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TransmissionFundamentalsChapter2ElectromagneticSignalFunctionoftimeCanalsobeexpressedasafunctionoffrequencySignalconsistsofcomponentsofdifferentfrequenciesTime-DomainConceptsAnalogsignal-signalintensityvariesinasmoothfashionovertimeNobreaksordiscontinuitiesinthesignalDigitalsignal-signalintensitymaintainsaconstantlevelforsomeperiodoftimeandthenchangestoanotherconstantlevelPeriodicsignal-analogordigitalsignalpatternthatrepeatsovertime
s(t+T)=s(t) -¥<t<+¥whereTistheperiodofthesignalTime-DomainConceptsAperiodicsignal-analogordigitalsignalpatternthatdoesn'trepeatovertimePeakamplitude(A)-maximumvalueorstrengthofthesignalovertime;typicallymeasuredinvoltsFrequency(f)Rate,incyclespersecond,orHertz(Hz)atwhichthesignalrepeatsTime-DomainConceptsPeriod(T)-amountoftimeittakesforonerepetitionofthesignalT=1/fPhase()-measureoftherelativepositionintimewithinasingleperiodofasignalWavelength()-distanceoccupiedbyasinglecycleofthesignalOr,thedistancebetweentwopointsofcorrespondingphaseoftwoconsecutivecyclesSineWaveParametersGeneralsinewaves(t)=Asin(2ft+)Figure2.3showstheeffectofvaryingeachofthethreeparameters(a)A=1,f=1Hz,=0;thusT=1s(b)Reducedpeakamplitude;A=0.5(c)Increasedfrequency;f=2,thusT=½(d)Phaseshift;=/4radians(45degrees)note:2radians=360°=1periodSineWaveParametersTimevs.DistanceWhenthehorizontalaxisistime,asinFigure2.3,graphsdisplaythevalueofasignalatagivenpointinspaceasafunctionoftimeWiththehorizontalaxisinspace,graphsdisplaythevalueofasignalatagivenpointintimeasafunctionofdistanceAtaparticularinstantoftime,theintensityofthesignalvariesasafunctionofdistancefromthesourceFrequency-DomainConceptsFundamentalfrequency-whenallfrequencycomponentsofasignalareintegermultiplesofonefrequency,it’sreferredtoasthefundamentalfrequencySpectrum-rangeoffrequenciesthatasignalcontainsAbsolutebandwidth-widthofthespectrumofasignalEffectivebandwidth(orjustbandwidth)-narrowbandoffrequenciesthatmostofthesignal’senergyiscontainedinFrequency-DomainConceptsAnyelectromagneticsignalcanbeshowntoconsistofacollectionofperiodicanalogsignals(sinewaves)atdifferentamplitudes,frequencies,andphasesTheperiodofthetotalsignalisequaltotheperiodofthefundamentalfrequencyRelationshipbetweenDataRateandBandwidthThegreaterthebandwidth,thehighertheinformation-carryingcapacityConclusionsAnydigitalwaveformwillhaveinfinitebandwidthBUTthetransmissionsystemwilllimitthebandwidththatcanbetransmittedAND,foranygivenmedium,thegreaterthebandwidthtransmitted,thegreaterthecostHOWEVER,limitingthebandwidthcreatesdistortionsDataCommunicationTermsData-entitiesthatconveymeaning,orinformationSignals-electricorelectromagneticrepresentationsofdataTransmission-communicationofdatabythepropagationandprocessingofsignalsExamplesofAnalogandDigitalDataAnalogVideoAudioDigitalTextIntegersAnalogSignalsAcontinuouslyvaryingelectromagneticwavethatmaybepropagatedoveravarietyofmedia,dependingonfrequencyExamplesofmedia:Copperwiremedia(twistedpairandcoaxialcable)FiberopticcableAtmosphereorspacepropagationAnalogsignalscanpropagateanaloganddigitaldataDigitalSignalsAsequenceofvoltagepulsesthatmaybetransmittedoveracopperwiremediumGenerallycheaperthananalogsignalingLesssusceptibletonoiseinterferenceSuffermorefromattenuationDigitalsignalscanpropagateanaloganddigitaldataAn脖al四og统S差ig箭na元li外ngDi弄gi翼ta管l射Si搜gn云al盼in翼gRe飘as轧on念s疾fo言r投Ch相oo拼si羽ng易D洞at贝a闹an拌d岁Si慌gn底al参C肾om怕bi象na锯ti慈on筑sDi赶gi栋ta矩l启da苍ta陷,票di东gi拒ta腰l嫂si食gn她alEq意ui绢pm亲en睬t兆fo添r项en肺co扬di漫ng判i盾s磁le察ss束e葱xp巴en栋si爹ve雅t尚ha忧n秋di优gi盛ta捐l-问to沉-a扶na动lo资g逮eq姓ui杨pm吗en档tAn钻al盗og霞d沫at傻a,恋d挖ig甘it室al放s浮ig希na地lCo怕nv安er晌si泳on腿p脆er俱mi钉ts针u议se贤o秩f紫mo欠de楼rn扶d难ig糖it够al滥t馋ra湾ns前mi纲ss愚io政n纸an承d妄sw烛it紧ch插in颗g闯eq受ui轻pm玻en叔tDi闻gi万ta臭l订da铸ta幅,吐an筑al辨og亏s绢ig标na介lSo热me古t架ra蓬ns较mi脂ss急io栽n泻me肯di谣a虫wi茄ll法o绸nl吧y赔pr皂op酒ag尊at颤e烧an肯al芳og衫s规ig话na惨lsEx驼am芝pl虹es街i扩nc子lu吨de界o粱pt眠ic水al堂f姓ib吨er名a伤nd处s南at法el倘li惰teAn劲al毙og锦d念at波a,陆a秘na伪lo戏g民si协gn懂alAn孤al似og帖d骆at表a迈ea策si末ly构c嘴on水ve境rt寒ed执t背o遣an膛al统og朋s走ig准na将lAn狼al惊og缠T死ra支ns我mi镇ss伴io粗nTr兆an砌sm驴it堵a身na待lo缓g涉si善gn屯al猾s萌wi挺th故ou评t泉re未ga海rd滔t昨o止co僚nt村en每tAt计te筒nu巧at样io园n覆li诉mi依ts怕l葬en湖gt宴h复of右t鱼ra驳ns士mi恐ss户io俭n号li挨nkCa粘sc回ad虾ed隶a械mp制li旨fi喘er蔑s顶bo舒os待t溉si永gn锹al票’s洁e屯ne掘rg颗y丙fo制r劲lo驴ng袭er欣d污is牙ta雄nc笔es绵b堤ut抄c垮au稍se询d韵is封to桥rt趟io响nAn猪al笼og坐d塔at卧a朵ca蔽n意to鱼le滤ra敢te颂d铅is煎to尘rt等io备nIn缺tr耍od狼uc努es寻e步rr著or呀s爬in味d扰ig样it经al很d杂at强aDi杂gi温ta他l烛Tr奋an疾sm睛is川si朽onCo溪nc觉er垒ne农d施wi武th蚁t喝he肆c投on丝式te枝nt江o腹f般th宋e铃si怖gn惨alAt桂te组nu津at多io双n战en桨da驱ng护er末s夸in慈te仿gr议it创y柱of跑d蚊at掘aDi牌gi鸦ta男l肠Si茅gn孔alRe罚pe穷at涝er需s今ac领hi胀ev草e旬gr惯ea沃te摘r排di亿st答an典ceRe匪pe拜at音er烂s某re摧co留ve浑r态th肠e环si惰gn烟al然a阁nd据r宴et法ra叫ns泪mi框tAn嫩al红og锹s棒ig机na柄l涛ca抖rr测yi历ng踢d新ig框it库al饲d除at替aRe井tr猪an版sm叼is唇si庄on根d株ev盗ic婚e锡re减co钳ve杀rs弄t战he国d宋ig齿it乌al毅d台at白a粘fr寇om苏a娱na许lo案g搜si止gn旬alGe花ne皆ra霜te滴s擦ne背w,浸c厦le扬an水a匹na请lo努g们si煮gn李alAb捉ou欣t鸣Ch腥an局ne录l俱Ca蠢pa捐ci币tyIm浙pa虫ir梅me同nt排s,站s吨uc蛮h伞as碧n踪蝶oi翠se招,幻玉li易mi右t腿da在ta狡r财at括e浸th励at氏c伶an厕b该e浙ac身hi劈燕ev归edFo释r很di酒gi痰ta翼l滤da询ta郑,尾to杰w取ha闲t歼ex谱te瞧nt奔d沫o卧im算pa糟ir差me米nt没s准li绿mi筹t怠da鞠ta傲r炒at爱e?Ch拣an衔ne港l泉Ca亩pa监ci沙ty兽–荡t结he忌m迈ax苦im员um翅r商at挎e混at珠w佳hi台ch影d狠at悼a忆ca窄n掘be灾t将ra漂ns找mi亮tt按ed系o游ve表r径a潮gi立ve仇n膀co条mm绢un神ic币at初io乱n烧pa扣th唐,膏or和c名ha友nn册el呢,扰un只de挖r秘gi缠ve镰n苍co蚀nd转it棍io萄nsCo锹nc夜ep勤ts裳R湾el冷at住ed幼t萍o浪Ch梦an筛ne抬l拌Ca陆pa通ci抖tyDa柿ta厉r座at痛e锣-俭ra涛te侍a五t院wh经ic粘h览da始ta径c露an忍b序e寻co躬mm豪un著ic纵at正ed锡(佩bp骑s)Ba俱nd酬wi阻dt毛h纠-酷th薄e银ba峰nd伙wi息dt葡h冠of婆t虾he惜t庄ra酱ns烛mi织tt察ed晌s丘ig寻na赛l问as望c拳on甜st宿ra特in焰ed盈b主y抵th熟e么tr课an贩sm访it靠te限r妇an玻d玩th澡e途na夫tu灶re艇o喜f积th失e鼓tr轰an刃sm葬is出si句on腐m充ed招iu露m骗(H院er雄tz块)No蜡is控e书-谊av玻er匀ag昼e谊le押ve品l抬of贵n还oi种se映o荐ve串r招th激e汤co祝mm望un统i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