专业英语全部复习资料123

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1、一.翻译P58.Thesignal-processingblockatthetransmitterconditionsthesourceformoreefficienttransmission.Forexample,inananalogsystem,thesignalprocessormaybeananaloglow-passfilterthatisusedtorestrictthebandwidthofm(t).Inahybridsystem,thesignalprocessormaybeananalog-to-digitalconverter(ADC).This

2、producesa“digitalword”thatrepresentssamplesoftheanaloginputsignal.Inthiscase,theADCinthesignalprocessorisprovidingsourcecodingoftheinputsignal.Inaddition,thesignalprocessormayalsoaddparitybitstothedigitalwordtoprovidechannelcodingsothaterrordetectionandcorrectioncanbeusedbythesignalpro

3、cessorinthereceivertoreduceoreliminatebiterrorsthatarecausedbynoiseinthechannel.Thesignalattheoutputofthetransmittersignalprocessorisabasebandsignalbecauseithasconcentratednearf=0.Thetransmittercarriercircuitconvertstheprocessedbasebandsignalintoafrequencybandthatisappropriateforthet

4、ransmissionmediumofthechannel.Forexample,ifthechannelconsistsofafiberopticcable,thecarriercircuitsconvertthebasebandinputtolightfrequencies,andthetransmittedsignals(t)islight.1.randomaccessmemory（RAM）2.InternationalTelecommunicationsUnion（ITU）3.pubiictelecommunicat/onsnetwork（PTN）4.bin

5、ary-codednumber5.negative-feedbackamplifer6.adaptiveequalization7stored-programcontrol(SPC)8.quadratureamplitudemodulation(QAM)9.linearintegratedcircuit10.commonemittercircuit高保真度、带通信号、电磁感应、多径衰落、方框图、扩频系统、单边带、频率配置、电离层反射、差错控制码、二填空P58.Ifthechannel___basebandsignals,nocarriercircuitsarenee

6、ded,ands(t)canbeoutputoftheprocessingcircuitatthetransmitter.Carriercircuitsareneededwhenthetransmissionchannelis__inabandoffrequenciesaroundfc>>0.Inthiscase,s(t)issaidtobea___becauseitisdesignedtohavefrequencieslocatedinabandaboutfc.Forexample,an____modulated(AM)broadcastingstationw

7、ithanassignedfrequencyof850kHzhasacarrierfrequencyoffc=850kHz.The___ofthebasebandinputinformationwaveformm(t)intothebandpasssignals(t)iscalledmodulation.P23.Wehaveseenthattheop-amp’sisahigh-gaindirectcoupledvoltageamplifierwithhighinputimpedanceandlowoutputimpedance.Inpractice,theou