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1、FineTuningYourTuningRangeByWayneNB6MCopyright2001WanttobeabletosetyourtuningrangeontheSW30+,MH101Project,oranyotherrigwhichusestuningdiodesinitsVFO,soastomakefulluseofthelowendoftheband,rightdowntowithinaKhzofthebottomofyourlegalportionoftheband,without
2、havingtoworryaboutgettingoutofbandandintotrouble?Hereisoneeasywaytodoit.TheVFOoftheSW30+transceivermakesuseofaselectionoflowvalueNP0capstosetthetuningrange.Oncetherigiscompleted,thebuildinginstructionstellyoutoconnectadummyload,transmit,andlocateyoursig
3、nalonanother,calibrated,receiver.Ofcourse,aFrequencyCountercouldbeused,instead.Then,usingtheformulaprovided,theappropriatevaluecapacitorisselectedandinstalledas"C-7",paddingtheexistingcapacitanceoftheVFOtankcircuitsoastolowerthefrequencytherequiredamoun
4、t.Mostofuswouldbequiteupsetatinadvertentlytransmittingoutofband.So,wetendtoselectthevalueofcapacitancethatputsthelowendofourtuningrangeasclosetothebandedgeaspossible,butwhichmaystillleaveusafew,orevenseveral,Khzabovethebottomoftheband.Whattodo?Onecoulde
5、ithercompressorspreadtheturnsoftheVFOcoiltomakeacloseradjustment,butthismaynotbepreciseenough.Inmycase,selectingthe68pfcapsuppliedwiththekitleftthelowendofmytuningrangeat10.085Mhz.Thenextlowervaluesupplied,47pf,leftthelowendofthetuningrangeatabout10.110
6、.ThefrequencycouldhavebeenadjusteddownwardfromthatpointbycompressingtheturnsoftheVFOcoil,andthenanchoringtheminplacewithepoxyor"Q"Dope,orwhichevertypeofpottingcompoundonechoosestouse.Havinga56pfNP0caponhand,thatwasinstalled,whichputthelowendofthetuningr
7、angeat10.096Mhz.Sincetheupperendofthetuningrangewasnow10.132Mhz,abovetheuseful"CW"portionofthe30MeterBand,thatcapwasleftinplaceandthelowendofthetuningrangewasadjustedelectronically,byinstallingaresistorbetweenthe"ground"contactofthetunepotandthegroundle
8、aditselfsothatthelowestpositionofthetunepottunestherigabout800Hzabovethebottomoftheband.Here'showtodeterminetheamountofresistanceneeded.Oncethecorrectvalueofcapacitanceisinstalled,ortheVFOcoilturnsarecompressedorspreadsoastosetth
