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1、隨著現代社會的快速發(fā)展,人們對電子產品的要求越來越高,因而電子產品無論從制作上述是從銷售上都要求很高。小功率調幅發(fā)射機常用于通信系統(tǒng)和其它無線電系統(tǒng)屮,特別是在屮短波廣播通信的領域里更是得到了廣泛應用。原因是調幅發(fā)射機實現調幅簡便,調制所占的頻帶窄,并且與之對應的調幅接收設備簡單,所以調幅發(fā)射機廣泛地應用于廣播發(fā)射。發(fā)射機的主要任務是完成有用的低頻信號到高頻載波的調制,將其變?yōu)樵谀骋恢行念l率上具有一定帶寬、適合通過天線發(fā)射的電磁波。高頻部分一般包括主振蕩器、緩沖放大、倍頻器、屮間放大、功放推動級與末級功放。主振器的作用是產生頻率穩(wěn)定的載波。為了提高頻率穩(wěn)定性,主振級往往釆用石英
2、品體振蕩器,并在它后而加上緩沖級,以削弱后級對主振器的影響。在以前應用最廣泛的是調頻接收機,隨著科學技術的發(fā)展,出現了超外差式調頻接收機。低頻部分包括話筒、低頻電壓放大級、低頻功率放大級與末級低頻功率放大級。低頻信號通過逐級放大,在末級功放處獲得所需的功率電平,以便對高頻末級功率放大器進行調制。關鍵詞:高頻功率放大器、振蕩器、調頻發(fā)射機、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