in a logic system.logic probe A test probe with a built-in amplifierand (usually) indicating LEDs; its tip is touchedto various test nodes in a digital logic circuit totrace logic levels and pulses.

418 logic relay • long-term input offset voltage stabilitylogic relay See BISTABLE RELAY.logic swing In a logic circuit, the difference betweenthe voltage corresponding to the high stateand the voltage corresponding to the low state.logic symbol 1. A symbol used to represent a logicelement in a circuit diagram. 2. A symbol used torepresent a logic connective.log-log graph See LOGARITHMIC GRAPH.LOGO A high-level computer programming languageused for robot control and as an educationaid. It is especially useful for teaching childrenhow to operate computers and computerizedrobots. Statements are simple enough so thatelementary-school children can learn to writeshort programs.log-periodic antenna Also called log-periodic dipolearray (LPDA). A broad-spectrum, multiband directionalantenna in which the lengths and spacing ofthe radiator and elements increase logarithmicallyfrom one end of the antenna to the other.log polar navigation A computerized navigationsystem in which polar-coordinate data is convertedinto rectangular-coordinate data. In thetransformation process, the logarithm of the radius(range) is taken. This results in improvedimage resolution at close range, although it sacrificesresolution at greater ranges.log taper In a potentiometer or rheostat, resistancevariations that correspond to the logarithm ofshaft rotation, or vice versa. Compare LINEARTAPER. Also see TAPER.long Abbreviation of LONGITUDE.long-distance communication 1. Radio communicationbetween stations separated by distancestoo great for ground-wave propagation to be effective.2. In telephone service, communicationsthat require the dialing of an area code in additionto the local exchange number.long-distance loop A direct telephone line connectinga subscriber’s station to a long distanceswitchboard.long-distance reception Reception of radio signalsfrom stations beyond the range of groundwavepropagation. See also LONG-DISTANCECOMMUNICATION, 1.long-distance transmission Transmission of radiosignals to points beyond the range of groundwavepropagation. See also LONG-DISTANCECOMMUNICATION, 1.longitude Abbreviation, long. Angular displacement,measured in degrees around the earth’scircumference, to the east and west of the primemeridian that passes through Greenwich, England.Compare LATITUDE. Also see MERIDIAN.longitude effect The variation (caused by theearth’s rotation and magnetic field) of thestrength of cosmic rays arriving at different longitudeson the surface of the earth.longitudinal current Current flowing in the samedirection in the parallel wires of a pair (the returncircuit is via ground).longitudinal parity Parity associated with bitsrecorded on one track of a magnetic storagemedium to indicate whether the number of bits iseven or odd.longitudinal redundancy A computer condition,generally affecting magnetic tape records, inwhich the bits in each track of a record do notmeet the required parity, as determined by aLONGITUDINAL REDUNDANCY CHECK.longitudinal redundancy check A parity checkperformed on a block of characters or bits (for example,on a track of a magnetic disk). A paritycharacter is generated and transmitted as thelast character of the block; thus, each longitudinalblock has either even or odd parity.longitudinal wave A wave in which the movementof particles in a medium is parallel with the directionof propagation.Max Max Max Maxlongitudinal wavelong line 1. A single-wire antenna whose length isgreater than the length of the wave fed to it forpropagation. Also see LONG-WIRE ANTENNA.2. In wire telegraphy, an electrical line that hasgreat physical length. 3. In electronics theory, atransmission line of indeterminate length, butwhose characteristics remain stable and predictableto infinity.long-persistence screen A cathode-ray-tubescreen on which the image remains for a time afterthe electron beam has passed.long-play Abbreviation, LP. Descriptive of phonographdiscs designed to play at 33.3 revolutionsper minute (rpm). Also see MICROGROOVERECORD.long-play record See MICROGROOVE RECORD.long-range navigation See LORAN.long-range radar Radar that can detect targets atdistances of 200 miles or more.long skip Ionospheric radio-wave propagation,usually via the F layer, between or among stationsseparated by large geographic distances.The wave angles of departure (from transmittingstations) and arrival (at receiving stations) arevery small relative to the horizon. CompareSHORT SKIP.long-term drift Gradual change in the value of aquantity, such as voltage or frequency, observedover a long period, in contrast to that noted for abrief interval. Compare SHORT-TERM DRIFT.long-term input offset voltage stability Expressedin microvolts per month. The extent to

long-term input offset voltage stability • Lorentz force 419which the input offset voltage in an integrated circuitstays stable over long periods of time.long-term stability Stability reckoned over a periodof weeks, months or years, as contrasted tothat noted for brief intervals of time (minutes orhours).long throw A speaker design term that describes awoofer moving through long excursions; the objectiveis to provide good low-frequency responsewith low distortion.long waves Low-frequency radio waves, particularlythose in the frequency range of 30 kHz to300 kHz (10 km to 1 km).long-wire antenna A horizontal or sloping wire antennameasuring a full wavelength or more andfed at a high-current point or at one end. As thewire is made longer, the main radiation/responselobes get more nearly in line with the antenna,and their amplitudes increase. As the wire ismade shorter, the main lobes get farther from theaxis of the antenna, and their amplitudes decrease.This antenna can produce high gain andexcellent low-angle radiation, provided it isstraight, is at least several wavelengths long, andis clear of obstructions. However, it cannot be rotatedconveniently to change the direction inwhich maximum gain occurs. Also, a great deal ofreal estate is needed at medium and high frequencies.lookup A computer programming technique inwhich a data item identified by a key is selectedfrom an array.loop 1. An electrical circuit consisting of elementsconnected in series. 2. In a standing-wave system,a maximum-response point (e.g., currentloop and voltage loop). Compare NODE, 2. 3. SeeLOOP ANTENNA. 4. A signal path (e.g., feedbackloop). 5. A one- or two-turn coil for lowimpedancecoupling. Also see LINK, 1. 6. In acomputer program run, the repetitious executionof a series of instructions that terminates whensome specified condition is satisfied by a relationaltest, at which point the next instruction inthe main program is obeyed.loop antenna 1. A small portable receiving antennain the form of a wire coil. 2. A half-waveconductor bent into a circle or square. The conductoris broken at the point opposite the feedpoint. It can be used for transmitting and receiving.3. A full-wavelength, continuous conductorbent into a circle or square. It can be used fortransmitting and receiving.loop checking A method of checking the accuracyof data transmitted over a data link by returningsignals received at one terminal to the transmittingterminal for comparison with the originaldata.looped amplification See FEEDBACK FACTOR.looping plug A double phone-plug unit for simultaneouslyplugging into two phone jacks. Completes(loops) the circuit between the two jacks.looping plugloop-input signal A signal introduced into a feedbackcontrol loop.loop pulsing The regular, intermittent breaking ofthe direct-current path at the transmitting end ofa transmission line; also called DIAL PULSING.loop resistance The resistance of the electricalpath around a complete loop (see LOOP, 1).loop response time In a security system, thelength of time between the first sensing of an abnormalcondition (e.g., an intrusion) and therecognition of that condition by the controller.loopstick antenna See FERRITE-ROD ANTENNA.loop test A means of locating a discontinuity in acircuit by creating a closed loop, including thesuspected fault point.loose coupling Coupling that transfers only smallamounts of energy, as when a primary and secondarycoil are spaced so far apart that the coefficientof coupling is small. Compare CLOSECOUPLING.loosely coupled twin In computer operations, asystem in which two processors, each having itsown operating system, are used with switches sothat they can use common peripherals. Also seeSWITCH.lopplar Acronym for laser Doppler radar. Also abbreviatedas ladar.lorac A radio-navigation system that operates bymeans of phase comparison. Similar to LORAN.Trade name of Seismograph Service Corporation.loran A long-range radionavigation system inwhich two pairs of ground stations transmitpulsed signals that are used by aircraft and shipsto determine their positions. The name is anacronym for long-range navigation.loran C A radionavigation system that operates ata frequency of 100 kHz. It operates on the hyperbolicprinciple.loran D A radionavigation system similar to loranC. It is used by aircraft, operates independent ofground stations, and prevents unwanted enemydetection of aircraft position.Lorentz force For a charge Q moving with velocityv in a magnetic field B and an electric field E, theforce F = Q(E + (v × B)).

420 loss • lower sideband suppressed carrierloss Energy that is dissipated without doing usefulwork in a circuit or system. See POWER LOSS.loss angle For an insulating material, 90 degreesminus the PHASE ANGLE.loss index For an insulating material, the productof the POWER FACTOR and the DIELECTRICCONSTANT.lossless data compression A process in whichthe number of bits in a data file is reduced byeliminating redundancies, without sacrificingany of the precision or detail in the file. Compressionof text and programs must usually belossless. Image compression need not generallybe lossless. Compare LOSSY DATA COMPRES-SION.lossless line A perfect transmission line (i.e., onehaving no resistance loss, no dielectric loss, andno radiation loss). It is not realizable in practice,but useful in some theoretical calculations.loss tangent See DISSIPATION FACTOR, 1.lossy data compression A process in which thenumber of bits in a data file (especially a digitalimage) is reduced by eliminating redundancies,with some sacrifice of precision or detail. In imagecompression, some loss can usually be tolerated,allowing larger compression ratios than would bepossible if zero loss were mandatory. Lossy compressionis not generally acceptable for text filesand programs. Compare LOSSLESS DATA COM-PRESSION.lossy line A line or cable having comparativelyhigh or excessive attenuation per unit length.loudness The amplitude of sound, especially in audioreproduction equipment, such as a highfidelitystereo amplifier. Also called VOLUME.loudness control See COMPENSATED VOLUMECONTROL.loudness curves See AUDIBILITY CURVES.loudness switch/button In a high-fidelity audioamplifier, a switch or button that can be actuatedwhen music is played at low loudness. Increasesthe volume of the bass relative to the midrangeand treble.loudspeaker A transducer that converts electricalimpulses into sound waves of sufficient volume tobe heard easily by a number of listeners situatedat some distance from the device. Also calledspeaker.loudspeaker damping See DAMPED LOUD-SPEAKER.loudspeaker dividing network See CROSSOVERNETWORK.low 1. The logical digit 0. 2. Of relatively smallmagnitude (e.g., LOW VOLTAGE and LOW-FREQUENCY). 3. In a rechargeable cell or battery,the condition of being near the end of the dischargecycle.low band 1. The low or lowest frequency bandused in communications, testing, or processingin a given situation. 2. Television channels 2 to6 (54 to 88 MHz). 3. In two-way radio operations,those radio channels between 30 MHzand about 70 MHz.low battery 1. The condition of a battery needingreplacement or recharging. 2. An indicating devicethat shows when a battery needs to be replacedor recharged.low-battery bias current The current into a designatedpin of an integrated circuit required forproper operation of the LOW-BATTERY INDICA-TOR.low-battery indicator A device, such as a lightemittingdiode (LED) and associated circuitry,that gives a visible indication of the condition ofLOW BATTERY.low-capacitance probe A test probe in which capacitancehas been minimized to reduce loadingand detuning of the circuit under test.low earth orbit Acronym, LEO. An artificial satelliteorbit that is comparatively low in altitude, resultingin a short orbital period (in some cases less than 2hours). See also LEO SATELLITE SYSTEM.low-energy criterion See VON HIPPEL BREAK-DOWN THEORY.lower sideband Abbreviation, LSB. In an amplitude-modulatedwave, the lower band of frequenciesequal to the difference between the carrierfrequency and the modulating frequency. CompareUPPER SIDEBAND.lower sideband suppressed carrier Abbreviation,LSSC. A single-sideband transmission techniquein which the lower sideband is transmitted,but the upper sideband and carrier are suppressed.Compare DOUBLE SIDEBAND SUP-PRESSED CARRIER and UPPER SIDEBANDSUPPRESSED CARRIER.

lowest usable frequency • low power 421lowest usable frequency Abbreviation, LUF. Thelowest frequency that can be used successfully ata given time for communication via the ionosphere.Compare MAXIMUM USABLE FRE-QUENCY.low filter A highpass filter that removes lowfrequencyaudio noise from the modulating waveformof a broadcast station. The result is a lowerlevel of transmitted hum and rumble.low-frequency Abbreviation, LF. 1. Pertaining toradio frequencies in the band from 30 kHz to 300kHz (wavelengths from 10 kilometers to 1 kilometer).Also see RADIO SPECTRUM. 2. Pertaining toaudio frequencies below 500 Hz.low-frequency compensation 1. In videoamplifierdesign, special measures, such as useof high coupling and bypass capacitances, toboost low-frequency gain. 2. Use of special circuitsto increase the low-frequency response of an audioamplifier. Also see BASS BOOST, 1, 2.low-frequency direction finder Abbreviation,LDF. A direction finder operated in or below thestandard amplitude-modulation (AM) broadcastband, that is, below 1.605 MHz.low-frequency padder See OSCILLATOR PAD-DER.low-frequency parasitics Parasitic oscillations ofa frequency lower than that being processed bythe amplifier or generated by the oscillator inwhich they occur.low-level 1. A logic term for the more negative ofthe two (binary) logic levels. 2. Having an amplitudethat is below that normally available in comparablecircuits or systems. 3. In computeroperations, pertaining to programming languages(such as assembly language or machine language)that control the machine, but do not directlyinterface with the operator.low-level audio signal In audio operations, a signalthat has not been amplified by any means(e.g., the output of a dynamic microphone). CompareHIGH-LEVEL AUDIO SIGNAL.low-level contact A switch or relay contact intendedfor use with low values of current and voltage.low-level input current 1. A test used to check aninput pull-up resistor in an integrated circuit toensure that the fan-in is as specified. 2. The currentflowing from an input when the highest lowleveloutput voltage specified is applied to theinput of the device.low-level language A computer programming languagein which each instruction has only oneequivalent machine code. Examples are machinelanguage and assembly language. CompareHIGH-LEVEL LANGUAGE.low-level logic Abbreviation, LLL. In digitalcomputeroperations, any logic system thatoperates at low voltage or current levels.low-level modulation Modulation of a radio ortelevision transmitter at a stage preceding the finalradio-frequency (RF) power amplifier.low-level output current 1. A test to ascertainthat the fan-out and current-sinking capability ofan integrated circuit are as specified. 2. The currentflowing into an output with input conditionsthat cause the output to be at logic low.low-level signal 1. A signal with small amplitude.2. A signal with peak-to-peak voltage so low thatit does not drive an amplifier circuit out of the linearrange of operation.low-loss material A material, particularly a dielectric,having low electrical loss at a given frequency.Also see LOSS.low-noise Pertaining to circuits, especially weaksignalcommunications receiving amplifiers andconverters, designed to generate the smallestpossible amount of internal noise.low-noise down converter In a satellite televisionreceiving system, a circuit that converts the signalsfrom the dish antenna to frequencies thatcorrespond to the channels on a conventionaltelevision set.low order The lesser-value place(s) of characters ordigits in the hierarchy of a group (number orword). For example, 5 and 6 are low-order digitsin the number 123,456.low-order position The extreme right-hand (leastsignificant) position in a number or word.low-pass filter A combination of capacitance, inductance,and/or resistance, intended to producelarge amounts of attenuation above a certain frequencyand little or no attenuation below that frequency.The frequency at which the transitionoccurs is called cutoff. At cutoff, the power attenuationis 3 dB with respect to the minimum attenuation.At frequencies below cutoff, the powerattenuation is less than 3 dB. At frequenciesabove cutoff, the power attenuation is more than3 dB. The simplest circuit consists of a series inductoror a parallel capacitor. The inductancecapacitance(LC) circuit has a combination ofseries inductors and parallel capacitors. In theresistance-capacitance (RC) circuit, resistors aresubstituted for the inductors. Compare BAND-PASS FILTER, BAND-REJECTION FILTER,HIGH-PASS FILTER.low power Abbreviation, LP. Power considerablylower than that ordinarily encountered in aInLC C Clow-pass filterLOut

422 low power • lugparticular application. The term is arbitrary; severalhundred watts might be regarded as lowpower in one situation, whereas a fraction of awatt would be implied in another.low-print recording tape Magnetic tape that isless susceptible to print-through than conventionaltape.low Q For a component or circuit, a low quotient forthe ratio of reactance to resistance (X/R). This is arelative term because a particular Q value consideredlow in one situation might be high in othercircumstances. Also see FIGURE OF MERIT, 1.low tension See LOW VOLTAGE.low voltage 1. A voltage considerably lower thanthat ordinarily encountered in a particular application.The term is arbitrary; several hundredvolts might be regarded as low in one situation,and a fraction of a volt would be implied in another.2. In a television receiver, the supply voltageapplied to all points other than thehigh-voltage circuit or the picture tube.low-voltage rectifier In a television receiver, therectifier that supplies power for the low-voltagestages. See LOW VOLTAGE, 2.LP 1. Abbreviation of LOW POWER. 2. Abbreviationof LONG PLAY. 3. Abbreviation of low pressure.L pad An attenuator consisting of one series armand one shunt arm, arranged in such a way thatthe schematic representation of the circuit resemblesan inverted capital letter L. It is noted forits constant input resistance or impedance as theamount of attenuation is varied.LPB Abbreviation of LIGHTED PUSHBUTTON.L P band A section of the L BAND extending from390 to 465 MHz.lpm Abbreviation of lines per minute: the outputspeed of a line printer.lpW Abbreviation of lumens per watt; lm/W is preferred.Lr Symbol for LAWRENCIUM.L + R, L – R The sum and difference of the left (L)and right (R) channel signals in a stereo highfidelitysound system. The L + R signal is the inphasecombination of the two channels; the L – Rsignal is the out-of-phase combination.L regulator See L-TYPE VOLTAGE REGULATOR.LRR Abbreviation of LONG-RANGE RADAR.LR time constant See INDUCTANCE-RESIS-TANCE TIME CONSTANT.LSA diode Abbreviation for limited-space-chargeaccumulationdiode. A solid-state diode that actsas a microwave oscillator.LSB 1. Abbreviation of LOWER SIDEBAND. 2. Abbreviationof LEAST-SIGNIFICANT BIT.L S band A section of the L band that extends from900 to 950 MHz.LSC Abbreviation of LEAST-SIGNIFICANT CHAR-ACTER.LSD Abbreviation of LEAST-SIGNIFICANT DIGIT.L section 1. A filter section whose schematic representationhas the general shape of an invertedcapital letter L. 2. An attenuator circuit whoseschematic representation has the general shapeof an inverted capital letter L. 3. A network sectionconsisting of a series (input) impedance armand a shunt (output) impedance arm. See L PAD.4. A right-angle bend in coaxial cable (see ELL).LSI See LARGE-SCALE INTEGRATION.LSSC Abbreviation of LOWER SIDEBAND SUP-PRESSED CARRIER.L T band A section of the L BAND extending from780 to 900 MHz.LTROM Abbreviation of LINEAR-TRANSFORMERREAD-ONLY MEMORY.L-type antenna See INVERTED-L ANTENNA.L-type voltage regulator A simple voltage regulatorcontaining a series current-limiting resistorand shunt regulator (zener diode, VR tube, voltage-dependentresistor, etc.). The schematicrepresentation resembles an inverted capitalletter L.+−FrompowersupplyoutputR1UnregUnreg+ + +Reg+VRFrompowersupplyoutputR1L-type voltage regulatorReg + (High)VRReg + (Low)VR− − −lt-yr Abbreviation of LIGHT-YEAR.Lu Symbol for LUTETIUM.Lucalox General Electric’s translucent ceramic; itschief constituent is polycrystalline alumina. Thematerial has many applications in electro-optics.Lucite Trade name for METHYL METHACRYLATERESIN.Luddites During the Industrial Revolution, peoplewho sabotaged automated factory equipment becausethey believed the machines would putthem out of work. The word comes from the nameof Ned Ludd, their supposed leader. The term issometimes applied nowadays to people who fearcomputers, robots, and other technological innovationsbecause of real or imagined threats topersonal job security.LUF Abbreviation of LOWEST USABLE FRE-QUENCY.lug 1. A contact attached to the end of a wire leadto facilitate connection to a binding post. 2. A

lug • LZT 423contact attached to a terminal strip, to whichwire leads are soldered.lum Abbreviation of LUMEN. The preferred (SI)form is lm.lumen Abbreviation, lm, and sometimes l or lum.The SI unit of luminous flux; it is equal to thelight that is emitted in one steradian (the unitsolid angle) by a uniform point source of one candela.Also see CANDLE POWER, ILLUMINANCE,LUMINOUS INTENSITY, SOLID ANGLE, andSTERADIAN.lumen-hour Abbreviation, lm-hr. The amount oflight that a source having a luminous flux of oneLUMEN delivers in a time period of one hour.luminaire A complete and self-contained lightingsystem, for television-studio use or photographicuse. The kit includes all of the needed parts andaccessories.luminance The amount of light emitted or scatteredby a surface. This property is expressed incandelas per square meter (cd/m 2 ).luminance channel In a color television circuit,the channel that processes the Y SIGNAL.luminance signal See Y SIGNAL.luminescence The production of visible light, butnot heat, by a material stimulated by radiation orelectron bombardment. See ELECTROLUMINES-CENT CELL and LUMINESCENT SCREEN.luminescent cell See ELECTROLUMINESCENTCELL.luminescent screen A cathode-ray tube whosescreen is coated with a material that glows underthe influence of ionizing radiation, X rays, or electronbeams.luminiferous ether See ETHER, 1.luminosity The luminous efficiency of radiant energy,as given by the ratio of luminous flux to radiantflux (lumens per watt) for a specificwavelength.luminosity factor Abbreviated K, and expressed inlumens per watt. The luminous intensity dividedby the actual radiant intensity at a given wavelengthof visible light.luminous energy The energy in visible electromagneticradiation.luminous flux The rate of transfer or flow of luminousenergy.luminous intensity Luminous flux through a unitsolid angle, expressed in candelas. Also see CAN-DELA.lumistor An amplifier or coupling device in whichthe input signal varies the brilliance of a lamp,electroluminescent cell, or light-emitting diode,and a photocell (or other light-sensitive device)picks up the fluctuating light and uses it to modulatean output current. In a compact lumistor,the light-emitting and light-sensing componentsare separate layers in a wafer or block of material.Compare LIGHT AMPLIFIER.lumped Pertaining to a property that is concentratedat or around a single point, rather than be-SignalinputElectroluminescentcellLightrayslumistorPhotoconductivecellLoadresistorSignaloutputing distributed through a circuit (e.g., lumped capacitanceand lumped inductance).lumped capacitor See DISCRETE CAPACITOR.lumped component A discrete component (i.e.,one that is self-contained). Compare DISTRI-BUTED COMPONENT.lumped constant The total value of any singleelectrical property in an electrical or electroniccomponent.lumped-constant delay line A delay line having discretecapacitance and inductance components.Compare DISTRIBUTED-CONSTANT DELAY LINE.lumped impedance A reactance and/or resistancemanifested in a definite location. Examples areordinary components, such as capacitors, inductors,and resistors.lumped inductor See DISCRETE INDUCTOR.lumped parameter Any circuit parameter that canbe considered as a discrete parameter—even if itis not made up of a single component.lumped resistor See DISCRETE RESISTOR.lutetium Symbol, Lu. A metallic element of therare-earth group. Atomic number, 71. Atomicweight, 174.967.lux The unit of illuminance, equivalent to one LU-MEN per square meter.Luxemberg effect The generation of interferenceby cross-modulation of two or more signalswhose paths intersect in the same region of theionosphere.luxmeter A device for measuring visible illuminance.LV Abbreviation of LOW VOLTAGE.LVDT Abbreviation of LINEAR VARIABLE DIFFER-ENTIAL TRANSFORMER.Lw Symbol for LAWRENCIUM; more commonly Lr.lx Abbreviation of LUX.L X band A section of the L BAND that extends from950 MHz to 1.15 GHz.L Y band A section of the L BAND that extends from725 to 780 MHz.L Z band A section of the L BAND that extends from1.450 to 1.550 GHz.LZT Abbreviation of LEAD ZIRCONATE-TITANATE,a ceramic used in electronics.

M 1. Abbreviation of prefix MEGA-. 2. Symbol forMUTUAL INDUCTANCE. 3. Symbol for MODI-FIED INDEX OF REFRACTION.m 1. Abbreviation of prefix MILLI-. 2. Symbol forMASS. 3. Abbreviation of METER. 4. Abbreviationof MILE. (Also, mi.) 5. Symbol for MODULA-TION COEFFICIENT.m 2 Abbreviation of square meter, the SI unit ofarea.m 3 Abbreviation of cubic meter, the SI unit of volume.MA 1. Abbreviation of MAGNETIC AMPLIFIER.(Also, magamp.) 2. Abbreviation of MEGAMPERE.mA Abbreviation of MILLIAMPERE.Mache unit A unit of radioactivity equivalent to13.47 disintegrations per second (3.64 × 10 –10curie) per liter. It represents the concentration ofradon gas per liter (when all radiation is absorbed)that will result in a saturation current of10 –3 esu (not to be confused with MACH NUM-BER).machine address See ABSOLUTE ADDRESS.machine code See MACHINE LANGUAGE.machine cycle In a machine whose operation isperiodic, a complete sequence constituting a periodof operation.machine error In a computer or data-processingsystem, an error attributable to a hardware failure,rather than to a software fault.machine instruction A computer program instructionwritten in MACHINE LANGUAGE.machine knowledge General term for data storedin an artificially intelligent computer system, andthe ability of the computer to use that data inmeaningful ways.machine language Computer program instructionsand data represented in binary form. In thehierarchy of programming languages, it is thelowest; the computer works directly with it. Allhigh-level languages are translated to machinelanguage by an assembler, compiler, interpreter,or monitor system.machine learning In artificial intelligence, a computer’sability to learn through repeated calculationsfor particular problems.machine logic 1. The way that a computer’s functionalparts are interrelated. 2. The facilitywhereby a computer solves problems.machine operation The performance by a computerof a built-in function (e.g., subtraction).machine operator A person participating in implementingand overseeing the processing of computerprograms.machine word In computer operations, the addressof a memory location composed of the fullnumber of bits normally handled by each registerof the machine.machining In industrial robotics, the mechanicalmodification of parts during assembly. Examples:drilling, welding, sanding, polishing, and painting.Mach number For a medium such as air, the ratioof the speed of a body in motion to the speed ofsound in the medium. (Not to be confused withMACHE UNIT.)macro 1. A control shortcut, in which a functionrequiring the actuation of several switches is abbreviated,via a microcomputer, so that it can beexecuted by actuating only one or two switches.2. Abbreviation of MACROINSTRUCTION.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

macro- • magnetic balance 425macro- Prefix denoting extremely large. CompareMICRO-.macro assembly program An assembly programwhose source statements are translated to severalmachine-language instructions.macroinstruction A source program instructionthat becomes several machine-language instructionswhen operated on by a compiler.macroknowledge In artificial intelligence, knowledgein the large sense (i.e., knowledge about information).Example: a set of definitions in anexpert system. Compare MICROKNOWLEDGE.macroprogram A computer program consisting ofmacroinstructions.macrosonics The theory and applications of highamplitudesound waves.madistor A component that produces changes incurrent by means of magnetic-field effects. It isused as an oscillator or amplifier.MADT Abbreviation of MICROALLOY DIFFUSEDTRANSISTOR.MAG Abbreviation of MAXIMUM AVAILABLE GAIN.magamp Acronym for MAGNETIC AMPLIFIER.magazine A tape or film cartridge.magenta One of the primary pigments used incolor printers. It has a pinkish-red hue.magnal CRT base An 11-pin base typical of manycathode-ray tubes.magnesium Symbol, Mg. A metallic element.Atomic number, 12. Atomic weight, 24.305.magnesium fluoride phosphor A substance usedas a phosphor coating on the screen of a verylong-persistencecathode-ray tube. The fluorescenceand phosphorescence are orange.magnesium silicate phosphor A substance usedas a phosphor coating on the screen of a cathoderaytube. The fluorescence is orange-red.magnesium tungstate phosphor A substanceused as a phosphor coating on the screen of acathode-ray tube. The fluorescence is very lightblue.magnet A device or body of material that has theability to attract to itself pieces of iron and othermagnetic metals, and the ability to attract or repelother magnets. Also see ELECTROMAGNET,PERMANENT MAGNET, and TEMPORARY MAG-NET.magnet armature See KEEPER.magnet battery A group of several magnets placedtogether in parallel (i.e., with similar poles touchingor resting nearby) to act as a single magnet.magnet charger A device that produces an intensemagnetic field for restoring weakened magnets orfor making new magnets.magnetic 1. Pertaining to MAGNETISM. 2. PossessingMAGNETISM. 3. Capable of being magnetized.2. See MAGNETIC MATERIAL.magnetic air-gap A space between two magneticpoles, either the same (in which case the force isrepulsive) or opposite (in which case the force isattractive).magnetic amplifier An iron-core device that usesthe principle of the saturable reactor to obtainamplification. In its simplest form, it consists ofinput and output coils wound on a core ofsquare-loop magnetic metal. The input coil consistsof two identical windings connected inseries-opposition so that currents in the outputwinding cannot induce voltage in the input winding.The output coil is connected in series with aload and an alternating-current (ac) supply. Asmall ac signal applied to the input windingcauses a large change in the impedance of theoutput winding and, therefore, a large change inthe voltage across the load.acpowersupplymagnetic amplifierLoaddccontrol-signalinputmagnetic analysis See MASS SPECTROMETER.magnetic attraction 1. The force that causes amagnetic pole to draw to itself an opposite magneticpole. Thus, a north pole attracts a southpole, and a south pole attracts a north pole. CompareMAGNETIC REPULSION. 2. The force thatcauses a magnetic pole to draw to itself a piece ofmagnetic material, such as iron or steel.magnetic axis A straight line joining the poles of amagnet.magnetic bearing The azimuth, or compass direction,measured with respect to magnetic north(the direction of the north geomagnetic pole). It isusually expressed in degrees and can be read directlyfrom a compass.magnetic azimuth An azimuth bearing relative tomagnetic north (the direction of the north geomagneticpole).magnetic balance An instrument for measuringthe force, either attractive or repulsive, betweentwo objects that are magnetized, or between a

426 magnetic balance • magnetic field intensitymagnet and a magnetic substance. The devicecan also be used for measuring the intensity of amagnetic field, either from a permanent magnet,an electromagnet, or from the earth.magnetic bias A steady magnetic force applied toanother magnetic field to set the latter’s quiescentpoint (e.g., sensitizing a relay by using a permanentmagnet to lower the relay draw-in point).magnetic blowout 1. The extinction of an electricarc by a strong magnetic field. 2. The apparatusfor accomplishing the action described in 1.magnetic bottle A container envisioned for atomicfusion reactions, and that would consist of amagnetic field. Conventional containers cannotwithstand the extremely high temperatures involvedin atomic fusion.magnetic braking See ELECTROMAGNETICBRAKING.magnetic bridge An instrument comparable to theWHEATSTONE BRIDGE, used to measure magneticpermeability.magnetic bubble memory See BUBBLE MEM-ORY.magnetic capacity The maximum magnetization agiven material can receive.magnetic card A computer storage medium in theform of a card that can be selectively magnetizedor imprinted with magnetic ink to represent data.magnetic cartridge A variable-reluctance phonographpickup. As the stylus moves in the groove,the vibrations are translated into electric currentsby a magnet and coil.magnetic centering Centering the beam in a televisionpicture tube by means of an electromagneticfocusing coil, a permanent magnet, or both.magnetic character A letter, numeral, or othersymbol written or printed in (visible) magnetic inkfor its automatic sensing or reading in computingand signaling operations.magnetic circuit The closed path determined by aline of magnetic flux or by a set of lines of flux.magnetic clutch A clutch in which the magnetismof one rotating member causes a second memberto lock in and rotate. There need not be physicalcontact between the two.magnetic coil The winding in an electromagnet orsimilar device.magnetic compass A direction-indicating deviceusing a horizontally suspended magnetic needleas the indicator. The needle tends to point in thedirection of the north geomagnetic pole. CompareGYROCOMPASS.magnetic component See ELECTROMAGNETICCOMPONENT.magnetic conductivity See PERMEABILITY.magnetic constant The absolute permeability offree space. It is approximately 1.26 × 10 –6 H/m.magnetic controller A controller that uses electromagnetsfor some of its functions.magnetic core The iron core of an electromagnet,choke, transformer, relay, or similar device.magnetic coupling See INDUCTIVE COUPLING.magnetic course In navigation, a course referencedto geomagnetic north, rather than geographicnorth.magnetic crack detector See ELECTROMAG-NETIC CRACK DETECTOR.magnetic creeping A gradual increase in the magnetizationof a material under the influence of asteady magnetizing force.magnetic cycle 1. For a material in an alternatingmagnetic field, the change in magnetic flux as afunction of time. 2. The change in the magneticfieldpolarity of the earth. This polarity reversesevery few thousand years.magnetic damping The production of a dampingeffect or drag in a machine or meter by means ofmagnetic action on a moving member, in accordancewith LENZ’S LAW.magnetic declination See DECLINATION.magnetic deflection See ELECTROMAGNETICDEFLECTION.magnetic density The concentration of magneticflux in a region, expressed as the number of linesper unit area of cross section.magnetic dip At a particular location on theearth’s surface, the angle between the terrestrialmagnetic field and a horizontal line.magnetic dipole 1. A molecule or particle with anorth and south magnetic pole. 2. Any pair of adjacentnorth and south magnetic poles.magnetic direction finder Abbreviation, MDF. Atype of compass operated by an electric signal deliveredby a gyrostabilized magnetic-compassmovement.magnetic disk A rotating disk coated with a layerof magnetic material for the recording, storageand retrieval of information. They are available invarious sizes, configurations, and storage capacities.Commonly used with personal computers.Also see DISKETTE and HARD DISK.magnetic doublet See DOUBLET, 2.magnetic drive A device in which mechanicalmovement is conveyed from one moving part toanother by means of a magnetic clutch.magnetic drum See DRUM.magnetic effect of electric current The presenceof a magnetic field around a conductor carryingelectric current.magnetic equator Also called geomagnetic equator.An imaginary circle around the earth, along whicha magnetic needle shows no dip. It is near, butslightly displaced from, the geographic equator,and is midway between the geomagnetic poles.magnetic feedback Feedback by means of inductivecoupling between the output and input circuitsof a system. It can be positive or negative.magnetic field The space around a magnetic poleor magnetized body in which magnetic energyacts.magnetic field intensity See MAGNETIC INTEN-SITY.

magnetic field strength • magnetic media 427− +NSOutputInputmagnetic feedbackmagnetic field strength See MAGNETIC INTEN-SITY.magnetic-field viewer A device for visually examininga magnetic field. It consists of a clear plasticwatchcase filled with iron-oxide particles inliquid suspension. When it is placed within amagnetic field, the particles align themselves inthe direction of the magnetic lines of flux.magnetic-film memory A magnetic memory inwhich memory cells consist of a thin film (thickfilm in some instances) of a magnetic material depositedon a substrate. Information is written intoand read out of the cell through coils. Also calledthin-film memory.magnetic flip-flop A bistable multivibrator usingmagnetic amplifiers or square-loop cores in placeof transistors.magnetic flux The intensity of a magnetic fieldthrough a given area. The unit of magnetic flux isthe weber, and the symbol is F. It can loosely beexpressed as the number of lines passing througha region of a certain area or of a unit area, suchas one square meter. See FLUX.magnetic flux density See FLUX DENSITY.magnetic flux linkage The passage of magneticlines of flux through separate materials or circuits,thereby coupling them magnetically.magnetic focusing See ELECTROMAGNETIC FO-CUSING.magnetic force The force exerted by a magnet on abody of magnetic material, or on another magnet,within its field.magnetic friction 1. See HYSTERESIS, 1. 2. Theresistance experienced by a magnetic materialmoving in a magnetic field.magnetic fluxmagnetic gap A space separating the materials ina magnetic circuit. This break is either an airspace or one filled with a comparatively thin pieceof nonmagnetic material (e.g., the gap in a chokecoilcore).magnetic head See MAGNETIC PICKUP HEADand MAGNETIC RECORDING HEAD.magnetic hysteresis See HYSTERESIS, 1.magnetic inclination See MAGNETIC DIP.magnetic induction 1. The magnetization of amagnetic material, such as iron or steel, when itis placed in a magnetic field. 2. The induction ofan alternating voltage in a conductor by a nearbyalternating magnetic field. Also see ELECTRO-MAGNETIC INDUCTION.magnetic ink Writing or printing ink that is a suspensionof finely divided particles of magneticmaterial. Also see MAGNETIC CHARACTER.magnetic instability 1. The tendency of a magneticrecording medium to deteriorate with time.2. Any fluctuation in the intensity of a magneticfield.magnetic intensity The free-space strength of amagnetic field at a particular point. Specifically,the force (in dynes) that the magnetic field wouldexert on a unit magnetic pole placed at that point.magnetic iron oxide See MAGNETITE.magnetic leakage The usually undesired extensionof magnetic flux beyond the confines of amagnetic body, such as the core of a choke.magnetic lens See ELECTROMAGNETIC LENS.magnetic line of flux See LINE OF FLUX, 2.magnetic load An electromagnetic device operatingon the output of an electrical source. Such devicesinclude actuators, alarms, electromagnets,magnetic tapes and disks, relays, and loudspeakers.magnetic loudspeaker See MAGNETIC SPEAKER,1, 2.magnetic material 1. A material, such as magnetite,that exhibits natural magnetism. 2. A material,such as iron or steel, that is capable ofbeing magnetized.magnetic media Any medium that stores data astiny magnetic fields; in particular, MAGNETICDISK or MAGNETIC TAPE.

428 magnetic memory • magnetic shieldingmagnetic memory 1. See RETENTIVITY. 2. A digitalmemory circuit using magnetic fields to storedata bits. Example: BUBBLE MEMORY.magnetic meridian The circle of the celestialsphere that passes through the zenith andearth’s magnetic poles.magnetic mine A naval mine detonated by a magneticswitch that is closed by the proximity of thesteel hull of a ship.magnetic modulator A core-type device that issomewhat similar to a magnetic amplifier usedfor amplitude modulation. Modulating currentpasses through the control winding, and the carriercurrent through the output winding.magnetic moment Unit, joule per tesla. For amagnet, the product of pole strength and the distancebetween poles.magnetic needle The pivoted magnetic pointer ina magnetic compass.magnetic north See NORTH MAGNETIC POLE.magnetic oxide Iron oxide used as the sensitivecoating of magnetic recording tape.magnetic pickup 1. A phonograph pickup of thevariable-reluctance type (see VARIABLE-RELUC-TANCE PICKUP). 2. A magnetic transducer (suchas a phono cartridge, tape recording head, orsimilar input element).magnetic-pickup head In a tape recorder, thetransducer that receives up magnetic impulsesfrom the passing tape and converts them into alternatingcurrents. These currents are amplifiedto obtain the original sound. Compare MAG-NETIC RECORDING HEAD.magnetic-plate wire Wire in which a magneticmetal has been plated on top of a nonmagneticmetal.magnetic poles 1. The points in a MAGNET atwhich the magnetic lines of flux converge. 2. Thepoints on the earth at which the geomagneticlines of flux converge. See NORTH MAGNETICPOLE and SOUTH MAGNETIC POLE.magnetic pressure See MAGNETOMOTIVEFORCE.magnetic printing 1. Also called magnetic printthrough.In a recording material, such as magnetictape, the transfer of information from onepart of the material to another part (or from onemedium to another) by the magnetic field of therecorded material. This phenomenon, which isalso called PRINT-THROUGH, sometimes occursin recording tape on a reel. 2. Conventionallithography, letterpress, or other reproductionprocess in which MAGNETIC INK is used.magnetic print-through See MAGNETIC PRINT-ING, 1.magnetic probe A loop or coil inserted in an electromagneticfield to sample the magnetic component.See, for example, WAVEGUIDE PROBE.Compare ELECTRIC PROBE.magnetic recording 1. The recording of sounds ordata by varying the magnetization of a medium,TapeMotion of tapemagnetic recordingModulatingwaveformsuch as a magnetic disk or tape. 2. A magneticmedium on which data has been recorded.magnetic recording head In a tape recorder, thetransducer that receives current impulses(analogs of the original sound vibrations) from anamplifier and converts them into magnetic impulsesthat magnetize spaces on the passingtape. Compare MAGNETIC PICKUP HEAD.magnetic recording medium 1. A magnetic cylinder,disk, drum, tape, or wire used in the recordingof sound or data. 2. The sensitive materialwith which any of these is coated.magnetic relay A relay having a permanent magnetin whose field a coil, bar, or reed moves toopen or close a pair of contacts.magnetic remanence See RESIDUAL MAG-NETISM.magnetic repulsion The force that causes a magneticpole to push away a similar magnetic pole,although they are not in mutual contact. Thus,two north poles repel each other, and so do twosouth poles. Compare MAGNETIC ATTRACTION.magnetic-resonance accelerator See CYCLO-TRON.magnetics 1. Collectively, magnetic componentsand equipment. 2. Collectively, magnetic materials.3. A branch of physics dealing with magnetsand magnetism.magnetic saturation The condition in which amagnetic material passes all of the magnetic linesof flux that its permeability allows. Increasing theintensity of the magnetizing force will produce noincrease in magnetization.magnetic scan See ELECTROMAGNETIC DE-FLECTION.magnetic screen See ELECTROMAGNETICSHIELD.magnetic shield See ELECTROMAGNETICSHIELD and MAGNETIC SHIELDING.magnetic shielding 1. Enclosing a magnetic fieldto confine its flux, thus preventing interaction

magnetic shielding • magnetic whirl 429with outside bodies. 2. Devices (such as boxes,cans, or shells of iron, steel, or a magnetic alloy)used for the purpose described in 1.magnetic shift register A shift register using magneticflip-flops.magnetic shunt A device that allows the usefulmagnetic flux of an instrument’s magnet to becontrolled. The device consists of a piece of magneticmaterial near the magnet in an electricalmeasuring instrument.magnetic south See MAGNETIC SOUTH POLE.magnetic speaker 1. A loudspeaker that is essentiallyan enlarged earphone with a horn that conveysand intensifies the sound from the vibratingdiaphragm. 2. A loudspeaker in which the vibrationof a diaphragm or reed in the field of a permanentmagnet is conveyed by a pin to a paper orcomposition cone. Compare DYNAMIC SPEAKER.magnetic storage 1. A data bank or memory thatstores information in the form of magnetic fields.2. The data on a magnetic tape or disk.magnetic storm A disturbance in the earth’s magneticfield that typically follows a solar flare. Oftencauses interference to radio communicationsat low, medium and high frequencies.magnetic strip A strip of powdered iron or ferriteon the back of an identification card, bank cashcard, or credit card, that carries a code to identifythe account number and verify that the secret entrycode (if any) is correct, or that the credit isgood.magnetic susceptibility See SUSCEPTIBILITY.magnetic switch 1. In security systems, a switchkept open by the presence of a magnet attachedto a door, window, or other movable object. Whenthe object is moved, the magnet moves away fromthe switch, closing the switch and actuating analarm. 2. A REED SWITCH operated by a magneticfield.magnetic tape Plastic tape coated with a film ofmagnetic material; it can be magnetized along itslength to record sounds, video signals, and computerinformation.magnetic-tape core A strip of magnetic metalwound spirally to create a toroid (donut) shape.Such construction is sometimes used in choke ortransformer cores. Also see TOROID.magnetic tape deck See TAPE DECK.magnetic tape drive See TAPE TRANSPORT.magnetic tape head See MAGNETIC PICKUPHEAD and MAGNETIC RECORDING HEAD.magnetic tape library In a computer installation,the place where magnetic tape files are kept, ormagnetic tape files and the records needed to utilizethem.magnetic tape parity As a safeguard against losinginformation bits during the transfer of informationbetween magnetic tape and a memorydevice, a technique in which an extra bit is generatedand added to characters under certain conditions,to make the output uniform temporarily.Lack of uniformity in output then serves as an errorindicator. The original quantity is recoveredby dropping the extra bit following a parity check.magnetic tape reader A tape deck for playing backdata on magnetic tape.magnetic tape recorder A recorder-reproducerusing magnetic tape.magnetic test coil See SEARCH COIL.magnetic thick film A film of magnetic material atleast 10 -6 meter in thickness, deposited on a substrate.Compare MAGNETIC THIN FILM.magnetic thin film A film of magnetic material,less than 10 -6 meter in thickness, deposited on asubstrate. Compare MAGNETIC THICK FILM.magnetic transducer A transducer that uses acoil, magnet, or both, to convert displacementinto variable magnetic fields or electric currents.Common varieties are the inductance type, transformertype, and generator type. CompareCAPACITIVE TRANSDUCER, CRYSTALTRANSDUCER, and INDUCTIVE TRANSDUCER.magnetic tuning In a microwave oscillator, ameans of tuning in which a ferrite rod in the cavityresonator is made to have adjustable magnetizationso that the resonant frequency of thecavity varies and the frequency of the oscillator isthus adjustable. It is also used at ultra-high frequencies(UHF) and occasionally at very-high frequencies(VHF).magnetic-vane meter See IRON-VANE METER.magnetic vector In an electromagnetic field, thevector representing the magnetic component. It isperpendicular to the electric vector.magnetic viscosity A property of certain materials,described in terms of the time required tomagnetize a given substance to a specified level.magnetic whirl One of the circular magnetic linesof flux around a straight conductor that carrieselectric current.Magneticfluxlinemagnetic whirlCurrent-carryingwire

430 magnetic wire • magnetostrictionmagnetic wire The thin wire used in wire recordingand playback. See WIRE RECORDER.magnetism The property of having or causing amagnetic field. It occurs when magnetic dipolesare aligned and when electric charge carriers arein motion.magnetite A natural magnetic oxide of iron. Alsocalled LODESTONE.magnetization curve A curve depicting the magnetizationof a material versus the applied magnetizingforce. See, for example, HYSTERESISCURVE.magnetizer A device for magnetizing magnetic materials,as in the making of permanent magnets.Also see MAGNET CHARGER. Compare DEMAG-NETIZER.magnetizing current 1. A current that sets up amagnetic field of useful intensity. 2. The halfcycleof an alternating current or the polarity of adirect current flowing through a coil wound on apermanent magnet (as in a headphone, permanent-magnetloudspeaker, or polarized relay) thatincreases magnetic field strength. Compare DE-MAGNETIZING CURRENT. 3. The field current ofa dynamo.magnetizing force 1. Magnetomotive force (ingilberts) divided by spatial distance (in meters). 2.The intensity of a magnetic field that causes amaterial to become magnetized.magnet keeper See KEEPER.magnet meter See MAGNET TESTER.magnet motor See PERMANENT-MAGNET MOTOR.magneto See PERMANENT-MAGNET GENERATOR.magnetocardiogram Abbreviation, MCG. A record,made by a MAGNETOCARDIOGRAPH, of the pulsatingmagnetic field of the heart. It is used as adiagnostic aid.magnetocardiograph An instrument that producesa record of the pulsating magnetic fieldgenerated around the torso by natural ion currentsin the heart.magnetoelectric generator See MAGNETOGEN-ERATOR.magnetofluid mechanics See MAGNETOHYDRO-DYNAMICS.magnetofluidynamics See MAGNETOHYDRODY-NAMICS.magnetogasdynamics See MAGNETOHYDRODY-NAMICS.magnetoionic duct A propagation path for radiowaves between two points that have the samegeomagnetic longitude on the surface of theearth. The radio waves tend to travel with the geomagneticlines of flux at some frequencies undercertain conditions.magnetoionics The study of the effects of the geomagneticfield on the propagation of radio waves.magnetogenerator See PERMANENT-MAGNETGENERATOR.magnetograph An instrument for automaticallyrecording a magnetic field.magnetohydrodynamic generator A device usingmagnetohydrodynamic principles to generateelectric power directly from gases. In the generator,a hot gas is passed through an intense magneticfield; a pair of collector plates picks upelectrons from the ionized gas.magnetohydrodynamic gyroscope A gyroscopewhose spin is obtained by a rotating magneticfield circulating a conducting fluid, such as mercury,around a closed loop. Also see MAGNETO-HYDRODYNAMICS.magnetohydrodynamic power generator SeeMAGNETOHYDRODYNAMIC GENERATOR.magnetohydrodynamics Abbreviation, MHD. Thetheory and application of phenomena producedby electrically conductive fluids and gases in electricand magnetic fields.magnetometer An instrument for measuring thestrength and direction of magnetic fields.magnetomotive force Abbreviation, mmf. Unit,ampere. The phenomenon that is sometimes descriptivelycalled magnetic pressure. It is analogousto electromotive force (and to waterpressure) and is the agent that produces a magneticfield.magneton See BOHR MAGNETON.magneto-optical rotation The tendency of a magneticfield to rotate the plane of polarization oflight passing through a substance. Also seeKERR MAGNETO-OPTICAL EFFECT.magneto-optical technology A computer datastoragetechnology that uses lasers to guide theread/write head in a magnetic disk drive. Thisgreatly increases the amount of data that can beeffectively stored on, and retrieved from, a magneticdisk.magneto-optical valve See KERR MAGNETO-OPTICAL EFFECT.magnetopause The high-altitude limit of the MAG-NETOSPHERE.magnetoplasmadynamics See MAGNETOHYDRO-DYNAMICS.magnetoresistance The phenomenon whereby theresistance of a material, such as a semiconductor,changes when it is exposed to a magneticfield. Also see MAGNETORESISTOR.magnetoresistor A material (such as bismuthwire, indium antimonide, or indium arsenide)whose resistance varies with the strength of amagnetic field in which it is placed.magnetosphere In the upper atmosphere, a regionextending thousands of kilometers from theearth, in which charged particles are trapped bythe earth’s magnetic field.magnetostatic field A stationary magnetic field,such as that produced by a permanent magnet.magnetostriction The expansion or contraction ofa bar or rod of magnetic material (such as Invar,Monel metal, Nichrome, nickel, or Stoic metal) inproportion to the strength of an applied magneticfield. Magnetostrictive vibration in such a rod is

magnetostriction • main memory 431Charged cosmicparticleMagnetosphereevated temperature) inside the body, as in heatinga cancerous tumor for therapeutic purposes.magnetron A microwave vacuum tube consistingof a diode (with a cylindrical anode) throughwhich the field of a powerful external permanentmagnet passes. The magnetic field causes electronsleaving the cathode to travel in spiral pathsbetween the electrodes. This action gives the tubea negative-resistance characteristic, resulting inoscillation when the tube is connected in an appropriatecircuit. Some magnetrons have a builtinresonant cavity.magnetospherecomparable to piezoelectric vibration in a quartzcrystal.magnetostriction filter See ULTRASONIC FIL-TER, 1.magnetostriction oscillator An oscillator whosefrequency is controlled by a magnetostrictive rod(see MAGNETOSTRICTION). The dimensions ofthe rod and the type of metal it contains determineits vibration frequency and, accordingly, theoperating frequency of the oscillator.+−magnetostriction oscillatorOutputMagnetostrictiverodmagnetostrictive delay line A delay line in whichthe signal is propagated through a magnetostrictiverod. Also see MAGNETOSTRICTION.magnetostrictive microphone A microphone inwhich sound vibrations produce changes in amagnetostrictive element, which, in turn, areconverted into output-voltage changes. Also seeMAGNETOSTRICTION.magnetostrictive transducer A transducer inwhich some phenomenon, such as vibration orpressure, produces changes in a magnetostrictionelement, which in turn are converted into outputvoltagechanges. Also see MAGNETOSTRICTION.magnet protector See KEEPER.magnetrode The trademark of a radio-frequencydevice for externally producing hyperthermia (el-SPlatePlateMagnetsCathodeN2ndplate1stplatemagnetronCathodeΒ− Β+magnet steel A high-retentivity alloy of chromium,cobalt, manganese, steel, and tungsten,used in the manufacture of permanent magnets.magnet tester An instrument used to measure theflux of a magnet. Also see FLUXMETER.magnet wire Insulated wire (usually solid copper)of 14 to 40 gauge, so called because of its originalmajor use in winding the coils of electromagnets.magnitude 1. General expression for degree, size,or extent. 2. Signal strength (amplitude). 3. For anumber or vector quantity, the absolute value orlength. 4. A measure of the relative or absolutebrightness of celestial objects.mAh Abbreviation of milliampere-hour.main British expression for the alternating-current(ac) utility power available in a house or building.main bang 1. In a radar display, the pip or pulseresulting from the actual transmitted signal. Thispulse is blanked out. 2. In a spectrum analyzer,the pip corresponding to a frequency of zero, andcaused by the local oscillator.mainframe 1. The chassis containing the centralprocessor and arithmetic and logic circuits for alarge computer. 2. The general term for a large,powerful computer.main lobe Also called major lobe. In a directionalantenna system, the portion of the directivity patternrepresenting the greatest transmitted signalgain and/or the greatest received signal response.Also see MINOR LOBE, SIDE LOBE.main memory The principal (immediate process)memory unit in a digital computer or dataprocessingsystem.

432 main path • manualsystem (e.g., major feedback loop). Compare MI-NOR LOOP.make 1. The closing of a pair or set of contacts.2. To close a pair or set of contacts.make-before-break contacts A pair of contacts inwhich the movable arm closes with the next contactbefore breaking with the previous one. CompareBREAK-BEFORE-MAKE CONTACTS.make time The time required for a relay to latchcompletely, or for a switch (either mechanical orelectronic) to close completely. Compare BREAKTIME.male plug A plug having one or more protrudingcontacts in the form of pins, blades, or prongs.Compare FEMALE PLUG and HERMAPHRO-DITIC PLUG.male plugmain path In a computer program, the sequence ofinstruction execution disregarding the executionof subroutines.main program The part of a computer programother than a subroutine.main routine See MAIN PROGRAM.mains 1. In a power-distribution center, the linesthat supply the entire system. An example is theset of lines leading into a house. 2. The utility wiresand associated outlets in a house or building.maintenance The process of keeping a system, circuit,or component in operating condition, withminimal down time.maintenance routine A computer program usedby computer service personnel for diagnosis duringa regular service interval.major beats The principal beats produced in abeat-note system; they are usually the sumand/or difference of two fundamental frequencies.Compare MINOR BEATS.major face In a hexagonal quartz crystal, one ofthe three larger faces. Compare MINOR FACE.majority carrier The predominant charge carrierin processed semiconductor material. Electronsare the majority carriers in n-type material; holesare the majority carriers in p-type material. CompareMINORITY CARRIER.majority logic A logic gate in which the output ishigh whenever the majority of its inputs is high,regardless of which inputs are high. Thus, in afive-input gate of this type, the output is highwhen any three or more of the inputs are high.major lobe See MAIN LOBE.major loop The principal path for the circulation ofinformation or control signals in an electronicMalter effect The tendency for a layer of semiconductorhaving a high secondary emission ratio tobecome positively charged when bombarded byelectrons. This occurs when a thin insulator separatesthe semiconductor from a metal plate. Theinsulator must be very thin (on the order of 10 –7meters). This results in a potential difference ofup to about 100 volts.manganese Symbol, Mn. A metallic element.Atomic number, 25. Atomic weight, 54.938.manganese-dioxide depolarizer In a dry cell,manganese dioxide mixed with powdered carbon,the mixture being a depolarizing agent. Also seeDEPOLARIZER.manganin A low-temperature-coefficient alloyused in making wire for precision resistors. A typicalcomposition is: copper (84 percent), manganese(12 percent), and nickel (4 percent).manipulator A robot arm and end effector, as usedin mechanical processes.man-made interference See HUMAN-MADE IN-TERFERENCE.man-made static See HUMAN-MADE INTERFER-ENCE.manometer An instrument for measuring gas orvapor pressure—especially at low levels.manpack A portable radio transceiver that can beused while walking.mantissa 1. The portion of a logarithm to the rightof the decimal point. Thus, in 3.952502 (log 108964), the mantissa is 0.952502. 2. The fixedpoint part of a number in scientific notation;thus, in 4 × 10 3 , the mantissa is 4.manual 1. Actuated or operated directly by mechanicalmeans, rather than automatically. 2. A

manual • maser 433book, or a set of online information files, detailingthe operation and maintenance procedures for adevice or system.manual input Use of a keyboard, mouse, trackball,or other electromechanical input device to enterdata into a computer program or system.manual operation In data processing, an operationin which automatic machines are not involved.manual telegraphy Telegraphy that consists signalstransmitted by a hand-operated key andrecorded by hand (pen, pencil, or typewriter).manual tuning Tuning performed entirely by adjustingvariable circuit components by hand.manual word generator A device by which an operatorcan originate information words for inputinto computer memory.manufacturing automation protocol In a factoryusing computer-controlled robots, the set of standardsfor data communication between therobots and the controller and/or between individualrobots. It keeps the factory operatingsmoothly.MAR Abbreviation of MEMORY-ADDRESS REGIS-TER.Marconi antenna A quarter-wave radio transmittingor receiving antenna operated against anearth ground.Marconi effect The undesired tendency of an entirereceiving antenna system, including lead-inor feeders, to act as a MARCONI ANTENNA.margin1. A gap or space between two objects,such as adjacent plates of a capacitor. 2. Clearance.3. The maximum error that can be toleratedwithout risk of improper or abnormal operation.4. In a teletypewriter, the range of adjustments inwhich the error frequency is acceptable.marginal relay A relay having a small differencebetween its on and off currents or voltages.marginal test As performed on equipment in acomputer installation, a test to either determinethe cause of an intermittent malfunction, or verifyan equipment’s operating tolerances.marine broadcast station A coastal station thatbroadcasts information of interest to shipping:time, weather, ocean currents, etc.marine radio Radio communications betweenseagoing vessels or between vessels and shorestations.marine radiobeacon station A land-based radionavigationstation whose transmitted signals areused for taking bearings.mariner’s compass See MAGNETIC COMPASS.mark 1. In telegraphy, the dot or dash portion of acharacter, as opposed to the dead space betweensuch portions. 2. The intelligence part of a similarsignal (such as sound, light, etc.). 3. The high(logic 1) state represented by a binary bit, as opposedto the low (logic 0) state. 4. A characteridentifying the end of a data set. Also calledMARKER (see MARKER, 2).marker 1. A pip that indicates a particular frequencyon a response curve displayed on an oscilloscopescreen. 2. A character that identifiesthe end of a data set. Also called MARK (seeMARK, 4).marker beacons Individual coded-signal transmittersplaced along a radio range and indicatingfeatures of the course marked by them.marker frequency 1. A known frequency that canbe used to identify a spot-frequency harmonic ofa frequency-standard signal. 2. A known accuratesignal used to identify the limit of a radioband. 3. The frequency at some point on a responsecurve as identified by a marker pip (seeMARKER).marker generator An oscillator that supplies amarker pip (see MARKER).mark hold In telegraphy, an unmodulated signalmeaning information is not being sent.mark reading The reading by an optical scanningdevice of marks made in specific areas of a document;the process also includes the marks’ conversionto digital signals for input to a computer.mark scanning See MARK READING.mark sensing A process similar to MARK READ-ING, except that the marks are sensed electrically.marker trap A wave trap that supplies a dip-typemarker pip when used in conjunction with a radio-frequencytest oscillator (see MARKER).market scanner Also called bar-code reader. A devicethat scans a black-bar binary label printedon a carton or other package (or magazine), andindicates the price of the merchandise on thereadout of the checkout register.mark-to-space ratio In radiotelegraphy, the ratioof the duration (mark) of a dot to the interval(space) between successive dots.Marx generator An impulse-type high-voltagedirect-current generator circuit in which severalcapacitors are charged in parallel through a highresistancenetwork. When the capacitor voltagereaches a critical high value, discharge occurs inseries through spark gaps, producing a highvoltagepulse for each discharge.maser A low-noise microwave amplifying device inwhich a microwave input signal causes highenergy-statemolecules of ammonia or ruby to fallto the low-energy state and, as a result, to emitlarge amounts of energy as an output signal. Thename is an acronym for microwave amplificationby stimulated emission of radiation.ac inputMarx generator

434 mask • master program filemask 1. A kind of stencil through which plating,electrodeposition, or diffusion can be done.2. The viewing screen, or GRATICULE, of an oscilloscope.3. To obliterate a signal with a strongerone. 4. A bit or character pattern used to changeor extract bit positions in another pattern.masking 1. The use of a MASK of any type. 2. Thetendency of one effect or phenomenon to obscureanother. It applies especially in audio systems,where certain sounds impair the ability of a listenerto hear other sounds that occur at the sametime. 3. The extent to which one effect or phenomenonobscures another.Masonite Masonite Corporation’s tough fiberboardused for panels and bases of some electronicequipment.mass The quantity of matter in a body. Like weight,mass is expressed in kilograms in the metric (SI)system and in pounds in the English system. Fora given piece of material, mass can be determinedby dividing the weight by the acceleration of gravity.mass data Data in excess of the maximum amountthat can be stored in the main (internal) storageunit of a digital computer (i.e., that which canonly be accommodated by external media such asmagnetic disks or tapes).mass-energy equation Energy (E) is the product ofa given mass (m) and the square of the speed oflight (c 2 ): E = mc 2 . It is also called the Einsteinequation.mass number 1. Symbol, A. A number representingthe total of neutrons and protons in the nucleusof an atom. The approximate mass of anatom is equal to A × m p , where m p is the total proton(rest) mass. 2. The number indicating thesum of nuclear protons and neutrons in an atom.It is usually written following the symbol for theatom: thus, U238 is uranium having 238 nucleons.An isotope of an element will have a differentmass number than that of the normal atom.mass of electron at rest Symbol, m e . The amountof matter in an electron; m e = 9.1093897 ×10 –31 kg.mass of neutron at rest Symbol, m n . The mass ofa neutron in the nucleus of an atom; m n =1.6749286 × 10 –27 kg.mass of proton at rest Symbol, m p . The massof a proton in the nucleus of an atom; m p =1.6726231 × 10 –27 kg.mass resistivity 1. The resistance of a wire onemeter long having a mass of one gram. It varies,depending on the composition of the wire. 2. Theresistance of a wire one mile long having a weightof one pound. It varies, depending on the compositionof the wire.mass spectograph An instrument used to analyzechemical compounds and mixtures interms of their distinctive mass spectra, exhibitedby ionized samples of the materials in amagnetic field.mass spectrometer Abbreviation, MS. An instrumentthat permits rapid analysis of chemicalcompounds via the MASS SPECTRUM.mass spectrum An electron spectrum that can beused to identify a chemical element. Different elementshave nuclei with different charge-to-massratios. This results in each element having aunique mass spectrum.mass storage In a computer system, a magnetic oroptical storage medium capable of holding largeamounts of data. Examples: magnetic diskette,magneto-optical diskette, external hard disk,compact-disk read-only memory (CD-ROM), andmagnetic tape.mass unit See ATOMIC MASS UNIT.master 1. The primary or main element or devicein a system. 2. A primary data medium or recordingfrom which copies are made. 3. A primaryreference standard. See the following severaldefinitions.master clock 1. In a digital computer, the primarygenerator of timing pulses. 2. A standard timeclock that drives other (slave) clocks, or to whichclocks of lesser accuracy can be referred.master console In a computer system, an equipmentwith panel instruments and controls, whichpermits operations to be governed, monitored,and controlled by a human operator.master control 1. The main control circuit in asystem. 2. A point from which signals or programsare distributed in a communications orbroadcast system.master data Also called archives. In a computerrecord, data elements that remain unaltered for along time, and from which copies are made.master file A computer file of data used routinelyand remaining unchanged for a long time.master gain control The principal gain control inan audio amplifier or mixer [i.e., the one used toadjust the gain (volume) of the entire system].master instruction tape Magnetic tape on whichvarious related computer programs are recorded.master library tape See MASTER PROGRAM FILE.master oscillator Abbreviation, MO. The main oscillatorin an electronic system (e.g., the oscillatorstage in an oscillator-amplifier type of radiotransmitter). This oscillator can be either selfexcitedor crystal-controlled.master oscillator-power amplifier Abbreviation,MOPA. A type of transmitter or signal generatorin which a frequency-determining oscillatordrives a power amplifier, which in turn deliversan output signal. Because the oscillator is isolatedfrom the output load, this arrangement hasgreater stability than one in which the oscillatoralone supplies power to the load.master pattern The etching pattern used for manufactureof a batch of identical printed-circuitboards.master program file A reel of magnetic tape onwhich is recorded the programs regularly used in

matching pad An inductance-capacitance (LC)network for matching the impedance of a load tothe output impedance of a signal generator.matching stub See STUB.matching transformer An audio-frequency (AF) orradio-frequency (RF) transformer used to matchone purely resistive impedance to another.matchtone A transistorized, single-frequency audiooscillator that can be used to monitor transmasterprogram file • maxima and minima 435a data-processing installation. It is also calledmaster library tape.master record In a data-processing system, thecurrent record (usually stored on a disk or tape)that will be used for the next computer run.master relay A relay that operates other (slave) relays.Compare SLAVE RELAY.master station See KEY STATION.master switch A switch that can actuate or deactuatean entire installation or system.master tape 1. In sound recording and reproduction,a magnetic tape that contains material fromwhich other tapes and discs can be made. 2. Inautomation, a magnetic tape on which isrecorded the basic signal sequence for controllinga process and other recorders. 3. In data processing,a magnetic tape that must not be erased.master volume control See MASTER GAIN CON-TROL.masurium See TECHNETIUM.MAT Abbreviation of MICROALLOY TRANSISTOR.match 1. To mate devices, signals, impedances,etc. for optimum compatibility in terms of signaltransfer, equipment interfacing, and other optimizingqualities. 2. The condition of being compatiblymated, physically or electrically.matched components Circuit components (capacitors,coils, diodes, resistors, transistors, etc.)that are carefully selected for similar or particularlycompatible operating characteristics.matched filter 1. A filter with input and outputimpedances matched to the input line and outputload, respectively. 2. A filter designed for separatinga signal with a particular waveform fromother signals and noise.matched impedance A usually non-reactiveimpedance that has the same value as that of anotherimpedance with which it is operated. Maximumpower is transferred between impedancesthat are matched.matched load A purely resistive load, the impedanceof which is the same as the characteristicimpedance of the feed line. This results inoptimum power transfer from the line to the load.matched pair A pair of matched components offeredin a single package.matched transmission line A transmission lineterminated in a purely resistive impedance whosevalue is identical to the characteristic impedanceof the line. Such a line transfers all of its energyto its load without reflection; no standing wavesare on the line.Voltage (volts)100806040200Gen.mitted radiotelegraph signals. The carrier wavefrom the transmitter is rectified by a small semiconductordiode, whose direct-current outputpowers the oscillator.Mateucci effect The generation of a potential differencein a helically wound, ferromagnetic wirewhen its magnetization fluctuates.mathematical check A test of the validity of theresult of an arithmetic process (by using alternatemethods, for example).mathematical logic 1. A branch of mathematicsthat involves the theoretical behavior of varioussystems of reasoning. 2. See BOOLEAN ALGE-BRA. 3. See DIGITAL LOGIC.mathematical model See MODEL, 2.mathematical subroutine Within a computer program,a subroutine serving as an arithmetic function(i.e., one for performing an operation notintegral to the monitor program).matrix 1. A high-speed switching or memory arrayused in counters and computers. 2. Generally,any two-dimensional array of objects. 3. A devicefor solving linear simultaneous equations, consistingof a rectangular array of coefficients.matrix printer See WIRE PRINTER.mat switch A form of PRESSURE SENSOR used insome security systems. When weight appears onthe mat, switches close, actuating an alarm.matterVoltageCurrentRelative positionLine(50 ohms)matched transmission lineThe building material of the universe thatoccupies space and has mass that can be measured.See, for illustration, ATOMIC THEORY andSTATES OF MATTER.matter waves See DE BROGLIE WAVES.max Abbreviation of MAXIMUM.maxima Points along a curve at which a functionreaches a local maximum value. Also see MAX-IMA AND MINIMA.maxima and minima 1. The loops and nodes ofcurrent or voltage on an antenna or transmissionline. 2. The lobes and nulls in a directivity pattern.3. The bright and dark bands in a visiblelightinterference pattern. 4. In radar reflections,regions of localized maximum and minimum543210Current (amperes)Load(50 ohms)

436 maxima and minima • Maxwell’s equationsLocalmaximaymaximaintensity. 5. The study and solution of maximum,minimum, and inflection points on the curve of afunction.maximal flatness For an amplifier or network, thecondition in which peaks are not present in thenormal passband response.maximum Abbreviation, max. The highest value ina range or set. Also see MAXIMA AND MINIMAand PEAK.maximum available gain Abbreviation, MAG. Theamplification provided by a circuit or devicewhose input and output impedances are correctlymatched to source and load.maximum current 1. Symbol, I m or I max . The highestvalue reached by an alternating-current halfcycleor by a pulse current. Also called PEAKCURRENT. 2. The highest value of current in aseries of current values.maximum power 1. Symbol, P m or P max . The highestvalue of power that an equipment can becalled upon to supply. 2. The highest value ofpower in a series of measurements or calculations.maximum-power discharge current For a cell orbattery, the current at which the greatest amountof power is delivered.maximum power output See MAXIMUM POWER,1.maximum power transfer The condition in whichthe largest amount of power is delivered by asource to a load.maximum power transfer theorem Maximumpower is transferred from a generator to a loadwhen the impedance of the load equals the internalimpedance of the generator. Compare COM-PENSATION THEOREM, NORTON’S THEOREM,RECIPROCITY THEOREM, SUPERPOSITIONTHEOREM, and THEVENIN’S THEOREM.maximum rating 1. The highest value of a quantity(e.g., current, voltage, or power) that can safely beused with a given device. 2. The highest value of aquantity afforded by a given device (e.g., maximumcapacitance of a variable capacitor).xmaximum record level 1. In a magnetic tape,magnetic disk, or phonograph disc, the highestamplitude of input signal that can be recordedwith an acceptable amount of distortion. 2. Therecording-head current or power that results inthird-harmonic distortion of three percent.maximum signal level 1. In an amplitude-modulatedsignal, the peak power. 2. In an amplitudemodulatedfacsimile or television system, theamplitude that results in a black or white picture(depending on whether the highest amplitudeproduces black or white).maximum undistorted power output Abbreviation,MUPO. The highest power that an active amplifyingdevice will deliver before significantdistortion occurs.maximum usable frequency Abbreviation, MUF.The highest frequency that can be used successfullyat a given time, between two specific geographiclocations, for communication via theionosphere.maximum voltage 1. Abbreviation, E m , E max , V m ,or V max . The peak value reached by an alternating-currentvoltage half-cycle, or by a voltagepulse. 2. The highest value of voltage in a seriesof voltage measurements or calculations.maximum wattage See MAXIMUM POWER.maxterm form In mathematical calculations, thefactored form of a function, expressed as a productof sums. For example, the maxterm form off(x) = x 2 + 5x + 6 is f(x) = (x + 2) (x + 3).maxwell Symbol, Mx. The cgs unit of magneticflux, equivalent to one line of flux or 10 –8 weber.Maxwell bridge A four-arm alternating-currentbridge for measuring inductance against a standardcapacitance.Maxwell’s equations A set of four equations developedby James Clerk Maxwell in 1864 and 1873,describing vector quantities pertaining to points inspace subjected to varying electric and magneticforces. Through his classic presentation, MaxwellGenDetMaxwell bridge

Maxwell’s equations • measurand 437predicted the existence of electromagnetic waves,whose later discovery made radio possible.Maxwell’s law Also called Maxwell’s rule. Everypart of an electric circuit is acted upon by a forcetending to move it in the direction that results inthe maximum magnetic flux being enclosed.maxwell-turn A unit of magnetic coupling (linkage)equal to 1 maxwell per turn of wire in a coil linkedby magnetic flux. Also see MAXWELL.mayday In radiotelephony, a word spoken as aninternational distress signal equivalent to SOS inradiotelegraphy. The word is the phonetic equivalentof the French m’aidez (help me).MB Abbreviation of MIDBAND.Mb Abbreviation of MEGABAR.MBB Abbreviation of MAKE BEFORE BREAK.MBM Abbreviation of magnetic bubble memory.MBO Abbreviation of MONOSTABLE BLOCKINGOSCILLATOR.MBS Abbreviation of magnetron beam switching.mc 1. Symbol for MILLICURIE (mCi is preferred).2. Symbol for METER-CANDLE.Mc 1. Symbol for MEGACURIE (MCi is preferred).2. Obsolete abbreviation of megacycle(s), a termsuperseded by MEGAHERTZ.MCG Abbreviation of MAGNETOCARDIOGRAM.McLeod gauge An instrument for measuring gasunder low pressure. A measured volume of thegas under test is first compressed (to a lowerknown volume) to a pressure more easily measuredvia a mercury manometer and the applicationof Boyle’s law.MCM Abbreviation of MONTE CARLO METHOD.McProud test A simple test for checking the trackingefficiency of a phonograph pickup and arm formicrogroove discs.Mc/s Obsolete abbreviation of megacycle(s) persecond, a term superseded by MEGAHERTZ.MCS 1. Abbreviation of Master of Computer Science.2. Abbreviation of missile control system.MCW Abbreviation of MODULATED CONTINUOUSWAVE.Md Symbol for MENDELEVIUM.MDAS Abbreviation of medical data acquisition system.m-derived filter A filter whose inductance (L) andcapacitance (C) values are derived by multiplyingthose of a constant-k filter by a factor m betweenzero and 1. This factor is a function of the ratiof Ï /f c , where f Ï is the frequency of infinite attenuation,and f c is the cutoff frequency. This type of filterexhibits sharper response than the equivalentconstant-k filter.MDI Abbreviation of MAGNETIC DIRECTION INDI-CATOR.M-display See M-SCAN.MDS Abbreviation of MINIMUM DISCERNIBLESIGNAL.m e Symbol for MASS OF ELECTRON AT REST.Meacham oscillator A highly stable radiofrequencyoscillator consisting of an amplifierCrystalRFamplifierMeacham oscillatorRF outputprovided with a feedback circuit containing afour-arm bridge, one arm of which is a quartzcrystal, and another, a tungsten-filament lampacting as a nonlinear resistor. Also called bridgestabilizedoscillator.mean 1. A general term meaning average. 2. SeeARITHMETIC MEAN. 3. See GEOMETRIC MEAN.mean charge 1. In an object that is nonuniformlycharged, the average charge per unit distance,area, or volume. 2. In a capacitor carrying a fluctuatingcurrent, the average amount of chargeheld by the plates.mean free path 1. In acoustics, the average distancethat sound waves travel before striking abarrier or reflecting surface. 2. The average distancethat sound waves travel between reflections(echoes) in a chamber. 3. In a gas tube, the averageof all the free paths of electrons at a specifiedtemperature.mean life 1. Symbol, L. The average life of a radioactivesubstance [i.e., the time taken for 1/e(e = base of natural logarithms) of the substanceto disintegrate]. 2. The time required for excess carriersinjected into a semiconductor to recombinewith carriers of opposite sign. Also called averagelife.mean proportional See GEOMETRIC MEAN.mean time before failure Abbreviation, MTBF.The average length of time that a component orsystem will perform before the first failure occurs.It is generally specified in hours.mean time between failures Abbreviation, MTBF.The average length of time that a component orsystem will perform before failure occurs—eitherinitially or after repair or replacement. It is generallyspecified in hours.measured A quantity that is presented to an instrumentfor measurement.measured service Any service in which chargesare assessed per unit-time usage block. Onlinecomputer services are a common example. Insome cases, other factors, such as distance, affectthe cost per unit time; most long-distancetelephone services fall into this category.measurand Any quantity that is measured with aninstrument.

438 measurement • medium-scan televisionmeasurement 1. The process by which the magnitude,extent, or duration of a parameter is found.2. The value of a parameter, as obtained, accordingto 1.measurement error The difference between themeasured value of a quantity and its true value.Also see NEGATIVE ERROR OF MEASUREMENTand POSITIVE ERROR OF MEASUREMENT.measurement range In a measuring device, therange within which the error is smaller than aspecified value.mechanical analogs Familiar mechanical devices,systems, or effects with which certain electricalcounterparts can be compared for ease in teachingor understanding (e.g., inductance comparedwith mass, capacitance with elasticity, voltagewith pressure, and current with velocity).mechanical axis In a quartz crystal, the axis perpendicularto the faces of the hexagon. Also seeY-AXIS, 2.mechanical bandspread Bandspread tuning obtainedby reduction-ratio gearing of the tuningmechanism. Compare ELECTRICAL BAND-SPREAD.mechanical bias 1. A steady pull applied by aspring to the armature of a relay to sensitize it bydecreasing the distance that the armature mustmove to close the contacts. 2. Bending of a relayframe to position the armature closer to the magnetfor the purpose defined in 1.mechanical damping Damping action obtainedentirely by mechanical devices (such as weights,dashpots, etc.).mechanical equivalent of heat The amount ofmechanical work required to produce a unitquantity of heat. For example, 4.183 joules canbe converted into 1 calorie of heat.mechanical equivalent of light The expression ofluminous energy in equivalent power units. Inpractical measurements, this is taken as the totalpower output of a lamp minus the power absorbedby a transparent jacket used to removethe infrared and ultraviolet rays.mechanical filter See ULTRASONIC FILTER, 1.mechanical joint A union of electrical conductorsconsisting exclusively of a junction or splice madewithout brazing, soldering, or welding.mechanical load An electromechanical device thatuses the output of an electrical source. Such devicesinclude actuators, brakes, clutches, meters,motors, and relays.mechanical rectifier A vibrator or commutatorused to change an alternating current into adirect current by selecting and passing onlypositive or negative half-cycles. Also seeELECTROMECHANICAL RECTIFIER.mechanical scanner 1. A mechanical device forscanning an object or scene and breaking it intohorizontal lines that are converted to signals. 2. Adevice that scans the reproducer lamp in a mechanicaltelevision receiver. See, for example,NIPKOW DISK.mechanical switch A switch actuated by movingor sliding a lever, pressing a button, or otherwiseapplying mechanical pressure.mechanical time constant For a torque motor,the ratio of moment of inertia to damping factor.Compare ELECTRICAL TIME CONSTANT.mechanical wave filter See ULTRASONIC FIL-TER, 1.mechanics The branch of physics concerned withforces and motion and the laws of gases and liquids.It is subdivided into kinematics and kinetics.mechatronics Combination of the words mechanicsand electronics, referring to the use of electromechanicaldevices (especially robots) inmanufacturing. The term was originally coined inJapan.median 1. The middle value in a sequence of numbers.For example, in the series: 1, 2, 3, 4, 5, 6, 7,the median is 4. Compare ARITHMETIC MEANand GEOMETRIC MEAN. 2. In a statistical distribution,the value s in the domain so that the areaunder the curve for all values less than s is equalto the area under the curve for all values greaterthan s.medical electronics See ELECTROMEDICAL EN-GINEERING.medical robot 1. A robot used in a doctor’s office,or in a hospital to assist doctors and nurses.There are various applications, some of whichhave provoked controversy (e.g., robotic surgicalassistant). It generally performs simple, noncriticaltasks. It has been suggested as a means of entertaininghospital patients—especially children.2. See BIOMECHANISM.medium In a computer system, that storage deviceonto or into which data is recorded for input intomemory (e.g., magnetic disk, magnetic tape, opticaldisk, etc.).medium-frequency Abbreviation, MF. Pertainingto frequencies in the range 300 kHz to 3 MHz,representing wavelengths from 1000 meters to100 meters.medium of propagation The substance (or vacuum)through which electromagnetic energy istransmitted (e.g., outer space, the atmosphere, ora dielectric material).medium-scale integration A method of manufacturingintegrated circuits, in which there are atleast 10, but less than 100, individual gates oneach chip. Abbreviated MSI.medium-scan television A television (TV) communicationsmedium in which the scanningrate is slowed down compared to regular (fastscan)TV, but is faster than the commonly usedslow-scan TV. It provides some conception ofmotion, although not as realistic as fast-scanTV.

medium tension • meltback transistor 439medium tension Medium voltage. A relative term,but generally referring to common alternatingcurrentutility voltage (e.g., 117 volts or 234volts).medium wave Abbreviation, MW. Pertaining towavelengths corresponding to medium frequencies(see MEDIUM-FREQUENCY) (i.e., those inthe 100- to 1000-meter range).meg 1. Colloquialism for MEGOHM(s). 2. Colloquialismfor MEGABYTE(s).mega- Abbreviation, M. 1. A prefix meaning million(s),(i.e., 10 6 or 1,000,000). 2. In digital dataapplications, a prefix meaning 2 20 or 1,048,576.megabar Abbreviation, Mb. A cgs unit of high pressure.1 Mb = 10 6 bars = 10 11 pascals. Also seeBAR, 1.megabit A unit of digital data equal to 2 20(1,048,576) bits. Also see BIT.megabyte Abbreviation, M or MB. A unit of digitaldata equal to 2 20 (1,048,576) bytes. Also see BYTE.megacurie Abbreviation, MCi. A large unit of radioactivityequal to 3.71 × 10 6 disintegrations persecond; 1 MCi = 10 6 curies. Also see CURIE.megacycle See MEGAHERTZ.megaelectronvolt Abbreviation, MeV. A large unitof electrical energy; 1 MeV = 10 6 eV. Also seeELECTRONVOLT.megahertz Abbreviation, MHz. A unit of frequency;1 MHz = 10 6 Hz = 1,000,000 Hz.megampere Abbreviation, MA. A unit of high current;1 MA = 10 6 A = 1,000,000 A.megaphone 1. A hand-held microphone/amplifier/loudspeakerused to amplify the voice of aperson who must be heard over an appreciablearea. 2. A simple horn for amplifying the voice.megarutherford Abbreviation, Mrd. A large unit ofradioactivity equal to 1 trillion (10 12 ) disintegrationsper second; 1 Mrd = 10 6 rd = 1,000,000 rd.Also see RUTHERFORD.megavolt Abbreviation, MV. A unit of extremelyhigh voltage; 1 MV = 10 6 V = 1,000,000 V.megavolt-ampere Abbreviation, MVA. A unit of extremelyhigh reactive power; 1 MVA = 10 6 VA =1,000,000 VA. Also see VOLT-AMPERE.megawatt Abbreviation, MW. A unit of high power;1 MW = 10 6 W = 1,000,000 W. Also see WATT.megawatt-hour Abbreviation, MWh. A large unit ofelectrical energy or of work; 1 MWh = 10 6 Wh =1,000,000 Wh = 3.6 × 10 9 joules. Also see WATT-HOUR.megger An instrument containing an internalhigh-voltage direct-current power supply, usedfor measuring high values of resistance. CompareMEGOHMMETER.meg-mike 1. Colloquialism for MEGOHM-MICRO-FARAD(s). 2. Colloquialism for MEGOHM-FARAD(s).megohm Symbol, M. A unit of high resistance, reactance,or impedance; 1 M = 10 6 ohms =1,000,000 ohms.megohm-farads For a large capacitor, the productof leakage resistance (megohms) and capacitance(farads). Also see MEGOHM-MICROFARADS.megohmmeter A special ohmmeter for measuringresistances in the megohm range.megohm-microfarads For a capacitor, the productof leakage resistance (megohms) and capacitance(microfarads). The figure is an expression for therelative insulation resistance of a capacitor.Meissner circuit An oscillator tuned by means ofLECHER WIRES (parallel-conductor resonant circuits).It is used primarily at ultra-high frequencies(UHF).GatetuningMeissner circuitDraintuningOutput+12 VMeissner effect In a superconductive material, theabrupt loss of magnetism when the temperatureof the material is reduced to a value below thatrequired for superconductivity.Meissner oscillator See MEISSNER CIRCUIT.meitnerium Symbol, Mt. Also called unnilenium(Une). Atomic number, 109. The most commonisotope has atomic weight 266. Classified as atransition metal. It is human-made and notknown to occur in nature.mel An expression of apparent or perceived soundpitch. A tone of 1 kHz, at a level of 40 dB, with respectto the threshold of hearing, represents 1mel. The perceived pitch depends, to some extent,on the intensity of the sound, as well as on theactual frequency.M electron In certain atoms, one of the electronswhose orbits are outside of and nearest to thoseof the L electrons.meltback process The technique of remelting adoped semiconductor material and allowing it torefreeze to form a grown junction.meltback transistor A grown-junction transistorproduced by the MELTBACK PROCESS.

440 melting point • mercury cellmelting point Abbreviation, mp. The temperatureat which a solid starts becoming liquid at a pressureof one atmosphere. Compare FREEZINGPOINT and MIXTURE MELTING POINT.memory 1. The section of a digital computer thatrecords and holds data until it is necessary. Inpersonal computers, the term generally refers toRANDOM-ACCESS MEMORY and READ-ONLYMEMORY, contained in integrated circuits (ICs).Compare STORAGE. 2. See MEMORY DRAIN.memory address register In computer storage, aregister in which is stored the address ofoperands in other locations.memory area A portion of computer memory reservedfor a specific type of data. Also called area.memory capacity As a function of the number ofmemory locations available, the number of bytesthat can be stored. It is usually specified in kilobytes,megabytes, or gigabytes. Also see GIGA-BYTE, KILOBYTE, and MEGABYTE.memory cycle 1. The period of execution of a sequenceof operations. 2. The complete operationalcycle for inputting data to memory orretrieving it.memory dialing In a telephone set, a feature thatallows rapid dialing of stored digits. The simplestversion is the “redial” feature, in which the mostrecently dialed number is rapidly dialed at thetouch of a button. Some sets can store several differentnumbers, usually including area codes,and sometimes country codes as well.memory drain Also called battery memory. A phenomenonoccasionally exhibited by nickel–cadmium cells and batteries, in which the usefulampere-hour capacity is reduced even though theunit is not physically damaged. The depth of thecharge cycle decreases to a fraction of its ratedvalue. The problem can usually be overcome bydischarging the cell or battery fully, then rechargingfully, and repeating the process several times.See also NICKEL–CADMIUM.memory dump In computer operations, to eitherprint out what is stored in some of or all of thememory locations or transfer the data from abank of memory cells to some external storagemedium.memory effect See MEMORY DRAIN.memory guard In a computer, hardware or softwarethat keeps certain memory locations frombeing addressed by a program being run.memory location In a computer memory, a placewhere an information unit (word or character)can be stored; the stored information can be retrievedby appropriate addressing instructions.memory organization packets In artificial intelligence(AI) and expert systems, a method of arrangingcomputer memory into general rules orstatements. The statements are used by softwareto derive models, forecasts, diagnoses, etc.memory power Computer memory efficiency interms of data processing (cycle) speed.memory protection A hardware device in a multipleprogramming computer that prevents programsfrom being altered by other operatingprograms in the installation.memory register In a digital computer, a registerused in all instruction and data transfers betweenthe memory and other sections of the machine.memory unit See MEMORY.mendelevium Symbol, Md. A radioactive elementproduced artificially. Atomic number, 101.Atomic weight, 258 (approx.).menu In computer operations, a list of commandsfor using various functions of the system.MEP Abbreviation of mean effective pressure.mercuric iodide Formula, HgI 2 . A compoundwhose crystals are useful at room temperature asdetectors in high-resolution gamma-ray spectroscopy.mercury Symbol, Hg. A metallic element. Atomicnumber, 80. Atomic weight, 200.59. The onlymetal that is liquid at room temperature. It isused extensively in switches, certain high-voltagerectifiers, high-vacuum pumps, and thermometers.mercury arc The arc discharge occurring in mercuryvapor between solid or liquid (mercury) electrodes.The discharge emits ultraviolet radiation.mercury-arc rectifier A heavy-duty rectifier tubeutilizing ionized mercury vapor. The two generaltypes are MERCURY-VAPOR RECTIFIER andMERCURY-POOL RECTIFIER.mercury battery Also called mercuric-oxide battery.A set of two or more mercury cells stackedone atop the other, electrically connected in series.The resulting battery has a cylindricalshape. A set of four cells provides approximately5.4 volts under no-load conditions; a battery ofseven cells provides 9.5 volts; a battery of ninecells provides 12 volts. See MERCURY CELL.mercury cadmium telluride Formula HgCdTe.An alloy used as a semiconductor in certain transistors,integrated circuits, and infrared detectors.mercury cell Also called mercuric-oxide cell. Anelectrochemical cell having a button-like shape,small enough to fit inside a wristwatch. Theunit is housed in a steel container and has amercuric-oxide cathode, amalgamated-zinc anode,and potassium hydroxide and zinc-oxide electrolyte.The potential difference under no-loadconditions is 1.35 volts, with a high ratio ofstored energy per unit mass. The cell has a flatdischarge curve; the voltage remains essentiallyconstant until the charge is almost depleted, andthen the voltage drops rapidly. There has been adecrease in the use of mercury cells and batteriesin recent years, because mercury is toxic. Unlessthese cells are discarded in a special way, themercury from them can cause dangerous contaminationof soil and water.

mercury delay line • meson 441mercury delay line A delay line in which delay isobtained by propagating the signal through apipe of mercury.mercury diffusion pump A vacuum diffusionpump using mercury vapor.mercury displacement relay A form of switchingrelay in which the electrical contact is made bymoving mercury.mercury-jet switch A multipoint switch using a jetof mercury instead of the conventional wiper arm,for high-speed operation and reduced wear.mercury memory A recirculating memory using amercury delay line. Also see DELAY LINE andDELAY-LINE MEMORY.mercury-pool cathode In certain industrial electrontubes, such as the ignitron, a cathode electrodeconsisting of a pool of mercury.mercury-pool rectifier A type of mercury-arc rectifierwhose cathode is a pool of mercury. In onetype, the arc is initiated by tilting the tube momentarilyto bring the mercury into contact witha third electrode, thus causing a starting currentto flow through the pool. In another type, the ignitron,a starter electrode is in continual contactwith the mercury.mercury pump See MERCURY DIFFUSION PUMP.mercury rectifier See MERCURY-POOL RECTI-FIER and MERCURY-VAPOR RECTIFIER.mercury relay A relay in which at least one of thecontacts is mercury.mercury storage See MERCURY MEMORY.mercury switch A switch consisting essentially oftwo or more stiff wire electrodes and a drop ofmercury hermetically sealed in a glass tube. Tiltingthe tube causes the mercury to flow towardone end, where it immerses the electrodes, providinga conductive path between them.mercury-vapor lamp A glow lamp emitting bluegreenlight that causes ionization of mercury vaporby an electric current.mercury-vapor rectifier A tube-type high-voltagediode rectifier containing a small amount of mercurythat vaporizes and ionizes during tube operation.mercury-vapor tube 1. See MERCURY-VAPORLAMP. 2. See MERCURY-VAPOR RECTIFIER.mercury-wetted reed relay A reed relay in whichthe reeds are wetted with mercury in a pool bycapillary action. The film of mercury forms a tinybridge when the reeds open; when this bridge separates,a clean, high-speed break occurs withoutcontact bounce. Compare DRY-REED SWITCH.merge 1. In computer operations, to make a singleset or file from two or more record sets. 2. In wordprocessing, to create a corrected master recordingfrom two input media: the original masterrecording and the recording that contains thecorrections.meridian 1. A great circle passing through earth’sgeographic poles and a given point on the surfaceof the earth. 2. A line of longitude on a map orglobe. Also see TIME ZONE, ZERO MERIDIAN,and ZONE TIME.mesa A flat-topped, protruding region in a semiconductorwafer. The mesa is produced by etchingthe surrounding part of the material. Somebipolar transistors are manufactured in this way.mesa diffusion A method of manufacturing bipolartransistors. The different semiconductor materialsare first diffused together. Then part of theresulting wafer is etched away, resulting in amesa shape.mesa transistor A diffused planar transistor inwhich the silicon area around the base has beenetched away to reduce collector-to-base capacitance;the base-emitter region remains elevatedlike a high plateau (mesa).EmitterAlloyedregionBasemesa transistorDiffused regionCollectorSemiconductorMESFET A form of field-effect transistor combiningdepletion-mode and enhancement-mode properties.A Schottky barrier forms the gate electrode.mesh 1. A combination of the elements that form aclosed path in a network. 2. The closed figure(such as the delta or star) obtained by connectingpolyphase windings together. 3. A grid, screen, orsimilar structure in a vacuum tube.mesh equations Equations describing fully thecurrent and voltage relations in a network ofmeshes (see MESH, 1).Mesny circuit A push-pull ultra-high-frequency(UHF) oscillator whose gate or base tank is a pairof parallel wires short-circuited by a slider; thedrain or collector tank is a similar pair of wires.The frequency is varied by moving the slidersalong the wires.mesochronous A condition for signals in whichsignificant instants pass at identical averagespeeds, such as bits per second.meson An unstable nuclear particle first observedin cosmic rays. A meson can be electrically positive,negative, or neutral. Its mass lies betweenthat of the electron and proton.

442 mesotron • meteorographmesotron See MESON.message 1. In communications, a body of informationsent from a source (transmitter) to a destination(receiver). 2. Data entered into atransaction-processing system.message exchange In a digital communicationschannel, a hardware unit that carries out certainswitching functions that would otherwise have tobe done by a computer.message switching system A data communicationssystem having a central computer that receivesmessages from remote terminals, storesthem, and transfers them to other terminals asneeded.metadyne See DC GENERATOR AMPLIFIER.metal An elemental material that exhibits severalfamiliar properties (such as luster, ductility, malleability,good electrical and heat conductivity,relatively high density, and the ability to emitelectrons). Common examples are aluminum,copper, gold, lead, and silver. Compare METAL-LOID and NONMETAL.metal-base transistor A bipolar transistor inwhich the base is a metal film, and the emitterand collector are films of n-type semiconductormaterial.metal-ceramic construction The building of certainelectronic components by bonding ceramicparts to metal parts. Also see CERMET.metal-film resistor A fixed or variable resistor inwhich the resistance element is a film of a metalalloy deposited on a substrate such as a plastic orceramic.metal finder See METAL LOCATOR.metallic binding forces In a crystal, the bindingelectrostatic force between cations and electrons.Also called electron-gas binding forces.metallic bonding See BONDING, 1 and METALLICBINDING FORCES.metallic circuit A circuit, such as a two-wire telephoneline, in which earth ground is not a part ofthe circuit. Compare GROUND-RETURN CIR-CUIT.metallic crystal A crystal substance in which positiveions and free electrons exist; it is, therefore,a good electrical conductor.metallic insulator A short-circuited quarter-wavesection of transmission line that acts as an insulatorat the quarter-wavelength frequency.metallicize To make a circuit fully metallic, aswhen two wires are used instead of one wire anda ground connection. (Not to be confused withMETALLIZE.)metallic rectifier A dry rectifier using a metal diskor plate coated with a material (such as selenium,an oxide, or a sulfide).metallic tape Recording tape made from metal,rather than from plastic. Noted for its excellentaudio-reproduction characteristics.metallize To treat, coat, or plate with a metal. (Notto be confused with METALLICIZE.)metallized capacitor A capacitor in which eachface of a dielectric film is metallized to form conductiveplates.metallized-paper capacitor A paper-dielectric capacitorwhose plates are metal areas electrodepositedon each side of a paper film.metallized-polycarbonate capacitor A fixed capacitorin which the dielectric is a polycarbonateplastic film, and the plates are metal areas electrodepositedon each face of the film.metallized resistor See METAL-FILM RESISTOR.metal locator An electronic device for locatingmetal deposits, pipes, or wires underground, inwalls, or under floors. It operates via the disturbancethat these objects cause to a radiofrequencyor magnetic field.metalloid An element that has some of the propertiesof a metal. Examples of metalloidal elementswidely used in electronics are antimony, arsenic,germanium, silicon, and tin.metal master See ORIGINAL MASTER.metal negative See ORIGINAL MASTER.metal-oxide resistor A resistor in which the resistancematerial is a film of tin oxide deposited on asubstrate.metal-oxide semiconductor field-effect transistorAbbreviation, MOSFET. A field-effect transistorin which the gate electrode is not a pnjunction (as in the junction field-effect transistor),but a thin metal film insulated from thesemiconductor channel by a thin oxide film.Gate-control action is entirely electrostatic. Alsocalled insulated-gate field-effect transistor. Alsosee DEPLETION-TYPE MOSFET, DEPLETION-ENHANCEMENT-TYPE MOSFET, and EN-HANCEMENT-TYPE MOSFET.metal-oxide varistor A VOLTAGE-DEPENDENTRESISTOR in which the resistance material is ametallic oxide, such as zinc oxide.metal-plate rectifier See METALLIC RECTIFIER.metal tube A vacuum tube housed in a metal envelopefor self-shielding and mechanical ruggedness.metamer A visible-light beam that is identical incolor (hue), but different in concentration (saturation),with respect to a reference color.meteor-burst signals Momentary signals, or increasesin signal strength, resulting from reflectionof electromagnetic energy from meteorionization trails. See METEOR SCATTER, 1.meteor ionization trail A cloud of ions left in theupper atmosphere as a meteor passes. This cloudtends to reflect radio signals at certain frequenciesfor a short period of time. During a meteorshower, there could be a sufficient number ofsuch trails to allow continuous over-the-horizoncommunication when other over-the-horizonmodes are unusable.meteorograph An instrument for the simultaneousmeasurement of various meteorological phenomenasuch as temperature, humidity, etc.

meteorology • metrology 443meteorology The science of the atmosphere, especiallythe study of weather and climate. (Not to beconfused with METROLOGY.)meteor-scatter propagation The reflection of radiosignals from the ionized trails produced by meteorsas they pass through the upper atmosphere.This can result in over-the-horizon radio communicationor reception. A meteor produces a trailthat persists for a few tenths of a second up to severalseconds, depending on the size of the meteor,its speed, and the angle at which it enters the atmosphere.This is not sufficient time for the transmissionof very much information, but during ameteor shower, ionization can be almost continuous.Meteor-scatter propagation has been observedat frequencies considerably above 30 MHz.meteor-trail reflections Momentary reflection ofsignals by the ionized trails of meteors passingthrough a signal path.F layerE layerIonizedtrailsmeteor-trail reflectionsMeteorpathsmeter 1. An instrument for measuring and indicatingthe value of a particular quantity. See, forexample, CURRENT METER and VOLTMETER.2. Abbreviation, m. A unit of linear measureand of electrical wavelength, equivalent to1.65076373 × 10 6 wavelengths (in a vacuum) of theradiation corresponding to the transition betweenthe two levels of the krypton-86 atom, andapproximately equal to 39.37 inches. 3. To supplyin specific increments or by a governed amount.meter alignment See VISUAL ALIGNMENT.meter-ampere A unit of transmitted radio signalintensity. Determined by multiplying the antennacurrent (in amperes) by the height (in meters) ofthe antenna above ground.meter-candle Abbreviation, mc. A metric unit of illuminance,equivalent to the illumination on asurface 1 meter from a light source of 1 candlepower. Compare FOOT-CANDLE and LUX.meter equivalent The number of meters equal to agiven English measure of length (e.g., the meterequivalent of 3 feet is approximately 0.9144).meter-kilogram-second Abbreviation, mks. Thesystem of units in which the meter is the standardunit of length, the kilogram is the standardunit of mass, and the second is the standard unitof time. Compare CENTIMETER-GRAM-SECONDand INTERNATIONAL SYSTEM OF UNITS.meter multiplier See MULTIPLIER RESISTOR.meter protector A nonlinear resistor, such as avaristor or semiconductor diode, used to preventoverswing in an electric meter by limiting the currentflowing through it.meter rating The maximum reading on a meter, ator below which the accuracy is within a specifiedlimit, but above which the error might exceedthat limit.meter rectifier A light-duty semiconductor diodeor bridge circuit, used to change alternating current(ac) to direct current (dc) for deflection of aD’Arsonval-type dc milliammeter or microammeter.meter relay A sensitive relay that is essentially amoving-coil meter, whose pointer closes against astationary contact mounted at some point alongthe scale.meter resistance Symbol, R m . The internal resistanceof an electric meter. In a simple D’Arsonvalmeter, it is the resistance of the movable coil. Inmore-complicated meter circuits, it is the resistanceof the parallel combination of the coil andMETER SHUNT.meter scale factor See SCALE FACTOR, 1.meter sensitivity See VOLTMETER SENSITIVITY.meter shunt A resistor connected in parallel withan ammeter, milliammeter, or microammeter toincrease the range of currents that the device canmeasure.meter torque See DEFLECTING TORQUE.meter-type relay See METER RELAY.methyl methacrylate resin Also known by thetrade name Lucite. A plastic insulating material.Dielectric constant, 2.8 to 3.3. Dielectricstrength, 20 kV/mm.metre Abbreviation, m. Alternate spelling of meterwhen used to specify displacement or wavelength.See METER, 2.metric system The decimal system of weights andmeasures based on the meter, kilogram, and second.Also see CENTIMETER-GRAM-SECOND,METER-KILOGRAM-SECOND, and INTERNA-TIONAL SYSTEM OF UNITS.metric ton Abbreviation, MT. A metric unit ofweight equal to 1000 kilograms or 1.1023 Englishtons.metric waves British designation for electromagneticenergy having wavelengths ranging from 10meters down to 1 meter, corresponding to frequenciesfrom 30 MHz up to 300 MHz.metrology The science of weights and measures,including electrical standards and electronic instrumentsand measurements. (Not to be confusedwith METEOROLOGY.)

444 metronome • microcomponentmetronome A mechanical or electronic device thatproduces audible beats (ticks). It is commonlyused in setting the tempo for music, and for audiblytiming certain processes.MeV Abbreviation of MEGAELECTRONVOLT(s).MEW Abbreviation of MICROWAVE EARLY WARN-ING.mF Abbreviation of MILLIFARAD.MF 1. Abbreviation of MEDIUM FREQUENCY.2. Abbreviation of MIDFREQUENCY.MFD Abbreviation of MAGNETOFLUID DYNAMICS(see MAGNETOHYDRODYNAMICS).MFSK Abbreviation of MULTIPLE FREQUENCY-SHIFT KEYING.Mg Symbol for MAGNESIUM.mg Abbreviation of MILLIGRAM.MGD Abbreviation of MAGNETOGASDYNAMICS(see MAGNETOHYDRODYNAMICS).MHD Abbreviation of MAGNETOHYDRODYNAM-ICS.MHD generator See MAGNETOHYDRODYNAMICGENERATOR.MHD gyroscope See MAGNETOHYDRODYNAMICGYROSCOPE.MHD power generation See MAGNETOHYDRO-DYNAMIC GENERATOR.mho Obsolete term for the standard unit of electricalconductance. See SIEMENS.mhp Abbreviation of MILLIHORSEPOWER.MHz Abbreviation of MEGAHERTZ.mi Abbreviation of MILE. (Also, m.)MIC Abbreviation of MICROWAVE INTEGRATEDCIRCUIT.mic Abbreviation of MICROPHONE.mica A dielectric mineral of complex silicate composition,easily separated into numerous thin, transparentsheets. It is widely used as a capacitordielectric and high-temperature electrical insulator.Dielectric constant, 2.5 to 7. Dielectricstrength, 50 to 220 kV/mm. Also see MUSCOVITE.mica capacitor A component that is made by alternatelystacking metal sheets and layers of mica,or by applying silver ink to sheets of mica. Themetal sheets are wired together into two meshedsets, forming the two terminals of the capacitor.This type of capacitor is noted for low loss. Voltageratings can be up to several thousand volts ifthick sheets of mica are used. But these capacitorsare physically bulky in proportion to their capacitance.The main application is in radioreceivers and transmitters. Compare CERAMICCAPACITOR, ELECTROLYTIC CAPACITOR,PAPER CAPACITOR, PLASTIC-FILM CAPACITOR,TANTALUM CAPACITOR.MICR Abbreviation of MAGNETIC INK CHARAC-TER RECOGNITION.micro- 1. A prefix meaning MILLIONTH(S) (i.e.,10 –6 ). 2. A prefix meaning extremely small (as inmicrostructure). Compare MACRO-.microalloy diffused transistor Abbreviation,MADT. A MICROALLOY TRANSISTOR having aCoatingLeadsMetalelectrodesmica capacitorThin layerof micauniform base region that is diffused into thewafer before the emitter and collector electrodesare produced by alloying.microalloy transistor Abbreviation, MAT. A transistorhaving tiny emitter and collector electrodesthat are formed by alloying a thin film of impuritymaterial with a collector pit and emitter pit facingeach other on opposite surfaces of the semiconductorwafer. Also see SURFACE-BARRIERTRANSISTOR.microammeter A usually direct-reading instrumentused to measure current in the microampererange. Also see CURRENT METER.microampere A small unit of current, equal to 10 –6(0.000001) A.microbalance A sensitive electronic weighing device.One type uses one or more servo amplifiersfor the balancing operation.microbar A cgs unit of low pressure, equal to 10 –6b or 0.1 pascal. Also see BAR, 1 and MILLIBAR.microbarograph A barograph that is sensitive tosmall changes in pressure.microbeam An energy beam (ray) having extremelysmall cross section.microcircuit An extremely small circuit fabricatedupon and within a substrate, such as a semiconductorchip. Also see INTEGRATED CIRCUIT.microcode 1. See MICROINSTRUCTION. 2. A codefor MICROPROGRAMMING.microcomponent A tiny component in an electroniccircuit. Examples are the resistors, capacitors,diodes, and transistors fabricated onto anintegrated-circuit chip.

microcomputer • micromodule 445microcomputer 1. A computer contained withina single integrated circuit (IC). The simplestsuch devices perform elementary functions andare available for a few dollars. More sophisticateddevices control radio receivers and transmitters,television sets, automobiles, aircraft,and robots. The most advanced devices can beprogrammed to provide electrical impulses tocontrol erratically functioning body organs,move the muscles of paralyzed persons, andtranscribe speech to writing or vice versa. CompareMICROPROCESSOR. 2. In general, anysmall computer.microcrystal A crystal that is invisible to thenaked eye.microcurie A small unit of radioactivity equal to3.71 × 10 4 disintegrations per second or 10 –6curie. Also see CURIE.microelectrode 1. An electrode used in MICRO-ELECTROLYSIS. 2. A tiny electrode, especiallyone of those used in integrated circuits and incertain biological applications.microelectrolysis Electrolysis of tiny amounts ofmaterial. Also see ELECTROLYSIS, 1.microelectronic circuit 1. A tiny electronic circuitother than an INTEGRATED CIRCUIT (i.e., oneassembled in a small space with small discrete orintegrated components). 2. See MICROCIRCUIT.microelectronic device See MICROELECTRONICCIRCUIT.microelectronics The branch of electronics dealingwith extremely small components and circuitsfabricated on substrates. Also see INTEGRATEDCIRCUIT.microelectrophoresis Electrophoresis of singleparticles.microelectroscope A very sensitive electroscopeused to detect minute quantities of electricity.microelement A tiny component (capacitor, resistor,coil, semiconductor device, or transformer)mounted on a wafer and used in a MICROCIR-CUIT.microelement wafer A microwafer on which a microelementis mounted or deposited.microfarad Abbreviation, µF. A unit of capacitanceequal to 10 -6 (0.000001) F.microfarad meter 1. A dynamometer-type meterthat indicates the value of a capacitor directly inmicrofarads. Such instruments operate froman alternating-current power line. 2. A directreadingcapacitance meter.microfiche A method of storing printed informationon small film cards. The pages are reducedand arranged in order from left to right and top tobottom. The card is inserted into a projecting machineto allow retrieval of the information. Thephotographic method is similar to that used inMICROFILM.microfilm A method of storing printed or photographicinformation. The pages are reduced andarranged sequentially on a strip of film, usually35-mm size. The film is inserted into a projectingdevice for retrieval of the information.microgalvanometer A highly sensitive GALVA-NOMETER.microgauss A magnetic unit equal to 10 –6(0.000001) gauss.microgram A metric unit of weight or mass equalto 10 –6 (0.000001) gram.microgroove record A phonograph disc with avery fine groove (200 to 300 per inch), designedfor playback at 33 1 ⁄3 revolutions per minute (rpm).microhenry Symbol, µH. A unit of inductance,equal to 10 –6 (0.000001) H.microhm Symbol, µΩ. A unit of low resistance, reactance,or impedance, equivalent to 10 –6(0.000001) ohm.microhm-centimeter A unit of low resistivity,equal to 10 –6 (0.000001) ohm-cm. See OHM-CENTIMETER and RESISTIVITY.microhmmeter An instrument for measuring ultra-lowresistance. Such an instrument musthave a special provision for canceling the effectsof contact and lead resistance.microinch A unit of linear measure equal to 10 -6(0.000001) inch.microinstruction A machine-code instructionthat controls the operation of a computer directly(i.e., it is a “wired-in” instruction, or one set byDIP switches, independent of programs loadedinto the machine).microknowledge In artificial intelligence (AI), detailedmachine knowledge. It includes logic rules,computer programs, and data in memory. CompareMACROKNOWLEDGE.microliter A unit of volume, equal to 10 –6(0.000001) liter.microlock A special form of phase-locked-loopsystem, used especially with radar to improve thesignal-to-noise ratio.micromanipulator A machine that permits handlingtiny parts in very small areas. An example ofits use is in placing connections close together inmicrocircuits.micrometer 1. An instrument for measuring verysmall thicknesses, diameters, etc. 2. Also calledmicron. The SI unit of length, equal to 10 –6(0.000001) meter, or 10 –3 (0.001) millimeter.micromho See MICROSIEMENS.micromicro- See PICO-.micromicrofarad See PICOFARAD.micromicrohenry See PICOHENRY.micromicron A unit of linear measure equal to10 –12 meter, or 10 –6 (0.000001) micrometer.micromillimeter See NANOMETER.microminiature Pertaining to an extremely smallbody, component, or circuit; the last adjective inthe sequence of those describing size: standard,small, midget, miniature, subminiature, and microminiature.micromodule A small, encapsulated circuit, consistingof smaller components. The components

446 micromodule • microsyncan be discrete, can consist of integrated circuits,or can be a combination of both. The module iseasily removed and replaced by means of a pluginsocket.micron See MICROMETER.microphone A transducer that converts soundwaves, especially speech and music, into electricalvoltage analogs.microphone amplifier A sensitive, low-distortion,low-noise amplifier used in voice wireless transmittersand public address systems. Most amplifiersof this type have a tailored frequencyresponse, passing audio between about 300 Hznd 3000 Hz, and attenuating audio outside this arange. The range 300 Hz to 3000 Hz is sufficientto convey intelligible voice signals, and also allowsfor audio-frequency-shift keying (AFSK) andslow-scan television (SSTV) audio input.Mic.+12 Vmicrophone amplifierOutputmicrophone boom A device used to hang a microphone,with the base out of the way. It is oftenused in radio broadcasting.microphone hummer See HUMMER.microphone input In an audio amplifier, a jack orother receptacle provided for connection to an externalmicrophone. It can also be used with otherlow-level audio apparatus. The jack is connectedto a MICROPHONE AMPLIFIER that provideshigh gain with minimum internal noise.microphone oscillator See HUMMER.microphonics Ringing (electrical noises) set up bythe vibration of a component having loose or movableelements. For example, ringing noises aregenerated in some circuit boards when they receivea physical blow.microphonograph A recorder of very low-intensitysound.microphonoscope An electronic stethoscope, usingamplification to enhance the response.microphotograph An extremely small photograph,often of a pattern or mask used in producingtransistors and integrated circuits. Not to be confusedwith photomicrograph, a photograph takenthrough a microscope.microphotometer A sensitive instrument for measuringsmall-area light intensity.microphysics The branch of physics concernedwith atoms, molecules, and subatomic particles.micropower Extremely small amounts of power—especially the very low direct-current supplypower required by some transistors.microprocessor The integrated circuit (IC), alsoknown as a chip, that coordinates the actions of acomputer and does the calculations. It is locatedon the motherboard (sometimes called the logicboard). These devices get more powerful everyyear. Physically, this translates to an increasingnumber of digital switching transistors per chip.The number of digital switches that can be fabricatedonto a semiconductor chip of a particularsize is ultimately limited by the structure of matter.Compare MICROCOMPUTER.microprogram 1. In computer operations, a routineof microinstructions that provides a computera specific function, independent of thoseestablished by programs being run or by themonitor program. Also see MICROINSTRUCTION.2. In the direction of a computer, use of a routinethat is stored specifically in the memory, insteadof elsewhere.microprogramming In the direction of a computer,the use of a routine that is stored specificallyin the memory, instead of elsewhere.micropulsation Also called micropulse. A pulse ofextremely short duration.microradiometer A sensitive detector of heat andinfrared radiation, consisting essentially of athermopile carried by the moving coil of a galvanometer.microrutherford A unit of radioactivity equal toone disintegration per second or 10 –6 (0.000001)rutherford. Also see RUTHERFORD.microsecond A unit of time measure equal to 10 –6(0.000001) second.microsiemens A unit of conductance equal to 10 –6(0.000001) siemens.microspectrophotometer An extremely sensitivespectrophotometer for examining light from tinyareas.microstrip A microwave component that is, in effect,a single-wire transmission line operatingabove ground.microsyn A device that translates rotational positioninto an electrical signal. Similar to aSELSYN. It is used for such purposes as rotatordirectionreading.

microsystems electronics • midrange speaker 447microsystems electronics The technology of electronicsystems using tiny electronic components.Also see INTEGRATED CIRCUIT, MICROELEC-TRONIC CIRCUIT, MICROELEMENT, MICRO-ELEMENT WAFER, and MICROWAFER.microvolt A unit of low voltage, equal to 10 –6(0.000001) volt.microvolter An accurate, external attenuator(usually for an audio signal generator) providingstepped and continuously variable output in microvoltsand millivolts.microvoltmeter A usually direct-reading instrumentused to measure voltages in the microvoltrange. An input amplifier boosts the test voltagesufficiently to deflect the indicating meter.microvolts per meter A unit of radio-frequency(RF) field strength. It refers to the RF voltage (inmicrovolts) between an antenna and ground, dividedby the height of the antenna (in meters)above ground. Compare MILLIVOLTS PER ME-TER.microvolts per meter per mile A means of expressingabsolute radio-frequency (RF) fieldstrength. Generally, the numerical value is basedon the field strength, in MICROVOLTS PER ME-TER, at a distance of 1 statute mile (5280 feet)from the source.microwafer A wafer of insulating material, such asa ceramic, on which one or more microelementsare mounted and terminals deposited or plated.microwatt A unit of low power, especially electricalpower, equal to 10 –6 (0.000001) watt.microwattage See MICROPOWER.microwattmeter An instrument for measuringpower in the microwatt range. Such an instrumentobtains its sensitivity from a built-in inputamplifier.microwave See MICROWAVES.microwave security system A circuit using microwaveradio-frequency energy to detect intruders.When an object moves within the field, theintensity of the field changes at one or morepickup sensors, triggering an alarm.microwave acoustics See ACOUSTOELECTRON-ICS and ACOUSTIC DELAY LINE.microwave dish A dish antenna for use at microwavefrequencies.microwave early warning Abbreviation, MEW. Ahigh-power early warning radar system that affordslarge traffic-handling capacity and longrange.microwave filter A bandpass filter built into awaveguide for use at microwave frequencies.microwave frequencies The general expressionfor radio frequencies above the ultra-high range,that is, 3 GHz or more, but below the frequenciesof infrared energy. This corresponds to radiowavelengths of 10 centimeters or less.microwave integrated circuit Abbreviation, MIC.An integrated circuit designed for use at microwavefrequencies.microwave lens See WAVEGUIDE LENS.microwave mirror A reflector of microwaves.microwave oven A device consisting essentially ofa radio-frequency heater using a magnetronoscillator. It produces microwave energy thatcauses heating of certain substances via excitationof the molecules.microwave plumbing Collectively, the waveguides,tees, elbows, and similar fixtures andconnections used in microwave setups.microwave radio relay The use of microwaves torelay radio, television, and control signals frompoint to point.microwave refractometer An instrument usingmicrowaves (around 10 GHz) to measure the refractiveindex of the atmosphere.microwave region See MICROWAVE FREQUEN-CIES and MICROWAVES.microwave relay See MICROWAVE RADIO RELAY.microwave relay system A series of microwavetransmitter-receiver stations for relaying communicationsin several line-of-sight hops.microwaves Radio-frequency electromagnetic energyat wavelengths shorter than about 10 centimeters,but longer than the wavelengths ofinfrared energy. See also MICROWAVE FRE-QUENCIES.microwave spectrum See MICROWAVE FRE-QUENCIES and MICROWAVES.microwave transistor A transistor whose semiconductorproperties and special fabrication enableit to operate at microwave frequencies.microwave tube A KLYSTRON, MAGNETRON, orsimilar tube, used to generate or amplify microwaveradio-frequency signals.midband Abbreviation, MB. The region whose limitsare immediately above and below a MIDFRE-QUENCY; the limits are usually specified for aparticular case.midband frequency See MIDFREQUENCY.midfrequency The center frequency in a specifiedband of frequencies.midget Of reduced size (smaller than small andlarger than miniature).MIDI Acronym for MUSICAL INSTRUMENT DIGI-TAL INTERFACE.midpoint voltage The voltage at the terminals of acell or battery when it has been dischargedhalfway (i.e., when the amount of energy used upis equal to the amount of energy remaining).midrange Pertaining to audio frequencies in themiddle of the human hearing range, where theear is the most sensitive. These frequencies lie betweenthe BASS and TREBLE.midrange horn A MIDRANGE SPEAKER equippedwith a flared horn to give the device a unidirectionalsound-emission pattern. It is used primarilyin high-power systems and by popular musicbands or high-end audio enthusiasts.midrange speaker A loudspeaker operating mostefficiently at frequencies in the middle of the

448 midrange speaker • milliroentgenaudio spectrum. Such a speaker is intermediatein performance between a WOOFER and aTWEETER.midsection The center section of a multisection filterhaving an odd number of sections; thus, thesecond section of a three-section filter.migration See ION MIGRATION.mike 1. See MICROPHONE. 2. See MICROFARAD.3. See MICROMETER.MIL Abbreviation of military.mil 1. A small unit of linear measure; 1 mil = 10 –3(0.001) inch = 0.0254 mm. 2. Thousand, as in nparts per mil.mile Abbreviation, m or mi. A large unit of linearmeasure, 1 mi = 1.609 km = 5280 feet.military robot A robot designed and used for thepurpose of executing some task in warfare. Thetwo general types are: human-operated andcomputer-controlled. An example of a humanoperatedmilitary robot is an aircraft that is flownby remote control by a ground-based pilot. Thesame robot, or a whole fleet of them, might beflown by a computer using sophisticated EXPERTSYSTEMS.mill A telegraph operator’s typewriter.Miller oscillator A crystal oscillator circuit inwhich the crystal is connected between the controlelectrode and ground. The tuned tank is connectedin the output circuit. The internalcapacitance of the active device provides feedbackcoupling. Sometimes called conventional crystaloscillator.milli- Abbreviation, m. A prefix meaning thousandth(s):10 –3 (0.001).Miller oscillator+12 VOutputmilliammeter A usually direct-reading instrumentfor measuring current in the milliampere range.Also see CURRENT METER.milliampere Abbreviation, mA. A unit of currentequal to 10 –3 (0.001) ampere.milliampere-hour Abbreviation, mAh. A unit oflow current drain or charging rate, equal to 10 -3(0.001) ampere-hour. Also see AMPERE-HOURand BATTERY CAPACITY.millibar Abbreviation, mb. A unit of low pressureequal to 10 –3 (0.001) bar or = 100 pascals.millicurie Abbreviation, mCi. A small unit of radioactivityequal to 3.71 × 10 7 disintegrations persecond, or 10 –3 (0.001) curie. Also see CURIE.millifarad Abbreviation, mF. A seldom-used unit ofcapacitance, equal to 10 –3 (0.001) farad or 1000microfarads.milligram Abbreviation, mg. A metric unit ofweight equal to 10 –3 (0.001) gram.millihenry Abbreviation, mH. A unit of inductance,equal to 10 –3 (0.001) henry.millihorsepower Abbreviation, mhp. A unit ofpower equal to 10 –3 (0.001) horsepower or 0.746watt. Also see HORSEPOWER.millilambert Abbreviation, mL. A small unit ofbrightness equal to 10 –3 (0.001) lambert.milliliter Abbreviation, ml. A metric unit of volumeequal to 10 –3 (0.001) liter.millimaxwell Abbreviation, mMx. A small unit ofmagnetic flux equal to 10 –3 (0.001) maxwell or10 –11 weber.millimeter Abbreviation, mm. A metric unit of linearmeasure equal to 10 –3 (0.001) meter or0.03937 inch.millimeter equivalent The number of millimetersequal to a given English measure fraction (e.g.,the millimeter equivalent of 5 ⁄16 inch is 7.937).millimeter waves Wavelengths between 0.6 and10 mm (frequencies from 30 to 500 GHz).millimicro See NANO-.millimicrofarad See NANOFARAD.millimicrohenry See NANOHENRY.millimicron Abbreviation, mm. A unit of wavelengthequal to 10 –3 micron or one nanometer (10 –9 meter).millimilliampere See MICROAMPERE.millimole Abbreviation, mmol. A unit in chemistryequal to 10 –3 (0.001) mole.milliohm A small unit of resistance, reactance, orimpedance, equal to 10 –3 (0.001) ohm.milliohmmeter An ohmmeter for measuring resistancesin the milliohm range.million electronvolt(s) See MEGAELECTRON-VOLT.milliphot A unit of illumination equal to 10 –3(0.001) phot.millipuffer See PUFFER.milliradian Abbreviation, mrad. A unit of angularmeasure equal to 10 –3 (0.001) radian.milliroentgen Abbreviation, mr. A small unit of radioactivedosage; 1 mr = 10 –3 (0.001) roentgen =2.57976 × 10 –7 Ci/kg.

millirutherford • minor lobe 449millirutherford Abbreviation, mrd. A small unit ofradioactivity equal to 1000 disintegrations persecond; 1 mrd = 10 –3 (0.001) rutherford.millisecond Abbreviation, ms or msec. A smallunit of time equal to 10 –3 (0.001) second.millitorr Abbreviation, mT. An obsolete unit of lowpressure equal to 10 –3 (0.001) torr, or 0.133322pascal. Also see TORRICELLI.millivolt Abbreviation, mV. A unit of voltage equalto 10 –3 (0.001) volt.millivoltmeter A usually direct-reading instrumentfor measuring low electric potential. Itssensitivity is provided by a high-gain amplifieroperated ahead of the indicating meter.millivolt potentiometer Abbreviation, MVP. A potentiometer-typenull instrument for accuratelymeasuring small direct-current voltages, such asthose delivered by a thermocouple. Also see PO-TENTIOMETRIC VOLTMETER.millivolts per meter Abbreviation, mV/m. A unitof radio-frequency (RF) field strength. It refers tothe RF voltage (in millivolts) developed betweenan antenna and ground, divided by the height (inmeters) of the antenna above ground. CompareMICROVOLTS PER METER.milliwatt Abbreviation, mW. A unit of power equalto 10 –3 (0.001) watt.milliwattmeter An instrument for measuringpower in milliwatts. Such instruments usuallyobtain their sensitivity from a built-in preamplifier.Mills cross A radio-telescope antenna, consistingof two collinear or phased arrays with a commonintersecting lobe. The result is high resolution.mil-spec security See LEVEL-3 SECURITY.min 1. Abbreviation of MINIMUM. 2. Abbreviationof MINUTE.mineral An element or compound that occurs naturallyin the earth’s crust. Most minerals arecrystalline and many of these have found use inelectronics. Some have been produced artificially.mineral oil A natural liquid insulant derived frompetroleum. Dielectric constant, 2.7 to 8.0. Powerfactor, 0.08 to 0.2 percent at 1 kHz.mineral-oil capacitor An oil capacitor whose paperdielectric has been impregnated with mineraloil, which is also the filler.miniature Very small (smaller than midget andlarger than subminiature).miniature cell An electrochemical cell of verysmall size (e.g., a button cell of the kind used incameras and watches).miniaturization The technology of minimizing thephysical size of a circuit or system, while maintainingits ability to accomplish a given task.minicalculator A pocket-size electronic calculator.minicomputer General term for a computer that ismore sophisticated than a MICROCOMPUTER,but less powerful than a MAINFRAME.mini connector A jack or plug having two or threeconductors, and measuring 1 ⁄8 (0.125) inch in di-ameter. It is commonly used with audio equipment.minifloppy A smaller than standard flexible magneticdisk (floppy).minima Points along a curve at which a functionreaches a local minimum value. Also see MAXIMAAND MINIMA.yminimaxLocalminimaminimum Abbreviation, min. The smallest value ina range or set. Also see MAXIMA AND MINIMA.minimum detectable signal A signal whose intensityis just higher than the threshold of detection.minimum discernible signal Abbreviation, MDS.The lowest input-signal amplitude that will producea discernible output signal in a radio receiver.miniscope A very-small-sized, lightweight oscilloscope.minitrack A system used to track an earth satellite,using signals transmitted to the satellite by aline of ground radio stations.minometer A radioactivity-measuring instrumentcomposed of an ionization chamber and a stringgalvanometer.minor beats Secondary or extraneous beats producedin a beat-note system, caused by varioussum and difference frequency byproducts of theheterodyne process. Compare MAJOR BEATS.minor bend A bend in a rectangular waveguide,made without twisting.minor cycle See WORD TIME.minor face In a hexagonal quartz crystal, one ofthe three smaller faces. Compare MAJOR FACE.minority carrier The type of charge carrier presentin relatively small numbers in a processed semiconductormaterial. Electrons are minority carriersin p-type material; holes are minority carriersin n-type material. Compare MAJORITY CAR-RIER.minor lobe In a directional antenna system, anylobe other than the main lobe(s). Such a lobe representsreduced sensitivity and/or power gain

450 minor lobe • mixturerelative to the main lobe. Also see MAIN LOBE,SIDE LOBE.minor loop A subordinate path for the circulationof information or control signals in an electronicsystem (e.g., minor feedback loop). Compare MA-JOR LOOP.minute 1. Abbreviation, min. A unit of measure oftime equal to 60 seconds or 1 ⁄60 hour. 2. Also calledminute of arc. Symbol (‘). A unit of arc measureequal to 1 ⁄60 angular degree or 60 seconds. 3. Generalterm meaning “extremely small.”MIR Abbreviation of memory-information register.mirror 1. A device consisting chiefly of a highlypolished or silvered surface that reflects a largepart of the radiation (such as light) striking it.2. Radar-interference material (see CHAFF). 3. Toreflect, as by a mirror.mirror galvanometer A galvanometer in which amirror is moved by the coil. The mirror either reflectsa spot of light along an external scale, or itreflects the scale, which is then read through asmall telescope.mirror-galvanometer oscillograph See ELEC-TROMECHANICAL OSCILLOSCOPE.mirror image 1. An image or curve that is exactlyreversed relative to a straight line or flat plane,compared to a reference image or curve. CompareBILATERAL SYMMETRY. 2. For a quarter-waveMarconi antenna, the extra quarter-wave elementsupplied by the earth. 3. For an antenna at a distanced above a ground plane, an effective antennaat an equal distance d below the groundplane.AntennaImageλ/4λ/4mirror image, 2Groundmirror-reflection echo A false radar echo or set ofechoes, caused by reflection of the radar beamfrom a plane surface prior to its encountering thetarget or targets. The beam can also be reflectedfrom one target to another.mirror-type meter A meter whose movable coilcarries a small mirror (rather than a pointer) thatreflects a beam of light to produce a spot on atranslucent scale.misaligned head In a tape recorder, a record or apickup head that is incorrectly oriented, with respectto the passing tape.misfire Failure of a gas tube or mercury-arc tubeto ignite at the correct instant.misleading precision In electronic calculationsand data recording, greater precision than the instrumentsor conditions justify. Also see SIGNIF-ICANT FIGURES.mismatch The condition resulting from joining twocircuits, or connecting a line to a circuit, in whichthe impedances are substantially different.mismatched impedances Impedances that areunequal, and thus do not satisfy the conditionsfor maximum power transfer.mismatch factor For a load not perfectly matchedto a driving circuit, the ratio of current flowing inthe load to the current that would flow in the loadif its impedance were perfectly matched to theoutput impedance of the driving circuit.mismatch loss For a load that is mismatched to asource, the ratio P 1 /P 2 , where P 1 is the power amatched load would absorb from the source, andP 2 is the power actually absorbed by the mismatchedload.mistor A variable-resistance device, used to detectthe presence of a magnetic field and to measuremagnetic-field strength.MIT Abbreviation of MASTER INSTRUCTION TAPE.mix 1. To produce a beat signal (either the sum orthe difference frequency) from two input signals.2. The proportion of powdered iron and other inertsubstances in a ferromagnetic transformercore. Different mixes result in different operatingcharacteristics.mixdown A method of combining recorded soundfrom two or more audio tracks, and recording theresult onto an audio tape or disc. It is used to createspecial audio effects.mixed-base notation A number system in whichthe base (radix) alternates between two digit positions.Also called mixed radix notation.mixed calculation A mathematical calculation orexpression in which more than one operation isused.mixed modulation Modulation of several kinds coexistingin a system. Thus, a small amount of undesiredfrequency modulation might accompanyamplitude modulation, or vice versa.mixed number A number having integral (whole)and fractional parts (e.g., 3.14159).mixer 1. A device, such as a transistor or semiconductordiode, used to mix two input signals anddeliver an output equal to their difference and/orsum (see MIXING). 2. See AUDIO MIXER. 3. Anydevice that combines two or more signals, yieldingone output signal whose nature is determinedby the characteristics of the circuit.mixer noise Electrical noise that occurs in aMIXER.mixing Combining several signals so that some desiredmixture of the original signals is obtained.Compare MODULATION.mixture 1. A combination of two or more signalsthat retain their characteristics—even when theyinteract to produce beat-frequency products. 2. A

mixture • moderator 451Input1Input 1Input 2+PassiveInput2ActivemixerOutputOutputdiffusion of one substance throughout another,without a solution or a chemical reaction resulting.mixture melting point Abbreviation, mmp. Thetemperature at which a mixture of solid substancesstarts turning into a liquid at 1 atmosphereof pressure. This melting point dependsupon the melting points of the substances andtheir relative concentration in the mixture. Alsosee MELTING POINT and MIXTURE.mks Abbreviation of METER-KILOGRAM-SECOND.mL Abbreviation of MILLILAMBERT.ml Abbreviation of MILLILITER.mm Abbreviation of MILLIMETER.mmf Abbreviation of MAGNETOMOTIVE FORCE.mmol Abbreviation of MILLIMOLE.mmp Abbreviation of MIXTURE MELTING POINT.mmv Abbreviation of MONOSTABLE MULTIVI-BRATOR.Mn Symbol for MANGANESE.m n Symbol for MASS OF NEUTRON AT REST.mnemonic 1. Pertaining to MEMORY or to memorysystems. 2. A memory code or device.mnemonic code In computer operations, a programmingcode, such as assembly language,that, although easily remembered by the programmer,requires subsequent conversion to machinelanguage.mntr Abbreviation of MONITOR. (Also, mon.)MO Abbreviation of MASTER OSCILLATOR.Mo Symbol for MOLYBDENUM.mobile communications 1. Radio communicationsbetween or among stations on board movingor stationary land, waterborne, or airbornevehicles. 2. Radio communications between atleast one fixed station and one or more moving orstationary land, waterborne, or airborne stations.mobile radio service See MOBILE COMMUNICA-TIONS.mobile receiver A radio, television, or other receiveraboard a moving or stationary land, waterborne,or airborne vehicle.mobile-relay station A fixed station that receives asignal from a MOBILE STATION and retransmitsit to one or more other mobile stations.mobile station A station installed and operatedaboard a moving or stationary vehicle. The vehiclemight be on land, under water, or in the air.Compare PORTABLE STATION.mobile transmitter A radio, television, or othertransmitter aboard a moving or stationary vehicle.The vehicle might be on land, under water, orin the air.mobility See CARRIER MOBILITY.mockup See DUMMY, 1.mod 1. Abbreviation of MODULATOR. 2. Abbreviationof MODULUS. 3. Abbreviation of MODIFICA-TION.mode 1. One of the ways a given resonant systemcan oscillate. 2. One of the ways that electromagneticenergy can be propagated through a deviceor system. See MODES OF PROPAGATION.3. The method via which intelligence is conveyedin a communications or broadcast signal. SeeEMISSION MODE. 4. Resonance of sound waveswithin an acoustic chamber.mode coupling The exchange or interaction of energybetween identical modes (see MODE, 1, 2).mode filter A waveguide filter that separateswaves of different propagation mode, but of thesame frequency (see MODES OF PROPAGATION).model 1. A working or mockup version of a circuit,system, or device, illustrative of the final version.2. A mathematical representation of a process,device, circuit, or system. Example: the Rutherfordmodel of the atom.modeling The creation of an object in three-dimensionalcomputer graphics.modem See MODULATOR-DEMODULATOR.mode purity In a modulated radio-frequency signal,the condition in which no undesirable typesof modulation exist. For example, a frequencymodulatedsignal in which there is zero amplitudemodulation.moderator A substance, such as graphite orheavy water, used to slow neutrons in an atomicreactor. Also see ACCELERATOR, 1 and REAC-TOR, 2.

452 modes of propagation • modulation capabilitymodes of propagation The configurations inwhich microwave energy can be transmittedthrough a WAVEGUIDE.modes of resonance In a microwave cavity, theconfigurations in which resonant oscillation canexist, depending on the way the cavity is excited.modification 1. Changing the configuration of acircuit, device, or system, usually to a minor extent,to tailor its characteristics for a specific purpose.2. Changing some aspect of a signal for aspecific purpose (e.g., reducing the emissionbandwidth to allow more signals to fit within agiven band of frequencies). 3. In computer operations,changing program addresses and instructionsby performing logic and arithmetic on them,as if they were data. Also see PROGRAM MODIFI-CATION.modified alternate mark inversion A signal thatis similar to alternate mark inversion (AMI), butcontains certain differences that are specified bya rigorous set of standards for the particular signal.modifier A data item used to change a computerprogram instruction so that it can be used to implementdifferent successive operations. Also seePROGRAM MODIFICATION.modifier register See INDEX REGISTER.modify To perform a MODIFICATION to a circuit,device, system, signal, program address, etc.moding A fault characterized by oscillation of aMAGNETRON in undesirable modes.modular technique See BUILDING-BLOCK TECH-NIQUE.modulated amplifier A usually high-frequencyamplifier whose output is varied in some way forthe purpose of conveying intelligence. CompareMODULATED OSCILLATOR. In the amplitudemodulation of an amplifier, there is little or nodisturbance of the carrier frequency. Also seeMODULATION.modulated beam 1. An electron beam (as in acathode-ray tube), whose intensity is varied by adesired signal. 2. A light beam whose intensity isvaried for communications or control purposes.modulated carrier A carrier wave whose amplitude,frequency, or phase is varied to convey intelligence.modulated continuous wave Abbreviation, mcw.A high-frequency carrier wave modulated by acontinuous, lower-frequency wave, as in MCWtelegraphy.modulated CW See MODULATED CONTINUOUSWAVE.modulated electron beam See MODULATEDBEAM, 1.modulated light beam See MODULATED BEAM,2.modulated oscillator A usually high-frequencyoscillator whose output is varied in some way toconvey intelligence. Compare MODULATED AM-PLIFIER. Also see MODULATION.RF in+6 VAF inmodulated amplifier+6 VOutmodulated-ring pattern See GEAR-WHEEL PAT-TERN and SPOT-WHEEL PATTERN.modulated stage A transmitter, amplifier, or oscillatorin which the signal information is impressedon the carrier.modulated wave See MODULATED CARRIER.modulatee A stage or circuit upon which modulationis impressed (e.g., a MODULATED AMPLI-FIER or a MODULATED OSCILLATOR).modulating electrode 1. In an oscilloscope, anelectrode (usually the intensity electrode) to whicha signal can be applied to intensity-modulatethe electron beam. 2. In a cathode-ray tube, theelectrode to which the video signal is applied.modulating signal Intelligence that modulates acarrier (e.g., binary data in radioteletype, or musicin broadcasting).modulation Combining two signals with the resultthat some aspect of one signal (the carrier) is variedby and in sympathy with the other (the modulatingsignal). Usually, the carrier has afrequency considerably higher than that of themodulating signal.modulation bars A form of television interferencein which an amplitude-modulated signal causeshorizontal bars, alternating light and dark, to appearon the picture screen. The higher the modulatingfrequency, the closer together the barsappear. In severe cases, the bars completely obliteratethe picture.modulation capability The maximum percentageof modulation a transmitter will permit before

modulation capability • modulator-demodulator 453modulation barsnonlinearity occurs. Also see MODULATION LIN-EARITY.modulation characteristic For an amplitudemodulatedwave, the ratio of the instantaneousamplitude of the modulated signal to the instantaneousmodulating voltage.modulation code In a modulated transmitter, asystem of modulation in which certain signalvariations or pulses represent particular characters.Examples are ASCII, BAUDOT CODE, andMORSE CODE.modulation coefficient Symbol, m. A figure expressingthe depth (extent) to which a signal isamplitude-modulated. For a signal in which theupward modulation is equal to the downwardmodulation, m = (E m – E c )/E c , where E c is thepeak-to-peak voltage of the unmodulated signal,and E m is the peak-to-peak voltage of the modulatedsignal. For full (100%) modulation, m = 1.modulation depth See DEPTH OF MODULATION.modulation distortion 1. In a modulated signal,envelope distortion introduced by the modulationprocess or by the receiver circuit. 2. Externalcross modulation (see CROSS MODULATION, 1).modulation envelope See ENVELOPE, 1.modulation-envelope distortion Undesirable distortionin the ENVELOPE of the modulating intelligencein an amplitude-modulated or single-sidebandsignal at the output of a radio transmitter.modulation factor See MODULATION COEFFI-CIENT.modulation frequency Abbreviation, f m . The frequencyof a modulating signal.modulation linearity In a modulated signal, thedegree to which the instantaneous signal amplitudeor frequency follows the instantaneous amplitudeof the modulating signal.modulation meter See PERCENTAGE-MODULA-TION METER.modulation monitor 1. A linear detector with apickup coil (or antenna) and headphones for listeningto an amplitude-modulated signal. 2. SeePERCENTAGE-MODULATION METER. 3. A devicethat displays the modulation characteristicsof a signal (e.g., the envelope for amplitude modulationand single sideband or the frequency-vs.time function for frequency modulation).modulation noise See NOISE BEHIND THE SIG-NAL.modulation percentage A measure of the extentto which a signal is amplitude modulated. It is expressedas the MODULATION COEFFICIENTmultiplied by 100.modulation ratio For a modulated signal, the quotientM r /M i , where M r is the percentage of radiated-signalmodulation, and M i is the percentageof current modulation.modulator A device or circuit for modulating a carrier.modulator cell See KERR CELL.modulator crystal A transparent piezoelectric crystalto which a signal voltage can be applied to modulatea beam of polarized light passing through it.modulator-demodulator Also called modem. 1. Adevice that converts binary data to audiofrequency-shift-keyed(AFSK) analog signals, andvice-versa. It is commonly used to interface computersand terminals with telephone lines and radiotransceivers. 2. A circuit or device, such as aData inAmplifierA/DconverterComputermodulator-demodulatorData outAmplifierD/Aconverter

454 modulator-demodulator • molecular conductancebiased diode or diode bridge, that can perform eithermodulation or demodulation.modulator driver An amplifier stage that deliversexcitation current, voltage, or power to a modulatorstage.module An assembly containing a complete selfcontainedcircuit (or subcircuit), often miniaturizedand made for plug-in operation.modulometer Any instrument, such as a percentage-modulationmeter, used to measure the degreeof modulation of a signal. Often, it can alsomeasure other signal characteristics (e.g., carriershift, extraneous amplitude modulation, and extraneousfrequency modulation).modulo n check In computer operations, a techniquefor verifying the validity of a number usedas an operand. The number being so checked isdivided by another number to provide a remainder(check digit) that goes with the number. Afterthe number is, for example, transmitted throughsome part of a computer system, it is again dividedby the original divisor, and if the remainderis the check digit, the data has retained its integrity.modulus 1. Absolute magnitude. Also see ABSO-LUTE VALUE and IMPEDANCE. 2. Abbreviation,mod. In computer operations, a whole numberthat indicates the number of states a counter sequencesthrough in each cycle. 3. Abbreviation,mod. A number (constant or coefficient) expressingthe degree to which some property is possessedby a material or body (e.g., modulus ofelasticity, shear modulus, and bulk modulus). 4. Aconstant by which a logarithm to one base mustbe multiplied to obtain a logarithm of the samenumber to another base.modulus of elasticity The stress-to-strain ratio ina material under elastic deformation.moire In a television or facsimile picture, an effectproduced by the convergence of straight lines.When the lines are nearly parallel to the scanninglines, the converging lines appear irregular.moisture meter See ELECTRIC HYGROMETERand ELECTRONIC HYGROMETER.mol Abbreviation of MOLE.molar conductance See MOLECULAR CONDUC-TANCE.molar polarization Any molecule in an electricfield undergoes a small displacement of the positiveand negative electrical centers. This resultsin an electric dipole.molar solution A solution, such as an electrolyte,containing 1 mol of solute per liter of solvent.Compare NORMAL SOLUTION.mold 1. To form matter into a desired shape, as bypouring liquefied material into a container or liquefyingthe material in the container, then allowingthe liquid material to solidify. In hot molding,the material is melted in the container and thencooled to hardness; in cold molding, the materialis shaped without heat and it solidifies with time.2. The hollow container used to shape a material,as in 1.molded capacitor A capacitor that is molded intoa protective body of insulating material. Also seeMOLD, 1, 2 and MOLDED COMPONENT.molded ceramic capacitor A ceramic-dielectriccapacitor enclosed in a molded housing. Alsosee MOLD, 1, 2; MOLDED CAPACITOR; andMOLDED COMPONENT.molded coil See MOLDED INDUCTOR.molded component A part (such as a capacitor,coil, or resistor) that is completely enclosed in aprotective material (such as a plastic) that ismolded around it. Also see MOLD, 1, 2.molded electrolytic capacitor A solid-dielectricelectrolytic capacitor enclosed in a molded housing.Also see MOLD, 1, 2; MOLDED CAPACI-TOR; MOLDED COMPONENT; and SOLID-ELECTROLYTIC CAPACITOR.molded glass capacitor A glassplate-dielectric capacitorenclosed in a molded glass housing. Alsosee GLASS CAPACITOR; MOLD, 1, 2; MOLDEDCAPACITOR; and MOLDED COMPONENT.molded inductor An inductor that is molded into aprotective housing of insulating material. Also seeMOLD, 1, 2 and MOLDED COMPONENT.molded mica capacitor A mica-dielectric capacitorenclosed in a molded housing. Also see MICACAPACITOR; MOLD, 1, 2; MOLDED CAPACITOR;and MOLDED COMPONENT.molded mud A molding compound that has inferiorelectrical characteristics. Also see MOLD, 1,2 and MOLDED COMPONENT.molded paper capacitor A paper-dielectric capacitorenclosed in a molded housing. Also seeMOLD, 1, 2; MOLDED CAPACITOR; MOLDEDCOMPONENT; and PAPER CAPACITOR.molded porcelain capacitor A capacitor enclosedin a body of molded porcelain. Also see MOLD, 1,2; MOLDED CAPACITOR; MOLDED COMPO-NENT; and PORCELAIN.molded resistor A resistor that is molded in a protectivehousing of insulating material. Also seeMOLD, 1, 2 and MOLDED COMPONENT.molded transistor A transistor that is encapsulatedin a protective molding compound, such asepoxy resin. Also see MOLD, 1, 2 and MOLDEDCOMPONENT.mole Abbreviation, mol. 1. The amount of substancein a system containing as many specifiedentities (atoms, molecules, ions, subatomic particles,or groups of such particles) as there areatoms in 12 grams of carbon 12. 2. It is alsocalled the Avogadro constant. A unit of quantityin chemistry, equal to approximately 6.022 ×10 23 .molectronics See MOLECULAR ELECTRONICS.molecular circuit See MONOLITHIC INTE-GRATED CIRCUIT.molecular conductance For a solution, such asan electrolyte, the product of specific conductivity

molecular conductance • monitor system 455and the volume (in liters) of a solution that contains1 gram molecule of the solute. Also seeSOLUTE; SOLUTION, 1; and SOLVENT, 1, 2.molecular conductivity See MOLECULAR CON-DUCTANCE.molecular electronics The technique of processinga single block of material so that separate areasperform the functions of different electroniccomponents. The entire block constitutes a circuit(e.g., a MONOLITHIC INTEGRATED CIR-CUIT).molecular magnets According to the moleculartheory of magnetism, the elemental magnetsformed by individual molecules.molecular theory of magnetism Each molecule ina piece of magnetic metal is itself a magnet (possessinga north and a south pole). These tinymagnets are thought to be normally oriented atrandom, but when the material is magnetized byan external force, they align themselves with eachother.molecular weight Abbreviation, mol wt. In amolecule of a substance, the sum of the atomicweights of the constituent atoms.molecule The basic particle of a compound; eachmolecule usually contains two or more atoms.For example, the formula AgNO 3 represents silvernitrate, each molecule of which contains oneatom of silver (Ag), one atom of nitrogen (N), andthree atoms of oxygen (O).moletronics See MOLECULAR ELECTRONICS.mol wt Abbreviation of MOLECULAR WEIGHT.molybdenum Symbol, Mo. A metallic element.Atomic number, 42. Atomic weight, 95.94. It isused in the grids and plates of certain vacuumtubes.momentThe tendency to produce motion arounda point, as by torque, or the product of a quantityand the distance to a point. The moment of forceis expressed as the product Fd, where F is forceand d is distance.momentary-contact switch A switch that maintainscontact only while it is held down. Such adevice is usually a pushbutton switch, although itmight be a toggle switch, a slide switch, or a leverswitch.momentary switching Switching of short duration,often characterized by a quick make andbreak immediately following activation of theswitch. Compare DWELL SWITCHING.moment of inertia For a torque motor, the inertiaof the armature around the axis of rotation. Alsosee MOMENT.mon 1. Abbreviation of MONITOR. 2. Abbreviationof MONAURAL.monatomic 1. Pertaining to a molecule with onlyone atom. 2. Pertaining to a molecule with onlyone replaceable atom or radical.monatomic molecule A molecule having a singleatom (e.g., argon, helium, and neon). CompareDIATOMIC MOLECULE.monaural 1. Pertaining to an audio system havingone channel. 2. Pertaining to hearing with oneear, as opposed to BINAURAL.monaural recorder A single-track recorder, as opposedto a stereophonic recorder.Monel metal An alloy of nickel (67%), copper(28%), iron, manganese, and other metals (5%).Its resistivity is approximately 42 microhmcentimetersat 20°C.monimatch An amateur version of the reflectedpowermeter and SWR meter.RFinputVmonimatchRFoutputmoniscope A special cathode-ray tube that producesa stationary picture for testing televisionequipment. Its name is a contraction of monitorand scope.monitor 1. A device that allows the sampling of asignal or quantity. Examples: line-voltage monitor,television monitor, and modulation monitor. 2. Acathode-ray-tube (CRT) computer display.monitor head A separate playback head includedin some tape recorders for listening to the tape asit is being recorded.monitoring The act, process, or technique of observingan action while it is in progress or checkinga quantity while it is varying. Examples:carrier monitoring, modulation monitoring, andline-voltage monitoring.monitoring amplifier An auxiliary amplifier usedin monitoring an audio-frequency system.monitoring antenna A usually small pickup antennaused with a signal monitor or monitoringreceiver.monitoring key In a telephone system, a deviceused to listen to a two-way conversation.monitoring receiver A radio or television receiverused specifically to monitor a transmission directly.monitoring station In a security system, a centralcontrol location from which personnel can observethe input from sensors, cameras, and otherdevices at remote locations throughout the securedarea.monitor system A computer program usuallystored in the read-only memory (ROM) suppliedby the hardware vendor. It controls the implementationof programs written by the user, andthe operation of peripherals associated with

456 monitor system • monovalentprogram runs and inputting or outputting data toor from memory. Also called executive program.monkey chatter The characteristic sound of a single-sideband(SSB) signal when the receiver ismistuned, or when the receiver is set for thewrong sideband.monk’s cloth A coarse drapery fabric sometimesused to soundproof the walls and ceiling of a radiostudio or recording booth.mono See MONAURAL.mono- Prefix meaning single.monobrid circuit An integrated circuit in whicheither several monolithic IC chips are interconnectedto form a larger, single-package circuit, ormonolithic IC chips are interwired with thin-filmcomponents into a single-package circuit. Thename is a contraction of monolithic hybrid.monochromatic 1. Being of one color (hue) in nature.2. Being of a single wavelength in nature(pertaining to radiation of any kind). 3. Pertainingto black-and-white television.monochromaticity Consisting of one color of visiblelight. The brightness can vary from black tomaximum.monochromatic power density At a given temperature,the energy radiated per square centimeterof blackbody surface per second per unitwavelength range. Also see BLACKBODY andBLACKBODY RADIATION.monochromatic sensitivity Sensitivity to light ofone color only.monochrome television Black-and-white television.monoclinic crystal A crystal having three axes ofunequal length; two of them intersect obliquelyand are perpendicular to the third [e.g., the typeof crystal found in one form of sulfur (monoclinicsulfur)].monocrystalline material See SINGLE-CRYSTALMATERIAL.monode A one-element device, such as a filamenttypelamp, thermistor, voltage-dependent resistor,barretter, etc.monogroove stereo A method of making a stereophonicphonograph disc in which both channelsare recorded as a single groove.monolayer A thin film having a thickness of onemolecule.monolithic integrated circuit An integrated circuit(IC) formed in a single block or wafer of semiconductormaterial. The name is derived from theGreek monolithos (“one stone”). Compare HY-BRID INTEGRATED CIRCUIT and THIN-FILM IN-TEGRATED CIRCUIT.monometallic Containing or using only one metal.monomolecular film See MONOLAYER.monophonic recorder See SINGLETRACK RE-CORDER.monophonic system A single-channel sound system.Compare STEREO SYSTEM.monopole antenna See QUARTER-WAVE MONO-POLE.monopulse In radar and electronic-navigation operations,using one pulse to determine azimuthand elevation simultaneously.monorange speaker A loudspeaker that reproducesmost of the full audio range. Also called extendedrange speaker. Compare TWEETER andWOOFER.monostable Having one stable state.monostable blocking oscillator Abbreviation,MBO. A blocking oscillator that behaves somewhatlike a one-shot multivibrator. The oscillatordelivers a single output pulse each time it receivesan input (trigger) pulse.monostable multivibrator A multivibrator thatdelivers one output pulse for each input (trigger)pulse. Also called one-shot circuit and single-shotmultivibrator. Compare ASTABLE MULTIVIBRA-TOR and BISTABLE MULTIVIBRATOR.Input+5 V−5 Vmonostable multivibratorOutputmonostatic reflectivity The property whereby, forcertain reflectors (such as a tricorner reflector),all incident rays are reflected in exactly the oppositedirection from which they arrive.monotone A sound or series of sounds having asingle, constant pitch (frequency).monotonicity In a digital-to-analog converter, acondition where the output either remains thesame or increases for any single increase in theinput code.monovalent See UNIVALENT.

Monte Carlo method • motorboating filter 457Monte Carlo method 1. The use of statistical samplingin the approximate solution of an engineeringproblem. 2. In computer operations, theconstruction of mathematical models from randomlyselected components taken from representativestatistical populations.Moog synthesizer An electronic device that can bemade to simulate virtually any sound, includingthat of musical instruments and the humanvoice, through the use of several audio oscillators,whose output can be controlled to producetones of various harmonic content, duration, attack,and decay periods.moonbounce Also called earth-moon-earth (EME).Radio communication, usually at very-high frequencies(VHF) or ultra-high frequencies (UHF),in which the moon is used as a passive reflector.This is a popular mode among some amateur radiooperators.Earthmoon bounceMoonMOPA Abbreviation of MASTER OSCILLATOR/POWER AMPLIFIER.morphological electronics See MOLECULARELECTRONICS.Morse 1. See MORSE CODE. 2. Telegraphy (wire orradio). 3. To signal by means of the Morse code.Morse code Either of two similar binary codesused in radio and wire telegraphy. It uses shortpulses (dots or dits) and long pulses (dashes ordahs) to represent letters of the alphabet, numerals,and punctuation marks. It usually refers tothe CONTINENTAL CODE, but occasionally itrefers to the AMERICAN MORSE CODE.MOS Abbreviation of metal-oxide-semiconductor.mosaic 1. See PHOTOMOSAIC. 2. The pattern oftiny photoelectric particles in a television cameratube that convert the image into electriccharges.mosaic crystal A form of imperfect crystal. The defectshave certain properties, one of which is tocause additional energy levels in semiconductormaterials manufactured from such crystals.MOS capacitor A capacitor using metal-oxidesemiconductor(MOS) technology. It is used inMOS integrated circuits. A silicon substrateforms one electrode (generally p-type material).An oxide layer forms the dielectric. An electrodeforms the other plate of the capacitor. The capac-itance might be variable by changing the appliedvoltage at the metal gate electrode.MOSFET Abbreviation of METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR.MOSROM Abbreviation of metal-oxide-semiconductorread-only memory (see READ-ONLY MEM-ORY).MOST Abbreviation of metal-oxide-semiconductortransistor.most significant character Abbreviation, MSC. Inpositional number representation, the leftmostcharacter in a significant group, such as a word.most significant digit Abbreviation, MSD. In anumber, the leftmost digit that is not zero (zerobeing insignificant in this context).mother 1. A term or prefix referring to a componentthat supports (or appears to support) othersimilar components (e.g., MOTHERBOARD). 2. Aterm referring to the source from which samplesor components are derived (e.g., MOTHER CRYS-TAL). 3. A mold that has been electroformed froma master phonograph disc.motherboard In a computer or data-processingdevice, the circuit board on which most of themain circuitry is mounted.mother crystal A natural quartz crystal fromwhich is produced the piezoelectric plates andother components used in electronics.motion detector A device for sensing the movementor stopping of a body, such as a rotatingshaft. Various sensors are used in different detectors:magnetic, photoelectric, capacitive, etc.motion frequency The natural frequency (especiallythat of oscillation) of a servo.Motion Picture Experts Group Abbreviation,MPEG. A data-compression standard used foranimated digital video. It is useful in computervideoconferencing and telecommuting, and forthe development of multimedia presentations.motion-picture pickup In television operations, acamera (and the technique for using it) for pickingup scenes directly from motion-picture film.motion sensor In security systems, a set of devicesthat produces an output signal wheneveranything moves within a certain area. Suchequipment might use infrared, ultrasound,microwaves, capacitive effects, thermal sensors,air-current detectors, sound detectors, videocameras, or a combination of these.motor 1. A machine for converting electrical energyinto mechanical energy. 2. The drivingmechanism of a loudspeaker.motorboard The basic mechanism of a taperecorder, embodying motor, flywheel, capstan,rollers, etc., assembled on a board or panel.motorboating A repetitive, low-frequency poppingor puffing noise sometimes observed in malfunctioningaudio circuits. It was so named becauseof its resemblance to the sound of a motorboat.motorboating filter In an audio amplifiercircuit, a simple filter installed to prevent

458 motorboating filter • M scanMOTORBOATING caused by unwanted positivefeedback. Also see DECOUPLING FILTER.motor capacitor See MOTOR-RUN CAPACITORand MOTOR-START CAPACITOR.motor constant The ability, expressed numerically,of a torque motor to convert electric inputpower into torque.motor converter An electromechanical device forconverting alternating current to direct current.motor-driven relay An electromechanical relaywhose contacts are opened and closed by a rotatingmotor.motor effect Magnetic force between adjacent current-carryingconductors.motor-generator A combination of motor and generatorin a single machine assembly. A commonarrangement is a low-voltage motor turning ahigh-voltage generator. The machine shafts canbe coupled, or the motor can turn the generatorthrough a belt, chain, or gear train.motor meter A meter in which the movable elementis essentially a continuously rotating motor.See, for example, KILOWATT-HOUR METER.motor-run capacitor A power-factor-boosting capacitorconnected (together with its auxiliarywinding) in parallel with the main winding in aninduction motor. Also see CAPACITOR MOTOR.motor-speed control A method of controlling thespeed of a motor by varying the magnitudeand/or phase of its current. Electronic devicesusually use diode, diac, or triac circuits.motor-start capacitor A capacitor that, with anauxiliary winding, is switched into a motor circuitduring the starting period, and is automaticallydisconnected (with the winding) after the motorreaches normal running speed. Also see CAPACI-TOR MOTOR.motor starter See STARTING BOX.mould See MOLD.mount 1. A mechanical device with which a componentis attached to a circuit board or chassis.2. The attachment of a circuit board to achassis. 3. The hardware with which an antennais attached to a mast. 4. The hardwarewith which a microphone is attached to a boomor other support. 5. In general, any attachinghardware.Mountain standard time Abbreviation, MST. Localmean time at the 105th meridian west ofGreenwich. Also see GREENWICH MEAN TIME,STANDARD TIME, TIME ZONE, and COORDI-NATED UNIVERSAL TIME.mounting flange The portion of a speaker frame,usually made of metal, that is equipped withholes for attachment to a cabinet or panel.mouse A pointing device commonly used with personalcomputers. It is about the size of a candybar. The computer operator moves the displaypointer or cursor by sliding the mouse on a flatsurface. Functions and commands are executedby pressing a button (clicking) on the device.mouth The radiating end of a horn (antenna, loudspeaker,etc.).MOV Abbreviation of METAL-OXIDE VARISTOR.movable-coil meter See D’ARSONVAL METER.movable-coil modulator See ELECTROMECHANI-CAL MODULATOR.movable contact The traveling contact in a relayor switch. Compare FIXED CONTACT.movable-iron meter See IRON-VANE METER.movies on demand In television, a system thatmakes it possible for subscribers to choose theprograms they want to see, and also to choose theviewing times for the programs.moving-coil galvanometer A galvanometer whosemovable element is a coil of fine wire suspendedor pivoted between the poles of a magnet.moving-coil microphone See DYNAMIC MICRO-PHONE.moving-coil motor The driving mechanism of amoving-coil DYNAMIC SPEAKER.moving-coil pickup See DYNAMIC PICKUP.moving-coil speaker See DYNAMIC SPEAKER.moving-conductor microphone See VELOCITYMICROPHONE.moving-diaphragm meter A headphone used as asensitive indicator in alternating-current bridgemeasurements.moving element In an electromechanical device,the portion that moves physically under variableoperating conditions.moving-film camera An oscilloscope camera inwhich the film is drawn past the lens continuouslyat a constant speed, rather than being advancedframe by frame, as in a motion-picturecamera.moving-iron meter See IRON-VANE METER.moving-vane meter See IRON-VANE METER.mp Abbreviation of MELTING POINT.m p Symbol for MASS OF PROTON AT REST.MPEG Abbreviation for MOTION PICTURE EX-PERTS GROUP.MPG Abbreviation of microwave pulse generator.mph Abbreviation of miles per hour. Also, mi/h.MPO Abbreviation of maximum power output.mps 1. Abbreviation of meters per second. Also,m/s. 2. Abbreviation of miles per second. Also,mi/s.MPT Abbreviation of MAXIMUM POWER TRANS-FER.MPX Abbreviation of MULTIPLEX.MR Abbreviation of MEMORY REGISTER.mrad Abbreviation of MILLIRADIAN.MRIA Abbreviation of Magnetic Recording IndustryAssociation.mrm Abbreviation of milliroentgens per minute.MS Abbreviation of MASS SPECTROMETER.m 2 /s Abbreviation of meters squared per second.The unit of kinematic viscosity.M scan In radar operations, a modified A-scan displayin which a pedestal signal is moved along thebase line to a point where it coincides with the

M scan • multiband receiver 459base line of the reflected signal to determine thedistance to the target.msec Abbreviation of MILLISECOND. Also, ms.msg Abbreviation of MESSAGE.MSI Abbreviation of MEDIUM SCALE INTEGRA-TION.MST Abbreviation of MOUNTAIN STANDARDTIME.MT Abbreviation of METRIC TON.MTR Abbreviation of MAGNETIC TAPE RE-CORDER.mtr Alternate abbreviation of METER.MTS Abbreviation for MULTICHANNEL TELEVI-SION SOUND.M-type backward-wave oscillator A broadband,voltage-tuned oscillator in which the electrons interactwith a backward traveling radio-frequencywave. Compare O-TYPE BACKWARD-WAVE OS-CILLATOR.mu Symbol, µ. 1. Abbreviation of the prefix MI-CRO-. 2. Expression for AMPLIFICATIONFACTOR. 3. Expression for PERMEABILITY.4. Expression for MICRON. 5. Expression for ELEC-TRIC MOMENT. 6. Expression for INDUCTIVITY.7. Expression for MAGNETIC MOMENT. 8. Expressionfor MOLECULAR CONDUCTIVITY.µ 1. Symbol for MU.µA Abbreviation of MICROAMPERE.µ B Symbol for BOHR MAGNETON.µb Abbreviation of MICROBAR.µCi Abbreviation of MICROCURIE.µ e Symbol for ELECTRON MAGNETIC MOMENT.µF Abbreviation of MICROFARAD.µg Abbreviation of MICROGRAM.µH Abbreviation of MICROHENRY.µin Abbreviation of MICROINCH.µl Abbreviation of MICROLITER.µmm Abbreviation of micromillimeter (see NANO-METER).µ n Symbol for NUCLEAR MAGNETON.µ o Symbol for FREE-SPACE PERMEABILITY CON-STANT.µ p Symbol for PROTON MAGNETIC MOMENT.µP Abbreviation of MICROPROCESSOR.µrd Abbreviation of MICRORUTHERFORD.µS Abbreviation of MICROSIEMENS.µs Abbreviation of MICROSECOND. (Also, µsec.)µV Abbreviation of MICROVOLT.µV/m Abbreviation of MICROVOLTS PER METER.µW Abbreviation of MICROWATT.MUF Abbreviation of MAXIMUM USABLE FRE-QUENCY.mu factor See MU, 2.mu law In communications, a companding standardgenerally used in the United States andCanada.Muller tube A tube that conducts by means of ionizationof an internal gas. It is used for radiationdetection.multiaddress In a computer, a multiple memorylocation.multiband amplifier A radio-frequency power amplifiercapable of operation on more than one frequencyband. The bands are often (but notalways) harmonically related. Compare WIDE-BAND AMPLIFIER.multiband antenna A single antenna, such as oneused in amateur radio and television reception,operated in several frequency bands or channels.The bands are often (but not always) harmonicallyrelated.Balancedfeed lineRadiating elementsBalunRadioRadiating elementTransmatchmultiband antennaCoaxialfeed lineCoaxiallineRadiomultiband device A device (such as a tuner, receiver,transmitter, or test instrument) that operatesin several selectable frequency bands.multiband oscilloscope See WIDEBAND OSCIL-LOSCOPE.multiband receiver A communications receivercapable of operation on more than one frequencyband. Such a receiver might, but does not necessarily,provide continuous coverage over a wide

460 multiband receiver • multipath transmissionrange of frequencies. Compare WIDEBAND RE-CEIVER.multicasting The use of two frequency-modulation(FM) broadcast stations, or one FM station andone television station, to broadcast separately thetwo channels of a stereo program. The program ispicked up simultaneously with two receivers.multicavity magnetron A magnetron whose anodeblock has two or more cavities.multicellular horn A loudspeaker in front of whichare placed rectangular cells through which thesound passes.multichannel Pertaining to a radio-communicationsystem that operates on more than onechannel at the same time. The individual channelsmight contain identical information, or theymight contain different signals.multichannel analyzer A test instrument, such asa spectrum analyzer, that splits an input intoseveral channels for testing.multichannel television sound Abbreviation,MTS. In television broadcasting, audio transmittedon more than one channel to provide stereosound to subscribers.multichip circuit A MICROCIRCUIT composed ofinterconnected active and passive chip-type components.multichip integrated circuit An INTEGRATEDCIRCUIT composed of circuit elements on separate,interconnected chips.multicontact switch A switch having more thantwo contacting positions.multicoupler An impedance-matching device usedto couple several receivers to a single antenna.multielement antenna A directive antenna havingmore than one element. Such antennas includephased arrays and parasitic arrays. Common examplesare the LOG-PERIODIC ANTENNA, theQUAD ANTENNA, and the YAGI ANTENNA.multiemitter transistor 1. A bipolar transistorhaving more than one emitter. 2. A bipolar powertransistor having several emitters connected inparallel in the transistor structure.multiframe A set of frames in a signal that are adjacentto each other in time (consecutive) and positionedaccording to an alignment signal.multigun CRT A cathode-ray tube (CRT) havingmore than one electron gun.multihop propagation Propagation of a radio waveby several successive reflections between theionosphere and the surface of the earth.multilayer circuit A circuit consisting of severalsections printed or deposited on separate layers,which are subsequently stacked in a sandwichlikemanner.multilayer coil A coil in which the turns of wireare wound in several complete layers, one on topof the other. Compare SINGLE-LAYER COIL.multilevel password protection See HIERARCHI-CAL PASSWORD PROTECTION.multimedia 1. In computing, the use of video,voice, music, electromechanical control, and/ordata transfer at the same time. Useful in education,entertainment, business, and gaming applications.2. The use of voice, images, data, and/orvideo in a communications system or network,and, in particular, in wireless applications. An exampleis videoconferencing between a corporateoffice and the user of a handheld computerequipped with a wireless modem.multimedia computer A personal computer designedespecially for multimedia use. It includesa sound board, speakers, a microphone, and aCD-ROM (compact-disk read-only memory) drive.It often has a large-screen, high-resolution monitor(17 inches or greater diagonal measure).multimeter A meter that allows measurement ofdifferent quantities (e.g., current, voltage, and resistance);the functions are usually made availablethrough a selector switch.multimode operation 1. In radio communication,the use of two or more transmitters simultaneously,operating in different modes [e.g., one usingsingle-sideband (SSB) and another usingfrequency modulation (FM)]. 2. The transmissionof visible light or infrared energy through an opticalfiber in more than one mode at the same time.3. The operation of any device in more than one ofits modes simultaneously.multipactor A microwave switching tube capableof operating at high power levels. Characterizedby high operating speed.multipath cancellation A phenomenon sometimesobserved in radio-wave propagation. Separate signalcomponents arrive at the receiver in equal amplitude,but opposite phase. Also see MULTIPATHFADING and MULTIPATH RECEPTION.multipath delay In MULTIPATH RECEPTION, thelag between signal components arriving over differentpaths.multipath effect At a receiver, the difference in arrivaltime of multipath signals. Also see MULTI-PATH DELAY.multipath fading In radio communication, variationsin the received signal that result from phasingvarious components of the transmitted signalthat are propagated over different paths. At low,medium, and high frequencies, this effect is usuallythe result of ionospheric fluctuation. At veryhighand ultra-high frequencies, it could occur asa result of changes in the state of the interveningatmosphere or, occasionally, reflection from objects,such as aircraft.multipath reception Reception of a signal overmore than one path. This often results in fading(see MULTIPATH FADING) and other undesirableeffects, such as ghosting in television reception.multipath transmission 1. Transmission of a signalover two or more paths. Also see MULTIPATHRECEPTION. 2. See MULTIHOP PROPAGATION.

multiphase system • multiplex stereo 461TransmitterIonized layermultipath receptionReceivermultiphase system See POLYPHASE SYSTEM.multiple access system A timesharing data processingsystem that can be used by a number ofpeople at remote locations, usually through peripheralsother than conventional terminals (e.g.,cash registers linked to a computer system for inventorycontrol).multiple-address code In computer operations, aninstruction code that requires the user to specifythe address of more than one operand per instruction.multiple address instruction A computer programinstruction specifying the address of morethan one operand.multiple break 1. Interruption of a circuit at severalpoints. 2. Contact bounce.multiple-chip circuit See HYBRID INTEGRATEDCIRCUIT.multiple connector In a flowchart, a symbolshowing the merging of several flowlines.multiple ionization Successive ionization, aswhen an ion repeatedly collides with electrons.Also see DOUBLE IONIZATION.multiple-length number In computer operations,a number occupying more than one register.multiple-loop feedback system A feedback systemusing more than one feedback loop. Anexample is a tunable audio amplifier (seePARALLEL-TEE AMPLIFIER) in which a negativefeedbackpath provides tuning, while a positivefeedbackpath sharpens selectivity.multiple modulation See COMPOUND MODULA-TION.multiple precision arithmetic An arithmetic processusing several words (bit groups) for anoperand to ensure accuracy.multiple programming 1. Computer operation inwhich several programs in memory share peripheralsand processor time. 2. Programming acomputer so that several logic or arithmeticoperations can be carried out at the same time.multiple-purpose meter See MULTIMETER.multiple-purpose tester A multimeter sometimescombined with some other instrument, such as atest oscillator.multiple reel file In a data-processing system, amagnetic tape data file of more than one reel.multiple speakers A group of more than two loudspeakers,usually operated from a single amplifiersystem.multiple-stacked broadside array A stacked arrayin which a number of collinear elements arestacked above and below each other. Also seeBROADSIDE ARRAY and COLLINEAR AN-TENNA.multiple station Descriptive of a communicationsnetwork in which more than one terminal is used.multiple-unit steerable antenna A shortwave antennasystem intended to prevent or minimize theeffects of fading in received signals. It consistsprincipally of a number of rhombic antennasfeeding the receiver. The system utilizes the variouswaves arriving at different angles. An electricsteering system causes the antennas to be selectedautomatically in the best combination andwith their outputs in the proper phase. Also seeDIVERSITY RECEPTION.multiple winding See DRUM WINDING.multiplex Pertaining to a communications orbroadcasting system in which multiplexing isused. See MULTIPLEXING, 1, 2, 3.multiplex adapter A special circuit (or auxiliaryunit) used in frequency-modulated radio receiversfor stereophonic reception from a stationtransmitting a multiplex broadcast. Also seeMULTIPLEXING, 1 and MULTIPLEX STEREO.multiplex code The transmission of multiple signalsover a single medium, using a code (such asMorse, Baudot, or ASCII). See MULTIPLEXING, 2,3.multiplex data terminal A computer terminal actingas a modem by virtue of its accepting andtransferring signals between its input/output devicesand a data channel.multiplexer A device that allows two or more signalsto be transmitted simultaneously on a singlecarrier wave, communications channel, or datachannel. See MULTIPLEXING, 2, 3.multiplexing 1. A process in which a comparativelylow-frequency carrier is modulated, thenmixed with a signal that has a higher frequency.Also see SUBCARRIER and SUBSIDIARY COM-MUNICATION AUTHORIZATION. 2. The simultaneoustransmission of numerous relativelylow-frequency signals on a single carrier having ahigher frequency. Also called frequency-divisionmultiplexing. 3. The transmission of numeroussignals on a single channel by breaking each signalinto timed fragments (intervals) and transmittingthe fragments in a rotating sequence. Alsocalled time-division multiplexing. 4. In certain digitallight-emitting-diode (LED) displays, the lightingof various parts of the display in a rapidlyrotating sequence.multiplex stereo The use of multiplexing to broadcastboth channels of a stereophonic program ona single carrier wave. See MULTIPLEXING, 1, 2.

