The Illustrated Dictionary of Electronics - Loscha

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.