AN-PRC-74A_serv_TM11-5820-590-35_1975.pdf

J t 1M11-5820-590-35 DEPARTMENT 0 FTHEARMY TEe H.NICALMANUAL DS, GS, AND DEPOT MAINTENANCE MANUAL RADIO SET AN/PRC-74 This copyisareprintwhich includescurrent pagesfromChanges1and2. HEADQUA RTER5,DEPARTMENT0 FTHEARMY JULY1966 FurnishedunderUnitedStatesGovernmentContractNo.DA-36- 039-AMC-06547(E).Shallnotbeeitherreleased outsidetheGovernment orused, duplicatedordisclosed in wholeorinpartformanufactureor procurementwithoutthewrittenpermissionofHUGHESAIRCRAFT COMPANY,exceptfor:(i)emergencyrepairoroverhaulworkbyorfor theGovernment,wheretheitemorprocessconcerned isnototherwise reasonablyavailabletoenabletimelyperfonnanceof work;or(ii)release to aforeignGovernment,astheinterestsoftheUnitedStatesmayre- quire;providedthatineithercasetherelease, use, duplicationordis- closurehereofshallbesubjecttotheforegoinglimitations.This legend shall bemarkedonanyreproductionhereof on wholeorpart. . . CHANGE NO.2 TM115820-590-35 C2 HEADQUARTERS DEPARTMENTOFTHEARMY WASHINGTON,DC22August1975 Direct Support, General Support, and Depot Maintenance Manual RADIO SETS AN/PRC.74ANDAN/PRC.74AAND POWER SUPPLY PP-4514/PRC.74 TM11-5820-590-35,21July1966,ischangedasfollows: 1.Neworchangedmaterialis indicatedbya verticalbarinthemargin. 2.Removeandinsertpages as indicatedinthepagelist below: RemoveJXlUe81mertP(JJe8 11and121-1and1-2 1-9and1-101-9and1-10 5-1through5-4.1and5-55-1through5-6 None5.1-1through5.1-9 3.Filethischangesheetinthefront ofthemanualfor reference purposes. ByOrder oftheSecretaryoftheArmy: Official: VERNEL. BOWERS Major General, United StatesArmy TheAdjutantGeneral FREDC.WEYAND General, UnitedStatesArmy ChiefofStaff Distribution: To be distributedinaccordance with DAForm12-51,(qtyrqrblockNo.351)DirectandGeneral Supportmaintenancerequirementsfor ANIPRC-74. Thisnlanualcontainscopyrightedinformation TM11-5820-590-35 TECHNICALMANUAL ( No. 11-)820-590-35 HEARQUARTEJRS DEPARTMENTOFTHEARMY WASHINGTON,D.C.,21July1966 DS,GS,andDepotMaintenanceManual RADIOSETAN/PRC-74 1-1,1-1 1-1-1-3 1-3-1-7 1-8-1-12 1-12-1-15 1-15-1-18 1-18-1-20 1-20 1-21-1-22 1-22 1-23-1-24 2-1-2-102-1-2-10 2-11-2-172-14-2-22 1-1,1-2 1-3-1-5 1-f-1-9 1-10-1-20 1-21-1-28 1-29-1-38 1-39-1-45 1-46-1-48 1-49-1-53 1-54,1-.frequencyrangeofthissignalis 3.75meto 13.749 meandis 1,750 kc abovetheradioset operatingfrequency. SectionV.RFMODULE ANALYSIS 1-21.General (fig.1-1) TheRFmoduleperformstwofunctions:in thereceive modeofoperation,itconvertsthe incomingRFfromthepoweramplifiermodule to a 1,750-kc inrtermediake frequency;inthe transmitmode of operation,itconvertsthe 1,750-kcintermediatefrequencytothetransmit frequency,F,igure1-1shows howthesignals areroutedduringthetwomodesofoperation. a.Receive Mode.Duringthereceive mode ofoperation,theRFinputfromthepower amplifiermodule is coupledthroughthecon- tactsofrelay K1 (denergized)totheTRFam- plifier.TheTRFamplifierconsists ofthree RFtunedcircuitsandanRFamplifier.The RFtunedcircuitsaretunedtotheoperating frequencyandareconnectedinseriestoin- creasetheselectivity oftheTRFamplif.ier. OutputfromthethirdRFtunedcircuitsis coupledthroughthecontactsofrelay K2(de- energized) to balancedmixerZl.Inthebal- anced mixer,theoutputfromthethirdRF tuned circuits is heterodynedwitha signal fromthesynthesizer module.Thesynthesizer n10duleoutputsignal is 1,750kcabovethe operatingfrequencyoftheradioset.There- sultantoutputfromthebalancedmixeris a 1,750-kcintermediatefrequency appliedtothe IFaudio module.Theinputfromthesynthe- sizer module is amplifiedbythesynthesizer 1-12 amplifierstage.Thesynthesizertunedcircuits thatfollowrthesyntehsizeramplifierstageare tunedwitha section ofthes,amegangedcap- acitorusedbythetunedcircuitsoftheTRF amplifier.Theresonantfrequencyofthesyn- thesizertunedcircuitis