HP-492A-494A-Manual-SN-010 电路图.pdf

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1、HP Archive This vintage Hewlett Packard document was preserved and distributed by Pleasevisituson the web! Scanned by on-line curator: Tony Gerbic * For FREE Distribution Only * RadioFans.CN 收音机爱 好者资料库 HEWLETT-PACKARDCOMPANY 4.2A/4.4A TRAVELING-VVAVE AMPLIFIER RadioFans.CN 收音机爱 好者资料库 ) ) ) 001442 OP

2、ERATINGANDSERVICEMANUAL MODEL492A AND MODEL494A SERIALSPREFIXED:010- TRAVELING-WAVEAMPLIFIERS Copy,;ghHEWLETT.ACICA.DCOMANY1962 lS01AGEMILLROAD,ALOALTO,CALlFO.NIA,U.S.A. Printed:JAN1962 RadioFans.CN 收音机爱 好者资料库 Model492Aj494A Tableof Contents ListsofIllustrationsandTables TABLEOFCONTENTS SectionPage

3、SectionPage IGENERAL INFORMATION 1-1IVPRINCIPLES OF OPERATIO(contd) 1-1.Description1-14-10.TravelingWaveTube 4-1 1-6.InstrumentIdentification 1-24-15.GridModulation.4-4 1-8.TravelingWaveTubeWarranty1-24-17.Helix Modulation .4-4 4-22.Constant-Amplitude,Linear IIINSTALLATION 2-1SawtoothGenerator4-5 2-

4、1.MechanicalInspection2-1 2-3.PowerRequirements.2-1VMAINTENANCE.5-1 2-5.PowerCable.2-15-1.Introduction. 5-1 2-8.Installation2-15-3.CleaningtheAirFilter5-1 2-12.RepackagingforShipment2-15-5.TestEquipment .5-1 5-7.Repair.5-3 IIIOPERATING INSTRUCTIONS 3-15-8.CabinetRemoval5-3 3-1.Introduction.3-15-10.T

5、ubeReplacement.5-3 3-3.PreliminaryOperatingProcedure3-15-12.TravelingWaveTubeCapsule 3-6.HelixControl3-1Replacement5-3 3-8.SaturationPowerOutput3-15-17.ChangingtheFrequencyRange 3-12.BandwidthConsiderations.3-1ofthe492Aor494A5-5 3-14.ConstantGainorConstantOutput5-21.Adjustments5-5 Amplification3-35-

6、22.ExcessiveHelixCurrent5-5 3-18.BufferAmplifications3-35-24.ChassisHelixControl5-5 3-20.AmplitudeModulation3-35-26.Anode VoltageControl.5-5 3-24.PulseModulation.3-65-28.RegulatedPowerSupply5-5 3-27.LimitedPhaseModulation.3-65-30.Troubleshooting. 5-6 3-29.UnlimitedPhaseModulation and5-32.Performance

7、Checks5-7 FrequencyShifting .3-65-33.GainCheck.5-7 3-34.HomodyneDetection3-75-36.OutputPowerCheck5-7 3-37.FrequencyModulation3-95-39.NoiseFigureCheck5-7 5-42.Hum andSpuriousModulation Check5-8 ) IVPRINCIPLESOFOPERATION.4-1 4-1.Introduction.4-1VIREPLACEABLEPARTS.6-1 4-3.MagnetPowerSupply.4-16-1.Intro

8、duction6-1 4-5.RegulatedPowerSupply4-16-4.OrderingInformation6-1 LISTOFILLUSTRATIONSANDTABLES NumberIllustrationTitlePage 4-3.Cutaway ViewofaTWTCapsuleandMagnet ShowingtheImportantElements. .4-3 4-4.Cutaway View of anEncapsulatedTWT.4-3 4-5.SimplifiedCircuitofaConstantAmplitude, VariableSlope Sawtoo

9、thGenerator4-5 5-1.TopViewofModels 492A and 494A.,5-2 5-2.Bottom ViewLookingTowardstheFront PanelofModels492A and 494A .5-4 5-3.RearView of Models 492Aand494A5-4 5-4.TestSetupforGain, OutputPower,and NoiseFigurePerformanceChecks5-7 5-5.TestSetupforHum andSpurious ModulationPerformanceCheck . .5-8 5-

