全省种粮大户情况汇总表Titl.ppt

ChelmsfordAmateurRadioSocietyAdvancedCourseTransmittersPart 2 Mixers Modulation MixersinTransmitters NeedtorecallandexpandIntermediatecourseonmixersandmodulationinTransmitters IngeneralVFOs CrystalOscillatorsandSynthesisersdonotdirectlygeneratethefinalRFOutputfrequency Mixersareusedtocombinetwoormorefrequencysourcesaspartofthemodulationandup conversionscheme Needtounderstandthatspuriousoutputscanalsooccur aswellasdeviationissuesonFM Mixers TwofrequenciescanbecombinedinamixercircuitResultisthecreationofsumanddifferencefrequencies NOTE Overdrivingamixer underdrivingtheLOport orpoorsuppressionofharmonicscanresultinotherunwantedspuriousmixerproducts IfPSUisolationispoor mainshumsidebandscanalsobeinadvertentlyadded MixerasaModulator MixermaybeusedasanAMmodulatorAMhascarrierandtwosidebandsMostpowerisinthecarriersignalExcessiveaudiocausesover modulation BalancedMixers ABalancedMixerisusedtocreateSSBasitwillnullifythecarriercomponenttoleavethetwosidebandsRFIsappliedtocentretapswhichresultsinnullnetcarrierAMcanbegeneratedbydeliberatelyunbalancingit AM SSBBandwidth SSBhasanumberofadvantagesNocarrier sopowerisnotwastedHalfthebandwidthofAMNoRFpowerwithoutmodulatingaudioSmallerPSULessheat CarrierandUnwantedSidebandissuppressedcomparedtonormalAM reducingbandwidth FMModulator ColpittsOscillatorwithFrequencyModulationbyVaricapDiodeL1andC1setnominalfrequency whichisvariedbyCDFMBandwidthismorecomplexassidebandsextendwiderthanAM TransmitterUpConversion SSBgenerationandothermodulationisperformedatloworintermediatefrequenciestoeasedesign filteringetcThismustbeup convertedtofinalRFfrequencybyanothermixerExample SSBfor2mbandmaybegeneratedata6MHzIFItisthenaddedtoa138MHzRFLOtoproducea144MHzoutputNotethatusingamultiplier especiallyforSSB woulddestroythefrequencyandbandwidthrelationships ModulationTerms FMDeviationreferstothemaxshiftawayfromthenominalcarrierNarrowvsWidebandFM TheFMsectionof2mthebandhasbeenre channelisedto12 5kHzspacing vs25kHzonmostof70cmsPeakDeviationis2 5kHzfor12 5kHzchannelspacingand4 8 5kHzfora25kHzspacing WideTxdeviationonnarrowbandreceiverswillinterfereinadjacentchannels ItwillalsogetclippedbyIFfilters discriminatorsandresultinchoppyreceivedaudio acommonissueforolderradioson2m AMDepth AMDepthreferstotheextentofAMmodulation If100 depthisexceeded clipping distortionoccursAMDepth m b a andisoftenexpressedasapercentage FMBandwidth UnlikeAM FMhasawholeseriesofcontinuoussidebandswhichextendbeyondthenominaldeviationAgoodguideisCarsonsRule FMBandwidth 2x MaximumAudioFreq PeakDeviation orBW 2 Fmax f Examples For70cms BW 2x 3kHz 5kHz 16kHz needa25kHzFMChannel At2m BW 2x 2 8kHz 2 5kHz 10 6kHz fora12 5kHzChannel EmissionCodes Beawareofemissioncodes SometimeusedforLogs NoVsetctodescribetransmittermodulationCommonmodulationsusecodes A1A HandSent On Offkeyingofthecarrier MorseA3E AmplitudeModulatedVoiceTelephony AMF3E FrequencyModulatedAudio FMJ3E SingleSidebandDatamodulationF1B DirectFrequencyshiftkeyingF2B FSKAudioonanFMTransmitterJ2B FSKAudioonanSSBTransmitter DataModulation F1B DirectFrequencyshiftkeying FSKDatadirectlymodulatedtherfcarrierfrequencyF2B FSKAudioonanFMTransmitter alsoknowasAFSKDatausesapairofAudiotones theAudioisasubcarrierJ2B FSKAudioonanSSBTransmitterAudiotones eg1275 1445HzforRTTY directlyinitiatecarrieroutput