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1、随着现代社会的快速发展，人们对电子产品的要求越来越高，因而电子产品无论从制作上述是从销售上都要求很高。小功率调幅发射机常用于通信系统和其它无线电系统屮，特别是在屮短波广播通信的领域里更是得到了广泛应用。原因是调幅发射机实现调幅简便，调制所占的频带窄，并且与之对应的调幅接收设备简单，所以调幅发射机广泛地应用于广播发射。发射机的主要任务是完成有用的低频信号到高频载波的调制，将其变为在某一中心频率上具有一定带宽、适合通过天线发射的电磁波。高频部分一般包括主振荡器、缓冲放大、倍频器、屮间放大、功放推动级与末级功放。主振器的作用是产生频率稳定的载波。为了提高频率稳定性，主振级往往釆用石英
2、品体振荡器，并在它后而加上缓冲级，以削弱后级对主振器的影响。在以前应用最广泛的是调频接收机，随着科学技术的发展，出现了超外差式调频接收机。低频部分包括话筒、低频电压放大级、低频功率放大级与末级低频功率放大级。低频信号通过逐级放大,在末级功放处获得所需的功率电平，以便对高频末级功率放大器进行调制。关键词：高频功率放大器、振荡器、调频发射机、功率放大器AbstractWiththerapiddevelopmentofmodernsociety,peopletotheelectronicproductoftheincreasinglyhighdemand,sotheelectroni
3、cproductsintermsofproductionorsalesisdemanding.LowpowerAMtransmitterisoftenusedincommunicationsystemsandotherradiosystems,especiallyinthemedium-andshort-waveradiocommunicationfieldismorewidelyapplied.ThereasonissimpletoachieveamplitudemodulationAMtransmitter,occupiesanarrowfrequencyband,andt
4、hecoiTespondingamplitudemodulationreceiverhastheadvantagesofsimpleequipment,soamtransmitteriswidelyusedinradiotransmitter.Thetransmitterfsmaintaskistocompletetheusefulsignaloflowfrequencytohighfrequencymodulatedcarrier,toturnitintoacenterfrequencyatacertainbandwidth,suitableforelectromagneti
5、cwavesemittedbytheantenna・Thehighfrequencyportiongenerallyincludeamasteroscillator,abufferamplifier,multiplier,intermediateamplifier,poweramplifierdriverstageandthefinalpoweramplifier.Themainisolatoreffectisgeneratedbyafrequencystabilizedcarrier.Inordertoimprovethefrequencystability,vibratio
6、nleveloftenusesthequartzcrystaloscillator,andbehinditwithbuffer,toweakenthebackstageonthemainisolatoreffect.InthepastthemostwidelyusedistheFMreceiver,withthedevelopmentofscienceandtechnology,appearedthesuperheterodyneFMreceiver.Thelowfrequencypartcomprisesamicrophone,alow-frequencyvoltageamp
7、lificationstage,lowfrequencypoweramplifierstageandthefinalstageofthelowfrequencypoweramplifierstage.Lowfrequencysignalsthroughtheprogressiveenlargement,inthefinalpoweramplifiertoobtainthedesiredpowerlevel,forhighfrequencypoweramplifiermodulation.Ke