always 1,750 kc above thatoftheTRFtunedcircuits.Theresonant frequencyofalltheRFtunedcircuitsinthe RFmodule isvariedsimultaneouslyby.the control panelPEAKNOISE control b.TransmitMode.Duringthetransmit modeofoperation,theRFmodule receives a 1,750-kc lower sideband signalfromtheIFau- dio module.Thesiognalis ooupledtothebal- anced m,ixerandheterodynedwiththeampli- fied 3.75-mcto13.749-mcRFinputfromthe synthesizermodule.Thedifference frequency ourtputofthebalancedmixeristheupperside- bandoftheselected channelandis coupled throughthe00ntactsofrelay K1 (en(3-rgized) to theTRFamplifier,andfromthere(through thecontactsofenergizedrelayK2)tothe poweramvlifiermodule. 1-22.FirstRFTunedCircuits (fig.7-8) Inputsignalsfromthepoweramplifiermod- ule tothefirstRFtuned circuitsarereceived atconnector J702andcoupledthroughthecon- tao1:JsofrelayK1 (deenerglized)toswikhS1A. RFGAINCONTROL TOPOWER AMPLIFIER MODULE FROM GAIN CONTROLI CIRCUITS r-R-1 FROM,II AM8-.-,1STRFTUNED2.0RFTUNEDRF3DRFTUNED MODULEICIRCUITSCIRCUITSAMPLIFIERCIRCUITSH.O-r-.ILTRANSMIT TI-T4T5-T8QIT9-T12IRFOUTPUT I ITRANSMIT II /I1/I L II/1III II1I,II l-jl-/-/-1-.,-_-1I TRANSMIT:-t_/-.I-i-7-./MK IIfI l-_.L_-;_,-:; I +12V TRANSMITI FROMPOWERI SUPPLYf I SYNTHESIZER IITUNEDCIRCUITS. T13-T16 II GANGED TO;STEP FREQUENCY ADJUSTIPEAKNOISE-/f SYNTHESIZER.L _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _CONTROLI/ MODULE-7-7 I1 II ,I INPUT FROM3.75MCTO13.749MCISYNTHESIZER SYNTHESIZER.AMPLIFIER MODULEQ2. TRANSMIT RF BALANCED MIXER ZI RECEIVE RF TRANS,MITI.75MCIF TOANDFROM RECEIVE.IFAUDIO MODULE NOTE: LClINDICATES EQUIPMENT MARKING. TM5820-590-35-55 FigU161-1. RF11Wdule, block diagram. . - !. Cit,) - - I x: Ill.) 1: VI TM11-5820-590-3;5 SwitchSIAis one section of a six-wafer, four- position, gear-drivenrotaryswitchthatselects thetuned circuit,s oftheRFmoduleandisgear driven fromtheMCselector switch ofthesyn- thesizermodule. Theinputsignal is switched bySlAto one offourtankcircuitsinthefirst RFtuned circuits.Thetankcircuit used is de- terminedbythebandsettingofswitchSlA. Inband1,theinputisappHedtothBprimary oftransformerT701;inband2,theinputis appliedtotheprimaryofT702; etc. a.Theradiosetfrequencyrangeandsynrthe- izerrangeforeachofthefourbandsare showninthefollowingchart: RwndnumberRf!langeSynJthesizer I(me)(me) 1,2to2.9993.75to4.749 23.to4.99094.75to6.749 35to7.9996:7,5to9.749 48to11.9999.75to13.749 b.Foralloperatingbands,tuningcapacitor C701A is placedinparallel wi.ththecapaci- toroftheselect,edtankcircuit. Capacitor C701 consists offourgang-tuned capacitors (C701A throughC701D) whichareadjusted simultan- eously withthePEAKNOISE controllo- cated onthecontrol panel oftheradio set.The outputsigIlatI ofthefirstRFtuned circuits is sup.plied by oneofthesecondary windings of tunedtTansformers T701throughT704.Th tankcircuitsthatarenotusedareloadedbyre- sistorR3topreventinter8JCtionwiththese- lectedtankoircuit.Theoutputfromthese- lectedtransformeris cOllnectedthroughSlA andcoupledthroughcapacitorC8totheSec- ondRFtunedcircuits. c.Inthecalibration mode, a 10-kc calibration signalfromthefrequencygeneratormodule is supplied totheRFmodule.The 10-kc signal is fedtothefirstRFtuned circuitsthrough jackJ701,thenfiltered by a resistance-induc- tance(RL)networkcomposed of resistorsRl, R2,andR15,andinductors L4 and L5. 1-23.SecondRF Tuned Circuits ThesecondRFtunedcircuitsconsistof switchSIB, tunedtransformersT705through T708,andcapacitors C710throughC713.The 1-14 inputsignalisroutedthroughSIBto theselectedtankciJ:1cuit.Eachtank circuithasatappedtransformertomatch theimpedance oftransistorQl.RedstorR4 is connectedtothethreetankcircuitsthatare notused.Thepurpose of R4 is the same as R3.Variable garrg.tunedPEAKNOISE cap- acitorC701B, in parrallelwithC9, tunesthese- Jectedtankcircuitformaximumoutputatthe desired frequency intheband.Theoutput frDm,the selooted secondrftunedcircuits is coupledthroughswitchSIBand capacitor C15 tothebaseoftransistorQl. 