1、INTELLIGENTFREQUENCYMODULATIONOFCAMPUSBROADCASTINGSYSTEMFMradioisthewaytheFMaudiosignaltransmission/thecarrierwavefrequencymodulationwiththeaudiosignalchangescenterfrequencyinthecarrier(notthecenterfrequencymodulationago)onbothsidesofchange/secondchangetheoffsetfrequencyandaudiosignalthesamemodulati
2、onfrequency/suchasthefrequencyofaudiosignal1KHz/thecarrierfrequencyoffsetchangesinthenumberoftimespersecond1K/Thesizeofoffsetwiththeamplitudeofaudiosignalsize/FMtransmittersinthedomesticSpecificationslimittoallowthemaximumfrequencyoffset75KHz/thefrequencyresponse80-10000Hz(3dB)/harmonicradiation-60d
3、B(forafundamental0dB)/thefrequencystabilityof110-6/letternoiseratio50dB/totalharmonicdistortion0/1%/transmittingfrequency87-108MHz/thegeneralprovisionsoftheschoolinthe70-87MHzbetween/Intelligentbroadcastingsystemoncampusasaninnovativeandpracticalequipmentofmoderneducation/inlinewiththecountrysindust
4、ryandtheMinistryofEducationseducation-orientedinformationtoandiswidelyconsideredanalternativeschooloftraditionale-ringandear-piercingloudspeakersbroadcastingthegreenenvironment-friendlyproducts/Thesystemwiththelatestcomputernumericalcontroltechnology/high-fidelityaudiotechnology/createdthemusic(ormu
5、sicringtones)insteadofe-ringprecedent/Broadcastsystem/whichisindispensableforeachschool/oneoftheinfrastructure/althoughinrecentyearsvideoandnetworktechnologyintherapiddevelopmentofthebroadcastingsystembutstillitspracticality/economy/conveniencewasavarietyofunits/placesofapplication/Existingtypesofsc
6、hoolsinChinaarebasicallythepublicaddresssystem/itmainlyusedforvariouspublicoccasions/suchasallofpublicbroadcasting/notification/broadcastavarietyofliteraryandartisticprograms/recognitionofadvancedschooltoconvenetheGeneralAssembly/suchas/Withmoderninformationtechnology/multi-mediateachinginschoolstok
7、eepXinhuanetwidelypopular/themajorityofprimaryandsecondaryschoolstousevoicebroadcastingsystemoflanguageteachinginthecontinuingincreaseindemand/thetraditionalschoolpublicaddresssystemforbroadcastinganumberofsmall-scale/suchas/canteenmealsputonmusic/atdifferentlevelsondifferentclassesofvoicetrainingin
8、themorningandeveningbroadcastsofquartershaveachoiceofbroadcastingdifficulttoachieve/Schoolscannotmeettheteachingvoice/voicetrainingneeds/SmartcampusFMradiosystemisbasedonthecurrentschoolsystemfunctionsonthecampusradiogrowingdemandtodevelopasetofinteractiveintelligentFMradiosystem/ithasnowiringPole/c
9、overingawiderangeofunlimitedexpansion/installationandmaintenanceconvenience/investmentProvince/abeautifulclearsoundqualitycharacteristics/Thesystemiscurrentlyasetofmoreadvancedintelligentbroadcastingsystem/Sincethebirthofradiotechnology/informationtransmissionandinformationprocessinghasalwaysbeenits
10、majortask/Toeffectivelylauncharadiosignalout/thesizeoftheantennaandthesignalwavelengthmustbethesameorderofmagnitude/Inordertoeffectivelycarryouttransmission/mustbetobringinformationtothedozensoflow-frequencysignalmodulationMHzmorethanafewhundredMHzhigh-frequencyoscillationsignal/andthensentbytheante
11、nna/Inordertoreducethefactorsthatcausedinstabilityinthesystem/andenhancethereliabilityofthesystem/thesystemmustincludeautomaticgaincontrol/automaticfrequencycontrolandautomaticphasecontrol(PLL)circuitincludingthefeedbackcontrol/Theperformanceofphase-lockedloopcircuitinwhichitisparticularlyimportantT
12、heuseofphase-lockedloopFMprogramsdirectly/sothatitnotonlyhasaveryhighfrequencystability(about10-6)/alsohasarelativelyhighamountofthemaximumoffset/TheoverallintegrationoftheFMtransmittercontrolsignals/usedasthecoreoftheBH1417chipcircuitdesign/chipcrystaloscillatortoprovidebenchmarksfortheoscillationf
13、requencysignalsource/thesourceoscillationfrequencysynthesizerusingPLLmode/TheuseofFMmodulationsignalisaddeddirectlyontotherealizationofvoltage-controlledoscillator/VCOvaractordiodesandbytheBJToscillatorcomposedofthree-pointcapacitance/RFpoweramplifierusingahighefficiencyClassCamplifier/BH1417-housec
