資源描述：
《ARM外文翻譯外文.doc》由會員上傳分享，免費在線閱讀，更多相關(guān)內(nèi)容在教育資源-天天文庫。
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
