当前位置:考试网  > 试卷库  > 职业资格  > 其它  > 通信工程师考试  > 通信专业实务  > 简述移动通信系统中发信机的主要作用。
试题预览

简述移动通信系统中发信机的主要作用。

查看答案
收藏
纠错
正确答案:

答:发信机的主要作用是将所要传送的信号首先对载波信号进行调制,形成已调载波,已调载波信号经过变频(有的发射机不经过这一步骤)成为射频载波信号送至功率放大器,经功率放大器放大后送至天馈线。

答案解析:

暂无解析

你可能感兴趣的试题

通信卫星能源系统又称电源系统,由()组成。

研究表明,通过改变馈入各振子的信号相位,可以改变无线天线主瓣的下倾角度。

无线市话的网络接口采用开放的()信令接口。

下列编号中包含PLMNID的是()。

移动通信系统中的收信机的主要作用是把天线接收下来的射频载波信号首先进行低噪声放大,然后经过变频、中频放大和解调后还原出原始信号,最后经中频放大器放大输出。

热门试题 更多>
PARTVREADINGCOMPREHENSION Inthissectiontherearefourpassagesfollowedbyquestionsorunfinishedstatements,eachwithfoursuggestedanswersmarkedA,B,CandD.Choosetheonethatyouthinkisthebestanswer. TEXTA Racket,dinclamor,noise,whateveryouwanttocallit,unwantedsoundisAmerica'smostwidespread nuisance.Butnoiseismorethanjustanuisance.Itconstitutesarealandpresentdangertopeople'shealth.Day andnight,athome,atwork,andatplay,noisecanproduceseriousphysicalandpsychologicalstress.Nooneis immunetothisstress.Thoughweseemtoadjusttonoisebyignoringit,theear,infact,neverclosesandthe bodystillresponds—sometimeswithextremetension,astoastrangesoundinthenight. Theannoyancewefeelwhenfacedwithnoiseisthemostcommonoutwardsymptomofthestressbuilding upinsideus.Indeed,becauseirritabilityissoapparent,legislatorshavemadepublicannoyancethebasisof manynoiseabatementprograms.Themoresubtleandmoreserioushealthhazardsassociatedwithstress causedbynoisetraditionallyhavebeengivenmuchlessattention.Nevertheless,whenweareannoyedormade irritablebynoise,weshouldconsiderthesesymptomsfairwarningthatotherthingmaybehappeningtous, someofwhichmaybedamagingtoourhealth. Ofmanyhealthhazardstonoise,hearinglossisthemostclearlyobservableandmeasurablebyhealth professionals.Theotherhazardsarehardertopindown.Formanyofus,theremaybeariskthatexposuretothe stressofnoiseincreasessusceptibilitytodiseaseandinfection.Themoresusceptibleamongusmayexperience noiseasacomplicatingfactorinheartproblemsandotherdiseases.Noisethatcausesannoyanceandirritability inhealthpersonsmayhaveseriousconsequencesforthesealreadyillinmindorbody. Noiseaffectsusthroughoutourlives.Forexample,thereareindicationsofeffectsontheunbornchildwhen mothersareexposedtoindustrialandenvironmentalnoise.Duringinfancyandchildhood,youngstersexposed tohighnoiselevelsmayhavetroublefallingasleepandobtainingnecessaryamountsofrest. Why,then,istherenotgreateralarmaboutthesedangers?Perhapsitisbecausethelinkbetweennoiseand manydisabilitiesordiseaseshasnotyetbeenconclusivelydemonstrated.Perhapsitisbecausewetendto dismissannoyanceasapricetopayforlivinginthemodernworld.Itmayalsobebecausewestillthinkof hearinglossasonlyanoccupationalhazard. 1.InParagraph1,thephrase"immuneto"areusedtomean___. A.unaffectedby B.hurtby C.unlikelytobeseenby D.unknownby 2.Theauthor'sattitudetowardnoisewouldbestbedescribedas___. A.unrealistic B.traditional C.concerned D.hysterical 3.Whichofthefollowingbeststatesthemainideaofthepassage? A.Noiseisamajorproblem;mostpeoplerecognizeitsimportance. B.Althoughnoisecanbeannoying,itisnotamajorproblem. C.Noiseisamajorproblemandhasnotyetbeenrecognizedassuch. D.Noiseisamajorproblemaboutwhichnothingcanbedone. 4.Theauthorcondemnsnoiseessentiallybecauseit___. A.isagainstthelaw B.canmakesomepeopleirritable C.isanuisance D.inagangertopeople'shealth 5.Theauthorwouldprobablyconsiderresearchabouttheeffectsnoisehasonpeopletobe___. A.unimportant B.impossible. C.awasteofmoney D.essential
