The Illustrated Dictionary of Electronics - Loscha

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