462 multiplex telegraphy • multiprogrammingSubcarrieroscillatorMixerRFamplifierfTuned tomfOutModulatorReactancemodulatedoscillatorPoweramplifierIn+12 VAF amp.AF amp.Outputmultiplier amplifierSubsidiaryinputMaininputmultiplexing, 1.multiplex telegraphy 1. A system of wire telegraphyin which two or more messages are sent simultaneouslyin one or both directions. 2. Asystem of radiotelegraphy in which two or moremessages can be sent simultaneously on thesame carrier wave.multiplex telephony 1. A system of wire telephonyin which two or more messages can besent simultaneously in one or both directionsover the same line. 2. A system of radiotelephonyin which two or more messages can be sent simultaneouslyon the same carrier wave.multiplication 1. The arithmetic process wherebya certain factor is added to itself the number oftimes indicated by another factor (the multiplier).2. A method of increasing a quantity, magnitude,or rate by some desired factor. See, for example,FREQUENCY MULTIPLIER and VOLTAGE MUL-TIPLIER.multiplier 1. See FREQUENCY MULTIPLIER.2. See VOLTAGE MULTIPLIER. 3. A circuit ordevice for performing arithmetic multiplication.4. See VOLTMETER MULTIPLIER.multiplier amplifier A frequency-multiplying amplifier(such as a doubler, tripler, or quadrupler),whose output circuit is tuned to an integral multipleof the input frequency. Compare STRAIGHT-THROUGH AMPLIFIER.multiplier phototube See PHOTOMULTIPLIERTUBE.multiplier prefix A prefix that, when affixed to thename of a quantity (e.g., Hertz and byte) indicatesthe amount, usually a power of 10 or a power of2, by which that quantity is to be multiplied. Alsocalled prefix and prefix multiplier. See PREFIXEStable in Appendix B. Also see, for example,GIGA-, KILO-, MEGA-, MICRO-, MILLI-, NANO-,and PICO-.multiplier probe 1. A resistor-type test probe for avoltmeter, which increases the range of the meterand, therefore, acts as a voltmeter multiplier. 2. Avoltage-multiplier type of test probe for a voltmeter,which multiplies the test voltage before it is appliedto the instrument (e.g., voltage-doubler probe).multiplier register In a computer, a register thatretains a number during a multiplication operation.multiplier resistor A resistor connected in serieswith a current meter (usually a milliammeter ormicroammeter) to make it a voltmeter. Also calledVOLTMETER MULTIPLER.multiplier tube See PHOTOMULTIPLIER TUBE.multipoint circuit A transmission circuit or system,in which information can be entered or retrievedat two or more locations.multipoint distribution service In radio broadcasting,the transmission of programs via microwavelinks from a central facility to variouslocal stations.multipolar Pertaining to the presence of more thantwo magnetic poles.multipolar machine A motor or generator havinga number of poles in its armature and field.multiposition relay A relay having more than twopositions of closure. See, for example, SELECTORRELAY.multiposition switch A switch having more thantwo contacting positions. See, for example, SE-LECTOR SWITCH and STEPPING SWITCH.multiprocessing 1. In a computer system, therunning of more than one program at once.2. The use of more than one microprocessorsimultaneously in a single computer. Also calledparallel processing. 3. See TIME SHARING.multiprogramming Also called multitasking. In acomputer system, a technique that allows two ormore programs to be executed at the same time.

multipurpose meter • Musical Instrument Digital Interface 463multipurpose meter An electric meter that performsseveral functions, usually availablethrough a function selector. Examples: VOLTAM-METER, VOLT-OHMMETER, and VOLT-OHM-MILLIAMMETER.multirange instrument An instrument providedwith several separate ranges, usually selectableby range switching (e.g., five-range voltmeter,two-scale ammeter, and four-band oscillator).multisection filter A filter having two or more selectivesections connected in cascade.multisegment magnetron See MULTICAVITYMAGNETRON.multiskip propagation See MULTIHOP PROPAGA-TION.multistage device A device having several stagesoperating in cascade or otherwise coordinatedwith each other (e.g., a five-stage amplifier).multistage feedback Feedback (positive or negative)between several stages in a system, as opposedto feedback between the output and inputof a single stage.multistage oscillation Oscillation resulting frompositive feedback between or among two or morestages of an amplifier chain, as opposed to oscillationoccurring between the output and input ofa single amplifier stage.multistage X-ray tube An X-ray tube providingelectron acceleration by means of successivering-shaped anodes—each biased to a highervoltage than the preceding one.multiswitch A switch having a number of polesand contacts.multitester An instrument, such as a multimeteror a combined signal generator and oscilloscope,that performs a number of different test functions.multitrack recording 1. A recording on two ormore tracks (e.g., multitrack disk and multitracktape). 2. Making a recording on a tape or discwith two or more tracks.multiturn loop antenna A small loop antenna(whose diameter measures less than approximately10 degrees of phase in free space) that hastwo or more turns of wire or tubing. The loop hassignificant inductance. A capacitor, connected inparallel or in series with the loop, can produce anarrowband frequency response.multiturn potentiometer A potentiometer whoseshaft must be rotated through several completerevolutions to cover the full resistance range.multivalent Having a valence greater than 2. CompareUNIVALENT.multivibrator A circuit usually containing two transistorsin a resistance-capacitance (RC) coupledamplifier, whose output is capacitance-coupled tothe input. The two stages switch each other alternatelyin and out of conduction at a frequency determinedby the R and C values. Also see ASTABLEMULTIVIBRATOR, BISTABLE MULTIVIBRATOR,and MONOSTA-BLE MULTIVIBRATOR.multiwire antenna An antenna having more thanone wire in the radiating section. In early flat-topantennas, such wires were usually connected togetherat one end.multiwire doublet antenna A doublet antennahaving more than one wire in its radiator. A commonform is the folded dipole, in effect two closelyspaced dipole radiators connected together atboth ends, one being center-fed.Mumetal A high-permeability alloy of iron andnickel, valued especially for use as a magneticshield for cathode-ray tubes.Munsell color system A system for specifying colorsin terms of hue, saturation, and brilliance,according to charts. Also see COLOR MATCHING.Muntz metal See YELLOW METAL.MUPO Abbreviation of MAXIMUM UNDISTORTEDPOWER OUTPUT.Murray-loop bridge A specialized form of Wheatstonebridge in which two of the resistance armsare supplied by a two-wire line (such as a telephoneline). By means of resistance measurementsmade with the bridge, the distance from anoffice or station to a ground fault on the line canbe determined.MUSA Abbreviation of multiple-unit steerable antenna.muscovite Formula, KH 2 Al 2 (SiO 4 ) 3 . A high-gradevariety of mica having low dielectric loss.Musical Instrument Digital Interface Acronym,MIDI. A computer language used in electronicmusic. It “tells” the computer when to play a note,how long to play it, and how loud to play it. It alsosets the tempo of the music, based on how long a

464 Musical Instrument Digital Interface • Mylarquarter-note lasts. It controls the operation of amusic synthesizer, and allows two or more synthesizersto communicate.musical quality See TIMBRE.musical scale A series of tones between a giventone and its second harmonic, scaled in intervalsof 1 ⁄8 octave. The most common example can befound on a piano. Variations exist (e.g., 13-notescale, six-note scale, and five-note scale).music chip An integrated circuit for producingvarious musical effects (such as tones, percussion,etc.).music power For a power amplifier, the short-termoutput power obtained in the reproduction of musicwaveforms, in contrast to root-mean-square(rms) or effective power output.music synthesizer A set of oscillators, usually operatedwith a computer, used to create or playingelectronic music. Also see MOOG SYNTHESIZERand MUSIC INSTRUMENT DIGITAL INTERFACE.music under Pertaining to low-volume, continuous,background music, often added to presentations,radio and television advertisements,educational programs, etc.muting1. Disabling a receiver or amplifier underno-signal or weak-signal conditions. 2. Softeningor muffling a sound.+AmplifierstageMutingtransistormutingmuting circuit 1. An interference-preventing devicethat automatically shuts off a radio receiverduring the operation of a transmitter, and viceversa. 2. A squelch circuit. 3. In a stereo receiver,an electronic element that cuts off all audio whenno signal is present or when the receiver is beingtuned between carriers.muting switch A switch or relay that cuts off a receiverduring periods of transmission, or when receptionis not desired. Generally, a cutoff voltageis applied to one of the intermediate-frequency+stages to accomplish muting. In some cases, theaudio-frequency circuit is disabled.mutual antenna coupling Electromagnetic couplingbetween or among antennas when they areplaced too close together. Usually, it is an undesirablephenomenon.mutual capacitance Inherent capacitance betweentwo conductors.mutual-capacitance attenuator An attenuatorthat, in its simplest form, is essentially ashielded, two-plate variable capacitor.mutual conductance See TRANSCONDUCTANCE.mutual impedance An impedance shared by twoor more branches of a circuit.mutual inductance Symbol, M. Unit, henry. Theproperty shared by neighboring inductors or inductivedevices that enables induction to occur. Amutual inductance of 1 henry is present when acurrent change of 1 ampere per second in one inductorinduces 1 volt across another inductor.Also see INDUCTANCE.mutual-inductance attenuator An attenuatorconsisting essentially of two coupled coils (inputand output), whose spacing can be graduallychanged.mutual-inductance bridge See CAREY-FOSTERMUTUAL-INDUCTANCE BRIDGE.mutual induction The action whereby the magneticfield produced by alternating current in oneconductor produces a voltage in another isolatedconductor.mutual interference 1. See ADJACENT-CHANNEL INTERFERENCE. 2. Any kind ofinterference between or among radio-frequencycommunications circuits.mutually exclusive events Two or more events (ordata points) so that the occurrence of one preventsthe occurrence of the other(s). That is, twoevents cannot take place simultaneously.MV 1. Abbreviation of MEGAVOLT. 2. Abbreviationof MULTIVIBRATOR.mV Abbreviation of MILLIVOLT.MV Abbreviation of MEDIUM VOLTAGE.MVA Abbreviation of MEGAVOLT-AMPERE.mV/m Abbreviation of millivolts per meter.mVP Abbreviation of MILLIVOLT POTENTIOME-TER.MW Symbol for MEGAWATT.mW Symbol for MILLIWATT.mw Abbreviation of MEDIUM WAVE.MWH Abbreviation of MEGAWATT-HOUR.mW RTL Abbreviation of milliwatt resistor-transistorlogic or low-power resistor-transistor logic.Mx Abbreviation of MAXWELL.Mycalex Trade name for an insulating materialconsisting of mica bonded with glass. Dielectricconstant, 6 to 8. Resistivity, 10 13 ohm-cm.Mylar A DuPont registered trademark. A tough,plastic insulating material commonly used as amagnetic tape base. Dielectric constant, 2.8 to3.7. Dielectric strength, 7000 V/mil.

Mylar capacitor • myriametric waves 465Mylar capacitor A capacitor in which the dielectricfilm is Mylar.Mylar tape Magnetic recording tape using a Mylarfilm as the substrate.mym Abbreviation of MYRIAMETER.myoelectricity 1. Bioelectric pulses of 10- to1000-mV amplitude produced by muscular activityand detectable by electrodes attached to theskin. Also see ELECTROMYOGRAM, ELEC-TROMYOGRAPH, and ELECTROMYOGRAPHY. 2.The study of phenomena, as defined in 1.myogram See ELECTROMYOGRAM.myograph See ELECTROMYOGRAPH.myography See ELECTROMYOGRAPHY.myriameter Abbreviation, mym. A metric unit oflinear measure equal to 10 kilometers (10 4 meters).myriametric waves British designation for electromagneticenergy having wavelengths from100 kilometers down to 10 kilometers, correspondingto frequencies from 3 kHz up to30 kHz.

N 1. Symbol for NUMBER. 2. Symbol for NITRO-GEN. 3. Abbreviation for NEWTON. 4. Abbreviationof NUMBER (also, No.). 5. Symbol for the setof natural (counting) numbers (0, 1, 2, 3, . . . ).n 1. Abbreviation of prefix NANO-. 2. Symbol forNUMBER. 3. Symbol for a term (e.g., a multiplier)having an assigned value. 4. Symbol for part ofan expression or operator (as in 2n, n - 1, n 2 , etc.).5. Symbol for INDEX OF REFRACTION. 6. Symbolfor amount of substance (unit, mole).NA 1. Abbreviation of not available (as on a specificationssheet). 2. Abbreviation of not applicable.N A Symbol for AVOGADRO’S CONSTANT.Na Symbol for SODIUM.nA Abbreviation of NANOAMPERE.NAB Abbreviation of NATIONAL ASSOCIATION OFBROADCASTERS.NAB curve In audio-frequency operations, thestandard magnetic tape playback equalizationcurve developed by the National Association ofBroadcasters (NAB).NAE Abbreviation of National Academy of Engineering.NAND circuit Also called NOT-AND circuit. A binarydigital circuit whose output is high (logic 1) if anyof the input signals are low (logic 0); the output islow only when all the inputs are high. The performanceof the NAND circuit is the inverse of that ofthe AND circuit.NAND gate A gate that performs the function of aNAND circuit.nano- Abbreviation, n. A prefix meaning billionth(s)(i.e., 10 –9 ).nanoampere Abbreviation, nA. A unit of current;1 nA equals 10 –9 ampere.ABA B C001101011110NAND circuitnanofarad Abbreviation, nF. A unit of capacitance;1 nF equals 10 –9 farad.nanohenry Abbreviation, nH. A unit of low inductance;1 nH equals 10 –9 henry.nanometer Abbreviation, nm. A unit of short wavelengthor displacement; 1 nm equals 10 –9 meter.nanosecond Abbreviation, ns. A time interval of10 –9 second.nanotechnology The design and construction ofsuperminiature electronic and electromechanicaldevices. For example, microscopic, computercontrolledrobots might someday be used as programmableantibodies to fight infectious diseases,or to build integrated circuits, atom by atom.nanovolt Abbreviation, nV. A unit of low voltage;1 nV equals 10 –9 volt.nanovoltmeter A sensitive voltmeter for measuringpotential in the nanovolt range.CCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

nanowatt • natural frequency 467nanowatt Abbreviation, nW. A unit of low power;1 nW equals 10 –9 watt.nanowattmeter A meter for measuring power inthe nanowatt range.NAP Abbreviation of nuclear auxiliary power.napier See NEPER.Napierian base Symbol, e. An irrational number,equal to approximately 2.718282, and used asthe NAPIERIAN LOGARITHM base.Napierian logarithm Abbreviation, ln or log e . Alogarithm to the base e (see NAPIERIAN BASE).Also called NATURAL LOGARITHM. CompareCOMMON LOGARITHM.NAPU Abbreviation of nuclear auxiliary power unit.narrative A computer program statement that,rather then being an instruction, merely describesthe purpose of what follows (usually thesteps in a routine or a block of instructions) as adebugging or program modification aid. In a programwritten in BASIC, such a statement is precededby the abbreviation REM, for remark. Alsocalled COMMENT.narrowband 1. A frequency band in which the differencebetween upper and lower limits is smallcompared with bandwidths typical of the servicespecified. 2. Pertaining to a radio-frequency emissionwhose bandwidth is limited or restricted. 3.Pertaining to a circuit or device that operates overa comparatively small range of frequencies. 4. Ina digital network, a channel having a bandwidthof 64 kbps or less.narrowband amplifier An amplifier whose passbandis restricted to a fraction of the frequencyspread common to the amplifier’s application.narrowband FM See NARROWBAND FREQUENCYMODULATION.narrowband frequency modulation Abbreviation,NBFM or NFM. Frequency modulation in whichInputTunedcircuit+12 Vnarrowband amplifierOutputthe maximum instantaneous frequency deviationis no greater than the highest modulating frequency.narrowband interference Signal interferencewhose bandwidth is narrow, compared with thatof the circuit affected.narrowband voice modulation Abbreviation,NBVM. A scheme via which an analog voice signalis compressed into a band of frequencies narrowerthan that normally required for effectivecommunication.narrow bandwidth Pertaining to a radio-frequencyemission whose bandwidth is comparatively narrow(e.g., a small fraction of the available spectrumspace in the frequency band being used).narrow-sector recorder A directional radio receiverfor locating sources of atmospheric noise.NARTB Abbreviation of National Association of Radioand Television Broadcasters.NAS Abbreviation of National Academy of Sciences.National Association of Broadcasters Abbreviation,NAB. A countrywide organization of radioand television broadcasters.National Bureau of Standards Abbreviation, NBS.An agency in the U.S. that maintains values forphysical constants in the Standard International(SI) System of Units. It also maintains radiobroadcast stations that transmit standard timeand frequency signals.National Electrical Manufacturers AssociationAbbreviation, NEMA. A countrywide organizationof manufacturers of electrical and electronicequipment and supplies.National Electric Code Abbreviation, NEC. Safetyregulations and procedures issued by the NationalFire Protection Association for the installationof electrical wiring and equipment in theUnited States. Although the code is advisory fromthe Association’s standpoint, it is enforced to variousdegrees by local authorities.National Television Standards Committee Abbreviation,NTSC. A U.S. organization of televisioncompanies and other interested organizations. Itdeveloped the original black-and-white and colortelevision standards that were approved by theFederal Communications Commission.natural-decay curve See EXPONENTIAL DE-CREASE.natural antenna frequency The fundamental resonantfrequency of an electromagnetic antenna.natural disintegration 1. The decay of a radioactivesubstance as a result of the continuous emissionof particles and rays. 2. Also called half life.The time required for half of a quantity of a radioactivesubstance to decay into a different isotopeor element.natural electricity 1. Atmospheric electricity.2. The electricity in living organisms, that is, BIO-ELECTRICITY.natural frequency See NATURAL RESONANTFREQUENCY.

468 natural-growth curve • near infrarednatural-growth curve See EXPONENTIAL IN-CREASE.natural interference Interference from atmosphericand celestial sources, as opposed to human-madeinterference.natural language A spoken or written human language(such as French or Japanese), as opposedto a computer language (such as machine language,C++, or LISP). Translation between naturallanguage and machine language is importantin optical character recognition, speech recognition,and speech synthesis.natural logarithm See NAPIERIAN LOGARITHM.natural magnet A material, such as magnetite(lodestone), found in nature and exhibiting permanentmagnetism.natural magnetism Magnetism found in somenatural materials (see NATURAL MAGNET) and inthe earth itself.natural number 1. Any nonnegative whole number,that is, a member of the set N = (0, 1, 2, 3, . . .).2. See NAPIERIAN BASE.natural period The time required for one completewave cycle to occur in a device at its NATURALRESONANT FREQUENCY.natural radiation Noise in the form of radiationemitted by natural radioactive substances, cosmicrays, etc. Also called BACKGROUND RADIATION.natural resonance Resonance resulting from theunique physical constants of a body, circuit, orsystem. Also see NATURAL RESONANT FRE-QUENCY.natural resonant frequency 1. The frequency atwhich a circuit or device responds with maximumamplitude to applied signals. 2. The frequency atwhich a circuit or device generates maximum energy.3. The frequency at which an object vibratesat maximum amplitude.natural wavelength The wavelength correspondingto the NATURAL RESONANT FREQUENCY ofa circuit, device, or object.nautical mile A nautical unit of linear measureequal to 1.852 kilometers (1.1508 statute miles).nav 1. Abbreviation of navigation. 2. Abbreviationof navigational.Navaglobe A radionavigation system used at verylowor low frequencies over long distances.NAVAIDS Abbreviation of NAVIGATIONAL AIDS.navar A radar system in which a ground radarscans the immediate vicinity of an airport, observesthe flight activity, and transmits such observationsto aircraft in flight. The name is acontraction of the term navigation and ranging.navigation aid An electronic device or system,such as radar or radio direction finding, that assistsin the navigation of vehicles on land, at sea,or in the air.navigation beacon A beam that provides aircraftand ships with navigational aid.NAWAS Abbreviation of National Attack WarningSystem.Nb Symbol for NIOBIUM.nb Abbreviation of NARROWBAND.NBFM Abbreviation of NARROWBAND FRE-QUENCY MODULATION. Also abbreviated NFM.NBS Abbreviation for NATIONAL BUREAU OFSTANDARDS.NBTDR Abbreviation of narrowband time-domainreflectometry.nbw Abbreviation of NOISE BANDWIDTH.NC 1. Abbreviation of NORMALLY CLOSED. 2. Ondrawings, abbreviation of no connection. 3. Abbreviationof NUMERICAL CONTROL.N/C Abbreviation of NUMERICAL CONTROL.nc Abbreviation of no connection.n-channel junction field-effect transistor Abbreviation,NFET. A junction field-effect transistor inwhich the gate junction is formed on a bar or dieof n-type semiconductor material.SourcenGateppn-channel junction field-effect transistorDrainn-channel MOSFET A metal-oxide-semiconductor(MOS) field-effect transistor in which the channelis n-type material.NCMT Abbreviation of NUMERICALLY CONTROL-LED MACHINE TOOL.NCS Abbreviation of net control station(s).N curve A negative-resistance voltage-currentcurve having a shape roughly resembling an uppercaseletter N. Compare S CURVE.Nd Symbol for NEODYMIUM.N display A radar display in which the target isrepresented by a pair of vertical blips, whose amplitudeindicates target direction and whose positionalong the horizontal base line (as determinedby lining up a pedestal signal with the blips) isread from the pedestal-adjustment calibration.n-doped zinc-oxide ceramic A nonlinearresistancematerial used in the manufacture ofsome voltage-dependent resistors.NDR Abbreviation of NONDESTRUCTIVE READ.NDT Abbreviation of NONDESTRUCTIVE TEST.Ne Symbol for NEON.near-end crosstalk Crosstalk originating at, ornear, the telephone subscriber line in which theinterference is noticed.near field 1. The radiation field within a radius of1 wavelength from a transmitting antenna. 2. Thesound field near a loudspeaker or other reproducer.near infrared Pertaining to electromagnetic radiationof 3 to 30 micrometers in wavelength.

near ultraviolet • negative exponent 469near ultraviolet That part of the ultraviolet spectrumnearest the visible light wavelengths. Theseare the least-penetrating ultraviolet rays. Theyare also called soft ultraviolet.near video on demand In television, a local servicein which various programs/videos are broadcastat specified times.near zone See NEAR FIELD, 1.NEB Abbreviation of noise equivalent bandwidth.NEC Abbreviation of NATIONAL ELECTRIC CODE.necessary bandwidth The minimum bandwidthneeded (with a given emission) to transmit informationat a required rate and of a required quality.In general, as data speed increases (asmeasured in bits per second, baud, or words perminute), the minimum required bandwidth increases.For slow-speed Morse code signals, itcan be as small as a few Hertz; for fast-scan television,it is several megahertz.neck The straight portion of a cathode-ray-tube(CRT) envelope (i.e., the part between the baseand the flared portion).NEDA Abbreviation of National Electronic Distributors’Association.needle 1. The stylus of a phonograph cartridge.2. The pointer of an indicating meter. 3. One ofthe electrodes in a voltage-measuring spark gap(see NEEDLE GAP). 4. The slender, pointed metaltip of a test probe.needle chatter See NEEDLE TALK.needle drag In disc recording and reproduction,friction between the needle (stylus) and disc. Alsocalled stylus drag.needle electrode See NEEDLE, 3, 4.needle gap A spark gap composed of two needleshaving an adjustable air gap between theirpoints. An unknown high voltage is measured interms of the gap width necessary for sparking.needle memory A computer memory in whichthe dual-state elements are thin magnetic needles.needle pointer The pointer of a meter or compass.needle pressure See VERTICAL STYLUS FORCE.needle probe See NEEDLE-TIP PROBE.needle scratch In disc recording and reproduction,noise resulting from vibration of the needle(stylus) because of an irregular groove surface.Also called surface noise.needle talk Direct radiation of sound by the stylusof a phonograph pickup. Also called needle chatter.needle telegraph A telegraph in which the Morsecode characters are converted into magnetic needledeflections.needle test point See NEEDLE, 4.needle-tip probe A test probe that terminates in asharp point. Also see NEEDLE, 4.needle voltmeter See NEEDLE GAP.neg Abbreviation of NEGATIVE.negate 1. To insert the NOT operation in front of adigital expression. 2. To change logic 1 to logic 0(high to low) or vice versa.negation The logical NOT operation (see NOT) indigital systems. Also see NAND CIRCUIT, NORCIRCUIT, NOR GATE, NOT CIRCUIT, and NOT-OR CIRCUIT.negation element In a computer system, a devicethat can give the reverse of a condition, event, orsignal.negative 1. Possessing NEGATIVE ELECTRIFICA-TION. 2. In voice communications, a word oftenused for “no,” especially when interference is presentor signals are weak. 3. Pertaining to a realnumber less than zero. 4. An image whose shadingsare opposite to those in the scene.negative acceleration A decrease in speed or velocity;also called deceleration.negative acknowledgment character In a handshakingor forward-error-correction (FEC) system,a response by the receiving station thatindicates a missed bit or bits.negative angle 1. An angle in the third or fourthquadrant in a system of rectangular coordinates.2. An angle measured clockwise from the positivex-axis in a rectangular coordinate system. ComparePOSITIVE ANGLE.negative bias A steady, negative direct-current voltageor current applied continuously to an electrodeof a device, such as a transistor to establishthe operating point. Compare POSITIVE BIAS.negative bus See NEGATIVE CONDUCTOR.negative charge An electric charge consisting of aquantity of NEGATIVE ELECTRIFICATION. Alsosee CHARGE, 1; ELECTRIC CHARGE; and UNITELECTROSTATIC CHARGE. Compare POSITIVECHARGE.negative conductor The conductor or wire connectedto the negative terminal of a current,power, or voltage source. Compare POSITIVECONDUCTOR.negative electricity See NEGATIVE CHARGE andNEGATIVE ELECTRIFICATION.negative electrification Electrification characterizedby an excess of electrons. For example, whena glass rod is rubbed with a silk cloth, the clothbecomes negatively charged because electronsare transferred from the glass to the cloth. Similarly,when a neutral atom acquires an extra electron,the atom becomes negatively chargedbecause it has an excess of electrons. ComparePOSITIVE ELECTRIFICATION.negative electrode 1. An electrode connected tothe negative terminal of a current, power, or voltagesource. 2. The negative output terminal of acurrent, power, or voltage source, such as a batteryor generator.negative error of measurement An error of measurementin which the difference between a measuredvalue and the true or most probable valueis negative. Compare POSITIVE ERROR OF MEA-SUREMENT.negative exponent In mathematical notation, anexponent indicating that a number is to be raised

470 negative exponent • negative resistanceto a negative power. Raising a number x to a negativepower –n means taking the reciprocal of thenumber raised to the power n. That is, x –n = 1/x n ;for example, 10 –2 = 1/10 2 = 1/100 = 0.01.negative feedback Feedback that is out of phasewith the input signal. Also called INVERSE FEED-BACK, DEGENERATION, and DEGENERATIVEFEEDBACK. Compare POSITIVE FEEDBACK.Input+−+V ccFeedbackresistornegative feedbackOutputnegative-feedback amplifier An amplifier inwhich negative feedback is used to improve performanceor modify response.negative function A trigonometric function havingthe negative sign. In a rectangular coordinatesystem, the sine function is negative in the thirdand fourth quadrants, the cosine in the secondand third, and the tangent in the second andfourth. Compare POSITIVE FUNCTION.negative gain A misnomer for FRACTIONAL GAIN,arising because fractional gain can be expressedin negative decibels.negative ghost In a television picture, a ghost withnegative (see NEGATIVE, 4) shading.negative ground In a direct-current power system,the connection of the negative pole to commonground.negative image 1. A picture in which the blacks,whites, and shades in between are the reverse ofthose in the scene (see NEGATIVE, 4). 2. An abnormalimage that has the reverse shading describedin 1.negative impedance An impedance that displaysthe same behavior as that of NEGATIVE RESIS-TANCE.negative ion An atom with an excess of electronsand, consequently, a net negative charge. Alsocalled ANION. Compare POSITIVE ION.negative-ion generator A device for generatingnegative ions and circulating them into the surroundingair. This is believed by some people tobe beneficial to health.negative lead See NEGATIVE CONDUCTOR.negative-lead filtering Power-supply filtering inwhich the choke coils and capacitors are in thenegative direct-current lead, rather than in thepositive lead (the usual position). One advantageof this arrangement is the lower insulation requirementof the choke.negative light modulation In television imagetransmission, the condition in which transmittedpower is increased by a decrease in the initial intensityof light. Compare POSITIVE LIGHT MOD-ULATION.negative line See NEGATIVE CONDUCTOR.negative logic 1. Binary logic in which a high negativestate represents logic 1, and a low negativestate represents logic 0. 2. Binary logic in whicha low positive state represents logic 1, and a highpositive state represents logic 0. Compare POSI-TIVE LOGIC.negative measurement error See NEGATIVE ER-ROR OF MEASUREMENT.negative modulation Amplitude-modulated televisiontransmission in which the transmittedpower decreases as image brightness increases.Compare POSITIVE MODULATION.negative modulation factor For an amplitudemodulatedwave having unequal positive andnegative modulation peaks, a ratio expressing themaximum negative deviation from the average forthe envelope. Compare POSITIVE MODULATIONFACTOR.negative number A real number less than zero(i.e., one to which the minus sign is assigned).negative peak The maximum negative instantaneouscurrent or voltage in an alternatingcurrentwaveform.negative-peak voltmeter An electronic meter formeasuring the NEGATIVE PEAK voltage of an alternating-currentwaveform.negative phase-sequence relay A relay that respondsto the negative phase sequence in apolyphase circuit. Compare POSITIVE PHASE-SEQUENCE RELAY.negative picture modulation See NEGATIVEMODULATION.negative picture phase In a television signal, thepicture-signal voltage swing from zero to negative,in response to an increase in brightness.Compare POSITIVE PICTURE PHASE.negative plate The negative member of a batterycell; electron flow is from the plate through theexternal circuit.negative pole See NEGATIVE ELECTRODE, 1, 2.negative positive zero Abbreviation, NP0. Pertainingto temperature-compensating capacitors havinga temperature coefficient of capacitance thatchanges sign within a specified temperature range.negative potential 1. The potential measured at anegative electrode, with respect to the positiveelectrode or to ground. 2. Potential less than thatof the earth as a reference.negative resistance 1. A decrease in voltage acrossa device as the current through it increases, andan increase in voltage as the current decreases.2. A decrease in current through a device as the

negative resistance • nemo 471voltage across it increases, and an increase incurrent as the voltage decreases. This is opposite tothe behavior of an ohmic (positive) resistance. Alsosee N-CURVE, NEGATIVE-RESISTANCE REGION,NEGATIVE RESISTOR, and S CURVE.+CurrentNegativeresistanceregionnegative resistance+Voltagenegative-resistance amplifier A simple circuit inwhich a negative-resistance device, such as aTUNNEL DIODE, cancels the positive resistanceof the circuit, causing amplification or oscillation.negative-resistance device See NEGATIVE RE-SISTOR.negative-resistance diode 1. See TUNNEL DIODE.2. A reverse-biased germanium diode (and occasionallya silicon diode) that exhibits NEGATIVERESISTANCE. 3. A special diode tube that, whenoperated at ultrahigh frequencies, exhibits negativeresistance because of transit-time effects.negative-resistance magnetron A split-anodemagnetron operated at a combination of anodevoltage and magnetic field strength correspondingto cutoff; it exhibits negative resistance tovoltage applied symmetrically between the anodehalves. The frequency of oscillation is determinedby an external tank circuit.negative-resistance oscillator An oscillator thatconsists of a negative-resistance device connectedacross a tuned circuit. The arrangementoscillates because the negative resistance cancelsthe positive resistance (losses) of the tuned circuit.See, for example, NEGATIVE-RESISTANCEMAGNETRON and TUNNEL-DIODE OSCILLA-TOR.negative-resistance region In certain devices, aportion of the voltage-versus-current curve havingnegative slope (i.e., the current decreases asthe voltage increases, or vice versa). Also see NCURVE, NEGATIVE RESISTANCE, and S CURVE.negative-resistance repeater A repeater that producesgain by means of NEGATIVE RESISTANCEeffects.negative resistor Any device exhibiting NEGATIVERESISTANCE.negative space charge The cloud of electrons(negative particles) in the region surrounding anemitter, such as the hot cathode of a vacuumtube.negative temperature coefficient Abbreviation,NTC. A number expressing the amount by whicha quantity (such as the rating of a component) decreaseswhen the temperature is raised. The coefficientis stated as a percentage, or as a certainnumber of parts per million (ppm) per degreetemperature rise. Compare POSITIVE TEMPERA-TURE COEFFICIENT and ZERO TEMPERATURECOEFFICIENT.negative terminal See NEGATIVE ELECTRODE,2.negative torque In an electric motor, a torque thatacts against the operating torque.negative transmission In a television or facsimilesystem, the condition in which brighter light correspondsto lower transmitted power, and dimmerlight corresponds to higher transmitted power.negative valence The valence of a negative ion.Also see VALENCE.negator A logical NOT element [i.e., one that outputsthe complement of an input bit (1 for 0 andvice-versa)].negatron The term that specifically differentiatesthe familiar ELECTRON from a POSITRON (positiveelectron).NEI Abbreviation of noise equivalent input.neighborhood node A local site at which a fiberoptictelevision (video) signal is converted to a cablesignal.NEL Abbreviation of National Electronics Laboratory.NELA Abbreviation of National Electric Light Association.N electron In certain atoms, an electron whose orbitis outside of, and nearest to, those of the Melectrons.NEMA Abbreviation of National Electrical Manufacturers’Association.nematic crystal A normally transparent liquidcrystal that becomes opaque when an electricfield is applied to it, and becomes transparentagain when the field is removed. The crystal materialis cut in the form of a letter or numeral andprovided with a reflecting backplate for displayreadouts in calculators, watches, and variouselectronic devices.nematic-crystal display A device in which an electricallycontrolled film of nematic-crystal materialis used to transmit and interrupt light from alamp or from a reflecting mirror, in this way displayingcharacters in whose shape the film hasbeen formed.nematic liquid In a liquid-crystal display (LCD), anormally clear liquid that becomes opaque in thepresence of an electric field.nemo A radio or television program that is pickedup from a location outside the studio. Also calledfield pickup or remote.

472 neodymium • neperneodymium Symbol, Nd. A metallic element of therare-earth group. Atomic number, 60. Atomicweight, 144.24.neodymium-YAG laser A laser that uses neodymiumand yttrium-aluminum-garnet (YAG)crystal. It is used in medical applications, such assurgery and various other jobs where high precisionis required. Generally, it is a low-to-mediumpowerlaser.neomatachograph An instrument used in psychologyto measure complex reaction time. CompareNEOMATACHOMETER.neomatachometer An instrument used in psychologyto measure simple reaction time. CompareNEOMATACHOGRAPH.neon Symbol, Ne. An inert-gas element. Atomicnumber, 10. Atomic weight, 20.179. Neon, presentin trace amounts in the earth’s atmosphere,is used in some glow tubes, readout devices, andindicator lamps.neon bulb A (usually small) neon-filled gas diode.It has a characteristic pink glow and is ignited bya firing voltage for the particular unit. Also calledneon glow lamp and neon tube.neon-bulb flip-flop A flip-flop circuit (bistable multivibrator)using two neon bulbs as the bistablecomponents.neon-bulb gate A gate circuit containing a neonbulb biased below the firing point. A trigger voltageadded to the bias voltage raises the applied voltageand fires the bulb, producing an output pulse.neon-bulb logic Logic circuits composed of neonbulbgates.neon-bulb memory See NEON-BULB STORAGE.neon-bulb multivibrator A multivibrator usingtwo neon bulbs as the switching components.neon-bulb oscillator A simple relaxation oscillatorconsisting essentially of a neon bulb, capacitor,resistor, and direct-current supply. The frequencyof the sawtooth-wave output depends principallyon the capacitance and resistance values. Themaximum operating frequency is limited to about5 kHz by the deionization time of the gas.neon-bulb overmodulation indicator The applicationof a neon-bulb overvoltage indicatoras a monitor for amplitude-modulated radiofrequencysignals. The bulb flashes each time themodulation percentage exceeds a predeterminedvalue. Also called neon-bulb modulation alarm.neon-bulb overvoltage indicator A relatively simplecircuit in which a neon bulb flashes each timea voltage monitored by the circuit exceeds a predeterminedvalue. The flash shows that the portionof the voltage presented to the bulb hasexceeded the firing potential.neon-bulb peak indicator See NEON-BULBOVERVOLTAGE INDICATOR.neon-bulb ring counter A ring counter composedof neon-bulb flip-flops. The maximum countingspeed is limited by the deionization time of the neonbulbs to approximately 300 events per second.+150 VFrequencyadjustmentNeonbulbneon-bulb oscillatorOutputneon-bulb sawtooth generator A relatively simplerelaxation oscillator using a neon bulb, capacitor,and resistor. The output is a sawtooth wave,whose frequency is determined principally by thecapacitance and resistance values.neon-bulb scale-of-two circuit A scale-of-two circuit(frequency halver) using neon bulbs as thebistable elements.neon-bulb storage A storage (memory) device composedof neon bulbs. A fired bulb (representing abit of stored information) remains fired untilturned off by an erase signal.neon-bulb stroboscope A stroboscope in which aneon bulb supplies the light flashes. The circuit isessentially that of the neon-bulb oscillator, theflash rate being continuously variable by an adjustablefrequency control.neon-bulb voltage regulator A simple circuit utilizingthe constant voltage drop across a firedneon bulb as a regulated voltage. The usual circuitconfiguration is a neon bulb and currentlimitingresistor in series with a power supply.neon-bulb volume indicator A neon-bulb overvoltageindicator used in some tape recorders toshow when the volume exceeds a predeterminedlevel—especially when the volume is high enoughto cause an unacceptable amount of distortion.neon glow lamp See NEON BULB.neon lamp See NEON BULB.neon pilot lamp A neon bulb used as a pilot lampoperated from the power-line circuit of an electronicequipment. Also called neon pilot light.neon tube See NEON BULB.NEP Abbreviation of NOISE EQUIVALENT POWER.NEPD Abbreviation of noise equivalent power density.neper Abbreviation, Np. A Napierian-logarithmicunit expressing a ratio of power levels; Np = log e(P 1 /P 2 ) 1/2 , where P 1 and P 2 are the power valuesbeing compared and e is the Napierian logarithmbase, equal to approximately 2.71828. The neperis related to the decibel (dB), a similar unit based

neper • network analog 473on common logarithms, in the following manner:1 Np = 8.686 dB; 1 dB = 0.1151 Np.neptunium Symbol, Np. A radioactive metallic elementproduced artificially. Atomic number, 93.Atomic weight, 237.05.Nernst effect The appearance of a voltage betweenthe opposite edges of a metal strip that is conductingheat longitudinally when the strip isplaced in a magnetic field perpendicular to theplane of the strip.HeatedmetalstripB field90°Nernst effectNernst-Ettinghausen effect In a piezoelectric crystal,the tendency for a temperature gradient to existas a result of applied electromagnetic fields.Nernst lamp An incandescent lamp in which thefilament material is a mixture of magnesia andcertain rare oxides (such as yttria). A surroundingcurrent-carrying coil heats the filament, loweringits resistance and causing it to glow, afterwhich it continues to operate on a low current.nerve center The most essential part of a controlsystem or communication network.nerve current In an animal organism, the smallelectrical current that flows along nerve fibers.nervous breakdown The upset of a function in a digitalcomputer (which becomes disabled as a result).NESC Abbreviation of National Electrical SafetyCode.nested loops See NESTING.nesting In digital computers and data processing,the inclusion of one or more loops or subroutinesinside a larger loop or subroutine. Nested loops,for example, can be used to assign values todouble-subscripted variables.NET Abbreviation of noise equivalent temperature.net 1. An effective, useful, or resultant quantity(e.g., NET CAPACITANCE). 2. Colloquialism forcommunications network. See NETWORK, 2.net authentification A password or other specialidentification used in a radio network.net capacitance The resultant capacitance in acircuit in which capacitances act in combinationwith each other.net component The total value of two or more passivecomponents of the same sort. See, for example,NET CAPACITANCE, NET CURRENT, NETIMPEDANCE, NET INDUCTANCE, NET POWER,NET REACTANCE, NET RESISTANCE, and NETVOLTAGE.net current The current flowing in a circuit inwhich currents aid or oppose each other.net gain For an amplifier, the amount of gain remainingafter all losses in the device have beensubtracted.net impedance The impedance of a circuit inwhich impedances act in combination with eachother.net inductance The inductance of a circuit in whichinductances act in combination with each other.net loss For an amplifier or other system, the algebraicsum of gains and losses between two pointsin the system.net power The resultant power observed whenpower signals aid or oppose each other in a singlecircuit or system.net radiometer A device for measuring the differencein intensity between radiation entering theearth’s surface and radiation leaving it. This isgenerally visible light or infrared radiation fromthe sun.net reactance Symbol, X t . The combined inductivereactance (X L ) and capacitive reactance (X C ) in acircuit or device.net resistance The resistance of a circuit in whichresistances act in combination with each other.net voltage The resultant voltage at a point wherevoltages aid or oppose each other.network 1. A circuit arrangement of electroniccomponents, sometimes redundant in its design[e.g., resistance-capacitance (RC) network]. 2. Agroup of interconnected computers, communicationsstations, or other facilities, often organizedfor simultaneous operation and data transfer.3. To conduct research or gather informationusing a group of interconnected computers,communications stations, or other facilities.network analog A circuit or circuits representingvariables and used to express and solve a mathematicalrelationship between the variables.

474 network analysis • neutral wirenetwork analysis The rigorous examination of anetwork to determine its properties and performance.Compare NETWORK SYNTHESIS.network analyzer An analog or digital circuit forsimulating and analyzing a network (see NET-WORK, 1) by means of measurements and calculationsfrom the model so obtained.network assurance The construction and operationof a network in such a manner that failurescan be quickly and easily located and corrected.network calculator An analog or digital device fordetermining the component values and performanceof a given network (see NETWORK, 1).network constant The value of a passive component(capacitance, inductance, resistance, etc.)used in a network (see NETWORK, 1).network filter A transducer that passes or rejectssignals, depending on their frequency.network interface unit Abbreviation, NIU. A device,provided to each subscriber, that connectstelephones, television sets, and personal computersto an electrical or fiberoptic cable. Envisionedas an integral component of the multimedia IN-FORMATION SUPERHIGHWAY.network provisioning The control of a network bymeans of computer software, rather than viamanual rearrangement of system devices.network relay 1. A relay that provides protectionof the circuits in a network (see NETWORK, 1); acircuit breaker. 2. In a communications network(see NETWORK, 2), the reception and retransmissionof a message by a human operator.network synthesis The design and fabrication of anetwork (see NETWORK, 1) by rigorous engineeringmethods to achieve a prescribed performance.network theorems See COMPENSATION THEO-REM, MAXIMUM POWER TRANSFER THEOREM,NORTON’S THEOREM, RECIPROCITY THEO-REM, SUPERPOSITION THEOREM, andTHEVENIN’S THEOREM.network topology The analysis of networks (seeNETWORK, 1) with signal-flow diagrams. Componentsof the diagram represent signal paths, openloops, closed loops, and node points.network transfer function A function describingthe overall processing of energy by a network (seeNETWORK, 1); it is equal to V o /V i , where V i is theinput voltage and V o is the output voltage of thenetwork.Neuman’s law A property of mutual inductances.For a given orientation and environment for twoinductors, the value of the mutual inductancedoes not change, regardless of the magnitude,frequency, or phase of the currents in the coils.That is, mutual inductance is subject only to thephysical environment surrounding the coils.neuristor A two-terminal semiconductor devicethat simulates the behavior of a neuron (nervecell) and allows machines to duplicate some ofthe neurological phenomena observed in the humanbody.neuroelectricity Low-voltage electricity in the nervoussystem of a human being or animal.neuron A nerve cell in a living organism.neurosurgery assistance robot An electromechanicaldevice, controlled by a human operatorand assisted by computers, that helps to performsimple neurosurgical operations requiring extremeprecision and steadiness. One procedurefor which a robot has been used is the drilling ofholes in the skull prior to brain surgery.neutral 1. Having no electric charge; thus, anatom is normally neutral because its internalpositive charges neutralize its internal negativecharges. 2. Devoid of voltage (e.g., a neutral line).3. Pertaining to a chemical, especially a solution,that is neither acidic nor alkaline.neutral bus See NEUTRAL WIRE.neutral circuit 1. A deenergized circuit (i.e., a“dead” one). 2. In a teletypewriter system, a circuitin which current flows in one direction.neutral conductor See NEUTRAL WIRE.neutral ground A ground connection to a neutralwire or to the neutral point of a circuit.neutralization The process of balancing out positivefeedback in an amplifier to prevent selfoscillation.Also see NEUTRALIZING CAPACITORand NEUTRALIZING COIL.neutralization indicator A neon bulb or radiofrequencymeter used during neutralization of anamplifier. When the amplifier is properly neutralized,the bulb or meter will show zero signal withno input to the amplifier, indicating that the circuitis not oscillating.neutralize To eliminate positive feedback in a radio-frequencyamplifier.neutralized amplifier An amplifier in which neutralizationhas been performed to prevent self-oscillation.neutralizing capacitor In a capacitively neutralizedcircuit, a small capacitor that serves as acoupler of signal energy from the output backto the input in reverse phase, to cancel selfoscillationof the circuit.neutralizing circuit Any component or set of componentsthat is used to neutralize a radiofrequencyamplifier.neutralizing coil In an inductively neutralized circuit,a small coupling coil that picks up signal energyfrom the output and applies it in reversephase to the input, to cancel circuit self-oscillation.neutralizing tool A nonconducting screwdriverlikedevice for adjusting a neutralizing capacitoror coil. It is usually made of fiber or plastic.neutralizing voltage The feedback voltage that cancelsself-oscillation in the process of neutralization.neutralizing wand See NEUTRALIZING TOOL.neutral line See NEUTRAL WIRE.neutral relay See UNPOLARIZED RELAY.neutral wire In a polyphase power-transmissionsystem, the line (wire) that does not carry currentuntil the system is unbalanced.

neutrodon • nickel–iron 475neutrodon See NEUTRODYNE.neutrodyne A radio-frequency amplifier that isneutralized by feeding energy through a small capacitorfrom a tap on the secondary coil of thecollector or drain output transformer back to thebase or gate.neutron An uncharged atomic particle having amass approximately equal to that of the proton.The neutron is present in the nucleus of everyatom, except that of hydrogen.neutron age 16.7% of the mean square displacementof a neutron as it moves through a specifiedenergy range.neutron rest mass See MASS OF NEUTRON ATREST.new candle See CANDELA.newton (Sir Isaac Newton.) Symbol N. The SI unitof force. A force of 1 newton imparts an accelerationof 1 meter per second per second to amass of 1 kilogram. The newton is equal to 10 5dynes.Newton’s laws of motion Three natural laws discoveredin 1686 by Sir Isaac Newton. First law: Abody at rest or in motion tends to remain in thatstate, unless it is acted upon by some force. Secondlaw: A body tends to accelerate or deceleratewhen it is acted upon by a force, the accelerationor deceleration being directly proportional to theforce and inversely proportional to the mass ofthe body. Third law: For every action or actingforce, there is an equal and opposite reaction orreacting force.nexus An interconnection point in a system.NF Abbreviation of NOISE FIGURE.nF Abbreviation of NANOFARAD.NFET Abbreviation of N-CHANNEL JUNCTIONFIELD-EFFECT TRANSISTOR.NFM Abbreviation of NARROWBAND FREQUENCYMODULATION. Also abbreviated NBFM.NFM reception Reception of a signal having NAR-ROWBAND FREQUENCY MODULATION. Standarddiscriminators and ratio detectors can beused. Slope detection can be achieved with anamplitude-modulation (AM) receiver by tuningslightly to one side of the center frequency of theFM signal.NFM transmission Transmission of a signal viaNARROWBAND FREQUENCY MODULATION. Asimple method consists of frequency modulatingthe master oscillator of the transmitter at themodulation frequency. Phase modulation canalso be used.NFPA Abbreviation of National Fire Protection Association(see NATIONAL ELECTRIC CODE).NFQ Abbreviation of night frequency.NG 1. Abbreviation of NEGATIVE GLOW. 2. Abbreviationof no good, used for marking inoperativeor malfunctioning components.nH Abbreviation of NANOHENRY.nhp Abbreviation of NOMINAL HORSEPOWER.Ni Symbol for NICKEL.nibble In computer operations, a four-bit word.NICAD Acronym for NICKEL–CADMIUM.NiCd Chemical symbol for NICKEL–CADMIUM.Nichrome A nickel-chromium alloy used in theform of a wire or strip for resistors and heater elements.nickel Symbol, Ni. A metallic element. Atomicnumber, 28. Atomic weight, 58.69. Nickel is familiaras an alloying metal in some resistancewires and as the material used in some electrontubeelements.nickel–cadmium Acronym, NICAD. Chemicalsymbol, NiCd. A mixture used in certainrechargeable electrochemical cells and batteries.In recent years, these cells and batteries havebeen largely replaced by nickel–metal-hydride(NiMH) and lithium-based units. These batteriesmust be disposed of in a special way because ofthe toxic cadmium they contain. CompareNICKEL–METAL-HYDRIDE.nickel–cadmium battery 1. A battery of nickel–cadmium cells. 2. Loosely, a nickel–cadmiumcell. See also NICKEL–CADMIUM.nickel-cadmium cell A small, rechargeable, electrochemicalcell. The anode is cadmium, the cathodeis nickel hydroxide, and the electrolyte is potassiumhydroxide. See also NICKEL–CADMIUM.Cadmiumanode+Nickelhydroxidecathodenickel-cadmium cell−Potassiumhydroxideelectrolytenickel hydroxide Chemical symbol, NiOH. A compoundused in certain rechargeable electrochemicalpower supplies. Examples are nickel–cadmium(NiCd or NICAD) and nickel–metal-hydride (NiMH)batteries, used in older notebook computers.nickel–iron Chemical symbol, NiFe. A mixture usedfor a specialized rechargeable electrochemical cellin which the active positive plate material consistsof nickel hydroxide. The active negative plate materialis powdered iron oxide mixed with cadmium,and the electrolyte is potassium hydroxide.

476 nickel-iron battery • noctovisionnickel-iron battery See EDISON BATTERY.nickel-metal–hydride Chemical symbol, NiMH. Amixture used in certain rechargeable electrochemicalcells and batteries. This type of cell or batteryis less likely than nickel–cadmium units to developbattery memory or memory drain, in which theampere-hour capacity is reduced because of repeatedpartial discharging. In addition, the chemicals inNiMH cells and batteries are less toxic than thosein NICADs. Compare NICKEL–CADMIUM.nickel–metal-hydride battery 1. A small,rechargeable, nickel-based electrochemical battery,similar to the nickel–cadmium (NICAD) type.2. Loosely, a nickel–metal-hydride cell. SeeNICKEL–METAL-HYDRIDE.nickel–metal-hydride cell A small, rechargeable,nickel-based electrochemical cell, similar to thenickel–cadmium type. See also NICKEL–METAL-HYDRIDE.nickel-oxide diode A diode fabricated from nickeloxidesemiconductor material.nickel silver An alloy of copper, nickel, and zinc,sometimes used for making resistance wire. Alsocalled GERMAN SILVER.Nicol prism An optical component for producing oranalyzing plane-polarized light. It consists of twoprisms of Iceland spar cemented together. Lightentering the device strikes the interface, wherethe ordinary ray is totally reflected and the extraordinaryray passes through, both rays beingplane-polarized perpendicular to each other.NIDA Abbreviation of numerically integrating differentialanalyzer.NIF Abbreviation of NOISE IMPROVEMENT FAC-TOR.NiFe Chemical symbol for NICKEL–IRON.night effect A phenomenon sometimes observedat frequencies below approximately 500 kHz. Direction-findingsignals received between sunsetand the following sunrise appear to come from atransmitter that moves slowly back and forth.night-effect errors In radio direction-finding, inaccurateor uncertain readings resulting from theNIGHT EFFECT.night range The distance over which signals froma given transmitter are consistently received aftersunset.ni junction In a semiconductor device, the junctionbetween an n-type layer and an intrinsic layer.nil 1. Colloquialism for negligible. 2. British expressionfor zero. Also, nought. 3. Colloquialismfor nothing.NiMH Chemical symbol for NICKEL–METAL-HYDRIDE.niobium Symbol, Nb. A metallic element chemicallyresembling tantalum. Atomic number, 41.Atomic weight, 92.91.NIPO Abbreviation of negative input/positive output.NIR Abbreviation of NEAR INFRARED.nit In digital-computer operations, a unit of dataequal to 1.44 bits.nitrocellulose See CELLULOSE NITRATE.nitrogen Symbol, N. A gaseous element. Atomicnumber, 7. Atomic weight, 14.007. Nitrogen isthe most-abundant component (about 78%) ofthe Earth’s atmosphere.NIU Abbreviation of NETWORK INTERFACE UNIT.Nixonite A trade name for cellulose acetate, aplastic.Nixonoid A trade name for cellulose nitrate, aplastic.NJCC Abbreviation of National Joint Computer Conference.n layer A semiconductor layer doped to providecurrent carriers that are predominantly electrons.Compare P LAYER.n-level logic 1. A multilevel form of logic, with ndifferent possible states. 2. In a computer, theconnection of up to n logic gates.NLR 1. Abbreviation of nonlinear resistance. 2. Abbreviationof NONLINEAR RESISTOR.NLS Abbreviation of NO-LOAD SPEED.N/m 2 Abbreviation of newtons per meter squared(pascals).Nm 2 /kg Newton meters squared per kilogram, theSI unit of the gravitational constant.NMAA Abbreviation of National Machine AccountantsAssociation.NMOS A metal-oxide semiconductor device madeon a p-type substrate whose active carriers, electrons,migrate between n-type source and draincontacts.NMR 1. Abbreviation of NUCLEAR MAGNETICRESONANCE. 2. Abbreviation of NORMAL-MODE REJECTION.n-n junction In a semiconductor device, especiallyan integrated circuit, the junction between twon-type regions having somewhat different properties(sometimes designated n 1 and n 2 ).NO Abbreviation of NORMALLY OPEN.No Symbol for NOBELIUM.No. Abbreviation of NUMBER.no-address instruction In digital computer operations,an instruction requiring no reference tostorage or memory for its execution.nobelium Symbol, No. A radioactive element producedartificially. Atomic number, 102. Atomicweight, approximately 259 (varies with isotope).Nobili’s rings See ELECTRIC RINGS.noble Chemically inert or inactive. For example,noble metals oxidize less rapidly than base metals.noble gas An inert rare gas (such as argon, helium,krypton, neon, or xenon). It is used in electronicglow devices.noble metal A comparatively nonreactive metal(such as gold, silver, or platinum).noctovision A television transmission system usinginfrared rays instead of visible light to scanthe object. This makes it possible to televise imagesin complete visual darkness (hence, the prefixnocto-, meaning “night”).

no-charge machine fault time • noise current 477no-charge machine fault time Unproductive computertime resulting from errors or a malfunction.nodal point See NODE.node 1. The terminal point at which two or morebranches of a circuit meet, or a point that iscommon to two circuits. 2. In a standing-wavesystem, a zero point or minimum point, e.g.,current node. Compare LOOP, 1. 3. A databasemanagement system expression defining thelocation of information about a record, user,field, etc. 4. A point at which a satellite crossesthe equator. See also ASCENDING NODE, DE-SCENDING NODE.NodeCurrentDisplacementnode, 2Nodenodules 1. Oxide particles that protrude above thesurface of magnetic tape. 2. In a planar patterndescribing radiation or pickup characteristics (asfor antennas, microphones, loudspeakers), asmall peak aligned in a direction other than thatof the main lobe.no-field release In the starting box for a shunt motor,the electromagnet that normally holds thearm in full-running position; it is connected in serieswith the field winding. When the field currentis lost, the arm is released, disconnecting the armaturefor safety. Compare NO-VOLTAGE RE-LEASE.noise 1. A random-frequency current or voltagesignal extending over a considerable frequencyspectrum and having no useful purpose, unlessit is intentionally generated for test purposes.2. Dissonant, interferential sound; unlike harmonioussound, it is disagreeable. 3. In audio operations,unwanted hiss and/or hum. 4. Extra bitsor bytes that must be removed from digital databefore it can be useful.noise abatement The elimination or reduction ofnoise intensity—especially a measure in a programconcerned with noise pollution in the environment.noise analysis The measurement of the amplitudeand spectral distribution of noise and the determinationof its character.noise analyzer An instrument for evaluating thenature of noise in a communications system. See,for example, NOISE METER. Noise analyzers aresometimes adapted for vibration analysis.noise-balancing system A bridge circuit insertedbetween a receiver and antenna for balancing outinterferential signals resulting from nearbypower-line leaks or similar causes.noise bandwidth Abbreviation, NBW. A figure obtainedby dividing the area under the poweroutput-vs.-frequencycurve of a device by thepower amplitude at the noise frequency of interest.noise behind the signal Noise caused by, but exclusiveof, a signal.noise blanker A device that cuts off one of the intermediate-frequencystages of a radio receiver duringa noise pulse. The noise blanker is effective againsthigh-amplitude impulses of short duration.noise-canceling antenna A specialized receivingantenna system that uses two elements, one intendedfor receiving primarily the desired signal(s)and the other intended for receivingprimarily local human-made noise. The outputsfrom the two elements are combined so that thenoise impulses appear out of phase, but of equalamplitude. Because one element is located in afavorable position for reception of desired signalswhile the other element is not, the desiredsignals do not cancel at the receiver input. As aresult, the signal-to-noise ratio is greatlyimproved, compared with the use of the signalantenna alone.noise-canceling microphone A microphone thatdiscriminates against background sounds. It isusually directional and relatively insensitive, requiringthe user to talk directly into it at closerange.noise clipper A biased-diode circuit used as anautomatic noise limiter. The device cuts off allsignals above a predetermined amplitude on thetheory that noise peaks are high-level transientsin an otherwise uniform signal. Noise is reducedat the sacrifice of system reproduction fidelity.noise criteria An expression for the level of ambientacoustic noise.noise current Noise-generated current.

478 noise-current generator • noise-reducing antennanoise-current generator A noise generator thatsupplies a useful current. Compare NOISE-VOLTAGE GENERATOR.noise digit A digit (usually zero) generated duringnormalization of a floating-point number. SeeNORMALIZE.noise diode A reverse-biased semiconductor diodethat produces a standard noise voltage.noise elimination The nearly complete removal ofnoise effects from a system. Noise can never beeliminated altogether because the movement ofelectrons and atoms generates some electricaland thermal noise. However, in some digital systems,the effects of noise can be almost totallyovercome. Compare NOISE SUPPRESSION.noise equivalent power Abbreviation, NEP. Thepower that produces an rms signal-to-noise ratioof 1 in a detector.noise factor For a circuit, especially a communicationsreceiver or weak-signal amplifier, the ratioR 1 /R 2 , where R 1 is the signal-to-noise power ratio ofan ideal circuit, and R 2 is the signal-to-noise ratio ofthe circuit under test. Compare NOISE FIGURE.noise figure The NOISE FACTOR of a circuit, expressedin decibels. If N is the noise factor expressedas a ratio, then noise figure N dB can bedetermined by N dB = 10 log 10 N.noise filter A filter designed to suppress noise thatwould otherwise enter an electronic circuit (e.g., apower-line noise filter).noise floor 1. In a receiver, the level of noise in microvoltsthat determines the weakest signal thatcan be heard or accurately received. 2. In a spectrumanalyzer, the level of noise that determinesthe weakest signal that will be visibly displayed.noise generator A device for generating preciseamounts of noise voltage for test purposes.noise grade 1. The relative level of radiofrequencybackground noise, over all electromagneticfrequencies, in a particular geographiclocation. The noise grade is generally lowestnear the poles and highest near the equator.2. The mathematical function of relative electromagneticnoise intensity versus latitude andlongitude.noise immunity The degree to which a circuit ordevice is insensitive to extraneous energy—especiallynoise signals.noise-improvement factor Abbreviation, NIF. Fora radio receiver, the ratio SN i /SN o , where SN i isthe input signal-to-noise ratio and SNo is the outputsignal-to-noise ratio.noise killer 1. See AUTOMATIC NOISE LIMITER.2. See NOISE FILTER. 3. See NOISE BLANKER.noiseless alignment See VISUAL ALIGNMENT.noise level 1. The amplitude of ambient electricalnoise generated outside an electronic system ofinterest. 2. The amplitude of electrical noise generatedin an electronic system of interest. 3. Theintensity of ambient acoustic noise.noise limiter See AUTOMATIC NOISE LIMITER.noise margin In a binary logic circuit, the differencebetween operating and threshold voltages.noise-measuring set See NOISE METER.noise meter An instrument for measuring acousticnoise level. It consists essentially of a sensitive,multirange voltmeter provided with amicrophone, amplifier, and attenuators. The meterscale reads noise level directly in decibels.Readable signalsAmplitude axisMike Amp. µΑSignals belownoise floornoise floor, 2.FrequencyaxisNoisefloorDo not appearin displaynoise meternoise power The power component of a noisesignal.noise power ratio The ratio of noise power at theoutput of a circuit (such as a receiver) to the noisepower at the input.noise pulse A random short-duration noise burstwhose amplitude exceeds the average peak noiselevel.noise quieting In a radio receiver, the reduction(in decibels) of background noise, with respect toa signal of interest.noise ratio See NOISE POWER RATIO.noise-reducing antenna A receiving antenna havinga balanced transmission line and usuallysome form of noise-balancing system for reducingelectrical noise picked up by the antenna.

noise reduction • nominal value 479noise reduction See NOISE SUPPRESSION.noise residue The residual output (see NULLVOLTAGE, 1) of a balanced bridge, caused entirelyby noise.noise silencer A noise-limiting circuit that removesnoise-pulse transients with little or no effecton the signal from which the noise isremoved. Compare NOISE CLIPPER.noise source See NOISE GENERATOR.noise spike See NOISE PULSE.noise suppression 1. In communications, the reductionof noise amplitude to a level that is noncompetitivewith desired signals. 2. In audiorecording and reproduction, reduction of unwantednoise (e.g., hiss) to the greatest extentpossible without degrading the fidelity of the desiredaudio. Compare NOISE ELIMINATION.noise suppressor A device for eliminating electricalnoise or reducing its amplitude. See, for example,AUTOMATIC NOISE LIMITER and NOISEBLANKER.noise temperature At a given frequency, the temperatureof a passive system that has the samenoise power per unit bandwidth as that observedat the terminals of a device under test.noise voltage The voltage component of an electricalnoise signal.noise-voltage generator A signal generator thatsupplies an alternating-current waveform containingrandom-frequency pulses of relativelyuniform distribution over a given frequency spectrum.Compare NOISE-CURRENT GENERATOR.noisy mode During normalization of a floatingpointnumber, the generation of digits, excludingzero, as part of the fixed-point part (see NOR-MALIZE).NOL 1. Abbreviation of National Ordnance Laboratory.2. Abbreviation of Naval Ordnance Laboratory.no-load current 1. Output-electrode current (e.g.,drain, plate, or collector current) when a device isnot delivering output to an external load. 2. Currentflowing in the primary winding of an unloadedtransformer.no-load losses Losses in an unloaded transformer(see NO-LOAD CURRENT, 2).no-load speed The rotational speed of an unloadedmotor.no-load voltage The open-circuit output voltage ofa power supply, amplifier, generator, or network.nominal 1. Named, rated, or specified. The nominalvalue of a speaker, for example, might be 8 ohms,even though the actual impedance value dependson the frequency of the applied signal. 2. Approximate,and specified as a typical example only, forthe purpose of identifying the operating or valuerange. For example, an automotive circuit mighthave a nominal rating of 12 volts—even though itcan be operated at 10 volts to 14.6 volts.nominal band In a facsimile signal, the wavebandextending between zero and the maximum frequencyof modulation.nominal bandwidth 1. For a filter, the differencef c2 f c1 , where f c1 is the nominal lower cutoff frequencyand f c2 is the nominal upper cutoff frequency.2. For an allocated communicationchannel, the total bandwidth, including upperand lower guard frequencies. 3. The intended andspecified bandwidth of a given channel, regardlessof the bandwidth of the signal on that frequencyat any given time.AmplitudeChannelXNominalbandwidthChannelYNominalbandwidthnominal bandwidth, 2Freq.nominal capacitance The rated (“label”) value of acapacitor. Also see NOMINAL VALUE.nominal current The rated (“nameplate”) value ofrequired current or of current output. Also seeNOMINAL VALUE.nominal horsepower The rated (“nameplate”)horsepower of a machine, such as a motor. Alsosee NOMINAL VALUE.nominal impedance The rated impedance of a circuitor device. Also see NOMINAL VALUE.nominal inductance The rated (“label”) value of acoil’s inductance. Also see NOMINAL VALUE.nominal line pitch In a television raster, the averagecenter-to-center separation between adjacentlines.nominal line width 1. For a television raster, thefactor 1/n, where n is the number of lines perunit width for the direction in which the linesprogress. 2. In facsimile, the average center-tocenterseparation of scanning or recording lines.nominal power factor The rated (“nameplate”)value of power factor of a device. Also see NOMI-NAL VALUE.nominal power rating The rated (“nameplate”)value of power output, power drain, or power dissipation.Also see NOMINAL VALUE.nominal Q The rated (“nameplate”) value of Q of acapacitor, inductor, transformer winding, or tankcircuit. Also see NOMINAL VALUE.nominal rating See NOMINAL, 1, 2.nominal resistance The rated (“label”) value of a resistoror similar device. Also see NOMINAL VALUE.nominal speed The highest speed of a dataprocessingunit or system, disregarding slowdownsbecause of factors other than computational operations.nominal value A named, specified, rated, or labeledvalue, given without reference to tolerance.

480 nominal value • nonharmonic oscillationsThis can differ significantly from the actual value.For example, the nominal value of a capacitormight be 100 pF; but if the tolerance is ±10 percent,the actual capacitance might be any valuebetween 90 pF and 110 pF.nominal voltage 1. The rated (“nameplate”) valueof required voltage or of voltage output. Also seeNOMINAL VALUE. 2. In a cell or battery, the MID-POINT VOLTAGE.nomogram See ALIGNMENT CHART.nomograph See ALIGNMENT CHART.nomography The geometric representation of amathematical function or relation by means ofalignment charts.nonaccountable time The period during which acomputer system is unavailable to the user (becauseof a power outage, for example).nonarithmetic shift See LOGICAL SHIFT.nonblinking meter A digital meter that does notalternate, or oscillate, between two different valueswhen the measured parameter is betweentwo discrete values. Instead, the display isrounded off to the nearest value, and the displayremains at that value continuously.nonblocking system In a telephone communicationsnetwork, a system that ensures a circuitwill be completed when necessary. That is, at notime is it impossible for a connection to be made.Under conditions of extremely heavy usage, thequality of communications might be degraded,but the connection will not be cut off.nonbridging contact In a switch or relay, a movablecontact that leaves one stationary contactbefore contacting another.nonchargeable battery A primary battery (i.e., onethat cannot ordinarily be recharged). An exampleis a battery of common zinc-carbon or alkalinecells.noncoherent Pertaining to electromagnetic radiationin which the wave disturbances are not allprecisely aligned in frequency and phase.nonconductor See DIELECTRIC.noncontact temperature measurement The useof infrared or optical electronic equipment tomeasure the temperature of bodies withouttouching them.noncorrosive flux A solder flux that does not corrodethe metals to which solder is applied.noncrystalline Pertaining to materials that possessnone of the characteristics of crystals. CompareCRYSTALLINE MATERIAL.nondestructive read In digital computer andcounter operation, the process of reading datawithout erasing it as a result. The name is alsoapplied to the readout device.nondestructive test Abbreviation, NDT. A testthat does little or no irreversible harm to the testsample. Compare DESTRUCTIVE TEST.nondeviated absorption Absorption that slowswaves by a negligible amount; also, normal skywaveabsorption.nondirectional antenna An antenna that displaysequally intense radiation or equally sensitive receptionin all directions within a specified plane.An example is a vertical dipole antenna, which isnondirectional in the horizontal plane.nondirectional microphone A microphone thatresponds equally well to sound from any direction;an omnidirectional microphone.nondissipative load A purely reactive load. Insuch a load, the only power consumed is thatwhich is dissipated in the inherent resistance(losses) of the load.nondissipative stub A stub that exhibits only slightlosses; it consumes no power, except that dissipatedin small, inherent losses. Also see STUB.nonelectrical Not electrical in nature. The term iscommonly used to designate the mechanicalparts of electromechanical systems, such asrobots and servomechanisms.nonelectrolyte A substance that does not ionize inwater solution. Compare ELECTROLYTE.nonelectronic meter A meter that uses no electronicdevices (such as transistors, liquid crystals,light-emitting diodes, or integrated circuits).Also called conventional meter.nonequivalence operation See EXCLUSIVE-OROPERATION.nonerasable storage In digital-computer anddata-processing operations, storage media thatcannot be erased under ordinary circumstances.A common example is CD-ROM (compact-diskread-only memory).nonferrous metal A metal or alloy that does notcontain iron, and is not related to iron in thesense that it is not attracted to magnets.nonflammable Pertaining to a material that is resistantto burning.nonharmonic frequency A frequency that has nointegral numerical relationship to another frequencyof interest. Compare HARMONIC FRE-QUENCY.nonharmonic oscillations Parasitic oscillationsthat do not occur at the fundamental frequencynor at any harmonic frequency of an oscillator oramplifier in which they appear.Relative attenuation (dB)0204060FundamentalsignalNonharmonicoscillationsHarmonics0 2 4 6 8 10Relative frequencynonharmonic oscillations

nonillion • nonoscillating detector 481nonillion The number 10 30 , so called becausewhen written out, the number contains ninegroups of three zeros (following the first 1000).noninductive capacitor A wound capacitor inwhich the edges of one of the spiral windings areconnected together to minimize the inductance ofthe roll. Compare INDUCTIVE CAPACITOR.noninductive resistor A wirewound resistor constructedso that the magnetic field of the coil isself-canceling. Therefore, the inductance is practicallyeliminated.noninterlaced scanning In the display of a videoimage, the presentation of all the raster lines in asingle scan. It is commonly used in cathode-raytube(CRT) computer monitors. This process minimizes“jerkiness” in rapidly moving images.noninverting connection Connection to the noninvertinginput of a differential or operational amplifier.Also see NONINVERTING INPUT. CompareINVERTING CONNECTION.noninverting input In a differential or operationalamplifier, the input that provides an output signalin phase with the input. Compare INVERTINGINPUT.noninverting transponder In a communicationssatellite, a transponder in which the downlinkband is “rightside-up” in frequency relative to theuplink band. That is, the highest downlink frequencycorresponds to the highest uplink frequency,and the lowest downlink frequencycorresponds to the lowest uplink frequency.Compare INVERTING TRANSPONDER. Also seeDOWNLINK, TRANSPONDER, UPLINK.nonionic 1. Possessing none of the properties ofions. 2. Electrically neutral.nonionizing radiation Electromagnetic radiationthat does not cause ionization of gases under agiven set of conditions. Examples: radio signals,television signals, and visible light.nonlinear 1. Pertaining to components, circuits, ordevices in which the instantaneous output signalamplitude is not directly proportional to the instantaneousinput signal amplitude. The graph ofinstantaneous output versus instantaneous inputis a curve, not a straight line. Example:CLASS-C AMPLIFIER. 2. Pertaining to components,circuits, or devices in which a specifiedvalue is not directly proportional to some otherspecified value. Example: NONLINEAR CAPACI-TOR.nonlinear bridge See VOLTAGE-SENSITIVEBRIDGE.nonlinear capacitor A capacitor whose valuevaries nonlinearly with applied voltage. Also seeVOLTAGE-VARIABLE CAPACITOR, 1, 2.nonlinear coil See SATURABLE REACTOR.nonlinear dielectric A material (such as processedbarium-strontium titanate) whose dielectricconstant varies with applied voltage.nonlinear distortion Distortion caused by nonlinearresponse of an amplifier or component. Thiscauses different parts of the signal to be amplifiedor transmitted by different amounts; therefore,the amplitude variations in the output signal differfrom those in the input signal.nonlinear inductor See SATURABLE REACTOR.nonlinearity 1. The condition of being NONLIN-EAR. In an amplifier, this means that the outputsignal is not a faithful reproduction of the inputsignal, and distortion occurs. 2. A measure of theextent to which a circuit is nonlinear. Expressedas a percentage of peak-to-peak full-scale output,the maximum extent to which the output differsfrom a perfect reproduction of the input.nonlinearity error An error in received signals resultingfrom nonlinearity in one or more of thestages in the communications circuit.nonlinear mixing The mixing of signals as a resultof the nonlinear response of a device (such as asemiconductor diode operated in its square-lawregion) through which they are passed simultaneously.Also see MIXER and MIXING.nonlinear network A circuit that produces distortionin an input waveform; the output and inputwaves are not related by a linear function.nonlinear quantizing A method of signal quantizingin which the intervals are not all the same sizeor duration.nonlinear resistor A resistor whose valuevaries with applied voltage. Also see VOLTAGE-DEPENDENT RESISTOR.nonlinear response Any response for which thecorresponding plot is not a straight line; doublingthe independent variable, for example, does notdouble the dependent variable.nonloaded Q See UNLOADED Q.nonmagnetic 1. Possessing no magnetism. 2. Incapableof being magnetized.nonmathematical Pertaining to materials andmethods that rely upon physical description andqualitative procedures instead of mathematicaldevelopment, prediction, and quantitative procedures.nonmetalAn elemental material devoid of the propertiesexhibited by metals (e.g., luster, good ductility,electrical conductivity, heat conductivity, andmalleability). Examples: carbon, phosphorus, sulfur.Compare METAL and METALLOID.nonmetallic conduction Collectively, ionic conductionin liquids and gases, conduction indielectrics by small leakage currents, andthermionic conduction in a vacuum.nonmicrophonic Without microphonic properties,e.g., a nonmicrophonic integrated circuit does notproduce electrical ringing when physically struck.nonnumeric character A character that is not anumeral, i.e., a symbol or letter.nonohmic response 1. Nonlinear resistance or reactance.Compare OHMIC RESPONSE. 2. SeeNEGATIVE RESISTANCE.nonoscillating detector A detector devoid of positivefeedback action and, therefore, unable to

482 nonoscillating detector • nonsynchronous vibratorgenerate a signal on its own. Compare OSCIL-LATING DETECTOR.nonplanar 1. Existing in three spatial dimensions.2. Pertaining to a circuit that cannot be fabricatedon a two-dimensional board without theuse of jumper wires.nonpolar 1. Having no pole(s). 2. Pertaining toatoms that share electrons to complete theirouter shells. 3. Not polarized nor requiring polarization.Example: a 100-pF disk ceramic capacitoris nonpolar because it can be used in circuitswithout consideration of voltage polarity.nonpolar crystal A crystal in which lattice pointsare identical.nonpolarized electrolytic capacitor An electrolyticcapacitor that has no definite negativeand positive terminals and, consequently, can beused in alternating-current circuits, as well as indirect-current circuits. See also NONPOLAR, 3.OxidefilmAnodesElectrolytepasteOxidefilmnonpolarized electrolytic capacitornonpolarized reactor A saturable reactor in whichthe lines of flux produced in the three-leg core bythe coils on the two outer legs oppose each otherin the center leg. When direct current (dc) ispassed through the coil on the center leg to saturatethe core, operation remains the same for eitherdc polarity. Compare POLARIZED REACTOR.nonpolarized relay See UNPOLARIZED RELAY.nonprint code In telegraphy, a code used to startteleprinter functions excluding printing.nonreactive circuit A circuit containing pure resistanceonly.nonrechargeable battery See NONCHARGEABLEBATTERY.nonrecurrent Pertaining to phenomena that donot repeat periodically. Thus, a single sweep in anoscilloscope is nonrecurrent.nonrecurrent sweep See NONREPETITIVE SWEEP.nonregenerative detector A detector having noregenerative feedback. Such a detector is stable,but relatively insensitive. Compare REGENERA-TIVE DETECTOR.nonregenerative receiver A radio receiver inwhich no local signal whatever is generated.nonrepetitive phenomena See NONRECURRENT.nonrepetitive sweep In an oscilloscope, a singlehorizontal sweep of the electron beam, initiatedeither by the operator or by the signal under observation.Also called SINGLE SWEEP. CompareRECURRENT SWEEP.nonreset timer A timer that must be reset manually.nonresident routine A computer routine not permanentlystored in memory. Compare RESIDENTROUTINE.nonresonant 1. Pertaining to a resonant circuit ordevice operated at some frequency other than oneof its resonant frequencies. Thus, reactance ispresent at the operating frequency. See RESO-NANCE. 2. Pertaining to a circuit or device thatexhibits pure resistance (without reactance) overa wide range of frequencies.nonresonant lines Transmission lines so dimensionedand operated that they do not resonate atthe operating frequency.nonresonant load An alternating-current loadthat is either purely resistive or is detuned fromthe fundamental and harmonic frequencies of thesource from which it is operated.nonreturn to zero In the magnetic recording ofdigital data, the system in which the current flowingin the write-head coil is sustained (i.e., doesnot return to zero) after the write pulse.nonsalient pole A nonprojecting (often flush) pole.Compare SALIENT POLE.nonsaturated color 1. Visible light that consists ofenergy at more than one wavelength. 2. A color thatcontains some white, in addition to the pure color.nonsaturated logic A logic circuit in which transistorsare prevented from saturating. This resultsin higher operating speed than SATURATEDLOGIC using the same transistors.nonshorting switch A multiple-throw switch thatdisconnects one circuit before completing another;that is, no two poles are ever connected simultaneously.nonsinusoidal waveform A waveform whose curvecannot be represented by the equation y = c sina(x + b), where a, b, and c are constants, y is thedependent variable (usually instantaneous amplitudeor frequency), and x is the independentvariable (usually time), for any real-number valuesof a, b, and c. Examples: BACK-TO-BACKSAWTOOTH, SAWTOOTH, and SQUARE WAVE.The COSINE WAVE is sinusoidal, being a SINEWAVE shifted in phase by 90 degrees.nonsymmetrical wave See ASYMMETRIC WAVE.nonsynchronous Unrelated in cyclic quality toother such qualities in the system.nonsynchronous network A communications networkin which the clocks are not all synchronized.nonsynchronous vibrator A power-supply vibratorthat is essentially a single-pole, double-throwswitch providing no mechanical rectification.A separate rectifier must be used. Compare

nonsynchronous vibrator • normal-mode rejection 483VIBRATOR-TYPE RECTIFIER. Also see VIBRA-TOR-TYPE POWER SUPPLY.nontechnical Pertaining to circuits, devices, systems,or phenomena described in lay terms, usingconcise graphics and little or no mathematics. Anexample is the simplified explanation of the operationof a spread-spectrum radio transmitter.nontonal components See NOISE, 3.nontrigger voltage For a thyristor, the maximumgate-to-cathode voltage that can be applied withouttriggering the device. The amplitude of interferentialsignals, including noise, must be belowthis level to prevent accidental triggering.nonuniform field An electric or magnetic fieldwhose intensity is not the same at all points.nonvolatile memory Memory whose data is retainedeven when power is removed for extendedperiods. This type of memory requires no backuppower source. The main advantage of this type ofmemory is the fact that the data is not lost in caseof a power interruption. Memory should not beconfused with storage. Magnetic, magnetooptical,or optical disks (including hard drives) arestorage media, not memory. Memory data can bestored and retrieved much faster than storagedata, because memory uses no mechanical parts.Also see RANDOM-ACCESS MEMORY, READ-ONLY MEMORY. Compare VOLATILE MEMORY.nonvolatile storage A computer storage mediumin which the data does not require a source ofpower to be retained. Examples: MAGNETICDISK, MAGNETIC TAPE, and COMPACT-DISKREAD-ONLY MEMORY.no-op instruction An instruction that commandsa computer to perform no operation, other thanto proceed to the following instruction.NOR circuit Also called NOT-OR CIRCUIT. In computerand control operations, a circuit that deliversa zero output signal, except when two or moreinput signals are zero. The NOR circuit functionis the inverse of that of the OR circuit.NOR gate A gate that performs the functions of aNOR circuit.norm The average or ambient condition.ABA0011B0101C1000NOR circuitCnormal 1. Pertaining to the most commonly observedset of conditions or parameters. 2. Standard.3. Perpendicular; oriented at right angles.4. Pertaining to a NORMAL DISTRIBUTION.5. Pertaining to a NORMAL SOLUTION. 6. Pertainingto an atom at its lowest energy state. SeeNORMAL STATE OF ATOM.normal curve See BELL-SHAPED CURVE.normal distribution In a statistical evaluation, aprobability distribution represented by the socalledbell-shaped curve. The maximum probabilityoccurs at the 50-percent value.normal-distribution curve See BELL-SHAPEDCURVE.normal electrode A standard electrode used inelectrode-potential measurements.normal fault An unintended path between the hotterminal of a load and ground.normal fault plus grounded neutral fault A combinationof NORMAL FAULT and GROUNDEDNEUTRAL FAULT.normal glow discharge In a glow-discharge tube,the discharge region between the Townsend dischargeand the abnormal glow in which currentincreases sharply, but a constant voltage drop ismaintained across the tube.normal impedance A transducer’s input impedancewhen the load impedance is zero.normal induction curve A saturation curve for amagnetic material. Also see BOX-SHAPED LOOPand SATURABLE REACTOR.normalize In computer programming, to use floating-pointnumbers to modify the fixed-point partof a number so that it is within a desired range.normalized admittance The quantity 1/Z n , whereZ n is NORMALIZED IMPEDANCE.normalized frequency The unitless number representedby the ratio f/f r , where f r is a reference frequencyand f is a frequency of interest. Responseplots are sometimes conveniently drawn on thebasis of normalized frequency, the reference (orresonant) frequency being indicated as 1, twicethe reference frequency as 2, etc.normalized impedance A value of impedance dividedby the characteristic impedance of a waveguide.normally closed Abbreviation, NC. Pertaining to aswitch or relay whose contacts are closed whenthe device is at rest. Compare NORMALLY OPEN.normally open Abbreviation, NO. Pertaining to aswitch or relay whose contacts are open when thedevice is at rest. Compare NORMALLY CLOSED.normal mode Pertaining to a device or system operatedin its usual or most common manner.normal mode A state of acoustic resonance in anenclosure, such as a speaker cabinet or a room.normal-mode rejection Abbreviation, NMR. In adigital direct-current voltmeter, the level of noiseon the applied voltage that will be rejected by theinstrument. Compare COMMON-MODE REJEC-TION.

484 normal position • notch sweepnormal position In a switch or relay, the state ofthe contacts when the device is at rest.normal solution A solution, such as an electrolyte,in which the amount of dissolved material ischemically equivalent to 1 gram-atomic weightof hydrogen per liter of the solution. CompareMOLAR SOLUTION.normal state of atom The condition in which anatom is at its lowest energy level. For the hydrogenatom, for example, the state in which theelectron is in the lowest-energy orbit.normal-through A feature in an audio PATCH BAYor PATCH PANEL that connects two sockets bydefault. The top socket and the one immediatelybelow it are connected, even when a patch cord isnot plugged into either of them.northern lights See AURORA.north magnetic pole The north pole of the equivalentbar magnet constituted by the EARTH’SMAGNETIC FIELD. The north magnetic pole liesclose to the geographic north pole. CompareSOUTH MAGNETIC POLE.north pole 1. See NORTH MAGNETIC POLE.2. The earth’s geographic north pole. 3. SeeNORTH-SEEKING POLE.north-seeking pole Symbol, N. The so-callednorth pole of a magnet. When the magnet is suspendedhorizontally, this pole points in the directionof the earth’s north magnetic pole. CompareSOUTH-SEEKING POLE.Norton’s equivalent An equivalent circuit basedon NORTON’S THEOREM, replacing a Theveninequivalent for a current-actuated device, such asa bipolar transistor. Also see THEVENIN’S THEO-REM.Norton’s theorem With reference to a particularset of terminals, any network containing anynumber of generators and any number of constantimpedances can be simplified to one constant-currentgenerator and one impedance. Theequivalent circuit will deliver to a given load thesame current that would flow if the outputterminals of the original circuit where shortcircuited.Compare COMPENSATION THEOREM,MAXIMUM POWER TRANSFER THEOREM,RECIPROCITY THEOREM, SUPERPOSITIONTHEOREM, and THEVENIN’S THEOREM.NOT In binary logic, an operation that changeshigh to low and vice versa. Also see NAND CIR-CUIT, NOR CIRCUIT, NOR GATE, NOT CIRCUIT,and NOT-OR CIRCUIT.NOT-AND circuit See NAND CIRCUIT.notation The way that numbers, quantities, or formulasare represented (e.g., binary notation, Polishnotation, and scientific notation).notch A dip in frequency response, typical of aband-suppression (band-elimination) filter orother frequency-rejection circuit. ComparePEAK, 3.notch amplifier An amplifier containing a notchfilter or other arrangement that permits it to re-Attenuation, dB010203040200 800 1400Audio frequency, Hznotchject one frequency or a given band of frequencieswhile passing all higher and lower frequencies.notch antenna An antenna with a slot in the radiatingsurface, for the purpose of obtaining a directionalresponse.notcher See NOTCH FILTER.notcher-peaker A circuit or device that can be setto perform either as a NOTCH FILTER or PEAKFILTER.notch filter A circuit that exhibits high attenuationat and near a single frequency and little or noattenuation at all other frequencies. This type ofdevice is used in some radio communications receivers,and can reduce interference caused bystrong, unmodulated carriers within the passband.The notch frequency is adjustable, so thatthe deep null can be tuned to any frequencywithin the receiver passband. A properly designedcircuit can produce attenuation in excessof 40 dB in the center of the notch. Some sophisticatedtypes, especially audio designs, can providemore than 60 dB of attenuation at the notchfrequency. Audio notch filters employ operationalamplifiers with resistance-capacitance (RC) circuits.In some audio notch filters, the notchwidth (sharpness) and frequency are both adjustable.Compare BAND-REJECTION FILTER.notch gate In radar, a gate that determines theminimum and maximum range.notch sweep An oscilloscope sweep that expandsonly a small portion (notch) of the pattern on thescreen, leaving the portions on either side of thenotch untouched. Thus, the first dozen or so

notch sweep • n-type conduction 485cycles might appear at the normal sweep speed,the next two cycles expanded, and the remainingtwo or three at normal sweep speed.NOT circuit A logic circuit that provides an outputpulse when there is no input pulse, and viceversa. Also called COMPLEMENTER, NEGATOR,and INVERTER.note See BEAT NOTE.notebook computer A portable personal computer,also called a laptop computer. It is aboutthe size of a typical three-ring notebook, and generallycontains a DISKETTE DRIVE, a HARDDISK, a MODEM, and attachments for peripherals,such as printers. It uses rechargeable batteriesand can be operated for approximately two tosix hours between battery charges.NOT gate A digital circuit that inverts a logical condition—eitherfrom high (logic 1) to low (logic 0) orvice versa. Also called an inverter.NOT-OR circuit A logical OR CIRCUIT combinedwith a NOT CIRCUIT.novelty calculator See SPECIAL-PURPOSE CAL-CULATOR.November Phonetic alphabet code word for the letterN.novice 1. A beginner class of amateur radio license.2. Any beginner or inexperienced practitioner.no-voltage release In the starting box for a shuntmotor, the electromagnet that normally holds thearm in full-running position. It is connected directlyacross the power line to disconnect the motorin the event of power failure. When the arm isreleased, it falls to its off position, thereby preventingburnout that would result if the motorwere left connected to the line in the full-runningposition when power resumed. Compare NO-FIELD RELEASE.noys scale A scale of apparent acoustic noise,based on a linear function instead of the morecommon logarithmic function.Np 1. Symbol for NEPTUNIUM. 2. Abbreviation ofNEPER.N p Symbol for number of primary turns in a transformer.n-phase system A polyphase system having nphases.npin transistor A junction transistor having an intrinsiclayer between a p-type base and an n-typecollector. The emitter is a second n-type layer onthe other side of the base.N plant See NUCLEAR POWER PLANT.n-plus-one address instruction A computer programinstruction containing two addresses, oneof which specifies the location of an upcoming instructionto be executed.NPM Symbol for counts per minute.npnp device A semiconductor switching devicehaving three junctions. Examples: FOUR-LAYERDIODE, and SILICON-CONTROLLED RECTI-FIER. Also called pnpn device.npn transistor A bipolar transistor in which theemitter and collector layers are n-type semiconductormaterial, and the base layer is p-typesemiconductor material. Compare PNP TRAN-SISTOR.NP0 Abbreviation of NEGATIVE POSITIVE ZERO.NP0 capacitor A fixed capacitor exhibiting temperature-compensatingability over a wide temperaturerange, in which the coefficient has negative,positive, and zero values.NPS Symbol for counts per second.N radiation X rays emitted as a result of an electronbecoming an N electron.NRD Abbreviation of NEGATIVE-RESISTANCEDIODE.N region See N LAYER.NRZ Abbreviation of NONRETURN TO ZERO.N s Symbol for number of secondary turns in atransformer.ns Abbreviation of NANOSECOND.N scan See N DISPLAY.N scope Colloquialism for a radar set using an NDISPLAY.nsec Alternate abbreviation of NANOSECOND.Ns/m 2 Newton-seconds per meter squared, theunit of dynamic viscosity.n-space A coordinate system in n variables. It isgenerally of mathematical interest. The coordinatesare written (x 1 , x 2 , x 3 , . . . ,x n ) and are calledordered n-tuples.NSPE Abbreviation of National Society of ProfessionalEngineers.NTC Abbreviation of NEGATIVE TEMPERATURECOEFFICIENT.nth harmonic An unspecified harmonic, having afrequency of n times the fundamental frequency,where n is some positive integer. Also see HAR-MONIC and HARMONIC FREQUENCY.nth term An unspecified term in a mathematicalsequence or series.NTP Abbreviation of NORMAL TEMPERATUREAND PRESSURE.NTSC Abbreviation of National Television StandardsCommittee.NTSC color signal The color-television signal specifiedby the National Television Systems Committee.In the signal, the phase of a 3.58-MHz signalvaries with the instantaneous hue of the transmittedcolor, and the amplitude varies with theinstantaneous saturation of the color.NTSC triangle On a chromaticity diagram, a trianglewhose sides encompass the range of colorsobtainable from the additive primaries.NTSC-type generator A special radio-frequencysignal generator for color-television tests. It providesseparate, individually selected color barsthat are fully saturated. The signals are strictly inaccordance with NTSC standards.n-type conduction In a semiconductor, currentflow consisting of electron movement. CompareP-TYPE CONDUCTION.

486 n-type material • null detectorn-type material Semiconductor material that hasbeen doped with a donor-type impurity and, consequently,conducts a current via electrons. Germanium,for example, when doped with arsenic,becomes n-type. Compare P-TYPE MATERIAL.n-type semiconductor See N-TYPE MATERIAL.nuclear battery See ATOMIC BATTERY.nuclear bombardment In nucleonics, the bombardingof the nucleus of an atom with subatomicparticles, usually neutrons.nuclear charge The net positive charge of the nucleusof an atom.nuclear clock A chronometer based on the rate ofdisintegration of a radioactive material.nuclear energy Energy resulting from the splittingof the nucleus of an atom or from the fusion ofnuclei. Also see ATOMIC ENERGY, ATOMICPOWER, NUCLEAR FISSION, NUCLEAR FUSION,NUCLEAR REACTOR, and NUCLEUS.nuclear fission A nuclear reaction resulting fromthe bombardment of nuclei in the atoms of certainradioactive materials. The bombardmentwith neutrons creates two new nuclei (by splitting)and several new neutrons that split severalother nuclei, producing still more nuclei and neutrons,etc. The result is a chain reaction that canlead to a violent explosion if not checked. CompareNUCLEAR FUSION.nuclear force A strong attraction that holds togetherpairs of nucleons in an atomic nucleus.This prevents an electric charge of protons fromdriving the nucleus apart. Nuclear force acts onlyover very minute distances. At greater distances,electrostatic repulsion is stronger.nuclear fusion A nuclear reaction resulting fromthe violent collision of the nuclei of the atoms of ahydrogen isotope (such as deuterium) at extremelyhigh temperature. The process producesmore energy than does NUCLEAR FISSION, andleaves no hazardous radioactive waste.nuclear magnetic resonance An atomic phenomenonin which a particle, such as a proton, ina steady magnetic field “flips over” when an alternatingmagnetic field is applied perpendicular tothe steady field.nuclear magnetic resonance imaging Abbreviation,NMRI. The use of NUCLEAR MAGNETICRESONANCE effects to produce a picture of internalbody organs. Using computers, threedimensionalrenditions can be generated. It isuseful in medicine as a diagnostic aid.nuclear medicine A branch of medicine involvingthe use of radioactive isotopes in diagnosing andtreating disease. A radioactive isotope is putinside the body and it tends to accumulate incertain areas. Abnormal concentration ofradioisotopes might indicate abnormal body activityin a certain area.nuclear pile See NUCLEAR REACTOR.nuclear power plant A power-generating plant usinga NUCLEAR REACTOR.nuclear reaction 1. A reaction in which a heavyatomic nucleus is split into two or more lighter nuclei,with an accompanying release of radiant energy.Also called NUCLEAR FISSION. 2. A reactionin which two or more light nuclei combine to forma heavier nucleus, accompanied by the release ofradiant energy. Also called NUCLEAR FUSION.nuclear reactor 1. A device in which nuclear fissioncan be initiated and controlled. At the centerof the reactor is a core of nuclear fuel, such as afissionable isotope of uranium. The core is surroundedby a graphite moderator jacket that is, inturn, surrounded by a coolant jacket; the wholeis surrounded by a thick concrete shield. Neutron-absorbingrods are inserted through variouswalls to different depths in the fuel to control thereaction. Also called atomic pile. 2. A controllednuclear fusion device, not yet perfected, but underdevelopment. It would provide all the benefitsof an atomic pile (fission reactor), but would bemore efficient and would not produce hazardousradioactive waste.nuclear recoil An observable vibration of anatomic nucleus when it disintegrates.nuclear resonance The condition wherein a nucleusabsorbs a gamma ray emitted by an identicalnucleus.nuclear service robot A remotely controlled (teleoperated)robot used for general work in environmentswhere the level of radioactivity is too highfor humans (e.g., the maintenance of a nuclearreactor). It could also be used, if necessary, forsuch tasks as disarming nuclear warheads andcleaning up after a nuclear accident.nucleon A proton or neutron in the nucleus of anatom.nucleonics The branch of physics concerned withnucleons and nuclear phenomena. The name isan acronym for nuclear electronics.nucleon number See MASS NUMBER.nucleus The center or core of an atom. Containsneutrons, protons, and other particles. The netelectric charge of the nucleus is positive, and isequal to the sum of the negative charges of the orbitalelectrons of the atom.null 1. The condition of zero output current or voltageresulting from adjusting or balancing a circuit,such as a bridge. 2. A local minimum in aninterference pattern or directivity pattern.null balance In potentiometric-measuring circuitsfor comparing one voltage to another, the balancecondition in which no current flows through thegalvanometer.null current In potentiometric-measuring circuitsfor comparing one voltage to another, the galvanometercurrent remaining at null when thenull point is not fully zero.null detection Direction finding by means of anantenna with a bidirectional or unidirectionalnull response.null detector See BRIDGE DETECTOR.

null frequency • N zone 487nucleusNucleusElectronshellsnull frequency The frequency at which a frequency-sensitivecircuit, such as a Wien bridge ortwin-tee network, can be balanced.null meter See BRIDGE DETECTOR.null method See ZERO METHOD.null point In a balanced circuit, such as a bridgeor potentiometer, the point of zero output voltage(or current) or minimum output voltage (or current).null potentiometer 1. The variable resistor thatconstitutes one arm of a four-arm bridge and isused to balance the bridge. 2. A potentiometriccircuit using the null method to compare one voltagewith another. Also see POTENTIOMETER, 2.null setting 1. The setting of a bridge circuit orother null device that balances the circuit. 2. Theelectrical zero setting of an electronic voltmeter.null voltage 1. In a conventional bridge, the outputvoltage remaining when the bridge is set forits best null. 2. For a voltage-sensitive bridge, theinput voltage that will produce zero output voltage.number The mathematical representation of aquantity. It is generally used in electronics to denotecoefficients, magnitudes, component values,frequencies, etc.number cruncher A computer with great computationalpower, but one not necessarily able toprocess large amounts of data (such as payroll information).number system A systematic sequence of numbersbased on a radix and a logical arrangement.See, for example, BINARY NUMBER SYSTEM andDECIMAL NUMBER SYSTEM.numeral A member of a digit set in a number system.numerical analysis A mathematical approach tosolving problems numerically, including findingthe limits of error in the results.numerical code A code having a character set restrictedto digits.numerical control A method of programmingcomputer-controlled mechanical devices, used insome early robots. An automated system in whichnumber sequences fed to a digital computercause it to control machines or processes in amanufacturing operation.nV Abbreviation of NANOVOLT.nW Abbreviation of NANOWATT.nybble A piece of digital information that is largerthan a bit and smaller than a byte. CompareGULP.Nylon The trade name for a synthetic fiber-formingpolyamide, useful for electrical insulation.Nyquist criterion of stability With reference to aNYQUIST DIAGRAM for a feedback amplifier, theamplifier is stable if the polar plot of loop amplificationfor all frequencies from zero to infinity is aclosed curve that neither passes through nor enclosesthe point 1 + j0.Nyquist diagram A graph of the performance of areactive feedback system (such as a degenerativeamplifier) that depicts the variation of amplitudeand phase of the feedback factor with frequency.The plot is polar and accounts for the real andimaginary components.(Imaginary)jyNyquist diagramPhasex (Real)Nyquist noise rule The power dissipated in a resistorbecause of thermal noise at a given frequency.The derivative of frequency, with respectto power, is equal to the absolute temperaturetimes the Boltzmann constant.N zone See N LAYER.

O 1. Symbol for OXYGEN. 2. Abbreviation of OUT-PUT.o 1. Symbol for OUTPUT. (Also, OUT; both are usedas subscripts.) 2. Symbol for ORIGIN.O 2 Symbol for OXYGEN.O 3 Symbol for OZONE.OAT Abbreviation of OPERATING AMBIENT TEM-PERATURE.object code 1. In a computer system, the machinelanguageoutput of the compiler, directedto the computer. 2. In a computer, the high-leveloutput of the compiler, directed to the operator.3. The assembly language, directed to the compilerfor translation between machine languageand high-level language and vice versa.object language The computer language that acompiler derives from a high-level (source) language(such as C++, LISP, etc.); it is usually machinelanguage, but it can be an intermediatecode that requires further conversion.object-oriented graphics Also called vector graphics.In computer graphics, the use of equations torepresent curves in a coordinate plane to defineshapes, rather than defining the shapes pixel-bypixel.object-oriented language A computer programthat uses on-screen objects, called icons, to representcommands. A movable device, such as amouse or trackball, is used to move an arrow orother pointer to the icon; then a button is pressedto carry out the function indicated by the icon.object-oriented programming Abbreviation, OOP.A computer programming language that buildssophisticated programs from basic programscalled modules.object program A machine or high-level languageversion of a user’s computer program, as producedby a compiler.object recognition In robotic systems, anymethod used to identify specific objects, accordingto characteristics, such as shape, texture,weight, etc. Common schemes use bar-code labelsand machine vision. More-complex methodsmake use of pattern-recognition programs.oblique-incidence transmission Transmission ofradio signals via ionospheric reflection.oblique mode In acoustics, a resonance within aroom that involves all four walls, the floor, andthe ceiling.oboe A system of radar navigation in which a pairof ground stations measures the distance to anairborne transponder beacon and then transmitsthe information to the aircraft.obsolescence-free Pertaining to a design or processthat is not likely to become obsolete in thenear future. Compare OBSOLESCENCE-PRONE.obsolescence-prone Pertaining to a design or processsubject to being soon outdated. CompareOBSOLESCENCE-FREE.OBWO Abbreviation of O-TYPE BACKWARD-WAVEOSCILLATOR.o/c Abbreviation of OPEN CIRCUIT.occluded gas Gas that has been absorbed or adsorbedby solid material, such as glass or metals,and that must be eliminated during the evacuationof an electronic device, such as a vacuumtube. Also see OUTGASSING.occultation 1. The passage of the moon or otherplanetary body in front of a more distant celestialobject, resulting in the cutting off of electromag-Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

occultation • odometry 489netic radiation from that object. 2. The eclipsingof one object by another.occupied band A frequency band used by at leastone transmitting station regularly.occupied bandwidth For a given emission, thecontinuous band of frequencies (f 2 f 1 ) for whichthe mean (average) radiated power above f 2 andbelow f 1 is 0.5 percent of the total mean radiatedpower.occupied orbit In an atom, an orbit in which anelectron is present.Ocean Phonetic alphabet code word for the letter O.OCR Abbreviation of OPTICAL CHARACTER REC-OGNITION.oct Abbreviation of OCTAL.octal Abbreviation, oct. Based on the number eight.See, for example, OCTAL NUMBER SYSTEM.octal digit One of the figures in the group 0through 7 used in the OCTAL NUMBER SYSTEM.octal notation See OCTAL NUMBER SYSTEM.octal number system The base-eight system ofnumber notation. It uses digits 0 through 7.Compare BINARY NUMBER SYSTEM and DECI-MAL NUMBER SYSTEM. The octal system is oftenused as shorthand for otherwise-cumbersome binarynumbers. The binary number is separatedinto groups of three digits from right to left; eachsuch group is then converted into its decimalequivalent, with the result being the octal form ofthe binary number [e.g., binary 111 001 011 = octal713 (111 = decimal 7; 001 = decimal 1; and011 = decimal 3)].Decimal Octal0 01 12 23 34 45 56 67 78 109 1110 1211 1312 1413 1514 1615 1716 20octal number systemoctal-to-decimal conversion Conversion of numbersin the octal number system to numbers inthe more-familiar decimal number system.This is done by expressing the octal number seriallyin powers of eight. Thus, octal 12 = (1 × 8 1 ) +(2 × 8 0 ) = 8 + 2 = decimal 10.octant One-eighth of a circle; therefore, 45 degrees,or 0.5 quadrant.octave 1. The range of frequencies between a givenfrequency ( f ) and twice that frequency (2f ).2. The range of frequencies between a given frequency( f ) and half that frequency ( f/2).octave band A band of frequencies one octave wide(see OCTAVE).octave-band noise analyzer A noise analyzer havingbandpass-filter channels whose center frequenciesare one octave apart.octave-band pressure level Sound pressure levelwithin an OCTAVE BAND.octave pressure level See OCTAVE-BAND PRES-SURE LEVEL.OCTL Abbreviation of OPEN-CIRCUITED TRANS-MISSION LINE.octonary signal An eight-level signaling code.octonary system See OCTAL NUMBER SYSTEM.OD Abbreviation of OUTSIDE DIAMETER.odd-even check A method of checking the integrityof data transferred in a computer system, in whicheach word carries an extra digit to show whetherthe sum of ones in the word is odd or even.odd harmonic In a complex waveform, a harmonicthat is an odd-numbered multiple of the fundamentalfrequency (e.g., third harmonic, fifth harmonic,etc.). Compare EVEN HARMONIC.odd-harmonic intensification In a complex waveform,emphasis of the amplitude of odd harmonics,with respect to that of even harmonics, aproperty of some multivibrators and nonsinusoidalwaves.odd line In a conventional television picture, oneof the 262.5 odd-numbered horizontal linesscanned by the electron beam in developing theodd-line field. Compare EVEN LINE.odd-line field On a conventional television screen,the complete field obtained when the electronbeam has traced all the odd-numbered lines.Compare EVEN-LINE FIELD.odd-line interlace See ODD-LINE FIELD.odd parity check A computer check for an oddnumber of ones or zeros in digital data.Odex Trade name for a series of autonomousrobots developed by Odetics, Inc. They use legsfor locomotion. Noted for their ability to maneuverin places that most robots cannot reach.odograph An electromechanical or electronic plotterthat traces the path of a vehicle on a map, oron the image of a map as portrayed on a displayscreen.odometer An electromechanical device that indicatesthe speed of, and distance covered by, amoving vehicle or robot. Some such devices give aconstant position indication, via mathematicalintegration of the measured velocity (speed anddirection), relative to time. It can function in one,two, or three dimensions.odometry A method of speed, velocity, and/or positionsensing. It is commonly used in mobile

490 odometry • ohmic contactvehicles and mobile robots. The mostsophisticatedsystems give a constant indicationof position on the basis of a starting point (origin)and mathematical integration of the velocity(speed and direction), with respect to time. It canfunction in one, two, or three dimensions.Oe Symbol for OERSTED.oersted Symbol, Oe. The cgs unit of magnetic fieldintensity; 1 Oe = 79.58 A/m. Formerly the unit ofreluctance.off-air alarm A device that gives a visible or audibleindication when the carrier of a transmitter islost. In its most rudimentary form, the deviceconsists of a radio-frequency relay that actuatesa bell, buzzer, horn, or lamp.off-center display A radar display whose centerpoint does not correspond to the location of theantenna.off-center-fed antenna An antenna in which afeeder is attached to one side of the center pointof the radiator. See, for example, WINDOM AN-TENNA.off-center feed The connection of a feed line to anantenna radiator at some point other than thephysical center of the radiator.λ/4 3λ/4off-center feedoff delay The interval during which a circuit remainson after the control signal has beenswitched off. Compare ON DELAY.off-ground 1. An above- or below-ground operatingvoltage. 2. The ground return for a voltage, as definedin 1, not common with the system ground.offhook In a telephone system, the condition inwhich the receiver is removed from its receptacle,or in which the line is otherwise engaged (e.g., afax machine or modem is in use).off isolation A measure of the extent to which anopen switch isolates the output from the input,specified as the output voltage divided by the inputvoltage. For percentage, multiply this quantityby 100. The ideal value is zero (or zeropercent).off-limit In a stepping relay, a condition in whichthe armature has gone past the limit of its travel.offline 1. In a computer installation, equipmentthat is not controlled by the central processor.2. In computers and data processing, operationsthat are not under the direct real-time control ofa central processor. 3. A computer memory facilityor device not connected to a central processor.4. In personal computing, the use of a computerby itself (i.e., not connected in a network). CompareONLINE.offline editing In video production, a process inwhich copies are made of the original recording;these copies are edited in a trial-and-errorscheme to develop the final presentation. CompareONLINE EDITING.offloadingThe use of computers and/or robots toperform repetitive, mundane tasks, leaving peoplefree to do more interesting things. Example: apersonal robot that mows the lawn.off-on operation See ON-OFF OPERATION.off period 1. The interval during which an on-offcircuit or device is off. 2. The time during whichan equipment is shut down.offset An imbalance between the halves of a normallysymmetrical circuit, such as that of a differentialamplifier. Also see OFFSET CURRENTand OFFSET VOLTAGE.offset adjustment range The change in offset voltage,in millivolts or in microvolts, that can be affectedby means of the external offset adjustmentcircuit(s).offset current For an operational amplifier, the inputcurrent when the offset voltage is zero.offset voltage For an operational amplifier, theparticular value of direct-current bias voltage requiredat the input to produce zero output voltage.off state1. The condition of an on-off circuit or device,such as a flip-flop, that is off. Compare ONSTATE, 1. 2. The condition in which a circuit ordevice is shut down. Compare ON STATE, 2.off-state voltage The voltage drop across a semiconductordevice, such as a diode, rectifier, orthyristor, when the device is in its normal off(nonconducting) state. Compare ON-STATEVOLTAGE.off-target jamming In radio or radar jamming, theuse of a remote jamming transmitter that will notbetray the location of the base station.off time The period during which no useful work isbeing performed, as of equipment when it is notfunctioning because of a circuit breakdown.OGL Abbreviation of OUTGOING LINE.OGO Abbreviation of orbiting geophysical observatory.ohm Symbol, ´Ω. The basic unit of resistance, reactance,or impedance. A resistance of 1 ohmpasses a current of 1 ampere in response to anapplied emf of 1 volt.ohmage Electrical resistance or resistivity expressedin ohms.ohm-centimeter A unit of volume resistivity (seeRESISTIVITY): the resistance of a centimetercube of the material under measurement. Alsosee MICROHM-CENTIMETER.ohmic component A resistive or reactive circuit ordevice exhibiting an OHMIC RESPONSE.ohmic contact A usually very-low-resistance connectionbetween two materials that provides

ohmic contact • oil diffusion pump 491bilateral linear conduction. It exhibits none of theproperties of a rectifying junction or a nonlinearresistance.ohmic heating 1. Heating caused by current passingthrough a resistive material (i.e., I 2R losses inthe material). 2. In an electric field, heat generatedby charged particles when they collide withother particles.ohmic loss Loss resulting from the direct-currentresistance in a circuit or transmission line.ohmic region The portion of the response curve ofa negative-resistance device that exhibits positive(ohmic) resistance. The E-I curve of a tunneldiode, for example, has two such positivesloperegions with a negative-slope (negativeresistance)region between them.ZeroadjustVoltmetermARangeswitch+ −UnknownresistanceohmmeterCurrent0OhmicregionNonohmic(negative-resistance)regionOhmicregionVoltageohmic regionohmic resistance A resistance exhibiting OHMICRESPONSE.ohmic response Response that follows OHM’SLAW: I = E/R. In strictly ohmic devices, neitherresistance nor reactance changes with current orvoltage. Compare NONOHMIC RESPONSE.ohmic value Electrical resistance expressed inohms, or in multiples or fractions of ohms (kilohms,megohms, milliohms, etc.)ohmmeter An instrument for the direct measurementof electrical resistance. It usually consistsof a milliammeter or microammeter, a battery,and several switchable resistors having very closetolerances. The scale is calibrated in ohms; theswitch selects multiplier factors (e.g., ×100,×10,000, ×1,000,000). The scale is usually reversed(i.e., 0 is at the extreme right and “infinity”is at the extreme left).ohmmeter zero 1. The condition of proper adjustmentof an ohmmeter, indicating zero resistancefor a direct short circuit. 2. The potentiometer, orother control, used for adjusting an ohmmeter toobtain a reading of zero with a short circuit.ohm-mile A rating meaning 1 mile of wire having aresistance of 1 ohm.ohms adjust The rheostat or potentiometer used toset the pointer of an ohmmeter before it is used totake resistance readings.Ohm’s law The statement of the relationshipamong current, voltage, and resistance. In adirect-current circuit, current varies directlywith voltage and inversely with resistance: I = E/R,where I is the current in amperes, E is the voltagein volts, and R is the resistance in ohms. Foralternating current, Ohm’s law states that I =E/X = E/Z, where X is reactance and Z isimpedance.ohms per square The resistance (in ohms) betweentwo parallel edges of a square of thin-film resistancematerial.ohms-per-volt A specification that indicates thesensitivity and impedance of a voltmeter. In general,the higher the rating, the better. When measuringvoltage in high-impedance circuits, therating should be as high as possible. Field-effecttransistor(FET) voltmeters and vacuum-tubevoltmeters have the highest ratings.oil-burner control An electronic system for startingand stopping the operation of an oil burner toprevent puffback and to interrupt the supplywhen the flame becomes erratic.oil calorimeter A calorimeter used to measurepower in terms of the rise in temperature of oilheated by the electrical energy of interest.oil capacitor A capacitor impregnated or filledwith oil, such as high-grade castor or mineral oil.Also see OIL DIELECTRIC.oil circuit breaker A circuit breaker filled with ahigh-grade insulating oil for cooling and arc elimination.oil-cooled transformer A heavy-duty transformer,through which oil is circulated for heat removaland arc prevention.oil dielectric A highly refined oil used as an electricalinsulating material (e.g., between the platesof a capacitor). Familiar examples are castor oil,mineral oil, and the synthetic oil chlorinateddiphenyl.oil diffusion pump See OIL PUMP.

492 oiled paper • one-lungeroiled paper Insulating paper impregnated with oilfor waterproofing and to increase its dielectricstrength.oil-filled cable A cable whose insulation is impregnatedwith oil that can be maintained at a constantpressure.oil-filled capacitor See OIL CAPACITOR.oil-filled circuit breaker See OIL CIRCUITBREAKER.oil-filled transformer A transformer whose case isfilled with an insulating oil.oil fuse cutout A fuse cutout that is filled with aninsulating oil. Compare OPEN-FUSE CUTOUT.oil-immersed transformer See OIL-FILLED TRANS-FORMER.oil-impregnated capacitor See OIL CAPACITOR.oil pump A vacuum diffusion pump using oil insteadof mercury. Also see DIFFUSION PUMP.oil switch A switch enveloped by insulating oil.OLRT Abbreviation of online real time (operation).OM Amateur radio jargon for OLD MAN: chief(male) operator, or husband of female operator.omega A phase-dependent radionavigation systemusing single-frequency, time-shared, ICW transmissionsfrom two or more locations.omnibearing A navigational bearing obtained bymeans of OMNIRANGE.omnibearing converter An electromechanical devicein which an OMNIRANGE signal and vehicleheading information are combined, the outputbeing a signal that is fed to a meter.omnibearing indicator Abbreviation, OBI. An omnibearingconverter with a dial and pointer.omnibearing line In an OMNIRANGE system, oneof the imaginary lines extending from the geographiccenter of the omnirange.omnibearing selector A device that can be setmanually to a selected omnibearing.omniconstant calculator A calculator that addsor multiplies numbers in succession in such amanner as to arithmetically or geometrically increasethe exponent as a single button is repeatedlypressed.omnidirectional 1. Pertaining to a device thatresponds equally well to acoustic or electromagneticenergy from any direction in threedimensions. 2. Pertaining to a device that radiatesacoustic or electromagnetic energy equallywell in any direction in three dimensions. 3. Also,NONDIRECTIONAL. Pertaining to an antennathat intercepts or radiates equally well in any azimuth(horizontal) direction.omnidirectional antenna See NONDIRECTIONALANTENNA.omnidirectional hydrophone A hydrophone thatpicks up underwater sounds coming from any direction.omnidirectional microphone A microphone thatpicks up sounds coming from any direction.omnidirectional radio range See OMNIRANGE.omnidirectional range See OMNIRANGE.omnidirectional range station Abbreviation,ORS. A radionavigation station for OMNIRANGEservice.omnigraph A Morse-code generator that operatesvia marked or perforated paper tape.omnirange A radionavigation system in whicheach station in a chain broadcasts a beam in alldirections. It usually operates at very-high frequencies(VHF) or ultra-high frequencies (UHF).Pilots of aircraft home on a particular station bytuning it in and noting its bearings.OMR Abbreviation for OPTICAL MARK RECOGNI-TION.on air See ON THE AIR.on-call channel An assigned radio channel ofwhich exclusive, full time use is not demanded.on-course curvature In navigation, the rate atwhich the course of a vehicle deviates with referenceto the distance along the true course.on-course signal A single-tone-modulated signalindicating to an aircraft pilot following a radiobeam that the flight is substantially on course.on current See ON-STATE CURRENT.on delay An interval during which a circuit remainsoff after an actuating signal has been supplied.Compare OFF DELAY.on-demand system A system, especially in computerand data-processing operations, that deliversinformation or service immediately uponrequest.ondograph An electromechanical device thatgraphically draws alternating-current waveformson paper.ondoscopeA radio-frequency (RF) energy detectorthat consists of a neon bulb attached to the endof an insulating rod. When a bulb is held in an intenseRF field, the field energy ionizes the gas inthe bulb, causing it to glow without direct connectionto the RF circuit.one-address code In computer programming, acode in which the address in an instruction refersto only one memory location.one condition See ONE STATE.one-digit adder See HALF ADDER.one-element rotary antenna A directional antennaconsisting of a radiator only (no directorsor reflectors) that can be rotated. A straight, rigid,half-wave rotatable dipole is the most commonconfiguration.one-for-one compiler A compiler that generatesone machine language instruction from onesource language instruction.one-input terminal In a flip-flop, the input terminalthat must be energized to switch the circuit toits logic 1 output.one-level address See ABSOLUTE ADDRESS.one-level subroutine In a computer program, asubroutine in which no reference is made to othersubroutines.one-lunger Colloquialism for a radio transmitterconsisting entirely of a one-transistor oscillator.

one output • on-state current 493one output See ONE STATE.one-output signal The signal that results fromreading a computer memory unit that is in thelogic 1 state.one-output terminal In a flip-flop, the output terminalthat is energized when the circuit is in itslogic 1 state.one-plus-one address A method of computer programmingin which instructions contain two addressesand an operation, the addresses referringto the location of the next instruction and the locationof the data to be used.ones complement Binary notation in the radixminus-one-complementform.one shot See MONOSTABLE MULTIVIBRATOR.one-shot circuit See MONOSTABLE MULTIVI-BRATOR.one-shot multivibrator See MONOSTABLE MUL-TIVIBRATOR.one-sided wave A waveform consisting of only negativeor positive half-cycles. Example: a rectifiedalternating-current signal.one state Also, logic 1 state. The high, on, or truelogic state of a bistable device, such as a flip-flop.Compare ZERO STATE. In binary notation, theone state is represented by the digit 1.one-third-octave band A frequency band that is 1 ⁄3octave wide; that is, the difference betweenthe upper-frequency limit (f 2 ) and the lowerfrequencylimit (f 1 ) is one-third of an octave. Alsosee OCTAVE BAND.one-to-one assembler An assembler computerprogram that produces a machine language instructionas a result of translating a sourcelanguagestatement.one-to-one correspondence A mapping betweentwo sets A and B so that every element in set Ahas exactly one correspondent in B, and every elementin B has exactly one correspondent in A.O network A four-impedance network containingtwo series (upper and lower) arms and two shunt(input and output) arms.InputR SH1R S1R S2O networkR SH2Outputone-way communication 1. The transmission of amessage to one or more stations that receive only.Compare TWO-WAY COMMUNICATION. 2. SeeBROADCASTING.one-way conduction See UNILATERAL CONDUC-TIVITY.one-way radio See ONE-WAY COMMUNICATION.one-way repeater In wire telephony, a device thatamplifies and retransmits a signal in the directionthe signal was traveling when it arrived atthe repeater. Compare TWO-WAY REPEATER.one-way valve A diode or rectifier (British variation).on interval See ON TIME.online 1. Descriptive of equipment under the controlof a central processor. 2. Pertaining to operationsbeing controlled by a central processor.3. Relating to a computer storage device independentof a central processor. 4. In personal computing,the use of a computer in a network (e.g.,with a modem for operation on the Internet).Compare OFFLINE.online data reduction Processing data as it entersa computer system.online editing In video production, the final phaseof editing. The original recording (not copies) isused to prepare the presentation, based on thetrials that were performed using the copies. CompareOFFLINE EDITING.online service A computer network accessible viatelephone lines, television cable systems, and/orradio. It is generally available to owners of personalcomputers. It provides such services aselectronic mail, special-interest forums, news,weather, sports, shopping, and general information.on-off keying Keying, as in radiotelegraphy andwire telegraphy, by switching a signal source onand off to form dots and dashes or a binary code,rather than alternately changing the amplitude orfrequency of the signal.on-off operation A switching operation, especiallythat performed by nonmechanical (fully electronic)circuits.on-off ratio 1. For a circuit or device, the ratio ofoff time to on time. 2. For a pulse, the ratio ofpulse duration to the dead space between pulses.on-off switch 1. In electronic equipment, theswitch by which the equipment can be started orstopped. It can be, but is not necessarily, thepower-line or B-plus switch. 2. An electronic circuitor stage that is designed to operate as a conventionalswitching element when triggered by anappropriate signal.on period See ON TIME.ONR Abbreviation of Office of Naval Research.on resistance See ON-STATE RESISTANCE.on state 1. For a switch or switching device (suchas a flip-flop), the condition of the device when itconducts current or delivers an output voltage.Compare OFF STATE, 1. 2. The condition of a circuitor device that is activated for operation.Compare OFF STATE, 2.on-state current The current flowing through asemiconductor device (such as a diode, rectifier,or thyristor) when it is conducting. Also see ON-STATE VOLTAGE.

494 on-state resistance • open-frame machineon-state resistance The resistance of a voltagedependentresistor that is conducting current.on-state voltage The voltage drop across a semiconductordevice (such as a diode, rectifier, orthyristor) when the device is conducting current.Also see ON-STATE CURRENT.on the air 1. The state of a radio station that istransmitting. 2. In broadcasting, the condition inwhich the transmitter is operational and thesound and/or video from the studio is being disseminated.on time The length of time a switch or switchingdevice (such as a flip-flop) remains on.on voltage See ON-STATE VOLTAGE.OOP Abbreviation of OBJECT-ORIENTED PRO-GRAMMING.op 1. Abbreviation of OPERATE. 2. Abbreviation ofoperator (see OPERATOR, 1). 3. Abbreviation ofOPERATION. 4. Abbreviation of operational.opacimeter 1. An instrument for measuring theextent to which a material blocks light. 2. An instrument,such as a field-strength meter, used tomeasure the effectiveness of an electrical shieldingmaterial in blocking radio waves, X rays, orother radiation.opacity The condition of being opaque. This appliesto all forms of radiation. For example, amaterial can be opaque to light rays, but betransparent to radio waves, or it can be transparentto gamma rays while being opaque to alphaparticles.op amp See OPERATIONAL AMPLIFIER.op code Abbreviation of OPERATION CODE.open-air line See OPEN-WIRE LINE.open-back cabinet A loudspeaker enclosure inwhich the space behind the speaker is open to theroom.open capacitance The value of a variable capacitorwhose rotor plates have been rotated completelyout of mesh with the stator plates. CompareCLOSED CAPACITANCE.open-center display A radar display in which aring around the center indicates zero range.open-chassis construction A method of assemblingelectronic equipment by mounting componentsand wiring them on an unenclosed chassis,often without a front panel. Similar to breadboardconstruction.open circuit 1. A discontinuous circuit (i.e., onethat is broken at one or more points and, consequently,cannot conduct current nor present avoltage at its extremities). Compare CLOSEDCIRCUIT. 2. Pertaining to no-load conditions, forexample, the open-circuit voltage of a battery.3. For a bipolar transistor, the operating characteristicsunder independent input and output conditions.open circuit breaker A circuit breaker whose contactsare open.open-circuit current Current flowing in the primarywinding of an unloaded transformer.open-circuited line See OPEN-CIRCUITEDTRANSMISSION LINE.open-circuited transmission line Abbreviation,OCTL. An unterminated transmission line inwhich the conductors at the far end are not connectedtogether.open-circuit impedance For a transmission lineor a four-terminal network, the input or drivingpointimpedance when the output end of the lineor network is open-circuited.open-circuit jack A telephone jack that introducesa break in a circuit until a plug connected to aclosed external circuit is inserted.open-circuit plug See OPEN PLUG.open-circuit resistance For a four-terminal network,the input or driving-point resistance whenthe output end of the network is unterminated.open-circuit signaling A system of signaling inwhich no current flows until the signal circuit isin active operation. In a simple telegraph circuit,for example, current flows only when the key ispressed (to form a dot or dash).open-circuit alarm system A security system inwhich all the actuating sensors are normallyopen and connected in parallel. When one of thesensors is actuated, it closes, causing a short circuitthat triggers the alarm.open-circuit voltage See NO-LOAD VOLTAGE.open-collector configuration In an integrated circuit,an output scheme utilizing no internal pullupresistor. Wired-OR outputs can thus haveopposite states without risk of damage to the device.open component An open-circuit component (e.g.,an open diode, coil, resistor, etc.).open core A magnetic core having a cylindricalshape. A disadvantage of this core configuration,in some applications, is that much of the magneticflux extends outside the core. CompareCLOSED CORE.open-core choke A choke coil wound on an opencore. Also called OPEN-CORE INDUCTOR. CompareCLOSED-CORE CHOKE.open-core transformer A transformer wound onan open core. Compare CLOSED-CORE TRANS-FORMER.open-delta connection See VEE-CONNECTIONOF TRANSFORMERS.open-ended Pertaining to a circuit or device thatcan be built upon without modifying its originalconfiguration.open-end stub A stub that is neither shortcircuitednor terminated at its far end.open-end stub tuning Adjustment of an OPEN-END STUB, by pruning its length, for optimumoperation at a given frequency.open-entry contact In a connector, an unprotected,opening contact of the female type.open feeder See OPEN-WIRE LINE.open-frame machine See OPEN GENERATOR andOPEN MOTOR.

open-fuse cutout • open-wire transmission line 495open-fuse cutout A type of enclosed-fuse cutouthaving an exposed fuse holder and support. CompareOIL FUSE CUTOUT.open generator An unsealed generator (i.e., onethat has openings in its housing for air circulation).open line 1. See OPEN-WIRE LINE. 2. See OPEN-CIRCUITED TRANSMISSION LINE.open loop 1. In a control system, a feedthroughpath having no feedback and that is not selfregulating.2. In an operational amplifier, theconfiguration in which there is no feedback, andin which the device operates at maximum gain.3. A loop within a program from which the computerautomatically exits after a specific numberof iterations.Input+−+V ccopen loop, 2.Outputopen-loop bandwidth The bandwidth of an openloopdevice, such as an amplifier, without feedback.Also see OPEN LOOP.open-loop control system A control system havingno feedback and that is not self-regulating.An example is a fluid-level gauge that indicatesthe height of fluid in a tank, but that cannot correctthe level automatically. Compare CLOSED-LOOP CONTROL SYSTEM.open-loop differential voltage gain For a differentialamplifier, the overall voltage gain (when eitherinput is used) when the amplifier has nofeedback.open-loop gain The overall gain (ratio of output toinput) of an open-loop device, such as an amplifierwithout feedback. Also see OPEN LOOP.open-loop input impedance The input impedanceof an open-loop device, such as an amplifier withoutfeedback. Also see OPEN LOOP.open-loop output impedance The output impedanceof an open-loop device, such as an amplifierwithout feedback. Also see OPEN LOOP.open-loop output resistance The output resistanceof an open-loop device, such as an amplifierwithout feedback. Also see OPEN LOOP andOPEN-LOOP IMPEDANCE.open-loop system 1. A circuit in which the inputand output currents are independent. 2. A robotthat does not use a servo system. It depends entirelyon alignment and precision for positioningaccuracy. 3. An electromechanical device thatdoes not use corrective feedback.open-loop voltage gain The overall voltage gain ofan open-loop amplifier (i.e., one having no feedback).Also see OPEN LOOP.open magnetic circuit A magnetic circuit inwhich a complete path is not provided for magneticflux. See, for example, OPEN CORE. CompareCLOSED MAGNETIC CIRCUIT.open motor An unsealed motor (i.e., one that hasopenings in its housing for air circulation).open-phase protection Use of an automatic device,such as an open-phase relay, to interruptthe power to a polyphase system when one ormore phases are open-circulated.open-phase relay In a polyphase system, a protectiverelay that opens when one or more phasesare open-circuited. Also see OPEN-PHASE PRO-TECTION.open plug A phone plug to which no external connectionsare made; it is used to hold the blades ofa jack as if they were plugged in.open-reel A tape-recording system in which thetape, during record or playback condition, iswound into a take-up reel that is physically separatefrom the tape reel. Also called reel-to-reelarrangement.open relay 1. A relay in its open-contact state. 2. Arelay having an open-circuited coil. 3. An unenclosedrelay.open routine In computer operations, a routinethat can be inserted directly into a larger routineand requires no link to the main program.open subroutine In computer operations, a subroutinethat can be inserted into a larger instructionalsequence and must be recopiedwhenever it is required. Also called direct-insertsubroutine.Open Systems Interconnection Reference ModelAbbreviation, OSI-RM. A standard set of protocolsfor computer network communication. Itconsists of seven levels, also called layers: physicallayer, link layer, network layer, transportlayer, session layer, presentation layer, and applicationlayer.open temperature pickup A temperature transducerthat must be placed directly in contact withthe monitored medium.open volume Pertaining to the maximum-gain operationof a sound-reproducing system (i.e., operationat full volume).open wire 1. An unterminated wire. 2. A wire supportedabove the surface of the earth and oftenungrounded. 3. See OPEN-WIRE LINE.open-wire feeder See OPEN-WIRE LINE.open-wire line A transmission line or feeder usuallyconsisting of two straight, parallel wires heldapart by bars of low-loss insulating material atregular intervals along the line.open-wire loop A branch line connected to a mainopen-wire line.open-wire transmission line See OPEN-WIRELINE.

496 open-wire wavemeter • operating ratioopen-wire wavemeter See LECHER WIRES.operand In computer operations, a quantity thatenters into or results from an operation.operate 1. To manipulate according to an establishedprocedure (e.g., to operate an instrument).2. To perform according to specifications, in thesense that an electronic circuit functions.operate current A signal current or trigger currentrequired to actuate a device. Compare OPERATEVOLTAGE.operate delay See OPERATE TIME, 1.operate interval See OPERATE TIME, 2.operate time 1. The interval starting after the applicationof an operate current or voltage to a device,and ending when the device operates. 2. Theperiod during which an electronic equipment is inoperation. Also see OPERATING TIME, 1.operate voltage The signal voltage or trigger voltagerequired to actuate a device. Compare OPER-ATE CURRENT.operating ambient temperature Abbreviation,OAT. The maximum or recommended temperaturein the space immediately surrounding anequipment in operation.operating angle In an amplifier circuit, the excitation-signalcycle, in degrees, during which drain,collector, or plate current flows. Class-A amplifiersoperate for 360 degrees of the input signalcycle; class-AB amplifiers operate for more than180 degrees, but less than 360 degrees of the inputsignal cycle; class-B amplifiers operate for180 degrees of the input signal cycle; class-C amplifiersoperate for less than 180 degrees of theinput signal cycle.operating bias In a circuit containing transistors,diodes, or vacuum tubes, the value(s) of directcurrentbias required for normal operation.operating code The code used by the operator in acomputer or data-processing system.operating conditions The environment in which acircuit or system functions in normal use.operating current The current required by a deviceduring its operation. Compare IDLING CUR-RENT.operating cycle The sequence of events in the operationof a device. For example, the repetitive operationof a neon-bulb relaxation oscillator is asequence of three events: (1) slow charge of capacitor,(2) firing of bulb, and (3) abrupt dischargeof capacitor.operating frequency 1. The fundamental frequencyat which a circuit or device is operated. 2.The frequency of the current, voltage, or powerdelivered by a generator.operating frequency range 1. The range of operatingfrequencies, expressed as a minimum andmaximum, for a communications receiver, transmitter,or transceiver. 2. For an integrated-circuitoscillator, the minimum and maximum frequency,and all frequencies in between, at whichthe device is guaranteed to operate.operating life The maximum period (from secondsto years) over which a device will operate beforefailure (from which it usually cannot recover).Compare SHELF LIFE.operating line A line drawn across a family ofcurves depicting the performance of a device. Itintersects each curve at a single point and graphicallydisplays the performance of the device for agiven condition. Thus, an operating line on a familyof output curves for a transistor might depictoperation with a given load resistor.Collector current (I c )Operating line:E c = 10 VCollector voltage (E c )operating lineI B = 200 µAI B = 100 µAI B = 50 µAI B = 20 µAoperating overload The extent and/or duration ofoverload to which an equipment can be exposedduring customary operation, and still continue toproperly function.operating point On the response curve for a device,the point indicating the quiescent level ofoperation (such as determined by a fixed biasvoltage or current). An alternating-current signalapplied at this point oscillates above and belowthe point as a mean.operating-point shift A movement of an operatingpoint due to faulty operation of a circuit or device,or to a value change in some critical component.operating position 1. The control point in a system,[i.e., the place where an operator (see OPER-ATOR, 1) normally functions]. 2. The actual orrecommended physical orientation of a deviceduring its operation (e.g., a vertical operating positionfor a power vacuum tube).operating power 1. The power actually used by adevice during its operation. 2. The antenna powerof a radio station.operating ratio For a given period, the ratio t o /t,where t o is the time during which an equipment isoperating correctly, and t is the duration of theperiod.

operating station • optical character reader 497operating station In a computer installation, oneor more consoles for the control of a dataprocessingsystem by an operator.operating system Abbreviation, OS. In a computer,a set of programs that oversee the functioning ofthe hardware and application software. It workswith the basic input/output system (BIOS).operating temperature The actual or recommendedtemperature of a device during its operation.operating-temperature range For a given device,the spread between maximum and minimum valuesof operating temperature.operating time 1. The interval during which anequipment is in operation. 2. The period correspondingto OPERATING ANGLE.operating-time characteristic For a coil-type relay,the relationship between operating time andoperating power.operating voltage The voltage required by a device,or measured at the device, during its operation.Compare IDLING VOLTAGE.operation 1. The working of a circuit or device (i.e.,its performance). 2. A process usually involving asequence of steps (e.g., a mathematical operation).operational amplifier Also called an op amp. Aspecialized linear integrated circuit (IC) that consistsof several transistors, resistors, diodes, andcapacitors, interconnected to produce gain over awide range of frequencies. A single amplifier cancomprise an entire IC, or an IC can contain severalamplifiers. The dual op amp and the quad opamp are common variants. Some ICs contain oneor more amplifiers in addition to other circuits.The devices can be used with resistance-capacitance(RC) network combinations to build activefilters for use at audio frequencies.operational differential amplifier An OPERA-TIONAL AMPLIFIER preceded by a DIFFEREN-TIAL AMPLIFIER.operational readiness In statistical analysis, theprobability that a system will, at a certain time,be correctly operating or ready to operate.operational reliability Reliability determined empiricallyfrom a study of the actual operation of adevice or system under controlled conditions.Also called ACHIEVED RELIABILITY.operational transconductance amplifier Abbreviation,OTA. An integrated-circuit amplifier thatdiffers from the conventional operational amplifierin that its output current is proportional to itsinput-signal voltage.operation code In computer operations, the partof an instruction that specifies an operation.operation decoder In a digital computer, the circuitthat reads an OPERATION CODE and directsother circuitry in the execution of the code.operation envelope See WORK ENVELOPE.operation number In computer programming, anumber that indicates the position in the programof a particular operation or subroutine.operation part In a computer program, the partof an instruction containing the OPERATIONCODE.operation register In a digital computer, the registerthat stores the operation code of an instruction.operations research A branch of computer engineering,devoted to the solution and/or optimizationof functions of many variables.operation time The interval between the instant ofapplication of all voltages to a circuit, and the instantwhen the current reaches a specified percentageof its final steady value.operator 1. A person who performs an operation(see OPERATE, 1). 2. In mathematics, a symbolindicating an operation (e.g., j, +, –, ×, etc.).operator j See J OPERATOR.opposition 1. The state of two quantities that are180 degrees out of phase with each other. 2. Astate in which two effects or quantities operateagainst each other in some manner (e.g., physically,mathematically, electrically, etc.).opt Abbreviation of OPTICAL.Optacon An electronic aid for the blind. It has acamera that scans printed matter and a devicethat forms corresponding raised letters that canbe read, as would Braille, with the fingertips. Thename is a contraction of optical to tactile converter.optical 1. Generating or sensing visible light.2. Visible electromagnetic radiation in the rangeof approximately 390 to 750 nanometers wavelength.optical ammeter A type of OPTICAL PYROMETERthat measures the current flowing through the filamentof an incandescent lamp.optical antenna A photosensitive device intendedfor the reception of modulated-light or modulated-infraredsignals. Usually consists of aconvex lens or a concave reflector and asemiconductor photodetector.optical axis The z-axis of a quartz crystal (seeZ-AXIS, 4).optical character reader A device that uses OPTI-CAL CHARACTER RECOGNITION to discernprinted characters.

498 optical character recognition • optical sound recordingoptical character recognition Abbreviation, OCR.In computer and data-processing operations, thereading of alphabetical, numerical, and othercharacters from hard copy (usually printed matter)by photoelectric methods. It converts thecharacters into digital data that can be stored incomputer memory, on disks and tapes, andtransmitted via digital communications networks.It can also allow a computer or robot toread signs, maps, etc.optical communications One-way or two-waycommunications via modulated visible light. Itcan be conducted through optical fibers, theatmosphere, water, or any other transparentmedium.optical coupler A coupling device consisting essentiallyof a light source (actuated by an inputsignal) mounted in an opaque housing with alight-sensitive device (that delivers the outputsignal). In its simplest form, the arrangementconsists of a light-emitting diode (LED) and aphotodiode.Input Mod. Amp. Outputoptical coupleroptical detector An integrated-circuit (IC) thatprovides light-to-voltage conversion. Its directcurrentoutput voltage is proportional to the intensityof light impinging on its sensor.optical encoder An electronic device that measuresthe extent to which a mechanical shaft hasrotated. It can also measure the rate of rotation(angular speed). It consists of a light-emittingdiode (LED), a photodetector, and a disk with alternatelight and dark bands (chopping wheel). Itis commonly used in digital controls and jointedrobot arms.optical fiber A glass or plastic medium throughwhich light is propagated for optical-communicationspurposes. The refractive characteristics ofthe fiber keep the visible light inside.optical lever A device for amplifying the effect of asmall rotation. The rotating member carries asmall mirror that reflects a light beam over acurved scale, the distance through which thelight spot travels on the scale being proportionalto the distance between the scale and the rotatingmirror. In this way, the deflection on the scale isseveral times the length of the arc described bythe mirror, the rotation being thus amplified.optical link See OPTICAL COUPLER.optical mark recognition A method of data transferthat involves the use of optical techniques.optical maser See LASER.MirrorMeterbearingoptical leverStationarylight sourceScreenwith scaleImageoptical mode The vibration mode that produces anoscillating dipole in a crystal lattice.optical pattern A Christmas-tree-like pattern producedby parallel rays of light striking a phonodisk. Also see DIFFRACTION.optical playback See OPTICAL SOUND REPRO-DUCER.optical pyrometer A pyrometer for measuring thetemperature of a hot body in terms of the intensityand color of light it emits.optical scanner An electronic device that convertshard-copy text and graphics into digital formsuitable for processing and storage in a computer.There are several types; the most commonresembles a small photocopy machine and isknown as a flatbed scanner. See OPTICAL SCAN-NING.optical scanning An electronic process that convertshard-copy text and graphics into digitalform suitable for processing and storage in acomputer. Text scanners work in conjunctionwith specialized software. The optical scannerand software together form the equivalent of audiospeech recognition and sound interpretation.Usually, scanners are employed to convertprinted matter to digital data. However, scanningtechnology can also be used at a distance, for example,by a robot for the purpose of reading roadsigns.optical sound recorder A photoelectric machinefor recording sound on photographic film. Alsosee OPTICAL SOUND RECORDING.optical sound recording A system for recordingsound on photographic film, as in sound motionpictures. The sound is picked up by a microphoneand amplified to vary the intensity of a lightsource. The film passing this modulated beam becomesexposed to a variable-width or variabledensitytrack corresponding to the modulation(see VARIABLE-DENSITY SOUND RECORD andVARIABLE-WIDTH SOUND RECORD). When de-

optical sound recording • Orange Book 499veloped film is played back, its sound track modulatesa light beam in the reproducer by actuatinga photocell or phototube to produce the audio signal,which is then amplified.optical sound reproducer A photoelectric machinefor reproducing sound on film. A light beamin the device is modulated by the passing soundtrack, and it, in turn, modulates photocell or phototubecurrent, which is amplified to drive a loudspeaker.Also see OPTICAL SOUND RECORDING.optical system Collectively, the functional arrangementof lenses, mirrors, prisms, and relateddevices in optoelectronic apparatus.optical tachometer An optoelectronic instrumentfor measuring (by means of reflected-light variations)the speed of a body, such as a rotatingshaft, without electrical or mechanical attachmentsto the latter.optical thermometer See OPTICAL PYROMETER.optical twinning A kind of defect in which twotypes of quartz occur in the same crystal. CompareELECTRICAL TWINNING.optical type font A special type (printing) styledesigned for use with OPTICAL CHARACTERRECOGNITION equipment.optical wand A pencil-like optical probe, used toread bar codes from a printed page and translatethe codes into information that is then loadedinto a computer or calculator.optic axis See OPTICAL AXIS.optic flow See EPIPOLAR NAVIGATION.optics 1. The science of light, its measurement,application, and control. 2. A system of lenses,prisms, filters, or mirrors used in electronics todirect, control, or otherwise modify light rays.optimization The adjustment or manipulation ofthe elements of a process or system for the bestoperation or end result.optimize 1. To manipulate a set of variables or parametersfor the best possible performance of acircuit or system. 2. To maximize the value of amultivariable function.optimum angle of radiation For a given altitude ofthe ionosphere, the angle, with respect to thehorizon, at which a radio signal should be transmittedfrom a specific geographic location to provideoptimum reception at some other specificlocation. This angle varies, depending on the altitudeof the ionospheric layer from which signalsare returned, the distance between the transmittingand receiving stations, and the number ofhops taken by the signal between the earth andthe ionosphere.optimum bunching In a velocity-modulated tube,such as a klystron, the bunching associated withmaximum output.optimum collector load The ideal load impedance(see OPTIMUM LOAD) for a particular transistoroperated in a specified manner.optimum coupling The degree of coupling betweentwo circuits tuned to the same frequencythat results in maximum energy transfer. Alsocalled CRITICAL COUPLING.optimum current The value of current that producesthe most-effective performance of a circuitor device.optimum frequency See OPTIMUM WORKINGFREQUENCY.optimum load The value of load impedance thatproduces maximum transfer of power from a generatoror amplifier.optimum plate load The ideal load impedance (seeOPTIMUM LOAD) for a particular electron tubeoperated in a specified manner.optimum Q The most effective figure of merit for acapacitor, inductor, or tuned circuit at a specifiedfrequency.optimum reliability The value of reliability thatensures minimum project cost.optimum voltage The value of voltage that resultsin the most effective performance of a circuit ordevice.optimum working frequency In radio transmissioninvolving reflection from the ionosphere, thefrequency of use that results in the most reliablecommunication between two points.optoelectronic coupler An assembly consisting ofan LED and a phototransistor. An input signalcauses the diode to glow, and the light activatesthe transistor, which in turn delivers an outputsignal of higher amplitude than that of the inputsignal.optoisolator A light-emitting diode (LED) or infrared-emittingdiode (IRED) and a photodiodecombined in a single package with a transparentgap between them. The LED or IRED converts anelectrical signal to visible light or IR; the photodiodechanges the visible light or IR back into anelectrical signal. This device eliminates interstageimpedance reflections that can plague systemsthat employ electronic coupling. Even the mostdrastic changes in load impedance have no effecton the impedance “seen” by the signal source.The devices can also protect expensive equipmentagainst electrical transients; for example, intelephone-line modems used with personalcomputers.optoelectronics A branch of electronics that involvesthe use of visible light for communicationsor data-transfer purposes.optoelectronic transistor A transistor having anelectroluminescent emitter, transparent base,and photoelectric collector.optophone A photoelectric device for convertinglight into sounds of proportionate pitch to enableblind persons to “see” by ear.Orange Book Trade name (Sony and Philips) for aspecialized format for compact-disc recordable(CD-R) computer data storage media. It allowsrecording of data onto, as well as retrieval of datafrom, an optical compact disc. See also GREENBOOK, RED BOOK, and YELLOW BOOK.

500 orange peel • orthiconoscopeorange peel On a phonograph disc, a mottled surfacethat produces high background noise; socalled from its resemblance to an orange peel.orbit 1. Also called shell. The median path of anelectron around the nucleus of an atom. 2. Thecircular or elliptical path of an artificial satellite(e.g., a communications satellite) around theearth. 3. The elliptical path of the moon aroundthe earth. 4. The elliptical path of the earth or anotherplanet around the sun. 5. Any closed, usuallycircular or elliptical path, that an objectfollows around another object.orbital-beam multiplier tube An electronmultiplyingUHF oscillator or amplifier tube inwhich a positively charged electrode focuseselectrons in a circular path.orbital electron An electron in orbit around thenucleus of an atom.orbital period The length of time required by asatellite to go around a celestial body, usually theearth. It can vary from about 90 minutes for verylow orbits to months or even years for orbits beyondthat of the moon. The moon’s period isabout a month.OR circuit Also called inclusive-OR circuit. In digitalsystems and other switching circuits, a logicgate whose output is high (logic 1) when any ofthe input signals is high. The output is low (logic0) only when all of the inputs are low. CompareAND CIRCUIT.AInputsBA0011B0101C01112-input OR circuitCOutputorder 1. An instruction to a digital computer.2. Sequence.OR element See OR CIRCUIT.ordered pair A set of two variables or numbersthat can be mapped one-to-one onto a set ofpoints in a plane. The most familiar example is(x,y), used to depict the Cartesian (rectangular)coordinate system on which characteristic curvesand other functions are plotted.order of interference The position of an interferencefringe that depends on whether the interferencearises from one, two, three, or morewavelength differences. Generally, the first fringeresults from a difference of one wavelength, thesecond fringe from a difference of two wavelengths,etc. The center fringe indicates that thetwo signals are exactly in phase; that is, the differenceis zero wavelengths.order of logic 1. A mathematical expression forthe complexity of a system of logic. 2. The relativespeed with which logical information is processedin a system.order tone A warning signal to receiving operatorsin the form of a tone transmitted over a trunkpreceding the transmission of an order.ordinary ray As a result of the double refraction ofelectromagnetic waves, the member of a pair ofrays that follows the usual laws of refraction. Alsosee O WAVE. Compare EXTRAORDINARY RAY.ordinary wave See O WAVE.ordinate In the rectangular coordinate system, apoint located on the vertical axis.organ 1. A computer subsystem. 2. An electronicdevice used for the purpose of generating music.organic decay See EXPONENTIAL DECREASE.organic electricity Electricity in the living tissuesof animals and plants.organic growth See EXPONENTIAL INCREASE.organic semiconductor A semiconductor materialconsisting of, or combined with, some compoundof carbon.OR gate See OR CIRCUIT.orientation 1. The direction or position of an objectin space, expressed in terms of coordinatevalues. 2. In a teleprinter, the calibration oralignment that determines the speed of responseto a received character.orientation of quartz plates See CRYSTAL AXESand CRYSTAL CUTS.orifice An opening or window, such as that in aloudspeaker enclosure or waveguide, throughwhich energy is transmitted.origin1. The starting point in a coordinate system.2. Relative to address modification in computeroperations, an address to which a modifier isadded to derive a variable operand address.original lacquer In disc-recording operations, anoriginal recording made on a lacquer-surfaceddisc that is subsequently used to make a master.original master In disk recording, the master discproduced from a wax or lacquer disc (see ORIGI-NAL LACQUER) by means of electroforming.origin distortion The change in the shape of awave as it swings through zero (polarity).OR operation See OR CIRCUIT.ORS Abbreviation of OMNIDIRECTIONAL RANGESTATION.orthicon A television camera tube somewhat similarto the iconoscope, but which provides internalamplification of light and, accordingly, can beused in dimmer places than the iconoscope. Lightamplification is provided by an arrangement similarto that of a photomultiplier tube.orthiconoscope See ORTHICON.

orthoacoustic recording • oscillator keying 501orthoacoustic recording 1. A system of discrecording in which the inherent differencesbetween high-frequency recording and lowfrequencyrecording are compensated to providereproduction that more closely resembles theactual sound. 2. A disc made by the methoddefined in 1.orthogonal axes Perpendicular axes [e.g., those ina Cartesian (rectangular) coordinate system].Os Symbol for OSMIUM.OS Abbreviation of OPERATING SYSTEM.osc Abbreviation of OSCILLATOR.OSCAR Abbreviation for Orbiting Satellite CarryingAmateur Radio. A satellite with a transponderthat has an uplink in one amateur band and adownlink in another amateur band.osciducer See OSCILLATING TRANSDUCER.oscillate 1. To fluctuate in amplitude in a uniformmanner. 2. To vary above and below a specifiedvalue at a constant rate.oscillating arc A small arc, especially one producedby slow-opening relay contacts, that generateshigh-frequency oscillations.oscillating circuit A closed circuit containing inductance,capacitance, and inherent resistance,in which energy passes back and forth betweeninductor and capacitor at a frequency determinedby the inductance (L) and capacitance (C) values.oscillating crystal 1. A piezoelectric plate maintainedin a state of oscillation in a circuit. See, forexample, CRYSTAL OSCILLATOR and QUARTZCRYSTAL. 2. An oscillating semiconductor diode(see NEGATIVE-RESISTANCE DIODE, 1, 2).oscillating current See OSCILLATORY CURRENT.oscillating detector A detector provided with positivefeedback; therefore, it is capable of generatinga signal of its own. CompareNON-OSCILLATING DETECTOR.oscillating diode 1. A semiconductor diode biasedinto its negative-resistance region so that it oscillatesin a suitable circuit. 2. An oscillating tunneldiode. 3. Any of several microwave diodes, suchas the IMPATT diode, which will oscillate in asuitable system. 4. See MAGNETRON. Also seeDIODE OSCILLATOR.oscillating field An alternating electric or magneticfield.oscillating rod A rod of magnetostrictive metalmaintained in a state of oscillation in a circuit.See, for example, MAGNETOSTRICTION andMAGNETOSTRICTION OSCILLATOR.oscillating transducer A transducer in which aninput quantity varies a frequency proportionatelyfrom its center value.oscillating wire A wire of magnetostrictive metalmaintained in a state of oscillation in a circuit.See, for example, MAGNETOSTRICTION andMAGNETOSTRICTION OSCILLATOR.oscillationThe periodic change of a body or quantityin amplitude or position (e.g., oscillation of apendulum, voltage, or crystal plate).oscillation constant For an oscillating inductance-capacitance(LC) circuit, the expression(LC) 1/2 , where L is the inductance in henrys and Cis the capacitance in farads. The reciprocal of theOSCILLATION NUMBER.oscillation control A manual or automatic devicefor adjusting the frequency or amplitude of thesignal generated by an oscillator.oscillation efficiency The ratio, as a percentage,of the alternating-current (signal) power output ofan oscillator (P out ) to the corresponding directcurrentpower input (P in ). Efficiency = 100P out /P in .oscillation number For an oscillating circuit, thenumber of complete oscillation cycles that occurin 6.28 (2 pi) seconds.oscillation test 1. A test of an oscillator to determineif a signal is being generated. 2. A test fortransistors wherein the transistor is used as anoscillator to give a rough indication of its conditionin terms of oscillation amplitude.oscillation transformer A tank coil of a radiotransformer—especially one that includes an outputcoupling coil.oscillator A device that produces an alternatingor pulsating current or voltage electronically.The term is sometimes used to describe anyalternating-current-producing device other thanan electromechanical generator.oscillator circuit The specific manner in whichthe components of an OSCILLATOR are interconnected.The three general types are: positivefeedback,negative-resistance, and relaxation.oscillator coil A tapped coil that provides the inputand output windings required for an oscillator circuit.Such coils are used in signal generators, oscillators,and superheterodyne receivers.oscillator-doubler A circuit consisting of an oscillatorand a frequency doubler (e.g., a crystal oscillatorwhose output frequency is twice thecrystal frequency).oscillator drift A usually gradual change in frequencyof an oscillator caused by such factors aswarmup time, voltage variations, capacitancechange, inductance change, or change in transistorcharacteristics.oscillator frequency The fundamental frequencyat which an oscillator operates. It can be determinedby a tuned circuit, crystal, cavity, sectionof waveguide or transmission line, or by a resistance-capacitancecircuit.oscillator harmonic interference In a superheterodynereceiver, interference that is the beatproduct of local oscillator harmonics and receivedsignals.oscillator interference Radio-frequency interferencecaused by signals from the high-frequencyoscillator of a receiver.oscillator keying Keying by making and breakingthe signal output, direct-current (dc) power, or dcbias of the oscillator stage of a radiotelegraphtransmitter.

502 oscillator-mixer • oscillatory current+oscillator keyingOutputoscillator synchronization The locking of an oscillatorin step with another signal source, suchas a frequency-standard generator.oscillator tracking In a superheterodyne receiver,the constant separation of the oscillator frequencyfrom the signal frequency by an amountequal to the intermediate frequency at all settingsof the tuning control.oscillator transmitter A radio transmitter consistingonly of a radio-frequency oscillator and itspower supply. The oscillator can be modulated invarious ways [e.g., on-off keying, frequency-shiftkeying, voice amplitude modulation (AM), voicefrequency modulation (FM)].oscillator trimmer In a superheterodyne receiver,a small, limited-range capacitor connected inparallel with the oscillator coil for tracking oscillatortuning at the high end of a band. CompareOSCILLATOR PADDER.oscillator tuning The separate, often ganged, tuningof the oscillator stage in a circuit.oscillator-mixer 1. A combination stage in whicha transistor functions as a local oscillator andmixer in a receiver or test instrument. 2. A devicedesigned specifically to function as a local oscillatorand mixer.oscillator-mixer-detector 1. In a superheterodynereceiver, a stage in which the functions ofhigh-frequency oscillator, mixer, and first detectorare performed by a single transistor. 2. A devicedesigned specifically to function as a localoscillator, mixer, and detector.oscillator-multiplier A single circuit that serves simultaneouslyas an oscillator and frequency multiplier.See, for example, OSCILLATOR-DOUBLER.oscillator padder In a superheterodyne receiver, asmall, limited-range variable capacitor connectedin series with the oscillator coil for tracking oscillatortuning at the low end of a band. CompareOSCILLATOR TRIMMER.oscillator power supply 1. The direct-current oralternating-current power supply for an oscillator.2. See OSCILLATOR-TYPE POWER SUPPLY.oscillator radiation The emission of radiofrequencyenergy by the oscillator stage of asuperheterodyne receiver. Also see OSCILLATORINTERFERENCE.oscillator-radiation voltage The radio-frequencyvoltage at the antenna terminals of a superheterodynereceiver that results from signal emissionby the oscillator stage.oscillator stabilization 1. The automatic compensationof an oscillator circuit for the frequencydrift resulting from changes in temperature, current,voltage, or component parameters. 2. Theautomatic stabilization of the operating point ofan oscillator circuit against variations resultingfrom changes in temperature, supply current orvoltage, or component parameters.Variabletunedcircuit+oscillator tuningOutputoscillator-type power supply A high-voltage,direct-current (dc) power supply in which a radiofrequency(RF) oscillator generates a low-voltagealternating current (ac). This ac voltage isstepped up by an RF transformer, and is finallyrectified to obtain high-voltage dc.oscillator-type transmitter See OSCILLATORTRANSMITTER.oscillator wavelength The fundamental wavelengthat which an oscillator operates. It isusually expressed in meters, centimeters, ormillimeters. It can be determined by a tuned circuit,crystal, cavity, section of waveguide ortransmission line, or by a resistance-capacitancecircuit.oscillatory current A current that alternates periodically,particularly the current in an inductance-capacitance(LC) tank circuit that results

oscillatory current • out of phase 503from the oscillation of energy back and forth betweenthe inductor and capacitor.oscillatory discharge An electrical discharge,such as that of a capacitor, that sets up an OS-CILLATORY CURRENT.oscillatory surge A current or voltage surge thatincludes both positive and negative excursions.oscillatory transient See OSCILLATORY SURGE.oscillistor A device consisting essentially of a barof semiconductor material positioned in a magneticfield; it will produce oscillations under certainconditions.oscillogram 1. The image produced on the screenof an oscilloscope. 2. A permanent, usually photographic,record made from the screen of an oscilloscope.oscillograph 1. An instrument that makes a permanentrecord (photograph or pen recording) of arapidly varying electrical quantity. Also calledrecorder (see RECORDER, 2). Compare OSCILLO-SCOPE. 2. An obsolete term for OSCILLOSCOPE.oscillograph recorder A direct-writing recorder(see RECORDER, 2).oscillography The use of a graphic oscillationrecorder (OSCILLOGRAPH).oscillometer A device used for determining thepeak amplitude of an oscillation.oscilloscope An instrument that presents forvisual inspection the pattern representingvariations in an electrical quantity. Also seeCATHODE-RAY OSCILLOSCOPE. Compare OS-CILLOGRAPH.oscilloscope camera A special high-speed, shortfocuscamera with fixtures for attachment to anoscilloscope to record images from the screen.Standard and instant-film types are available.oscilloscope differential amplifier An amplifierthat processes the difference between two signals,for the purpose of displaying on an oscilloscopeor oscillograph.oscilloscope tube A cathode-ray tube for use in anoscilloscope. It contains an electron gun, acceleratingelectrode, horizontal and vertical deflectingplates, and a fluorescent screen.Os-Ir Symbol for OSMIRIDIUM.OSI-RM Abbreviation of OPEN SYSTEMS INTER-CONNECTION REFERENCE MODEL.OSL Abbreviation of orbiting space laboratory.osmiridium Symbol, Os-Ir. A natural alloy of osmiumand iridium.osmium Symbol, Os. A metallic element of theplatinum group. Atomic number, 76. Atomicweight, 190.2.osmotic pressure The force that causes the positiveions to pass out of a solution toward a metalbody immersed in an electrolyte. Also seeHELMHOLTZ DOUBLE LAYER.OSO Abbreviation of orbiting solar observatory.osteophone A bone-conduction hearing aid.OTA Abbreviation of OPERATIONAL TRANSCON-DUCTANCE AMPLIFIER.OTL Abbreviation of OUTPUT-TRANSFORMER-LESS.O-type backward-wave oscillator Abbreviation,OBWO. A backward-wave oscillator using harmonicshaving opposing phases.ounce Abbreviation, oz. A unit of weight equal to 1 ⁄16pound or 28.35 grams.ounce-inch Abbreviation, oz-in. A unit of torqueequal to the product of a force of 1 ounce and amoment arm of 1 inch. Compare POUND-FOOT.outage 1. Loss of power to a system. 2. Loss of areceived signal.outboard components 1. Discrete components(capacitors, coils, resistors, or transformers) connectedexternally to an integrated circuit. 2. Discretecomponents connected externally to anyexisting electronic device.outcome In statistical analysis, the result of an experimentor test. An outcome can be numerical ornonnumerical.outdoor antenna An antenna erected outside,usually high above the surface of the earth clearof obstacles. It generally provides superior performancecompared with an INDOOR ANTENNA.Also reduces the probability of radio-frequencyinterference (RFI) when used for transmitting.outdoor booster A signal preamplifier mounted onan outdoor television receiving antenna for improvedreception.outdoor transformer A weatherproof distributiontransformer installed outside the building it services.outer conductor The outer metal cylinder orjacket of a coaxial cable or coaxial tank. CompareINNER CONDUCTOR.outgassing 1. In the evacuation of electronic devices,such as vacuum tubes, the removal of occludedgases from glass, ceramic, and metal bymeans of slow baking and by flashing an internalmetal getter (such as one of magnesium). 2. Theproduction of gases in certain electrochemicalcells and batteries during the final stage of charging.outgoing line A power or signal line that leaves adevice, facility, or stage. Compare INCOMINGLINE.outlet A female receptacle that delivers a signal oroperating power to equipment plugged into it.outline flowchart In computer operations, a preliminaryflowchart showing how a program will bedivided into routines and segments, input andoutput functions, program entry points, etc.out-of-line coding Instructions for a computerprogram routine stored in an area of memoryother than that in which the routine’s program isstored.out of phase Pertaining to the condition in whichthe alternations or pulsations of two or more separatewaves or wave phenomena, having identicalfrequencies, are out of step with each other. CompareIN PHASE.

504 out-of-phase current • output coupling transformerout of phaseout-of-phase current Reactive current in an alternating-currentcircuit (i.e., current that is out ofphase with voltage. Also see QUADRATURE CUR-RENT).out-of-phase voltage Voltage across a reactance; socalled because it is out of phase with the current.outphaser A device that converts a sawtooth waveto a square wave. It is used in electronic organsand synthesizers.outphasing modulation A system of modulationin which the sideband frequencies are shifted90 degrees from the phase position in an amplitude-modulatedwave. The resulting constantenvelopewave is then amplified with highefficiency and low distortion by a class-C stage;then the signal is reconverted to an amplitudemodulatedone by phase shifting the carrier, withrespect to the sidebands.out-plant system A data-processing system inwhich a central computer receives data from remoteterminals.output 1. Energy or information delivered by acircuit, device, or system. Compare INPUT, 1. 2.The terminals at which energy or information istaken from a circuit, device, or system. CompareINPUT, 2.output admittance Symbol, Y o . The internal admittanceof a circuit or device, as “seen” at theoutput terminals; the reciprocal of OUTPUTIMPEDANCE. Compare INPUT ADMITTANCE.output amplifier See FINAL AMPLIFIER.output area In a computer system, the portion ofstorage holding information for delivery to an outputdevice. Also called output block.output axis For a gyroscope that has received aninput signal, the axis around which the spinningwheel precesses.output block See OUTPUT AREA.output buffer 1. A circuit that follows an oscillatorand reduces the effects of variable load impedanceon the oscillator frequency or signal amplitude.2. An amplifier, usually with a voltage gain of 6 dB,that follows a video multiplexer. The amplifierdrives a coaxial transmission line.output bus driver In a computer, a device thatamplifies output signals sufficiently to providesignals to other devices without undue loading ofthe supply line (bus).output capability The maximum power or voltageoutput that a circuit can deliver without distortionor other improper operating conditions.output capacitance Symbol, C o . The internal capacitanceof a circuit or device, as seen at theoutput terminals. Compare INPUT CAPACI-TANCE.output capacitive loading For an operational amplifierat unity gain, the maximum capacitancethat can be connected to the output of the amplifierbefore phase shift increases to the point of oscillation.output capacitor 1. In a capacitance-coupled circuit,the output coupling capacitor. Compare IN-PUT CAPACITOR. 2. The last capacitor in apower-supply filter circuit.output capacity The maximum output capabilityof a device or system expressed in appropriateunits, such as current, voltage, power, torque,horsepower, etc.output choke The last choke (inductor) in apower-supply filter circuit.InputL1C1L2output chokeOutput chokeC2Outputoutput circuit The circuit or subcircuit that constitutesthe output portion of a network or device.Also see OUTPUT and OUTPUT TERMINALS.Compare INPUT CIRCUIT.output-circuit distortion Distortion in the outputportion of a circuit or device (such as a transistoror transformer), usually caused by an overload ornonlinear response.output conductance Symbol, G o . The internalconductance of a circuit or device, as “seen” atthe output terminals. It is the reciprocal of OUT-PUT RESISTANCE. Compare INPUT CONDUC-TANCE.output control 1. The gain control of an amplifier.2. The level control of a variable power supply.output coupling capacitor See OUTPUT CAPACI-TOR.output coupling transformer See OUTPUTTRANSFORMER.

output current • output transformer 505output current 1. Symbol, I o . The current deliveredby a source, such as a battery, generator, oramplifier. Compare INPUT CURRENT, 1. 2. Symbol,I o . Current flowing in the output leg or electrodeof a circuit or device. Compare INPUTCURRENT, 2.output device 1. A load device, such as a resistor,loudspeaker, lamp, relay, motor, etc., that utilizesthe output energy delivered by a generator,amplifier, or network. 2. A device, such as an outputtransformer, that serves to transfer energy orinformation from a circuit or device. Compare IN-PUT DEVICE. 3. In computer operations, a devicethat presents the results of computer operationin a comprehensible form. Examples: printer,monitor, disk drive, tape drive, modem, etc.output efficiency The efficiency of a device, suchas a generator or amplifier, in delivering an outputsignal. For an amplifier, the efficiency (Eff % ) isgiven as a percentage by the formula Eff % =100P o /P i , where P i is the direct-current power input,and P o is the alternating-current (signal)power output.output equipment See OUTPUT DEVICE, 3.output filter The direct-current filter of a powersupply operating from alternating current. Alsosee CAPACITOR-INPUT FILTER and CHOKE-INPUT FILTER.output gap A device via which current or power isintercepted from an electron beam in a beampowertube.output impedance Symbol, Z o . The impedance“looking” into the output terminals of an amplifier,generator, or network. Compare INPUTIMPEDANCE.output indicator A device, such as an analog meter,digital meter, or bar-graph meter, that providesa visual indication of the output-signalamplitude of an equipment.output leakage current In an open-collector integratedcircuit, the current from collector to emitterwith the output in the “off” condition and acertain specified voltage applied to the device. Itcan be expressed in milliamperes or microamperes.output limiting A process for automatically maintainingthe amplitude of the signal delivered by agenerator or amplifier. See, for example, AUTO-MATIC GAIN CONTROL, AUTOMATIC MODULA-TION CONTROL, VOLUME COMPRESSION, andVOLUME LIMITER.output load See OUTPUT DEVICE, 1.output load current 1. The current through theoutput load of an amplifier. Generally, this currentis expressed in root-mean-square (rms) form.2. The highest rms current that an amplifier candeliver to a load of a specified impedance.output meter A meter that gives a quantitative orqualitative indication of the output of an amplifieror generator. See, for example, OUTPUT-POWERMETER.output offset In an integrated circuit, the voltageat the output when the inputs are grounded.output port The output terminal of a logic device.output power Symbol, P o . The power deliverable byan amplifier, generator, or circuit. Also calledpower output. Compare INPUT POWER.output-power meter A type of direct-readingwattmeter for measuring the power output of anamplifier or generator.output regulator A circuit or device that automaticallymaintains the output of a power supply orsignal source at a constant amplitude.output resistance Symbol, R o . The internal resistanceof a circuit or device, as “seen” at the outputterminals. Compare INPUT RESISTANCE.output routine In computer operations, a routine(program segment) that performs the work involvedin moving data to an output device, oftenincluding intermediate transferals and modifyingthe data as necessary.output section See OUTPUT AREA.output sink current In an integrated circuit, for aspecified set of conditions at the input and output,current into the output as measured in milliamperesor microamperes.output source current In an integrated circuit, fora specified set of conditions at the input and output,the current out of the output, as measuredin milliamperes or microamperes.output stage The last stage of an amplifier. Deliversthe signal to the load.output terminals Terminals (usually a pair) associatedwith the output of a circuit or device (seeOUTPUT, 1, 2). Compare INPUT TERMINALS.output tank In a transmitter or power generator, aparallel-tuned combination of inductance and capacitancein the collector, drain, or plate circuit,that is generally tuned to resonance at the operatingfrequency. IT optimizes efficiency and couplesthe signal to the load. Compare INPUT TANK.output transformer The output-coupling transformerthat delivers signal voltage or power froman amplifier, generator, or network to a load or toanother circuit. Compare INPUT TRANSFORMER.Input+Outputtankoutput tank+Output

506 output-transformerless • overdesignoutput-transformerless Abbreviation, OTL. Pertainingto an oscillator, amplifier, or generatorthat requires no output coupling transformer.output transistor A transistor in the final stage ofan amplifier or generator; usually, it is a powertransistor.output tube A vacuum tube in the final stage of anamplifier or generator; usually, it is a power tube.output unit See OUTPUT DEVICE.output voltage 1. Symbol, E o or V o . The voltage deliveredby a source, such as a battery, generator,or amplifier. Compare INPUT VOLTAGE, 2. 2.Symbol, E o or V o . The voltage across the outputleg or electrode of a circuit or device. Compare IN-PUT VOLTAGE, 2.output voltage compliance In an integrated circuit,the voltage range over which the output canbe made to swing, while keeping the operation ofthe circuit within a certain maximum allowablenonlinearity limit. It is measured in volts or millivolts.output voltage noise In an integrated circuit, theoutput noise over a given range of frequencies, asmeasured in peak-to-peak millivolts or microvolts.It can also be measured as the rootmean-square(rms) value.output voltage swing In an integrated circuit witha specified load, the output-voltage change measuredas a difference between maximum andminimum in volts or millivolts.output voltage tracking For an integrated-circuitdual regulator, the difference between the absolutevalues of the output voltages of a dual regulator.It can be expressed as a specific voltage oras a percentage of the specified output voltage ofthe device.output winding The secondary coil of an outputtransformer.outside antenna See OUTDOOR ANTENNA.outside booster See OUTDOOR BOOSTER.outside diameter Abbreviation, OD. The outermostdiameter of a body or figure having two concentricdiameters (e.g., tubing or conduit).Compare INSIDE DIAMETER.outside lead See FINISH LEAD.outside transformer 1. See OUTDOOR TRANS-FORMER. 2. A transformer mounted outside ofan equipment in whose circuit it is included.External mounting can eliminate hum in theequipment circuit, and can help to preventoverheating.oven 1. Also called crystal oven. A chamber providinga closely controlled operating temperature foran electronic component, such as a quartz crystal.2. An enclosure in which electronic equipmentcan be tested at selected, precise hightemperatures. Compare COLD CHAMBER.overall feedback Positive or negative feedbackaround an entire system (such as a publicaddresssystem), as opposed to feedback confinedto one stage or a few stages within the system.overall gain The total gain of an entire system(such as a multistage amplifier), as opposed tothat of one or several stages.overall loudness The apparent intensity of anacoustic disturbance, generally measured withrespect to the threshold of hearing, and expressedin decibels, relative to the threshold level.overbiased unit A component, such as a transistoror vacuum tube, whose bias current or voltageis higher than the correct value for a given modeof operation. Compare UNDERBIASED UNIT.overbunching In a velocity-modulated tube, suchas a Klystron, the condition in which the bunchervoltage exceeds the value required for optimumbunching.overcharging In a secondary cell or battery, theapplication of charging current longer than necessaryto obtain full charge. This can sometimescause problems, such as cell heating.overcompounded generator A dynamo-type generatorhaving a compound field winding in whichthe series-field winding increases the field intensitybeyond the point needed to maintain the outputvoltage. Compare UNDERCOMPOUNDEDGENERATOR.overcompounding A characteristic of electromechanicalmotors, resulting in increased runningspeed with decreasing load resistance.overcoupled transformer A transformer havinggreater than critical coupling between its primaryand secondary windings. In tuned circuits, suchas intermediate-frequency (IF) transformers, thisproduces a double-peak response.overcoupling Extremely close coupling (seeCLOSE COUPLING).overcurrent A current greater than the specified,nominal, or desired level. Compare UNDERCUR-RENT.overcurrent circuit breaker A circuit breaker thatopens when current exceeds a predeterminedvalue.overcurrent protection The use of a circuitbreaker, relay, or other device to protect a circuitor system from damage resulting from an excessiveflow of current.overcurrent relay A protective relay that opens acircuit when current exceeds a predeterminedvalue. Compare UNDERCURRENT RELAY.overcutting In disc recording, the condition inwhich an excessively high amplitude signalcauses the stylus to cut through the wall betweenadjacent grooves. Compare UNDERCUTTING.overdamping Damping greater than the criticalvalue (see DAMPING ACTION, 2). Compare UN-DERDAMPING.overdesign Also called overengineering. 1. To usean unnecessarily high safety factor in the designof equipment. 2. To design equipment for performancesuperior to that which is required in theintended application. 3. A design that resultsfrom operations defined in 1 and 2.

overdrive • overload recovery time 507overdrive In an analog amplifier, an undesirableoperating condition that occurs with the applicationof excessive input signal voltage or power.This results in increased distortion, nonlinearity,excessive harmonic generation, and excessiveoutput signal bandwidth. In a high-fidelity audiosystem, such a condition grossly degrades thequality of the sound. The amplifying device (transistoror vacuum tube) is in or near saturationduring part of the signal cycle. This reduces theefficiency of the circuit, can cause excessive collector,drain, or plate current, and can overheatthe base–collector (B-C) junction of a bipolartransistor. In the worst case, it can destroy thecomponent.overdriven amplifier See OVERDRIVEN UNIT.overdriven unit An amplifier, oscillator, or transducerwhose driving signal (current, voltage,power, or other quantity) is higher than thatwhich the device can properly or efficiently handlefor correct or intended operational performance.overdub In audio recording, a method of combiningtwo or more signals onto a single tape track.For example, a live voice can be recorded on atape containing pre-recorded music.overexcited Receiving higher than normal excitation,as in radio-frequency amplifiers or alternating-currentgenerators.overflow 1. In computer or calculator operation,the condition in which an arithmetic operationyields a result exceeding the capacity of the locationor display for a result. 2. The carry digit thatresults from the condition described in (1).overflow indicator 1. In a digital calculator, a displaythat indicates that a numerical value is toolarge or too small to be shown with the availablenumber of decimal places. 2. In data processing,a display that indicates the presence of too manybits or characters for the available storagecapacity.overflow position In a digital computer, an auxiliaryregister position for developing the overflowdigit (see OVERFLOW, 1, 2).overflow record In data processing, a record thatwill not fit the storage area allotted for it, and thatmust be kept where it can be retrieved, accordingto some reference stored in its place.overflow storage In a calculator or computer, extrastorage space, allowing a small amount ofoverflow without loss of accuracy.overhanging turns The turns in the unused portion(s)of a tapped coil.overhead line A power or transmission line suspendedabove the ground between poles or towers.over-horizon radar A form of radar used at highfrequencies, in which pulses are transmitted andreceived. The signals are returned to earth via theionosphere, both in the forward and reflected directions,making it possible to detect such thingsas missile launchings from thousands of milesaway.over-horizon transmission See FORWARD SCAT-TER.overinsulation Use of excessive insulation for aparticular application. Compare UNDERINSULA-TION.over insulation The insulation (usually a strip oftape) laid over a wire brought up from the centerof a coil. Compare UNDER INSULATION.overlap 1. The time during which two successiveoperations are performed simultaneously. 2. In afacsimile or television system, a condition in whichthe scanning line is wider than the center-tocenterseparation between adjacent scanning lines.overlap radar A long-range radar situated in onesector and covering part of another sector.overlay 1. A sheet of transparent or translucentmaterial laid over a schematic diagram for thepurpose of tracing connections that have beenmade in wiring an equipment from the diagram.2. In computer operations, a method whereby thesame internal storage locations are used for differentparts of a program during a program run.It is used when the total storage requirements forinstructions exceed the available main storagecapacity.overlay transistor A double-diffused epitaxialtransistor having separate emitters connected togetherby means of diffusion and metallizing toincrease the edge-to-area ratio of the emitters.This design raises the current-handling ability ofthe transistor. Also see DIFFUSED TRANSISTORand EPITAXIAL TRANSISTOR.overload 1. Current or power drain in excess of therated output of a circuit or device. 2. An excessivedriving signal.overload circuit breaker See CIRCUIT BREAKER.overloaded amplifier A power amplifier deliveringexcessive output power. Compare UNDER-LOADED AMPLIFIER, 2.overloaded oscillator An oscillator from whichexcessive power is drawn, causing instability,frequency shift, lowered output voltage, andoverheating.overload indication Any attention-catchingmethod, such as an audible or visual alarm, forwarning that a prescribed signal or power levelhas been exceeded.overload level The amount of overload that cansafely be applied to an equipment (see OVER-LOAD, 1).overload protection The use of circuit breakers,relays, automatic limiters, and similar devices toprotect equipment from overload damage by reducingcurrent or voltage, disconnecting thepower supply, or both.overload recovery time Following an overdrive atthe input of an integrated-circuit device, the timerequired for the output to resume its normalcharacteristics.