10、6.Models 492A and494ASchematicDiagram5-9 NumberIllustrationTitlePage 1-1.Model 492ATravelingWaveAmplifier1-1 1-2.TravelingWaveTubeWarranty1-2 3-1.OperatingControls.3-0 3-2.TypicalGainandPowerOutput Characteristics.3-2 3-3.BlockDiagramof aCircuitusedto MaintainConstant-LevelOutputPower fromaTWTAmplif

11、ier3-3 3-4.BlockDiagramofanAutomaticGain ControltoMaintainConstantAmpli- ficationfroma TWTAmplifier3-3 3-5.TypicalPlotofOutput VoltagevsGrid Voltageofa Model 492A3-4 3-6.TypicalPlotofOutput VoltagevsGrid Voltageofa Model 494A.3-5 3-7.RFPhaseShiftProducedby Helix Mod3-7 3-8.OffsetFrequencyProducedbyS

12、awtooth ModulationoftheHelix .3-7 3-9.BlockDiagramof aLinear(Homodyne) ) DetectionSystem.3-8 3-10.BlockDiagramof aCircuittoProduce an FM Signal with aTWTAmplifier3-8 4-1.BlockDiagram,Models 492A and 494A4-0 4-2.TWTandHowitWorks.4-2 00144-2 1-1. 3-1. 5-1. 5-2. 5-3. 6-1. 6-2. TableTitle Specifications

13、. . . . . MaximumOperatingCurrentsfor Models492A and 494A . . RecommendedTestEquipment TubeReplacementList TroubleshootingChart. . ReferenceDesignation Index ReplaceableParts. . . . 1-0 3-1 5-1 5-3 5-6 6-2 6-5 iii Section I Table1-1 Model 492A/494A Table1-1,Specifications Model 492A-o-= .J 800 .J 70

14、0 z 600 :) 500 0. :) 400 0 300 200 100 0 +10+5o-5-10-15-20-25-30-35-40-45-50-55 GRIDB I A SVOLT SG-M-36 Figure3-5.TypicalPlotof OutputVoltagevsGridVoltageofa Model 492A 3-4 00144-2 Model 492A/494A Section III Figure3-6 ) 1600+-+-1 -.:.bp-MODEL494A TYPICALMODULATIONCHARACTERISTICS INPUT -6OBM -21OBM

15、-250BM -280BM -31OBM OUTPUT -0DB -30B .-_6DB -,-,-9DB -12DB FREQUENCY:9000Me HELIXVOLTAGE:OPTIMIZEDATEg=O FOREACHCURVE. OUTPUT:DBBELOW SATURATION OUTPUTATEg=0 , , , . . . ,. ,., ,., :. 800-fI 400+-rl-T-;-+-ir-1-+-+-+- ., .1 . . 200+-+-,r-d-.:.;-r-11-+-+-+- ., .,. :.-.:.:. 0-_+_-_+_-1f_-=:.:.!-_+_-_+

16、-_l 1400+-+- 1200 0 .J o .J .J ) +10 o -10 GRID -20-30 BIASVOLTS -40-50 G-M-37 -60 Figure3-6.TypicalPlotofOutputVoltageVBGridVoltageof a Model 494A 00144-23-5 SectionIII Paragraphs3-23to3-30 output.Thelinearmodulationregionextendsfrom approximately+4volts(wherebeamde-focusing occurs)toapproximately-

17、15volts(wheretherfout- putbecomesanexponentialfunction of thegridvolt- age).Thislinearoperatingregionpermitsupto30% modulationwithlessthan 2.5%envelopedistortion and upto50%modulationwithlessthan5%distortion. Envelopedistortionincreasesrapidlyabove50%modu- lation.Inpulseworkthetwtmaybebiasednearor b

18、elowcut-offandtherfdriveadjustedforsaturation outputatthepeakamplitudeofthemodulatingpulse. However,thegridvoltageatthepeakofthemodu- latingsignalmustnotcausede-focusing(approxi- mately+4to+ 8volts)norexcessiveaverageelectrode current,seetable3-1.Thetransientresponseofthe 492Aor494A to astepfunction

