多功能电子医药盒毕业设计内容英文.doc

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1、英文原文RadioReceiverAblockdiagramforamodernradioreceiverisshowninFig..2-4.Theinputsignalstothisradioareamplitude-modulatedradiowaves.Thebasicelectroniccircuitsinclude:antenna,tuner,mixer,localoscillator,IFamplifier,audiodetector,AFamplifier,loudspeaker,andpowersupply.Fig.1ABlockDiagramFor

2、ModernRadioReceiverAnyantennasystemcapableofradiatingelectricalenergyisalsoabletoabstractenergyfromapassingradiowave.Sinceeverywavepassingthereceivingantenna.Inducesitsownvoltageintheantennaconductor,itisnecessarythatthereceivingequipmentbecapableofseparatingthedesiredsignalfromtheunwa

3、ntedsignalsthatarealsoinducingvoltagesintheantenna.Thisseparationismadeonthebasisofthedifferenceinfrequencybetweentransmittingstationsandiscarriedoutbytheuseofresonantcircuits,whichcanbemadetodiscriminateverystronglyinfavorofaparticularfrequency.Ithasalreadybeenpointedthat,bymakingante

4、nnacircuitresonanttoaparticularfrequency,theenergyabstractedfromradiowavesofthatfrequencywillbemuchgreaterthantheenergyfromwavesofotherfrequencies;thisalonegivesacertainamountofseparationbetweensignals.Stillgreaterselectiveactioncanbeobtainedbytheuseofadditionalsuitablyadjustedresonant

5、circuitslocatedsomewhereinthereceiverinsuchawayastorejectallbutthedesiredsignal.Theabilitytodiscriminatebetweenradiowavesofdifferentfrequenciesiscalledselectivityandtheprocessofadjustingcircuitstoresonancewiththefrequencyofadesiredsignalisspokenofastuning.Althoughintelligibleradiosigna

6、lshavebeenreceivedfromthestationsthousandsofmilesdistant,usingonlytheenergyabstractedfromtheradiowavebythereceivingantennamuchmoresatisfactoryreceptioncanbeobtainedifthereceivedenergyisamplified.Thisamplificationmaybeappliedtotheradio-frequencycurrentsbeforedetection,inwhichcaseitiscal

7、ledradio-frequencyamplificationoritmaybeappliedtotherectifiedcurrentsafterdetection,inwhichcaseitiscalledaudio-frequencyamplification.Theuseofamplificationmakespossiblethesatisfactoryreceptionofsignalsfromwavesthatwouldotherwisebetooweaktogiveanaudibleresponse.Theprocessbywhichthesig