508 overload relay • oxidation-reduction potentialoverload relay A relay actuated when circuit currentexceeds a predetermined value. CompareUNDERLOAD RELAY.overload time The maximum length of time thatan equipment can safely be subjected to an overloadlevel of current.overmodulation Modulation in excess of a prescribedlevel—especially amplitude modulationgreater than 100%. Compare COMPLETE MODU-LATION and UNDERMODULATION.Relative amplitudeovershootOvershootTimeCarrier levelovermodulationTimeovermodulation alarm See OVERMODULATIONINDICATOR.overmodulation indicator A device, such as aneon bulb, incandescent lamp, light-emittingdiode, analog meter, or digital meter, adapted togive an alarm when the modulation percentage ofa signal exceeds a predetermined value.overpotential See OVERVOLTAGE.overpower relay A relay actuated by a rise inpower above a predetermined level. Compare UN-DERPOWER RELAY.overpressure For a pressure transducer, pressurein excess of the maximum rating of the device.override 1. To intentionally circumvent an automaticcontrol system. 2. To bridge a functionalstage of a system.overscanning The deflection of the beam of a cathode-raytube beyond the edges of the screen.overshoot 1. The momentary increase of a quantitybeyond its normal maximum value (e.g., thespike sometimes seen on a square wave becauseof the overswing of a rising voltage). 2. Momentaryovertravel of the pointer of an analog meter.overswing See OVERSHOOT, 2.overtemperature protection The use of an automaticdevice, such as a thermal relay or thermostat,to disconnect a device from the powersupply when the device’s temperature becomesexcessive.overthrow See OVERSHOOT, 2.overtone See HARMONIC.overtone crystal A piezoelectric quartz crystalthat oscillates at odd multiples of the frequencyfor which it was cut. This allows crystal operationat frequencies otherwise obtainable only from afundamental-frequency crystal ground so thin asto be prohibitively fragile.overtone oscillator A crystal oscillator using anOVERTONE CRYSTAL.overtravel See OVERSHOOT, 2.overvoltage A voltage higher than a specified orrated value. Compare UNDERVOLTAGE.overvoltage circuit breaker A circuit breaker thatopens when voltage exceeds a predeterminedvalue.overvoltage protection The use of a special circuitor device to protect equipment from excessivevoltage. When voltage increases beyond the overvoltagelimit, the protective circuit causes shutdown.overvoltage relay A relay actuated when voltagerises above a predetermined value. Compare UN-DERVOLTAGE RELAY.overwrite In computer operations, to record newdata over existing data (e.g., to update the files ona magnetic disk or tape).Ovshinsky effect In thin-film solid-state devices,the tendency for switches to have the same characteristicsfor currents in either direction.O wave One (the ordinary) of the pair of componentsinto which an ionospheric radio wave is divided byEarth’s magnetic field. Compare X WAVE.Owen bridge A wide-range four-arm bridge thatmeasures inductance in terms of a standard capacitanceand bridge-arm resistances.own coding Additional program steps added tovendor-supplied software so that it can be modifiedto fit special needs.ox Abbreviation of OXYGEN.oxidation 1. The combination of a substance withoxygen. Generally a slow process, such as thecorrosion of iron or aluminum in the atmosphere.The process is accelerated by the presence ofmoisture and/or high temperatures. 2. The lossof electrons from a cell or battery during discharge.oxidation-reduction potential The potential atwhich oxidation occurs at the anode of an electrolyticcell, and at which reduction occurs at thecathode.

oxide-coated cathode • ozone monitor 509oxide-coated cathode See OXIDE-COATED EMIT-TER.oxide-coated emitter An electron-tube cathode orfilament coated with a material, such as thoriumoxide, for increased electron emission at lowemitter temperatures.oxide-coated filament See OXIDE-COATEDEMITTER.oxide film 1. The thin film of iron oxide that constitutesthe recording surface of a magnetic diskor tape. 2. The layer of copper oxide formed onthe copper plate of a copper-oxide rectifier.oxide-film capacitor An electrolytic capacitor, socalled because the dielectric is a thin oxide film.oxide rectifier A solid-state rectifier using a junctionbetween copper and copper oxide. Also calledCOPPER-OXIDE RECTIFIER.oximeter A photoelectric instrument for measuringthe oxygen content of the blood. It operates bypassing visible light through the earlobe, and analyzingthe color and intensity of the emergingbeam. Also called ANOXEMIA TOXIMETER.oxygen Symbol, O. Abbreviation, O 2 . A gaseous element.Atomic number, 8. Atomic weight, 15.999.Constitutes 21% of Earth’s atmosphere. It readilycombines with various elements to form compounds(see OXIDATION).oxygen analyzer An electronic gas analyzer designedespecially to measure oxygen content. Theoperation of this instrument is based on the paramagneticproperties of oxygen.oxygen recombination In nickel-cadmium (NICAD)cells and batteries, a process in which oxygen isgenerated in the vicinity of the positive electrode,and is reduced with water in the vicinity of thenegative electrode. This produces battery heating.oz 1. Abbreviation of OUNCE. 2. Abbreviation ofOZONE.oz-in Abbreviation of OUNCE-INCH.ozocerite An insulating mineral wax. Dielectricconstant, 2.2. Dielectric strength, 4 to 6 kV/mm.Also spelled OZOKERITE.ozone Symbol, O 3 . An allotropic form of oxygen. Itsformula indicates that each molecule has threeatoms. Produced by the action of ultraviolet rays(or electrical discharge) on oxygen, its characteristicodor (somewhat like weak chlorine) can oftenbe detected around sparking contacts or in theair after a thunderstorm.ozone layer In the earth’s atmosphere, a layer ofozone gas in the upper troposphere and lowerstratosphere. It is produced by ultravioletradiation from space, mainly from the sun. Theozone layer tends to block ultraviolet radiation,reducing the amount that reaches the surface ofthe earth.ozone monitor An instrument for measuring theconcentration of ozone in the atmosphere. Oneversion measures the extent to which ultravioletradiation is absorbed by a sample of air; thegreater the absorption, the higher the ozone concentrationin the sample.

P 1. Symbol for POWER. 2. Symbol for PLATE (of avacuum tube). 3. Symbol for PHOSPHORUS. 4.Abbreviation of PRESSURE. 5. Symbol for PRI-MARY. 6. Abbreviation for prefix PETA-. 7. Symbolfor PERMEANCE. 8. Abbreviation of POINT.p 1. Abbreviation of prefix PICO-. 2. Subscript forPEAK. 3. Abbreviation of POUND. 4. Abbreviationof POINT (often capitalized). 5. Subscript for PRI-MARY. 6. Subscript for PLATE (of a vacuumtube). 7. Abbreviation of PITCH. 8. Abbreviationof PER.PA 1. Abbreviation of POWER AMPLIFIER. 2. Abbreviationof PULSE AMPLIFIER. 3. Abbreviationof particular average. 4. Abbreviation of pilotlessaircraft. (Also, P/A.) 5. Abbreviation of PUBLICADDRESS (as in PA system).Pa 1. Symbol for PROTACTINIUM. 2. Symbol forPASCAL.pA Abbreviation of PICOAMPERE.pacemaker See CARDIAC STIMULATOR.pacer See CARDIAC STIMULATOR.Pacific Standard Time Abbreviation, PST. Localmean time at the 120th meridian west of Greenwich.Also see GREENWICH MEAN TIME, STAN-DARD TIME, TIME ZONE, and COORDINATEDUNIVERSAL TIME.packA technique for maximizing a computer memorydevice’s storage capacity, wherein more thanone information item is stored in a single storageunit. Also called crowd.package1. The enclosure for an electronic deviceor system. This includes a wide range of housings,from the simple encapsulation of miniaturetransistors to forced-air-cooled enclosures forheavy power units. 2. To assemble and house anelectronic equipment, or to design a housing forit, in accordance with good engineering techniques.3. A computer program of general use foran application (e.g., payroll package).package count The number of discrete packagedcircuits in a system.packaging density 1. See VOLUMETRIC EFFI-CIENCY. 2. Computer storage capacity in termsof the number of information units that can becontained on a given segment of a magneticmedium. Also called PACKING DENSITY. 3.Within a given integrated circuit, the capacity interms of the number of active devices that can becontained on a single silicon chip.packet 1. A unit of digital information in PACKETCOMMUNICATIONS. It consists of a header followedby a certain number of data bits or bytes.2. See WAVE PACKET. 3. See PACKET COMMU-NICATIONS. 4. See PACKET RADIO.packet communications A method via which datais exchanged through a network between oramong people or computers. Information is sentand received in blocks of information calledpackets. Each packet is routed individuallythrough the network according to the most efficientpossible path at the time of its transit. Atthe destination, the packets are reassembled intothe original signal. This scheme makes more efficientuse of network resources than continuousconnectionor single-path methods. However,when network usage is heavy, there can be a delayin the arrival of a sufficient number of packetsto produce an intelligible received signal.packet radio The transmission and reception ofPACKET COMMUNICATIONS data via radio.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

packet switching • panel meter 511packet switching In telephony, a method of connectionin which data is exchanged between subscribersby splitting the data into units (packets).Each packet is sent over the optimum path at thetime of transmission. The signal path can, andusually does, vary from packet to packet. At thedestination, the packets are reassembled into theoriginal singal. The connection is in effect nonexistentduring periods of silence (no data transmittedby either subscriber). Compare CIRCUITSWITCHING.packing In the button of a carbon microphone,bunching and cohesion between the carbon granules.packing density The number of discrete packagecircuits within a given surface area or volume.packing factor 1. See VOLUMETRIC EFFICIENCY.2. In computer operations, the number of bitsthat can be recorded in a given length of magneticmemory surface. Also called PACKING DENSITY.pack transmitter A portable transmitter that canbe strapped to the operator’s back.pack unit A portable transceiver that can bestrapped to the operator’s back or carried on ananimal’s back.PACM Abbreviation of pulse-amplitude code modulation.pad 1. An attenuator network (usually a combinationof resistors) that reduces the amplitude of asignal by a desired amount while maintainingconstant input and output impedance. 2. In computeroperations, to make a record a fixed size byadding blanks or dummy characters to it. 3. Tolower the frequency of an inductance-capacitance(LC) circuit by adding capacitance to an alreadycapacitively tuned network.padder See OSCILLATOR PADDER.padding capacitor See OSCILLATOR PADDER.padding character In a digital communications system,a character that is inserted solely for the purposeof consuming time while no meaningfulcharacters are sent. The insertion of such charactersmaintains the synchronization of the system.paddle-handle switch A toggle switch the lever ofwhich is a flattened rod. Compare BAT-HANDLESWITCH, ROCKER SWITCH, and SLIDE SWITCH.PADT Abbreviation of POST-ALLOY-DIFFUSEDTRANSISTOR.paddle-handle switchpage A display of text data on a computer displaythat completely fills the screen.page printer A computer peripheral that prints amessage in lines on a page, according to an establishedformat, rather than in a single line.pager 1. A public-address system used for summoningpurposes. 2. See BEEPER, 2.page turning The successive display of pages (seePAGE).pair 1. Two wires, especially two insulated conductorsin a cable. 2. A set of two particles or chargecarriers (e.g., electron-hole pair). 3. A set of twotransistors or vacuum tubes, operating togetherin push-pull or parallel in a power amplifier.paired cable A cable consisting of separate twistedpairs of conducting wires.paleomagnetism The study of certain rocks andminerals to determine the nature of the earth’smagnetic field at the time the rocks were formed.When the age of the rock is determined by meansof radioactive dating, and numerous rock samplesare found covering many different eras, thenature of the earth’s magnetic field can begraphed over time.palladium Symbol, Pd. A metallic element of theplatinum group. Atomic number, 46. Atomicweight, 106.42.palletizing In industrial robots, the automaticplacing of objects in a tray according to a computerprogram.Palm See HANDHELD COMPUTER.Palmer scan In radar, a method of simultaneouslyscanning the azimuth and the elevation.PalmPilot See HANDHELD COMPUTER.palmtop computer See HANDHELD COMPUTER.PAM Abbreviation of PULSE-AMPLITUDE MODU-LATION.Pan In radiotelephony, a spoken word indicatingthat an urgent message is to follow. It is equivalentto the XXX of radiotelegraphy.pan 1. To make a panoramic sweep [e.g., to sweepa wide area with a beam (as from an antenna), orto sweep a wide band of frequencies with a suitabletuning circuit]. 2. A panoramic sweep madeas defined in 1. 3. In audio engineering, to graduallyshift from one audio channel to another orfrom one reproducer to another.pan and tilt 1. An azimuth-elevation mounting fora television camera. 2. The simultaneous movementof a television camera in the vertical andhorizontal directions.pancake coil See DISK WINDING.panel A flat surface on which are mounted the controlsand indicators of an equipment, for easy accessto the operator.panel lamp 1. See ELECTROLUMINESCENTPANEL. 2. See PANEL LIGHT.panel light A pilot light for illuminating the frontpanel of a piece of equipment.panel meter A usually small meter for mountingon, or through an opening in, a panel.

512 panic button • parallel capacitorspanic button In a security system, a button orswitch that immediately triggers an alarm when itis closed.panoramic adapter An external device that can beconnected to a receiver to sweep a frequencyband and indicate carriers on the air as pips on ascreen at the corresponding frequency points.Also called pan adapter.panoramic display 1. A wide-angle display. 2. Aspectrum-analyzer display that shows a widerange of frequencies, from zero to well above themaximum frequency in the monitored system.panoramic radar An omnidirectional radar (i.e.,one that transmits wide-beam signals in all directionswithout scanning).panoramic receiver A receiver that displays pipson a screen to show carriers on the air in a givenfrequency band. All frequencies in the band arepresented along the horizontal axis of the screen.panpot A potentiometer with which panning canbe achieved (see PAN, 3).pan-range A form of radar display in which targetmotion can be ascertained.pantography The transmission of radar informationto a distant location for observation or recording.Papa Phonetic alphabet code word for the letter P.paper advance mechanism In a data-processingsystem, the part of a printer that moves (sometimesby computer control) the paper through theprinter.paper capacitor A component that is made byplacing paper, soaked with mineral oil, betweentwo strips of foil. The assembly is rolled up, andwire leads are attached to the two pieces of foil.Finally, the rolled-up foil and paper are enclosedin a cylindrical case. These components aresometimes found in radio-frequency (RF) electronicequipment. They have values ranging fromabout 0.001 microfarads (µF) to 0.1 µF, and canhandle low to moderate voltages, usually up toabout 1000 volts. Compare CERAMIC CAPACI-TOR, ELECTROLYTIC CAPACITOR, MICACAPACITOR, PLASTIC-FILM CAPACITOR,TANTALUM CAPACITOR.PAR Abbreviation of PRECISION APPROACHRADAR.par Abbreviation of PARALLEL.parabola A plane curve that is the locus of pointsthat are equidistant from a fixed point (the focus)FoilPaperFoilPaperpaper capacitorand a fixed straight line (the directrix). In theCartesian xy-plane, the general equation is y =ax2 + b, where a and b are constants.parabola control See VERTICAL-AMPLITUDECONTROL, 2.parabola generator A circuit for generating aparabolic-waveform signal.parabolic microphone A directional microphonemounted at the principal focus of a parabolicsound reflector; the front of the microphone facesthe inside of the parabola. It is useful for detectingsounds from great distances.parabolic reflector Also called paraboloidal reflector.A reflector having the shape of a paraboloid.It is particularly useful for focusing or directingradiation. For example, if a radiator, such as anantenna rod, is placed at the focus of theparaboloid, a beam of parallel rays will be emittedby the reflector.paraboloid The surface generated by a PARABOLArotated about its axis of symmetry.paraffin A relatively inexpensive, easily available,solid, white petroleum wax. At one time, it wasused to impregnate capacitors and coils and towaterproof paper used for insulating purposes.parallaxThe apparent shift in the position of a relativelynearby object when the observer moves oralternately blinks either eye. Thus, a pointer-typemeter will seem to give different readings whenviewed from different angles. Some meters havemirrored scales to eliminate this effect.parallel1. Pertaining to the type of operation in acomputer when all elements in an informationitem (e.g., bits in a word) are acted upon simultaneously,rather than serially (one at a time).2. The condition in which two comparably sizedobjects or figures are equidistant at all facingpoints. 3. Pertaining to the shunt connection ofcomponents or circuits.parallel access In computer operations, inputtingor outputting data to or from storage in whole elementsof information items (a word, rather thana bit at a time, for example).parallel adder In a computer or calculator, anadder in which corresponding digits in multibitnumbers are added simultaneously. Also seePARALLEL, 1.parallel antenna tuning Antenna-feeder tuning inwhich the tuning capacitor is connected in parallelwith the two feeder wires. Compare SERIESANTENNA TUNING.parallel arithmetic unit See PARALLEL ADDER.parallel capacitance 1. A capacitance connectedin parallel (shunt) with some other component.2. The capacitance between the turns of a coil.Also see DISTRIBUTED CAPACITANCE.parallel capacitors Two or more capacitors connectedin parallel (shunt) with each other. Thetotal capacitance is equal to the sum of theindividual capacitances. Also see PARALLELCIRCUIT.

parallel circuit • parallel operation 513parallel circuit A circuit in which the componentsare connected across each other (i.e., so that thecircuit segment could be drawn showing componentleads bridging common conductors as rungswould across a ladder). Compare SERIES CIR-CUIT.parallel-component amplifier An amplifier stagein which the active devices (transistors or vacuumtubes) are connected in parallel with eachother for increased power output. Also see PAR-ALLEL CIRCUIT.parallel-component oscillator An oscillator stagein which transistors are connected in parallelwith each other for increased power output. Alsosee PARALLEL CIRCUIT.parallel computer A computer equipped to handlemore than one program at a time, but notthrough the use of multiple programming ortime-sharing.parallel-cut crystal See Y-CUT CRYSTAL.parallel-diode half-wave rectifier See PARALLELLIMITER.parallel-fed amplifier An amplifier circuit in whichthe direct-current operating voltage is applied inparallel with the alternating-current output voltage.Also see PARALLEL FEED.parallel-fed oscillator An oscillator circuit inwhich the direct-current operating voltage is appliedin parallel with the alternating-current outputvoltage. Also see PARALLEL FEED.parallel feed 1. The presentation of parallel alternating-current(ac) and direct-current (dc) voltagesto a device. 2. The presentation of a dcoperating voltage in parallel with the ac outputvoltage of a device (as in a parallel-fed amplifier oroscillator). Also see SHUNT FEED.parallel gap welding A welding technique usingtwo electrodes separated by a gap.parallel gate circuit 1. A gate circuit using twobipolar transistors with parallel-connected collectorsand emitters, and a common collector resistor.The input signal is applied to one base, andthe control signal to the other. 2. A gate circuitusing two field-effect transistors with parallelconnecteddrains and sources, and a commondrain resistor. The input signal is applied to onegate, and the control signal to the other.parallel inductance An inductance connected inparallel (shunt) with some other component.parallel inductors Inductors connected in paralleland separated or oriented to minimize the effectsof mutual inductance. Also see PARALLEL CIR-CUIT.parallel inverse feedback In a single-ended audioamplifier circuit, a simple system for obtainingnegative feedback: A high resistance is connectedfrom the output-transistor collector or drain tothe driver-transistor collector or drain.parallel limiter A limiter (clipper) circuit in whichthe diode is in parallel with the signal. CompareSERIES LIMITER.Positive limiting0 0v inNegative limiting0 0v inparallel limiterparallel-line tuning At ultra-high frequencies(UHF) and microwave frequencies, the use of twoparallel wires or rods for tuning. A straight shortcircuitingbar is slid along the wires to accomplishtuning.parallelogram A two-dimensional geometric figurethat has four sides. Opposite pairs of sides are parallel.Opposite interior angles have equal measure.yxxparallelogramparallelogram of vectors A graphic device for findingthe sum of two vectors. A parallelogram isconstructed for which the two vectors are adjacentsides. The sum of the vectors is representedby the diagonal of the parallelogram.parallel operation In computer operations, the simultaneoustransmission of all bits in a multibitword over individual lines, as compared with theserial transmission of a word bit by bit.v outv outy

514 parallel output • parallel-wire lineparallel output A digital output consisting of twoor more lines, all of which carry data at the sametime.parallel processing In computer operations, thesimultaneous processing of several different programsthrough separate channels. CompareSERIAL PROCESSING.parallel Q Symbol, Q p . The figure of merit of a parallelcircuit of inductance, capacitance, and resistance.parallel resistance 1. A resistance connected inparallel (shunt) with some other component.2. The resistance between the plates of a capacitor.3. The resistance across a coil.parallel resistors Resistors connected in parallel.If the individual resistances are represented byR 1 , R 2 , R 3 , . . ., Rn, then total resistance R t isequal to 1/(1/R 1 + 1/R 2 + 1/R 3 + . . . + 1/R n ). Alsosee PARALLEL CIRCUIT.parallel resonance Resonance in a circuit consistingof a capacitor, inductor, and alternatingcurrentsource connected in parallel. At theresonant frequency, the inductive reactance isequal in magnitude, but opposite in effect, to thecapacitive reactance. The capacitor current andinductor current are maximum, the line currentis minimum, and the circuit impedance is maximum.Compare SERIES RESONANCE.parallel-resonant circuit A resonant circuit inwhich the capacitor, inductor, and alternatingcurrentsource are connected in parallel. CompareSERIES-RESONANT CIRCUIT.parallel-resonant trap A wavetrap consisting of aparallel-resonant inductance-capacitance (LC)circuit. Compare SERIES-RESONANT TRAP.parallel-resonant trapparallel-resonant wavetrap See PARALLEL-RESONANT TRAP.parallel-rod oscillator An ultra-high-frequency(UHF) oscillator tuned by means of two straight,parallel quarter- or half-wave rods, one rod connectedto the base or gate of a transistor, and theother rod connected to the collector or drain.parallel-rod tuning Adjustment of the resonant frequencyof a section of open-wire transmission line.A movable shorting bar allows quarter-wave resonance.The impedance at resonance is very high.Input1 /4 WavelengthMoveableshorting barparallel-rod tuningparallel-series Also called series-parallel. Pertainingto an arrangement of components, usuallysimilar (e.g., resistances), consisting of parallelcircuits connected in series with each other, or ofseries circuits connected in parallel with eachother. Usually, the component values or ratingsare all identical, so currents and/or voltages areequally shared among them. Also see PARALLELCIRCUIT and SERIES CIRCUIT.parallel-series capacitors Capacitors connectedin PARALLEL-SERIES, usually to obtain highervoltage and/or current ratings than an individualcapacitor can provide.parallel-series inductors Inductors connected inPARALLEL-SERIES and separated or oriented tominimize the effects of mutual inductance.parallel-series resistors Resistors connected inPARALLEL-SERIES, usually to obtain a higherpower rating than an individual resistor can provide.parallel storage In a computer, storage in whichall information items can be made available in thesame amount of time.parallel-tee amplifier A bandpass amplifier havinga parallel-tee network in its negative-feedbackpath. The null frequency of the network determinesthe pass frequency of the amplifier.parallel-tee measuring circuit A parallel-tee networkused for measuring circuit constants. Alsocalled TWIN-TEE MEASURING CIRCUIT.parallel-tee network A resistance-capacitance(RC) network containing two tee sections (with Rand C elements opposite in the tees) connected inparallel. The network produces a null at one frequency.Also called TWIN-T NETWORK.parallel-tee oscillator A resistance-capacitancetuned oscillator having a parallel-tee network inits negative-feedback path. The null frequency ofthe network determines the oscillator frequency.parallel transfer A form of digital informationtransfer, consisting of two or more lines thatcarry data at the same time.parallel-wire line A transmission line consisting oftwo parallel wires whose separation is kept

parallel-wire line • parasitic capacitance 515constant by dielectric rods (open-wire line) or asolid dielectric web (ribbon line).parallel-wire tank In an ultra-high-frequency(UHF) amplifier or oscillator, a resonant circuitconsisting of two separate parallel wires connectedto the transistor(s) or tube(s) at one end,and short-circuited or tuned at the other end.paramagnet A paramagnetic substance (see PARA-MAGNETISM). Compare DIAMAGNET.paramagnetic Possessing PARAMAGNETISM.Compare DIAMAGNETISM.paramagnetism The state of having a magneticpermeability slightly greater than 1. CompareDIAMAGNETISM.parameter1. An operating value, constant, or coefficientthat can be either a dependent or an independentvariable (e.g., a transistor-electrodecurrent or voltage). 2. The ratio of one coefficientto another, where both are either fixed or variable(e.g., transconductance of a vacuum tube).parameter word In a computer memory, a placehaving a capacity of a word (bit group) in which isstored a parameter for a program.parametric amplifier A radio-frequency poweramplifier based on the action of a voltage-variablecapacitor in a tuned circuit.parametric amplifier diode See VARACTOR.parametric converter A frequency converter inwhich a parametric device, such as a varactor, isused to change a signal of one frequency to a signalof another frequency. Also see PARAMETRICDOWN-CONVERTER and PARAMETRIC UP-CONVERTER.parametric diode A variable-capacitance diode(see VOLTAGE-VARIABLE CAPACITOR, 1).parametric down-converter A parametric converterin which the output signal is of a lowerfrequency than the input signal. ComparePARAMETRIC UP-CONVERTER.parametric equalizer A set of audio filters similarto a GRAPHIC EQUALIZER, except that the centerfrequencies are adjustable, rather than fixed.The center frequencies are selected by the operator;then the attenuation level (in decibels) is setfor each frequency. It is used in audio recordingstudios.parametric modulation Modulation in which eitherthe inductance or capacitance of a tank circuitor coupling device is varied at themodulation frequency.parametric oscillator An oscillator that generatesvisible light energy by means of a parametric amplifierand a tunable cavity.parametric up-converter A parametric converterin which the output signal is of a higher frequencythan the input signal. Compare PARA-METRIC DOWN-CONVERTER.parametron See PHASE-LOCKED OSCILLATOR.paramistor A device consisting of several digitalcircuit elements that use parametric oscillators.paramp Abbreviation of PARAMETRIC AMPLIFIER.paraphase inverter A single-transistor phase inverterin which the two out-of-phase output signalsare obtained by taking one output from thecollector or drain, and the other output fromthe emitter or source. Thus, the 180-degreephase difference between collector/drain andemitter/source is exploited.+ 12 VInparaphase inverterOut YOut Xparasitic See PARASITIC OSCILLATION.parasitic antenna See PARASITIC ARRAY, PARA-SITIC ELEMENT.parasitic array Any of several types of directionalantenna employing parasitic elements, sometimesin combination with phasing, to obtain directivityand gain. Common examples include theYagi and quad. Arrays with numerous parasiticelements (usually directors) can produce upwardsof 15 dBd forward gain. When severalhigh-gain arrays are phased, the realizablegain becomes greater still. Two-element, threeelement,and four-element arrays are commonbelow 30 MHz. At very-high and ultra-high frequencies,especially above 100 MHz, bays of antennasof this type are used in satellitecommunications and radio astronomy. See PAR-ASITIC ELEMENT, QUAD ANTENNA, YAGI AN-TENNA.parasitic capacitance Stray capacitance. It can beinternal or external to a circuit and can introduceundesirable coupling or bypassing.

516 parasitic choke • pass amplifierparasitic choke A small radio-frequency chokecoil (with or without a shunting resistor) thatsuppresses or eliminates parasitic oscillation in apower amplifier.parasitic director In a multielement directionalantenna, a parasitic element acting as a director;usually, it is a few percent shorter than the drivenelement.parasitic element An electrical conductor thatcomprises an important part of an antenna system,but that is not directly connected to the feedline. Such elements are used for the purpose ofobtaining directivity and power gain. They operatevia electromagnetic coupling to the driven element(s).The principle of operation was firstdiscovered by the Japanese engineers Yagi andUda, who observed that antenna elements parallelto a driven element but not connected to anything,at a specific distance from the drivenelement, and having a certain length, cause theradiation pattern to show gain in one directionand loss in the opposite direction. See DRIVENELEMENT, PARASITIC ARRAY, PARASITIC DI-RECTOR, PARASITIC REFLECTOR.parasitic-element directive antenna See PARA-SITIC ARRAY.parasitic eliminator See PARASITIC SUPPRES-SOR.parasitic excitation Excitation of a beam-antennaelement without a direct connection to the transmitter.Thus, a director or reflector element canbe excited by the field of the radiator element.parasitic inductance Stray inductance (e.g., theinternal inductance of a wirewound resistor).parasitic oscillation Extraneous, useless oscillationpresent as a fault in an electronic circuit,particularly a radio-frequency power amplifier.parasitic reflector In a multielement beam antenna,a parasitic element acting as a reflector;usually, it is a few percent longer than the drivenelement.parasitic resistance Stray resistance (e.g., the inherent,internal resistance of a multilayer coil).parasitic suppressor A small resistor, coil, or parallelcombination of the two, connected in serieswith the plate or collector of a vacuum tube ortransistor to eliminate parasitic oscillations in aradio-frequency power amplifier.PARD Abbreviation of PERIODIC AND RANDOMDEVIATION.parity 1. At par (with respect to the even-or-oddstate of the characters in a group). 2. Having thequality that the number of bits (or the number ofsimilar bits) are even or odd, as intended.parity bit 1. In computer operations, a logic 1added to a group of bits so that the number of 1sin the group is, according to specification, even orodd. 2. In computer operations, a check bit thatcan be a logic 1 or 0, depending on the parity (seePARITY, 1) of the total of 1s in the bit group beingchecked.parity check A check of the integrity of data beingtransferred by adding the bits in, for example, aword, and then determining the parity bit neededand comparing that with the transmitted paritybit.parity error An error disclosed by a parity check.parity tree A digital device used to check parity.parsec Abbreviation, pc. The distance at which themean radius of the earth’s orbit around the sunsubtends an angle of 1 second of arc; 1 pc =3.0857 × 10 13 kilometers or 3.2616 light years.part See CIRCUIT COMPONENT, 1.part failure The usually destructive breakdown ofa circuit component.partial One of the frequencies in a complex musicaltone. It might be a harmonic of the fundamentalfrequency, although this is not always thecase.partial carry The temporary storage of some or allof the carry information in a digital calculation.particle 1. A tiny, discrete bit of matter. 2. A unitof matter smaller and lighter than an atom. See,for example, ANTIPARTICLE, ELECTRON, ME-SON, NEUTRETTO, NEUTRINO, NEUTRON, NU-CLEON, POSITRON, and PROTON.particle accelerator See ACCELERATOR, 1.particle theory of radiation In physics, a modelthat explains the nature of electromagnetic radiation(radio waves, infrared, visible light, ultraviolet,X rays, and gamma rays) in terms of discreteparticles. Each particle, called a PHOTON, carriesa certain amount of energy that depends on thewavelength of the radiation.particle velocity 1. The speed and direction ofthe particles from a source of atomic radiation.2. The speed and direction of the molecules in themedium of an acoustic disturbance.partitioning In computer operations, breakingdown a large block of data into smaller blocksthat can be better handled by the machine.parton model A model for atomic nuclei, in whichprotons and neutrons are made up of smallerparticles called partons. Subparticles have beenfound, commonly called quarks.Pascal A high-level computer programming language,similar to BASIC or FORTRAN in structure.It is used in some schools to teach computerprogramming.pascal Symbol, Pa. The SI (derived) unit of pressure;1 Pa = 1 N/m 2 = 1.4503 × 10 –4 lb/in 2 .Paschen-Back effect See ZEEMAN EFFECT.Paschen’s law For a two-element, parallel-plate,gas-discharge tube, the plate-to-plate sparkingpotential is proportional to Pd, where P is the gaspressure, and d is the distance between plates.pass amplifier A tuned amplifier having the responseof a bandpass filter. Like the filter, theamplifier passes one frequency (or a narrowband of frequencies) readily while rejecting orattenuating others. Compare REJECT AMPLI-FIER.

passband • passive reflector 517passband The continuous spectrum of frequenciestransmitted by a filter, amplifier, or similar device.Compare STOPBAND.passband ripple Multiple low-amplitude attenuationvariations within the passband of a filter ortuner, resulting in a ripple pattern on the nose ofthe response curve.Relativefreq.,kHzPassbandat 3 dB down1020Ripplerequires no power for its characteristic operation).Examples: conventional resistor, capacitor,inductor, diode, rectifier, and fuse. Compare AC-TIVE COMPONENT, 1.passive comsat See PASSIVE COMMUNICATIONSSATELLITE.passive decoder A decoder that responds to onlyone signal code, rejecting all others.passive detection In reconnaissance, detecting atarget without betraying the location of the detector.passive electric network See PASSIVE NET-WORK.passive frequency multiplier A frequency multiplierthat does not require a power supply, butoperates only from the input signal energy. Usuallyconsists of one or more semiconductor diodes,sometimes in conjunction with inductors and/orcapacitors. The output signals appear at integralmultiples of the input frequency.−6 −4 −2+2 +4 +64050Attenuation,dB60passbandpassband ripplepassivation The process of growing a thin oxidefilm on the surface of a planar semiconductor deviceto protect the exposed junction(s) from contaminationand short circuits. See, for example,PLANAR EPITAXIAL PASSIVATED TRANSISTORand PLANAR TRANSISTOR.passive absorber A substance that reflects minimalsound energy. Examples include acousticalceiling tile and thick carpeting.passive circuit A circuit consisting entirely of nonamplifyingcomponents, such as capacitors, resistors,inductors, and diodes.passive communications satellite A communicationssatellite that reflects electromagnetic waves,but does not contain a transponder; that is, itdoes not receive and retransmit the signals. Alsocalled passive comsat. Compare ACTIVE COM-MUNICATIONS SATELLITE.passive component A device that is basicallystatic in operation (i.e., it is ordinarily incapableof amplification or oscillation and usuallypassive infrared sensor A device that detects infrareddirectly, such as that given off by humansbecause of their body heat. It does not generateenergy of any kind. It is used in some intrusiondetection systems.passive mixer A signal mixer using only passivecomponents (diodes, nonlinear resistors, andnonlinear reactances) (i.e., one without activecomponents, such as transistors). Passive mixersintroduce some loss. Compare ACTIVEMIXER.passive modulator A modulator using only passivecomponents (diodes, nonlinear resistors, andnonlinear reactances) (i.e., one without activecomponents, such as transistors). Passive modulatorsintroduce some loss. Compare ACTIVEMODULATOR.passive network A network composed entirely ofpassive components (i.e., one containing no generatorsand providing no amplification).passive radiator See DRONE CONE.passive reflector A metal surface used to reflectelectromagnetic energy at ultra-high and microwavefrequencies.

518 passive transponder • PbX inY inpassive mixerOutpassive transponder A device that allows a machine,such as a computer or robot, to identify anobject. A bar-code reader is a common example.Magnetic labels, such as those on credit cardsand bank cash cards, are another example. It isso named because it does not transmit data; it requiresa sensor for data detection.password As a security device in computer operations,a group of characters upon whose presentationto the system via a terminal the user isallowed access to memory or control of information.password retry limitation A security feature thatprevents hackers from making repeated guessesat passwords in an attempt to break into a computer,network, or database. If more than threeunsuccessful entries are made in succession, forexample, the system will not accept further accessattempts for a certain preprogrammedlength of time, say 1 hour.paste In “dry” batteries and electrolytic capacitors,a gelatinous electrolyte.patch 1. A temporary signal path, as between a radioreceiver and a telephone or, conversely, betweena telephone line and a radio transmitter.2. To make quick, usually temporary connections,as with a patch cord. 3. Instructions entered byan unconditional branch to a computer programfor the purpose of correction.patch bay 1. See PATCH PANEL. 2. A set of patchpanels.patch cord A flexible line of one or more conductorswith a jack or connector at each end, used tointerconnect (patch) circuit points exposed for thepurpose on a panel or breadboard.Patchett tone control A dual tone-control circuitusing a variable series resistance-capacitance(RC) filter for treble boost, and a variable shuntRC filter for bass boost. The input signal is appliedin parallel to both filters. The outputs arecombined in an audio mixer.patching The interconnection of two or more signalmedia or lines.patch panel A panel on which the terminals of asystem are accessible for interconnection, tests,etc. It is used especially in high-fidelity audiorecording systems. It was once commonly used inmanual telephone-switching applications.patch up 1. To replace faulty or damaged parts inan electronic system with roughly appropriatesurrogates to restore operation quickly (usuallyunder emergency conditions). Also see DOCTOR.2. To wire a circuit quickly using patch cords forpreliminary test and evaluation.patent 1. A document awarded by a governmentbody, giving to an inventor the exclusive right toexploit an invention for a specified number ofyears. Formally called letters patent. 2. Themonopoly granted by a document, as definedin 1.path1. The route over which current flows. 2. Inradio and navigation, the imaginary line extendingdirectly between transmitter and receiver (ortarget). 3. In a computer program, the logical orderof instructions.pathometer A form of lie detector that indicateschanges in the electrical resistance of the humanbody.pattern 1. An established sequence of steps in aprocess. 2. An arrangement of terms in a matrix.3. The graphical representation of a varyingquantity (e.g., an alternating-current wave pattern).4. The image on the screen of an oscilloscope,or the record traced by an oscillograph.5. The graphic polar representation of the radiationfield of an antenna. 6. The arrangement of bits ina word or field.pattern recognition In machine-vision systems, amethod of identifying an object or decoding dataaccording to geometric shape. Optical characterrecognition (OCR) is an example. The machinerecognizes combinations of shapes, and deducestheir meanings via a computer program.pause editing In the editing of audio tape recordings,the use of a “pause” switch to temporarilystop the tape when necessary.PAV Abbreviation of PHASE-ANGLE VOLTMETER.pawl In a mechanical stepping device, as in a nonelectricclock, a device made to engage the slopingsprockets on a wheel to ensure shaft rotation inone direction only.PAX Abbreviation of PRIVATE AUTOMATIC EX-CHANGE.pay-per-view Abbreviation, PPV. Television servicein which each subscriber pays only for individuallyselected programs.pay TV See SUBSCRIPTION TV.Pb Symbol for LEAD.

P band • peak envelope power 519P band A radio-frequency band extending from 225to 390 MHz.PBX Abbreviation of PRIVATE BRANCH EX-CHANGE.PC 1. Abbreviation of PERSONAL COMPUTER.2. Abbreviation of PRINTED CIRCUIT. 3. Abbreviationof PHOTOCELL. 4. Abbreviation of POSITIVECOLUMN. 5. Abbreviation of POINT-CONTACT.6. Abbreviation of PERCENT (also, pct.). 7. Abbreviationof PROGRAM COUNTER.pc 1. Abbreviation of PICOCOULOMB. Also, pC(preferred). 2. Abbreviation of PICOCURIE. Also,pCi (preferred). 3. Abbreviation of PARSEC.pC Abbreviation for PICOCOULOMB.PCB Abbreviation of PRINTED-CIRCUIT BOARD.PC board See PRINTED-CIRCUIT BOARD.PC diode See POINT-CONTACT DIODE.p-channel JFET See P-CHANNEL JUNCTIONFIELD-EFFECT TRANSISTOR.p-channel junction field-effect transistor Abbreviation,PFET. A junction-type FET in whichthe gate junction has been formed on a bar ordie of p-type semiconductor material. CompareN-CHANNEL JUNCTION FIELD-EFFECT TRAN-SISTOR.p-channel MOSFET A metal-oxide semiconductorfield-effect transistor in which the channel iscomposed of p-type silicon. Also see DEPLETION-TYPE MOSFET, DEPLETION-ENHANCEMENT-TYPE MOSFET, and ENHANCEMENT-TYPEMOSFET.pCi Symbol for PICOCURIE.PCL Abbreviation of PRINTED-CIRCUIT LAMP.PCM Abbreviation of PULSE-CODE MODULATION.PCM-FM Pertaining to a carrier that is frequencymodulated by information that is pulse-codemodulated. Also see FREQUENCY MODULATIONand PULSE-CODE MODULATION.PCM-FM-FM Pertaining to a carrier that is frequencymodulated by one or more subcarriersthat are frequency modulated by information thatis pulse-code modulated. Also see FREQUENCYMODULATION and PULSE-CODE MODULATION.PCM level In a pulse-code-modulated signal, oneof several different possible signal conditions.PCM-PM Pulse-code modulation that is accomplishedby varying the phase of the carrier wave.PC relay See PRINTED-CIRCUIT RELAY.PCS Abbreviation for PERSONAL COMMUNICA-TION SERVICE.PC transistor See POINT-CONTACT TRANSISTOR.PD 1. Abbreviation of PLATE DISSIPATION. 2. Abbreviationof PULSE DURATION. 3. Abbreviationof PROXIMITY DETECTOR. 4. Abbreviation ofPOTENTIAL DIFFERENCE.Pd Symbol for PALLADIUM.PDA Abbreviation for personal digital assistant. SeeHANDHELD COMPUTER.PDAS Abbreviation of programmable data acquisitionsystem.P display See PLAN POSITION INDICATOR.PDM Abbreviation of PULSE-DURATION MODULA-TION.PDM-FM Pertaining to a carrier that is frequencymodulated by one or more subcarriers that arefrequency modulated by pulses that are pulsedurationmodulated. Also see FREQUENCYMODULATION and PULSE-DURATION MODULA-TION.PDM-FM-FM Pertaining to a carrier that is frequencymodulated by one or more subcarriersthat are frequency modulated by pulses that arepulse-duration modulated. Also see FREQUENCYMODULATION and PULSE-DURATION MODULA-TION.PDM-PM Pertaining to a carrier that is phase modulatedby pulse-duration-modulated information.Also see PHASE MODULATION and PULSE-DURATION MODULATION.PDT Abbreviation of PACIFIC DAYLIGHT TIME.PDVM Abbreviation of PRINTING DIGITAL VOLT-METER.PE 1. Abbreviation of POTENTIAL ENERGY. 2. Abbreviationof PROFESSIONAL ENGINEER. 3. Abbreviationof PROBABLE ERROR.peak 1. The maximum value of a quantity. 2. In analternating-current cycle, the maximum positiveor negative current or voltage point. 3. The frequencyat which the transmission by a bandpasscircuit or device is maximum (attenuation isminimum), evidenced by a maximum in thefrequency-response curve.peak amplitude 1. The maximum positive or negativecurrent or voltage of a wave. 2. The maximuminstantaneous power of a signal.peak anode (plate) current The maximum instantaneouscurrent flowing in the anode (plate) circuitof a vacuum tube.peak anode (plate) voltage The maximum instantaneousvoltage applied to the anode (plate) of avacuum tube.peak chopper See PEAK CLIPPER.peak current Abbreviation, I p . The highest valuereached by an alternating-current half-cycle or acurrent pulse. Also called MAXIMUM CURRENT.peak detector See PEAK PROBE.peak distortion 1. The maximum instantaneousdistortion in a signal, generally expressed as apercentage. 2. Distortion of a modulated signal atenvelope peaks.peaked sawtooth A wave composed of a sawtoothand peaking-pulse components. The deflectionvoltage of a magnetic-deflection cathode-ray tuberequires this waveform to produce a current sawtoothin the deflecting coils.peaked waveform An alternating-current waveformhaving nearly pointed positive and negativehalf-cycles. Such a wave contains appreciablethird-harmonic energy.peak envelope power Abbreviation, PEP. For a linearradio-frequency (RF) power amplifier handlinga modulated signal, the average RF output

520 peak envelope power • peak-to-peak voltageLimiting levelpeaked sawtoothAmplitudeTimepower during a single RF cycle at the highestpeak of the modulation envelope.peaker 1. See PEAK FILTER. 2. See PEAKINGTRANSFORMER.peaker-notcher See NOTCHER-PEAKER.peak factor For an alternating-current wave, theratio E m /E rms or I m /I rms , where E m is the maximumvoltage, E rms is the effective (root-mean-square)voltage, I m is the maximum current, and I rms is theeffective current.peak filter A frequency-selective circuit, such as abandpass filter, for producing a peak response(see PEAK, 3).peak inductor current In a switching regulator,the maximum instantaneous current through theinductor when the device is switching at its fullyrated duty cycle.peaking The adjustment of a control or device formaximum indication on a meter or other display.peaking coil A small inductor used to compensatethe frequency response of a circuit, such as avideo amplifier or video detector. Both series andshunt peaking coils are used.peaking transformer A transformer whose outputwaveform is sharply peaked (of short duration,with respect to a cycle). The effect is obtained bymeans of a special core that, because it containslittle iron, saturates easily.peak inverse voltage Abbreviation, PIV. Oftenused interchangeably with the term PEAK RE-VERSE VOLTAGE. 1. The peak value of the voltageapplied to a rectifier diode in the reversedirection. 2. The maximum value of reverse voltagethat a rectifier diode will tolerate according toits specifications.peak level lamp In audio recording and reproduction,a bulb or light-emitting diode (LED) thatilluminates when sound peaks exceed apredetermined amplitude.peak limiting 1. A method of limiting the maximumamplitude of a signal. When the instantaneouspeak amplitude, either positive or negative,exceeds a certain value, the output is clipped atthat value. 2. In pulse-code modulation, the effectresulting from the application of an input signalin excess of the virtual decision value.peak modulated power In an amplitudemodulatedwave, the maximum instantaneoussignal power (including the carrier andsidebands). In 100-percent sinusoidal modulation,the peak modulated power is four times the unmodulatedcarrier power.peak limitingLimiting levelpeak point The highest current point in the current-voltageresponse curve of a tunnel diode.Immediately beyond this point, the currentdecreases as the applied voltage is increased,indicating a negative-resistance region. CompareVALLEY POINT.peak power 1. Symbol, P p . Unit, watt. Alternatingcurrentpower that is the product of the peak voltage(E p ) and the peak current (I p ). For E p in voltsand I p in amperes, the peak power in watts isgiven by P p = E p I p . 2. The highest output powerthat an amplifier or device can produce withoutexcessive distortion. 3. The maximum instantaneouspower that a speaker can handle withoutrisk of damage.peak probe A voltmeter test probe containing adiode circuit whose direct-current output voltageis close to the peak value of the applied alternating-currenttest voltage.peak recurrent forward current For a semiconductordiode, the maximum repetitive instantaneousforward current as measured underspecified conditions of operation.peak reverse voltage Abbreviation, PRV. In semiconductoroperations, the peak value of the voltageapplied in reverse polarity across thejunction. It is often used interchangeably with theterm PEAK INVERSE VOLTAGE.peak signal level The maximum instantaneoussignal power or voltage specified for particular operatingconditions.peak-to-peak Abbreviations, p-p or pk-pk. For analternating-current waveform, pertaining to thearithmetic difference between the positive peakand negative peak values of current or voltage.peak-to-peak probe A voltmeter test probe containinga diode circuit whose direct-current outputvoltage is close to the peak-to-peak value ofthe applied alternating-current test voltage.peak-to-peak voltage The arithmetic sum of positiveand negative peak voltages in an alternatingcurrent(ac) wave. Thus, a symmetrical sine-waveac voltage of 115.0 V rms has a peak value of162.63 V and a peak-to-peak value of 325.3 V.Also see PEAK VOLTAGE.

peak torque • PEP transistor 521+Amplitude−+Amplitude−+Amplitude−pk-pkpk-pkpk-pkpeak-to-peak voltageTimeTimeTimepencil 1. A beam of electrons or other particles orrays that either converges to, or diverges from, aspecific point. 2. A pair of geometric entities sharinga property (e.g., lines intersecting at a singlepoint).pendulum switch A device that closes a circuitwhen subjected to physical shock. One type consistsof a dangling element resembling a pendulum,with one or more nearby contacts.penetrating frequency For a particular layer ofthe ionosphere, the lowest high frequency atwhich a vertically propagated wave penetrates thelayer (i.e., it is not reflected back to earth). Alsocalled CRITICAL FREQUENCY.penetrating radiation Ionizing radiation thatpasses through otherwise opaque materials. Arelative term; low-energy X rays are less penetratingthan high-energy X rays, which, in turn, areless penetrating than gamma rays.penetrating rays See COSMIC RAYS.penetration depth See DEPTH OF PENETRATION.pent Abbreviation of PENTODE.pentavalent element An element whose atomshave five valence electrons (e.g., antimony or arsenic).pentode A five-electrode vacuum tube in which theelectrodes are an anode, cathode, control grid,screen grid, and suppressor grid.pentode field-effect transistor A field-effect transistorwith three separate gates.pentode transistor A bipolar transistor with threeemitters.peak torque Symbol, T p . For a torque motor, themaximum useful torque at maximum recommendedinput current.peak voltage Abbreviation, E p . The highest valuereached by an alternating-current voltage half cycle,or by a voltage pulse. Also called MAXIMUMVOLTAGE.peak voltmeter 1. An alternating-current (ac) voltmeterthat responds to the peak value of the appliedvoltage. 2. An ac voltmeter that responds tothe average value of the applied voltage—eventhough its scale reads in peak volts.pea lamp A miniature incandescent bulb, sometimesused as a control-panel or meter light.PEC Abbreviation of PHOTOELECTRIC CELL.pedestal See BLANKING PEDESTAL.pedestal level See BLANKING LEVEL.pel See PIXEL.Peltier effect A drop below ambient temperatureat the junction between two dissimilar metalswhen an electric current is passed through thejunction.PEM Abbreviation of photoelectromagnetic.pen-and-ink recorder A graphic recorder in whicha fountain-pen-type stylus inscribes an ink lineon a paper chart. Also called pen recorder.BCE 1E 2E 3pentode transistorpenumbra 1. That part of a shadow in which thelight source is not fully obscured by the eclipsingobject. 2. In a sunspot, the outer part of the spot;it is less dark than the inner portion.PEP 1. Abbreviation of PLANAR EPITAXIAL PASSI-VATED. 2. Abbreviation of PEAK ENVELOPEPOWER.PEP diode See PLANAR EPITAXIAL PASSIVATEDDIODE.PEP reading wattmeter A wattmeter that showsthe peak envelope power output of a transmitter.PEP transistor See PLANAR EXPITAXIAL PASSI-VATED TRANSISTOR.

522 perceived level • peripheral electronperceived level The level of a disturbance, particularlysound, as sensed by a person. It is generallyexpressed in decibels, with respect to acertain threshold value. The threshold is assignedan intensity of 0 dB.percent An expression of a fraction, in terms ofhundredths. A quantity of x percent indicates afraction of x/100. Percent is usually abbreviatedby the symbol %.percentage error The amount by which a measuredvalue differs from the true value, expressedas a percentage (the number of parts per 100 thatthe measurement is in error).percentage-modulation meter An instrumentthat provides direct readings of the modulationpercentage of an amplitude-modulated signal.The meter scale or dial is graduated in incrementsfrom 0 to somewhat more than 100 percent.percentage uncertainty The maximum possibleerror in a measurement, expressed as a percentageof the measured value. Also see UNCER-TAINTY IN MEASUREMENT.percent distortion Symbol, %D. In the determinationof harmonic distortion, the total harmonicvoltage expressed as a percentage of the fundamentalvoltage, plus total harmonic voltage; %D =100E h /E t , where E h is the total voltage of the harmoniccomponents, and E t is the total signal voltage(fundamental plus harmonics).percent modulation See MODULATION PER-CENTAGE.percent modulation meter See PERCENTAGE-MODULATION METER.percent ripple The amount of ripple voltage in thedirect-current (dc) output of a rectifier or generator,expressed as a percentage of the nominal dcoutput voltage.perfect crystal A crystal without defects or impurities.The atoms are arranged in a regular patternwith no faults.perforated board A plastic panel provided with anumber of small holes in orderly columns androws for the insertion of the pigtails of components,or of push-in terminals to facilitate quickassembly of prototype circuits. Also called perfboard.performance curve A curve depicting the behaviorof a component or circuit under specified conditionsof operation. Such a curve, for example,might display the variation of output power withinput power, the variation of frequency with voltage,etc. Compare CHARACTERISTIC CURVE.performance test A test made primarily to ascertainhow a system behaves. The test is concernedwith normal operation, whereas a diagnostic testis a troubleshooting procedure. Compare TROU-BLESHOOTING TEST.perigee 1. The point at which an earth-orbitingsatellite attains its lowest altitude. It occurs oncefor every complete orbit. At this point, the satellitetravels faster than at any other point in the orbit.2. The altitude, measured from the earth’s surfaceor the earth’s center, of an earth-orbitingsatellite at its closest approach.perihelion 1. The point at which a solar-orbitingsatellite attains its lowest altitude. It occurs oncefor every complete orbit. At this point, the satellitetravels faster than at any other point in theorbit. 2. The altitude, measured from the sun’ssurface or the sun’s center, of a solar-orbitingsatellite at its closest approach.perimeter protection The use of a security systemto restrict or prevent access to a designated area,using sensors and/or barriers around the boundariesof the area.period Symbol, T. Unit, second. The duration of acomplete alternating-current cycle or of anycyclic event; T = 1/f, where f is the frequencyin Hertz. Also see CYCLE, FREQUENCY, andHERTZ.periodic and random deviation Abbreviation,PARD. In the direct-current output of a rectifier,the combined PERIODIC DEVIATION, includingripple, noise, hum, and transient spikes.periodic curve A curve that repeats its shape ineach period (e.g., a sine curve).periodic deviation Repetitive deviation of a quantityfrom its normal value (e.g., ripple in thedirect-current output of a rectifier).periodic function A mathematical function that isrepresented by a periodic curve (e.g., the sinefunction y = sin x).periodicity In a transmission line, the tendencyfor power to be reflected at a point or pointswhere the diameter of the line changes.periodic law The observation that when the chemicalelements (see ELEMENT, 3) are arranged inincreasing order of atomic number, their physicaland chemical properties recur periodically. Alsosee PERIODIC TABLE.periodic table A table in which the chemical elements(see ELEMENT, 3) are arranged accordingto the periodic law. The vertical columns in thetable, labeled groups, contain elements possessingrelated properties (e.g., silicon and germaniumin group IV). The rows, labeled periods,depict the periodic shift in the properties of the elements.peripheral1. Pertaining to equipment accessory toa central system (e.g., peripheral input/outputdevices online or offline to computers, datarecorders, and indicators). Also see ANCILLARYEQUIPMENT. 2. Peripheral equipment in a computersystem (e.g., printers, modems, externaldisk drives, tape drives, etc.).peripheral buffer As part of a peripheral in a computersystem, a storage unit in which datatemporarily resides on its way to or from thecentral processing unit. Also called INPUT/OUTPUT BUFFER.peripheral electronSee VALENCE ELECTRON.

peripheral equipment • persistor 523peripheral equipment See PERIPHERAL, 1, 2.peripheral interface adapter Abbreviation, PIA.An integrated circuit that acts as an input/outputport to interface a microprocessor with peripheraldevices.peripheral transfer In a computer system, thetransfer of a unit of data between peripherals, orbetween a peripheral and the central processingunit.Permalloy A high-permeability alloy of iron andnickel.permamagnetic speaker See PERMANENT-MAGNET SPEAKER.permanent magnet A body that is always magnetized(i.e., without the application of electricityand without requiring the presence of anothermagnet). Compare TEMPORARY MAGNET.permanent-magnet erase Erasure of magnetictape by the field of a permanent magnet. Typically,it is a two-step process: a magnet eraseswhat it can of the signal, leaving any residualmagnetization for erasure by a second magnet.permanent-magnet focusing In a cathode-raytube, the focusing of the electron beam by meansof permanent magnets.permanent-magnet generator An electromechanicalgenerator in which the field (either stationaryor rotating) is provided by a multipole permanentmagnet. Also called magneto.permanent-magnet loudspeaker See PERMA-NENT-MAGNET SPEAKER.permanent-magnet magnetizer A magnetizer usinga permanent magnet as the magnetic-fieldsource.permanent-magnet meter An indicating meter inwhich a movable coil rotates between the poles ofa permanent magnet. Compare ELECTRODY-NAMOMETER and IRON-VANE METER.permanent-magnet motor A motor having a permanent-magnetfield.permanent-magnet relay A polarized relay usinga permanent magnet.permanent-magnet speaker An acoustic loudspeakerin which the core is a strong permanentmagnet (as opposed to a direct-current electromagnet).Also see MAGNETIC SPEAKER.permanent storage See NONVOLATILE MEMORY.permeability Unit, H/m. A quantitative indicatorof the extent to which a material concentratesmagnetic flux: for a given constant magnetic-fieldintensity, the ratio of magnetic flux density in thematerial to the magnetic flux density in air.permeability curve See B-H CURVE.permeability-tuned oscillator A radio-frequencyoscillator in which the frequency is varied or adjustedby moving a ferromagnetic core in and outof the coil of an inductance-capacitance (LC)tuned circuit.permeability tuning Variation of the resonant frequencyof an inductance-capacitance LC circuitby changing the position of a magnetic coreFerromagneticcoreCoilpermeability tuningCoilformwithin the inductor. This type of tuning is used inamplifiers, oscillators, filters, and wavetraps.permeameter An instrument for measuring permeability.permeance Unit, Wb/A. In a magnetic circuit, theease with which a magnetic field is established.The reciprocal of RELUCTANCE.Permendur A high-permeability magnetic alloycontaining equal parts of iron and cobalt. At saturation,the flux density of this material can be 2teslas (20,000 gauss).Perminvar A high-permeability magnetic alloy ofcobalt, iron, and nickel. At saturation, the fluxdensity of this material can approach 1.2 teslas(12,000 gauss).permittivity See DIELECTRIC CONSTANT.permutation A selection of several factors or objectsfrom a group, in a specific ordered sequence.For example, one of the permutations of the elementsof the set (1, 2, 3, 4, and 5) is the orderedsequence 4, 1, 3, 5, 2.permutation modulation A method of modulationaccomplished by varying the sequence of digitalbits.peroxide of lead In a lead-acid cell or battery, acompound of lead and oxygen that composes thepositive electrode or electrodes.persistence 1. The effect whereby the retina of theeye continues to register a projected scene for approximately0.05 second after the scene disappears.This allows perception of a sequence ofvideo frames as a continuous moving image.2. The tendency of certain phosphors to glow afterthe excitation has been removed. Thus, after theelectron beam in a cathode-ray tube has passedover the screen, the phosphor might continue toglow for a certain time along the path traced bythe beam. Some phosphors, such as those usedin high-speed oscilloscopes, have virtually nopersistence, whereas others have long persistence.persistent oscillations Successive oscillations ofconstant amplitude. Also called CONTINUOUSWAVE.persistor A device used at low temperatures fortemporary memory storage that operates betweensuperconducting and normal conditions.

524 personal communications service • phase coincidencepersonal communications service Abbreviation,PCS. Also called digital cellular. An enhancedwireless network using digital modulation,cellular repeaters, and facilitating telephone andInternet connections. Emphasis is on maximizinguser mobility and portability, and minimizingblind zones. Compare CELLULAR COMMUNICA-TIONS.personal computer A small computer equippedwith a keyboard, display, hard disk, diskettedrive(s), a modem or fax/modem, one or more serialdata ports, and one or more parallel dataports. They are used extensively by individualsand businesses for record keeping, data processing,communications, word processing, graphics,etc.; they are also used in schools as an educationalaid.personal digital assistant Abbreviation, PDA. SeeHANDHELD COMPUTER.personal equation The value of systematic errorfor a person observing specific phenomena ormaking measurements.personality Characteristics that make an intelligentcomputer or robot human-like. In general,the more powerful the computer, the more personalityit can have, depending on the installedsoftware. In some cases, certain malfunctions ina computer can produce personality quirks.personal robot A usually autonomous robot intendedfor use by individuals. The most commonexamples are robot toys, programmable with aPERSONAL COMPUTER, intended for the educationand entertainment of children. More sophisticateddevices can perform domestic tasks, suchas cleaning floors and mowing lawns.peta- Abbreviation, P. A prefix meaning 10 15 .petagram Abbreviation, Pg. A large unit of mass orforce, equal to 10 15 grams or 10 12 kilograms.petameter Abbreviation, Pm. A large unit of (astronomical)distance, equal to 10 15 meters or 10 12kilometers.pF Abbreviation of PICOFARAD.pf Symbol for POWER FACTOR.PFET Abbreviation of P-CHANNEL JUNCTIONFIELD-EFFECT TRANSISTOR.PFM Abbreviation of PULSE-FREQUENCY MODU-LATION.PG Abbreviation of POWER GAIN.Pg Abbreviation of PETAGRAM.pH 1. Symbol for hydrogen-ion concentration. Numerically,pH is the negative logarithm of the effectivehydrogen-ion concentration in gramequivalents per liter. The scale runs from zero to14, on which 7 denotes neutrality relative to acidityvs. alkalinity; values between zero and 7 denoteacidity, and values between 7 and 14 denotealkalinity. 2. Abbreviation of PICOHENRY.phantom Radio interference in the form of a beatnote (heterodyne), resulting from interference betweentwo strong carriers, often from local radiostations. When the phantom frequency lieswithin the tuning range of a receiver, the phantomcan be tuned in as a separate signal. Butwhen the phantom corresponds to the intermediatefrequency (IF) of the receiver, it will ride intothe IF amplifier and be present as an untunableinterferential signal.phantom channel In a properly phased highfidelitystereo sound system, the apparent soundsource centered between the left- and right-channelloudspeakers.phantom circuit In wire telephony, a third circuitthat has no wires; it results from a method (usingrepeating coils) of making two other circuits dothe work of (this third) one.phantom signal Also called bogey. In a radar system,a signal that does not correspond to an actualtarget. The origin of the phantom signal orecho cannot be readily determined.phantom target See ECHO BOX.phase angle Unit, degree or radian. In an alternating-current(ac) circuit, the lag or lead betweenthe instant that one alternating quantity reachesits maximum value and the instant that anotheralternating quantity reaches its maximum value.It is usually given in degrees (a complete cycle being360 degrees) along the horizontal axis of thetime-versus-magnitude graph of the ac quantity.phase-angle voltmeter An instrument that indicatesboth the magnitude and phase of a voltage.phase coincidence For signals having the samefrequency, the condition of their coinciding interms of instantaneous amplitudes, so positivepeaks of the first signal correspond to positivepeaks of the second signal, and negative peaks ofthe first signal correspond to negative peaks ofthe second signal. For periodic waves that do notchange their characteristics with time, this is thesame thing as being shifted by an integral multipleof 360 degrees in phase. Compare PHASEOPPOSITION.

phase compensation • phase opposition 525phase compensation In an operational amplifier,compensation for excessive phase shift in thefeedback.phase compressor A push-pull phase-inverter circuitin which a capacitor is connected betweeneach collector or drain and the opposite outputterminal to attenuate in-phase components, suchas even-numbered harmonics.phase constant A figure providing the rate (in degreesof phase per unit length) at which the phaselag of the current or voltage field component in atraveling wave increases linearly in the propagationdirection.phase corrector A circuit that returns a signal to acertain phase after the signal has passed througha circuit or medium that has caused phase distortion.phased antenna See PHASED ARRAY.phased array Also called phased antenna. An antennasystem having two or more driven elementsfed with a certain relative phase, and spaced at acertain distance, resulting in a directivity patternthat exhibits gain in some directions and little orno radiation/response in other directions. Suchan array can have two elements, producing a unidirectionalcardioid or bidirectional figure-eightpattern. More complex arrays have several elements,usually vertical antennas, strategicallypositioned and fed with signals of specified phaseto produce a highly tailored pattern. The most sophisticatedsystems have rotatable or steerableradiation/response patterns.phase-delay equalizer See DELAY EQUALIZER.phase detector See PHASE-SENSITIVE DETEC-TOR.phase diagram A graphical representation ofwaves having equal frequency, but differing inphase. The phase difference for two identicalwaveforms is greater than or equal to zero degrees,but less than 360 degrees.phase difference 1. The difference (in time, angle,or fractional cycle) between the instants at whichtwo alternating quantities reach a given value.2. For a dielectric, the complement of PHASE AN-GLE; that is, 90 degrees minus the phase angle indegrees.phase discriminator See DISCRIMINATOR, FOS-TER-SEELEY DISCRIMINATOR, RATIO DETEC-TOR, and TRAVIS DISCRIMINATOR.phase distortion Distortion characterized by input/outputphase shift between various componentsof a signal passed by a circuit or device.phase inverter A resistance-capacitance-coupledamplifier with a single-ended input and a pushpulloutput. This circuit enables a push-pull amplifierto be driven without an input transformer.phase-locked loop Abbreviation, PLL. An oscillatorthat combines the flexibility of a conventionalvariable-frequency oscillator (VFO) with the stabilityof a crystal oscillator. The oscillator outputis passed through a programmable divider thatSignalinput(from IF)PhasecomparatorVoltagecontrolledoscillatorFilter Amplifier OutputControlvoltagephase-locked loopdivides the frequency by a specific integral valuen chosen by the operator. The output frequencyof the divider is locked, by means of a phase comparator,to the signal from a crystal-controlledreference oscillator. As long as the output fromthe divider is exactly at the reference-oscillatorfrequency, the two signals are in phase, and theoutput of the phase comparator is zero volts dc. Ifthe VCO frequency changes, the phase alsochanges, and the phase comparator produces adc error voltage. The error voltage is applied to theVCO, causing the VCO frequency to correct itself.This maintains the VCO frequency at precisely ntimes the reference-oscillator frequency.phase-locked oscillator An oscillator in which theinductance or the capacitance is varied periodicallyat half the driving frequency.phase margin In an integrated-circuit amplifier,the extent to which the device shifts the phase ofa signal more or less than one-half cycle (180 degrees)for a certain signal voltage.phase modulation Abbreviation, PM. A method ofmodulation in which the phase of the carrier currentis varied in accordance with the instantaneousmodulating-signal voltage. The result issimilar to FREQUENCY MODULATION.phase modulator A circuit or stage that producesPHASE MODULATION.phase multiplier A circuit used for the purpose ofphase comparison between signals. The frequencyof the measured signal is multiplied, resultingin multiplication of the phase difference.This improves the sensitivity of the measuringapparatus.phase opposition For signals having the same frequency,the condition of their being inverted relativeto each other in terms of instantaneousamplitudes, so positive peaks of the first signalcorrespond to negative peaks of the second signal,and negative peaks of the first signal correspondto positive peaks of the second signal. Thisis not the same thing as being shifted by an odd

526 phase opposition • phase windingsPhaseshiftAmplitudeTimephase shiftintegral multiple of 180 degrees in phase,although in practice, with sine waves and squarewaves, the effect is the same. Compare PHASECOINCIDENCE.phase resonance See VELOCITY RESONANCE.phase reversal 1. The inversion of an alternatingcurrent(ac) signal. The instantaneous amplitude(current or voltage) is multiplied by anegative constant. Thus, the positive half-cyclesbecome negative, and the negative half-cyclesbecome positive. 2. A phase shift of ±180degrees (± 1 ⁄2 cycle) in an ac signal.phase-rotation relay See PHASE-SEQUENCE RE-LAY.phase-rotation system A system for producingsingle-sideband signals without using selectivefilters. In one such system, two balanced modulatorsare used. One of these receives carrier andmodulating voltages that are 90 degrees out ofphase with voltages that are fed to the other balancedmodulator.phase-sensitive detector Abbreviation, PSD. Adetector for frequency modulation (FM) andphase modulation (PM). It delivers a directcurrentoutput voltage whose value is proportionalto the difference in phase between a referencesignal and the signal from a local oscillator.phase-sequence relay In a polyphase system, a relayor relay circuit that is actuated by voltagesreaching maximum positive amplitude in a predeterminedphase sequence. Also called PHASE-ROTATION RELAY.phase shift 1. A change in the displacement, as afunction of time, of a periodic disturbance havingconstant frequency. 2. The magnitude of achange, as defined in 1, measured in fractions ofa wavelength or in electrical degrees.phase-shift bridge A four-arm-bridge circuit forshifting the phase of an alternating-current signal.Such a circuit is often used (with one armvariable) to shift the phase of the firing voltage fora thyratron.phase-shift discriminator See FOSTER-SEELEYDISCRIMINATOR.phase shifter A circuit, such as an inductancecapacitance(LC) or resistance-capacitance (RC)network, or a device, such as a Helmholtz coil orphase-shifting capacitor, that introduces a phaseshift between input and output signals.phase-shifting capacitor A special four-stator,one-rotor variable capacitor that, with a transformer-coupledresistance-capacitance (RC) circuit,provides 360 degrees of continuouslyvariable phase shift for one rotation of the rotor.The rotor plate turns like a cam under the statorsbecause of the off-center insertion of the rotorshaft.phase-shift oscillator A single-stage oscillator inwhich the required 180-degree phase shift in thesignal (fed back from output to input) is obtainedby passing the output through a phase-shiftingnetwork.phase-shift-type distortion meter A distortionmeter in which the output signal of a device undertest is compared with a distortion-free inputtest signal. The output signal phase is shifted 180degrees, with respect to the input, and the twoamplitudes are made equal. If there is no distortion,the signals cancel each other, and the resultis zero. Any remaining signal is proportional tothe total harmonic distortion (THD).phase-splitting circuit A circuit that produces,from a single input signal, two output signals differingin phase.phase-splitting driver A PHASE INVERTER usedas the driver of a push-pull amplifier.phase velocity The velocity of a wave, provided bythe product of the frequency and the wavelength.phase windings In an alternating-current generator,windings that deliver voltages that differ in phase.

phasing capacitor • phonetic alphabet 527phasing capacitor In a crystal filter, a small variablecapacitor that constitutes one arm of afour-arm bridge in which the crystal is anotherarm. Adjustment of this capacitor balances thebridge, thus preventing the undesirable passageof a signal through the capacitance of the crystalholder.phenol-formaldehyde plastics A family of plasticinsulating materials made with phenolic resin,and occasionally used as dielectrics and air-corecoil forms. Some of the trade names for these materialsinclude Bakelite, Catalin, Durez, Durite,Formica, and Micarta.phenolic insulants See PHENOL-FORMALDE-HYDE PLASTICS.phenolic resin A synthetic resin made by condensingphenol (carbolic acid) with formaldehyde.phenomenon An event or circumstance that canbe verified by the senses, as opposed to one subjectto theory or speculation (e.g., the phenomenonof magnetic attraction).Phillips gate A device that allows measurement ofthe gas pressure in a confined chamber. A currentis passed through the gas. The magnitude ofthe current, for a given gas, is a function of thegas pressure and temperature.Phillips screw A screw with a pair of slots in itshead. The slots are arranged like an x. Phillipsscrews are available in many different sizes, as areordinary screws. The x-shaped pair of slots reducesthe tendency for the screwdriver to slip outof the screw head as the screw is rotated.Phi phenomenon The illusion of motion resultingfrom the rapid presentation to the eye of picturesshowing objects in a succession of different positions.Television and motion pictures exploit thisillusion. Also see PERSISTENCE.pH meter An instrument used to measure theacidity or alkalinity of solutions. Also see PH, 1.phon A unit of apparent change in loudness discernedby a listener. Unlike the decibel, the phonincludes compensation for the ear’s nonlinear responseto attendant frequency changes. At a frequencyof 1 kHz, a change in loudness of 1 phonis the equivalent of 1 decibel.phone 1. Telephone (wire or radio). 2. To establishcommunication via telephone. 3. Colloquialismfor voice communication (radiotelephone), particularlyvia amateur-radio single sideband on thehigh-frequency bands (160 through 10 meters).4. A minimal, unique speech sound. Also calledSOUND UNIT.phoneme An individual sound or syllable in thehuman voice, with a characteristic amplitude-vs.frequency spectral pattern. It is important inspeech recognition and speech synthesis. Computerscan be programmed to identify and transcribethese sounds; computers can also beprogrammed to generate the sounds from textdata.phone jack The female mating device for a PHONEPLUG.phone monitor A simple device for listening toamplitude-modulated radio transmissions totest their quality. In its most rudimentary form,it consists of a pickup antenna, semiconductor-diodedetector, and high-resistance headphones.phone patch A device for establishing a connection(patch) between radio and wire-telephone facilities.Also see PATCH.phone plug A type of plug originally designed forpatching telephone circuits, now widely used inelectronics and instrumentation. In its conventionalform, it has a rod-shaped neck thatserves as one contact, and a ball on the tip ofthe neck, but insulated from it, that serves asthe other contact. Typical diameters are 1 ⁄8 inchand 1 ⁄4 inch.phone test set An instrument for checking theperformance of a radiotelephone transmitter. Theset combines the functions of field-strength meter,modulation indicator, and aural monitor.Sometimes it includes a volt-ohm-milliammeterfor troubleshooting the transmitter.phonetic alphabet Words whose initial letters areused to identify the letters of the alphabet for

528 phonetic alphabet • phosphor copperwhich they stand. These words are spoken in radiotelephonyto identify letters that, if spoken bythemselves, might not be clearly heard.Phonetic alphabetPhonetic(Capitals indicateLetteremphasis)AAL-faBBRAH-voCCHAR-lieDDEL-taEECK-oFFOX-trotGGOLFHho-TELIIN-diaJJu-li-ETTEKKEE-lowLLEE-maMMikeNNo-VEM-berOOS-carPpa-PAQQue-BECKRROW-me-ohSsee-AIR-ahTTANG-goUYOU-ni-formVVIC-torWWHIS-keyXX-rayYYANK-keyZZOO-loophonetic alphabet code word In radio and wiretelephony, a word chosen for its easy recognitionby ear to identify the letter of the alphabet withwhich it begins. For example: Golf for G, Juliet forJ, X-ray for X.phonics See ACOUSTICS, 1.phonocardiogram The record made by a PHONO-CARDIOGRAPH.phonocardiograph An instrument that makes agraphic record of heart sounds.phono cartridge The vibration-to-electricity transducer(pickup) of a phonograph; it is actuated bythe stylus (needle). Common types are ceramic,variable-inductance, and variable-reluctance. SeePHONOGRAPH and PHONOGRAPH DISC.phonocatheter A microphone that can be insertedinto the body for the purpose of listening to thefunctions of internal organs.phonograph A device for reproducing soundrecorded on disc. It consists of a turntable, anamplifier, and one or more speakers.phonograph cartridge See PHONO CARTRIDGE.phonograph disc A thin, lightweight disc, usuallymade of vinyl or similar plastic, on which audiofrequencysignals are recorded as irregularities ina spiral groove. In reproduction, these irregularitiescause vibration in a PHONO CARTRIDGE asthe turntable rotates.phonograph oscillator See PHONO OSCILLATOR.phono jack Also called RCA jack. A jack similar toa PHONE JACK, designed especially for the quickconnection and disconnection of coaxial cablesused with audio and low-frequency devices.phonon A unit of energy resulting from vibration,as of a piezoelectric crystal.phono oscillator A small radio-frequency (RF) oscillatormodulated by the audio-frequency (AF)voltage from a phonograph. The modulated RFsignal is picked up by a remote radio receiver(usually in the same room), and the sound is reproducedthrough a loudspeaker connected tothe receiver.phono plug Also called RCA plug. A plug similar toa PHONE PLUG, designed especially for the quickconnection and disconnection of coaxial cablesused with audio and low-frequency devices.phono plugphonoreception The hearing of high-frequencysounds.phonorecord A PHONOGRAPH disc.phonoselectroscope A special type of stethoscope,in which the main heartbeat is attenuated. Thismakes abnormal sounds more audible. The devicecan be adjusted in various ways to listen forabnormalities characteristic of various heart diseases.phosphor A substance that glows when an electronbeam strikes it. Such a substance is used asa coating on the screens of cathode-ray tubes.See also BEAT ZINC SILICATE; CADMIUMBORATE, SILICATE, and TUNGSTATE; CAL-CIUM PHOSPHATE, SILICATE, and TUNG-STATE; MAGNESIUM FLUORIDE, SILICATE, andTUNGSTATE; ZINC ALUMINATE; ZINC BERYL-LIUM SILICATE; ZINC BERYLLIUM ZIRCONIUMSILICATE; ZINC BORATE; ZINC CADMIUM SUL-FIDE; ZINC GERMANATE; ZINC MAGNESIUMFLUORIDE; ZINC ORTHOSILICATE; ZINC OX-IDE; ZINC SILICATE; and ZINC SULFIDE.phosphor bronze A form of bronze whose elasticity,hardness, and toughness have been greatlyimproved by the addition of phosphorus. Themetal is used for brushes, springs, switch blades,and contacts.phosphor copper An alloy of copper and phosphorusused in the manufacture of PHOSPHORBRONZE.

phosphorescence • photoelectric efficiency 529phosphorescence The property of some materialsthat ordinarily fluoresce to continue to glow afterthe stimulus (light or an electron beam) has beenremoved. Compare FLUORESCENCE.phosphorescent screen A viewing screen coatedwith a phosphor (e.g., oscilloscope screen).phosphorous Exhibiting the properties of phosphor(e.g., glowing after stimulation with light).Not to be confused with PHOSPHORUS.phosphorus Symbol, P. A nonmetallic element ofthe nitrogen family. Atomic number, 15. Atomicweight, 30.974. It is used as a dopant in semiconductorprocessing.phot The cgs unit of illumination: The direct illuminationproduced upon a one-centimeterdistantsurface by a uniform point source of oneinternational foot-candle. Equivalent to one lumenper square centimeter.photocathode 1. The photomosaic of a video cameratube. 2. The light-sensitive cathode in a phototube.PhotoCD Trade name for an image-recording systemdeveloped by Kodak, in which photographscan be stored on compact discs. Viewing is accomplishedusing personal computers.photocell See PHOTOELECTRIC CELL.photocell amplifier An amplifier used to boost theoutput of a photocell. With respect to the natureof the input signal, it can be an alternatingcurrent(ac) or direct-current (dc) amplifier, dependingon whether the output of the photocell ismodulated dc or pure dc.photochemical effect The phenomenon wherebycertain substances undergo chemical change whenexposed to light or other radiant energy. An exampleof such a substance is the silver bromide, silverchloride, or silver iodide on photographic film.photoconductive cell A photoelectric cell, such asthe cadmium-sulfide type, whose resistance isproportional to the intensity of light impingingupon it. The photoconductive cell acts as a lightsensitivevariable resistor in a current path. Alsosee PHOTOCONDUCTIVE MATERIAL.photoconductive effect The tendency for the electricalresistance of a substance to change wheninfrared radiation, visible light, or ultraviolet radiationstrikes it. Different substances exhibit differentdegrees of this effect.photoconductive material A substance that exhibitsdecreased electrical resistance when exposedto infrared rays, visible light, or ultraviolet.Some photoconductive substances are cadmiumselenide, cadmium sulfide, germanium, lead sulfide,selenium, silicon, and thallous sulfide. Alsosee ACTINOELECTRIC EFFECT.photoconductivity The phenomenon whereby theelectrical resistance of certain materials (such ascadmium sulfide, cadmium selenide, germanium,selenium, and silicon) is lowered upon exposureto infrared rays, visible light, or ultraviolet. Alsosee PHOTOCONDUCTIVE MATERIAL.photoconductor 1. See PHOTOCONDUCTIVE MA-TERIAL. 2. See PHOTOCONDUCTIVE CELL.photocurrent See PHOTOELECTRIC CURRENT.photo-Darlington Also, photodarlington. 1. A phototransistorfabricated as a Darlington amplifierfor high output current. 2. A combination of photodiode(see LIGHT-SENSITIVE DIODE) and Darlingtonamplifier.photodecomposition Chemical breakdown by theaction of radiant energy. Also called photolysis.photodetachment The removal of an electron froman atom or ion, resulting from the impact of aPHOTON.photodetector 1. An illumination meter that usesa PHOTOCELL. 2. See OPTOELECTRONIC COU-PLER.photodielectric effect The tendency for the dielectricconstant of a substance to change wheninfrared radiation, visible light, or ultravioletradiation strikes it. Different substances exhibitdifferent degrees of this effect.photodiffusion effect See DEMBER EFFECT.photodiode See LIGHT-SENSITIVE DIODE.photodisintegration In the nucleus of an atom,disintegration resulting from PHOTON bombardment.photoelasticity The tendency for the lighttransmissioncharacteristics of a substance tochange with externally applied forces.photoelectric alarm An alarm actuated when alight beam impinging on a photocell is interrupted.photoelectric amplifier 1. An amplifier for boostingthe output of a photosensitive device. 2. AnOPTOELECTRONIC COUPLER possessing gain.photoelectric cell A device that converts infrared,visible-light, or ultraviolet energy into electricityor electrical effects. It can function by producinga voltage (see PHOTOVOLTAIC CELL, SELENIUMCELL, SILICON CELL, SOLAR CELL, and SUNBATTERY) or by acting as a light-sensitive resistor(see LIGHT-SENSITIVE DIODE, PHOTOCON-DUCTIVE CELL, and SELENIUM CELL).photoelectric constant The quantity h/e, where his Planck’s constant and e is the unit electroncharge.photoelectric counter A counting device (electromechanicalor fully electronic) that counts objectsas they interrupt a light beam impingingupon a photocell.photoelectric disintegration See PHOTODISIN-TEGRATION.photoelectric effect The phenomenon wherebytemporary changes occur in the atoms of certainsubstances under the influence of infrared, visiblelight, or ultraviolet radiation. Some of thesematerials undergo a change in their electrical resistance,whereas others generate electric current(see, for comparison, PHOTOCONDUCTIVE MA-TERIAL and PHOTOVOLTAIC MATERIAL).photoelectric efficiency See QUANTUM YIELD.

530 photoelectric field-effect transistor • photographic sound recordingphotoelectric field-effect transistor SeePHOTOFET.photoelectricity Electricity produced by the actionof light on certain materials, such as cesium,selenium, and silicon. Also see PHOTOEMISSIONand PHOTOVOLTAIC CELL.photoelectric material See PHOTOCONDUCTIVEMATERIAL and PHOTOEMISSIVE MATERIAL.photoelectric multiplier A device that internallyamplifies the current resulting from bombardmentby infrared, visible light, or ultraviolet radiation.A PHOTOMULTIPLIER TUBE is an exampleof such a device.photoelectric photometer An instrument thatuses a photoelectric device for the purpose ofmeasuring the intensity of infrared radiation, visiblelight, or ultraviolet radiation.photoelectric proximity sensor A device thatuses a light-beam generator, a photodetector, anamplifier, and a microprocessor to detect thepresence of nearby objects. It is useful in robotguidance systems.photoelectric pyrometer An optical pyrometer inwhich a photocell and appropriate filters act insteadof the human eye.photoelectric relay A relay actuated directly by aphotocell or a photocell and amplifier. This type ofrelay is the basis of some PHOTOELECTRICALARM devices.photoelectric sensor 1. See ELECTRIC EYE.2. See PHOTOELECTRIC PROXIMITY SENSOR.3. See PHOTOELECTRIC CELL.photoelectric smoke alarm An alarm that istripped by a PHOTOELECTRIC SMOKE DETEC-TOR when the density of smoke exceeds a safelevel.photoelectric smoke control A system for makingautomatic adjustments to a burning processwhen the smoke density exceeds a prescribedlevel. The initial element in the system is a PHO-TOELECTRIC SMOKE DETECTOR.photoelectric smoke detector A smoke detectorin which a photocell, photodiode, phototransistor,or phototube is excited by a light beam passingthrough the air. The cell output currentdecreases when smoke fills the air. This currentchange trips an alarm or deflects an indicatingmeter when the density of the smoke exceeds aprescribed level.photoelectric tape reader A punched-tape readerusing a photocell, photodiode, phototransistor, orphototube to sense light passing through theholes.photoelectric transducer A photocell, photodiode,phototransistor, or phototube used as a sensor.photoelectric tube See PHOTOTUBE.photoelectric wattmeter A power-measuring instrumentuseful for the approximate measurementof radio-frequency power. It consists of anincandescent lamp sharing an opaque enclosurewith a photovoltaic cell. The power to be mea-RFinputphotoelectric wattmetermAsured is applied to the lamp, which glows proportionately.The light excites the cell, causing it todeliver a direct current proportional to the power.This current deflects a milliammeter or microammeter.The meter can be calibrated to read directlyin watts.photoelectromotive force The electromotive force(voltage) produced by a photovoltaic cell.photoelectron An electron displaced within, orejected from, an atom, as the result of infrared,visible light, or ultraviolet radiation striking theatom.photo-emf See PHOTOELECTROMOTIVE FORCE.photoemission The ejection of electrons from certainmaterials, such as cesium, when these materialsare exposed to infrared, visible light, orultraviolet radiation. Also see PHOTOEMISSIVEMATERIAL.photoemissive material A substance that emitselectrons when exposed to infrared, visible light, orultraviolet radiation. A typical use of such a materialis in the coating of the light-sensitive cathodeof a phototube. The metals cesium, potassium, rubidium,and sodium are photoemissive.photofabrication 1. A method of circuit-boardmanufacturing. The etching pattern is placedover the circuit-board material, the board isplaced in a special solution, then the assembly isexposed to visible light. The light interacts withthe solution to dissolve the metal in areas exposedto the light, but not in areas covered by theetching pattern. 2. The technique in 1, applied tothe manufacture of integrated circuits.photoFET A FIELD-EFFECT TRANSISTOR that exhibitsproperties similar to those of a bipolarPHOTOTRANSISTOR.photoflash See ELECTRONIC FLASH, 1.photoglow tube See DISCHARGE LAMP.photogram The permanent shadow produced byan object placed between a light source and photographicpaper.photographic exposure meter See EXPOSUREMETER, 1.photographic recorder A graphic recorder thatuses a light beam, deflected by galvanometermovement, that moves across photographic filmor paper to produce a trace representing a varyingquantity.photographic sound recording See OPTICALSOUND RECORDING.

photograph reception • photon 531photograph reception 1. The use of FACSIMILE toprint photographs transmitted in analog form viawire or radio. 2. The use of a computer, equippedwith a modem and graphics software, to displayand/or store photographs transmitted in digitalform via wire or radio.photograph transmission 1. The use of FACSIM-ILE to scan and send photographs in analog formvia wire or radio. 2. The use of a computer,equipped with a modem and video camera or opticalscanner, to digitize and send photographsvia wire or radio.photoionization The ejection of electrons fromatoms or molecules by the action of infrared, visiblelight, or ultraviolet radiation.photoisolator See OPTOELECTRONIC COUPLER.photojunction cell A photocell consisting of a semiconductorpn junction. The cell is useful mainlyfor its photoconductivity, although infrared, visiblelight, or ultraviolet energy striking the junctionproduces a small amount of photovoltaic action.photokinesis Light-induced motion, as in a RA-DIOMETER.photolithographic process A method of producingintegrated circuits and printed circuits by photographing(often at considerable reduction) anenlarged pattern of the circuit on a suitable lightsensitizedsurface of metal or semiconductor, andchemically etching away unwanted portions ofthe surface.photolysis See PHOTODECOMPOSITION.photomagnetic effect Light-sensitive magneticsusceptibility in some materials.photomap A photo taken of terrain from a high altitudeand usually overlaid with a reference grid.photomask In PHOTOFABRICATION, the transparentfilm or template on which the etching patternis drawn.photometer An instrument used to compare theluminous intensity of two light sources.photometric measurement of power See PHOTO-ELECTRIC WATTMETER.photometry The science of visible-light measurement.The response of the human eye is used asthe basis for preferred sensors (those used withphotometric instruments, which have spectralsensitivity curves resembling those of the eye).Compare RADIOMETRY.photomosaic In a television camera tube, the flatphotocathode screen on which the image is projectedby the lens system and scanning electronbeam. The surface of the screen is covered withtiny light-sensitive droplets. Also see DISSECTORTUBE, ICONOSCOPE, and ORTHICON.photomultiplier tube A type of PHOTOTUBE thatdelivers high output current for a given light intensityby utilizing the secondary emission of electrons.The initial light-sensitive cathode emitselectrons; these strike a specially placed metalplate with a force that dislodges more electrons.These electrons, together with the initial emission,Relative perceived brightness forlight source of constant intensity0200 300 400 500 600 700 800PhotomosaicIncidentelectronbeamViolet IndigoElectron gunBlueGreenWavelength (nm)photometryphotomosaicYellow Orange RedLightFocusinglensReturned, modulatedelectron beamAnodeOutputare reflected to a second plate, where they dislodgestill more electrons. This process continuesfrom deflection plate to deflection plate throughthe tube. The final plate deflects the accumulatedelectrons to the anode (collector electrode).photon A quantum of radiant energy whose energyconstant W (in joules) is equal to hf, where h isthe PLANCK CONSTANT and f is the frequency inHertz.

532 photoneutron • pickoffphotoneutron A neutron released by PHOTODIS-INTEGRATION.photophone 1. A telephone-type communicationsystem using a modulated light beam transmittedbetween stations. 2. A process for recordingsound on motion-picture film (see OPTICALSOUND RECORDING).photorelay See PHOTOELECTRIC RELAY.photoresistive cell See PHOTOCONDUCTIVECELL.photoresistive material See PHOTOCONDUC-TIVE MATERIAL.photoresistivity See PHOTOCONDUCTIVITY.photoresistor See PHOTOCONDUCTOR, 1, 2.photosensitive device A light-sensitive electronicdevice. See, for example, PHOTOCONDUCTIVECELL, PHOTODIODE, PHOTOFET, PHOTOMUL-TIPLIER TUBE, PHOTOTRANSISTOR, PHOTO-TUBE, and PHOTOVOLTAIC CELL.photosphere The luminous layer at the surface ofa star.photoswitch A light-activated switch. Some photoswitchescontain an electromechanical relay; others,such as the light-activated silicon-controlledswitch, have no moving parts.phototimer An electronic timer for timing photographicprocesses.phototransistor A transistor in which currentcarriers emitted as a result of illumination constitutean input-signal current. This current isamplified by the transistor. The output signaldelivered by the transistor, accordingly, islarger than the output of an equivalent photodiode.phototube An electron tube that converts light energyinto electrical energy by acting as a lightsensitiveresistor. Characteristically, the tubecontains an illuminated cathode coated with aphotoemissive material, and an anode wire situatednearby. Light energy causes electrons to beemitted from the cathode in amounts proportionalto light intensity; the electrons are attractedby the anode, which is connectedexternally to a positive direct-current voltage.photovoltaic cell Also called solar cell. A semiconductordiode, usually made from silicon, thatconverts visible light, infrared, and/or ultravioletdirectly into electric current. The device consistsof a flat P-N junction; the assembly is transparentso that radiant energy can fall directly on the P-type silicon. Metal ribbing, forming the positiveelectrode, is interconnected with tiny wires. Thenegative electrode is a metal backing, placed incontact with the N-type material. The componentproduces about 0.5 to 0.6 volts in direct sunlightunder no-load conditions.photovoltaic material A substance that generatesa voltage when exposed to light. The principalsubstances exhibiting this effect are silicon, selenium,and germanium. Also see ACTINOELEC-TRIC EFFECT.GlasspnMetal baseRelative current86420MetalribbingSaturation current0 2 4 6 8 10Relative light intensityphotovoltaic cellphotran A light-sensitive, four-layer semiconductordevice, used for switching purposes.physical properties The distinguishing characteristicsof matter, apart from its chemical properties.Included are boiling point, density, ductility,elasticity, electrical conductivity, hardness, heatconductivity, index of refraction, malleability, meltingpoint, specific heat, and state (solid, liquid,gaseous, or plasma).physical quantity A quantity expressing the actualnumber of physical units under consideration,as compared with a dimensionless number.Examples: 50 volts, 39 kilometers, and 30 picofarads.Compare DIMENSIONLESS QUANTITY.physics The science of energy and matter and theirinteractions. Physics is subdivided into severalfields, including mechanics, thermodynamics,acoustics, optics, and electricity/magnetism.Many subdivisions are within the traditionalfields.P i Symbol for INPUT POWER.picket fencing An effect often observed at veryhighfrequencies (VHF) and ultra-high frequencies(UHF), in which movement of the transmittingstation antenna, the receiving stationantenna, or both antennas causes rapid fading.The fading is the result of phase effects betweenthe direct wave and indirect wave(s). These effectsare most pronounced with vertically polarizedantennas.PIA Abbreviation of PERIPHERAL INTERFACEADAPTER.pickoff 1. To monitor a voltage, current, or othercharacteristic in an active circuit, without dis-+−

pickoff • Pierce oscillator 533turbing the operation of the circuit. 2. A device forelectronically monitoring linear or angular displacement.pickup 1. A device that serves as a sensor of a signalor quantity. This covers a wide variety ofitems, including temperature sensors, vibrationdetectors, microphones, phonograph pickups, etc.2. Collectively, energy or information that is received(e.g., sound pickup).pickup arm The pivoted arm that holds the cartridgeand stylus of a phonograph.pickup cartridge See PHONO CARTRIDGE.pickup current 1. The current required to close arelay. 2. Current flowing through, or generatedby, a pickup.pickup pattern The directional pattern of a microphoneor other transducer that converts acousticenergy into electrical signals.pickup voltage 1. The voltage required to close arelay or circuit breaker. 2. The voltage deliveredby a pickup.pico- 1. Abbreviation, p. A prefix meaning 10 –12 .2. A prefix meaning extremely small.picoammeter A usually direct-reading instrumentused to measure current in the picoampererange. Also see CURRENT METER.picoampere Abbreviation, pA. A small unit of currentequal to 10 –12 ampere.picocoulomb Abbreviation, pC. A small unit ofelectrical quantity equal to 10 –12 coulomb.picocurie Abbreviation, pCi. A small unit of radioactivityequal to 10 –12 curie.picofarad Abbreviation, pF. A small unit of capacitanceequal to 10 –12 farad.picohenry Abbreviation, pH. A small unit of inductanceequal to 10 –12 henry.picosecond Abbreviation, ps or psec. A small unitof time equal to 10 –12 second.pi coupler See COLLINS COUPLER.picovolt Abbreviation, pV. A small unit of voltageequal to 10 –12 volt.picovoltmeter A usually direct-reading electronicinstrument used to measure electromotive forcein the picovolt range.picowatt Abbreviation, pW. A small unit of powerequal to 10 –12 watt.pictorial See PICTORIAL WIRING DIAGRAM.pictorial diagram See PICTORIAL WIRING DIA-GRAM.pictorial wiring diagram A wiring diagram in theform of a drawing or photograph of the components,as opposed to one of circuit symbols. Thecomponents are shown in their positions in thefinished equipment, and the wiring as lines runningbetween them.picture black In facsimile or television, the signalcondition resulting from the scanning of a blackportion of the image.picture detector See VIDEO DETECTOR.picture diagram See PICTORIAL WIRING DIA-GRAM.picture element See PIXEL.picture information In a television signal, thevariable-amplitude component (i.e., the one carryingenergy corresponding to the picture elements)that fills the space between blankingpulses.picture-in-picture Abbreviation, PIP. In some televisionreceivers, a feature that allows simultaneousviewing of two programs. One programoccupies the full screen, and another programappears in a small portion of the screen.picture reception 1. See PHOTOGRAPH RECEP-TION. 2. The reception of television signals.picture transmission 1. See PHOTOGRAPHTRANSMISSION. 2. The transmission or broadcastingof television signals.picture tube The cathode-ray tube used in a televisionreceiver to display the image. Also calledKINESCOPE.−+ElectrongunGridsSignalinputHousingDeflectingplatesorcoilspicture tubePhosphorscreenpie chart See CIRCLE GRAPH.Pierce oscillator A simple crystal oscillator inwhich the crystal is connected directly betweenthe input and output terminals of the active device(usually a bipolar or field-effect transistor). Atuned inductance-capacitance (LC) circuit mightbe included, but is not required.Y1RFCB+B−Pierce oscillatorRFoutput

534 pie winding • pinch rollerpie winding A method of coil winding in which twoor more separate, multilayer coils are connectedin series and placed along a common axis. It issometimes used in radio-frequency chokes tominimize capacitance among the windings.piezo- A prefix meaning pressure (see PRESSURE,2).piezodielectric A substance that, when stretchedor compressed, exhibits a change in dielectricconstant.piezoelectric accelerometer An accelerometerusing a piezoelectric crystal, whose voltage outputis proportional to acceleration.piezoelectric ceramic A ceramic material that deliversa voltage when deformed, or that changesin shape when a voltage is applied to it.piezoelectric crystal A crystal (such as quartz,Rochelle salt, tourmaline, or various synthetics)that delivers a voltage when mechanical force isapplied between its faces, or that changes itsshape when a voltage is applied between its faces.piezoelectric earphone See CRYSTAL EAR-PHONE.piezoelectric filter See CRYSTAL FILTER andCRYSTAL RESONATOR.piezoelectricity Electricity produced by deforming(squeezing, stretching, bending, or twisting) certaincrystals, such as those of quartz, Rochellesalt, or tourmaline.piezoelectric loudspeaker See CRYSTAL LOUD-SPEAKER.piezoelectric microphone See CERAMIC MICRO-PHONE and CRYSTAL MICROPHONE.piezoelectric oscillator See CRYSTAL OSCILLA-TOR.piezoelectric pickup See CRYSTAL PICKUP.piezoelectric resonator See CRYSTAL FILTERand CRYSTAL RESONATOR.piezoelectric sensor See CRYSTAL TRANS-DUCER.piezoelectric transducer See CRYSTAL TRANS-DUCER.piezoid A complete piezoelectric crystal device.piezoresistance In certain substances, the tendencyof the resistance to change with stretchingor compression.piezo tweeter A tweeter of the piezoelectric type(see CRYSTAL LOUDSPEAKER).pi filter An unbalanced filter section having oneseries arm and two shunt arms; its schematicrepresentation has the general shape of the uppercaseGreek letter pi.piggyback component See OUTBOARD COMPO-NENT.piggyback control See CASCADE CONTROL.piggyback tuner A separate ultra-high-frequency(UHF) television tuner operated in conjunctionwith the very-high-frequency (VHF) tuner of thereceiver.pigtail 1. A usually long and sometimes flexiblelead, such as the pigtail of a fixed capacitor.InputInputpi filtersOutputOutput2. Descriptive of a device containing a long leador leads, and usually mounted by such leads.pile 1. See VOLTAIC PILE. 2. See NUCLEAR REAC-TOR. 3. A battery of electrochemical cells. 4. Anypacked group of particles or granules.pillow speaker A small, flat loudspeaker intendedfor use under a pillow.PILOT Acronym for programmed inquiry learning orteaching. A straightforward high-level computerprogramming language, used in computerassistedinstruction (CAI).pilot lamp See PILOT LIGHT.pilot light A usually small, incandescent or neonlamp. When glowing, it serves as a signal that apiece of equipment is in operation.pilot model A preliminary model of a circuit or deviceconstructed primarily to test the efficacy of aproduction process. The pilot model usually followsthe PROTOTYPE.pilot production The often small-scale productionof a device in a special assembly line apart fromthe main line in a factory.pilot regulator A variable-gain circuit that maintainsa constant output—even if the input amplitudechanges.PIM Abbreviation of PULSE-INTERVAL MODULA-TION.pi mode In a vane-anode magnetron, the mode ofoperation in which adjacent vanes have radiofrequencyvoltages of opposite polarity.pin 1. A semiconductor junction consisting of alayer of instrinsic semiconductor material situatedbetween n and p layers. 2. A slender,straight, stiff prong used as a terminal or lockingdevice (see, for example, BASE PIN and BAYONETBASE).pinchoff In a junction field-effect transistor, thecondition in which the gate voltage causes thetwo depletion regions to meet and close the channelto obstruct drain-current flow.pinchoff voltage In a junction field-effect transistor,the lowest value of gate voltage that will producepinchoff.pinch roller In a tape recorder, a rubber-tired, rotatingcylinder that helps to pull the tape past therecording and/or playback heads.

pincushion • pitch 535pincushion A type of television picture distortionin which each side of the raster sags toward centerscreen. Also see ANTIPINCUSHIONING MAG-NETS.pincushion-correction generator A circuit forgenerating a deflection signal to correct pincushiondistortion (see PINCUSHION). One form consistsof a parabola generator and op-amp-typedifferentiator.pin diode A silicon junction diode having a lightlydoped intrinsic layer serving as a dielectric barrierbetween p and n layers.pi network See COLLINS COUPLER.ping An acoustic pulse; it can be audible sound orultrasound.pinhole 1. A tiny hole present as a defect in a filmof dielectric, semiconductor, or metal. 2. A tinyaperture that acts as a universal lens by permittingthe passage of a very small bundle of lightrays. The smaller the aperture, the greater thedepth of field.pinhole detector An electronic device for findingpinholes in materials. Also see PINHOLE, 1.pin jack A jack into which a pin plug is inserted forquick connection.pink noise Acoustical noise whose amplitude isinversely proportional to the frequency within alimited frequency spectrum. In the extreme, itcreates a hissing sound. Compare WHITENOISE.pinoutA diagram of an integrated circuit depictingthe locations of the pins for various functions. Itgenerally takes the form of a rectangle for the circuititself, and short lines for the pins with designatorsprinted next to the lines.pin plugA plug consisting of a slender metal pininserted between the blades of a PIN JACK for aquick connection. The plug usually has a smallinsulated back for convenient handling.pin straightener A device for straightening thepins of a transistor, integrated circuit, or otherelectronic component.pin switch A switch that changes state when asmall pin is pushed or pulled.pin-usage factor For an integrated circuit, thenumber of gate equivalents per package pin. Alsosee GATE EQUIVALENT.PIO Abbreviation of parallel input/output.pion A subatomic particle consisting of one quarkand one antiquark.PIP Abbreviation of PICTURE-IN-PICTURE.pip See BLIP.pi pad A resistance-type attenuator having a seriesarm, a shunt input arm, and shunt output arm;its name is derived from its resemblance to theGreek letter pi. Also see PAD.pipe radiator A waveguide having an open endfrom which microwave energy is radiated.Pirani gauge A type of vacuum gauge in which aheated filament, composing one arm of a fourarmresistance bridge, is sealed into the vacuumsystem. The bridge is balanced before evacuationstarts. As evacuation progresses, the heat removedfrom the filament becomes proportional tothe pressure in the system, and the resistance ofthe filament changes accordingly. The bridge isthen rebalanced, and the difference between initialand subsequent null conditions indicate theextent of the vacuum when the bridge has beenappropriately calibrated.pi section An unbalanced filter or tuner sectionwhose schematic representation has the generalshape of the uppercase Greek letter pi.pi-section coupling Use of a PI SECTION for couplinga radio transmitter to an antenna. Also seeCOLLINS COUPLER and PI-SECTION TANK.pi-section filter A pi section used as either a lowpassor high-pass filter, depending on the positionof the capacitors in the circuit.pi-section tank A pi section used as the collector,drain, or plate tank circuit of a radio-frequencypower amplifier, and also serving as an antennacoupler.piston 1. The movable element (cone) of a loudspeaker.2. The movable, solid plunger of a trimmercapacitor that consists of a plug within acylinder.piston directivity Directivity of sound emitted bythe piston of a loudspeaker (see PISTON, 1). Asthe frequency of the audio signal increases, radiationfrom a loudspeaker tends to be concentratedalong the axis of the piston.pit1. A microscopic depression in a compact disc;scatters and/or absorbs light from the laser,rather than reflecting it. Compare LAND, 1. 2. Ina printed-circuit board, a pockmark in a componentor foil run. 3. A pockmark in a metallic substance,resulting from corrosion.pitchInputpi padOutput1. The frequency of a sound, either in generalterms (e.g., low, midrange, and high) or as aspecific quantity (e.g., 2450 Hz). 2. The distancebetween the peaks of adjacent grooves on aphonograph disc. 3. The distance between adjacentthreads of a screw. 4. The distance betweencenters of turns in a coil (see PITCH OF WIND-ING) 5. The number of teeth or threads per unitlength. 6. The distance along its axis a propellermoves in a revolution. 7. Up-and-down motion ofa robot end effector or other electromechanicaldevice. 8. The extent or range of movement, asdefined in 7.

536 pitch of winding • plasma diodepitch of winding In a coil, the distance from thecenter of one turn to the center of the adjacentturn in a single layer of winding.PIV Abbreviation of PEAK INVERSE VOLTAGE.pivot The sometimes jeweled, stationary memberof the bearing in an analog meter movement.pi-wound choke A choke coil consisting of severalseries-connected sections, mounted on a singlecore and separated to reduce internal capacitance.pix Abbreviation of PICTURE.pixel Contraction of picture element. The smallestbit of data in a video image. Also called pel. Thesmaller the size of the pixels in an image, thegreater the resolution for a given image area.pixel aspect ratio In a video image, the ratio ofPIXEL height to pixel width.pix tube See PICTURE TUBE.PL Abbreviation for PRIVATE LINE.place effect An apparent change in the perceivedpitch of a sound, caused by variations in the waythe waves interact inside the human ear.planar diffusion In the production of a semiconductordevice, the diffusion of all the elementsinto one face of a wafer. Consequently, connectionsto the elements all lie in one plane. Also seeEPITAXIAL PLANAR TRANSISTOR and PLANARTRANSISTOR.planar diode A semiconductor diode, having a pnjunction that lies entirely within a single plane.planar epitaxial passivated diode A junctiondiode that, like the planar epitaxial transistor,has been manufactured by planar diffusion, thenpassivated to protect the junction. Also see EPI-TAXIAL GROWTH, EPITAXY, PASSIVATION, andPLANAR DIFFUSION.PL/1 A computer programming language that is ahybrid of scientific and commercial types (like AL-GOL and COBOL), the combined features beingpowerful problem-solving and mass-datahandlingabilities.planar epitaxial passivated transistor A planarepitaxial transistor that has been passivated toprotect the exposed junctions. Also see EPITAX-IAL PLANAR TRANSISTOR, PLANAR TRANSIS-TOR, EPITAXIAL TRANSISTOR, PASSIVATION,and PLANAR TRANSISTOR.planar transistor A transistor in which the emitter,base, and collector elements terminate on thesame face (plane) of the silicon wafer. A thin filmof silicon dioxide is grown on top of the wafer toinsulate the exposed junctions after the leadshave been attached (i.e., the transistor is passivated).Planck constant Symbol, h. Unit, joule-second.The constant of proportionality in the fundamentallaw of the quantum theory, stating thatradiant energy is composed of quanta proportionalto the frequency of the radiation; h = q/f =6.62608 × 10 –34 J•s, where q is the value of thequantum and f is the frequency in Hz.CollectorBaseEmitternpnplanar transistorOxidefilmplane of polarization The plane containing the directionof propagation and the electric field vectorof a plane-polarized wave (see POLARIZATION, 3and POLARIZED LIGHT).plane-polarized light See POLARIZATION, 3 andPOLARIZED LIGHT.plane-reflector antenna A directive antenna inwhich the reflector is a sheet of metal or a metalscreen. In a corner-reflector antenna, the reflectoris a folded sheet, or two sheets joined alongone edge.planetary electron See ORBITAL ELECTRON.planimeter A mechanical instrument for measuringthe area of a closed figure. The outline of thefigure is traced with the pointer of the device, andthe area is read from a pair of dials. In this application,the planimeter does the work of integralcalculus.PLANNER A high-level computer programminglanguage sometimes used in artificial intelligence.It is a “goal-oriented” language in that itseeks a solution to a problem using variousschemes, as necessary.plan position indicator Abbreviation, PPI. A radardisplay on whose screen small spots of light reconstructthe scanned vicinity, revealing objects,such as buildings, boats, aircraft, etc. The distancefrom the center of the screen to a spot depictsthe range of an object, and the radial anglereveals its bearing.plant In computer operations, to put the result ofan operation specified by a routine in a storagelocation from which it will be taken for implementationof an instruction further on in the program.plaque resistor A flat, noninductive, power resistor,often used as a dummy load during highfrequencypower measurements.plasma A usually high-temperature gas that is sohighly ionized that it is electrically conductiveand susceptible to magnetic fields; it is recognizedas one of the states of matter. Also seePHYSICAL PROPERTIES.plasma diode A diode in which a plasma substanceproduces conduction in one direction, butnot in the other.

{plasma length • plated magnetic wire 537plasma length See DEBYE LENGTH.plasma oscillation In a plasma, a form of electricfieldoscillation of the rapidly moving electrons.plasma torch A torch, used for such high-heat applicationsas melting metal, in which a gas isheated by electricity to the high temperature atwhich it becomes a plasma.plasmatron A form of amplifier tube sometimesused at ultra-high and microwave frequencies. Itis similar to a thyratron. An inert gas is exciteduntil it becomes a plasma, producing amplificationunder certain operating conditions.Plastacele See CELLULOSE ACETATE.plastic A synthetic material usually made fromvarious organic compounds through polymerization(see POLYMERIZE). Plastics can be moldedinto solid shapes and are available as films. Examples:celluloid, cellulose acetate, cellulose nitrate,polyethylene, and polystyrene. Also seeTHERMOPLASTIC MATERIAL and THERMOSET-TING MATERIAL.plastic-film capacitor A capacitor made usingpolyester, polyethylene, or polystyrene. Themethod of manufacture is similar to that for papercapacitors when the plastic is flexible. Stackingmethods can be used if the plastic is morerigid. The geometries can vary, and these capacitorsare therefore found in several differentshapes. Capacitance values for plastic-film unitsrange from about 50 pF to several tens of microfarads.Most often they are in the range of 0.001 µFto 10 µF. Plastic-film capacitors are employed inaudio equipment, and also in wireless transmittersand receivers. The efficiency is good, althoughnot as high as that for mica-dielectricunits. Compare CERAMIC CAPACITOR, ELEC-TROLYTIC CAPACITOR, MICA CAPACITOR, PA-PER CAPACITOR, TANTALUM CAPACITOR.plasticizer A substance added to a plastic to makeit softer or more flexible.plastic-leaded chip carrier Abbreviated PLCC. Asurface-mounted package for an integrated circuit.It is small in size and has high electrical andmechanical reliability.plate 1. The anode of an electron tube. 2. One ofthe electrodes of a primary or secondary batterycell. 3. One of the electrodes of a capacitor.plateau In a response curve, a region in which anincrease in the independent variable produces nofurther change in the dependent variable. Example:the saturation region in a common-basetransistor collector-current curve.plate blocking capacitor A capacitor connectedbetween the plate of an electron tube and theplate tank. It allows the direct-current supplyvoltage to be applied directly to the plate withoutit passing through the tank coil, while at thesame time preventing the tank coil from shortcircuitingthe plate power supply. The capacitorfreely transmits alternating-current signal energyto the tank.yy = f (x)plateauPlateauplate capacitance See PLATE-CATHODE CAPACI-TANCE.plate-cathode capacitance Symbol, C PK . Unit, pF.The internal capacitance between the plate andcathode of an electron tube. Also called OUTPUTCAPACITANCE.plate characteristic For an electron tube, the familyof plate current-vs-plate voltage curves for variousgrid-bias voltages.plate circuit The external circuit associated withthe plate of an electron tube.plate-circuit relay A direct-current relay operatedin series with the plate of an electron tube.plate conductance Symbol, g P . Unit, siemens.Conductance of the internal plate circuit of anelectron tube. The value of static g P is equal to theplate current divided by the plate voltage (I P /E P ).The value of dynamic g P is equal to the derivativeof the static g P : d IP /d EP . Plate conductance is thereciprocal of PLATE RESISTANCE.plate current Symbol, I P . Direct current flowing inthe plate circuit of an electron tube.plate-current shift A change in the plate currentof a radio-frequency power amplifier during amplitudemodulation. The action discloses faultyoperation because the average plate currentshould remain constant during modulation.plate dissipation Abbreviation, PD. Unit, watt.Power expended in the plate of an electron tube.For an unloaded tube, PD = E P I P , where E P is thedirect-current (dc) plate voltage in volts, and I P isthe dc plate current in amperes. For a loadedtube, PD = P o – P i , where P o is the alternatingcurrent(ac) power output of an amplifier oroscillator in which the tube operates, and P i is thedc plate power input.plated magnetic wire A wire with a ferromagneticouter coating on a core that is not magnetic.x

538 plated-wire memory • plate-type capacitorplated-wire memory See WIRE MEMORY.plate-grid capacitance Symbol, C PG or C GP . Unit,pF. The internal capacitance between the plateand control grid of an electron tube. Also calledINTERELECTRODE CAPACITANCE and FEED-BACK CAPACITANCE.plate load The power-consuming load into whichthe plate circuit of an electron tube operates. Inan intermediate stage of a multistage amplifier,this load is the grid circuit of the following tube.plate load impedance Symbol, Z LP . Unit, ohm. In atube circuit, the (output) impedance that is acconnectedbetween the plate and ground, or dcconnectedbetween the plate electrode and dcplate power supply.plate meter A direct-current ammeter or milliammeterthat indicates the plate current of anelectron tube.plate modulation A method of AMPLITUDE MOD-ULATION in which a modulating voltage is superimposedon the direct-current plate voltage of ahigher-frequency amplifier or oscillator.platen The “roller” in a teletypewriter or impactprinter. It supports the paper against impact bythe print head; it also helps to move the paperthrough the machine.plate-neutralized amplifier A vacuum-tube radiofrequencypower amplifier in which a neutralizingcapacitor is connected between the control gridand the free end of a center-tapped plate-tankcoil.plate power Symbol, P P . Unit, watt. Power in theplate circuit of an electron tube; P P = E P I P , whereE P is the plate voltage in volts and I P is the platecurrent in amperes.plate power input See PLATE POWER.plate power output The output signal power deliveredby the plate circuit of an electron tube. ComparePLATE POWER INPUT.plate power supply The (usually direct current)power supply that furnishes energy to the plate ofan electron tube.plate pulse modulation A method of obtainingpulse modulation by injecting high-voltage pulsesinto the plate circuit of a vacuum-tube amplifier.plate relay A relay operated in series with the plateof an electron tube.plate resistance Symbol, r P . Unit, ohm. Resistanceof the internal plate circuit of an electron tube.The static value of r P is equal to E P /I P , where E P isthe plate voltage in volts, and I P is the plate currentin amperes. The dynamic value is dE P /dI P .plate saturation In an electron tube, the point atwhich, while plate voltage is increasing, the plateattracts all the electrons emitted by the cathode(i.e., the point beyond which no further significantincrease in plate current results from a furtherincrease in plate voltage).plate-screen capacitance Symbol, C PS . Unit, pF.The internal capacitance between the plate andscreen grid of an electron tube.plate-screen modulation A method of AMPLI-TUDE MODULATION in which the modulatingvoltage is superimposed simultaneously on thedirect-current plate and screen voltages of ahigher-frequency amplifier or oscillator.plate series compensation In an audio amplifier,the use of a plate decoupling circuit to obtain afixed amount of bass boost.plate shunt compensation The addition of a networkto the plate-output circuit of a tube to boostthe bass response of an amplifier.plate spacing 1. The distance between plates in afixed capacitor. This dimension is usually thesame as dielectric thickness. 2. The distance betweenplates in a variable capacitor. Also calledcapacitor air gap.PlatespacingPlateplate spacing, 1PlateDielectricplate supply voltage Symbol, E BB . The output voltageof a plate power supply.plate tank A resonant inductance-capacitance(LC) circuit operated from the plate of an electrontube.plate tank capacitance The capacitance requiredto tune a PLATE TANK to resonance.plate tank inductance The inductance of the coilin a PLATE TANK.plate tank Q Figure of merit (see Q) of a plate tank,a function of the load resistance and the tank inductance-to-capacitance(L/C) ratio.plate tank voltage The audio-frequency or radiofrequencyvoltage developed across the plate tankof an electron-tube circuit.plate tuning Tuning an electron-tube circuit byvarying the capacitance, inductance, or both inthe plate tank.plate tuning capacitance See PLATE TANK CA-PACITANCE.plate tuning inductance See PLATE TANK IN-DUCTANCE.plate-type capacitor A capacitor having flat metalplates, rather than concentric cylinders, a cylinderand rod, etc.

plate voltage • plug-in meter 539plate voltage Symbol, E P . The direct-current voltageapplied to the plate of an electron tube.plate winding 1. An inductor connected in seriesbetween the plate of a vacuum tube and the positivepower-supply voltage. 2. The primary windingof a plate-circuit output transformer.platiniridium A natural alloy of PLATINUM andIRIDIUM.platinotron A form of traveling-wave vacuum tubeused as an amplifier at ultra-high and microwavefrequencies. There are two output connections.platinum Symbol, Pt. A precious metallic element.Atomic number, 78. Atomic weight,195.08. It is sometimes used for plating of relayand switch contacts, and for certain parts ofvacuum tubes.platinum metals The rare metals IRIDIUM, OS-MIUM, PALLADIUM, PLATINUM, RHODIUM, andRUTHENIUM. They do not react readily withother elements.platinum-tellurium thermocouple A thermocoupleusing the junction between platinum and telluriumwires; it is used in thermocouple-typemeters.platter 1. One of the individual disks in a computerHARD DISK drive. 2. The rotating turntablein a PHONOGRAPH.playback The reproduction of recorded material inaudio-tape, audio-disc, video-tape, or video-discsystems.playback computer system A personal computerand associated peripherals, equipped for reproducingmultimedia that has been recorded onCD-ROM.playback head In a magnetic recorder/reproducer,the head that picks up the signal from the tape ordisc for reproduction. Also called read head andplay head.playback loss In disc recording, the difference (at aparticular point on the disc) between the recordedlevel and the reproduced level.player A semiconductor layer that is doped to providecurrent carriers that are predominantlyholes. Compare N LAYER.player A device or system that reproduces (playsback) data from a tape or disc, but cannot beused to record data onto the tape or disc.play head See PLAYBACK HEAD.playthrough The condition in which an amplifierdelivers a small output signal when the gain controlis set to zero.PLC Abbreviation of POWER-LINE COMMUNICA-TION.PLCC Abbreviation of PLASTIC-LEADED CHIPCARRIER.plethysmograph A medical-electronic device thatallows the monitoring of the amount of blood indifferent parts of the body.PLL Abbreviation of PHASE-LOCKED LOOP.PLM Abbreviation of pulse-length modulation (seePULSE-DURATION MODULATION).PLO Abbreviation of PHASE-LOCKED OSCILLA-TOR.plot 1. A curve depicting the variations of onequantity, with respect to another. 2. To generate,print, or display a curve of the type defined in 1.plotter A machine that plots (see PLOT, 2) automatically,often by the direction of a computer.PL tone encoder An audio oscillator and modulatorthat cause a subaudible-tone modulation of asignal for use in restricted communications systems.plug A usually male quick-connect device that canbe inserted into a JACK to make a circuit connection,or be pulled out of the jack to break the connection.See, for example, MALE PLUG, PHONEPLUG, POWER PLUG, and POLARIZED POWERPLUG.plug-and-jack connection A connection made byinserting a PLUG into a JACK.plug fuse A fuse provided with an Edison base forscrewing into a socket.pluggable Capable of being completely removedfrom the rest of the system without the need forremoving any wiring. Pluggable components andcircuit boards simplify the servicing of electronicequipment.plug-in See PLUG-IN COMPONENT and PLUG-INUNIT.plug-in capacitor A capacitor with pins or ferrulesthat can be quickly inserted into, or removedfrom, a socket.plug-in coil A coil wound on a form having pinsthat can be quickly inserted into, or removedfrom, a socket.plug-in coil form An insulating form with basepins that mate with socket terminals so that acoil wound on the form can be quickly insertedinto, or removed from, a circuit.plug-in component A component or module, suchas a transistor, capacitor, coil, lamp, etc., providedwith pins, clips, or contacts for easy insertioninto, or removal from, a circuit. See, forexample, PLUG-IN CAPACITOR, PLUG-IN COIL,PLUG-IN FUSE, PLUG-IN LAMP, PLUG-IN ME-TER, PLUG-IN RESISTOR, PLUG-IN TRANS-FORMER, and PLUG-IN UNIT.plug-in fuse A cartridge fuse having a metal ferruleon each end for insertion into a matching clip foreasy installation and removal.plug-in fuseplug-in lamp A lamp with base pins for quick insertioninto, or removal from, a socket.plug-in meter A meter with pins or banana plugs forquick insertion into, or removal from, a circuit.

540 plug-in resistor • point defectplug-in resistor A resistor with pins or ferrules forquick insertion into, or removal from, a socket.plug-in transformer A small transformer with pinsfor quick insertion into, or removal from, asocket.plug-in unit A unit, such as a tuned circuit, amplifier,or meter, that has pins or contacts for easyinsertion into, or removal from, a larger piece ofequipment.plumber’s delight An antenna whose construction,including that of the mast, is entirely ofmetal rods or tubing, with no insulating parts.Short circuits and grounds are prevented bymaking all attachments and joints at points thatare at zero voltage, with respect to the standingwavepattern.Plumbicon A television camera tube, similar to theVIDICON, with a lead-oxide target. It is noted forhigh sensitivity. The image lag time is shorterthan in the conventional vidicon.plumbing Collectively, the waveguides, tees, elbows,and similar pipelike devices and fixturesused in microwave setups.plunger-type meter A meter in which an iron orsteel plunger is pulled into a coil by the magnetismproduced by a current flowing in the coil.The plunger is attached to a pointer that movesover the scale.plutonium Symbol, Pu. A radioactive metallic elementthat is artificially produced. Atomic number,94. Atomic weight, approximately 244.PM 1. Abbreviation of PERMANENT MAGNET.2. Abbreviation of PULSE(D) MODULATOR.3. Abbreviation of post meridian. 4. Abbreviationof PHASE MODULATION.Pm 1. Symbol for PROMETHIUM. 2. Abbreviationof PETAMETER.Pm Symbol for MAXIMUM POWER.PME Abbreviation of photomagnetoelectric.PMG Abbreviation of PERMANENT-MAGNET GEN-ERATOR.PMM Abbreviation of PERMANENT-MAGNETMAGNETIZER.PMOS Abbreviation of P-CHANNEL METAL-OXIDESEMICONDUCTOR.PMU Abbreviation of portable memory unit.PN 1. Abbreviation of POLISH NOTATION. 2. Abbreviationof POSITIVE-NEGATIVE (often lowercase).pn Abbreviation of POSITIVE-NEGATIVE.pn boundary See PN JUNCTION.pnip transistor A junction transistor having an intrinsiclayer between an n-type semiconductorbase and one of the p-type semiconductor layers.pneumatic computer A computer that uses fluidlogic [i.e., one in which information is stored andtransferred by the flow of a fluid (gas or liquid)and pressure variations therein].pn junction The boundary between p-type and n-type semiconductor materials in a single block orwafer of the materials. The junction cannot beduplicated by merely touching two pieces of material(one n-type and one p-type) together, howeversmooth their mating faces.pn-junction diode A diode consisting of the junctionbetween p-type and n-type regions in thesame wafer of semiconductor material.PNM Abbreviation of PULSE-NUMBERS MODULA-TION.pnpn device See NPNP DEVICE.pnp transistor A bipolar junction transistor inwhich the emitter and collector layers are p-typesemiconductor material, and the base layer isn-type semiconductor material. Compare NPNTRANSISTOR.Po Symbol for POLONIUM.Po Symbol for OUTPUT POWER or POWER OUT-PUT.POGO Abbreviation of polar orbiting geophysicalobservatory.point 1. A dot indicating the place of separationbetween the integral and fractional parts of anumber (e.g., decimal point). Also called RADIXPOINT. 2. A precisely defined location in threedimensionalspace that has theoretically zerolength, zero width, and zero depth (e.g., focalpoint). 3. The place on a graph in any number ofdimensions, at which two or more curves or coordinatesintersect. 4. A set of operating conditionsfor a component, device, or system (e.g., cutoffpoint, operating point). 5. A defined condition atwhich some specific physical phenomenon occurs(e.g., melting point).point charge An electric charge imagined to occupya single point in space; thus, it has neitherarea nor volume.point contact The point at which the sharplypointed tip of a wire or rod conductor touches asecond conductor (e.g., the contact between a“cat whisker” and a semiconductor wafer).point-contact diode A semiconductor diode havinga fine wire (“cat whisker”), whose point is inpermanent contact with the surface of a wafer ofsemiconductor material, such as germanium orsilicon.point-contact junction The pn junction electroformedunder the point at which the “catwhisker” touches the semiconductor wafer in apoint-contact diode or transistor.point-contact transistor A transistor having twofine wires (“cat whiskers”) that serve as the emitterand collector electrodes. The pointed tips of thewires are nearly in contact with (a few mils apartfrom) the surface of a wafer of semiconductor material,such as germanium. The semiconductorserves as the base electrode. This device was a predecessorof the JUNCTION TRANSISTOR.point counter A Geiger counter tube in which thecentral electrode is a pointed, fine wire. Also seePROPORTIONAL COUNTER.point defect 1. In a semiconductor substance orpiezoelectric crystal, the absence of an atom from

point defect • polarization 541its place in the lattice structure. 2. The presenceof an extra atom in the lattice structure.point effect The tendency of an electrical dischargeto occur more readily at a sharp pointthan at a blunt surface (as of an electrode).pointer A pointed blade, stiff wire, or inscribed lineon a transparent blade; it moves over a scale toindicate a setting or the value of a quantity. Alsocalled NEEDLE.pointer-type meter An analog meter in which apointer moves over a calibrated scale.point impedance 1. The impedance observed at agiven point in a circuit. 2. In a transmission line,the intensity of the electric field divided by the intensityof the magnetic field at a given point.points of saturation For a magnetic core, saturationas evidenced by a leveling-off of the positiveand negative halves of the magnetization curve.point source A source from which electromagneticradiation emanates, and that appears as a geometricpoint from a great distance.point mode Descriptive of cathode-ray-tube displayoperation (in a computer system), in whichdata is portrayed as plotted dots.point-to-point communication Communicationbetween two stations whose location can be preciselyspecified.point-to-point motion A method of robot armmovement in which the device can attain onlycertain positions. The coordinates of each stoppingpoint are stored in the robot controller (computer)memory.point-to-point station A radio station that providesPOINT-TO-POINT COMMUNICATION.point-to-point wiring A method of wiring an electroniccircuit in which wires are run directly betweenthe terminals or components, usually bythe shortest practicable route. It is used mainlyin high-voltage circuits, such as power amplifiers.Compare CABLED WIRING.poise The cgs unit of absolute viscosity; 1 poise isthe absolute viscosity of a fluid that requires ashearing force of 1 dyne to move a 1-sq-cm areaof one of two parallel layers of the fluid (1 cmapart) with a velocity of 1 cm per second, with respectto the other layer. The comparable SI unit isthe newton-second per meter squared (N • s/m 2 );1 poise = 0.1 N • s/m 2 .polar axis 1. In a crystal, the axis of rotation notperpendicular to a reflection plane. 2. Thestraight line connecting epicenters of electric,magnetic, or gravitational poles in a system.3. The axis about which the earth or anotherplanet rotates.polar coordinate conversion See POLAR COOR-DINATE TRANSFORMATION.polar-coordinate geometry A two-dimensionalsystem for movement of industrial-robot arms. Itis based on a system of POLAR COORDINATES,in which a radius and a direction angle are assignedto each point in the working plane.polar coordinates The magnitude and direction ofa vector in a defined plane, listed as a radius(magnitude) in combination with an angle (direction)between the vector and the polar axis.(r,θ)Origin: r = 00 2 4 6 8polar coordinatespolarimeter An instrument for measuring theamount of polarized light in a ray that is only partiallypolarized.polariscope An instrument used in the observationor testing of materials under POLARIZED LIGHT.polarity 1. The condition of being electrically positiveor negative. 2. The condition of being magneticallynorth or south. 3. The orientation of thepositive and negative poles in a battery or powersupply relative to a circuit. 4. The orientation of amagnetic field, relative to the surrounding environment.polarity blanking See POLARITY INHIBIT.polarity inhibit In some instruments, especiallythose having automatic polarity, the automaticblanking of the polarity sign.polarity-sensitive relay A direct-current relay actuatedonly when coil current flows in one direction.One of the simplest versions is a relayhaving a semiconductor diode connected in serieswith its coil.polarity shifter A potentiometer connected to twodirect-current sources so that a pair of outputterminals has plus and minus polarities at oneextreme of potentiometer adjustment, and minusand plus at the other extreme. At the center of therange, the output voltage is zero.polarity switch A double-pole, double-throwswitch connected between a pair of direct-currentinput terminals so that the polarity of a pair ofoutput terminals can be interchanged.polarization 1. In a radio wave, the orientation ofthe electric lines of flux, with respect to the surroundingenvironment (e.g., horizontal polarizationand vertical polarization). 2. The disabling ofa battery cell by the formation of insulating gason one of the plates. 3. The condition in whichtransverse waves of light are confined to a specific(e.g., horizontal or vertical) plane.θr

542 polarization diversity • polarizing filterpolarization diversity A form of reception inwhich two separate receivers, tuned to the samesignal, are connected to independent antennas.One antenna is vertically polarized and the otheris horizontally polarized. The result is a reductionin fading caused by ionospheric effects on the polarizationof the incoming signal.VerticalantennaBoth antennasat least λ/2 apartHorizontal antennapolarized plug A plug that can be inserted into asocket or receptacle in only one way to ensuresafe and foolproof operation.Larger pinis groundpolarized plugRXpolarization diversitypolarization error In the operation of a loop antenna(e.g., that of a direction finder), null errorcaused by waves arriving with polarization oppositethat of the loop (thus, vertically polarizedwaves at a horizontal-plane loop, and vice versa).polarization fading In radio reception, a form offading that results from changes in the polarizationof the arriving signal with respect to the receivingantenna. When the polarization of thearriving signal coincides with that of the receivingantenna, the received signal strength is maximum.When the received-signal polarization is atright angles to the receiving antenna, the signalstrength is minimum.polarization modulation A method of impressinginformation on a signal by changing the polarizationof the radiated electromagnetic field.polarization selectivity For a photoemissive surface,the condition in which the ratio of photocurrentsfor two different angles of plane polarizationof the light incident to the surface differs from theratio of the corresponding amounts of lightabsorbed by the surface. Also see PHOTO-EMISSION; PHOTOEMISSIVE MATERIAL; andPOLARIZATION, 3.polarized capacitor A conventional electrolytic capacitor,so called because one particular terminalmust be connected to the more positive of the twoconnection points. Compare NONPOLARIZEDELECTROLYTIC CAPACITOR.polarized light Visible light waves whose electriclines of flux are confined more or less to a singleplane. This effect can be obtained via filtering; italso occurs naturally under certain conditions.Scattered sunlight is polarized to some extent bythe atmosphere. Light is polarized to some extentwhen it reflects from a plane surface. Also see PO-LARIZING FILTER.polarized power plug A polarized plug for connectionof equipment to an alternating-current utilitypower source.polarized reactor A saturable reactor in which thelines of flux produced in the three-leg core by thecoils on the two outer legs are added in the centerleg. Consequently, the flux can reinforce or opposethe controlling current in the coil on thecenter leg, depending on the direction of the current.Compare NONPOLARIZED REACTOR.polarized receptacle A receptacle constructed sothat it can receive a plug in only one way, thuspreventing incorrect connections.Larger pinsocket isgroundpolarized receptaclepolarized relay A relay actuated by one polarity ofdirect current, or by one particular phase of alternatingcurrent. Such a relay sometimes containsan armature-centering permanent magnet.polarized socket See POLARIZED RECEPTACLE.polarized X rays X-ray waves whose electric linesof flux are more or less oriented in a specificplane, as when they are scattered by carbonblocks. See, for illustration, POLARIZATION, 3and POLARIZED LIGHT.polarizing filter A light filter that consists essentiallyof microscopic heraphathite plastic plate.The plate can be rotated to cause light passing

polarizing filter • polygraph 543through it to be polarized in any particular planebetween horizontal and vertical, depending onthe degree of rotation. Also see POLARIZEDLIGHT.polarography In chemistry, a form of qualitative orquantitative analysis utilizing IE curves obtainedwhen the voltage is gradually increased across asolution in ELECTROLYSIS.polar orbitAn orbit that carries a satellite over thegeographic polar regions of the earth. This type oforbit is oriented at, or nearly at, 90 degrees withrespect to the equator, and can have a periodranging from about 90 minutes to several weeksor even months. Low-earth-orbit (LEO) satellitesgenerally have such orbits.EquatorSatelliteorbitNorthpolepolar orbitEarthpolar-orbiting satellite Any satellite in a POLARORBIT.polar planimeter See PLANIMETER.polar relay See POLARIZED RELAY.polar response The horizontal-plane directionalresponse of an antenna or other transducer.pole 1. An extremity or terminus that possessesPOLARITY. Examples: magnetic pole and electricpole. 2. The movable member of a switch. 3. Oneof the frequencies at which a transfer functionbecomes infinite.pole face The smooth end surface of a pole piece.pole piece 1. A section of specially shaped iron orsteel that is attached to a magnetic core. 2. Halfof a two-piece magnetic core that terminates in apole.pole shoe In an electric motor, the section of thefield pole nearest the armature.poles of impedance For a reactive network, thefrequencies at which the impedance is infinite.Compare ZEROS OF IMPEDANCE.poles of network function The values at which anetwork function is infinite. Compare ZEROS OFNETWORK FUNCTION.poles of transfer function The frequencies atwhich a transfer function becomes infinite. CompareZEROS OF TRANSFER FUNCTION.police robot A proposed robotic machine, eitherautonomous or remotely controlled (teleoperated),that would be used to assist in law enforcement,particularly in dangerous operations.poling The deliberate adjustment of electromagnetic-fieldpolarity.Polish notation In Boolean algebra, a form of notationwherein the variables in a statement arepreceded by the operators.polling In data transmission, a technique in whichchannels being shared by more than one terminalare tested to find one over which data iscoming in, or to ascertain which is free fortransmission.polonium Symbol, Po. A radioactive metallic element.Atomic number, 84. Atomic weight, approximately209.polychromatic radiation 1. Visible-light radiationhaving more than one wavelength; in particular,covering a broad range of wavelengths. 2. Electromagneticradiation over a broad band of wavelengths.polycrystalline material A substance, such as asemiconductor, of which even a very smallsample consists of a number of separate crystalsbound tightly together. Compare SINGLE-CRYSTAL MATERIAL.polydirectional microphone See OMNIDIREC-TIONAL MICROPHONE.polyelectrolyte An ELECTROLYTE having highmolecular weight.polyester A resin made by reacting a dihydroxy alcoholwith a dibasic acid.polyester backing A polyester tape on the surfaceof which iron oxide is deposited to yield a magneticrecording tape.polyethylene A plastic insulating material. Dielectricconstant, 2.2. Dielectric strength, 585 V/mil.polyethylene disc A phonograph disc made ofpolyethylene.polygonal coil A coil wound on a form having apolygonal, rather than circular cross section.Some polygonal forms have as many as 12 sidesin cross section.polygraph An instrument for measuring andrecording electrical signals proportional to bloodpressure, skin resistance, breathing rate, andother reactions that vary under emotional stress.Also called LIE DETECTOR. Compare PATHOME-TER.

544 polymer • positionpolymer A compound that is the product of polymerization,resulting from the chemical union ofmonomers. Also see POLYMERIZE.polymerize To unite monomers or polymers of thesame kind to form a molecule having a highermolecular weight.polyphase In alternating-current circuits, pertainingto the existence or generation of two or morespecific electrical phases. Compare SINGLEPHASE.polyphase antenna An antenna consisting of twodipole radiators mounted perpendicular to eachother at their midpoint and excited 90 degreesout of phase. The radiation pattern is approximatelycircular in the plane of the elements. Alsocalled TURNSTILE ANTENNA.90° Phase shiftpolyphase antennapolyphase generator 1. A dynamo-type generatorof polyphase power (two-phase, three-phase,etc.). 2. See POLYPHASE OSCILLATOR.polyphase oscillator An oscillator circuit that generatespolyphase alternating current. The circuitcontains separate oscillators for each phase. Athree-phase circuit, for example, has three symmetricaloscillators with matched inductance andcapacitance values.polyphase power 1. The total dissipated power ina polyphase alternating-current circuit. 2. Polyphasealternating current provided for utility purposes.polyphase rectifier A rectifier of polyphase alternatingcurrent generally obtained from a threephasepower line through a transformer. Theseveral common circuits usually contain a diodefor each phase. Such rectifiers offer the advantageof higher ripple frequency than is obtainableby single-phase operation. For a three-phase rectifier,for example, the ripple frequency is threetimes the line frequency; for a six-phase rectifier,it is six times the line frequency.polyphase system An alternating-current circuitin which voltages or currents are normally out ofphase with each other by some fixed amount. Familiartypes are two-phase and three-phase.polyphase transformer An alternating-currenttransformer specifically designed for use in circuitsthat have two or more simultaneous currentphases.polypropylene A plastic material commonly usedas an electrical insulator. Dielectric constant,2.0. Dielectric strength, 600 V/mil.polyrod antenna A tapered dielectric antenna,usually made of polystyrene, for directional microwavetransmission.polysilicon A polycrystalline form of silicon (seePOLYCRYSTALLINE MATERIAL).polystyrene A clear, colorless thermosetting-typeplastic. It is widely used as an insulating materialin radio-frequency circuits and, to some extent,as a dielectric film in fixed capacitors. Dielectricconstant, 2.4 to 2.9. Dielectric strength, 20 to 28kV/mm.polystyrene capacitor A high-Q capacitor inwhich the dielectric film is polystyrene.polyvinyl chloride Abbreviation, PVC. A plasticinsulating material. Dielectric constant, 3.6 to4.0. Dielectric strength, 800 V/mil.pool cathode In an industrial electron tube, acathode consisting of a pool of mercury.pool-cathode tube An industrial electron tube usinga pool cathode. Examples: excitron, ignitron,and mercury-arc rectifier.popcorn noise A temperature-dependent, randomshotelectrical noise. In a radio receiver or audiocircuit, this noise resembles the sound of poppingcorn. It occurs in some operational amplifiers.population In statistical analysis, the total groupof items, quantities, or values under consideration.Sometimes called universe.porcelain A hard, white, usually glazed ceramicused as a dielectric and insulant. Dielectric constant,6 to 7.5. Dielectric strength, 40 to 100V/mil. Also called china.porcelain capacitor A ceramic-dielectric capacitorin which the dielectric is composed of porcelain ora related substance.porcelain insulator An electric insulator fabricatedfrom porcelain.porch See BACK PORCH and FRONT PORCH.port 1. In a circuit, device, or system, a point atwhich energy or signals can be introduced or extractedin a particular manner (e.g., two-port circulatorand I/O port). 2. An aperture in aloudspeaker enclosure.portable-mobile station See MOBILE STATION.portable station A communications station thatcan be carried from one location to another. Aportable station differs from a mobile station inthat a portable station does not usually operatewhile in motion, whereas a mobile station does.ported reflex enclosure A loudspeaker cabinetwith openings that facilitate bass (low-frequency)sound reproduction.pos 1. Abbreviation of POSITIVE. 2. Abbreviationof POSITION.position 1. The location of a point or object with respectto one or more (usually fixed) references.2. The setting of an adjustable device, such as apotentiometer, rotary switch, or variable capacitor.

positional notation • positive ghost 545positional notation A method of representingnumbers in which the number is indicated by thepositions and value of the component digits. Thedecimal number system belongs in this category(e.g., the decimal number 1284.67 is equal to 1 ×10 3 + 2 × 10 2 + 8 × 10 1 + 4 × 10 0 + 6 × 10 –1 + 7 ×10 –2 ).positional number system See POSITIONAL NO-TATION.positional representation See POSITIONAL NO-TATION.position-control potentiometers In an oscilloscope,potentiometers used to control the voltageapplied to the horizontal and vertical deflectingplates to position the spot on the screen. Also seeCENTERING CONTROL.position controls See POSITION-CONTROL PO-TENTIOMETERS.position feedback In a servo or other control system,feedback current, or voltage that is proportionalto the position assumed by a member.position fixing The determination of a positionfrom the intersection on a map of two lines derivedfrom the direction-finding pickups of two transmittingstations. Also see DIRECTION FINDER.position indicator In a tape recorder, a counterwhose numbered wheels revolve when the reelsdo, thus aiding in locating a desired spot on thetape. Also called tape counter.positioning circuit The circuit associated with ahorizontal or vertical centering control (see CEN-TERING CONTROL).position sensing 1. In robotics and navigationsystems, a method of determining location, relativeto the surrounding environment. 2. Anymethod via which a robot can accurately determinethe location(s) of its end effector(s).position sensor An electronic circuit that detectsphysical displacement, and transmits a signalproportional to the displacement.positioning control See CENTERING CONTROL.positive 1. Possessing positive (plus) directcurrentelectrical polarity. 2. Pertaining to realnumbers greater than zero. 3. A photographicimage whose shadings are the same as those inthe scene.positive angle 1. In a system of rectangular coordinates,an angle in the first or second quadrant.2. In rectangular coordinates, an angle measuredcounterclockwise from the positive x-axis.Compare NEGATIVE ANGLE.positive bias A positive voltage or current appliedcontinuously to an electrode of a device (as to atransistor base) to maintain the device’s operatingpoint. Compare NEGATIVE BIAS.positive bus See POSITIVE CONDUCTOR.positive charge An electrical charge characterizedby having relatively fewer electrons than a negativecharge. Also see CHARGE, 1; ELECTRICCHARGE; and UNIT ELECTROSTATIC CHARGE.Compare NEGATIVE CHARGE.positive conductor The conductor or line connectedto the positive terminal of a current,voltage, or power source. Compare NEGATIVECONDUCTOR.positive electricity See POSITIVE CHARGE andPOSITIVE ELECTRIFICATION.positive electrification Electrification characterizedby a deficiency of electrons. For example,when a glass rod is rubbed with a silk cloth, therod becomes positively charged because electronsare rubbed off the glass onto the silk. Similarly,when an atom loses an electron, it becomes electrifiedpositively because it has a deficiency of electrons.Compare NEGATIVE ELECTRIFICATION.positive electrode 1. An electrode connected tothe positive terminal of a current, voltage, orpower source. 2. The positive terminal of a current,voltage, or power source, such as a batteryor generator.positive electron See POSITRON.positive element See POSITIVE ELECTRODE, 1.positive error of measurement An error of measurementin which the difference between a measuredvalue and the true or most probable valueis positive. Compare NEGATIVE ERROR OF MEA-SUREMENT.positive exponent A positive superscript indicatingthat a number (x) is to be raised to the positiventh power. Thus, in the expression xn, thevalue of n is greater than zero. Compare NEGA-TIVE EXPONENT.positive feedback Feedback that is in phase withan input signal. Also called REGENERATION andREGENERATIVE FEEDBACK. Compare NEGA-TIVE FEEDBACK.InputFeedbackresistor+−+V ccpositive feedbackOutputpositive function A function having the positivesign. In the rectangular coordinate system, thetrigonometric sine function is positive in the firstand second quadrants, the cosine in the first andfourth, and the tangent in the first and third.Compare NEGATIVE FUNCTION.positive ghost In a television picture, a ghost withpositive shading (see POSITIVE, 3). Also seeGHOST.

546 positive-going • positive resistorpositive-going Pertaining to a signal whose valueis changing in a positive direction. This is not restrictedto signals of actual positive polarity; adecreasing negative voltage, for example, ispositive-going as it falls in the direction of zero—even if it never crosses the zero line.positive grid In an electron tube, a control gridwhose bias or signal voltage is positive, with respectto the cathode.positive-grid oscillator A microwave oscillator circuitin which the control grid of a triode tube isoperated at a positive direct-current potential,and the plate at a negative potential. Electronsmove back and forth between cathode and plate,through the grid, and thus give rise to an oscillatingcurrent.positive ground A direct-current electrical systemin which the positive power-supply terminal isconnected to the common ground. It is not generallyused in North America.positive half-alternation See POSITIVE HALF-CYCLE.positive half-cycle That half of an alternatingcurrentcycle in which the current or voltage increasesfrom zero to maximum positive and returnsto zero.positive image 1. A picture in which the blacks,whites, and grays correspond to those in the actualscene (see POSITIVE, 3). 2. A normal television picture(i.e., one that has the shading described in 1).positive ion An atom that has a deficiency of electronsand, consequently, exhibits a net positivecharge. Also called CATION.positive lead See POSITIVE CONDUCTOR.positive light modulation In television transmission,the condition in which transmitted powerincreases as the light intensity increases. CompareNEGATIVE LIGHT MODULATION.positive line See POSITIVE CONDUCTOR.positive logic 1. Binary logic in which a low positivestate represents logic 0, and a high positivestate represents logic 1. 2. Binary logic in whicha high negative state represents logic 0, and a lownegative state represents logic 1. Compare NEG-ATIVE LOGIC.positive magnetostriction A form of MAGNE-TOSTRICTION in which the physical size of asubstance is directly proportional to the intensityof the surrounding magnetic field.positive measurement error See POSITIVE ER-ROR OF MEASUREMENT.positive modulation In amplitude-modulatedtelevision transmission, the increase in transmittedpower when the brightness of the scene increases.Compare NEGATIVE MODULATION.positive modulation factor For an amplitudemodulatedwave having unequal positive andnegative peaks, a ratio expressing the maximumpositive deviation (increase) from the averagevalue of the envelope. Compare NEGATIVE MOD-ULATION FACTOR.positive number A real number, whose value isgreater than zero. Compare NEGATIVE NUMBER.positive peak The maximum amplitude of a positivehalf-cycle or positive pulse.positive-peak clipper A peak clipper that levels offthe positive half-cycle of an alternating-currentwave to a predetermined level.positive-peak modulation Amplitude modulationof the positive peaks of a carrier wave.positive-peak voltmeter An electronic voltmeterfor measuring the amplitude of the positive peakof an alternating-current (ac) wave. In its simplestform, it consists essentially of a directcurrent(dc) microammeter with a diode orientedto pass the positive half-cycle. A series capacitorin the circuit is charged to approximately thepeak value of the applied ac voltage. CompareNEGATIVE-PEAK VOLTMETER.+Input−+Vpositive-peak voltmeter+−Dischargeswitchpositive phase-sequence relay A phase-sequencerelay that responds to the positive phase sequencein a polyphase circuit. Compare NEGA-TIVE PHASE-SEQUENCE RELAY.positive picture modulation See POSITIVE MOD-ULATION.positive picture phase In a television signal, theswinging of the picture-signal voltage from zero topositive, in response to an increase in brightnessin the scene. Compare NEGATIVE PICTUREPHASE.positive plate 1. The positive member of an electrochemicalcell or battery. Electrons flow to thisplate from the negative plate, through the externalcircuit. 2. A vacuum-tube plate that is biasedpositively, as in a conventional tube circuit.positive pole See POSITIVE ELECTRODE, 1, 2.positive potential 1. The voltage at a positive electrode(with respect to the negative electrode).2. Voltage greater than that at ground as a reference.positive power See POSITIVE EXPONENT.positive resistance Ohmic resistance (see OHMICRESPONSE). Compare NEGATIVE RESISTANCE.positive resistor A resistor whose value does notchange with current or voltage changes. CompareNEGATIVE RESISTOR.

positive temperature coefficient • potential energy 547positive temperature coefficient Abbreviation,PTC. A number expressing the amount by which aquantity (such as the value of a component) increaseswhen temperature is increased. The coefficientis stated as a percentage of the rated valueper degree, or in parts per million per degree.Compare NEGATIVE TEMPERATURE COEFFI-CIENT and ZERO TEMPERATURE COEFFICIENT.positive transmission In facsimile or television, aform of amplitude modulation in which the picturebrightness is directly proportional to the signalstrength at any given instant of time.positive valence The valence of a positive ion.positron A positively charged particle having thesame mass as that of the electron, and the samemagnitude of electric charge, but positive (insteadof negative). Sometimes called positive electron.post See BINDING POST.post- Prefix meaning “following,” “subsequent to,”or “behind.”post-accelerating electrode In a cathode-raytube, the high-voltage electrode that producesPOST-DEFLECTION ACCELERATION of the electronbeam. Also called INTENSIFIER ELEC-TRODE.postacceleration See POST-DEFLECTION ACCEL-ERATION.post-alloy-diffused transistor Abbreviation,PADT. A transistor in which electrodes are diffusedinto the semiconductor wafer after otherelectrodes have been alloyed.post-conversion bandwidth The bandwidth of asignal after it has been converted from one frequencyto another.post-deflection accelerating electrode SeePOST-ACCELERATING ELECTRODE.post-deflection acceleration In a cathode-raytube, the intensification of the electron beamfollowing beam deflection. Also see POST-DEFLECTION CRT.post-deflection CRT An oscilloscope tube providedwith a high-voltage intensifier electrode inthe form of a ring encircling the inside flare of thetube, between the deflecting plates and thescreen. The deflected electron beam is acceleratedby this electrode. This arrangement allowsthe beam to be deflected at low velocity and highsensitivity, then to be accelerated for a brighterimage.post edit The editing of data in a computer output.postemphasis See DEEMPHASIS.post-equalization 1. In sound recording and reproduction,equalization during playback. ComparePREEQUALIZATION. 2. See DEEMPHASIS.postmortem An investigation into the cause offailure of a circuit, device, or system.postmortem dump At the end of a computer programrun, a dump to supply information for debuggingpurposes.post office box A type of wheatstone bridge thatcontains resistance coils in a special box. Thecoils are connected so that they can be replacedby shorting connectors.pot 1. See POTENTIOMETER. 2. See DASHPOT.3. Abbreviation of POTENTIAL. 4. To encapsulate acircuit in a potting compound, such as epoxy resin.potassium Symbol, K. A metallic element of the alkali-metalgroup. Atomic number, 19. Atomicweight, 39.098.potassium chloride Formula, KCl. A compoundused as a phosphor coating on the screen of anearly permanent-persistence cathode-ray tube.The fluorescence is magenta or white, as is thephosphorescence.potassium cyanide Formula, KCN. A highly toxicsalt that is an electrolyte in some forms of electroplating.potassium dihydrogen phosphate Abbreviation,KDP. An inorganic ferroelectric material.pot core A magnetic core for a coil, made of ferriteor of powdered iron, consisting of a central rod, asurrounding potlike enclosure, and a lid. The rodpasses through the center of the coil, and the potand lid completely enclose the coil. This arrangementprovides a completely closed magnetic circuitand coil shield.Slot for coilpot coreSlot forcoilClampingboltpotential See ELECTROMOTIVE FORCE.potential barrier The electric field produced oneach side of a semiconductor junction by minoritycarriers (i.e., by holes in the n-layer and electronsin the p-layer) that face each other acrossthe junction, but cannot diffuse across the junctionand recombine.potential coil The shunt coil in a conventionalwattmeter.potential difference See ELECTROMOTIVEFORCE and VOLTAGE.potential divider See VOLTAGE DIVIDER.potential drop 1. A voltage difference between twopoints in a circuit. 2. The voltage across a resistorin a direct-current circuit.potential energy Energy resulting from the positionof a body or particle (e.g., the energy stored

548 potential energy • power amplifierin something lifted against gravity and held in itsnew position) or from the position of charges (e.g.,the energy stored in a charged capacitor). CompareKINETIC ENERGY.potential gradient See VOLTAGE GRADIENT.potential profile A rectangular-coordinate displayof the VOLTAGE GRADIENT across a body (e.g.,the cross section of a transistor).potential transformer A small step-up transformerfor increasing the range of an alternatingcurrentvoltmeter.potentiometer 1. A variable resistor used as a voltagedivider. The input voltage is applied across theentire resistance element and the output voltageis taken from the wiper, relative to one end of theelement. One end is usually grounded (at zero potential).2. A null device whose operation is basedon a variable resistor, and is used for precise voltagemeasurements. The unknown voltage is appliedto the input of a variable resistor whosesettings are known with great accuracy; the resistanceis adjusted for an output voltage that exactlyequals the voltage of a standard cell (asindicated by a null between the two voltages). Theunknown voltage is then determined from the resistanceand the standard-cell voltage.potentiometer noise In a current-carrying potentiometer,electrical noise generated when thewiper blade rubs against the resistance element,or by contact between the blade and element.potentiometric recorder A type of graphicrecorder. It consists essentially of a resistancecalibratedpotentiometer, a standard cell, and agalvanometer. When an unknown voltage (E x ) isapplied to the input terminals of the potentiometerand the potentiometer is set for null, E x = E s(R 2 /R 1 ), where Es is the voltage of the standardcell, R1 is the input resistance of the potentiometer,and R2 is the output resistance of the potentiometer.Potier diagram An illustration of the phase relationshipbetween current and voltage in an alternating-currentcircuit that contains reactance.POTS Acronym for plain old telephone service,meaning basic service without optional features(such as call waiting, conference calling, call forwarding,etc.).potted circuit A circuit embedded in plastic orwax to protect it against the environment, and/orto minimize the effects of physical vibration (seePOTTING).potted component An electronic part embeddedin a suitable plastic or wax to protect it againstthe environment, and/or to minimize the effectsof physical vibration (see POTTING).potting A process of embedding a component orcircuit in a solid mass of plastic or wax held in acontainer. The process is similar to encapsulation,except that in potting, the container (envelope)remains as part of the assembly. CompareENCAPSULATION.potting material A substance, such as a resin orwax, used for potting electronic gear. Also calledpotting compound.pound 1. Abbreviations, lb, p. A unit of weightequal to 16 avoirdupois ounces. 2. Abbreviation,lbf. A unit of force approximately equal to 4.448newtons. 3. Abbreviation, lbm. A unit of mass approximatelyequal to 0.4536 kilogram.poundalA unit of force equal to approximately13825.5 dynes or 0.138255 newton. One poundalis the force that, when acting for one second, willimpart a speed of one foot per second to a onepoundmass.pound-footAbbreviation, lb-ft. A unit of torqueequal to the product of a force of one pound anda moment arm of one foot. Compare OUNCE-INCH.pounds per square inch absolute Abbreviation,psia. Absolute pressure (i.e., the sum of atmosphericpressure and the pressure indicated by agauge). Compare POUNDS PER SQUARE INCHGAUGE.pounds per square inch gauge Abbreviation,PSIG. The value of pressure indicated by a gauge,without correction for atmospheric pressure.Compare POUNDS PER SQUARE INCH ABSO-LUTE.powdered-iron core A magnetic core consisting ofminute particles of iron, each coated with a filmto insulate it from others, molded into a solidmass. Because of its low eddy-current loss, thistype of core is usable in radio-frequency transformersand coils, where it increases the inductanceof the winding.power1. Symbol, P. Unit, watt. The rate of doingwork, or producing or transmitting energy. Indirect-current circuits, and in alternating-currentcircuits containing no reactance, power is theproduct of the root-mean-square current andvoltage. See, for example, AC POWER, APPARENTPOWER, DC POWER, KILOVOLT-AMPERE,POWER FACTOR, REACTIVE KILOVOLT-AMPERE, REACTIVE VOLT-AMPERE, TRUEPOWER, VOLT-AMPERE, WATT, and WATTLESSPOWER. 2. The product obtained by multiplyinga quantity x by itself n times, written xn. For example,2 4 = 2 × 2 × 2 × 2 = 8; here, 8 is the fourthpower of 2. Compare ROOT, 1. 3. The exponent inan expression, as defined in 2.power amplification 1. The amplification of a signalhaving a certain power (wattage) to produce asignal having greater power. 2. The signal powerincrease, expressed as a ratio or as a figure indecibels, resulting from the process defined in 1.Also called POWER GAIN.power amplification ratio See POWER AMPLIFI-CATION, 2 and POWER GAIN.power amplifier An amplifier that delivers usefulamounts of power to a load, such as one or morespeakers. Compare CURRENT AMPLIFIER andVOLTAGE AMPLIFIER.

power-amplifier device • power grid 549Inputpower amplifierpower-amplifier device A high-current tube ortransistor designed especially for high poweroutput. Such a device does not always providesignificant voltage amplification, but always providespower amplification. Compare VOLTAGE-AMPLIFIER DEVICE.power at peak torque Symbol, Pp. For a torquemotor, the input power in watts needed for peaktorque at stall at a winding temperature of 25 degreesCelsius.power attenuation 1. A reduction of power level.2. See POWER LOSS.power bandwidth For a high-fidelity audio amplifier,the difference between the maximum andminimum frequencies at which the amplifier canproduce at least 50 percent of its maximumpower output, with less than a certain amount oftotal harmonic distortion (usually 10 percent).power blackout A situation in which all electricpower is lost to utility subscribers in a defined region.power consumption 1. For a direct-current device,the normal operating voltage multiplied bythe normal drawn current. 2. For an alternatingcurrentcircuit, the root-mean-square voltagemultiplied by the root-mean-square current.power control The adjustment of the output voltageof a power supply, usually by means of a variableautotransformer, silicon-controlled rectifier,thyratron, or similar device.power cutoff frequency Symbol, f co . The frequencyat which the power gain of a transistor drops 3 dBbelow its low-frequency value.power derating For a temperature higher than thespecified ambient temperature, a deliberate reductionof the power dissipated by a componentor device. This is done to prevent failure of thecomponent or device. Also see DERATING, DER-ATING CURVE, and DERATING FACTOR.power difference An expression of the power lostin a circuit when power is absorbed by a dielectricmaterial.power diode A heavy-duty diode that is usuallyused in power-supply service. Also called rectifierdiode.+Outputpower dissipation Abbreviation, PD. The powerconsumed by a device during normal operation.This power is not available in the electrical outputof the device. An example is the direct-currentpower dissipated in the collector circuit of a highfidelityaudio amplifier.power divider A circuit that distributes power, in apredetermined manner, among various loads.power drain The amount of power drawn by a device.It can be operating power or standby power.power dump See DUMP, 2.power equations Variations of the basic powerequation: P = EI = E 2 /R = I 2 R, where P is thepower in watts, E is the voltage in volts, I is thecurrent in amperes, and R is the resistance inohms.power factor Abbreviation, PF. In an alternatingcurrentcircuit, the ratio (expressed either as adecimal or a percentage) of true power (power actuallyconsumed) to apparent power (simpleproduct of voltage and current). The power factoris equal to the cosine of the phase angle. Also seeAC POWER.power-factor balance In a capacitance bridge, aseparate null adjustment for the internal resistancecomponent of a capacitor under measurement.The dial of the variable component for thisadjustment reads directly in percent power factorin some bridges.power-factor correction To raise the power factorof an inductive circuit by inserting a parallel capacitance.In power circuits, this affords improvedeconomy of operation because the currentdrain is brought more in line with that of a resistivecircuit.power-factor meter An instrument that gives directreadings of power factor (lead or lag). Onesuch meter uses a dynamometer-type movement(see ELECTRODYNAMOMETER) in which the rotatingelement consists of two coils fastened togetherat right angles.power-factor regulator A device that regulates thepower factor of an alternating-current line.power-factor relay An alternating-current relayactuated by a rise or fall in power factor, with respectto a predetermined value.power frequency 1. See POWER-LINE FRE-QUENCY. 2. The frequency of an alternatingcurrentgenerator. 3. The output frequency of apower inverter (see INVERTER, 1).power-frequency meter An instrument for measuringpower-line frequency. It can use electromechanicaldevices, or can directly count thenumber of alternations per second.power gain Abbreviations, PG or PG dB . The extentto which power is increased by a power amplifier.It can be expressed as the ratio of power output topower input as PG = P o /P i , or in decibels asPG dB = 10 log 10 (P o /P i ).power grid An aggregation of power-generatingstations, transmission lines, and associated

550 power grid • power surgeequipment, usually extending over hundreds ofmiles and embracing several communities, so operatedthat individual members can deliver powerto the system or draw power from it, according tolocal demand.power ground The power-supply ground for a circuitor system.power-handling capacity 1. The amount of powerthat a device can dissipate, either continuously orintermittently, without suffering damage. 2. Themaximum input power that can be tolerated by anamplifier transistor or tube without overheating.power hyperbola For a semiconductor device orvacuum tube, a curve plotted from the device’scurrent and voltage values, which provide thepower value when multiplied (e.g., a 2-watt curvefor the direct-current collector input of a powertransistor).power input See INPUT POWER.power-input control The adjustment of the outputof a power supply by varying the alternatingcurrentinput to the power transformer. Usually,a variable autotransformer is operated ahead ofthe power transformer. See, for example,VARIABLE TRANSFORMER and VARIAC.power inverter See CHOPPER POWER SUPPLY.power-level indicator 1. See DB METER. 2. SeeOUTPUT POWER METER.power line The line through which electrical energyis received by a subscriber.power-line communication Abbreviation, PLC.Carrier-current telephony or telegraphy overpower lines that are common to transmitting andreceiving stations. Also see WIRED WIRELESS.power-line filter 1. A heavy-duty radio-frequency(RF) filter inserted in the power line close to a devicethat generates RF energy, such as a radiotransmitter. It prevents transmission of RF energyvia the power line. 2. An RF filter inserted inthe power line, where it enters the power supplyof a sensitive electronic device, such as a computeror high-fidelity audio amplifier. It preventsRF energy on the power line from entering the devicevia the power supply.power-line frequency The frequency of the alternatingcurrent and voltage available over commercialpower lines. In the United States, it is60 Hz; in some countries, it is 50 Hz.power-line monitor An expanded-scale alternating-currentvoltmeter for the continuous monitoringof power-line voltage.power-line pickup The interception of radiofrequencyenergy by utility power lines acting asreceiving antennas. This energy can enter a sensitiveelectronic device, such as a computer or a highfidelityaudio amplifier, via the power supply.power loss The power dissipated in a component.It generates heat while doing no useful work.Represents energy loss, except when the generationof heat is the end purpose.power-loss factor Symbol, F p . In interstage coupling,the ratio of available power (with the couplingnetwork in place) to the available powerwhen the network is disconnected.power meter See WATTMETER.power modulation factor In amplitude modulation,the ratio of the peak power to the average power.power oscillator A heavy-duty oscillator deliveringuseful power output.power output See OUTPUT POWER.power-output meter See OUTPUT POWER ME-TER.power pack An external power-line-operated unitsupplying alternating or direct current for the operationof electronic equipment.power pentode A heavy-duty pentode vacuum tubedesigned to deliver relatively high output power.power plug A plug for insertion into a power-lineoutlet.power programmer A device that adjusts radaroutput power, in accordance with the target distance.power rating 1. The specified power required by anequipment for normal operation. 2. The specifiedpower output of a generator or amplifier.power reactive See REACTIVE VOLT-AMPERE.power rectifier A heavy-duty semiconductor diodeused to rectify alternating current for powersupplypurposes.power relay A heavy-duty relay designed to switchsignificant amounts of power. The heavy contactsand armature require high actuating current;this necessitates a larger coil than is used inlighter-duty relays.power resistor A heavy-duty resistor (i.e., one designedto carry large currents without overheating).power stack A selenium rectifier consisting of anumber of rectifier plates stacked in series forhigher voltage handling.power supply 1. A device, such as a generator or atransformer-rectifier-filter arrangement, that producesthe power needed to operate an electronicequipment. 2. A reserve of available power (e.g.,the power line, an installation of batteries, etc.).power-supply filter A low-pass filter that is usedto remove the ripple from the output of a powersupplyrectifier. See, for example, BRUTE-FORCEFILTER.power-supply rejection ratio The ratio of the output-voltagechange for an amplifier, oscillator, orother circuit, to the change in power-supply voltage.It is determined on an instantaneous basis.power-supply sensitivity In an operational amplifier,sensitivity of the offset to variations in thepower-supply voltage.power surge 1. A momentary increase in the voltageon a utility line. 2. An abnormally high voltagethat sometimes exists for the first severalmilliseconds after utility power is restored followinga blackout.

power switch • preamplifier 551+Fromrectifier−Filterchokespower-supply filterpower switch The switch for controlling power to apiece of equipment. Also see ON-OFF SWITCH.power switching Switching operating power onand off. There are two principal methods: One involvesmaking and breaking the connections betweenequipment and the power line; the otherinvolves making and breaking the output of aline-operated or battery-type power supply.power tetrode A heavy-duty tetrode vacuumtube designed to deliver relatively high outputpower.power-to-decibel conversion Abbreviation, P dB .Power expressed in decibels, with respect to a referencepower level. Determined by the formulaP dB = 10 log 10 (P x /P ref ), where P x is the given powerlevel and P ref is the reference power level.power transfer 1. The passage of power from agenerator to a load. 2. The passage of power fromone circuit to another.power transfer theorem See MAXIMUM POWERTRANSFER THEOREM.power transformer A transformer designed solelyto supply operating power to electronic equipment—eitherdirectly or through a rectifier-filtercircuit. Because a power transformer is used atlow (power-line) frequencies, its core does not requirethe high-grade iron used in audio transformers,nor are special winding techniquesneeded to reduce the leakage inductance and interwindingcapacitance.power transistor A heavy-duty transistor designedfor power-amplifier and power-control service.power triode A heavy-duty triode vacuum tube designedto deliver relatively high output power.power tube A heavy-duty electron tube designed todeliver useful amounts of power. See, for example,POWER PENTODE, POWER TETRODE, andPOWER TRIODE.power unit 1. A power supply (see POWER SUP-PLY, 1). 2. A unit of power measurement. See,for example, KILOWATT, MEGAWATT, MICRO-WATT, MILLIWATT, PICOWATT, and WATT.+Filtereddc−power user In personal or business computing, aserious user who has extensive, up-to-dateknowledge of hardware and software.power winding In a magnetic amplifier or saturablereactor, the output winding (i.e., the windingthrough which the controlled current flows).Poynting vector In an electromagnetic wave, thevector product of instantaneous electric intensityand magnetic intensity.PP Abbreviation of peripheral processor.PP 1. Symbol for PLATE POWER. 2. Symbol forPEAK POWER.ppb Abbreviation of parts per billion.PPI Abbreviation of PLAN POSITION INDICATOR.pp junction In a semiconductor wafer, the boundarybetween two p-type regions that have somewhatdifferent properties.PPM Abbreviation of PULSE-POSITION MODULA-TION.ppm 1. Abbreviation of parts per million. 2. Abbreviationof pulses per minute.pps Abbreviation of pulses per second.ppt Abbreviation of parts per thousand.PPV Abbreviation of PAY PER VIEW.Pr Symbol for PRASEODYMIUM.practical component A circuit component consideredin proper combination with the stray componentsinherent in it. Thus, a resistor has residualinductance and capacitance, an inductor hasresidual capacitance and resistance. CompareIDEAL COMPONENT.practical units A set of physical/electrical unitsespecially suited to a particular application. Forexample, in direct-current electrical applications,practical units are the AMPERE, OHM, VOLT,and WATT.praetersonics See ACOUSTOELECTRONICS;ACOUSTIC DELAY LINE; SURFACE-WAVE AM-PLIFIER; SURFACE-WAVE FILTER.pragilbert The unit of MAGNETOMOTIVE FORCEin the absolute mks (Giorgi) system.pragilbert per weber The unit of RELUCTANCE inthe absolute mks (Giorgi) system.praoersted The unit of MAGNETIZING FORCE inthe absolute mks (Giorgi) system.praseodymium Symbol, Pr. A metallic element ofthe rare-earth group. Atomic number, 59. Atomicweight, 140.908.preaccelerating electrode In the electron gun of acathode-ray tube, the high-voltage electrode thatprovides initial acceleration to the electron beam.pre-alarm signal An audio and/or visual indicatorthat an alarm will sound if an area is not clearedwithin a short time. An example is a voice recordingin a car alarm system (e.g., “Stand back!”).preamplifier 1. A high-sensitivity, low-noise amplifierthat usually uses a high-gain field-effecttransistor (FET) and is used to enhance thesensitivity of a radio communications receiver.They are especially used at frequencies above

552 preamplifier • preset counterpreamplifierapproximately 15 MHz, where most of the noisecomes from the receiver, rather than from outsidesources. 2. A low-noise amplifier used for boostingweak signals for television reception. 3. A lownoise,low-level amplifier used for boosting signallevels from transducers, such as microphones orphotocells.prebiased relay A relay through which is maintaineda steady current that is just lower thanthat needed to close the relay. The actuating signal,then, need only be a small amount of additionalcurrent.precedence effect See FUSION, 1.precipitation 1. Water falling from the atmospherein some form (rain, snow, hail, or sleet). See PRE-CIPITATION STATIC. 2. The amount of precipitationoccurring in a given period of time at aspecific location. 3. Separation of a solid materialfrom a solution, as a result of a chemical or physicalaction.precipitation static 1. Radio noise that sometimesoccurs when it rains or snows. It can bemistaken for artificially generated noise. 2. Radionoise caused by atmospheric electricity arisingfrom rain, snow, ice crystals, hail, or dust clouds,through which an aircraft carrying the radio flies.precipitator See DUST PRECIPITATOR.precipitron See DUST PRECIPITATOR.precision 1. Pertaining to electronic hardware, especiallytest instruments and measuring devices,designed and built to function with a high degreeof accuracy. 2. The relative accuracy of a meter orother indicating device. 3. The accuracy of the resultsof an experiment, test, or measurement.precision approach radar A radar aimed along theapproach path to guide an aircraft during approach.precision instrument An instrument possessinghigh accuracy and stability (i.e., one capable ofreproducing readings or settings for various trialsunder set circumstances).precision potentiometer 1. A POTENTIOMETERpossessing highly accurate resistance calibration,linearity, and repeatability of settings. 2. Apotentiometer-type voltage-measuring instrument.+Outputpreconduction current 1. The cutoff current in atransistor. 2. In a thyratron, the small (anode)current flowing before the tube is fired.predetermined counter A counter programmed tocount to a desired number and stop.predistortion See PREEMPHASIS.pre-Dolby 1. To record a tape with DOLBY compression.2. A tape that has been recorded withDolby compression.preemphasis In frequency modulation, the introductionof a rising-response characteristic (responserises as modulation frequency increases).Compare DEEMPHASIS.preequalization 1. In sound recording and reproduction,equalization during recording. 2. SeePREEMPHASIS.preferred values of components A number systemused by the Electronics Industries Association(EIA) for establishing the values ofcomposition resistors and small fixed capacitors.prefix multiplier See MULTIPLIER PREFIX.prefix notation As used with complex expressionsinvolving many operators and operands, a type ofnotation in which the expressions, rather thancontaining brackets, are given a value, accordingto the relative positions of operators andoperands.preform1. A small wafer, usually dry-pressedfrom powdered plastic, from which the body of acomponent, such as a capacitor or resistor, isheat-molded. Also called a pill or biscuit. 2. Thepreformed slab used in molding a phonographdisc. 3. To shape a moldable circuit before fixingthe final configuration or package.preliminary information For manufactured electroniccomponents, data that is released prior tothe actual availability of the device. Subject tochange when units are produced.premix A molding compound of reinforced plastic.prerecorded disc A phonograph disc on which arecording has been made (i.e., a recorded disc).prerecorded tape Magnetic tape on which a programor data has been recorded. Also calledRECORDED TAPE.p region See P LAYER.prescaler A device operated ahead of a counter toestablish a new, usually higher-frequency, rangeover which frequency measurements can bemade.preselector A tuned or untuned radio-frequencyamplifier operated ahead of a radio or televisionreceiver to boost the sensitivity of the receiver.presence 1. In sound reproduction, the quality ofbeing true to life. 2. The effect of boosted uppermidrangefrequencies in music.preset counter A pulse counter that delivers oneoutput pulse for a number of successive inputpulses, determined by the settings of countercircuitcontrols. Thus, a preset counter mightgive an output pulse for each train of 125 inputpulses.

preset element • primary coil 553preset element In automation and control, an elementthat can be preset to a given level or value,and to which other elements can then be referred.preset switch In the circuit of a PRESET COUN-TER, a multiposition rotary switch that can be setto determine the number of input pulses thatmust be received for the circuit to deliver oneoutput pulse.preshoot A downward-moving transient pip thatsometimes precedes the rise of a pulse.Relative amplitude−PreshootpreshootTimepreshoot amplitude The peak voltage of a PRE-SHOOT, measured from the zero line to the valleyof the preshoot.preshoot time The width of a PRESHOOT, measuredalong the horizontal base line (time axis).pressing 1. A process by which phonographicdiscs are fabricated from plastic. 2. A discpressed from plastic.press-to-talk microphone A microphone thatuses a PRESS-TO-TALK SWITCH for actuation.press-to-talk switch A switch in a microphone oron the end of a control cord. It is used to actuatea transmitter, telephone, or recorder when theoperator wishes to speak.pressureAbbreviation, P or p. 1. Force per unitarea. It can be expressed in any appropriate unitsof force and area (e.g., newtons per square meter,pounds per square inch, grams per square centimeter,etc.). 2. The application of force over partor all of a surface. 3. Compression. 4. See TEN-SION, 1.pressure amplitude The pressure caused by anacoustic disturbance. It is usually measured indynes per square centimeter.pressure capacitor An enclosed fixed or variablecapacitor, whose breakdown voltage increaseswhen the air pressure rises inside the container.pressure contact 1. Electrical contact made bypressing two conducting surfaces together (tocomplete a circuit). 2. A contact for obtaining thecondition described in 1.pressure-gradient microphone See PRESSUREMICROPHONE.pressure microphone A microphone that receivessound waves at only one side of its diaphragm.This one-sided exposure results in the displacementof the diaphragm by an amount proportionalto the instantaneous pressure of the sound waves.pressure pad In a tape recorder, a small pad thatholds the tape against one of the heads.pressure pickup See PRESSURE TRANSDUCER.pressure roller In a tape recorder, a rubber-tiredroller that presses the tape against the capstan.pressure sensor A device that detects the presenceof, and/or measures, physical force within a specificarea. One simple device uses two metalplates separated by electrically resistive foam.Pressure compresses the foam and reduces theresistance between the plates. This resistancechange can be detected and measured.pressure switch A switch that is opened or closedby a change in pressure within a system.pressure transducer A sensor for converting pressureinto proportionate current or voltage. Someuse strain gauges; others use piezoelectric crystals,potentiometers, and other variable elements.pressure zone A region of high air pressure that isimmediately adjacent to a surface reflecting anacoustic (sound) wave.pressure-zone microphone A microphone equippedwith a deflector that helps to guide acousticenergy toward the diaphragm.prestore To place data in memory before it is intendedfor use.pretuned stage A stage, such as one in an intermediate-frequencyamplifier or single-frequencyreceiver, that is preset to a frequency, rather thanbeing continuously tuned.prf Abbreviation of PULSE REPETITION FRE-QUENCY.pri Abbreviation of PRIMARY.primaries See PRIMARY COLORS.primary 1. See PRIMARY WINDING. 2. See PRI-MARY STANDARD.primary battery A battery composed of primarycells.primary block A fundamental group of channels inpulse-code modulation, combined by means oftime-division multiplexing.primary capacitance 1. The distributed capacitanceof the primary winding of a transformerwhose secondary winding is unloaded. CompareSECONDARY CAPACITANCE, 1. 2. A series orshunt capacitance used to tune the primary coilof a radio-frequency transformer. Compare SEC-ONDARY CAPACITANCE, 2.primary cell An electrochemical cell that does notrequire, and generally will not accept, an electricalcharge in order to function. Once it has beendischarged, the cell must usually be thrownaway. Compare STORAGE CELL. Also see CELL,DRY CELL, and STANDARD CELL.primary circuit 1. The circuit associated with theprimary winding of a transformer. 2. The circuitryassociated with the input to a device or system.primary coil See PRIMARY WINDING.

