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双工无线语音数据传输系统的设计 Triplewirelessvoicedatatransmissionsystemdesign Student:Liufigure,physicsandinformationengineeringcolleges Instructor:XiaoYunhong,JianghanUniversity Everyday,inourworkandinourleisuretime,wecomeincontactwithanduseavarietyofmoderncommunicationmedia,themostcommonbeingthetelephone,radio,television,andtheInternet.Thoughthesemediaweareabletocommunicate(nearly)instantaneouslywithpeopleondiffidentcontinents,transactourdailybusiness,andreceiveinformationaboutvariousdevelopmentsandeventsofnotethatoccurallaroundtheworld.Electronicmailandfacsimiletransmissionhavemadeitpossibletorapidlycommunicatewrittenmessageacrossgreatdistances. Wirelesscommunications.ThedevelopmentofwirelesscommunicationsstemsfromtheworksofOersted,Faraday,Gauss,Maxwell,andHertz.In1820,Oersteddemonstratedthatanelectriccurrentproducesamagneticfield.OnAugust29,1831,MichaelFaradayshowedthataninducedcurrentisproducedbymovingamagnetinthevicinityofaconductor.Thus,hedemonstratedthatachangingmagneticfieldproducesanelectricfield.Withthisearlyworkasbackground,JamesC.Maxwellin1864predictedtheexistenceofelectromagneticradiationandformulatedthebasictheorythathasbeeninuseforoveracentury.Maxwell’stheorywasverifiedexperimentallybyHertzin1887. In1894,asensitivedevicethatcoulddevicethatcoulddetectradiosignals,calledthecoherer,wasusedbyitsinventorOliverLodgetodemonstratewirelesscommunicationoveradistanceof150yardsatOxford,England.GuglielmoMarconiiscreditedwiththedevelopmentofwirelesstelegraphy.Marconidemonstratedthetransmissionofradiosignalsatadistanceofapproximately2kilometersin1895.Twoyearslater,in1897,hepatentedaradiotelegraphsystemandestablishedtheWirelessTelegraphandSignalCompany.OnDecember12,1901,MarconireceivedaradiosignalatSignalHillinNewfoundland,whichwastransmittedfromCornwall,England,adistanceofabout1700miles. Theinventionofthevacuumtubewasespeciallyinstrumentalinthedevelopmentofradiocommunicationsystem.ThevacuumdiodewasinventedbyFlemingin1904andthevacuumtriodeamplifierwasinventedbyDeForestin1906,