1-24.Amplifier ThesignalfromthesecondRFtuned cir- euits is coupledthroughC15tothebae ofRF amplifierQl.The gainoftheRFamplifier is controlledbya pooitive voltagefromthegain eOnrtroilcircuit(para1-55).Thegain control voltage is connectedtothebaseofQlthrough inductorLl.Resistor R6, diodeCRl,andby- rasscapacitor C14formpartofa voltage di- vidernetworkforthegaincontrol circuit. DiodeCRIalso providestemperaturecompen- ootion fc,rthebase-to-emiltter junction ofQ1. InductorLlkeepsRFoutofthegain control circuit/soEmitterbasis developed by R7. In- ductor L2 istheloadfortrans,istorQl.De- coupling is accomplishedbycapacitorC16. Theoutputsignal is coupledthroughC18and SICtooneoffourtankcircuits in thethird RFtuned circuits. 1-25.ThirdRFTuned Circuits Thefour.tankdrcuttsinthethirdRFtuned circuitsareformedbytheprimarywindingsof transformersT709throughT712andcapaci- t.ors C720throughC723.ResistorR8 loadsthe threeunusedtankcircuits.Theecondary w,indrings oftransformersT709throughT712 provide lowimpedanceoutputstobalanced nlixerZ1.Outputfromtheselectedtankcir- cuit is oonnected tothebalancedmixerthrough switchSIDandcontactsofrelayK2(deener- gized). 1-26.Balanced Mixer Balancedmixer21operatesinboththere- ceive andtransmitmodes of operation.Inthe receive mode of operation,thebalancedmixer receivesaninputfromthethirdRFtunedcir- cuttsandfromthesynthesizer tuned circuits. Theoutputofthebalancedmixeris coupled throughtransformerT717 andjackJ705 tothe IFaudio module. The resonant frequencyfor T707andC38 is 1,750 kc.Inthetransmit modeofoperation,thebalancedmixerre- ceives aninputfromtheIFudiomodule andfromthesynthesizer tuned circuitsThe npper and lower sideband outputsfromthe balanced mixerareconnected throughthecon- tacts of relayKl(energized)ItothefirstRF tuned circuits. 1-27.Synthesizer Amplifier ThesYnthizeramplifier receivesinputsig- nalsfromthefrequency synthesizer module. Inputsignalsarecoupledthroughcapacitor C25 tothebaseoftransistoramplifierQ2.Resis- torR9 providestheproperimpedance match- ingwiththefrequency SYnthesizer module. Base biasforQ2is developed across voltage divider network RIOandRll.The loadfor TM11-5820-0590-35 thecollectorcircuitofQ2is provided by in- ductor L3.CapacitorG26,andresistor R12 form a decoupling network.Emitterbias is developed across resistor R13. Capacitor C27 isanemitterbypass capacitor. Capacitor C28 couplestheoutputofQ2toMeSJtepfrequency selectorSIF.The synthesizer amplifieroutput is switched byS1Fandrouted totheselected synthesizer tuned circuit. 1Synthesizer Tuned Circuit Fourtankcircuits inthesynthesizer tuned circuits stageareformed bytheprimarywind- ingoftransformersT713 throughR716in parallelwithcapaoitors C30, C731, C32, C733, C35, C734, C37, and C736.Capacitor C701D (PEAKNOISE control)isplacedinparallel (through sw1tchS1F)withthetuned circuit elected.Tunedcircuitsnotusedare loaded by resistor R14.The output fromthe selected synthesizer tunedcircuitis coupled through switch section S1E tothebalanced mixer. SectionVI.IFAUDIO MODULE ANALYSIS 1-29.General (fig.7-9) TheIFaudio module is used in boththe transmitand receive operaJtion oftheradio set. Inteceive mode of operation,theIFaudio module :f:iltersandamplifiestheIFsignal in- putof1,750 kc and demodulatesittoanaudio output.Intransmitmode of operation,theIF audio amplifier convertstheaudioinputsig- nalsorkeyedinputsigna;lstoa single-side- band 1,750-kc intermediate frequencyoutput whichissupplied totheRFmodule.Figure 9isablockdiagramoftheIFaudio module. a.Receive Mode.Inreceive