554 primary colors • printprimary colors See COLOR PRIMARY.primary current The current flowing in the primarywinding of a transformer. Also calledTRANSFORMER INPUT CURRENT. CompareSECONDARY CURRENT.primary electron The electron possessing thegreater energy after a collision between two electrons.Compare SECONDARY ELECTRON.primary emission Emission arising directly from asource, such as the cathode of an electron tube.Compare SECONDARY EMISSION.primary frequency standard A device that generatesunmodulated signals at precise frequencies.It generally uses a highly stable crystal oscillatorthat can be referred to a time standard and periodicallycorrected. A string of multivibrators, togetherwith harmonic amplifiers and buffers,divide, and multiply the fundamental crystal frequency.The resulting signals provide markers forcalibrating receivers and test equipment. CompareSECONDARY FREQUENCY STANDARD.Also see PRIMARY STANDARD.primary impedance 1. The impedance of the primarywinding of a transformer whose secondarywinding is unloaded. Compare SECONDARYIMPEDANCE, 1. 2. An external impedance presentedto the primary winding of a transformer.Compare SECONDARY IMPEDANCE, 2.primary inductance The inductance of the primarywinding of a transformer whose secondarywinding is unloaded. Compare SECONDARY IN-DUCTANCE.primary kVA The kilovolt-amperes in the primarycircuit of a transformer. Compare SECONDARYKVA.primary measuring element A detector, sensor,or transducer that performs the initial conversionin a measurement or control system. Such an elementconverts a phenomenon into a signal thatcan be transmitted to appropriate instrumentsfor translation and evaluation.primary power Power in the primary circuit of atransformer. Also see PRIMARY KVA and PRI-MARY VA. Compare SECONDARY POWER.primary radiator 1. The driven element of a directiveantenna system that incorporates parasiticelements. 2. The driven element of a directive antennathat uses a reflector, such as a screen ordish.primary resistance The direct-current resistanceof the primary winding of a transformer. CompareSECONDARY RESISTANCE.primary standard A usually stationary source of aquantity (e.g., capacitance, frequency, time, inductance,resistance, etc.). This source is so precise,and is maintained with such care, that itcan be used as a universal reference. CompareSECONDARY STANDARD.primary turns Symbol, N p . The number of turns inthe primary winding of a transformer. CompareSECONDARY TURNS.primary utilization factor Abbreviation, UF p . Fora transformer in a rectifier circuit, the ratio ofdirect-current power output to primary voltamperes.Numerically, the primary utilizationfactor is higher than the secondary utilizationfactor, but is less than 1. Also see SECONDARYUTILIZATION FACTOR and UTILITY FACTOR.primary VA The volt-amperes in the input circuitof a transformer. Compare SECONDARY VA.primary voltage The voltage across the primarywinding of a transformer. Also called transformerinput voltage. Compare SECONDARY VOLTAGE.primary winding The normal or usual input windingof a transformer. Also called primary coil.Compare SECONDARY WINDING.prime meridian See ZERO MERIDIAN.prime mover A machine, such as a gas engine,steam engine, or water turbine, that converts anatural force or material into mechanical power.primitive oscillation period In a complex oscillationwaveform, the shortest period for which adefinite repetition occurs; the highest fundamentalfrequency.principal axis The line passing through the centerof the spherical part of a lens, mirror, or dish reflector.principal focus The focal point of rays arrivingparallel to the principal axis of a lens, mirror, ordish reflector.Principal focusprincipal focusPrincipal axisprincipal mode See DOMINANT MODE.principal ray The path described by an electron enteringan electron lens parallel to the lens’ axis, orby an electron leaving this lens parallel to the axis.print 1. The material transferred from a typewriteronto paper. 2. The command, in a computer sys-

print • private branch exchange 555tem, that causes data to be placed on paper oronto the output screen. 3. The alphanumeric outputof a computer or data terminal.printed capacitor A two-plate capacitor formed ona printed circuit.printed circuit A pattern of conductors (correspondingto the wiring of an electronic circuit)formed on a board of insulating material, such asa phenolic, by photo-etching, silk-screening ofmetallic paint, or by the use of pressure-sensitivepreforms. The leads or pins of discrete componentsare soldered to the printed metal lines atthe proper places in the circuit, or the componentscan be formed along with the conductors.Also see ETCHED CIRCUIT.printed-circuit board A usually copper-clad plasticboard used to make a printed circuit.printed-circuit lamp A baseless lamp having flexibleleads for easy soldering or welding to aprinted circuit.printed-circuit relay A usually small relay providedwith pins or lugs for easy solder connectionto a printed circuit.printed-circuit switch A rotary switch whose contactsand contact leads are printed on a substrate.printed-circuit template Also called etching pattern.A drawing for the purpose of makingprinted-circuit boards by photographic means.printed coil A flat, spiral coil formed on a printedcircuit.printed-circuit templateprinted component A component formed on thesubstrate of a printed circuit. See, for example,PRINTED CAPACITOR, PRINTED COIL, andPRINTED RESISTOR.printed display See DATA PRINTOUT, 2.printed element See PRINTED COMPONENT.printed inductor See PRINTED COIL.printed resistor A resistor printed or painted on aprinted circuit.printed wiring The printed or etched metal linesthat serve as the conductors in a printed circuit.printer In computer and calculator operations andin measurement procedures, a readout devicethat prints a permanent record of output data.There are several types, including the dot-matrixprinter, the daisy-wheel printer, the inkjet printer,and the laser printer. Some printers, such as thedaisy-wheel type, can render only text data;others, such as the laser type, can print highresolutiongraphic images, sometimes in color.printing calculator 1. An electronic calculatorthat supplies a printed record of the results of acalculation. 2. For a programmable calculator,the results, a record of program steps, and plotsof curves.printing digital voltmeter Abbreviation, PDVM. Adigital voltmeter that delivers a printed record ofa voltage reading, in addition to the usual digitalreadout of the voltage.printing telegraph 1. A telegraph that prints thereceived message on a tape or page. 2. See TELE-TYPEWRITER.printing wheel See PRINT WHEEL.print format The form of data transmitted by acomputer program to a printer (e.g., plain text,graphics, color graphics, etc.).printout See DATA PRINTOUT, 1, 2.print-through In prerecorded magnetic tape on areel or cassette, the transfer of magnetism betweenlayers of the rolled-up tape.print wheel In a daisy-wheel printer, the rotatablewheel on whose rim the letters, numbers, andother symbols are inscribed in relief.priority indicator In data transmission, a codethat specifies the order of importance of a messagein a group of messages to be sent.priority processing In multiple programming operations,a system for ascertaining the order ofprocessing for different programs.privacy code 1. A subaudible tone used in cordlesstelephone systems to reduce the chances ofinterference between phones operating on thesame channel in close proximity. 2. A subaudibletone used in radio transmissions, especially inconjunction with repeaters, to allow only thosestations with the proper code to be received. 3. Atone-burst sequence at the beginning of a transmissionthat actuates a receiver, allowing onlythose stations with the proper code to be received.privacy equipment Devices, such as speechscramblers and digital encryption programs, thatprovide some measure of secrecy in communications.privacy switch In a telephone amplifier, a switch(usually a pushbutton) for muting outgoing messages.private automatic exchange Abbreviation, PAX. Adial telephone system for use within an organizationand having no connection to the central office.Compare PRIVATE BRANCH EXCHANGE.private branch exchange Abbreviation, PBX. Atelephone system, complete with a private manuallyoperated switchboard and individual telephonesets, installed and operated on private

556 private branch exchange • programpremises but having trunk-line connection to thecentral office. Compare PRIVATE AUTOMATICEXCHANGE.private line 1. A communication circuit in whichthe use is limited, by electronic means, to certainsubscribers. 2. A subaudible-tone system used torestrict access to a communications system. Thetone frequency is predetermined. For access tothe system, a transmitted signal must containthe tone of the appropriate subaudible frequency,in addition to the voice or other information.probability 1. The branch of mathematics concernedwith the likelihood of an event’s occurrence.It has many applications in quality controland physics. 2. The mathematical likelihood thatan event will occur.probable error Abbreviation, PE. The value of errorabove and below which all other error values areequally likely to occur.probe 1. A usually slender pencil-like implementwith a pointed metal tip and a flexible, insulatedlead. It is used to contact live points in a circuitunder test (e.g., voltmeter probe and oscilloscopeprobe). 2. A device used to sample a radiofrequencyvoltage or current at a desired point(e.g., WAVEGUIDE PROBE). 3. A pickup deviceshaped like a probe for insertion into closequarters (e.g., PROBE THERMISTOR).probe meter See PROBE-TYPE VOLTMETER.probe thermistor A thermistor of slender constructionfor insertion into an area in which thetemperature is to be monitored or controlled.probe thermocouple A thermocouple in the formof a slender probe for insertion into close quartersfor temperature sensing or temperature control.probe tip See PROD.probe-type voltmeter A voltmeter installed in along probe or wand. Kilovoltmeters are sometimesconstructed in this fashion, with a longmultiplier resistor housed in the probe.probing A process for locating, or determining theexistence of, external artificial interference (e.g.,power-line noise) in a radio communications circuit.problem-oriented language Any high-level computerprogramming language that allows the userto write programs as statements in terms applicableto the field of interest (e.g., COBOL’s statementsin English for problems relating tobusiness).problem reduction In artificial intelligence, a processin which problems are made easier by breakingthem down into smaller logical parts.process control The control of a process, such asone of manufacturing, by means of computers.processor 1. A circuit or device used to modifya signal in response to certain requirements(e.g., clipper and waveshaper). 2. See DATA-PROCESSING MACHINE. 3. See CENTRAL PRO-CESSING UNIT. 4. See MICROPROCESSOR.prod The metal tip of a probe (see PROBE, 1).product 1. The result of mixing or heterodyning oftwo or more signals. 2. The result of modulatingone signal with another. 3. The result of combiningor processing a signal or signals in a specifiedmanner. 4. The saleable end result of a manufacturingprocess. 5. The result obtained when twoor more quantities are multiplied by each other.product detector A detector circuit whose outputis the product of two signals applied simultaneouslyto the circuit. In a single-sideband receiver,for example, one of the signals is the incomingsignal; the other, the signal from the local beatfrequencyoscillator.IFLocal osc.+12 Vproduct detectorOutproduction lot A manufactured set of components,circuits, or systems, intended for sale. Allof the units in the lot are identical. The finishedproduct is suitable (presumably) for consumeruse.production unit One unit in a production lot; afinished unit, ready for use by a consumer.product modulator A modulator whose output isequal or proportional to the product of carriervoltage and modulating voltage.product of sine waves The result of multiplyingone sine wave by another with attention beingpaid to the power factor. In the case of a resistivecircuit, where the power factor is equal to 1, allvoltage-current (EI) products are positive, and areequal to the true power. A product wave has negativehalf-cycles when the circuit contains reactance.professional engineer A person licensed by a stateboard of examiners to work independently as anengineering. Also see PE and REGISTERED PRO-FESSIONAL ENGINEER.program 1. In computer operations, a detailed sequenceof instructions representing an algorithm

program • promethium cell 557(the necessary steps in solving a problem) thatcan be implemented by a computer. 2. The contentof a radio or television broadcast during aspecified period of time. 3. In audio recording, thecomposite output from the mixer, used to makethe master tape or disc.program address counter See INSTRUCTIONREGISTER.program amplifier A broadcast preamplifier usedat the studio or a remote location.programatics The study of computer programming.program circuit In wire telephony, a circuit capableof handling music and other audio data thatcovers a wide band of frequencies.program compatibility The condition in which aprogram written for one computer can be usedwith another computer having a different architecture.program controller In a central processor, a unitthat controls the sequence and execution of programinstructions.program counter See CONTROL REGISTER.program file A flexible reference system for softwarelibrary maintenance.program flowchart A representation of a computerprogram in the form of a flowchart. Each functionand transition point is indicated by a box in thechart. A user can follow the flowchart and determinethe outcome of the program for any givenset of input parameters.program library A collection of computer or programmable-calculatorprograms. Usually, itmeans the collection of programs used in a givencomputer system, often a software package suppliedby the hardware vendor. It might also be acatalog of programs with instructions for their use.programmable calculator A calculator that can beprogrammed to perform a chain of operations in agiven order repetitively.programmable read-only memory In a computer,a read-only memory (ROM) that can store a program.program maintenance The ongoing correcting,updating, and modification of computer programsbelonging to a system.programmed dump A dump that occurs during aprogram run, according to a program instruction.programmed halt During a computer programrun, a temporary cessation resulting from an interruptor halt instruction.programmed instruction See MACRO INSTRUC-TION.programmed timer See CYCLE TIMER.programmer A person who writes computer programs.program modification 1. In computer programmingoperations, a change in the effect of instructionsand addresses during a program run byperforming arithmetic and logical operations onthem. 2. Rewriting, or adding a patch to, a computerprogram. Also see PATCH, 3.program register See CONTROL REGISTER.program segment A unit within a computer programthat is stored with others in memory at thetime of the program’s execution, or sometimes, asoverlays loaded individually when the entire programexceeds memory capacity.program specification A description of the stepsinvolved in the solution of a problem, from whicha programmer devises a computer program.program step An instruction in a computer program.program tape In computer operations, a magneticor paper tape that contains programs for a systemor application.program timer 1. A programmed timer (see CY-CLE TIMER). 2. A timing unit that controls theduration of a program.progressive scanning Non-interlaced televisionraster scanning, in which the lines are tracedfrom top to bottom in succession. Conventionaltelevision broadcasting uses INTERLACEDSCANNING.progressive wave A wave disturbance that travelsthrough a theoretically perfect homogeneousmedium. This can be a compression (longitudinal)wave, a transverse wave, or an electromagneticwave.projected cutoff For an amplifier circuit, the operatingpoint at which crossover distortion vanishes.The direct-current bias voltage (grid orgate) required for projected cutoff is somewhatlower than the value corresponding to conventionalcutoff of plate or drain current.project engineering A field of engineering dealingwith the coordination of a complete project.projection television Large-screen television forviewing by a relatively large group, usually accomplishedvia a projection tube and optical system.projection tube A cathode-ray tube, especially atelevision picture tube, capable of producing abright image that can be projected onto a largescreen by means of a lens system.projector 1. A device that transmits a visible imageonto a surface for reproduction. 2. In general, anydevice that transmits a signal into space.PROLOG Acronym for programming in logic. Ahigh-level computer programming language, similarto LISP, used in artificial intelligence. The operatorinputs facts and rules; the computer, ineffect, derives theorems from the facts by followingthe logical rules.PROM Abbreviation of PROGRAMMABLE READ-ONLY MEMORY.promethium Symbol, Pm. A metallic element ofthe rare-earth group, produced artificially.Atomic number, 61. Atomic weight, approximately145. Formerly called illinium.promethium cell A radioactive battery cell usingan isotope of promethium. Radioactive particlesfrom this substance strike a phosphor, causing it

558 promethium cell • protective gapto glow. Self-generating photocells then convertthis light into electricity.PROM programmer An electronic device that canstore a computer program in a PROGRAM-MABLE READ-ONLY MEMORY (PROM). It uses abuilt-in keyboard.prompt In computer operations, a message receivedby an operator from an operating systemor an individual program. For example, in diskoperating system (DOS), it could be the statement“Bad command or file name.”prompting In computer or programmed-calculatoroperations, the entry of a special, required variablewhen the machine halts and awaits such entry.prong See PIN.prony brake An arrangement for measuring themechanical power output of a rotating machine.It is a special form of friction brake consisting ofa band passed around a pulley on the rotatingshaft of the machine under test and held at eachend by a spring balance.propagation 1. The extension of energy into andthrough space. Thus, radiant energy is propagatedfrom and by its source. 2. A phenomenonresulting from the extension of energy into andthrough space. Thus, radio waves can be spokenof as a propagation.propagation constant For waves transmittedalong a line, a number showing the effect the linehas on the wave. This is a complex figure [i.e., onecontaining a real-number component (the attenuationconstant) and an imaginary-number component(the phase constant)].propagation delay 1. Symbol, t pd . In an integrated-circuitlogic gate, the time taken for a logicsignal to be propagated across the gate. 2. In digital-circuitoperation, the time required for alogic-level change to be transmitted through oneor more elements.propagation delay-power product See DELAY-POWER PRODUCT.propagation factor The ratio E/E o , where E is thecomplex electric-field strength at a point to whicha wave has been propagated, and E o is the complexelectric-field strength at the point of origin.Also called propagation ratio.propagation loss The path loss of an electromagneticdisturbance between the transmitting andreceiving antennas.propagation mode See WAVEGUIDE MODE.propagation ratio See PROPAGATION FACTOR.propagation time In digital-circuit operation, thetime required for a binary bit to be transferredfrom one point to another in the system.propagation velocity See VELOCITY OF PROPA-GATION.proportional action An action, such as amplificationor conversion, that produces an outputsignal proportional to the input signal.proportional amplifier An amplifier in which theinstantaneous output amplitude is proportionalto the instantaneous input amplitude.proportional control A voltage-regulation systemin which the feedback correction voltage is proportionalto the output-voltage error.proportional counter A Geiger tube having apointed-wire (or ball-tipped-wire) anode. The voltagedeveloped across the load resistor is proportionalto the number of ions created by theradioactive particles entering the tube.proprioceptor A set of transducers and associatedcircuitry that allows a computerized robot to constantlysense the positions of its end effectors, anduse this data in carrying out programmed tasks.prosodic features Variations in voice tone and emphasisthat lend meaning and implication tospoken statements. It is important in advancedcomputer speech recognition and speech synthesissystems. Two sentences with identical wordingcan have greatly different meanings, depending onthese factors (e.g., “You are!” versus “You are?”).prosthesis An electromechanical artificial humanlimb or body part. Examples: artificial legs, artificialhands, and artificial respirators. Some suchdevices are computer-controlled; others can bemanipulated by nerve impulses.protactinium Symbol, Pa. A relatively short-livedradioactive metallic element. Atomic number, 91.Atomic weight, 231.04 Formerly called protoactinium.protected area A region to which access is restricted,and that is secured by an alarm system,surveillance cameras, or other intrusion-preventionsystems.protected location In computer storage, a locationwhose contents are protected from mutilationor erasure by making the location usableonly by following a special procedure (e.g., usinga password).protection In a multiple processing computer system,preventing interference between data or programs.protective bias In the final power amplifier of a radiotransmitter, external direct-current bias appliedto the base, gate, or grid. Prevents runawayin collector, drain, or plate current when the biascaused by the driving signal is lost.protective capacitor A power-line bypass capacitor.protective device 1. A component that breaks acircuit in the event of excessive voltage or currentfrom the power supply. 2. A device that preventsexcessive power from being delivered to a load bya driving circuit.protective gap 1. A spark gap connected in parallelwith a component, or between a line andground as protection against high-voltage transientsand surges. 2. A spark-gap-type lightningarrester.

protective resistor • pseudo-instruction 559ToantennaProtectivegapsTwo-wirefeed lineprotective gapTuningnetworkprotective resistor 1. A bleeder resistor connectedin parallel with a filter capacitor in a high-voltagedirect-current power supply to discharge the capacitorautomatically, thus preventing electricshock. 2. A series resistor that limits the currentgoing through a device.+Protectiveresistorprotective resistor, 2.protector 1. A fast-acting power-disconnect device,such as a circuit breaker or fuse, that acts toprotect electronic equipment. 2. A device or connection,such as a safety ground or ground-faultinterrupter, that protects an operator from electricshock. 3. See CONTACT PROTECTOR.protium The light isotope of hydrogen, having anatomic mass of 1.protoactinium See PROTACTINIUM.protocol 1. A set of parameters for a digital communicationssignal. 2. The method by which aprocedure is followed; a uniform set of governingregulations. It ensures proper operation of a systemor network.+proton A positively charged particle in the nucleusof an atom. The mass of a proton is approximately1840 times the mass of an electron.proton rest mass See MASS OF PROTON ATREST.proton-synchrotron A synchrotron that uses frequencymodulation of the radio-frequency acceleratingvoltage. It can accelerate protons toenergies of several billion electronvolts.prototype The preliminary design or model of a deviceor system. It is often modified numeroustimes before the final design is attained. ComparePILOT MODEL.proustite Crystalline silver arsenide trisulfide. Artificialcrystals of this compound are used in tunableinfrared-ray instruments.proximity alarm A capacitance relay used to actuatean alerting-signal device when an area is intrudedupon or a person is too close to aprotected object. Also called INTRUSION ALARM.proximity detector See PROXIMITY SENSOR.proximity effect 1. The influence of highfrequencycurrent flowing in one conductor onthe distribution of current flowing in an adjacentconductor. 2. In an audio system, the result ofplacing a microphone too close to a person’smouth. Under these conditions, some spokenconsonants (e.g., B, F, P, and T) produce clappingor booming sounds.proximity fuse An electronic device situated in thenose of a missile. When the missile is near thetarget, the fuse transmits a signal that is reflectedback from the target; this reflected signal detonatesthe missile.proximity relay See CAPACITANCE RELAY.proximity sensing The ability of a machine, especiallya robot, to detect when an object is near.This is an aid in robot navigation because it preventscollisions. Some devices can measure thedistance from a robot, or from a robotic end effector,to a nearby object.proximity sensor A device that indicates the presenceof a nearby body. Such a device uses someform of circuit, such as that of a CAPACITANCERELAY, that changes its operating characteristicswhen an object enters its field.proximity switch See CAPACITANCE RELAY.PRR Abbreviation of PULSE REPETITION RATE.PRV Abbreviation of PEAK REVERSE VOLTAGE.PS Abbreviation of POWER SUPPLY.ps Abbreviation of PICOSECOND. (Also, psec.)PSD Abbreviation of PHASE-SENSITIVE DETEC-TOR.psec Abbreviation of PICOSECOND. (Also, ps.)pseudocode In a computer system, an instructionor code symbol that affects the operation of theprogramming in an indirect manner.pseudo-instruction In computer programming operations,data representing an instruction and requiringtranslation by a compiler or assembler.

560 pseudo-offlining • pullingpseudo-offlining During input/output operationsin a computer system, maximizing hardware bydisconnecting slow devices from the process inquestion.pseudo-operation In computer operations, an operationthat, rather than being performed byhardware, is carried out by special software or bymacroinstruction.pseudo-random numbers Numbers that, althoughproduced by a computer operating on an algorithmfor their generation, are useful for an applicationrequiring random numbers.pseudo-stereophonic effect A somewhat heightenedbinaural effect obtained when two loudspeakersare situated, relative to the listener, sothat a transit-time difference of 1 to 30 millisecondsresults.ShortpathLevelequalizerListenerHi-fiAmp.OutLongpathpseudo-stereophonic effectpsf Abbreviation of pounds per square foot. (Also, lbper sq ft, lb/ft 2 .)psi 1. Abbreviation of pounds per square inch.(Also, lb per sq in, lb/in 2 .)psia Abbreviation of POUNDS PER SQUARE INCHABSOLUTE.psig Abbreviation of POUNDS PER SQUARE INCHGAUGE.psi particle A massive elementary particle thatrepresents a resonance in an electron-positroninteraction.PSK Abbreviation of PHASE-SHIFT KEYING.PSM Abbreviation of pulse-spacing modulation,more commonly called PULSE-INTERVAL MODU-LATION.psophometer A device used to measure noise in awire communications system. It provides quantitativereadings based on typical human observations.psvm Abbreviation of phase-sensitive voltmeter.PSWR Abbreviation of power standing-wave ratio.psychoacoustics A field of acoustics, overlappingwith psychology, concerned with the effects ofsounds on human beings.PT Abbreviation of Pacific Time.Pt Symbol for PLATINUM.PTC Abbreviation of POSITIVE TEMPERATURECOEFFICIENT.PtIr Symbol for PLATINIRIDIUM.PTM Abbreviation of PULSE-TIME MODULATION.PTO Abbreviation of PERMEABILITY-TUNED OS-CILLATOR.PTT Abbreviation for press-to-talk. See PRESS-TO-TALK MICROPHONE; PRESS-TO-TALK SWITCH.PTV Abbreviation of public television.p-type conduction In a semiconductor, currentflow consisting of the movement of holes. CompareN-TYPE CONDUCTION.p-type material Semiconductor material that hasbeen doped with an acceptor-type impurity and,consequently, conducts current mainly via holemigration. Germanium, for example, when dopedwith indium, becomes p-type. Compare N-TYPEMATERIAL.p-type semiconductor An acceptor-type semiconductor(i.e., one containing an excess of holes inits crystal lattice).PU Abbreviation of PICKUP.Pu Symbol for PLUTONIUM.public-address amplifier A high-gain, high-poweraudio amplifier designed especially for the reproductionof speech and music at large gatherings.public-address system A system of sound reproductionespecially designed for use at large gatheringsindoors or outdoors. The system includesmicrophones, a public-address amplifier, loudspeakers,and sometimes recorders and playbackdevices. Also called PA system.puck drive In a tape recorder, a speed-reductionsystem for driving the flywheel from the shaft ofthe (high-speed) motor. In some machines, a rubbertire mounted on the flywheel is driven,through friction, by the motor shaft. In others, anintermediate rubber-tired wheel is placed betweenthe motor shaft and the rim of the flywheel.puffer A meter or bridge for measuring small valuesof capacitance. The name comes from thespoken sound of pF, the abbreviation of PICO-FARAD.pulldown Descriptive of a circuit, device, or individualcomponent used to lower the value (e.g.,impedance) of a circuit to which it is connected.pull-in current The current required to close a relay.pulling 1. The abnormal tendency of one circuit tocause another to slip into tune with it. This oftenresults from coupling (intended or accidental)that is too tight. Thus, when two oscillators feed acommon circuit, such as a mixer, one might pullthe other into tune with itself. 2. Lowering of acrystal frequency by an external reactance.

pull-in voltage • pulse droop 561pull-in voltage The voltage required to close a relay.pull switch A mechanical switch actuated by apulling action.pullup Descriptive of a circuit or component usedto raise the value (e.g., impedance) of a circuit towhich it is connected.pulsar An extremely dense, rapidly rotating collapsedstar that produces radio signals at regularintervals. The pulse frequency varies from lessthan one hertz to several tens or hundreds ofhertz.pulsating direct current A direct current that periodicallyrises and falls between zero and a maximumvalue (or between two positive or negativevalues) without changing polarity. Thus, it is possibleto have either a pulsating positive current ora pulsating negative current. Also see DIRECTCURRENT.Voltage+10+8+6+4+20pulsating direct currentTimepulsating wave See PULSATING DIRECT CUR-RENT.pulse A transient signal that is usually of short duration,constant amplitude, and one polarity. Atypical example is a narrow positive or negativespike.pulse amplifier An amplifier having wide frequencyresponse and low distortion, used for amplifyingsteep-sided pulses of short duration.pulse-amplitude modulation Abbreviation, PAM.A method of conveying information in wirelesscommunications. A train of pulses is transmitted.The strength of each individual pulse varies accordingto the modulating waveform. Normally,the pulse amplitude increases as the instantaneousmodulating-signal level increases (positivemodulation). However, this can be reversed sothat higher audio levels cause the pulse amplitudeto go down (negative modulation).pulse bandwidth For an amplitude pulse, the minimumbandwidth occupied. The faster the riseand/or decay times of a pulse, the greater thebandwidth. The greater the pulse frequency, thegreater the bandwidth.pulse code A code in which groups of pulses representdigits.pulse-code modulation Abbreviation, PCM. Amethod of conveying information in wireless communications.A train of pulses is transmitted. Theintelligence-carrying signal is sampled periodicallyand the amplitude is converted into binarycode. The code might allow for eight levels(000 to 111), 16 levels (0000 to 1111), 32 levels(00000 to 11111), or 64 levels (000000 to 111111).pulse-code-modulation binary code A pulse codeused in communications not in the form of linetransmission. Individual values are denoted bybinary numbers.pulse-code modulation multiplex equipment Amultiplexer/demultiplexer for signal conversionbetween a single signal and multiple-channel signals.It uses both pulse-code modulation andtime-division multiplexing.pulse-count divider A circuit or device that receivesan input of a certain number of pulses (or pulsesper second) and delivers an output that is a functionof that quantity. See, for example, DIVIDE-BY-SEVEN CIRCUIT and DIVIDE-BY-TWO CIRCUIT.pulse counter A circuit or device that indicates thenumber of pulses presented to it in a given timeinterval.pulse counting Counting pulses in a sequence. Atlow speed (pulse repetition rate), this can be donewith an electromechanical dial-type counter. Athigh speed, a fully electronic circuit is required.pulse delay circuit A monostable multivibratoradapted to deliver its single output pulse a predeterminedtime after the input pulse has been applied.pulse dialing A form of telephone dialing in whicheach digit is formed by a series of pulses, usuallyat 10 to 20 Hz. The pulses are the equivalent ofdisconnecting the line for a few milliseconds. Eachdigit has the corresponding number of pulses, exceptdigit 0, which is formed by 10 pulses.pulse droop Distortion observable as a downwardslopingtop on the oscilloscope trace of a pulse. Itcan be quantified in volts, millivolts, microvolts,amperes, milliamperes, or microamperes.Voltage+8+6+4+20pulse droopDroopTime

562 pulsed laser • pulse-time modulationpulsed laser A laser in which flashes (pulses) ofhigh-intensity light excite the lasing medium.pulse duration The time period during which apulse exists (i.e., its width on an oscilloscope display).pulse-duration modulation Abbreviation, PDM.See PULSE WIDTH MODULATION.pulse equalizer A MONOSTABLE MULTIVIBRA-TOR adapted to deliver pulses of equal amplitude,shape, and width—even when it receives triggerpulses of different kinds.pulse fall time The time required for the trailingedge of a pulse to fall from 90 to 10 percent of itspeak amplitude. Compare PULSE RISE TIME.pulse-forming line A circuit used in radar for producinghigh-intensity pulses. Inductances andcapacitances are combined in a long string, andthe effect is to generate high-amplitude radiofrequencypulses.pulse-frequency modulation Abbreviation, PFM.See PULSE-INTERVAL MODULATION.pulse generator A signal generator that producespulses. A general-purpose generator of this sortwill produce pulses of adjustable amplitude, duration,shape, and repetition rate.pulse-height discriminator A circuit or devicethat passes only pulses whose amplitudes exceeda predetermined level.pulse interval The interval between successivepulses.pulse-interval modulation Abbreviation, PIM.Also called pulse-frequency modulation (PFM) orpulse-numbers modulation (PNM). A method ofconveying information in wireless communications.A train of pulses is transmitted. Everypulse has the same amplitude and the same duration,but their rate fluctuates with the modulatingwaveform. When there is no modulation, thepulses are evenly spaced with respect to time. Anincrease in the instantaneous data amplitudemight cause pulses to be sent more often (positivemodulation) or less often (negative modulation).pulse inverter A single-stage, wideband, lowdistortion,common-emitter, or common-sourceamplifier. The output-pulse waveforms aretherefore inverted, with respect to the input-pulsewaveforms.pulse jitter In a pulse train, a disturbance characterizedby random changes in the spacing betweenpulses.pulse-length modulation See PULSE-DURATIONMODULATION.pulse load The load impedance for a pulse generator.pulse mode See PULSE MODULATION.pulse modulation See PULSE-AMPLITUDE MOD-ULATION, PULSE-CODE MODULATION, PULSE-INTERVAL MODULATION, PULSE-POSITIONMODULATION, PULSE-WIDTH MODULATION.pulse modulator 1. A modulator that deliverspower or voltage pulses for modulating a carrier.2. A device that modulates pulses (see PULSEMODULATION, 2).pulse narrower A circuit or device that reduces theduration (width) of a pulse.pulse-numbers modulation Abbreviation, PNM.See PULSE-INTERVAL MODULATION.pulse operation Intermittent operation of a circuit,in the form of discrete pulses.pulse oscillator Any oscillator with an output thatconsists of a series of pulses.pulse-position modulation Abbreviation, PPM. Amethod of conveying information in wireless communications.A train of pulses is transmitted. Thetiming of each individual pulse varies accordingto the modulating waveform. The pulsesoccur earlier or later than the nominal (zeromodulation)time, depending on the instantaneousamplitude of the modulating signal.pulse rate See PULSE REPETITION RATE.pulse ratio The ratio of pulse height (amplitude) topulse width (duration).pulse regeneration Restoration of the originalwaveform and frequency to a pulse. It eliminatesdistortion caused by circuits or propagation conditions.pulse repetition frequency Abbreviation, PRF.See PULSE-REPETITION RATE.pulse-repetition rate Abbreviation, PRR. Thenumber of pulses per unit time; usually pulsesper second (pps).pulse rise time The time required for the leadingedge of a pulse to rise from 10 to 90 percent of itsmaximum amplitude. Compare PULSE FALLTIME.pulse scaler A circuit actuated by the reception ofa definite, predetermined number of inputpulses.pulse-shaping circuit 1. A circuit for producing apulse from a wave of some other shape (e.g., sinewave). 2. A circuit for tailoring a pulse to desiredshape, amplitude, and duration.pulse spacing The interval between successivepulses.pulse-spacing modulation Abbreviation, PSM. SeePULSE-INTERVAL MODULATION.pulse-steering diode In a flip-flop circuit, a diodethrough which the trigger pulse must pass toswitch the circuit. Because of the unidirectionalconductivity of a diode, pulses of only one polarityare passed.pulse stretcher 1. A shaping circuit that widens apulse (i.e., increases its duration). 2. A circuit,such as a special monostable multivibrator, thatgenerates a pulse that is wider than the triggerpulse.pulse stuffing See JUSTIFICATION, 2.pulse tilt The sloping of the normally flat top of apulse either up or down. Also see PULSE DROOP.pulse time See PULSE DURATION.pulse-time modulation See PULSE-POSITIONMODULATION.

pulse train • purity control 563pulse train A series of successive pulses of usuallyone kind.pulse transformer A transformer designed to accommodatethe fast rise and fall times of pulsesand similar nonsinusoidal waveforms. Suchtransformers often use special core materials andare made using special winding techniques.pulse transmitter 1. A device that transmits a seriesof pulses. 2. A pulse-modulated transmitter.3. See PULSE MODULATOR.pulse waveform The general shape of a pulse as itappears on an oscilloscope display. The variousforms range from positive or negative halfsinusoids,through rectangles, to thin-line spikes.pulse width The horizontal dimension of a pulse(i.e., its duration).pulse-width modulation Abbreviation, PWM. Alsocalled pulse-duration modulation (PDM). Amethod of conveying information in wireless communications.A train of pulses is transmitted.The width (duration) of each individual pulsevaries according to the modulating waveform.Normally, the pulse width increases as the instantaneousmodulating-signal level increases(positive modulation). However, this can be reversedso that higher audio levels cause the pulsewidth to decrease (negative modulation).Modulatingwaveformpulse-width modulationPulseamplitudepump 1. In a parametric amplifier, the oscillatorthat supplies the signal that periodically variesthe reactance of the varactor. 2. The pumpingsignal in 1. 3. To perform the operation (pumping)described in 1. 4. To increase the energy levelof an atom or molecule (by exposing it to electromagneticradiation) to such an extent that oscillationor amplification occurs. A ruby laser, forexample, produces its intense, coherent beam asa result of pumping. 5. The radiation used topump an atom or molecule. 6. The device producingthe radiation required to pump an atom ormolecule.pump frequency The frequency of a PUMP voltage.pumping A method of laser actuation. A series ofpulses, at the resonant frequency of the lasingmaterial, is injected to cause laser output.pump oscillator An oscillator for producing apump voltage.pump voltage The voltage of a pumping signal.Also see PARAMETRIC AMPLIFIER and PUMP,1, 2.punch 1. A tool for cutting holes in metal chassis,panels, and boxes for electronic equipment. 2.High signal strength.punch-in editing In audio recording, a featurethat allows convenient insertion of newmaterial on a tape. The tape recorder can beswitched instantly from Play to Record, andback again, whenever the operator wants to addmaterial.punchthrough In a bipolar transistor, the potentiallydamaging condition resulting when the reversebias of the collector is increased to a voltagehigh enough to spread the depletion layer entirelythrough the base. This tends to effectively connectthe emitter to the collector.punchthrough region The conduction region associatedwith higher-than-punchthrough voltage,in which bipolar-transistor current is excessive.Also see PUNCHTHROUGH.punchthrough voltage The voltage that causesPUNCHTHROUGH in a given bipolar transistor.puncture voltage See BREAKDOWN VOLTAGE, 1.Pupin coil One of several loading coils that can beinserted at intervals in series with a telephoneline to cancel line-capacitance effects and, thus,improve the clarity of speech.pure tone An audio-frequency (AF) tone having essentiallyno harmonic content; a sine-wave AFtone.pure wave A wave containing no distortion products.purging The removal of an undesired gas or othersubstance from a system by introducing a materialto displace it.purifier A power-line operated alternating-currentelectromagnet that can be manually rotated infront of a color-television picture tube to demagnetizethe tube. Also called a DEGAUSSER.purity 1. In color television, complete saturationof a hue. 2. In a waveform, complete freedomfrom distortion. 3. The extent to which spurioussignals are attenuated in the output of a radio ortelevision transmitter. Also called spectralpurity.purity adjustment In a color-television picturetube, adjustment of each purity control for purecolor.purity coil A variable-current coil around the neckof a color-television picture tube that is used toadjust color purity.purity control For a purity coil, the variable resistorthat controls the current for color correction.

564 purity magnet • push-push multiplierpurity magnet A ring-magnet collar around theneck of a color-television picture tube to adjust,by rotation, color purity.purple plague Corrosion that occurs when aluminumand gold are placed in contact.pushbutton tuner A radio or television tuner utilizingpushbutton tuning.pushbutton tuning The tuning of a circuit to variousfrequencies in single steps by means of pushbuttonswitches.pushdown list In data processing, a method ofamending a list. A new item entered at the topmoves each existing item one position down.pushdown stack Also called first-in/last-out. A digitalread-write memory in which data bits emergein reverse sequence from the order they go in. Ifdata bit x enters the pushdown stack before databit y, then x will come out after y. CompareFIRST-IN/FIRST-OUT.push-in terminal A circuit contact or tie point,usually of thin, springy material, that can be insertedinto a hole in a perforated board.push-pull Pertaining to a circuit in which two activedevices are used, with the inputs and outputsboth placed in phase opposition. In theoutput circuit, even harmonics are canceled, andodd harmonics are reinforced.Inputpush-pull+12 VOutputpush-pull amplifier An amplifier stage in which,for increased power output, two active devices areoperated 180 degrees out of phase with eachother in opposite halves of a symmetrical circuit.Also see PUSH-PULL CIRCUIT.push-pull circuit A symmetrical circuit in whichtwo active devices operate on separate halves ofthe input-signal cycle and deliver a combinedoutput signal.push-pull deflection In an oscilloscope, the applicationof deflection voltage to a pair of deflectingplates 180 degrees out of phase with each other.For this purpose, the output amplifier in the horizontalor vertical deflection channel is a pushpullstage.push-pull doubler See PUSH-PULL MULTIPLIER.push-pull microphone A set of two microphones,in which the audio-frequency outputs are inphase opposition.push-pull multiplier A push-pull amplifier with itsoutput circuit tuned to an odd-numbered multipleof the input frequency. This circuit is unsuitablefor even-harmonic operation, but has somemerit as an odd-harmonic multiplier (e.g., atripler or quintupler). Also see PUSH-PUSH MUL-TIPLIER.push-pull oscillator An oscillator stage in which,for increased power output, two active devices areoperated 180 degrees out of phase with eachother in opposite halves of a symmetrical circuit.Also see PUSH-PULL CIRCUIT.push-pull/parallel amplifier An amplifier stage inwhich tubes or transistors are connected inpush-pull/parallel for increased power output.Also see PARALLEL-COMPONENT AMPLIFIER,PUSH-PULL AMPLIFIER, and PUSH-PULL/PAR-ALLEL CIRCUIT.push-pull/parallel circuit A push-pull circuit inwhich two or more active devices are connected inparallel on each side of the circuit. This arrangementgives increased power output over that ofthe conventional push-pull circuit. See, for example,PUSH-PULL/PARALLEL AMPLIFIER andPUSH-PULL/PARALLEL OSCILLATOR.push-pull/parallel oscillator An oscillator stagein which active devices are connected inpush-pull/parallel for increased power output.Also see PARALLEL-COMPONENT OSCILLATOR,PUSH-PULL OSCILLATOR, and PUSH-PULL/PARALLEL CIRCUIT.push-pull recording A type of film sound trackconsisting of two side-by-side images 180 degreesout of phase with each other.push-pull transformer A transformer having acenter-tapped winding for operation in a pushpullcircuit.push-push Pertaining to a circuit in which two activedevices are used, with the inputs connectedin phase opposition, and the outputs connectedin parallel. The result is reinforcement of the evenharmonics, and cancellation of the fundamentalfrequency and all odd harmonics.push-push circuit See PUSH-PUSH MULTIPLIER.push-push multiplier An amplifier circuit containingtwo active devices with their inputs connectedin phase opposition and their outputs connectedin parallel. This circuit is unsuitable for fundamental-frequencyand odd-harmonic operation,

push-push multiplier • PZT 565Inputpush-pushOutput+12 Vbut has some merit as an even-harmonic multiplier(e.g., a doubler or quadrupler). Also seePUSH-PULL MULTIPLIER.push-to-talk switch See PRESS-TO-TALKSWITCH.pushup list In data processing, a method ofamending a list, whereby new items are added atthe end of the list; all other items retain their originalpositions. Compare PUSHDOWN LIST.pV Abbreviation of PICOVOLT.PVC Abbreviation of POLYVINYL CHLORIDE.pW Abbreviation of PICOWATT.PWM 1. Abbreviation of PULSE-WIDTH MODULA-TION. 2. Abbreviation of PLATED-WIRE MEM-ORY.pwr Abbreviation of POWER.Pyralin See CELLULOSE NITRATE.pyramidal horn antenna A rectangular horn antennathat is flared in two dimensions. The hornwidth and height both increase linearly with increasingdistance (in the direction of maximumradiation/response) from the feed point.pyramidal wave See BACK-TO-BACK SAWTOOTH.Pyrex A heat-resistant glass having numerous applicationsin electronics and chemistry.pyrheliometer An instrument used to measure infraredradiation.pyroelectricity In certain crystals, electricity generatedby temperature change, and in particular,by the application of heat.pyroelectric lamp See NERNST LAMP.pyroelectric material A crystalline material thatgenerates an output voltage when it is heated.pyrolysis The process whereby heat changes asubstance into one of several different substancesby rearranging its atoms.pyromagnetic effect In a material or circuit, thecombined effect of heat and magnetism.pyrometer An instrument, other than a thermometer,used for the measurement of temperature.See, for example, OPTICAL PYROMETER.Pythagorean scale A sound scale defining a specifictype of relationship among audio tones. If xand y are related by the Pythagorean scale andare adjacent in frequency, then a specific frequency( f ) exists, so x = f 2 and y = f 3 .Pythagorean theorem A theorem of plane geometry.For a right triangle, with sides of lengths a, b,and c, where c is the side opposite the right angle,it is always true that a 2 + b 2 = c 2 .p-zone See P LAYER.PZM Abbreviation of PRESSURE-ZONE MICRO-PHONE.PZT Abbreviation of LEAD ZIRCONATE TITANATE.

Q 1. The figure of merit of a capacitor, inductor, orinductance-capacitance (LC) circuit, equal to thereactance divided by the resistance. 2. Symbol forelectrical charge. 3. Occasional symbol for SE-LECTIVITY. 4. See Q BAND. 5. See Q OUTPUT.q 1. Symbol for quantity of electricity (incoulombs). 2. Symbol for the charge carried by anelectron (the charge carried by a hole is representedby –q). 3. Symbol for the value of a quantum.QA Abbreviation of QUALITY ASSURANCE.Q adjustment The separate null adjustment forthe Q value of a component being tested in animpedance bridge having separate resistive andreactive balances.Q-antenna An antenna in which the transmissionline (feeder) is matched in impedance to the centerof the radiator by means of a Q-matching section.QAVC Abbreviation of QUIET AUTOMATIC VOL-UME CONTROL.Q band The radio-frequency band 36 to 46 GHz. Itis subdivided as follows: Q a , 36 to 38 GHz; Q b , 38to 40 GHz; Q c , 40 to 42 GHz, Q d , 42 to 44 GHz;and Q e , 44 to 46 GHz.Q bar One of the parallel metal tubes in aQ-matching section. Also see Q ANTENNA.Q booster See Q MULTIPLIER.Q bridge An alternating-current bridge used principallyto determine the Q of capacitors andinductors. Bridges are usually used foraudio-frequency Q determinations; resonant-typeQ meters are generally used for measurement ofradio-frequency Q.FeederRadiating elementQ-antennaQ-matchingsectionCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

QC • quad 567QC Abbreviation of QUALITY CONTROL.QCE Abbreviation of QUALITY-CONTROL ENGI-NEERING or QUALITY-CONTROL ENGINEER.Q channel In American (NTSC) color television, the508-kHz-wide green-magenta color informationtransmission band.QCT Abbreviation of QUALITY-CONTROL TECHNI-CIAN.QCW In the local oscillator and associated circuitryof a color television receiver, a 3.85-MHz CW signalof Q PHASE.QCW signal In a color television receiver, the componentof the chrominance signal that is 90 degreesout of phase with the in-phase component.Q demodulator In a color television receiver, thedemodulator that combines the chrominance signaland the color-burst oscillator signal to recoverthe Q signal (see Q SIGNAL, 2).QED 1. Abbreviation of QUANTUM ELECTRODY-NAMICS. 2. Abbreviation of quod erat demonstrandum,Latin for “which was to bedemonstrated.” Also, Q.E.D. Often written at theconclusions of valid logical proofs and derivations.Q factor See Q.QFM Abbreviation of QUADRATURE MODULA-TION.QM Abbreviation of QUADRATURE MODULATION.Q-matching section A linear radio-frequencyimpedance-matching transformer consisting oftwo straight, rigid, parallel metal conductors thatare used to match a feeder to an antenna. Thesection is 1 ⁄4 wavelength long at the operating frequency.The diameters and center-to-centerspacing of the conductors are such that the characteristicimpedance of the matching section isequal to the geometric mean of the feeder characteristicimpedance and the radiation resistance ofthe radiator. Also see Q ANTENNA and QUAR-TER-WAVELENGTH MATCHING STUB.Q meter A usually direct-reading instrument fordetermining the Q of a capacitor, inductor, or inductance-capacitance(LC) circuit. Most Q metersare operated at radio frequencies, but audiofrequencyinstruments are available.Q modulation Amplitude modulation obtained byvarying the effective Q of a radio-frequency tankcircuit in step with a modulating component. SeeABSORPTION MODULATION.QMQB Abbreviation of quick make/quick break.Q multiplier A positive-feedback (regenerative)amplifier that increases the effective Q of a tunedcircuit, and thereby sharpens its response, whenits input is connected across the tuned circuit.Q output The reference output of a flip-flop.Q phase A color-television carrier signal that is 147degrees out of phase with the color subcarrier.Q point The point or points at which a load line intersectsa device characteristic (such as the collectorcurve of a transistor or plate curve of atube) and that identifies the quiescent operatingpoint.ReverseQ pointReversevoltageReverseload lineForwardcurrentReversecurrentForward voltageForward Q point.Q points on diode characteristicForwardload lineQRD Abbreviation of QUADRATIC RESIDUE DIF-FUSOR.Q-section transformer See Q-MATCHING SEC-TION.Q signal In color television, the quadrature componentof the chrominance signal, equal to +0.48(R-Y) and to +0.41(B-Y), where B is the blue camerasignal, R is the red camera signal, and Y is the luminancesignal.Q signals A set of three-letter groups, each beginningwith the letter Q, used for simplified telegraphand radiotelegraph communication, andsometimes rapid voice communication (in radiotelephony).Each signal represents a commonlyused phrase or message.QSL card A card verifying communication with, orthe reception of signals from, the station sendingthe card. Such verification is common in the amateurradio service and with some shortwavebroadcast and CB stations.QSO Amateur radiotelegraph abbreviation forTWO-WAY COMMUNICATION.Q spoiler A device or circuit that produces QSPOILING in a laser.Q spoiling The technique of inhibiting laser actionduring an interval when an ion population excessis pumped up. When the laser is subsequentlytriggered by Q switching, a more powerful pulseof light results than would be otherwise obtained.Q switching A laser-switching action obtainablewith Kerr cells or rotating reflecting prisms,which consists of holding the Q of the laser cavityto a low value during an ion-population buildup,then abruptly switching the Q to a higher value.Q transformer See Q-MATCHING SECTION.qty Abbreviation of QUANTITY.quad 1. A combination of four components, such asdiodes, transistors, etc., in a single housing. Thecomponents are usually carefully matched. 2. In acable, a combination of four separately insulatedconductors (sometimes, two twisted pairs) twisted

568 quad • quadrilliontogether. 3. Abbreviation of QUADRANT. 4. SeeQUAD ANTENNA. 5. See QUADROPHONIC.quad antenna A directional antenna similar to theYagi, except that full-wavelength loops are usedinstead of straight elements. A two-element arraycan consist of a driven element and a reflector, orit can have a driven element and a director. Athree-element system has one driven element,one director, and one reflector. The director hasa perimeter of about 0.97 electrical wavelength,the driven element measures exactly 1 electricalwavelength around, and the reflector has aperimeter of about 1.03 electrical wavelength. Additionaldirector elements can be added to the basicthree-element quad design to form arrayshaving any desired numbers of elements. Thegain and directivity increase as the number of elementsincreases. Compare YAGI ANTENNA.RadiatorFeederquad antennaReflectorStubquadded cable See QUAD, 2.quadding Redundancy obtained by connectingcomponents in series-parallel for enhanced reliabilityand/or increased power-handling capacity.quad latch A set of four interconnected flip-flopsthat is used for digital data storage.quadrant 1. A specific 90-degree arc of a circle.2. One of the four parts formed on a plane surfaceby rectangular coordinates and designated I, II,III, and IV in a counterclockwise direction, startingwith the upper-right quadrant. 3. An altitudemeasuringinstrument.quadrantal deviation The part of magneticcompassdeviation caused by the induction oftransient magnetism into the horizontal soft ironof a vessel by the horizontal component ofterrestrial magnetism.quadrantal error See QUADRANTAL DEVIATION.quadrant electrometer An electrometer whoseprincipal parts are quadrants (a pillbox-shapedbrass chamber split into four parts) and a needle (aflat, bowtie-shaped aluminum vane) suspended bya platinized quartz fiber between the quadrants.QuadrantNeedleNeedlequadrant electrometerMirrorQuartz fiberQuadrantquadraphonic sound Sound recording and reproductioninvolving four channels.quadraphony Music recording or playback inwhich four distinct information channels areused. Also called four-channel stereo.quadratic equation A second-degree equation[i.e., one in which the highest exponent is 2 (thesquare of an unknown) (e.g., ax2 + bx + c = 0)].quadratic residue diffusor Abbreviation, QRD. Inacoustics, a sound-reflection grating that scatters(diffuses) sound waves almost uniformly inall directions. The depths of the indentations inthe grating are determined according to aQUADRATIC EQUATION.quadrature The state of (cyclic events or points)being 90 degrees out of phase.quadrature amplifier An amplifier circuit that introducesa 90-degree phase shift. Such amplifiersare used in control devices, test instruments,transmitters, and color television receivers.quadrature axes The vertical axes in the complexnumberplane (i.e., the +j and –j axes).quadrature carrier See Q PHASE.quadrature component 1. The reactive componentof an alternating current or voltage. 2. A vectorperpendicular to a reference vector. 3. Theimaginary-number component in a complexnumberexpression.quadrature current Reactive current in an alternating-currentcircuit.quadrature modulation In-phase modulation oftwo carrier components having a 90-degree phasedifference.quadrature number See IMAGINARY NUMBER.quadrature-phase subcarrier signal See QCWSIGNAL.quadrature portion In color television, the portionof the chrominance signal having the same(or opposite) phase as that of the Q-signalmodulatedsubcarrier, and that is 90 degrees outof phase with the in-phase portion.quadrature sensitivity The sensitivity of a transducerto motions in a direction that is perpendicularto the normal axis of response.quadrature voltage A voltage 90 degrees out ofphase with another (reference) voltage.quadrilateral 1. Pertaining to an object havingfour sides. 2. A four-sided plane polygon.quadrillion The number 1,000,000,000,000,000(10 15 ).

quadripartite • quantized pulse modulation 569quadripartite Having four parts.quadripole network A four-terminal network,usually with input- and output-terminal pairs.quadrivalent Having a valence of 4. Tin, for example,is quadrivalent. Also called TETRAVALENT.quadruped robot A robot with four legs that canmove independently. It offers better stability thanthree-legged designs. Functions well in mobilemachines that must navigate irregular terrain.quadrupler 1. A rectifier circuit that delivers a direct-currentoutput voltage approximately equalto four times the peak value of the alternatingcurrentinput voltage. 2. An amplifier or other circuitthat delivers an output signal of four timesthe frequency of the input signal.quadruplex circuit A data circuit in which two messagesare carried in each direction simultaneously.quadrupole 1. A combination of two dipoles, producinga force that varies inversely with thefourth power of distance. 2. A four-pole magnetused in some synchrotrons and linear acceleratorsto focus and bend a particle beam. 3. A systemconsisting of two dipoles of equal andopposite direct moment.qualification The quality-control or qualityassurancescheme used in the production ofcomponents, circuits, or systems. Certainminimum requirements must be met for a deviceto obtain qualification.qualitative test A test performed to determine thegeneral mode of operation or the presence of certainfactors, without regard to numerical values.Compare QUANTITATIVE TEST.quality 1. In audio-frequency applications, fidelityof transmission or reproduction. 2. The degree ofconformity of a product to specifications.quality assurance The outcome of measures takento bring performance into conformity with specifications.See QUALITY, 2.quality control The surveillance of selection, manufacturing,and testing operations to ensure conformityof a product to specifications.quality-control engineering The branch of engineeringconcerned principally with the technicalmethods of quality control and statistical methodsof assessing quality (see QUALITY, 2).quality-control technician A technician whoseprincipal duty is the performance of operations inthe areas of incoming inspection, manufacturingsupport, and product testing. Sometimes statisticalevaluations are required.quality engineering A field of engineering that dealswith quality assurance and quality control in theproduction of components, circuits, and systems.quality factor See Q.quality-factor bridge See Q BRIDGE.quality-factor meter See Q METER.quanta Plural of QUANTUM.quantimeter An instrument used to measure thequantity of X rays to which a body has been exposed.quantitative test A test performed to determinethe numerical values (and their relationships)connected with observable phenomena. CompareQUALITATIVE TEST.quantity 1. A parameter (e.g., collector current,grid voltage, etc.). 2. In calculations, a positive ornegative real number. 3. Electrical charge, usuallyspecified or measured in coulombs (seeCOULOMB). Also called electrical quantity.quantization The conversion of a quantity havinginfinitely many possible values or levels (such asan analog signal) into one that can attain only afinite number of defined values or levels (such asa digital signal). The number of levels is usuallysome integral power of 2 (i.e., 2, 4, 8, 16, 32, etc.).This allows the levels to be represented as binarynumbers.Amplitude111110101100011010001000Timequantizationquantization distortion Distortion introduced bythe process of QUANTIZATION in a communicationsor broadcast signal.quantization distortion power The level of thedistortion in a signal resulting from QUANTIZA-TION. It is expressed in microwatts, milliwatts, orwatts. It can also be expressed as a percentage, oras a level in decibels, relative to the power level ofthe input signal.quantization error The difference between the actualvalues of quantities and their quantized values.quantization noise Noise introduced by the processof QUANTIZATION in a communications orbroadcast signal.quantize 1. To perform the process of QUANTIZA-TION. 2. To split a quantitative commodity, suchas energy into its smallest measurable incrementalunits.quantized pulse modulation Pulse modulation involvingQUANTIZATION. Examples are PULSE-CODE MODULATION and PULSE-NUMBERSMODULATION.

570 quantizer • quarter wavelengthquantizer A circuit or device that selects the digitalsubdivision into which an analog quantity isplaced (e.g., an analog-to-digital converter).quantizing See QUANTIZATION.quantometer An instrument for measuring magneticflux.quantum 1. Abbreviation, Q. Plural, quanta. Inphysics, the elemental unit or particle of electromagneticenergy. The energy contained in onesuch particle is directly proportional to the frequency,and inversely proportional to the wavelength.2. See PHOTON. 3. Any discrete unitderived by QUANTIZATION.quantum chromodynamics A term coined by ProfessorMurray Gell-Mann for the theory of quarksand gluons.quantum counter A radiation-counter tube with awindow for the admission of light to the cathode.quantum efficiency See QUANTUM YIELD.quantum electrodynamics A branch of quantummechanics that involves the motions of electrons,photons, and muons caused by electromagneticaction. Quantum electrodynamics takes relativisticeffects into account.quantum electronics The branch of electronicsconcerned with energy states in matter.quantum equivalence The principle that one electronis emitted for each photon absorbed by a material(when the photon has the necessary energy).quantum jump The abrupt movement of a particlefrom one discrete energy state to another.quantum level The orbit or ring occupied by anelectron in an atom.quantum mechanics A branch of physics concernedwith the behavior of matter and energy, onthe basis of observable data.quantum noise A noise signal arising from randomvariations in the average rate at whichquanta impinge upon a detector.quantum number A number that describes the energylevel, or change in energy level, for a particle.quantum statistics A branch of QUANTUM ME-CHANICS concerned with the distribution of elementaryparticles through various quantizedenergy levels.quantum theory The theory that the emission orabsorption of energy by atoms or molecules occursin discrete packages or units, rather thancontinuously. Each unit is the emission or absorptionof an energy packet called a QUANTUM.Thus, radiant energy is thought to be divided intoquanta.quantum transition The movement of an electronfrom one energy level to another within an atom.quantum yield The photoelectric efficiency of alight-sensitive surface in terms of the number ofelectrons emitted for each absorbed quantum oflight.quark A hypothetical particle having a fractionalelectrical charge; quarks are thought to be constituentsof other subatomic particles.quarter-deflection method A method of measuringhigh-frequency resistance, involving the useof a sine-wave signal source, a standard noninductivevariable resistor, and a square-law radiofrequencyammeter.quarter-phase See TWO-PHASE.quarter wave 1. The length of time correspondingto 90 electrical degrees in a wave disturbance.2. The distance in space, or along a wire or feedline that corresponds to 90 electrical degrees in awave disturbance.quarter-wave antenna An antenna in which theradiator is an electrical quarter-wavelength longat the operating frequency.Groundradials1/4-waveradiatorquarter-wave antennaCoaxiallineEarthquarter-wave attenuator In a transmission line orwaveguide, two energy-absorbing structures separatedby an odd number of quarter wavelengthsso that the reflection from one structure is canceledby that from the other.quarter-wave balun A balun using quarter-waveelements. One form of this device consists ofa grounded quarter-wavelength-long cylinderclosed at one end and open at the other, formatching an unbalanced low-impedance line to abalanced high-impedance line.quarter wavelength Symbol, λ/4. The distance thatcorresponds to 90 degrees of phase as an electromagnetic(EM) field is propagated. In free space, itis related to the frequency by a simple equationL ft = 246/fwhere L ft represents λ/4 in feet, and f representsthe frequency in megahertz. If λ/4 is expressed inmeters, then the formula isL m = 75/f

quarter wavelength • quartz plate 571where L m represents the displacement in meters.In general, if v is the velocity factor (expressed asa ratio) in a given medium, then:L ft = 246v/fandL m = 75v/fCompare FULL WAVELENGTH, HALF WAVE-LENGTH.quarter-wavelength line A transmission line orfeeder that is a quarter-wavelength long at theoperating frequency. Also called quarter-waveline.quarter-wavelength matching stub An arrangementconsisting of a quarter-wavelength-longparallel-wire section of transmission line, usedfor matching the impedance of a nonresonantfeeder to that of an antenna. It is similar to a Q-MATCHING SECTION, except that flexible transmissionline (e.g., ladder line) is used, rather thanrigid metal rods or tubing.quarter-wave monopole A nondirectional UHFvertical antenna requiring no ground. The radiatoris 1 ⁄4 wavelength long, and is an enlargeddiameterouter sleeve connected to the outerconductor of the coaxial feeder. The two sectionssimulate a half-wave antenna.quarter-wave plate A plate of double-refractingcrystalline material whose thickness allows theintroduction of a quarter-cycle phase differencebetween the ordinary and extraordinary componentsof light transmitted by it.quarter-wave radiator An antenna consisting of asingle, usually straight, active element that measuresan electrical quarter wavelength from endto end. When operated against electrical ground,the element exhibits resonance. A simple quarter-wavelength(λ/4) conductor with a highlength-to-diameter ratio measures approximately95 percent of λ/4 in free space. The element canbe much shorter than free-space λ/4 yet remainresonant when operated against electrical groundif inductance is inserted in series with the radiator.The element can be much longer than freespaceλ/4 yet remain resonant when operatedagainst electrical ground if distributed capacitancesare inserted in series with the radiator.quarter-wave resonance Resonance at the operatingfrequency in a quarter-wave antenna.quarter-wave resonant line A section of transmissionline (such as open-wire line or coaxial cable)that is a quarter-wavelength long at the operatingfrequency. Such a section is useful in impedancematching and in various radio-frequency testsand measurements.quarter-wave stub See QUARTER-WAVE TRANS-FORMER.quarter-wave support In a coaxial line, a quarterwavemetal stub that can be used, instead of aninsulator, to separate the inner and outer conductors.quarter-wave termination In a waveguide, a set oftwo metal barriers separated by 90 electrical degrees.One barrier totally reflects the energy strikingit. The other barrier allows some energy topass through. Resonance occurs in the space betweenthe barriers.quarter-wave transformer A quarter-wave resonantline short-circuited at one end by an adjustableslider. This arrangement is useful forradio-frequency impedance matching.quarter-wave transmission line See QUARTER-WAVE LINE.quartic equation A fourth-degree equation of theform ax 4 + bx 3 + cx 2 + dx + e = 0, where a, b, c, d,and e are constants. Also called BIQUADRATICEQUATION.quartz A mineral that is a variety of natural silicondioxide, or an artificially grown material of thesame sort. In the natural state, quartz occurs inhexagonal crystals having pyramidal ends. It hasvarious uses in electronics; one of the most commonis the manufacture of piezoelectric crystals.quartz bar A comparatively large, thick piezoelectricquartz plate used in standard-frequency oscillatorsand in sharply tuned low-frequencyfilters. Common resonant frequencies are 50 kHz,100 kHz, and 1000 kHz.quartz crystal A natural or artificial piece ofquartz cut to specific dimensions, usually selfcontainedin a solder-in or plug-in enclosure. Thedevice acts as a highly stable selective circuit. Itexhibits a sharp resonance at the frequency forwhich it is cut, and at harmonics of this frequency.It is used as the frequency-determiningelement in precision oscillators.quartz-crystal oscillator See CRYSTAL OSCILLA-TOR.quartz-crystal resonator See CRYSTAL RES-ONATOR.quartz delay line An acoustic delay line usingquartz to transmit the sound waves.quartz-fiber electroscope An electroscope using agold-plated quartz fiber, instead of gold leaves.quartz-halogen lamp An incandescent, usuallylow-voltage lamp used in automotive headlights,and in some home and office lighting appliances.It provides greater efficiency than conventionalincandescent lamps.quartz lamp A mercury-vapor lamp with a transparentquartz (instead of glass) envelope. Unlikeglass, quartz readily passes the ultraviolet raysgenerated by the mercury discharge.quartz lock A circuit that uses a CRYSTAL OSCIL-LATOR to regulate frequency, timing, or speed. Itis used in electronic clocks and watches, televisionreceivers, synthesized radio receivers, transmitters,transceivers, high-fidelity turntables, etc.quartz oscillator See CRYSTAL OSCILLATOR.quartz plate A piezoelectric plate cut from a quartzcrystal. The plate is itself often called a crystal.Also see CRYSTAL AXES and CRYSTAL CUTS.

572 quartz resonator • quick-break fusequartz resonator See CRYSTAL RESONATOR.quartz timepiece A watch or clock having as itscontrol element a time-determining quartz crystal.quasi- A prefix meaning “to some extent” or “similarto,” as in quasi-optical radio wave (a radiowave that behaves like a light ray).quasi-bistable circuit A trigger-operated multivibrator.It operates as a flip-flop when the triggerfrequency is sufficiently high.quasi-instruction In a computer program, a dataitem appearing as an encoded instruction, butthat is not acted upon.quasi-linear feedback system A system in whichthe feedback elements are nearly linear, but notentirely linear.quasi-negative Pertaining to a voltage that isnegative, with respect to some other voltage, butwhose absolute polarity is positive. For example,+0.5 volt is quasi-negative, with respect to+5.5 volts.quasi-optical Behaving like light. The term is usedto describe certain extremely short radio waves orother radiations that, like light rays, follow lineof-sightpaths and can be directed, reflected, refracted,or diffused.quasi-optical path A line-of-sight path followed byvery short radio waves, such as microwaves.quasi-positive Pertaining to a voltage that is positive,with respect to some other voltage, butwhose absolute polarity is negative. For example,–0.5 volt is quasi-positive, with respect to–5.5 volts.quasi-random A set of numbers considered to berandom, but chosen according to an algorithm.quasi-rectangular wave A wave whose shape approachesthat of a rectangular wave, but thatpossesses a small amount of tilt and/or curvature.quasi-scientific A term that is sometimes appliedto the design of electronic systems or to the appraisalof circuit behavior, using an intuitive,rather than analytical approach.quasi-sine wave A waveform that is not a perfectsine curve, but is close enough to be consideredsinusoidal, for all practical purposes.quasi-single sideband A modulated waveform thatsomewhat resembles single sideband, in whichparts of both sidebands are present.quasi-square wave A waveform that is not a perfectsquare, but is close enough to be consideredsquare for all practical purposes. It is sometimesapplied to a rectangular wave when a squarewave is desired.quasi-technical A term sometimes applied to qualitativetests, as opposed to quantitative tests.quaternary 1. Pertaining to a base-4 numbersystem. 2. Of an atom, joined to carbon atoms forfour bonds. 3. The fourth member of a 4-unit set.Quebec Phonetic alphabet code word for theletter Q.Amplitude+−quasi square waveTimequench 1. To suddenly bring to an end (e.g., toquench an oscillation). 2. To cool quickly, as inthe quenching of a heated metal object. 3. To extinguishthe discharge in a gas tube.quench capacitor A capacitor that prevents aspark from arcing across an inductor when currentflow abruptly stops.quench frequency See QUENCHING FRE-QUENCY.quenching action Typical operation of a superregenerativecircuit, in which regeneration is increasedto nearly the point of oscillation and thenreduced; this action is repeated at an ultrasonicfrequency and results in very high sensitivity.Also see QUENCHING FREQUENCY, QUENCHOSCILLATOR, and SUPERREGENERATIVE CIR-CUIT.quenching frequency The frequency at which regenerationin a superregenerative circuit is increasedand decreased.quench oscillator In some superregenerative circuits,the separate ultrasonic oscillator that producesthe required quenching action.quench resistor A resistor in a quenching networkthat prevents a spark from occurring across aninductor when current flow stops.queue A list of data, steps in a process, or commandsawaiting execution in a specific order.queuing theory A branch of mathematical electronics,dealing with the optimum order in whichsteps should be executed to obtain a particularend result.quibinary code In computer operations, a binarycodeddecimal system in which each decimal digitis represented by seven bits occupying placeswhose values are 8, 6, 4, 2, 0, 1, and 0.quibinary decade circuit A decade counter consistingof a ring-of-5, followed by a single binarystage.quick break An operating characteristic of aswitch, relay, or circuit breaker whereby the contactsopen rapidly—even when the actuating currentor mechanical force is slow-acting.quick-break fuse A fuse in which the wire meltsand breaks almost instantly when the currentrating is exceeded. Also called quick-blow fuse.Compare SLOW-BLOW FUSE.

quick-break switch • QWERTY 573quick-break switch A switch that opens rapidly—even if its handle or lever is moved slowly by theoperator. This action minimizes arcing and preventschatter. Compare QUICK-MAKE SWITCH.quick charge The process of charging a battery,such as a nickel-cadmium (NICAD) or nickelmetal-hydride(NiMH) type, at a relatively rapidrate, at high charging current. It is sometimesused to charge a battery from a state of almost totaldischarge. Compare TRICKLE CHARGE.quick-disconnect The characteristic of a connectorthat enables its mating halves to be separatedquickly and simply, to break the circuit in whichit is situated.quickening liquid A solution of mercuric cyanide ormercuric nitrate, into which objects can be dippedprior to electroplating with silver. The process ensuresgood adhesion of the silver to the object.quick make An operating characteristic of aswitch, relay, or circuit breaker, whereby the contactsclose rapidly—even when the actuating currentor mechanical force is slow acting.quick-make switch A switch that closes rapidly—even if its handle or lever is moved slowly by theoperator. Compare QUICK-BREAK SWITCH.quick printer A high-speed printer, used with adata terminal or computer. A relative term, dependingon the user and the application.quicksilver See MERCURY.quick-stop control A control on tape recorders andsome dictating machines that allows the operatorto stop the tape, but keep the machine in the playor record mode. Also called pause control.QuickTime Trade name (Apple Computer, Inc.) forsystem software commonly used in MULTIMEDIAapplications with personal computers.QUICKTRAN For multiaccess computer systems, acomputer programming language based on FOR-TRAN and offering facilities, through the use ofremote terminals, for running, testing, debugging,and compiling programs.quiescent carrier operation A modulation systemin which the carrier is present only during modulation(i.e., it is suppressed at all other times).Also called controlled-carrier transmission.quiescent-carrier telephony A carrier-current(wired-wireless) telephone system in which thecarrier is suppressed when there is no voice oralerting signal.quiescent component In an electronic device, acomponent that is momentarily nonfunctional.quiescent current Operating current (usually a directcurrent) flowing in a circuit or componentduring zero-signal or no-drain intervals. Alsocalled IDLING CURRENT.quiescent operation Zero-signal operation of a device,such as a transistor, diode, magnetic amplifier,or similar component.quiescent period The no-signal interval duringwhich equipment is not operating—even thoughit is energized.quiescent point The point on the characteristiccurve of a transistor, diode, or similar device, denotingthe zero-signal operating conditions.quiescent push-pull Denoting a push-pull stage,especially an audio power-output amplifier, inwhich the direct-current signal is essentiallyzero.quiescent state The inactive, or resting, state ofan active component, such as a transistor or vacuumtube.quiescent value The zero-signal value of currentor voltage for any component supplied with operatingpower.quiet AGC See DELAYED AUTOMATIC GAIN CON-TROL.quiet automatic gain control See DELAYED AU-TOMATIC GAIN CONTROL.quiet automatic volume control See DELAYEDAUTOMATIC GAIN CONTROL.quiet AVC See DELAYED AUTOMATIC GAIN CON-TROL.quiet battery A direct-current source specially designedand filtered to minimize noise componentsin its output.quieting Noise-voltage reduction in the output of afrequency-modulation (FM) receiver when an unmodulatedcarrier is received. Also called noisequieting.quieting level In a frequency-modulation (FM) receiver,the limiter threshold point.quieting sensitivity In a frequency-modulation(FM) receiver, the lowest input-signal amplitudeat which the output signal-to-noise ratio is belowthe specified limit.quiet tuning A system of tuning in which the outputof a receiver is muted until a station is tunedin properly.quinary code See BIQUINARY CODE.quinary counter A decade counter consisting of afive-stage ring.quinhydrone electrode A pH meter electrode consistingof a platinum wire in a solution of quinhydrone(C 12 H 10 O 4 ). Also see PH METER.quintillion The number 1,000,000,000,000,000,000 (10 18 ).quintupler 1. A rectifier circuit that delivers a direct-currentoutput voltage equal to about fivetimes the peak value of the alternating-currentinput voltage. 2. A circuit that delivers an outputsignal at the fifth harmonic of the input signal.QWERTY The standard typewriter and computerkeyboard layout. The name is derived from thefirst several letters in the top letter row: Q, W, E,R, T, and Y.

R 1. Symbol for RESISTANCE. (Also, r.) 2. Radiotelegraphabbreviation for ROGER. 3. Symbolfor RELUCTANCE. 4. Abbreviation of RADIUS.r 1. Symbol for ROENTGEN. 2. Symbol for correlationcoefficient. 3. Abbreviation of RADIUS. (Also,abbreviated R.)r e Symbol for CLASSICAL ELECTRON RADIUS.RA 1. Abbreviation of right ascension. 2. Abbreviationof RANDOM ACCESS.rabbit ears An indoor antenna, sometimes usedwith a television receiver, consisting of two verticalwhips (usually telescoping), the angle betweenwhich is adjustable.RAC Abbreviation of RECTIFIED ALTERNATINGCURRENT.R ac Symbol for AC RESISTANCE. (Also, r ac .)race Incorrect interpretation of the clock pulses bya digital circuit. Also called racing. The circuit improperlyattempts to do many operations duringone clock pulse, rather than a single operation.RACES Abbreviation of Radio Amateur Civil EmergencySystem.raceway See WIRE DUCT and WIREWAYS.rack An upright frame for holding equipment ofRACK-AND-PANEL CONSTRUCTION.rack-and-panel construction A method of buildingelectronic equipment on a chassis attachedhorizontally or vertically to a vertical panel. Aftercompletion of a unit, the panel is fastened inplace on a RACK. Several such panels fill therack.rack and pinion A device used for mechanical adjustmentof a control, such as the tuning controlin a radio receiver. A gear engages a serrated rod.As the gear is turned, the rod moves lengthwise.rack up In computer operations, a way of displayingdata, in which a new line added to the alreadycompletely occupied screen bumps up what hasforgone, thus eliminating the top line.racon Acronym for radar beacon.rad 1. A unit of ionizing radiation received by abody (dose) equal to 0.001 J/kg. 2. Abbreviationof RADIAC. 3. Abbreviation of RADIAN. 4. Abbreviationof RADIO. 5. Abbreviation of RADIX.radarStraight,toothed rodScalerack and pinionPointerShaftRound,toothed gear1. A microwave system for detecting objectsand determining their distance, direction, heading,speed, and other characteristics. Signalsfrom the transmitter are reflected back to thetransmitter site by the object, and the reflection(sometimes along with the transmission) is displayedon a cathode-ray screen. The name is anCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

adar • radial 575acronym for radio detection and ranging. 2. Thetheory and application of radio detection andranging systems as defined in 1.radar altitude The distance of an aircraft abovethe surface of the earth, as determined by radar.This value varies with the terrain over which theaircraft passes.radar antenna Any antenna used for transmittingand/or receiving radar signals.radar astronomy The use of radar equipment toobserve and map planets, moons, and asteroids,and to measure their distance from the earth orfrom a spacecraft.radar beacon A radar transceiver that, on receiptof radar signals, transmits encoded signals fromwhich the operator can take a bearing.radar beam The cone-shaped main lobe of energyemitted by a radar antenna. The narrower thebeam, the greater the resolution of the radar system.radar clutter Visual interference on a radar screencaused by reflections from ground or sea.radar countermeasures Abbreviations, RCM andrad CM. In wartime, any method of interferingwith enemy radar, such as jamming or use of decoys.radar detector 1. A device used in automobilesand trucks to detect the proximity of police orhighway-patrol radar. 2. A device used in militaryapplications, especially aviation, to indicate thepresence of radar.radar display The scheme via which a radar setportrays the relative positions of the objects thatproduce echoes. The most common is the azimuth/rangedisplay, showing compass bearings(usually in degrees clockwise from geographicnorth) and radius from the transmitter (usuallyin miles or kilometers). Altitude above mean sealevel can be displayed for individual echoes.radar homing A method of missile homing inwhich radar is used to track a target.radar speed trap A radar system used by trafficpolice to spot speeding vehicles.radar telescope The transmission and receptionunit used in radar astronomy. Compare RADIOTELESCOPE.RadCM Abbreviation of RADAR COUNTERMEA-SURES. (Also, RCM.)radial 1. One of several conductors used to enhancethe performance of an unbalanced, vertical antenna.These can be constructed from wire ormetal tubing, and generally measure one-quarterwavelength or more. When a vertical antenna ismounted at the earth’s surface, the ground conductivityis improved by these conductors, whichrun outward from the base of the radiator, and areconnected to the shield of a coaxial feed line. Thegreater the number of radials of a given length, themore the ground loss is reduced. Also, the longerthe radials for a given number, the better. If a verticalradiator is mounted with its base more thanone-quarter wavelength above the earth’s surface,there need only be three or four conductorsmeasuring exactly one-quarter wavelength.See GROUND-MOUNTED VERTICAL ANTENNA,GROUND-PLANE ANTENNA. 2. Pertaining to thedistance from the center of a circle to its periphery.3. Pertaining to the distance from the center of asphere to its surface. 4. Extending or emanatingoutward in a straight line from a defined point.VerticalradiatingelementRadialRadialCoaxialfeed lineradials

576 radial ground • radioactiveradial ground An earth connection composed ofradials buried in the ground.radial lead A lead (pigtail) attached perpendicularto the axis of a component, such as a resistor orcapacitor.radian Abbreviation, rad. The angle at the center ofa circle subtended by an arc whose length isequal to the radius. Equal to approximately57.2958 degrees.radiance The radiant flux emitted by an object. Radianceis measured in terms of the amount of energycontained in a unit solid angle (steradian)with the source at the apex.radians-to-degrees conversion The conversion ofradian angular measure into degrees. To changeradians to degrees, multiply the number of degreesby 57.2958. Thus, 0.7854 radian = 45 degrees.Compare DEGREES-TO-RADIANS CON-VERSION.radiant efficiency The ratio of the radiant energyemitted by a source to the energy consumed bythe source. The radiant energy is generally specifiedwithin a certain range of wavelengths. An exampleis the incandescent light bulb, which hasrelatively low radiant efficiency in the visiblespectrum between about 750 and 390 nanometers.radiant energy 1. Any form of energy emitted by asource and propagated through space as an electromagneticdisturbance. Included are radiowaves, infrared, visible light, ultraviolet, X rays,and gamma rays. 2. Electromagnetic disturbancesat infrared and shorter wavelengths.radiant flux The rate at which radiant energy isemitted.radiation 1. The emission of energy or particles(e.g., waves from an antenna, X rays from an X-ray tube, energy from a radioactive material, heatfrom a body, etc.). 2. Radio waves, infrared, visiblelight, ultraviolet, X rays, or gamma rays.3. Ionizing emissions from radioactive substances(e.g., alpha particles, beta particles, neutrons,gamma rays, etc.).radiation angle The horizontal or vertical angle atwhich electromagnetic waves are radiated froman antenna. Measured between the central axis ofthe main lobe and the horizon, or between thecentral axis of the main lobe and geographicnorth.radiation belts See VAN ALLEN RADIATIONBELTS.radiation counter An instrument used for determiningthe intensity of atomic-particle radiation,X rays, or gamma rays. It operates by means ofionization of a gas in a sealed tube.radiation field The portion of the electromagneticfield that is propagated by a radiator, as opposedto the induction field.radiation intensity For a directional radio transmittingantenna, the radiated power per steradianin a given direction.AntennaAverage terrain(horizontal)radiation angleMaximumradiationAngleradiation loss Loss of energy through radiationfrom a conductor. Also see LOSS.radiation pattern A graphical representation ofthe intensity of the electromagnetic field in variousdirections from a radiator, such as a transmittingantenna. It is usually shown in either thehorizontal plane or a specific vertical plane containingthe antenna. Also see LOBE.radiation physics The study of radiation and itseffects on matter. Radiation physics is especiallyconcerned with ionizing radiation, but it can involveany kind of particle or electromagnetic energy.radiation pressure Pressure exerted on a surfaceby impinging electromagnetic radiation.radiation resistance The inherent resistance atthe feed point of a resonant radio antenna.radiation sickness General physiological symptomsresulting from a short-term overdose ofX rays, gamma rays, or atomic-particle radiation.radiator 1. The element of an antenna from whichradio energy is directly radiated, as opposed tothe transmission line, lead-in, reflector, or director.2. See LOUDSPEAKER.radio 1. Wireless electrical communication, i.e., bymeans of electromagnetic waves. 2. See RADIORECEIVER. 3. See RADIO TRANSCEIVER. 4. SeeRADIO TRANSMITTER. 5. To communicate by radio.radio- 1. A prefix meaning “pertaining to wirelesselectrical communication.” Examples: radiotelephoneand radiotelegraph. 2. A prefix meaning“using radio waves.” Examples: radiosonde, radiolocator,and radiothermics. 3. A prefix meaning“pertaining to using or possessing radioactivity,”or “pertaining to X rays.” Examples: radiograph,radioisotope, and radiologist.radioactive Having the property of emitting alpha,beta, and (sometimes) gamma rays as the resultof nuclear disintegration. Also see HALF-LIFE.

adioactive element • radio-frequency choke 577radioactive element A chemical element that isRADIOACTIVE (e.g., uranium). Also called radioelement.radioactive isotope See RADIOISOTOPE.radioactive tracer A quantity of radioactive materialput into a system so that its path can be monitoredby means of a radiation detector. Anexample is the introduction of radioactive bariuminto the large intestine. The flow and concentrationof the barium gives an indication of the functioningof the lower intestine.radioactive transducer A pickup device for detectingand measuring radioactivity (e.g., Geiger-Mueller tube).radioactivity counter See GEIGER COUNTERand SCINTILLATION COUNTER.radio altitude See RADAR ALTITUDE.radio amateur An electronics hobbyist licensed tooperate two-way wireless communications stationsin various assigned frequency bands, withoutreceiving payment for services rendered.Radio Amateur Civil Emergency System Abbreviation,RACES. A civil-defense organization of licensedamateur radio stations. Also see RADIOAMATEUR.radio astronomy The observation, study, andanalysis of radio-frequency electromagnetic emissionsfrom bodies or points in space, and thestudy of these bodies through their radiations.radioautograph See AUTORADIOGRAPH.radio beacon 1. A radio transmitter of directionfindingor guidance signals. 2. Also called radiobeam. The signals transmitted by a radio beacon,as defined in 1.radio beam 1. Antenna radiation focused in onedirection. 2. See RADIO BEACON, 2.radiobiology A field of biology concerned with theinfluence of radiant energy or radioactivity on livingorganisms.radio broadcast A radio transmission directed tonumerous, nonspecific receivers—especially by astation in the broadcast service. Also called RA-DIOCAST. Also see BROADCAST SERVICE, 1, 2.radio car An automobile equipped with a two-wayradio.radio carbon Radioactive carbon (i.e., carbon 14).radiocast See RADIO BROADCAST.radio channel A single, usually narrow radiofrequencyband within a larger band, in whichstations are authorized to transmit signals of aspecified type. Also see CHANNEL, 1; CHANNELSEPARATION; and CHANNEL WIDTH.radiochemistry The chemistry of radioactive substances.radio communication Wireless communicationcarried on by means of radio-frequency electromagneticwaves.radio compass See DIRECTION FINDER.radioconductor A substance or body whose electricalconductivity is affected by radio waves, andthat can be used as a sensor of such waves.radio control See REMOTE CONTROL.radio direction finder See DIRECTION FINDER.radio Doppler 1. A change in the frequency of a radiosignal emitted by a source having radial motion,with respect to the receiver. 2. An electronicdevice used to measure radial speed by means ofthe Doppler effect at radio frequencies.radio-electronics The branch of electronics specificallyinvolved with wireless communications.radioelement See RADIOACTIVE ELEMENT.radio engineer A trained professional skilled in thephysics and mathematics of radio communications,and in the theory and application of basicelectronics engineering and related subjects. Alsosee RADIO ENGINEERING.radio engineering The branch of electronics engineeringdevoted to the theory and operations ofradio communication.radio field strength The intensity of radio wavesat a given point. Also see FIELD INTENSITY, 2and RADIO MAP.radio frequency Abbreviation, RF. 1. Consistingof, or pertaining to, alternating currents at frequenciesabove about 9 kHz (the lowest allocatedradio communications frequency). 2. Consistingof, or pertaining to, electromagnetic fields whosewavelengths are longer than those of infrared,but shorter than about 33 kilometers (correspondingto a frequency of 9 kHz). Also see RA-DIO SPECTRUM.radio-frequency amplifier 1. In a superheterodynecircuit, the channel in which the incomingsignal is amplified. Compare INTERMEDIATE-FREQUENCY AMPLIFIER. 2. Broadly, an amplifierof radio-frequency signals.radio-frequency choke Abbreviation, RFC. A lowinductancecoil used to block radio-frequency(RF) alternating currents. Many RF chokes haveair cores; some have cores of ferrite or powderediron.In(General bipolar circuit)+12 Vradio-frequency amplifier, 2Out

578 radio-frequency current • radiolocationradio-frequency current Symbol, I RF . 2. The intensityof a generated radio-frequency (RF) signal,usually expressed in microamperes. 2. Loosely,any measurable RF signal.radio-frequency heating The generation of heat inan object by an intense radio-frequency electromagneticfield. See, for example, DIATHERMY, 1;DIELECTRIC HEATING; and INDUCTION HEAT-ING.radio-frequency interference Abbreviation, RFI.1. Annoying electrical noise in radio-frequency(RF) amplifiers, detectors, and instruments.2. Undesired RF signals that compete with desiredones in amplifiers, receivers, and instruments.3. The unwanted interception and demodulationof a strong RF signal by an audio-frequency (AF)device, such as a telephone set or high-fidelitystereo amplifier.radio-frequency meter An instrument for measuringsignals of RADIO FREQUENCY (9 kHz andabove).radio-frequency oscillator Abbreviation, RFO. Anoscillator (self-excited or crystal-controlled) foroperation at radio frequencies. In such an oscillator,stray components, efficiency, and generallosses are of primary concern. Also see RADIOFREQUENCY.radio-frequency power Symbol, P RF . Alternatingcurrentpower at radio frequencies.radio-frequency resistance The total in-phase resistanceexhibited by a conductor at radio frequencies.This opposition to current includesdirect-current resistance and the in-phase componentscaused by skin effect, shielding, and thepresence of dielectrics.radio-frequency selectivity The selectivity of a radio-frequency(RF) channel, such as the RF amplifierand first detector of a superheterodynecircuit.radio-frequency transformer Abbreviation, RFtransformer. A device used for the purpose ofimpedance matching, antenna tuning, or interstagecoupling at frequencies above the range ofhuman hearing (approximately 20 kHz and up).The device might consist of solenoidal windingswith an air core, solenoidal windings with apowdered-iron or ferrite core, or toroidal windingswith a powdered-iron or ferrite core. Thewindings are designed to minimize distributedcapacitance and direct-current resistance.When no reactance is present, the impedancetransferratio is equal to the square of the turnsratio. Compare AUDIO-FREQUENCY TRANS-FORMER.radio-frequency transistor 1. A transistor capableof providing significant amplification at radiofrequencies. 2. A transistor operable at frequenciesabove 100 kHz.radiogenic Produced by radioactivity.radiogoniometer A radio compass (see DIREC-TION FINDER and GONIOMETER, 1).radiogram A (usually printed out) message transmittedand received via radiotelegraphy or radioteletype.The term is an acronym for radiotelegram.radiograph 1. To contact by sending a RADIO-GRAM. 2. An X-ray photograph.radio homing 1. A method of homing that uses thetracking of a target on the basis of a radio signalemitted by that target. 2. A method of keeping amissile on track via radio remote control.radio interference 1. Interference to radio communication,from whatever cause. 2. See RADIO-FREQUENCY INTERFERENCE.radioisotope A radioactive isotope (natural or artificial)of a normally nonradioactive chemical element(e.g., radioactive carbon). Also see ISOTOPE.radio jamming See JAMMING.radio knife A surgical instrument consisting essentiallyof a needle that forms a high-frequency arc.The arc simultaneously cuts and cauterizes tissue.radiolocation A process whereby the position of avehicle, aircraft, or ocean-going vessel is determined.The simplest method is the directionalmethod. Two or three fixed receiving stations areused. Radio direction-finding (RDF) equipment isemployed at each station, in conjunction with atransmitter aboard the vessel, to establish thebearings of the vessel with respect to each station.Radar can also be used to locate vessels. Inwartime, enemy craft can sometimes be locatedby visual or infrared apparatus. Satellites can locateenemy ships and missiles, in some caseswith an error smaller than the length of the vesselitself. Compare RADIONAVIGATION.ReceiverXReceiver ZVesselradiolocationReceiverY

adiolocator • radio spectroscope 579radiolocator See RADAR.radiological system See X-RAY THERAPY SYS-TEM.radiologist A specialist skilled in RADIOLOGY.radiology The science embracing the theory anduse of X rays and radioactive substances in thediagnosis and treatment of diseases and ailments.radiolucency 1. The property of a material that allowsionizing radiation to pass through it with littleor no absorption. 2. The extent to which amaterial transmits ionizing radiation.radioluminescence Visible light emitted from a radioactivematerial. A good example is radium; itwas once used on wristwatch dials so that theycould be seen in the dark.radiolysis Chemical decomposition brought aboutby radiation.radioman A radio technician or operator.radio map A map of a geographic area, on whichlines are drawn connecting measured points ofequal field strength for signals from a radio stationat the approximate center of the area.radiometeorograph See RADIOSONDE.radiometer A device for detecting and measuringthe strength of radiant energy. One form consistsof a set of vanes blackened on one side andmounted on pivots in a partially evacuated glassbulb. Visible light or infrared causes the vane assemblyto rotate, the speed being proportional tothe intensity of the light.GlassenveloperadiometerLightradiometry The science and art of measuring radiationin the infrared, visible, and ultraviolet regionsof the electromagnetic frequency spectrum.Compare PHOTOMETRY.radio micrometer See MICRORADIOMETER.radionavigation The use of radio apparatus, usuallyin conjunction with computers, by personnelaboard moving vessels, for the purpose of plotting,correcting, and maintaining a course. The intersecting-linemethod is simplest. Two or threeland-based transmitters are needed. Their locationsmust be accurately known. A directionfindingdevice on the vessel is used to determinethe bearings of each of the transmitters. Aircraftradionavigation can be performed with the aid ofradar. The most sophisticated radionavigationtechniques employ the Global Positioning System(GPS). Computers are used to project the courseof a craft based on its current position, its speed,and the direction of its movement. Course correctionsare made by choosing the desired courseand having the computer calculate speed and/ordirection changes. Compare RADIOLOCATION.radio net A group of radio stations operating togetherin an organization, often on or near thesame frequency.radio network See RADIO NET.radio operator A technician licensed to operate atransmitter in the radio, television, or radar services.radiopaque Opaque to X rays or other ionizing radiation.Compare RADIOPARENT.radioparent Transparent to X rays or other ionizingradiation. Compare RADIOPAQUE.radiophone See RADIOTELEPHONE.radiophoto A photograph transmitted and receivedby radio. Also see FACSIMILE.radio pill See ENDORADIOSONDE.radio prospecting The use of radio-frequency devicesto locate underground or underwater metalsand mineral deposits. Also see METAL LOCATOR.radio range A radio station providing navigationalaid to airplanes.radio receiver The complete apparatus that selects,amplifies, demodulates, and reproduces aradio signal for purposes of communication, asdistinct from facsimile receiver, remote-control receiver,telemetry receiver, television receiver, etc.radiosensitivity 1. The property of being sensitiveto ionizing radiation. Most photographic filmshave this property. 2. The extent to which a substanceor device is sensitive to ionizing radiation.radio service technician An electronics technicianskilled in the repair and maintenance of radioequipment—especially receivers.radiosonde A balloon-carried combination of radiotransmitter and transducers, for sending to aground monitoring station signals revealing suchatmospheric conditions as temperature, humidity,and pressure. It is used mainly for gatheringmeteorological data at high altitudes.radiosonobuoy See SONOBUOY.radio spectroscope A device used by radio astronomersto obtain the radio-frequency profile ofa distant star or galaxy. It generally consists of a

580 radio spectroscope • radiothermicsgraph, obtained by scanning the radio spectrumand plotting signal intensity as a function of frequencyor wavelength.radio spectrum The continuum of frequenciesuseful for radio communication and control.Classified in the following manner: Very low frequency(VLF), 9 to 30 kHz; low frequency (LF), 30to 300 kHz; medium frequency (MF), 300 to 3000kHz; high frequency (HF), 3 to 30 MHz; very highfrequency (VHF), 30 to 300 MHz; ultrahighDecimillimetricMillimetricCentimetricDecimetricMetricDecametricHectometricKilometricMyriametricToinfrared,visible light,ultraviolet, X rays,gamma rays0.1 mm 3 THz1 mm 300 GHz1 cm 30 GHz10 cm 3 GHz1 m 300 MHz10 m 30 MHz100 m 3 MHz1 km 300 kHz10 km 30 kHz30 km 10 kHz100 km 3 kHzTo lower audioand subaudioradio spectrumEHFSHFUHFVHFHFMFLFVLFMicrowavesfrequency (UHF), 300 to 3000 MHz; super high frequency(SHF), 3 to 30 GHz; extremely high frequency(EHF), 30 to 300 GHz.radiostat See CRYSTAL FILTER.radio station 1. The location at which a radiotransmitter and/or receiver is/are installed.2. The complete set of equipment for a radio receivingand/or transmitting installation, includingthe studio, linking apparatus, and antennas. 3. Astandard broadcast station.radio technician A professional skilled in the construction,testing, repair, and maintenance of radioequipment, and sometimes in its design, and whousually works under the supervision of a radio engineer.Also see RADIO SERVICE TECHNICIAN.radiotelegram See RADIOGRAM.radiotelegraph 1. Pertaining to the theory and applicationof, and the equipment for, Morse codetransmission and/or reception via radio. 2. Aninstallation for Morse code transmission and/orreception via radio. 3. The transmission and/orreception of Morse code signals via radio.radiotelegraph code See CONTINENTAL CODE.radiotelegraph distress signal See SOS.radiotelegraph monitor See KEYING MONITOR.radiotelegraphy The transmission and/or receptionof telegraphic communications, usuallyMorse code, by means of radio.radiotelephone 1. Pertaining to the theory and applicationof, and the equipment for, voice transmissionand/or reception via radio. 2. Aninstallation for voice transmission and/or receptionvia radio. 3. The transmission and/or receptionof voice signals via radio.radiotelephone distress signal See MAYDAY.radio/telephone patch See PHONE PATCH.radiotelephony The transmission and/or receptionof audio signals, usually human voices, bymeans of radio.radio telescope A directional antenna and associatedequipment for receiving and evaluating theradio-frequency electromagnetic radiation fromspace—especially from celestial objects (such asthe sun, planets, stars, nebulae, galaxies,quasars, etc.). See RADIO ASTRONOMY.radioteletype 1. Pertaining to the theory and applicationof, and the equipment for, text datatransmission and/or reception via radio. 2. Aninstallation for text data transmission and/or receptionvia radio. 3. The transmission and/or receptionof text data signals via radio.radioteletypewriter A teletypewriter adapted toradio, rather than wire service; it is used in someRADIOTELETYPE installations. In recent years,personal computers and terminals have largelyreplaced adapted teletypewriters for this purpose.radiotherapy The use of X rays and/or radioactivesubstances in the treatment of disease and disorders.radiothermics The science of the generation ofheat by means of radio-frequency current.

adiothermy • random feed 581radiothermy See DIATHERMY.radio thorium Radioactive THORIUM.radiotracer See TRACER.radio transceiver A RADIO RECEIVER and RADIOTRANSMITTER built into a single unit, and generallyintended for use in two-way communication.radio transmitter The complete apparatus thatgenerates radio-frequency power, modifies it withthe data needed for communication, and deliversthe product to an antenna for radiation intospace. Here, the radio transmitter is distinguishedfrom similar equipment: facsimile transmitter,remote-control transmitter, telemetrytransmitter, television transmitter, etc.radio-transparent material 1. A substancethrough which radio waves pass with little or noattenuation. 2. A substance through whichX rays, gamma rays, or high-speed subatomicparticles can pass with little or no attenuation.radiotrician Acronym for radio electrician. See RA-DIO SERVICE TECHNICIAN.radio tube 1. A VACUUM TUBE used at radio frequencies.2. A vacuum tube used as an amplifier,local oscillator, detector, or mixer in an early radioreceiver.radiovision See TELEVISION.radio watch See WATCH.radio waves Electromagnetic waves in the RADIOSPECTRUM.radio window That portion of the radio-frequencyelectromagnetic spectrum that passes throughthe atmosphere, rather than being refracted orabsorbed. The wavelength range is about 20 metersto 5 millimeters, or 15 MHz to 60 GHz. Thelower limit of this range is affected by ionosphericconditions. The upper frequency limit depends onvarious factors, including relative humidity anddust content of the air.radium Symbol, Ra. A rare radioactive metallicelement. Atomic number, 88. Atomic weight,226.025.radius The straight-line distance from the center ofa circle or sphere to its periphery.radius vector In spherical or polar coordinates, aline segment drawn from the pole, or origin, andrepresenting the vector magnitude.radix The number indicating the number of symbolsin a system of numerical notation, and thepowers of which give the place values of the system.Thus, 10 is the radix of the decimal system,and 2 is the radix of the binary system. Alsocalled BASE.radix point In a number, the point (dot or period)separating the integral and fractional digits. Itsspecific name depends on the system of notationinvolved: binary point, decimal point, etc.radome A plastic shell housing a radar antenna—especially aboard an aircraft.radon Symbol Rn. A gaseous radioactive elementthat results from the disintegration of radium.Atomic number, 86. Atomic weight, 222.rad/s Abbreviation of radians per second, the SIunit of angular velocity.rad/s 2 Abbreviation of radians per second squared,the SI unit of angular acceleration.radux A continuous-wave, low-frequency radionavigationsystem. Position is determined by comparingthe phase of two signals sent fromdifferent locations.RAID Acronym for REDUNDANT ARRAY OF INDE-PENDENT DISKS.rainbow generator A test-signal generator thatproduces a full color spectrum, a pattern resemblingthe successive coloration of a rainbow, onthe screen of a color-television receiver. Also seeRAINBOW PATTERN.rainbow pattern A test pattern for servicing acolor-television receiver. It consists of a full colorspectrum, thus taking its name from its resemblanceto a rainbow. Also see RAINBOW GENER-ATOR.RAM Abbreviation of RANDOM-ACCESS MEM-ORY.ramp A sawtooth wave with a linear rise and apractically instantaneous decay; its name wasderived from its resemblance to an incline.AmplituderampTimeramp generator A test-signal generator that producessawtooth-wave signals. Also see RAMP.R and D Abbreviation of research and developmentor research and design. (Also, R&D.)random access Abbreviation, RA. In computer anddata-processing operations, pertaining to storageor memory in which data can be recovered in anyorder.random-access memory In computer and dataprocessingsystems, a memory providing accesstime that is independent of the address.random deviation Irregular RIPPLE.random-fed antenna An antenna that uses RAN-DOM FEED.random feed A method of connecting a transmissionline to an antenna, wherein the feed point isnot necessarily at the center and not necessarilyat a current loop or voltage loop. This techniqueis rarely used; it generally results in some radiationfrom the feed line.

582 random noise • ratio detectorrandom noise Electrical noise in which the pulsesor fluctuations have no discernible pattern of occurrence(i.e., they are haphazard in frequencyand amplitude).random number A number derived by chance. It isused in statistical analysis for various purposes.random number generator Hardware or softwarethat provides a sequence of numbers or digitsthat are random for the purpose of a given statisticalapplication.random occurrence See CHANCE OCCURRENCE.random variable In statistics, a variable that canhave a number of values, each of the same probability.random winding A coil winding in which the turnsare wound haphazardly to reduce distributed capacitance.range 1. The limits within which a circuit or deviceoperates (i.e., the territory defined by such limits).Examples: current range, frequency range,and voltage range. 2. The difference between theupper and lower limits of deflection of a meter.3. The distance over which a transmitter operatesreliably. 4. A clear area for testing antennas.5. The distance between a radar station and atarget. 6. The possible values for a quantity orfunction that lie between given limits.range capacitor See TRIMMER CAPACITOR.range-height indicator Abbreviation, RHI. A radardisplay in which the horizontal axis shows distanceto the target, and the vertical axis shows elevationof the target.range mark See DISTANCE MARK.range plotting The creation of a graph of the distance(range) to objects, as a function of directionor orientation in two or three dimensions. Commonlyused in robot guidance systems.range resistor See TRIMMER RESISTOR.range sensing The measurement of distances toobjects via electronic methods such as radar,sonar, vision systems, etc. Commonly used inrobot guidance systems.ranging 1. Any means of determining the distancefrom a station or vehicle to an object or objects.2. Any of several methods for a vehicle, vessel,aircraft, spacecraft, or robot to navigate in its environmentby measuring, and keeping track ofchanges in, the distance between itself and one ormore objects or beacons.rank 1. To arrange in a specific sequence accordingto significance. 2. A place in such a sequence.Rankine scale A temperature scale on which thefreezing point of water is 491.69 degrees, and theboiling point 671.69 degrees. Absolute zero isrepresented by 0 degrees. For conversion tokelvins, multiply degrees Rankine by 5/9.rapid drift A fast change of a quantity or setting(usually in one direction) with time.rapid printer See QUICK PRINTER.raser A device that produces coherent electromagneticwaves at radio frequencies; the radiofrequencyequivalent of a LASER.raster The rectangle of light (composed of unmodulatedlines) seen on the screen of a televisionpicture tube when no signal is present.ratchet circuit See COMMUTATOR, 2 and ELEC-TRONIC RATCHET.rate action See DERIVATIVE ACTION.rate effect In a four-layer semiconductor device,the tendency for the switch to conduct undesirablyas a result of a transient spike.rate-grown transistor See GRADED-JUNCTIONTRANSISTOR.rate gyro A special gyroscope for measuring angularrates.rate of change 1. The extent to which the value ofa dependent variable changes in accordance witha specified change in an independent variable(usually time). 2. A quantitative expression of thespeed with which a dependent variable changes,with respect to an independent variable (usuallytime).rate signal A signal whose amplitude is proportionalto the derivative of a variable, with respectto time.rate time In automatic-control operations, thetime over which the addition of DERIVATIVE AC-TION advances PROPORTIONAL ACTION.ratio-arm bridge A simple four-arm bridge inwhich the balancing potentiometer supplies thetwo arms, one on each side of the slider at allsettings.R xDetR sR a R bR x = R aR bR sratio-arm bridgeratio arms Two impedance arms serving to establishthe numerical ratio of a bridge circuit.ratio control In automatic-control operations, asystem in which the controlled variable is in aprescribed ratio to another variable.ratio detector A frequency-modulation (FM) seconddetector resembling the FOSTER-SEELEYDISCRIMINATOR, except that one of the two

atio detector • reactance 583diodes is reversed and the junction point of theload resistors is grounded. In an FM circuit usinga ratio detector, no limiter is required. The ratio ofthe direct-current outputs is proportional to theratio of the instantaneous signal voltages appliedto the two diodes.ratio meter An instrument that compares two differentsignals (and indirectly their sources) anddelivers a reading of their ratio.rational number A number that can be expressedin the form a/b, where a and b are integers and bis not equal to zero.rational operation Any of the conventional arithmeticoperations: multiplication, division, addition,or subtraction.ratio of geometric progression In a geometricprogression, the ratio of one value to the next.ratio of similitude The ratio of the lengths of correspondingsides in similar geometric figures.rat race See HYBRID RING.raven red A variety of red oxide of iron, a commercialred paint used as the magnetic coating ofearly recording tapes.raw ac Unrectified alternating current (ac) or voltage.raw data Data that has not been processed in anyway.rawinsonde A RADIOSONDE tracked by a radio directionfinder to determine wind velocity. Thename is an acronym from radar wind radiosonde.raw tape See BLANK TAPE.ray 1. A line of radiant energy. Such a line (e.g.,the path of a single photon of visible light) isimagined to arise from a point source and havezero width. 2. A thin beam of radiant energy(e.g., the beam of electrons in a cathode-raytube). 3. A quantity of radiant energy or ionizingradiation (e.g, gamma ray). 4. One of numerouslines converging toward, or emanating from, aspecific point. 5. A vector representing the directionin which an electromagnetic field or acousticdisturbance travels. 6. Also called half line.The set of points on a line consisting of a definedorigin and all the points on one side of the origin.Example: the positive reactance axis in an AR-GAND DIAGRAM.Raydist A continuous-wave, medium-frequencyradionavigation system. The position is determinedaccording to the phase difference betweentwo signals transmitted from different locations.Rayleigh-Carson theorem An expression of thereciprocal relationship between the transmittingand receiving properties of an antenna. If voltageE applied to antenna A causes current I to flow ata given point in antenna B, then the same voltage(E) applied at that point in antenna B will produceidentical current I (same magnitude and phase)at the point in antenna A, where voltage Eoriginally was applied. Also see RECIPROCITYTHEOREM.Rayleigh distribution A probability-density function,used to describe the behavior of sky-waveelectromagnetic signals.Rayleigh’s law The hysteresis loss in a magneticmaterial varies in proportion to the cube of themagnetic induction.Rb Symbol for RUBIDIUM.R B Symbol for BASE RESISTANCE. (Also, r B .)RC 1. Abbreviation of RESISTANCE-CAPACI-TANCE. 2. Abbreviation of RADIO-CON-TROLLED. 3. Abbreviation of REMOTE CONTROL.R c 1. Symbol for COLLECTOR RESISTANCE. (Also,r C .) 2. Symbol for COLD RESISTANCE.RCA jack See PHONO JACK.RCA plug See PHONO PLUG.RC circuit See RESISTANCE-CAPACITANCE CIR-CUIT.RC-coupled amplifier See RESISTANCE-CAPACI-TANCE-COUPLED AMPLIFIER.RC coupling See RESISTANCE-CAPACITANCECOUPLING.RC filter See RESISTANCE-CAPACITANCE FILTER.RCL 1. Abbreviation of RECALL. 2. Abbreviation ofRESISTANCE-CAPACITANCE-INDUCTANCE.RCM Abbreviation of RADAR COUNTERMEA-SURES. (Also, radCM.)RC phase shifter See RESISTANCE-CAPACI-TANCE PHASE SHIFTER.RC time constant See RESISTANCE-CAPACI-TANCE TIME CONSTANT.RCTL Abbreviation of RESISTOR-CAPACITOR-TRANSISTOR LOGIC.RC tuning See RESISTANCE-CAPACITANCE TUN-ING.RCV Abbreviation for receive. (Also, rcv.)RCVR Abbreviation for RECEIVER. (Also, rcvr, rx.)rd Abbreviation for rutherford.R & D See R AND D.R D Symbol for DRAIN RESISTANCE.R d 1. Symbol for DIODE RESISTANCE. (Also, r d .)2. Symbol for DISTRIBUTED RESISTANCE.R-DAT Abbreviation of ROTARY DIGITAL AUDIOTAPE.R dc Symbol for DC RESISTANCE. (Also, r dc .)RDF Abbreviation of RADIO DIRECTION FINDER.Re Symbol for RHENIUM.R e Symbol for EMITTER RESISTANCE. (Also, r E .)REA Abbreviation of Rural Electrification Administration.reachthrough See PUNCHTHROUGH.reachthrough region See PUNCHTHROUGH RE-GION.reachthrough voltage See PUNCHTHROUGHVOLTAGE.reactance Symbol, X. Unit, ohm. The oppositionoffered to the flow of alternating current by purecapacitance, pure inductance, or a combinationof the two. Reactance introduces phase shift. Alsosee CAPACITIVE REACTANCE and INDUCTIVEREACTANCE. Compare RESISTANCE.

584 reactance chart • readthroughreactance chart A nomograph for capacitance, inductance,and frequency.reactance factor The ratio of the alternatingcurrentresistance of a conductor to the directcurrentresistance. The reactance factor generallyincreases as the frequency increases because ofskin effect and because the length of the conductormight be a sizable part of the wavelength ofthe transmitted energy.reactance modulator A frequency modulator usinga variable reactance, usually a varactor diodein the oscillator.AFin− +Varactorbiasreactance modulatorToosc.Circuitreactance transistor A transistor used as a REAC-TANCE MODULATOR.reaction-time meter See NEOMATACHOGRAPHand NEOMATACHOMETER.reactive absorber In acoustics, a device that dissipatesimpinging sound waves by means of reflection,resonance, and other effects, besidesdissipation in the form of heat.reactive attenuator An attenuator that functionsby means of reactance, rather than by means ofresistance.reactive current The component of alternatingcurrent that is not in phase with the voltage.Compare RESISTIVE CURRENT.reactive kilovolt-ampere Abbreviation, kVAR. Aunit of high apparent power; it is the product ofkilovolts and amperes in a reactive component ofa circuit. Also see APPARENT POWER, KILO-VOLT-AMPERE, REACTIVE VOLT-AMPERE, andVOLT-AMPERE.reactive load 1. A load device that is capacitive orinductive, rather than resistive. 2. A load devicethat contains reactance as well as resistance.reactive power See REACTIVE KILOVOLTAM-PERE and REACTIVE VOLT-AMPERE.reactive volt-ampere Abbreviation, VAR. A unit ofapparent power; it is the product of volts and amperesin a reactive component of a circuit. Also seeAPPARENT POWER, KILOVOLT-AMPERE, REAC-TIVE KILOVOLT-AMPERE, and VOLT-AMPERE.reactor 1. An inductor, especially one having verylow internal resistance, used principally for its inductivereactance. 2. A chamber in which the nucleiof atoms are split to provide atomic energy.Also see NUCLEAR REACTOR. 3. In industrialchemistry, a vat in which reactions take place.read 1. In computer operations, to extract datafrom memory or a storage medium and (usually)transfer it to another area of memory or othermedium. Compare WRITE. 2. In digital communications,to transcribe data into printed form. 3. Inradiotelegraphy, to listen to Morse-code signalsand comprehend the text without necessarilywriting it down. 4. To observe and note the indicationof an instrument, such as a meter.readability In electronic communications, the degreeto which a desired signal can be recognizedand interpreted in a given context.readback In a multiplexer, a feature that facilitatesinspection of the contents of the control latch.reader A device that transcribes digital signals ormarkings into meaningful data. Examples:Morse-code reader and bar-code reader.read head In a magnetic memory or in a taperecorder or wire recorder used for data recording,the head that picks up the magnetic pulses fromthe drum, tape, disk, or wire. Compare WRITEHEAD.reading rate The number of input characters persecond that a computer or other data-processingdevice handles.read-only memory Abbreviation, ROM. In a computeror calculator, a memory unit in which instructionsor data are permanently stored for useby the machine or for reference by the user. Thestored information is read out nondestructively.readout lamp An electron tube containing severalcathodes, filled with a gas (such as neon), andused as a numeric or alphanumeric display device.Each cathode is connected to a separate pinon the base. A single anode is common to allcathodes. The cathode(s) to which a voltage is appliedglow(s), showing the shape of a numeral, letterof the alphabet, or other symbol. In recentyears, this type of display has been replaced bylight-emitting diodes (LEDs) and liquid-crystaldisplays (LCDs).readout pulse In a random-access memory (RAM),a pulse applied to the word line, facilitating readoutof the information in a certain storage slot.read pulse In computer operations, a pulse thatactivates the read function (see READ). CompareWRITE PULSE.read rate The number of data units an input readdevice can transcribe per unit of time [e.g., bitsper second (bps) and words per minute (wpm)].readthrough 1. The reception of signals betweentransmitted pulses at the same frequency.2. The continuous monitoring of a signal beingjammed. Any change in the frequency, modulation,or other characteristics of the signal can

eadthrough • receiver front end 585then be detected, and the jamming signaladjusted accordingly.read time The period during which data is beingtransferred from a computer storage unit.read-write channel In computer operations, achannel over which activity between a centralprocessing unit and a specific peripheral occurs.read-write head An electromagnetic transducerused for both reading and writing data. See READand WRITE.read-write memory 1. A small data storage bankfor short-term use. The contents of the memoryare easily changed. 2. See RANDOM ACCESSMEMORY.real address See ABSOLUTE ADDRESS.real axis The axis of the real-number component ofa COMPLEX NUMBER (i.e., the horizontal axis inan ARGAND DIAGRAM).real component The real-number part of a COM-PLEX NUMBER.real image The image formed on a screen whenrays from the object converge on passing througha lens. Compare VIRTUAL IMAGE.ObjectLensreal imageScreenImagereal number A number in the category that includeszero, all rational numbers, and all irrationalnumbers. Also see COMPLEX NUMBER,IMAGINARY NUMBER, IRRATIONAL NUMBER,and RATIONAL NUMBER.real power The apparent power multiplied by thepower factor in an alternating-current circuitcontaining reactance. Real power is the differencebetween the apparent power and the reactivepower. Actual radiated or dissipated power cannotexceed the real power.real time Pertaining to the operation of a computer,communications, or data processing system inwhich events are represented or acted on as theyoccur. Data is processed as it becomes available,usually through the use of time-sharing, directaccessstorage devices, and remote terminals.real-time clock A device that produces periodicsignals that reflect the interval between events. Itis sometimes used to indicate time of day.rear end The low-frequency portion of a superheterodynereceiver (i.e., the intermediatefrequencyamplifier, second detector, andaudio-frequency amplifier). Compare FRONT END.rear projection A method of big-screen televisionpicture reproduction. The image is focused onto atranslucent, flat surface. The viewer is positionedon the side of the screen opposite to the projectingbeam.Reaumur scale A thermometer scale on which zerois the freezing point of water and 80 degrees is theboiling point of water. Compare ABSOLUTESCALE, CELSIUS SCALE, FAHRENHEIT SCALE,and RANKINE SCALE.rebecca The airborne interrogator in the BritishREBECCA-EUREKA SYSTEM.rebecca-eureka system A British 90-milehoveringradar navigation system that consists ofan airborne interrogator (rebecca) and a groundtransponder beacon (eureka).rebroadcast The retransmission of a radio broadcastsimultaneously by a station other than theoriginator. Also see AUTOMATIC RELAY STATION.rebroadcast station See AUTOMATIC RELAY STA-TION.recalescence During the cooling of a metal, thesudden release of heat. Also see RECALESCENTPOINT. Compare DECALESCENCE.recalescent point In a metal whose temperature isbeing lowered from a higher value, the temperatureat which heat is suddenly released. CompareDECALESCENT POINT.recall Abbreviation, RCL. In computers and calculators,an instruction that brings material fromthe memory for examination or use. The oppositeinstruction is STORE.receiver 1. A device or system operated at the destinationend of a communication link; it accepts asignal and processes or converts it for local use.Also see specific entries for various types of receiver.2. The earpiece of a telephone. 3. A radiobroadcast-band tuner integrated with a generalpurposepreamplifier and power amplifier, andcontaining standard jacks for input and output ofaudio signals to and from peripheral equipment.receiver detector In a wireless communications orbroadcast receiver, a circuit that extracts the informationfrom the signal. The design depends onthe type of emission to be received. See also DIS-CRIMINATOR, ENVELOPE DETECTOR, PHASE-LOCKED LOOP, PRODUCT DETECTOR, RATIODETECTOR.receiver dynamic range A quantitative measure ofthe ability of a wireless receiver to maintain afairly constant output, and yet to maintain itsrated sensitivity, in the presence of signals rangingfrom very weak to extremely strong. This figure isspecified in decibels. It is typically 100 dB or morein a well-engineered communications receiver.receiver front end The portion of a wireless communicationsor broadcast receiver consisting ofthe first radio-frequency (RF) amplifier, and oftenalso including bandpass filters between this amplifierand the antenna. The dynamic range andsensitivity of a receiver are determined by the performanceof this stage. These two characteristicsare among the most important for any receiver.

586 receiver front end • recombination rateLow-noise, high-gain amplifiers are the rule.Field-effect transistors are commonly used.receiver IF chain In a wireless communications orbroadcast receiver, the series of radio-frequency(RF) amplifier stages in which most of the gaintakes place. These stages are also where the bestpossible RF selectivity is obtained. The intermediatefrequency (IF) on which the amplifiers worksis a constant frequency. This simplifies the designof the amplifiers to produce optimum gainand selectivity. Crystal-lattice filters or mechanicalfilters are commonly used in these stages toobtain the desired bandwidth and response.receiver mixer In a superheterodyne wireless communicationsor broadcast receiver, a stage thatconverts the variable input signal frequency to aconstant intermediate frequency (IF), or a stagethat converts the first IF to a second IF usuallyhaving a lower frequency. This type of circuit isnonlinear, and combines the signal with a carrierfrom a local oscillator (LO). The output is eitherthe sum or the difference of the signal frequencyand the LO frequency.receiver muting See MUTING, 1.receiver noise figure A quantitative measure of theability of a wireless receiver to respond to desiredsignals while rejecting unwanted noise. This canbe quantified in various ways. In general, thelower the noise figure, the better the sensitivity.Gallium–arsenide field-effect transistors (GaAs-FETs) are well known for the low levels of noisethey generate, even at quite high frequencies.Other types of FETs can be used at lower frequencies.Bipolar transistors tend to be noisy.See also NOISE FACTOR, NOISE FIGURE.receiver post-detector stages In a wireless communicationsor broadcast receiver, one or morestages of amplification and/or filtering employedto refine the detector output to a form suitable forfeeding a speaker, headset, printer, fax machine,slow-scan television picture tube, computer,electromechanical device, or other peripheralequipment.receiver primaries See DISPLAY PRIMARIES.receiver selectivity A quantitative measure of theability of a wireless receiver to respond to a desiredsignal, but not to undesired ones. The frequencywindow is established by a preselector inthe early RF amplification stages, and is honed toprecision by bandpass filters in later amplifierstages. The preselector passes energy within arange of about plus-or-minus 10 percent of thesignal frequency; other frequencies are attenuated.This reduces the chance for strong, out-ofbandsignals to impair the performance ofthe receiver. The narrowband filter in the finalintermediate-frequency (IF) stage responds onlyto energy within the actual signal band. Thisminimizes adjacent-channel interference. Insome receivers, yet another bandpass filter isused in the audio-amplifier stages.receiver sensitivity A quantitative measure of theability of a wireless receiver to recover weak signalsand process them into readable data. Themost common expression is the number of signalmicrovolts that must exist at the antenna terminalsto produce a certain signal-to-noise ratio(S/N). Sometimes, the signal-plus-noise-to-noiseratio (abbreviated S+N/N) is given. The front end,or first RF amplifier stage, of a receiver is themost important stage with regard to sensitivity.Sensitivity is directly related to the gain of thisstage, but the amount of noise the stage generatesis even more significant. A good front endshould produce the best possible S/N or S+N/Nratio at its output. All subsequent stages amplifythe front-end noise output as well as the frontendsignal output.receiving set RADIO RECEIVER.receiving station A station that ordinarily only receivessignals (i.e., it makes no type of transmission).Compare TRANSMITTING STATION.receptacle 1. See SOCKET. 2. The half of a connectorthat is mounted on a support, such as apanel, and that is therefore stationary.recharge In certain cells and batteries, the restorationof chemical energy following use so that thedevice is ready to deliver its full rated electric current.Also see RECHARGEABLE.rechargeable Pertaining to a secondary cell or batterythat can accept a restoration of chemical energyfollowing use, and thus can be completelycharged and discharged numerous times. Examples:nickel-metal-hydride (NiMH) battery andlead-acid battery.reciprocal impedances See INVERSE IMPED-ANCES.reciprocal ohm See SIEMENS and MHO.reciprocation 1. The determination of a mathematicalreciprocal value from a given value.2. The transmission of a message in response toa received message.reciprocity in antennas See RAYLEIGH-CARSONTHEOREM.reciprocity theorem When a voltage E acrossbranch A of a network causes a current I to flowin branch B of the network, the voltage can be appliedacross branch B to cause the same value ofcurrent to flow in branch A. Compare COM-PENSATION THEOREM, MAXIMUM POWERTRANSFER THEOREM, NORTON’S THEOREM,SUPERPOSITION THEOREM, and THEVENIN’STHEOREM.recombination The refilling of holes by electronsin a semiconductor.recombination current In a transistor circuit,base current resulting from recombination.recombination rate In a semiconductor material,the speed at which the electrons and holes recombine.It can be expressed as the timerequired for a certain proportion of charge carriersto recombine.

ecompile • rectified alternating current 587recompile In computer operations, to COMPILEagain, usually according to program amendmentsfollowing debugging, or to create a different formof a program so that it will be compatible withother hardware.record 1. See PHONOGRAPH DISC. 2. A chart deliveredby a graphic recorder. 3. To make one ofthe foregoing. 4. In data processing, a constituentof a file. 5. In data processing, a data unit portrayinga specific transaction.record blocking In data processing operations,making data blocks from groups of records sothat the blocks can, in a single operation, betransferred to a nonvolatile storage medium,such as diskette or tape.record count A usually running total of a file’srecords.recorded disc A phonograph disc on which arecording has been made. Also called PRERE-CORDED DISC.recorded tape Magnetic tape containing recordedmaterial. Also called PRERECORDED TAPE.Compare BLANK TAPE.recorder 1. A machine for preserving sound, video,or data signals in the sequence in which they occur(e.g., DISC RECORDER, TAPE RECORDER,and WIRE RECORDER). 2. A machine for makinga permanent visual record (photographically orby stylus) of an electrical phenomenon. Examples:DRUM RECORDER and OSCILLOGRAPH.record head See RECORDING HEAD.recording density In a magnetic storage medium,the number of information units (bits, bytes, etc.)represented by magnetized areas, per unit area orlength.recording disc A phonograph record on which materialhas not been recorded, or from whichrecorded material has been removed. ComparePRERECORDED DISC.recording head In a magnetic recorder/reproducer,the head that magnetizes the medium inaccordance with sounds or other signals. Alsocalled RECORD HEAD and WRITE HEAD. ComparePLAYBACK HEAD.Recording Industry Association of America Abbreviation,RIAA. An organization that sets standardsfor audio recording and reproduction in theUnited States.recording instrument A measuring instrument,such as a voltmeter or ammeter, that makes apermanent record of its deflections. Also seeRECORDER, 2.recording loss 1. Loss of data during a recordingprocess. 2. Loss resulting from recording efficiencyof less than 100 percent; audio power loss.recording tape Magnetic tape on which nothinghas been recorded, or from which all data hasbeen erased. Compare PRERECORDED TAPE.recovery time 1. Symbol, t r . The time required fora semiconductor pn junction to attain its highresistancestate when the bias voltage is suddenlyswitched from forward to reverse. 2. The time requiredfor a circuit to recover from momentaryoverdrive. 3. The time required for a computersystem to stabilize following a degenerative operation.4. The time required for switching a memoryfrom the write to the read mode. It ismeasured as the length of time from switchingout of the write mode until meaningful signals occurat the output. 5. In a transceiver, the time requiredfrom the completion of a transmittedsignal until the receiver is activated.rect Abbreviation of RECTIFIER.rectangular coordinates See CARTESIAN COOR-DINATES.rectangular scan 1. A method of beam scanning ina cathode-ray tube, in which the beam moves sequentiallyin parallel lines to cover a rectangularregion. Used in television. 2. In radar, a twodimensionalscan, covering a specific rectangularregion.rectangular wave An alternating or pulsating currentor voltage whose rise and decay times are essentiallyzero, and whose maxima and minimaare essentially flat, but not necessarily of equalduration. The SQUARE WAVE is a special type ofrectangular wave.+Amplitude−rectangular waveTimerectangular waveguide A waveguide having a rectangularcross section.rectification The conversion of alternating currentinto pulsating direct current by any means otherthan the use of a motor-generator. Also see REC-TIFIER.rectification efficiency The ratio (expressed as apercentage) of the direct-current output voltageto the peak alternating-current input voltage of arectifier.rectified alternating current The unfiltered, pulsatingdirect-current output of a rectifier. It consistsof the unidirectional half-cycles passed bythe rectifier (one per cycle for half-wave rectification,and two per cycle for full-wave rectification).

588 rectifier • reductionismrectifier Abbreviation, rect. An electronic or electromechanicaldevice that converts alternatingcurrent into pulsating direct current.rectifier diode A heavy-duty tube or semiconductordiode designed primarily to change alternatingcurrent to pulsating direct current in powersupplies.rectifier filter A circuit containing parallel capacitance,sometimes in combination with series inductance,intended for smoothing out the ripplein the output of a power-supply rectifier.−1 0 1 2 3 4 5 6 7 8Movement of paper+4+3+2+10−1−2−3−4Penrectilinear chartrectifier-filter system The rectifier plus powersupply-filtercombination for converting alternatingcurrent into direct current.rectifier photocell A photovoltaic cell consisting oftwo layers of material with a semiconductor junctionbetween them. The device produces directcurrent when exposed to visible light, infrared, orultraviolet radiation.rectifier probe A diode-type probe used with adirect-current (dc) voltmeter to measure radiofrequency(RF) voltage. The diode rectifies the RFsignal and presents to the meter a dc voltage proportionalto the peak RF voltage.rectifier stack An assembly of separate rectifierdisks or plates in series on a central bolt, as inmost selenium rectifiers.rectifier tube A two-element electron tube, oncecommonly used for converting alternating currentinto pulsating direct current in high-voltage,high-current power supplies.rectifier-type meter See DIODE-TYPE METER.rectilinear chart A graphic-recorder chart inwhich the crossing coordinates are arcs, ratherthan straight lines, to correspond to the swing ofthe pen. Also see STRIP CHART.rectilinear scan See RECTANGULAR SCAN, 1.recurrent network A circuit in which several sectionsof identical configuration (e.g., L sections)are cascaded.recurrent phenomenon A phenomenon that repeatsitself periodically.recurrent sweep In an oscilloscope, a repetitivehorizontal sweep of the beam occurring at a frequencydetermined by the settings of the sweepcontrols. Also called REPETITIVE SWEEP. CompareNONREPETITIVE SWEEP.recursion 1. Generating a complete sequence offunctions or numbers by applying an algorithm toinitial values in the sequence. 2. In computerprogramming and artificial intelligence, a logicalprocess containing loops in calculation or reasoning.recursive Relating to a procedure or set of stepsthat repeat endlessly.Red Book The first format developed for compactdiscdata storage media, developed by Sony andPhilips. It is commonly used in digital audio systems.See also CD-ROM, GREEN BOOK, OR-ANGE BOOK, and YELLOW BOOK.red-green-blue Abbreviation, RGB. In video applications,the three primary colors from which allother colors are derived. Also see COLOR TELE-VISION.red gunIn a three-gun color-television picturetube, the electron gun whose (correctly adjusted)beam strikes only the red phosphor dots on thescreen.red oxide of iron An iron oxide of the general formulaFe 2 O 3 , used as the magnetic coating ofrecording tape. Also see IRON OXIDE.red oxide of zinc See ZINCITE.red-tape operation An operation or functionneeded for organizational purposes, but that doesnot directly contribute to the completion of thetask at hand.reduced instruction set computer Abbreviation,RISC. A computer architecture in which programinstructions are simplified to obtain enhancedprocessing speed. It is useful especially in complexgraphics, animation, multimedia, and scientificwork requiring many calculations.reductio ad absurdum A method of obtaining aconclusion by proving that its negation results ina contradiction. It is sometimes used in computerprogramming involving mathematical proofs.reduction In an electrochemical cell or battery, atransfer of electrons to the active chemical.reductionism The theory that all human thoughtprocesses, including emotion and intuition, can

eductionism • reflected power 589be reduced to digital logic, and thus can be duplicatedby a sufficiently powerful computer. It is ofinterest to researchers in artificial intelligence.reductionist A person who subscribes to the theoryof REDUCTIONISM.redundancy 1. The repetition of components in acircuit (e.g., series or parallel connection of them)so that one will be available for circuit operationif the other fails. 2. Having available more thanone method for performing a function. 3. Havingon hand several copies of data as a safeguardagainst data loss.redundancy check A check for the integrity of digitizeddata to which extra bits have been addedfor the purpose (e.g., parity check).redundant 1. Pertaining to any two units of datathat resemble each other in such a manner that ifeither unit is removed, no information is lost fromthe system. 2. A unit of data that contains informationalready present in the system.redundant array of independent disks Acronym,RAID. A set of data storage media used to storevideo programs.red video voltage In a three-gun color-televisioncircuit, the red-signal voltage that actuates thered gun.reed A usually thin metal blade, leaf, or strip usedin vibrators, reed-type relays, reed-type oscillators,and similar devices.reed oscillator See REED-TYPE OSCILLATOR.reed relay See DRY-REED SWITCH andMERCURY-WETTED REED RELAY.reed-relay logic Logic circuits using reed relays.Also see RELAY LOGIC.reed switch 1. A frequency-sensitive switch inwhich the movable contact is mounted on the tipof a thin, metal strip (reed). The reed is actuatedby an alternating-current (ac) coil. The reedcloses the contacts when the ac excitation is at itsnatural frequency. 2. See DRY-REED SWITCH.reed-type oscillator An electromechanical audiofrequencyoscillator whose frequency is controlledby a vibrating metal strip (reed) instead ofa tuning fork. Also see HUMMER.reed-type switch See REED SWITCH.reel 1. The spool around which a magnetic tape orvideo film is wound. 2. A spool containing magnetictape or video film.reentrant cavity A resonant cavity in which one ormore sections are directed inward to confine theelectric field to a small volume.reentrant winding A winding of wire that returnsto its starting point—especially in a motor armature.ref Abbreviation of REFERENCE.reference address As a point of reference, an addressfor instructions having relative addresses.reference amplifier A voltage-regulation deviceconsisting of a transistor and Zener diode in thesame envelope.reference angle In radar, the angle of incidence ofthe beam against a target surface, measured withrespect to the normal (perpendicular) line at thesurface.reference antenna A standard antenna, such asan isotropic radiator or a half-wave dipole, usedto establish a reference for determining the relativegain of another antenna.reference bias current In a reference amplifier,the input current that subtracts from the referencecurrent. It is generally measured in microamperes.reference current range In a digital-to-analog converter,the difference between the maximum andminimum reference current for which the deviceis within specifications for resolution.reference diode A Zener diode whose constantvoltage drop is used as a direct-current referencepotential in calibrator circuits and voltage regulators.reference dipole See REFERENCE ANTENNA.reference electrode For use with a pH meter, anelectrode that provides a reference potential.reference input slew rate In a digital-to-analogconverter, the average rate of change in outputfor a given change in the reference input. It is expressedin milliamperes or microamperes per microsecond.reference level A specific value of a quantity (e.g.,current, frequency, power, or voltage) to whichother values of the same quantity are referred.reference time The point at which a trigger pulseattains 10 percent of its maximum amplitude.reference tone A standard audible tone of knownfrequency [e.g., 440 Hz (representing A belowmiddle C)]. Sometimes the intensity as well, asthe frequency, is specified.reference white level The television picture signalvalue representing the uppermost limit for peakwhite signals.R eff Symbol for EFFECTIVE RESISTANCE.reflectance 1. See MISMATCH FACTOR. 2. The reflectedpart of the radiant flux striking a surface.It is expressed as a fraction of the total incidentradiation.reflected binary code See CYCLIC CODE.reflected electromagnetic field In a transmissionline, the electromagnetic energy not absorbed bythe load when an impedance mismatch exists betweenthe load and the line. See INCIDENTPOWER and REFLECTED POWER.reflected impedance In a coupled circuit, theimpedance in the secondary that appears in theprimary circuit, or vice-versa, as if it were reflectedthrough the coupling transformer.reflected power In a transmission line not perfectlymatched to a load at the feed point, an expressionof the amount of electromagnetic fieldreflected from the feed point, rather than absorbedby the load. In general, this can be expressedin watts or as a percentage of theincident power. It is not a true indicator of the

590 reflected power • refractivityloss caused by the mismatch because the reflectedfield is usually all returned again when itarrives back at the transmitter.reflected-power meter A radio-frequency instrument,connected between a source and a load,that can measure INCIDENT POWER and RE-FLECTED POWER.reflected ray The ray that is reflected by the surfaceof a body or region it strikes. Compare INCI-DENT RAY and REFRACTED RAY.reflected resistance 1. In a transformer, the effectiveresistance across the primary winding whena resistive load is connected to the secondary.2. In a transmission line, the resistance at the inputend when a load is connected to the output end.reflected wave 1. An electromagnetic wave reflectedby the ionosphere or by the surface of the earth.Compare INCIDENT WAVE and REFRACTEDWAVE. Also see IONOSPHERE and IONOSPHERICPROPAGATION. 2. A wave that is bounced off anobstruction, such as a building or mountain.reflecting galvanometer A galvanometer having alight-beam pointer.reflecting shell See IONOSPHERE.reflection1. The turning back of a ray by a surfaceit strikes. Examples of reflecting media are thesurface of the earth, the polished surface of a material,and a layer of the ionosphere. CompareREFRACTION. 2. The return of energy to thesource by the mismatched end of a transmissionline or by the end of a radiator.reflection error In a radar, radionavigation, or radiolocationsystem, an error in the readingcaused by reflections of the signal from objectsother than the intended signal source or object.reflection factor See MISMATCH FACTOR.reflection law When a ray strikes a smooth reflectingsurface, the angle of incidence is equal to theangle of reflection.Incident rayReflected rayreflection lawTangent planeSurface = Angle of incidence = Angle of reflectionreflection loss 1. Loss caused by the reflection ofan electromagnetic field at a discontinuity in atransmission line. 2. Loss that occurs when anelectromagnetic wave is reflected from a surfaceor object.reflection phase grating A device that diffusessound waves by diffraction effects. The acousticequivalent of an electromagnetic-wave DIF-FRACTION GRATING.reflective code See GRAY CODE.reflectivity 1. See MISMATCH FACTOR. 2. Thedegree to which a point, plane, or surface reflectsthe radiation (light, for example) that strikes it.reflectometer 1. See REFLECTED-POWER ME-TER. 2. A type of photometer used to measure reflection.reflector 1. A smooth, metal surface or wire screenfor reflecting radio waves. See, for example,PARABOLIC REFLECTOR. 2. A length of wire,rod, or tubing used in a parasitic antenna to reflectradio waves. Compare DIRECTOR and RADI-ATOR. 3. A polished surface for reflecting visiblelight or infrared rays (i.e., a mirror). 4. See RE-PELLER.reflector element See REFLECTOR, 2.reflector satellite A satellite whose skin reflectsradio waves.reflector voltage In a reflex Klystron, the reflectorto-cathodevoltage.reflex baffle A loudspeaker BAFFLE constructedso that some of the sound radiated to the rear ofthe diaphragm is transmitted forward (afterphase shift) to boost acoustic radiation at somefrequencies.reflex bunching In a Klystron, electron bunchingfollowing direct-current-field-induced reversal ofthe velocity-modulated electrons. Also see RE-FLEX KLYSTRON.reflex circuit A radio receiver circuit in which asingle transistor is used successively for differentfunctions. For example, one active device can actas a mixer and as a radio-frequency amplifier.reflex Klystron A Klystron having only one cavity.This cavity serves first as the buncher and then,as the electrons are turned around and caused topass through again, as the catcher.refracted ray The ray that is refracted by a body orregion through which it passes. Compare INCI-DENT RAY and REFLECTED RAY.refracted wave An electromagnetic wave that is refractedby the ionosphere. Compare INCIDENTWAVE and REFLECTED WAVE. Also see IONO-SPHERE and IONOSPHERIC PROPAGATION.refractionThe bending of an energy ray as itpasses through media that cause a change in thespeed of propagation. It can occur with radiowaves, infrared, visible light, ultraviolet, X rays,gamma rays, and sound waves.refractive index See INDEX OF REFRACTION.refractivity The extent of the ability to refract, givenas the quantity (v 1 /v 2 ) – 1, where v 1 is the phase

efractivity • rejection filter 591velocity in free space, and v 2 is the phase velocityin the medium through which a wave passes.refractory A heat-resistant, nonmetallic ceramicmaterial.refrigerator A chamber used to maintain a circuitor component at a constant temperature that islower than the ambient temperature. This deviceis analogous to the oven, which maintains ahigher temperature than the surroundingmedium. A refrigerator can be used to maintainprecise frequency for a reference oscillator.regeneration 1. The processing of a distorted signalso that it has its original characteristics.2. Positive feedback generally used for the purposeof causing oscillation, or for detection in a regenerativereceiver. See POSITIVE FEEDBACK.regeneration period The period during which theelectron beam scans a cathode-ray tube screen torestore changes to the screen surface.regenerative amplifier An amplifier that uses regenerationto increase its gain and/or selectivity.regenerative detector A detector provided with regenerativefeedback. Although such a detector issensitive, it can be unstable. Compare NONRE-GENERATIVE DETECTOR.regenerative feedback Feedback producing regeneration(i.e., positive feedback). Compare DE-GENERATIVE FEEDBACK.regenerative IF amplifier An intermediatefrequencyamplifier in which regeneration is introducedto boost sensitivity and, sometimes,selectivity.regenerative reading A method of reading data(see READ) so that it is automatically restored, bywriting, to locations from which it came.register In computer systems, an arrangement ofseveral storage devices, such as flip-flops, forstoring a certain number of digits (a two-bit register,for example, requires two flip-flops).register capacity The range of values for quantitiesthat can be handled by a register.registered professional engineer A title grantedby a state board of examiners to a person licensedto work as an engineer.register length The number of characters or bitsthat can be held in a register, according to its capacity.registration The accurate alignment of terminalsor other points on different components or on oppositesides of a board so that when the surfacescontaining those points are overlaid, all pointsmate precisely.regulated power supply A power supply whoseoutput is held automatically to a constant level orwithin a narrow range, regardless of loading variations.regulating transformer See VOLTAGE-REGULAT-ING TRANSFORMER.regulation 1. In general, the adjustment or controlof a component, device, or system. 2. Automaticcontrol. See, for example, SELF-REGULATION.3. See CURRENT REGULATION. 4. See VOLT-AGE REGULATION.regulator 1. A device that automatically holds aquantity to a constant value (e.g., a voltage regulator).2. A device via which a quantity can be varied(e.g., potentiometer, rheostat, and variableautotransformer).regulator diode A semiconductor diode—especiallya Zener diode used as a two-terminal voltageregulator.reinitialization The setting of all lines in a microcomputeror microprocessor to logic zero automaticallywhen power is removed, then reapplied.reject amplifier A tuned amplifier having the responseof a band-suppression filter. Like the filter,the amplifier rejects or severely attenuatesone frequency (or band of frequencies) while readilypassing lower and higher frequencies. ComparePASS AMPLIFIER.reject filter See REJECTION FILTER.rejection circuit A circuit performing the functionof a REJECTION FILTER.rejection filter A filter that suppresses one frequency(or band of frequencies) while passing allother frequencies.Inputrejection filterOutput

592 rejection notch • reluctance motorrejection notch A sharp dip in the transmissioncharacteristic of a crystal filter. It provides rejection-filteraction at the notch frequency. Also seeCRYSTAL RESONATOR and REJECTION FILTER.rejectivity The degree to which a selective circuitrejects an unwanted signal. Compare TRANSMIT-TIVITY.rejuvenation See REACTIVATION.rel Symbol, R. The cgs unit of reluctance, equivalentto gilberts per maxwell.relative accuracy In a measuring instrument, theerror determined as a percentage of the actualvalue; the difference between the actual and measuredvalues, divided by the actual value, thenmultiplied by 100.relative address In the address part of a computerprogram instruction, a number specifying a locationrelative to a BASE ADDRESS. When the baseaddress is added to the relative address, it yieldsthe ABSOLUTE ADDRESS.relative error The ratio of the absolute error to theexact value of a quantity.relative gain The current, voltage, or power gain,measured, with respect to a reference standard.relative humidity Abbreviation, rh. The ratio, as apercentage, of the amount of moisture in the airto the amount the air could contain at a giventemperature. Compare ABSOLUTE HUMIDITY.relative luminosity Luminosity measured with respectto a reference level.relative permeability The ratio of the permeabilityof a given material to the permeability of anothermaterial (or of the same material under differentconditions).relative power Power level specified with respectto another (often reference) power level.relative uncertainty The uncertainty of a measurementdivided by the measured value. Themaximum value that this quotient can have is 1.Also see UNCERTAINTY IN MEASUREMENT.relative visibility Response of the human eye tolight. This is relative because the eye does not seeequally well throughout the visible spectrum. Thepeak response of the human eye is around 5.4 ×10 14 Hz; this represents yellow-green light. Photoelectricdevices have peak responses that can differconsiderably from this value.relativity theory See EINSTEIN’S THEORY.relaxation A delayed change in circuit conditions,as a result of change in the input.relaxation inverter An inverter circuit in whichthe direct-to-alternating-current conversion deviceis a RELAXATION OSCILLATOR.relaxation oscillator An oscillator whose operationresults from the buildup of a charge in a capacitor,followed by sudden discharge of the capacitor,the sequence being repeated periodically. In onecircuit, a capacitor is connected in series with aresistor and a direct-current power supply, and aneon bulb is connected in parallel with the capacitor.The output is a sawtooth wave.relaxation time 1. The time required for an exponentiallydecreasing variable to fall to 1/e (approximately36.8 percent) of its initial value,where e is the natural-logarithm base (approximately2.71828). 2. For a gas, the time requiredfor it to return to its original state after havingbeen disturbed.relay 1. A signal-actuated switching device. Inmost instances, a relatively weak current or voltageis used to make the relay switch a higher currentor voltage. A relay can be electromechanicalor fully electronic (no moving parts). See, for example,ELECTROMECHANICAL RELAY andELECTRONIC RELAY. 2. A repeater station. 3. Incommunications, to receive a message and retransmitit en route from a source to a destination.relay amplifier See RELAY DRIVER.relay booster See RELAY DRIVER.relay driver A direct-current amplifier (usually onestage) used to actuate an electromechanical relayin response to a low-powered signal.relay flip-flop See BISTABLE RELAY.relay logic Abbreviation, RL. In computer andindustrial-control operations, a logic system usingelectromechanical relays as flip-flops (seeBISTABLE RELAY).relay transmitter See AUTOMATIC REPEATERSTATION.release time 1. The interval between the instantpower is removed from a relay and the instantthe armature is released sufficiently to operatethe contacts. 2. The time between one control inputbecoming inactive and another becoming active.3. The time required for reception toresume in a transceiver, once transmission hasstopped. 4. An expression for the rapidity withwhich an automatic gain control reverts to maximumsensitivity following the reception of astrong signal.reliability 1. The dependability of operation of adevice or circuit under specified conditions.2. The proportion of units that still work after aset of units has been in use for a specified lengthof time.reliability engineering The branch of engineeringdevoted to the theory and application of reliability;based on fundamental engineering and advancedstatistical concepts.reluctance Symbol, R. SI unit, A/Wb; cgs unit, rel.In a magnetic circuit, the opposition to the establishmentof a magnetic field; it is analogous to resistancein electric circuits.reluctance motor An electric motor having asquirrel-cage rotor with some of its teeth grounddown, and a shaded-pole or split-phase type ofstator that supplies a rotating magnetic field.When starting, this motor comes up to speed likean induction motor, but the protruding teeth ofthe rotor then follow the field in the manner of thepoles of a hysteresis motor.

eluctivity • replacement 593reluctivity Specific reluctance (i.e., the reluctanceof a sample of magnetic material one centimeterlong and one square centimeter in cross section).Reluctivity is the reciprocal of permeability.rem Acronym for roentgen equivalent man, anamount of ionizing radiation having the same effecton the body as a one-roentgen dose of gammaor X radiation.remagnetizer A magnetizer used principally to restoreweakened permanent magnets.remainder 1. The result of subtracting one quantity(the subtrahend) from another (the minuend).Also called DIFFERENCE. 2. In division, the numericalvalue left over after the integral part ofthe quotient has been determined; it becomes thefractional part when divided by the divisor. Forexample, in 25/3, the remainder is 1.remanence See RESIDUAL MAGNETISM.remanent flux density See REMANENCE.remodulator Any device that changes the modulationof a signal from one form to another, such asfrom frequency modulation to amplitude modulation,without loss of intelligence.remote alarm In security systems, an alarm thatoccurs at a location different from where an intrusionoccurs (e.g., at the headquarters of a securitycompany).remote control Control of distant devices by mechanicalmeans or by radio-frequency signalssent from a transmitter especially designed forthe purpose; in the latter case, it is sometimescalled radio control.remote-control receiver The complete device thatselects, amplifies, and demodulates or rectifies aradio signal for control of a circuit or mechanismat a distance from the transmitter of the controlsignal. Some receivers have self-contained antennas.remote-control transmitter The complete devicethat generates radio-frequency power, adds to itthe signals needed for remote control, and radiatesthe modified power.remote-control system The complete set of hardwareunits and software programs facilitating theoperation of a computer or robot from a distance.remote data terminal In a computer system, aterminal connected to the central processor by atelephone line or radio link. It is used for thetransfer of data without providing control of thesystem. Also called remote data station.remote error sensing A method of regulation usedin some power supplies. The voltage across theload, or the current through the load, is determinedby remote control. The power-supply outputis adjusted to compensate for losses in thesystem.remote job entry In computer operations, the keying-inof input data at a site physically distantfrom the central processor.remote tuning The electrical or radio tuning of acircuit or device from a distance.rendering In three-dimensional computer animation,the software process in which all the aspectsof the model are combined to obtain the presentation.rep 1. Acronym for roentgen equivalent physical,an amount of ionizing radiation that, upon absorptionby body tissue, will develop the energy ofa one-roentgen dose of gamma or X radiation.2. Colloquial abbreviation for repetition, as in reprate. 3. Colloquial abbreviation for representative,as in service representative.repeatability The ability of an instrument, system,or method to give identical performance or resultsin successive instances.repeater A receiver/transmitter device that retransmitsa signal it receives from anothersource, often simultaneously. In this way, a signalcan be transmitted on several frequencies, orthe service area of the original station can be extended.Also see ONE-WAY REPEATER and TWO-WAY REPEATER.ReceiveantennaReceiverIsolatorrepeaterTransmitantennaTransmitterrepeater station See AUTOMATIC REPEATERSTATION and REPEATER.repeating decimal A decimal fraction in whichgroups of digits recur endlessly (e.g., 25/99 =0.252525. . .).repeller An electrode, especially in a velocity-modulatedtube, for reversing the direction of an electronbeam.repertoire The instruction set for a particular objector source computer programming language.repetition instruction In a loop in a computerprogram, an instruction that causes the repetitiveimplementation of one or more instructions.repetitive phenomenon See RECURRENT PHE-NOMENON.repetitive sweep See RECURRENT SWEEP.replication In an electronic system, especially in acomputer, the redundancy of hardware units toprovide standby facilities in case of failure.replacement A component or circuit that can besubstituted directly for another; it fits exactly intoplace and functions exactly like the component itreplaces, without modification to the equipment.

594 report • resiliencereport 1. The results of testing and evaluation of adevice, organized into a written document. 2. Theoutput of a computer, printed on paper for permanentreference.report program generator Abbreviation, RPG. Acomputer programming language with which programscan be produced for the generation of businessreports.reproduce head See PLAYBACK HEAD.reproducing stylus A stylus for the playback ofmaterial from a phonograph disc.reproduction 1. The recovery of data from storage,and its presentation in original form. 2. Data obtainedby the process defined in 1. 3. See PLAY-BACK.reproduction loss See PLAYBACK LOSS.repulsion A force that pushes objects away fromeach other, as between similar electric charges orsimilar magnetic poles. Compare ATTRACTION.Also see LAW OF REPULSION.repulsion-induction motor An alternatingcurrentmotor arranged to start as a REPULSIONMOTOR and run as an INDUCTION MOTOR, butwith better regulation than that of the latter.repulsion motor An alternating-current motorhaving an armature and commutator similar tothose of a direct-current motor, and a stator similarto that of a split-phase motor, without theauxiliary starting winding. Repulsion caused bythe negative half-cycle of torque is utilized to drivethe armature, by placing the brushes in such away that they close the coils only when the latterare in position to receive this repulsive action.repulsion-start motor An alternating-current motorthat starts as a REPLUSION MOTOR but atapproximately 75 percent of full speed. Its commutatoris automatically short-circuited and themotor runs as an INDUCTION MOTOR. Also seeREPULSION INDUCTION MOTOR.request slip In computer operations, peripheraland memory needs for a program given in a writtenstatement.reradiation Radiation of energy by a body that hasbeen exposed to radiation, as when a receivingantenna retransmits a signal.rerecording A recording of played-back material.reroute 1. In computer operations, to establish newchannels between peripherals and main memory.2. To establish new circuit paths, physically (as bychanging conductor orientation) or electronically(as by selecting an alternate signal bus).rerun See ROLLBACK.res 1. Abbreviation of RESISTANCE or RESISTOR.(Also, R and r.) 2. Abbreviation of RESEARCH. 3.Abbreviation of RESOLUTION.reset 1. The clearing of a flip-flop of data in storage(i.e., the setting of the flip-flop to its zero state). 2.In a computer program, an instruction to initializethe value of a variable. 3. In a security system,a function that terminates an alarm signal followingan intrusion, and renders the system operationalagain so that it can detect subsequent intrusionsshould they occur.reset action 1. The return of a circuit or device toits normal operating condition. 2. A method ofadjusting a circuit to compensate for the severityof an abnormal condition. The extent of readjustmentis determined by the extent of the departurefrom normal conditions.reset generator A circuit or device that generates apulse for resetting a flip-flop or counter. Also seeRESET and RESET TERMINAL.reset pulse A pulse that resets (see RESET, 1) astorage cell in a computer memory.reset terminal In a flip-flop, the zero-input terminal.Compare SET TERMINAL.reset time The elapsed time between a malfunctionand the completion of the reset action.reset timer A device that returns a circuit or deviceto its initial state after a specified time delay.reserve In multiple programming computer operations,to allocate memory areas and peripheralsfor a program.reserve battery A battery in which the electrolyteis in a special standby chamber outside of the interelectrodesection while the battery is on theshelf. When the battery is readied for service, theelectrolyte is caused to flow into position betweenthe electrodes, either by heating the battery,shocking it mechanically, or inverting it.residual amplitude modulation See INCIDENTALAM.residual charge The electric charge remaining in acapacitor after it has been initially discharged. Itresults from dielectric absorption.residual current A current that continues to flowin a circuit after removing power. The duration ismeasured in nanoseconds or microseconds.residual frequency modulation 1. See INCIDEN-TAL FM. 2. Frequency modulation of the fundamentalfrequency of a Klystron by noise oralternating-current heater voltage.residual gas Minute quantities of gas remaining ina vacuum tube after evacuation.residual magnetism Magnetism remaining in amaterial, such as iron, after the magnetizing forcehas been removed.residual modulation 1. Modulation of a signal byhum or noise. 2. See INCIDENTAL AM. 3. See IN-CIDENTAL FM.residual voltage In the output of a null device,such as a bridge, a usually small voltage still presentat null and preventing zero balance.residue check In computer operations, the verificationof the result of an arithmetic operation usingthe remainders generated when each operand is dividedby a special number; the remainder is transmittedalong with the operand as a check digit.resilience Also called fault resilience. The ability ofan electronic device or system, especially a computer,to keep functioning after part of it hasfailed.

esin • resistance-inductance circuit 595resin A natural or synthetic organic substancethat is polymeric in structure and largely amorphous.Various plastics are made from syntheticresins.resistance 1. Symbol, R or r. Unit, ohm. In a device,component, or circuit, the simple oppositionto current flow. Resistance by itself causes nophase shift. In a purely resistive circuit, R = E/I,where R is the resistance in ohms, E is the voltagein volts, and I is the current in amperes. 2. Aproperty of circuits, devices, or substances thatcauses impinging energy to be dissipated by conversionto heat. Compare REACTANCE.resistancePer kilometer of solid copper wire for American Wire Gauge(AWG) 1 through 40.AWG ohms/km AWG ohms/km1 0.42 21 432 0.52 22 543 0.66 23 684 0.83 24 865 1.0 25 1106 1.3 26 1407 1.7 27 1708 2.1 28 2209 2.7 29 27010 3.3 30 35011 4.2 31 44012 5.3 32 55013 6.7 33 69014 8.4 34 87015 11 35 110016 13 36 140017 17 37 170018 21 38 220019 27 39 280020 34 40 3500resistance alloys Metallic alloys used in the manufactureof resistance wire and resistance elements.Such alloys include CONSTANTAN,GERMAN SILVER, MANGANIN, MONEL METAL,and NICHROME.resistance balance A device used to balance a circuit,by means of the insertion of resistances.resistance brazing A method of brazing in whichmetal is heated by passing a current through it.The I 2 R loss, or dissipated power, occurs in theform of heat.resistance bridge A bridge (see BRIDGE, 2) formeasuring resistance only.resistance-capacitance Abbreviation, RC. Pertainingto a combination of resistance and capacitance(e.g., RESISTANCE-CAPACITANCE CIRCUIT).resistance-capacitance bridge 1. A four-arm nullcircuit containing only resistors and capacitors.Also see BRIDGE, 1. 2. An alternating-currentbridge (see BRIDGE, 2) for measuring resistanceand capacitance.resistance-capacitance circuit A circuit containingonly resistors and capacitors. There are no inductors.resistance-capacitance-coupled amplifier Amultistage amplifier circuit in which RESIS-TANCE-CAPACITANCE COUPLING is used betweenstages and at the input and output pointsof the circuit.resistance-capacitance coupling Coupling, especiallybetween stages in a circuit, using blockingcapacitors and supply-path resistors.resistance-capacitance filter A power-supply filteror wave filter containing only resistors and capacitors.The resistors are in the positionsoccupied by inductors in inductance-capacitancefilters.resistance-capacitance-inductance Abbreviation,RCL. Pertaining to a combination of resistance,capacitance, and inductance.resistance-capacitance phase shifter A phaseshifter containing only resistors and capacitors toobtain the desired shift.RCE R E C+E R0E C −resistance-capacitance phase shifterresistance-capacitance time constant Symbol, t.The time constant (see ELECTRICAL TIME CON-STANT) of a circuit containing (ideally) only resistanceand capacitance; t = RC, where t is inseconds, R is in ohms, and C is in farads. CompareRESISTANCE-INDUCTANCE TIME CONSTANT.resistance-capacitance tuning Tuning of a circuit,such as that of an amplifier or oscillator, bymeans of a variable resistor or ganged units ofthis type. See, for example, PARALLEL-TEE AM-PLIFIER, PARALLEL-TEE OSCILLATOR, andWIEN-BRIDGE OSCILLATOR.resistance-coupled amplifier See RESISTANCE-CAPACITANCE-COUPLED AMPLIFIER.resistance drop The voltage drop across a resistor,or across the inherent resistance of a device.resistance-inductance Abbreviation, RL. Pertainingto a combination of resistance and inductance(e.g., RESISTANCE-INDUCTANCE CIRCUIT).resistance-inductance bridge 1. A four-arm nullcircuit containing only resistors and inductors.Also see BRIDGE, 1. 2. An alternating-currentbridge (see BRIDGE, 2) for measuring resistanceand inductance only.resistance-inductance circuit A circuit containingonly resistors and inductors. There are no capacitors.