19、appliedtothegridis approximately15nsec. 3-23.Amplitudemodulationisaccompaniedbysome incidentalphasemodulbtion oftherfsignal,amount- ingtoapproximately90phaseshiftoftherfcarrier fora 10 dbchangeinthemodulatedrfoutputlevel. Inpracticethisphasemodulationisunimportantwhen usingtheconventionalsquare-lawc

20、rystaldetectors, butisimportantindetectionsystemswheretheout- putisa functionoftherfcarrierphase. 3-24.PULSEMODULATION. 3-25.Thereisconsiderablylatitudeintheadjustment ofmodulationcharacteristicswhenpulsemodulating anrfsignalusingthe492Aorthe494A;seefigures 3-5and3-6.Thecwinputlevel,themodulation- p

21、ulseamplitude,andthegridbiasdeterminethe characteristicsoftherfoutputpulseasfollows: a.Thecwinputsignalprimarilydeterminesthe maximumpossibleleveloftherfoutputpulseand whetherornotthetwtcanbeoperatedintosaturation. b.Thepeak-to-peakamplitudeofthemodulating pulseprimarilydeterminestheon-offratioofthe

22、rf outputpulse. c.Thegridbiaslevelprimarilydeterminestherf outputlevelsattainedduringthepulse-onandpulse- offtimesandalso,inconjunctionwiththemodulating pulse,determinestherfinputlevelnecessaryto saturatethetwt.TheGRIDBIAScontrolalways shouldbesetsothatthetwtgridwill notdrawcur- rent(approximately4v

23、oltspositive)duringthepulse- onperiod. 3-26.Topulsemodulatetherfsignalbeingamplified inthe492Aor494A,refertofigures3-5or3-6and proceedasfollows: a.Determineifthetwtisto bedrivenintosatura- tionandiftherfoutputmustbeataspecificlevel. b.SettheGRIDBIAScontrolforzerobias. c.Connecttherfinputsignaltothet

24、wt andadjust itsleveltoproducethedesiredrfpulseoutputlevel. d.Determinetheon-offvoltageratiorequiredin therfoutputpulse. 3-6 Model 492A/494A e.Usingthegraphinfigure3-5determinethe magnitudeofmodulationpulserequiredtoproducethe desiredon-offratio. f.SettheGRIDBIAScontroltoobtainthevoltage determinedi

25、nstepe.,Le.,thepeakvoltageofthe modulatingpulse.ThebiasVOltagemaybemeasured atthepinjackonthefrontpanel. g.ConnectthemodulatingpulsetotheGRIDMOD. connectorandadjustitsamplitudetothevoltagede- terminedinstepe toproducethedesiredon-offratio intherfoutputpulse.Sincethegridofthetwtiscon- necteddirectlyt

26、otheGRIDMOD.jack,adccom- ponentinthemodulatingsignalwillaffectthegrid bias.Also,ifcapacitivecouplingisusedthemodu- latingsignalwilldrivethegridofthetwtaboveand belowthedclevelestablishedbythegridbias,an amountdeterminedbythedutycycleofthemodulating signal.TheGRIDBIAScontrolmustbeadjustedto compensat

27、eforboth oftheseeffects. h.Toincreasetheon-offratiooftherfoutput pulse,increasetheamplitudeofthemodulationpulse, atthesametimeadjustthegridbiassothatthegrid will not bedrivenbeyond 4voltspositive,seetheNote paragraph3-21. Note Largeinputmodulatingpulses,above15 volts,tendtoshock-excitethehelix,produ

28、c- ingringingonthetop oftherfoutputpulse and a slowrisetime.Ifthetraveling-wave tubeisoperatednearsaturationthiseffectis minimizedandbetterpulsecharacteristics areobtained. 3-27.LIMITEDPHASEMODULATION. 3-28.Thesignalbeingamplifiedinthe492Aor494A canbephase-modulatedby applyingvoltagetothe HELIX MOD.