14、onsistsofthreebasiccomponents/phasedetector(PD)/loopfilter(LPF)andvoltage-controlledoscillator(VCO)/Phasedetectorisaphasecomparisondevice/theinputsignalSi(t)andvoltage-controlledoscillatoroutputsignalSo(t)tocomparethephase/resultingintwosignalscorrespondingtotheerrorvoltagephaseSe(t)/Loopfilteristof
15、ilterouttheerrorvoltageSe(t)inthehighfrequencycomponentsandnoiseinordertoensuretheperformanceoftherequestedlooptoincreasethestabilityofthesystem/VCOcontrolvoltagebySd(t)thecontrol/sothatthefrequencyofVCOfrequencytotheinputsignalside/untiltheeliminationofthelockfrequencydifference/Phase-lockedlooppha
16、seerrorisarealcontrolsystem/BycomparingtheinputsignalandVCOphasedifferencebetweenoutputsignals/resultingintheerrorcontrolvoltagetoadjusttheVCOfrequency/soastoachievethesamefrequencywiththeinputsignal/Beganitsworkintheloop/iftheinputsignalfrequencyandvoltage-controlledoscillatorfrequencyisdifferentfr
17、omthetwosignalsduetotheinherentfrequencybetweenthepoor/isboundtohavebeenchangesinphasedifference/phasedetectoroutputvoltageontheerrorwithinacertainrangechange/Inthiserrorvoltagecontrol/voltage-controlledoscillatorfrequencyischanging/Ifthevoltage-controlledoscillatortochangethefrequencyoftheinputsign
18、alwithfrequencyequaltothestabilityconditionsaremetinthisfrequencystabilized/Achievestability/theinputsignalandVCOoutputsignalfrequencydifferencebetweenthezero/adifferenceofnochangeovertime/theerrorvoltagetoafixedvalueintothelooponthelockstate/Loudspeakersbroadcasttheselectedenvironmentshouldinprinci
19、plebeselectedasthespecificationsofdifferentspeciessuchastheradiospeakers/theceilingintheceilingoftheroom/tousetheembedded/non-afterspeakerenclosuresofsmallpox/Simplestructureofthesespeakers/butthepricesarerelativelycheap/andeasyconstruction/Themaindrawbackisthatafterthecoverisnoteasilyinsects/rodent
20、sbite/Theonlyframeworkintheceilingwithouttheceilingoftheinteriorsurface(suchasopen-frameshoppingmalls)tousethelifting-styleballafterthespeakerorspeakerenclosureceiling/Duetoaceilingequivalenttotheinfinitebaffle/sotheconditionsintheceilingunderthehoodaftertheuseofloudspeakerswillnotcauseashortcircuit
21、/Andthereisnoceilingwhenthesituationisverydifferent/ifstillfreeofsmallpoxafterspeakerenclosures/theeffectwillbepoor/Inprinciple/shouldbeusedwhenhoistingspeaker/However/toolargeinvestmentandcanalsobeusedforsmallpoxafterthespeakerenclosures/Afterthespeakershaverearhoodcoversmallpoxisnotonlytheroleofth
22、egeneralmechanicalprotection/andtosomeextentplaytheroleofanti-short-circuit/校园自动锁相调频发射原理调频广播是以调频方式进行音频信号传输的，调频波的载波随着音频调制信号的变化而在载波中心频率（未调制以前的中心频率）两边变化，每秒钟的频偏变化次数和音频信号的调制频率一致，如音频信号的频率为1KHz，则载波的频偏变化次数也为每秒1K次。频偏的大小是随音频信号的振幅大小而定。在国内调频发射机技术指标允许最大频偏***在75KHz，频率响应80-10000Hz（3dB），谐波辐射强度-60dB（以基波为0dB），频率稳定度110
23、-6，信噪比50dB，失真度0/1%，发射频率87-108MHz，学校一般规定在70-87MHz之间。校园智能广播系统作为一种新颖实用的现代教育设备，符合国家的产业导向和教育部的教育信息化要地，被广泛认为是替代学校传统电子***和刺耳高音喇叭广播的绿色环保型产品。该系统凭借最新的计算机数字控制技术、高保真音响技术，开创了以音乐（或音乐***）代替电子***的先例。广播系统是每个学校不可缺少的基础设施之一，尽管近几年来视频技术和网络技术在飞速的发展，但广播系统仍以它的实用性、经济性、便捷性被各种单位、场所应用。我国现有的各类学校基本上都有公共广播系统，它主要用于各种公共场合，如进行全校的公共广播、通知
24、、课间操、播送各种文艺节目、表扬先进、召开全校大会等。随着现代信息技术的不断发展，多媒体教学在广大中小学校不断普及，广大中小学利用广播系统进行语音语言教学的需求在不断的增加，传统的公共广播系统对于学校一些小规模的广播，如：就餐时对食堂放音乐、不同年级不同班级上语音训练课、早晚对宿舍广播等有选择的广播难以实现。也不能满足学校语音教学、语音训练的需求。校园智能调频广播系统是根据当前学校对校园广播系统功能的要求不断增加，开发的一套交互式智能调频广播系统，它具有无需立杆架线，覆盖范围广，无限扩容，安装维护方便，投资省，音质优美清晰的特点。该系统是目前国内较为先进的一套智能广播系统。无线电技术诞生以来/
25、信息传输和信息处理始终是其主要任务。要将无线电信号有效地发射出去/天线的尺寸必须和电信号的波长为同一数量级。为了有效地进行传输/必须将携带信息的低频电信号调制到几十MHz几百MHz以上的高频振荡信号上/再经天线发送出去。为减小各种因素引起的系统不稳定，增强系统的可靠性，系统必须包括自动增益控制、自动频率控制和自动相位控制(锁相环)在内的反馈控制电路。其中锁相环电路的性能就显得尤其重要。采用锁相环直接调频的方案，使其不仅具有很高的频率稳定度（约10-6），还具有比较高的最大频偏量。整体集成化控制信号的调频发射，采用芯片BH1417为核心的电路设计，芯片内晶振为振荡源提供基准频率信号，振荡源采用PLL
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