596 resistance-inductance phase shifter • resistors in series-parallelresistance-inductance phase shifter A phaseshifter containing only resistors and inductors toobtain the desired phase shift.RLE RE LE L E Rresistance-inductance phase shifterresistance lamp An incandescent bulb inserted inseries with a circuit to provide a dropping resistance.Such a lamp is capable of dissipating alarge amount of power, shows very little reactanceat low frequencies, and is inexpensive.resistance magnetometer A magnetometer whoseoperation is based upon the change of electricalresistance of a material (such as bismuth wire)placed in the magnetic field under test.resistance material A substance, such as carbonor German silver, whose resistivity is highenough to enable its use as a lumped resistor.See, for example, RESISTANCE ALLOYS and RE-SISTANCE METAL.resistance metal A metal, such as iron, whose resistivityis high enough to enable its use as alumped resistor. Also see RESISTANCE ALLOYS.resistance pad An attenuator composed of noninductiveresistors.resistance standard A highly accurate and stableresistor used in precision measurements of resistance.Also see PRIMARY STANDARD and SEC-ONDARY STANDARD.resistance strain gauge An electrical strain gaugein which the stressed element is a thin resistancewire.resistance strip A strip of metallic or nonmetallicresistance material. Also see RESISTANCE AL-LOYS and RESISTANCE METAL.resistance temperature detector A transducerconsisting of a specially made resistor whose resistancevaries linearly with temperature.resistance thermometer An electronic thermometerwhose operation is based on the change of resistanceof a wire as it is heated or cooled.resistance transducer See RESISTIVE TRANS-DUCER.resistance tuning See VARIABLE-RESISTANCETUNING.resistance welding An electrical or electronicwelding process in which the workpieces areheated by current flowing through the inherentresistance of their junction.resistance wire Wire made of a metal or alloy thatexhibits significant resistivity. See, for example,RESISTANCE ALLOYS and RESISTANCE METAL.resistance-wire sensor A specific length of resistancewire, properly mounted, whose resistanceis proportional to a sensed phenomenon (such asstrain, temperature, presence of gas, pressure,etc.). See, for example, ELECTRICAL STRAINGAUGE, GAS DETECTOR, and PRESSURETRANSDUCER.resistive current The component of alternatingcurrent that is in phase with voltage. Also calledWATT CURRENT. Compare REACTIVE CURRENT.resistive cutoff frequency Symbol, f rco . The frequencybeyond which a tunnel diode ceases to exhibitnegative resistance.resistive load A load device that is essentially apure resistance.resistive losses Losses resulting from the resistanceof a circuit or device, and usually appearingas heat.resistive transducer A transducer in which thesensed phenomenon causes a change in resistance,which in turn produces a correspondingchange in output current or voltage. CompareCAPACITIVE TRANSDUCER, CRYSTAL TRANS-DUCER, INDUCTIVE TRANSDUCER, MAGNETICTRANSDUCER, and PHOTOELECTRIC TRANS-DUCER.resistive trimmer See TRIMMER RESISTOR.resistive voltage The voltage across the resistancecomponent in a circuit. In an alternating-currentcircuit, the resistive voltage is in phase with thecurrent.resistivity Symbol, r. Resistance per unit volumeor per unit area. It can be expressed in terms ofohms per cubic meter or ohms per square meter.Also see MICROHM-CENTIMETER and OHM-CENTIMETER.resistor A device having resistance concentrated inlumped form. Also see RESISTANCE and RESIS-TIVITY.resistor-capacitor-transistor logic Abbreviation,RCTL. A form of RESISTOR-TRANSISTOR LOGICin which capacitors are used to enhance switchingspeed.resistor color code See COLOR CODE.resistor core A form around which a resistancewire can be wound for the purpose of constructinga high-power resistor.resistor decade See DECADE RESISTOR.resistor diode A usually forward-biased semiconductordiode that acts as a VOLTAGE-DEPEN-DENT RESISTOR.resistor FET See ELECTRONIC RESISTOR.resistor fuse See FUSIBLE RESISTOR.resistors in parallel See PARALLEL RESISTORS.resistors in parallel-series See PARALLEL-SERIES RESISTORS.resistors in series See SERIES RESISTORS.resistors in series-parallel See SERIES-PARALLEL RESISTORS.

esistor substitution box • resonant-line oscillator 597resistor substitution box A self-contained assortmentof common-value resistors arranged to beswitched one at a time to a pair of terminals. Introubleshooting and circuit development, any ofseveral useful fixed resistance values can thus beobtained.resistor transistor See ELECTRONIC RESISTOR.resistor-transistor logic Abbreviation, RTL. A circuitin which the logic function is performed byresistors, and an inverted output is provided bytransistors.resnatronA form of vacuum tube that is used asan oscillator and amplifier at ultra-high and microwavefrequencies. It is essentially a cavity resonator.resolution1. The degree to which closely adjacentparts of an image can be differentiated. 2. The reductionof a problem by means of logical analysis.3. The ability of a vision or ranging system to distinguishbetween objects that are close togetherin terms of radial distance, direction, or absoluteseparation.resolution ratio In a television image, the ratio ofhorizontal resolution to vertical resolution.resonance 1. The state in which the natural responsefrequency of a circuit coincides with thefrequency of an applied signal, or vice versa,yielding intensified response. 2. The state inwhich the natural vibration frequency of a bodycoincides with an applied vibration force, or viceversa, yielding reinforced vibration of the body.resonance bridge An alternating-current bridge(see BRIDGE, 2) in which one or two arms areseries-resonant or parallel-resonant, the otherarms being resistances. Also see SERIES-TYPERESONANCE BRIDGE and SHUNT-TYPE RESO-NANCE BRIDGE.resonance curve A graph of the insertion gain orloss of a component, device, circuit, or system toCurrent or voltageFrequencyresonance curvef 0variations in the frequency of an applied sound orsignal. Such curves are almost always plotted inrectangular coordinates with frequency as the independentvariable on the horizontal axis. The dependentvariable, plotted on the vertical axis, canbe any characteristic that displays a peak or dipat the resonant frequency or frequencies. In radiofrequencycircuits, such parameters include current,voltage, attenuation, gain, and impedance.resonance theory of hearing The theory thatsound waves pass down the auditory canal andcause the eardrum to vibrate. Behind theeardrum is a system of three bones leading to thecochlea. The cochlea consists of fibers that resonate.Therefore, they vary in length and tension.Various groups of fibers are activated by differentsounds, and the vibrations are transmitted tonerves leading to the brain.resonance radiation Electromagnetic radiationfrom an energized substance, resulting frommovement of electrons from a higher to lower energylevel. When an electron moves from a higherto a lower orbit, a photon, having a definite wavelength,is emitted.resonant cavity A chamber whose size reinforcesenergy injected into it at a natural frequency,which is determined by the chamber’s dimensions.Such cavities can be used with acoustic orelectromagnetic waves.resonant circuit A circuit whose constants arechosen for maximum circuit response at a givenfrequency. Examples: parallel-resonant circuitand series-resonant circuit. Also see RESONANCEand RESONANT FREQUENCY.resonant current Current flowing in a tuned circuitat resonance.resonant feeder An antenna feeder that is resonantat the operating frequency.resonant filter A filter containing at least one series-or parallel-resonant arm for sharp response.Thus, a power-supply filter of this kind mighthave a parallel-resonant arm acting as a wavetrapat the ripple frequency.resonant frequency Symbol, f r or f o . The naturalfrequency at which a circuit oscillates or a devicevibrates. In an inductance-capacitance circuit(series-resonant or parallel-resonant), the reactancescancel at the resonant frequency, leavingonly resistance.resonant-gate transistor A transistor embodyinga tiny tuning fork for resonance at low frequencies,thus eliminating bulky coils and capacitors.resonant line A transmission line that is resonantat the operating frequency.resonant-line amplifier See LINE-TYPE AMPLI-FIER.resonant-line circuit A circuit using resonantlines as a tank. See, for example, LINE-TYPEAMPLIFIER and LINE-TYPE OSCILLATOR.resonant-line oscillator See LINE-TYPE OSCILLA-TOR.

598 resonant-line wavemeter • reverberation systemresonant-line wavemeter See LECHER WIRES.resonant rise See VOLTAGE RISE.resonant-slope amplifier See DIELECTRIC AMP-LIFIER.resonant-slope detector See SLOPE DETECTOR.resonant suckout The drawing of radio-frequencyenergy out of the energized part of a coil or transmissionline by the part not intended to be energized,when the latter resonates at the samefrequency.resonant-voltage rise See VOLTAGE RISE.resonant-voltage stepup See VOLTAGE RISE.resonate 1. To exhibit RESONANCE—either electricallyor acoustically. 2. To adjust a variablefrequencyelectrical or acoustical device so that itexhibits RESONANCE at a specific frequency.resonator A device that produces or undergoesresonance. See, for example, HELMHOLTZ RES-ONATOR and RESONANT CAVITY.resource A part of a computer system that can beused for a specific application as a unit (e.g.,printer, PCMCIA standard adapter card, tapedrive, etc.).responder The transmitting section of a transponder.response The behavior of a circuit or device (especiallyin terms of its dependent variables), in accordancewith an applied signal (e.g., frequencyresponse and current-vs.-voltage response).response curve A graph depicting the performanceof a circuit or device. Examples: attenuation-vs.-frequencycurve and current-vs.-voltagecurve.response time The interval between the instant asignal is applied to or removed from a circuit ordevice and the instant that the circuit acts accordingly.restart Following a malfunction or error occurringduring a computer program run, to go back to anearlier point in the program.resting state See QUIESCENT STATE.restore See RESET.resultant 1. The vector that results from the additionof two or more vectors. 2. A quantity that resultsfrom mathematical operations performed onother quantities.retarding magnet See DRAG MAGNET.retentivity 1. The property whereby a material retainsmagnetism imparted to it. 2. A quantitativemeasure of the extent to which a material retainsmagnetism imparted to it.retention period In computer operations, the timeduring which the data on a magnetic medium(disk or tape) must be kept intact.retrace 1. In a cathode-ray tube, the return of thescanning beam to its starting point. 2. In a cathode-raytube, a line traced on the screen by thescanning beam as it returns to its starting point,if RETRACE BLANKING is not used.retrace blanking Obliteration of the RETRACE ofthe electron beam in a cathode-ray tube. It rendersthe retrace line invisible on the screen sothat it will not interfere with the display.retrace line See RETRACE, 2.retrace ratio For the swept beam in a cathode-raytube, the ratio of the scanning velocity in thetrace direction to the scanning velocity in the RE-TRACE direction.retrace time In a cathode-ray tube, the amount oftime required for the scanning beam to movefrom the end of one trace or line to the beginningof the next.retrofit To supply something with specially designedor adapted parts that were not availablewhen it was made.retrograde orbit For an artificial earth satellite, anorbit whose direction is east-to-west, relative tothe earth’s surface.return 1. See RETRACE. 2. See RETURN CIRCUIT.3. See RETURN POINT. 4. In an electronic circuit,the electrical ground and ground current path.return circuit The circuit through which currentreturns to a generator.return instruction In a computer program, an instructionin a subroutine directing operationback to a specific point in the main program.return interval See RETRACE TIME.return line See RETRACE, 2.return point 1. The point to which circuits are returned(e.g., a common ground point). 2. The terminalpoint of a return circuit.return ratio See FEEDBACK FACTOR.return time See RETRACE TIME.return to zero 1. Abbreviation RZ or RTZ. In themagnetic recording of data, a method in which thewrite current returns to zero following the writepulse. Compare NONRETURN-TO-ZERO. 2. Alogic system in which the zero and one states arerepresented by zero voltage and a discrete voltage.return trace See RETRACE, 1, 2.REV 1. Abbreviation of REENTRY VEHICLE. 2. Abbreviationof REVERSE.rev 1. Abbreviation of REVOLUTION. 2. To quicklyand substantially increase the angular velocity ofa motor.reverberation 1. Multiple reflections of soundwaves from the inside surfaces of an enclosedchamber. 2. The dying-out of sound waves in anenclosed chamber as the waves reflect repeatedlyfrom the inside surfaces. 3. In sound recordingand/or reproduction, an electronically producedecho. It is used for special effects—especially inelectronic music systems. 4. See RESONANCE, 2.reverberation chamber A room in which the walls,floor, and ceiling absorb very little sound, resultingin echoes. To avoid standing waves, the roomis designed so that no two surfaces are exactlyparallel.reverberation system A system of devices operatedwith an electronic organ to simulate the effectof reverberation in a large room, such as achurch auditorium.

everberation time • revolution 599reverberation time In an enclosed chamber, thetime required for a sound to die down to a specifiedlevel (usually -60 dB) after the disturbancehas stopped.reverberation unit A device for producing artificialechoes—especially in the operation of electronicmusic systems.reverse 1. To alter the direction of a current or processor motion of an object so that the new directionis exactly opposite the previous direction.2. In a directional wattmeter, the reflected-powerindication or switch position.reverse AGC Automatic gain control in which asignal-dependent voltage is fed back to an earlierstage to adjust its gain automatically. CompareFORWARD AGC.reverse bias Reverse voltage or current in a transistoror a semiconductor diode. Compare FOR-WARD BIAS.−npn+reverse engineering A design process in which aspecific device or system is copied functionally,but not literally.reverse Polish notation Abbreviation, RPN. A systemof notation for expressing mathematical operationsin which the operators follow theoperands being manipulated. It is a mode of entryfor some calculators (e.g., the operation 7 × 2might be entered by pressing keys in this order:7, ENTER, 2, ×).reverse recovery time See RECOVERY TIME, 1.reverse resistance Symbol, R r . The resistance of areverse-biased pn junction. Also called BACK RE-SISTANCE. Compare FORWARD RESISTANCE.reverse voltage Symbol, E r or V r . Direct-currentvoltage applied to a pn junction so that thep-type material is electrically more negative thanthe n-type material. Also called BACK VOLTAGE.Compare VOLTAGE.reverse-voltage capacitance The internal capacitanceof a reverse-biased semiconductor pn junction.reverse voltage drop The voltage drop across asemiconductor pn junction that is biased in thereverse (low-conduction) direction.reversible counter A counter that, by a controlsignal, can have the value it is holding either increasedor decreased.reversible permeability The permeability of a ferromagneticsubstance when the magnitude of thealternating-current field is arbitrarily small.reversing switch 1. A switch that reverses the polarityof a direct-current voltage. 2. A switch thatreverses the direction of motor rotation.pnp_++Input−Gangedoutputreverse biasreverse breakdown See AVALANCHE.reverse breakdown voltage See AVALANCHEVOLTAGE.reverse characteristic The current-vs.-voltage responseof a semiconductor junction that is biasedin the reverse (low-conduction) direction. CompareFORWARD CHARACTERISTIC.reverse conduction The very small current conductionthrough a pn junction when it is reversebiased.Compare FORWARD CONDUCTION.reverse current Symbol, I r . The current that flowsthrough a pn junction when it is reverse-biased.Also called back current. Compare FORWARDCURRENT.reversing switchrevolute geometry A method by which a robotarm can move freely in three dimensions. The entireassembly rotates from the base in a horizontalplane through a complete circle (360 degrees).An elevation joint at the base moves the arm fromhorizontal to vertical (90 degrees). A joint in themiddle of the arm can bend through about 180degrees.revolution Abbreviation, r or rev. One complete rotation(i.e., 360 degrees of circular travel).

600 revolving field • Rieke chartrevolving field See ROTATING FIELD.rewind To run a magnetic tape on a transport at ahigh speed, in the direction opposite to that associatedwith the play mode.rewrite In computer operations, to return informationread from a storage location to that locationby recording.R F Symbol for FILAMENT RESISTANCE.RF Abbreviation of RADIO FREQUENCY.RF amplifier See RADIO-FREQUENCY AMPLI-FIER.RFC Abbreviation of RADIO-FREQUENCY CHOKE.RF heating See RADIO-FREQUENCY HEATING.RFI Abbreviation of RADIO-FREQUENCY INTER-FERENCE.RF inverse feedback A negative-feedback systemfor radiophone transmitters, in which a portion ofthe modulated radio-frequency (RF) signal is rectified,and the resulting direct-current voltage isfiltered and applied as bias to one of the audiostages in the proper polarity for degeneration.RF lamp A lighting lamp, used with radiofrequency(RF) alternating current, rather thanthe conventional 60-Hz utility current. This resultsin better efficiency, and allows much more light tobe generated with a given filament lamp, as comparedwith 60-Hz current.RF motion detector In security systems, an intrusiondetection and alarm system that sensesDoppler-effect-induced changes in the frequencyor phase of a radio-frequency (RF) electromagneticfield. The Doppler effect results from motionof objects in the secured area.RFO Abbreviation of radio-frequency oscillator.RF power supply See OSCILLATOR-TYPE POWERSUPPLY.RF preamplifier A sensitive, radio-frequency amplifiercircuit intended for improving the signal-tonoise(S/N) ratio in a wireless receiver. Generallyplaced between the receiver and the antenna orfeed line. Some such devices are tunable; othersare broadbanded. See also PREAMPLIFIER.RF probe See RECTIFIER PROBE.RF resistance See RADIO-FREQUENCY RESIS-TANCE.RF selectivity See RADIO-FREQUENCY SELEC-TIVITY.RF transformer See RADIO-FREQUENCY TRANS-FORMER.RF transistor See RADIO-FREQUENCY TRANSIS-TOR.R g Symbol for GRID RESISTANCE.R G Symbol for GATE RESISTANCE.RGB Abbreviation of RED-GREEN-BLUE.RGT Abbreviation of RESONANT-GATE TRANSIS-TOR.Rh Symbol for RHODIUM.R/h Abbreviation of ROENTGENS PER HOUR.R H 1. Symbol for HEATER RESISTANCE. 2. Symbolfor HOT RESISTANCE.rh Abbreviation of RELATIVE HUMIDITY.rhenium Symbol, Re. A metallic element. Atomicnumber, 75. Atomic weight, 186.207. It is used insome thermocouples.rheostat A wirewound variable dropping resistor ofthe rotary type or slider type.EndcontactAdjustablecontactEnd contactsrheostatEndcontactAdjustablecontactR HF Symbol for high-frequency resistance (seeRADIO-FREQUENCY RESISTANCE).RHI Abbreviation of RANGE-HEIGHT INDICATOR.rhodium Symbol, Rh. A metallic element. Atomicnumber, 45. Atomic weight, 102.906.rhombus A four-sided geometric plane figure, inwhich all four sides have equal length, and oppositeangles have equal measure.rhombic antenna See DIAMOND ANTENNA.rho-theta A radio-navigation system in which asingle transmitting station is used, and the positionis determined, according to polar coordinates(distance and direction).rhumbatron A RESONANT CAVITY—especiallyone in a KLYSTRON.RI Abbreviation of RADIO INTERFERENCE.R i Symbol for INPUT RESISTANCE. (Also, R in .)RIAA Abbreviation of RECORDING INDUSTRY AS-SOCIATION OF AMERICA.RIAA curve The amplitude-versus-frequency functionused in recording and reproduction of longplaying(33.3 rpm) phonograph discs, andspecified by the Recording Industry Associationof America (RIAA). The RIAA curve takes advantageof the sensitivity of the human ear at variousfrequencies to reduce the level of audible noise.ribbon microphone See VELOCITY MICROPHONE.ride gain In broadcasting, the operations of constantlyadjusting the audio modulation of thetransmitter for optimum operation.Rieke chart A visual aid, similar to the SMITHCHART, used with traveling-wave tubes in the

Rieke chart • ripple 601ultra-high-frequency (UHF) and microwave frequencybands for determining the optimum loadimpedance.rig Colloquialism for a radio communications installation—especiallya transmitter or transceiver.It is commonly used among amateur radiooperators.right-angle line section See ELL.right-hand lay See DIRECTION OF LAY.right-hand polarized wave See CLOCKWISE-POLARIZED WAVE.right-hand rule for induced emf See FLEMING’SRIGHT-HAND RULE.right-hand rule for wire A simple rule for indicatingthe direction of the magnetic field surroundinga straight wire that carries current. When thewire is grasped in the right hand with the thumbpointing in the direction of current flow, the fingerscurl in the direction of the magnetic field.right-hand taper Potentiometer or rheostat taperin which most of the resistance is in the clockwisehalf of rotation, as viewed from the front. CompareLEFT-HAND TAPER.right justified In a computer memory location, adata item that takes up consecutive bit positions,from right to left.Right-Leduc effect A phenomenon somewhatanalogous to the Hall effect. When a metal stripconducting heat is placed in a magnetic field perpendicularto the plane of the strip, a temperaturedifference develops across the strip.right shift In computer operation, a shift wherebyword bits are displayed to the right; the effect isdivision in a right arithmetic shift.rim drive 1. In a tape recorder, a driving method inwhich the motor shaft is provided with a smoothpulley that transfers motion directly to the rubber-tiredrim of the flywheel. 2. A driving methodfor a phonograph turntable in which a rotatingwheel contacts the outer edge of the platter.R in Symbol for INPUT RESISTANCE. (Also, R i .)ring1. The core of a toroidal coil. 2. See HYBRIDRING. 3. See RING MODULATOR. 4. See RINGINDUCTOR. 5. See RING MAGNET. 6. See RING-ING.ring armature A motor or generator armature havinga ring winding.ringback In a telephone system, the signal sentfrom the receiving (destination) telephone setback to the sending (source) set, indicating thatthe signal is being received. This consists of atone, interrupted by pulses at intervals of about0.05 second. The signal stops when the destinationset is taken off the hook. Also see RING-DOWN.ring circuit 1. See RING MODULATOR. 2. Awaveguide hybrid-tee resembling a ring havingradial branches. 3. In amateur radio operations,a circuit connected to a telephone line and radiotransmitter. The radio transmitter is energizedand modulated with an identifiable signal eachtime the telephone rings, so the telephone can beanswered via remote control.ring counter An electronic counter in which successivecascaded stages form a ring (i.e., the laststage in the chain is connected to the first stageso that the counter advances through the cycle,stage by stage, repetitively).ringdown In a telephone system, the signal sentfrom the transmitting (source) set to the receiving(destination) set, causing the destination set toring. Also see RINGBACK.ring head In tape recorders, a recording and playbackhead that consists essentially of a metal ringwith a gap at one point, and on which the coilsare wound.ring inductor 1. An inductor consisting of a singleturn of wire, or of a conductor bent into a loop.2. See SHADING COIL.ringing Self oscillation in a pulsed inductancecapacitancecircuit, sustained by the circuit’s flywheelaction (hysteresis), and usually producinga damped wave.ringing coil In the horizontal oscillator in a televisioncircuit, a small, adjustable coil (shunted by acapacitor) used to produce a sharp rise in inputsignalvoltage.ringing current In wire telephony, an alternatingcurrent superimposed on the direct operatingcurrent. Produces RINGDOWN.ringing time See RING TIME, 1.ring magnet A permanent magnet in the shape ofa ring or donut.ring main An electric power main that is closed toform a ring. This results in two independent electricalpaths between any two points in the circuit.If one path is interrupted, power can still betransmitted to any other point in the circuit froma power station.ring modulator A double-balanced diode-typemodulator circuit; its name is derived from thering-like arrangement of the four diodes.ring oscillator A self-excited oscillator in whichtwo sets of two transistors are operated in pushpull/parallel.ring shift In computer operation, the cyclic shiftingof digits from one end of a register to theother.ring time 1. The period of a damped oscillation—especially one set up in an inductance-capacitancecircuit by a pulse. 2. The time required foran ECHO BOX signal to decay below the displaylevel.ring winding A winding in which the turns of thecoil are laid on the outside of a ring-shaped coreand passed through its center, resulting in adonut coil with a core.ripple 1. A small alternating-current component inthe output of a direct-current power supply withinadequate filtering. 2. In computer and dataprocessingoperations, the serial transmission ofdata.

602 ripple amplitude • Rochelle saltring windingCoreripple amplitude The peak or peak-to-peak valueof ripple in a power supply (see RIPPLE, 1).ripple counter A binary counter consisting of flipflopscascaded in series. A pulse must pass sequentiallyfrom the input, through each stage, tothe output of the chain.ripple current Current flowing in a circuit as theresult of ripple voltage (see RIPPLE AMPLITUDE).ripple factor The ratio of the RIPPLE AMPLITUDEto the direct-current voltage output of a powersupply.ripple frequency The frequency of a ripple component(see RIPPLE, 1). In power supplies usinghalf-wave rectification, this frequency is normally60 Hz (the line frequency); in full-wave supplies,it is normally 120 Hz (twice the line frequency).ripple percentage See PERCENT RIPPLE.ripple torque Symbol, T R . In a torque motor, thesmall fluctuation in torque resulting from commutatorswitching action.ripple voltage See RIPPLE AMPLITUDE.RISC Abbreviation of REDUCED INSTRUCTIONSET COMPUTER.rise 1. See VOLTAGE RISE. 2. See RISE TIME.3. An increase in the amplitude of a pulse or wave.rise cable 1. A vertical feeder cable. 2. A verticalsection of a feeder cable.rise time The time required for a pulse to rise from10 percent to 90 percent of its peak amplitude.Compare FALL TIME.RJE Abbreviation of REMOTE JOB ENTRY.R k Symbol for cathode resistance.RL 1. Abbreviation of RESISTANCE-INDUCTANCE.2. Abbreviation of RELAY LOGIC.R L Abbreviation of LOAD RESISTANCE.RL bridge See RESISTANCE-INDUCTANCEBRIDGE.RL circuit See RESISTANCE-INDUCTANCE CIR-CUIT.R LF Symbol for low-frequency resistance.RL phase shifter See RESISTANCE-INDUCTANCEPHASE SHIFTER.R m Symbol for METER RESISTANCE.r m Symbol for emitter-collector transresistance of abipolar transistor.rms Abbreviation of ROOT MEAN SQUARE.rms converter See ROOT-MEAN-SQUARE CON-VERTER.rms current See EFFECTIVE CURRENT.rms meter A current meter or voltmeter whose deflectionis proportional to the root-mean-square(rms) value of current or voltage. In most meters,the deflection is proportional to either the peakvalue or the average value, but the scale of anrms unit is graduated on the basis of sine-waveinput.rms value See EFFECTIVE VALUE.rms voltage See EFFECTIVE VOLTAGE.Rn Symbol for RADON.R n 1. Symbol for NEGATIVE RESISTANCE. (Also,–R.) 2. Symbol for null resistance.R o Symbol for OUTPUT RESISTANCE. (Also, R out .)roaming 1. In cellular communications, an idealcondition in which the user of a mobile orportable wireless telephone set can travelthroughout a specified geographic region with no“dead zones” or interruption in service. 2. For amobile or portable cellular telephone subscriber,the act of traveling throughout a large geographicregion and, in particular, among different statesor countries.robot 1. An electromechanical device or system capableof reliably performing complex and/orrepetitive tasks. It can be controlled by a humanoperator or by a computer. 2. A usually autonomousdevice, as defined in 1, built to physicallyresemble a human being, with a head, twoarms, and some form of locomotion.robot generations Agreed-on milestones or criteriain the evolution of robots and smart machines.First generation: Before 1980. Mainlymechanical, stationary, physically rugged, no externalsensors, no artificial intelligence. Secondgeneration: 1980–1990. Tactile sensors, visionsystems, position sensors, pressure sensors, microcomputercontrol, programmable. Third generation:After 1990. Mobile, autonomy or groupcontrol, artificial intelligence, speech recognition/synthesis,teleoperation, navigation systems.Fourth generation: In conceptual stages.Highly intelligent, capable of building otherrobots, capable of doing many human tasks.robot gripper A robotic END EFFECTOR designedspecifically to grasp objects. The two basic designsare: hand-like and specialized. Hand-likegrippers are engineered according to the notionthat the human hand has evolved to near perfection,and should be mimicked in robots. Specializedgrippers are built by trial-and-error methodsand often bear little resemblance to humanhands.robotics The science and art of robot design, construction,operation, and maintenance.Rochelle salt Sodium potassium tartrate, a substancewhose crystals are piezoelectric. Such crystalsare used in some microphones, loudspeakers,and transducers. Also called SEIGNETE SALT.

ock • rotary beam 603rock Slang for QUARTZ CRYSTAL.rockbound Pertaining to an oscillator or radiotransmitter whose frequency is determined by aquartz crystal, and is, therefore, not variable overa significant range.rocker switch A toggle switch whose lever is a speciallyshaped bar. The bar is rocked back andforth to operate the switch. Compare BAT-HANDLE SWITCH, PADDLE SWITCH, and SLIDESWITCH.onoffrocker switchrod 1. A unit of length or distance; 1 rod = 5.029meters. 2. A bar of material with special properties.rod antenna See FERRITE-ROD ANTENNA.rod magnet A permanent magnet in the shape of arod with circular or elliptical cross section.roentgen Abbreviation, r. A unit of ionizing radiation;1 r is the quantity of radiation that produces1 esu of electricity (positive or negative) per cubiccentimeter of air at standard temperature andpressure. In average tissue, 1 r produces ionizationequivalent to an energy concentration of2.58 × 10 –4 C/kg (93 ergs per gram). Also see MIL-LIROENTGEN.roentgen equivalent man See REM.roentgen equivalent physical See REP.roentgen ray See X RAY.roger A communications signal meaning “Acknowledged.”Roget spiral A spring-like wire device that contractsin proportion to the magnitude of the currentflowing through it.role indicator In computer operations, a codeclassifying a keyword as a part of the speech (e.g.,noun).roll 1. In a display terminal having a line length ofless than the standard 80 characters, an operatingfeature that allows the operator to follow thetext along. The cursor remains fixed near the centerof the displayed line, while the text movesfrom right to left. 2. Vertical movement of a televisionpicture, resulting from lack of vertical synchronization.rollback In computer operations, the runningagain of a computer program or portion of theprogram. Also called RERUN.roller inductor A variable inductor, usually of theair-core type, with a shaft attached that allowsthe whole assembly to be rotated; a wheel contactprovides a movable tap. Such an indicator is continuouslyvariable and is often used in such devicesas antenna-tuning networks.rolling In television, the apparent continuous upwardor downward movement of the picture,resulting from lack of vertical synchronizationbetween the transmitter and receiver.rolloff 1. The rate at which a dependent variable(e.g., output amplitude) diminishes above or belowa certain critical value of the independentvariable (e.g., frequency). It pertains especially tofrequency response in audio devices and systems.2. Attenuation of the bass and/or treble responseor output in an audio system.ROM Abbreviation of READ-ONLY MEMORY.Romeo Phonetic alphabet code word for the letterR.Romex cable A form of wire cable with a coveringthat is highly resistant to the environment.roof mount A metal bracket for fastening an antennamast to a roof.room noise Ambient acoustic noise in a room.room resonance Acoustic resonance caused bythe geometry and contents of a room.room temperature Abbreviation, RT. 1. The temperatureof the chamber in which a test or fabricationis carried out. It is commonly used todistinguish between operations that can be performedat the ambient temperature and thosethat require an oven or a cold chamber. 2. A temperaturetypical of an indoor environment, approximately21 degrees Celsius (70 degreesFahrenheit).room tone A qualitative expression for the suitabilityor behavior of an enclosed area for a givenacoustic application. It affected by factors (suchas resonances or lack thereof, echoes or lackthereof, overall room size and proportions, andbackground noise).root mean square Abbreviation, rms. The squareroot of the arithmetic mean (average) of thesquares of a set of values.root-mean-square converter A device that convertsan input signal of any waveform into adirect-current signal of the same value as theEFFECTIVE VALUE of the input signal.root-mean-square current See EFFECTIVE CUR-RENT.root-mean-square value See EFFECTIVE VALUE.root-mean-square voltage See EFFECTIVE VOLT-AGE.ROP Abbreviation of record of production.rosin A substance derived chemically from an extractof pine wood, and used in some solders.rotameter A fluid flow gauge consisting of a floatwithin a glass tube having incremental markings.rotary amplifier See AMPLIDYNE.rotary antenna See ROTATABLE ANTENNA.rotary beam A beam antenna, such as a Yagi, thatcan be rotated in a (usually horizontal) plane to

604 rotary beam • roundingallow transmission and/or reception in variousdirections. Also see ROTATABLE ANTENNA.rotary-beam antenna See ROTARY BEAM.rotary converter A dynamo (electric machine)having a direct-current armature connected to acommutator on one end of the shaft and to sliprings on the other end. When the machine is operatedas a direct-current motor, it delivers an alternating-currentoutput, and vice versa. Alsocalled DOUBLE-CURRENT GENERATOR.rotary dialing An older style of telephone dialing inwhich a rotary pulse generator is used to dial thedigits.rotary digital audio tape Digital audio tape usedwith a recording/playback system that uses a rotatinghead or heads.rotary encoder An optical analog-to-digital (A/D)converter that operates by passing a light beamthrough a rotating disk. The amplitude of theanalog input signal at any moment causes a certainangular rotation of the disk, cutting off thelight beam, according to the nature of the patternon the disk. The resulting modulated light beamhas digital characteristics and can be detectedusing photocells.rotary inverter A motor-generator used to changea direct-current input voltage into an alternatingcurrentoutput voltage.rotary-motion sensor A transducer that deliversan output voltage proportional to the arc overwhich its shaft has been turned.rotary power amplifier See DC GENERATOR AM-PLIFIER.rotary relay An electromechanical relay in which apivoted armature rotates to open or close the contacts.The meter relay is an example.rotary selector switch See ROTARY SWITCH.rotary stepping relay See STEPPING SWITCH.rotary stepping switch See STEPPING SWITCH.rotary switch A switch in which a blade moves ina circle or in arcs over the contacts.rotary transformer A motor-generator used tochange an input voltage into a lower or higheroutput voltage.rotatable antenna An antenna that can be turnedto change the orientation of its main lobe (directionof greatest forward gain) in a specific plane(usually horizontal).rotating amplifier See DC GENERATOR AMPLI-FIER.rotating antenna An antenna that constantlyturns to scan a given area (e.g., a RADAR AN-TENNA).rotating-capacitor modulator A frequency modulatorconsisting of a motor-driven variable capacitor.Also see WOBBULATOR.rotating field An alternating-current electric ormagnetic field, such as that generated by the statorsof some motors, that revolves between poles.rotating interrupter A commutator (see COMMU-TATOR, 1).MastTowerrotating machines Electromechanical devices(such as motors, generators, amplidynes, rotaryconverters, etc.) that utilize magnetic flux to convertangular motion or displacement into electricalenergy, or vice-versa.rotating memory See DISK MEMORY and DRUMMEMORY.rotating voltmeter See GENERATING VOLT-METER.rotator A motor-driven, remotely controlled mechanismfor turning a directional antenna in a specificplane.rotor 1. A rotatable coil—especially in a motor orgenerator. Compare STATOR, 1. 2. The rotatingmember of a motor or generator. Compare STA-TOR, 2. 3. The rotating-plate assembly of a variablecapacitor. Compare STATOR, 3.rotor blade The wiper arm of a rheostat or potentiometer.rotor coil See ROTOR, 1.rotor plate The rotating plate(s) of a variable capacitor.Compare STATOR PLATE.roulette pattern A circular pattern for frequencyidentification with an oscilloscope, consisting ofloops around the screen’s circumference. CompareGEAR-WHEEL PATTERN, LISSAJOUS FIG-URE, and SPOT-WHEEL PATTERN.roundingAntennarotatable antennaRotator1. A method of approximating a quantityby reducing the number of significant digits. Forexample, rounding 3.44 to two significant digitsyields 3.4; rounding 3.46 to two significant digits

ounding • rumble 605yields 3.5. Compare TRUNCATION. 2. The approximationof a value to a specified number ofdecimal places or significant digits. 3. Smoothingof the corners of a square wave or sawtooth wave,resulting in lengthening of the transition timefrom one state to another.rounding error The error resulting from therounding of a number (see ROUNDING, 1, 2).round offTo shorten an otherwise lengthy numberby replacing numerical digits with zeros and increasingthe final nonreplaced digit by 1 if theleftmost replaced digit is 5 or greater. Thus,3.141592653 can be rounded off to 3.1416 or3.14.round-up A form of numerical approximation, inwhich a number with a value of n.5 or greater isassigned the value n + 1. This is a feature of manycalculators using scientific notation or a fixednumber of decimal places.R out Symbol for OUTPUT RESISTANCE. (Also, R o .)route1. To physically position wires or conductingcircuit paths by planning and deliberation. 2. Thepath over which conductors are positioned. 3. Apath over which signals or information can becarried.routine1. In computer operations, the completesequence of instructions for performing an operation(i.e., a program or program segment). 2. Atest or measurement procedure. 3. An assemblyor manufacturing procedure. 4. A standard troubleshootingprocedure.row In a matrix, a horizontal arrangement or set ofvalues.R P 1. Symbol for PLATE RESISTANCE. (Also, r P .)2. Symbol for POSITIVE RESISTANCE. 3. Symbolfor PARALLEL RESISTANCE. (Also, R par .) 4. Symbolfor PRIMARY RESISTANCE. (Also, R pri .)R par Symbol for PARALLEL RESISTANCE. (Also,R P .)r parameters 1. Device or network parameters expressedas resistances. 2. Transistor parametersin terms of resistance values in the equivalent teenetwork. Compare G PARAMETERS and H PA-RAMETERS.RPG Abbreviation of REPORT PROGRAM GENER-ATOR.rpm Abbreviation of revolutions per minute.rpm meter See ELECTRONIC TACHOMETER andSTROBOSCOPE.RPN Abbreviation of REVERSE POLISH NOTA-TION.R pri Symbol for PRIMARY RESISTANCE. (Also,R P .)rps Abbreviation of revolutions per second.RPT Radiotelegraphic abbreviation of repeat.R req 1. Symbol for REQUIRED RESISTANCE.2. Symbol for SCREEN RESISTANCE.R RF Symbol for RADIO-FREQUENCY RESIS-TANCE.R SSymbol for SOURCE RESISTANCE in a fieldeffecttransistor.R s 1. Symbol for SERIES RESISTANCE. (Also, R ser .)2. Symbol for SECONDARY RESISTANCE. (Also,R sec .)R sec Symbol for SECONDARY RESISTANCE. (Also,R s .)R ser Symbol for SERIES RESISTANCE. (Also, R s .)RST flip-flop A conventional flip-flop subject to theoperations of reset, set, and trigger.RST system In the amateur radio service, amethod of reporting signal quality in terms ofreadability, strength, and tone.R sweep In an oscilloscope or spectrum analyzer,an expanded portion of the trace produced by along triggered sweep. It permits detailed analysisof a small portion of a displayed waveform or frequencyband.RT 1. Abbreviation of RADIOTELEPHONE. 2. Abbreviationof ROOM TEMPERATURE.rt Abbreviation of RIGHT.R T 1. Symbol for THERMAL RESISTANCE. 2. Symbolfor total resistance. (Also, R t .)R t Symbol for total resistance.RTD Abbreviation of RESISTANCE TEMPERA-TURE DETECTOR.RTL Abbreviation of RESISTOR-TRANSISTORLOGIC.RTTY Abbreviation of RADIOTELETYPE.RTZ Abbreviation of RETURN TO ZERO. (Also, RZ.)Ru Symbol for RUTHENIUM.rubberA natural insulating material; an elastomerexhibiting rapid elastic recovery. Dielectric constant,2 to 3.5. Dielectric strength, 16 to 50kV/mm. Also called India rubber. Compare HARDRUBBER.rubber-covered wire Wire insulated with a jacketof rubber.rubidium Symbol, Rb. A metallic element. Atomicnumber, 37. Atomic weight, 85.468.ruby laser A laser using a ruby rod as the resonantelement.100-percentreflectorRuby crystalHelicalflash tuberuby laser95-percentreflectorOutputruby maser A maser in which the resonant materialis ruby.Ruhmkorff coil See INDUCTION COIL.rumble 1. Low-frequency acoustical noise of a frequencybelow about 50 Hz. 2. Low-frequencyelectrical noise in an audio circuit of a frequency

606 rumble • R-Y signalbelow about 50 Hz. 3. Vibrations that can occurin a poorly designed or malfunctioning phonographturntable.rumble filter An audio high-pass filter havingsharp cutoff below 50 Hz, for eliminating rumblearising from irregularities in the rotation of aphonograph turntable. Also see RUMBLE, 3.run 1. The execution of a computer routine or program.2. To execute a routine or program. 3. Tocause a routine or program to be executed. 4. Acommand that causes a routine or program to beexecuted.runawayIn a current-carrying circuit or device, especiallya semiconductor, a rapid increase in currentthat causes the temperature to rise, in turnresulting in a further increase in current. Unlesspreventive measures are taken, this will ultimatelydamage or destroy the component.run chart In computer operations, a flowchartshowing the organization and order of pertinentprograms to be run.running accumulator A computer storage unithaving registers linked so that data is transferredunidirectionally from one to the other, and inwhich only one register is accessible from the outside.running open 1. The condition of a mechanicalteleprinter running continuously in the absenceof a signal. The teleprinter operates, but nothingis printed; this keeps the machine in synchronization.2. Operation of a transmitter at themaximum rated level of input or output power.running-time meter See ELAPSED-TIME METER.run time 1. The period of time during which acomputer program is executed. 2. The length oftime required for a computer program to be executed.rupture 1. The usually rapid and violent tearingapart, or breaking through, of an insulating materialsubjected to excessive voltage. 2. The cleanopening of relay, circuit-breaker, or switch contactsto interrupt a current-carrying circuit.rush Broadband audio background noise, such asthat arising from superheterodyne receivers andhigh-gain amplifiers. Its name is derived from resemblanceto the gentle rushing of wind. CompareHISS, 1, 2.ruthenium Symbol, Ru. A rare metallic element.Atomic number, 44. Atomic weight, 101.07.rutherfordAbbreviation, rd. A unit of radioactivityequal to 10 6 disintegrations per second (2.7 × 10 –5curie). Also see KILORUTHERFORD, MEGA-RUTHERFORD, MICRORUTHERFORD, andMILLIRUTHERFORD.Rutherford atom An early concept of the nature ofthe atom, proposed by Rutherford in 1912. In thismodel, negatively charged electrons orbit a central,positively charged nucleus in a manner similarto the way planets orbit the sun. CompareBOHR ATOM.rutherfordium Symbol, Rf. Also called unnilquadium(Unq) and kurchatovium (Ku). Atomic number, 104.The most common isotope has atomic weight 261.Classified as a transition metal. It has a half-life onthe order of a few seconds to a few tenths of a second(depending on the isotope), is human-made,and is not known to occur in nature.RW Abbreviation of radiological warfare.R x Symbol for unknown resistance.RY Abbreviation of RELAY.ryotron A form of inductive semiconductor switch,operated at cold temperatures to maximize conductivity.R-Y signal In a color-television circuit, the signalrepresenting primary red (R) minus luminance(Y). A primary red signal is obtained when theR-Y signal is combined with the luminance (Y)signal. Compare B-Y SIGNAL and G-Y SIGNAL.

S 1. Symbol for SCREEN GRID of a vacuum tube.2. Symbol for SHELL of a tube or semiconductordevice. 3. Symbol for SULFUR. 4. Symbol for DE-FLECTION SENSITIVITY. 5. Symbol for SWITCH.6. Symbol for ELASTANCE. 7. Abbreviation ofSYNC. 8. Symbol for SECONDARY. 9. Abbreviationfor SIEMENS. 10. Abbreviation of SINE. 11.Symbol for ENTROPY.s 1. Symbol for distance or DISPLACEMENT.2. Symbol for SCREEN GRID of a vacuum tube.3. Symbol for STANDARD DEVIATION. 4. Abbreviationfor SECOND.SA Abbreviation of SUBJECT TO APPROVAL.S A band A section of the S band, extending from3100 to 3400 MHz.sabin A unit of sound absorption; 1 sabin representsa surface that can absorb sound at thesame rate as 1 square foot of a perfectly absorbentsurface.SADT Abbreviation of surface alloy diffused-basetransistor.SAE 1. Abbreviation of SHAFT-ANGLE ENCODER.2. Abbreviation of Society of Automotive Engineers.safe noise level A level of acoustic intensity equalto 85 dB above the threshold of hearing. At soundlevels higher than this, eardrum damage is possible.safety factor A figure denoting the extent of overloadthat a device can withstand before breakingdown.safety ground A connection made between equipment(usually the metal chassis, panel, case, orB-minus circuit) and the earth as a protectivemeasure against fire and electric shock.safety switch See ELECTRICAL INTERLOCK.UnitXUnitYsafety groundUnitZsal ammoniac Formula, NH 4 Cl. Ammonium chloride,the principal ingredient in the gelatinouselectrolyte of some dry cells and batteries.salient pole A pole, such as the polepiece of a motoror generator, that projects from the rest of thestructure (rotor assembly or motor frame).Salisbury chamber A radio-frequency test chamberin which the walls are non-reflective at variousfrequencies, thus simulating free space.salt-spray test A test to assess the life and performanceof electronic equipment in a marine environment.The equipment is sprayed, usually witha saltwater mist, and various electrical parametersare measured at prescribed time intervals.samarium Symbol, Sm. A metallic element of therare-earth group. Atomic number, 62. Atomicweight, 150.36.sample 1. A selection of quantities, events, or objects,taken at a specific time or time interval foranalysis or testing. 2. To take a sample, as definedin 1. 3. To test a quantity (current, voltage,temperature, pressure, etc.) or a materialCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

608 sample • saturation(electrolyte, insulant, corrosion, rust, etc.) takenfrom a larger group or body.sample and hold A method of storing a variablesignal for detailed examination.sampled data system A system that can be eitheranalog or digital, and that works from samples ofthe input signals.sampler In audio systems, a device that digitizesand stores sound for a brief interval of time.sample size In statistics, the number of items inthe sample space chosen for analysis.sample space In statistics, the set of events, numbers,or other items chosen for analysis.sampling 1. Observation of a signal at variouspoints in a circuit, without affecting the operationof the circuit. 2. The conversion of analog signalsto binary signals—especially for use in digitalcommunications systems and in computers. 3. Instatistics and probability, a set of function valuescorresponding to specifically chosen points in thedomain.sampling rate The frequency with which samplesare taken [e.g., 1/hr (one sample per hour) or10/min (10 samples per minute)].sampling window See WINDOW, 2.sand load A microwave power dissipator in whichthe absorptive material is a mixture of sand andcarbon.sapphire needle See SAPPHIRE STYLUS.sapphire stylus A jewel-tipped stylus for discrecording and playback. It is noted for durability.sat 1. Abbreviation of saturate. 2. Abbreviation ofSATURATION. 3. Abbreviation of SATELLITE.satd Abbreviation of saturated.satellite An artificial object sent into orbit aroundthe earth or another planet. See, for example, AC-TIVE COMMUNICATIONS SATELLITE and PAS-SIVE COMMUNICATIONS SATELLITE.satellite communication Communication via oneor more satellite transponders. Usually both stationsare on the ground, although sometimes oneor both stations are airborne or in space.satellite processor 1. In a computer, a microprocessorthat is subsidiary to the central processingunit (CPU). 2. In a data-processing system, a CPUused to handle the running of programs of secondaryimportance to the system’s main application.satellite television The broadcasting and receptionof television (TV) signals via earth-orbiting satellite.Usually, the satellite is in a geostationary orbit.The receiving station employs a dish antenna,a tuner, a digital-to-analog (D/A) converter (if thesignals are digital), and a TV receiver.satisfy To make a statement of inequality or anequation true (e.g., x = 2 satisfies the equation2x = x 2 ).saturable capacitor A voltage-variable ceramic orsemiconductor capacitor in which variations incapacitance stabilize at a reasonably constantvalue after a particular voltage level is reached.saturable-core magnetometer A MAGNETOME-TER in which the sensor is a saturable magneticcore with a winding. The readout is proportionalto the change in permeability of the core producedby the magnetic field under test.saturable reactor An inductor consisting essentiallyof a coil wound on a core of magneticmaterial whose magnetic flux can easily reachsaturation level. The inductance and, accordingly,the reactance of the device can be varied by passinga direct current through the coil simultaneouslywith the alternating current to be controlled.saturable transformer A transformer having a saturablecore that permits automatic regulation ofan alternating-current voltage.saturated color A visible color whose energy isconcentrated at a single wavelength or in a narrowband of wavelengths. Also called pure color.saturated logic Any form of digital-logic circuit inwhich the transistors are either completely cut offor completely saturated. It is characterized by relativeimmunity to noise, high speed, and highinput-level requirements.saturated operation 1. The operation of a magneticcore at or beyond its saturation point (i.e.,in the region where an increase in coil currentproduces no change in core magnetization).2. The operation of a transistor or vacuum tubebeyond its saturation point (i.e., in the regionwhere an increase in voltage produces no changein current, or vice versa). Compare UNSATURATEDOPERATION.saturated solution A solution, such as an electrolyte,that contains all of the solute that it ordinarilywill hold at a given temperature andpressure. Compare SUPERSATURATED SOLU-TION. Also see SOLUTE; SOLUTION, 1 and SOL-VENT, 2.saturating current See SATURATION CURRENT.saturation 1. See SATURATION POINT. 2. Thestate of purity of a color. In general, the greater

saturation • scale down 609the saturation, the narrower the bandwidth of theelectromagnetic energy. The highest possible saturationis represented by energy at a single wavelength[e.g., light of 700 nanometers (nm) appearsas highly saturated red, and light of 400 nm appearsas highly saturated violet]. Compare HUE.3. The condition of a ferromagnetic material inwhich it can accommodate no additional magneticflux. 4. The condition of a dielectric materialin which it can accommodate no additional electricflux.saturation current In a device, the current flowingat and beyond the SATURATION POINT.saturation flux 1. The magnetic flux density thatwill saturate a given sample of magnetic material.2. The electric flux density that will saturate agiven sample of dielectric material.saturation flux density See SATURATION INDUC-TION.saturation induction For a magnetic material, themaximum possible flux density.saturation limiting Output peak clipping that occurswhen a transistor or vacuum tube is driveninto saturation during part of the input cycle.Compare CUTOFF LIMITING.saturation point On a voltage-current conductioncurve, the point beyond which a further increasein voltage produces no appreciable increase incurrent.Collector/drain currentBase/gate voltagesaturation pointSaturationpointsaturation resistance The voltage-to-current ratiofor a saturated semiconductor.saturation switching The on/off switching operationin which a transistor is in its saturated statewhen conducting.saturation value 1. In a transistor, field-effecttransistor, or vacuum tube, the lowest level of theinput current, voltage, or power that results insaturation. 2. The maximum obtainable outputlevel for a given circuit. 3. In a magnetic material,the smallest level of magnetizing force that resultsin the maximum possible flux density.saturation voltage The (usually direct-currentoutput) voltage appearing across a device operatingin its saturation region (e.g., the collector volt-age of a switching transistor in its switched-onstate).SAVOR Abbreviation of SIGNAL-ACTUATEDVOICE RECORDER.sawtooth An alternating or pulsating wave of currentor voltage that is characterized by a gradualrise in amplitude followed by a rapid fall, or viceversa; its name is derived from its graphic resemblanceto the teeth of a saw.AmplitudesawtoothTimeSB 1. Abbreviation of SIDEBAND. 2. Abbreviationof SIMULTANEOUS BROADCAST.Sb Symbol for ANTIMONY.S band A radio-frequency band extending from1550 to 5200 MHz. For subdivisions of this band,see S A BAND, S C BAND, S D BAND, S F BAND, S GBAND, S H BAND, S Q BAND, S S BAND, S T BAND,S W BAND, S Y BAND, and S Z BAND.SBC Abbreviation of SINGLE-BOARD COMPUTER.SBDT Abbreviation of SURFACE-BARRIER DIF-FUSED TRANSISTOR.SBT Abbreviation of SURFACE-BARRIER TRAN-SISTOR.SC 1. Abbreviation of SUPPRESSED CARRIER.2. Abbreviation of SHORT CIRCUIT. 3. On drawings,the abbreviation for silk-covered.Sc Symbol for SCANDIUM.sc 1. Abbreviation of SINGLE CRYSTAL. 2. Abbreviationof SCALE. 3. Abbreviation of sine-cosine.4. Abbreviation of science.SCA Abbreviation of SUBSIDIARY COMMUNICA-TION AUTHORIZATION.SCA adapter An auxiliary tuner unit for separatingthe SCA subcarrier from a main frequencymodulatedsignal on which it is superimposed.Also see SCA SUBCARRIER and SUBSIDIARYCOMMUNICATIONS AUTHORIZATION.scalar quantity A quantity having magnitude, butfor which direction is not specified. CompareVECTOR QUANTITY.scale 1. A graduated line or curve for indicatingvalues of a quantity. 2. An ordered set of values.3. An ordered series of quantities, such as tones,frequencies, voltages, etc. (e.g., musical scale).scale division The space between consecutivegraduations on a scale (see SCALE, 1).scale down In computer operations, to adjust agroup of quantities according to a fixed factor sothat it can be accommodated by hardware orsoftware.

610 scale expansion • scanning yokescale expansion Spreading out the divisions inpart of a scale (see SCALE, 1).scale factor 1. A figure by which the readings froma particular scale must be multiplied or divided togive the true values of measured quantities. 2. Afigure via which values in one system of notationare converted to those in another system. 3. Inscaling down (see SCALE DOWN), the factor bywhich a group of quantities is adjusted. 4. Theratio of output frequency to input voltage for avoltage-to-frequency converter.scale-factor adjustment In some meters, an adjustmentthat allows full-scale deflection to be setat any desired value (within certain limits) of applied-signalamplitude.scale-factor error The absolute value of the differencebetween the actual scale factor and the idealscale factor for a multiplier circuit.scale-factor tolerance The extent to which a measuredvalue for the scale factor differs from thecomputed value. It is generally given as a percentage.scale length The end-to-end dimension of a scale(see SCALE, 1), in inches, centimeters, geometricdegrees, or number of divisions.scale multiplier See SCALE FACTOR, 1.scale-of-two counter A circuit that delivers oneoutput pulse for two successive input pulses.scale-of-10 counter A circuit that delivers oneoutput pulse for 10 successive input pulses.scale-of-ten scaler See SCALE-OF-10 COUNTER.scaler A circuit or device for extending the frequencyrange of another device (e.g., a circuit thatextends the range of a 1-MHz counter to 100MHz).scale range The difference between the lowest andhighest values on a scale.scale span See SCALE RANGE.scaling The fact, and the implications of the fact,that the mechanical strength of a structure increasesin proportion to the square of linear dimensionwhile the weight increases, according tothe cube of linear dimension. Thus, weight increasesmore rapidly than strength as a structure,composed of a given material, is madelarger. It is important in the design of large antennasand support structures.scaling adder An inverting OPERATIONAL AMPLI-FIER used to weight and sum multiple voltages.scaling circuit A circuit, such as one or more flipflops,that will deliver one output pulse after apredetermined number of input pulses have beenreceived; therefore, it will provide pulse or frequencydivision. See, for example, SCALE-OF-TWO COUNTER.scaling factor For a scaler, the number of inputpulses required for one output pulse.scaling ratio See SCALING FACTOR.scan 1. To traverse a range, field, or dimension.2. The amount of traversal in 1. 3. See SWEEP.4. To sample or reproduce an image in a single-lineelement, as in facsimile or television. 5. A singleline resulting from 4. 6. In information retrievaloperations, to inspect each record in a file or constituentof a list. 7. To check communications ordata channels for availability.scan conversion In television reception, the scanningof each line twice to convert a conventionalimage into one that can be displayed on a highdefinitionpicture tube.scan-converter tube A face-to-face assembly of acathode-ray tube and a vidicon in one envelope.scandium Symbol, Sc. A metallic element. Atomicnumber, 21. Atomic weight, 44.956.scan frequency See SCANNING FREQUENCY.scanner A device, especially a radio receiver,equipped with a circuit that searches communicationsor data channels for signals.scanner amplifier An amplifier for boosting ascanning signal. Also see SCAN, 1, 3, 4.scanning 1. In a cathode-ray tube or camera tube,the synchronized movement of the electron beam(or other marker) from right to left and/or fromtop to bottom. 2. The intermittent, but repetitive,monitoring of two or more communications channelsin rotating sequence. 3. The movement of aradar beam for the purpose of obtaining coverageover a specified area.scanning antenna A transmitting or receiving antenna(such as a rotating one) that covers a generallycircular region.scanning beam The deflected electron beam in acathode-ray tube. Also see SCAN, 1, 2, 3, 4, 5.scanning circuit A circuit for producing a scan(see SCAN, 2, 4).scanning frequency The number of scans per unittime, usually expressed in lines, sweeps, or channelsper second or per minute. Also called SCAN-NING RATE.scanning line A single line sampled or producedby a scanning process, as in facsimile, television,and graphic recording.scanning line frequency See SCANNING FRE-QUENCY.scanning linearity Uniformity of scanning rate. Ina linear scan, for example, scan speed is the sameat all points along a line.scanning loss The effective reduction in radar sensitivitythat occurs as the beam scans a givenarea, rather than remaining in a fixed orientation.scanning rate See SCANNING FREQUENCY.scanning receiver A receiver whose tuning is automaticallyand continuously swept through afrequency band to detect all signals in the band.scanning sonar A form of distance-measuring ordepth-finding sonar, in which the receiving transducerscans to find the direction of the echo orechoes.scanning speed The rate at which a line, region, orquantity is scanned or at which samples aretaken.scanning yoke See YOKE, 2.

scan rate • scientific notation 611scan rate 1. The rate at which a controlled quantityis checked periodically by a control computer.2. See SCANNING FREQUENCY.scan tuning Repetitive, automatic sweeping of afrequency band by a tuned circuit containing avaractor, whose capacitance is periodically variedby a sawtooth voltage.SCARA Abbreviation of SELECTIVE COMPLIANCEASSEMBLY ROBOT ARM.SCA subcarrier An auxiliary carrier (commonly67 kHz) superimposed on a main frequencymodulatedcarrier to convey subsidiary communications,such as music without commercials. Also seeSUBSIDIARY COMMUNICATION AUTHORIZATION.scatter To disperse or diffuse transmitted electromagneticradiation.scattering 1. The tendency of a concentrated beamof energy to be spread out when it passes througha given medium or substance. 2. The spreadingout of radio waves as they pass through the ionosphereor troposphere.schematic diagram An electronic circuit diagram.Also called WIRING DIAGRAM and schematic.schematic symbol A graphic symbol used to representelectronic components in a circuit diagram.Schering bridge A four-arm capacitance bridge inwhich the unknown capacitance is comparedwith a standard capacitance. This bridge is frequentlyused in testing electrolytic capacitors, towhich a direct-current polarizing voltage is appliedduring the measurement.R X balance R 1C XR XC 1R 2C SC X = C S (R 2 /R 1 )R X = R 1 (C 1 /C S )IonosphereC XbalanceTransmittingstationEarthscatteringReceivingstationscatter read In data processing, to distribute datafrom an input record to several storage areas.scatter transmission See BACK SCATTER andFORWARD SCATTER.S C band A section of the S BAND extending from2000 to 2400 MHz.scc Abbreviation of SINGLE-COTTON-COVERED(WIRE).SCDSB Abbreviation of SUPPRESSED CARRIERDOUBLE-SIDEBAND (see DOUBLE-SIDEBANDSUPPRESSED CARRIER).SCE Abbreviation of saturated calomel electrode.sce Abbreviation of SINGLE-COTTON-ENAMELED(WIRE).SCEPTRON Acronym for SPECTRAL COMPARA-TIVE PATTERN RECOGNIZER.schedule In computer operations, to establish theorder of importance of jobs to be run, and assignthe necessary resources for those jobs.schedule method A method of waveform analysisinvolving the evaluation of instantaneous amplitudesat numerous points in time. The values areobtained at specific intervals from the image ofone complete wave cycle, as displayed on an oscilloscopeor plotted on a graph.Schering bridgeSchmidt optical system In projection television, alens system used between the bright-image picturetube and the screen.Schmitt limiter See SCHMITT TRIGGER.Schmitt trigger A multivibrator that producesuniform-amplitude output pulses from a variable-amplitudeinput signal. This circuit hasmany applications, one being the conversion of asine wave into a square wave.Schottky diode A solid-state diode in which ametal and a semiconductor form the pn junction.Electrons injected into the metal have a higherenergy level than the charge carriers in a semiconductor,and energy storage at the junction islow because current flow is not accompanied byhole movement. Also known as HOT-CARRIERDIODE.Schottky logic A form of integrated-injection logicwith enhanced operating speed.Schottky noise The random noise resulting fromthe emission of charged particles, usually electronsor holes, from an electrode in an amplifyingdevice. This noise is usually of a wideband nature.scientific language Any computer programminglanguage used primarily for mathematical or scientificapplications.scientific notation The expression of very largeand very small numbers as a fixed-point part(mantissa) and a power of the radix (usually 10).

612 scientific notation • seaborgiumGenerally, the mantissa is greater than orequal to 1, but less than 10; the power of 10 is adjustedaccordingly. Thus, for example, 203,700 =2.037 × 10 5 ; 0.000533 = 5.33 × 10 –4 . See alsoSIGNIFICANT FIGURES.scintillating crystal A crystal, such as one ofsodium iodide, that sparkles or flashes when exposedto radioactive particles or rays.scintillation 1. In radar operations, the apparentrapid displacement of a target from its mean position.2. A momentary flash of light produced ina phosphor or scintillating crystal when a highvelocityparticle strikes it. 3. A small fluctuationin radio field intensity at a receiving point.scintillation counter A radiation counter consistingessentially of a scintillating crystal in combinationwith a photomultiplier tube. Flashes fromthe excited crystal cause the tube to deliver outputpulses that are totaled and indicated.scintillator material A substance, such as crystallinesodium iodide, that scintillates under certainstimuli.scissoring A method of interrupting the electronbeam in a cathode-ray tube when the beamwould not land on the phosphor screen.SCLC Abbreviation of SPACE-CHARGE-LIMITEDCURRENT.sco Abbreviation of SUBCARRIER OSCILLATOR.scope Colloquialism for OSCILLOSCOPE.Scott oscillator See PARALLEL-TEE OSCILLA-TOR.scp Abbreviation of SPHERICAL CANDLEPOWER.SCR Abbreviation of SILICON-CONTROLLED REC-TIFIER.scrambled signal Any signal in which (for secrecyor exclusivity) the elements are disarranged accordingto an encryption algorithm. Thus, intelligentreception is possible only if the signal isprocessed via a suitable decryption algorithm.Example: SCRAMBLED SPEECH.scrambled speech Voice transmission in whichthe frequencies have been inverted to preventeavesdropping. It is automatically unscrambled(by reinversion) at the receiver to restore intelligibility.scrambler circuit A circuit containing filters andfrequency inverters for scrambling speech.scratch filter An audio-frequency low-pass filterthat suppresses high-frequency noise caused byfriction between a phonograph disc and the needle.Inputscratch filterOutputscratchpad memory In computers, a low-capacitymemory that stores an intermediate result of acalculation.scratch tape Magnetic data tape that can be overwrittenfor any purpose.screen 1. See SCREEN GRID. 2. See SHIELD.3. The front surface of a cathode-ray tube. 4. Thesurface of a computer or terminal display.screen angle In radar, the angular difference betweenthe actual horizon and the plane perpendicularto the line connecting the radar set withthe center of the earth.screen current Symbol, I S or I SG . The current flowingin the screen circuit of an electron tube.screen grid In a vacuum tube, a grid element betweenthe control grid and plate. It reduces theinternal grid-plate capacitance, and consequentlyprevents self-oscillation when the tube is used ina straight-through amplifier.screen-grid neutralization Neutralization of anamplifier that uses a tetrode vacuum tube. Suchcircuits require smaller neutralizing capacitancesthan those used in triode amplifiers becauseof the lower interelectrode capacitance of thescreen-grid tube.screen illumination Edge lighting of the transparentscreen of an oscilloscope, to make the lines ofthe graticule more clearly visible.screen material See PHOSPHOR.screen resistance Symbol, R S or R SG . The internalresistance presented by the screen-grid/cathodepath of an electron tube.screen room See CAGE.screen voltage Symbol, E S or E SG . The voltage atthe screen grid of an electron tube.scribing The etching of a semiconductor wafer tofacilitate breaking the wafer into smaller pieces.ScriptX A high-level programming language usedin the writing of software for personal computers—especiallyin multimedia. Developed byKaleida Laboratories.SCS Abbreviation of SILICON-CONTROLLEDSWITCH.SCT Abbreviation of SURFACE-CHARGE TRAN-SISTOR.S curve 1. The voltage-versus-current curve for anegative-resistance device. Compare N CURVE.2. The response curve for a frequency-modulationdiscriminator or ratio detector.SD Abbreviation of STANDARD DEVIATION.S D band A section of the S BAND extending from4200 to 5200 MHz.SDF Abbreviation of static direction finder.SDR See SOFTWARE-DEFINED RADIO.Se Symbol for SELENIUM.seaborgium Symbol, Sg. Also called unnilhexium(Unh). Atomic number, 106. The most commonisotope has atomic weight 263. Classified as atransition metal. It has a half-life on the order of1 second or less, is human-made, and is notknown to occur in nature.

sea clutter • secondary frequency standard 613sea clutter Collectively, the radar echoes that thesea reflects.seal 1. The point at which a lead or electrode entersor leaves and is secured to an envelope, case,or housing. Such a point is often tightly closedagainst the passage of air in or out of the envelope.2. To close off a circuit or component fromtampering.sealed dry battery A set of electrochemical drycells that can be installed without concern for orientationor position. Example: 9-volt “transistorbattery.”sealed meter 1. A meter that is tightly closedagainst the entry of moisture and foreign materials.2. A meter that is locked or otherwise protectedagainst tampering.sealing compound A substance (such as wax,pitch, or plastic) used to enclose and protect electronicdevices.search 1. To scan or sweep through a range ofquantities or through a region of interest. 2. Toexamine (usually in some prescribed order) itemsof information in a computer memory to findthose satisfying a given criterion.search coil An inductive probe (exploring coil)used to sample magnetic fields.search oscillator A variable-frequency oscillatorused to locate and identify signals by the heterodynemethod.search probe 1. See SEARCH COIL. 2. A capacitiveprobe used to sample electric fields.search radar A radar that displays a target almostimmediately after that target enters a scannedarea.search time The time needed to test items duringa search (see SEARCH, 2).sea return See SEA CLUTTER.seasonal effects In ionospheric propagation, thechanges produced as a result of the revolution ofthe earth around the sun. The path of the sunacross the sky, and the length of the day, are primarilyresponsible for such effects.seasonal static Atmospheric electrical interference,most prevalent during the summer.S E band A section of the S BAND extending from1550 to 1650 MHz.sec 1. Abbreviation of SECOND. 2. Abbreviation ofSECTION. (Also, sect.) 3. Abbreviation of SEC-ONDARY. 4. Abbreviation of SECANT.secant Abbreviation, sec. The trigonometric functionrepresenting the ratio of the hypotenuse of aright triangle to the adjacent side (c/b). The secantis the reciprocal of the cosine; sec x = 1/cos x.second 1. Abbreviation, s and sec. A unit of time.The mean solar second is 1/86,400 of a mean solarday, and is 1/60 minute or 1/3600 hour.2. Symbol ("). A unit of arc measure. 1" = 1/3600geometric degree.secondaries See SECONDARY COLORS.secondary 1. See SECONDARY WINDING. 2. SeeSECONDARY STANDARD.secondary battery See STORAGE BATTERY.secondary calibration The calibration of an instrument,based on a reference instrument calibratedagainst an absolute source.secondary capacitance 1. The distributed capacitanceof the secondary winding of a transformerwhose primary winding is unloaded. ComparePRIMARY CAPACITANCE, 1. 2. A series or shuntcapacitance used to tune the secondary coil of aradio-frequency transformer. Compare PRIMARYCAPACITANCE, 2.FromIF amp.secondary capacitance, 2SecondarycapacitanceTo nextIF amp.secondary cell See STORAGE CELL.secondary circuit 1. The circuit associated withthe secondary winding of a transformer. 2. SeeOUTPUT CIRCUIT.secondary coil See SECONDARY WINDING.secondary color 1. A color prepared by mixing twoprimary colors. 2. In television operations, anydisplayed color composed of two or more colorprimaries.secondary current The current flowing in the secondarywinding of a transformer. Also calledTRANSFORMER OUTPUT CURRENT. ComparePRIMARY CURRENT.secondary electron 1. The electron possessing thelesser energy after a collision between two electrons.Compare PRIMARY ELECTRON. 2. Anelectron ejected by secondary emission.secondary emission The action whereby electronsin the atoms at the surface of a target are ejectedas a result of bombardment by a beam of (primary)electrons. Thus, in an electron tube, electronsfrom the cathode strike the plate with aforce that drives secondary electrons out of theplate, into the surrounding space.secondary emitter A source of secondary electrons(e.g., the plate of an electron tube or a dynodein a photomultiplier tube).secondary failure The failure of a component orcircuit, resulting from the failure of some othercomponent. For example, the pass transistor in apower supply might burn out, causing the outputvoltage to increase; this increased voltage candamage equipment connected to the supply.secondary frequency standard A device for generatingsignals of accurate frequency, but that does

614 secondary frequency standard • secular equilibriumnot possess the very high stability and extremeaccuracy of a primary frequency standard. Thesecondary standard is periodically checkedagainst a PRIMARY FREQUENCY STANDARDand appropriately corrected.secondary impedance 1. The impedance of thesecondary winding of a transformer whose primarywinding is unloaded. Compare PRIMARYIMPEDANCE, 1. 2. An external impedance presentedto the secondary winding of a transformer.Compare PRIMARY IMPEDANCE, 2.secondary inductance The inductance of the secondarywinding of a transformer whose primarywinding is unloaded. Compare PRIMARY INDUC-TANCE.secondary kVA The kilovolt-amperes in the secondarycircuit of an operating transformer. ComparePRIMARY KVA.secondary power The power in the secondary circuitof a transformer. Also see SECONDARY KVAand SECONDARY VA. Compare PRIMARY POWER.secondary radiation 1. The (sometimes random)reradiation of electromagnetic waves, as from areceiving antenna. 2. Rays emitted by atoms ormolecules when the latter are struck by other radiation.secondary rays Rays emitted by atoms or moleculesthat have been bombarded by other rays ofthe same general nature. Examples: secondary Xrays and secondary beta rays.secondary resistance The direct-current resistanceof the secondary winding of a transformer.Compare PRIMARY RESISTANCE.secondary standard An accurate source of aquantity (capacitance, frequency, inductance, resistance,etc.), that is referred periodically to aprimary standard for correction.secondary storage In computer and data-processingoperations, storage that is auxiliary to themain storage. Also called backing storage.secondary turns The number of turns in the secondarywinding of a transformer. Compare PRI-MARY TURNS.secondary utilization factor For a transformer ina rectifier circuit, the utility factor of the secondarywinding (ratio of direct-current power outputto secondary volt-amperes).secondary VA The volt-amperes in the secondarycircuit of a transformer. Compare PRIMARY VA.secondary voltage The voltage across the secondarywinding of a transformer. Also calledTRANSFORMER OUTPUT VOLTAGE. ComparePRIMARY VOLTAGE.secondary winding The normal output winding ofa transformer. Also called SECONDARY COIL.Compare PRIMARY WINDING.second breakdown In a large-area power transistor,a destructive breakdown caused by thermalrunaway.second-breakdown voltage The collector voltage atwhich second breakdown occurs in a transistor.second-channel attenuation See SELECTANCE, 2.second-channel interference In a given channel,interference arising from authorized signals twochannels removed.second detector In a superheterodyne receiver,the intermediate-frequency detector. CompareFIRST DETECTOR.second-level address In a computer program instruction,an address giving the location of theaddress of a required operand. Also called indirectaddress.sect Abbreviation of SECTION. (Also, sec.)section 1. A subcircuit or stage of a larger circuit(e.g., the oscillator section of a receiver). 2. Thesmaller unit described in 1, when self-containedand operated independently (e.g., filter section).3. See PROGRAM SEGMENT.sectionalized antenna A set of collinear radiatingelements, placed end-to-end with reactances betweenthem, for the purpose of modifying the radiationpattern.sectionalized winding 1. A method of winding acoil in complete, multilayer sections that arestacked side by side or top to bottom, a techniquethat reduces distributed capacitance. 2. A coilwound, as defined in 1.sector On a magnetic disk, a specific portion of atrack.sectoral horn antenna An (usually sheetmetal)antenna with the shape of a horn of rectangularcross section. It is flared in one dimension only.FlareddimensionMaximumradiation/responseTowaveguidesectoral horn antennasector display In a radar, a display that allows thecontinuous observation of a portion of thescanned area.secular equilibrium The state in which a radioactivesubstance changing into another substance

secular equilibrium • selective fading 615is decaying as fast as the second substance is beingformed.secular variation A slow change in the intensity ofthe terrestrial magnetic field.secure mode In a security system, the condition ofbeing fully activated.securite In radiotelephony, a spoken word (pronouncedsay-kyoor-ee-tay) identifying a transmissionconcerning safety. Equivalent to TT inradiotelegraphy.security code 1. A set of alphanumeric characters(letters and/or numbers) or switch settings thatactivates or deactivates a security system. 2. SeePASSWORD.security robot In a smart home, a robot that assistsin protection of a home or business, and itsoccupants, from intrusion, burglary, or attack. Ifan intruder enters the property, the securityrobot might drive the offender away or detain theoffender until police arrive. The robot might employiris-print detection or facial feature detectionto identify an intruder from a distance. The robotwould be linked to the home computer via abroad-bandwidth, high-speed wireless system.Compare SENTRY ROBOT. Also see SMARTHOME OR BUSINESS.security system A set of electronic (and sometimesalso electromechanical) devices designed todo one or more of the following: restrict access toa premises or computer system, detect abnormalconditions, detect unauthorized entry, alert humanoperators of abnormal conditions, alert ownersand/or authorities of unauthorized entry to apremises, and (in some cases) provide physicalprotection of property.Seebeck effect The development of an electromotiveforce in a junction of two dissimilar metals(a thermocouple) when the temperature of thejunction is different from that of the rest of themetal.Seebeck emf The electromotive force resultingfrom the Seebeck effect.seed crystal A small single crystal from which alarger single crystal (e.g., germanium or silicon) isgrown. Also see CZOCHRALSKI METHOD.seeing-eye robot A robot that serves in the capacityof a seeing-eye dog, to help visually impairedpeople in their daily activities.seek See SEARCH.seek area An area of direct-access storage to whichare assigned specific records and from which therecords can be accessed quickly.segment 1. The portion of a line or curve lying betweentwo points. 2. See PROGRAM SEGMENT.segmental meter An expanded-scale meter (seeSCALE EXPANSION).segmented encoding law An approximation of asmooth encoding law, done by means of linearpartitions or segments. The greater the number ofsegments, the more accurate the approximation.segmenting See PARTITIONING.segment mark A character indicating the divisionbetween tape file sections.segue (Pronounced SEG-way.) A smooth transitionfrom one sound or channel to another (e.g., betweenmusical selections in a radio broadcast).The first selection decreases in volume as the secondselection increases. There is some overlap.Seignette salt See ROCHELLE SALT.seismic detector A vibration sensor used in sometypes of intrusion-detection systems.seismogram A record produced by a SEISMO-GRAPH.seismograph An instrument for detecting andrecording earth tremors. Indicates the direction,magnitude, and time of a quake.seismometer See SEISMOGRAPH.seismoscope An instrument that shows the occurrenceand time of an earthquake. Compare SEIS-MOGRAPH.select To accept or separate a unit, quantity, orcourse of action from all those available (in agroup, mixture, or series).selectance 1. For a resonant circuit, the ratioEr/Ex, where Er is the voltage at resonance, andEx is the voltage at a specified nonresonant frequency.2. For a receiver, the figure S2/S1, whereS1 is the sensitivity of the receiver in a given frequencychannel, and S2 is the sensitivity in anotherspecified channel.selected mode In an encoder, a mode in which oneoutput is read and the others are ignored.selective Pertaining to a device or system, such asa radio receiver, with a high degree of SELECTIV-ITY.selective absorption The attenuation or absorptionof some frequencies or bands of frequencies,with little or no attenuation at other frequenciesor bands of frequencies.selective amplifier An amplifier that can betuned, with the desired degree of sharpness, to asingle frequency or band of frequencies. Radiofrequencyamplifiers are generally tuned bymeans of inductance-capacitance (LC) circuits;audio-frequency amplifiers are usually tuned bymeans of resistance-capacitance (RC) circuits.selective calling The calling, alerting, or alarmingof a desired station without interfering with otherstations.selective compliance assembly robot arm Abbreviation,SCARA. An electromechanical device designedespecially for use in assembly lines. Ituses cylindrical coordinate geometry to allow precise,programmable movements in three dimensions.selective dump In computer operations, a dump(see DUMP) affecting a small, specific memoryarea.selective fading Fading caused by propagationconditions, whose effects differ at slightly differentfrequencies. In an amplitude-modulated signal,this effect causes the sidebands and carrier

616 selective fading • self-excited oscillatorto arrive in various phase relationships, with resultingdistortion in the received signal.selective interference Interference confined to anarrow band of frequencies.selective polarization See POLARIZATION SE-LECTIVITY.selective reflection In the reflection of electronsdirected into a crystal by means of an electrongun, the tendency of the electrons to be reflectedmore readily when they strike the crystal at certainspeeds.selective relay 1. A relay or relay circuit tuned toopen or close at one signal frequency. 2. A relayor relay circuit adjusted to open or close at onevalue of current or voltage.selective trace In computer operations, a diagnosticprogram used to analyze certain areas ofmemory or specific kinds of program instructions,for debugging purposes.selectivity 1. The ability of a circuit or device topass signals of one frequency and reject signalsat other frequencies. 2. The degree to which a circuitor device passes signals of one frequency andrejects signals at other frequencies.selectivity control In some equipment (such asreceivers, crystal filters, wave analyzers, and vibrationmeters) an adjustment that permits variationof selectivity.Selectoject A fully electronic, continuously tunable,notcher-peaker that is resistance-capacitancetuned. The name is an acronym for select orreject.selector 1. A channel switch in a radio or televisionreceiver. 2. See SELECTOR SWITCH.selector channel In data-processing and computersystems, a data transmission channel controllingthe information flow between peripheralsand a central processing unit.selector pulse In digital communications, an identifyingpulse that represents a certain group ofbits or data.selector relay A device, such as a stepping switch,that actuates one of a number of available circuitson receipt of a predetermined number ofpulses.selector switch A (usually rotary) multipositionswitch that allows an operator to select fromamong several options (such as frequency channels,frequency bands, or selective filters).selenium Symbol, Se. A nonmetallic element.Atomic number, 34. Atomic weight, 78.96. It isused in the manufacture of some diodes, rectifiers,and photocells.selenium cell A photoelectric cell that uses speciallyprocessed selenium as the light-sensitivematerial. It can be operated as a photoconductivecell or a photovoltaic cell.selenium diode A junction diode in which thesemiconductor material is specially processed selenium.Also see JUNCTION DIODE.selenium photocell See SELENIUM CELL.selenium rectifier A disk- or plate-type power rectifierutilizing the junction between selenium andaluminum or selenium and iron.self-bias For a transistor or vacuum tube, inputelectrodebias voltage resulting from the flow ofoutput-electrode current through a resistor commonto both circuits. Also called AUTOMATICBIAS.self-biasself-capacitance The inherent internal capacitanceof a device other than a capacitor.self-checking number A number whose digitshave a value that determines the check digit attachedto it; thus, it can be verified following itstransfer between storage locations or peripherals.self-cleaning contacts Switch or relay contactsthat clean themselves automatically by means ofwiping action.self-contained device A device containing allparts and sections (e.g., main circuit, power supply,meter, loudspeaker, etc.) needed for full operation(i.e., no auxiliary equipment is needed).self-controlled oscillator See SELF-EXCITED OS-CILLATOR.self discharge The tendency of an electrochemicalcell or battery to gradually lose stored energywhen not in use.self-discharge rate A quantitative expression ofthe speed with which SELF DISCHARGE occursin an electrochemical cell or battery when it isstored without being used.self-energy Symbol, E. The energy mc 2 , in joules,of a particle traveling at the speed of light c(2.9979 × 10 8 meters per second) and whosemass is m kilograms.self erasing In a magnetic tape, the unwantederasing of data near a highly magnetized region.self-excited generator An alternating-currentgenerator in which the field coils are suppliedwith direct current produced by the machine itself.Compare SEPARATELY EXCITED GENERA-TOR.self-excited oscillator An oscillator consisting ofan amplifier that supplies its own input signalthrough positive feedback, and whose oscillationfrequency depends entirely on circuit constants,

self-excited oscillator • self-sustained oscillations 617such as the capacitance and inductance in a tankcircuit. Compare CRYSTAL OSCILLATOR, FORKOSCILLATOR, HUMMER, and MAGNETOSTRIC-TION OSCILLATOR.self-excited oscillator+Outputself-focus picture tube A television picture tube inwhich the electron gun has an automatic, electrostaticfocusing arrangement.self-generating photocell See PHOTOVOLTAICCELL.self-generating transducer A voltage-producingtransducer, such as a piezoelectric pickup or dynamicmicrophone.self-healing capacitor A capacitor, such as a wetelectrolytic unit, in which the dielectric is restoredto its normal condition after a high-voltagebreakdown.self-heated thermocouple A thermocouple inwhich the passage of an applied current producesthe heat necessary for the activation of the thermocouple.self-heating thermistor A thermistor heated toabove ambient temperature by the current passingthrough it. Also called DIRECTLY HEATEDTHERMISTOR. Compare INDIRECTLY HEATEDTHERMISTOR.self impedance The effective or measured impedanceat a circuit point.self-inductance 1. The inductance of an inductor.2. The inherent internal inductance of a deviceother than an inductor.self-induction Induction that occurs in a singlecircuit. An instance is the generation of an opposingvoltage across a coil by an alternating currentflowing through it. Compare INDUCTION.Also see INDUCTANCE.self-latching relay A relay that remains in thestate that it has been switched (i.e., locked openor closed) until a subsequent signal is received.self-modulated oscillator A circuit, such as ablocking oscillator, in which oscillation occurssimultaneously at two frequencies, one modulatingthe other.self-organizing Pertaining to a computer or systemthat can change the arrangement of data filesfor particular purposes.self-powered device A device that requires no externalsource of power (i.e., it is equipped with aself-contained battery or a generator).self-pulsing blocking oscillator A blocking oscillatorthat produces a train of radio-frequencypulses. Compare SINGLE-SWING BLOCKING OS-CILLATOR.self-quenching detector A super-regenerative detector(see SUPER-REGENERATIVE CIRCUIT) inwhich the low-frequency quenching voltage issupplied by the regenerative detector itself. Alsosee QUENCHING ACTION and QUENCH OSCIL-LATOR. Compare SEPARATELY QUENCHED DE-TECTOR.self-quenching oscillator A circuit, such as ablocking oscillator, in which oscillation is periodicallyswitched off automatically, resulting in aself-interrupted wave train.self-rectifying vibrator A vibrator-type powersupply in which one vibrator reed chops the direct-currentinput to the primary winding of thetransformer, and a second vibrator reed rectifiesthe alternating-current output delivered by thesecondary winding. Also see VIBRATOR RECTI-FIER.self-rectifying X-ray tube An X-ray tube operatedwith alternating-current anode voltage.self-regulation The ability of a circuit or device tocontrol its output automatically, according tosome predetermined plan, by using output errorto correct operation or to vary the input.self reset 1. The action of a circuit breaker to reapplypower after a certain elapsed time. 2. The actionof any device, returning a circuit or system tonormal automatically.self-resetting loop In a computer program, a loopin which instructions cause locations used in theloop to assume their condition prior to the loop’sexecution.self-resistance The inherent internal resistance ofa device other than a resistor.self-resonant frequency The frequency at which adevice will resonate naturally (without externaltuning). Thus, an inductor will self-resonate withits distributed capacitance; similarly, a capacitorwill resonate with its stray inductance.self-saturation In a magnetic amplifier, saturationresulting from rectification of the saturablereactoroutput current.self-starting motor An alternating-current motorthat starts running as soon as voltage is applied(i.e., no external mechanical force is needed). Alsosee SHADING COIL.self-sustained oscillations Oscillations maintainedby means of positive feedback (inductiveor capacitive) from the output to the inputof a circuit. See, for example, SELF-EXCITEDOSCILLATOR.

618 self-test • semiresonant lineself-test Any arrangement whereby a device orsystem determines, without the aid of an externaloperator, whether or not it is operating correctly.self-ventilated motor See OPEN MOTOR.self-wiping contacts See SELF-CLEANING CON-TACTS.selsyn See AUTOSYN and SYNCHRO.SEM 1. Abbreviation of SINGLE-ELECTRON MEM-ORY. 2. Abbreviation of SCANNING ELECTRONMICROSCOPE.semantic network A reasoning scheme sometimesused in artificial intelligence. Logical state-mentsor sentences are broken down into nodes (generallynouns) and relationships (generally verbsand modifiers). This allows statements to bemapped in a way that is easy for computers tostore and modify.semiautomatic key Also called bug. A telegraphkey that mechanically produces a string ofMorse-code dots (short pulses) when its lever ispressed to one side (usually toward the right),and continuous circuit closure when the lever ispressed to the opposite side (usually toward theleft). Dashes are manually sent by the operator.semiconductor A material whose natural resistivitylies between that of conductors and insulators(e.g., GERMANIUM, SILICON, SELENIUM, andGALLIUM ARSENIDE).semiconductor capacitor A miniaturized componentthat takes advantage of reverse biasingin a semiconductor P-N junction. When a voltagesource is connected across a diode so that itdoes not conduct, the diode acts as a capacitor.The capacitance varies depending on how muchreverse voltage is applied to the diode. Thegreater the reverse voltage, the smaller the capacitance.Some diodes are especially manufacturedto serve this function. This phenomenoncan be useful in the fabrication of integrated circuits(ICs). See also INTEGRATED CIRCUIT,VARACTOR.semiconductor counter A device for measuringthe intensity of ionizing radiation (such as alphaparticles, beta particles, or gamma rays) using aphotodiode and sensing circuit.semiconductor device A component (such as adiode, photocell, rectifier, or transistor) that exploitsthe properties of a semiconductor.semiconductor diode A solid-state diode, as opposedto a vacuum-tube diode or gas-tube diode.Examples: germanium diode, selenium diode, andsilicon diode.semiconductor junction Within a body of semiconductormaterial, the area of physical contactbetween two regions (usually n and p) having oppositeelectrical properties.semiconductor laser See LASER DIODE.semiconductor material See SEMICONDUCTOR.semiconductor-metal junction The area ofphysical contact between a metal and a semiconductor.semiconductor photosensor A semiconductorphotodiode or phototransistor, as opposed to aphototube.semiconductor rectifier A heavy-duty semiconductordiode (or assembly of such diodes) designedprimarily to change alternating current todirect current in power-supply units. Rectifierscommonly are made from copper oxide, germanium,magnesium-copper sulfide, selenium, orsilicon. Also see JUNCTION DIODE and METERRECTIFIER.semiconductor resistor A tiny resistor manufacturedfrom semiconductor material, especially onethat is etched onto the chip of an integrated circuit(IC). The thickness, and the types and concentrationsof impurities added, determine the resistanceof the component. Such resistors can handleonly a tiny amount of power because of their smallsize. But because IC circuits are designed to consumeminimal power, this is not a problem. Thesmall signals produced by ICs can be amplified,using circuits made from discrete components, if itis necessary to obtain higher signal power. Seealso INTEGRATED CIRCUIT.semidirectional Pertaining to a transducer thatexhibits different directional characteristics atdifferent frequencies.semiduplex operation A two-frequency communicationsystem that operates in duplex at one endof the link, and in simplex at the other end. Alsosee DUPLEX OPERATION and SIMPLEX TELEG-RAPHY.semilogarithmic graph Also called semilog graph.A graph in which one axis is logarithmic and theother axis is linear.Logarithmic scaley107532y = x1x0 2 4 6 8 10linear scalesemilogarithmic graphsemimetal An elemental substance that exhibitssome, but not all, of the properties of a metal (e.g.,antimony and arsenic). Also called METALLOID.semiresonant line An open-wire transmission linecut approximately to resonant length at the frequencyof operation.

semitone • sequential 619semitone See HALF STEP.sender See TRANSMITTER, 1, 3.sending-end impedance See DRIVING-POINTIMPEDANCE.sending set 1. See RADIO TRANSMITTER. 2. Anequipment for transmitting electromagneticwaves. Also see TRANSMITTER, 1.sensation level The level of sound that produces atingling or noticeable sensation in the ear.sense 1. To check the condition of a switching device,such as a gate. 2. See READ.sense amplifier A device that produces a controlsignal when some characteristic of the input signalchanges.sense determination In a direction finder thatprovides an ambiguous indication (two readings180 degrees apart), the process of deducing, orthe ability of the apparatus to deduce, the true directionfrom which the signal is coming.sense resistor A (usually low-value) resistor usedto sense current in a circuit without introducinga significant loss. The voltage drop across this resistoris proportional to the current and can beapplied to a voltmeter, oscilloscope, or other instrumentfor measurement or observation.sensing circuit 1. A circuit that samples a quantity.2. In a voltage regulator, the circuit thatmonitors the output voltage and delivers a controlvoltage proportional to the output-voltage error.sensing window See WINDOW, 2.sensitive communications Two-way communicationsof an emergency or priority nature, or involvingthe security of government operations.sensitive device A device that responds to a signalof low amplitude.sensitivity 1. The ability of a circuit or device torespond to a low-level applied stimulus. 2. For areceiver, the input-signal (in microvolts or millivolts)required for a specified output level. 3. Fora galvanometer, microamperes or milliamperesper scale division. 4. The ohms-per-volt rating ofa voltmeter. Also see VOLTMETER SENSITIVITY.sensitivity adjustment 1. An input gain control inan amplifier circuit. 2. The radio-frequency gaincontrol of a receiver. 3. A control or switch that isused to select the range or threshold of a piece oftest equipment.sensitivity control A manual or automatic devicefor adjusting the sensitivity of a circuit or device.sensitometer An instrument used to measure thesensitivity of certain materials to light.sensor 1. A device that samples a phenomenon,and delivers a proportionate current or voltage interms of which the intensity of the phenomenoncan be measured, or with which control actioncan be initiated. 2. An electronic device that detectsabnormal conditions (e.g., smoke and heat)and delivers a warning signal to human operatorsand/or computers. 3. An electronic device thatdetects intrusion to a premises and delivers awarning signal to human operators and/or computers.sentry robot In a smart home or business, a robotthat alerts the owner to abnormal conditions. Itcan detect fire, burglars, or water in places itshould not be. It might also detect abnormal temperature,barometric pressure, wind speed, humidity,or air pollution. A wireless link alerts theowner via a device similar to a common beeper.Compare SECURITY ROBOT. Also see SMARTHOME OR BUSINESS.separately excited generator An alternatingcurrentgenerator whose field coils are suppliedwith direct current from another generator or froma battery. Compare SELF-EXCITED GENERATOR.separately quenched detector A superregenerativedetector (see SUPERREGENERATIVE CIR-CUIT) in which the quenching voltage is suppliedby a separate low-frequency oscillator. Also seeQUENCHING ACTION and QUENCH OSCILLA-TOR. Compare SELF-QUENCHED OSCILLATOR.separation See CHANNEL SEPARATION.separation energy The energy required to removea proton or neutron from the nucleus of an atom.The separation energy depends on the atomicnumber.separator 1. See FILTER, 1. 2. A perforated orporous plate of insulating material (usually plasticor wood) for holding active plates apart in astorage cell. 3. In computer operations, a charactermarking the division between logical dataunits. Also called data delimiter.septate cavity A coaxial cavity containing a SEP-TUM between the inner and outer conductors.septate waveguide A waveguide containing one ormore septa (see SEPTUM) to control power transmission.septum A thin metal vane used as a reflector in awaveguide or cavity.sequence 1. A succession of objects, parameters,or numbers. 2. An ordered set of numbers—eachof which is related to its predecessor by a specificmathematical function.sequence checking routine In computer operations,a routine that verifies the order of items ofdata.sequence control register In a computer memory,a register whose contents determine the instructionto be implemented next.sequence programmer A timing device that can bepreset to start or stop various operations at predeterminedtimes.sequencer A device that initiates or terminatesevents in a desired sequence.sequence relay A relay whose several contactsclose in a predetermined order.sequence timer A timer in which separate delaycircuits are actuated in a predetermined sequence.sequential In computer operations, a term denotingoperations on data items in which the items

620 sequential • series equivalent of parallel circuit(e.g., records in a file) are taken in an order determinedby key values, rather than in the order inwhich the items are physically arranged.sequential access memory Any semiconductormemory in which data can be recalled or addressedonly in a certain specified order.sequential analysis In statistics, using an unspecifiednumber of observations as samples fromwhich a result is derived. Each observation isaccepted or rejected, or another observation ismade.sequential color television The successive transmissionof the three primary colors in a televisionsystem, and their reproduction at the receiver inthe same order. Also see DOT-SEQUENTIAL SYS-TEM, FIELD-SEQUENTIAL SYSTEM, and LINE-SEQUENTIAL SYSTEM.sequential control Computer operation in whichthe order of instruction implementation is thesame as the order of instruction storage.sequential relay See SEQUENCE RELAY.sequential scanning Rectilinear television scanningin which the center-to-center distance betweensuccessive lines is the same as the nominalline width.sequential switch 1. A switch that provides selectionof two or more ports in a rotating succession.2. In a television system, a switch that allows themonitoring technician to select any of the camerasfor viewing.sequential timer See SEQUENCE TIMER.ser 1. Abbreviation of SERIES. 2. Abbreviation ofSERIAL.serial 1. Pertaining to the performance of steps, orthe occurrence of elements (such as data itemson magnetic tape), in succession. 2. An order,row, or sequence in which one item follows another(as opposed to parallel).serial access Access to data file records in their orderin a storage medium.serial adder See SERIAL ARITHMETIC UNIT.serial arithmetic unit In computer operations, anarithmetic unit in which digits are handled in order.Compare PARALLEL ADDER.serial bit Data in which the bits of each byte orword are sent or received one at a time.serial memory A register in which the input andoutput data is stored and retrieved one bit at atime.serial-parallel 1. Pertaining to data transfer that isserial in one sense and parallel in another sense.For example, entire words might be serially transmittedwithin a system, but the constituent bitsof each word might be transferred in parallel.2. See PARALLEL-SERIES.serial processing In computer operations, the sequentialprocessing of several different programsthrough a single channel. Compare PARALLELPROCESSING.serial storage In computer operation, storage inwhich elements are entered in order and areavailable only in the same order. Compare PAR-ALLEL STORAGE.serial transfer The propagation of informationalong a single path, in which data bits are sentone after the other.series 1. The sum of a mathematical sequence (seeSEQUENCE, 2). 2. Pertaining to the connectionof elements or components end-to-end (see SE-RIES CIRCUIT).series addition See SERIES-AIDING.series-aiding The condition in which two seriesvoltages or magnetic fields are added together.Compare SERIES-BUCKING.series antenna tuning Antenna-feeder tuning inwhich a separate tuning capacitor is connected inseries with each wire. Compare PARALLEL AN-TENNA TUNING.Two-wirelineInputseries antenna tuningseries bucking The condition in which two seriesvoltages or magnetic fields oppose each other.Compare SERIES-AIDING.series capacitance Capacitance acting, or connected,in series with another capacitance orother quantity.series capacitors Capacitors connected in series.If the individual capacitors have values C1, C2,. . . , Cn, then the total capacitance Ct is equal to1/(1/C1 + 1/C2 + . . . + 1/Cn). Also see SERIESCIRCUIT.series circuit A circuit whose components are, ineffect, connected in a string (i.e., end-to-end).Compare PARALLEL CIRCUIT.series-diode half-wave rectifier See SERIES-DIODE RECTIFIER.series-diode rectifier A rectifier circuit in whichthe diode is connected in series with the sourceand load. Compare SHUNT-DIODE RECTIFIER.series dropping resistor See DROPPING RESIS-TOR.series equivalent impedance A series impedancethat will draw the same current (magnitude andphase) drawn by a given parallel circuit connectedacross the same single-phase source.series equivalent of parallel circuitEQUIVALENT IMPEDANCE.See SERIES

series-fed amplifier • serrated rotor plate 621series-fed amplifier An amplifier circuit in whichthe operating voltages are applied in series withthe alternating-current signal voltages. Also seeSERIES FEED.series-fed oscillator An oscillator circuit in whichthe direct-current operating voltage is applied inseries with the alternating-current output voltage.Also see SERIES FEED.series feed The application of alternating-current(ac) and direct-current (dc) voltages in series to adevice. Example: the presentation of the dc operatingvoltages for an amplifier in series withthe ac signal voltages (see SERIES-FED AMPLI-FIER).series feedback A feedback system in which thefeedback signal is presented to the input point inseries with the input signal. Compare SHUNTFEEDBACK.series field A magnetic field produced by a serieswinding in a motor or generator.series generator An electric generator in which thearmature and field windings are connected in series.Compare SHUNT GENERATOR.series inductance 1. Inductance acting, effectively,in series with some other quantity (e.g., theinherent inductance of a wirewound resistor).2. An inductance connected in series with otherinductances, or with some other quantity (e.g.,capacitance and resistance).series inductors Inductors connected in series,and separated or oriented in a way that minimizesthe effects of mutual inductance. Assumingzero mutual inductance, if the individual inductorshave values L1, L2, . . . , Ln, then the total inductanceLt is equal to L1 + L2 + . . . + Ln. Also seeSERIES CIRCUIT.series limiter A limiter (clipper) circuit in whichthe diode is essentially in series with the signal.Compare PARALLEL LIMITER.series loading The series insertion of reactancesin a circuit for the purpose of impedancematching.series magnetic circuits A combination of severalmagnetic paths in line so that flux extendsthrough each path in sequence; this is analogousto the passage of electric current successivelythrough series-connected resistors.series motor An electric motor whose armatureand field windings are connected in series. CompareSHUNT MOTOR.series operation The operation of units in succession,necessitating sequential current flowthrough each. Also see SERIES CIRCUIT.series opposition See SERIES BUCKING.series-parallel See PARALLEL-SERIES.series-parallel capacitors See PARALLEL-SERIESCAPACITORS.series-parallel inductors See PARALLEL-SERIESINDUCTORS.series-parallel resistors See PARALLEL-SERIESRESISTORS.series regulator A voltage regulator circuit inwhich the controlled device is in series with theload. Compare SHUNT REGULATOR.series resistance 1. Resistance acting in serieswith another resistance or with another quantity(e.g., capacitance and inductance). 2. The inherentresistance that acts effectively in series withthe plates of a capacitor. 3. The resistance of thewire in a coil, acting effectively in series with theinductance.series resistors Resistors connected in series witheach other. If the individual resistors have valuesR1, R2, . . . , Rn, then the total resistance Rt isequal to R1 + R2 + . . . + Rn. Also see SERIESCIRCUIT.series resonance Resonance in a circuit consistingof a capacitor, inductor, and an alternatingcurrentgenerator in series. At the resonant frequency,the inductive reactance and thecapacitive reactance cancel, so the net reactanceis zero. The capacitor current and inductorcurrent are maximum and equal, and the circuitimpedance is minimum. Compare PARALLELRESONANCE.series-resonant circuit A resonant circuit inwhich the capacitor, inductor, and generator areconnected in series. Also see SERIES RESO-NANCE. Compare PARALLEL-RESONANT CIR-CUIT.series-resonant trap A wavetrap consisting of aseries-resonant inductance-capacitance (LC) circuit.Compare PARALLEL-RESONANT TRAP.series-resonant wavetrap See SERIES-RESO-NANT TRAP.series-shunt circuit See PARALLEL-SERIES.series tee junction See E-PLANE TEE JUNCTION.series tracking capacitor See OSCILLATOR PAD-DER.series-type frequency multiplier A varactor frequency-multipliercircuit in which the varactor isin series with the input and output. CompareSHUNT-TYPE FREQUENCY MULTIPLIER.series-type resonance bridge A resonance bridgein which the impedance arm is a series-resonantcircuit. Compare SHUNT-TYPE RESONANCEBRIDGE.series winding 1. In a motor or generator, a windingconnected in series with the armature. 2. Amethod of motor or generator construction inwhich the field winding is connected in serieswith the armature.series-wound generator See SERIES GENERA-TOR.series-wound motor See SERIES MOTOR.serrated pulse A pulse having a notched or slottedtop. An example is the vertical sync pulse in television.serrated rotor plate In a variable capacitor, an externalrotor plate that is slotted radially. This altersthe capacitance-variation curve of thecapacitor to allow alignment of sensitive apparatus

622 serrated rotor plate • sexadecimal number system(e.g., the tracking of radio-frequency tunedcircuits in a radio receiver).serrated vertical sync pulse In television, the verticalsync pulse notched at twice the horizontalsweep frequency.service 1. To maintain or repair electronic equipment.2. To provide maintenance or repair of electronicequipment.serviceability ratio For a device or system, the ratiots/(ts + td), where ts is serviceable (operational)time, and td is downtime (non-operationaltime).serviceable time The cumulative time duringwhich an operator-monitored (but not necessarilyoperated) device or system is capable of normaloperation.service area For a broadcast or communicationsstation, the useful coverage area.service band 1. For a communications system, theband of frequencies in which operation is normallycarried out. 2. A band of frequencies specificallyassigned, by government regulation, to acertain communications service or services.service channel The band of frequencies that aparticular broadcast or communications stationoccupies, when the carrier frequency is held constant.service charge The amount charged by a technicianfor installation, maintenance, or repair ofequipment. It is often performed on a per-hourbasis.service maintenance For a cell or battery, the relativeamount of energy capacity (percentage offull-charge capacity) available at a given time, orafter a certain length of time in normal use.service meter 1. An energy (“power”) meter. Alsosee KILOWATT-HOUR METER. 2. A rugged multimeterused by a service technician.service oscillator A signal generator designed expresslyfor troubleshooting and repair service.service switch 1. The main switch controlling theelectric service to a building or other place of installation.2. In television repair, a switch on therear of a chassis. The switch facilitates adjustmentof screen controls by removing vertical deflectiontemporarily.service-type instrument An instrument havingreasonable accuracy and a degree of ruggednessso that it is suitable for field or shop use.Examples: SERVICE METER and SERVICE OS-CILLATOR. Compare LABORATORY-GRADEINSTRUMENT.servo amplifier A highly stable amplifier designedexpressly for use in a SERVOMECHANISM.servo loop In a control system (particularly a servoamplifier), the output-to-input feedback loop,through which automatic control is performed.servomechanism Also called servo. A self-correcting,closed-loop control system. It usually usesan electromechanical device, such as a motor,that controls some electronic device. Error signals,supplied by the controlled electronic device,cause the motor to run in such a way as to optimizeor stabilize the system.servomotor A motor operated by the output signalof a servo amplifier. Depending on the end applicationof the servo system, the motor signal mightor might not be corrected.servo oscillation In a servo system, a back-andforthmovement or fluctuation, relative to theoptimum setting or position. It Results from impropersystem adjustment. Sometimes the systemstabilizes at the optimum after a short periodof oscillation; in some cases, the oscillation continuesindefinitely.servo robot A (usually industrial) robot whose motionsequence is programmed into a computer.The robot follows the instructions given by thecomputer, and makes precise, timed movementson that basis. Different computer programs allowdifferent motion sequences, so a single robot canbe used for various tasks.servo system An automatic control system usingone or more servomechanisms.set1. A piece of equipment or a system (e.g., radioset). 2. In a flip-flop circuit, an input that is notcontrolled by the clock. 3. To adjust a circuit ordevice, such as a flip-flop, to a desired operatingpoint or condition. 4. A class of numbers, things,or events. 5. In computer programming, to initializea variable (i.e., to assign a label to a location).set analyzer A combination test instrument designedoriginally for troubleshooting radio receivers.It consists of a multimeter and transistortester or vacuum-tube tester.set noise Electrical noise arising inside a radio ortelevision receiver, as opposed to that picked upfrom the outside.set pulse A pulse used to adjust a device to a certainstate (see SET, 3).set terminal In a flip-flop, the one-input terminal.Compare RESET TERMINAL.setting The position or value to which an adjustabledevice is set for a particular purpose.settling time 1. In a digital voltmeter, the time requiredbetween the application of a test voltageand the final display of an accurate readout. 2. Ina digital-to-analog converter, the time betweenhalf of the level change over all inputs and the arrivalof the output to a level within a certain toleranceof its specified final level. It is defined foreither full-scale to zero or zero to full-scale.set up To arrange and prepare equipment for operation.setup See SET, 1.set-up time 1. The time required to install and testan electronic system, and to ready the system foroperation. 2. In a digital gate, the length of timethat a pulse must be held to produce a change ofstate.sexadecimal number systemNUMBER SYSTEM.See HEXADECIMAL

sexagesimal number system • shaft-position indicator 623sexagesimal number system A number systemwhose radix is 60.SF 1. Abbreviation of SAFETY FACTOR. 2. Abbreviationof SINGLE FREQUENCY. 3. Abbreviationof STANDARD FREQUENCY. 4. Abbreviation ofSTABILITY FACTOR.SFA Abbreviation of SINGLE-FREQUENCY AMPLI-FIER.S F band A section of the S BAND extending from1650 to 1850 MHz.sferics In wireless broadcast or communicationsreception, random electromagnetic noise generatedby the earth’s atmosphere. Some of thisnoise is thermal in origin; some originates in thunderstorms.Sometimes this noise is called static.pole of a motor. Current induced in the coilcauses a momentary flux shift that approximatesa rotating field that self-starts a simple singlephaseinduction motor. 2. A coil used in a simpleac relay to prevent chatter.shading ring See SHADING COIL.shading signal In a television camera, a signal thatincreases the gain of the amplifier while the beamscans a dark part of the image.shadow area A region in which signal attenuationor the absence of a signal results from theSHADOW EFFECT.ObstructionShadowareaTransmittershadow areaSFO 1. Abbreviation of SINGLE-FREQUENCYOSCILLATOR. 2. Abbreviation of STANDARD-FREQUENCY OSCILLATOR.SFR Abbreviation of SINGLE-FREQUENCY RE-CEIVER.SFR-Chireix-Mesny antenna See CHIREIX-MESNY ANTENNA.SG Abbreviation of SCREEN GRID.S G band A section of the S BAND extending from2700 to 2900 MHz.SGCS Abbreviation of silicon gate-controlled switch(see SILICON-CONTROLLED SWITCH).shaded-pole motor An induction-type alternatingcurrentmotor using shading coils on the fieldpoles for self-starting with a single-phase supply.shading Electronic enhancement of a televisionpicture, resulting in a different brightness overvarious portions of the background, as comparedwith the actual situation. It can be used, for example,to make certain subjects stand out fromthe background.shading coil 1. A single, short-circuited turn (copperring) encircling the tip of the core of a coil thatcarries alternating current (ac), such as the fieldshadow attenuation 1. The attenuation of electromagneticenergy caused by an obstacle. It is generallymeasured in decibels. 2. The attenuation ofelectromagnetic energy produced by the curvatureof the earth.shadow effect The obstruction of radio waves byobjects in their path.shadow mask See APERTURE MASK.shadow meter See SHADOW TUNING INDICATOR.shadow region See SHADOW AREA.shadow tuning indicator A tuning meter in whichthe indicating medium is a shadow whose widthis proportional to meter current.shaft The rodlike part of an adjustable component(such as a potentiometer or variable capacitor) towhich a rotating (or turning) member is attached.shaft-angle encoder An electronic system for convertingshaft rotation into direct binary or decimalreadings.shaft lock A device for fastening the shaft of an adjustablecomponent (such as a potentiometer, rotaryswitch, or variable capacitor) in position at aparticular setting.shaft-position encoder See SHAFT-ANGLE EN-CODER.shaft-position indicator A device that delivers ananalog or digital output signal proportional to thearc of rotation of a shaft.

624 shaker • shock-excited oscillatorshaker See VIBRATOR, 2.shake table A platform, actuated by a vibrator, onwhich components can be mounted for a vibrationtest.shallow-diffused junction A pn junction made bydiffusing the impurity material for a short distanceinto the semiconductor wafer. CompareDEEP-DIFFUSED JUNCTION.shape factor 1. For a tuned circuit, the ratio of the60-dB bandwidth to the 6-dB bandwidth. 2. For afilter, the ratio of bandwidth at high attenuationto that at low attenuation.shaping network A combination of components forchanging the natural response of a circuit to a desiredresponse (i.e., a curve-changing circuit).shared file A data file that is available for use bymore than one system simultaneously.shared files system A data-processing systemhaving one direct-access storage device fromwhich information can be accessed by more thanone computer.sharpener 1. A circuit or device for increasing theselectivity of another circuit or device. 2. A circuitor device for decreasing the rise or fall time of apulse or square wave. 3. A circuit or device forsteepening the response of a filter.sharpness See SELECTIVITY.sharp pulse A pulse having extremely fast rise andfall times and narrow width (i.e., a spike).shaving The physical modification of a phonographdisc, or other permanent recording surface,in preparation for rerecording.S H band A section of the S BAND extending from3700 to 3900 MHz.sheath See POSITIVE-ION SHEATH.shelf corrosion In a dry cell in storage, deteriorationof the negative electrode because of local actionin the zinc.shelf life 1. The longest period of time that electronicequipment can be continuously kept instorage before deterioration of materials or degradationof performance occurs. 2. The longest periodof time that a battery can be stored withoutuse before it must be discarded or recharged.shell 1. An electronic orbit (imaginary shell) in anatom. 2. The envelope of a component (e.g., theouter casing of a power transistor or the housingof a plug). 3. The rigid case in an audio or videotape cassette.shell-type choke See SHELL-TYPE INDUCTOR.shell-type core A core that completely surroundsthe coil(s) of a choke or transformer.shell-type inductor An inductor in which the corecompletely surrounds the coil.shell-type transformer A transformer in whichthe core completely surrounds the coils.shf Abbreviation of SUPERHIGH FREQUENCY.shield A metallic partition or box for confining anelectric or magnetic field.shield baffle A sheet-type shield. Also see BAFFLE,2 and SHIELD PARTITION.shield box A shield having a general box shape,and which is usually enclosed on all sides.shield braid Tubing woven from wire, throughwhich an insulated wire is passed and thusshielded.shield can A cylindrical shield, usually enclosedon all sides.shield disk A flat shield having a disk shape. Alsosee BAFFLE, 2; SHIELD BAFFLE; and SHIELDPARTITION.shielded cable Cable completely enclosed within ametal sheath that is either flexible or rigid.shielded wire A single strand of insulated wirecompletely enclosed in a flexible or rigid shield.shield partition A wall-type shield usually consistingof a single, flat sheet of metal, sometimesbent into an angle. Also called BAFFLE SHIELD(see BAFFLE, 2).shield plate See BAFFLE, 2; SHIELD BAFFLE;SHIELD DISK; and SHIELD PARTITION.shield room See CAGE.shield wire A (usually grounded) wire, near andparallel to another wire that it shields.shift 1. To move from one operating point to anotherin a characteristic curve, or in the operationof an equipment. 2. To transfer data from onepoint to another in a system, or move it left orright in a register.shift flip-flop circuit A flip-flop designed especiallyas a stage in a shift register.shift pulse In a shift register, a drive pulse that initiatesthe shifting of characters.shift register In computers, calculators, and storagesystems, a circuit (usually composed of flipflopsin cascade) in which pulses can be shiftedfrom stage to stage and finally out of the circuit.shingle-type photocell A device in which severalseparate photocells are series connected byslightly overlapping the ends of adjacent cells.ship station A radio or radar station installedaboard a ship that is not in port.ship-to-shore communication Radio communicationbetween a ship at sea and a land-based station.shock 1. See ELECTRIC SHOCK. 2. A signal appliedmomentarily to a circuit, as in the shock excitationof a tank. 3. A sudden, dramatic changein an environmental variable (such as temperature).4. Physical blows or vibration.shock absorber Any object or device intended forreducing physical vibration of a component, set ofcomponents, circuit, or system.shock device 1. A device for administering shocktherapy (see ELECTROSHOCK, 1). 2. An inductioncoil and associated primary supply for applyinghigh voltage to a wire fence.shock excitation Driving an inductance-capacitance(LC) tuned circuit into damped oscillationby momentarily applying a pulse.shock-excited oscillator A type of self-excited oscillatorin which the transistor is suddenly cut off

shock-excited oscillator • short skip 625R G+BGDTransmitterKInputLCOutputshock-excited oscillatorby applying a cutoff voltage to the gate or baseelectrode. This abrupt interruption of steadydrain or collector current shocks the tank intodamped oscillations.shock hazard 1. Any situation that presents thedanger of electric shock to attendant personnel.2. The existence of a potential difference that willcause a current of at least 5 mA to flow through aresistance of 500 ohms or more, for a prolongedperiod of time.Shockley diode See FOUR-LAYER DIODE.shock mount A structure that secures a microphonewhile minimizing the pickup of vibrationsthrough the table, floor, or other surface onwhich the microphone is placed.shock therapy See ELECTROSHOCK, 1.shoran Contraction of SHORT-RANGE NAVIGA-TION.shore effect The tendency of radio waves travelingalong a shore to be bent either toward or awayfrom the shore. It can occur because of differencesin surface conductivity and/or atmospherictemperature over land, as compared withwater.shore station A fixed, land-based radio stationthat communicates with ships at sea.shore-to-ship communication See SHIP-TO-SHORE COMMUNICATION.short circuit An often unintended low-resistancepath through which current bypasses a componentor circuit.short-circuit current In a power supply, the currentthat flows when the output is directlyshorted. Many power supplies have shutdown devicesthat cause the current to stop flowing whenthe output terminals are short-circuited; othersupplies effectively insert resistance in serieswith the load, if necessary, to limit the current.short-circuiting switch A rotary selector switch inwhich unused contacts are automatically shortcircuited.short-circuit parameter A parameter for whichzero resistance is assumed in the part of the cir-Landshore effectWatercuit under consideration. The current amplificationfactor (alpha) of a common-base-connectedtransistor is such a parameter because its collectorload resistance is assumed to be zero.shorted-stub tuning Tuning a stub to match afeeder to an antenna by sliding a short-circuitingbar along the two wires of the feeder.shorting bar A thick, metal strap for short-circuitingtwo binding posts.shorting link A sheet-metal strip for connectingtogether two binding posts.shorting loop In a telephone system, a device thatshort-circuits two specified points for the purposeof testing or line fault location.shorting stick A metal rod with an insulating handle,used to short-circuit a charged capacitor toremove the shock hazard.shorting switch See SHORT-CIRCUITINGSWITCH.short-line tuning Use of a parallel capacitance totune a transmission line that is less than a quarter-wavelong.short-range navigation Contraction, shoran. Navigationby means of SHORT-RANGE RADAR.short-range radar A radar having a 50- to 150-mile maximum line-of-sight range for a 1-squaremeterreflecting target that is perpendicular tothe radar beam.short skip Skip of only a few hundred miles range.Also see SHORT-SKIP COMMUNICATION.

626 short-skip communication • SIshort-skip communication Radio communicationvia the ionosphere over relatively short distances(400 to 1300 miles). See, for example,SPORADIC-E SKIP.short-term drift The gradual change in the valueof a quantity, such as frequency or voltage, observedover a comparatively brief interval, as opposedto change occurring over a long period.Compare LONG-TERM DRIFT.short-term effect The variation of any electricalparameter over a relatively brief time interval. Example:frequency drift over a short time period.Also called short-time effect.short-term stability Stability reckoned over acomparatively brief time interval, as opposed tostability for a long period. Compare LONG-TERMSTABILITY.short-time effect See SHORT-TERM EFFECT.shortwave 1. Pertaining to wavelengths shorterthan 200 meters (i.e., frequencies higher than1.50 MHz). 2. Pertaining to the frequencies abovethe standard amplitude-modulation broadcastband (above 1.605 MHz), but below 30 MHz.shortwave converter A superheterodyne converterfor adapting a longwave receiver (such as abroadcast receiver) for shortwave reception.shortwave listener Abbreviation, SWL. A radiohobbyist who receives, but does not transmit,shortwave signals.shortwave receiver Any radio receiver capable ofintercepting and demodulating signals in therange 1.705 MHz to 30 MHz.shortwave transmitter Any radio transmitter capableof producing energy in the range 1.705 MHzto 30 MHz.shot-effect noise Electrical noise caused by randomfluctuations in a current, as in a diode ortransistor. Also see EQUIVALENT NOISE RESIS-TANCE. Compare THERMAL NOISE.shotgun microphone A highly directional microphonesensitive only to sounds coming from aspecific direction; the response pattern has a narrowmain lobe. It name results from its long,cylindrical configuration.shot noise Electrical noise arising from intermittentimpulses, such as those produced by sparkdischarges, make-and-break contacts, etc. Itsname results from its resemblance to pistol shots.shrink The amount by which a material being measuredwith an electronic instrument decreases insurface dimension. Compare STRETCH.shrink tubing Plastic sleeving placed over a conductoror at a conductor/connector joint, andmade to shrink tightly with the application ofheat.shunt Synonym, parallel. 1. Pertaining to theconnection of one component across (in parallelwith) another (e.g., shunt resistor). 2. Pertainingto connection of components in such a mannerthat they each (or all) are subjected to identicalvoltages. 3. A deliberately produced short circuitbetween two specific points in a device or system.4. To deliberately bypass some part of a systemby means of a short circuit.shunt circuit See PARALLEL CIRCUIT.shunt-diode rectifier A rectifier circuit in whichthe diode is connected in parallel with the sourceand load. Compare SERIES-DIODE RECTIFIER.shunt-fed 1. Pertaining to a circuit or device inwhich the direct-current operating voltage and alternating-currentsignal voltage are applied inparallel to an electrode. 2. Pertaining to a basegroundedvertical antenna excited at some pointabove ground.shunt feed See PARALLEL FEED.shunt feedback A feedback system in which thefed-back signal is presented to the input of thenetwork in parallel with the input signal. CompareSERIES FEEDBACK.shunt generator An electric generator in which thearmature and field windings are connected inparallel. Compare SERIES GENERATOR.shunting effect The condition in which a quantity,such as stray capacitance or resistance, acts inparallel with another quantity. Example: theshunting (parallel) resistance of an electrolyticcapacitor.shunt leads Interconnecting wires used for thepurpose of attaching a shunting component to atest instrument.shunt limiter See PARALLEL LIMITER.shunt loading The parallel insertion of reactancein a circuit, for the purpose of impedance matching.shunt motor An electric motor whose armatureand field windings are connected in parallel.Compare SERIES MOTOR.shunt regulator A voltage-regulator circuit inwhich the controlled transistor or vacuum tube isin parallel with the output (load) terminals. CompareSERIES REGULATOR.shunt resistor 1. A resistor connected in parallelwith a meter or recorder to increase its currentrange. 2. A resistor connected in parallel with avoltmeter to convert it into a current meter. CompareMULTIPLIER RESISTOR.shunt-series circuit See PARALLEL-SERIES CIR-CUIT.shunt tee junction A waveguide H-PLANE TEEJUNCTION.shunt-type frequency multiplier A varactor frequencymultiplier circuit in which the varactor isin parallel with the input and output. CompareSERIES-TYPE FREQUENCY MULTIPLIER.shunt-type resonance bridge A resonance bridgein which the impedance arm is a parallel-resonantcircuit. Compare SERIES-TYPE RESO-NANCE BRIDGE.shunt-wound generator See SHUNT GENERATOR.shunt-wound motor See SHUNT MOTOR.SI Abbreviation of (Standard) INTERNATIONALSYSTEM OF UNITS.

S/I • sidetone 627S/I Abbreviation of signal-to-intermodulation ratio.Si Symbol for SILICON.sibilants 1. High-frequency (hissing) componentsof speech. 2. High-frequency sounds or audio signals.SIC Abbreviation of specific inductive capacity (seeDIELECTRIC CONSTANT).SiC Formula for SILICON CARBIDE.sideband 1. With respect to a carrier, one of theadditional frequencies generated by the modulationprocess. In simple amplitude modulation,the two sidebands are fc + fm and fc – fm, wherefc is the carrier frequency, and fm is the modulationfrequency. 2. Pertaining to sidebands as definedin 1.Relative amplitude (V)10050BandwidthLowersidebandCarrier(channel center)Uppersidebandsideband technique A method of using, for communicationsor other purposes, one or both of thesidebands of a modulated signal without the carrier.side-chain amplifier An auxiliary amplifier that isexternal to a main amplifier. Such an amplifiermight be used, for example, in a feedback channelor in a volume-compression or volumeexpansionchannel.side frequency See SIDEBAND.side lobe In certain directional antenna systems, aminor lobe in the horizontal-plane directivity patternthat appears at right angles, or nearly atright angles, to the main lobe. Such a lobe representsreduced sensitivity and/or power gain relativeto the main lobe. Also see MAIN LOBE,MINOR LOBE.RelativemodulatingfrequencyRelativemodulatingfrequencysidebandsideband attenuation See SIDEBAND CUTTING.sideband cutting Elimination or attenuation of thesidebands of a modulated signal by a circuit havinginsufficient bandwidth.sideband frequency The frequency of the modulation-generatedsignal accompanying a carrier.One sideband frequency is that of the carrier minusthat of the modulating signal; another is thesum of the carrier and the modulation frequency.See also SIDEBAND, 1.sideband interference 1. Interference arising fromone or both of the normal sidebands of a modulatedsignal. 2. Interference caused by spurioussidebands, resulting from overmodulation.sideband power The power contained in the sideband(s)of a signal.sideband slicing See SIDEBAND CUTTING.sideband splatter In an amplitude-modulated orsingle-sideband signal, the emission of sidebandenergy at frequencies other than withinthe designated channel. Also simply calledsplatter.sidelobe suppression Elimination of the sidelobe(s)from the radiation pattern of an antenna.sidestacked antennas Antennas mounted in ahorizontal line, parallel to each other, and connectedby a common coupler to a transmitter orreceiver.sideswiper A manual telegraph key operated bymoving the lever sideways, rather than up anddown.sidetone 1. In wire telephony, the reproduction bythe receiver of sounds picked up by the transmitterof the same telephone. 2. In radiotelegraphy,an audible tone actuated when the carrier istransmitted. It allows the sending operator tohear Morse code elements as they are sent.

628 sidetone telephone • signal rectificationsidetone telephone A telephone set with no provisionfor canceling the sidetone.siemens Symbol, S. The SI unit of conductance.The conductance of a component or medium insiemens is equal to the reciprocal of the resistancein ohms.Siemen’s electrodynamometer A spring-tensionmeter that operates by means of torque, with zerocurrent through the device representing zerotorque. It can be used for measurements of current,voltage, or power.Sierra Phonetic alphabet code word for the letter S.sig Abbreviation of SIGNAL.sign 1. Any indicator denoting whether a value ispositive or negative. 2. A graphic device indicatingan operation. Examples: + (addition), × (multiplication).3. Any symbol. An ampersand, forexample, is an “and” sign. 4. A characteristicsymptom of malfunction or improper operation(e.g., a high standing-wave ratio in an antennasystem is a sign of an impedance mismatch).signal An electrical quantity, such as a current orvoltage, that can be used to convey informationfor communication, control, calculation, etc.signal-actuated voice recorder Abbreviation, SA-VOR. A recorder that goes into operation automaticallywhen the speaker starts talking andstops when the speaker finishes.signal amplitude The intensity of a signal quantity(see SIGNAL).signal booster See PREAMPLIFIER.signal channel In a system, a channel throughwhich only signals flow, control and modifying impulsesbeing accommodated by other channels.signal circuit A circuit handling signal currentsand voltages to the exclusion of control and operatingcurrents and voltages.signal conditioner Any accessory device (such as apeak probe, demodulator probe, current shunt,etc.) used to modify or change the function of a basicinstrument (such as an electronic voltmeter).signal converter See CONVERTER, 1.signal current The current component of a signal,as opposed to operating current in a system.signal diode A diode designed primarily for lightdutysignal applications (detection, demodulation,modulation, curve changing), as opposed tothe heavy-duty applications of power diodes andrectifiers.signal distance In two words (bit groups) of thesame length, the number of corresponding bit positionswhose states differ. For example, the signaldistance between 01001 and 10011 is 3.signal-flow analysis A graphic method of analyzingcircuits, particularly those using feedback,through the use of diagrams in which straight arrowsrepresent transmission paths, dots representnodes, and curved arrows representfeedback paths.signal-flow diagram The transmission-path diagramused in SIGNAL-FLOW ANALYSIS.signal gain The gain of an amplifier circuit—especiallyif used in small-signal applications. Seealso AMPLIFICATION, and GAIN.signal generator An instrument that produces signalsof precise frequency and amplitude, usuallyover a wide range.signal ground 1. Any circuit point that remains atzero signal potential. 2. A connection to a pointthat is deliberately maintained at zero signal potential.signal/image ratio See SIGNAL-TO-IMAGE RA-TIO.signaling In a communications system, the exchangeof data in electrical form, either analog ordigital.signaling rate In data communications, the speedat which data is transmitted. It is commonly expressedin bits per second (bps). Also, it is sometimesexpressed in baud or in words per minute(wpm).signaling time slot In a communications signal, aspecified interval of time, starting at a certain instantin each signal frame. This interval is usedexclusively for the purpose of signaling.signal injection 1. The introduction of a signalinto a circuit. 2. A method of troubleshooting incommunications receivers. A signal generator isused to introduce a test signal into each stage,starting with the output and proceeding stage-bystagetoward the input, until the defective stageor component is located.signal injector A simple (usually single-frequency)signal generator used in troubleshooting to introducea test signal at selected points in a circuit,to locate malfunctioning stages or components.Also see SIGNAL INJECTION, 2.signal intensity See SIGNAL STRENGTH.signal inversion Phase reversal of a signal passingthrough a circuit, device or medium.signal level At a given point in a circuit, thestrength of a signal, with respect to a referenceamplitude.signal loss 1. A reduction in the amplitude of a signalas it passes through a system. 2. Thecomplete disappearance of a signal. 3. SeeFRACTIONAL GAIN.signal mixer See MIXER.signal/noise ratio See SIGNAL-TO-NOISE RATIO.signal notcher See NOTCH FILTER.signal peaker See PEAK FILTER.signal power The amplitude of a signal expressedin watts, milliwatts, or microwatts, as opposed toamplitude expressed as a current or voltage.signal processor Any device, (e.g., preamplifier,expander, amplitude limiter, delay network) insertedinto or added onto a system to modify aninput or output signal.signal rectification The conversion of an alternating-currentsignal into a proportionate directcurrentsignal, usually by means of a diodecircuit.

signal rectifier • silicon capacitor 629RFInsignal rectificationdcOutsignal rectifier See SIGNAL DIODE.signal regeneration See SIGNAL RESHAPING.signal reshaping 1. The processing of a signal sothat it acquires its original waveform. Also calledsignal regeneration. 2. Passing a digital signal ofany type through a circuit that delivers a uniformoutput pulse on a real-time one-to-onebasis.signal shifter 1. A device used for quickly changingthe frequency of a transmitted signal. 2. A devicethat automatically causes a transmittedsignal to be sent on a frequency that differs fromthe receiver frequency by a known and predeterminedamount. 3. See MIXER, 1. 4. See CON-VERTER, 1.signal squirter See SIGNAL INJECTOR.signal strength The amplitude of a signal, usuallyin terms of voltage. Current or power is specifiedin some applications.signal-strength meter 1. See FIELD-STRENGTHMETER. 2. See S-METER.signal synthesizer A special signal generator deliveringsignals whose frequency, amplitude, andwaveshape can be adjusted at will.signal time delay The time required for an elementof a signal to be transmitted through a circuit ornetwork. This delay results in phase shift in anamplifier.signal-to-distortion ratio In a receiver, the ratio ofthe desired signal to the level of distortion otherthan the specified signal. Usually expressed indecibels (dB).signal-to-image ratio Abbreviation, S/I. In a receiver,the ratio of signal amplitude to image amplitude,both being measured in the same units.It is usually expressed in decibels (dB).signal-to-noise-plus-noise ratio Abbreviation,(S+N)/N. In a receiver, the ratio of the combinedsignal and noise amplitude to the amplitude ofthe noise alone. It is usually expressed in decibels(dB). Peak voltages are used to determine this ratioin the case of pulse noise; root-mean-square(rms) voltages are used in the case of randomnoise.signal-to-noise ratio Abbreviations: S/N, SNR. Ina receiver, the ratio of signal amplitude to noiseamplitude. It is usually expressed in decibels+(dB). Peak voltages are used to determine this ratioin the case of pulse noise; root-mean-square(rms) voltages are used in the case of randomnoise.signal-to-noise-and-distortion ratio Abbreviation,SINAD. In a receiver, the ratio of the desiredsignal to the level of noise and distortion, otherthan the specified signal. It is usually expressedin decibels (dB).signal tracer A tuned or untuned detector/amplifierhaving an input probe and an output indicator(meter, loudspeaker, or both), for following atest signal through a circuit.signal voltage The voltage component of a signal,as opposed to the operating voltage of the circuitgenerating or passing the signal.signal wave 1. Any electromagnetic disturbance ofa periodic nature that is modulated to convey information.2. The visual illustration or renditionof an electromagnetic disturbance that is modulatedto convey information.signal winding In a magnetic amplifier or saturablereactor, the coil that receives the controlcurrent.signal window See WINDOW, 2.signal wobbulator A frequency modulator usedwith an unmodulated signal generator to providesweep signals for visual alignment. Also seeWOBBULATOR.sign bit A one-bit SIGN DIGIT.sign digit A character indicating the sign (positiveor negative) of the value of the field or word towhich it is attached (usually at the end).signed field In a computer record, a field having anumber whose sign is indicated by a SIGN DIGIT.significant digits See SIGNIFICANT FIGURES.significant figures In a numerical quantity, especiallyone expressed in scientific (power of 10) notation,those figures (digits) that depict a quantityto a required, relevant, or justifiable degreeof precision. For example, 173,201 expressedto three significant figures is 1.73 × 10 5 ;0.00477583 expressed to four significant figuresis 4.776 × 10 –3 . See also SCIENTIFIC NOTATION.silencer See AUTOMATIC NOISE LIMITER.silent alarm In security systems, the transmissionof a warning signal to attendant human operatorsand/or computers, without producing an audibleor visible warning to intruders.silent alignment See VISUAL ALIGNMENT.silent piano See ELECTRONIC PIANO.silica pencil A rod of silicon dioxide heated to emitinfrared rays.silicon Symbol, Si. A metalloidal element. Atomicnumber, 14. Atomic weight, 28.086. Silicon isabundant in the earth’s crust. It is used in manysemiconductor devices, including integrated circuits,diodes, photocells, rectifiers, and transistors.silicon capacitorPACITOR.See VOLTAGE-VARIABLE CA-

630 silicon carbide • silver-oxide cellsilicon carbide Formula, SiC. A compound of siliconand carbon valued as a semiconductor, anabrasive material, and a refractory substance.The commercial product is made by heating carbonand sand to a high temperature in an electricresistance furnace. Also called CARBORUNDUM.silicon cell A type of photovoltaic cell using speciallyprocessed silicon as the light-sensitive material.This cell has a comparatively high voltageoutput.silicon-controlled rectifier Abbreviation, SCR. Afour-layer semiconductor device commonly usedin power control applications (e.g., light dimmersand motor-speed controls). The electrodes arecalled the anode, the cathode, and the gate. Thecontrol signal is applied to the gate.silicon-controlled switch Abbreviation, SCS. Afour-terminal semiconductor switching devicesimilar to the SILICON-CONTROLLED RECTI-FIER. It is used for light-duty switching.silicon crystal detector 1. See SILICON JUNC-TION DIODE. 2. See SILICON POINT-CONTACTDIODE. 3. A point-contact diode in which a lumpof silicon is contacted by either a fine wire (catwhisker) or a blunt-tipped steel screw underpressure.silicon detector See SILICON CRYSTAL DETEC-TOR.silicon-diffused transistor A silicon bipolar transistorfabricated by diffusion techniques. It ischaracterized by high power-dissipation tolerance.silicon diode A semiconductor diode in which thesemiconductor material is specially processed silicon.Also see SILICON JUNCTION DIODE andSILICON POINT-CONTACT DIODE.silicon dioxide Formula, SiO 2 . A compound of siliconand oxygen. In the passivation of transistorsand integrated circuits, a thin layer of silicondioxide is grown on the surface of the wafer toprotect the otherwise exposed junctions.silicone A polymeric material characterized by arecurring chemical group containing oxygen andsilicon atoms in the main chain as links. Varioussilicone compounds have numerous uses in electronics.silicon junction diode A semiconductor diode usinga pn junction in a silicon wafer. Compare SIL-ICON POINT-CONTACT DIODE.silicon on sapphire Abbreviation, SOS. Pertainingto integrated-circuit fabrication in which a siliconepitaxial layer is grown on a sapphire substrate.silicon oxide A compound containing both siliconmonoxide and silicon dioxide, and having dielectricproperties. It is used in the manufacture ofmetal-oxide-semiconductor (MOS) devices.silicon photocell A photocell using a silicon pnjunction as the light-sensitive medium.silicon photodiode A silicon diode constructed sothat radiant energy can strike the barrier betweenthe P- and N-type materials. A reverse biasis applied. When light falls on the P-N junction,current flows. The current is proportional to theintensity of the impinging energy, within certainlimits. The greatest sensitivity is in the near infrared(IR). When energy of variable brightnessfalls on the P-N junction under conditions of reversebias, the output current follows the intensityvariations. This makes the device useful infiberoptic communications systems.silicon point contact The contact between apointed metal wire (cat whisker) and a siliconwafer.silicon point-contact diode A diode in which atungsten wire (cat whisker) contacts a wafer ofsingle-crystal silicon. It is useful at ultra high frequencies(UHF). Compare SILICON JUNCTIONDIODE.silicon rectifier A semiconductor rectifier consistingessentially of a junction between n- and p-type silicon inside a specially processed wafer orplate of single-crystal silicon.silicon resistor See CRYSTAL RESISTOR.silicon solar cell A relatively heavy-duty photovoltaiccell using specially processed silicon asthe light-sensitive material.silicon steel A high-permeability, high-resistancesteel containing 2 to 3 percent silicon. It is usedas core material in transformers and other electromagneticdevices.silicon transistor A transistor in which the semiconductormaterial is single-crystal silicon.silk-enameled wire Wire whose insulation is alayer of silk on top of an enamel coating.silver Symbol, Ag. A precious metallic element.Atomic number, 47. Atomic weight, 107.87. It isused in circuits where low resistance and high Qare mandatory.silver arsenide trisulfide See PROUSTITE.silver-dollar construction Printed-circuit assemblyon a disk-shaped board, about the size of aU.S. silver dollar.silver-mica capacitor A fixed capacitor made bypainting or depositing a silver layer (capacitorplate) on both faces of a thin mica film (dielectricseparator).silver migration The undesirable tendency of silverto be removed from one location and depositedin another under adverse environmentalconditions.silver-oxide battery A set of two or more silveroxidecells stacked one atop the other, electricallyconnected in series. The resulting battery has acylindrical shape. A set of four cells provides approximately6 volts under no-load conditions; abattery of six cells provides 9 volts; a battery ofeight cells provides 12 volts. See also SILVER-OXIDE CELL.silver-oxide cell An electrochemical cell having abutton-like shape, small enough to fit inside awristwatch. There are several available sizes andthicknesses, all with similar appearance. The

silver-oxide cell • single cotton enameled wire 631generated potential difference under no-load conditionsis 1.5 volts, with a high ratio of stored energyper unit mass. The cell has a flat dischargecurve; the voltage remains essentially constantuntil the charge is almost depleted, and then thevoltage drops rapidly.silver solder A solder consisting of an alloy of silver,copper, and zinc. It has a comparatively highmelting temperature. Also see HARD SOLDER.silverstat A multiconductor device used to adjustthe balance of a resistance or reactance bridge.similar decimals Two or more decimal numbersthat have the same number of digits to the rightof the radix point (e.g., 3.14 and 6.39, or 1.234and 1.000).simple quad A combination of two parallel paths—each containing two elements in series.simple tone A pure sine-wave tone (i.e., one havingnegligible harmonic content).simplex channel An information channel for unidirectionaltransmission.simplex system 1. In data communications, a systemthat transmits data in only one direction.Compare FULL DUPLEX SYSTEM and HALF DU-PLEX SYSTEM. 2. In voice communications viaradio, a direct path over a single channel, usedalternately for transmitting and receiving at eachstation.simplex telegraphy Wire telegraphy in which onlyone message at a time can be sent over a line.simplification of circuits See CIRCUIT SIMPLIFI-CATION.simulation 1. Imitation of the performance of aprocess, device, or system. 2. The use of a mathematicalmodel to represent a physical process,device, or system. 3. The use of a computer,sometimes with virtual reality hardware and software,to mimic a real-life situation.simulator1. A software or hardware system capableof simulation (see SIMULATION, 2). 2. A computerprogram whose implementation allowsprograms written for one computer to be compatiblewith another computer. 3. A system of equipmentfor simulation (see SIMULATION, 1).simulcast1. To broadcast a program over two ormore different channels at the same time. 2. Tobroadcast a program over two or more differenttypes of mode, for example, television and radio,at the same time. 3. A program broadcast overtwo or more channels or modes at the sametime.simultaneous access See PARALLEL ACCESS.simultaneous broadcasting See SIMULTANEOUSTRANSMISSION.simultaneous computer See PARALLEL COM-PUTER.simultaneous transmission The transmission ofthe same information in two or more channels, orby means of two or more processes, at the sametime.sin Abbreviation of SINE.sin –1 Symbols for the inverse of the sine function,also called the arc sine.sine Abbreviation, sin. The trigonometric functiona/c, the ratio of the opposite side of a right triangleto the hypotenuse.SINAD See SIGNAL-TO-NOISE-AND-DISTORTIONRATIO.sine galvanometer A galvanometer in which thesine of the angle of deflection is proportional tothe current. Compare TANGENT GALVANOME-TER.sine law The variation in radiation intensity in anydirection from a linear source is proportional tothe sine of the angle between the axis of thesource and the direction of interest.sine potentiometer A POTENTIOMETER whoseoutput is proportional to the sine of the anglethrough which the shaft has rotated.sine wave A periodic wave that can be representedby a sine curve (i.e., its amplitude is directly proportionalto the sine of a linear quantity, such asdisplacement or time). Compare COSINE WAVE.0°90°180° 360°270°sine wavesinging Audible oscillation in a circuit or device,such as the low-level buzz emanating from the filamentof a lamp dimmed with a phase-controlcircuit.single-address coding In computer programming,the use of instruction words that contain the addressfor the location of the data to be operatedon, and no other addresses.single-board computer Abbreviation, SBC. A computerbuilt entirely on one circuit board.single-button microphone A carbon microphonehaving only one button attached to the diaphragm.Also see BUTTON MICROPHONE.single-channel codec A form of CODEC intendedfor operation on a single signal source, ratherthan in a multiplexed system.single-chip codec An integrated circuit containedentirely on one chip and in one package that canaccomplish all CODEC functions. It can be a single-channeldevice or multiplexed.single-cotton-covered wire Wire insulated withone layer of cotton.single cotton enameled wire Wire insulated withone layer of cotton on top of an enamel coating.

632 single-crystal • single-layer solenoidsingle-crystal Pertaining to the internal structureof a crystalline material, in which the characteristiclattice is continuous throughout any sizepiece of the material. Also called MONOCRYS-TALLINE.single-crystal material A substance, such as asemiconductor, of which a sample, regardless ofsize, consists of only one crystal (i.e., there are nograin boundaries). Also see SINGLE-CRYSTAL.Compare POLYCRYSTALLINE MATERIAL.single-crystal pulling See CZOCHRALSKIMETHOD.single-dial control Adjustment of a multistagesystem via one rotatable, calibrated control attachedto a ganged arrangement that tunes allstages simultaneously.single-diffused transistor A transistor in whichonly one diffusion of an impurity substance ismade. Thus, in a diffused-base transistor, a singlediffusion provides the base region and at thesame time creates the emitter-base and collectorbasejunctions. Compare DOUBLE-DIFFUSEDTRANSISTOR.single-electron memory Abbreviation, SEM. Acomputer memory in which the movement of oneelectron can change a logic bit from 1 (high) to 0(low) or vice versa.single-element rotary antenna See ONE-ELEMENT ROTARY ANTENNA.single-ended circuit A circuit that has one endgrounded, as opposed to a double-ended circuitand push-pull circuit.single-ended deflection In an oscilloscope or similardevice, horizontal or vertical deflection providedby a single-ended deflection channel.Compare PUSH-PULL DEFLECTION.single-ended input An input circuit with one terminalgrounded (or the equivalent ungroundedinput circuit). Also called unbalanced input. CompareBALANCED INPUT.single-ended multiplexer A group of analogswitches that selects from several analogsignals.single-ended output An output circuit with oneterminal grounded (or the equivalent ungroundedoutput). Also called unbalanced output. CompareBALANCED OUTPUT.single-ended push-pull circuit An arrangement,such as a complementary symmetry circuit, thatprovides push-pull output with single-ended input,but does not require transformers.single-frequency Also called fixed-frequency. Pertainingto circuits or devices that normally operateat one frequency only (e.g., single-frequencyoscillator).single-frequency amplifier An amplifier that normallyoperates at only one frequency (or within avery narrow band of frequencies) (e.g., an intermediate-frequencyamplifier, or a selective audiofrequencyamplifier used for harmonic analysis orbridge balancing).single-frequency duplex Two-way communicationsover one medium or frequency. Voice-actuated(VOX) or break-in devices are used at bothends of the circuit.single-frequency oscillator An oscillator that normallydelivers a signal at only one frequency untilit is switched to another frequency (e.g.,crystal-controlled oscillator).single-frequency receiver A radio or television receiverthat normally operates at one carrierfrequency, rather than being tunable. Such receiversare used in monitoring specific programs,picking up standard-frequency signals, and insimilar applications.single-gun color picture tube A color-televisionpicture tube in which the image is produced by asingle beam that scans the red, green, and bluecolor-phosphor dots sequentially.single-hop propagation Long-distance radio-wavepropagation involving only one encounter withthe ionosphere, and involving no intermediate reflectionsfrom the earth’s surface.single-hop return distance The return distance,as a function of the angle of departure from a radiotransmission, from a layer of the ionosphere.The illustration shows the maximum possibledistance under average conditions and assumingan angle of departure of zero degrees.Angle of departure80°60°40°20°E layerF layer0°0 500 1000 1500 2000 2500 3000single-hop return distance (miles)single-image response In an oscilloscope presentation,a single pattern, as opposed to a doubletracepattern.single-inline package Abbreviation, SIP. A flat,molded component package having terminal pinsalong one edge. All the pins lie along a commonline.single-junction transistor See UNIJUNCTIONTRANSISTOR.single-layer coil A coil whose turns are woundside by side in one layer.single-layer solenoid See SINGLE-LAYER COIL.

single-line tap • single-track recorder 633single-inline packagesingle-line tap In a telephone system, a connectionthat provides or designates a separate line(e.g., to serve a single household).single-loop feedback Feedback through only onepath.single phase Pertaining to the presence or generationof one alternating-current phase only. ComparePOLYPHASE.single-phase full-wave Pertaining to a rectifier operatedfrom a single-phase alternating-current (ac)power line, and rectifying both half-cycles of acvoltage. Compare SINGLE-PHASE/HALF WAVE.single-phase/full-wave bridge A bridge rectifieroperated from a single-phase alternating-currentsupply, usually from the untapped secondarywinding of a transformer. Compare SINGLE-PHASE/FULL-WAVE CIRCUIT and SINGLE-PHASE/HALF-WAVE CIRCUIT.single-phase/full-wave circuit A rectifier circuitin which each half-cycle of single-phase alternatingcurrent is rectified by a separate diode suppliedfrom the ends of a center-tapped winding ofa transformer. Compare SINGLE-PHASE/FULL-WAVE BRIDGE and SINGLE-PHASE/HALF-WAVE CIRCUIT.single-phase/half-wave Pertaining to a rectifieroperated from a single-phase alternating-current(ac) power line, and rectifying only one half-cycleof ac voltage.single-phase/half-wave circuit A rectifier circuitin which a diode, output load, and single-phasealternating-current supply are connected in series,only one half-cycle of the cycle being passedby the diode. Compare SINGLE-PHASE/FULL-WAVE CIRCUIT and SINGLE-PHASE/FULL-WAVE BRIDGE.single-phase rectifier See SINGLE-PHASE/FULL-WAVE BRIDGE, SINGLE-PHASE/FULL-WAVE CIRCUIT, and SINGLE-PHASE/HALF-WAVE CIRCUIT.single-point ground One ground connection towhich all channels of a circuit are returned. Sucha common connection eliminates or greatly minimizesthe common coupling often encounteredwhen separate ground points are used.single-pole double-throw Abbreviation, SPDT. Descriptiveof an electrical, electronic, or mechanicalswitch with a pole that can be connected toeither of two adjacent poles, but not to both.single-pole single-throw Abbreviation, SPST. Descriptiveof an electrical, electronic, or mechanicalswitch with a pole that can be connected to anadjacent pole (or disconnected from it) at will. It isused to provide the make and break function in asingle circuit.single rail 1. A one-conductor communicationsmedium with a ground return. 2. A one-conductordata line, with a ground return.single shot Also called one shot. Pertaining to circuitoperation in which a single input pulse applied to aswitching device (such as a multivibrator) causes itto deliver a single output pulse, rather than switchto a stable “on” state. A MONOSTABLE MULTIVI-BRATOR operates in this mode.single-shot multivibrator See MONOSTABLEMULTIVIBRATOR.single sideband Abbreviation, SSB. Pertaining to asystem of modulation in which one of the sidebandsfrom an amplitude-modulated signal is attenuatedor canceled out, leaving only onesideband. The carrier is generally suppressed also.single-sideband suppressed-carrier Abbreviation,SSSC or SSBSC. Pertaining to a system of modulationin which the carrier and one sideband from anamplitude-modulated signal are suppressed; onlythe remaining sideband is transmitted. Sometimesthis mode is simply called SINGLE SIDEBAND.single signal Pertaining to a mode of reception inwhich signals appear on only one side of zerobeat, enhancing selectivity and reducing interferenceamong received signals. Most superheterodynereceivers have this feature; mostdirect-conversion receivers do not.single-signal receiver A superheterodyne receiverthat achieves high selectivity via a selective filterin the intermediate-frequency amplifier chain.Signals appear on only one side of zero beat, in aband whose width can be adjusted or selected forvarious values from about 200 Hz to 3 kHz.single silk-covered wire Wire insulated with onelayer of silk.single-skip propagation See SINGLE-HOP PROP-AGATION.single-step operation See STEP-THROUGH OP-ERATION.single sweep In an oscilloscope, a single time-axisdeflection of the electron beam. Also see SWEEP,1, 2. Compare RECURRENT SWEEP.single-sweep blocking oscillator A blocking oscillatorthat cuts off after generating a single cycleor pulse.single-throw switch A single-action switch withtwo or more poles.single-tone keying Modulated continuous-wavekeying. A single audio-frequency tone is used toamplitude-modulate or frequency-modulate thecarrier.single-track recorder A recorder, such as a magnetic-taperecorder or a graphic recorder, thatpermits recording along only one track.

634 single-trip multivibrator • skin depthsingle-trip multivibrator See MONOSTABLEMULTIVIBRATOR.single-tuned circuit A circuit tuned by varyingonly one of its components [e.g., an intermediatefrequencytransformer in which only the secondarycoil (rather than both primary andsecondary) is tuned].single-turn coil 1. A coil consisting of a single turnof wire, tubing, or strip. 2. See RING INDUCTOR.3. See SHADING COIL.single-turn potentiometer A potentiometer thatcan be adjusted through its entire resistancerange by no more than one full rotation of theshaft. Usually, the turning range is somewhatless than a full circle (e.g., 300 degrees).single-wire-fed antenna See WINDOM ANTENNA.single-wire line 1. See SINGLE-WIRE TRANSMIS-SION LINE. 2. A single wire used for communicationor control purposes. The earth furnishes thereturn path.single-wire transmission line An antenna transmissionline or feeder consisting of one wire only(see, for example, WINDOM ANTENNA).sink 1. A device or circuit into which currentdrains. 2. See HEATSINK.sink circuit The circuit associated with a load orother sink. Compare SOURCE CIRCUIT, 2.sinker A piece of semiconductor material used toreduce the base-collector junction resistance in abipolar transistor.sintering A process in which various solid bodiesare formed from fusible powders at temperaturesbelow their melting points. Example: sinteredmagnetic core.sinusoidal Having the shape and properties of aSINE WAVE.SIO Abbreviation of serial input/output.SIP Abbreviation of SINGLE-INLINE PACKAGE.six-phase rectifier A polyphase rectifier circuitoperated from a three-phase supply. The outputripple frequency is six times the supply frequency.PrimariesSecondariessix-phase rectifierLoadSJD Abbreviation of SILICON JUNCTION DIODE.skating In a phonograph turntable, the tendencyof the tone arm to swing toward the spindle duringrecord play, independent of the action producedby the stylus following the groove.skeletal code A generalized computer routineneeding only certain parameters to be usable fora specific application.skeleton bridge A bridge consisting of an adjustablearm (potentiometer) and a pair of bindingposts for each of the other three arms. Suitableresistors, capacitors, or inductors are connectedto the binding posts to set up the bridge circuitdesired.DetGenskeleton bridgeskeleton-type assembly 1. A method of electronic-equipmentconstruction in which a minimumof supporting members is used. An exampleis the use of an open framework, instead of achassis, to support components. 2. An assemblyof electronic equipment, consisting essentially ofa foundation unit (containing the basic circuitry)and plug-in units for setting up various completeequipments.skew 1. A condition resulting from failure of thehorizontal synchronization in facsimile or television.The picture appears distorted, and appearsas a non-rectangular parallelogram. 2. In a printdisplay, nonalignment of columns resulting froman incorrect number of line spaces in each line.3. In a probability function, an accumulation ofvalues toward either side of center.skewing 1. The bending of a curve away from itsnormal shape. 2. In a differential amplifier, theoffset between two signals. Also see OFFSET.Skiatron A special form of cathode-ray tube, withthe fluorescent coating replaced by a screen ofhalide crystals that darken, instead of glow, whenexposed to the electron stream.skin depthThe depth to which current penetratesbelow the surface of a conductor, as a result ofthe SKIN EFFECT.

skin effect • slider 635skin effect The tendency of high-frequency alternatingcurrent to travel along the surface of aconductor; the high-frequency reactance is loweralong the outside than at the center of a conductor.This tends to increase the resistivity of solidconductors at high alternating-current frequencies,as compared with low frequencies and directcurrent.skip 1. Ionosphere-reflected radio transmissions.2. In a computer program, an instruction whosesole function is that of causing a jump to the nextinstruction.skip distance For a signal propagated via the ionosphere,the distance from the transmitter to thepoint at which the returned skywave strikes theearth.skip fading For a signal propagated via the ionosphere,changes in signal strength caused byfluctuations in the altitude and/or contour of theionized layer(s).skip zone See ZONE OF SILENCE.skirt selectivity 1. The bandwidth between pointsof high attenuation (usually 30 dB or 60 dB) onthe selectivity curve in a communications receiver.2. The relative steepness of the attenuation-vs.-frequencycurve in a communicationsreceiver.SKM Abbreviation of sine-cosine multiplier.skyhook 1. Colloquialism for ANTENNA. 2. A wireantenna supported by a captive balloon or kite.sky noise Radio noise originating in outer space.skywave A radio wave propagated by ionosphericreflections and/or refractions. CompareGROUND WAVE.XmtrIonized layerEarthskywaveRcvrskywave correction A factor applied to long-rangeradionavigation signals to account for the timedelay resulting from ionospheric propagation.skywire See OUTSIDE ANTENNA.slab 1. A relatively thick body of quartz, ceramic,semiconductor, or dielectric. 2. See SUBSTRATE.slap back The return of sounds by an acousticallyreflective object or surface a short distance away,resulting in almost immediate echoes.slashed-field-gun CRT A straight-gun televisionpicture tube (see STRAIGHT-GUN CRT). Becausethe gap between the anodes in this tube isslanted, the electrostatic field is diagonal, causingthe electron and ion beams to be diverted atan angle.slave flash A photoflash operated by the light flashfrom another such unit.slave relay A relay operated by, and whose actionfollows, a MASTER RELAY.SLC Abbreviation of STRAIGHT-LINE CAPACI-TANCE.sleeping sickness A gradual increase in transistorleakage current.sleep machine An electronic device sometimesused as an aid for relaxation or sleeping. It consistsof a wideband audio-frequency noise generatorthat produces low-level sounds similar to thenoise of waves on a beach or a light wind throughtrees.sleeve antenna A vertical antenna in which theupper half is a quarter-wave rod connected to theinner conductor of a coaxial feeder, and the lowerhalf is a quarter-wave metal sleeve connected tothe outer conductor of the feeder. Also calledCOAXIAL ANTENNA.sleeving A material in tubular form that can beslipped over another material [e.g., insulatingsleeving for wires (spaghetti)].slew rate In an operational amplifier, the rate atwhich the output can be driven between its limits.SLF Abbreviation of STRAIGHT-LINE FRE-QUENCY.slice A semiconductor wafer cut from a singlecrystalingot.slicer See CLIPPER-LIMITER.slide-back meter An electronic voltmeter in whichan unknown alternating-current signal voltageapplied to the input of an amplifier stage isbucked by an internal, adjustable, accuratelyknown signal voltage. The internal voltage is adjusteduntil a null occurs, indicating that its magnitudeis equal to that of the unknown voltage.sliderFirstanodeCathodeControl gridStrongmagnetWeakmagnetIon beamslashed-field-gun CRTElectronbeamA flat-spring contact that slides along theturns of a resistance or inductance coil to varythe coil’s resistance or inductance. Also called aWIPER.

636 slide-rule dial • slotted lineslide-rule dial A dial mechanism having a straightscale that resembles a slide rule.slide switch A switch actuated by sliding a blockshapedbutton. Compare BAT-HANDLE SWITCH,PADDLE SWITCH, and ROCKER SWITCH.onslope detector An amplitude-modulation (AM) receivingcircuit detuned to one side of resonance(i.e., to a point along the skirt of the selectivitycurve) to detect a frequency-modulated (FM) signal.The FM swing occurs along the slope of theresonance curve. Slope detection is useful in narrowbandFM when conventional FM circuitry isnot available.offslide switchslide wire A simple potentiometer consisting of asingle, straight piece of resistance wire with asliding contact. Also see SLIDE-WIRE RESISTOR.slide-wire bridge A simple four-arm bridge inwhich the adjustable element is a single, straightresistance wire along which a clip or slider ismoved, and that supplies two arms of the bridge(one on each side of the slider).slide-wire resistor A variable resistor consisting ofa single wire (straight or coiled) along whoselength a slider is moved to vary the resistance.sliding contact A contact that mates with anothercontact, or moves along a contacted surface, witha sliding motion. Also called SELF-CLEANINGCONTACT and WIPING CONTACT.slip 1. In an eddy-current brake, coupling, ordrive, the difference in speed between the fieldmagnets and the iron eddy-current ring. 2. In asynchronous motor, the difference between rotorspeed and stator speed.slip clutch In a gear or rack-and-pinion drive system,a device that releases the load if the torquebecomes excessive. The gears then slip instead ofbeing damaged.slip ring See COLLECTOR RING, 1.slip speed See SLIP, 2.slope 1. The slant of a line (graph) in rectangularcoordinates, depicted as the ratio of the change inthe dependent variable y to the change in the independentvariable x. If (x 1 ,y 1 ) and (x 2 ,y 2 ) are twopoints on the line, then slope m is determined bym = (y 2 – y 1 )/(x 2 – x 1 ). 2. The slant of a line in rectangularcoordinates as defined in 1, when theline is tangent to a curve (graph) at a specifiedpoint. 3. The skirt(s) of a selectivity curve, particularlyin a communications receiver, where asmall change in frequency results in a significantchange in gain or attenuation. 4. The ratio of theextent of change in a quantity to the extent ofchange in some other quantity, when a causal relationexists between the magnitudes of thequantities. Example: See SLOPE RESISTANCE.slope resistance The ratio of a small change involtage to a small change in current at an electrodeor in a component.slop-jar capacitor See WATER CAPACITOR.slop-jar rectifier See ELECTROLYTIC RECTIFIER.slot 1. In the armature of a motor or generator, agroove in which the windings are laid. 2. Thenotch in the response curve of a crystal filter.slot antenna A microwave antenna that radiatesenergy through a slot cut in a surface, such asthe metal skin of an aircraft.slot cell A reinforcing, dielectric material (such asplastic) placed in the slot of a ferromagnetic core.slot coupling Coupling microwave energy betweena waveguide and a coaxial cable by means of twoslots, one in the waveguide and the other in theouter conductor of the cable.slot-discharge resistance See CORONA RESIS-TANCE.slot insulation 1. Insulation of wires in the slots ofthe armature of a motor or generator (see SLOT,1). 2. A material in the form of tape or sheets,used for the purpose defined in 1.slot radiator See SLOT ANTENNA.slotted line A device consisting of a sectionof air-dielectric coaxial line arranged for microwavemeasurements. The outer conductor isa metal cylinder, and the inner conductor is aconcentric metal rod. The cylinder is provided

slotted line • small signal 637with a lengthwise slot through which a smallpickup probe extends for sampling the electromagneticfield inside the device. The probe isattached to a carriage that slides along agraduated scale on the outside of the cylinder.Radio-frequency energy is injected into one endof the line through a coaxial cable; as the probemoves along, response points are indicated byan external detector connected to the probe. Thescale is read at these points to determine frequency,standing-wave ratio, impedance, andpower. An alternate form of slotted line uses asection of slotted waveguide, instead of a sectionof coaxial line.slotted rotor See SERRATED ROTOR PLATE.slotted section See SLOTTED LINE.slotted waveguide See SLOTTED LINE.slot width 1. The width of a slot in the armature ofa motor or generator (see SLOT, 1). 2. The bandwidthof the notch in the response curve of aband-suppression filter of any kind. See, for example,NOTCH FILTER.slow-acting relay Any relay designed to operate atsome finite period following the application of theactuation voltage.slow-blow fuse A fuse in which the melting wirebreaks apart slowly. The time delay allows thefuse to withstand momentary current surges thatdo not damage the protected equipment, but thatwould cause a fast-blow fuse to break the circuitneedlessly.slow-break, fast-make relay A relay that opensslowly and closes rapidly.slow-break, slow-make relay A relay that opensslowly and closes slowly.slow charge Storage-battery charging in which alow current is passed through the battery over along period of time. It ensures that the ratedampere-hour capacity will be restored to thebattery.slow death1. The gradual deterioration of transistorperformance. 2. The gradual deterioration inthe performance of a component, circuit, device,or system.slow drift The gradual change of a quantity or setting(usually in one direction). Compare FASTDRIFT.slow-make, fast-break relay A relay that closesslowly and opens rapidly.slow-make, slow-break relay A relay that closesslowly and opens slowly.slow-operate, fast-release relay See SLOW-MAKE-FAST-BREAK RELAY.slow-operate, slow-release relay See SLOW-MAKE-SLOW-BREAK RELAY.slow-release, fast-operate relay See SLOW-BREAK-FAST-MAKE RELAY.slow-release, slow-operate relay See SLOW-BREAK-SLOW-MAKE RELAY.slow storage A form of memory with long storageand recovery time.slow time scale An extended time scale, i.e., onelarger than the time unit of the system underconsideration.SLS Abbreviation of SIDELOBE SUPPRESSION.slug 1. A movable core of ferromagnetic material,used to tune (varying the inductance of) coil bychanging its position along the axis of the coil.Also see SLUG-TUNED COIL. 2. A copper ring attachedto the core of a relay for time-delay purposes(see SLUG-TYPE DELAY RELAY).slug-tuned coil A coil whose inductance is variedby means of a ferromagnetic slug that slides inand out of the coil.slug tuner A tuner for a radio or television receiveror test instrument, using slug-tuned coils.slug-type delay relay A delayed-response relay thatachieves time delay through the action of a heavycopper slug on the core. The slug forms a lowresistance,short-circuited single turn in which acurrent is induced by the magnetic flux, resultingfrom energizing the relay. The resulting flux of theslug opposes the buildup of relay-coil flux.slumber switch An alarm-reset switch on an electronicclock radio. If the alarm activates, theslumber switch (usually a pushbutton device)can be pressed to turn off the alarm for a predeterminedlength of time. Also called snooze button.SLW Abbreviation of STRAIGHT-LINE WAVE-LENGTH.Sm Symbol for SAMARIUM.small-current amplifier 1. A direct-current (dc)amplifier for low-level input currents (i.e., currentsof 1 milliampere or less). 2. An amplifier(such as a silicon-transistor unit) requiring verylow dc operating current.small-scale frequency response For an analogcircuit, the output frequency at which the level is–3 dB, relative to the maximum level, with a smallsignal at the input, normally 1 volt peak-to-peak.small loop antenna A closed loop antenna withone to several turns and a circumference lessthan 0.1 wavelength at the highest operating frequency.This antenna is suitable for wireless reception,but generally not for transmissionbecause the radiation resistance is extremely low.The antenna is least responsive along its axis,and is most responsive in the plane defined by itsturn(s). The null along the axis is sharp and deep.A capacitor can be connected in series or parallelwith the loop to provide a resonant response. Thistype of antenna can reduce interference causedby human-made noise or strong local signals. It isalso useful for radio direction finding (RDF) at frequenciesup to approximately 20 MHz. CompareFERRITE-ROD ANTENNA, LARGE LOOP AN-TENNA.small signal A low-amplitude signal. Such a signalcovers so small a part of the operating characteristicof a device that operation is essentially linear.Compare LARGE SIGNAL.