29、connector.Thisvoltagevariesthe electron-beamvelocitybychangingthepotentialbe- tweenthecathodeandthehelix-apositivevoltage changeacceleratestheelectronbunchesandadvances thephaseoftherfoutputsignal;anegativechange slowsthemandretardsthephaseoftheoutputsignal. Theresultantphasedeviationintheoutputsign

30、alis directlyproportionaltotheappliedvoltage.Thede- greeofphasedeviationproducedislimitedbythe rangeofhelixvoltagesthatproducesamplification, andbytheamountofincidentalamplitudemodulation permissibleintherfoutput.Phasedeviationof 3600 ispossiblewiththeoutputamplitudeheldtovariations ofapproximately1

31、-1/2db andisobtainedwith ahelix voltagevariationoflessthan 50volts.Theactual voltagerequiredforaphaseshiftof3600varieswith theoperatingfrequencyandfromtube-to-tube. 3-29.UNLIMITEDPHASEMODULATIONAND FREQUENCYSHIFTING. 3-30.Althoughthelimitedphasedeviationdescribed inparagraph3-27isusefulinsomeapplica

32、tions,un- limitedphasedeviationhasamuchwiderrangeof usage.Itisparticularlyusefulbecausethefrequency 00144-2 Model 492A/494A Section III Paragraphs3-31to3-36 G-l-7 TIME DESIREDOUTPUT(Ftl FREQUENCY+-_-_-_-A._-L._-l -1-INPUTFREQUENCY(Fl UNDESIREDOUTPUT ( F ) FREQUENCY2 HIGH Figure3-8.OffsetFrequencyPro

33、ducedby Sawtooth Modulation oftheHelix LOW SAWTOOTHMODULATION APPLIEDTOHELIX 3-31.Inpracticalapplications,aconstantamplitude linear-slopesawtoothgeneratorisused toproduce thesawtoothwaveforms.Iftheamplitude8fthesaw- toothvoltageisadjustedtoproducea 360shift,one cycleofthecwsignalwill be addedorsubtr

34、acted duringeachsawtooth, andthefrequencyshiftpro- duced intheoutput will beequaltothe sawtoothrepe- titionrate.Sawtoothvoltageshavingnegativeslopes (seefigure3-7)produceadecreasein the outputfre- quency (delay inphase).Conversely,sawtoothvolt- agesof theoppositeslopecauseanincreaseinoutput frequenc

35、y. of the inputsignalcanbeshiftedby apredetermined amount.Unlimitedphasedeviationiseffectivelysim- ulatedby continuouslyrepeatingexact3600phase deviations.Thisisaccomplishedby modulatingthe travelingwave tubehelixwiSha sawtoothwaveform, eachsawtoothproducing360phaseshift,asshown infigure3-7.Anrfoutp

36、utfrequencythatisshifted inrelationtothe inputfrequencyisthus produced,as shown infigure3-8. O HIGH SAWTOOTHMODULATION APPLIEDTOHELIX LOW PHASEDIFFERENCE BETWEENINPUTAND OUTPUTWAVES frequencyshiftwithitsrelativelysmallpowercontent wouldberejectedbymostnarrowbandcircuits.In systemswheretheundesiredfr

37、equencyshiftfalls withinthepassband of theequipmentundertest,a negativepulsecanbeappliedtotheGRID MOD.con- nectortocutoff the twtbeamcurrentduringthefly- backtime.Thismethodreducestheundesiredfre- quencyshiftalthoughitproducessomesmalltran- sientsandleavessmalltimeintervalsduringwhich thereisnosigna

38、loutput.Practicalapplicationsof offsetfrequenciesincludethemeasurementofex- tremelyhighswrsaccuratecalibrationofattenu- atorsoverwideamplituderanges(paragraph3-34), frequencyshiftingofmicrowaveradiorelaychannels forretransmission,productionofmixerfrequencies forradarandothermicrowavereceivers,etc. G

39、-l-I TIME.3-34.HOMODYNEDETECTION. Figure3-7.RFPhaseShiftProducedby Helix Modulation 3-32.With sawtooth modulation,thedesiredoutput frequencyshift(Finfigure3-8)occursduringthe sawtoothformatioJtime,andisproportionaltothe rateofchangeof voltage.Duringthe sawtoothfly- backtimethe outputphaseisshiftedin

