ARM外文翻译外文.doc

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1、Highlysensitiveandselectivesingle-tunedfour-bandcrystalradiosetusinganewcontrawounddual-valueinductor,andhavinga'sharpselectivitysetting';alongwithawaytomeasuretheunloadedQofanL/CresonatorByBenH.TongueTheCrystalRadioSetDesign,ina(large)Nutshell:·Thedesignapproachistodiv

2、idetheAMbandintoseveralsub-bandsinanattempttokeeptheselectivityrelativelyconstantandtheinsertionpowerlosslowacrossthewholeband.·ThefirststepistodividetheBCbandintotwohalves:bandA(520-943kHz)andbandB(943-1710kHz).Two-stepshuntinductivetuningisemployedtoswitchbetweenbands

3、.Atankinductanceof250uHisusedinbandAand62.5inandB.·BandAisfurthersubdividedintotwobands:sub-bands1(520-700kHz)and2(700-943kHz).ThebandBisalsosubdividedintotwobands:sub-band3(943-1270kHz)and4(1270-1710kHz).·Inthenormalselectivitymode,twodifferentresonantRFresistancelevel

4、s,measuredatthetopofthetunedcircuit(point'A'inFig.5),areusedatthecenterofthesub-bands.Thisimpedancelevelisabout125kohmsatthecenterofsub-bands1and3.Itis250katthecenterofsub-bands2and4(excludingtheresistivelossesofthecomponentsused).Theseresistancevaluesaremadeupofaparall

5、elcombinationofthetransformedRFantenna-groundsystemresistanceandtheinputRFresistanceofthediode.Thesetworesistancesshouldbeequaltoeachothertoachieveminimuminsertionpowerloss,atthedesignbandwidth.Thismeansthatthetransformedantenna-groundsystemanddiodeRFresistancesareeacha

6、bout250kinsub-bands1and3and500kinsub-bands2and4atpoint'A'.ThetwodifferenttransformedRFantenna-groundsystemresistancevaluesareachievedbyproperadjustmentofavariablecapacitorinserieswiththeantenna(C7inFig.5).ThehigherdiodeRFtankloadingresistancevalueforsub-bands2and4areach

7、ievedbytappingthediodeontothetankatapointthatis70%oftheturnsupfromground.Thetankisnottappedforsub-bands1and3andconnectionistothetopofthetank.Inthesharpselectivitymodethediodeistappedhalfoftheturnsdownonthetankfromthepointusedfornormalselectivity.·Theweak-signalRFinputan

8、daudiooutputresistancesofadiodedetectorareapproximatelythesameandequalto0.026*n/Isohms(Ismeansdiodesaturationc