638 small-signal analysis • smoke detectorsmall-signal analysis Analysis of circuit or componentoperation in which it is assumed that thesignals deviate from (fluctuate to either side of)the steady bias levels by only a small amount.Also see SMALL SIGNAL.small-signal bandwidth The frequency at whichthe output signal of an analog circuit decreases to–3 dB, relative to the value for direct current. Theoutput voltage is generally set at 0.1 volt peak-topeakfor testing this value so that the circuit isnot overdriven.small-signal component 1. A coefficient or parameter(such as amplification, transconductance,dynamic resistance, etc.) calculated ormeasured under conditions of small-signal operation.Also see SMALL SIGNAL and SMALL-SIGNAL EQUIVALENT CIRCUIT. 2. A devicedesigned for operation at low signal levels.small-signal diode See SIGNAL DIODE.small-signal equivalent circuit For a given transistorcircuit, the equivalent circuit for low signal levels(i.e., at amplitudes lower than saturation andcutoff levels). Also see EQUIVALENT CIRCUIT.small-signal operation Operation at low signalamplitudes (i.e., at signal levels that do not extendinto the saturation or cutoff levels of a transistor,diode, or other component).small-signal transistor A transistor designed forlow-level applications, such as the amplificationof small voltages and currents and low-voltageswitching. Compare POWER TRANSISTOR.SmallTalk A high-level computer programminglanguage that uses a graphical user interface(GUI). It is used in complex design and research,and in robotics.smart home or business An electronically controlledhome or business, in which computersand robots take care of cooking, dish washing,floor scrubbing, waste removal, laundry, yardmaintenance, snow removal, and other mundanechores. Intrusion detection and fire preventionare constantly maintained. In some cases, intruderscan actually be identified or detained;fires can be extinguished by controlled sprinklersystems or remotely controlled robots. Sometasks can be monitored and controlled directly bythe owner from remote locations, via telephonelines or wireless.smartness The ability of an electronic system, especiallya computer or control system, to performa complete series of operations, substituting alternativesteps, where necessary—all with a minimumof instructions from, and supervision by,human operators.smearing In television or facsimile, a form of picturedistortion caused by an excessively narrow receivingbandpass. The image appears fattened andhorizontally blurred. Contrast might also be lost.smectic crystal A liquid crystal in which themolecules are arranged in parallel layers andcannot slide past each other.S meter In a radio communications receiver, a metergraduated in S units and/or decibels to indicatethe strength of a received signal.135S unitsS units79S meterSmith chart A curvilinear graph on which complex-numberimpedance values can be plotted. Itis useful in evaluating the behavior of radiofrequencycircuits, transmission lines, andantenna systems—especially with regard toimpedance mismatches and standing-wave ratio.0 − j40−50SWR 10:1−25−100ReactanceResistance50 + j050 − j50SWR = ∞ :1(Worst possiblemismatch)0 Short2550100∞ Open20dBdB50 + j50Smith chart4060SWR = 4:1+25SWR = 2:1+1000 + 40+50smoke alarm A device that produces audibleand/or visible signals in the presence of smoke orunusual gases in the air. Also see PHOTOELEC-TRIC SMOKE ALARM.smoke control See PHOTOELECTRIC SMOKECONTROL.smoke detector Any circuit or device used tosense the presence of smoke or noxious gases.

smoke detector • software 639Some types detect changes in the ionizationpotential of the air; others sense changes inthe dielectric constant of the air. Also seePHOTOELECTRIC SMOKE DETECTOR.smoke sensor See SMOKE DETECTOR.smooth 1. Relatively free from surface irregularity.2. To reduce or eliminate irregularities in the voltageor current from a direct-current powersource. 3. To reduce or eliminate irregularities indata or signal amplitude.smoothing choke A power-supply filter chokehaving a core with an air gap that prevents saturationat maximum rated direct current. CompareSWINGING CHOKE.smoothing factor For a power-supply filter, aquantity approximately equal to 6.28fRC, where fis the alternating-current frequency in Hertz, R isthe filter resistance (in an RC filter) or the seriesreactance of the choke (in an LC filter) in ohms,and C is the filter capacitance in farads.smoothing filter 1. A filter for smoothing the alternating-currentripple component of a directcurrentpower supply following rectification. Itcan consist of one or more parallel capacitors oflarge value, and one or more series chokes oflarge inductance. 2. A low-pass filter used at theoutput of a digital-to-analog (D/A) converter foreliminating high-frequency components generatedby sampling.SMPTE Abbreviation of SOCIETY OF MOTION PIC-TURE AND TELEVISION ENGINEERS.smudge See SQUEEZEOUT.SN Abbreviation of semiconductor network.S/N Abbreviation of SIGNAL-TO-NOISE RATIO.Sn Symbol for TIN.snake 1. A long, strong, flexible wire or strip usedto pull other wires through electrical conduits. 2.To route wires or cables through a group of circuits,components, or boards.snap-action switch A switch that snaps quicklyinto the on or off position to prevent arcing andconsequent premature contact deterioration.snap diode A semiconductor diode in whichswitch-off time after carrier storage is extremelyshort (e.g., under 1 nanosecond).snap magnet A magnet that reduces the tendencyfor arcing in relay-control instruments, therebyminimizing electromagnetic interference and prolongingcontact life.snap-on connector An electrical connector thatlocks in place, reducing the chance that it will detachunless it is deliberately removed.snapshot dump During a computer program run,a dump, for debugging purposes, of certain storageareas.snap switch See SNAP-ACTION SWITCH.sneak current Unintended current flow through apath that is auxiliary to a main circuit.sneak path A path through which current isaccidentally detoured; it is usually a leakagepath.Snell’s law A rule of physics that applies to visiblelight passing from air (or a vacuum) to somemedium with an index of refraction c. If the lightray strikes the medium at an angle u, relative to aline normal (perpendicular) to the surface, andpasses into the medium at angle v relative to thenormal, then (sin u)/(sin v) = c.sniffer See EXPLORING COIL.sniperscope A telescope, snooperscope, or starlightscope for a carbine or rifle.(S+N)/N Abbreviation of SIGNAL-PLUS-NOISE-TO-NOISE RATIO.SNOBOL Acronym for string-oriented symbolic language,a computer-programming language formanipulating character strings.snooperscope 1. An infrared-sensitive device thatpermits viewing objects and surroundings in totaldarkness. It presents the image on a fluorescentscreen. 2. A rifle-mounted starlight scope.snow A type of television picture interference thattypically occurs when the signal-to-noise ratio islow (the reception is marginal or poor). Characterizedby countless tiny out-of-focus light spots,whose rapid, random motion mimics the appearanceof falling snow.SNR Abbreviation of SIGNAL-TO-NOISE-RATIO.soak value The smallest value of current that willcause saturation of a relay core.Society of Motion Picture and Television EngineersAbbreviation, SMPTE. A group that decideson various procedures in video recordingand reproduction, both on magnetic media (tapeor disk) and on film.socket A (usually female) fixture into which a plug,integrated circuit, or other component is insertedfor easy installation in, or removal from, a circuit.socket punch See PUNCH, 2.sodium Symbol, Na. A metallic element of the alkali-metalgroup. Atomic number, 11. Atomicweight, 22.9898.sodium silicate See WATER GLASS.sodium-vapor lamp A gas-discharge lamp containingneon and a small amount of sodium. Afterthe filaments of the lamp are lighted for a shorttime, the heat vaporizes the sodium, and the filamentsare disconnected by an automatic switch.Under the influence of the voltage across thelamp, the sodium vapor glows with a characteristicyellow light.sofar A system for pinpointing the source of underwatersounds (coming from as far away as 2000miles) through triangulation. The name is anacronym for sound fixing and ranging.soft-drawn wire Wire that is highly malleable, andis therefore easily bent and unbent. CompareHARD-DRAWN WIRE.soft iron A grade of iron, used in some cores, thatis easily demagnetized.soft solder A low-melting-point solder.software 1. Vendor-supplied or user-generatedprograms or groups of programs for a computer

640 software • soldering gunor computer system. 2. The detailed instructionsfor performing a particular operation with a calculatoror a computer.software-defined radio Abbreviation, SDR. 1.Wireless communications in which the modulationwaveforms and protocols are generated anddecoded by computer software. This allows asingle, microcomputer-controlled radio receiver,transmitter, or transceiver to operate in a varietyof services that use different protocols. Changingthe modulation waveform or protocol requiresonly a change in the program run by a microcomputerthat controls the radio. 2. A receiver,transmitter, or transceiver that employs thetechnology defined in (1). 3. The use of wirelessequipment that employs the technology definedin (1).soft X rays Low-frequency (long-wavelength)X rays. Such radiation has relatively poor penetratingpower. Compare HARD X RAYS.sol 1. Abbreviation of SOLUTION. 2. Abbreviationof SOLUBLE.solar access For a specific property or location, theavailability of direct exposure to the sun’s rays asa source of energy.solar absorption index A quantitative measure ofthe effect of the sun on the ionospheric absorptionof radio waves.solar activity See SOLAR RADIATION andSUNSPOT cycle.solar battery A battery composed of solar cellsconnected in series and/or parallel for increasedoutput.solar cell A photovoltaic power transducer thatconverts visible light to electricity. It is called acell because its output is a low direct-currentvoltage. Such cells can be connected in seriesand/or parallel to provide useful electric poweroutput.solar cycle See SUNSPOT CYCLE.solar energy 1. The total energy arriving from thesun, over a given period of time and within a specificsurface area, at a given location on the surfaceof the earth. 2. Any energy derived entirelyfrom the sun.solar-energy conversion Any process that changessolar radiant energy into another useful form.solar flareA violent storm on the surface of thesun. These events tend to occur near the peak ofthe 11-year sunspot cycle. They cause an increasein the level of radio noise that comes fromthe sun, and they emit high-speed subatomicparticles that reach earth a few hours after thefirst appearance of the flare. Because the particlesare electrically charged, they are acceleratedby the geomagnetic field. Sometimes a geomagneticstorm results, producing aurora near thepoles and deterioration of ionospheric radiopropagationconditions.solar flux An indicator of general solar activity. Thesolar noise level is measured at a particular frequency,such as 2800 MHz. The solar flux tends tobe highest during periods of the greatest sunspotactivity and immediately following a solar flare.solar laser See SUNLIGHT-POWERED LASER.solar noise Broadband electromagnetic noise generatedby the sun. In particular, noise that occursat radio frequencies and affects satellite, moonbounce,and space communications. This noisevaries in intensity with the 11-year sunspot cycle,being generally higher at and near sunspot maxima.A solar flare can cause a sudden and dramaticincrease in the noise at all wavelengths.See SOLAR FLARE.solar panel An array consisting of a number of series-connectedor series-parallel-connected solarcells mounted on a flat plate.solar power Useful amounts of electricity obtainedfrom suitable arrays of solar cells.solar radiation Electromagnetic energy of variouswavelengths originating in the sun. Such radiation,after passing through the earth’s atmosphere,consists mostly of infrared rays andvisible light. Some ultraviolet rays also reach theearth’s surface.solar relay See SUN SWITCH.solar switch See SUN SWITCH.solar wind Continuous emission of high-speed subatomicparticles by the sun. It causes distortion ofthe lines of flux in the earth’s magnetic field. It becomesmore intense following a solar flare.solder1. A metal alloy (usually of tin and lead) thatis melted to electrically and mechanically joinpieces of other metals. Also see HARD SOLDERand SOFT SOLDER. 2. To join metals with solder.solderSolder Melting point Principaltype (°F/°C) usesTin-lead 50 : 50, 430/220 Electronicrosin-corecircuitsTin-lead 60 : 40, 370/190 Electronicrosin-corecircuits,low-heatTin-lead 63 : 37, 360/180 Electronicrosin-corecircuits,low-heatTin-lead 50 : 50, 430/220 Non-electronicacid-coremetal bondingSilver 600/320 High-current,high-heatsoldering Joining (usually nonferrous) metal partswith solder, a lead-alloy substance. CompareBRAZING.soldering gun An electric soldering iron having thegeneral shape of a handgun. The element heatsand cools more rapidly than the element in a

soldering gun • solution 641typical soldering iron. The element is heated bypressing a device similar to the trigger on a pistol.soldering iron An electric or nonelectric tool havinga heated tip for melting solder.solderless breadboard A foundation (see BREAD-BOARD, 1) on which a circuit can be assembledby plugging components into tiny jacks withoutthe use of solder.solderless connection A connection betweenleads, or between leads and terminals, accomplishedentirely through crimping, pinching,splicing, or wire wrapping. Solder is not used.Also see WIRE-WRAP CONNECTION.solderless terminal A terminal to which a solderlessconnection can be made. Also see WRAPPOST.solenoid 1. A coil of wire having a single layer,wound on a cylindrical form. 2. A multilayer coilused as an electromagnet, and usually having astraight, iron core.solenoidMetalrodsolenoid switch A switch consisting of a solenoidcoil (see SOLENOID, 2) into which a core is pulledby the magnetic field to close a pair of contacts.solid 1. One of the states of matter. It is characterizedby a definite shape and volume, and byatoms that maintain a fixed position, relative toeach other. Compare GAS, LIQUID, and PLASMA.2. An enclosed, defined volume of three-dimensionalspace. 3. In communications, descriptiveof error-free reception of a series of coded signals.4. In printing and data transmission, a largeprint area whose entire surface is of equal andmaximum intensity (of ink, light, or darkness).solid angle Unit, steradian. The angle within theapex of a cone formed by all line segments betweenthe center of a sphere and a defined circleon the surface of the sphere.solid circuit Any circuit consisting of a single pieceof hardware that is not normally separated intosmaller parts.solid conductor See SOLID WIRE.solid electrolyte A solid substance affording ionicaction similar to that in a liquid electrolyte.solid electrolytic capacitor A capacitor using asolid electrolyte.solid ground See DIRECT GROUND.solid-state Pertaining to devices and circuits inwhich the flow of charge carriers (electrons andholes) is controlled in specially prepared blocks,wafers, rods, or disks of solid materials. Semiconductordevices, such as transistors and integratedcircuits, are solid-state components.solid-state battery An atomic battery consistingessentially of a photovoltaic cell in combinationwith a quantity of radioactive material, whose radiationcauses the cell to generate electricity.solid-state camera A video camera device thatmakes use of solid-state technology. The target isa matrix of charge-coupled devices (CCDs). Whenlight strikes these devices, charge carriers areseparated in a manner similar to that in a photovoltaiccell. The matrix is scanned according to aparticular scheme, and the voltages developed ineach CCD combine to produce the video signaloutput.solid-state capacitor See SOLID ELECTROLYTICCAPACITOR.solid-state chronometer Any semiconductor deviceto indicate or measure time.solid-state circuit See MONOLITHIC INTE-GRATED CIRCUIT.solid-state lamp 1. See LIGHT-EMITTING DIODE.2. See LASER DIODE. 3. See ELECTROLUMI-NESCENT CELL.solid-state maser A device, such as the rubymaser, in which the stimulated medium is a solidmaterial.solid-state photosensor A semiconductor photodiodeor phototransistor, as opposed to a phototube.solid-state physics The branch of physics concernedwith the nature and applications of suchsolids as electronic semiconductors.solid-state relay 1. A sensitive relay consisting ofa conventional electromagnetic relay preceded bya transistorized amplifier. 2. A completely electronicrelay (i.e., one without moving parts) inwhich switching transistors provide the on andoff states. 3. See THYRISTOR.solid-state thermometer An electronic thermometerutilizing one or more solid-state components,such as transistors, integrated circuits, orthermistors.solid-state thyratron See SILICON-CONTROL-LEDRECTIFIER and SILICON-CONTROLLED SWITCH.solid-state tube A semiconductor device (diode,rectifier, transistor, SCR, etc.) whose housing andbase allow it to replace directly an electron tube.solid tantalum capacitor A capacitor using tantalumas a solid electrolyte.solid wire Wire consisting of a single strand ofmetal. Compare STRANDED WIRE.solute A substance that is dissolved in some othersubstance. Also see SOLUTION, 1.solution 1. A well-diffused mixture of two or moresubstances. It can consist of a gas in a liquid, agas in a solid, a gas in a gas, a liquid in a solid, or

642 solution • SOSa solid in a solid. A solution, typically, is molecular(i.e., there is no chemical reaction between itsconstituents). Also see SATURATED SOLUTION;SOLUTE; SOLVENT, 1; and SUPERSATURATEDSOLUTION. 2. The result of solving a problem ormaking a calculation. Also called answer or result.solution conductivity The electrical conductivityof a solution, such as an electrolyte. The conductivity(and conversely, the resistance) depends onthe number and mobility of ions in the solution.solution-conductivity bridge A direct-currentbridge specially designed and calibrated to measurethe conductivity of chemical solutions.solution pressure In an electrolyte into which ametal body is immersed, the force that causes themetal to tend to pass into solution as positiveions and to form a Helmholtz double layer.solvent1. A fluid that dissolves other materials.2. The constituent of a solution that dissolves oneor more other constituents. Thus, in a saltwatersolution, water is the solvent and salt the solute.Also see SOLUTION, 1.SOM Abbreviation of start of message.Sonalert Tradename for a small, but loud, soundreproducer used with solid-state circuits foralarm purposes.sonar A system of detection and ranging by meansof sonic and ultrasonic signals. In this system ofecho ranging, the distance to an underwater objectis determined from the time it takes a soundsignal to reach the object and be reflected back tothe transmitter. The name is an acronym forsound navigation and ranging.FishSonartransmitterBottomsonarSonarreceiverAcoustic wavesSubmarinesonde A device for automatically gathering meterologicaldata at high altitudes. An example is theradiosonde.sone A unit of loudness for an individual listener.The level of 1 sone is the loudness of a 1000-Hztone that is 40 dB above the particular listener’sthreshold of hearing.sonic altimeter An altimeter (see ABSOLUTE AL-TIMETER) using sound waves. The time requiredfor a transmitted wave to reach a target and bereflected back to the transmitter is proportionalto the distance between the transmitter and thetarget.sonic boom An explosive sound occurring whenthe shock wave produced by an aircraft flying atsupersonic speed strikes the earth.sonic delay line A delay line using electroacoustictransducers and an intervening medium throughwhich a sound wave is transmitted.sonic depth finder See ACOUSTIC DEPTHFINDER.sonic thermocouple A thermocouple whose heatabsorbingproperties are enhanced by subjectingit to acoustic vibrations.sonobuoy A buoy equipped with an acoustic receiverand radio transmitter. The device isparachuted into the water, where it receives submarinesounds and transmits them to a monitoringstation. Several sonobuoys communicatingwith a computer will track the path of a submarine.sonovoxAn electronic device used to produce specialsound effects when it is held against thethroat of the operator. The special sounds areformed into words by the operator’s mouth.SOP Abbreviation of standard operating procedure.sophisticated electronics Advanced electronicstheory and operations, usually dealing with complexdevices or systems and requiring rigorousanalysis to describe their operation and deviseapplications. Compare UNSOPHISTICATEDELECTRONICS.sorption processes Processes whereby certainsubstances (e.g., activated charcoal) occlude andretain gases and vapors. A chamber containingsuch a substance is often useful in the productionof a vacuum. Sorption includes both absorptionand adsorption.sort1. To group information items using theirkeys. Also see KEY. 2. To group information itemsaccording to some system of classification, as toprint an alphabetical list of words stored in a randomsequence.sorting routine A computer program for sequencingdata items according to key words (values inspecific fields) of the different records.SOS 1. The international radiotelegraph distresssignal; equivalent to mayday in radiotelephony. Itconsists of three dits (“dots”), followed by threedahs (“dashes”), followed by three more dits.2. Abbreviation of SILICON ON SAPPHIRE.

sound • sound power level 643sound The vibratory or wave phenomenon to whichthe sense of hearing is responsive. Conducted bywaves in solids, liquids, and gases; not propagatedthrough a vacuum.sound absorption The nonreflection and nontransmissionof acoustic energy by a body or medium,and the attendant conversion of the acoustic energyinto another form of energy (usually heat).sound absorption coefficient A quantitative expressionof the extent to which a surface absorbsacoustic energy (as opposed to reflecting, transmitting,diffusing, or scattering it).sound amplifier 1. An audio amplifier—especiallythe sound channel of a television system. 2. A device,such as a horn or reflector, that directlyboosts the intensity of sound at a given listeningpoint.sound analyzer An instrument, often a wave analyzerequipped with a microphone, for measuringsuch characteristics of sound as amplitude, frequency(pitch), and harmonic content (timbre).sound articulation See ARTICULATION.sound bars In a television picture, horizontal barsresulting from interference between the audioand video channels of the receiver.sound carrier In a television signal, the frequencymodulatedcarrier that transmits the audio partof the program. Compare VIDEO CARRIER.sound chamber An air enclosure, usually a box orcan, for modifying the acoustic qualities of soundor of an audio signal.sound detector The discriminator or ratio detectorthat demodulates the sound signal in a televisionreceiver circuit.sound-energy density Sound energy per unit volume,expressed in joules per cubic meter or ergsper cubic centimeter.sound-energy flux The average rate of flow ofsound energy through a specified area, as expressedin ergs or joules per second.sound field A volume of space or material containingsound waves.sound film Motion-picture film on which a soundtrack is recorded. Also see OPTICAL SOUNDRECORDING.sound flux The rate of flow of sound energy, usuallyexpressed in terms of sound pressure at apoint or over a unit area normal to the directionof sound propagation.sound gate An optical device used to convert thesound track of a movie film into electrical impulses.sound generator Any combination of oscillator,amplifier, and transducer (loudspeaker or headphones)for producing sound waves.sound-hazard integrator An instrument used tomeasure cumulative noise exposure received bypersons in noisy environments. One such instrumentprovides direct readings in percent of permissibleexposure.sound IF amplifier In a television receiver circuit,the separate amplifier for the sound intermediatefrequency. See, for illustration, INTERCARRIERRECEIVER and SPLIT-SOUND RECEIVER.sound-level meter See SOUND SURVEY METER.sound marker A marker indicating the soundcarrierpoint on a television alignment curvedisplayed on an oscilloscope screen.sound-marker generator A special radiofrequencysignal generator (or a special circuit ina television-alignment generator) for the productionof a sound marker.sound mirage See ACOUSTIC MIRAGE.sound mix In sound recording or reproduction, thecomposite output from an audio mixer circuit.sound-on-film recording See OPTICAL SOUNDRECORDING.sound-on-sound recording The simultaneousrecording (on a single track on magnetic tape) ofnew material with previously recorded material.The old recording is not erased.sound-operated relay 1. A relay operated indirectlyfrom sound, through the medium of apickup microphone and amplifier. 2. A relay havinga delicately poised armature that operates directlyfrom sound vibrations.Mic.AudioamplifierTocontrolledcircuits orsystemssound-operated relayRectifierFilterdcamplifierRelaysound power The total sound energy per unit timeproduced by a sound source, as expressed in ergsper second or in watts.sound power level The extent, in decibels, by whichSOUND POWER exceeds one picowatt (10 –12 watt).

644 sound pressure • source followersound pressure 1. The force exerted by soundwaves on a surface area, expressed in dynes persquare centimeter (as an rms value over 1 cycle).The sound pressure is proportional to the squareroot of sound-energy density. 2. The instantaneousdifference between actual air pressure andaverage air pressure at a given point.sound pressure level The extent, in decibels, viawhich SOUND PRESSURE exceeds 20 micropascals(2.0 × 10 –5 pascal).sound probe A transducer used to receive acousticvibrations for detection or measurement purposes.sound recording The electrical recording of sound,using cylinder, disc, tape, wire, or other comparablestorage medium.sound-recording system A complete, integratedarray of equipment for recording sound, includingsuch components as microphones, amplifiers,pickups, filters and other shaping networks,attenuators, level indicators, andrecording mechanisms. Compare SOUND-REPRODUCTION SYSTEM.sound reinforcement Intensification of sound byhorns, resonant chambers, or other acousticaldevices.sound relay See SOUND-OPERATED RELAY.sound reproduction The electrical reproduction ofsound from recordings on vinyl discs, magnetictapes, magnetic discs, compact optical disbs, etc.sound-reproduction system A complete, integratedarray of equipment for the playback ofrecorded sound, including such components astape or record players, amplifiers, filters andother shaping networks, attenuators, level indicators,loudspeakers, and headphones. CompareSOUND-RECORDING SYSTEM.sound spectrograph A device that produces a displayof sound amplitude vs. frequency. Similar toa SPECTRUM ANALYZER, except that it operatesat audio frequencies (about 20 Hz to 20 kHz) andis actuated by acoustic disturbances, rather thanby electromagnetic signals.sound spectrum The continuous band of frequencies(about 20 Hz to 20 kHz) constitutingaudible sounds, and sometimes the immediatelyadjacent (subaudible and superaudible) frequencies.sound stage The apparent dimensions of a soundsource.sound survey meter A portable instrument formeasuring the intensity and other characteristicsof sound.sound sweetening In audio recording or reproduction,the modification of the sound to achievesome desired effect.sound system A sound-recording system, soundreproductionsystem, or a combination of the two.sound takeoff In a television receiver circuit, thepoint at which the frequency-modulated soundsignal is extracted from the complex signal.sound track The variable-density or variable-widthrecording on one side of the film in sound-on-filmrecording and reproduction. Also see OPTICALSOUND RECORDING.sound transducer See ACOUSTIC TRANSDUCER.sound-transmission coefficient See ACOUSTI-CAL TRANSMITTIVITY.sound trap In a television receiver circuit, a wavetrapthat prevents the sound signal from enteringthe picture channels.sound unit See PHONE, 2.sound wave The vibratory phenomenon producedin a medium by acoustic energy. A sound wave inair consists of alternate compressions and rarefactionsof the air. Also see ACOUSTIC WAVE.source 1. The origin of a signal or electrical energy(e.g., a transmitting station). 2. In a field-effecttransistor, the electrode that is equivalent to theemitter of a common-emitter-connected bipolartransistor, or the cathode of a vacuum tube.3. That which is being transcribed to magnetictape. 4. Manufacturer, wholesaler, or retailer.source circuit 1. The circuit associated with thesource electrode of a field-effect transistor. 2. Agenerator circuit. Compare SINK CIRCUIT.source code See SOURCE LANGUAGE.source computer A computer for compiling asource program.source-coupled multivibrator A multivibrator circuitusing field-effect transistors, in which feedbackcoupling is achieved with a common sourceresistor for the two FETs. This circuit is equivalentto the emitter-coupled bipolar-transistortypemultivibrator.source data automation A means of storing amaster data file for easy duplication, whenevernecessary.source deck An audio or video tape player that reproducesoriginal recordings in the editing process.source follower A field-effect-transistor circuit inwhich the output is taken across a resistor betweensource and ground. This circuit is equivalentto the emitter follower, and is a unity-gainstage whose impedance-transformation characteristicsmake it ideal in signal conditioning,buffering, and impedance-matching applications.C in+dcSignalinput R gR sC outSignaloutputsource follower

source impedance • special character 645source impedance 1. The impedance of a generatorin a circuit. 2. The impedance of the sourceelectrode of a field-effect transistor.source language A computer programming languagefrom which is derived (by a compiler) themachine (object) language on which the computeroperates.source program A computer program written in asource language.south magnetic pole The south pole of the equivalentbar magnet constituted by earth’s magneticfield (see EARTH’S MAGNETIC FIELD). The southmagnetic pole lies close to the geographic southpole. Compare NORTH MAGNETIC POLE.south-seeking pole Symbol, S. The so-calledsouth pole of a magnet. When a bar magnet issuspended horizontally, this pole points toearth’s south magnetic pole. Compare NORTH-SEEKING POLE.SP Abbreviation of STACK POINTER.sp 1. Abbreviation of single pole. 2. Abbreviation ofspecial.space-charge field 1. The electric field existingwithin a group of charged particles. 2. The electricfield existing in a plasma.space diversity See DIVERSITY RECEPTION.space-diversity reception See DIVERSITY RE-CEPTION.space division A method of data transfer in whichdifferent paths are used for the transmission ofdifferent signals.space-division switch A switch having two or moreports and different paths connecting the ports.space lattice The three-dimensional, redundantpattern formed by atoms and molecules in a crystaland having a shape that is characteristic of aparticular crystalline material.spacer An insulating rod or bar that serves to holdapart the conductors of a two-wire, four-wire, orcoaxial air-dielectric transmission line.space suppression Following the printing of a lineby a printer, the prevention of normal paper travel.space-time-space switch Abbreviated STS switchor STSS. A large switching array with two spaceswitch blocks and a time switch block betweenthem.space wave One of the components of an electromagneticground wave. The space wave, unlikethe surface wave, is not earth-guided. It has twocomponents: the direct wave and the groundreflectedwave.spaghetti Slender, varnished-cambric tubing usedas slipover insulation for wires and busbars.span On an instrument scale, the difference betweenthe highest value and the lowest value.spark See ELECTRIC SPARK.spark absorber 1. See SPARK SUPPRESSOR. 2.See KEY-CLICK FILTER.spark coil A small induction coil. Its name is derivedfrom its initial purpose of supplying thehigh voltage for spark plugs in gas engines.spark energy The energy dissipated by an electricarc or spark.spark gap A device consisting essentially of twometal points, tips, or balls that are separated by asmall air gap. A high voltage applied to the electrodescauses a spark to jump across the gap.sparking distance The maximum separation ofthe electrodes of a spark gap at which a givenvoltage will produce a spark.sparking voltage The lowest voltage that willcause a spark to jump across a gap of a givenwidth.spark killer See SPARK SUPPRESSOR.sparkover A discharge in air, a vacuum, or a dielectric.It is characterized by sparking betweenelectrodes in the medium.spark plate In some automobile radios, a noiseinterference-eliminatingbypass capacitor inwhich the chassis is one plate.spark-plug suppressor A small resistive deviceconnected in series with a spark plug to suppresselectrical noise arising from the ignition in an internalcombustion engine.spark quencher See SPARK SUPPRESSOR.spark suppressor A resistor, capacitor, and/ordiode used to eliminate or minimize sparking betweenmake-and-break contacts.spark suppressorTo keyedcircuitspark-suppressor diode See SUPPRESSORDIODE.spatial distribution The three-dimensional directionalpattern of a transducer (such as an antenna,microphone, or speaker).spc 1. Abbreviation of silicon point contact. 2. Abbreviationof silver-plated copper.SPDT Abbreviation of SINGLE-POLE/DOUBLE-THROW (switch or relay).speaker See LOUDSPEAKER.speaker damping See DAMPED LOUDSPEAKER.speaker-level audio In a sound reproduction system,radio receiver, or other audio circuit, an audio-frequencysignal of sufficient amplitude todrive a speaker or speaker system directly, withoutthe need for additional amplification.speaking arc A method of modulated-light transmission.An electric arc is modulated by audiofrequencysignals.special character A printed, displayed, or encodedcharacter other than a numeral or letter, such as

646 special character • speech clippingan ampersand (&) or a pound sign (#). Also calledSYMBOL.special effects Various techniques used in filmmaking,computer animation, and videotaperecording for achieving certain visual scenes orimages.special-purpose computer A computer designedto handle problems or be suitable for applicationsof a specific category; a dedicated computer.special-purpose calculator An electronic calculatorintended for essentially “nonmathematical”purposes, such as biorhythm data, astrologicalinformation, metric conversions, musical composing,etc.specific address See ABSOLUTE ADDRESS.specification 1. For an electronic device, a statementof performance over specific parameters.Example: for a high-fidelity stereo amplifier, 50watts per channel over a frequency range of 10 Hzto 30 kHz, with less than 1 percent total harmonicdistortion. 2. A precise listing of requirementsor expectations.specific conductivity Conductance per unit volume.In SI units, this is expressed in siemens percubic centimeter (S/cm 3 ).specific dielectric strength For an insulant, thedielectric strength per millimeter of thickness.specific gravity Abbreviation, sp gr. The ratio ofthe density of a material to the density of a substanceaccepted as a standard (usually water at 4degrees Celsius or 39.2 degrees Fahrenheit).specific inductive capacity See DIELECTRICCONSTANT.specific resistance See RESISTIVITY.specific sound-energy flux See SOUND INTEN-SITY.spectral comparative pattern recognizer Acronym,SCEPTRON. Equipment used to classifyautomatically complex signals obtained frominformation that has been converted into electricalsignals.spectral density For a complex signal, the amountof energy contained within a given band of frequencies.spectral energy distribution The occurrence ofdifferent amounts of energy in different areas of aspectrum (as in a visible-light spectrum, soundspectrum, or radio-frequency spectrum).spectral response The characteristic of a device,such as a photocell or the human eye, that describesthe device’s sensitivity to radiations ofvarious frequencies in a given spectrum.spectral sensitivity The color response of a lightsensitivedevice.spectrograph A recording SPECTROMETER.spectrometer 1. An instrument used to measurespectral wavelengths. 2. An instrument used tomeasure the index of refraction. 3. See MASSSPECTROMETER.spectrophotometer A photoelectric instrument forchemical analysis. In the device, light passingthrough the material under analysis is broken upinto a spectrum that is examined with a photoelectriccircuit, which, in turn, plots a spectrogram.spectroscope An instrument that resolves a radiationinto its various frequency components andpermits measurement of each.spectrum A band of frequencies or wavelengths(e.g., radio spectrum, visible-light spectrum, andsound spectrum).spectrum analyzer 1. An automatic wave analyzerwith a visual display (oscilloscope). 2. A scanningreceiver with a screen that shows a plot of signalsand their bandwidths over a specific frequencyband.SignalsNoise floorspectrum analyzer, 2.Amplitude axisFrequencyaxisSignalsspecularity A qualitative or experimentally derivedexpression of the efficiency with which aDIFFRACTION GRATING works.specular reflection Reflection in which the reflectedray is in the same plane as the incidentray, as in reflection from an extremely smoothsurface.speech amplifier A (usually low-level) audio amplifierdesigned especially for speech frequencies.It is generally used to amplify the signals from amicrophone.speech clipper A device, such as a biased diode,(see POSITIVE PEAK CLIPPER) for holding speechsignals to a constant amplitude. CompareSPEECH COMPRESSOR. Also see SPEECH CLIP-PING.speech clipping The use of a limiting circuit tomaintain the output-signal amplitude of a speechamplifier against fluctuations in the intensity of

speech clipping • speed of transmission 647speech input. The resulting signal requires filteringto remove harmonics generated by the process.Compare SPEECH COMPRESSION.speech compression Automatic regulation of thegain of a speech amplifier to maintain its outputsignalamplitude against speech-input fluctuations.Compare SPEECH CLIPPING.speech compressor A circuit or device, such as anautomatic-gain-control (agc) system, for performingspeech compression. Compare SPEECH CLIP-PER.speech digit signaling A method of digital signaling,where time slots generally used for encodedaudio or video are used alternately for signaling.speech frequencies See VOICE FREQUENCIES.speech intelligibility The quality of reproducedspeech that makes it easily understood by a reasonablyproficient user of the language. For goodspeech intelligibility, a circuit should transmitfrequencies between 300 Hz and 3000 Hz withminimal distortion. Increased bandwidth improvesfidelity, but does not provide a significantincrease in intelligibility for normal speech.speech inverter See SCRAMBLER CIRCUIT.speech power 1. The alternating-current power inan electric wave corresponding to speech, as opposedto that in a sine wave. 2. Sound power in aspeech transmission.speech recognition The ability of a device totranslate audible spoken words, phrases, or sentencesinto binary digital signals that can be usedby machines, such as computers and robots.speech recognizer An electronic device that translatesaudible spoken words, phrases, or sentencesinto binary digital signals that can be usedby machines, such as computers and robots.speech scrambler See SCRAMBLER CIRCUIT.speech synthesis The ability of a device to translatebinary digital signals from a machine, suchas a computer or robot, into audible, coherentspoken words, phrases, or sentences.speech synthesizer An electronic device thattranslates binary digital signals from a machine,such as a computer or robot, into audible, coherentspoken words, phrases, or sentences.speed key 1. A semiautomatic key for manual generationof Morse code characters. 2. A similar,fully automatic key used especially for highspeedtelegraphy.speed of light Symbol, c. The speed at which electromagneticwaves propagate in a vacuum; approximately299,792 kilometers per second(186,282 miles per second).speed of sound The speed at which acoustic wavespropagate. It depends on the nature of themedium. In air, at ordinary temperatures, it isapproximately 344 meters (1129 feet) per second.In fresh water, it is approximately 1463 meters(4800 feet) per second.speed of transmission The amount of data sent ina given unit of time. It is generally measured inMic.PhonemevocabularyTo computeror robotA/Dconverterspeech recognizerPauseinserterInflectioninserterPhonemeselectorOpticalcharacterrecognizerspeech synthesizerPatternanalyzerComparatorVocabularySpkr.Texthardcopy

648 speed of transmission • spiral distortionbits per second (bps), characters per second (cps),characters per minute (cpm), or words per minute(wpm). It is used primarily for digital codes.speedup capacitor See COMMUTATING CAPACI-TOR.SPFW Abbreviation of SINGLE-PHASE FULL-WAVE.sp gr Abbreviation of SPECIFIC GRAVITY.sphere 1. A closed surface in three-dimensionalspace, represented by the set of all pointsequidistant from a specified center point. 2. Asolid in three-dimensional space, represented bythe set of all points on or within a closed surface,as defined in 1.sphere gap A spark gap in which the spark passesbetween two polished metal spheres. When theair gap is adjustable, unknown high voltages canbe measured in terms of the largest gap width atwhich sparking occurs. Compare NEEDLE GAP.sphere-gap voltmeter See SPHERE VOLTMETER.sphere voltmeter A gap voltmeter using a SPHEREGAP.spherical aberration In a spherical lens, mirror, orreflecting dish, distortion as a result of the spherical(as opposed to paraboloidal) shape of the surface.This causes the focus to be elongated into ashort line segment along the principal axis.spherical angle An angle formed by the intersectionof two arcs on the surface of a sphere.spherical coordinate geometry A scheme forguiding a robot arm in three dimensions viaSPHERICAL COORDINATES. The length (radius)of the arm can be varied, as can the elevation (latitude)and azimuth (longitude).spherical coordinates A method of defining apoint (P) in three-space using two angles (latitudeand longitude) and a radial distance (r) from theorigin.spherical degree A unit equal to 1 ⁄720 of the surfacearea of a sphere.spherical distance The length of the shortest arc(lying on a great circle) connecting two specifiedpoints on a sphere.spherical divergence The manner in which energynormally propagates from a fixed point source inthree dimensions. Wavefronts expand from thesource in the form of spheres, whose centers areat the point source.spherical reflector A microwave reflector (dish)whose contour is that of a sphere, rather thanthat of a paraboloid.spherical wave A wave characterized by wavefrontsthat are concentric spheres.spheroidal antenna A sheetmetal or wire-meshantenna having the cross section of a sphere thatis flattened at the ends of one axis.SPHW Abbreviation of SINGLE-PHASE HALF-WAVE.spider 1. The flat, round, springy part that holds theapex of the vibrating cone of a dynamic speaker.2. A quickly assembled, chassisless hookup inwhich the pigtails of components form the wiringand the mechanical support for a circuit.spiderweb antenna A set of dipole antennas fordifferent frequencies, arranged in a common(usually horizontal) plane. The result is a broadbandantenna.Radiatorsspiderweb antennaRadiatorsFeed linespiderweb coil A flat, single-layer coil in which astrand of wire is woven over and under thespokes of a wheel-like form, and having the generalappearance of a spiderweb. The criss-crosswinding reduces distributed capacitance bybreaking up the parallelism of adjacent turns.spike 1. A current or voltage pulse of extremelyshort duration. 2. A sharp transient, such as anovershoot on a pulse or square wave.spike suppressor A clipper or similar device for removinga spike from a signal voltage.spin A quantity of angular momentum possessedby a subatomic particle. It can be positive, negative,or zero, but it always exists in integral multiplesof 1 ⁄2.spindle1. The pivoted shaft that carries the movableelement and rotates between the pivots in ameter movement. 2. The rotor of an alternator—especially when the rotor is a permanent magnet.3. The rotating shaft in a motor, generator, orsimilar electric machine.spinning electron An electron having nonzero angularmomentum.spinthariscope An optical device for observing theeffect of alpha particles emitted by a radioactivesubstance, from the scintillations they produceupon striking a small, fluorescent screen.spiral coil See DISK WINDING.spiral distortion A form of television camera-tubedistortion caused by spiraling of the electrons asthey are emitted from the photocathode. The resultis a twisted image.

spiral-rod oscillator • spot modulation 649spiral-rod oscillator A parallel-line-type oscillatorin which the lines are rods that are rolled up intospirals to conserve space. Also see LINE-TYPEOSCILLATOR.spiral sweep 1. A means of sweeping the electronbeam in a cathode-ray tube to produce a spiraltrace on the screen. 2. The circuit for producingsuch a sweep.spiral trace See SPIRAL SWEEP.spiral winding See DISK WINDING.spkr Abbreviation of speaker (see LOUDSPEAKER).splatter See SIDEBAND SPLATTER.splatter-suppression filter In an amplitude-modulated(AM) or single-sideband (SSB) radio transmitter,a low-pass filter inserted between theoutput of the audio amplifier and the audio inputof the modulator. It suppresses high-frequencyaudio components that would otherwise causesideband splatter.splaying The construction of a room or auditoriumso that the walls do not meet at right angles. It isuseful in optimizing the acoustic characteristicsof the enclosure because it tends to reduceacoustic resonant effects.splice 1. A physical or electrical connection betweentwo wires, made by tightly winding theends together. Solder is often applied for additionalmechanical strength and electrical continuity.2. A physical connection between twolengths of magnetic tape, made in such a way asto cause minimal disturbance in reproduced audio,video, or data. 3. To prepare a joint, as definedin 1 or 2.splicer A device for making a SPLICE.splicing block A device specifically designed to facilitateeasy splicing of audio, video, or digitalmagnetic tape.splicing tape A durable, flexible adhesive designedto hold a magnetic-tape splice together.spline-based modeling In video animation and advancedcomputer graphics, a scheme that usescurve-generating formulas (e.g., Bezier curves) tocreate lifelike images.split-anode magnetron A magnetron in which theplate (anode) consists of two semicylinders withthe cathode at their axis.CathodeEnvelopeOne-halfanodeOne-halfanode(Magnet not shown)split-anode magnetronsplit-load phase inverter See PARAPHASE IN-VERTER.split-phase motor A fractional-horsepower, alternating-currentmotor that starts like a two-phasemotor and runs like a single-phase motor. Afterthe machine approaches approximately 75 percentof full speed, a centrifugal switch cuts outthe starting winding.split projector An acoustic transmission devicewith several independently operated transducers.split-reed vibrator See SELF-RECTIFYING VIBRA-TOR.split-rotor plate See SERRATED ROTOR PLATE.split-stator capacitor A variable capacitor havingtwo separate stator sections and a common rotorsection.split-sound receiver A television receiver circuit inwhich the sound signal is separated from thecomposite signal shortly after pickup by the antenna,and is amplified separately from the videosignal. Compare INTERCARRIER RECEIVER.splitter A device used to couple two or more televisionreceivers to a single antenna.spool See REEL.sporadic-E layer ionization Occasional, scatteredionization in the E-layer of the ionosphere.sporadic-E propagation At certain radio frequencies,the long-distance propagation of electromagnetic(EM) waves via the E layer of theionosphere. This layer exists at an altitude of approximately50 miles (80 km) above sea level. Thismode of propagation tends to be intermittent, andconditions can change rapidly. It is most likely tooccur between 20 MHz and 150 MHz. Occasionally,it is observed at frequencies as high as 200MHz. The propagation range is normally severalhundred miles, but occasionally can occur overdistances of 1,000 to 1,500 miles. The standardfrequency modulation (FM) broadcast band issometimes affected by this propagation. Thesame is true of the lowest television (TV) broadcastchannels, especially channels 2 and 3. SeeIONOSPHERE.SPOT Abbreviation of satellite position and tracking.spot brightness In a cathode-ray tube, the relativebrilliance of the glowing dot or trace produced onthe screen by the electron beam.spot check 1. To take a random sample or to makea random test by arbitrarily selecting a single itemfrom a run of similar items and subjecting it toanalysis, examination, performance, or parametricevaluation, etc. 2. A random sample or test.spot frequency 1. A single frequency or signal towhich other frequencies can be referred. 2. A frequencyor signal that acts as a limit marker (e.g., todefine the edges of an allocated frequency band).spot jamming Deliberate interference to a radio signalat some frequency and at some specific time.spot modulation In a cathode-ray tube, modulationof the brightness of the spot (and, accordingly,of the image) produced on the screen by the

650 spot modulation • square-law meterelectron beam. Also see INTENSITY MODULA-TION.spot welding A method of electrical welding inwhich the parts to be joined are held together,overlapping, between the points of two electrodes,between which a current is passed to heat theparts at the spot of contact.spot-wheel pattern A frequency-identifying wheelpattern produced on an oscilloscope screen by intensity-modulatinga circular trace. The circulartrace is produced by applying a standardfrequencysignal to the horizontal and vertical inputterminals 90 degrees out of phase. A square-wavesignal of unknown frequency is applied to the intensity-modulation(z-axis) input terminals. Thesquare wave chops the circle into a number ofbright sectors or spots. The unknown frequency(fx) equals Nfs, where N is the number of spots inthe circle, and fs is the standard frequency. CompareGEAR-WHEEL PATTERN.sprat Acronym for small portable radar torch. Aportable radar unit that uses a Gunn diode togenerate microwave energy. The range is about500 meters ( 1 ⁄3 mile).spray coating 1. Applying a protective coat of insulatingmaterial to a conductor or component byspraying it with a liquid substance and allowing itto dry. Compare DIP COATING. 2. The coat applied,as defined in 1.spreader 1. An insulator used to separate thewires of an air-spaced transmission line. 2. Anyof the rods composing the supporting structure ina cubical quad antenna.spreading current In a semiconductor, currentcaused by the movement of charge carriers by circuitousroutes, that is, in paths that deviate significantlyfrom straight lines.spreading loss Energy lost during the transmissionof radiation.spreading resistance In a semiconductor device,the resistance that is a consequence of electricalpaths through material that is not along straightlines between electrodes.spread spectrum 1. A method of transmission inwhich the occupied bandwidth of the signal is deliberatelyincreased, or spread out, over a muchwider range than it would normally occupy withconventional modulation. 2. A signal transmitted,as defined in 1.spring coil See SOLENOID, 1.spring contact See FLEXIBLE CONTACT.sprite In video and animated computer graphics, abrief insert, such as a little insect that scurriesacross the screen, or a face that pops in andsmiles. It is used primarily for effect.SPST Abbreviation of SINGLE-POLE/SINGLE-THROW (switch or relay).spurious emission From a radio or televisiontransmitter, an unintended and unwantedoutput signal on a frequency other than thefundamental signal frequency. It can begenerated by faulty modulation, amplification,and/or oscillation.spurious oscillation 1. Oscillation in a normallynonoscillatory circuit. 2. In an oscillator, simultaneousoscillation at a frequency other than thenormal one.spurious response In a communications receiver,a signal that appears to be on a certain frequency,when, in fact, the received signal is noton that frequency. It often results from inadequateimage rejection.spurious-response ratio The ratio of the transmission(or gain) of a circuit of a desired signal to itstransmission (or gain) for a spurious signal at thesame setting of the circuit (e.g., signal-to-imageratio).spurious sidebands In an amplitude-modulated(AM) or single-sideband (SSB) radio signal, sidebandenergy at frequencies outside the nominalsignal band, usually resulting from impropermodulation, inadequate filtering, improper envelopeclipping, or nonlinear amplification.Sputnik The first orbiting artificial earth satellite.It was launched by Russia (then known as theUnion of Soviet Socialist Republics) in 1957.sputter 1. A layer of material obtained by sputtering(see SPUTTERING, 1). 2. To carry out the processof sputtering (see SPUTTERING, 1).sputtering 1. A technique for electrically depositinga film of metal on a metallic or nonmetallicsurface. In a vacuum chamber, the piece of metalto be deposited is made the cathode of a highvoltagecircuit, with respect to a nearby anodeplate. The high voltage causes atoms to be ejectedfrom the surface of the cathode and strike thesurface of an object placed in their path, becomingdeposited on it as a film of cathode metal.Compare EVAPORATION, 1. 2. The disintegrationof a vacuum-tube cathode through ejection ofsurface atoms from the cathode by impingingpositive ions.sq Abbreviation of SQUARE.S Q band A section of the S BAND, from 2400 to2600 MHz.SQC Abbreviation of STATISTICAL QUALITY CON-TROL.SQR 1. Abbreviation of SQUARE ROOTER. 2. Inthe BASIC computer-programming language, afunction that computes the square root of a positivenumber.S quad See SIMPLE QUAD.square-law demodulator See SQUARE-LAW DE-TECTOR.square-law detector A detector whose output isproportional to the square of the root-meansquare(rms) value of the input. Also calledWEAK-SIGNAL DETECTOR.square-law meter 1. A meter whose deflection isproportional to the square of the quantity appliedto it. Also see CURRENT-SQUARED METER. 2. Ahigh-impedance electronic voltmeter, whose

square-law meter • ssc 651deflection is proportional to the square of the appliedvoltage.square-law modulator A circuit or device that accomplishesamplitude modulation of one signalcurrent by another, by simultaneously passingthe two currents through a component, such as anonlinear resistor, having a square-law response.square-law response Circuit or component operationthat results in an output signal, proportionalto the square of the input.square rooter An analog or digital device used toextract the square root of a number.square wave An alternating or pulsating current orvoltage whose rise and decay times are essentiallyzero, and whose maxima and minima are essentiallyflat. The duration of the maxima is equal tothe duration of the minima. A special form ofRECTANGULAR WAVE.square-wave amplifier An amplifier designed tooperate with square waves.square wavesquare-wave converter See SQUARING CIRCUIT.square-wave generator A signal generator deliveringan output signal that has a square waveform.Compare SQUARING CIRCUIT, 1.square-wave testing Testing the response of a circuitor device, such as an amplifier, by observingthe extent to which it distorts a square-wavesignal passing through it (a measure of highfrequencyresponse).squaring circuit 1. A circuit (such as a twin-diodeclipper, overdriven amplifier, or Schmitt trigger)that converts a sine wave or pulse into a squarewave. 2. A circuit whose instantaneous outputsignalamplitude is equal to the square of the instantaneousinput-signal amplitude.squarish wave 1. A signal whose oscilloscope traceis nearly, but not exactly, the same as that of asquare wave. 2. A rectangular wave that is not asquare wave; that is, whose maxima and minimaare not of the same duration. See RECTANGULARWAVE and SQUARE WAVE.squawker 1. In a three-way speaker system, themidrange speaker. 2. Any slave station in a multistationintercom network.squeal A high-pitched interferential sound, suchas that encountered in spuriously oscillating systems.squeezeout In optical character recognition (OCR),a condition in which errors occur because theprinted characters have excessive ink at theedges. Also called smudge.squegging A choking-type cutoff action in a circuitcaused by an excessively strong signal.squegging oscillator An oscillator that starts andstops oscillating intermittently as a result ofSQUEGGING.squelch See SQUELCH CIRCUIT.squelch amplifier An amplifier that can be controlledby a squelch signal. Also see SQUELCHCIRCUIT.squelch circuit One of several circuits that automaticallydisable a receiver or amplifier, exceptwhen incoming signals exceed a predeterminedthreshold amplitude. This action mutes theequipment, eliminating annoying backgroundnoise and unwanted signals. Also called MUTINGCIRCUIT.squelch signal The activating or deactivating signaldelivered by a SQUELCH CIRCUIT.squiggle See BLIP, 2.squint 1. The angular resolution of a radar antenna.2. The angular difference between theantenna axis and the major lobe of a radar transmitter.squirrel-cage induction motor See SQUIRREL-CAGE MOTOR.squirrel-cage motor An induction-type alternating-currentmotor using a squirrel-cage rotor.squirrel-cage rotor In an alternating-current motor,a rotor composed of straight copper barsembedded in a laminated soft-iron core andshort-circuited at the ends by rings. Its name isderived from its resemblance to a revolving squirrelcage.squirter See SIGNAL INJECTOR.SR 1. Abbreviation of SILICON RECTIFIER. 2. Abbreviationof silicone rubber (see SILICONE).3. Abbreviation of SHIFT REGISTER.S-R Abbreviation of SEND-RECEIVE.Sr Symbol for STRONTIUM.sr Abbreviation of STERADIAN.SRAM Abbreviation of static random-access memory.S-rays See SECONDARY RAYS.SRF Abbreviation of SELF-RESONANT FRE-QUENCY.S-RF meter A dual-function meter in a radiotransceiver. In the receiving mode, the meter indicatesS units. In the transmit mode, the meterindicates relative output power.SRR Abbreviation of SHORT-RANGE RADAR.SS 1. Abbreviation of SOLID STATE. 2. Abbreviationof SINGLE SHOT. 3. Abbreviation of smallsignal. 4. Abbreviation of SINGLE SIGNAL. 5. Abbreviationof same size. 6. Abbreviation of stainlesssteel.SSB Abbreviation of SINGLE SIDEBAND.S S band A section of the S BAND extending from2900 to 3100 MHz.SSBSC Abbreviation of SINGLE-SIDEBAND SUP-PRESSED CARRIER.ssc Abbreviation of single-silk-covered (wire).

652 S scale • staggered tuningS scale A scale of numbers used in radio communications,and especially in amateur radio, to reportthe approximate strength of signals: S1,faint signals; S2, very weak signals; S3, weak signals;S4, fair signals; S5, fairly good signals; S6,good signals; S7, moderately strong signals; S8,strong signals; S9, extremely strong signals. Alsosee S METER.sse Abbreviation of single-silk-enameled (wire).SSI Abbreviation of SMALL-SCALE INTEGRATION.SSL Abbreviation of SOLID-STATE LAMP.SSSC Abbreviation of SINGLE-SIDEBAND SUP-PRESSED CARRIER. (Also, SSBSC.)ST Abbreviation of SINGLE THROW.sta 1. Abbreviation of STATION. (Also stn.) 2. Abbreviationof STATIONARY.stab Abbreviated form of stabilizer (see STABI-LIZER, 4).stability 1. The condition in which an equipmentor device is able to maintain a particular mode ofoperation without deviation. 2. The condition inwhich the setting or adjustment of a device remainsat a particular point without movement.3. The condition in which a quantity remainsconstant, with respect to time, temperature, oranother variable. 4. The ability of inks used in opticalcharacter recognition to retain their colorafter exposure to light or heat.stability factor Abbreviation, SF. For a bipolartransistor, the derivative dI c /dI co , where I c is thesteady-state collector current and I co is the collectorcutoff current.stabilized platform See STABLE PLATFORM.stabilizer 1. See DAMPING DIODE. 2. See DAMP-ING RESISTOR. 3. A device or circuit for the selfregulationof current or voltage. 4. A chemicalused to control or arrest a reaction.stabilizing windings Auxiliary field windings usedto prevent speed runaway in shunt motors.Stabistor Trade name for a type of voltage-regulatingsemiconductor diode.stable device A device whose characteristics andperformance remain substantially unchangedwith time or variations in temperature, appliedpower, or other quantities.stable element 1. A component that maintains itsvalue or ratings, despite widely variable environmentalconditions. 2. A navigational instrumentthat maintains its orientation at all times.stable platform A gyro-type device used tostabilize objects in space, and to provide accurateinformation regarding attitude (pitch, roll, andyaw).stable state A stable condition, such as the highand low states of a flip-flop. The flip-flop has twostable states and will remain in one until it isswitched to the other, whereupon it will then remainin that latter state until switched back tothe former. Compare UNSTABLE STATE.stack 1. A piled assembly of capacitor plates andseparating dielectric films. 2. An assembly ofselenium rectifier plates (see POWER STACK).3. To assemble a stacked array. 4. A temporarystorage area consisting of a small group of registersin a computer memory.stacked array An antenna system in which two ormore identical antennas, such as dipoles, Yagis,or halos, are placed one above the other or sideby-side.It provides additional forward gain, and,in some cases, enhances the front-to-back ratioand/or front-to-side ratio.stacked arraystacked-dipole antenna A stacked array of halfwavedipole antennas.stacking The combination of two or more identicalantennas, such as dipoles, Yagis, or halos, in aSTACKED ARRAY to provide enhanced forwardgain. It can also enhance the front-to-back ratioand/or front-to-side ratio. Stacking can be donevertically or horizontally.stack pointer Abbreviation, SP. A register indicatingthe last data item to be entered in a stack (seeSTACK, 4).stage A complete functional unit of a system (e.g.,amplifier stage, oscillator stage, modulator stage,etc.).stage-by-stage elimination See SIGNAL INJEC-TION.stage gain The amplification provided by a singlestage in a system.stage loss The loss introduced by a single stage ina system.stagger 1. An error in facsimile reception, occurringas a constant discrepancy in the position ofthe received dot. 2. To deliberately tune a set ofresonant circuits, especially in a bandpass filter,to one side or the other of the center frequency.staggered tuning The tuning of the input and outputcircuits of a single stage, or the tuning of

staggered tuning • standard signal generator 653successive stages to slightly different frequenciesto obtain flat-top response.stagger tuning See STAGGERED TUNING.stagger-wound coil See BASKET-WEAVE COILand SPIDERWEB COIL.staircase circuit See STAIR-STEP CIRCUIT.staircase generator A circuit or device for generatinga STAIR-STEP WAVE.staircase wave See STAIR-STEP WAVE.stair-step circuit A circuit that converts a series ofequal-amplitude pulses into a stair-step wave.stair-step wave A nonsinusoidal wave characterizedby a multistep rise and a steep fall. It is socalled from its resemblance to the cross section ofa staircase.broadcast bands range from 54 MHz to 806 MHzin several sections, designated in channels from 2through 69. Also see BROADCAST SERVICE, 1.standard candle See CANDELA.standard cell A highly refined primary cell usedto supply a precise direct-current voltage forelectronic measurements. The Weston standardcell contains a mercury positive electrode, cadmiumamalgam negative electrode, and cadmiumsulfate electrolyte, and delivers 1.0183volts at 20 degrees Celsius. Also see ZINCSTANDARD CELL.stair-step wavestall torque The torque produced when a motorshaft is prevented from turning.stalo Acronym for stabilized oscillator.stand-alone photovoltaic system A solar-powerplant that uses large banks of rechargeable electrochemicalbatteries, such as the lead–acid type,to store electric energy as it is supplied by photovoltaicsduring hours of bright sunshine. The energyis released by the batteries at night or ingloomy daytime weather. This system does notdepend on the electric utility companies. Althoughthis scheme offers independence from theutility companies, a blackout will occur if the systemgoes down. Compare INTERACTIVE PHOTO-VOLTAIC SYSTEM.standard 1. A precise specification governing thedimensions and characteristics of a device or system(e.g., military standard). 2. A highly accuratephysical or electrical quantity to which similarquantities can be compared (e.g., standard frequency).3. The device or system that produces astandard quantity as defined in 2 (e.g., frequencystandard). 4. Having conventional and widely acceptedcharacteristics.standard atmosphere Abbreviation, atm. Air pressureat sea level (1.013 Pascals, or about 14.7pounds per square inch). Also called ATMO-SPHERE.standard broadcast band Any of numerous frequencybands allocated to conventional broadcaststations. In the United States, theamplitude-modulation (AM) radio broadcast bandextends from 535 to 1705 kHz, and the frequency-modulation(FM) radio broadcast bandextends from 88 to 108 MHz. The television (TV)standard deviation In statistical analysis, thesquare root of the mean of squares of deviationfrom the mean.standard frequency A highly precise frequency towhich other frequencies can be compared foridentification or measurement.standard-frequency oscillator A stable, preciseoscillator that delivers a standard frequency. Alsosee PRIMARY FREQUENCY STANDARD andSECONDARY FREQUENCY STANDARD.standard-frequency signal A calibration and referencesignal that is broadcast on a standard frequency,such as those transmitted on 2.5, 5, 10,and 15 MHz by the National Bureau of Standards.standard pitch The tone corresponding to thefrequency 440 Hz (in music, the note A abovemiddle C).standard signal generator A (usually continuouslyvariable) high-grade generator of modulatedand unmodulated radio-frequency testsignals. A general-purpose instrument of thistype usually covers a wide range (e.g., 15 kHz to100 MHz) in several tuning bands. For calibration,a standard signal generator is referred to aprimary frequency standard or secondary frequencystandard.

654 standard subroutine • statestandard subroutine A usually vendor-suppliedcomputer program segment applicable to morethan one program and used as needed as a subroutine.standard temperature and pressure The conditionwhere the temperature is zero degrees Celsiusand the pressure is one atmosphere.Abbreviated STP.standard time Official civil time in a particular region.See TIME ZONE.standby 1. The state in which equipment is out ofoperation, but can be immediately activated. Alsocalled IDLING. 2. A state of readiness on the partof personnel, equipment, or systems.standby battery An emergency power source for abattery-powered installation.standby current The CURRENT DRAIN of a circuit,device, or system when in the standby condition.standby equipment See EMERGENCY EQUIP-MENT.standby operation Keep-alive operation during astandby interval (see STANDBY).standby power The power drawn by an equipmentconnected to the power supply, but out of operation.standby power supply A circuit containing a battery,an automatic switch, and sometimes apower inverter. When utility power fails, theswitch actuates the supply, and the battery suppliespower to essential devices or systems. Similarto an UNINTERRUPTIBLE POWER SUPPLY.standing wave A stationary distribution of currentor voltage along a line because of the interactionsbetween a wave transmitted down the line and awave reflected back; it is characterized by maximum-amplitudepoints (loops) and minimumamplitudeor zero points (nodes).Voltage standing wavesFeed linestanding wavestanding-wave distortion Distortion of current orvoltage caused by standing waves on a transmissionline terminated in an impedance that containsreactance, and/or that differs from thecharacteristic impedance of the line.standing-wave indicator 1. A device, such as alamp or meter, used to detect standing waves.2. Standing-wave meter (see SWR BRIDGE).standing-wave loss The additional loss, over thematched-line loss, that occurs in a transmissionline when the standing-wave ratio (SWR) is not 1.standing-wave meter See SWR BRIDGE.standing-wave ratio Abbreviation, SWR. 1. Theratio between the maximum and minimum voltagealong a transmission line. This quantity issometimes specifically called voltage standingwaveratio (VSWR). 2. The ratio between themaximum and minimum current along atransmission line. 3. The ratio of load impedanceto feed-line characteristic impedance or viceversa, whichever is greater than or equal to 1.Ideally, the SWR is equal to 1 or 1:1, representinga load impedance that is purely resistive and hasthe same value as the characteristic impedance ofthe feed line. A high standing-wave ratio causesincreased loss in the line and can also result inexcessive conductor heating or dielectric breakdown.standoff insulator An insulator (usually of thepost type) that is used to hold a wire or componentaway from a chassis or base.star 1. In a gravity-battery cell, the copper electrode.The name is derived from its star shape.2. A star-shaped circuit of three-phase components.Also see WYE CONNECTION.star connection See WYE CONNECTION.Stark effect The influence of a strong transverseelectric field on the spectrum lines of a gas.starlight scope A device capable of viewing in apparenttotal darkness. Its operation depends onits ability to provide high amplification of extremelylow light levels, such as that of objects reflectingthe light from a moonless, but starlit, sky.star rectifier See WYE RECTIFIER.starter 1. An ignitor electrode in an ignitron (seeIGNITOR). 2. See STARTING BOX.starting box A special rheostat for starting a motorgradually in steps. The device is provided with anelectromagnet for holding the arm in the maximum-speedposition and releasing it when poweris interrupted.starting rod An ignitor electrode in an ignitron (seeIGNITOR).starting voltage 1. For a gas tube, the minimumvoltage that will initiate the glow discharge. 2. Inappropriate solid-state devices (e.g., a diac), thevoltage at which conduction between electrodesoccurs.start lead The lead attached to the first turn of a coil.Also called inside lead. Compare FINISH LEAD.start/stop multivibrator See MONOSTABLEMULTIVIBRATOR.stat- A prefix denoting ELECTROSTATIC.statampere The cgs electrostatic unit of current;1 statampere = 3.335640 × 10 –10 ampere.statcoulomb The cgs electrostatic unit of charge;1 statcoulomb = 3.335640 × 10 –10 coulomb.state 1. The present condition (i.e., on or off, trueor false, 1 or 0, high or low) of a bistable device,such as a flip-flop. 2. The physical or electrialcondition or status of a component, device,circuit, or system.

statement • statics 655statement The contents of a line in a sourcelanguagecomputer program.state of charge The amount of charge, measuredin coulombs or ampere hours, in a storage cell orbattery at a given time. A measure of the availableremaining energy in the cell or battery.statfarad The cgs electrostatic unit of capacitance;1 statfarad = 1.112650 × 10 -12 farad.stathenry The cgs electrostatic unit of inductance;1 stathenry = 8.987554 × 10 11 henry.static 1. Pertaining to that which is constant inquantity (e.g., static collector current of a transistor).2. Pertaining to that which is at rest (e.g.,static electricity). 3. The radio noise (sferics) producedby electric discharges in the atmosphere,usually lightning. 4. Pertaining to a test-andmeasurementmode for a unit or device, withoutsubjecting the unit or device to regular operation.Compare DYNAMIC.static base current See DC BASE CURRENT.static base resistance See DC BASE RESIS-TANCE.static base voltage See DC BASE VOLTAGE.static cathode current See DC CATHODE CUR-RENT.static cathode resistance See DC CATHODE RE-SISTANCE.static cathode voltage See DC CATHODE VOL-TAGE.static characteristic An operating characteristicdetermined from constant, rather than alternatingor fluctuating, values of independent and dependentvariables. Examples: the direct-current(dc) characteristics of diodes, transistors, and integratedcircuits. Compare DYNAMIC CHARAC-TERISTIC.static charge Energy stored in a stationary electricfield; electricity at rest.static collector A device that grounds the rotatingwheels of a motor vehicle, thereby removing thestatic electricity generated by the friction of thetires on the roadway.static collector current See DC COLLECTORCURRENT.static collector resistance See DC COLLECTORRESISTANCE.static collector voltage See DC COLLECTORVOLTAGE.static convergence In a color-television picturetube, the convergence of the three undeflectedelectron beams at the center of the aperturemask.static device A device with no moving parts.static discharge resistor A fixed resistor connectedbetween the earth and the high side of thepower line in a television receiver to drain off atmosphericelectric charge.static drain current See DC DRAIN CURRENT.static drain resistance See DC DRAIN RESIS-TANCE.static drain voltage See DC DRAIN VOLTAGE.static dump In computer operations, a dump occurringat a predetermined point in a programrun or at the end of the run.static electricity Energy in the form of a stationaryelectric charge, such as that stored in capacitorsor produced by friction or induction.static emitter current See DC EMITTER CUR-RENT.static emitter resistance See DC EMITTER RE-SISTANCE.static emitter voltage See DC EMITTER VOLTAGE.static flip-flop A flip-flop (see BISTABLE MULTIVI-BRATOR) using direct-current operating voltages.A single pulse switches the unit from on to off,and vice versa. Compare DYNAMIC FLIP-FLOP.static forward current transfer ratio Symbol,H FE . An expression of gain in a bipolar transistor.It can range from a factor of just a few times up tohundreds of times. Mathematically,H FE = I C /I Bwhere I C is the collector current and I B is the basecurrent. The H FE rating is important because itgives engineers an indication of the greatest currentamplification that can be obtained with aparticular transistor.static frequency multiplier A magnetic-core device,similar to a magnetic amplifier or peakingtransformer, that provides harmonics by distortinga sine-wave signal.static gate current See DC GATE CURRENT.static gate resistance See DC GATE RESISTANCE.static gate voltage See DC GATE VOLTAGE.static grid current See DC GRID CURRENT.static grid voltage See DC GRID VOLTAGE.static hysteresis The condition in which the magnetizationof a material (when it has the same intensityas the magnetizing force) is different whenthe force is increasing than when the force is decreasing,regardless of the time lag. CompareVISCOUS HYSTERESIS.static induction See ELECTROSTATIC INDUC-TION.static machine See ELECTROSTATIC GENERA-TOR.static memory Also called nonvolatile memory. Ina computer, a data memory medium (such asprogrammable read-only memory, or PROM) inwhich information is stored until it is altered orerased. It does not require a source of power tomaintain the integrity of the data. CompareVOLATILE MEMORY.static mutual conductance See STATIC TRANS-CONDUCTANCE.static plate current See DC PLATE CURRENT.static plate resistance See DC PLATE RESIS-TANCE.static plate voltage See DC PLATE VOLTAGE.statics The study of forces, bodies, poles, charges,or fields at rest or in equilibrium. CompareDYNAMICS.

656 static skew • step counterstatic skew In magnetic tape recording or playback,the amount of lead or lag time of one track,with respect to another. Ideally, the static skewshould be zero or practically zero.static source current See DC SOURCE CURRENT.static source resistance See DC SOURCE RESIS-TANCE.static source voltage See DC SOURCE VOLTAGE.static storage Also called nonvolatile storage. In acomputer, a data storage medium (such as magneticor optical disk) in which information isstored until it is altered or erased. It does not requirea source of power to maintain the integrityof the data. Virtually all data storage media are ofthis type, as contrasted with memory, which is oftenvolatile (see STATIC MEMORY and VOLATILEMEMORY).static stability The ability of a robot to maintainits balance while standing still. A robot with twolegs is generally poor in this respect. This is oneof the reasons why humanoid robots (androids)are difficult to engineer. A minimum of three legsis necessary for good static stability.static subroutine In computer programming, asubroutine that always serves the same purpose[i.e., it does not need to be tailored (according toparameters) for a specific application].station 1. An installation consisting of a transmitter,receiver, or both. 2. A test-equipment installationor position. 3. A computer installationincluding peripherals.stationary battery A (usually wet storage) batterynot normally moved when in use.stationary state A particular energy state for anatom represented by its electrons being in shellsat specific energy levels.stationary wave See STANDING WAVE.station authorization The legal privilege assignedto a broadcast or communications station, allowingthat station to be used for the purpose oftransmitting electromagnetic signals.station license See STATION AUTHORIZATION.statistical quality control Quality control basedupon the techniques of probability and statisticsin analyzing findings, making predictions, andformulating procedures for sampling.statmho The cgs electrostatic unit of directcurrentconductance; 1 statmho = 1.112650 ×10 –12 siemens.statoersted The cgs electrostatic unit of magnetizingforce; 1 statoersted = 265.458 A/m(3.33585 × 10 –11 oersted).statohm The cgs electrostatic unit of direct-currentresistance; 1 statohm = 8.987554 × 10 11 ohm.stator 1. A stationary coil. Compare ROTOR, 1. 2.The stationary member of a motor or generator.Compare ROTOR, 2. 3. The stationary-plate sectionof a variable capacitor. Compare ROTOR, 3.stator coil A stationary coil (see STATOR, 1, 2).stator plate(s) The stationary plate(s) of a variablecapacitor. Compare ROTOR PLATE.stator plateStatorplatesstator section See STATOR, 3.statoscope An aircraft altimeter that shows smallchanges in altitude.statvolt The cgs electrostatic unit of electromotiveforce; 1 statvolt = 299.7925 volts.statweber The cgs electrostatic unit of magneticflux; 1 statweber = 299.7925 webers (2.997925 ×10 10 maxwells).S T band A section of the S BAND, extending from1850 to 2000 MHz.std Abbreviation of STANDARD.steady-state component A quantity whose valueremains constant during normal operation of acircuit or device, as opposed to an alternating,fluctuating, or transient component.steerable antenna A directional antenna having arotatable major lobe.steering diode See DIRECTIONAL DIODE.Stefan-Boltzmann constant Value, 5.67051 ×10 –8 Wm –2 K –4 .Stefan-Boltzmann law The thermal-radiation lawthat shows the total emissive power of a blackbodyto be proportional to the fourth power of theabsolute temperature of the body.stenode See CRYSTAL FILTER.step 1. A computer program instruction. 2. A singleaction in the operation, maintenance, or troubleshootingof equipment. 3. A specific incrementin a quantity (such as frequency, voltage, current,etc.). 4. A sharp or rapid change in the value of aquantity.step-by-step operation See STEPTHROUGH OP-ERATION.step change A single-increment change in a value.step circuit A circuit that produces a step (sharpchange of slope) in the response curve of an amplifier.step counter 1. A stair-step circuit arranged tocount input pulses. The output capacitor of thecircuit discharges when a predetermined numberof input pulses has raised the capacitor voltage tothe level required to trigger a counter. 2. In a computeror calculator, a circuit or device that countsthe steps in an operation (such as division, multiplication,or shifting) called for by an instruction.

step-down ratio • stop amplifier 657step-down ratio In a circuit or device, such as astep-down transformer or cathode follower, theratio of the low output voltage to the high inputvoltage. Compare STEP-UP RATIO.step-down transformer A transformer deliveringan output voltage that is lower than the inputvoltage. In such a transformer, the secondary(output) winding contains fewer turns than theprimary (input) winding. Compare STEP-UPTRANSFORMER.step function See UNIT FUNCTION.step generator 1. A signal generator that deliversa step function (see UNIT FUNCTION). 2. A circuitor device that generates a STAIR-STEP WAVE.stepped leader The probing flow of electronsthrough the atmosphere preceding a lightningstroke. Once the path has been established, thedischarge takes occurs along the ionized pathdetermined by the stepped leader. It is so calledbecause the electrons move in hesitations,jumping several meters with each advance orstep.stepper motor A motor in which the shaft advancesin uniform angular steps, instead of rotatingcontinuously. These motors are extensivelyused in robotic devices. When such a motor isstopped and its coils are carrying current, theshaft resists turning.stepping relay See STEPPING SWITCH.stepping switch A multiposition rotary switch inwhich an electromechanical ratchet mechanismadvances to the next contact position each timethat a pulse of current is received.step-through operation A way of operating a computer,usually during a debugging operation, inwhich program instructions are executed one at atime by direction of the user. Also called singlestepoperation and step-by-step operation.step-up ratio In a circuit or device, such as a stepuptransformer or voltage amplifier, the ratio ofthe high output voltage to the low input voltage.Compare STEP-DOWN RATIO.step-up transformer A transformer delivering anoutput voltage that is higher than the input voltage.In such a transformer, the secondary (output)winding contains more turns than theprimary (input) winding. Compare STEP-DOWNTRANSFORMER.steradianA unit of solid-angle measure. A coneshapedsolid angle that has a vertex at the centerof a sphere (of radius r), that cuts off a portion ofthe sphere’s surface whose outer perimeter is acircle, and that has an area (as measured on thesphere’s surface) of r 2 . Also see SOLID ANGLE.Sterba array See BARRAGE ARRAY.Sterba curtain See BARRAGE ARRAY.stereo 1. Contraction of STEREOPHONIC. 2. Generalterm for a two-channel high-fidelity audio reproductionsystem.stereo-adaptable Pertaining to a television receiveror videocassette recorder (VCR) that requires aspecial circuit to obtain stereo sound from MultichannelTelevision Sound signals. CompareSTEREO-READY.stereo amplifier A two-channel amplifier for binauralreproduction (see BINAURAL).stereophonic Pertaining to equipment or techniquesfor producing a (somewhat) three-dimensionalperspective of sound reproduction.stereophonic sound system See STEREO SYSTEM.stereo-irrelevant Pertaining to sound componentsin a stereo system that are of equal magnitudein both (or all) channels. Thus, thesecomponents sound the same whether the systemis reproducing stereophonic sound or monauralsound.stereo phono cartridge A phono cartridge capableof reproducing sound from stereo discs.stereo-ready Pertaining to a television receiver orvideocassette recorder (VCR) that can deliverstereo sound from Multichannel Television Soundsignals without the need for a decoding circuit.Compare STEREO-ADAPTABLE.stereo recording A method of recording in whichtwo independent sound channels are transferredto some medium simultaneously, with the intentionthat the two channels be reproduced at thesame time.stereoscopic television Television in which thereproduced image appears three-dimensional.stereo system A multichannel, high-fidelity soundreproduction system including an amplifier andvarious other components, such as a radio receiver,compact-disc (CD) player, tape player,turntable, and speakers.stereotape Magnetic tape bearing more than onechannel (usually two channels) for the recordingand reproduction of stereophonic sound.sterilizer Any electronic device, such as an ultravioletgenerator, used to kill germs.stethoscope An electronic or nonelectronic instrumentused by physicians to listen to the heartbeatand other body sounds, and by techniciansto listen to mechanical sounds.still 1. A stationary picture on television. 2. A picturetransmitted or received by means of facsimile.3. A print on photographic paper of a negative.still television See FACSIMILE.stinger A brief, loud sound burst, such as a musicalchord, sometimes used for effect in recordedaudio or audio-visual presentations.stn Abbreviation of STATION. (Also, sta.)STO Abbreviation of STORAGE FUNCTION.stochastic The condition in which, at any instant,a given variable can assume a state dependent onprevious states, as well as chance elements (e.g.,words uttered extemporaneously by a speaker arerandom in that they cannot be predicted), whilealso being dependent, by the application of grammar,on previously spoken words (i.e., previousstates).stop amplifierSee REJECT AMPLIFIER.

658 stopband • storage registerAMtunerCDplayerTapeplayerTurntableFMtunerLeftspeakerstereo systemAmplifierRightspeakerstopband The continuous spectrum of frequenciesrejected by a filter, selective amplifier, or otherband-suppression device.stopband ripple Single or multiple attenuationpeaks within the stopband of an elliptic filter,where the frequency of the attenuation peak(s)is/are associated with the resonant circuit(s) inthe filter.stop code See HALT INSTRUCTION.stop element In digital transmission, a bit or set ofbits indicating the end of a character, and servingto inform the receiving device of the end of thecharacter.stop filter See BAND-SUPPRESSION FILTER.stopper resistor See STOPPING RESISTOR.stopping capacitor See BLOCKING CAPACITOR.stopping coil See CHOKE COIL.stopping resistor A parasitic-suppressing resistor,usually inserted in series with the inputand/or output of a power amplifying device. Alsocalled stopper resistor.storage 1. In computer operations, a medium onwhich data can be kept for an extended period oftime. Examples: magnetic disk, magnetic tape,optical disk. 2. The transferring of data frommemory to a more permanent medium. CompareMEMORY. 3. The retention of data of any kind,such as an oscilloscope image or video display,for use at a later time. 4. The retention of electricenergy or charge, as in a capacitor or electrochemicalcell. 5. The retention of energy in theform of a magnetic field, as in an inductor. 6. Theretention of potential energy in any form.storage allocation The assignment of computermemory areas to certain kinds of information, asoutlined in a source program and implementedby a compiler.storage battery A rechargeable battery; the technicalterm is secondary battery. Also see STOR-AGE CELL.storage capacity 1. The amount of data that canbe stored in a specific medium, such as a harddisk, diskette, or tape. Generally measured inbytes, kilobytes, megabytes, gigabytes, or terabytes.2. The energy-delivering capability of astorage battery in terms of ampere-hours, milliampere-hours,or other current-time units for aspecific rated voltage.storage cell 1. An electrochemical cell whose potentialcan be restored by charging it with electricity.Compare PRIMARY CELL. Also see CELL.2. The smallest part of a computer storagemedium. 3. In computer data storage, the partthat can hold a data unit (e.g., a bit).storage CRT See STORAGE TUBE.storage cycle In computer operation, the periodduring which a location of a cyclic storage devicecannot be accessed.storage density The number of data units (e.g.,bytes, kilobytes, or megabytes) that can be storedin a given length or area of a storage medium.storage device A medium into which data can beplaced and kept for later use. Examples: magneticdisk, magneto-optical disk, optical disk,and magnetic tape.storage dump See DUMP.storage function Abbreviation, STO. The so-called“memory” function of a microcomputer chip. Itcauses data to be inserted into memory or storagefor later use. It is commonly used in programmablecalculators, automatic-dialing telephones, and radioreceivers. Also called memory function.storage laser A laser that stores intense energy beforeflashing.storage life See SHELF LIFE.storage mesh In the cathode-ray tube (CRT) of astorage oscilloscope, a fine metal mesh electrodethat serves as the target on which the image iselectrostatically stored. Also see STORAGE TUBE.storage oscilloscope An oscilloscope that retainsa displayed image until the display is erased. Alsosee STORAGE TUBE.storage register In computers and calculators, astorage unit composed of flip-flops. In computers,it is independent of the central processing unit(CPU).

storage temperature • stray field 659storage temperature 1. The recommended temperaturefor storing specified electronic components.2. The particular temperature at whichelectronic components have been stored.storage time 1. The interval during which carriersremain in a semiconductor-junction device afterthe bias has been removed. Also see DIODE RE-COVERY TIME. 2. For a switching semiconductordevice, the time required for the amplitude of theoutput pulse to fall from maximum to 90% ofmaximum after the input pulse has fallen to zero.3. In a computer, the time required for data to betransferred from random-access memory (RAM)to nonvolatile storage (e.g., hard disk).storage tube A cathode-ray tube that retains informationin the form of images on a special electrodeuntil erased by a signal.store 1. To place data in a nonvolatile medium(such as a hard disk, diskette, optical disk, magnetictape, etc.). 2. To place in the memory of acalculator or computer. 3. In computing, a commandthat causes data to be placed in a nonvolatilemedium. In some applications, this iscalled save. 4. A nonvolatile medium on whichdata has been placed for future use or for archivalpurposes.stored base charge The carriers that remain in thebase layer of a bipolar transistor immediately afterthe forward bias has been interrupted. Thischarge maintains collector current momentarily.stored-energy welding A method of electric weldingin which electrical energy is stored slowly,then released at the rate required for the welding.STP See STANDARD TEMPERATURE AND PRES-SURE.straight adapter An inline coaxial fitting for joiningtwo fixture-terminated coaxial lines in series.straight angle An angle measuring 180 degrees.straight dipole A (usually center-fed) dipole antennahaving only one radiator. Also see DIPOLEANTENNA.straightforward Pertaining to data transmission inone direction only.straight-gun CRT A cathode-ray tube (CRT) inwhich the electron gun projects the beam in astraight line through the deflecting elements tothe screen. Compare BENT-GUN CRT.straight-line capacitance Abbreviation, SLC. Pertainingto a variable capacitor for which thesetting-vs.-capacitance curve is a straight line;the capacitance variation is linear. CompareSTRAIGHT-LINE FREQUENCY and STRAIGHT-LINE WAVELENGTH.straight-line coding See STRAIGHT-LINE PRO-GRAMMING.straight-line frequency Abbreviation, SLF. Pertainingto a variable capacitor in a tuned circuitfor which the setting-vs.-frequency curve is astraight line; the frequency variation is linear.Compare STRAIGHT-LINE CAPACITANCE andSTRAIGHT-LINE WAVELENGTH.straight-line programming During the writing ofa computer program, avoiding the creation ofloops by repeating a series of instructions to reduceexecution time.straight-line tracking In a phonograph turntable,linear lateral stylus movement (as opposed to motionalong an arc) as the disc is played. This ensuresthat the stylus is always at the optimumangle in the disc groove. The result is improvedsound reproduction, and longer disc and styluslife because of minimal friction between the stylusand groove.straight-line wavelength Abbreviation, SLW. Pertainingto a variable capacitor in a tuned circuitfor which the setting-vs.-wavelength curve is astraight line; the wavelength variation is linear.Compare STRAIGHTLINE CAPACITANCE andSTRAIGHT-LINE FREQUENCY.straight-through amplifier An amplifier in whichthe input and output circuits are tuned to thesame frequency. Compare MULTIPLIER AMPLI-FIER.strain A force that compresses or squeezes a body.Compare TENSION, 1.strain gauge See ELECTRIC STRAIN GAUGE.strain-gauge bridge A four-arm resistance bridgein which an ELECTRIC STRAIN GAUGE formsone arm. The resistance of the gauge changes becauseof strain. The amount of strain can be determinedby balancing the bridge.strain-gauge transducer A transducer, other thana strain sensor, that uses strain gauges to convertvalues of pressure into their electricalanalogs (e.g., pressure transducer and straingaugephonograph pickup).strain pickup A phonograph pickup using a straingauge to convert sound vibrations into a varyingelectric current.strand A single solid conductor in a STRANDEDWIRE.stranded wire A conductor composed of severalnon-insulated wires twisted together to providemechanical flexibility. Compare SOLID WIRE.stratosphere The portion of earth’s upper atmospherebeginning at a height of approximately 10miles and extending to the ionosphere.stray capacitance Inherent capacitance in a placewhere it can be detrimental, such as that betweenthe turns of a coil or between adjacent areas in acircuit. Also see STRAY COMPONENT.stray component An electrical property that existsas an inherent, and usually undesirable, side effectin a circuit or device. Thus, for example,STRAY CAPACITANCE unavoidably exists betweenparallel conductors, and STRAY INDUC-TANCE is present in all wiring.stray field The portion of an electric or magneticfield that extends beyond the immediate vicinityof the circuit with which it is associated, andwhich is, therefore, capable of interfering withother circuits or devices.

660 stray inductance • stylus frictionstray fieldFieldinteractswith nearbycomponentsstray inductance Inherent inductance in a placewhere it can be detrimental (e.g., inductance inthe coil of a wirewound resistor). Also see STRAYCOMPONENT.stray resistance Inherent resistance in a placewhere it can be detrimental, such as leakage resistancein a dielectric, and wire resistance in aninductor.streaking In television or facsimile, a form of distortionin which the image appears enlarged inthe horizontal, but not the vertical.stress 1. See STRAIN. 2. See TENSION, 1. 3. Theforce per unit area that produces STRAIN or TEN-SION on a body.stretch The amount by which a material beingmeasured with an electronic device increases insurface dimensions. Compare SHRINK.stretched string A long, thin wire or string that vibratesat a certain frequency, causing standingwaves. It generally exhibits a specific fundamentalfrequency and integral harmonics of this frequency.As the wavelength is cut in half, thefrequency doubles.strike To initiate a discharge, as in striking a gastube.striking voltage See STARTING VOLTAGE.string 1. In computer operations, a set of items ina sequence determined by the order of keys. 2. Ina computer memory, a sequence of bits or characters.3. Any group of series-connected componentsor circuits.string electrometer See BIFILAR ELECTROME-TER.string variable A string of characters, usuallyforming a word or phrase, represented by a variablename and character string symbol (BASIC’s$, for example) in a computer program.strip chart A longitudinal, as opposed to circular,chart for graphic recording. In a rectilinear chart,both coordinates are straight; in a curvilinearchart, the crosswise coordinates are arcs.strip core A ferromagnetic core material made froma strip of the substance. The method of manufactureresults in superior ferromagnetic qualities,but also imparts a polarization to the material.strip fuse A fuse in which the fusible element is aflat strip of low-melting-point metal. CompareWIRE FUSE.strobe 1. See ELECTRONIC FLASH, 1. 2. SeeSTROBOSCOPE.strobe light 1. See ELECTRONIC FLASH, 1. 2. SeeSTROBOSCOPE.Strobolume Trade name for a type of high-outputstroboscope.stroboscope 1. An instrument that emits bright,adjustable-rate flashes of light. When this light illuminatesan object that is rotating or vibratingat a fixed period, and the flash rate is made tomatch that period, the object seems to stand stilland can be examined for flaws or faulty operation(and its speed can be measured). 2. A rotatable,slotted disk for producing the effect defined in 1.stroboscopic disk A rotatable disk with alternatingwhite and black radial regions, used in conjunctionwith a strobe light for precise measurement ofthe speed of a phonograph turntable.strobotron A gas tetrode tube used as the flashinglight source in a stroboscope.stroke speed See SCANNING FREQUENCY.strong coupling See CLOSE COUPLING.strontium Symbol, Sr. A metallic element of the alkaline-earthgroup. Atomic number, 38. Atomicweight, 87.62. It is used in some ceramic dielectrics,such as barium-strontium titanate.Strowger exchange A telephone system incorporatingStrowger switches.Strowger switch A switch with one input and 100individually selectable outputs. It is used withtelephone switching networks. The telephone dialcode causes a contact to move vertically and horizontallyin such a way that a particular output isconnected to the input. Each output has aunique dial code and each dial code has a uniqueoutput.structured programming Computer programmingusing a limited number of procedural sets, whileminimizing branches to make the program asforward-going as possible. This allows it to beeasily modified or debugged.STS switch See SPACE-TIME-SPACE SWITCH.stub A (usually short) section of transmission linethat is patched onto a longer line for tuning orimpedance matching.Stubs gauge See BIRMINGHAM WIRE GAUGE.stub tuner A tuning unit consisting of a stub witha short circuit that can be moved along the stub.stub trap See INTERFERENCE STUB.stub-type wavetrap See INTERFERENCE STUB.stuffing bits In a digital communications system,extra bits inserted into some words so that all thewords are the same length.styli Plural of STYLUS.stylus 1. The “needle” that conveys vibrations to orfrom the disk in phonograph-disc recording orplayback. 2. One of the pins in the print head ofa dot-matrix printer.stylus drag See NEEDLE DRAG.stylus friction Rubbing of the stylus against therecord groove in phonograph-disc playback.

stylus pressure • subsidiary communication authorization 661stylus pressure See VERTICAL STYLUS FORCE.stylus printer See WIRE PRINTER.stylus scratch See NEEDLE SCRATCH.sub Abbreviation of subtract.sub- Prefix denoting under, below, less than, orlower than, with respect to size, value, or rank.Compare SUPER-.subassembly A completely fabricated unit thatforms part of a larger unit into which it easily fits.subatomic particle 1. Any of various particles thatcomprise atoms of matter. 2. A particle smallerthan an atom. See, for example, ANTI-PARTICLE,ELECTRON, MESON, NEUTRETTO, NEUTRINO,NEUTRON, NUCLEON, POSITRON, and PROTON.subaudible 1. Pertaining to any frequency fallingbelow the limit of human hearing, that is, lessthan about 20 Hz. 2. Any sound that is too low inamplitude to be heard.subaudible tone A signal, usually a steady, sinewavetone, sent along with a radio signal. Thetone frequency varies from about 20 Hz to 200Hz, below the audio cutoff frequency of most voicecommunications systems. Subaudible tones areused mainly for privacy. The receiver is programmedto receive only signals having the correctsubaudible tone frequency.suballocation A portion of a radio-frequencybroadcast or communications band that is legallyset aside for specific purposes or users, e.g., theExtra-class segment of the 40-meter amateur-radioband.subband 1. A portion of a frequency band with specificcharacteristics. 2. A portion of a radiofrequencybroadcast or communications band thatis set aside, legally or by convention, for specificpurposes [e.g., the single-sideband (SSB) portionof the 20-meter amateur-radio band].subcarrier A modulated carrier wave that composesthe modulating signal for another carrier wave.subcarrier band The band of frequencies in whicha subcarrier signal is transmitted.subcarrier frequency modulation In a system inwhich a carrier frequency is obtained by beating alow-frequency radio-frequency (RF) signal with ahigh-frequency RF signal, the application of frequencymodulation to the low-frequency component.The technique is sometimes used insweep-frequency signal generators.High - freq.RF osc.Low-freq.RF osc.ReactancemodulatorMixersubcarrier frequency modulationOutsubcarrier oscillator In a color-television receiver,the oscillator operating at the burst (chrominance-subcarrier)frequency of 3.579545 MHz.subchassis An auxiliary chassis on which one sectionof a larger piece of equipment is completelyassembled and wired.subfrequency See SUBHARMONIC.subharmonic An integral submultiple of a fundamentalfrequency. Thus, for example, the 10thsubharmonic of 15 MHz is 1.5 MHz.submarine cable An underwater cable designed towithstand continuous immersion.submarine robot A robot designed for underwateroperation. It can be operated via telepresence orby simple remote control, usually using a conventionalor fiberoptic cable. Some underwaterrobots have manipulators attached; others areequipped only with cameras, lights, and propulsiondevices.subminiature jack A female connector with an insidediameter of 3 ⁄32 inch.subminiature plug A male connector with an outsidediameter of 3 ⁄32 inch.submultiple A fractional multiple, usually in referenceto a frequency. For example, 7.2 MHz is asubmultiple of 14.4 MHz. See SUBHARMONIC.subpanel The front panel of a removable unit ormodule that forms a part of a larger unit.subroutine In a computer program, a sequence ofinstructions for carrying out a section of the program’sfunction. It is usually entered (led to) by aconditional branch (jump) instruction in the mainprogram.subscriber An individual user of a communicationsnetwork or service.subscript A small number or letter written to thelower right (and occasionally to the lower left) ofanother number or letter to identify the latterfrom others of the same designation (e.g., a 5 , S n ).Compare SUPERSCRIPT.subscription TV A television (TV) service paid forby subscribing viewers. The signals are scrambledso as to be useless to nonsubscribers, andlegitimate subscribers are provided with a decoderto unscramble the telecasts.subset 1. In statistics and set theory, a set whosemembers are all contained in a larger set. 2. Atelephone handset or deskset (subscriber’s set).3. A modulator/demodulator for makingbusiness machines compatible with telephonecircuits.subsidiary communication authorization Abbreviation,SCA. An authorization provided by theFederal Communications Commission (FCC) for afrequency-modulation (FM) broadcast station totransmit, in addition to its main program, a secondprogram within the assigned bandwidth usuallyconsisting of commercial-free backgroundmusic on a subcarrier that can be detected onlywith a special receiver or with a special adapterattached to a standard FM receiver.

662 subsidiary feedback • sun batterysubsidiary feedback Feedback other than themain feedback in a system.subsonic frequencies Frequencies below therange of hearing, that is, less than about 20 Hz.Also called ULTRALOW FREQUENCIES and SUB-AUDIBLE FREQUENCIES.substation An intermediate electricity-distributinglocation from which electrical energy is transformedand transmitted to users within a givengeographical area.substitution capacitor A capacitor used temporarilyin place of another of usually the samevalue, as in troubleshooting. Also see CAPACI-TOR SUBSTITUTION BOX.substitution inductor An inductor used temporarilyin place of another of usually the samevalue, as in troubleshooting. Also see INDUCTORSUBSTITUTION BOX.substitution method 1. A method of measuring aquantity (such as capacitance, inductance, or resistance)in which the value of the unknownquantity is determined in terms of the amount ofa standard quantity that must be removed to restorethe test circuit to its original state of balance.2. A method of troubleshooting in whichgood components are substituted for bad ones ina circuit (see, for example, SUBSTITUTION CA-PACITOR, SUBSTITUTION INDUCTOR, SUBSTI-TUTION RESISTOR, SUBSTITUTION SPEAKER,and SUBSTITUTION TRANSFORMER).substitution resistor A resistor used temporarilyin place of another of usually the same value, asin troubleshooting. Also see RESISTOR SUBSTI-TUTION BOX.substitution speaker A loudspeaker used temporarilyin place of another, as in troubleshooting.substitution transformer A transformer usedtemporarily in place of another having the samecharacteristics, as in troubleshooting.substrate A plate, wafer, panel, or disk of suitablematerial on (or in) which the components of aunit, such as an integrated or printed circuit, aredeposited or formed.subterranean 1. Pertaining to components, systems,or devices installed underground. It is applicableespecially to cables. 2. Pertaining to aphenomenon, such as the propagation of electriccurrents or acoustical waves, that occurs underground.subterranean acoustical communication A methodof communication that uses low-frequencysound waves, such as SONAR, to communicatevia conduction through earth or water.subtracter See ELECTRONIC SUBTRACTER.subtractive color A color formed by mixing subtractiveprimary pigments.subtractive primaries Broad-spectrum pigmentsused in printing to produce a wide variety of colorsthrough filtering. These primaries are cyan(blue-green), magenta (pink-red), yellow, andsometimes black. They are used to print imagesthat have been filtered through additive-primarylenses.subtrahend In the process of subtraction, thequantity that is subtracted from another (theminuend) to produce the remainder or difference.subwoofer A speaker designed to effectively reproduceextremely low audio frequencies, in somecases, subaudible (below 20 Hz).successive derivatives Successive repetition ofthe operation of differentiating a function, whichyields the first derivative, second derivative, andso on to the nth derivative.successive integration The operation of double ortriple integration.Suhl effect A reduction in hole life that occurs in asemiconductor material in the presence of a magneticfield.suite 1. A group of computer programs run successivelyas a job. 2. A bundled, high-end softwarepackage used especially in business computing.sulfate Contraction of lead sulfate.sulfation In a lead-acid storage cell, the formationof disabling lead sulfate during discharge of thecell.sulfur Symbol, S. A nonmetallic element. Atomicnumber, 16. Atomic weight 32.06.sulfur hexafluoride A gas used as a coolant andinsulant in some power transformers.sulfuric acid Formula, H 2 SO 4 . An acid used in dilutesolution as the electrolyte of a lead-acid battery.This highly corrosive fluid also has manyindustrial uses.sum The result obtained by adding two or moreterms. Compare SUMMATION.sumcheck See SUMMATION CHECK.sum frequency 1. In an amplitude-modulated carrier,the upper sideband frequency (i.e., the sidebandequal to the carrier frequency plus themodulating frequency). Compare DIFFERENCEFREQUENCY. 2. In superheterodyne operation,an intermediate frequency equal to the signal frequencyplus the local-oscillator frequency.summation 1. The sum of a finite number ofterms. Thus, the total resistance of n resistorsconnected in series is the summation of all R (resistance)terms. 2. A frequency equal to the sumof two other frequencies.summation check In computer operations, acheck carried out on a group of digits. The resultof adding the digits, and disregarding any overflow,is a check digit that can be compared with astandard value for the operation to verify the integrityof data.summer 1. See ADDER. 2. See SUMMING AMPLI-FIER.summing amplifier An operational amplifierwhose output is the sum, or is proportional to thesum, of several inputs.sun battery A set of photovoltaic cells connected inseries, parallel, or series-parallel to produce usefuloutput voltages and currents.

S units • supermodulation 663V 1V 2V 0nV 3 V c0 = − V 1i = 1summing amplifierS units In radio (especially amateur radio), gradationsreflecting the strength of received signals.Typically, a value of S9 (9 s-units), representing“extremely strong signals,” is equal to a strengthof 50 microvolts. The next lower S unit (S8) is6 dB lower in voltage (i.e., 25 microvolts); S7 is12 dB below S9 (i.e., 12.5 microvolts), etc.sun lamp An incandescent or fluorescent lamp withhigh ultraviolet output, used in medicine for thetreatment of certain skin disorders. It can also beused for skin tanning; most physicians discouragehabitual use of the lamps for this purpose.sunlight lamp A lamp that produces visible lightwhose spectral distribution is similar to that oftypical daylight. It generally produces more blueand violet light than a conventional lamp. It issometimes used for indoor lighting in winter athigh latitudes, and/or to enhance plant growth.sunlight-powered laser A laser whose action isstimulated by sunlight collected by a system ofmirrors and lenses. The life of the device is long,compared with that of conventional lasers.sun-pumped laser See SUNLIGHT-POWEREDLASER.sun relay See SUN SWITCH.sunspot An area on the sun’s surface that is visibleas a dark, irregular region of variable size, generallyseveral thousand miles across. Sunspots arebelieved to be comparatively cool regions associatedwith solar magnetic disturbances. The numberof sunspots is correlated with the frequencyand intensity of solar flares (see SOLAR FLARE).sunspot cycle Regular periodic variation of sunspotactivity. The time between peaks in activityis approximately 11 years.sun switch A photoelectric switch or relay actuatedby sunlight and used for various domesticand industrial purposes, such as switchinglights, operating window shades, etc.sup Abbreviation of SUPPRESSOR.super Contraction of supersonic.super- Prefix denoting over, above, greater than, orhigher than, with respect to size, value, or rank.Compare SUB-.superaudible frequency See ULTRASONIC FRE-QUENCY.superbeta transistor A transistor or transistorcombination, such as a Darlington pair (seeCOMPOUND CONNECTION), that provides a veryhigh current amplification factor (beta).Relative sunspot numbers1970 1980 1990 2000sunspot cyclesupercardioid microphone A microphone that ishighly sensitive in one direction and insensitivein all other directions. The directional pattern issimilar to a CARDIOID PATTERN, but is exaggeratedalong the axis of optimum response.superconducting cable A cable in which superconductivityis achieved by surrounding the cablewith liquid helium to lower its temperature tonear absolute zero.superconductivity The virtual disappearance ofresistance in some metals cooled to temperaturesin the vicinity of absolute zero. Also see CRYO-GENICS, CRYOSTAT, and CRYOTRON.superconductor A material or device that displayssuperconductivity.super flatpack An integrated-circuit package ofthe flatpack type having considerably more componentsand leads than those in the conventionalflatpack.superhet Contraction of superheterodyne.superheterodyne circuit A circuit in which the incomingsignal in a first detector (or mixer) beatswith the signal of a local oscillator, resulting in alower (intermediate) frequency, which then is amplifiedby an intermediate-frequency (IF) amplifier.This IF signal is detected by a seconddetector whose output is amplified by an audiofrequency(AF) amplifier. Because the IF amplifieroperates at a single (fixed) frequency, it can beadjusted for optimum selectivity and gain. Alsocalled superhet circuit.superheterodyne receiver A radio or television receiverusing a SUPERHETERODYNE CIRCUIT.superhigh frequency See RADIO SPECTRUM.Supermalloy An alloy having a maximum permeabilityof 10 6 .supermodulation A type of amplitude modulation(AM) in which one radio-frequency (RF) powerstage continuously generates the carrier, and asecond (usually identical) RF power stage is gatedinto full operation at the proper instant by the audiomodulation to add additional RF power (correspondingto 100% modulation) to the signal. Atthe same time, the carrier amplitude is decreasedby the proper amount to fulfill the conditions of a

664 supermodulation • surface-barrier transistorsignal amplitude swing between zero and twicemaximum for 100% modulation.superposition In a complex wave, the manner inwhich the constituent waves combine. The instantaneousvalue of the complex wave is equal tothe vector sum of the instantaneous values of allthe constituent waves.superposition theorem In a network of linear elements,if a voltage E 1 in branch A causes a currentI 1 to flow through branch C, and if a voltageE 2 in branch B (which might be identical withbranch A) causes a current I 2 to flow throughbranch C, then E 1 in branch A and E 2 in branchB applied simultaneously will cause a currentequal to I 1 + I 2 to flow through branch C. CompareCOMPENSATION THEOREM, MAXIMUM POWERTRANSFER THEOREM, NORTON’S THEOREM,RECIPROCITY THEOREM, and THEVENIN’STHEOREM.superpower An arbitrary term denoting very highpower. In the rating of standard broadcast stations,it has come to signify 1,000,000 watts (onemegawatt) radio-frequency (RF) power output.superradiance In a laser, a rapid increase in intensityof fluorescent-line emission with increasingexcitation power.superregenerative circuit A regenerative detectorcircuit in which regeneration is periodically increasedalmost to the point of oscillation, then decreased.This quenching action takes place at asupersonic rate (typically at 50 or 100 kHz) sothat the quenching is inaudible. The result is thatmuch more regeneration is afforded, without thedetector going into oscillation, than is possible bysimply increasing the regeneration manually. Anextremely sensitive detector is the result.supersaturated solution A solution that containsmore solute than it normally would hold. Supersaturatedsolutions are obtained through specialtechniques and are extremely unstable. CompareSATURATED SOLUTION. Also see SOLUTE; SO-LUTION, 1; and SOLVENT, 2.superscript A small number or letter written to theupper right of another number or letter, theBASE, to indicate the power to which the basemust be raised. Example: 10 5 , e x , y 2 . Also calledEXPONENT. Compare SUBSCRIPT.supersensitive relay A relay that operates with acurrent of less than one milliampere, or with avoltage of less than one millivolt.supersonic flow In a gas or liquid, movement ofthe medium at a speed greater than the speed ofsound in that medium. Supersonic flow results ina greatly increased resistance or drag because ofshock waves that form in the medium.supersonic frequency See ULTRASONIC FRE-QUENCY.supersonics See ULTRASONICS.supervised line In a security system, a wire or foilstrip that carries electrical current. If the currentchanges in such a line, an alarm is actuated.supervisor 1. In a computer, a set of routines thatoversees the operation of the system. The supervisorroutines are coordinated by the central processingunit. 2. The execution of such a set ofroutines. 3. A microcomputer that oversees theoperation of a security system.supervisory circuit In a security system, a linkbetween a sensor and the central computer orcontrol device. This link can be via electric currentthrough a wire or cable, but other methodscan be used, such as fiberoptics, line-of-sight optics,infrared, ultrasonic, or radio.supply 1. See CURRENT SUPPLY. 2. See POWERSUPPLY. 3. See VOLTAGE SUPPLY.supply current Alternating or direct current availablefor operating a circuit, device, or system.supply frequency The frequency of an alternatingcurrentpower supply.supply power The maximum power that can be reliablydelivered by an alternating-current ordirect-current power supply.supply reel In a reel-to-reel tape recorder or player,the reel that is initially full, and that graduallyempties as the tape moves through the machine.supply voltage The voltage of an alternating-currentor direct-current power supply.suppressed carrier A carrier that has been canceledor filtered out of a carrier/sideband combination.suppressed-carrier double sideband See DOU-BLE-SIDEBAND and SUPPRESSED CARRIER.suppressed-zero instrument A meter or graphicrecorder in which the zero point is off-scale or upscale,but has been brought to scale-zero bymeans of mechanical adjustment or use of abucking voltage.suppressor 1. A filter used to suppress radio interference.2. See AUTOMATIC NOISE LIMITER. 3.See SPARK SUPPRESSOR. 4. In a pentode vacuumtube, a gridlike element between the screengrid and the plate, used to suppress secondaryemission. Also see GRID, 2 and PENTODE.suppressor circuit The circuit associated with thesuppressor electrode of a vacuum tube.suppressor diode A semiconductor diode used toprevent inductive kickback in circuits, to eliminateor reduce transients, or to prevent arcing betweenmake-and-break contacts.suppressor grid See SUPPRESSOR, 4.suppressor modulation A method of modulationin which a modulating voltage is superimposedon the suppressor voltage of a pentode radiofrequencypower amplifier tube.suppressor pulse A pulse that prevents electronflow.surface analyzer A device designed for the measurementof surface flatness or uniformity.surface-barrier diffused transistor See MICRO-ALLOY DIFFUSED TRANSISTOR.surface-barrier transistor Abbreviation, SBT. Apnp transistor made by means of electrolysis andelectroplating: Two fine streams of indium sulfate

surface-barrier transistor • surveillance radar 665EmitterCollectorsurface-barrier transistorBasesolution are placed on axially opposite points onthe faces of an n-type wafer. At the same time, adirect current is passed through the wafer andsolution in such a direction as to remove semiconductormaterial electrolytically from the faces;the tiny sprayed areas are etched away. When thedesired wafer thickness is reached at the pointsof impact, the etching process is arrested by reversingthe direction of current flow. This reversalcauses an indium dot to be plated on each oppositeface in the etched-out pit. Leads are attachedto the collector and emitter dots and to the wafer(base).surface-charge transistor A semiconductor deviceconsisting essentially of two narrowly separatedplates (source electrode and receiver electrode)deposited on the film-insulated surface of a siliconchip, and a third, overlapping electrode (thetransfer gate) deposited on, but insulated from,the other electrodes. An input signal stores acharge in the capacitor formed by the source electrodeand chip. A subsequent trigger signal appliedto the transfer gate transfers the charge tothe receiver electrode, where it becomes an outputsignal (often amplified, with respect to the inputsignal).surface effect An effect (such as current, resistance,or resistivity) observed on the surface of asample of material, rather than throughout thebody of the material. Compare BULK EFFECT.surface insulation A coating applied to the surfacesof core laminations to prevent the passageof currents between laminations.surface leakage Leakage of current over the surfaceof a dielectric material, as opposed to leakagethrough the interior of the material.surface noise See NEEDLE SCRATCH.surface recombination rate For a semiconductor,the rate at which electrons and holes recombineat the surface. Compare VOLUME RECOMBINA-TION RATE.surface resistivity The resistance of a unit area ofa material, measured between opposite edges.Compare VOLUME RESISTIVITY. Also see RESIS-TIVITY.surface tension The tendency of the surface of aliquid to “shrink.” This property varies with differentliquids and is caused by a net molecularforce directed inward from the surface.surface wave 1. The earth-guided component of aground wave. (The other component is the SPACEWAVE.) 2. An acoustic wave traveling along thesurface of a plate in a surface-wave amplifier orsurface-wave filter.surface-wave amplifier An amplifying device consistingessentially of a surface-wave filter towhich has been added a direct-current-biased n-type silicon electrode, which is separated fromthe crystal substrate of the filter by a very thinoxide layer. Amplification is produced by interactionbetween the electron current in the siliconand the piezoelectric field of the filter. Also seeACOUSTOELECTRONICS.surface-wave filter An acoustoelectronic deviceconsisting essentially of a crystal plate havingelectrodes at each end. An alternating-current(ac) input signal applied to one electrode sets upacoustic waves that travel along the surface of theplate to the other electrode, where they generatean ac output voltage by piezoelectric action. Theresonant frequency of the device is governed bythe dimensions of the crystal plate. Also seeACOUSTOELECTRONICS.surge A sudden rise or flow of current or voltage.surge absorber See SURGE SUPPRESSOR.surge arrester See SURGE SUPPRESSOR.surge current A heavy current that flows initiallyinto a capacitor when a charging voltage is applied.surge impedance Symbol, Z o . The impedance seenby a pulse applied to a transmission line; Z o = L/C(approximately), where L and C are the inductanceand capacitance, in microhenrys and microfarads,per unit length of the line. Also calledCHARACTERISTIC IMPEDANCE.surge protector Misnomer for SURGE SUPPRES-SOR.surge suppressor A semiconductor device used toabsorb potentially destructive transients or overvoltageson a utility power line. It has a three-wirecord for plugging into a 117-volt outlet, a powerswitch, and several three-wire outlets for connectionto sensitive electronic equipment (such aspersonal computers, videocassette recorders,television sets, hi-fi amplifiers, etc.).surround See SUSPENSION, 1.Surround Sound The trade name for a multichannelsound system for use with television receiversand videocassette players. Some televised movies,especially on cable and satellite networks, delivermultichannel sound through receiving/recordingsystems equipped with special decoders.surveillance 1. A method of monitoring a specificarea or volume for intrusion or other disturbance.2. A means of monitoring a specified portion ofthe electromagnetic spectrum for unauthorizedsignals.surveillance radar An air-traffic-control radar thatsupplies continuous information regarding theazimuth and distance of aircraft inside a selectedradius around an airport.

666 susceptance • swingsusceptance Symbol, B. Unit, siemens. The reactivecomponent of admittance, as distinguishedfrom conductance.susceptibility The capacity of a substance to becomemagnetized, expressed as the ratio of magnetizationto the strength of the magnetizingforce.suspension 1. In a speaker, the flexible, circular orelliptical structure via which the cone is attachedto the frame. 2. The wire or metallized fibersupporting the movable coil of a galvanometer.3. Particles of a substance and the liquid in whichit is mixed, but not dissolved. 4. The substance,as defined in 3.suspension galvanometer A meter with a lightbeamapparatus for lengthening the arc throughwhich the pointer travels. When the beam of lightis cast a long distance, a tiny movement of thecoil will cause considerable movement of the image.sustained oscillations Oscillations that continueas long as power is supplied to the oscillationgenerator. Also see CONTINUOUS WAVE. CompareDAMPED OSCILLATIONS.sustaining voltage The voltage at which secondcollectorbreakdown occurs in a transistor (seeSECOND BREAKDOWN).S video In animation, a scheme that separatesbrightness and color. It can enhance the video insome applications.SW Abbreviation of SHORTWAVE.sw Abbreviation of SWITCH. (Also, S or s.)swamping resistor 1. A noninductive resistor connectedin parallel with the input circuit of a class-B linear amplifier for automatic regulation of theexcitation. 2. A resistor connected in series withthe emitter of a bipolar transistor to minimize theeffects of temperature-induced variations in junctionresistance.swarf The string of material that threads off a discduring sound recording.S W band A section of the S BAND, extending from3400 to 3700 MHz.sweep 1. To deflect the electron beam in a cathoderaytube, usually horizontally, to provide a timebase. 2. The circuit for achieving the particulardeflection described in 1.sweep circuit A circuit, such as a deflection generator(e.g., a sawtooth oscillator), for producing asweep signal. Also see SWEEP.sweep delay In an oscilloscope, the process of initiatingthe sweep of the electron beam at some selectedinstant after the signal has started.sweep-delay circuit In an oscilloscope or radar,the circuit for delaying the sweep until the start ofthe signal. Also see DELAYED SWEEP.sweeper 1. See SWEEP GENERATOR. 2. SeeSWEEP-SIGNAL GENERATOR.sweep frequency 1. The frequency at which theelectron beam in a cathode-ray tube is deflectedalong the reference axis. 2. The frequency atwhich the carrier frequency is increased and decreasedby a sweep-signal generator. 3. In an oscilloscope,the number of times that the tracemoves across the screen in one second. It is equalto the reciprocal of the SWEEP PERIOD.sweep generator 1. A device that causes the electronbeam in a cathode-ray tube to scan at aknown speed. 2. An oscillator that generates asignal that rapidly varies in frequency. It is usedfor the testing and adjustment of bandpass filtersand other selective circuits.sweeping receiver See SCANNING RECEIVER.sweep magnification In an oscilloscope, increasingor multiplying the sweep frequency, thus reducingthe time per horizontal division. Thisincreases the maximum frequency of waveformsthat can be analyzed, and allows closer inspectionof high-frequency signal components.sweep magnifier In an oscilloscope, a circuit forachieving sweep magnification.sweep oscillator See SWEEP GENERATOR.sweep period The duration, in seconds, of onecomplete cycle of sweep signal in an oscilloscope.It is equal to the reciprocal of the SWEEP FRE-QUENCY.sweep signal The (usually linear, sawtooth) signalused to sweep the beam of an oscilloscope tube.Also see SWEEP, 1, 2.sweep-signal generator A signal generator thatsupplies a signal whose frequency varies automaticallyand periodically throughout a given band.Frequencyf maxf minTimesweep-signal generatorsweep test A method of testing the attenuationvs.-frequencycharacteristics of a selective circuit,using a radio-frequency sweep generator.sweep time The actual time required for a singlesweep by a deflecting signal; t = 1/f, where t issweep time in seconds, and f is sweep frequencyin hertz.sweep voltage The peak voltage amplitude of thesweep signal.SWG Abbreviation of standard wire gauge.swing The maximum change exhibited by a varyingquantity (e.g., amplitude swing and frequencyswing).

swinging choke • symmetrical conductivity 667swinging choke A filter choke that exhibits relativelyhigh inductance when low current flowsthrough it, and lower inductance when high currentflows through it. This inductance, whichswings under conditions of varying load current,permits the use of a high-resistance bleeder resistor.Compare SMOOTHING CHOKE.Swiss-cheese packaging A method of packagingan electronic circuit, in which components are insertedinto the assembly through holes drilled orpunched in parallel, stacked printed-circuitboards.switch 1. A circuit or device (electronic, electromechanical,or mechanical) for opening and closinga circuit or for connecting a line to one of severaldifferent lines (e.g., rotary selector switch). 2. Tochange the logic state of a circuit or device. 3. Ina computer program, a branch instruction directingthe program to a line number dependent onthe value of a variable or result (e.g., BASIC’sGOTO). 4. To cause an electrical circuit to changestate, as from low to high or vice versa.switch current 1. The current flowing through aswitch. 2. The current flowing through a switchingdiode or transistor. 3. The minimum currentnecessary to produce switching of a transistor,specified in milliamperes or microamperes.switchgear Collectively, devices and systems formaking and breaking circuits—either automaticallyor manually.switchhook In a telephone set, the spring-andswitchdevice that engages the line when the receiveris lifted.switching characteristics Technical data describingthe performance and capabilities of switchingdevices and circuits.switching circuit An on-off type of circuit containingelectronic or mechanical switches.switching diode See COMPUTER DIODE.switching frequency The frequency at which arepetitive switch operates. Also see SWITCHINGRATE.switching mode Operation in which a device, suchas a transistor or diode functions as a binary digitaldevice, rather than as an analog device. Thecurrent is generally either zero (cutoff or pinchoff)or some value that depends on the bias and onthe applied voltage.switching rate The rate (e.g., closures per second)at which a repetitive switch operates. Also seeSWITCHING FREQUENCY.switching speed The time required for a switch toopen or close or for a switching device to changestates (as from cutoff to saturation). Also seeSWITCHING TIME.switching time The time required, after the applicationof a pulse, for an electronic switch tochange state. Also see SWITCHING SPEED.switching transistor A transistor designed especiallyfor on-off operation. Such units exhibitshort recovery time and low capacitance.switching voltage The largest voltage that aswitching device can handle without malfunctioning.switch leakage current 1. The current flowingthrough a switching device when it is supposed tobe nonconducting. 2. In a switching transistor,for a given voltage, the leakage current betweenthe emitter and collector when the device is supposedto be nonconducting.SWL Abbreviation of SHORTWAVE LISTENER.SWR Abbreviation of STANDING-WAVE RATI0.SWR bridge A four-arm resistance bridge for measuringvoltage standing-wave ratio. This radiofrequencybridge has noninductive resistors inthree of its arms and the device under test in thefourth arm. The bridge is balanced first with anequivalent noninductive resistor that replacesthe device, and the output voltage is noted. Thenthe device is substituted for the test resistor, andthe change in voltage is noted. The standing-waveratio is determined from the voltage ratio.SWR meter See SWR BRIDGE.S Y band A section of the S BAND, extending from2600 to 2700 MHz.syllable compandor A device that compresses orexpands the amplitude of an audio signal. Thetime constant is fast enough to allow response toindividual syllables. Compression is generallyused at the transmitting station, and expansionat the receiving station.sym 1. Abbreviation of symmetrical. 2. Abbreviationof SYMBOL.symbol 1. A letter or graphic device representing aquantity or term [e.g., I (current), f (frequency),etc.]. 2. A conventional device denoting a mathematicaloperation (e.g., +, /). 3. In a circuitdiagram, a pictorial device representing acomponent.symbolic address An address in a sourcelanguagecomputer program (i.e., the arbitrarylabel used by the programmer).symbolic language See SOURCE LANGUAGE.symbolic logic A system for representing logicalrelationships, such as those acted upon by computerand switching circuits, by means of symbolsthat are usually nonnumerical. Also seeBOOLEAN ALGEBRA.symmetrical circuit A circuit having identicalconfigurations on each side of a dividing line,such as the ground bus. A push-pull circuit is anexample.symmetrical communications 1. Two-way communicationsin which the volume of transmitteddata is the same, or nearly the same, in both directions.2. Two-way communications in whichthe speed of transmitted data is the same, ornearly the same, in both directions. CompareASYMMETRICAL COMMUNICATIONS.symmetrical conductivity Identical conductivityfor both positive and negative electricity. CompareASYMMETRICAL CONDUCTIVITY.

668 symmetrical FET • synchronous clocksymmetrical FET See SYMMETRICAL FIELD-EFFECT TRANSISTOR.symmetrical field-effect transistor A field-effecttransistor whose source and drain terminals canbe interchanged without affecting circuit operation.Also called BIDIRECTIONAL TRANSISTOR.Compare UNILATERAL FIELD-EFFECT TRAN-SISTOR.symmetrical input See BALANCED INPUT.symmetrical output See BALANCED OUTPUT.symmetrical transistor See BIDIRECTIONALTRANSISTOR.symmetrical wave A wave whose positive and negativehalf-cycles are identical in shape and peakamplitude.symmetry 1. The condition of having the sameshape on each side of an axis. 2. The condition ofconducting positive and negative currents equallywell. 3. The condition in which a circuit is identicalon both sides of a reference line, such as theground line.sympathetic vibration Resonant vibration of onebody in response to the vibration of another body.sync 1. Contraction of SYNCHRONIZATION.2. Contraction of SYNCHRONISM.sync amplifier In a television circuit, the amplifierused to increase the amplitude of the sync pulsesafter they are separated from the composite videosignal.sync generator A circuit that produces the synchronizationpulses in a television transmitter.synchro A dynamo-electric-control device that,when connected to a similar device and the alternating-currentpower line, permits remote control.Thus, when the rotor of one synchro is turned to acertain position, the rotor of the other assumes thesame position. Also see AUTOSYN and SELSYN.synchrocyclotron A type of cyclotron in which thevariation in mass, because of increased velocity,of the charged particles is compensated, resultingin higher energy for the particles.synchro differential A synchro that receives twoinput signals and delivers a single output signal.The inputs can be two electrical signals, or oneelectrical signal and one mechanical signal.synchrodyne receiver A direct-conversion receiverin which the local oscillator frequency orphase is locked into synchronism with the incomingsignal carrier frequency or phase.synchroflash A flash that is synchronized with theshutter of a camera.synchro generator The transmitting member of asynchro system.synchro motor The receiving member of a synchrosystem.synchronism 1. The condition of being in step, aswhen two motors are running in synchronismwith each other and the power frequency, orwhen two relays open and close in step. 2. Thecondition of being in phase, as when two pulsesoccur simultaneously.RF amp.DetectorAF amp.SignalControlvoltageSpeakersynchrodyne receiverFrequencycomparatorVoltagecontrolledoscillatorSignalsynchronization The coincidence of one processor operation with another, as in the synchronizationof an oscillator frequency by means of an appliedstandard-frequency voltage, in which casethe oscillator frequency becomes that of the standardsignal.synchronized clamping A type of clamping inwhich an output voltage is maintained at a predeterminedfixed value until a synchronizingpulse is applied, whereupon the output followsthe input.synchronized multivibrator See DRIVEN MULTI-VIBRATOR.synchronizer A computer storage device used betweentwo devices transmitting data at differentspeeds, to counteract this differential (as abuffer).synchronizing signal A signal used to synchronizeanother signal, usually in frequency.synchronous The condition of operating in step(phase) with some reference signal.synchronous clock 1. An alternating-currentclock driven by a synchronous motor. Although60-Hz models are common, such clocks are notrestricted to low-frequency ac operation; 1-kHztypes, for example, are used in some primaryfrequency standards. 2. The timing source in asynchronous computer.

synchronous computer • synthesizer 669synchronous computer A computer whose operationsare timed by single-frequency clock signals.synchronous contacts The rectifying contacts of asynchronous vibrator (see VIBRATOR-TYPE REC-TIFIER).synchronous converter A synchronous machinethat can run on alternating current and generatedirect current, or vice versa. Also called ROTARYCONVERTER.synchronous gate A gate whose output is synchronized,according to the input signal.synchronous generator An alternator operating insynchronism with one or more other alternators.Also see SYNCHROSCOPE, 2.synchronous induction motor An alternatingcurrentmotor that is intermediate between thefractional-horsepower reluctance motor and themultiple-horsepower three-phase, synchronousmotor. The synchronous induction machinestarts like an induction motor and runs like asynchronous motor.synchronous inputs In a computer flip-flop, inputsthat accept pulses only at the command ofthe clock.synchronous machine See SYNCHRONOUS IN-DUCTION MOTOR.synchronous motor See SYNCHRONOUS INDUC-TION MOTOR.synchronous network A communications networkin which all clocks are set so that they run at thesame rate, their increments are identical in duration,and transitions occur simultaneously orwith a specified phase difference. Such a systemallows for greatly enhanced signal-to-noise ratiofor a given amount of transmitter power, and alsoreduces the bandwidth necessary for a single signalso that many more signals can be placed in agiven frequency band.synchronous orbit See GEOSTATIONARY ORBIT.synchronous satellite See GEOSTATIONARYSATELLITE.synchronous speed For an alternating-current(ac) machine, the speed corresponding to the acfrequency.synchronous transmission A method of signaltransmission in which individual symbols aresent at a specified rate, according to a clock thatalso governs the receiver.synchronous vibrator See VIBRATOR-TYPE REC-TIFIER.synchroscope 1. An oscilloscope having a highspeedsweep triggered by a synchronizing signal.Such an instrument is valuable for viewing highspeedpulses. 2. A pointer-type instrument usedto indicate the synchronism between two poweralternators.synchro system A circuit or system using synchrosfor the transmission and reception of positioningsignals. Also see SYNCHRO.synchrotron A particle accelerator that uses ahigh-frequency electrostatic field and a low-CollectorsynchrotronLinearacceleratorCircularacceleratingchamberfrequency magnetic field to impart very highvelocity to the particles.sync pulse 1. A pulse used to control the frequencyor repetition rate of an oscillator or othergenerator. 2. In a television system, a pulsetransmitted as part of the composite video signalto control scanning. Also see HORIZONTAL SYNCPULSE and VERTICAL SYNC PULSE.sync separator In a television receiver circuit, astage used to separate and deliver the syncpulses from the composite video signal. See, forexample, DIODE SYNC SEPARATOR.sync signal See SYNCHRONIZING SIGNAL.sync takeoff The point in the video amplifier circuitof a television receiver at which the compositevideo signal is sampled to extract the syncpulses.syntax 1. The rules by which computer programstatements are structured. 2. The way that awritten or spoken sentence is constructed. It isimportant in speech recognition and speech synthesis.synthesis The rigorous (usually mathematical) designof an electronic circuit or device and the accurateprediction of its performance. CompareANALYSIS.synthesizer 1. See SIGNAL SYNTHESIZER. 2. Acircuit synthesizer (i.e., a device that allows awide variety of circuits to be set up temporarily orsimulated, for testing and evaluating). Sometimes,a specially programmed computer servesthis purpose. 3. A keyboard on which music canbe played, and whose output can be adjusted tosimulate the sounds of various musical instruments.4. See MOOG SYNTHESIZER.

670 synthetic bass • S Z bandsynthetic bass An apparent accentuation of bassnotes resulting from intermodulation distortionin an amplifier.synthetic crystal An artificially produced crystal,such as synthetic quartz.synthetic resin An artificially produced resin. Alsosee THERMOPLASTIC MATERIAL and THER-MOSETTING MATERIAL.syntony See RESONANCE.syst Abbreviation of SYSTEM.system 1. An integrated assemblage of hardwareand/or software elements operating together toaccomplish a prescribed end purpose (e.g., servosystem, operating system, and communicationssystem). 2. A methodology incorporating fixedand ordered procedures for accomplishing an endpurpose. 3. A self-contained computer workstation.systematic error See CUMULATIVE ERROR.system engineering See SYSTEMS ENGINEER-ING.system of units A set of fundamental units fordefining the magnitudes of all physical variables.The most common system of units is the standardinternational (SI) system.systems analysis In computer system operation,analyzing the way something is done and devisinga better alternative by isolating the problem area,scrutinizing the system as it stands, studyingwhat is thereby disclosed, devising the alternateapplication of software and/or hardware, disseminatingthe revised operational procedure, andoverseeing the implementation of the new method.systems engineering The branch of engineeringdevoted to the design, development, and applicationof complete systems. The approach takesinto consideration all elements in a system orprocess and their integration.systems flowchart A flowchart showing the interrelationshipof activities in a system.S Z band A section of the S BAND, extending from3900 to 4200 MHz.

T 1. Symbol for TRANSFORMER. 2. Abbreviation ofprefix TERA-. 3. Symbol for thermodynamic temperature.4. Symbol for TRITIUM. 5. Abbreviationof TON. (Also, t and tn.) 6. Abbreviation of TESLA.7. Symbol for KINETIC ENERGY. 8. Symbol forPERIOD. 9. Symbol for true.t 1. Symbol for TIME. 2. Abbreviation of TON.(Also, T and tn.) 3. Symbol for CELSIUS TEM-PERATURE. (Also, T.) 4. Abbreviation of TARGET.5. Abbreviation of technical. 6. Abbreviation ofTENSION.Ta Symbol for TANTALUM.tab On the keyboard for a computer, typewriter,terminal, or word-processing system, a key thatmoves the cursor a specified number of spacestoward the right. It also performs various otherfunctions in menu-driven or graphical computerinterfaces.tableIn an internal or external computer memory,an array (i.e., a list or matrix) of data that canbe recalled using keys (e.g., single- or doublesubscriptedvariables).table look-at Abbreviation, TLA. In computer operations,finding the position of a data item in atable by implementing an algorithm.table look-up Abbreviation, TLU. In computer operations,locating items in a table by inspectingwhat is in the table, key by key.tabulate In data processing, to combine the totalsfor data item groups having the same key.tabulation 1. The printout of what has been tabulated(see TABULATE). 2. The computer-programdirectedmovement of the cursor on acathode-ray-tube display, or of a typewriter carriage,to certain positions in a line.tabulator See TAB.tacan A pulse-type UHF air navigation system inwhich a station is interrogated by signals from anaircraft to provide bearing and range information.The name is an acronym for tactical air navigation.tach Abbreviated form of tachometer.tachometer See ELECTRONIC TACHOMETER.tachometer generator A small, dynamo-type electricgenerator that delivers a voltage proportionalto the rotational speed of a shaft to which it is attached.tachyon A high-speed subatomic particle thoughtto move faster than the speed of light.tactical air navigation See TACAN.tactical radar A radar system used in military operations.tactile sensor A device that provides an intelligentmachine with a sense of “touch”: temperature,pressure, force, texture, and torque. It is importantin robotics, and also in some computer applications,such as virtual reality (VR).T-adapter See TEE-JUNCTION.tag 1. In data-processing and computer operations,the identification of digits or charactersforming part of a record. 2. An encoded price tag(i.e., a passive transponder or barcode strip). It iscommonly used in retail stores.tag converter A device that senses the informationon tags (see TAG, 2) and transfers it to a computersystem.tail 1. The decay of a waveform from maximumamplitude to zero amplitude. 2. Any pulse thatfollows a main pulse as a result of the mainpulse.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

672 taillight monitor • tap changerAmplitudetailTailTimetaillight monitor An electronic device for warninga motorist of taillight failure.tail pulse 1. A pulse with a fast rise time, but aslow decay time. 2. See TAIL, 2.takedown In computer operations, the process ofclearing output peripherals for upcoming programruns.take-down time The duration of the TAKEDOWNprocess.take-up reel In a reel-to-reel tape recorder/reproducer,the reel on which the tape accumulatesduring recording or reproduction.talk-back circuit See INTERPHONE.talk-listen switch A transmit-receive switch in anintercommunication system (see INTERCOM).talk power See SPEECH POWER.tally 1. To obtain a sum or total. 2. The rows ofoperands, subtotals, and totals that an addingmachine prints.tally reader A device that, via optical characterrecognition (OCR), can read the digits and symbolson a tally (see TALLY, 2).tamper switch A device that closes a circuit or actuatesan alarm when a certain set of conditionsis altered.tan Abbreviation of TANGENT.tan –1 Arc tan (inverse tangent function).tandem transistor An assembly of two seriesconnectedtransistors in the same envelope.tangent 1. Abbreviation, tan. The ratio of the sideopposite to the side adjacent to an acute angle ina right triangle. 2. A line that intersects a curve ata single point without crossing the curve. 3. Aplane that intersects a curved surface at a singlepoint.tangent galvanometer A galvanometer in whichthe current is proportional to the tangent of theangle of deflection. Compare SINE GALVANO-METER.tangential mode In acoustics, the reflection ofsound waves from four surfaces in a room havingsix interior surfaces.tanh Abbreviation of HYPERBOLIC TANGENT.tank 1. A parallel-resonant inductance-capacitancecircuit in the output of a radio-frequencyamplifier. 2. A circuit in which is stored electricalenergy of frequencies in a range whose midpointis resonance for the circuit. 3. See MERCURYDELAY LINE.tantalum Symbol, Ta. A metallic element of thevanadium family. Atomic number, 73. Atomicweight, 180.95. Tantalum is used in the elementsof some electron tubes and in some electrolyticcapacitors.tantalum capacitor A type of electrolytic capacitorthat uses tantalum rather than aluminum. Thetantalum can be foil, as is the aluminum in a conventionalelectrolytic capacitor. It might also takethe form of a porous pellet, the irregular surfaceof which provides a large area in a small volume.An extremely thin oxide layer forms on the tantalum.These capacitors have high reliability andexcellent efficiency, and are used in military applicationsbecause they have a low failure rate.They can be used in audio and digital circuits inplace of aluminum electrolytic capacitors. Themain disadvantage of tantalum capacitors is thatthey are comparatively expensive. Compare CE-RAMIC CAPACITOR, ELECTROLYTIC CAPACI-TOR, MICA CAPACITOR, PAPER CAPACITOR,PLASTIC-FILM CAPACITOR.LeadTantalumLeadtantalum capacitorElectrolyteMetal casetantalum detector A radio-frequency contact detectorconsisting essentially of a fine tantalumwire whose point lightly touches the surface of asmall pool of mercury.tantalum-nitride resistor A resistor consisting ofa thin film of tantalum nitride deposited on asubstrate. Also see THIN FILM.T-antenna See TEE-ANTENNA.tap A connection made to an intermediate point ona coil, resistor, or other device. See, for example,CENTER TAP and TAPPED COMPONENT.tap changer A device that facilitates adjustment ofthe turns ratio of a transformer by changing the

tap changer • target acquisition 673tap on the primary winding, the secondary winding,or both. It also facilitates the adjustment ofthe impedance-transfer ratio. It can be used forpower supplies or audio- or radio-frequencytransformers.tape 1. Magnetic tape. 2. Insulating tape. 3. Tomake a magnetic tape recording (audio, video,and/or digital data).tape cable 1. A form of cable in which all of theconductor centers lie in the same plane. 2. A flatcable, commonly used in situations, where repeatedflexing occurs.tape cartridge A holder and the reel of blank orprerecorded magnetic ( 1 ⁄8-inch audio or widervideo) tape it contains, which can be inserted intoa recorder/reproducer without having to threador otherwise handle the tape for either playing orrewinding.tape comparator In a data-processing or computersystem, a machine that compares tapesgenerated from the same input, for differences inthe data thereon; it is a character-by-characterprocess.tape core A ring-type magnetic core made bytightly winding metal tape in several layers for thedesired thickness.tape counter See POSITION INDICATOR.tape deck In a tape recorder/reproducer, the completetape-transport mechanism (drive, heads,equalization circuitry, and preamplifiers).tape drive 1. See TAPE TRANSPORT. 2. See TAPEDECK. 3. A tape recorder/reproducer for computerdata, used for backup and/or archiving.tape file A data file recorded on magnetic tape.tape group An assembly of two or more tape decks.tape label On a reel or cassette of magnetic tapecontaining a data file, a record at the beginning orend that contains information about the file.tape loop An endless loop of magnetic tape.tape magazine See TAPE CARTRIDGE.tape mark 1. A character that subdivides the magnetictape file on which it is recorded. Also calledCONTROL MARK. 2. A character marking the endof a length of magnetic tape on a reel. Also calledEND-OF-TAPE MARK.tape plotting system In computer operations, asystem for operating a digital incremental plotterusing the information on magnetic tape.taper In a potentiometer or rheostat, the rate ofchange in resistance during uniform rotation ofthe shaft. See, for example, LINEAR TAPER andLOG TAPER.tape recorder A machine for recording audio,video, or data signals on magnetic tape; it canusually also play back the recorded material.tapered potentiometer A potentiometer having atapered resistance winding (see TAPERED WIND-ING).tapered winding A resistance winding (in a rheostator potentiometer) in which the resistancechange per unit length of winding is nonuniform(see, for example, LOG TAPER). However, a windinghaving uniform resistance change is oftencalled LINEAR TAPER.tape skew A condition in which a magnetic tapepasses between the recording or playback headsin an irregular way. The result is that the variouschannels, or tracks, are not always perfectlyaligned.tape sort The (computer) operation of sorting datain a magnetic tape file into a record-keydeterminedsequence.tape splicer A mechanism that aligns and securesthe overlapping ends of broken magnetic tape sothat they can be cut (often with an integral cutter)to form butted ends, and taped into a splice.tape station See TAPE DECK.tape-to-head contact See HEAD-TO-TAPE CON-TACT.tape transmitter A transmitter that receives itssignal input from a recorded tape.tape transport In a tape deck or reproducer, thedevice that moves the tape past the heads.tape unit 1. See TAPE DECK. 2. See TAPE GROUP.tape verifier In computer operations, a device thatchecks the integrity of data on paper tapethrough comparison with an original document.tape width In magnetic tape, the dimension perpendicularto tape travel; in general, the greater thetape width, the more tracks the tape can contain.tape-wound core See TAPE CORE.tapped coil An inductor to which one or more intermediateconnections (taps) are made at appropriateturns to provide intermediate values ofinductance.tapped component A coil, transformer, choke, resistor,or other component in which an intermediateconnection is made. See, for exampleTAPPED COIL.tapped inductor See TAPPED COIL.tapped resistor A resistor in which one or more intermediateconnections (taps) are made to appropriateparts of the resistance element to providesteps of resistance.tapped transformer A transformer having one ormore tapped windings.tapped winding A transformer or choke windingwith one or more taps. Also see TAP and TAPPEDCOIL.tap switch A multiposition switch used to connectan external circuit to various taps on a component.Also see SELECTOR SWITCH and TAP.target 1. The bombarded electrode in an X-raytube. 2. The scanned storage element in a televisioncamera tube. 3. In radar operations, thescanned object. 4. An object intended for nuclear-particlebombardment. 5. A goal—especiallyin a production process (deadline, desirednumber of units, etc.).target acquisition 1. The moment at which a targetcomes within the range of a radar system.2. The observation of a new target on a radar screen.

674 target discrimination • tee-equivalent circuitOutputV115 VacSecondarytapped transformerPrimarytarget discrimination The extent to which a radarsystem can distinguish between two targets thatare close together. Also called target resolution. Itis specified in linear units (such as meters, kilometers,or miles).target identification Any method by which theidentity of a radar target is determined.target voltage In a television camera tube, thebackplate-to-cathode voltage.task environment The characteristics of the spacein which an autonomous robot works. It dependson such factors as the intended application(s),the required speed at which the robot(s) mustwork, and the human/robotic or computer/robotic interface.task-level programming In robotics, the writing ofprograms to perform sequences of actions. Acomplex process, it is a primitive level of artificialintelligence (AI). An example is a program that directsa robot to prepare and serve a meal.taut-band meter A movable-coil meter in whichthe conventional spiral springs of the coil are replacedby two tightly stretched, thin, straightmetal ribbons, whose twist provides torque thatreturns the pointer to zero after a deflection.Tb Symbol for TERBIUM.BS Abbreviation of talk between ships.Tc Symbol for TECHNETIUM.TCCO Abbreviation of TEMPERATURE-CON-TROLLED CRYSTAL OSCILLATOR.T circuit See TEE NETWORK.T circuit parameters See R PARAMETERS.T circulator See TEE CIRCULATOR.TCL Abbreviation of TRANSISTOR-COUPLEDLOGIC.TCM Abbreviation of thermocouple meter (seeTHERMOCOUPLE-TYPE METER).TDM Abbreviation of TIME-DIVISION MULTIPLEX.TDR 1. Abbreviation of TIME-DELAY RELAY (seeDELAY RELAY). 2. Abbreviation of TIME-DOMAIN REFLECTOMETRY.TDS Abbreviation of TIME-DELAY SPECTROME-TRY.TE Abbreviation of transverse electric (see, for example,TRANSVERSE ELECTRIC MODE).Te Symbol for TELLURIUM.teach box A robot-control device via which an operatorcan program the machine to carry out specificmovements. The operator manipulatescontrols, and the robot’s computer stores thedata. When the data is accessed, the robot reproducesthe motions.tearing In a television picture, the abnormal conditionin which poor synchronization causes thehorizontal lines to be irregularly displaced. Theeffect resembles cloth being torn.technetium Symbol, Tc. A metallic element producedartificially. Atomic number, 43. Atomicweight, 98. Formerly called masurium.technician 1. A person who repairs faultyelectronic equipment. 2. A person who assistswith the design and debugging of a system prototype.3. A person who operates an electronicsystem.technocentrism Overdependence on, and/or obsessionwith, the products of technology, particularlycomputers.tee Pertaining to a network, connection, or configurationwhose geometric shape or schematic representationresembles an uppercase letter T.tee adapter See TEE JUNCTION.tee antenna An antenna consisting of a horizontalradiator with a vertical lead-in or feeder connectedto its center point.InsulatorHorizontalsectionAntennatunertee antennaInsulatorVerticalsectiontee circuit See TEE NETWORK.tee circulator In microwave systems, a tee-shapedjunction of three waveguides with a ferrite post atthe junction.tee-equivalent circuit An equivalent circuit inwhich the components are arranged in the formof a tee. See, for example, TEE NETWORK andR PARAMETERS.

tee junction • telephone amplifier 675tee junction 1. A tee-shaped splice between twowires. 2. A tee-shaped fixture for splicing one coaxialline perpendicularly to another. 3. A tee-shapedsection for joining one waveguide perpendicularlyto another. Also called WAVE GUIDE TEE.tee junctiontee network A three-terminal network resemblinga tee.tee pad A three-resistor pad in which two series resistorsand a shunt resistor are arranged to forma tee.tee switch A combination of three switches arrangedto form a tee; two switches are in serieswith a shunt switch in between. If the seriesswitches are open and the shunt switch is closed,isolation is greatly improved, compared to a singleseries switch.Teflon FEP A plastic insulating material. Dielectricconstant, 2.1. Dielectric strength, 2800 V/mil.Teflon TFE A plastic insulating material. Dielectricconstant, 2.2. Dielectric strength, 600 V/mil.tel 1. Abbreviation of TELEPHONE. 2. Abbreviationof TELEGRAPH. 3. Abbreviation of TELE-GRAM.telautograph A device that transmits and receiveshandwriting, drawings, and similar material. Atthe receiver, a pen follows the movements of asimilar pen at the transmitter.teleammeter A TELEMETER for measuring currentgenerated at a remote point.telecamera See TELEVISION CAMERA.telecast A television program for general reception.The term a contraction of television broadcast.telechir A remotely controlled, autonomous robot.See TELEOPERATION and TELEPRESENCE.telecommunication Communication, usually betweenwidely separated points, by electrical orelectronic means.telecontrol See REMOTE CONTROL and TELEOP-ERATION.telefacsimile See FACSIMILE.telegram Abbreviation, tel. A (usually printed-out)message transmitted and received via telegraphor teletypewriter. Compare CABLEGRAM and RA-DIOGRAM.telegraph Abbreviation, tel. An instrument fortransmitting and receiving messages by means oftelegraphy. In its simplest form, it consists of akey and a sounder powered by a battery. Also seePRINTING TELEGRAPH, 1, 2.telegraph channel 1. The frequency band assignedto a particular telegraph station. 2. Thefrequency band occupied by a telegraph signal.telegraph code Broadly, Morse code. Wire telegraphyoften uses a special version, such as theAmerican Morse code.telegraph key See KEY, 1.telegraph sounder See SOUNDER.telegraph system A complete, integrated, coordinatedarrangement of equipment for communicationby means of telegraphy. Included aretelegraph keys or keyers, sounders or printers,relays, switchboards, wire lines and cables, andpower supplies.telegraphyThe branch of electrical communicationsthat deals with the transmission and receptionof messages by means of prearrangedcodes—especially over wires. Also see MORSE, 1,2, 3; MORSE CODE; and WIRE TELEGRAPHY.telemeter1. An indicating instrument that measuresthe value of a quantity generated at a distantpoint or measures and transmits the value.2. The action afforded by the device in 1.telemetering See TELEMETRY.telemeter receiver See TELEMETRIC RECEIVER.telemeter transmitter See TELEMETRIC TRANS-MITTER.telemetric receiver A system that selects, amplifies,and demodulates or rectifies a radio signal,and actuates indicating instruments, recorders,or data processors.telemetric transmitter A specialized transmitterthat generates radio-frequency (RF) power, addsto it signals delivered by data transducers, anddelivers the modulated power to an antenna fortransmission to a distant telemetric receiver.telemetryThe transmission of data signals over adistance, either by radio or wire, and the receptionand application of the signals to indicatinginstruments, recorders, etc.teleoperation The remote control of autonomousrobots. A human operator can control the speed,direction, and other movements of a robot fromsome distance away. See also TELEPRESENCE.telephoneAbbreviation, tel. An instrument fortransmitting and receiving messages by means oftelephony. In its simplest form, it consists of amicrophone, earphone, switching and ringing devices,wire line or cable, and power supply. Alsosee HANDSET.telephone accessories Devices (such as answeringmachines, speaker phones, facsimile machines,etc.) used in conjunction with a telephone set.telephone amplifier A small audio amplifier, usuallywith a self-contained loudspeaker, for increasingthe sound volume of a telephone output.Some amplifiers of this kind are connected to the

676 telephone amplifier • televisetelephone line, and others receive sound from thetelephone receiver.telephone-answering machine See ANSWERINGMACHINE.telephone bypass capacitors A set of fixed capacitorsinstalled between each wire in a telephoneline and an electrical ground to bypass radiofrequencyenergy. It can reduce or prevent radiofrequencyinterference (RFI) to telephone sets anddata terminals.telephone data set A device that converts signalsfrom a data terminal for passage over a telephonecircuit to a data-processing center.telephone dialer In a security system, a circuitthat automatically dials one or more telephonenumbers, alerting the recipient(s) that an emergencyexists at a given location.telephone induction coil A small telephone-tolineimpedance-matching transformer used intelephone systems.telephone patch See PHONE PATCH.telephone pickup A device for receiving conversationsfrom a telephone to which it isn’t directlyconnected.telephone plug See PHONE PLUG.telephone-radio patch See PHONE PATCH.telephone receiver The handheld part of a telephoneset, containing the microphone and earphone,and, in some cases, the dialing keypad.telephone repeater An amplifier and associatedequipment used to boost the amplitude of a telephonesignal at an appropriate point along theline.telephone service entrance The point at whichthe telephone wiring in a house or building connectsto the outside telephone line.telephone silencer A device for muting a telephoneor its bell.telephone system A complete, integrated, and coordinatedarrangement of equipment for communicationby means of telephony. Included aretelephones, switchboards and associated equipment,wire lines and cables, and power supplies.Also see DIAL TELEPHONE SYSTEM, HANDSET,PRIVATE AUTOMATIC EXCHANGE (PAX), PRI-VATE BRANCH EXCHANGE (PBX), and TELE-PHONE.telephone test set See PHONE TEST SET.telephone transmitter The sound pickup unit(microphone) of a telephone. Also see TRANSMIT-TER, 2.telephony The branch of electrical communicationdealing with the transmission and reception ofsounds—especially over wires. Also see WIRETELEPHONY.Telephoto 1. The transmission and/or receptionof photographs by means of FACSIMILE. 2. Aphotograph transmitted and/or received bymeans of FACSIMILE.telephoto lens A camera lens providing a telescopiceffect.Telephoto receiver See FACSIMILE RECEIVER.Telephoto transmitter See FACSIMILE TRANS-MITTER.telepresence An advanced form of robotic TELE-OPERATION, in which a human operator has theimpression of being at the robot’s location. It includesvision systems, pressure sensors, soundsensors, tactile sensors, and electromechanicalcontrol devices. The operator uses, or wears,equipment similar to that used for VIRTUAL RE-ALITY (VR).teleprinter A terminal telegraph printing machine.Also see PRINTING TELEGRAPH, 1, 2.TelePrompTer A device that presents a runningdisplay on a screen before a television announcer,performer, or speaker, of dialogue.teleran A ground-to-air communications system.Ground-based radar pictures are transmitted, viatelevision, to aircraft.telescoping antenna A vertical antenna consistingof separate lengths of metal tubing of progressivelysmaller diameter so that one can slide intoanother. The antenna can be pulled out to fulllength or compressed to the length of the largestdiametersection.telescoping antennateletext A method of communication in which avideo image is sent of a page of printed material.telethermoscope A device for measuring the temperatureof distant objects.Teletorque See AUTOSYN and SYNCHRO.Teletype 1. The transmission and/or reception oftext messages in digital form, displayed orprinted at a distant location. 2. See TELETYPE-WRITER.teletype grade A term descriptive of a circuit havingthe quality necessary for communication viatelegraphy.Teletypesetter An electronic system for operatinga distant Linotype.teletypewriter A variety of printing telegraph usingelectric typewriters and associated equipment.The message is typed on the keyboard atthe transmitting station and is typed out in correspondingletters at the receiving station. Thesame typewriter is able to send and receive messages.Also see RADIOTELETYPEWRITER.teletypewriter exchange Abbreviation, TWX. Acenter for switching and routing teletypewritercommunications. Also see TELETYPEWRITER.teleview To observe a scene or program via television.televise 1. To convert a scene into a televisionsignal. 2. To broadcast a scene or program viatelevision.

television • temperature derating 677television 1. Abbreviation, TV. The transmissionand/or reception, via electromagnetic fields, wirecable, and/or fiberoptic cable, of images, usuallywith sound. 2. A system for receiving signals, asdefined in 1. 3. Video programs or data, with orwithout sound, transmitted via electromagneticfields, wire cable, and/or fiberoptic cable.television band See UHF TELEVISION CHANNELSand VHF TELEVISION CHANNELS.television camera The pickup device that scans ascene and delivers a series of electrical signalsthat can be used to reconstruct the image on thescreen of a picture tube.television-camera tube See CAMERA TUBE,ICONOSCOPE, and ORTHICON.television channel A radio-frequency band allocatedexclusively for the transmission of a televisionsignal. In conventional broadcasting, thisband is usually 6 MHz wide. See, specifically,UHF TELEVISION CHANNELS and VHF TELEVI-SION CHANNELS.television engineer A trained professional skilledin video electronics engineering, as well as in basicengineering and associated subjects.television engineering The branch of electronicsengineering devoted to the theory and applicationof television.television interference Abbreviation, TVI. Interferenceto the reception of television signals, usuallyoccasioned by signals from radio services orcomputers, or by electrical noise.televisor 1. A television transmitter or receiver.2. A person or entity responsible for the broadcastof television programs or signals.televoltmeter A TELEMETER for measuring voltagegenerated at a remote point.telewriter See TELAUTOGRAPH.Telex 1. A teleprinter system that operates via thetelephone lines, and was once commonly used bybusinesses for sending and receiving short messages.It has largely been supplanted by computerizeddata communications systems. 2. A hard-copymessage sent or received by such a system.telluric currents Also called terrestrial currents.A flow of electrical charge carriers, primarily electrons,in the earth.tellurium Symbol, Te. A rare, metalloidal elementrelated to selenium. Atomic number, 52. Atomicweight, 127.60.TE mode See TRANSVERSE ELECTRIC MODE.temp 1. Abbreviation of temperature. (Also, T.)2. Abbreviation of temporary. 3. Abbreviation ofTEMPLATE.temperament The tuning of a keyboard-type musicalinstrument to produce a nearly perfect diatonicscale.temperature Symbol, T. A quantitative measure ofthe heat exhibited by an object or phenomenon.Also see THERMOMETER SCALE.temperature coefficient A figure that states theextent to which a quantity drifts or varies underthe influence of changing temperature. It is generallyexpressed in percent per degree (%/°C) orin parts per million per degree (ppm/°C).temperature-compensated crystal oscillationOscillation in a crystal oscillator, in which thecrystal and/or circuit is automatically compensatedagainst frequency drift caused by temperaturechange.temperature-compensating component A circuitcomponent, such as a capacitor or resistor, whosetemperature coefficient is equal in magnitude andopposite in sign to that of a conventional componentto which it is connected to cancel temperature-inducedvariation in the latter’s value.Tank capacitorTuningcontrolTemperaturecompensatingcapacitortemperature-compensating componenttemperature compensation The use of a device,such as a temperature-compensating component,to correct a temperature-induced deviationin the value of a conventional component.temperature control 1. The adjustment of temperature.2. The automatic maintenance of temperatureat a desired level, as in atemperature-controlled oven. 3. A device for controllingtemperature, as defined in 1 or 2.temperature-controlled crystal oscillator Abbreviation,TCCO. A high-precision crystal oscillatorin which the crystal plate (and sometimes the circuitry,as well) is held at constant temperature.temperature degree See DEGREE, 2 and THER-MOMETER SCALE.temperature derating Deliberate reduction of operatingcurrent and/or voltage of a device to aspecific temperature to ensure proper operation.Also see DERATING, DERATING CURVE, andDERATING FACTOR.

678 temperature gradient • terrain echoestemperature gradient A range of temperaturevariation, such as the rate of change of temperature,with respect to change of power dissipation,or the rate of change of temperature with spatialdisplacement.temperature inversion See INVERSION, 1.temperature meter An indicator (usually a directcurrentvoltmeter or millivoltmeter) whose scalereads directly in degrees.temperature scale See THERMOMETER SCALE.temperature-sensitive resistor See THERMIS-TOR.temperature shock See THERMAL SHOCK.temperature-to-voltage converter A circuit or device,such as a thermocouple, that delivers anoutput voltage proportional to an applied temperature.template 1. A diagram, usually drawn on paper, toshow the locations at which components shouldbe placed or tasks should be performed. It istaped or cemented temporarily to the work, andthe points are transferred to the latter by prickpunching.2. A stencil-like plate with alphanumericand circuit symbols, used as a drafting aid.Sometimes called “drafting stencil.”temporary magnet 1. A body that exhibits magnetismonly briefly after it has been exposed toanother magnet. Compare PERMANENT MAG-NET. 2. See ELECTROMAGNET.temporary storage 1. In computer and data-processingoperations, the storage of data or instructionsonly until they are needed. Also calledINTERIM STORAGE. 2. Locations in a computermemory set aside during a program run for holdingintermediate results of operations.TEM wave See TRANSVERSE ELECTROMAG-NETIC WAVE.ten code A set of abbreviations used by two-wayradio operators. Each “ten signal” represents aspecific statement or query.tension 1. A force that tends to stretch, pull tight,or pull apart. Compare STRAIN. 2. A term referringto VOLTAGE—especially in a utility powertransmission line.ten-turn potentiometer A precision potentiometerwhose shaft must be turned through 10 completerevolutions to cover the entire resistancerange. Also see HELICAL POTENTIOMETER andMULTITURN POTENTIOMETER.T-equivalent circuit See TEE-EQUIVALENT CIR-CUIT.tera- Abbreviation, T. 1. A prefix meaningtrillion(s), (i.e., 10 12 ). 2. A prefix meaning 2 40 .tera-electronvolt Abbreviation, TeV. A large unitof energy; 1 TeV = 10 12 electronvolts. Also seeELECTRONVOLT.terahertz Abbreviation, THz. A unit of extremelyhigh frequency equal to 10 12 Hz. Also called Fresnel.teraohm A unit of high resistance, reactance, orimpedance equal to 10 12 ohms.terawatt Abbreviation, TW. A large unit of power;1 TW = 10 12 W.terbium Symbol, Tb. A metallic element of therare-earth group. Atomic number, 65. Atomicweight, 158.93.terbium metals A group of rare-earth metals, includingeuropium, gadolinium, terbium, and occasionallydysprosium.term In an algebraic expression, constants, variables,or combinations of these, separated by operationsigns (e.g., the expression 4xy + z has twoterms).terminal 1. A connection point at the input, output,or an intermediate point of a device, or apoint at which a voltage is to be applied. 2. Ametal tab or lug attached to the end of a lead forconnection purposes. 3. Pertaining to the end of aseries of events, etc. (e.g., terminal tests). 4. In adata-communications system, a point of data inputor output. Also called data terminal. If it doesnot have computing capability of its own, it is oftencalled a dumb terminal.terminal block A group of several terminals, intendedfor interconnection of circuits, mountedon a solid insulating block.terminal board An insulating board carrying severallugs, tabs, or screws as terminals (see TER-MINAL, 2). Also see TERMINAL STRIP.terminal guidance The navigation of a missile oraircraft to help it reach its target or destination.terminal impedance The internal impedance of adevice measured at the input or output terminals.terminal point of degradation The point at whichdegradation of a circuit or component is complete.Also see DEGRADATION FAILURE.terminal repeater A telephone repeater operatedat the end of a line.terminal strip A strip of insulating material, suchas plastic or ceramic, on which are mounted oneor more screws, lugs, or other terminals. Also seeTERMINAL, 2.terminal strip (lug-type)terminal voltage The voltage at the output terminalsof an unloaded battery or generator.ternary code See TRINARY NUMBER SYSTEM.ternary fission The splitting of an atomic nucleusinto three nuclear pieces. Also see FISSION.ternary number system See TRINARY NUMBERSYSTEM.terrain echoes Radar images caused by reflectionsfrom hills, mountains, and other natural terrestrialsurface features. Also see GROUNDCLUTTER.

terrestrial magnetism • texture sensing 679terrestrial magnetism See EARTH’S MAGNETICFIELD.tertiary coil A third winding (see TERTIARYWINDING).tertiary winding A third winding on a transformeror magnetic amplifier.tesla Symbol, T. A unit of magnetic flux density; 1T = 1 weber per square meter = 10 4 gauss.Tesla coil A special type of air-core step-up transformerfor developing high voltage at radio frequencies.It consists essentially of a low-turnprimary coil, through which radio-frequency (RF)current flows, and a multiturn secondary coil,across which the high voltage, is developed.test A procedure consisting of one or several steps,in which (1) the mode of operation of a circuit ordevice is established, (2) the value of a componentis ascertained, or (3) the behavior of a circuit ordevice is observed.test bench An equipment installation intended forthe testing, repair, or debugging of electronic devicesby a technician.test data Data used to test a computer program,including samples within limits that might be encounteredduring the program’s implementation.tester 1. See TEST INSTRUMENT. 2. A technicianwho primarily makes tests and measurements.testing window See WINDOW, 2.test instrument A device for checking the operationof a circuit or the value of a component. Thisclass of instrument is usually less accurate thanmeasurement instruments. Also see TEST SET.test lead The flexible, insulated wire attached to atest prod.test pattern A picture-and-line display on thescreen of a television picture tube, used to checksuch features as aspect ratio, linearity, contrast,etc.test point A terminal intended for connection oftest equipment in the repair or debugging of a circuit.Often, test points are labeled by the lettersTP followed by numerals (such as TP1, TP2, etc.).test probe See PROBE, 1.test prod A stick-type probe (see PROBE, 1) with aflexible, insulated lead terminating in a plug orlug for attachment to an instrument.test prodstest program In computer operations, a programdevised to check the functioning of hardware.Also called utility and test routine.test run In computer operations, using test data tocheck the operation of a program, by comparingthe results obtained thereby with what shouldideally result.test set A combination of instruments assembledon a single panel, and usually enclosed in a carryingcase, for convenience in making tests.test signal 1. A signal used for conducting a test ofa component, circuit, or system. 2. In radiotelegraphy,a special signal signifying that the transmittingstation is testing equipment. Also seeVEE SIGNAL.test-signal generator A device, such as an oscillator,for producing a signal for testing equipment(see TEST SIGNAL, 1).test tape A magnetic tape containing signals fortesting equalization, frequency response, headadjustment, stereo balance, etc. in an audiotaperecorder, high-fidelity sound system, computertape drive, or videocassette recorder.tetravalent See QUADRIVALENT.tetrode An electron tube in which the principalelectrodes are cathode, control grid, screen, andplate.tetrode transistor 1. A bipolar transistor with twoemitters. 2. A dual-gate field-effect transistor.Btetrode transistorCE 1 E 2TeV Abbreviation of TERA-ELECTRONVOLT.T e value The temperature at which a centimetercube of glass or ceramic exhibits 1 megohm of resistance.TE wave See TRANSVERSE ELECTRIC MODE.text editor A computer program for finding andchanging data in a file.texture map In computer graphics, the topographicalqualities of the surface of a three-dimensionalrendition. For example, the image of anorange would have a “bumpy” texture map; theimage of a peach would have a “fuzzy” texturemap.texture sensing The ability of a robotic end effectorto determine the relative smoothness or

680 texture sensing • thermal shockroughness of a surface. One common schemeuses reflected light or infrared. Scattered reflectionsindicate a rough or matte surface.tgt Abbreviation of TARGET.TH Abbreviation of true heading.Th Symbol for THEORIUM.TH Symbol for heater temperature.thallium Symbol, Tl. A metallic element. Atomicnumber, 81. Atomic weight, 204.38.thalofide cell An evacuated photoconductive cellusing thallium oxysulfide as the light-sensitivematerial.THD Abbreviation of TOTAL HARMONIC DISTOR-TION.theory A reasonable proposition put forth to accountfor the behavior of, or the relationships between,bodies and forces, or to explain conceptsand their relations. When a theory has stood upunder exhaustive tests, it might reveal a scientificlaw.therm A gas heating unit. 1 therm = 100,000British thermal units (10 5 Btu).thermal agitation Random movement of particles(such as electrons) in a substance, because ofheat.thermal-agitation noise See THERMAL NOISE.thermal ammeter See HOT-WIRE AMMETER.thermal anemometer See HOT-WIRE ANEMO-METER.thermal conductivity The heat-conducting abilityof a material. Compare electrical conductivity (seeCONDUCTIVITY).thermal conductivityThermal conductivityElement(mW/m/°C)Aluminum 22.0Carbon 2.4Chrominum 6.9Cooper 39.0Gold 30.0Iron 7.9Lead 3.5Magnesium 16.0Mercury 0.8Nickel 8.9Platinum 6.9Silicon 8.4Silver 41.0Thorium 4.1Tin 6.4Tungsten 20.0Zinc 11.0thermal-conductivity device An instrument orcontrol unit using a heated filament whose temperatureand, accordingly, conductivity is variedby some sensed phenomenon. See, for example,GAS DETECTOR, HEATED-WIRE SENSOR, HOT-WIRE ANEMOMETER, HOT-WIRE FLOW-ME-TER, and HOT-WIRE MICROPHONE.thermal-conductivity gasmeter See GAS DETEC-TOR.thermal detector 1. See BOLOMETER. 2. In a securityor fire-protection system, a device thatcloses a circuit or actuates an alarm if the temperaturerises to a specific level.thermal emf See SEEBECK EFFECT.thermal gasmeter See GAS DETECTOR.thermal imaging See THERMOGRAPHY.thermal instrument See HOT-WIRE METER andTHERMOCOUPLE-TYPE METER.thermally sensitive resistor See THERMISTOR.thermal meter See HOT-WIRE METER and THER-MOCOUPLE-TYPE METER.thermal neutron A neutron that is essentially inthermal equilibrium with the surrounding mediumor environment.thermal noise Frequency-independent electricalnoise caused by the agitation of particles (e.g.,atoms and electrons) in a material by heat. Thermalnoise is proportional to bandwidth, resistance,and absolute temperature.thermal radiation See HEAT.thermal recorder A graphic recorder in which astrip of paper coated with a thin layer of opaquewax is drawn between a knife-edge platen and aheated writing stylus that melts the wax beneathits point, exposing the underlying black paper asa fine line.thermal resistance Symbol, RT. For a semiconductordevice, the rate of change of junction temperature,with respect to power dissipation; RT =dT/dP, where RT is in degrees Celsius per milliwatt,T is the temperature in degrees Celsius, andP is the power in milliwatts.thermal resistor A resistor that is sufficientlytemperature-sensitive to be used as a heat sensor.Examples: thermistor and germaniumdiode.thermal response time For a power-dissipatingcomponent, the elapsed time between the initialchange in power dissipation and the moment atwhich the temperature has changed by a specifiedpercentage (usually 90%) of the total value.thermal runaway A destructive process resultingfrom cumulative temperature effects. In bipolartransistors, this can occur if the collector currentincreases as the temperature rises. As the unitgets hotter, the collector-base junction dissipationincreases, generating still more heat. Theultimate result, if the process continuesunchecked, is destruction of the component. Theprocess can also occur in certain batteries whenthey are charged too rapidly or at excessively hightemperatures.thermal shock The effect of applying heat or coldto a device so rapidly that abnormal reactions occur,such as rapid (often catastrophic) expansionsand contractions.

thermal switch • thermoelectric junction 681thermal switch A switch actuated by a temperaturechange. Types vary from the simple thermostatto complex servosystem switches with atemperature-transducer input.thermal time-delay relay A delay relay utilizingthe slow-heating and slow-cooling property of oneof its components.thermion An ion or electron emitted by a hot body,such as the heated cathode of a vacuum tube.thermionic Pertaining to thermions and their applications.thermionic cathode A heated cathode, in contrastto a cold cathode, used as an emitter of electronsor ions. Also see THERMION.thermionic current Current caused by thermionicemission—especially in an electron tube.thermionic detector A vacuum-tube detector.Also see THERMION and THERMIONIC EMIS-SION.thermionic diode A hot-cathode diode tube.thermionic emission The emission of electrons bya hot body, such as the filament or cathode of avacuum tube. Also see THERMION and HOTCATHODE.thermionics The study of electron emission fromobjects or materials at high temperature.thermionic tube An electron tube (i.e., one inwhich electrons or ions are emitted by a heatedcathode). Also see THERMION, THERMIONICCURRENT, and THERMIONIC EMISSION.thermionic work function The energy required toforce an electron from inside a heated cathodeinto the surrounding space (in thermionic emission).Also see WORK FUNCTION.thermistor A temperature-sensitive resistor, usuallymade from specially processed oxides ofcobalt, magnesium, manganese, nickel, uranium,or mixtures of such substances. Thermistors areavailable with either a positive or negative temperaturecoefficient of resistance. The name is acontraction of thermally sensitive resistor.SemiconductorlayerthermistorMetalelectrodesthermistor bridge A four-arm bridge (see BRIDGE,1) in which one arm is a thermistor and, therefore,is temperature sensitive.thermistor power meter A radio-frequencypower-measuring instrument based on a thermistorbridge.thermistor probe A temperature probe containinga thermistor as the sensing element.thermistor thermometer An electronic thermometerin which the temperature-sensitive elementis a thermistor.thermoammeter See THERMOCOUPLE-TYPEMETER.thermocouple A device consisting essentially of abond between two wires or strips of dissimilarmetals (such as antimony and bismuth). Whenthe bond is heated, a direct-current voltage appearsacross it.ElectrodesthermocoupleGlass envelopethermocouple bridge A four-arm bridge (seeBRIDGE, 1) in which one arm is a thermocouple;therefore, it is temperature sensitive, as well asbeing voltage-productive.thermocouple meter See THERMOCOUPLE-TYPEMETER.thermocouple-type meter A radio-frequency (RF)meter consisting of a thermocouple and directcurrent(dc) ammeter, milliammeter, or microammeter,connected in series. The thermocoupleis heated, directly or indirectly, by an applied RFcurrent, and the resulting dc output deflects themeter pointer.thermodynamics The science dealing with the relationshipsbetween heat and mechanical energyand their interconversion. Also see CARNOTTHEOREM, FIRST LAW OF THERMODYNAMICS,SECOND LAW OF THERMODYNAMICS, andTHIRD LAW OF THERMODYNAMICS.thermoelectric cooler A cooling device based onthe Peltier effect.thermoelectric effect The production of thermoelectricityby certain materials.thermoelectricity Heat-produced electricity, as inthermocouple operation.thermoelectric junction A junction between twoconductors that exhibits variable characteristicsunder conditions of changing temperature.

682 thermoelectric series • thin-film resistorthermoelectric series A series of conducting metals,sequenced so that if a thermocouple is madefrom two of the metals, current flows at the hotjunction from the metal occurring earlier in theseries.thermoelectron An electron emitted by a hot cathode.Also see THERMION and THERMIONICEMISSION.thermoelement A thermocouple, especially aminiature one, used in a THERMOCOUPLE-TYPEMETER.thermogalvanometer See THERMOCOUPLETYPE METER.thermography A means of locating or mapping bydetecting infrared images. It can be in the form oflive video, similar to television, or in the form ofphotographs, using infrared film. Many commoncameras can be used with infrared film to makeinfrared photographs (thermographs).thermojunction The junction of the two metals ina thermocouple. A voltage appears when the dissimilarmetals are heated.thermoluminescence Luminescence resultingfrom the moderate heating of certain materials.thermomagnetic effect The effects of temperatureon the magnetism of a body, or vice versa.thermometer A (usually direct reading) device formeasuring temperature. Also see ELECTRONICTHERMOMETER and THERMOMETER SCALE.thermometer scale The scale on a thermometer,graduated in degrees, from which temperature isread. For a description of different scales, seeABSOLUTE SCALE, CENTIGRADE SCALE,FAHRENHEIT SCALE, REAUMUR SCALE, andRANKINE SCALE. The Kelvin scale is the same asthe absolute scale, and the Celsius scale is thesame as the centigrade scale.thermonuclear reaction A nuclear reaction inwhich energy is released when lighter atoms areconverted into heavier atoms at temperatures inthe millions of degrees Celsius. Also see FISSION,FUSION, and NUCLEAR REACTOR.thermopile A device consisting of two or morethermocouples connected in series for increasedvoltage output.thermoplastic material A plastic that can be resoftenedby applying heat after having beenmolded into a desired shape. Example: polystyrene.Compare THERMOSETTING MATERIAL.thermorelay See THERMOSTAT.thermosensitivity Sensitivity of a circuit or deviceto heat.thermosetting material A plastic that cureschemically (will not ordinarily soften again whenheat is applied) after having been heat-moldedinto a desired shape. Example: Bakelite. CompareTHERMOPLASTIC MATERIAL.thermostat A temperature-sensitive switch. In onecommon form, a movable contact is carried by astrip of bimetal and the stationary contact ismounted nearby.thermostatic switch See THERMOSTAT.thermoswitch See THERMOSTAT.theta wave A form of brain wave that occurs atextremely low frequencies, and is associated withsleep or mental incoherence.Thevenin’s theorem The proposition that, withreference to a particular set of terminals, a networkcontaining a number of generators and constantimpedances can be simplified to a singlegenerator in series with a single impedance.The equivalent circuit will deliver to a given load,the same current, voltage, and power delivered bythe original network. Compare COMPENSATIONTHEOREM, MAXIMUM POWER TRANSFER THE-OREM, NORTON’S THEOREM, RECIPROCITYTHEOREM, and SUPERPOSITION THEOREM.thick film A film of selected material (conductive,resistive, dielectric, etc.) applied to a substrate bypainting, photography, or similar process. See,for example, PRINTED CIRCUIT. Compare THINFILM. Typically, thick films are 1 mil or more inthickness.thick-film component A unit, such as a capacitoror resistor, fabricated by thick-film techniques.See, for example, PRINTED COMPONENT. Alsosee THICK FILM. Compare THIN-FILM COMPO-NENT.thick-film resistor A resistor fabricated by thickfilmtechniques. See, for example, PRINTEDRESISTOR. Also see THICK FILM. CompareTHIN-FILM COMPONENT.thick magnetic film See MAGNETIC THICK FILM.thin film An extremely thin layer (less than 1 mil)of a selected material (conductive, resistive, semiconductive,dielectric, etc.) electrodeposited orgrown on a substrate. Compare THICK FILM.thin-film capacitor A capacitor made by electrodepositinga thin film of metal on each side ofa grown layer of oxide, as in an integrated circuit.Also see THIN FILM.thin-film component A unit (such as a capacitor,resistor, diode, or transistor), fabricated by thinfilmtechniques. Also see THIN FILM. CompareTHICK-FILM COMPONENT.thin-film integrated circuit An integrated circuitin which the components and “wiring” are producedby depositing (or growing) and processingmaterials on a semiconductor slab or wafer (thesubstrate). Compare HYBRID INTEGRATED CIR-CUIT and MONOLITHIC INTEGRATED CIRCUIT.thin-film memory In a computer, a storage meiumthat is a magnetic thin film (see THIN FILM)on a nonmagnetic substrate (often glass) and thatcan be magnetized to represent digital data.thin-film microelectronic circuit An integratedcircuit that occupies (essentially) two dimensions;that is, a very thin integrated circuit.thin-film resistor A resistor fabricated by thinfilmtechniques (see THIN FILM) (e.g., TANTA-LUM-NITRIDE RESISTOR). Compare THICK-FILM RESISTOR.

thin-film semiconductor • three-phase rectifier 683thin-film semiconductor A very shallow layer ofsemiconductor material, such as single-crystalsilicon, electrodeposited on a substrate. Also seeTHIN FILM.thin-film transistor A transistor fabricated bythin-film techniques. Also see THIN FILM andTHIN-FILM COMPONENT.thin magnetic film See MAGNETIC THIN FILM.third-generation computer A computer in whichthe active discrete components are integrated circuits.Third Law of Thermodynamics As the temperatureof absolute zero is approached in an isothermalprocess involving a solid or liquid, the changein entropy approaches zero; and the entropy of asubstance is zero at absolute zero.third-octave band See ONE-THIRD-OCTAVEBAND.thirty-channel multiplex A form of pulse-codemodulated(PCM) multiplex using eight digits andthe A-law. There are 30 speech channels and twoutility channels.Thomson bridge See KELVIN BRIDGE.Thomson effect The liberation or absorption ofheat (depending on the material of interest) whenan electric current flows from a warmer to acooler part of a conductor.Thomson heat The amount of thermal energytransferred because of Thomson effect.Thomson voltage The voltage drop between twopoints on a conductor that are at different temperatures.thoriated-tungsten filament In a vacuum tube, afilament made of tungsten to which thorium oxidehas been added to increase the emissionof electrons. Also see THERMION and THER-MIONIC EMISSION.thorium Symbol, Th. A radioactive metallic element.Atomic number, 90. Atomic weight,232.04. Thorium, when heated, is a copious emitterof electrons, so the filaments or cathode cylindersof some electron tubes are coated with one ofits compounds.thoron Symbol, Tn. A radioactive isotope of RADON.three-address instruction A computer programinstruction having three addresses, two foroperands and one for the result (of the operationcalled for).three-channel stereo A form of stereophonicsound recording and reproduction in which threedistinct channels are used; these are usually designatedthe left, right, and center channels.three-coil meter See ELECTRODYNAMOMETER.three-conductor jack A female connector in whichtwo separate conductors are provided, in additionto the ground conductor.three-conductor plug A male connector in whichtwo separate conductors are provided, in additionto the ground conductor.three-dimensional television See STEREO-SCOPIC TELEVISION.SleevecontactTip contactRing contactthree-conductor jackSleeveRingthree-conductor plugTipthree-electrode tube See TRIODE.three-element tube See TRIODE.three-gun picture tube A color-television picturetube having a separate gun for each primary color(red, green, and blue).three-halves-power law See CHILD’S LAW.three-junction transistor A pnpn or npnp transistor.Also see NPNP DEVICE.three-phase bridge rectifier A bridge-rectifier circuitfor three-phase alternating current. Twodiodes are provided for each phase. The ripplefrequency is six times the line frequency. Also seeBRIDGE RECTIFIER, POLYPHASE RECTIFIER,and THREE-PHASE CIRCUIT.three-phase circuit The circuit of a three-phasesystem. See THREE-PHASE SYSTEM and, specifically,DELTA CONNECTION and WYE CONNEC-TION.three-phase current Current in a three-phase circuit.The currents in the three legs differ in phaseby 120°.three-phase four-wire system See FOUR-WIREWYE SYSTEM.three-phase generator A (usually dynamo-type)generator of three-phase current or voltage. SeeTHREE-PHASE SYSTEM.three-phase half-wave rectifier A half-wave rectifiercircuit for three-phase alternating current.One diode is provided for each phase. The ripplefrequency is three times the line frequency. Alsosee HALF-WAVE RECTIFIER, POLYPHASE REC-TIFIER, and THREE-PHASE CIRCUIT. CompareTHREE-PHASE BRIDGE RECTIFIER.three-phase motor An alternating-current motoroperating on three-phase power. Above fractional-horsepowersize, the three-phase motor issmoother running and more simply structuredthan the single-phase counterpart.three-phase power The total power dissipated ordelivered in a three-phase alternating-currentcircuit.three-phase rectifier A rectifier for three-phase alternatingcurrent. At least one diode is included

684 three-phase rectifier • thumbwheel switchfor each phase. Also see POLYPHASE RECTIFIER,THREE-PHASE BRIDGE RECTIFIER, THREE-PHASE CIRCUIT, and THREE-PHASE HALF-WAVE RECTIFIER.three-phase system An alternating-current electricalsystem in which three currents or voltagesexist simultaneously. They are of equal amplitude,but are 120° out of phase with each other.three-phase, three-wire system An electrical systemhaving three conductors, with an alternating-currentphase difference of 120° betweenconductor pairs.three-phase-to-single-phase transformer An alternating-currenttransformer with three-phaseinput and single-phase output (one terminal isgrounded).three-phase-to-two-phase transformer An alternating-currenttransformer with three-phase inputand two-phase output, the output currentsare 180° out of phase with each other.three-phase voltage Voltage in a three-phase alternating-currentcircuit. The voltages across thethree legs differ by 120°.three-quarter bridge A bridge rectifier havingdiodes in three arms and a resistor in the fourth.three-space A mathematical continuum in whicheach point is uniquely defined by three variablesin an ordered triple, such as (x,y,z), and each orderedtriple corresponds to exactly one point inthe space. A common coordinate system is theCartesian system consisting of three axes, x, y,and z—each mutually perpendicular and intersectingat the origin (0,0,0).three-space coordinates Any set of coordinatesused for locating points or plotting graphs inthree dimensions.three-state logic See TRI-STATE LOGIC.three-way speaker A set of three individual speakerscontained in a single cabinet: a woofer (lowfrequencyspeaker), a midrange speaker, and atweeter (high-frequency speaker). It is common inhigh-fidelity music reproduction systems. CompareTRIAXIAL SPEAKER.three-wire system 1. An electric-power feed systemusing three wires, the center one (neutral)being at a potential midway between the potentialacross the other (outer) two. 2. See THREE-PHASE and THREE-WIRE SYSTEM. 3. See TWO-PHASE and THREE-WIRE CIRCUIT.threshold 1. The initial (observable) point of an effect(e.g., threshold of hearing). 2. A predeterminedpoint, such as of minimum current or voltage, forthe start of operation of a circuit or device.threshold component A value of current, voltage,sound intensity, etc., selected as the minimumlevel at which a circuit or device is to operate insome prescribed manner, or beyond which acertain condition will prevail. Also see THRESH-OLD, 1, 2.threshold current 1. The minimum value of currentat which a certain effect takes place. 2. Thesmallest amount of forward current that flowsthrough a diode. 3. In a gas, the smallest level ofcurrent for which a discharge will maintain itselfunder variable conditions.threshold detector A device that prevents a signalfrom passing until its peak amplitude reaches acertain value.InputOnOffthreshold detectorOutputthreshold frequency 1. The cutoff frequency or frequenciesin a band-pass, band-rejection, low-pass,or high-pass filter. 2. The lowest frequency for ametal or semiconductor junction at which incidentradiation gives rise to the photoelectric effect.threshold of hearing The minimum intensity levelat which sounds are audible in an environmentcontaining essentially no background acousticnoise.threshold of pain The intensity level at whichhearing a sound causes physical discomfort. Thisis approximately 120 dB above the THRESHOLDOF HEARING for most people.threshold signal The weakest signal that can bedetected in a receiving system.throat See HORN THROAT.throat microphone A small microphone operatedin contact with the user’s throat.throttle The feedback control device in a regenerativedetector or amplifier.throughput In computer operations, an overallquantitative indicator of processing power, expressedin terms of the amount of data processedin a given period of time.throw-out spiral On a phonograph disc, a lead-outgroove.thulium Symbol, Tm. A metallic element of therare-earth group. Atomic number, 69. Atomicweight, 168.93.thumbwheel potentiometer A potentiometer operatedby means of a knurled knob (usually protrudingperpendicularly through a panel) that isturned with the thumb or with a finger.thumbwheel switch A switch operated by meansof a knurled knob (usually protruding perpendicularlythrough a panel) that is turned with thethumb or with a finger.

thy • time-interval mode 685thy Abbreviation of THYRATRON.thyratron A gas triode or gas tetrode used principallyfor switching and control purposes. Thyratronaction differs from that of the vacuum tubein the unique behavior of the thyratron controlelectrode (grid): Anode current starts to flowabruptly when grid voltage reaches a particularvalue, at which point the grid provides no furthercontrol; anode current continues to flow until theanode voltage is either interrupted or reversed.thyratron inverter An inverter circuit (see IN-VERTER, 1) using thyratrons as the switchingdevices. Also see THYRATRON.Thyrector A silicon diode exhibiting very high resistance(approaching that of an insulator) up toa certain voltage, beyond which the unit switchesto a low-resistance conducting state.thyristor 1. A pnpn-type bistable semiconductordevice having anode, cathode, and gate terminalsthat is used as an electronic switch. 2. Thegeneric term for all thyratronlike solid-state devices,such as the silicon-controlled rectifier.Thyrite Ceramic silicon carbide, a nonlinear resistancematerial, or a resistor made of this material.The resistance of Thyrite decreases sharplyas the applied voltage is increased. Thyrite resistorsare used in voltage regulators, equipmentprotectors, lightning arresters, curve changers,and similar devices.THz Abbreviation of TERAHERTZ.Ti Symbol for TITANIUM.tickler A (usually small) coil, through which energyis inductively fed back from the output to theinput of a circuit to induce oscillation.tickler coil See TICKLER.tickler-coil regeneration Positive feedback obtainedvia inductive coupling between a small coil(tickler) in the output circuit of an amplifier, anda (usually larger) coil in the input circuit. Also seeTICKLER.+12 VInOutTicklertickler-coil regenerationtickler oscillator An oscillator circuit in whichpositive feedback is obtained through inductivecoupling between an output (tickler) coil and aninput coil.tie A bracket, clamp, clip, ring, or strip for holdingseveral wires tightly as a cable or bundle.tie cable 1. A cable that connects two distributingpoints in a telephone system. 2. Any cable thatinterconnects two circuits.tie point A lug, screw, or other terminal to whichwires are connected at a junction.tie-point strip A terminal strip with lugs to whichconductors can be soldered.tight coupling See CLOSE COUPLING.tilt switch A device, such as a mercury switch,that is actuated by tilting it to a certain angle.timbre The quality that distinguishes the sound ofone voice or instrument from that of another,largely because of harmonic content.time Symbol, t. 1. The instant at which an eventoccurs. 2. The instant at which a time-base variablereaches a given value. 3. The interval betweentwo instants, commonly called duration orlength of time. Also see STANDARD TIME, TIMEBASE, TIME ZONE, and ZERO TIME.time base Time as the independent variable in aphysical relation or function. It appears in expressionssuch as pulses per second, feet perminute, watts per hour, etc.time compressor In audio recording and reproduction,a device that speeds up or slows downthe tempo without changing the audio frequencies.It is used for special effects.time constant See ELECTRICAL TIME CONSTANTand MECHANICAL TIME CONSTANT.time delay See DELAY, 1, 2.time-delay relay See DELAY RELAY.time-delay spectrometry In acoustics, a methodof simulating an echo-free environment within anenclosure that is actually not echo-free.time-division multiplexing Abbreviation, TDM. Indata and computer communications, a timesharingtechnique in which several terminals usethe same channel by transmitting data at regular,staggered intervals (i.e., one is active while theothers are idle). This gives the appearance of simultaneousreal-time operation.time-division-multiplex switch A switch with multipleports—each port corresponding to a certaintime slot in a time-division-multiplex scheme. Theinput and output (send and receive) ports are connectedby selecting the same TIME SLOT for each.time-domain reflectometry Abbreviation, TDR.Measuring the reflective characteristics of a deviceor system by superimposing the direct andreflected components of a step-formed test signalon a time-calibrated oscilloscope screen.time duration See TIME, 3.time-duration modulation See PULSE-DURA-TION MODULATION.time factor The ratio ta/tr, where ta is analog time(the relativistic duration of an event as simulatedby a computer), and tr is real time (the actual durationof the event). Also called TIME SCALE.time-interval mode In computer operations, operationthat allows a number of events to becounted between two points on a waveform.

686 time modulation • tolerancetime modulation Any form of modulation in whichthe instantaneous characteristics of a signal arevaried.timeout The expiration of an allotted time periodfor a given operation.timer 1. A device for automatically controlling theduration of an operation. See ELECTRONICTIMER. 2. A device for measuring the duration ofan operation.time sharing In computer operations, a methodfor interlaced (i.e., nearly simultaneous) use of amachine or facility by two or more persons oragencies. As the cost of computers diminishes, sodoes the need for time sharing. Also see TIME-DIVISION MULTIPLEXING.time-sharing dynamic allocator In computer storage,a program that allocates memory areas andperipherals to programs being entered into a timesharingsystem; it also controls program execution.timeshift 1. To receive a message at a significantlylater time than when it was sent. 2. To use avideocassette or videodisc recorder to view a televisionprogram at a later time than when it wastransmitted.time-shifting communications Any form of communicationsin which the recipient reads or viewsthe message(s) at a significantly later time thanthe message is sent from the source. A commonexample is electronic mail (e-mail) using onlinecomputer networks.time signals Special radio transmissions madeunder the auspices of the National Bureau ofStandards, for indicating Coordinated UniversalTime (UTC).time slot A specifically defined time interval in adata signal. It is of importance primarily in digitalcommunications, where a given time interval canbe high or low or at some discrete value.time-space-time switch A large switch consistingof a space block between two time blocks.time zone One of the 24 zones into which the globalmap is divided for the purpose of standardizingtime. Within these zones, mean solar time is determinedin terms of distance east or west of the zeromeridian at Greenwich (near London, England).Each zone is equal to 15 degrees of longitude, or1 hour. Four zones fall within the continentalUnited States: Eastern Standard Time (zone of the75th meridian), Central Standard Time (zone ofthe 90th meridian), Mountain Standard Time(zone of the 105th meridian), and Pacific StandardTime (zone of the 120th meridian). Also seeMERIDIAN, ZERO MERIDIAN, and ZONE TIME.timing extraction The retrieval of a timing signalfrom incoming data.timing pin current Measured in microamperes.The current that generates a timing waveform inan integrated-circuit voltage regulator.timing signal A repeating signal sent along withdata to control the synchronization of transmitterand receiver.tin 1. Symbol, Sn. A metallic element. Atomicnumber, 50. Atomic weight, 118.71. Tin is widelyused in electronics as a structural material, aconstituent of solder, and (in foil form) as theplates of some fixed capacitors. 2. To prepare thetip of a soldering gun or iron, or the stripped endof a wire or cable, by applying a coat of solder.tin-oxide resistor See METAL-OXIDE RESISTOR.tinsel Metal film strips interwoven with fabricthreads to provide a flexible cord, particularly forheadphones.tint control In a color-television receiver, the controlfor changing color hue.tip jack The mating connector for a tip plug.tip plug 1. A prod terminating in a phone tip. 2. Aplug-type connector terminating in a phone tip.tip plug, 2titanium Symbol, Ti. A metallic element. Atomicnumber, 22. Atomic weight, 47.88. Titanium entersinto some dielectric compounds (e.g., titaniumdioxide).titanium dioxide Formula, TiO 2 . A ceramic dielectricmaterial. Dielectric constant, 90 to 170.Dielectric strength, 100 to 210 V/mil.T junction See TEE JUNCTION.Tl Symbol for THALLIUM.T 2 L Abbreviation of TRANSISTOR-TRANSISTORLOGIC. (Also, TTL.)TLA Abbreviation of TABLE LOOK-AT.TLC Abbreviation of thin-layer chromatography.TLU Abbreviation of TABLE LOOK-UP.TM 1. Abbreviation of TRANSVERSE MAGNETIC.2. Abbreviation of technical manual.Tm Symbol for THULIUM.TM mode See TRANSVERSE MAGNETIC MODE.TM wave See TRANSVERSE MAGNETIC MODE.T network See TEE NETWORK.TNS Abbreviation of TRANSCUTANEOUS NERVESTIMULATOR.toggle A bistable device.toggle switch A switch having a mechanism thatsnaps into the on or off position at the oppositeextremes to which a lever is moved.tolerance The amount by which error is allowed ina value, rating, dimension, etc. It is usually

tolerance • torque amplifier 687tone modulation 1. The transmission of Morse,Baudot, or ASCII signals by audio-frequencymodulation of a radio-frequency carrier. 2. Anyrapid variation of the amplitude or frequency ofan audio tone.top cap A small metal cap on top of some electrontubes, serving as a direct, low-capacitance connectionto one of the internal elements—usuallythe control grid, but sometimes the plate.top loading A method of feeding a vertical antennaat or near the top.Feed linetoggle switchexpressed as a percent of nominal value, plusand minus so many units of measurement (orparts per million).toll call In a telephone system, a call that ischarged on a per-minute or per-second basis.ton Abbreviation, T, t, or tn. A unit of avoirdupoisweight; in the United States, it is usually taken tomean short ton, a unit equal to 907.20 kilograms(2000 lb). Compare METRIC TON.tone 1. The pitch (frequency) and timbre (relativeharmonic content) of a sound other than noise.2. A sound consisting of a periodic waveformhaving constant frequency; also called note.tone arm See PICKUP ARM.tone burst A test signal consisting of a singlefrequencysine wave sustained for a brief periodof time, usually having a rectangular envelope(rapid rise and decay).tone-burst entry In repeater systems, a techniquewhereby a short tone signal is used at the start ofa transmission to trigger a particular repeater sothat all repeaters in the system will not go intooperation simultaneously.tone-burst generator An oscillator and associatedcircuitry for producing a tone burst.tone control An adjustable device or circuit for modifyingthe frequency response of an amplifier (i.e.,for emphasizing bass, treble, or midrange pitches).tone dialing A method of telephone dialing thatuses standard tone pairs actuated via a keypadwith 12 keys representing digits 0 through 9 andsymbols # and *. Some keypads have four additionalkeys: A, B, C, and D.tone generator An oscillator for producing simpleaudio-frequency signals for communications,control, or testing.tone keying In wire and radio telegraphy, the representationof code characters by audiofrequencytones. Also see MODULATEDCONTINUOUS WAVE.tone localizer A localizer that provides lateralguidance for an aircraft by comparing the amplitudesof two modulating frequencies.Earthtop loadingRadiatingelementInsulatortopology 1. A branch of mathematics concernedwith the properties of surfaces and spaces. 2. Thedetails of layout of an integrated circuit. 3. Thecharacteristics of a surface.toroid See TOROIDAL COIL.toroidal coil A coil wound on a form that is shapedlike a donut. The form is made of powdered-ironor ferrite. Toroidal coils have certain advantagesover solenoidal coils: greater inductance for agiven physical size, better isolation properties,and higher Q factor. A disadvantage is that an aircore is not practical.toroidal coiltorque 1. The force that tends to produce a rotatingmotion. 2. Rotation of the plane of polarizationof light by some crystals.torque amplifier A device having rotating inputand output shafts and that delivers greatertorque at the output shaft than that required toturn the input shaft.

688 torque sensitivity • trackingtorque sensitivity Symbol, KT. For a torque motor,torque output per ampere of input current.torr A unit of pressure equal to the pressure requiredto support a column of mercury 1 millimeterhigh at 0°C and standard gravity; 1 torr =133.322 Pa (1333.2 microbars).torsion The effect on an object by torque applied toone end while the other is being held fast ortorqued in the opposite direction.torsion delay line A delay line in which the delayis manifested in a material that is torqued by mechanicalvibrations.torsion waves Waves that travel by means oftorque, instead of displacement or compression.The velocity of propagation depends on the modulusof rigidity and the density of the propagatingmedium.tot 1. Abbreviation of total. 2. To derive a sum ortotal.total breakaway torque For a torque motor, thesum of magnetic retarding torque and brushcommutatorfriction.total harmonic distortion Abbreviation, THD. Thedistortion caused by the combined action of allthe harmonics present in a complex waveform.An important specification in high-fidelity audioamplifiers.total distortion See TOTAL HARMONIC DISTOR-TION.total internal reflection 1. The reflection of visiblelight from a boundary between two substanceshaving different indices of refraction. When theangle of incidence, relative to the tangent to theboundary, is smaller than a certain value, as lighttravels through the more dense medium total reflectionoccurs at the boundary. 2. Reflection ofelectromagnetic waves from an ionized layer inthe atmosphere. This occurs at angles smallerthan a certain angle, relative to the tangent of theplane of the ionizing layer. In some cases, total internalreflection does not occur. Actually, mostionospheric reflection is really refraction; theelectromagnetic waves are bent by the ionizedlayer rather than reflected.total reflection Full return of a ray by a reflector,none of the energy being transmitted by or absorbedin the reflecting material.Higher indexof refractionLower indexof refractiontotal internal reflectionLight orradio beamtouchplate relay A capacitance relay in which thepickup element is a small, metal plate that actuatesthe relay when it is touched.tough dog A malfunctioning circuit that seeminglydefies all attempts to diagnose and correct itstrouble. Also see DOG.tourmaline crystal A piezoelectric and pyroelectriccrystal; a transparent plate of tourmaline hasthe ability to polarize light passing through it.Also see POLARIZATION, 3; POLARIZED LIGHT;and POLARIZER.tower 1. A usually tall and self-supporting openworkstructure used to support an antenna, andusually having three or four sides. 2. A metalstructure, as defined in 1, used as a vertical antenna.Townsend discharge In a glow-discharge tube, thedischarge that begins after the applied voltagereaches a given level. It is a low-current, non-selfsustainingdischarge. Compare ABNORMALGLOW and NORMAL GLOW DISCHARGE.touch screen A special cathode-ray tube (CRT) orvideo display unit that allows input of data viaphysical contact with the screen surface. Itemsare selected by simply touching the appropriatespot (“button” or icon) on the screen.TP Abbreviation of TRANSACTION PROCESSING.T pad See TEE PAD.TR Abbreviation of transmit-receive.tr 1. Symbol for RECOVERY TIME. 2. Symbol forRISE TIME.trace 1. A tiny or insignificant quantity. 2. Themovement of the electron beam across the face ofa cathode-ray tube. 3. A routine used for testingof, or for locating a fault in, a circuit or computerprogram. 4. The process of implementing such aroutine.trace element See MICROELEMENT.tracer A suitable substance or object introducedinto the human body and whose progressthrough the body can be followed (or its statemonitored) by means of electronic equipment.Tracers are sometimes used also in nonbiologicalsystems, such as pipelines.track 1. A discrete information band on a magneticdisk or tape. 2. To follow, as by a stylus, a phonodisc groove. 3. To follow, as by radar, a target.trackability An expression of the accuracy withwhich a phonograph stylus follows the irregularitiesin a disc.trackball A device for guiding the cursor or pointerin a computer. It is often used in laptop (notebook)computers. It resembles a ball bearing; theoperator moves the cursor or pointer by pushingon the bearing with a finger.track-drive locomotion A method of robotic locomotionusing two or more wheels that drive a belt(track). It uses the same principle as a militarytank.tracking Following in step, as when ganged circuitsresonate at the same frequency (or some

transceiver 1. A combination transmitter and receiver,housed in a single enclosure, with frequencycontrol and some ancillary stagescommon to both units. This design is economicalbecause it eliminates redundancy. Such a systemis more easily tuned than a separate transmitterand receiver if the operating frequency must bechanged often, but it can be difficult to carry outsplit-frequency or split-band communication ontwo frequencies that differ greatly. CompareTRANSMITTER–RECEIVER. 2. In computer practice,a read/write data terminal capable of transtracking• transfer function 689frequency difference) at all settings, or when amissile closely follows its guiding signal.tracking force See VERTICAL STYLUS FORCE.track label On a magnetic storage medium, arecord that identifies a track.tracking mode In tracking supplies, the usualmanner of operation in which the output of eachof the separate supplies automatically followsthat of the one being adjusted. Compare INDE-PENDENT MODE.tracking supplies Adjustable power supplies,packaged two or more to the unit, in which theoutput of each will automatically follow adjustmentmade to one of them.track pitch The distance between tracks (seeTRACK, 2).traffic 1. Collectively, messages handled by a communicationsstation. 2. Collectively, data and instructionshandled by a computer system incontinual use.trailer label At the end of a magnetic-tape orfloppy-disk file, a record signaling the end of thefile and often giving such information as thenumber of records in the file.trailer record At the end of a group of computerrecords, a record containing information relevantto the group’s processing.trailing edge The falling edge of a pulse. CompareLEADING EDGE.trans Abbreviation of TRANSVERSE.transaction The exchange of activity that occursbetween a computer, via a terminal, and the user,including any processing required (e.g., that involvedin adding records to, or deleting themfrom, a file).transaction file In data processing, a group ofrecords used to update a master file.transaction processing In computer operations,the use of a central processor for handling, modifying,or otherwise acting on information bytransactions.transaction tape Magnetic tape on which a transactionfile has been recorded.transadmittance For an active device, the ratiodI2/dE1, where I2 is the alternating-current (ac)component of the current in a second electrode(such as the drain), and E1 is the ac componentof voltage on a first electrode (such as the gate),with constant direct-current operating voltages.mitting and receiving information to and from achannel.transcendental functions Nonalgebraic functions.These include logarithmic functions, exponentialfunctions, trigonometric functions, andinverse trigonometric functions.transconductance 1. Symbol, gm. Unit, micromho.In an electron tube, the extent to whichplate current (IP) changes in response to a changein grid voltage (EG); gm = dIP/dEG. 2. Symbol,gfs. Unit, micromho. In a field-effect transistor,the extent to which drain current (ID) changes inresponse to a change in gate-to-source voltage(VGS); gfs = dID/dVGS.transconductance amplifier An amplifier inwhich the output current is a linear function ofthe input voltage.transcribe 1. To record material, such as a radioprogram, for future transmission. 2. In computeroperations, the intermedia transfer of data, asfrom tape to disk.transcriber A device used for intermedia datatransfer (e.g., one that can move the data on magnetictape to magnetic or optical disc).transcription A recording of material, such as arecord or tape of a radio program, for later use ina transmitter. See ELECTRICAL TRANSCRIP-TION.transcutaneous nerve stimulator Abbreviation,TNS. An electronic device for the temporary reliefof pain. In its use, electrodes taped to the skinover the painful area are connected to a portablegenerator of suitable pulse energy.transducerA device that converts one quantityinto another quantity, specifically when one ofthe quantities is electrical. Thus, a loudspeakerconverts electrical impulses into sound, a microphoneconverts sound into electrical impulses, aphotocell converts light into electricity, a thermocoupleconverts heat into electricity, etc.transducer amplifier An amplifier used expresslyto boost the output of a transducer.transducer efficiency For a transducer, the ratioof the output power to the input power.transductor See MAGNETIC AMPLIFIER.transfer 1. To move a signal from one point to another—especiallythrough a modifying circuit ordevice. 2. To transmit information or data fromone point or device to another, inside or outside asystem.transfer characteristic A figure or plot expressingthe output-input signal relationship in a circuitor device. Also see TRANSFER, 1.transfer efficiency In a charge-coupled device, theproportion of charge that is transferred undergiven conditions.transfer function 1. See TRANSFER CHARAC-TERISTIC. 2. An expression that mathematicallyshows how two entities or events occurringin different places or at different times arerelated.

690 transfer rate • transient responsetransfer rate The speed at which data can bemoved between a computer’s internal memoryand a peripheral.transferred charge In a circuit containing a capacitor,the net electric charge that moves aroundthe external circuit from one plate of the capacitorto the other.transform 1. See LAPLACE TRANSFORM. 2. Tochange the voltage or nature of an electrical parameter(e.g., high to low voltage and alternatingto direct current). 3. To change the form, but notthe content, of data.transformation constant See DISINTEGRATIONCONSTANT.transformer 1. A device using electromagnetic inductionto transfer electrical energy from one circuitto another (i.e., without direct connectionbetween them). In its simplest form, a transformerconsists of separate primary and secondarycoils wound on a common core offerromagnetic material, such as iron. When an alternatingcurrent flows through the primary coil,the resulting magnetic flux in the core induces analternating voltage across the secondary coil; theinduced voltage can cause a current to flow in anexternal circuit. Also see AIR-CORE TRANS-FORMER, INDUCTION, INDUCTIVE COUPLING,IRON-CORE TRANSFORMER, and TURNS RA-TIO. 2. A section of radio-frequency (RF) transmissionline used to match impedances. Also seeLINEAR TRANSFORMER.transformer input voltage See PRIMARY VOLT-AGE.transformer iron See SILICON STEEL.transformer loss The expression (in decibels) 10log 10 (P1/P2), where P1 is the calculated powerthat a given transformer should deliver to a particularload impedance, and P2 is the actualpower delivered.transformer oil A petroleum product in whichhigh-voltage, high-current transformers aresometimes immersed. The oil protects the windingsfrom environmental damage.transformer output current See SECONDARYCURRENT.transformer output voltage See SECONDARYVOLTAGE.transformer-type voltage regulator See VOLT-AGE-REGULATING TRANSFORMER.transformer utilization factor See UTILITY FAC-TOR.transient 1. A sudden, high-voltage spike in an alternating-currentsystem, caused by arcing orlightning. 2. A spurious signal in a hardcopyreceivingsystem. 3. Any short pulse attributableto external causes. 4. Existing for a short periodof time, or intermittently for short periods of time.Iron corePrimarySecondarySymbolPictorialtransformer, 1transformer-coupled amplifier An amplifier usingcoupling transformers between its stages or at itsinput and output points. Compare RESISTANCE-CAPACITANCE-COUPLED AMPLIFIER.transformer coupling The inductive couplingof circuits through a transformer. Also seeCOEFFICIENT OF COUPLING; INDUCTIVECOUPLING; MUTUAL INDUCTANCE; andTRANSFORMER, 1.transformer equivalent circuit An equivalent circuitdepicting the various parameters of a transformer(such as primary and secondaryresistances, primary and secondary reactances,core losses, etc.) and their relationship to eachother.transformer feedback Inductively coupled feedback(positive or negative) through a transformer.transformer input current See PRIMARY CUR-RENT.transient absorber See SURGE ARRESTER.transient arrester See SURGE ARRESTER.transient-based amplifier See CRYSTAL AMPLI-FIER, 2.transient current A momentary pulse of current.Also see TRANSIENT.transient response The response of a circuit to atransient, as opposed to its steady-state response,usually evaluated in terms of its ability toreproduce a square wave.

transient suppressor • transistor VOM 691transient suppressor See SURGE ARRESTOR.transient voltage A momentary pulse of voltage.Also see TRANSIENT.transient voltmeter An instrument that indicatesthe voltage of momentary signals. Usually, apeak-reading meter in the instrument displaysthe highest positive or negative value the transientattains (sometimes holding the deflectionfor reading later) and can respond to pulses of1 microsecond in duration.transistor An active (commonly three-terminal)semiconductor device capable of amplification,oscillation, and switching action. The name is acontraction of transfer resistor. Also see ALLOY-DIFFUSED TRANSISTOR, ALLOY TRANSISTOR,BIPOLAR TRANSISTOR, DIFFUSED-BASE TRAN-SISTOR, DIFFUSED EMITTER-AND-BASE TRAN-SISTOR, DIFFUSED-JUNCTION TRANSISTOR,DIFFUSED MESA TRANSISTOR, DIFFUSED PLA-NAR TRANSISTOR, DIFFUSED TRANSISTOR,DIFFUSION TRANSISTOR, DOUBLE-BASEJUNCTION TRANSISTOR, FIELD-EFFECT TRAN-SISTOR, FIELDISTOR, GERMANIUM TRANSIS-TOR, GROWN-DIFFUSED TRANSISTOR,GROWN-JUNCTION TRANSISTOR, JUNC-TION TRANSISTOR, MESA TRANSISTOR,METAL-OXIDE-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR, MICROALLOY DIFFUSEDTRANSISTOR, MICROALLOY TRANSISTOR,PHOTOTRANSISTOR, PLANAR EPITAXIALPASSIVATED TRANSISTOR, PLANAR TRANSIS-TOR, POINT-CONTACT TRANSISTOR, POWERTRANSISTOR, SILICON TRANSISTOR, SUR-FACE-BARRIER TRANSISTOR, SURFACE-CHARGE TRANSISTOR, TANDEM TRANSIS-TOR, THIN-FILM TRANSISTOR, THREE-JUNCTION TRANSISTOR, and UNIJUNCTIONTRANSISTOR.transistor amplifier An amplifier containing onlytransistors as the active components. Also calledtransistorized amplifier.transistor analyzer An instrument for measuringthe electrical characteristics of transistors. CompareTRANSISTOR TESTER.transistor battery A 9-volt electrochemical batteryconsisting of six tiny zinc–carbon or alkaline cellsin series. Each of the six cells supplies 1.5 volts.The ampere-hour capacity is small. The batteryhas a characteristic box shape with adjacent cliponterminals at one end. These batteries are usedin low-current electronic devices such as remotecontrolgarage-door openers, television channelchangers, remote videocassette recorder (VCR)controls, electronic calculators, and smokedetectors.transistor-coupled logic Abbreviation, TCL. Incomputer and automatic-control operations, logiccircuitry and systems using multi-emitter-coupledtransistors. Also see RESISTOR-TRANSIS-TOR LOGIC and TRANSISTOR-TRANSISTORLOGIC.transistor current meter An ammeter, milliammeter,or microammeter circuit containing anamplifier using only transistors. Also see ELEC-TRONIC CURRENT METER.transistorized voltmeter See TRANSISTORVOLTMETER.transistorized voltohmmeter An electronic voltmeter-ohmmetercombination using a transistorizedcircuit similar to that of a vacuum-tubevoltohmmeter.transistor keyer A power transistor acting as akeying device.transistor oscillator An oscillator using only transistorsas the active components. Also called transistorizedoscillator.transistor power supply A high-current, wellfiltered,direct-current power supply for operatingtransistor circuits.transistor radio Any small, portable, battery-poweredradio receiver whose active components aretransistors and/or other semiconductor devices.transistor-resistor logic See RESISTOR-TRANSISTOR LOGIC.transistor tester An instrument for checking thecondition of transistors (i.e., whether good orbad). Compare TRANSISTOR ANALYZER.transistor tetrode See DOUBLE-BASE JUNCTIONTRANSISTOR.transistor thyratron See SOLID-STATE THY-RATRON.transistor-transistor logic Abbreviation, TTL orT 2 L. In computer operations, a circuit in whichthe multiple-diode cluster of the diode-transistorlogic circuit has been replaced by a multipleemittertransistor.XInputYtransistor-transistor logicOutputtransistor voltmeter Abbreviation, TVM. A voltmetercontaining an amplifier that uses onlybipolar transistors. Also called transistorized voltmeter.Also see ELECTRONIC VOLTMETER.Compare FET VOLTMETER and VACUUM-TUBEVOLTMETER.transistor VOM See TRANSISTORIZED VOLT-OHMMETER.

692 transit angle • transversetransit angle For an electron, the angular frequencymultiplied by the time required to travelfrom one point to another.transit time The time taken by an electron totravel from one electrode to another—especiallyfrom the cathode to the plate in a vacuum tube.transistor element A metallic element whoseatoms have valence electrons in two shells. Examples:chromium, iron, and nickel.transition factor See MISMATCH FACTOR.transition region See BARRIER, 1.translation loss See PLAYBACK LOSS.translator 1. See COMPILER. 2. See ASSEMBLER.transliteration 1. To change the characters in onealphabet or code system to the characters in adifferent system. 2. The function that maps thecharacters in one alphabet or code system tothose in another.translucence 1. The transmission of radiation, especiallyvisible light, through a material. 2. Theextent to which a substance can transmit radiation—especiallyvisible light. 3. Pertaining to amaterial that partially or totally transmits radiation—especiallyvisible light.transmission gain Current amplification, poweramplification, or voltage amplification.transmission line 1. A single conductor or groupof conductors for carrying electrical energy fromone point to another. 2. A correctly dimensionedconductor or pair of conductors for carrying radio-frequencyenergy from a transmitter to an antennaor coupling device.transmission mode 1. In a transceiver, the conditionin which the transmitter is enabled and thereceiver is disabled. 2. In a waveguide, propagationvia transverse waves.transmission speed The number of information elements(words, code groups, data symbols, bits,and bytes) that can be generated or received perunit time (second or minute) by a system or operator.transmission wavemeter A (usually simple) inductance-capacitance-tunedwavemeter that providespeak response when tuned to the frequencyof a signal passing through it; also, the comparablemicrowave device. Compare ABSORPTIONWAVEMETER.transmit-receive switch A manually or electricallyoperated switch for transferring a single antennabetween a transmitter and receiver.transmittancy The relative ability of a substanceto transmit radiation. Transmittancy depends onthe frequency of the radiation, as well as the substance.transmitter 1. An equipment for producing andsending signals or data. 2. See MICROPHONE. 3.One who originates signals or data.transmitter–receiver A transmitter and receiverusually contained in a single enclosure, but withseparate and independent oscillators, mixers,and amplifiers. The main asset of this scheme isthe fact that it is possible to conduct splitfrequencycommunication on bands whose wavelengthsdiffer greatly. Another asset is the abilityof the system, with proper design, to operate infull-duplex mode. Installations of this type are oftenused in satellite communications. CompareTRANSCEIVER, 1.transmitting antenna An antenna designed expresslyfor the efficient radiation of electromagneticenergy into space.transmitting station A station that only transmitssignals (i.e., it engages in no official form of reception).Compare RECEIVING STATION.transmittivity The degree to which a selective circuittransmits a desired signal. Compare REJEC-TIVITY.transmultiplexer A device that changes a signalfrom one multiplexed form to another while maintainingall of the information contained in the signal.For example, a transmultiplexer mightconvert time-division-multiplex data to frequency-divisionmultiplex or vice-versa.transonic Equal to, or approximating, the speed ofsound in air (approximately 1100 feet per second).transparence The practically unimpeded transmissionof radiation, such as light, through a material.Compare OPACITY and TRANSLUCENCE.transponder An acronym for transmitter andresponder. 1. A combination transmitter–receiverthat automatically transmits an identificationsignal whenever it receives an interrogating signal.2. In a communications satellite, a broadbandrepeater that receives signals sent up fromthe earth, converts them to another frequency,and retransmits them back to the earth. Somesatellites have units that employ multiplexing,data storage and retrieval systems, and otherschemes to maximize the amount and variety ofdata they can handle.transponder overload A condition that occurswhen a satellite transponder is heavily used orwhen an excessively strong uplink signal is received.During heavy usage, all downlink signalsare consistently weaker than they are when thetransponder is not dealing with many signals. Ifan overly powerful uplink signal is received, alldownlink signals are attenuated intermittently;the greater the instantaneous power of the offendinguplink signal, the greater the instantaneousattenuation of all the downlink signals.See TRANSPONDER, 2.transport See TAPE TRANSPORT.transportable equipment Portable electronicequipment. See, for example, PORTABLE TRANS-MITTER.transuranium An element whose atomic numberis higher than that of uranium.transverse Occurring in a direction or directionsperpendicular to the direction of propagation.

transverse electric mode • triangulation 693transverse electric mode In a waveguide, the conditionin which the electric lines of flux are perpendicularto the direction of propagation.Compare TRANSVERSE MAGNETIC MODE. Alsosee WAVEGUIDE MODE.transverse electromagnetic wave An electromagneticwave having electric-field vectors and magnetic-fieldvectors perpendicular to the directionof propagation.transverse magnetic mode In a waveguide, thecondition in which the magnetic lines of flux areperpendicular to the direction of propagation.Compare TRANSVERSE ELECTRIC MODE. Alsosee WAVEGUIDE MODE.trap 1. See WAVETRAP. 2. In a semiconductorcrystal, an imperfection capable of trapping currentcarriers.trapezoid 1. A polygon having four sides, of whichonly two are parallel. 2. See TRAPEZOIDAL PAT-TERN. 3. See TRAPEZOIDAL WAVE.trapezoidal distortion In television or facsimile, aform of distortion in which the frame is wider atthe top than at the bottom, or vice versa.Top of screenBottom of screentrapezoidal distortiontrapezoidal pattern An oscilloscope pattern usedto check the percentage of modulation of an amplitude-modulatedwave. Its name is derived fromits trapezoidal shape.trapezoidal wave A nonsinusoidal wave that is acombination of a rectangular component and asawtooth component. It is the required waveformof the voltage applied to a magnetic deflecting coil(oscilloscope or television) to ensure a sawtoothwave of current in the coil.traveling-wave amplifier Abbreviation, TWA. Anamplifier based on the unique operation of thetraveling-wave tube.traveling-wave tube Abbreviation, TWT. A microwavetube containing an electron gun, helicaltransmission line, collector, and input and outputcouplers. A microwave signal is coupled intothe helix, through which it travels while the gunprojects an electron beam through the helix.xModulation (%) = 100 ( x − y ) x + ytrapezoidal patternWhen wave and electron velocities are equal, apower gain is obtained in the signal coupled outof the helix. Also see BACKWARD-WAVE OSCIL-LATOR.Travis discriminator A discriminator circuit inwhich the diodes are operated from separatelytuned halves of the secondary winding of the inputtransformer. Compare FOSTER-SEELEYDISCRIMINATOR.treasure locator See METAL LOCATOR.treble The higher portion of the sound spectrum—especially the upper end of the musical scale(middle C and above). Compare BASS.treble boost 1. Amplification of high audio frequencies(the treble notes) in an audio system—especially in high-fidelity music reproduction.2. The extent of amplification of high audiofrequencies in audio applications—especially inmusic reproduction. 3. A control that allowsadjustment of the relative treble gain in an audiosystem.treble control See TREBLE BOOST, 3.tree 1. A cause-and-effect chain with two or moreindependent branches. 2. A circuit with two ormore branches but no meshes.TRF Abbreviation of tuned radio frequency.TRF amplifier See TUNED RADIO-FREQUENCYAMPLIFIER.TRF receiver See TUNED RADIO-FREQUENCYRECEIVER.triac A three-terminal, gate-controlled, semiconductorswitching device. Compare DIAC.triangular wave See BACK-TO-BACK SAWTOOTH.triangulation A method of radiolocation in whichdirectional bearings are obtained for the signalsfrom two transmitters whose positions areaccurately known. The position of the receiver isindicated by the intersection of two lines on ay

694 triangulation • TrinitronGatetriacmap, drawn emanating from the transmitterlocations 180 degrees opposite their respectivebearings.Triax A double-shielded coaxial cable. A centerconductor is surrounded by two concentric, independentshield conductors.triaxial connector A male or female connectorhaving three concentric contacting surfaces. Bycontrast, the coaxial jack and coaxial plug haveonly two such surfaces.triaxial speaker A dynamic loudspeaker containingthree coils and three cones, for high-,low-, and middle-frequency ranges. It is, in effect,three speakers in one. It is commonly used inhigh-fidelity music reproduction systems. Alsocalled triaxial driver. Compare THREE-WAYSPEAKER.triboelectric Pertaining to frictional electricity.triboelectric series See ELECTROSTATIC SE-RIES.triboluminescence Luminescence produced bymeans of friction.trickle charge A continuous slow charge of a storagebattery, in which the charging rate is just sufficientto compensate for internal losses ornormal discharge.trickle charger A light-duty unit for charging abattery gradually at low current.tricorner reflector A device that reflects a ray ofincident energy at a 180-degree angle, regardlessof the direction from which the ray approaches.Thus, the ray will return to its source,unless some obstruction intervenes. It consistsof three mutually perpendicular reflecting planesurfaces that intersect in a common point. Thegeometry is identical to that in a typical room,where the ceiling meets two walls. It is useful atmicrowave, infrared, visible, and ultravioletwavelengths.triethanolamine An amino alcohol that precipitatesmetallic silver from a silver-nitrate solutionin the deposition of a silver surface on a substrate,such as glass or a ceramic.trig Abbreviation of TRIGONOMETRY.trigatron A form of electrically operated switch.The circuit is closed by the breakdown of an electricalgap.A 2A 1trigger 1. A pulse used to start or stop the operationof a circuit or device, such as a flip-flop. 2. Toplace a circuit or device into or out of operationwith a start or stop pulse, as defined in 1.trigger diode See DIAC and FOUR-LAYER DIODE.triggered multivibrator See DRIVEN MULTIVI-BRATOR.triggered sweep In an oscilloscope or similar device,a driven sweep.triggering point The voltage level at which the actionof an electronic switching device is initiated.Also see BREAKOVER POINT.trigistor A three-junction semiconductor devicethat exhibits two-state operation, and is useful asa flip-flop or switch. Also see NPNP DEVICE.trigonometric functions See CIRCULAR FUNC-TIONS and HYPERBOLIC FUNCTIONS.trigonometry The branch of mathematics devotedto the application of CIRCULAR FUNCTIONS in aplane. It is useful in electronics for determiningimpedance and phase.trim To make a fine adjustment, as of a tuningcontrol, balance control, output adjustment, etc.trimmer A low-valued variable capacitor, inductor,or resistor operated in conjunction with a mainunit (usually of the same sort) for vernieradjustment or range setting. See, for example,HIGH-FREQUENCY TRIMMER and OSCILLATORTRIMMER.trimmer capacitortrimmer.MountingcontactA variable capacitor used as aAdjustable screwPorcelainbasetrimmer capacitorDielectricMountingcontacttrimmer coil See TRIMMER INDUCTOR.trimmer inductor A variable inductor used as atrimmer.trimmer resistor A variable resistor used as atrimmer.trinary number system The base-3 system of notation.This system uses the digits 0, 1, and 2, thepositional values being successive powers of 3(e.g., decimal 14 equals trinary 112). Also calledternary number system.Trinitron 1. A single-gun color-television picturetube developed by Sony. 2. A television set using

Trinitron • tropospheric propagation 695this tube. The gun has three cathodes that modulatethe three color beams (red, green, and blue).The beams are accelerated by common grids andare focused at different angles by convergenceplates.Trinoscope See TRINITRON.triode A three-electrode tube or transistor, embodyingan anode, cathode, and a control electrodeas the principal elements.triple-diffused transistor A diffused transistor inwhich the base and emitter are diffused into thetop face of the chip, and the collector into the bottomface.triple diode An assembly of three (often closelymatched) semiconductor diodes in a singlehousing.tripler1. A rectifier that delivers a direct-currentoutput voltage at approximately triple the peakvalue of the alternating-current input voltage.2. An amplifier or other circuit that delivers anoutput signal at triple the frequency of the inputsignal.triplexer In radar, a device that facilitates the useof two receivers at the same time.R1 C2 CR3 +CR1acCR2in E rms C3+C1tripler, 1Tri-state logic Digital logic in which there arethree possible states, rather than the usual two.The conditions are defined as 0, 1, and undecided.Trade name of National Semiconductor.tritium Symbol, T or H 3 . An isotope of hydrogenwhose nucleus contains two neutrons and oneproton. Compare DEUTERIUM.TRL Abbreviation of transistor-resistor logic (seeRESISTOR-TRANSISTOR LOGIC).Trojan horse A program written with the maliciousintent of sabotaging the operating system and/orfiles in a computer. It is somewhat similar to aVIRUS; it is occasionally spread via softwarewhose origin is questionable or unknown.troposcatter See TROPOSPHERIC-SCATTERPROPAGATION.troposphere The portion of the atmosphere inwhich virtually all weather phenomena occur. Itextends from the surface to an altitude of 8 to 12miles above sea level.++−tropospheric bending A common type of radiowavepropagation that takes place when radiowaves are refracted in the lower atmosphere.This effect is most dramatic near weather fronts,where warm, relatively light air lies above cool,heavy air. The cooler air has a higher index of refractionthan the warm air, causing radiofrequencyelectromagnetic fields to be bentdownward at a considerable distance from thetransmitter. It is often responsible for anomaliesin reception of FM and TV broadcast signals.Compare TROPOSPHERIC DUCTING, TROPO-SPHERIC-SCATTER PROPAGATION.tropospheric ducting Also called duct effect. Aform of tropospheric propagation that occursclose to the earth’s surface at very-highfrequencies (VHF) and ultra-high frequencies(UHF). A duct forms when a layer of cool airbecomes sandwiched between two layers ofwarmer air. Total internal reflection of theelectromagnetic (EM) field takes place insidethe duct. For this phenomenon to providecommunications, both the transmitting andreceiving antennas must be located within thesame duct, and this duct must be unbroken andunobstructed between the two locations. A ductmight measure only a few feet from top to bottom,but cover thousands of square milesparallel to the surface. Compare TROPO-SPHERIC BENDING, TROPOSPHERIC-SCATTERPROPAGATION.tropospheric propagation Also called tropo. Overthe-horizonpropagation of radio-frequency electromagneticwaves that occurs as a result ofreflection, scattering, and/or refraction in thetroposphere, the lowest 10 or 12 miles of theearth’s atmosphere. At wavelengths shorter thanabout 15 m (frequencies above 20 MHz), refractionand reflection can take place within and betweenair masses of different density. The air alsoproduces some scattering of EM energy atwavelengths shorter than about 3 m (frequenciesabove 100 MHz). “Tropo” can often allow

696 tropospheric propagation • tuned circuitcommunications over distances of several hundredmiles. Also see TROPOSPHERIC BENDING,TROPOSPHERIC DUCTING, and TROPOSPHERIC-SCATTER PROPAGATION.tropospheric-scatter propagation Also called troposcatter.A form of tropospheric propagationthat occurs at frequencies above about 100 MHz,where the atmosphere has a scattering effect onradio waves. Dust in the air increases the scatteringeffect, but some troposcatter occurs regardlessof the weather. Troposcatter takes placemostly at low altitudes where the air is the mostdense. This mode can provide reliable communicationover distances of several hundred mileswhen the appropriate equipment is used. Communicationvia troposcatter requires the use ofhigh-gain antennas. Scatter is often observedalong with other modes of tropospheric propagation.Compare TROPOSPHERIC BENDING,TROPOSPHERIC DUCTING.troubleshoot 1. To look for the cause of equipmentfailure. 2. To look for flaws in computer softwareor to debug a program.troubleshooting test A test that is part of the procedurefor finding the cause of faulty electronicequipment operation. Also see DIAGNOSTICTEST. Compare PERFORMANCE TEST.trough value The minimum amplitude of a compositecurrent or voltage.true complement See RADIX COMPLEMENT.true ground The earth, as opposed to an artificialground, such as that provided by the radials ofa ground-plane antenna or an equipmentchassis.true power In an alternating-current (ac) circuit,the power actually dissipated in the resistivecomponent; the reactive component consumes nopower. In ac circuits containing reactance, thetrue power is less than the product of the voltageand current. Also see AC POWER and POWERFACTOR.truncation A method of approximating a quantityby cutting off its digits beyond a certain point. Forexample, 3.44 and 3.46, when truncated to twosignificant digits, both become 3.4. CompareROUNDING.trunk 1. A communications link between twopoints, one usually being external. 2. The interfacebetween a central processing unit and a peripheraldevice.trunk link In computer systems, an interface permittingaccess to main storage via a peripheral.truth table In logic analysis and logic circuit design,a table in which are listed all combinationsof input values and the corresponding output valuesfor a given logic function.ts Abbreviation of tensile strength.Tschebyscheff filter See CHEBYSHEV FILTER.TSS Abbreviation of TIME-SHARING SYSTEM.T switch See TEE SWITCH.TST switch See TIME-SPACE-TIME SWITCH.truth table(x + y)' + xzx y z x + y (x + y)' xz (x + y)' + xz0 0 0 0 1 0 10 0 1 0 1 0 10 1 0 1 0 0 00 1 1 1 0 0 01 0 0 1 0 0 01 0 1 1 0 1 11 1 0 1 0 0 01 1 1 1 0 1 1TTL Abbreviation of TRANSISTOR-TRANSISTORLOGIC. (Also, T 2 L.)TTT In radiotelegraphy, a signal indicating that amessage concerning safety is to follow (equivalentto securite in radiotelephony).TTY Abbreviation of TELETYPE.T-type antenna See TEE ANTENNA.T-type attenuator See TEE PAD.tube 1. Generic term for any electron tube (e.g.,vacuum tube, gas tube, cathode-ray tube, X-raytube, etc.). 2. Glow lamp: argon bulb, neon bulb,mercury-vapor lamp, etc.tube capacitances The internal capacitances betweenthe elements of an electron tube.tube diode A two-element (cathode and anode)electron tube for current rectification. Also seeDIODE.tube of flux A group of flux lines within a circularcross section. It can vary in diameter as the densityof the flux lines changes.tube parameters Operating coefficients of electrontubes (e.g., plate current, grid voltage, screencurrent, transconductance, amplification factor,etc.).tube tester An instrument for checking one ormore of the parameters of an electron tube.tubular capacitor A fixed capacitor consisting of awound section enclosed in a cylindrical can.tune 1. To adjust a selective circuit to accept or rejecta signal. 2. To correct the natural frequencyof vibration of a body. 3. To adjust a radio transmitterfor optimum output. 4. To adjust the frequencyof an oscillator—especially in a radiotransmitter or receiver. 5. To adjust the resonantfrequency of an antenna, antenna coupler, or antennasystem.tuned AF amplifier 1. An audio amplifier that iscontinuously tunable over a band of frequencies.2. An audio oscillator that is set to a fixed, precisefrequency. See, for example, PARALLEL-TEE AM-PLIFIER.tuned-base oscillator A self-excited, commonemitterconnected, bipolar-transistor oscillator inwhich the tuned tank is in the base circuit.tuned circuit A (usually series-resonant or parallel-resonant)circuit adjusted to accept or reject asignal. Also see RESONANCE.

tuned-collector oscillator • tunnel-diode amplifier 697tuned-collector oscillator A self-excited, common-emitterconnected, bipolar-transistor oscillatorin which the tuned tank is in the collectorcircuit.C1R1R2R3C3C2tuned-collector oscillator−+TV CCOutputtuned coupler An antenna coupler (transmatch)that can be adjusted independently of the transmitteror receiver with which it is used.tuned dipole A half-wave, center-fed, resonant antenna.tuned feeders An antenna feed line that is adjustedor trimmed so that the entire system (feedersand radiating element) is resonant at thetransmitted-signal frequency.tuned headphones Headphones used in radio-telegraphythat are fix-tuned to a single audio frequency(e.g., 1 kHz) by means of a small parallel capacitor.tuned line An antenna wire or transmission linethat provides a resistive load at a specific resonantfrequency.tuned pickup A pickup circuit or device (such as aradio-frequency sampling coil) that is tuned tothe signal frequency.tuned radio-frequency amplifier An amplifier circuitthat is continuously tunable over a specificband of radio frequencies.tuned radio-frequency receiver A radio receiverconsisting only of a tuned-radio-frequency amplifier,detector, and audio amplifier. Compare SU-PERHETERODYNE RECEIVER.tuned reed A vibrating reed whose length, width,and/or thickness have been adjusted so that itvibrates naturally at a desired frequency.tuned-reed frequency meter An audio frequencymeter using tuned metal reeds as the indicators.Also see POWER FREQUENCY METER, 2.tuned relay An electronic or electromechanical relaythat closes at one frequency. See, for example,REED SWITCH, 1.tuned signal tracer A signal tracer that can betuned sharply to the frequency of the test signalbeing traced.tuned transformer An audio-frequency or radiofrequencytransformer tuned via a capacitor inparallel with its primary winding and/or a capacitorin parallel with it secondary winding.tuner A circuit or device that can be set to selectone signal from a number of signals in a frequencyband.tungsten Symbol, W. A metallic element. Atomicnumber, 74. Atomic weight, 183.85. Also calledwolfram. It is used in switch and relay contacts,in the elements of some electron tubes, and in incandescent-lampfilaments.tuning 1. Adjustment of the frequency of a receiverto intercept a signal on a given frequency. 2. Adjustmentof a transmitter oscillator to a desiredfrequency. 3. Adjustment of an inductancecapacitancecircuit for resonance on a desiredfrequency. 4. Adjustment of an antenna orantenna system to a desired frequency. 5. Adjustmentof a radio-frequency amplifier for optimumperformance. 6. Alignment of a musical instrumentfor correct tone frequency.tuning capacitor A variable capacitor used to tunean inductance-capacitance circuit (seriesresonantor parallel-resonant).tuning coil A variable inductor used to tune an inductance-capacitancecircuit (series-resonant orparallel-resonant).tuning core See TUNING SLUG.tuning diode See VOLTAGE-VARIABLE CAPACI-TOR, 1.tuning fork A metal device that vibrates at a preciseaudio frequency when struck physically. Itusually has two prongs and looks something likea fork.tuning-fork oscillator See FORK OSCILLATOR.tuning indicator 1. A meter or display that indicateswhen a receiver is properly tuned to the frequencyof an incoming signal. 2. Sometimes, abridge null detector.tuning meter A meter-type resonance indicator.tuning potentiometer A single or ganged potentiometer(depending on the circuit in which it isused) used to vary the frequency response of aresistance-capacitance-tuned circuit, such asthe bridge-tee, parallel-tee or Wien-bridgecircuit.tuning slug A powdered-iron core that slides orscrews in and out of a coil to vary the inductance.tuning voltage An adjustable direct-current voltageused to vary the capacitance of a varactordiode (serving as the capacitor in a tuned circuit).tuning wand See NEUTRALIZING TOOL.tunnel diode A specially processed junction diodewhose forward conduction characteristic displaysnegative resistance.tunnel-diode amplifier A circuit that uses thenegative-resistance properties of a tunnel diode

698 tunnel-diode amplifier • two-phaseto produce gain. It is used primarily at ultra-highand microwave frequencies.tunnel-diode oscillator A circuit that uses thenegative-resistance properties of a tunnel diodeto produce oscillation at a specific frequency. It isused primarily at ultra-high and microwave frequencies.turbidimeter A device used to measure the turbidity(relative opaqueness) of liquids.turbidity meter See TURBIDIMETER.Turing machine A hypothetical model, conceivedby Alan Turing in the 1930s, devised as an exercisein problem solving. In effect, it was a computerprogramming language with a limitedinstruction set, operating in a computer with infinitememory and storage capacity.Turing test A scheme devised by Alan Turing, designedto test computers for artificial intelligence(AI). If the machine can fool a person into thinkingit is another person most of the time, then themachine in effect “passes” the test, indicatingthat it has some AI.turn One complete loop of a coil.turnaround time 1. The length of time required fora repair to be performed. 2. The length of time requiredfor a computer program to be completed.3. The time required for a trans-ceiver to switchfrom the full-transmit to the full-receive condition.turn factor For a given inductor core, the numberof turns (in a standard configuration) that resultsin an inductance of 1 H.turn-off time The time required for the operationof a circuit or device to cease completely after asignal or operating power has been removed.Compare TURN-ON TIME.turn-on time The time required for a circuit or deviceto come up to full (normal) operation afterapplication of a trigger or operating power. CompareTURN-OFF TIME.turnover pickup See DUAL PICKUP.turns ratio For a transformer, the ratio of thenumber of turns in the primary winding to thenumber of turns in the secondary winding.turnstile antenna A polyphase antenna that resemblesa turnstile gate.turntable 1. The motor-driven, rotating platter onwhich a phonograph disc rests during recordingor reproduction. 2. In a high-fidelity phonographsystem, the assembly containing the platter, asdefined in 1.turret tuner A television front-end tuner having aseparate tuned-circuit section for each channel.Turning a knob rotates a desired section into positionagainst switch contacts. Also called DE-TENT TUNER.TV 1. Abbreviation of TELEVISION. 2. Abbreviationof terminal velocity.T/V Abbreviation of temperature to voltage.TV decoder A device for unscrambling a televisionbroadcast that has been intentionally encryptedto prevent its use by unauthorized viewers. SeeSUBSCRIPTION TV.TV ghost See GHOST.TVI Abbreviation of TELEVISION INTERFERENCE.TVL Amateur radio abbreviation of television listener(looker).TVM Abbreviation of TRANSISTORIZED VOLT-METER.TVO Abbreviation of TRANSISTORIZED VOLT-OHMMETER. (Also, TVOM.)TVOM Abbreviation of TRANSISTORIZED VOLT-OHMMETER. (Also, TVO.)TV projector A combination electronic and opticaldevice for projecting television images on a largescreen.TV sound marker See SOUND MARKER.TVT Abbreviation of television terminal (computerperipheral).TW Abbreviation of TERAWATT.TWA Abbreviation of TRAVELING-WAVE AMPLI-FIER.tweeter A loudspeaker that favors the extreme treble(high) audio frequencies, ranging from 4000or 5000 Hz to more than 20,000 Hz. CompareWOOFER.twin diode See DUAL DIODE.twinlead See FLAT-RIBBON LINE.twin line See FLAT-RIBBON LINE.twin meter See DUAL METER.twin-T measuring circuit See PARALLEL-TEEMEASURING CIRCUIT.twin-T network See PARALLEL-TEE NETWORK.twisted pair A simple wire line used for communications.It consists of two wires twisted togetherto form a helix.twister A piezoelectric crystal, such as one ofRochelle salt, that generates a voltage whentorqued.twistor A magnetic-memory element consisting ofa winding of magnetic wire on a length of nonmagneticwire.two-channel amplifier See DUAL-CHANNEL AM-PLIFIER.two-channel recorder See DOUBLE-CHANNELRECORDER.two-electrode amplifier See DIODE AMPLIFIER.two-electrode tube See TUBE DIODE.two-element amplifier See DIODE AMPLIFIER.two-element beam A Yagi antenna consisting of adriven element and one parasitic element. Theparasitic element can be either a reflector, about5% longer than the resonant half wavelength atthe operating frequency, or it can be a director,about 5% shorter than a half wavelength at theoperating frequency.two-element tube An electron tube having twoprincipal electrodes (i.e., a tube diode).two-five code See BIQUINARY CODE.two-phase Pertaining to circuits or devices inwhich two components (two voltages, two

two-phase • Type A telephone line 699DrivenelementBoomBoomDirector Reflector Drivenelementtwo-element beamcurrents, or a current and a voltage) are 90° outof phase with each other.two-phase system See QUARTER-PHASE SYSTEM.two-phase, three-wire circuit A circuit using threeconductors, one of which (the common return) is90° out of phase with the other (outer) two.two-pincher gripper A simple robotic end effectorusing two tongs, and resembling large tweezers orneedle-nosed pliers. It grasps objects by “pinching”them.two-point tuning See DOUBLE-SPOT TUNING.two-space A two-dimensional mathematical continuumin which each point is uniquely definedby two variables in an ordered pair, such as (x,y),and each ordered pair corresponds to exactly onepoint in the continuum. A common scheme is theCartesian coordinate system; another scheme isthe polar coordinate system. See CARTESIANCOORDINATES and POLAR COORDINATES.two-space coordinates A coordinate system fordefining points in two-space. See CARTESIANCOORDINATES and POLAR COORDINATES.two-state device A device having two stable states(e.g., a flip-flop).two-state logic Digital logic in which there are twopossible conditions (called high and low, true andfalse, or 1 and 0).two-tone keying See FREQUENCY-SHIFT KEY-ING.two-track recording Recording on two adjacenttracks on magnetic tape. The separate recordingscan be in the same direction (as in stereo) or inopposite directions.two-way amplifier An amplifier whose input andoutput terminals can be used interchangeably.two-way communication The exchange of messagesbetween two or more stations that transmitas well as receive. Compare ONE-WAY COMMU-NICATION, 1.two-way radio 1. Any form of TWO-WAY COMMU-NICATION using electromagnetic waves. 2. A radiotransceiver—especially one used for voicecommunication at very-high or ultra-high frequencies.two-way repeater In telephony, a device that amplifiesand retransmits a signal in either direction.Also see TWO-WAY AMPLIFIER.two-way speaker A woofer/midrange speaker anda tweeter occupying the same enclosure, and interconnectedby a crossover network for widebandfrequency response.TWT Abbreviation of TRAVELING-WAVE TUBE.TWX Abbreviation of TELETYPEWRITER EX-CHANGE.Twystron A form of microwave-oscillator tube,similar to the Klystron.Type A telephone line A telephone line servingone subscriber (as opposed to a party line).

U 1. Symbol for URANIUM. 2. Abbreviation ofUNIT.u Symbol (ital.) for UNIFIED ATOMIC MASS UNIT.Ua Abbreviation of unit of activity (electroencephalography).UAM Abbreviation of underwater-to-air missile.ubiquitous carrier A current carrier (especially anelectron) whose velocity is so high, or mechanismof transfer so subtle, that it appears to be in twoplaces simultaneously. Thus, in the tunnel diode,during the interval of tunneling a single electron,appears to be on both sides of the barrier at thesame time.Ubitron A tube in which a periodic magnetic fieldcauses an electron beam to undulate. Through itstransverse velocity component, the beam interactswith a radio-frequency wave, and its kineticenergy is converted into radio-frequency energy.The ubitron can be used as an amplifier or oscillator.UCT Abbreviation of UNIVERSAL COORDINATEDTIME.UDC Abbreviation of universal decimal classification.UDOP Abbreviation of ultra-high-frequency Doppler.A 440-MHz phase-coherent tracking systemused to determine the velocity and position ofmissiles and space vehicles.UEP Abbreviation of underwater electric potential.UFET Abbreviation of unipolar field-effect transistor.(Also, UNIFET.) See UNIPOLAR TRANSISTOR.UFO See UNIDENTIFIED FLYING OBJECT.UG Abbreviation of underground.UHF Abbreviation of ULTRAHIGH FREQUENCY.UHF adaptor See UHF CONVERTER, 1.UHF capacitor A button-type capacitor. Becauseof its unique design, it is an efficient bypass capacitorat ultrahigh frequencies.UHF converter 1. A circuit, usually consisting of aradio-frequency amplifier and mixer, for convertingultra-high-frequency (UHF) signals to a lowerband of frequencies. 2. A circuit for convertingUHF television signals to very-high-frequency(VHF) signals so that they can be accommodatedby an older (VHF only) television receiver. SeeUHF TELEVISION CHANNELS and VHF TELEVI-SION CHANNELS.UHFinUHFamp.MixerOsc.HFamp.UHF converter, 1HFoutUHF diode A semiconductor diode whose rectificationefficiency is good at ultra-high frequencies.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

UHF generator • ultra-low frequencies 701UHF generator 1. An oscillating device (such as atransistor, tunnel diode, Klystron, or magnetron)used to produce radio-frequency energy at ultrahighfrequencies (UHF). 2. The equipment inwhich such a device is used. 3. An ultra-highfrequencytest-signal generator.UHF loop A (usually single-turn) loop antenna witha toroidal radiation pattern perpendicular to theloop; the antenna has a natural wavelength in theultra-high-frequency (UHF) range.UHF receiver A receiver tunable to frequencies inany band in the range 300 MHz to 3000 MHz.UHF television channels Television channels 14through 69, whose frequencies lie in the ultrahighrange.UHF transistor A transistor specially designed andfabricated for ultra-high-frequency (UHF) operation.It is characterized by extended beta cutofffrequency, low junction capacitance, and fast recoverytime.UHF translator A television broadcast translatorstation transmitting in an ultra-high-frequency(UHF) channel.UHF transmitter A transmitter that is speciallydesigned for operation at ultra-high frequencies.In such a transmitter, stray parameters are minimizedand special tubes or transistors are required.UHF tube A vacuum tube specially designed for ultra-high-frequencyoperation. It is characterizedby low interelectrode capacitance, low input andoutput capacitances, short electron transit time,and low lead inductance.UHF tuner 1. A superheterodyne receiver front endtunable in the ultra-high-frequency (UHF) range.It is usually arranged to deliver the mixer outputto a lower-frequency receiver. 2. A television receiverfront end tunable to the UHF channels.UHR Abbreviation of ULTRA-HIGH RESISTANCE.U index The difference between consecutive dailymean values of the horizontal component of thegeomagnetic field.UJT Abbreviation of UNIJUNCTION TRANSISTOR.UL 1. Abbreviation of UNDERWRITERS LABORA-TORIES. 2. Abbreviation of ULTRALINEAR.ULD Abbreviation of ULTRA-LOW DISTORTION.ULF Abbreviation of ULTRA-LOW FREQUENCY.U-line section A short section of coaxial cable orhardline having the shape of a squared U.ULSI See ULTRA-LARGE-SCALE INTEGRATION.ultimate attenuation The maximum attenuationin a circuit or device when it is operated outsideits passband, or within its stopband.ultimately controlled variable In an automatedsystem, the quantity or operation (e.g., liquidlevel, temperature, pressure, precision drilling,etc.), whose control is the end purpose of the system.ultimate-range ballistic missile A ballistic missilewhose range is greater than half the earth’s circumference(approximately 12,000 miles).ultimate ratio The limiting value of a ratio (i.e., thevalue approached by a ratio).ultimate sensitivity 1. In an instrument or system,the maximum degree of perception of, or responseto, a quantity or condition. 2. In a graphicrecorder, half the deadband.ultimate threshold See ULTIMATE SENSITIVITY,2.ultimate trip current For a specified set of environmentalconditions, the lowest value of currentthat will trip a circuit breaker.ultimate trip limits For a circuit breaker, themaximum and minimum current at which thebreaker trips and drops out.ultor anode The second anode of a television picturetube or oscilloscope tube.ultor element In a television picture tube, the elementthat receives the highest direct-currentvoltage. Also called ultor electrode. Also see UL-TOR ANODE.ultor voltage The high direct-current voltage appliedto the second anode of an oscilloscope tube ortelevision picture tube. Also see ULTOR ANODE.ultra- A prefix meaning above, larger than, greaterthan, or higher than. See the following several definitionsfor examples.ultra-atomic Pertaining to particles smaller thanatoms (i.e., SUBATOMIC).ultra-audible frequency A frequency higher thanthe highest audible frequency. Also called ULTRA-SONIC FREQUENCY and supersonic frequency.ultra-audion oscillator See ULTRAUDION OSCIL-LATOR.ultracentrifuge A centrifuge that spins at a veryhigh speed.ultrafast switch An electronic switch capable ofmicrosecond operation.Ultrafax A system for high-speed transmission ofprinted matter by facsimile, radio, or television.ultra-high frequency A radio frequency in therange 300 MHz to 3000 MHz, corresponding tofree-space wavelengths between 1 meter and10 centimeters.ultra-high-frequency band See UHF BAND.ultra-high resistance Resistance of 100 megohmsor higher.ultra-large-scale integration An integrated-circuitprocess that goes several orders of magnitudebeyond VERY-LARGE-SCALE INTEGRATION.More than 4 × 10 6 transistors could be on a singlechip.ultra-linear Pertaining to the most linear operationobtainable with state-of-the-art electronic equipment.ultra-linear amplifier A high-fidelity audiofrequencypower amplifier having wide frequencyresponse and very low distortion.ultra-low distortion Total harmonic distortion(THD) of less than 0.1 percent.ultra-low frequencies 1. Radio frequencies between300 Hz and 3 kHz, pertaining to

702 ultra-low frequencies • ultrasonic light diffractionwavelengths between 1000 kilometers and 100kilometers. 2. Audio frequencies lower than thosein the human hearing range.ultramicrometer An electronic instrument for extremelysmall linear measurements.ultramicroscope An optical microscope using refractedlight to illuminate minute particles.ultramicrowave Pertaining to wavelengths in therange 10 -3 to 10 -6 meter (300 GHz to 300 THz).ultraminiature See SUBMINIATURE.ultraphotic rays Collectively, infrared and ultravioletrays.ultrared rays See INFRARED RAYS.ultra-short waves Waves whose length correspondto ultra-high frequencies (i.e., wavelengths between0.1 and 1 meter).ultrasonic Of higher frequency than those that areaudible (supersonic). See, for example, ULTRA-SONIC FREQUENCY.ultrasonic bonding A method of bonding metal bymeans of physical vibration at frequencies abovethe human hearing range.ultrasonic brazing Forming a nonporous bond betweenmetal parts through the use of ultrasonicenergy and a second, different metal (or alloy)having a lower melting point.ultrasonic cleaning A method of cleaning delicateor intricately structured items (such as dentures,contact lenses, or jewelry) in which the soileditems are immersed in a fluid that is agitated byultrasonic transducers; the foreign particles areshaken away.ultrasonic cleaning tank A thick-walled stainlesssteeltank with ultrasonic transducers mountedwithin its walls and used for ultrasonic cleaning.ultrasonic coagulation The coagulation of a substancethrough ultrasonic agitation.ultrasonic communication Underwater telegraphiccommunication between ships and/orsubmarines by keying the echo-ranging sonarequipment.ultrasonic delay line A delay line, such as themercury type, through which an ultrasonic signalis propagated. The delay results from the relativelyslow propagation of the ultrasonic wavethrough the substance in the line.ultrasonic densitometer A density-measuring apparatuswhose operation is based on the time requiredfor an ultrasonic signal to penetrate thematerial under test, or for the signal to penetratethe material and be reflected back to the transmitter.ultrasonic depth finder See ACOUSTIC DEPTHFINDER.ultrasonic detector A device that responds to ultrasonicwaves by indicating their presence, intensity,and/or frequency.ultrasonic diagnosis The medical determination ofthe condition of tissues or structures within thebody, in terms of reflection of ultrasonic waves bythose tissues or structures. The technique is usefulin situations where other techniques, such asradiology or the use of catheter probes, are risky.Also see ULTRASOUND.ultrasonic disintegrator In biology and relatedfields, a device that uses ultrasonic energy to ruptureor shatter cells, tissues, or foreign bodies,such as kidney stones.ultrasonic drill A drill running at speeds correspondingto ultrasonic frequencies. The tool isvaluable in drilling hard or brittle materials andin dentistry.ultrasonic filter 1. A bandpass filter whose operationis based on the natural (ultrasonic) vibrationfrequency of small disks or rods of magnetostrictivemetal. See MAGNETOSTRICTION. Also calledmechanical filter. 2. Generally, a filter operatingat ultrasonic frequencies.ultrasonic flaw detector A system analogous toradar, in which an ultrasonic wave is transmittedthrough a solid material and is reflected back to adetector and display device to reveal flaws,cracks, and strain in the material.ultrasonic frequency For an acoustic disturbance,any frequency above the limit of humanhearing (higher than 20 kHz).ultrasonic generator 1. An oscillator that operatesat frequencies above the range of human hearing,and the output of which is intended for couplingto an electroacoustic transducer. 2. Any devicethat produces ultrasonic waves.ultrasonic grating constant For a sound waveproducing a diffraction spectrum, a figure indicatingthe distance between diffracting centers ofthe wave.ultrasonic heating The production of heat in aspecimen by means of ultrasonic energy directedinto or through it.ultrasonic image converter A device that makesvisible acoustic field patterns.ultrasonic inspection The use of ultrasonic wavesto detect internal flaws in solid materials, such asmetals. It is valued particularly because it is nondestructive.Also see ULTRASONIC FLAW DE-TECTOR.ultrasonic intrusion alarm A security system activatedwhen an intruder disturbs a pattern of ultrasonicwaves in the protected area; a sensitiverelay closes, setting off an alarm.ultrasonic level detector A level-monitoring systemin which an ultrasonic transmitter and detectorare mounted together on one wall of a tankor chamber. When the tank is empty, the transmittedsignal is reflected by the opposite wallback to the detector. When the liquid rises, thereflection time is reduced; this change is used tooperate a device that indicates that the tank hasbeen filled to a desired level.ultrasonic light diffraction Diffraction resultingfrom the periodic variation of light refractionwhen a beam of light passes through a longitudinalsound-wave field.

ultrasonic light modulator • ultraviolet altimeter 703Osc.ToalarmSensorUltrasonicwavesAmp.Movingobjectsultrasonic intrusion alarmultrasonic light modulator A device that modulatesa light beam passing transversely through afluid agitated by sound waves.ultrasonic material dispersion The use of the agitativeaction of high-intensity ultrasonic wavesto disperse or emulsify one substance in another.ultrasonic plating The use of ultrasonic energy todeposit or bond one material onto the surface ofanother.ultrasonic probe A rodlike director of ultrasonicenergy.ultrasonic relay An electronic relay actuated byultrasound.ultrasonics 1. The use of high-frequency acousticenergy in industry, medicine, research, and thehome. See ULTRASONIC FREQUENCY. 2. Theuse of high-frequency acoustic energy for medicaldiagnosis and treatment. 3. The branch ofphysics dealing with the effects and behavior ofacoustic disturbances at frequencies above therange of human hearing.ultrasonic soldering See ULTRASONIC BRAZING.ultrasonic sounding Determining the depth of abody of water in terms of the time taken for atransmitted ultrasonic signal to be reflected backto a transmitting point on the surface of the water.ultrasonic space grating A periodic variation inthe index of refraction when acoustic waves arepresent in a light-transmitting medium. Also seeULTRASONIC LIGHT DIFFRACTION.ultrasonic storage cell See ULTRASONIC DELAYLINE.ultrasonic stroboscope A stroboscope that usesan ultrasonically modulated beam of light.ultrasonic switch An electronic switch actuatedby ultrasound.ultrasonic therapy The use of ultrasonic energy inmedicine for treatment of certain disorders.ultrasonic thickness gauge An instrument thatdetermines the thickness of a specimen in termsof the propagation time (or echo time) of ultrasonicwaves through the specimen.ultrasonic transducer A transducer that convertselectrical energy into ultrasonic energy, or viceversa.Common types are the quartz crystal, ceramiccrystal, and magnetostrictive disk.ultrasonic waves Acoustic waves whose lengthcorresponds to ultrasonic frequencies (i.e., frequenciesabove 20 kHz).ultrasonic welding A below-melting-point techniqueof joining two metallic bodies by clampingthem tightly together and applying ultrasonic energy,rather than heat, in the plane of the desiredweld. Compare ULTRASONIC BRAZING.ultrasonic whistle A whistle whose pitch is beyondthe range of human hearing. Although someare of the simile (blown) type, others are (usuallyminiature) electronic sound generators. These devicescan be used for the remote control of televisionreceivers, garage-door openers, and otherequipment.ultrasonography A method of examining humantissues or organs by transmitting ultrasonicwaves into the body and receiving the echoes.ultrasound 1. Acoustic disturbances at frequenciesabove 20 kHz. 2. See ULTRASONIC FRE-QUENCY. 3. See ULTRASONOGRAPHY.ultraviolet 1. Electromagnetic radiation at wavelengthssomewhat shorter than those of visiblelight. Longwave or near ultraviolet extends fromapproximately 390 nanometers (nm) down to50 nm. Shortwave or far ultraviolet extends from50 nm down to 4 nm. 2. Pertaining to the behaviorand effects of electromagnetic radiation in therange of approximately 390 nm to 4 nm.Wavelength (angstroms)10 010 110 210 310 410 510 610 710 810 910 10X raysFar ultravioletNear ultravioletVisible lightInfared}EHFSHF RadioUHFultravioletwavesultraviolet altimeter An altimeter that uses ultravioletrays instead of radio waves to determine thealtitude of an aircraft or spacecraft.

704 ultraviolet lamp • unblanking intervalultraviolet lamp A lamp that delivers ultravioletrays. Common types are arc lamps and mercuryvaporlamps.ultraviolet light See ULTRAVIOLET RAYS.ultraviolet power The power (in watts) of ultravioletradiation.ultraviolet rays Radiation at frequencies in the ultravioletregion (i.e., between the highest visiblelightfrequencies and the lowest X-ray frequencies).ultraviolet therapy The use of ultraviolet rays byphysicians and other health personnel in thetreatment of certain disorders.ultraviolet wavelength The wavelength range ofultraviolet radiation [e.g., 390 nanometers (nm)to 4 nm].ultraviolet waves See ULTRAVIOLET RAYS.umbilical cord 1. A cord through which missilesand rockets are controlled and powered until theyare launched. 2. A cord connecting an astronautto his space vehicle during extravehicular activity(e.g., during a space “walk”).umbilical tower The vertical tower supporting theumbilical cords extending to a rocket in thelaunch position.umbra 1. The region of total (conical) shadow behindan object situated in the path of a radiation.2. The comparatively dark central region in asunspot.umbrella antenna An antenna consisting of anumber of wires, extending from the top of a verticalmast to points on a circle below, at the centerof which the mast is mounted. The wires areusually fed in parallel from the top.Umklapp process A process responsible for thermalresistance in nonconducting materials. It resultsfrom collision between phonons, orphonons and electrons.UMW Abbreviation of ULTRAMICROWAVE.unabsorbed field strength The field strength withno absorption between transmitter and detector.The unabsorbed field strength is an ideal quantity;the actual field strength over a given distanceis always less. It is expressed in volts per meter.unamplified back bias A negative-feedback voltagedeveloped across a fast-time-constant circuitwithin a single amplifier stage.unamplified feedback A positive or negative currentor voltage taken from the output of a systemand presented to the input without being boostedthrough auxiliary amplification.unamplified ALC Automatic level control (ALC) inwhich the control-signal voltage is taken from apoint in the circuit and fed to the controlled pointwithout being boosted by an auxiliary amplifier.Compare AMPLIFIED ALC.unattended operation Operation, as of an electronicallyprogrammed machine, with minimal (orno) human supervision.unattended time The period, excluding down timefor repair or checkout, during which a computeris unpowered.unattenuated Not reduced in intensity of amplitude.Thus, an unattenuated signal is one thathas retained its original strength during its transmissionthrough a system.unavailable energy The difference between thequantity of heat energy supplied to a system andthe available energy of the system.unbalance 1. Lack of balance or symmetry in a circuit,line, or system. 2. The condition in which abridge (or the equivalent) is not nulled.unbalanced circuit See SINGLE-ENDED CIRCUIT.unbalanced delta system A three-phase circuit inwhich the elements are connected in a triangular(delta) configuration, but are of unequalimpedance. In an unbalanced delta system, nodefinite relationship exists between line andphase currents. Compare BALANCED DELTASYSTEM.unbalanced input See SINGLE-ENDED INPUT.unbalanced line 1. A transmission line in whichone side (conductor) is grounded (e.g., a coaxialline). 2. A normally balanced transmission line inwhich the currents in the two halves are out ofbalance (i.e., they are not equal in amplitude andopposite in phase).unbalanced multivibrator A multivibrator inwhich the time constant of one base or gate circuitdiffers from that of the other base or gate circuit.The asymmetry results in short-durationoutput pulses separated by long time periods.unbalanced output See SINGLE-ENDED OUTPUT.unbalanced two-phase system A two-phase circuitin which the load elements are of unequalimpedance.unbalanced wire circuit A wire line whose (two)sides are dissimilar.unbalanced-wye system A three-phase circuit inwhich the elements are connected in the familiarwye, or star, configuration, but are of unequalimpedance.unbalanced-Y system See UNBALANCED-WYESYSTEM.unbalance-to-balance transformer A transformerfor matching an unbalanced transmission line toa balanced line (e.g., a coaxial line to a parallelwireline).unbiased limiting Peak limiting that results fromoverdriving an unbiased active device.unbiased unit A device or circuit operated withoutbias [e.g., a transistor without base bias (commonemitter and emitter follower) or emitter bias (commonbase)].unblanking Removal of the blanking pulse in acathode-ray-tube circuit (i.e., turning on thebeam).unblanking generator A (usually pulse-type) signalsource for turning on the beam of a blankedcathode-ray tube.unblanking interval The period during which thebeam of a cathode-ray tube is turned on. CompareBLANKING INTERVAL.

unblanking pulse • unconditional jump 705unblanking pulse A pulse that turns on the beamof a blanked cathode-ray tube. Compare BLANK-ING PULSE.unblanking time 1. See UNBLANKING INTERVAL.2. The instant at which unblanking begins.unbonded strain gauge A strain gauge that is notdirectly attached (by cement, for example) to thestrained surface.unbound electron A free electron (i.e., an electronnot confined to a shell within an atom).unbuffered output An output (signal, power, etc.)that is delivered directly from the generating devicewithout the benefit of an isolating stage,such as a buffer amplifier. Compare BUFFEREDOUTPUT.unbypassed emitter resistor In a common-emittertransistor circuit, an emitter resistor withouta bypass capacitor. The flow of output-signal currentthrough the resistor produces negative feedbackwithin a single stage.InputR C−V CCC IR B R EC OOutputunbypassed emitter resistor (R E )unbypassed source resistor In a common-sourcefield-effect transistor circuit, a source resistorwithout a bypass capacitor. The flow of outputsignalcurrent through the resistor produces negativefeedback within a single stage.uncage In a displacement gyroscope system, todisconnect the erection circuit.uncalibrated unit A component, circuit, or instrumentthat has never been calibrated or has notrecently been calibrated and, hence, is of questionableaccuracy.uncanny valley According to a theory put forth bycertain Japanese roboticists, a phenomenon thatcan occur among people as technology advances.As machines rapidly get more sophisticated, apoint is reached at which their human users becomeunnerved, partially offsetting the advantagesthe technology has to offer.uncased choke See UNSHIELDED CHOKE.uncased transformer See UNSHIELDED TRANS-FORMER.uncertainty in computation The degree of doubtconcerning the exactness of computations. Thisuncertainty is always greater than that of theroughest measurement used in obtaining data forthe computation. Uncertainty is closely related tothe tolerance of the instruments and formulasused.uncertainty in measurement The estimated maximumamount whereby the numerical value of ameasured quantity can differ from the true value.uncertainty principle The observation that highprecision in the location of an electron is obtainableonly at a sacrifice in the accuracy with whichthe momentum of the electron can be determined,and vice versa.uncharged Without an electric charge, as opposedto discharged (depleted of a charge).unclamp To switch off clamping action in a circuit.See CLAMPER and CLAMPING.uncoated filament 1. A plain filament (i.e., onewithout a coating of electron-increasing material).2. A stripped filament (i.e., one from which theelectron-increasing coating has been burned off).uncompensated Not modified to produce a desiredtype of performance, such as increased bandwidthor reduced temperature sensitivity. Example:an uncompensated amplifier put into servicein the (wide) video band. Compare COMPEN-SATED AMPLIFIER, COMPENSATED CAPACI-TOR, and COMPENSATED DIODE DETECTOR.uncompensated amplifier An amplifier without aprovision for the automatic or manual modificationor correction of its response. Compare COM-PENSATED AMPLIFIER.uncompensated capacitor A fixed or variable capacitorwithout a provision for the automatic ormanual correction or modification of its capacitanceor range or the improvement of its temperaturecoefficient. Compare COMPENSATEDCAPACITOR.uncompensated inductor A fixed or variable inductorwithout a provision for the automatic ormanual correction or modification of its inductanceor range or the improvement of its temperaturecoefficient.uncompensated resistor A fixed or variable resistorwithout a provision for the automatic or manualcorrection or modification of its resistance orrange or the improvement of its temperature coefficient.unconditional branch See UNCONDITIONALJUMP.unconditional jump In computer operations, a programinstruction that interrupts, without a relationaltest being made, the normal, orderedsequence of instructions and gives the address of(usually) the first instruction in a subroutine [e.g.,BASIC’s GOTO (line number)]. Also called unconditionalbranch. Compare CONDITIONAL JUMP.

706 unconditional stability • underloaded amplifierunconditional stability Stability of a system at allfrequencies and ages. Also called absolutestability.unconditional transfer See UNCONDITIONALJUMP.uncontrolled multivibrator A multivibrator thatis not synchronized with a signal source. Alsocalled ASTABLE MULTIVIBRATOR and FREE-RUNNING MULTIVIBRATOR.uncontrolled oscillator See SELF-EXCITED OS-CILLATOR.uncorrected power In an alternating-current circuit,a power value calculated without regard forpower factor (i.e., the volt-ampere product).uncorrected time Local standard time that hasnot been corrected in terms of the distance of thelocality from the nearest standard-time meridian.uncorrected tube A television picture tube operatedwithout antipincushioning magnets.uncoupled mode A mode of vibration existing in asystem concurrent with (but independent of)other modes.undamped galvanometer A galvanometer forwhich no provision has been made to limit overswingor prevent oscillation.undamped meter 1. A meter for which no provisionhas been made to limit overswing or preventoscillation. 2. A meter that is unprotected by ashort circuit for limiting vibratory movement ofthe pointer during transport.undamped natural frequency In the absence ofdamping, the oscillation frequency of a systemhaving one degree of freedom when a transientforce displaces the system momentarily from itsposition of rest.undamped oscillation Continuous-wave oscillation.Also see CONTINUOUS WAVE.undamped output circuit An audio power-amplifieroutput circuit that has not been designed sothat overswing of the loudspeaker cone is prevented.undamped speaker enclosure A loudspeaker cabinetfor which provision has not been made todeaden resonances and other undesired vibration.undamped wave See CONTINUOUS WAVE.undeflected beam A cathode-ray beam or a lightbeam in its normal position of rest (quiescence).underbiased unit A component, such as a transistoror vacuum tube, whose bias voltage or currentis lower than the prescribed value. CompareOVERBIASED UNIT.underbunching Less-than-optimum bunching ofelectrons in a velocity-modulated tube because oflowered buncher voltage.undercompounded generator A generator inwhich the output voltage varies inversely withload resistance.undercoupling Loose coupling, usually of anamount insufficient for optimum signal transfer.undercurrent A current of lower than specifiedstrength. Compare OVERCURRENT.undercurrent relay A relay that is actuated whencoil current falls below a predetermined level.undercut The removal of the metal under the edgeof the resist in a printed circuit by the etchant;thus the cross section of the conductor is reduced.undercutting A phonograph-disc groove that iscut too shallow or with reduced internal movementof the recording stylus.underdamping Insufficient damping of a system(i.e., not enough to prevent output oscillation followingapplication of a transient force).underdriven unit An amplifier, oscillator, ortransducer whose driving signal (current, voltage,power, or other quantity) is lower than the prescribedvalue. Compare OVERDRIVEN UNIT.underexcited Receiving lower-than-normal excitation,as in an underdriven final amplifier of a radiotransmitter. Compare OVEREXCITED.underflow In computer operations, the conditionin which a quantity entered into storage isshorter than the space provided for it (e.g., a 12-digit quantity in a 16-position register).underground antenna A transmitting or receivingantenna installed and operated below ground. Includedare buried antennas and antennas onequipment operated in tunnels, cellars, and similarareas.underground cable A cable that is buried in theearth.underground communication Communicationbetween a transmitter and receiver, both belowthe surface of the earth.underground image The below-ground mirror imageof an antenna; it combines with the actualantenna to form the complete radiation pattern.underground line A power line laid below the surfaceof the earth.underground receiver 1. A receiver situated completelybelow the surface of the earth. 2. A clandestinereceiver.underground reception Reception of an abovegroundstation’s transmissions by an undergroundreceiver. Compare UNDERGROUNDCOMMUNICATION.underground transmitter 1. A transmitter situatedcompletely below the surface of the earth. 2.A clandestine transmitter.under insulation The insulation (usually a strip oftape) laid under a wire brought up from the centerof a coil.underinsulation Inadequate or insufficient insulation.underlap In a facsimile or television picture, acrowding of the scanned lines.underload circuit breaker See CIRCUIT BREAKER.underloaded amplifier 1. An amplifier whose loadresistance (impedance) is less than the prescribedvalue. 2. A power amplifier delivering lessthan its rated output power. Compare OVER-LOADED AMPLIFIER.

underload relay • unequal alternation 707underload relay A relay actuated when circuit currentdrops below a predetermined value. CompareOVERLOAD RELAY.undermodulation Incomplete modulation of a carrierwave. Compare COMPLETE MODULATIONand OVERMODULATION.underpass The crossing of two conductors on asemiconductor wafer, without an electrical connection.underpower relay A relay actuated when powerdrops below a predetermined level. CompareOVERPOWER RELAY.underrate To assign a rating (e.g., current orpower) lower than the quantity of the rating anequipment can handle, or tolerate. For safety orreliability, apparatus sometimes is deliberatelyunderrated—especially in power output and maximumcurrent or voltage.undershoot On an oscilloscope screen or graph, amomentary swing of a current or voltage belowthe reference axis. Compare OVERSHOOT.Relative amplitude+−undershootUndershootTimeundershoot distortion Distortion caused by reductionof the maximum amplitude of a signalwavefront below the steady-state amplitude thatwould be reached by a prolonged signal wave.understudy See BACKUP.underthrow A form of signal distortion that occurswhen the modulating-waveform frequency is toohigh in proportion to the frequency of the wave itself.undervoltage A voltage of lower than specifiedvalue. Compare OVERVOLTAGE.undervoltage protection The automatic disconnectionof a load device from its driving sourcewhen the driving voltage falls below a predetermined(threshold) level. This action is sometimesaccomplished with a Zener diode (whose breakdownvoltage is equal to the threshold voltage) inseries with a disconnect relay.undervoltage relay A relay actuated when voltagedrops below a predetermined level. CompareOVERVOLTAGE RELAY.underwater antenna A transmitting or receivingantenna normally operated in a body of water. Itis usually associated with a submarine.underwater sound projector A hydroacoustictransducer that converts audio-frequency powerinto sound waves, which it radiates through abody of water to a receiver.Underwriters Code The advisory National ElectricalCode adopted by the National Fire ProtectionAssociation; it is often enforced by courts of lawand inspection agencies.Underwriters Laboratories Abbreviation, UL. Aprivate corporation that issues standards ofsafety for electrical components and equipment,and for their operation.undistorted power output For active amplifier devices,a specified maximum audio power outputlevel at which the total distortion does not exceeda specified low value (i.e., at which operation ispractically distortionless).undistorted wave 1. A sine wave that contains essentiallyno harmonic energy. 2. A nonsinusoidalwave whose shape corresponds exactly to theequation for the wave.undisturbed-one output In digital-memory operations,the one-output of a magnetic cell or othermemory unit that has received a full, rather thanpartial, read pulse. Compare UNDISTURBEDOUTPUT SIGNAL.undisturbed output signal In digital-memory operations,the output of a magnetic cell or othermemory unit previously set to one or zero, andthat has received a full, rather than partial, readpulse. Also called undisturbed response voltage.undisturbed response voltage See UNDIS-TURBED OUTPUT SIGNAL.undisturbed-zero output In digital-memory operations,the zero-output of a magnetic cell or othermemory unit that has received a full, rather thanpartial, read pulse. Compare UNDISTURBEDOUTPUT SIGNAL.Universal Truth Machine (UTM) A hypotheticalcomputer capable of proving any logically truestatement. According to the Incompleteness Theoremproved in 1930, such a machine cannot existfor a first-order logical system.undoped Pertaining to a pure semiconductor material(i.e., one containing no lattice-altering additives).undulating current A current, such as an alternatingor composite current, whose value oscillatesin the manner of a wave.undulation A wavelike alternation.undulatory theory The theory that light is transmittedby means of an undulating (wavelike) movementbetween the luminous object and the eye.unequal alternation In an alternating-currentwaveform, a form of asymmetry in which the positiveand negative half-cycles are not exact mirrorimages; they might vary in peak amplitude, duration,shape, etc.

708 unexpected halt • unidirectional responseAmplitudePositivehalf-cyclesNegativehalf-cyclesunequal alternationTimeunexpected halt During a computer program run,an undirected (unplanned) halt (e.g., one causedby a machine fault or program bug).unfiltered Not having been subjected to filteringaction. An example is the pulsating-directcurrentoutput of an alternating-current-operatedrectifier circuit.unfocused light source In a photoelectric system,a light source that delivers diffused light.unformed rectifier A newly fabricated semiconductorrectifier (especially selenium) or an electrolyticrectifier before it has been electroformedfor improved characteristics.unfurlable antenna An antenna that can be unrolledto increase its length, thereby lowering itsfundamental resonant frequency; it can also berolled up to decrease its length and increase itsfundamental resonant frequency.ungrounded item A component, circuit, or circuitpoint having no connection to ground, except aninadvertent one through common impedances orleakage paths.ungrounded system A system operated entirelyabove ground, any path to ground being accidental.unguided Without electronic guidance (pertainingto missiles, rockets, satellites, etc.).uni- A prefix (combining form) meaning one or singleand appearing in a number of electronicterms. See the following several definitions for examples.uniaxial 1. Having one axis. 2. Referred to one axis.uniaxial crystal A crystal having one optical axis.unibivalent electrolyte An electrolyte, such assodium carbonate (Na 2 CO 3 ), that dissociates intotwo univalent ions and one bivalent ion.Unicode Trade name for a 16- or 32-bit binary digitalcode that allows for the representation ofcharacters and glyphs in all the written languagesof the world. The 16-bit code contains65,536 code points; the 32-bit version containsmore than 1 million code points.uniconductor cable A cable having a single conductor,usually of braided or twisted wires.uniconductor waveguide A waveguide consistingof a metal sheath deposited on a solid dielectricof cylindrical or rectangular crosssection.unidentified flying object Abbreviation, UFO. Anobject claimed to have been seen in flight, but notidentified by reliable authorities as any knowntype of vehicle.unidirect To commutate (see COMMUTATOR).unidirectional 1. Flowing or acting in one directiononly. 2. Having a radiation or response sensitivitythat is maximum in primarily onedirection in space.unidirectional antenna See UNIDIRECTIONALARRAY.unidirectional array A beam antenna that radiatesin one direction only, or principally in one direction,unless rotated.unidirectional conductivity Electrical conductivityin only one direction; it characterizes an idealdiode.unidirectional coupler A directional coupler samplingonly one direction of transmission.unidirectional current A current that flows alwaysin the same direction, although it mightfluctuate in intensity.unidirectional elements Circuit elements, suchas diodes or transistors, that transmit energy inonly (or best in) one direction.unidirectional field-effect transistor See UNI-LATERAL FIELD-EFFECT TRANSISTOR.unidirectional hydrophone An underwater unidirectionalmicrophone.unidirectional loudspeaker A loudspeaker thatradiates sound substantially in one direction.unidirectional microphone A microphone that receivessound waves from one direction, usuallyfrom the front, minimum response usually beingfrom the sides and back.unidirectional network A network that transmitssignals in only one direction (i.e., the input andoutput terminals are not interchangeable).unidirectional pattern For a transducer (such asan antenna, speaker, or microphone), a radiationor response pattern that shows a pronouncedmaximum in one direction only.unidirectional pulse A single-polarity pulse.unidirectional pulse train A series of unidirectionalpulses.unidirectional response For a receiving transducer,such as an antenna or microphone, aresponse pattern that shows a pronouncedmaximum in one direction only.

unidirectional speaker • unilateral field-effect transistor 709270°0°180°unidirectional pattern90°unidirectional speaker See UNIDIRECTIONALLOUDSPEAKER.unidirectional transducer A transducer that operatesin one direction only (i.e., its input andoutput cannot be interchanged).unidirectional voltage A voltage that never changespolarity, although it might fluctuate in value.UNIFET Abbreviation of UNIPOLAR FIELD-EFFECT TRANSISTOR. (Also, UFET.)unified-field theory A theory, as yet unproved,that all forces in nature are interrelated and arecontrolled by the same causes and factors. AlbertEinstein worked on this theory after he successfullydeveloped the theories of relativity.unifilar Having (or wound as) one fiber, wire, filament,or thread.unifilar magnetometer A magnetometer in whicha bar is suspended at its center of gravity by asingle thread.unifilar suspension A method of meter constructionin which the moving part is suspended by asingle filament. The torque might be provided bythis filament or by a spring or other resisting device;the greater the displacement, the greater thetorque.uniform circular motion Motion at a uniform rateand describing a circle (e.g., a motor armature rotatingat a constant speed).uniform electric field An electric field in which allthe lines of flux are straight and parallel, and inwhich the electrostatic force has the same valueat all points (e.g., the field between two oppositelycharged, flat, parallel plates).uniform field See UNIFORM ELECTRIC FIELDand UNIFORM MAGNETIC FIELD.uniform frequency response Frequency responsethat is flat throughout a specified range. Such responseis characterized by the transmission of asignal with no introduced amplitude or phasedistortion.uniform line A transmission line having identicalelectrical properties over its entire length.uniform magnetic field A magnetic field in whichall the lines of flux are straight and parallel, andin which the magnetic force has the same value atall points.uniform plane wave A free-space plane wave at aninfinite distance from the generator, having constant-amplitudeelectric and magnetic field vectorsover the equiphase surfaces.uniform precession In regions of the uniformmagnetic field of a sample of material, the state inwhich the magnetic moments of all atoms areparallel and precess in phase around the magneticfield.uniform waveguide A waveguide having constantelectrical and physical characteristics along itsaxis.uniground 1. The grounding of a circuit at onepoint to reduce susceptibility to hum and noise.2. The point at which such a connection is made.unijunction transistor A semiconductor deviceconsisting of a thin silicon bar on which a singlepn junction acting as an emitter is formed nearone end. Two bases are provided—each an ohmicconnection made to one end of the bar. Alsocalled double-base diode.PictorialBase 1nBase 2pBase 1Base 2EmitterSymbolunijunction transistorEmitterunilateral area track A film sound track havingmodulation on only one edge of the opaque area.unilateral bearing In radio direction finding, abearing obtained with a finder that produces unilateralresponse and thereby eliminates 180-degree error.unilateral conductivity See UNIDIRECTIONALCONDUCTIVITY.unilateral element See UNIDIRECTIONALELEMENTS.unilateral field-effect transistor A field-effecttransistor whose source and drain terminals cannotbe interchanged. Also called ASYMMETRICALFIELD-EFFECT TRANSISTOR. Compare SYM-METRICAL FIELD-EFFECT TRANSISTOR.

710 unilateralization • unit recordunilateralization A system of neutralization usedin transistor amplifiers at very-high and ultrahighfrequencies, in which the internal capacitiveand resistive components are compensated bythe neutralization feedback.unilateralized amplifier A transistor amplifier inwhich both the internal resistive and capacitivecomponents are compensated by the neutralizingcircuit. Also see UNILATERALIZATION.unilateral network See UNIDIRECTIONAL NET-WORK.unilateral transducer See UNIDIRECTIONALTRANSDUCER.uninterruptible power supply Abbreviation, UPS.A device that provides a continuous utility currentto electronic devices in the event of a utilitypower dip or blackout. It contains a battery and apower inverter. These devices are used extensivelyin personal computing to prevent loss ofdata that could otherwise result from a utilitypower failure.union 1. The logical inclusive-OR operation. 2. SeeBOND, 1.union catalog In computer operations, the compiledlist of the contents of two or more tape ordisk libraries.unionic material A material having no ions (i.e.,one in which all atoms are neutral).uniphase antenna See COLLINEAR ANTENNA.UNIPOL Acronym for universal problem-orientedlanguage, a high-level computer-programminglanguage.unipolar 1. Having or using a single pole or polarity.2. Operating with one class of current carrier.unipolar armature An electric-motor armaturethat maintains its polarity throughout a completerevolution.unipolar field-effect transistor See UNIPOLARTRANSISTOR.unipolar induction Induction by only one pole of amagnet.unipolar input The input circuit of an instrumentor device designed for input signals of one polarityonly.unipolar pulse A pulse in which the current flowsin only one direction, or in which the voltage occurswith only one polarity.unipolar transistor A field-effect transistor (FET).It utilizes only one kind of carrier (electrons in then-channel FET, holes in the p-channel FET).Compare BIPOLAR TRANSISTOR.unipolar winding The winding of a UNIPOLAR AR-MATURE.unipole 1. An all-pass filter having one pole andfor which there is one zero. Also see ALL-PASSFILTER, POLES OF IMPEDANCE, and ZEROS OFIMPEDANCE. 2. A hypothetical, omnidirectionalantenna.unipotential cathode An indirectly heated tubecathode. Also called equipotential cathode. See IN-DIRECTLY HEATED CATHODE.unit 1. A named, single magnitude adopted as astandard by physical measurement. Thus, theunit of current is the ampere, the unit of frequencyis the hertz, the unit of capacitance is thefarad, etc. Also see ABSOLUTE SYSTEM OFUNITS, INTERNATIONAL SYSTEM OF UNITS,and CENTIMETER-GRAM-SECOND. 2. A singlepiece or assemblage of equipment, such as amplifier,converter, power supply, etc. 3. A quantity of1 implied when unit is the adjective describing aquantity (e.g., unit length means a distance of1 meter, 1 foot, etc.).unitary code In computer operations, a codebased on one digit. The number of times the digitis repeated indicates a given number.unit cell In crystals, the simplest polyhedron exhibitingall the structural features and which isrepeated to form the crystal lattice.unit charge See UNIT ELECTROSTATIC CHARGE.unit electric charge See UNIT ELECTROSTATICCHARGE.unit electrostatic charge An electrostatic pointcharge that will attract or repel a point charge ofequal strength 1 centimeter away in a vacuum,with a force of 1 dyne (10 –5 newton).unit function Symbol, H or 1. A time-dependentquantity that is zero before the start of a period(when time t is zero) and 1 for all values of tgreater than zero. It is approximated by a squarewave, and is useful in solving problems involvingtransients.unit length 1. A fundamental unit of distance ortime, used for reference in a measuring system.For example, in the mks (meter-kilogram-second)system, the distance unit length is the meter, andthe time unit length is the second. 2. The durationof a fundamental element, or bit, in a binarycodetransmission system.unitized construction The fabrication of an electronicequipment in subassemblies (such asmodules) that can be tested separately, and thatcan be easily replaced (plugged in) in the event ofindividual failure.unit line A line of electric or magnetic flux.unit magnetic pole See UNIT POLE.unit matrix A matrix whose main diagonal terms(all) are all at unity, the other terms being zero.unitooth Pertaining to the use in electrical machineryof one slot per pole per phase.unitor See OR GATE.unit pole The strength (magnetic flux) of a (hypothetical)magnetic pole that will attract or repela pole of equal strength 1 centimeter away in avacuum, with a force of 1 dyne; 1 unit pole =1.257 × 10 –7 weber.unit-ramp function A function whose value is zerobefore time t, and becomes equal to the time measuredfrom t at all other instants. The integral ofthe UNIT FUNCTION.unit record In computer operations, a completerecord consisting of many data elements and

unit record • universal-wound coil 711contained within one storage medium, such as amagnetic disk.unitrivalent electrolyte An electrolyte, such assodium phosphate (Na 3 PO 4 ), that dissociates intothree univalent ions and one trivalent ion.units position In a numbering system, the rightmostposition in a multidigit whole number; or, ifthe number contains a radix point, the digit immediatelyto the left of the radix point.unit-step function See UNIT FUNCTION.unitunnel diode A special form of semiconductordiode, used as an oscillator at ultra-high and microwavefrequencies.unit vector A vector that is 1 unit long in terms ofthe scale representing a factor of interest, andhas the same direction as the vector of interest.For example, if u is a unit vector, then 5u representsa vector having the same direction and fivetimes the magnitude of u.unity 1. The figure 1 implied. 2. A ratio of 1:1. 3. Again of 0 dB.unity coupling Tight coupling between two coils,the turns ratio often being 1 to 1 and the coils alwaysbeing closely interwound.Inputunity couplingOutputunity gain The condition in which the output amplitudeis the same as the input amplitude; thatis, a gain factor of 1, or 0 dB.unity-gain bandwidth 1. For an active filter, thebandwidth between the frequencies at which thegain is 0 dB. 2. For an operational amplifier havinga rolloff of 6 dB per octave, the frequency atwhich the open-loop gain is 0 dB.uni-univalent electrolyte An electrolyte that dissociatesinto two univalent ions [e.g., sodiumchloride (NaCl)].univ Abbreviation of universal.UNIVAC The name given to a family of digital computersand data-processing systems. The name isan acronym for Universal Automatic Computer.univalent Having a valence of 1. For example, in thecompound sodium chloride (NaCl), the sodium ion(Na+) and the chlorine ion (Cl–) are univalent.universal bridge A bridge for the measurement ofcapacitance (C), inductance (L), and resistance(R). Such a bridge often is a skeletal foundationcircuit with a provision for plugging L, C, or Rstandards in the various arms, as required. Alsocalled general-purpose bridge.universal coordinated time Abbreviation, UTC.Greenwich mean time coordinated by the InternationalTime Bureau for broadcast as signals(on WWV, for example).universal coupler 1. An arrangement of one ormore inductors and variable capacitors formatching a transmitter to virtually any antenna.One such device is the Collins coupler. 2. A devicefor matching numerous generator outputimpedances to numerous load impedances.universal filter An active filter that is continuouslytunable over a wide frequency range andthat offers low-pass, high-pass, bandpass, andband-suppression functions.universal frequency counter A digital frequencymeter usable at radio and audio frequencies.universal motor A small series-wound motor thatruns on direct current or single-phase alternatingcurrent. This type of motor is used in manyhousehold appliances and in motor-driven tools,such as portable electric drills, polishers, etc.universal output transformer An output transformerhaving a number of taps on its primaryand secondary windings for use with a wide varietyof impedances.universal product code Abbreviation, UPC. Thevariable-width-bar code appearing on price tagsor product labels, and yielding such informationas cost, size, and color when read by supermarket(or other retailer) optical characterrecognitionequipment. Also called universalvendor marking (UVM).universal receiver A radio receiver that can be operatedeither from alternating current or directcurrent (i.e., from utility power or battery power).universal shunt See AYRTON-MATHERGALVANOMETER SHUNT.universal time See GREENWICH MEAN TIME.universal transformer See UNIVERSAL OUTPUTTRANSFORMER.universal transmitter A radio transmitter thatcan be operated either from alternating current ordirect current (i.e., from utility power or batterypower).universal Turing machine In computer theory, aTURING MACHINE capable of simulating otherTuring machines.universal vendor marking See UNIVERSALPRODUCT CODE.universal winding A zigzag winding used to reducethe distributed capacitance of multilayer coils.Also called lattice winding and honeycomb winding.universal-wound coil A coil using a universalwinding. Such coils are common in intermediatefrequency(IF) transformers and in radiofrequency(RF) chokes.

712 univibrator • unsaturated operationunivibrator See MONOSTABLE MULTIVIBRATOR.unknown quantity Any variable quantity soughtin calculations; it is usually represented by lowercaseitalic letters from the second half of the alphabet(e.g., x, y, z).unlike charges Dissimilar electric charges (i.e.,positive and negative).unlike poles Dissimilar poles, such as the northand south poles of a magnet.unload 1. To remove data from a file. 2. To disconnectthe load from a circuit.unloaded amplifier See UNTERMINATED AMPLI-FIER.unloaded antenna An antenna operated withoutadded inductance or capacitance.unloaded-applicator impedance In dielectricheatingoperations, the unloaded impedance ofapplicator electrodes placed in their normalworking position without the dielectric-materialload in place.unloaded battery 1. A battery in the standby condition.2. A battery tested for open-circuit terminalvoltage (i.e., with no load, except the voltmeter).unloaded generator See UNTERMINATED GEN-ERATOR.unloaded line See UNTERMINATED LINE.unloaded potentiometer A potentiometer or voltagedivider with an open-circuited output.unloaded Q The Q factor (degree of selectivity) of acoil or tuned circuit that is activated by a signal,but that delivers no output to a load.unloaded transmitter A transmitter operated underopen-circuit conditions (i.e., without an externalload, such as an antenna or dummy resistor).unmanned factory A manufacturing plant runlargely by robots and computers. There mustgenerally be at least one human being, whosejob(s) is/are to oversee and maintain the operationof the machines.unmatched elements 1. Components (such as resistors,capacitors, semiconductors, etc.) havingdifferent values. 2. Mating elements or devicesnot having the same impedance. Also calledMISMATCH.unmodulated carrier See CONTINUOUS WAVE.unmodulated current A current whose characteristics(amplitude, phase, or frequency) are notvaried by a signal or by noise.unmodulated voltage A voltage whose characteristics(amplitude, phase, or frequency) are notvaried by a signal or by noise.unmodulated wave See CONTINUOUS WAVE.unnilennium See MEITNERIUM.unnilhexium See SEABORGIUM.unniloctium See HASSIUM.unnilpentium See DUBNIUM.unnilquadium See RUTHERFORDIUM.unnilseptium See BOHRIUM.unode See MONODE.unpack In computer operations, to remove datafrom a storage location into which, with otherdata, it has been packed (as a memory-conservationmeasure).unpolarized light Light in which the wave orientationis random around the axis of the beam.unpolarized plug A plug that can be inserted intoa socket in two or more different ways, thus increasingthe likelihood of a wrong connection.Compare POLARIZED PLUG.unpolarized receptacle A receptacle into which aplug can be inserted in two or more differentways, thus increasing the likelihood of a wrongconnection. Also called UNPOLARIZED SOCKET.Compare POLARIZED RECEPTACLE.unpolarized relay A relay that always closes inthe same direction, regardless of the direction ofcurrent in its coil. Also called nonpolarizedrelay.unpolarized socket A socket into which a componentor plug can be inserted in two or more differentways, thus increasing the likelihood ofwrong connections. Also called UNPOLARIZEDRECEPTACLE.unprotected antenna An outside antenna operatedwithout a lightning arrester or groundingswitch. Increases the risk of damage to equipment,such as radio receivers and transmitters,connected to the antenna. It also increases thedanger to personnel using the equipment.unrationalized systems of units Collectively, theabsolute centimeter-gram-second (cgs) electrostaticsystem of units, the absolute cgs electromagneticsystem of units, and the absolutemeter-kilogram-second (mks) system of units.unreflected ray See UNREFLECTED WAVE.unreflected wave 1. See DIRECT WAVE. 2. SeeGROUND WAVE. 3. An electromagnetic wave thatpenetrates the ionosphere and passes into space.unregulated Not held to a constant value. For example,an unregulated voltage is free to fluctuatein value.unregulated power supply A power supply whoseoutput current or voltage is not automaticallyheld to a constant value. Compare CONSTANT-CURRENT SOURCE and CONSTANT-VOLTAGESOURCE.uns Abbreviation of UNSYMMETRICAL.unsaturated core A magnetic core operated belowthe point of saturation (i.e., below the point atwhich an increase in coil current produces nofurther increase in magnetization of the core).unsaturated logic A digital-logic scheme in whichthe switching devices operate between the saturatedand cut-off conditions during either or bothof the high and low states.unsaturated operation Operation of a device at apoint below saturation [i.e., below the point atwhich (1) an increase in voltage produces no furtherincrease in current, or vice versa, or (2) anincrease in coil current produces no further increasein magnetization of a core]. CompareSATURATED OPERATION.

unsaturated standard cell • ununoctium 713Collector currentUnsaturatedoperationBase voltageunsaturated operationSaturationpointunsaturated standard cell See STANDARD CELL.unshielded cable A cable, such as a twisted pair ora multiwire twist, lacking a shielding jacket. Unlessspecial precautions are taken, such as transposingconductors, such a cable is susceptible tostray pickup and is capable of radiation.unshielded choke An uncased choke (i.e., one withouta protective and shielding metal housing).unshielded coil An inductor without a fieldconfiningenclosure.unshielded probe An instrument probe that has noshielding enclosure. Such a probe is desirable forsome tests, but it is subject to antenna-pickup effect,body capacitance, and stray-field pickup.unshielded stage In electronic equipment, a stageoperating entirely in the open (i.e., without electrostaticor magnetic shielding enclosures). It is,therefore, susceptible to stray pickup and is capableof radiation.unshielded transformer 1. An uncased transformer(i.e., one without a protective and shieldingmetal housing). 2. A transformer having noelectrostatic shield between its windings.unshift The mechanical action in a teletypewriterwhen the carriage moves from the figures positionto the letters position.unshunted current meter A single-rangeD’Arsonval milliammeter or microammeter thathas no shunt resistor. The resistance of the instrumentis, therefore, equal to the resistance ofthe movable coil.unsolder To separate wires, contacts, or fasteningsby melting the solder that holds them together.Also called DESOLDER.unsophisticated electronics Electronics theoryand operations of the simplest kind, involving littleor no mathematics. It is generally intended fora hobbyist audience. Compare SOPHISTICATEDELECTRONICS.unstable oscillation 1. Relaxation oscillation.2. The periodically interrupted oscillation characteristicof a blocking oscillation.unstable region The negative-resistance portion ofan N- or S-shaped response curve.unstable servo A servo having unlimited outputdrift.unstable state A condition, such as a negativeresistanceregion, that is difficult to maintainand often results in oscillation. The negativeresistanceregion of the tunnel diode forwardconductioncurve is evidence of such a state.Compare STABLE STATE.untapped winding A winding having two terminals,one at either end, and no intermediate terminalsor connections. Also called untapped coil.unterminated amplifier An amplifier operatedwithout a load device (i.e., under open-circuitoutput conditions).unterminated generator A generator operatedwithout a load device (i.e., under open-circuitoutput conditions).unterminated line A transmission line that is notterminated with an impedance (i.e., an openendedline).untriggered flip-flop A flip-flop that, at a particularinstant, receives no actuating pulse, and that,therefore, does not change state.untuned amplifier A radio-frequency amplifierthat is not tuned to a single frequency, but hasuseful gain over a wide band of frequencies. Examplesare the distributed amplifier and the videoamplifier.untuned filter See ALL-PASS FILTER.untuned line An aperiodic transmission line (i.e.,one that is only tuned to a particular frequencyby its own distributed characteristics).untuned transformer A transformer having simpleprimary and secondary windings and no tuningdevices (such as capacitors in series orparallel with the windings), and designed so thatits natural resonant frequency (because of distributedcapacitance) lies outside the specifiedrange of operation.ununbium Symbol, Uub. Atomic number, 112.The most common isotope has atomic weight277. Classified as a transition metal. It is humanmadeand not known to occur in nature.ununhexium Symbol, Uuh. Atomic number, 116.The most common isotope has atomic weight289. First reported in January 1999. It is a decompositionproduct of ununoctium, and it inturn decomposes into ununquadium. It is notknown to occur in nature.ununnilium Symbol, Uun. Atomic number, 110.The most common isotope has atomic weight269. Classified as a transition metal. It ishuman-made and not known to occur innature.ununoctium Symbol, Uuo. Atomic number, 118.The most common isotope has atomic weight293. It is the result of the fusion of krypton andlead, and decomposes into ununhexium. It is notknown to occur in nature.

714 ununquadium • uranium raysununquadium Symbol, Uuq. Atomic number, 114.The most common isotope has atomic weight285. First reported in January 1999. It is humanmade,and not known to occur in nature.unununium Symbol, Uuu. Atomic number, 111.The most common isotope has atomic weight272. Classified as a transition metal. It is humanmade,and not known to occur in nature.unused time See UNATTENDED TIME.unweighted average In the statistical analysis ofdata, an average calculated from terms notweighted by a factor. Compare WEIGHTED AV-ERAGE. Also see UNWEIGHTED TERM.unweighted term In the statistical analysis ofdata, a term not operated upon by a weightingfactor. Therefore, it has no extraordinary influenceon a final result, such as an average. CompareWEIGHTED TERM.unwind To eliminate all redundant or unnecessaryoperations in a computer system.up-and-downer amplifier In broadcasting andsound amplification, an auxiliary amplifier thatallows the level of sound effects and backgroundmusic to be controlled automatically without disturbingthe dialogue levels.UPC Abbreviation of UNIVERSAL PRODUCT CODE.upconv Abbreviation of UP CONVERTER.up convert In superheterodyne conversion, to heterodynea signal to an intermediate frequencyhigher than the signal frequency. CompareDOWN CONVERT.update In data-processing operations, to make afile reflect the current status of pertinent informationby using transactions for its modification.up-down counter See BIDIRECTIONAL COUNTER.uplink 1. The signal sent up to a satellitetransponder. 2. The frequency of the signal sentup to a satellite transponder.uplink frequency 1. The specific frequency of agiven signal sent up to a satellite transponder.2. The band of frequencies sent up to a satellitetransponder. There can be many signals in anuplink; there can also be many different stationssending uplink signals within the band.uplink power 1. The power output of the transmittersending the signal up to a satellite transponder.2. The effective radiated power of the stationsending the uplink signal.uplink station Any station that transmits a signal,or group of signals, up to a satellite transponder.upper atmosphere See IONOSPHERE, STRATO-SPHERE, and TROPOSPHERE.upper sideband Abbreviation, USB. In an amplitude-modulatedwave, the component whose frequencyis the sum of the carrier frequency andthe modulation frequency. Compare LOW-ERSIDEBAND.upper sideband, suppressed carrier Abbreviation,USSC. A single-sideband transmission techniquein which the upper sideband is transmitted, thelower sideband is suppressed, and the carrier issuppressed. Compare DOUBLE SIDEBAND,SUPPRESSED CARRIER, LOWER SIDEBAND,and SUPPRESSED CARRIER.Abbreviation for UNINTERRUPTIBLE POWERSUPPLY.UPSupside down 1. In radioteletype, a signal in whichthe MARK and SPACE signals are reversed in frequency.2. In single sideband, reception of a signalon the wrong sideband, resulting in “monkeychatter.”up time See SERVICEABLE TIME.upturn A usually sudden rise in a performancecurve. Compare DOWNTURN.upward modulation Modulation in which the outputcurrent of the modulated circuit increasesduring modulation. Compare DOWNWARD MOD-ULATION.UR Abbreviation of ULTRARED.uranium Symbol, U. A radioactive metallicelement. Atomic number, 92. Atomic weight,238.03.uranium 235 Symbol, U-235. An isotope of uraniumof mass number 235, used in atomic bombsand atomic power plants.uranium 238 Symbol, U-238. An isotope of uraniumof mass number 238, which, under fast-neutronbombardment, decays to become neptunium andthen plutonium (of mass number 239).uranium metals The group of heavy, radioactiveelements of atomic numbers 89 through 103.Also called the actinide series.uranium rays The ionizing radiation emitted byuranium. In 1896, Antoine Henri Becquerel

uranium rays • UVM 715observed that uranium salts emit rays (later identifiedas alpha, beta, and gamma) that can passthrough bodies opaque to light and are capable ofexposing a photographic plate. Also called Becquerelrays.urea formaldehyde resin A thermosetting, syntheticresin used in the manufacture of a numberof plastic dielectric bodies and formed by the reactionof urea with formaldehyde.urea plastic Any of several thermosetting plasticshaving a urea base and used as a dielectric andas a molding material in electronics (e.g., ureaformaldehyde resin).URSI Abbreviation of Union Radio Scientifique Internationale(International Radio Scientific Union).ursigram A broadcast message giving informationon sunspots, radio propagation, terrestrial magnetism,and related subjects. Also see URSI.usable frequency 1. Any frequency at which communicationscan be maintained between twopoints via ionospheric propagation. 2. Any frequencyat which a communications system is operational.usable sample 1. The portion of an oscilloscope ormonitor display that is visible on the screen. 2. Instatistics, a sample that is considered valid forcalculation purposes.USB Abbreviation of UPPER SIDEBAND.user friendliness 1. For electronic equipment andsystems, the quality of being easy for people tooperate. 2. The relative ease with which a machine,especially a computer, can be operated bypeople.useful life The elapsed time between the installationof an expendable component, circuit, or system,and the time it must be replaced.useful line In television, the portion of a scanningline that can be used for picture signals. Alsocalled AVAILABLE LINE.user group A group of hobbyists or company representativeshaving in common the ownershipand/or use of a specific brand of computer, andwho meet or otherwise interact to share their expertisewith, or programs, for, the machine. Alsoapplicable to similar groups of programmablecalculatorowners.user’s library A compilation of programs suppliedto (by the vendor) or generated by a user group.USM Abbreviation of underwater-to-surface missile.USSC Abbreviation of UPPER SIDEBAND, SUP-PRESSED CARRIER.UTC Abbreviation of UNIVERSAL COORDINATEDTIME.utility 1. An organization providing a public service,such as electric power or electronic communications.2. In computer operations, a programor set of programs intended for diagnosingand/or correcting hardware and software problems.utility box A general-purpose aluminum or steelbox, supplied in various convenient sizes (paintedor unpainted), used as a housing or shield forelectronic equipment.utility factor For a transformer used in a directcurrent(dc) power supply, the ratio of dc outputto required kilovolt-ampere (kVA) capacity.utilization factor See UTILITY FACTOR.UTL Abbreviation of unit transmission loss.UUM Abbreviation of underwater-to-underwatermissile.UV 1. Abbreviation of ULTRAVIOLET. 2. Abbreviationof UNDERVOLTAGE.Uvicon A television camera tube in which a conventionalvidicon scanning section is precededby an ultraviolet-sensitive photocathode, anelectron-accelerating section, and a special target.Uviol lamp An ultraviolet lamp using uviol glass—a special glass that is transparent to ultravioletrays.UVM Abbreviation of UNIVERSAL VENDORMARKING.

V 1. Abbreviation of VOLT. 2. Symbol (ital) forVOLTAGE or POTENTIAL. 3. Symbol for VANA-DIUM. 4. Symbol for VOLUME. 5. Symbol (ital)for RELUCTIVITY. 6. Abbreviation of VERTICAL.(Also, vert.)v 1. Abbreviation of VELOCITY. 2. Abbreviation ofVECTOR.VA Abbreviation of VOLT-AMPERE.V/A Abbreviation of volts per ampere (ohms).VAC Abbreviation of vector analog computer.vac Abbreviation of VACUUM.V ac Symbol for AC VOLTS. (Also, Vac.)vacancy In a crystal lattice, a position not occupiedby a nucleus.BondsVacanciesNucleivacancyvacuum A space from which all air and other gaseshave been removed to the greatest practicable extent.Some electronic parts, such as the elementsof an electron tube, are housed in an evacuatedspace to protect them from the deterioration thatwould result from open-air operation.vacuum capacitor A plate- or concentric-cylindertypecapacitor sealed in an evacuated glass tubeor bulb. The vacuum acts as the dielectric andprovides a dielectric constant of 1 and very highvoltage breakdown.vacuum deposition The electrical application of alayer of one material (such as a metal) to the surfaceof another (the substrate), carried out in avacuum chamber (e.g., evaporation and sputtering).Also see DEPOSITION and EVAPORATION,1.vacuum envelope The shell or tube of an electrontube, X-ray tube, or other electron device that requiresa vacuum.vacuum evaporation A method of manufacturingthin-film circuits by vaporizing a substance, andletting it accumulate or condense on a base.vacuum gauge An instrument for measuring thevacuum in a device being evacuated. One of theseveral varieties of this gauge uses the elementsof a triode, which are sealed in part of the vacuumsystem, some characteristic of the tube beingcontinuously monitored as the vacuumpumping progresses. Another uses a thermistorsealed in part of the system; the resistance of thethermistor changes proportionately during thevacuum pumping.vacuum impregnation The impregnation of a device(such as a capacitor, transformer, or chokecoil) in a vacuum chamber. The process causesthe pores in the device and its insulating materialsto be completely filled with the impregnant.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

vacuum level • V antenna 717vacuum level 1. The pressure, in millimeters ofmercury (mm/Hg). Normal atmospheric pressureis 760 mm/Hg. A perfect vacuum would be representedby 0 mm/Hg. 2. The proportion, or percentage,of normal atmospheric pressure in agiven environment.vacuum phototube A phototube enclosed in anevacuated envelope, as opposed to one that isgas-filled.vacuum pump A pump for removing air and gasesfrom electron tubes, X-ray tubes, lamp bulbs, etc.Such pumps include mechanical types, diffusiontypes, and combinations of these. Also see DIF-FUSION PUMP.vacuum range The range of a communicationssystem if propagation takes place through aperfect-vacuum (theoretical) medium.vacuum seal An airtight seal between adjoiningparts in an evacuation system.vacuum switch A switch that is enclosed in a vacuumbulb or tube to reduce contact sparking.vacuum thermocouple A thermocouple enclosedin a vacuum bulb with a small heater element.Radio-frequency current passed through theheater raises its temperature and causes thethermocouple to generate a proportional directcurrentvoltage.vacuum tube An electron tube from which virtuallyall air and gases are removed. Also see ELEC-TRON TUBE.vacuum-tube amplifier An amplifier using one ormore vacuum tubes, rather than semiconductordevices.vacuum-tube bridge A special bridge for determiningvacuum-tube characteristics by null methods.vacuum-tube characteristics The operating parametersof a vacuum tube, such as plate current,grid voltage, input resistance, interelectrodecapacitances, amplification factor, transconductance,etc., that describe tube performance.vacuum-tube coefficients See VACUUM-TUBECHARACTERISTICS.vacuum-tube current meter An ammeter, milliammeter,microammeter, or nanoammeter embodyingan amplifier that uses one or morevacuum tubes. Also see ELECTRONIC CURRENTMETER.vacuum-tube modulator A circuit using one ormore vacuum tubes to impress a modulating signalon a carrier.vacuum-tube rectifier 1. An alternating-to-directcurrentconverter circuit using one or more vacuumtubes, rather than gas tubes orsemiconductor devices. 2. A rectifier tube.vacuum-tube sweep A sweep oscillator using avacuum tube, rather than a gas tube. Also calledHARD-TUBE SWEEP.vacuum-tube voltmeter Abbreviation, vtvm. Avoltmeter using a tube-type amplifier. Also seeELECTRONIC VOLTMETER.val Abbreviation of VALUE.valence A unit showing the degree to which elementsor radicals (replaceable atoms or groups ofatoms) will combine to form compounds.valence band In the energy diagram for a semiconductor,the band of lowest energy. This band liesbelow the forbidden band (energy gap), which isbelow the conduction band. Also see ENERGYBAND DIAGRAM.valence bond In a semiconductor material, an interatomicpath over which shared electronstravel.valence electrons Electrons in the outermost orbitsof an atom. These electrons determine thechemical and physical properties of a material.Also see FREE ELECTRON.valence shells See ELECTRON SHELLS.validate To check data for correctness.validity 1. Correctness or accuracy of data. 2. Thelogical truth of a derivation or statement, basedon a given set of propositions.valley A dip between adjacent peaks in a curve orwave.valley current In a tunnel diode, the current at thevalley point.valley point The lowest point of finite current onthe current-voltage response curve of a tunneldiode. Immediately before this point, current decreaseswith increasing applied voltage (an indicationof negative resistance). Beyond this point,however, the current again increases with increasingvoltage. Compare PEAK POINT.valley voltage In a tunnel diode, the voltage at thevalley point.value 1. The level or magnitude of a quantity (e.g.,voltage value). 2. The worth of a system, procedure,device, etc., in terms of goal fulfillment orother criterion.valve Variation (Brit.) of ELECTRON TUBE. Theterm was applied to the first tube, a diode (theFleming valve), and is descriptive of the action ofa tube (a controller of electric current), ratherthan its appearance.vanadium Symbol, V. A metallic element. Atomicnumber, 23. Atomic weight, 50.94.Van Allen radiation belts Two high-altitude zonesthat surround the earth and consist of highenergysubatomic particles. These belts wereonce thought to preclude space travel by humansbeyond the immediate vicinity of the earth.Van de Graaff generator See BELT GENERATOR.vane-anode magnetron A magnetron having planeparallel walls between adjacent cavities.vane attenuator A waveguide attenuator consistingessentially of a slab (vane) of resistive materialthat slides laterally through the waveguide.vane instrument See IRON-VANE METER.vane-type magnetron See VANE-ANODE MAG-NETRON.vane-type meter See IRON-VANE METER.V antenna See VEE ANTENNA.

718 vapor lamp • variable inductorvapor lamp A discharge lamp consisting essentiallyof a glass tube filled with a small amount ofgas under low pressure and some element, suchas mercury or sodium. A high voltage is appliedbetween electrodes sealed into each end of thetube. The voltage causes the element to vaporize.This, in turn, ionizes the gas, causing it to glow.vapor pressure In a confined medium, the pressureof a gas, measured in atmospheres, poundsper square inch, or millimeters of mercury.VAR Abbreviation of VOLT-AMPERES REACTIVE.var Abbreviation of VARIABLE.varactor A semiconductor-type voltage-variablecapacitor. Sometimes called a varactor diode.varactor amplifier A dielectric amplifier using avaractor as the voltage-variable capacitor.varactor flip-flop A bistable multivibrator basedon the nonlinear performance of one or two varactors.varactor frequency multiplier A frequency multiplier(doubler, tripler, etc.) in which multiples of afundamental frequency result from the nonlinearaction of a varactor.C1C1 and L1 tuned to fC2 and L2 tuned to F xnL1RF input (f ) RF output (F xn )L2C2varactor frequency multipliervaractor tuning A method of tuning a circuit oradjusting the frequency of an oscillator, using aninductor and a varactor to obtain the desired frequency.The varactor acts as a variable capacitor.VAR-hour Abbreviation, VARh. Short for voltampere-reactive-hour,a unit of reactive energy;1 VARh can be represented by 1 VAR for 1 hour,2 VAR for 0.5 hour, 0.5 VAR for 2 hours, etc.VAR-hour meter An instrument that measures reactiveenergy.variable Abbreviation, var. A quantity whose valuechanges at some stated or calculable rate, and isgiven names in expressions or equations, such asx, y, or z. Compare CONSTANT. Also see DEPEN-DENT VARIABLE and INDEPENDENT VARIABLE.variable-area sound track See VARIABLE-WIDTHSOUND RECORD.variable block In computer operations, a unit ofdata, such as a group of records, whose size is dependenton data requirements (i.e., it is not fixed).variable-capacitance diode See VARACTOR.variable-capacitance transducer See CAPACI-TIVE TRANSDUCER.variable capacitor A capacitor that can be adjustedfrom a low value (practically zero) to somemaximum value. A step-type unit contains anumber of fixed capacitors that can be switchedin parallel with each other until, at the last step,all are in parallel. A continuously variable unithas a provision for moving one plate or set ofplates, relative to another plate or set of plates; orone plate might be moved, with respect to another,so that the distance between them ischanged. In a voltage-variable capacitor (such asa varactor), capacitance varies in accordancewith an applied direct-current voltage.variable-carrier modulation See QUIESCENT-CARRIER OPERATION.variable connector In a flowchart, a path leadingfrom a box in which a decision is made, to a numberof other points on the diagram.variable coupling Coupling that is adjustable. Inan inductively coupled circuit, the distance or anglebetween the coils is usually the adjustablefactor. In a capacitively coupled circuit, a variablecapacitor is generally used.variable-density sound record In photographicsound-on-film recording, a sound track made byvarying, in sympathy with the sound frequency,the amount of light reaching the film. CompareVARIABLE-WIDTH SOUND RECORD.variable-depth sonar A sonar device that can beplaced far below the surface, for the purpose ofdetecting objects or terrain at greater depths thanwould be possible with a surface-located sonardevice.variable-efficiency modulation See EFFICIENCYMODULATION.variable-erase recording In magnetic-tape operations,recording a signal by selectively erasing apreviously recorded signal.variable field 1. Any field with an intensity thatchanges with time. An electromagnetic field is acommon example. 2. In a computer record, a fieldthat is a variable block with a terminal symbol atthe end.variable-frequency oscillator Abbreviation, VFO.An oscillator (usually self-excited) whose frequencyis continuously variable.variable-inductance pickup A phonograph pickupin which vibration of the stylus causes the inductanceof a small coil to vary in sympathy withthe sound frequency.variable-inductance transducer A transducer inwhich a monitored quantity causes the inductanceof a coil to vary proportionately. The coilthereby offers a varying impedance to analternating-current supply voltage.variable inductor An inductor whose value can beadjusted from zero to a certain maximum. Thevariability might be in steps, provided by taps onthe inductor, or a sliding contact can be used.

variable inductor • VATE 719Several different inductors can be connected inseries and parallel combinations, with switchesto facilitate variability. One type of variable inductoruses a roller contact to allow continuousadjustment. See ROLLER INDUCTOR. Anothermethod of varying inductance is to change thepermeability of the core, such as by moving a rodof ferrite or powdered iron in and out of the coil.See VARICOUPLER and VARIOMETER.variable-pitch indication An audible signal usedin lieu of, or in conjunction with, a meter to indicatevoltage, current, logic state, etc. The higherthe value of the measured quantity, the higherthe pitch.variable-reluctance microphone A microphone inwhich the impinging sound waves cause correspondingvariations in the reluctance of an internalmagnetic circuit.variable-reluctance pickup A phonograph pickupin which the stylus causes an armature to vibratein a magnetic field, and consequently thereluctance of the magnetic circuit varies in sympathywith the audio frequency.variable-reluctance transducer A transducer inwhich the monitored quantity causes the reluctanceof an internal magnetic circuit to vary proportionately.variable-resistance pickup A phonograph pickupin which the vibration of the stylus causes the resistanceof an internal resistive element to vary insympathy with the sound frequency.variable-resistance transducer A transducer inwhich a monitored quantity causes the resistanceof an internal resistive element to vary proportionately.variable-resistance tuning Tuning of a selectiveresistance-capacitance (RC) circuit, such as aWien bridge or parallel-tee network, by varyingone or more of its resistance arms.variable resistor A resistor whose value can bevaried either continuously or in steps. Also seePOTENTIOMETER and RHEOSTAT.variable selectivity In a circuit or device, selectivitythat is adjustable. Example: a variableselectivityintermediate-frequency (IF) amplifier.variable-speed motor Any motor whose speed isadjustable, smoothly or in steps, under load.variable transformer A transformer (often an autotransformer)whose output voltage is adjustablefrom zero (or some minimum value) to maximum.For this purpose, one winding (usually the secondaryin a two-winding transformer) can have anumber of taps. Smooth variation can be providedby a wiper arm that slides over the turns ofthe winding.variable-width wound record In photographicsound-on-film recording, a sound track made byvarying the width of the track in sympathy withthe sound variations. Compare VARIABLE-DENSITY SOUND RECORD.Variac See VARIABLE TRANSFORMER.Varicap A voltage-variable capacitor of the semiconductor-diodetype. Also see VOLTAGE-VARIABLE CAPACITOR.varicoupler An adjustable radio-frequency transformerconsisting of a primary coil (usually therotor) and a secondary coil (usually the stator),the former being rotatable to vary the couplingbetween the coils. The inductance of the stator isvaried via a set of taps.varindor A coil having a special core and whose inductancevaries with the amount of direct currentflowing through the winding. Also see SAT-URABLE REACTOR.variocoupler A radio-frequency transformer inwhich one winding is rotatable, for the purpose ofadjusting the mutual inductance between the primaryand secondary. It is used in certain antenna-couplingapplications.variolosser A variable attenuator.variometer A continuously variable inductor consistingof two coils connected in series or paralleland mounted concentrically—one rotating insidethe other. Inductance is maximum when the coilsare perpendicular to each other, and minimumwhen they are parallel.varioplex A time-sharing method of transmittingand receiving wire telegraph signals. It allows theoptimum usage of available lines.varistor See VOLTAGE-DEPENDENT RESISTOR.Varley-loop bridge A four-arm, direct-currentbridge circuit in which one of the arms, a twowireline, is accidentally grounded at a distantpoint. By adjustment of the bridge, the resultingresistance indicates the distance to the fault.Line ALine BAccidentalgroundVarley loop bridgeLines tiedtogetherfor testVAR meter An instrument for measuring the apparent(VAR) power in a reactive circuit.varnished cambric Cotton or linen fabric insheets, tape or tubes, that has been varnishimpregnatedand baked. A common form of thisinsulating material, the slender tubing known asspaghetti, has largely been replaced by plastictubing.varnished-cambric tubing Slender tubes of varnishedcambric slipped over bare wires and busbarsto insulate them. Also called spaghetti.VATE Abbreviation of VERSATILE AUTOMATICTEST EQUIPMENT.

720 V B • vector power factorV B Symbol for BASE VOLTAGE of a bipolar transistor.V BB Symbol for base-voltage supply for a bipolartransistor.V beam system See VEE BEAM SYSTEM.V C Symbol for COLLECTOR VOLTAGE of a bipolartransistor.VCA Abbreviation of VOLTAGE-CONTROLLED AM-PLIFIER.V CC Symbol for collector-voltage supply of a bipolartransistor.VCCO Abbreviation of VOLTAGE-CONTROLLEDCRYSTAL OSCILLATOR. (Also, lowercase.)VCD Abbreviation of VARIABLE-CAPACITANCEDIODE.VCG Abbreviation of VOLTAGE-CONTROLLEDGENERATOR.VCO Abbreviation of VOLTAGE-CONTROLLED OS-CILLATOR.V connection of transformers See VEE CONNEC-TION OF TRANSFORMERS.VCR Abbreviation of VIDEO CASSETTE RE-CORDER.VCSR Abbreviation of voltage-controlled shift register.V-cut crystal See VEE-CUT CRYSTAL.VCXO Abbreviation of VOLTAGE-CONTROLLEDCRYSTAL OSCILLATOR. (Also, lowercase.)VD 1. Abbreviation of VOLTAGE DROP. 2. Abbreviationof vapor density.V D Symbol for drain voltage of a field-effect transistor.Vdc Symbol for DC VOLTS.VDU Abbreviation of VISUAL DISPLAY UNIT.vdcw Symbol for DC WORKING VOLTAGE. (Also,dcwv.)VDIG Abbreviation of VIDEO DIGITIZER.VDR 1. Abbreviation of VOLTAGE-DEPENDENTRESISTOR. 2. Abbreviation of VIDEODISCRECORDER.V drive Abbreviation for DRIVING VOLTAGE or OUT-PUT VOLTAGE.VE Abbreviation of value engineering.V E Symbol for EMITTER VOLTAGE of a bipolartransistor.vectograph A graphic three-dimensional representationof a scene composed of superimposed imagesphotographed through polarizing filters ofdifferent orientation, and reconstructed by a similarviewing technique.vector 1. A quantity having direction (in two orthree dimensions) and magnitude. 2. A graphicalrepresentation of a quantity, as defined in 1. Itconsists of a straight arrow indicating the direction,and whose length is proportional to themagnitude.vector addition The summation of two vectors, determinedby adding their corresponding componentvalues. In two dimensions, for example,suppose A = (x 1 ,y 1 ) and B = (x 2 ,y 2 ). Then A + B =[(x 1 + x 2 ),(y 1 + y 2 )]. The sum can be found geometricallyby constructing a parallelogram from thevectors, corresponding to the two known sides, asdetermined by the vectors. The sum is the vectororiginating at the point where the two vectorsoriginate, and extending the diagonal of theparallelogram.y(x 1 , y 1 )vector addition(x 1 x 2 , y 1 y 2 )(x 2 , y 2 )vector admittance The reciprocal of VECTORIMPEDANCE.vector cardiograph An electrocardiograph that indicatesthe magnitude and the direction of aheart signal.vector components 1. The Cartesian coordinatesof a vector, or its component angle and radius(polar coordinates). 2. Quantities that can be representedby means of vectors (e.g., impedanceand velocity).vector diagram A graphical representation of vectorquantities.vector function A function having both magnitudeand direction. Also see VECTOR; VECTOR COM-PONENTS, 2; and VECTOR QUANTITY.vector generator A device that graphically illustratesvectors.vectorial angle 1. The angle between a vector andthe horizontal axis. 2. The angle between two vectors.vector impedance Complex impedance (i.e., animpedance of the form R + jX, where R is resistance,X is reactance, and j is an operator indicatingthat the reactance is 90 degrees out ofphase, relative to the resistance).vector-mode display On a cathode-ray-tube display,the data representation in which points onthe screen are connected by straight lines.vector power The vector quantity (P a2 + P x2 ) 1/2 ,where P a is the active power and Px is the reactivepower.vector power factor The ratio P a /(P a2 + P x2 ) 1/2 ,where P a is the active power and Px is the reactivepower. In sine-wave situations, this ratio (ofx

vector power factor • velocity modulation 721active power to vector power) produces a figureidentical to the conventional power factor.vector quantity A quantity having both magnitudeand direction, and that can, therefore, berepresented by a vector.vectorscope A special oscilloscope for visual adjustmentof a color-television receiver by meansof a color-phase diagram.vector sum The resultant of two nonparallel vectors;therefore, the resultant of the forces orquantities represented by them. For example, reactanceand resistance can be represented by twoperpendicular vectors.vector voltmeter A voltmeter that indicates thephase as well as the amplitude of an alternatingcurrentvoltage.V EE Symbol for emitter-voltage supply of a bipolartransistor.vee antenna A center-fed antenna in which thetwo halves of the radiator form an angle considerablyless than 180 degrees.vee-beam system An elevation-measuring radarsystem in which fan-shaped vertical and inclinedbeams, intersecting at ground and rotating continuouslyaround the vertical axis, are radiatedby one antenna. Target elevation is determinedfrom the interval between successive echoes fromthe target.vee connection of transformers In a three-phasesystem, a method of connecting two transformersso that the line current and voltage equal thephase current and voltage. Also called open-deltaconnection.vee-cut crystal A piezoelectric plate cut from aquartz crystal so that its faces are not parallel tothe x, y, or z axis of the crystal. Also see CRYSTALAXES and CRYSTAL CUTS.vee particle A short-lived elementary particle thatresults when high-energy neutrons or protonscollide with nuclei. The particle can be positive,negative, or neutral, and gets its name from itscloud-chamber track.vee signal In radiotelegraphy, the letter V (di-di-didah)transmitted as a test signal, usually threetimes in rapid succession. It is used during onthe-airtransmitter tests, followed by the station’scall letters.vehicle An inert substance, usually a liquid, thatacts as a solvent, carrier, or binder for someother, more active substance. Thus, shellac canbe the vehicle for the metallic powder in a silverpaint used in silk-screening electronic circuits.vehicle smog-control device See COMPUTER-CONTROLLED CATALYTIC CONVERTER andEXHAUST ANALYZER.vel Abbreviation of VELOCITY.velocimeter 1. An instrument for measuring thevelocity of sound in various materials. 2. Anelectronic velocity meter—especially a radialvelocitymeter using Doppler radar. 3. An electronicflow meter.velocity Symbol, v. Abbreviation, vel. Unit, distanceper unit time [e.g., meters per second(m/s)]. 1. The change in the position of a bodyover a specified period of time. 2. The derivative ofdisplacement with respect to time. Compare AC-CELERATION.velocity constant See VELOCITY FACTOR.velocity error For a servomechanism in which theinput and output shafts rotate at the same speed,the angular displacement between them.velocity factor Abbreviation, v. For a transmissionline, the ratio of the speed of electromagneticwave propagation in the line to the speed of electromagneticwaves in a vacuum (299,792 kilometersper second). It can be expressed as a numberbetween 0 and 1, or as a percentage between 0and 100. In practical feed lines, v ranges fromabout 0.66 (for coaxial line with a solid polyethylenedielectric) to about 0.95 (for open-wire linewith widely separated spacers).velocity hydrophone A hydrophone whose output,like that of the velocity microphone, is proportionalto the instantaneous particle velocity inthe sound wave impinging on the device.velocity-lag error A lag (proportional to the inputvariationrate) between the input and output of adevice, such as a servomechanism.velocity level For a sound, the ratio v 0 , expressedin decibels:v 0 = 20 log 10 (v s /v r )where v s is the particle velocity of the sound, andv r is a reference particle velocity.velocity microphone A microphone in which thevibratory element is a thin, aluminum or Duraluminribbon suspended loosely between the polesof a strong permanent magnet. Vibration of thecorrugated ribbon in the magnetic field causes anaudio-frequency voltage to be induced across theribbon. The microphone is so called because itsoutput is proportional to the instantaneous particlevelocity in the sound wave impinging on theribbon. Also called ribbon microphone.velocity-modulated amplifier A circuit in whichradio-frequency amplification is obtained by velocitymodulation.velocity-modulated oscillator A vacuum-tubedevice in which an electron stream is velocitymodulated(see VELOCITY MODULATION) as itpasses through a resonant cavity (the buncher);the subsequent energy, of a higher intensity, isextracted from the bunched stream as it passesthrough another resonant cavity (the catcher).Feedback from catcher to buncher sustains oscillations.See, for example, KLYSTRON OSCILLATOR.velocity-modulated tube A vacuum tube utilizingvelocity modulation. See, for example, KLYSTRON.velocity modulation The process in which the inputsignal of a vacuum tube varies the velocity ofthe electrons in a constant-current electron beamin sympathy with the input signal.

722 velocity resonance • versatile automatic test equipmentvelocity resonance A state of resonance in whicha 90-degree phase difference is between the fundamentalfrequency of oscillation of a system andthe fundamental frequency of the applied signal.velocity sorting Selecting and separating electrons,according to their velocity.velocity spectrograph A device that uses electricor magnetic deflection to separate charged particlesinto various streams, according to their velocity.velocity variation See VELOCITY MODULATION.velocity-variation amplifier See VELOCITY-MODULATED AMPLIFIER.velocity-variation oscillator See VELOCITY-MODULATED OSCILLATOR.velometer An instrument used to measure the velocityof air (e.g., to determine wind speed).venetian-blind effect A television-display malfunctionin which the picture seems to appearthrough horizontal slits.Venn diagram A method of illustrating the relationshipamong various subsets within a specifieduniversal set. The subsets are shown asgeometric figures, usually circles.vented-baffle loudspeaker See ACOUSTICALPHASE INVERTER and BASS-REFLEX LOUD-SPEAKER.vent mount A metal bracket for fastening an antennamast to a (plumbing) vent pipe on a roof.ventricular fibrillation See FIBRILLATION.verification 1. The process of ensuring that twosets of data are identical. 2. The process of validating(see VALIDATE).vernier 1. An auxiliary scale along which a regular,linear scale (such as that of a tuning dial)slides. The vernier scale is graduated so thatwhen the main scale is set to an unmarked pointbetween two of its graduations, and the “0” pointon the vernier scale is used as the index, “1” onthe vernier scale will exactly coincide with “1” onthe main scale. The corresponding number on thevernier scale indicates the exact number of subdivisionsbetween two points on the main scale.Vernier arrangements are provided with the dialsof some precision analog instruments. 2. SeeVERNIER CAPACITOR. 3. See VERNIER DIAL.4. See VERNIER RESISTOR.w1Universal setMainreadinglineAux. scalexw2y1 2 34 56 78 9x1x2x3x5x4z1y3y1y2z2y4y5y670Reading issomewherebetween75 and 76vernier, 180Aux. scale lines up at 3,indicating 75.3zVenn diagramvent 1. An opening in an equipment enclosure forthe entry of cool air or the escape of warm air.2. In an electrolytic capacitor, a lightly coveredblowout hole for the relief of gas pressure in theevent of severe overload. 3. A small opening forrelieving gas pressure in an automobile battery.4. In a loudspeaker enclosure, such as the bassreflextype, an auxiliary opening that extends thelow-frequency range of the speaker.vented baffle A loudspeaker enclosure having theproper auxiliary opening(s) for coupling thespeaker to the surrounding air.w3vernier capacitor A low-capacitance variable capacitorconnected in parallel with a higher-capacitancefixed or variable capacitor for preciseadjustment of the total capacitance.vernier dial 1. A slow moving dial for fine tuningan adjustable device. The required reduction ratiois obtained with gears, friction wheels, or abelt-and-pulley combination. 2. A dial providedwith an accessory vernier scale.vernier resistor A low-resistance variable resistorconnected in series with a higher-resistance fixedor variable resistor to precisely adjust the total resistance.vernier rheostat See VERNIER RESISTOR.vers Abbreviation of VERSED SINE.versatile automatic test equipment Abbreviation,VATE. For troubleshooting the electronicsystems of missiles, a computer-controlled testerthat isolates faults through logical operations.

versed sine • vertical frequency response 723versed sine Abbreviation, vers. A trigonometricfunction equal to the difference between the cosineof an angle and one; vers x = 1 – cos x.vert Abbreviation of VERTICAL.vertex 1. The terminal point at which two or morebranches of a network meet. Also see NODE, 1.2. The point of intersection of two lines that forman angle.vertex plate In the reflector of a microwave antenna,a matching plate mounted at the vertex.vertical 1. The direction indicated by a line perpendicularto the plane of the horizon (e.g., a verticalaxis). 2. In the 45-45 recording process, thesignal resulting from sound that arrives simultaneouslyand 180 degrees out of phase at the twomicrophones and causes up-and-down movementof the cutting stylus.vertical amplification Gain provided by the verticalchannel of a device, such as an oscilloscope,cathode-ray electrocardiograph, or television receiver.Compare HORIZONTAL AMPLIFICATION.vertical amplifier The circuit or device that providesgain in the vertical channel of a device.Compare HORIZONTAL AMPLIFIER.vertical-amplitude control 1. See VERTICAL-GAIN CONTROL. 2. In a color television receiver,one of the three controls by which the amplitudeof the parabolic voltages applied to the coils of themagnetic-convergence assembly are adjusted.vertical angle of radiation The angle, with respectto the plane of the horizon, at which radiofrequencyenergy is propagated from a transmittingantenna.vertical antenna 1. An antenna that consists essentiallyof a single, straight, vertical conductor.2. An antenna that is mounted vertically, insteadof horizontally.vertical blanking See VERTICAL RETRACEBLANKING.vertical-blanking pulse In a television signal, thepulse at the end of each field that accomplishesvertical retrace blanking. Compare HORIZON-TAL-BLANKING PULSE.vertical-centering control See CENTERING CON-TROL.vertical channel The system of amplifiers, controls,and terminations that constitutes the path of thevertical signal applied to a device, such as an oscilloscope.Compare HORIZONTAL CHANNEL.vertical compliance In disc sound reproduction,the ease with which the stylus can move verticallywhile it is in position on the disc.vertical coordinates See CARTESIAN COORDI-NATES.vertical deflection 1. In an oscilloscope or televisionreceiver, the movement of the spot up anddown on the screen. Compare HORIZONTAL DE-FLECTION. 2. In a direct-writing recorder, up ordown deflection of the pen.vertical deflection coils In a cathode-ray tube,the pair of coils in a deflection yoke that providesthe electromagnetic field for the vertical deflectionof the electron beam. Compare HORIZONTAL DE-FLECTION COILS.vertical deflection electrodes See VERTICAL DE-FLECTION COILS and VERTICAL DEFLECTIONPLATES.vertical deflection plates In an oscilloscope (andin some early television picture tubes), a pair ofplates that provides the electrostatic field for verticaldeflection. Compare HORIZONTAL DEFLEC-TION PLATES.vertical dipole An antenna consisting of astraight, center-fed, half-wave conductor orientedvertically.1 /2-waveradiatingelementvertical dipoleFeed linevertical dynamic convergence During the scanningof points along a vertical line through thecenter of a color-television picture tube, the convergenceof the electron beams at the aperturemask. Compare HORIZONTAL DYNAMIC CON-VERGENCE.vertical field strength The field strength of signalsin a vertical plane passing through an antenna.Compare HORIZONTAL FIELD STRENGTH.vertical-field-strength diagram A plot of verticalfield strength.vertical frequency response The gain-frequencycharacteristic of the vertical channel of an instrument,such as an oscilloscope. Compare HORI-ZONTAL FREQUENCY RESPONSE.

724 vertical gain • vertical sweep ratevertical gain The overall amplification (gain) providedby the vertical channel of an instrument,such as an oscilloscope, graphical recorder, ortelevision receiver. Compare HORIZONTAL GAIN.vertical-gain control A control, such as a potentiometer,for adjusting vertical amplification.Compare HORIZONTAL-GAIN CONTROL.vertical-hold control In a television receiver, thecontrol for adjusting the frequency of the verticaloscillator so that the picture can be locked to preventvertical roll. Compare HORIZONTAL-HOLDCONTROL.vertical-incidence transmission Transmission ofa wave vertically to the ionosphere and the subsequentreflection of the wave to the earth.vertical-lateral recording In stereophonic discrecording, the recording of one signal vertically(see VERTICAL RECORDING) and the other laterally(see LATERAL RECORDING).vertical linearity Linearity of response (gain anddeflection) of the vertical channel of an oscilloscopeor television receiver. A linear picture isneither contracted nor expanded vertically in anypart of the screen. Compare HORIZONTAL LIN-EARITY.vertical-linearity control In an oscilloscope ortelevision receiver, the control whereby verticallinearity is adjusted. Compare HORIZONTAL-LINEARITY CONTROL.vertically polarized wave An electromagneticwave whose electric lines of flux are perpendicularto the plane of the horizon. Compare HORI-ZONTALLY POLARIZED WAVE.vertical-metal-oxide semiconductor field-effecttransistor Abbreviation, VMOSFET. A metaloxidesemiconductor field-effect transistor fabricatedso that the current flow within the device isvertical, instead of the usual horizontal, affordingseveral advantages over the conventional MOS-FET.vertical oscillator In a television receiver, the oscillatorthat generates the vertical sweep signal.Compare HORIZONTAL OSCILLATOR.vertical-output regulator In a television receiver,a voltage-dependent resistor used to stabilize thesweep voltage across the horizontal deflectioncoils—especially during warmup.vertical output stage In a television receiver, anoutput amplifier following the vertical oscillator.Compare HORIZONTAL OUTPUT STAGE.vertical polarization Pertaining to an electromagneticwave whose electric lines of flux are perpendicularto the plane of the horizon. In general,when the radiating element of an antenna is vertical,the electric lines of flux in the transmittedwaves are vertical, and the antenna is most sensitiveto incoming signals whose electric lines offlux are vertical. Compare HORIZONTAL POLAR-IZATION.vertical positioning control See CENTERINGCONTROL.vertical quantity The quantity measured alongthe y-axis of a graph, or represented by the verticaldeflection of an electron beam. CompareHORIZONTAL QUANTITY.vertical radiator See VERTICAL ANTENNA.vertical recording Disc recording in which thedepth of the groove is varied in sympathy with thesound. Also called HILL-AND-DALE RECORD-ING. Compare LATERAL RECORDING.vertical redundance In computer operation, theerror state when a character has an odd numberof bits in an even-parity system, or vice versa.vertical resolution The number of horizontalwedge-lines that can be easily seen in a televisiontest pattern before they blend. Compare HORI-ZONTAL RESOLUTION.vertical retrace In a cathode-ray device, such as anoscilloscope or television receiver, the rapid returnof the beam to its starting point at the top of thescreen after completely traversing the screen fromtop to bottom. Compare HORIZONTAL RETRACE.vertical retrace blanking In a television receiver,the automatic shutoff of the electron beam duringa vertical retrace period, to prevent an extraneousline being traced on the screen during this period.Also see BLACKOUT, 2; BLANKING INTERVAL,1, 2; BLANKING PEDESTAL; BLANKINGTIME; VERTICAL RETRACE; and VERTICALRETRACE PERIOD. Compare HORIZONTAL RE-TRACE BLANKING.vertical retrace period In a television receiver, theinterval during which the spot returns from thebottom to the top of the screen after having tracedall horizontal lines from top to bottom. CompareHORIZONTAL RETRACE PERIOD.vertical sensitivity The signal voltage required atthe input of a vertical channel to produce full verticaldeflection. Also see VERTICAL GAIN. CompareHORIZONTAL SENSITIVITY.vertical signal A signal serving as a vertical quantity(e.g., one that deflects the beam in a cathoderaytube upward and/or downward). CompareHORIZONTAL SIGNAL.vertical-speed transducer A transducer whoseelectrical output is proportional to the verticalspeed of an aircraft or missile carrying the transducer.vertical stylus force In disc sound reproduction,the downward force (in grams or ounces) that thestylus exerts on the disc.vertical sweep 1. In a cathode-ray tube, especiallya television picture tube, the movement of thespot up or down on the screen. Compare HORI-ZONTAL SWEEP. 2. The circuit that producesthis sweep.vertical sweep frequency The frequency at whichvertical sweep occurs. In a television receiver, it is60 Hz. Also called vertical sweep rate. CompareHORIZONTAL SWEEP FREQUENCY.vertical sweep rate See VERTICAL SWEEP FRE-QUENCY.

vestigial sideband 1. A portion of one sideband inan amplitude-modulated signal, remaining afterpassage through a selective filter. 2. An ampliverticalsynchronization • VHF oscillator 725vertical synchronization In a television receiver,synchronization of the vertical component ofscanning with that of the camera. Also see VER-TICAL SYNC PULSE. Compare HORIZONTALSYNCHRONIZATION.vertical sync pulse In a video signal, the pulsethat synchronizes the vertical component ofscanning in a television receiver with that of thecamera, and that triggers vertical retrace andblanking. Compare HORIZONTAL SYNC PULSE.vertical wave See VERTICALLY POLARIZEDWAVE.vertical width control See WIDTH CONTROL, 1,2.very high frequency Abbreviation, VHF. Radiofrequencies in the range 30 MHz to 300 MHz,corresponding to free-space wavelengths of 10meters to 1 meter. It is sometimes divided intoVHF low band (30 MHz to 50 MHz) and VHF highband (50 MHz to 300 MHz). Also see RADIOSPECTRUM, 1.very high resistance Abbreviation, VHR. Largevalues of resistance; usually expressed in megohms,gigohms, or teraohms.very-high-resistance voltmeter Abbreviation,VHRVM. A voltmeter using a low-range microammeteror picoammeter and a very high value ofmultiplier resistance (see VOLTMETER MULTI-PLIER).very-high-speed integrated circuit An integratedcircuit used for switching or other digital functionsat thousands, millions, or billions ofchanges of state per second.very-large-scale integration Abbreviation, VLSI.The inclusion of several complete systems, suchas computers, on a single integrated-circuit chip.This can extend several orders of magnitude beyondlarge-scale integration (LSI).very long range Abbreviation, VLR. Pertaining toground radar sets having a maximum slant rangeof over 250 miles. Compare VERY SHORTRANGE.very low frequency Abbreviation VLF. A radio frequencyin the range 10 kHz to 30 kHz, correspondingto wavelengths between 30 kilometersand 10 kilometers. Also see RADIO SPECTRUM,1.very low resistance Abbreviation, VLR. Values ofresistance less than 1 ohm, usually expressed inmilliohms or microhms.very short range Abbreviation, VSR. Pertaining toground radar sets having a maximum slant rangeof less than 25 miles. Compare VERY LONGRANGE.vestigial1. An effect that remains as a by-product,but that serves no directly applicable purpose.See, for example, VESTIGIAL SIDEBAND. 2. Unnecessary;extraneous.Workingsidebandf oFrequencyCarrierVestigialsidebandvestigial sideband, 2tude-modulated signal in which one sidebandhas been partially or largely suppressed. 3. Thesmall amount of energy emitted in the unusedsideband in a single-sideband transmitter.vestigial-sideband filter A filter operated betweenan amplitude-modulated transmitter and an antennato obtain a vestigial-sideband signal.vestigial-sideband signal An amplitude-modulatedsignal in which one of the sidebands hasbeen partially suppressed.vestigial-sideband transmission Transmission ofa signal containing a vestigial sideband. In television,for example, the upper sideband is transmittedfully, while the lower sideband is almostcompletely suppressed. The lower sideband is,therefore, a vestigial sideband.vestigial-sideband transmitter An amplitudemodulatedtransmitter equipped with the filtersor other subcircuits necessary for emitting a vestigial-sidebandsignal.VF Abbreviation of VIDEO FREQUENCY.V FB Abbreviation for feedback voltage in an integratedcircuit device. The term applies especiallyto operational amplifiers.VFO Abbreviation of VARIABLE-FREQUENCY OS-CILLATOR.V g Abbreviation of GENERATOR VOLTAGE. (Also,Eg.)VGA Abbreviation of VARIABLE-GAIN AMPLIFIER.V GD Symbol for GATE-DRAIN VOLTAGE of a fieldeffecttransistor.V GS Symbol for GATE-SOURCE VOLTAGE of afield-effect transistor.VHF Abbreviation of VERY HIGH FREQUENCY.VHF high band See VERY HIGH FREQUENCY.VHF low band See VERY HIGH FREQUENCY.VHF omnirange Abbreviation, VOR. A very-highfrequencyradionavigation system that providesradial lines of position.VHF oscillator A radio-frequency oscillator speciallydesigned to operate in the range 30 MHz to300 MHz.

726 VHF receiver • vibrocardiographyVHF receiver 1. A radio receiver specially designedto operate in the range of 30 MHz to 300 MHz.2. A television receiver for the VHF channels (seeVHF TELEVISION CHANNELS).VHF television channels Twelve 6-MHz-widechannels (television channels 2 through 13) between54 and 216 MHz.Channel Frequency (MHz)2 54.0 – 60.03 60.0 – 66.04 66.0 – 72.05 76.0 – 82.06 82.0 – 88.07 174 – 1808 180 – 1869 186 – 19210 192 – 19811 198 – 20412 204 – 21013 210 – 216VHF television channels(United States)VHF transmitter A radio or television transmitterspecially designed to operate in the range 30 MHzto 300 MHz.VHR Abbreviation of VERY HIGH RESISTANCE.VHRVM Abbreviation of VERY-HIGH-RESISTANCEVOLTMETER.VHS videocassette recorder A popular scheme forvideocassette recording, used in millions ofhouseholds in the United States alone. TypicalVHS cassette play times range from about twohours to more than eight hours.VHSIC Abbreviation for VERY HIGH SPEED INTE-GRATED CIRCUIT.VI 1. Abbreviation of VOLUME INDICATOR. 2. Abbreviationof VISCOSITY INDEX.V i Symbol for INPUT VOLTAGE. (Also, V in .)vibrating bell A bell with a striking mechanismthat oscillates, causing a continuous ringingsound.vibrating-reed frequency meter See POWER-FREQUENCY METER, 2.vibrating-reed oscillator An audio-frequency oscillatorin which an iron, steel, or alloy reed vibratingin a magnetic field acts like a tuning forkto control the oscillation frequency.vibrating-reed relay An electromechanical relay inwhich the movable contact is carried by the endof a thin, metal strip (reed) of iron or magnetic alloy.The strip is supported within the magneticfield of a coil carrying an alternating control current;when the frequency of this current correspondsto the natural (resonant) frequency of thereed, it vibrates vigorously enough to close thecontacts. Such a relay, consequently, is frequencyselective.vibrating-wire oscillator An oscillator similar tothe vibrating-reed oscillator, but using a wire, insteadof a reed.vibrating-wire transducer A transducer in whichthe fluctuating tension of a thin wire suspendedin a magnetic field frequency-modulates the operatingvoltage.vibration 1. The changing of the position or dimensionsof a body back and forth, usually at arapid rate, an action seen in the repetitive movementof a musical string, headphone diaphragm,loudspeaker cone, loose machine, etc. 2. See OS-CILLATION.vibration analyzer See VIBRATION METER.vibration calibrator A device that generates astandard vibration, usually at a fixed frequency,for calibrating vibration meters, pickups, transducers,etc.vibration galvanometer A type of alternatingcurrentgalvanometer. The natural frequency ofthe movable element of the instrument is madeequal to that of the alternating current undertest, to obtain a reading.vibration isolator In an electronic-equipment assembly,a cushioning support that protects theequipment from vibration.vibration machine See VIBRATOR, 2.vibration meter An instrument for measuring theamplitude and frequency of vibration (see VIBRA-TION, 1). It consists essentially of a vibrationpickup followed by a selective amplifier and an indicatingvoltmeter graduated in vibration units.vibration pickup A transducer that senses mechanicalvibration and converts it into a proportionateoutput voltage, or changes resistance insympathy with the vibration.vibrato In electronic musical instruments, a circuitor device that modulates a note by varying itsfrequency, amplitude, or both, at an extremelylow frequency (a few hertz).vibrator 1. See INTERRUPTER. 2. See VIBRATING-REED RELAY. 3. A device for shaking somethingunder test at selected frequencies and amplitudes.vibrator-type power supply A battery-operated,high-voltage power supply in which one vibrator(see INTERRUPTER) makes and breaks directcurrent flowing from the battery into the primarywinding of a step-up transformer, and another vibratorrectifies the high voltage delivered by thesecondary winding.vibrator-type rectifier A vibrator (see INTER-RUPTER) that connects one terminal of the secondarywinding of a transformer to an outputterminal each time that terminal is positive.When the negative half-cycle appears at thetransformer terminal, the vibrator is open. In thisway, the alternating-current output of the transformeris rectified.vibrocardiography A method of monitoring andrecording the movement of the chest cavity as aresult of the beating of the heart.

vibrograph • video IF amplifier 727VibratorDriver coilB RFC 1C1vibrator-type power supplyvibrograph A device for observing and recording vibration.vibrometer See VIBRATION METER.vibroscope An instrument for observing (andsometimes recording) vibration.Victor Phonetic alphabet communications codeword for the letter V.Victron A brand of polystyrene, a low-loss plasticinsulant that is especially useful at high radio frequencies.video 1. Pertaining to television—especially to itspicture circuitry or to circuits and devices relatedto television, but used for other purposes. 2. Thepicture portion of a television broadcast, as opposedto the sound (audio) portion. 3. Sometimes,a cathode-ray-tube terminal or display.4. Generally, television in adjective sense (e.g.,video play). 5. The images on a computer displayor monitor.video amplifier 1. In television, the widebandstage (or stages) that amplifies the picture signaland presents it to the picture tube. 2. A similarwideband amplifier, such as an instrument amplifieror preamplifier having at least a 4-MHzbandwidth.video animation Movement of graphic images on acathode-ray-tube display by the use of computermanipulationthrough special software, underthe direction of an operator using a keyboard,joystick, or digitizer.video buffer A unity-gain circuit that minimizesloading effects caused by having several videomultiplexer inputs connected to the same signalsource.video carrier The television carrier amplitudemodulatedby the picture information, synchronizationpulses, and blanking pulses.videocassette recorder Abbreviation, VCR. Amachine for recording television programs onmagnetic-tape cassettes (see CASSETTE, 1).videocast 1. Television broadcast. Also calledTELECAST. 2. To make a television broadcast.videocaster See TELECASTER.video CD-ROM A digital optical VIDEODISC, resemblingan audio or computer compact disc. Atypical disc can store more than an hour’s worthof conventional television programming.TC3RFC 2C2+dc output_video correlator A device used with radar to locateand identify a target with high precision.video detector In a television receiver, the demodulatorfor the video signal. This detector followsthe video intermediate-frequency amplifier andprecedes the video amplifier. It usually embodiesa relatively simple, wideband diode circuit.Last IF ampB+_+PeakingVideocoildet.diodelR1C1video detectorPeakingcoilR2detectorloadOutputVideo Digitizer Abbreviation, VDIG. A programdeveloped for multimedia video in personal computersystems.videodisc A flat magnetic or optical disc on whichaudio-visual programs are recorded, and fromwhich they can be played back into a televisionreceiver or multimedia personal computer.videodisc recorder Abbreviation, VDR. A machinefor recording television programs on discs comparableto those used for sound or data recording.video discrimination In radar, the use of a circuitor device to decrease the width of the videoamplifierpassband.video frequency 1. Pertaining to signals in the widepassband of a video amplifier: 30 Hz to 4 MHz.2. Pertaining to a device capable of operating overthe wide passband of a video amplifier (e.g., avideo-frequency alternating-current voltmeter).video-frequency amplifier An amplifier capable ofhandling signals of a wide frequency range (e.g.,direct current to 4 MHz). Also see VIDEO FRE-QUENCY, 1.video gain control In a television receiver, a gaincontrol for adjusting the video signal amplitude.In a color-television receiver, a pair of these controlspermits adjustment of the three color signalsto the proper amplitude ratio.video game A game, such as football, basketball,slot machine, tic-tac-toe, etc., played on thescreen of a television receiver or on a computer.videogenic Suitable for television.video IF amplifier In a television receiver, thebroadband intermediate-frequency (IF) amplifierof the video signal. In modern receivers, this IFamplifier also handles the sound signal.

