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时间:2018-11-22
《多功能电子医药盒毕业设计英文.doc》由会员上传分享,免费在线阅读,更多相关内容在学术论文-天天文库。
1、英文原文RadioReceiverAblockdiagramforamodernradioreceiverisshowninFig..2-4.Theinputsignalstothisradioareamplitude-modulatedradiowaves.Thebasicelectroniccircuitsinclude:antenna,tuner,mixer,localoscillator,IFamplifier,audiodetector,AFamplifier,loudspeaker,andpowersupply.Fig.1ABlockDi
2、agramForModernRadioReceiverAnyantennasystemcapableofradiatingelectricalenergyisalsoabletoabstractenergyfromapassingradiowave.Sinceeverywavepassingthereceivingantenna.Inducesitsownvoltageintheantennaconductor,itisnecessarythatthereceivingequipmentbecapableofseparatingthedesireds
3、ignalfromtheunwantedsignalsthatarealsoinducingvoltagesintheantenna.Thisseparationismadeonthebasisofthedifferenceinfrequencybetweentransmittingstationsandiscarriedoutbytheuseofresonantcircuits,whichcanbemadetodiscriminateverystronglyinfavorofaparticularfrequency.Ithasalreadybeen
4、pointedthat,bymakingantennacircuitresonanttoaparticularfrequency,theenergyabstractedfromradiowavesofthatfrequencywillbemuchgreaterthantheenergyfromwavesofotherfrequencies;thisalonegivesacertainamountofseparationbetweensignals.Stillgreaterselectiveactioncanbeobtainedbytheuseofad
5、ditionalsuitablyadjustedresonantcircuitslocatedsomewhereinthereceiverinsuchawayastorejectallbutthedesiredsignal.Theabilitytodiscriminatebetweenradiowavesofdifferentfrequenciesiscalledselectivityandtheprocessofadjustingcircuitstoresonancewiththefrequencyofadesiredsignalisspokeno
6、fastuning.Althoughintelligibleradiosignalshavebeenreceivedfromthestationsthousandsofmilesdistant,usingonlytheenergyabstractedfromtheradiowavebythereceivingantennamuchmoresatisfactoryreceptioncanbeobtainedifthereceivedenergyisamplified.Thisamplificationmaybeappliedtotheradio-fre
7、quencycurrentsbeforedetection,inwhichcaseitiscalledradio-frequencyamplificationoritmaybeappliedtotherectifiedcurrentsafterdetection,inwhichcaseitiscalledaudio-frequencyamplification.Theuseofamplificationmakespossiblethesatisfactoryreceptionofsignalsfromwavesthatwouldotherwisebe
8、tooweaktogiveanaudibleresponse.Theprocessbywhichthesig
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