40、 theopposite directionproducinganundesiredfrequencyshift(F2 infigure3-8).Iftheflybacktimeismadeextremely short,thisfrequencyisfarremovedfromthedesired frequencysincethedegreeoffrequencyshiftisin- verselyproportionaltotheflybacktime.Inaddition tobeingfarremovedfromthedesiredfrequencythe powerintheund

41、esiredfrequencyisverysmallsince itisproportionaltotheratioof flybacktimetosaw- toothtime. 3-33.Inatypicalcaseinvolving adesired50-kcfre- quencyshift,aI-microsecondflybacktimewould produceaI-megacyclefrequencyshiftintheopposite directionand wouldcontainonly5%ofthetotalpower intheoutputwave.Inpractice

42、,thisundesired 3-35.Theabilityof a twttoproduceanoffsetfre- quencythatisstablewithrespecttothesignalsource makesitanidealinstrumenttousein a homodyne (linear)detectionsystem.Thedifferencefrequency will be dependent uponthestabilityof the sawtooth generatorusedtomodulatethetwt helix, aproblem ofnocon

43、sequenceatthelow modulatingfrequencies involved. 3-36.Atypicallineardetectorsystemsuitablefor calibratingmicrowaveattenuatorsisillustratedin figure3-9.Thesignalgeneratorsuppliesasignal (f) bothtoacrystalmixerandtoatravelingwave tubeamplifier.Thetravelingwave tubeamplifieris sawtooth modulated toprod

44、uceanoffsetfrequency (f-f) whichisapplied totheattenuatortobecali- brated.Theoutputsignalfromtheattenuatoristhen combinedwith theoriginalsignal(f) inthemixerto produceabeatfrequency(f ) whoseamplitudeisdi- rectlyproportionaltotheahtplitudeof(f-fj)solong astheamplitudeof(f-fj)remainswithinthesquare-

45、lawregionof thecryStal.Thisbeatfrequencyis amplifiedbythetunedamplifierandtheoutputisin- dicatedby anacvoltmeter.Thelowersensitivity 01144-23-7 Section III Figures3-9and3-10 Model 492A/494A SAWTOOTH GENERATOR f, OFFSET FREQUENCY SINGLESIDEBANDGENERATOR -1 I ATTENUATORBEINGCALIBRATE /I I I I I I I f-

46、f,I I I I I I _JL_ I- I TRAVELINGWAVETUBETUBE AMPLIFIER SIGNAL GENERATOR COUPLER/ f VOLTMETER TUNEDAMPLIFIER LO-l- Figure3-9.BlockDiagramof aLinear(Homodyne)DetectionSystem INT.SWEEP OSCILLOSCOPE MIXER 30DBPAO TCONNECTOR TWTAMPLIFIER )20OB( DIRECTIONAL COUPLER SIGNALGENERATOR 4TO8KNC0USE-hp-MODEL492

47、A 7TO12.4MC.USEhpMODEL494A USEAPPROPRIATEDIRECTIONALCOUPLERS. ATTENUATORS.MIXERS.ETC. TO HELIX SLOPE-MODULATED SAWTOOTHGENERATOR .hp202A FUNCTIONGENERATOR M.O.P.A.MICROWAVEFREQUENCYMODULATIONSYSTEM LD-L-40B Figure3-10.BlockDiagramofaCircuittc?ProduceanFMSignal with a TWTAmplifier 3-800144-2 ) Model4

48、92A/494A limitisdeterminedbythecrystaland IFamplifier noiseandisapproximately-100dbm. ote When aswrindicator(suchasthej)Model 4158)calibratedforusewith asquare- lawdetectorisusedinplaceofthetuned amplifierandvoltmeter,thedbreadings mustbedoubled. 3-37.FREQUENCYMODULATION. 3-38.Narrow-bandfrequencymo

49、dulationcanbeob- tainedbyapplyingthemodulationsignaldirectlyto thehelixofthetwt;however,tofrequencymodulate with anappreciablefrequencydeviationitisfirst necessarytoproduceanoffsetfrequencyasdescribed inparagraph3-29.Thedeviationoftheoffsetfre- quencyshouldbeslightlygreaterthan1/2thetotal frequencydeviationdesired.Theoffsetfrequencyis t