试题分类: 专业英语四级
练习次数:1次
试题分类: 社区工作人员
练习次数:0次
Afriendofminewasfondofdrawinghorse.Hedrewthehorsesverywell,buthealwaysbeganthetail.NowitistheWesternruletobeginattheheadofthehorse,thatiswhyIwassurprised.Itstruckmethatitcouldnotreallymakeanydifferencewhethertheartistbeginsattheheadorthetailorthebelly(肚子)orthefootofthehorse,ifhereallyknowshisbusiness.Andmostgreatartistswhoreallyknowtheirbusinessdonotfollowotherpeople’srule.Theymaketheirownrules.Everyoneofthemdoeshisworkinawaypeculiar(奇特的)tohimself;andthepeculiaritymeansonlythathefindsitmoreeasytoworkinthatway. Nowtheverysamethingistruetoliterature(文学).Andthequestion,"HowshallIbegin?"onlymeansthatyouwanttobeginattheheadinsteadofbeginningatthetailorsomewhereelse.Thatis,youarenotyetexperienced(有经验的)enoughtotrusttoyourownpowers.Whenyoubecomemoreexperiencedyouwill neveraskthequestion,andIthinkthatyouwilloftenbeginatthetail--thatistosay,youwillwritetheendofthestorybeforeyouhaveeventhoughtofthebeginning. 1.Afriendofthewriter’sdrewthehorses____. A.verywell B.inthewayofwesternrule C.inthewayofhisownrule D.alloftheabove 2.Thewriterwassurprisedbecause____. A.theartistbegantodrawattheheadofthehorse B.theartistbegantodrawatthetailofthehorse C.theartistmadehisownrule D.theartistdidnotfollowotherpeople’srule 3.Youarenotyetexperiencedbecause____. A.youdon’tknowwheretobegin B.youwanttobeginattheheadinsteadofbeginningatthetail C.youalwaysaskedquestion D.youdonottrusttoyourownpowers 4.Whenyoubecomemoreexperiencedyouwill____. A.neveraskquestion B.oftenbeginatthetail C.shouldwritetheendofthestory D.shouldthinkofthebeginning 5.Thetopicofthepassageis______. A.Howtodrawahorse B.Howtowriteastory C.Howtomakeyourownrules D.Trusttoyourownpowers
试题分类: 初级(阅读)
练习次数:15次
ReadingComprehension SectionA Directions:Therearetenincompletesentencesinthissection.ForeachsentencetherearefourchoicesmarkedA,B,CandD.ChoosetheONEthatbestcompletesthesentence.Thenwritedowntherightanswerinthebracketsforeachsentence.Thissectiontotals10points,onepointforeachsentence. ()1.Wecansupplyallthebicyclesyourequired____________stockandarearrangingshipmentbyM.V.Mermaid. A.forB.from C.to D.against ()2.Wewouldliketoremindyouthatthe__________L/CmustreachusbeforeMarch10 sothatwecanmakeshipmentingoodtime. A.coveringB.cover C.coveredD.beingcovered ()3.Wehavereceivedyourletterof28March,___________ustomodifythepreviousarrangementsfortheshipmentofthecaptionedorder. A.askedB.toask C.beingaskedD.asking ()4.InourletterofMay5,wemade__________clearthatshipmentistobeeffectedinJune. A.youB.them C.thatD.it ()5.Wealwaysdeal_______________paymentbysightL/C. A.with B.in C.at D.on ()6.Thisofferis_____________toyourreplyreachingusbeforethe20thofFebruary. A.subjectingB.subject C.subjectedDtosubject ()7.____________weareappreciatingthegoodqualityofyourblacktea,weregretthatyourpriceappearstobeonthehighside. A.WhileB.When C.HoweverD.Therefore ()8.Weherebyauthorizeyouto___________onusat60daysaftersighttotheextentofUSD20,000.00. A.open B.establish C.draw D.build ()9.Ifpartiestoacontractdesiretosettledisputes,anarbitrationclauseisusuallymadeinthecontractwellbeforeadispute_____________. A.risesB.arisesC.lookD.appear ()10.Somecustomersrequestedusto_____________ourpricebecausetheyconsideredit toohigh. A.putdownB.getdownC.takedown D.bringdown
试题分类: 初级(阅读)
练习次数:3次
试题分类: 国家电网招聘考试
练习次数:4次
扫一扫,手机做题