728 video mapping • vinylvideo mapping A system of surveillance or mappingin which, for reference, the outlines of thearea being surveyed are superimposed electronicallyon the radar display of the area.video masking A form of radar signal processingin which ground clutter and other unwantedechoes are removed, making the desired targetsmore readily visible.video mixer A circuit or device for mixing the signalsfrom two or more television cameras.video modulation In television transmission, amplitudemodulation of the carrier wave withpulses and waves corresponding to the picture elements.video on demand Television service in which subscriberscan choose the programs they want towatch, and also the specific times for viewing.video random-access memory Abbreviation,VRAM. In computer systems, RANDOM-ACCESSMEMORY used primarily for enhancing the performanceof the display.video recording 1. Recording wideband material(such as a video signal) on a tape or disc. 2. Therecording made of a telecast. Also see VIDEO-TAPE RECORDER.video signal 1. In television, the amplitude-modulatedsignal containing picture information andpulses. Also see VIDEO, 2 and VIDEO MODULA-TION. 2. Broadly, a telecast signal, includingsound.Whitestsignal BlackDarkGrey Whitegrey} Blacker-than-blackregionvideotape recording 1. Abbreviation, VTR. Thetechnique of recording video signals on magnetictape. Also see VIDEO RECORDING, 1, 2 andVIDEOTAPE. 2. A tape on which a video signalhas been recorded.videotext A system that allows television viewersto dial up special material, such as stock marketquotations, weather data, sports scores, etc.vidicon A television camera tube in which the electronbeam scans a charged-density pattern thathas been formed and stored on the surface of thephotoconductor. It is commonly used in camcorders,closed-circuit television systems, androbot vision systems. Its assets include compactnessand sensitivity.viewfinder An accessory or integral device inwhich an image (formed optically or electronically)corresponds to the image viewed by thecamera with which it is used.viewing mesh In a cathode-ray storage tube, themesh on which the image is presented for viewingby the operator. Also see CHARGE-STORAGETUBE.viewing mirror In an oscilloscope-camera assembly,a flat, slant-mounted mirror that reflects the imageon the oscilloscope screen to the viewer’s eye.viewing screen In a cathode-ray device, such asan oscilloscope tube or television picture tube,the face on which the image appears.viewing time In a storage type cathode-ray tube,the length of time for which the image persists.viewing window See WINDOW, 2.Villard circuit 1. A voltage-doubler circuit usingonly one diode and two capacitors. The opencircuitdirect-current output voltage is approximatelytwice the peak value of thealternating-current input voltage. Also see VOL-TAGE DOUBLER. 2. See SELECTOJECT.Zero signalC1video signalacInput E rmsDE dc+ dcOutput_video stretching In some electronic navigationsystems, increasing the duration of a video pulse.video synthesizer A computerized device that producesgraphical renditions of objects or circuitsin three dimensions.videotape 1. A special magnetic tape for videorecording (see VIDEO RECORDING, 2). 2. Tomake a video recording.videotape recorder Abbreviation, VTR. A wideband,magnetic-tape recorder for producing videorecordings with a camera, or for making a recordof television programs, for subsequent reproduction(playback).C2E dc = 2.82 E rmsVillard circuit, 1Villari effect In certain magnetostrictive materials,the change in magnetic induction that accompaniesthe application of a mechanical stress in agiven direction. Also see MAGNETOSTRICTION.vinyl A general name for vinyl copolymer resins.

vinylidene chloride • visible spectrum 729vinylidene chloride A plastic insulant. Dielectricconstant, 3 to 5. Dielectric strength, 20 kV/mm.Vinylite-A A brand of the plastic polyvinyl acetate.Vinylite-Q A brand of the plastic polyvinyl chloride.vinyl resin A synthetic resin resulting from thepolymerization of compounds that contain thegroup CH 2 = CH–.violation In a security system, a condition that resultsin the actuation of an alarm. Example: anintruder breaks the light beam in an electric eye.virgin magnetic material Core or shield materialthat has never been magnetized. When virgin materialis first subjected to magnetization, the hysteresisloop starts at zero, but never returns tozero (see BOX-SHAPED LOOP).virgin neutron Any neutron that has not been involvedin a collision with another particle subsequentto its initial generation.virgin record See BLANK RECORD.virgin tape See BLANK TAPE.virtual address In computer operations, an addressthat must be modified to refer to a locationin main memory.virtual decision value In quantizing or encoding,a method of expressing the maximum input amplitude.Two values are extrapolated from actualdecision values—one at either end of the workingrange used.virtual height The altitude that a vertically propagatedelectromagnetic wave would reach beforereflection if its path in the ionosphere were astraight line. The actual distance at which thewave penetrates the ionosphere before reflectionis less than the virtual height.virtual image The image formed when rays from ascene diverge after passing beyond the focal pointof a convex lens. The scene appears inverted to anobserver. Compare REAL IMAGE.virtual memory 1. In a computer system, a meansof using two or more memory stores simultaneously.2. Auxiliary memory used in conjunctionwith the main, or core, memory.virtual ppi reflectoscope A device used to superimposea virtual image of a chart or map onto aplan-position indicator (ppi) radar display. Alsosee VIDEO MAPPING.virtual reality Abbreviation, VR. A general term forany of various high-level computer simulation orremote-control programs. The user often wears ahead-mounted display that provides vivid, threedimensionalimagery and binaural sound. It canbe used in robotic telepresence systems for precisionremote control.virus See COMPUTER VIRUS.vis 1. Abbreviation of visibility. 2. Abbreviation ofvisual.viscometer An instrument for measuring viscosity.There are several electronic versions of thisdevice. In one, a steel ball falls through a material(such as an oil) under test and distorts the magneticfield of a pickup coil, causing the deflectionof a meter by an amount proportional to thespeed of the ball and, consequently, to the viscosityof the fluid.viscosimeter See VISCOMETER.viscosity The resistance offered by a fluid (liquidor gas) to objects passing through it. The viscosityof pure water is low; that of heavy oil is high.Expressed in newton-seconds per meter squared.viscosity index Abbreviation, VI. A number indicatinghow well an oil retains its viscosity withtemperature changes; larger indexes are assignedto oils that are little influenced by variations intemperature.viscous-damped arm A phonograph pickup armwith an oil dashpot to prevent arm resonance andto slow the descent of the arm to the disc.viscous damping The use of a viscous fluid in thedashpot of a device (such as a relay, timer, orpickup arm) to provide damping. See, for example,DASHPOT RELAY.viscous hysteresis A slow, slight increase in themagnetization of a material when the magnetizingfield is constant. Compare STATIC HYSTERESIS.visibility factor See DISPLAY LOSS.visible radiation Electromagnetic radiation that isperceptible to the eye. Also see VISIBLE SPEC-TRUM.visible spectrum The band of electromagneticwavelengths that the human eye perceives as visiblelight. For most people, this band extendsfrom approximately 750 nanometers (nm), representingred light, down to 390 nm, representingviolet light. The visibility curve peaks in theyellow-green region at about 560 nm; 1 nm = 0.000Wavelength(angstroms)10 0X rays10 110 2 Ultraviolet10 3Visible light10 410 5 Infared10 610 7EHF10 8SHF waves10UHF}Radio 910 10visible spectrum

730 visible spectrum • voice frequencies000 001 meter = 10 –9 m. Also see ELECTROMAG-NETIC THEORY OF LIGHT.vision system A set of devices that allows a machine(computer or robot) to observe and respondto visual stimuli. Typically, it includes a camera[such as a vidicon or charge-coupled device(CCD)], a cable, electromagnetic or fiberoptic link,a receiver, and software for interpreting the images.visual alignment Optimization of a circuit (suchas a radio receiver) with the aid of meter deflections,rather than with audible indications. Alsocalled silent alignment.visual-aural radio range A radio aid to air navigation(characterized by an audible signal, meterdeflection, or both) used by the pilot of an aircraftto determine if the course is being followed.visual-aural range See VISUAL-AURAL RADIORANGE.visual-aural signal tracer A troubleshooting instrumentfor following a signal through a circuitby sensing it at successive points in the circuit.The signal strength is indicated by a meter and aloudspeaker.visual carrier frequency See VIDEO CARRIERand VIDEO-FREQUENCY, 1.visual communication 1. Transmission and receptionof signals by visible-light means, such asmodulated beams of flashing lights. 2. Transmissionand reception of messages by direct visualobservation, such as signal lights.visual display unit Abbreviation, VDU. 1. A computerperipheral consisting of a cathode-ray tube,a keyboard, and often a pointing device. 2. Adumb terminal for operation of a computer from aremote site.visual horizon 1. The distance from a given pointto the farthest visible point on the surface of theearth in a particular direction. 2. The enclosedgeometric plane figure on the surface of the earth,representing the set of farthest-visible points for aparticular location.visual telegraphy Telegraphy in which the receivedsignals are read from a visual device, suchas a blinking light, meter, or swinging pen.visual transmitter The equipment used to transmitthe picture portion of a television broadcast.visual transmitter power The peak power outputof a visual transmitter during normal operation.vitreous Pertaining to a material or surface resembling,or related to, glass (e.g., the vitreousenamel on certain types of resistors).VLF Abbreviation of VERY LOW FREQUENCY.VLR 1. Abbreviation of VERY LOW RESISTANCE.2. Abbreviation of VERY LONG RANGE.VLSI Abbreviation of VERY-LARGE-SCALE INTE-GRATION.V/m Abbreviation of VOLTS PER METER (a unit ofelectric field strength).VMOS Abbreviation of vertical-metal-oxide semiconductor.VMOSFET Abbreviation of VERTICAL-METAL-OXIDE SEMICONDUCTOR FIELD-EFFECTTRANSISTOR.V o Symbol for OUTPUT VOLTAGE. Also, V out .VOA Abbreviation of VOLT-OHM-AMMETER.vocabulary In computer-programming operations,a list of available operating codes and instructionsfor the computer. Also called INSTRUCTIONSET.Vocoder A device for reducing speech to frequencieslow enough for efficient transmissionthrough a limited-bandwidth channel. The termis a contraction of voice coder.VodaIn a telephone system that utilizes a radiolink (using the same frequency for transmissionin both directions) and land-line links, an automatic,voice-operated switching system for enablingthe transmitter and disabling the receiver,and vice versa. The name is an acronym for voiceoperateddevice, anti-sing.Vodacom Contraction of voice data communications.Voder An electronic device that synthesizesspeech. The term is an acronym for voice operationdemonstrator.vogad A type of automatic gain control for audioamplifiers and modulators. In a radio transmitter,it maintains 100% modulation of the carrier—evenwhen the speaker’s voice level varieswidely. The name is an acronym for voiceoperatedgain adjusting device.voice actuation See VOICE-OPERATED CON-TROL.voice analyzer A circuit that evaluates the characteristicsof human voices, such as the amplitudevs.-frequencyfunction or the amplitude-vs.-timefunction.voice band See VOICE FREQUENCIES.voice coil The moving coil of a dynamic microphoneor dynamic speaker.voice-controlled break-in A type of break-in operationfor radiotelephony, in which the transmitterautomatically switches on and the receiverswitches off immediately when the operator startstalking; the transmitter switches off and the receiverswitches on a moment after the operatorstops talking.voice-controlled relay An electronic relay that isactuated by the human voice.voice filter 1. A filter for passing, suppressing, ormodifying voice frequencies. 2. A parallelresonantcircuit inserted into a line that feedsseveral loudspeakers, to trap certain frequenciesand thereby improve the sound of the reproducedvoice.voice frequencies 1. The audio-frequency range ofhuman speech, from about 60 Hz to 8000 Hz. 2.The frequencies within the audio passband of atypical single-sideband voice transmitter or receiver.The lower limit is generally 200 Hz to 300Hz; the upper limit is about 2500 Hz to 3000 Hz.

voice-frequency carrier telegraphy • voltage-breakdown test 731voice-frequency carrier telegraphy A type of carrier-currenttelegraphy (see WIRED WIRELESS)in which the modulated carrier can be transmittedover a telephone line having a voice-frequencybandwidth.voice-frequency dialing A system of telephone dialinginvolving the conversion of direct-currentpulses into voice-frequency alternating-currentpulses.voice-frequency telephony Wire telephone communicationin which the frequencies of the electricwaves are identical to the frequencies of thesound waves (or very nearly so).voice grade Pertaining to a communications systemhaving a bandpass capable of transferring ahuman voice with reasonable intelligibility. SeeVOICE FREQUENCIES, 2.voice-grade channel 1. A telephone line and attendantequipment suitable for the transmissionof speech and certain other information, such ascontrol signals, digital data, etc. 2. In a radiotelephonetransmitter, a speech amplifier-modulatorchannel suitable only for voice frequencies.voice-operated control Abbreviation, vox. Pertainingto a device (such as a relay, automaticmodulation control, transmit-receive switch, etc.)that is actuated when the operator speaks into amicrophone.voice-operated device, anti-sing See VODA.voice-operated gain-adjusting device See VO-GAD.voice-operated loss control and suppressor Inwire telephony, a device that switches the lossfrom the transmitting line to the receiving linewhen the subscriber speaks, and vice versa.voice-over The simultaneous recording of a humanvoice (such as that of a narrator) along with othersounds (such as music, children playing, wind intrees, ocean waves, chirping birds, etc.). The voiceis generally louder than the other sounds.voice print A graphic recording of the speech frequenciesproduced by an individual and used asa means of identifying that individual.voice-recognition device See SPEECH RECOG-NIZER.voice security In voice communications system,the use of encryption and decryption, usually inthe form of digital algorithms, to “scramble”speech at the source and “unscramble” it at thedestination.voice-stress analyzer Abbreviation, VSA. An instrumentthat samples the spoken voice and producesa display from which the relative amount ofstress experienced by the speaker can be determined,and from which, in turn, probable truthor falsity of statements or answers can be inferred.voice synthesis device See SPEECH SYNTHE-SIZER.void space See VACUUM.vol Abbreviation of VOLUME.volatile 1. Capable of evaporating (e.g., volatile solventsused in the encapsulation of electronicequipment). 2. Explosive (noun and verb). 3. Pertainingto a state which is difficult to maintain(e.g., a VOLATILE MEMORY).volatile memory Memory, usually of the randomaccesstype, whose data vanishes when power isremoved unless some provision is made for memorybackup. The most common means of memorybackup is the use of an electrochemical cell orbattery. Modern memory chips need so little currentto store their data that a backup batterylasts almost as long in the circuit as it would onthe shelf. The main advantage of this type ofmemory is the fact that it can easily be erased ifdesired. Compare NONVOLATILE MEMORY.volatile storage See VOLATILE MEMORY.volatile store See VOLATILE MEMORY.Voldicon A form of semiconductor logic deviceused for analysis of analog signals. Trade name ofAdage, Inc.volt Abbreviation, V. The basic practical unit of differenceof potential (i.e., of electrical pressure); 1volt is the difference of potential produced acrossa resistance of 1 ohm by a current of 1 ampere.Also see KILOVOLT, MEGAVOLT, MICROVOLT,MILLIVOLT, NANOVOLT, and PICOVOLT.Volta effect See VOLTA’S PRINCIPLE.voltage Symbols, E, e, V, v. Electromotive force, ordifference of potential; E = IR, where I is currentand R is resistance. Also see VOLT.voltage-actuated device An electronic device,such as a field-effect transistor, that amplifies avoltage signal or is controlled by a voltage, anddraws virtually no signal current or control current.The opposite is a current-actuated device,such as a bipolar transistor.voltage amplification 1. Abbreviation, A v . Amplificationof an input-signal voltage to provide ahigher output-signal voltage. 2. Abbreviation, A v .The signal increase (V out /V in ) resulting from thisprocess. Also called voltage gain.voltage-amplification device A low-current devicedesigned especially for voltage amplification.It provides little or no power amplification.voltage amplifier An amplifier operated primarilyto increase a signal voltage. Compare CURRENTAMPLIFIER and POWER AMPLIFIER.voltage at peak torque Symbol, V p . For a torquemotor operated at 25°C, the voltage required toproduce peak torque at standstill.voltage attenuation 1. The reduction in voltage ata given point in a circuit. 2. For a device, the ratioof input voltage to output voltage when theoutput voltage is the lower quantity.voltage-balance relay A relay actuated by a voltagedifferential.voltage breakdown See BREAKDOWN VOLTAGE.voltage-breakdown test 1. A test in which themeasured voltage applied to an insulatingmaterial is continuously increased until the

732 voltage-breakdown test • voltage dividerbreakdown point is reached. 2. A test in whichthe measured reverse voltage applied to a semiconductorjunction is continuously increased untilthe reverse breakdown point is reached (seeAVALANCHE BREAKDOWN).voltage burden The voltage drop across a CUR-RENT SHUNT.voltage calibrator A device used to calibrate, interms of voltage, a meter scale, oscilloscopescreen, graphic-recorder chart, etc.voltage-capacitance curve A plot depicting thevariation of capacitance with applied voltage for avoltage-variable capacitor. For a varactor (variable-capacitancediode), capacitance varies inverselywith reverse direct-current voltage.voltage coefficient A figure that shows the extentto which a quantity drifts under the influence ofvoltage. It is generally expressed in percent pervolt or in parts per million per volt (ppm/V).voltage coefficient of capacitance For a voltagedependentcapacitor, the capacitance change perunit change in applied voltage.voltage coefficient of resistance For a voltagedependentresistor, the resistance change perunit change in applied voltage.voltage coil See POTENTIAL COIL.voltage comparator A device for comparing (usuallyonly two) voltages. The various types rangefrom simple, manually balanced potentiometersto analog or digital devices that automaticallycompare the applied voltages and provide a directreadout of either their difference or the percent ofunbalance.voltage control 1. A component or circuit that allowsthe adjustment of the output voltage of apower supply within a given range. 2. The adjustmentof the output voltage of a power supply tooptimize the performance of a circuit connectedto the supply. 3. Any form of circuit control thatis accomplished by the adjustment of the voltageat a given circuit point.voltage-controlled amplifier Abbreviation, VCA.An amplifier in which gain is controlled by meansof a voltage applied to a control terminal.voltage-controlled attenuator An attenuator circuitin which a transistor serves as a voltagevariableresistor. The output resistance of thetransistor varies inversely with the direct-currentbias voltage applied to the input electrode (base,emitter, or gate).voltage-controlled capacitor See VOLTAGE-DEPENDENT CAPACITOR.voltage-controlled crystal oscillator Abbreviation,VCCO or VCXO. A voltage-controlled oscillatorof the crystal-stabilized type.voltage-controlled generator Abbreviation, VCG.Any signal-generating device whose output frequencyis varied by changing one of the directcurrentoperating voltages of the device.voltage-controlled oscillator Abbreviation, VCO.An oscillator of the inductance-capacitance (LC)type that employs a varactor diode in the capacitiveportion of the tuned circuit. The varactor isplaced in series or parallel with the tuning capacitorand is isolated for direct current by blockingcapacitors. The frequency can be adjusted, withincertain limits, by nonmechanical means. The signalcan also be frequency modulated by applyingthe modulating voltage across the varactor.voltage-controlled resistor See VOLTAGE-DE-PENDENT RESISTOR.voltage corrector See VOLTAGE REGULATOR.voltage crest See VOLTAGE PEAK.voltage-current characteristic See VOLTAGE-CURRENT CURVE.voltage-current crossover The point at which avoltage-regulated supply becomes a currentregulatedsupply.voltage-current curve For a circuit or device, theplot of the interrelationship of current and voltage,with voltage as the independent variable.voltage-current feedback See CURRENT-VOLT-AGE FEEDBACK.voltage decay The exponential decrease of voltageacross a discharging capacitor. Also see EXPO-NENTIAL DECREASE.voltage-dependent capacitor A capacitor (such asa varactor) whose capacitance varies with appliedvoltage.voltage-dependent resistor A nonlinear resistorwhose value varies inversely with the voltage dropacross it. Also called varistor.voltage detector A circuit or device that deliversan output voltage only when the input voltage isof a prescribed value. Compare VOLTAGE DIS-CRIMINATOR.voltage-determined property A property (capacitance,current, frequency, or resistance) whosemagnitude depends on the value of an appliedvoltage. See, for example, VOLTAGE-DEPENDENTCAPACITOR, VOLTAGE-DEPENDENT RESISTOR,and VOLTAGE-CONTROLLED OSCILLATOR.voltage differential Symbol, dE or dV. An infinitesimalchange in voltage. Compare VOLTAGEINCREMENT.voltage-directional relay 1. A relay that is actuatedwhen voltage exceeds a certain value in agiven direction. 2. A relay that closes only whenthe applied voltage is in a specific direction.voltage discriminator A circuit or device whoseoutput voltage is zero when the input voltage is ofa prescribed value. When the input voltage isgreater than this value, the output is positive;when it is less, the output is negative.voltage distribution 1. The delivery of operatingvoltage throughout a circuit (e.g., high and lowdirect-current voltages in the various stages of acontrol circuit). 2. Sometimes, the distribution ofelectrical energy (“power” distribution).voltage divider A resistive or capacitive potentiometeror network used to divide an appliedvoltage by a desired amount.

voltage doubler • voltage peak 733acInput(E rms )E dc = 2(1.41)E rmsvoltage doubler A power-supply circuit that suppliesa direct-current output voltage of abouttwice the peak value of the alternating-current inputvoltage.voltage drift See DRIFT VOLTAGE.voltage drop Abbreviation, VD. The voltage (E) setup across a resistance (R) carrying a current (I);E = IR. For alternating current, reactance X andimpedance Z can be substituted for resistance,where applicable.voltage-equalizing resistors In a power-supply filter,resistors connected across each capacitor ina string of electrolytics connected in series towithstand a high voltage. The resistors protectthe capacitors by equalizing the voltage acrossthem.voltage-fed antenna An antenna in which thefeeder is attached to the radiator at a voltage loop(current node). Compare CURRENT-FED AN-TENNA.voltage feed The delivery of voltage to a device orcircuit at a point where voltage, rather than current,is dominant. Compare CURRENT FEED.voltage feedback A feedback signal consisting ofvoltage fed from the output to the input circuit ofan amplifier or other device. Compare CURRENTFEEDBACK and CURRENT-VOLTAGE FEED-BACK.voltage-frequency transducer 1. A device whoseoutput voltage is a function of the frequency of asignal at the input. 2. A device whose outputfrequency is a function of the voltage at theinput.voltage gain See VOLTAGE AMPLIFICATION.voltage generator See VOLTAGE SUPPLY.voltage gradient The voltage per unit length alonga defined path.voltage increment A change in voltage representedby E 2 – E 1 , where E 2 and E 1 are the voltagesat two defined points on a curve, and thedifference is finite (nonzero). Compare VOLTAGEDIFFERENTIAL.voltage input encoder An analog-to-digital encoderfor which the input is an analog voltage.C1C2voltage doubler+_dcOutput(E dc )See, for example, VOLTAGE-TO-SHAFT-POSI-TION ENCODER.voltage inverter A circuit or device whose voltageoutput has the sign opposite that of the inputvoltage. The device might or might not provideamplification.voltage jump 1. An upward transient in voltage.2. In a glow-discharge tube, a sudden break orincrease in voltage drop across the tube.voltage lag The condition in which voltage changesoccur after corresponding current changes. CompareCURRENT LAG and VOLTAGE LEAD.voltage lead The condition in which voltagechanges precede corresponding current changes.Compare CURRENT LEAD and VOLTAGE LAG.voltage level 1. A prescribed reference value ofvoltage (e.g., the black level in a television picturesignal). 2. The discrete value of a steady voltage,or the average value of a fluctuating voltage, asobserved or measured in a circuit.voltage limit The maximum or minimum level in avoltage range.voltage loop In a standing-wave system, such asan antenna or transmission line, a maximumvoltagepoint. Compare VOLTAGE NODE.voltage loss 1. Reduction of a voltage across aload, occurring because of a series resistance.2. The ratio, in decibels, between the input voltageto a transmission line and the output voltage atthe load end of the line, assuming that theimpedance is the same at both points.voltage maximum See VOLTAGE PEAK.voltage minimum See VOLTAGE TROUGH.voltage-mode switching circuit A resistor-transistor-logic(RTL) NAND or NOR circuit in which(in the off state) the transistor is cut off by the V BBbias voltage. The output is then approximatelyequal to the collector supply voltage, V CC . Theproper combination of input pulses overrides thecutoff bias, and the transistor switches on. Theoutput then drops to a level equal to V CC minusthe voltage drop across the external collector resistor.voltage multiplier A special type of rectifier circuitthat delivers a direct-current output voltage thatis a multiple of the peak value of the alternatingcurrentinput voltage, thus affording voltage stepupwithout a transformer. See, for example,VOLTAGE DOUBLER; VOLTAGE QUADRUPLER;QUINTUPLER, 1; and VOLTAGE TRIPLER.voltage node In a standing-wave system, such asan antenna or transmission line, a minimumvoltagepoint. Compare VOLTAGE LOOP.voltage of self-induction The voltage drop acrossan inductor, resulting from the flow of alternatingcurrent through the inductor; it is caused by selfinduction.voltage peak The highest value attained by a voltageduring an excursion. Also called voltage crestor voltage maximum. Compare VOLTAGETROUGH.

734 voltage-power directional relay • voltage-sensitive bridgeacInput(E rms )C1C2D1voltage quadruplervoltage-power directional relay A relay system inwhich two circuits are connected when their voltagedifference exceeds a predetermined value inone direction, and are disconnected when thevoltage in the opposite direction exceeds a predeterminedlevel.voltage quadrupler A special rectifier circuit thatsupplies a direct-current output voltage of approximatelyfour times the peak alternatingcurrentinput voltage.voltage quintupler See QUINTUPLER, 1.voltage-range multiplier 1. A multiplier resistor(see VOLTMETER MULTIPLIER) connected in serieswith a voltmeter that has an internal multiplier,to increase the range of the instrument.2. For an alternating-current voltmeter, an inputamplifier used to increase the sensitivity of the instrument.voltage rating 1. For a circuit or device, the recommendedmaximum voltage that can be applied,or the recommended working voltage, asspecified. 2. For a generator, the specified outputvoltage.voltage ratio The quotient of the voltages, E 1 /E 2 ,at two specific points in a circuit, device, or system.Examples: ratio of input voltage to outputvoltage and ratio of primary voltage to secondaryvoltage.voltage-ratio box See VOLT BOX.voltage reference See STANDARD CELL andZENER-DIODE VOLTAGE REFERENCE.voltage-reference cell See STANDARD CELL.voltage-reference diode A Zener diode biasedinto its Zener region. The voltage drop across thediode is comparatively constant. Under properconditions, it can be used for referencepurposes. Also see ZENER-DIODE VOLTAGEREFERENCE.voltage reflection coefficient In a reflected-wavesituation, the ratio E r /E i , where E i is the fieldstrengthvoltage of the incident wave, and Er isthe field-strength voltage of the reflected wave.D2D3D4E dc = 4(1.41)E rmsC3C4++dcOutput(E dc )voltage-regulated supply See CONSTANT-VOLT-AGE SOURCE.voltage-regulating transformer A special transformerin which a resonant circuit and core saturation(see SATURATED OPERATION, 1) are usedto provide a constant output voltage.voltage regulation The stabilization of a voltageagainst fluctuations in source or load.voltage-regulation constant Symbol, K v . For avoltage-regulated power supply, the ratiodE L /dE i , where dE i is a change in input voltage,and dE L is the corresponding change in load voltage.voltage regulator A circuit or device that holds anoutput voltage constant during variations in theoutput load or input voltage.voltage-regulator diode See ZENER-DIODEVOLTAGE REGULATOR.voltage-regulator transformer See VOLTAGE-REGULATING TRANSFORMER.voltage relay A relay or relay circuit that is actuatedby a discrete voltage, rather than by currentor power.voltage-responsive device See VOLTAGE-ACTU-ATED DEVICE.voltage rise The normal condition in a seriesresonantcircuit, in which the voltage across thecoil or capacitor is higher than the voltage appliedto the circuit.voltage saturation In a current-actuated device,such as a bipolar transistor, the situation inwhich an increase in current provides no increasein voltage drop beyond a certain point (the saturationpoint).voltage-sensitive bridge A bridge having a nonlinearelement (such as a voltage-dependent resistor)as one of the arms. Because of this element,the bridge can be balanced (with a given set ofother arms) at only one value of applied voltage.At lower voltages, the bridge becomes unbalancedin one direction; at higher voltage, in the oppositedirection.AdjustablevoltageinputNonlinear element (varistor,semiconductor diode, thermistor,tungsten-filament lamp, etc.)Outputvoltage-sensitive bridge

voltage-sensitive capacitor • voltaic pile 735voltage-sensitive capacitor See VOLTAGE-DEPENDENT CAPACITOR.voltage-sensitive resistor See VOLTAGE-DEPEN-DENT RESISTOR.voltage sensitivity 1. Particular responsiveness ofa circuit or device to voltage, rather than currentor power. See, for example, VOLTAGE-DEPEN-DENT CAPACITOR, VOLTAGE-DEPENDENT RE-SISTOR, and VOLTAGE RELAY. 2. SeeVOLTMETER SENSITIVITY.voltage-spectrum function The voltage-vs.-frequency curve at the output of a circuit ortransducer.voltage-stabilized supply See CONSTANT-VOL-TAGE SOURCE.voltage stabilizer See VOLTAGE REGULATOR.voltage-stabilizing diode See ZENER-DIODEVOLTAGE REGULATOR.voltage standard A device that delivers a voltage ofaccuracy and stability so that it can be used tocalibrate other voltage generators and test instruments.See, for example, STANDARD CELL andZENER-DIODE VOLTAGE REFERENCE.voltage standing-wave ratio Abbreviation, VSWR.In a standing-wave system, the ratio of the maximumvoltage to the minimum voltage.voltage supply A power supply whose usable outputis voltage, rather than current or power.When such a supply is not voltage-regulated, itcan only be used reliably with a very light load.voltage to chassis In electronic equipmentmounted on a metal chassis, the voltage betweenthe chassis and a given point in the circuit.voltage-to-frequency converter A device or circuitthat delivers an output frequency proportionalto an input voltage (usually direct current).Compare FREQUENCY-TO-VOLTAGE CON-VERTER.voltage to ground 1. In a circuit, the voltage measuredbetween a given point and the groundpoint. 2. The voltage measured between the earthand a line or piece of equipment.voltage to panel In electronic equipment mountedon a metal panel, the voltage between the paneland a given point in the circuit.voltage-to-shaft-position encoder An encoder forwhich the output is the rotation of a motor shaftover an arc proportional to an input voltage.voltage transformer 1. A transformer usedprimarily to supply voltage with little or nocurrent. 2. A small step-up transformer for increasingthe sensitivity of an alternating-currentvoltmeter. Also called POTENTIAL TRANS-FORMER.voltage tripler A rectifier circuit that, without atransformer, supplies a direct-current outputvoltage of approximately three times the peakvalue of the alternating-current input voltage.voltage trough The lowest value reached by a voltageduring an excursion. Compare VOLTAGEPEAK.acInput(E rms )C1D2D3D1voltage triplervoltage tuning A method of adjusting the frequencyof an oscillator or resonant circuit bymeans of a variable, direct-current voltage.voltage-tunable magnetron A magnetron oscillatorin which the output frequency is varied by adjustingthe direct-current voltage on the tube.voltage-tunable oscillator See VOLTAGE-CONTROLLED OSCILLATOR.voltage-turns ratio The turns ratio of a transformer,indicated by the ratio of primary voltageto secondary voltage, or vice-versa.voltage-type telemetry Telemetry based upon thevariation of a single voltage in sympathy with thechanges in a sensed phenomenon.voltage-variable capacitor 1. A specially processedsemiconductor diode of which the voltagevariablecapacitance of the junction is utilized.Also called VARACTOR. 2. A capacitor having aspecially processed nonlinear dielectric, such asbarium strontium titanate, whose capacitancevaries inversely with the applied direct-currentbias voltage.voltage-variable resistor See VOLTAGE-DEPEN-DENT RESISTOR.voltage vector In a vector diagram, a vector showingthe magnitude and phase of a voltage. CompareCURRENT VECTOR.voltaic Pertaining to chemically produced directcurrent. Sometimes interchangeable with galvanic.voltaic cell For the generation of a direct-currentvoltage, a primary cell consisting of two electrodesmade of different metals and immersed inan electrolyte. Also called GALVANIC CELL. Alsosee CELL, ELECTROMOTIVE SERIES, and PRI-MARY CELL.voltaic couple A pair of dissimilar metals (or othersubstances) that generate a direct-current voltagewhen they contact an electrolyte.voltaic pile A rudimentary primary battery consistingof a series of disks made of two differentmetals, stacked alternately with electrolytesoakedcloth or paper disks.C2E dc = 3(1.41)E rmsC3+_dcOutput(E dc )

736 voltaic series • volume-limiting amplifiervoltaic series See ELECTROMOTIVE SERIES.voltameter An electrolytic cell for determining thevalue of an unknown current, or of an unknownquantity of electricity, from the weight of metaldeposited out of an electrolyte onto the cathodeby the passage of current over an accuratelytimed interval.volt-ammeter A combination meter for measuringelectrical voltages and currents.volt-ampere Symbol, VA. Unit, watt. The simpleproduct of voltage and current in volts and amperes,yielding the true power in a direct-currentcircuit and the apparent power in an alternatingcurrentcircuit. Also see APPARENT POWER andTRUE POWER.volt-ampere-hour meter See VAR-HOUR METER.volt-ampere meter See VAR METER.volt-amperes reactive Abbreviation, VAR. Theproduct of volts and amperes for a purely reactivecircuit. This product does not produce the truepower because the power factor is neglected; itproduces only the apparent power. A true reactanceabsorbs power during one half-cycle of alternatingcurrent, and returns it to the generatorduring the next half-cycle.Volta’s law See VOLTA’S PRINCIPLE.Volta’s pile See VOLTAIC PILE.Volta’s principle Two dissimilar metals broughtinto contact (even in air) will generate a differenceof potential whose value is characteristic of themetals. Also see ELECTROMOTIVE SERIES.volt box A precision, potentiometer-type voltagedivider used in the calibration of meters andother instruments. The device is usually providedwith a set of terminal posts for selecting variousratios of output voltage to input voltage.volt-electron See ELECTRONVOLT.voltmeter A usually direct-reading instrumentused to measure voltage. Also see ELECTRONICVOLTMETER, FET VOLTMETER, TRANSISTORVOLTMETER, and VACUUM-TUBE VOLTMETER.voltmeter-ammeter See VOLT-AMMETER.voltmeter amplifier A wideband, flat-frequencyresponse,low-distortion preamplifier used toboost the sensitivity of an alternating-currentvoltmeter.voltmeter-millivoltmeter A voltmeter that providesseveral low ranges, as well as several highones. A familiar example is an alternatingcurrentvoltmeter, which has various full-scaleranges from about 1 millivolt to about 1000 volts.voltmeter multiplier A resistor connected in serieswith a current meter (usually a milliammeteror microammeter) to convert it into a voltmeter.voltmeter sensitivity Unit, ohm per volt. For avoltmeter, the total resistance of the instrument(multiplier resistance plus the resistance of themeter movement) divided by the full-scale deflectionof the meter. Thus, a 0-to-10 direct-currentvoltmeter with an input resistance of 100 kilohmshas a sensitivity of 10,000 ohms per volt.volt-milliammeter A combination meter for measuringvolts and milliamperes.volt-ohm-ammeter A multimeter for measuringvoltage, resistance, and current (in amperes).volt-ohmmeter A combination meter for measuringvoltage and resistance.volt-ohm-milliammeter Abbreviation VOM. Amultimeter for measuring voltage, resistance,and current (in milliamperes and microamperes).voltsensor See VOLTAGE DETECTOR.volts per meter Abbreviation, V/m or Vpm. Theunit of electric field strength.volume 1. Intensity of sound. Also called LOUD-NESS. 2. A circumscribed portion of space, eitherimaginary or actually occupied, and described bythree dimensions (e.g., sphere, ellipsoid, cube,pyramid, etc.). 3. In a computer system, a unit ofmagnetic storage medium (e.g., a diskette).volume compression The automatic reduction ofthe gain of an audio amplifier. The process differsfrom clipping (which “slices off” the tops of waves)in that compression (ideally) reduces the amplitudewhile preserving the waveform. CompareVOLUME EXPANSION.volume compressor A circuit or device (such as anautomatic-gain-control amplifier) for achieving volumecompression. Compare VOLUME EXPANDER.volume conductivity The reciprocal of VOLUMERESISTIVITY.volume control A variable resistor (usually a potentiometer)or a network of resistors (such as apad) for adjusting the gain, and, consequently,the output-signal loudness, of an amplifier.volume equivalent In wire telephony, speechloudness throughout the system, expressed interms of the trunk loss in a reference system andadjusted for equal loudness.volume expander A circuit or device for automaticallyboosting the volume of an audio-frequencysignal. Also see EXPANDER. Compare VOLUMECOMPRESSOR.volume expansion The technique of automaticallyincreasing the gain, and consequently theoutput-signal volume, of an audio amplifier. Alsosee VOLUME EXPANDER. Compare VOLUMECOMPRESSION.volume indicator A fast-acting alternatingcurrentmeter used to monitor the volume level inan audio channel in which the signal level isfluctuating. The scale is graduated in VOLUMEUNITS. Also called VU meter.volume lifetime In a homogeneous semiconductor,the interval between minority-carrier generationand recombination.volume limiter A circuit or device that automaticallyholds the volume level of an audio channelto a predetermined maximum. Also see VOLUMECOMPRESSION and VOLUME COMPRESSOR.volume-limiting amplifier An amplifier that functionsas a volume limiter through the action ofvolume-limiting subcircuits.

volume magnetostriction • vy 737BlackrangeRed range(high risk of distortion)volume indicatorvolume magnetostriction 1. The decrease in thetotal volume of certain ferromagnetic substancesunder the influence of a magnetic field. 2. The increasein the total volume of certain ferromagneticsubstances under the influence of amagnetic field.volume range Unit, decibel (dB). The difference betweenthe maximum and minimum volume levelsthat a device or system can accommodate.volume recombination rate Within the volume ofa semiconductor, the rate at which electrons andholes recombine.volume resistance The effective resistance,through a given medium, between two electrodesplaced within that medium.volume resistivity The resistance of a specific volumeof a material (e.g., the resistance betweenopposite faces of a 1-centimeter cube of the material).Also see MICROHM-CENTIMETER; OHM-CENTIMETER; RESISTIVITY.volumetric efficiency In an electronic assembly,the ratio of the volume of parts to the total volumeof the assembly.volumetric radar A radar providing a threedimensionaldisplay.volumetric sensor In security systems, a devicethat detects effects in a specifically defined threedimensionalregion, such as an entire room (fromfloor to ceiling).volume unit Abbreviation, VU. The unit of measurementof fluctuating alternating-currentpower, such as that of speech or music. Zero VUcorresponds to a reference power of 2.51 milliwatts,or +4 dBm (four decibels above 1 milliwatt).Volume units are measured with aVOLUME INDICATOR.volume-unit indicator See VOLUME INDICATOR.volunteer examiner In amateur radio, a personwho works with the Federal CommunicationsCommission (FCC) to administer license examinations.Such a person is not actually an employeeof the FCC, but serves on an independent,volunteer basis.VOM Abbreviation of VOLT-OHM-MILLIAMMETER.von Hippel breakdown theory The theory that,assuming no electron-energy distribution, breakdownoccurs at field intensities for which the recombinationrate of electrons and holes is lowerthan the rate of ionization by collision.von Neumann architecture In computer systems,a design scheme in which the bits are transmittedserially (one by one) along a single line or bus.VOR Abbreviation of very-high-frequency omnirange(see VHF OMNIRANGE).voter See MAJORITY LOGIC.vox Abbreviated form of VOICE-OPERATED CON-TROL.V P 1. Symbol for GATE-SOURCE PINCHOFF VOLT-AGE of a field-effect transistor. 2. Symbol forPLATE VOLTAGE.V p Symbol for VOLTAGE AT PEAK TORQUE.V particle See VEE PARTICLE.Vpm Abbreviation of VOLTS PER METER. (Also,V/m.)VR 1. Abbreviation of VIRTUAL REALITY. 2. Abbreviationof VOLTAGE REGULATOR.VRAM Abbreviation of VIDEO RANDOM-ACCESSMEMORY.V ref Abbreviation of reference voltage.vrr Abbreviation of visual radio range.V•s Abbreviation of volt-seconds (webers).V•s/A Abbreviation of volt-seconds per ampere(henrys).VSA Abbreviation of VOICE-STRESS ANALYZER.VSB Abbreviation of VESTIGIAL SIDEBAND.VSF Abbreviation of VESTIGIAL-SIDEBAND FILTER.V signal See VEE SIGNAL.vsr Abbreviation of VERY SHORT RANGE.VSWR Abbreviation of VOLTAGE STANDING-WAVE RATIO.vt 1. Abbreviation of VACUUM TUBE. 2. Abbreviationof variable time.VT fuse See PROXIMITY FUSE.VTL Abbreviation of VARIABLE-THRESHOLDLOGIC.vtm Abbreviation of VOLTAGE-TUNABLE MAG-NETRON.VTO Abbreviation of VOLTAGE-TUNABLE OSCIL-LATOR.VTR Abbreviation of VIDEOTAPE RECORDER orVIDEOTAPE RECORDING.VTVM Abbreviation of VACUUM-TUBE VOLT-METER.vt voltmeter See VACUUM-TUBE VOLTMETER.VU Abbreviation of VOLUME UNIT.vulcanized fiber A tough insulating material derivedfrom cellulose. Dielectric constant, 5 to 8.VU meter See VOLUME INDICATOR.VVCD Abbreviation of voltage-variable capacitordiode (see VOLTAGE-VARIABLE CAPACITOR, 1).VVV signal See VEE SIGNAL.VW Abbreviation of volts working (see WORKINGVOLTAGE).vy Abbreviation for very.

W 1. Symbol for WORK. 2. Abbreviation of WATT.3. Symbol for TUNGSTEN. 4. Symbol for EN-ERGY. 5. Abbreviation of west. 6. Abbreviation ofWIDTH.w 1. Abbreviation of WEIGHT. (Also, wt.) 2. Abbreviationof week.WAC Amateur radio abbreviation of Worked AllContinents, an award given to operators who haveengaged in verified two-way communication withstations on all continents.wafer 1. Semiconductor die. 2. A thin, flat disk,ring, or plate around which the contacts of a rotaryswitch are spaced. 3. A thin square or rectangleof dielectric material used as the dielectricmember in a fixed capacitor. 4. A plate cut from acrystal (e.g., a quartz wafer).wafer fabrication The various processes used inthe manufacture of semiconductor integrated circuits.wafer slicing Cutting plates from a mother crystal,as when piezoelectric plates are cut from a quartzcrystal.wafer socket A component socket consisting of aplastic or ceramic wafer with spring-type contactsfor gripping the pins.wafer switch A rotary switch whose contacts arearranged around the periphery of a plastic or ceramicwafer.Wagner ground A circuit (often a single potentiometer)that facilitates cancellation of stray reactancein an alternating-current bridge. Thebridge is balanced alternately with the bridgebalancecontrol and the Wagner control, untilthere is no further shift of null point when changingfrom one to the other.BridgebalancecontrolDetWagnercontrolGenWagner ground(with capacitance bridge)waiting time 1. See WARMUP TIME. 2. The delaybetween the time a data transfer to or from acomputer memory is called for and the actualtransfer of the data. Also called LATENCY.walkie-lookie A portable combination camera andtransmitter for remote television pickup. Atsports events and other gatherings, the unit isstrapped to the shoulder of the camera operator.walkie-talkie A portable, compact transceiver (ortransmitter-receiver).Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

wall absorption • water adsorption 739wall absorption Diminished radioactive emission(especially of beta and gamma rays) because ofabsorption by the radiating substance.wall box A wall-mounted (usually metal) box enclosingcircuit breakers, fuses, switches, etc.wall effect In an ionization chamber, the rise inionization because of electrons being released bythe walls of the chamber.wall energy In a ferromagnetic substance, the energyper unit area stored in a domain wall betweentwo regions of opposite magnetization.Wallman amplifier A cascode amplifier (see CAS-CODE).wall mount A metal bracket for fastening an antennato a wall.wall outlet A plug or socket, usually mounted in aprotective box or can and recessed in a wall thatcan be accessed from the front. It is commonlyused for supplying alternating-current power toappliances at 117 volts or 234 volts. It is alsoused in telephone and cable-television systems.wall plaque A loudspeaker so thin that, mountedin a frame (sometimes behind grill cloth), it canbe hung on a wall.wall plate A (usually rectangular) plate of metal orplastic for holding a wall outlet or wall switch.wall plug A male or female plug usually mountedin a protective box or can and recessed in a wall.Such a device can provide easy access to an antenna,telephone line, or load; or it can deliveralternating-current, direct-current, or radiofrequencypower.walls The sides of the groove cut into a record disc.wall socket A male or female socket usuallymounted in a protective box or can and recessedin a wall. Such a device can provide easy accessto an antenna, telephone line, or load; or it candeliver alternating-current, direct-current, orradio-frequency power.wall speaker See WALL PLAQUE.wall switch A switch usually mounted in a protectivebox or can and recessed in a wall.wall telephone A wall-mounted telephone set. Itgenerally fits over the jack, so the only cord is betweenthe main unit and the receiver.wall-through tube See LEAD-IN TUBE.Walmsley antenna A phased array consisting ofseveral full-wavelength loops.wamoscope A radar display tube that performsseveral microwave-receiver functions (detection,oscillation, amplification, etc.) as well as displayingan image. The name is an acronym for wavemodulationoscilloscope.wander See SCINTILLATION, 1.WAP Acronym for WIRELESS ACCESS PROTOCOL.warble 1. A periodic rise and fall in the pitch of amusical tone or combination of tones. 2. To riseand fall in pitch with a definite period.warble-tone generator An audio-frequency oscillatorwhose frequency is varied at a subaudiblerate over a fixed frequency range.warm junction The heated junction in a twojunctionthermocouple circuit. Also called HOTJUNCTION. Compare COLD JUNCTION.warmup The process of stabilizing an electronicequipment by allowing its temperature to rise tothe optimum level.warmup time The time required for an electroniccircuit to become fully operational, or to stabilize,after the power has been switched on.warning bell (buzzer) A bell (or buzzer) used as anaudible alarm in a WARNING DEVICE.warning device A device, such as an electronic signaler,for alerting a person to an emergency (intrusionon premises, danger to life and safety,etc.) or to the existence of an intrusion into a securedarea.warning lamp See WARNING LIGHT.warning light A lamp used as a visual alarm in awarning device.warpage Distortion of the normally straight sidesof a triangular wave.warping In multimedia computer graphics, achange in the shape of an object that occurssmoothly over a period of time.WAS Amateur radio abbreviation of Worked AllStates, an award given to operators who have engagedin verified two-way communication withstations in all states of the United States.washer capacitor A very thin donut capacitor.washer resistor A resistor made in the generalshape of a washer or ring and having a centerhole for a mounting screw or stacking rod.washer thermistor A thermistor made in the generalshape of a washer and having a center holefor a mounting screw or stacking rod.washer varistor A varistor made in the generalshape of a washer and having a center hole for amounting screw or stacking rod.washout process A method of fabricating bipolartransistors. The contact metal is deposited in thediffusion hole.waste instruction In a computer program, an instructionnot meant to be acted upon (e.g., oneused to take up space in the listing for some reason).Also called null instruction and dummy instruction.watch A work shift, as of electronic personnel (e.g.,radio station operators).watchcase receiver An earphone enclosed in asmall, round case with a screw-on cap. It is derivedfrom its resemblance to a large pocket watch.water absorption For a solid material, such as adielectric, the ratio of the weight of water absorbedby the material to the weight of the material.water-activated battery A battery that containsall the ingredients of its electrolyte, except water,which must be added when the battery is put intoservice.water adsorption The formation of a thin layer ofwater molecules on the surface of normally dry

740 water adsorption • WATSmaterial, but not by absorption. Also see AD-SORPTION.water analogy The useful, but not wholly accurate,teaching device of comparing an electriccurrent with the flow of water. In such a comparison,voltage is shown equivalent to water pressure,and current to the quantity (e.g., gallons) ofwater flowing in unit time.water battery A primary battery or cell using wateras the electrolyte.water calorimeter A calorimeter used to measurepower in terms of the increase in temperature ofwater heated by the electrical energy.water capacitor An emergency capacitor made bysetting one glass of water in another larger jar ofwater so that the two bodies of water are separatedby the walls of the smaller jar. The bodies ofwater, in which an electrolyte has been dissolved,form the “plates” of the capacitor, and the wall ofthe smaller jar serves as the dielectric betweenthem.ElectrodeJarsElectrodewater capacitorwater-cooled tube A power tube, such as a largeradio transmitting tube, cooled by the circulationof water in the space between the outside of thetube envelope and a surrounding jacket.water cooling A method of cooling components bypumping water through pipes surrounding them.water-flow alarm An electronic circuit that actuatesan alarm when the flow of water throughpipes or other channels changes from a predeterminedrate.water-flow control A servo system for automaticallymaintaining or adjusting the flow of waterthrough pipes or other channels.water-flow gauge See WATER-FLOW METER.water-flow indicator See WATER-FLOW METER.water-flow meter An instrument used to monitorthe flow of water through pipes or other channels,sometimes showing its direction as well as itsrate.water-flow switch In water-cooled systems (e.g.,water-cooled tubes), a switch that actuates analarm when the water slows or stops.water glass Sodium silicate, a substance used as afireproofing agent and protective coating.water ground An earth connection made by droppinga weighted wire into a body of water.water jacket In a water-cooled device, the outerjacket that, along with the outer wall of the cooledcomponent, forms a space through which thecooling water flows.water-level control A servo system that automaticallymaintains or adjusts the level of water insidea tank or other container.water-level gauge An electronic system that givesdirect water level readings inside a tank or othercontainer.water-level indicator See WATER-LEVEL GAUGE.water load 1. A makeshift, power-dissipating resistiveload (see DUMMY LOAD) consisting of acontainer of tap water or saltwater into which twowires are immersed. 2. A waveguide terminationcontaining water heated by the microwave energy.It is usable as a water calorimeter.water monitor A sensitive electronic instrumentfor checking radioactivity in a water supply.water-pipe ground An earth connection made byrunning a wire to the nearest cold-water pipe.This scheme works only with metal pipes devoidof insulating joints or splices.water power Hydroelectric power (i.e., electricalenergy produced by generators driven by water).water-pressure alarm An electronic circuit thatactuates an alarm when water in pipes or otherchannels changes from a predetermined level.water-pressure control A servo system for automaticallymaintaining or adjusting water pressurein pipes or other channels.water-pressure gauge See WATER-PRESSUREMETER.water-pressure indicator See WATER-PRESSUREMETER.water-pressure meter An instrument that directlyindicates water pressure in a pipe or tank.water-pressure switch A switch that actuates analarm when water pressure rises or falls.water pump In a water-cooled electronic system, the(usually rotary) pump that circulates the water.water resistor An electrolytic resistor in which theelectrolyte is tap water or diluted saltwater.water rheostat A variable water resistor. Usually,the resistance is varied by moving the immersedelectrodes closer together or farther apart.water tester An instrument for checking pH, electricalresistance, and other properties of water.water witching Locating underground water byelectronic methods.WATS Acronym for Wide Area Telephone Service. Aform of long-distance telephone service. Rates arecharged on a different basis than normal longdistanceservice. The system is especially favoredby businesses because it saves money for subscribersmaking a large number of calls in eachbilling period.

watt • wave direction 741watt Abbreviation, W. The practical unit of electricand other power. One watt is dissipated by a resistanceof 1 ohm through which a current of1 ampere flows. See also KILOWATT, MEGA-WATT, MICROWATT, and MILLIWATT.wattage Electrical power, especially when expressedin watts.wattage rating 1. The recommended output powerof a device. 2. The recommended power dissipationof a device.watt current The component of alternating currentthat is in phase with voltage. Also calledRESISTIVE CURRENT. Compare REACTIVECURRENT.watt-decibel conversion The conversion of apower level, such as the power output of an amplifier,in watts to the corresponding power levelin decibels, with respect to a reference level.Thus, n dB = 10 log 10 (P/P ref ), where P is the powerof interest (watts), and P ref is the reference level(e.g., one milliwatt).watt-hour Abbreviation, WH. The unit of electricalenergy or work; 1 WH = 3600 joules = 10 -3kWH. Also see ENERGY, KILOWATT-HOURS,POWER, and WATT-SECOND.watt-hour capacity The number of watt-hoursthat a storage battery can deliver reliably andsafely under specified operating conditions.watt-hour-demand meter A combination watthourmeter and demand meter.watt-hour efficiency For a storage battery, theratio of watt-hours output to watt-hours ofrecharge.watt-hour constant In an electric-energy meter,the number of watt-hours in one revolution of theindicating disk.watt-hour meter An instrument for measuringelectrical energy in watt-hours. One well-knowntype consists essentially of a small motor gearedto a row of four dial indicators. An eddy-currentdisk keeps the motor speed proportional to thewatt-hours consumed by a load, a value which isthe sum of the readings of the dials. Also calledSERVICE METER and KILOWATT-HOUR ME-TER.wattless current The component of alternatingcurrent that is out of phase with voltage. Alsocalled REACTIVE CURRENT. Compare RESIS-TIVE CURRENT.wattless power The apparent power in a reactivecircuit, indicated by the product of volts and amperes.There is no actual power consumption becausethe power taken by a reactance during ahalf-cycle is returned to the generator during thenext half-cycle. Also see AC POWER, APPARENTPOWER, REACTIVE KILOVOLT-AMPERES, andREACTIVE VOLT-AMPERES.wattless volt-amperes See WATTLESS POWER.wattless watts See WATTLESS POWER.wattmeter Abbreviation, WM. An instrument usedto measure electrical power. The scale usuallyreads directly in watts, kilowatts, milliwatts, ormicrowatts. Also see ELECTRONIC WATTMETER.watt-second Abbreviation, Ws. A small unit ofelectrical energy or work; 1 watt-second = 1 joule= 1/3600 watt-hour. Also see ENERGY andPOWER.watt-second constant In an electric-energy meter,the number of watt seconds in one revolution ofthe indicating disk.wave 1. A single oscillation of some property ofmatter or space, such as density, displacement,or field strength. It moves outward from a point ofdisturbance and grows weaker as it travels farther.Wave motion is associated with mechanicalvibration, sound, radio, heat, light,X rays, gamma rays, and cosmic rays. SeeSOUND and WAVELENGTH. 2. A single cycle ofalternating or pulsating current or voltage. Alsosee AC VOLTAGE, ALTERNATING CURRENT,PULSATING DC VOLTAGE, and PULSATING DI-RECT CURRENT.wave absorption The removal of energy from electromagneticwaves as they pass through certainmedia, such as solid bodies, water, and the atmosphere.Compare POLARIZATION, WAVE RE-FLECTION, and WAVE REFRACTION.wave amplitude The peak value of a wave. Also seeWAVE CREST and WAVE TROUGH.wave analyzer An instrument consisting essentiallyof a continuously tunable bandpass filterand an electronic alternating-current voltmeter.As the filter is tuned successively to the fundamentalfrequency of a complex wave and to itsvarious harmonics, the voltmeter shows the amplitudeof each of the components. Also see HET-ERODYNE WAVE ANALYZER.wave angle The angle, measured with respect tothe horizon, at which a radio wave is transmittedor received.wave antenna See BEVERAGE ANTENNA.wave attenuation The reduction of wave amplitude,with respect to distance from the source.waveband A band of radio frequencies. Also calledFREQUENCY BAND.waveband switch See BANDSWITCH.wave beam Unidirectional radiation from a directiveantenna.wave bounce See WAVE REFLECTION.wave clutter Radar interference caused by waveson a body of water, particularly large swells onthe ocean.wave converter A waveguide part, such as a baffle-plateor grating, that changes a wave patternfrom one type to another.wave crest The maximum value of a wave envelope.Compare WAVE TROUGH.wave cycle A complete single alternation of a wave.wave direction The direction in which an electromagneticwave travels. It is perpendicular to thewave front and depends (whether it is forward orbackward) upon the direction of the electric and

742 wave direction • waveguide flangemagnetic components. If either is reversed, wavedirection reverses; if both are reversed, the directionremains unchanged.wave duct 1. See DUCT, 1. 2. A tubular waveguidein which wave propagation is concentrated.wave envelope The outline described by the variousamplitude peaks of the cycles in an amplitude-modulatedwave. The envelope frequency isequal to the modulating frequency.wave envelopewave equation A second-degree partial differentialequation whose solution describes wave phenomena.wave filter A circuit or device that offers differentamounts of attenuation to signals of different frequencies.See BANDPASS FILTER, BAND-SUPPRESSION FILTER, HIGH-PASS FILTER, andLOW-PASS FILTER.waveform The shape of a wave described in termsof its resemblance to some well-known figure orto its conformity to the curve of the applicablewave equation (e.g., sinusoidal, square, sawtooth,cosine, rectangular, and triangular).waveform-amplitude distortion See AMPLITUDEDISTORTION.waveform analyzer See WAVE ANALYZER.waveform converter A circuit or device for changinga signal of one waveform (such as a sine wave)into one of another waveform (such as a pulse orsquare wave).waveform distortion The malfunction evidencedby a change of the waveshape of a signal passingthrough a circuit.waveform error In a quantity displayed by analternating-current test instrument, an errorcaused by the waveform of the measured signal.Thus, a voltmeter calibrated with a sine-wavevoltage is subject to error when a measured signalis nonsinusoidal. Also called waveform effect.waveform generator See FUNCTION GENERATOR.waveform influence See WAVEFORM ERROR.waveform monitor In television operations, an oscilloscopethat continuously displays the videowaveform.waveform synthesizer A variable-frequency signalgenerator that allows the tailoring of waveshapeto suit individual applications. A function genera-tor (see FUNCTION GENERATOR, 1) is such aninstrument, but it usually provides only a choiceof common waveshapes.wave front For a radio wave, the plane that is parallelto the perpendicular electric and magneticlines of flux. The wave propagates at right anglesto this plane.wave function A point function in a wave equation,specifying wave amplitude.wave group The resultant of several differentfrequencywaves traveling over a common path.waveguide A transmission line used at ultra-highand microwave radio frequencies. It is a hollowmetal pipe with a rectangular or circular crosssection. A rectangular waveguide must havesides measuring at least 0.5 wavelength andpreferably more than 0.7 wavelength. A circularwaveguide should be at least 0.6 wavelength indiameter, and preferably 0.7 wavelength or more.The characteristic impedance (Z 0 ) varies with frequency.In this sense, it differs from coaxial orparallel-wire lines, whose Z 0 values are independentof frequency.waveguide apparatus See WAVEGUIDE COMPO-NENTS.waveguide attenuator A device, such as an interposedenergy-absorbing plate, for signal attenuationin a waveguide.waveguide choke flange A waveguide flange thatpresents no impedance to the signal, and whichneed not be metallic for continuity.waveguide component A device adapted for connectionto, or insertion into, a waveguide system.Such components include waveguide parts andaccessories (e.g., splicing hardware, attenuators,loads, wavemeters, etc.).waveguide connector A fitting for joining waveguidesfor the efficient propagation of a signal.waveguide coupling See WAVEGUIDE CONNEC-TOR.waveguide critical dimension The cross-sectionaldimension that determines the cutoff frequencyfor a waveguide.waveguide cutoff In a waveguide, the highest orlowest frequency that can be propagated with lessthan a specified amount of attenuation per unitlength.waveguide directional coupler A directional couplermade of two parallel waveguides with a commonwall. Two slots cut in the wall allow part ofthe microwave energy propagated in one directionin the main waveguide to be extracted, and energytraveling in the opposite direction to be rejected.waveguide dummy load A waveguide section thatdissipates the microwave energy entering it.waveguide elbow 1. A curved bend in a waveguide.2. A waveguide connector with a bend.waveguide flange A flat, liplike fitting at the end ofthe pipe of a waveguide. It fastens waveguidesections together or attaches a waveguide

waveguide flange • waveguide tee 743Greaterthan 2λResistorplateConducting wiresButton resistorwaveguide dummy loadwaveguide elbowResistorrodCarbon-coated clothor graphited sandGreaterthan 2λcomponent, equipped with an identical flange, tothe end of a waveguide.waveguide frequency meter See WAVEGUIDEWAVEMETER.waveguide gasket A gasket that provides electricalcontinuity between mating waveguide sections.waveguide grating An array of wires mounted insidea waveguide, and that passes signals atsome frequencies while obstructing others.waveguide impedance Where the power P isknown, and voltage E and current I are defined,with respect to a type of wave and waveguide, thevalue is either E 2 /P or P/I 2 .waveguide junction A fitting that allows onewaveguide section to be joined at an angle to anothersection. See, for example, WAVEGUIDETEE and WAVEGUIDE WYE.waveguide lens A microwave lens consisting ofwaveguide sections that provide the requiredphase shifts.waveguide load See WAVEGUIDE DUMMY LOAD.waveguide mode The form of propagation indicatedby the field pattern in a plane transverseto the direction in which energy is propagatedthrough a waveguide. Common modes areTRANSVERSE ELECTRIC MODE, also called TEmode, and TRANSVERSE MAGNETIC MODE,also called TM mode.waveguide mode suppressor A filter that suppressesundesired propagation modes in a waveguide.waveguide phase shifter A shifter for adjustingthe phase of waveguide output energy, with respectto input energy.waveguide plunger A plunger-like device that reflectsincident microwave energy in a waveguide.waveguide post A transverse rod inside a waveguidethat acts as a parallel susceptance.waveguide probe A pickup probe (tip or loop, asrequired) for sampling the field inside a waveguide,or a similar injection probe for introducingenergy into a waveguide. Also see WAVEGUIDESLOTTED LINE.waveguide propagation 1. The transmission ofmicrowave energy through a waveguide by successivereflections between the inner walls.2. Propagation of very-high-frequency (VHF), ultrahigh-frequency(UHF), or microwave electromagneticfields through an atmospheric duct (seeDUCT, 1), as if through a waveguide. 3. Propagationof very-low-frequency (VLF) electromagneticfields through a waveguide-like duct between theionosphere and the earth’s surface.waveguide radiator An antenna consisting of anopen-ended waveguide with or without a horn. Itradiates microwave energy into space or to a reflector.waveguide resonator A waveguide section used asa cavity resonator (see RESONANT CAVITY).waveguide seal A protective cover for the end of awaveguide. The seal introduces very little microwaveattenuation, while preventing entry ofmoisture and debris.waveguide shim A thin, pliable metal sheet insertedbetween mating waveguide components for electricalcontinuity. Also see WAVEGUIDE GASKET.waveguide shutter An adjustable mechanical barrier,such as a rotatable vane, inserted into awaveguide to block or divert microwave energy.waveguide slotted line A section of waveguidehaving a slot that accommodates a movableprobe or coupling element.waveguide slug tuner A quarter-wave dielectricslug inserted into a waveguide so that its amountof penetration and position can be adjusted fortuning purposes.waveguide stub A stub consisting of a waveguidesection joined to a main waveguide at an angleand provided with a nondissipative termination.waveguide stub tuner An adjustable piston in awaveguide stub for tuning purposes.waveguide switch A switch consisting of a movablesection of waveguide that can be positionedfor coupling to one of several other waveguidesections; it thus passes the energy it receives toany of the other sections.waveguide system Microwave “plumbing” consistingof waveguides, their fittings and accessories,and associated components (such as attenuators,loads, wavemeters, etc.).waveguide taper A connector that is flared to allowcoupling between two waveguide sections havingdifferent cross-sectional sizes.waveguide tee In a waveguide assembly, a teeshapedjunction used to connect a section ofwaveguide in series or parallel with anothersection.

744 waveguide transformer • wave normalwaveguide transformer A waveguide componentthat functions as an impedance transformer.waveguide tuner In a waveguide system, an adjustabletuner providing impedance transformation.waveguide twist A length of waveguide whosecross section is rotated around the longitudinalaxis (e.g., from vertical to horizontal).wavelength Unit, meter. The displacement in onecomplete wave of an alternating or vibrating phenomenon,generally measured from crest to crestor from trough to trough of successive waves. Forelectromagnetic waves in free space, the wavelengthin meters is equal to 3 × 10 8 divided by thefrequency in Hertz. Also see WAVELENGTH-PERIOD-FREQUENCY RELATIONSHIPS.Greaterthan 2λwaveguide twistwaveguide wavelength In a uniform waveguideoperating at a given frequency and in a particularmode, the distance between similar points for360° phase shift.waveguide wavemeter A waveguide componentthat acts as an absorption wavemeter or transmissionwavemeter for identifying microwavefrequencies.MovableplungerVoltage probeMetal cylinderVwaveguide wavemeterVoltmeterSlot for slidingprobe along guideλBA AWave ofenergyEnergywaveguide wedge See WEDGE, 1.waveguide window A thin metal opening mountedtransversely inside a waveguide for impedancematchingpurposes. The edges of the slit in a capacitivewindow are perpendicular to the electricfield; in an inductive window, they are parallel tothe electric field.waveguide wye In a waveguide assembly, a wyeshapedjunction for joining three waveguide sections.wave heating Heating a material by energy absorbedfrom traveling electromagnetic waves.wave interference Interaction between two ormore waves, resulting in reinforcements and cancellationsof energy.wavelength constant The imaginary-numbercomponent of the propagation constant.wavelength shifter 1. A frequency shifter whoseperformance is indicated in units of wavelength,rather than in units of frequency. 2. In certainphotosensitive cells and tubes, a photofluorescentsubstance that raises the efficiency of thedevice by absorbing photons and then releasingones of longer wavelength.wave mechanics A theory of matter that viewssubatomic particles as complex wave patterns,and attempts to account for all physical processesin terms of wave phenomena.wavemeter An instrument for measuring the wavelengthor frequency of radio waves. One form consistsof a series-resonant circuit containing aninductor, variable capacitor, and diode-type meter.The dial of the capacitor is calibrated to readin MHz. The inductor picks up energy from theradio-frequency source of unknown frequency,the capacitor is tuned for peak deflection of themeter, and the unknown frequency is read from thedial. This instrument is often called an absorptionwavemeter because it absorbs a certain amount ofpower from the signal source under test. See alsoCAVITY WAVEMETER, COAXIAL WAVEMETER,LECHER WIRES, and SLOTTED LINE.wave motion Undulating motion (e.g., up anddown, and side to side). An electromagnetic wavehas undulating electric and magnetic componentsthat are both in phase and perpendicularto each other and to the direction of propagationof the wave.wave normal 1. The direction of propagation of anelectromagnetic wave. 2. A unit vector directed at

wave normal • way station 745a right angle to both the electric and magneticlines of flux in an electromagnetic wave.wave number The reciprocal of wavelength. Thisnumber denotes the number of waves per unitdistance.wave packet A short pulse composed of waves.wave packets Radiant energy resulting from anumber of wave trains of different wavelength.wave path The line along which a WAVE TRAIN ispropagated.wave polarization The direction (horizontal or vertical)of wave undulations (i.e., the plane of theundulations, with respect to the direction ofpropagation). In general, a vertical antennaradiates a vertically polarized wave, and ahorizontal antenna radiates a horizontallypolarized wave.wave propagation The movement of wavesthrough space or through some medium. Electromagneticwaves travel through space at the speedof light (approximately 3 × 10 8 meters, or 186,000miles, per second) and, like light, can be reflectedand refracted.wave reflection The reflection of electromagneticwaves by an obstruction, such as a solid body ora layer of the ionosphere. Compare WAVE AB-SORPTION, WAVE POLARIZATION, and WAVEREFRACTION.wave refraction Bending of the line of propagationof electromagnetic waves as they pass throughvarious media, such as the troposphere or theionosphere. Compare WAVE ABSORPTION,WAVE POLARIZATION, and WAVE REFLECTION.waveshape The overall contour of a wave—especiallyas revealed by a curve plotted for the particularwave equation. Also see WAVEFORM.waveshaping circuit A circuit that receives an inputsignal having a certain waveshape, and deliversan output signal having a different waveshape.For example, a squaring circuit converts a sinewave into a square wave at the same frequency.wave surface See WAVE FRONT.wave tail In a decaying pulse or signal envelope, theinterval between the beginning of the decay andthe point at which the amplitude reaches zero.wave telegraphy See RADIOTELEGRAPHY.wave telephony See RADIOTELEPHONY.wave theory of matter A physical theory that thecharge of an electron is distributed in space,rather than being focused at a point. Also seeWAVE MECHANICS.wave tilt A slight forward tilt of the electric fluxlines in a radio wave radiated at the surface of theearth by a vertical antenna.wave train A series of identical electromagneticwave cycles propagated at equal intervals; anelectromagnetic energy burst lasting at least severalcycles.wavetrap A resonant circuit consisting of an inductorand capacitor, either or both of which canbe adjustable for tuning, used to remove (trap) aInputwavetrapOutputsignal at the resonant frequency from a signalmixture.wave trough The minimum value of a wave envelope.Compare WAVE CREST.wave velocity The distance per unit time traversedby a wave passing through a given medium.wave winding See DRUM WINDING.wa-wa pedal A foot-operated device used with anelectronic musical instrument to produce a “wahwah”sound fluctuation.wax 1. Any of a series of organic materials havingimportant uses as dielectrics, impregnants, sealers,and lubricants in electronics. They are usuallysolid or semisolid, waterproof, and easilymelted. 2. In certain phonograph record discs, ablend of wax (see 1, above) and metallic soaps.Also see WAX MASTER, 2.wax cake See WAX MASTER, 1, 2.wax capacitor A fixed capacitor that has beendipped in or impregnated with a wax, such ashalowax.wax-dipped capacitor A fixed capacitor that hasbeen dipped in a wax for sealing against moisture.waxed paper See WAX PAPER.wax-filled capacitor A fixed capacitor impregnatedwith a wax for enhancing the properties of its dielectric(usually paper) and sealing the capacitorunit.wax master 1. In disc-recording operations, theoriginal recording made on a wax-surface disc.2. To make an original recording on a waxsurfacedisc.wax original See WAX MASTER.wax paper Wax-saturated paper used as a dielectricfilm in fixed capacitors and as an insulator.way-operated circuit A single or duplex circuitshared by three or more party stations.way point An important point selected on a radionavigationalcourse line.way station A station consisting of a teletypewriterconnected at an intermediate point in a line (i.e.,between, and in series with, other teletypewriterstations).

746 WAZ • weighted noise levelWAZ Amateur radio abbreviation of Worked AllZones, an award given to operators who have carriedon verified two-way communication with stationsin all communications zones of the world.WB Abbreviation of weather bureau.W B Abbreviation of base-region width (in a transistor).Wb Symbol for WEBER.Wb/m 2 Abbreviation of Webers per square meter(see TESLA).W C Abbreviation of collector-region width (in a transistor).WCEMA Abbreviation of West Coast ElectronicManufacturers’ Association.W/cm 2 Abbreviation of watts per square centimeter.WE Abbreviation of write enable.W E Abbreviation of emitter-region width (in a transistor).weak battery 1. A battery that has been depletedto the point that its output (no-load or full-load) istoo low to be useful. 2. A battery specially designedfor low-voltage output.weak color Lack of color vividness or poor contrastbetween colors in a color-television picture. Thecondition is often caused by some malfunction inthe chroma demodulator(s).weak contrast In a television picture, poor differentiationof adjacent tonal areas.weak coupling See LOOSE COUPLING.weak current An extremely small electric current.The term is relative; generally, it refers to currentsof a few microamperes or less.weak magnet 1. A magnet whose power has deterioratedconsiderably below a prescribed level.2. A body that normally is only slightly magnetic.weak signal A signal whose amplitude is very lowcompared with that of signals considered satisfactoryin a given application. Although the termis relative, it usually implies a signal that is noncompetitivewith other signals in a given environment.weak-signal detector A detector in which, at lowinput-signal amplitudes (weak-signal levels),the direct-current output is proportional to thesquare of the root-mean-square (rms) value of theinput-signal voltage.wearout The complete deterioration of a componentor system (i.e., beyond restoration to usefulservice).wearout failure Failure because of wearout, whichcan be predicted on the basis of known lifetimeand the deterioration characteristics of componentsand equipment.wearout point The instant of wearout, in terms ofpower output, watt-hour capacity, or some otherspecification.weather antenna An antenna dimensioned forreception exclusively in the 162.4- to 162.55-MHz weather band. See WEATHER TRANSMIS-SION.weathering Deterioration of electronic equipmentas a result of exposure to outdoor heat, cold,moisture, wind, and similar conditions.weather-protected machine A machine (usually agenerator or motor) whose vent holes are designedto prevent entry of dust, water, and debris.weather protection The coating, sealing, or treatingof electronic equipment for protection againstcorrosion, humidity, and temperature changes inoutdoor use.weather satellite A satellite designed to photographweather systems in infrared and/or visiblelight, and relay the pictures to earth via facsimileor television.weather sonde See RADIOSONDE.weather transmission The radio transmission ofmeteorological reports. Sometimes the transmissionsare combined with guidance transmissions,from which they can be separated by means of afilter in the receiver.weber Abbreviation, Wb. The SI unit of magneticflux and of the magnetic flux quantum; 1 Wb =10 8 maxwells = 1.257 × 10 –7 unit pole.Weber-Fechner law The law expressing the relationshipbetween a stimulus and the physiologicalreaction it produces: The sensation isproportional to the logarithm of the stimulus.weber per square meter Symbol, Wb/m 2 . SeeTESLA.weber turn A unit of magnetic flux linkage equal to10 8 maxwell turns.wedge 1. In a waveguide, a termination consistingof a tapered block or plate of carbon (or other dissipativematerial). 2. In a television test pattern,convergent, equally spaced lines for checking resolution.wedge bonding In integrated-circuit fabrication, amethod of bonding in which a thermocompressionbond (see COLD-COMPRESSION WELDING)is obtained through pressure from a wedgeshapedtool.Wehnelt cathode An oxide-coated cathode in anelectron tube.Wehnelt cylinder In a cathode-ray tube, thecathode-enclosing cylinder that concentrates theelectrons emitted by the cathode.weight 1. The amount of gravitational pull on abody or particle. 2. Extra significance given to aterm or value. See, for example, WEIGHTEDTERM. 3. The dot-to-space ratio in a Morse-codesignal.weight-density Symbol, d. Unit, kg/m 3 . Theweight per unit volume of a liquid, such as anelectrolyte or insulating oil; also called density.weighted distortion factor In the measurement ofharmonic distortion, a factor whose use allowsthe harmonics in the complex waveform to beweighted in proportion to their relationship.weighted noise level Unit, dBm. The noise levelweighted with respect to the 70-dB equalloudnesscontour of hearing.

welder 1. An electrical device, often electronicallycontrolled, for welding materials. 2. A person whooperates a device, as defined in 1.weldgate pulse In a welding device, the pulse thataffects the arc current; therefore, it also affectsthe intensity of the heat produced by the device.welding control An electronic system for controllingthe interval during which current is passedthrough a workpiece in spot welding or seamwelding. In this system, an electronic timer circuitdetermines the conduction time of thyraweighting• wet electrolytic capacitor 747MarkSpaceMarkSpaceMarkSpaceweighting1. Adjustment of a parameter to compensatefor some imbalance in a system. 2. Adjustmentof the dot-to-space ratio in a Morse codesignal. 3. Adjustment of the mark-to-space ratioin a digital communications signal.weighting filter A filter used in a communicationsnetwork to represent the characteristics of thetransmission passband.weighting network A network that weighs differently(in a prescribed ratio) the frequency componentsappearing in an output signal by offeringunequal attenuation to those frequencies.weightlessness switch See ZERO-GRAVITYSWITCH.Weir circuit In frequency-modulated signal transmission,a circuit used to stabilize the carrierwave. It compares the average carrier frequencywith the frequency of a standard crystal oscillator,obtaining a direct-current compensating voltage(proportional to frequency deviation) that isapplied to the frequency modulator. Also calledWeir stabilization circuit.Weiss constant In paramagnetism, a constantalso known as paramagnetic Curie temperature. Itcan be positive or negative, depending on the particularparamagnetic material. It is important indefining the behavior of certain paramagneticsubstances.weldTimeTimeTimeweight, 31:1Normal3:1Heavy1:3LightA strong bond of materials (usually metals)obtained by applying heat to areas to be joinedwhile they are held or pressed together. No foreignmetal is used, as is the case in brazing andsoldering. The required heat is sometimes obtainedby passing a high electric current throughthe materials.trons, ignitrons, or silicon-controlled rectifiers inthe welding circuit. The control system can alsoregulate the welding current.welding current The high electric current passedthrough a workpiece to produce the heat requiredfor welding.welding cycle The required sequence of steps (andthe time required) in making a weld electronically.welding time See WELD TIME.welding transformer For electronic welding, aspecial very-high-current step-down transformer.weld junction See WELD.weld polarity The polarity of welding current.Some materials require a certain direction of currentflow for a good weld.weld time The interval during which welding currentflows through the bodies to be bonded together.well counter A radiation-counter setup in which aradioactive sample and detector are enclosed togetherin a thick-walled (usually lead) cylinder tominimize background count.well-structured language An advanced form ofhigh-level computer programming language. It isused in graphical and control applications.Wenner element An adjustable, dual-slidewirebalancing resistor used in constant-current, laboratorypotentiometers to eliminate the necessityfor sliding contacts in the measuring circuit.Wenner winding A low-capacitance, low-inductancewinding for high-frequency wirewoundresistors in which the direction of the wire isreversed by looping alternate turns along theform.Wertheim effect The tendency for a potential differenceto develop between opposite ends of alength of wire, when the wire is placed parallel tomagnetic lines of flux and rotated.Western Union joint A strong splice of two wiresmade by tightly twisting a short portion of the tipof each wire along the body of the other. For increasedruggedness, the joint is often soldered.Also called Western Union splice.Weston cell See STANDARD CELL.Westrex system A system of sound recording inwhich signals from two separate microphonechannels are recorded on opposite walls of agroove on a disc.wet battery A battery of cells having a liquid electrolyte.wet Liquid, especially pertaining to the electrolytematerial in an electrochemical cell.wet cell A battery cell having a liquid electrolyte.Compare DRY CELL.wet-charged stand The length of time that a fullycharged, wet storage cell can stand idle before itscapacity drops by a specified amount.wet electrolytic capacitor An electrolytic capacitorin which the electrolyte is a liquid. The leakagecurrent in this type is higher than in the dry

748 wet electrolytic capacitor • whistle filterelectrolytic, but it is self-healing after momentaryvoltage breakdown. Compare DRY ELEC-TROLYTIC CAPACITOR.wet grab The adherence of a pressure-sensitivetape or sheet to a surface when very little pressureis used.wet rectifier See ELECTROLYTIC RECTIFIER.wet shelf life The specified shelf life of a discharged,wet storage cell. Compare DRY SHELFLIFE.wetted-contact relay See MERCURY-WETTEDREED RELAY.wetting Applying a mercury coating to a contactsurface.wetting agent A substance (such as an alcohol orester) that promotes the spreading and adhesionof a liquid or its absorption by a porous material.WG Abbreviation of WIRE GAUGE.WH Abbreviation of WATT-HOUR.wh Abbreviation of WHITE.Wheatstone bridge A four-arm balancing circuit(see BRIDGE), having resistors in each arm andused to measure an unknown resistance in termsof a standard resistance. The bridge supply is usuallydirect current, but alternating current can beused if all four resistances are nonreactive.R 1 R 2R 3R x = R 3 (R 2 /R 1 )R xWheatstone bridgewheel-drive locomotion The use of wheels formoving mobile apparatus such as robots. Offerssimplicity and low cost. The main disadvantage isthe inability to negotiate irregular terrain.Wheeler’s formula A formula for calculating theinductance of a multilayer air-core coil:L = (0.8a 2 n 2 )/(6a + 9l + 10b)where L is in microhenrys, a is the mean radius(inches) of the winding (axis to center of crosssection), b is the depth of winding (inches), l is thelength of winding (inches), and n is the number ofturns.alWheeler’s formula(dimensions illustrated)wheel pattern A frequency test pattern producedon an oscilloscope screen by z-axis modulation ofa circular trace. A sinusoidal axis signal producesa gear-wheel pattern, and a square-wave or pulsez-axis signal produces a spot-wheel pattern.wheel printer A printout device for computers andcalculators. It consists essentially of a rotatingmetal wheel around whose rim letters and numbersstand in relief. When the desired charactercomes into position, a hammer strikes it throughthe recording paper and carbon paper, printingthe character on the recording paper. Also calleddaisy-wheel printer.wheel static Static electricity (and the resultingradio interference) generated by friction betweenautomobile tires and the road.whiffletree switch In computer operations, a multipositionelectronic switching circuit, so calledfrom its circuit configuration, which resemblesthe contrivance used between a wagon and thehorse team pulling it.whip antenna A small-diameter, vertical rod (oftentelescoping) used as an antenna—especially inmobile communications, portable radio and televisionreceivers, field-strength meters, etc.whirl One of the circular, magnetic lines of fluxaround a straight wire carrying current.whisker 1. The pointer-wire electrode of a pointcontactdiode, point-contact transistor, or crystaldetector. 2. A slender filament of metal or ceramic,having high purity and high tensilestrength.whisker resistance In a semiconductor material,the resistance of a whisker component (seeWHISKER, 1).Whiskey Phonetic alphabet code word for the letterW.whistle A high-pitched tone (e.g., a beat note oracoustic feedback).whistle filter A notch filter used to eliminate awhistle in an amplifier or other audio-frequencycircuit. This filter can be of several versions,ranging from a simple resistance-capacitancebL 0.8 a2 n 26a 9l 10b

whistle filter • Wide Area Telephone Service 749(RC) null circuit tuned to remove the offendingfrequency to a feedback-type band-suppressionamplifier.whistle interference The appearance of extraneouswhistles in audio-frequency circuits. In someequipment, whistles result from oscillating amplifiers;in radio receivers, they are usually audiblebeat notes (heterodynes) produced by interferingcarriers.whistlerA type of very-low-frequency (VLF) radionoise. They are thought to be caused by electromagneticfields from distant lightning strokes,circulating in the earth’s magnetic field. Thename is derived from the peculiar sound thenoise makes in a VLF radio receiver.whistler mode propagation Radio transmissionfrom the northern hemisphere to the southernhemisphere along the flux lines of earth’smagnetic field.whistlestop See WHISTLE FILTER.whistling atmospheric See WHISTLER.white The color that results from mixing all the additiveprimary colors: red, green, and blue.white acid Hydrofluoric acid. Formula, HF. Usedas an etchant, especially of glass.white brass Brass that is more than 49% zinc.white compression In television transmission, reductionof gain at highlight levels in the picture.white-dot pattern In color-television tests with adot generator, the one-white-dot pattern obtainedwhen beam convergence has been secured.white lamp See DAYLIGHT LAMP.white level The lower-voltage point in a video signal,corresponding to full brilliance of the line onthe screen (i.e., to the condition of whiteness inthe picture).white light See WHITE RADIATION, 2.white noise Random noise (acoustic or electric)equally distributed over a given frequency band,an example being the noise resulting from therandom motion of free electrons in conductorsand semiconductors.white-noise generator A test device that generateselectrical noise over a wide frequency spectrum. Asimple type uses a reverse-biased silicon diode,the output of which is useful for testing audioamplifiers and radio receivers.white-noise record A phonograph record containingrecorded bands of white noise, each accompaniedby voice announcements (e.g., instructions),and used to test the frequency response of asound system.white object A body that reflects and diffuses lightof all wavelengths equally well.white peak In a television picture signal, the maximumexcursion in the white direction.white radiation 1. See WHITE NOISE. 2. Visiblelight radiated with more or less equal intensitythroughout the visible spectrum; seen as gray orwhite.white rasterSee CHROMA-CLEAR RASTER.white recording 1. In amplitude modulation,recording characterized by a correspondence ofmaximum received power to minimum recordingmediumdensity. 2. In frequency modulation,recording characterized by a correspondence oflowest received frequency to minimum recordingmediumdensity.white room See CLEAN ROOM.white saturation See WHITE COMPRESSION.white signal The facsimile signal (see FACSIMILE)corresponding to scanning the copy area havingmaximum density.white-to-black amplitude range 1. At a point in apositive amplitude-modulated (AM) facsimile system(see FACSIMILE), the ratio (in dB) of signalcurrent or voltage corresponding to white in thepicture to that for black in the picture. 2. At apoint in a negative AM facsimile system, the ratio(in dB) of signal current or voltage correspondingto black in the picture to that for white in thepicture.white-to-black frequency swing At a point in afrequency-modulated facsimile system, the frequencydifference fw – fb, where fb is the frequencycorresponding to black in the picture, andfw is the frequency corresponding to white.white transmission A system of picture or facsimiletransmission in which the maximum copydarkness corresponds to the smallest amplitude(in an amplitude-modulated transmitter) or thehighest instantaneous frequency (in a frequencymodulatedtransmitter). The opposite of BLACKTRANSMISSION.white X radiation X rays of the continuous, orgeneral, type.whizzer An attachment that can improve the highfrequencyreproduction in some audio loudspeakers.whole-number division Arithmetic division (as inthe division of binary numbers) in which the quotientis a whole number (i.e., division in which thedivisor is contained in the dividend an integralnumber of times).whorl See WHIRL.WHP Abbreviation of water horsepower.wick action 1. The absorption of a liquid by, andits flow through, a cloth or thread, such as a lampwick or lubricating wick. 2. The flow of moltensolder along and under the insulation of a wire.wicking See WICK ACTION.wide-angle diffusion A form of diffusion characterizedby the wide-angle scattering of light;causes the source to have the same brightness atall viewing angles.wide-area network A group of computers linkedtogether, but separated by large geographic distances.Links can be made via telephone lines orradio.wide-area serviceover long-distance wire lines.Wide Area Telephone ServiceA teletype network that operatesSee WATS.

750 wideband • width modewideband 1. Having a bandwidth greater than theminimum necessary to transmit a signal with acceptableintelligibility. 2. For a voice signal, havinga bandwidth greater than 6 kHz. 3. Havingthe capability to operate, without adjustment,over a broad and continuous range of frequenciesor wavelengths. 4. In a digital network, a channelhaving a bandwidth of more than 64 kbps butless than 2 Mbps.wideband amplifier An amplifier that exhibits reasonablyflat response to a broad band of frequencies.The term is relative, depending on theapplication.wideband antenna An antenna that transmits orreceives signals over a broad frequency range,usually without the need for tuning.wideband axis In a color-television signal, the directionof the fine chrominance primary phasor.wideband communications 1. Communicationscarried out over a band of frequencies wider thanthe minimum necessary for effective transfer ofthe information. 2. A method of transmitting andreceiving signals by deliberately varying thechannel frequency over a wide range. Also calledspread-spectrum communications.wideband generator A signal generator covering awide frequency range. Typical coverage in a laboratory-typeinstrument is 10 kHz to 1000 MHz.wideband oscilloscope An oscilloscope whose horizontal,vertical, and sweep channels operate overa wide band of frequencies. Although the termwideband is relative, a wideband oscilloscope isusually assumed to be capable of displaying bothradio and audio frequencies.wideband ratio The ratio B1/B2, where B1 is frequencybandwidth and B2 is intelligence bandwidth.wideband receiver A radio receiver that can tunein signals over a broad range of frequencies. Anexample is a communications receiver that cancover 10 kHz to 30 MHz continuously.wideband repeater A repeater capable of operatingover a wide range of input and output frequencies.Such repeaters are used in active communicationssatellites handling many differentchannels at the same time.wideband signal generator See WIDEBAND GEN-ERATOR.wideband sweep 1. In the operation of an oscilloscope,a repetitive sweep of the electron beam,the frequency of which is adjustable to any desiredpoint within a wide range. The basic sweeprate in simple oscilloscopes is restricted to theaudio-frequency spectrum (up to about 20 kHz),but a wideband sweep extends to much higherfrequencies, typically several tens of MHz. 2. Asweep circuit that produces the wideband sweepaction described in 1.wideband test meter An alternating-current (ac)meter that can measure quantities over a widefrequency range in its basic form (i.e., withoutspecial external probes or converters). An exampleis an electronic ac voltmeter with a range extendingfrom 10 Hz to 2.5 MHz.wide-base diode A junction diode in which the pregion is considerably wider than the n region.wide-open 1. Pertaining to wideband, untuned response.2. Pertaining to maximum-gain operation(e.g., a wide-open amplifier or receiver).wide-range ammeter An ammeter that employsone or more shunt resistances to increase thefull-scale deflection, usually by a power of 10 (10,100, 1000, etc.). The resistor must be capable ofcarrying the current without burning out.Shunts are used when it is necessary to measurevery large currents, such as hundreds of amperes.Shunts also allow a microammeter or milliammeterto be used as a multimeter with manycurrent ranges.wide-range reproduction High-fidelity audiofrequencyreproduction.width 1. The horizontal dimension of a pulse, usuallycorresponding to its effective duration; alsocalled PULSE DURATION. 2. The horizontal dimensionof an image, such as a television picture.Voltage+8+6+4+20Widthwidth, 1.Timewidth coding The modification of pulse durationaccording to a code.width coil See WIDTH CONTROL, 1.width control 1. In a television receiver, the variablecomponent for adjusting the swing of thehorizontal deflection voltage and, therefore, thewidth of the picture. It is often a slug-tuned coilconnected in parallel with a portion of the secondarywinding of the horizontal output transformer.2. Sometimes, the horizontal gain controlin an oscilloscope.width mode In electronic-counter operations, atime-interval mode in which the signal ismeasured.

width modulation • Wilson cloud chamber 751C Swidth modulation Modulation of the interval duringWien-bridge heterodyne eliminator A notch filterwhich a gate circuit is open.composed of a continuously variable Wien-bridgeWiedemann effect See DIRECT WIEDEMANN EF- circuit (see WIEN BRIDGE). The device is connectedFECT.in the audio-frequency channel of a radioWiedemann-Franz law For metals that are good receiver, and is tuned to remove a troublesomeelectrical conductors, the ratio of thermal conductivityto electrical conductivity is nearly constant,heterodyne whistle.Wien-bridge oscillator An oscillator in which theand is proportional to the absolutetemperature.frequency-selective feedback network is a Wienbridgecircuit (see WIEN BRIDGE). Also seeWien bridge A frequency-sensitive bridge in which BRIDGE-TYPE OSCILLATOR.two adjacent arms are resistances and the othertwo adjacent arms are resistance-capacitance(RC) combinations. One of the latter contains resistanceand capacitance in series; the other con-C5C4tains resistance and capacitance in parallel.C1Because the bridge can be balanced at only one R1R2C3Outputfrequency at a time, it is useful as a simple audioR4 R7C2R5frequency meter (see BRIDGE-TYPE AF METER).It is used also for capacitance and resistance R3 LP1R6measurements. When inductors are substituted+B +BC X portional to the absolute temperature.for the capacitors, the Wien bridge can be usedfor inductance measurements (see WIEN INDUC-TANCE BRIDGE).Wien-bridge oscillatorGenWien capacitance bridge A Wien bridge arrangedfor the measurement of unknown capacitance.Wien effect For an electrolytic substance, an increasein conductivity (decrease in resistivity)R 1 R 2that occurs when a very large voltage is placedacross the material. This voltage must be greaterthan approximately 1 megavolt per 50 cm.DetWien inductance bridge A Wien bridge containinginductors in place of capacitors and used for theR 3 R 4measurement of unknown inductance.Wien’s displacement law The wavelength of maximumradiation of a black body is inversely pro-Wien’s first law See WIEN’S DISPLACEMENTWien bridgeLAW.Wien’s laws See WIEN’S FIRST LAW, WIEN’SSECOND LAW, and WIEN’S THIRD LAW.Wien’s radiation law See WIEN’S SECOND LAW.Wien-bridge audio frequency meter See WIEN- Wien’s second law The emissive power of a blackBRIDGE FREQUENCY METER.body is proportional to the fifth power of the absoluteWien-bridge distortion meter A distortion metertemperature.in which a Wien bridge circuit is used to remove Wien’s third law An empirical law for the spectralthe fundamental frequency from the complexwaveform. The bridge is inserted between amplifierstages, and its notch response is sharpenedby means of overall negative feedback.Wien-bridge equivalent A resistance-capacitancenull circuit, such as the parallel-tee (twin-tee)network, which has the same balance equation asthe Wien bridge.Wien-bridge filter A Wien bridge used as a bandsuppressionfilter (notch circuit).Wien-bridge frequency meter A bridge-type audiofrequency meter in which the continuously variablefrequency-selective circuit is a Wien bridge.Also see BRIDGE-TYPE AF METER.distribution of energy radiated from a black bodyat a specified temperature. The distribution is acurve with a peak (maximum) at a wavelengththat depends on the temperature. The higher thetemperature, the shorter the wavelength at whichmaximum radiation occurs.willemite See ZINC ORTHOSILICATE PHOSPHORand ZINC SILICATE PHOSPHOR.Williams tube A type of electrostatic cathode-raystorage tube.Wilson chamber See WILSON CLOUD CHAMBER.Wilson cloud chamber An airtight chamber containingwater vapor or alcohol vapor at low pressure,and provided with a viewing window.

752 Wilson cloud chamber • wingRadioactive particles penetrating the chamberare made visible as droplets form trails when thevapor condenses on them.Wilson effect Electric polarization of a dielectricmaterial being moved in a magnetic field.Wilson electroscope A leaf-type electroscope (seeELECTROSCOPE) using a single leaf hanging vertically.Wilson experiment An experiment demonstratingthe WILSON EFFECT. It consists of rotatingabout its axis a hollow dielectric cylinder (whoseinner and outer surfaces are metallized) in a magneticfield parallel to the axis. The result: An alternatingvoltage appears between the metallizedsurfaces.Wimshurst machine A rotating machine used toproduce high-voltage static electricity. The machinecontains two glass disks, each havingseparate sectors of metal foil spaced around itsface. The disks rotate in opposite directions,and the foil sectors passing each other formvariable capacitors. Metal brushes pick upcharges from the sectors passing under themand deliver this energy to one or more Leydenjars for storage.wind charger A wind-driven generator used specificallyto supply direct current for charging storagebatteries.wind-driven generator A dynamo-type generator,either stationary or mobile, powered by a windmill-likedevice.wind gauge See ANEMOMETER.winding 1. A coil in an inductor or transformer(e.g., primary winding, secondary winding, outputwinding, etc.). 2. A coil in a motor or generator.winding arc The winding length of a coil, expressedin degrees.winding cross section The cross section of a multilayercoil.winding depth The depth of a multilayer coil, measuredfrom the outermost layer to the innermostlayer.winding factor For a transformer or choke coil (orfor a toroidal coil), the ratio of the total area ofwire in the window to the window area.winding length The length of a coil from the firstturn to the last in a single-layer coil, or from thefirst turn to the last in one layer of a multilayercoil when all layers are identical.winding space The window area of the core of atransformer or choke (see WINDOW, 3).wind loading 1. The total wind pressure on an antennasystem, generally measured in poundsor kilograms. The greater the wind speed,the greater the wind loading for a given antenna.The greater the exposed surface of the antenna,the greater the wind loading for a given windspeed. 2. The highest wind speed, in miles perhour or meters per second, that an antenna systemcan safely withstand, assuming no accumulationof ice on the antenna structure.Windom antenna 1. A multiband antenna inwhich a single-wire feeder is attached to a horizontalhalf-wave radiator wire somewhat off center,at a point about 1 ⁄6 wavelength from one endof the radiator. The antenna operates with reasonableefficiency at the first several harmonicsof the frequency at which it measures 1 ⁄2 wavelength.2. A similar antenna using a parallelwirefeeder.f 0 =3.5 MHzand harmonics135 FtFeed lineto Xmtr(300 ohms)44 FtWindom antenna, 2window 1. Radar-interference material (seeCHAFF). 2. An interval during which a circuit isgated open to permit signal sampling. During thisinterval, a window is figuratively open to thesignal. 3. The open spaces between the legs of aniron core for a transformer or choke coil. 4. Anelectromagnetic frequency band easily transmittedby earth’s atmosphere. 5. The period duringwhich conditions are ideal for a complex operation,such as a rocket or spacecraft launch. 6. Anapplication space in a computer program thatuses a graphical interface.window area See WINDOW, 3.window comparator A comparator that detectsvoltage levels within a certain range of values,rather than simply indicating whether a voltage ismore or less than a certain specified value.window corridor An area where window (see WIN-DOW, 1) has been dispersed.window jamming The disturbance of electroniccommunications, especially radar, by dumpingreflective material, such as metal foil, from an aircraft.Also see CHAFF; JAMMING; and WINDOW,1.Windows Trade name (Microsoft) for a personalcomputerinterface scheme. The several versionsall use selectable icons and menus.window strip An insulated, flat, metal strip forbringing an antenna lead-in through a window.The window can be closed on the strip.wind screen A foam covering that can minimizethe roar caused by wind blowing against oracross a microphone.wind shield A radio-transparent cover placed overa radar antenna to protect it against damage fromhigh winds. It is used especially in radar systemsaboard aircraft.wing In an antenna or other radiator, a (usuallyflat) member attached to, and sticking out from,

wing • wire gauge 753another member. Its name is derived from itscharacteristic shape.winterization The protective treatment and preparationof electronic equipment for winter storageor for operation in frigid regions.wipeout Severe interference that obliterates all desiredsignals.wipeout area An area in which WIPEOUT occurs.wiper 1. A thin metal blade or strip in sliding contactwith a coil or other element over which it isturned to vary some quantity (such as resistance,inductance, voltage, current, etc.). 2. A brush ina motor or generator.wiper arm See WIPER, 1.wiper blade See WIPER, 1.wiping action The movement of contacts againsteach other when they slide as they mate or withdraw.wiping contact A contact that makes and breakswith a sliding motion.wire 1. A metal strand or thread serving as a conductorof electricity. 2. To connect wires betweenpoints in a circuit. 3. See TELEGRAM. 4. To senda TELEGRAM.wire bonding 1. The interconnection of componentswithin a discrete package, by means of finewire conductors welded to the individual components.2. A method of temporarily splicing theouter conductors of two coaxial cables. 3. In general,any solderless method of splicing betweentwo conductors.wire broadcasting Broadcasting by means ofcarrier-current communication (see WIREDRADIO).wire cloth A net of fine wire, used as an electricalshield when air circulation is necessary.wire communication Communication carried onby means of signals transmitted over wire lines,as opposed to wireless (radio) communication.wire control The control of remote devices bymeans of signals transmitted over wire lines, asopposed to radio control.wire core A magnetic core consisting of a bundle ofiron (or magnetic alloy) wires.wired AND See DOT AND.wired-in component A component to which wiresare permanently connected in a circuit, as opposedto a plug-in component.wired OR See DOT OR.wired-program computer A computer in which instructionsare wired-in by making appropriateconnections to a panel with patch cords.wired radio The transmission and reception ofvoice and other sounds, telegraph signals, pictures,control signals, telemetry signals, and thelike by means of radio-frequency energy conductedby wire lines. Usually, the lines are usedprimarily for some other purpose (e.g., powerlines or telephone lines).wired-radio receiver The complete device or systemthat selects, amplifies, and demodulates orCouplerTransceiverTransceiverCouplerUtility linewired radioHotGroundNeutralrectifies a radio signal picked up from wires thatconduct it from a transmitting station.wired-radio transmitter The complete device orsystem that generates radio-frequency power,adds signals (for communication, remote control,telemetry, etc.), and delivers the power to wires orto a cable for reception at a distant point.wire drawing In the manufacture of wire, pullingmetal through special dies to form wire of selecteddiameter.wire dress The careful arrangement of wires in achassis to ensure optimum performance. Alsocalled lead dress (see DRESS).wire duct A conduit through which wires are run.Such ducts have several shapes, but generallyare rectangular.wired wireless See WIRED RADIO.wire-equivalent security See LEVEL-1 SECU-RITY.wire fuse A fuse in which the fusible element is awire of low-melting-point metal. Compare STRIPFUSE.wire gauge 1. A system for specifying the characteristicsof wire. See AMERICAN WIRE GAUGEand BIRMINGHAM WIRE GAUGE. 2. A wire numbergoverned by diameter (e.g., 18-gauge wire for#18 wire). 3. A tool or instrument for measuringwire diameter or for determining wire number.

754 wire gauze • wire splicewire gauze A fine screen of thin wires.wire grating See WAVEGUIDE GRATING.wire-guided Pertaining to guiding a machine, suchas a robot, by means of signals sent by wire fromthe control point.wire leads Leads that are (usually thin, flexible)wires, rather than pins, bars, strips, etc. An exampleis the wire leads of some transistors (as opposedto terminal pins).wireless 1. Pertaining to data communicationsand control systems that operate without wires(e.g., an infrared link between a notebook computerand a desktop computer). 2. An early namefor radio; it is still used in some countries. Sometimesfor specificity, radio is referred to as wirelesstelegraphy or wireless telephony. SeeRADIOTELEPHONY.wireless access protocol Acronym, WAP. A communicationsstandard used on a worldwide basiswith portable cellular telephone sets incorporatingelectronic mail, online service access, and/orInternet access.wireless broadcaster See WIRELESS MICRO-PHONE.wireless compass A radio compass (see DIREC-TION FINDER).wireless device A device that operates over a distance,without the use of interconnecting wires.wireless e-mail 1. The use of electronic mail(e-mail) in conjunction with a wireless Internet service.2. The use of a specialized portable wirelesscommunications device, resembling a strippeddowncomputer or an enhanced cell phone, tosend and receive e-mail messages.wireless intercom An intercom using wired-radiofor transmission and reception over the powerline from which it is operated. Also see WIREDRADIO.wireless Internet 1. The use of a personal computer,usually a notebook or portable, in conjunctionwith a wireless modem connected to theInternet. Services of this type are provided withhigh-end cellular telephone subscriptions. Assetsand limitations are similar to those associatedwith cell phone services. 2. The use of aspecialized portable or mobile wireless communicationsdevice, resembling a stripped-down computeror an enhanced cell phone, for basicInternet communications and informationretrieval.wireless microphone A device consisting of asmall radio-frequency oscillator modulated by themicrophone to which it is attached, and providedwith a tiny antenna. The modulated signal ispicked up and reproduced by a radio receiver.wireless modem 1. A modem that facilitates connectionof a computer to the Internet using a cellphone set. 2. A wireless transceiver that facilitatesconnection of a computer to the Internet. Acellular telephone connection can be included asan option. 3. Also called cordless modem. A pairof short-range (on the order of a few feet) radio orinfrared transceivers. One unit connects to a telephonejack or cable port, and the other unit connectsto a computer. Can protect a portablecomputer against damage by lightning, assumingthe computer uses batteries and is not connectedto utility mains.wireless tap A method of eavesdropping on communicationsin which a portion of the circuitmakes use of a radio-frequency wireless link. Aneavesdropping receiver can be positioned withinrange of the wireless transmitting antenna, andthe signals intercepted. The existence of such atap causes no change in the electronic characteristicsof any equipment in the system, so itsdeployment is difficult to detect even ifeavesdropping is anticipated.wireless telegraphy See RADIOTELEGRAPHY.wireless telephone 1. A radio transceiver interconnectedwith the telephone lines. 2. A telephonein which a short-range radio link replacesthe cord between the receiver and the base unit.It normally has a range of several hundred feet.wireless telephony See RADIOTELEPHONY.wire line One or more wires or cables conductingcurrents for communication, control, or measuringpurposes.wire link A line for wire communication or wirecontrol.wire-link telemetry Telemetry carried on over awire link.wireman 1. An electrician who specializes in theinstallation and servicing of electrical wiring.2. See LINEMAN.wire mile A unit of measure equal to the productns, where n is the number of separate, equallengthconductors in a line, and s is the length ofa conductor in miles.Wirephoto1. A system for transmitting and receivingphotographs over wire lines. Also calledTelephoto. See FACSIMILE. 2. A photographtransmitted and/or received, as defined in 1. 3. Atrademark for a photograph transmitted and receivedover telephone lines.wire printer A printout device consisting of a wirearray in which each wire is activated by an electromagnet.When a wire is selected (electrically),it is pushed against, and makes a dot on therecording paper. The letters and figures, then, aredot patterns. Compare WHEEL PRINTER.wire radio See WIRED RADIO.wire recorder In audio applications and datarecording, a machine that records sounds or datapulses in the form of magnetized spots on a thinwire.wiresonde A system for transmitting weather informationdata through a cable that holds a captiveballoon. Compare RADIOSONDE.wire splice A strong, low-resistance joint between(usually two) wires. See, for example, WESTERNUNION JOINT.

wire stripper • Wolf’s equation 755wire stripper A hand tool or power machine forcutting the insulating jacket on a wire and removingit without cutting or nicking the wire.wiretap 1. An instance of wiretapping. 2. A wiretappingdevice.wiretapper 1. A device for wiretapping. 2. A personwho practices wiretapping.wiretapping The act of making direct or indirectconnections to a communications line to overhearor record a conversation.wire telegraphy Telegraphic communication carriedon by means of signals transmitted over wirelines, as opposed to wireless (radio) telegraphy.wire telephony Voice communication carried onby means of signals transmitted over wire lines,as opposed to wireless (radio) telephony.wire tie See TIE.wire wave communication See WIRED RADIO.wireways Hinged-cover metal troughs for containingand protecting wires and cables. Also seeWIRE DUCT.wirewound potentiometer A potentiometer inwhich the resistance element is a coil of resistancewire wound on a cord bent into a cylinder,or on a rigid, circular core.wirewound resistor A resistor made from a coil ofwire that is a poor conductor. The wire is usuallywound around a cylindrical form; some componentsuse toroidal forms. The resistance is determinedby how well the wire metal conducts, by itsdiameter (gauge), and by its length. This type ofresistor can be manufactured to precision tolerance.If the wire gauge is heavy, it can dissipatelarge amounts of power. The component has inductivereactance, making it unsuitable for use atradio frequencies. Compare CARBON-COMPOSI-TION RESISTOR, FILM RESISTOR.wirewound rheostat A rheostat in which the resistanceelement is a coil of resistance wire woundon a card bent into a cylinder, or on a rigid, circularcore.wire wrap A method of circuit-board wiring in whichcomponents are interconnected by individual wireconductors, the ends of which are wrappedaround terminal posts using a special tool.wire-wrap connection An electrical connectionmade by tightly wrapping a bare wire around aspecial terminal.wire wrapwire-wrapping tool A device used to make a wirewrapconnection.wiring 1. The system of wires or similar conductorsconnected between circuit components. 2.Connecting and dressing such wires, as in wiringa circuit. 3. Collectively, the connections (eitheractual wire or printed metal lines or processedsemiconductor paths) between terminals andcomponents in an electronic circuit. 4. The processof installing or making such connections.wiring board The control panel of a computer (i.e.,a plugboard).wiring capacitance Unavoidable capacitance betweenwires in a circuit, or between the wires andnearby metal bodies.wiring connector A small (usually metal) fittingused to tie wires together.wiring diagram See CIRCUIT DIAGRAM.wiring impedance Unavoidable impedance in thewires in a circuit, and in associated terminalsand hardware conducting alternating current.This impedance is the vector sum of WIRING RE-ACTANCE and WIRING RESISTANCE.wiring inductance Unavoidable inductance in thewires in a circuit, and in associated terminalsand other hardware, through which alternatingcurrents flow.wiring reactance Unavoidable reactance in thewires in a circuit, and in associated terminalsand other hardware, conducting alternating current.This reactance is caused by WIRING CA-PACITANCE and/or WIRING INDUCTANCE.wiring resistance Unavoidable resistance in thewires in a circuit and in associated terminals andother hardware.Witka circuit A voltage-tripler circuit using onlytwo diodes and two capacitors. Its no-load directcurrentoutput voltage is approximately threetimes the peak value of the alternating-currentinput voltage. Also see VOLTAGE TRIPLER.wk 1. Abbreviation of WORK. 2. Abbreviation ofweek.WL 1. Abbreviation of WAVELENGTH. 2. Abbreviationof waterline.WM Abbreviation of WATTMETER.Wm 2 Symbol for watt square meter (unit of the firstradiation constant).W/(MK) Symbol for watts per meter kelvin (unit ofthermal conductivity).WMO Abbreviation of World Meteorological Organization.wobbulator A device that sweeps the frequencyof an oscillator. There are several types, from amotor-driven, rotating, tank capacitor to sophisticated,fully electronic variable capacitors orvariable inductors.wolfram See TUNGSTEN.Wolf’s equation A sunspot-number equation usedto forecast maximum usable frequency: R =k(10G + N), where R is relative sunspot number, kis a constant for the telescope used, G is the

756 Wolf’s equation • working voltagenumber of sunspot groups observed, and N is thetotal number of sunspots.Wollaston wire An extremely fine wire made bycoating platinum with silver, drawing it thinner,and dissolving the silver coat.womp A sudden surge in amplitude that causes aflare up of brightness in a television picture.woodpecker A slang term used to describe thesound of the signal from over-the-horizon radar.Operating in the high-frequency part of the spectrumand changing in wavelength, roughly followingthe maximum usable frequency, the signalconsists of repeated “spikes” that can interferewith routine communications.woodpecker filter A special type of blanking filterused to quiet a shortwave receiver during strong,brief “spikes.” It is similar to a noise blanker, butis designed to filter out the longer peaks characteristicof the over-the-horizon radar, known asthe WOODPECKER.Wood’s alloy See WOOD’S METAL.Wood’s metal A low-melting-point (159.8°F) alloycontaining bismuth (50%), cadmium (12.5%),lead (25%), and tin (12.5%). The alloy looks likelead and is used to mount rectifying crystals(such as galena) whose electrical sensitivitywould be destroyed by the high temperatures requiredto melt most soft metals.woofer A large loudspeaker, often a foot or more indiameter, designed specifically to reproduce verylow (bass) audio frequencies. It is commonly usedin high-fidelity stereo sound systems. CompareTWEETER.word 1. In computer operations, a group of bits orcharacters treated as a unit. 2. In telegraphy, adata unit consisting of five characters plus onespace.word-address format A method of addressing aword by means of a single character, such as thefirst letter of the word.word code 1. A cipher in which word meanings areinterchanged, rather than letter symbols. 2. Aword having an altered meaning in a cipher system,as defined in 1. For example, “word” mightmean “code.”word format The specific sequence of charactersthat forms a word of data.word generator A special signal generator that deliverspulses in selected combinations correspondingto digital words (see WORD, 1). It isused in testing computers and digital systems.word length 1. In computer operations, the numberof bits in a word. 2. In telegraphic communications(radio or wire), the average number ofletters in a word.word pattern The shortest meaningful word (seeWORD, 1, 2) that can be recognized by a machine.word processor 1. An electronic device, similar toa typewriter, used for writing. Words, phrases,sentences, or paragraphs can be changed,replaced, or deleted prior to the final printout.2. A computer used for writing, as defined in 1.3. Software that allows a computer to be used forwriting, as defined in 1.word rate In a communications or computer system,the number of words per unit time (e.g.,WORDS PER MINUTE).word size See WORD LENGTH.words per minute In telegraphy, a measure ofdata speed. It is approximately equal to the numberof characters (including spaces) per minutedivided by 6.word time In computer operations, the time requiredto process one word that is in storage.work 1. Symbol, W. Units: joule, erg, foot-pound,kilogram-meter. That which is accomplished bythe transfer of energy from one body to another,as when an exerted force causes a displacement.The amount of work performed is equal to forcetimes distance: W = Fd. 2. An amateur radio termmeaning to engage in two-way communicationwith another station.work areaIn computer operations, a temporaryarea of memory for data items being processed.Also called INTERMEDIATE STORAGE, WORK-ING MEMORY, and WORKING STORAGE.work coil The alternating-current-carrying coilthat induces energy in the workpiece in inductionheating.work envelope The range of motion over which arobot arm can move. It can be two-dimensional orthree-dimensional.work function Unit, eV. The energy required tobring an internal particle to the surface of a materialand out into space, as when an electron isemitted by the hot cathode of a vacuum tube. Thework function is the voltage required to extract 1electrostatic unit of electricity from the material.working data file A temporary accumulation ofdata sets that is erased or otherwise discarded afterits transferal to another medium.working life The expected or guaranteed lifetime ofa material, device, or system in actual operationor use. Compare SHELF LIFE.working memory See WORK AREA.working point The operating point of an active device(i.e., the point along one of the characteristiccurves around which operation is fixed).working Q The Q of a loaded circuit or device (e.g.,tank-circuit Q of a radio transmitter loaded withan antenna or dummy load).working range 1. The usable maximum distancebetween a transmitter and receiver in a wirelesscommunications circuit. 2. The allowed rangeover which specified parameters can vary in aparticular system while facilitating normal operation,or operation within rated specifications.working storage See WORK AREA.working voltage The (usually maximum) voltageat which a circuit or device can be operated continuouslywith safety and reliability.

workout • wrong color 757workout 1. A dry run; a test. Example: checking acomputer’s processing power using a set ofbenchmark programs. 2. An exacting test ofequipment; a burn-in procedure.workpiece The object heated by an induction or dielectricheater.worm A cylindrical gear whose spiral “teeth” resemblea screw thread.worm drive A mechanism for transferring motionfrom a tuning-knob shaft through a right angle tothe shaft of an adjustable component, such as apotentiometer or variable capacitor. The knobturns a threaded shaft that mates with a gearwheel.TocontrolknobTocomponentworm driveThreadedshaftGearwheelworst-case circuit analysis Analysis that seeksthe worst possible effects of variations in circuitparameters on circuit performance—especiallyvariations in component characteristics.worst-case noise pattern See DOUBLE-CHECK-ERBOARD PATTERN.worst-case design The design of electronic equipmentin such a way that normal operation is obtained—eventhough the characteristics of circuitcomponents might vary widely.woven resistor A resistance element made ofstrands of resistance material woven in the formof gauze.wow Slow, periodic variations in the pitch of reproducedsound because of variations in the speed ofthe drive mechanism. Its name is derived from itscharacteristic sound. Compare FLUTTER.wow meter An instrument that indicates theamount of wow produced by a turntable or othermoving part.Wpc Abbreviation of watts per candle.wpm Abbreviation of words per minute.wrap See WIRE-WRAP CONNECTION.wrap-around 1. The extent of curvature in magnetictape passing over the heads during recordingor playback. 2. An enclosure that resembles asheet (wrapped around a piece of electronicequipment). 3. In computer and data-processingoperations, a technique in which the display iscleared of data once it is filled (all available linesare occupied) and additional data is traced fromtop to bottom.wrap joint See WIRE-WRAP CONNECTION.wrapper A paper or tape wound around a component,such as a coil or capacitor, for insulationand protection.wrapping 1. See WRAPPER. 2. Insulating a wire orother conductor by wrapping insulating tapearound it.wrap post A terminal post, tip, pin, or lug used ina wire-wrap connection.wrap-up The (usually successful) completion of adesign, fabrication, test, or investigation.Wratten filter A light filter for separating colors. Itis available in transparent sheets of various colorsand is useful in photography and in severalphases of electronics, including the operation ofcolor meters and color matchers.wrinkle finish A pattern of fine wrinkles created byspecial paint when it dries on a surface, such asthat of a metal cabinet for a piece of electronicequipment.wrist-force sensor In robotics, a set of straingauges that detects the various forces in the jointconnecting an end effector to an arm, and sendssignals back to the robot controller. The controllercan use the signals to direct the movementsof the arm and end effector.write 1. In computer operations, to transfer datafrom one form of memory or storage to anotherform. Example: To transfer data in a computerfrom random-access memory (RAM) to the harddisk. Compare READ. 2. To produce an image onthe storage mesh in the cathode-ray tube of astorage oscilloscope.write enable ring See WRITE PERMIT RING.write gun See WRITING GUN.write head In a magnetic memory or in a taperecorder or wire recorder used for recording data,the head that magnetizes the drum, tape, disk, orwire. Compare READ HEAD.write pulse In computer operation, the pulse thatcauses information to be recorded in a magneticcell, or sets it to the one-state. Compare READPULSE.write time The time taken to write data to a storagedevice.writing gun In a storage oscilloscope, the electrongun that produces the image electronically on thestorage mesh. It is mounted in the rear of thecathode-ray tube. Compare FLOOD GUN.writing head See WRITE HEAD.writing rate In photographing the image on a cathode-raytube screen, the highest spot speed atwhich an acceptable picture can be made.writing speed See WRITING RATE.writing telegraph See TELAUTOGRAPH.wrong color The instance of an undesired color(e.g., purple instead of red) in a color-televisionpicture. The condition is often caused by a malfunctionof the chroma demodulator(s).

758 W/(sr•m 2 ) • wye-wye circuitW/(sr•m 2 ) Abbreviation of watts per steradiansquare meter.WT 1. Abbreviation of wireless telegraphy. 2. Abbreviationof WATERTIGHT.wt Abbreviation of WEIGHT.WUI Abbreviation of Western Union International.Wulf electrometer See BIFILAR ELECTROMETER.Wullenweber antenna An electronically steerableantenna composed of two concentric circular arraysof masts connected to the steering circuitry.WUX Abbreviation of Western Union telegram.WVdc Abbreviation of direct-current working voltage:the maximum continuous direct-currentvoltage that can safely be placed across a component.ww Abbreviation of wirewound.W/sr Abbreviation of watts per steradian (unit ofradiant intensity).WWV The call letters of a standard-frequency/standard-time broadcasting station operated bythe National Bureau of Standards and locatedin the continental United States. Also seeWWVH.WWVH The call letters of a standard-frequency/standard-time broadcasting station operated bythe National Bureau of Standards and located inHawaii. Also see WWV.wx Radiotelegraph abbreviation of weather.WXD International Telecommunications Unionsymbol for meteorological radar station.WXR International Telecommunications Unionsymbol for radiosonde station.wye adapter A connector that provides two outputsfor a single input, or vice versa. It is commonlyused in audio applications.wye box In a three-phase power-measuring setup,a special arrangement of two impedances, each ofwhich is equal to the impedance of the potentialelement of the wattmeter used in the setup. Thebox permits a single wattmeter to be used, whichindicates one-third the total power. Without thebox, three wattmeters would be needed.wye connection A method of connecting threewindings in a three-phase system so that one terminalof each winding is connected to the neutralpoint. It is shaped like the letter Y. Also calledstar connection.wye current Current through one of the branchesof a three-phase star (wye) connection.wye delta starter A starter circuit for a threephasesquirrel-cage induction motor. When thestarter switch is thrown in one direction, the statorof the motor is wye-connected for starting;thrown in the opposite direction, the stator isdelta-connected for continued operation.wye equivalent circuit A wye-connected threephasecircuit equivalent to a delta-connectedcircuit when the impedance of any pair ofcorresponding lines for both wye and delta arethe same; the third line is unconnected.wye junction See WAVEGUIDE WYE.wye-matched-impedance antenna An antenna inwhich the impedance of a nonresonant open-wirefeed line is matched to that of the center of the radiatorby spreading the end of the feeder wiresout into a Y-shaped or delta-shaped matchingsection. Also called DELTA-MATCHED-IMPEDANCE ANTENNA.wye point The star point in a three-phase system.Also see WYE CONNECTION.RadiatorTo transmitterFeedersMatching sectionInsulatingspreaderwye-matched-impedance antennawye potential In a three-phase armature, the voltagebetween a terminal and the neutral point.wye rectifier A three-phase rectifier circuit inwhich the transformer or generator windings arearranged in a wye connection.wye-wye circuit A circuit consisting a wyeconnectedgenerator and a wye-connected load.Sourcewye-wye circuitLoad

X 1. Symbol for REACTANCE. 2. Symbol for no connection.(Also, NC.) 3. Symbol for the HORIZON-TAL AXIS of a graph or screen in the rectangular(Cartesian) coordinate system. 4. Symbol for anunknown quantity.x 1. Symbol for number of carriers drawn from collectorto base of a transistor, for each carrier collected.2. Symbol for an unknown quantity. 3.Symbol for the HORIZONTAL AXIS of a graph orscreen in the rectangular (Cartesian) coordinatesystem.x amplifier The horizontal amplifier of an oscilloscopeor recorder. Compare Y AMPLIFIER and ZAMPLIFIER.X and Z demodulation Color television demodulationbased on the 60-degree difference betweenthe two reinserted 3.58-MHz subcarrier signals.The R-Y, B-Y, and G-Y voltages derived from thedemodulated signals control the three guns of thepicture tube. Compare Q MODULATION.x-axis1. The horizontal axis of a chart, graph, orscreen in the rectangular (Cartesian) coordinatesystem. 2. In a quartz crystal, the axis drawnthrough the corners of the hexagon.x-axis amplifier See X AMPLIFIER.XB Abbreviation of crossbar.X balance The reactance balance (either the variablecomponent or the adjustment of it) in animpedance bridge in which separate resistance(R) and reactance (X) balancing is provided.X band The frequency band extending from 5.2 to11 GHz.X bar A rectangular, piezoelectric quartz bar cutfrom a Z-section, whose faces are parallel to theX-axis and whose edges are parallel to the X-, Y-,and Z-axes. See CRYSTAL CUTS.X bridge An alternating-current bridge for measuringreactance.X C Symbol for CAPACITIVE REACTANCE.X channel The horizontal channel of an oscilloscopeor recorder. Compare Y CHANNEL and ZCHANNEL.X-channel gain See X GAIN.X component In a complex impedance, the reactivecomponent (either inductive or capacitive).x coordinate See ABSCISSA.X-cut crystal A piezoelectric plate cut with itsfaces perpendicular to the X-axis of a quartz crystal.See CRYSTAL CUTS.xcvr Abbreviation of TRANSCEIVER. Often capitalized.X deflection Horizontal deflection of the spot onthe screen of a cathode-ray tube. Compare Y DE-FLECTION.X diode The decoding diode in each of the X linesof a memory matrix. Compare Y DIODE.X direction The horizontal direction in deflectionsand in graphical presentations of data.X drive The driving source or energy for the X linesof a computer memory matrix.xducer Abbreviation of TRANSDUCER.Xe Symbol for XENON.xenon Symbol, Xe. An inert gaseous element.Atomic number, 54. Atomic weight, 131.29.Xenon is present in trace amounts in the earth’satmosphere and is used in some thyratrons, electriclamps, and lasers.xenon tube A flash tube filled with xenon.xerography A system for the reproduction ofprinted matter, drawings, and other graphic matter.It is an electrostatic process in which acharged photoconductive surface is exposed to anCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

760 xerography • X-ray photographimage of the material to be copied. A latent imageis formed on the surface and is developed (bydusting with black powder attracted to thecharged image) to make the image visible.xeroradiography Xerography using X RAYS.xerothermic A condition characterized by bothheat and dryness.Xerox 1. Name of a company that manufactures awide variety of office and computer equipment.2. Trade name for a XEROGRAPHY machine.3. The reproduction obtained by means ofXEROGRAPHY (generic term). 4. To make axerographic reproduction (generic term).X factor 1. An unknown or unidentifiable quantityor parameter. 2. See X COMPONENT.xformer Abbreviation of TRANSFORMER.X gain The gain (or gain control) of the horizontalchannel of an oscilloscope or X-Y recorder. CompareY GAIN and Z GAIN.X-H array See LAZY-H ANTENNA.XHV Abbreviation of EXTREMELY HIGH VACUUM.x intercept The x coordinate of the point at whicha line or plane intersects the X-AXIS.x irradiate To expose to X RAYS.xistor Abbreviation of TRANSISTOR.X L Symbol for INDUCTIVE REACTANCE.X line A horizontal line in a memory matrix. CompareY LINE.XLR connector A microphone connector with alocking device to prevent unintentional disconnection.It has three pins and is commonly usedwith balanced audio systems.X meter 1. An instrument for measuring reactanceand phase angle. 2. A form of simple capacitancemeter whose dial is direct-reading in microfarads,although the deflection is actually proportional tothe reactance of the capacitor under measurement.Constant-voltageac inputCapacitorunder testVery lowresistanceX meter, 2Electronicacvoltmeterxmission Abbreviation of transmission.xmit Abbreviation of transmit. Also, xmt.xmitter Abbreviation of TRANSMITTER. Also, xmtr.XMODEM In data transmission, an error-correctingmode in which data is sent in blocks of 128kilobytes (128K), or 131,072 bytes. The sourceand destination tally up the bytes in each block.If they agree, the next data block is sent. If theydo not agree, the current data block is retransmitted.Compare YMODEM and ZMODEM.xmt Abbreviation of transmit. Also, xmit.xmtr Abbreviation of TRANSMITTER. Also, xmitter.XOR Abbreviation of EXCLUSIVE-OR.xover Abbreviation of CROSSOVER.X particle See MESON.xponder Abbreviation of TRANSPONDER.X position 1. The alignment of a cathode-ray beamalong the horizontal axis of an oscilloscopescreen. 2. The position of a point, with respect tothe horizontal axis of a graph in the rectangular(Cartesian) coordinate system.XR Abbreviation of INDEX REGISTER.X radiation Electromagnetic energy in the form ofX rays.X-ray 1. Phonetic alphabet communications codeword for the letter X. 2. Pertaining to, or consistingof, X rays.X-ray astronomy The science of observing celestialobjects and the sky in the X-ray band of wavelengths.Generally, this must be done from abovethe earth’s atmosphere because the atmosphereabsorbs X rays.X-ray crystallography The science of observingatomic patterns in a crystal by means of X rays.X-ray detecting device 1. An X-ray instrument forspotting flaws in solid bodies. 2. A device, such asa fluoroscope, for showing the presence of X rays.X-ray diagnosis The use of X rays in the diagnosisof disease and in the observation of internal partsof the body.X-ray diffraction The diffraction of X rays by amaterial into or onto which they are directed.Also see X-RAY DIFFRACTION CAMERA andX-RAY DIFFRACTION PATTERN.X-ray diffraction camera A special camera thatfurnishes a photograph of the pattern created by Xrays diffracted by a material. See X-RAY DIFFRAC-TION and X-RAY DIFFRACTION PATTERN.X-ray diffraction pattern The pattern producedon film exposed to X rays diffracted by a material.Also see X-RAY DIFFRACTION and X-RAYDIFFRACTION CAMERA.X-ray goniometer An instrument used to find theposition of the axes of a quartz crystal. It uses Xrays reflected from the atomic planes of thecrystal.X-ray inspection The use of X rays in the examinationand study of the internal features of materialsand devices.X-ray laser A laser designed to emit coherentX rays in a narrow beam.X-ray load 1. An X-ray tube that is the terminalmember of an electronic system. 2. A body, mass,or material exposed to X rays.X-ray machine A device that generates X rays for aspecific purpose, such as medical diagnosis.X-ray photograph A photograph made by exposureto X rays, especially an X-ray shadowgram,

X-ray photograph • x-y recorder 761a picture made without a camera by interposingan object (such as a part of the human body) betweenan X-ray tube and photographic film.X-ray radiation See X RADIATION.X rays Invisible, electromagnetic radiation havingwavelengths ranging from approximately 0.01nanometer (10 –11 meter) to 0.15 nanometer (1.5 ×10 –10 meter). These waves are shorter than ultraviolet,but longer than gamma rays. They can beproduced by bombarding a target of heavy metal(such as tungsten) with a stream of high-speedelectrons in a vacuum tube. X rays have highpenetrating power, can expose photographic film,and cause some substances to fluoresce. Also seeX-RAY DIAGNOSIS, X-RAY INSPECTION, andX-RAY THERAPY.X-ray spectra The continuous band of ionizingelectromagnetic radiation having wavelengthsranging from approximately 0.01 nanometers to0.15 nanometers.X-ray spectrograph A spectrograph used to disperseand measure the wavelength of X rays.X-ray spectrometer A spectrometer with whichthe diffraction angle of X rays reflected from thesurface of a crystal can be measured. The deviceallows the characteristics and composition of almostany material to be studied.X-ray star A collapsed star that emits high-intensityenergy concentrated mainly in the X-ray regionof the electromagnetic spectrum.X-ray system Collectively, an X-ray tube and theassociated equipment required for a specific application,such as crystallography, irradiation, ormedical therapy.X-ray technician 1. A professional skilled in theoperation and maintenance of X-ray systems,who usually works under the supervision of anengineer. 2. A professional skilled in the medicaluse of X rays, who works under the supervision ofa medical doctor.X-ray therapy The use of X rays in the treatmentof certain physiological diseases.X-ray therapy system An X-ray system designedfor X-ray therapy.X-ray thickness gauge An instrument used tomeasure the thickness of metal, such as a continuouslymoving sheet of steel. The measurementis in terms of the amount of absorption ofan applied X-ray beam by the metal.X-ray tubeA specialized, very-high-voltage diode inwhich a high-speed electron beam bombards ananode (target) of heavy metal, such as tungsten,Anode(target)X raysElectronbeamX-ray tubeCathodecausing it to emit X rays. The target is tilted to reflectthe X rays through the glass wall of the tube.X section Abbreviation of cross section.X sink The circuit or device into which the X linesof a memory matrix feed. Compare Y SINK.X T Symbol for total reactance.xtal Abbreviation of CRYSTAL.xtalk Abbreviation of CROSSTALK.x unit A small unit of length, equal to approximately10 -13 meter or 10 -4 nanometer. Now seldomused, the x unit was once often used in theexpression of ultraviolet and X-ray wavelengths.X wave One (the extraordinary) of the pair of componentsinto which an ionospheric radio wave isdivided by the earth’s magnetic field. CompareO-WAVE.XXX In radiotelegraphy, a signal meaning urgent.X-Y counting A technique used with electroniccounters to determine the ratio of one frequency(X) to another (Y). When X is the higher frequency,the counter readout shows the numberof pulses of X producing one cycle of Y.XY-cut crystal A piezoelectric plate cut from aquartz crystal at such an angle that its electricalcharacteristics fall between those of the X-cutand Y-cut crystal.x-y plotter An output device similar to the x-yrecorder. It allows a digital computer to plotgraphs. Also called data plotter.x-y recorder An instrument that produces a permanentrecord (photographic print or directlyinked paper) of a variable quantity on a charthaving Cartesian (rectangular) coordinates.

Y 1. Symbol for ADMITTANCE. 2. Symbol forYTTRIUM. 3. Symbol for YOUNG’S MODULUS.y 1. Abbreviation of YEAR. (Also, yr.) 2. Abbreviationof YARD. (Also, yd.) 3. Symbol for the verticalaxis of a graph or screen in the rectangular(Cartesian) coordinate system.Y adapter See WYE ADAPTER.YAG Abbreviation of yttrium-aluminum-garnet, thestimulated substance in some lasers.Yagi antenna Also called Yagi-Uda array or beam.An antenna consisting of two or more parallel,straight elements, including at least one parasiticelement and at least one driven element. The elementsall lie in the same plane. Each driven elementis connected to the feed line, half-waveresonant, and center-fed. A two-element arraycan be formed by adding a director or a reflectoralongside a single driven element. An array withone director and one reflector, along with thedriven element, increases the gain and directivitycompared with a two-element system. The gainand directivity increase further as elements areadded. This is usually done by placing additionaldirectors in front of a three-element array. CompareQUAD ANTENNA.y amplifier The vertical amplifier of an oscilloscopeor recorder. Compare X AMPLIFIER and Z AMPLI-FIER.Yankee Phonetic alphabet communications codeword for the letter Y.yard Abbreviation, yd. A unit of linear measure inParasiticreflectorRadiatorFeederParasiticdirectors}Mastyagi antennathe English system. 1 yd = 3 ft = 36 inches =0.9144 meter.yaw Side-to-side movement in a vehicle or roboticend effector. Essentially horizontal displacementabout the vertical axis.yaw amplifier In an aircraft servo system, the unitthat amplifies the yaw signal (the signal proportionalto the deviation of the aircraft from the lineof flight).yaw meter An instrument for measuring the angleof yaw of an aircraft.y-axis 1. The vertical axis of a chart, graph, orscreen in the rectangular coordinate system.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

y-axis • ytterbium metals 7632. In a quartz crystal, the axis drawn perpendicularto the faces of the hexagon.y-axis amplifier See Y AMPLIFIER.Yb Symbol for YTTERBIUM.Y box See WYE BOX.Y channel See Y AMPLIFIER.Y-channel gain See Y GAIN.Y circulator An interconnection among threewaveguides. When power is applied to the junctionthrough one waveguide, the wave is transferredto the adjacent waveguide immediately tothe right or left.Y connection See WYE CONNECTION.y coordinate See ORDINATE.Y current See WYE CURRENT.Y-cut crystal A piezoelectric plate cut from aquartz crystal in such a way that the plane of theplate is perpendicular to the Y-axis of the crystal.See CRYSTAL AXES and Y-AXIS, 2.yd Abbreviation of YARD.Y deflection Vertical deflection of the spot on thescreen of a cathode-ray tube. Compare X DE-FLECTION.Y diode The decoding diode in each of the Y lines ofa memory matrix. Compare X DIODE.y direction The vertical direction in deflectionsand in graphical presentations of data.Y drive The driving source or energy for the y linesof a computer memory matrix. Compare X DRIVE.year Abbreviation, y or yr. The period of the earth’srevolution around the sun, with respect todistant stars: approximately 365.25 days or3.15576 × 10 7 seconds.Yellow Book A specialized format for compact-diskread-only memory (CD-ROM) computer data storagemedia, developed by Sony and Philips. It issimilar to RED BOOK, but it includes superior errorcorrection and storage capacity. See also CD-ROM, GREEN BOOK, ORANGE BOOK, and REDBOOK.yellow copper ore See CHALCOPYRITE.yellow metal A copper-zinc alloy that is 60% copper.yellow pyrites See CHALCOPYRITE.Y-equivalent circuit See WYE-EQUIVALENT CIR-CUIT.Y gain The gain (or gain control) of the verticalchannel of an oscilloscope or x-y recorder. CompareX GAIN and Z GAIN.yield In a phototube or photocell, the photoelectriccurrent per unit intensity of light.yield map A diagram of an integrated circuit showingthe locations of faulty components.yield strength The lowest stress for plastic deformationof a material, below which the material iselastic and above which it is viscous.yield value The amount of physical stress thatcauses a substance to become stretched permanentlyout of shape.YIG Abbreviation of yttrium-iron-garnet, a crystallinematerial used in certain types of acousticdelay lines, parametric amplifiers, and filters.YIG crystal A crystal of yttrium-iron-garnet. SeeYIG.YIG filter A filter using a YIG crystal and tunedelectromagnetically.YIG-tuned parametric amplifier A parametricamplifier in which tuning is accomplished by continuouslyvarying direct current through thesolenoid of a YIG filter.y intercept The y coordinate of the point at whicha line or plane intersects the y-axis.ylem The material from which the primordial fireballis thought to have been made, and fromwhich the entire known universe is believed tohave originated approximately 10 billion (10 10 )years ago.Y line A vertical line of a memory matrix. CompareX LINE.Y-matched-impedance antenna See WYE-MATCHED-IMPEDANCE ANTENNA.YMODEM In data transmission, an error-correctingmode in which data is sent in blocks of onemegabyte (1MB), or 1,048,576 bytes. The sourceand destination tally up the bytes in each block.If they agree, the next data block is sent. If theydo not agree, the current data block is retransmitted.Compare XMODEM and ZMODEM.yoke 1. The ferromagnetic ring or cylinder thatholds the pole pieces of a dynamo-type generatorand acts as part of the magnetic circuit. 2. Thesystem of coils used for magnetic deflection of theelectron beam in cathode-ray tubes.yoke method A method of measuring the permeabilityof a sample of magnetic material. It involvescompleting the magnetic circuit with aheavy yoke of soft iron.Young’s modulus Symbol, Y. The ratio of tensilestress to tensile strain.Y parameters The admittance parameters of afour-terminal network or device.Y point See WYE POINT.Y position 1. On a cathode-ray screen, the verticalposition of the beam spot. 2. On a graph, the positionof a point along the vertical axis.Y potential See WYE POTENTIAL.yr Abbreviation of YEAR. Also, y.Y rectifier See WYE RECTIFIER.Y signal In color television, the monochromaticsignal conveying brightness information.Y sink The circuit or device into which the Y linesof a memory matrix feed. Compare X SINK.ytterbium Symbol, Yb. A metallic element of therare-earth group. Atomic number, 70. Atomicweight, 173.04.ytterbium metals The rare-earth metals dysprosium,erbium, lutetium, holmium, thulium, andytterbium.

764 Yttralox • Y-Y circuitYttralox A transparent polycrystalline ceramiccomposed primarily of yttrium oxide, which hasmany applications in electro-optics.yttria Formula, Y 2 O 3 . Yttrium oxide, a white powderused in Nernst lamps.yttrium Symbol, Y. A metallic element of the rareearth-metalsgroup. Atomic number, 39. Atomicweight, 88.906.yttrium-iron-garnet See YIG.yttrium metal Any of the group of metals,including yttrium, erbium, holmium, lutetium,thulium, ytterbium, and sometimes dysprosium,gadolinium, and terbium.Yukon Standard Time Standard time of the ninthtime zone west of Greenwich, embracing theYukon Territory and a portion of southern Alaska.Y winding See WYE CONNECTION.Y-Y circuit See WYE-WYE CIRCUIT.

Z 1. Symbol for IMPEDANCE. 2. Symbol forATOMIC NUMBER. 3. Symbol for zenith distance(astronomy).z 1. Abbreviation of ZERO. 2. Symbol for ELEC-TROCHEMICAL EQUIVALENT. 3. Abbreviation ofZONE. 4. Symbol for the vertical axis of a threedimensionalCartesian graph.zag The short, straight deflection of a point or particle,or of waves along a jagged path in a directionopposite that of a ZIG; one of the componentsof ZIGZAG DEFLECTION.Zamboni pile A high-voltage electrochemical cellconsisting of an aluminum anode, a manganesedioxidecathode, and an aluminum-chloride electrolyte.Z amplifier The intensity-modulation amplifier inan oscilloscope. Compare X AMPLIFIER and YAMPLIFIER.Z-angle meter An instrument, commonly of thenull-balance type, that indicates the impedanceand phase angle of capacitors, inductors, andsometimes of inductance-capacitance-resistance(ICR) combinations.z-axis1. The intensity-modulation input of anoscilloscope, including the associated circuit.2. The video-signal input of a television picturetube, including the associated circuit. 3. Thethird axis in a three-dimensional coordinate system.4. The lengthwise axis of a quartz crystal.z-axis amplifier See Z AMPLIFIER.z-axis modulation See INTENSITY MODULATION.Z bar See Z-CUT CRYSTAL.z channel See Z AMPLIFIER.z-channel gain See Z GAIN.Z-cut crystal A plate cut from a quartz crystal sothat the plane of the plate is perpendicular to theZ-axis of the crystal and parallel to theX-axis. See CRYSTAL AXES.ZD Abbreviation of zero defects.Z deflection Deflection of a cathode-ray beam beyondthe (ordinarily defined) deflection area onthe tube screen.Zeeman effect The splitting of a spectral line of agas into closely spaced, polarized frequency componentsby an applied magnetic field.Zenely electroscope A sensitive alpha-ray electroscope(see ELECTROSCOPE) whose leaf is attractedby a metal plate biased at 50 to 200 volts.On touching the plate, the leaf becomes chargedand is repelled. But the gas ions around the leafneutralize the charge, and the leaf returns to theplate to repeat the action. This sequence causesthe leaf to oscillate, the number of oscillations persecond being proportional to the strength of theionizing source.Zener See ZENER DIODE.Zener breakdown See AVALANCHE BREAK-DOWN.Zener current See AVALANCHE CURRENT.Zener diode Also sometimes called avalanchediode or Zener. A semiconductor diode (usuallysilicon) specially fabricated to take advantage ofthe effects of avalanche breakdown. It is availablein a wide variety of configurations and ratings; itis commonly used as a voltage regulating devicein low-voltage power supplies.Zener-diode clipper A signal-amplitude clipperthat does not require direct-current bias becauseit uses a Zener diode. Clipping takes place atthe avalanche voltage. Zener diodes can beconnected back to back for alternating-currentclipping.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

766 Zener-diode coupling element • Zener kneeZener-diode coupling element A Zener diodeused as a direct coupling element between amplifierstages in an electronic system. When no signalis present, the resistance of the diode isextremely high because the direct-current voltagesof the diode-coupled amplifier stages reversebiasthe diode to below the avalanche point, andno current flows from one stage to the next. Thesignal raises the voltage enough to causeavalanche breakdown; the signal is thus readilytransmitted from one stage to the following one.+Battery_dc TypeCurrent-limitingresistorDiode+_Standarddc voltageB Current-limitingresistorac TypeacSourceDiodesStandardac outputDzener-diode voltage referencedc TypeCurrent-limitingresistorzener-diode coupling elementZener-diode voltage reference A device that utilizesthe constant voltage drop across a Zenerdiode operated in its breakdown region, to providea standard voltage for reference purposes. Itconsists essentially of a direct-current (dc) voltagesource, limiting resistor, and Zener diode. Foran alternating-current (ac) reference voltage, anac voltage source, limiting resistor, and two Zenerdiodes (connected in parallel, back to back) arerequired. Zener diodes can be connected in seriesto supply a higher reference voltage than can bedelivered by a single diode.Zener-diode voltage regulator A simple voltageregulator whose output is the constant voltagedrop developed across a Zener diode conductingin the reverse breakdown region. The simple regulatorcircuit consists of a Zener diode and an appropriatelimiting resistor connected in seriesacross the output terminals of an unregulateddirect-current power supply. For alternatingcurrentvoltage regulation, two Zener diodes canbe connected in parallel, back to back. Zenerdiodes can be connected in series to regulate ahigher voltage than can be accommodated by asingle diode.Unregulateddc inputUnregulatedac input+_ac TypeCurrent-limitingresistorZenerdiode +Zenerdiodeszener-diode voltage regulatorZener effect See AVALANCHE BREAKDOWN.Zener knee In the response of a reverse-biasedZener diode, the point of abrupt transition fromlow current (high resistance) to high current (lowresistance). For voltage regulation and voltage_Regulateddc outputRegulatedac output

Zener knee • zero capacitance 767standardization, the knee should be as sharp aspossible.Zener knee current In a Zener diode, the currentthat flows when the reverse bias reaches theavalanche voltage.Zener-protected MOSFET See GATE-PRO-TECTED MOSFET.Zener voltage The particular value of reverse voltageat which a Zener diode or other reversebiasedpn junction abruptly exhibits theavalanche effect. Depending on the Zener diode,this potential can be less than 10 volts, or asmuch as several hundred volts.zenith In the sky, the point directly overhead, exactly180 degrees opposite the direction of theearth’s center.Zeolite process A method using certain artificialZeolites (hydrous silicates) to soften water used insome electronic manufacturing and testing operations.zeppelin antenna Also called zepp. 1. A half-wavelengthradiator, fed at one end with a quarterwavelengthsection of open-wire line. The feedline can come away from the radiator at anyangle, usually 90 degrees or more. The antennawas originally used aboard zeppelins; the entiresystem was dangled in flight and the feed line wascollinear with the radiating element. Theimpedance at the feed point is high; theimpedance at the transmitter end of the feed lineis low. The antenna will operate satisfactorily at allharmonics of the design frequency. 2. A radiatorthat is an integral multiple of a half wavelength,fed with open-wire line of any length. A transmatchis employed at the transmitter and of thefeed line. This arrangement is popular among radioamateurs. The primary advantage of this an-AntennatunerParallel-wirelineRadiatorn(λ/2)n = 1,2,3 . . .zeppelin antennatenna is ease of installation; the main drawbackis the fact that the feed line radiates to some extentbecause the system is not perfectly balanced.zero 1. The number represented by the ciphersymbol (0). 2. To set a meter or other instrumentto its zero reading or condition. 3. To align one elementof a system precisely with another. 4. Incomputer operations, to set a register to zero.5. In computer operations, using zero pulses toreplace what is in a storage area.zero-access memory See ZERO-ACCESS STOR-AGE.zero-access storage Computer storage requiringnegligible waiting time (latency).zero-address instruction A computer instructionrequiring no address; the operation specified bythe instruction defines the locations of theoperands. Also called addressless instruction.zero adjust In an analog metering device, a mechanicalor electrical control that allows precisesetting of the reading to zero, when the parameterto be measured is actually zero.zero adjustment 1. The act of setting an instrumentor circuit to its zero reading or zero-operatingcondition. 2. A device or subcircuit used toset a meter to its zero reading. Also see ZEROSET, 1, 2.zero-angle cut An alternate term for X cut, as appliedto quartz crystal plates. Also see CRYSTALCUTS.zero axis In a plot of a variable quantity, the (usuallyhorizontal) reference line that indicates thezero value of the quantity.zero-axis symmetry The condition in which awaveshape is symmetrical about a zero axis.zero beatComplete absence of a beat note (i.e., silence),a condition occurring when the frequenciesof the beating signals (or their harmonics) areequal. See BEAT NOTE.zero-beat detector A device or circuit used tosense and indicate the condition of zero beat.zero-beat indicator See ZERO-BEAT DETECTOR.zero-beat method A means of adjusting the frequencyof one signal exactly to that of another(usually standard) signal by setting the first signalfrequency to zero beat with the second signalfrequency.zero-beat reception A system of reception entailingzero beating an incoming signal with the signalfrom a local oscillator. Also called homodynereception.zero-bias operation Operation of a transistor orvacuum tube without direct-current base, gate,or grid bias.zero-bias tube A vacuum tube designed for operation(particularly in a class-B power amplifier)without direct-current grid bias. In such a tube,the zero-signal plate current is very low becauseof the large amplification factor.zero capacitance 1. Absence of capacitance (atheoretically ideal condition). 2. In some circuits,

768 zero capacitance • zero polethe lowest capacitance point, to which all othercapacitances are referred.zero compensation The elimination or minimizingof the zero-signal output of a transducer or similardevice.zero compression See ZERO SUPPRESSION, 1.zero condition See ZERO STATE.zero current 1. Absence of movement of electricalcharge carriers. 2. In some circuits, the lowestcurrent level, to which all other currents are referred.zero-cut crystal A piezoelectric plate cut from aquartz crystal in such a way that the frequencytemperaturecoefficient is zero.zero-dB reference level An agreed-upon zero levelfor decibel ratings (which are by nature relative).Zero dBm, for example, corresponds to 1 milliwatt.Compare VOLUME UNIT.zero drift 1. The (usually gradual) drift of a zeropoint, such as the zero setting of an electronicvoltmeter. 2. The condition of no change in thevalue of a quantity.zero elimination See ZERO SUPPRESSION, 1.zero energy The condition in which energy is neithergenerated, consumed, nor dissipated.zero error 1. In instruments and measurements,an error so small that it can be considered inconsequential.2. In a radar system, the inherentdelay in the transmitter and receivercircuits.zero field emission Thermionic emission from acathode or hot conductor within a uniform electrostaticfield.zero fill See ZERO, 5.zero gravity The condition of weightlessness (i.e.,the state in which gravitational pull by a celestialbody is completely absent or has been nullified).zero-gravity switch A switch actuated automaticallywhen the condition of zero gravity is reached.zero impedance 1. Absence of impedance (a theoreticallyideal condition). 2. In some circuits, thelowest impedance level, to which all otherimpedances are referred.zero inductance 1. Absence of inductance (a theoreticallyideal condition). 2. In some circuits, thelowest inductance level, to which all other inductancesare referred.zero input 1. Complete absence of input (signal ornoise). 2. Absence of operating voltage or power toa system. 3. In a flip-flop, the input terminal thatis not receiving a trigger signal.zero-input terminal In a flip-flop, the input-signalterminal at which a trigger signal will switch theflip-flop output to zero. Also called zero terminaland RESET TERMINAL.zero instant See ZERO TIME.zero level The reference level for the comparison ofquantities. For example, it might be a voltage orcurrent level; in audio measurements, it is thezero-dB reference level.zero-line stability In an analog metering device,the ability of the instrument to maintain properzero adjustment over a period of time.zero magnet A permanent magnet used to set thepointer of a meter to zero.zero magnitude 1. For a quantity, the state of beingvalueless (i.e., a complete absence of thequantity). 2. In some tests, measurements, orcalculations, the lowest value of a quantity, towhich all other values are referred.zero meridian The meridian at Greenwich (nearLondon), England, from which longitude andstandard time are reckoned. Also see TIME ZONEand ZONE TIME.zero method A method of measurement entailingadjustment of a circuit or device (such as abridge, tee network, or potentiometer) for zero responseof the detector. Also called null method.zero modulation The momentary lack of modulationin a communications or broadcast system,as during a pause in speech.zero-modulation noise Noise produced by previouslyerased tape that is run under specified operatingconditions.zero output 1. Complete absence of output signalor output power, sometimes disregarding noiseoutput. 2. In a flip-flop, the normal condition ofno signal pulse at a particular output terminal.zero-output terminal In a flip-flop, the output terminalthat is not delivering an output pulse.zero phase In an alternating-current circuit, thecondition in which the current and voltage are instep. That is, the current peaks occur at exactlythe same times as the voltage peaks; the phasedifference between the current and voltage is zerodegrees.zero pole In a multiconductor line, the common orreference conductor.

zero potential • zero-zero 769zero potential 1. Complete absence of voltage.2. In some circuits, the lowest voltage, to whichall other voltages are referred. 3. The potential ofthe earth as a reference point.zero power 1. Complete absence of dissipatedpower. 2. In some circuits and systems, the lowestpower level, to which all other power valuesare referred.zero-power resistance In a thermistor, the resistanceat which power dissipation is zero.zero-power resistance-temperature characteristicFor a thermistor, a figure that reveals the extentto which zero-power resistance varies withthe temperature of the thermistor body.zero-power temperature coefficient of resistanceA temperature coefficient that revealsthe extent to which the temperature of the thermistorbody causes the zero-power resistance tochange (expressed in ohms per ohm per degreeCelsius).zero reactance 1. Absence of reactance (a theoreticallyideal condition in alternating-current circuits).2. In some circuits, the lowest reactance,to which all other reactances are referred.zero resistance 1. Absence of resistance (a theoreticallyideal condition). 2. In some circuits, thelowest resistance, to which all other resistancesare referred.zero scale current In a digital-to-analog (D/A)converter, the current into the output when alllogic inputs are low (off) and the output is at acertain predetermined value, in microamperes ormilliamperes.zero screw The mechanical zero adjuster of ameter.zero set 1. A (usually screwdriver-adjusted) mechanismfor setting the pointer of a meter to zero.2. An electrical circuit consisting of a resistancebridge or adjustable bucking voltage for setting ameter to read zero under specific conditions.VTVMcircuitR2R3zero set, 2Meter(dc µA)R4R1Zero-setcontrolB B zero shift See ZERO DRIFT.zero signal 1. The condition of complete absenceof signal. 2. A finite signal level used as a referencepoint against which all other signal levelsare measured.zeros of impedance For an alternating-currentnetwork, the frequencies at which the impedanceis zero. Also called zeros.zeros of network function The real or complexvalues at which the network function is zero.Compare POLES OF NETWORK FUNCTION.zeros of transfer function The frequencies atwhich a transfer function becomes zero. ComparePOLES OF TRANSFER FUNCTION.zero stability Constancy of the zero condition in aninstrument or system (i.e., absence of zero drift).zero state The low, zero, off, or false logic state of abistable device, such as a flip-flop or magneticcell. It might be actual zero output or a low-voltageoutput. Compare ONE STATE. In binarynotation and calculation, the zero state isrepresented by a cipher.zero suppression 1. In computer operation, automaticnonsignificant leading-zero cancellation.2. Absence or removal of a restraining medium,such as a noise-suppression voltage. 3. In an audiorecording system, the introduction of a voltageto cancel the steady-state component of theinput signal.zero temperature 1. The point from which temperaturesare reckoned on a thermometer scale.On the Celsius (centigrade) scale, zero degreescorresponds to the freezing point of pure water atstandard atmospheric pressure. On the Fahrenheitscale, zero degrees is 32 degrees colder thanthe freezing point of pure water at standard atmosphericpressure. On the Kelvin or Rankinescales, zero degrees corresponds to the completeabsence of thermal energy; it is the coldest possibletemperature. 2. A temperature point relativeto which all other temperatures are reckoned.zero temperature coefficient A temperature coefficienthaving the value zero (i.e., one that indicatesthere is no temperature-dependent drift of agiven quantity).zero terminal See ZERO-INPUT TERMINAL andZERO-OUTPUT TERMINAL.zero time 1. In some measurements, the first instantof time, to which all other instants are referred.2. See ZERO PHASE.zero time reference During one cycle of radar operation,the time reference of the schedule ofevents.zero vector A vector whose magnitude is zero.zero voltage See ZERO POTENTIAL.zero voltage coefficient A voltage coefficient havingthe value of zero (i.e., one that indicates thereis no voltage-dependent drift of a given quantity).zero-zero The atmospheric condition in which theceiling and visibility both are zero (i.e., extremelydense fog).

770 Z gain • Z meterZ gain The gain (or gain control) of the intensitychannel of an oscilloscope. Compare X GAIN andY GAIN.zig The short, straight deflection of a point or particle,or of a wave along a jagged path in a directionopposite that of ZAG; a component ofZIGZAG DEFLECTION.zigzag deflection Deflection of a particle, point, orobject in a path that contains side-to-side motion,as well as forward motion. Also see ZAG andZIG.zigzag rectifier A special version of the threephasestar (three-phase, half-wave) rectifier circuit.Direct-current (dc) saturation of thetransformer secondary is avoided by winding halfthe turns of each secondary on a separate core(i.e., each core carries two half-windings). The opposingflux resulting from different phases in thehalf-windings causes cancellation of the dc componentof flux in each core.zigzag reflections Multihop reflections of wavesalong a zigzag path, resulting from repeated reflectionswithin the ionosphere.zinc Symbol, Zn. A metallic element. Atomic number,30. Atomic weight, 65.39. It is used as thenegative-electrode material in dry cells and as aprotective coating for some metals used in electronics.ThreephaseinputABECzigzag rectifierFD+dc Output_zinc aluminate phosphor Either of two similarsubstances used as a phosphor coating forcathode-ray tube screens. One form glows blue;the other form glows red.zinc beryllium silicate phosphor A substanceused as a phosphor coating for cathode-ray-tubescreens. It glows yellow.zinc beryllium zirconium silicate phosphor Asubstance used as a phosphor coating for cathode-ray-tubescreens. It glows white.zinc borate phosphor A substance used as aphosphor coating for cathode-ray-tube screens. Itglows yellow-orange.zinc cadmium sulfide phosphor Either of twosimilar substances used as a phosphor coatingfor cathode-ray-tube screens. One form glowsblue; the other form glows red.zinc–carbon cell A common non-rechargeableelectrochemical cell. Produces approximately1.5 volts under no-load conditions. Zinc formsthe outer case or shell, and is the negative electrode.A carbon rod serves as the positive electrode.The electrolyte is a paste of manganesedioxide and carbon. The cell is inexpensive, andis commercially available in various sizes. Theshelf life is fairly long. Cells of this type work wellat moderate temperatures, and in applicationswhere the current drain is moderate to high.They function poorly at low temperatures. CompareALKALINE CELL.zinc germanate phosphor A substance used as aphosphor coating for cathode-ray-tube screens. Itglows yellow-green.zinc magnesium fluoride phosphor A substanceused as a phosphor coating for cathode-ray-tubescreens. It glows orange.zincolysis Electrolysis in a cell having a zincanode.zinc orthoscilicate phosphor Also called Willemite.A substance used as a phosphor coating forcathode-ray-tube screens. It glows yellow-green.zinc oxide A substance used as a phosphor coatingfor cathode-ray-tube screens. It glows bluegreen.It is also used in the manufacture ofcertain electronic components, such as resistors.zinc-oxide resistor A voltage-dependent resistorwhose active ingredient is zinc oxide.zinc silicate phosphor A substance used as aphosphor coating for cathode-ray-tube screens. Itglows blue.zinc standard cell A standard cell using zinc andmercury electrodes, and a mercurous sulfate excitantand depolarizer. Produces 1.4322 volts at15°C. Also called Clark cell. Compare WESTONCELL.zinc sulfide phosphor A substance used as aphosphor coating for cathode-ray-tube screens.Glows blue-green or yellow-green.ZIP Abbreviation of zinc-impurity photodetector.zip cord A simple two-conductor, flexible powercord.zirconia Preparations of zirconium (especiallyZr0 2 ), valued for their high-temperature dielectricproperties.zirconium Symbol, Zr. A metallic element. Atomicnumber, 40. Atomic weight, 91.22.Z marker A vertically radiating marker beacondefining the zone above a radio-range station.Z meter A device for measuring impedances. Instrumentsof this kind take four principal forms:(1) a direct-reading meter resembling an ohmmeter;(2) an adjustable circuit manipulated somewhatlike a bridge and that compares anunknown impedance with a standard resistance;

Z meter • zwitterion 771(3) an impedance bridge for evaluating the reactiveand resistive components of an unknownimpedance; (4) a section of transmission lineused with a signal source and voltmeter for measuringimpedance in terms of a standard resistorand/or standing waves.ZMODEMIn data communications, an error-correctionmode similar to XMODEM, except thatwhen an error is found during transmission of ablock of data, the source retransmits only thatportion of the block following the error. This improvesdata transmission speed because, whenan error occurs, the number of bytes retransmittedis generally fewer than the 128K block sizestandard in XMODEM. Compare XMODEM andYMODEM.Zn 1. Symbol for ZINC. 2. Symbol for AZIMUTH.Z 0 Symbol for CHARACTERISTIC IMPEDANCE.zone 1. On a magnetic disk, a group of trackswhose associated transfer rate is not the same asthat for the rest of the disk. 2. In computer operations,the area of a storage medium containingdigits. 3. In a computer system, a main memoryarea set aside for a particular purpose. 4. In a securitysystem, a specified area or region undersurveillance.zone blanking In a radar system, a method of extinguishingthe cathode-ray-tube beam during aportion of the antenna sweep.zone candle power In a given zone, the luminousflux per steradian, emitted by a light source undertest.zoned circuit In a security system, a circuit inwhich some areas are protected at all times, whilethe protection in other areas can be temporarilydisabled for entry or exit.zone leveling See ZONE REFINING.zone marker See Z MARKER.zone melting See ZONE REFINING.zone of silence The region between alternate reflectionsof a radio wave, in which no signal is detectable.Also called skip zone.zone plate antenna A rapid-scan radar antennahaving a reflector composed of confocal parabolasarranged in a circle.zone-position indicator A radar that reveals theposition of an object to a second radar having arestricted field.zone purification See ZONE REFINING.zone refining A method of purifying semiconductormaterials (such as germanium and silicon) inwhich a molten zone in an ingot of the materialmoves along the length of the ingot, dissolvingimpurities as it travels, eventually depositingthem at the end of the ingot, which is sawed off.This concentrated and segregated melting is accomplishedby means of radio-frequency heating.zone time In a given time zone, standard time interms of the number of hours that must be addedto local time to equal the time at the zero (Greenwich)meridian.zoning 1. A method of fabricating a microwavereflector in concentric, flat regions, producingthe same practical results as a continuousparaboloid. 2. In a communications system, thedivision of the coverage area into different geographicregions for a specific purpose.zoom 1. To rapidly change the focal length of atelevision or motion-picture camera lens so thatthe object seems to advance toward or recedefrom the viewer, remaining in focus as it does so.2. See ZOOM LENS. 3. To magnify the image in acomputer graphical user interface. A user can enlargea specific portion of the display, at the expenseof other portions. It is generally measuredin percent (e.g., 200% zoom represents a magnificationfactor of 2).zoom lens A continuously adjustable lens systemthat allows zoom effects to be obtained with atelevision or motion-picture camera, or a similararrangement for still cameras that obviates theneed for lens interchange when different focallengths are needed. The lens system, which canbe operated electronically, allows either narroworwide-angle views to be obtained without losingfocus at any time.Z parameters Device or network parameters expressedas impedances.ZPI Abbreviation of ZONE-POSITION INDICATOR.Z-plunger In a waveguide, a combination chokeand bucket plunger for radiation leakage reduction.Zr Symbol for ZIRCONIUM.Z signals A collection of letter groups, each startingwith the letter Z, used for simplified telegraphyand radiotelegraphy by the military services.Zulu Phonetic alphabet communications codeword for the letter Z.Zulu time Greenwich mean time. Also see ZEBRATIME.zwitterion An ion that carries both a positive anda negative charge.

This page intentionally left blank.

AppendixSchematic symbolsAAmmeter^Amplifier generalAmplifier, invertingAmplifier, operationalAND gateAntenna, balancedAntenna, generalAntenna, loopAntenna, loop, multiturnBattery− +Capacitor, feedthroughCapacitor, fixedCapacitor, variableCapacitor, variable, split-rotorCapacitor, variable, split-statorCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

774 Appendix ACathode, electron-tube, coldCathode, electron-tube, directly heatedCathode, electron-tube indirectly heatedCavity resonatorCell, electrochemical− +Circuit breakerCoaxial cableCrystal, piezoelectricDelay lineDiacDiode, field-effectDiode, generalDiode, GunnDiode, light-emittingDiode, photosensitive

Schematic symbols 775Diode, PINDiode, SchottkyDiode, tunnelDiode, varactorDiode, zenerDirectional couplerDirectional wattmeterWExclusive-OR gateFemale contact, generalFerrite beadFilament, electron-tubeFuseGalvanometerGGrid, electron-tubeGround, chassis

776 Appendix AGround, earthHeadsetHandset, doubleHeadset, singleHeadset, stereoLRInductor, air coreInductor, air core, bifilarInductor, air core, tappedInductor, air core, variableInductor, iron coreInductor, iron core, bifilarInductor, iron core, tappedInductor iron core, variableInductor, powdered-iron coreInductor, powdered-iron core, bifilar

Schematic symbols 777Inductor, powdered-iron core, tappedInductor, powdered-iron core, variableorIntegrated circuit, general(Design-show)Jack, coaxial or phonoJack, phone, two-conductorJack, phone, three-conductorKey, telegraphLamp, incandescentLamp, neonMale contact, generalMeter, generalMicroammeterµAMicrophone

778 Appendix AMicrophone, directionalMilliammetermANAND gateNegative voltage connection−NOR gateNOT gateOptoisolatorOR gateOutlet, two-wire, nonpolarizedOutlet, two-wire, polarizedOutlet, three-wireOutlet, 234-VPlate, electron-tubePlug, two-wire, nonpolarized

Schematic symbols 779Plug, two-wire, polarizedPlug, three-wirePlug, 234-VPlug, coaxial or phonoPlug, phone, two-conductorPlug, phone, three-conductorPositive voltage connection+PotentiometerProbe, radio-frequencyorRectifier, gas-filledRectifier, high-vacuumRectifier, semiconductorRectifier, silicon-controlled

780 Appendix ARelay, double-pole, double-throwRelay, double-pole, single-throwRelay, single-pole, double-throwRelay, single-pole, single-throwResistor, fixedResistor, presetResistor, tappedResonatorRheostatSaturable reactorSignal generatorSolar battery− +

Schematic symbols 781Solar cell− +Source, constant-currentSource, constant-voltage+−SpeakerSwitch, double-pole, double-throwSwitch, double-pole, rotarySwitch, double-pole, single-throwSwitch, momentary-contactSwitch, silicon-controlledSwitch, single-pole, rotarySwitch, single-pole, double-throwSwitch, single-pole, single-throw

782 Appendix ATerminals, general, balancedTerminals, general, unbalancedTest pointTPThermocoupleorTransformer, air coreTransformer, air core, step-downTransformer, air core, step-upTransformer, air core, tapped primaryTransformer, air core, tapped secondaryTransformer, iron coreTransformer, iron core, step-downTransformer, iron core, step-upTransformer, iron core, tapped primaryTransformer, iron core, tapped secondary

Schematic symbols 783Transformer, powdered-iron coreTransformer, powdered-iron core, step-downTransformer, powdered-iron core, step-upTransformer, powdered-iron core, tapped primaryTransformer, powdered-iron core,tapped secondaryTransistor, bipolar, NPNTransistor, bipolar, PNPTransistor, field-effect, N-channelTransistor, field-effect, P-channelTransistor, MOS field-effect, N-channelTransistor, MOS field-effect, P-channelTransistor, photosensitive, NPNTransistor, photosensitive, PNP

784 Appendix ATransistor, photosensitive, field-effect,N-channelTransistor, photosensitive, field-effect,P-channelTransistor, unijunctionTriacTube, diodeTube, heptodeTube, hexodeTube, pentodeTube, photosensitiveTube, tetrode

Schematic symbols 785Tube, triodeVoltmeterVWattmeterWWaveguide, circularWaveguide, flexibleWaveguide, rectangularWaveguide, twistedWires, crossing, connected(preffered)or(alternative)Wires, crossing, not connected(preffered)or(alternative)

AppendixBTables and dataConversion between Electrical SystemsSystemcgscgsProperty mks electromagnetic electrostaticCapacitance 1 farad 10 9 abfarad 9 10 11 statfarad10 9 F 1 abF 9 10 20 statF10 11 /9 F 10 20 /9 abF 1 statFCharge 1 coulomb 0.1 abcoulomb 3 10 9 statC10 C 1 abC 3 10 10 statC10 9 /3 C 10 10 /3aC 1 statCCharge density 1 coulomb/m 3 10 7 abcoulomb/cm 3 3 10 3 statcoulomb/cm 310 7 C/m 3 1 abC/cm 3 3 10 10 statCcm 310 3 /3 C/m 3 10 10 /3 aC/cm 3 1 statC/cm 3Conductivity 1 siemens/m 10 11 absiemens/cm 9 10 9 statSiemens/cm10 11 S/m 1 abS/cm 9 10 20 statS/cm10 9 /9 S/m 10 20 /9 abS/cm 1 statS/cmCurrent 1 ampere 10 1 abampere 3 10 9 statampere10 a 1 abA 3 10 10 statA10 9 /3 a 10 10 /3 abA 1 statACurrent density 1 ampere/m 2 10 5 abampere/cm 2 3 10 5 statampere/cm 210 5 A/m 2 1 abA/cm 2 3 10 10 statA/cm 210 5 /3 A/m 2 10 10 /3 aA/cm 2 1 statA/cm 2Electric field intensity 1 volt/m 10 6 abvolt/cm 10 4 /3 statvolt/cm10 6 V/m 1 abV/cm 10 10 /3 statV/cm3 10 4 V/m 3 10 10 aV/cm 1 statV/cmElectric potential 1 volt 10 8 abvolt 10 2 /3 statvolt10 8 V 1 abV 10 10 /3 statV3 10 2 V 3 10 10 aV 1 statVElectric dipole moment 1 coulomb-m 10 abC-cm 3 10 11 statC-cm0.1 C-m 1 abC-cm 3 10 10 statC-cm10 11 /3 C-m 10 10 /3 abC-cm 1 statC-cmCopyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

788 Appendix BSystemcgscgsProperty mks electromagnetic electrostaticEnergy 1 joule 10 7 erg 10 7 erg10 7 J 1 e 1 e10 7 J 1 e 1 eForce 1 newton 10 5 dyne 10 5 dyne10 5 N 1 d 1 d10 5 N 1 d 1 dFlux density 1 Weber/m 2 10 4 gauss (or abtesla) 10 6 /3 electrostatic unit10 4 Wb/m 2 1 G 10 10 /3 esu310 6 Wb/m 2 3 10 10 G 1 esuInductance 1 henry 10 9 abhenry 10 11 /9 stathenry10 9 H 1 abH 10 20 /9 statH9 10 11 H 9 10 20 abH 1 statHInductive capacity 1 farad/m 10 11 abfarad/cm 9 10 9 statfarad/cm10 11 F/m 1 abF/cm 9 10 20 statF/cm10 9 /9 F/m 10 20 /9 abF/cm 1 statF/cmMagnetic flux 1 weber 10 8 Maxwell 10 2 /3 electrostatic unit10 8 W 1 Mx 10 10 /3 esu3 10 2 W 3 10 10 Mx 1 esuMagnetic dipole moment 1 ampere-m 2 10 3 abampere-cm 2 3 10 13 statampere-cm 210 3 A-m 2 1 abA-cm 2 3 10 10 statA-cm 210 13 /3 A-m 2 10 10 /3 abA-cm 2 1 statA-cm 2Permeability 1 henry/m 10 7 abhenry/cm 10 13 /9 stathenry/cm10 7 H/m 1 abH/cm 10 20 /9 statH/cm9 10 13 H/m 9 10 20 abH/cm 1 statH/cmPower 1 watt 10 7 erg/s 10 7 erg/s10 7 W 1 e/s 1e/s10 7 W 1 e/s 1e/sResistance 1 ohm 10 9 abohm 10 11 /9 statohm10 9 ohm 1 abohm 10 20 /9 statohm9 10 11 ohm 9 10 20 abohm 1 statohm

Tables and data 789GREEK ALPHABETCapital Lowercase NameA α alphaB β beta γ gamma∆ δ or ∂ deltaE ε epsilonZ ζ zetaH η etaΘ θ or thetaI iotaK kappa lambdaM muN nu xiO omicron piP rho or sigmaT tau υ upsilon or phi chi psi omegaMathematical FunctionsSigns and symbols radix (base) point ≠ not equal to• multiplication symbol; logic AND function ∼ similar to infinity less than plus; positive; logic OR function not less than minus; negative much less than plus or minus; positive or negative greater than minus or plus; negative or positive not greater than times much greater than divided by ≤ equal to or less than divided by (expressive of a ratio) ≥ equal to or greater than equal to proportional to; varies directly as identical to; is defined by or → approaches or approximately equal to, congruent to is to; proportional to approximately equal to therefore

790 Appendix B@ at the rate of; at cost of x average value of x; x note natural number = 2.71828 f(x) or F(x) function of x pi 3.14159 . . . i 1 ( ) parentheses (use to enclose a group of terms)[ ] brackets (use to enclose a group of terms that j operator, equal to 1 includes one or more groups in parentheses) ∆x increment of x{ } braces (use to enclose a group of terms thatincludes one or more groups in brackets. dx differential of x∠ angle ∂x partial differential of x° degrees (arc or temperature)′ minutes; prime ∆ x∆ychange in x with respect to y′′ seconds; double prime⎥⎥ parallel to d xdyderivative of x with respect to y⊥ perpendicular tod. . . and beyond (x) d yderivative of x with respect to y (del or nabla) vector differential operator d y x derivative of x with respect to y ∂ x∂ypartial derivative of x with respect to yOperationsx y xadded to y; x OR y summationx y ysubtracted from x abx y, x y, multiplied by y; x AND yor xy Π productsummation between limits (from a to b)x y xdivided by y Π a product between limits (from a to b )bx/y or x x divided by y integraly1/x reciprocal of x bintegral between limits (from a to b)x n x raised to the indicated power of n x dy integral of x with respect to ynx indicated root n of x |a evaluated at aax : y xis to y | abevaluated between limits (from a to b)|x| absolute value of x, magnitude of x n! factorial of nX, X , or Xvector X

Tables and data 791PrefixesPrefix Quantity Symbolatto- 10 18 afemto- 10 15 fpico- 10 12 pnano- 10 9 nmicro- 10 6 milli- 10 3 mcenti- 10 2 cdeci- 10 1 ddeka- 10 dahecto- 10 2 hkilo- 10 3 kmega- 10 6 Mgiga- 10 9 Gtera- 10 12 Tpeta- 10 15 Pexa- 10 18 ERESISTOR COLOR CODEThe first three color bands supply the total resistance. The fourth color (if any ) gives the tolerance. Example: A5,600-ohm resistor would have green (first color, 5), blue (second color, 6) and red1 2 3 4 body1 2 3 4black = 0 black = 0 black = gold 5%brown = 1 brown = 1 brown = 0 silver 10%red = 2 red = 2 red = 00 no band 20%orange = 3 orange = 3 orange = 000yellow = 4 yellow = 4 yellow = 0000green = 5 green = 5 green = 00000blue = 6 blue = 6 blue = 000000violet = 7 violet = 7 gold = multiply by 0.1gray = 8 gray = 8 silver = multiply by 0.01white = 9 white = 9

This page intentionally left blank.

About the authorStan Gibilisco has authored or coauthored dozens of nonfiction booksabout electronics and science. He first attracted attention with UnderstandingEinstein’s Theories of Relativity (TAB Books, 1983). His Encyclopediaof Electronics (TAB Professional and Reference Books, 1985) andEncyclopedia of Personal Computing (McGraw-Hill, 1996) were annotatedby the American Library Association as among the best reference volumespublished in those years. Stan’s work has gained reading audiences in theFar East, Europe, and South America.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

This page intentionally left blank.

SOFTWARE AND INFORMATION LICENSEThe software and information on this diskette (collectively referred to as the “Product”) are the property ofThe McGraw-Hill Companies, Inc. (“McGraw-Hill”) and are protected by both United States copyright lawand international copyright treaty provision. You must treat this Product just like a book, except that youmay copy it into a computer to be used and you may make archival copies of the Products for the sole purposeof backing up our software and protecting your investment from loss.By saying “just like a book,” McGraw-Hill means, for example, that the Product may be used by any numberof people and may be freely moved from one computer location to another, so long as there is no possibilityof the Product (or any part of the Product) being used at one location or on one computer while it isbeing used at another. Just as a book cannot be read by two different people in two different places at thesame time, neither can the Product be used by two different people in two different places at the same time(unless, of course, McGraw-Hill’s rights are being violated).McGraw-Hill reserves the right to alter or modify the contents of the Product at any time.This agreement is effective until terminated. The Agreement will terminate automatically without noticeif you fail to comply with any provisions of this Agreement. In the event of termination by reason of yourbreach, you will destroy or erase all copies of the Product installed on any computer system or made forbackup purposes and shall expunge the Product from your data storage facilities.LIMITED WARRANTYMcGraw-Hill warrants the physical diskette(s) enclosed herein to be free of defects in materials and workmanshipfor a period of sixty days from the purchase date. If McGraw-Hill receives written notificationwithin the warranty period of defects in materials or workmanship, and such notification is determined byMcGraw-Hill to be correct, McGraw-Hill will replace the defective diskette(s). Send request to:Customer ServiceMcGraw-HillGahanna Industrial Park860 Taylor Station RoadBlacklick, OH 43004-9615The entire and exclusive liability and remedy for breach of this Limited Warranty shall be limited to replacementof defective diskette(s) and shall not include or extend to any claim for or right to cover any otherdamages, including but not limited to, loss of profit, data, or use of the software, or special, incidental, orconsequential damages or other similar claims, even if McGraw-Hill has been specifically advised as to thepossibility of such damages. In no event will McGraw-Hill’s liability for any damages to you or any other personever exceed the lower of suggested list price or actual price paid for the license to use the Product, regardlessof any form of the claim.THE McGRAW-HILL COMPANIES, INC. SPECIFICALLY DISCLAIMS ALL OTHER WARRANTIES, EX-PRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO, ANY IMPLIED WARRANTY OF MER-CHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Specifically, McGraw-Hill makes norepresentation or warranty that the Product is fit for any particular purpose and any implied warranty ofmerchantability is limited to the sixty day duration of the Limited Warranty covering the physical diskette(s)only (and not the software or in-formation) and is otherwise expressly and specifically disclaimed.This Limited Warranty gives you specific legal rights; you may have others which may vary from state tostate. Some states do not allow the exclusion of incidental or consequential damages, or the limitation onhow long an implied warranty lasts, so some of the above may not apply to you.This Agreement constitutes the entire agreement between the parties relating to use of the Product. Theterms of any purchase order shall have no effect on the terms of this Agreement. Failure of McGraw-Hill toinsist at any time on strict compliance with this Agreement shall not constitute a waiver of any rights underthis Agreement. This Agreement shall be construed and governed in accordance with the laws of New York.If any provision of this Agreement is held to be contrary to law, that provision will be enforced to the maximumextent permissible and the remaining provisions will remain in force and effect.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use

Suggested additionalreferencesCrowhurst, N. and Gibilisco, S., Mastering Technical Mathematics—2nd Edition. New York: McGraw-Hill,1999.Dorf, R., Electrical Engineering Handbook—2nd Edition. Boca Raton, FL: CRC Press, 1997.Gibilisco, S., Electronics Portable Handbook. New York: McGraw-Hill, 1999.Gibilisco, S., Electronics Formulas Pocket Reference. New York: McGraw-Hill, 1999Gibilisco, S., Mathematical and Physical Data, Equations, and Rules of Thumb. New York: McGraw-Hill,2001.Van Valkenburg, M., Reference Data for Engineers: Radio, Electronics, Computer and Communications.Indianapolis: Howard W. Sams & Co., 1998.Veley, V., The Benchtop Electronics Reference Manual. New York: McGraw-Hill, 1994.Copyright 2001 The McGraw-Hill Companies, Inc. Click Here for Terms of Use