modeofopera- tion,the1,750-kcsingle-sidebandilllPutis fromtheRFmodulethroughtheoontactsof deenergized relayK1andsuppliedtoIFpre- amplif,ierQl.TheoutputoftheIFpreampli- fieris appliedthroughcoupling circuitresistor R4andcapacitor C12tocrystal fiJ,terFLl. FilterFL1 increases the selectivity ofthere- ceiver by rejecting a portionofthecar:rersig- nal,thuslimitingthebandwidth ofthesignal Incalibration mode,rela:,K2 is energized andbypassesthecrystalfilterto preventthe calibration signal from being rejected. The out- putof the crystalfilteris appliedtoIFampli- fiertransistorsQ2andQ3.Thegaincontrol is appliedtoQ2oftheIFamplifier and oon- troIstheforwardgainofbothIFamplifiers. Output oftheIFampldfier is fedtothe de- raodulator,Q4.Inthedemodulator,there- ceived ssbIFsignal fromtheRFmodule is mixed with anunmodulated1,750-kc signal fromthefrequencygeneratormoduletopro- duceandaudio difference signal which is ap- pliedtotheaudio amplifier circuitstodrivethe headsetora small speaker.Inreceive mode of operation only, the circuits contained on cir- cuitboard assemblyA1(notshown)ofthe audio moduleareused. b.Transmit Mode.When the radiosetis in thetransmitmede of operation,IFaudio mod- ule audioinpUJtsarefroma microphone,or enabling ground from a telegraph key. Audio fromthemicrophone is amplified by micro- phone. amplifiersQ8,Q9,andQl0, thenap- pliedtooalancedmixerZ1whereitis mixed 1-15 1-32.IFAmplifier signal suppliedtoitinthe receive mode,and passonlythelower sidebandofthedouble- sideband signal suppliedtoitduringtransmit mode. This limiting action du:ring :the receive mode increasestheselectivityofthereceiver. CrystalnlterFL1 has considerBJble rejectionat thecarrierfrequency.Inordertopassthe calibrate signal (which isatthecarrierfre- quency when thesetis properly calibrated), K2 is energized bythe+12-volt calibrateand FL1 is bypassed. Theoutputof crystalfilter FL1 is routedtoIFamplifierQ2,Q3inthe receive mode.Inthetransmitmode,theout- putofFL1 is connectedthroughthecontacts of K3 (energized)toconnectorJ401. Connec- torJ401is conneoted totheRFmodwe. 1-30.IFPreamplifier (fig. 7-10) Duringthereceive mode of operation, the unfiltered 1,750-kc intermediate frequency sig- nal output oftheRFmoJJ.le is routedthrough connectorJ401 andthecontacts of relayK1 (deenergized) totheprimaryof tuned circuit transformerT401oftheIFpreamplifier.In thetransmitmodeofoperation, theinputto heIFpreamplifier tuned circuit is fromthe ,arm of resistor R434.Ineither mode of op- eration, T401 couplestheinputsignaltothe base ofIFpreampLifierQl.TransistorQ1is anmitter-followeramplifierwhkhdrives crystal filterFLl. TM11-5820-590-35 Cl withthe1,750-kc signal fromthefrequency generatormoduletoproduce a double-side- band suppressed-carrier signal. Resistor R432 adjuststhe audio levelinputtothebalanced mixer.Theoutputofthe bal,ancedmixeris thenroutedthroughthecontacts of relayK1 (energized) toIFpreamplifierQ1.Theam- plified double-sideband signal is fed to crystal filterFL1 which rejectsthelower sideband. ffhis action produces a single-sideband(ssb) signal which is then routed through the con- tactsof relay K3 (energized) totheRFmodule. A portion of the audio fromthemicrophone am- plifiers is suppliedtoreceive audio amplifiers Q5,Q6,andQ7formonitoring purposesat theoperators headset.Duringcw operation, the telegraph key ispressedtocause the 1,600-cpsoutputtoneaof tone oscillatorQ11to be activated.The cw hold circuit: consisting ofQ12and Q13,winhold the radiosetin a transmitmodefor2 secondsafterthtele- graphkey is pressed.rrherefore,duringthe time betweencharacterstheradiosetwill not change to a receive mode. The cw hold circuit operates onlyinthe cw transmission mode. Duringthetransmitmode of operation,+9- volt enable