2023学年完整公开课版RadioandSpectrumKnowledge（2022新）

Presenter:MiZhiqiangHunanModernLogisticsCollegeRadioandSpectrumKnowledgeContents1Radiosignalcharacteristics2Applicationofelectromagneticwaves3DivisionanddistributionofelectromagneticspectrumGuide0Intangiblestrategicresources-thestrategicsignificanceofradiospectrumresourcesRadiospectrumresources[Caseanalysisanddiscussion](1)Listthemainapplicationsofradioinourdailylife?(2)Asaninvisiblestrategicresource,whatroledoesradiofrequencyplayinthedevelopmentofnationaleconomy?Inhigh-frequencycircuits,therearethreemaintypesofradiosignalsthatwehavetodealwith:baseband(message)signals,high-frequencycarriersignals,andmodulatedsignals.Theso-calledbasebandsignalistheoriginalsignalbeforemodulation,andisalsocalledthemodulationsignal.1.TimeCharacteristics(1)Descriptionofsignal:Aradiosignal,whichcanbeexpressedasatimefunctionofvoltageorcurrent,isusuallydescribedbytimedomainwaveformormathematicalexpression.(2)Theconceptoftimecharacteristic:Thetimecharacteristicofradiosignalishowfastthesignalchangeswithtime.Thetimecharacteristicofthesignalrequiresthatthetimecharacteristic(suchastimeconstant)ofthecircuitthattransmitsthesignalcorrespondtoit.01Radiosignalcharacteristics2.SpectrumCharacteristicsThespectrumcharacteristicofradiosignalreferstothecharacteristicofeachfrequencycomponentinthesignal.Spectrumcharacteristicsincludeamplitude-frequencycharacteristicsandphase-frequencycharacteristics,whichreflectthedistributionoftheamplitudeandphaseofeachfrequencycomponentinthesignalrespectively.Formorecomplexsignals(suchasvoicesignal,imagesignal,etc.),itismoreconvenienttousespectrumanalysismethodtoexpressthem.Fortheperiodicsignal,itisexpressedasmanydiscretefrequencycomponents(theharmonicfrequencyrelationshipbetweenthecomponents),asshowninFigure2,whichisthespectrumofthesignalshowninFigure1.Forthenon-periodicsignal,itcanbedecomposedintocontinuousspectrumbyFouriertransformmethod,atwhichtimethenon-periodicsignalistheintegralofthecontinuousspectrum.Figure1SignaldecompositionFigure2Spectrumdiagram01Radiosignalcharacteristics3.PropagationCharacteristicsThepropagationcharacteristicsofradiosignalrefertoitstransmissionmode,transmissiondistance,transmissioncharacteristicsandsoon.Theyaremainlydistinguishedaccordingtotheirfrequencybandsorbands.Whentheelectromagneticwaveradiatesfromthetransmittingantenna,notonlytheenergyoftheelectromagneticwavewilldiffuse,butthereceivercanonlyreceiveaverysmallpartofit.Moreover,intheprocessofpropagation,theenergyofelectromagneticwavewillbeabsorbedorreflectedbytheionosphereontheground,buildingsorhighaltitude,orrefractedorscatteredintheatmosphere,resultinginagreatattenuationoftheintensitywhenitreachesthereceiver.Accordingtothephenomenaoccurringinthepropagationprocessofradioelectromagneticwave,thepropagationmodesofelectromagneticwavecanbedividedintodirect(lineofsight)propagation,diffraction(groundwave)propagation,refractionandreflection(skywave)propagationandscatteringpropagation,etc.asshowninFig.3.Thefrequencyofradiosignalsisthekeyfactordeterminingthemodeandcharacteristicsoftransmission.01RadiosignalcharacteristicsAccordingtothephenomenaoccurringinthepropagationprocessofradioelectromagneticwave,thepropagationmodesofelectromagneticwavecanbedividedintodirect(lineofsight)propagation,diffraction(groundwave)propagation,refractionandreflection(skywave)propagationandscatteringpropagation,etc.asshowninFig.2-3.Thefrequencyofradiosignalsisthekeyfactordeterminingthemodeandcharacteristicsoftransmission.01Radiosignalcharacteristics3.PropagationCharacteristicsTheWayofElectromagneticWavePropagationRadiowavecanbedividedintoskywave,groundwaveandspacewave.(1)GroundwavepropagationRadiowavesbelowtheHFband(<3MHz)propagatealongtheearth'ssurface(orseasurface)tothereceivingpoint,sotheyarealsocalledgroundwaves(surfacewaves).Mediumandlongwavesaremainlypropagatedbygroundwaves.(2)SkywavepropagationTheradiowave(shortwave)workinginHFband(3MHz-30MHz)iscalledskywave.Skywavestravelinstraightlines,notalongtheearth'ssurface.Reflectionsandrefractionsoccurwhenskywavesreachtheionosphereataltitudesof60to200miles.TheionospherecanreflectskywaveshundredsofmilesawayfromEarth.Itcanrealizelong-distancetransmissionofradiosignals.

01Radiosignalcharacteristics3.PropagationCharacteristics01RadiosignalcharacteristicsFig.3MainpropagationmodesofradiowavesRaySuitableforultrashortwaveandmicrowave(a)DirectpropagationIonosphere(60-600kmfromtheground)Theprimaryreflectiondistanceisabout400km.Suitableformediumandshortwave(c)SkywavepropagationSuitableformediumandlongwave(b)Groundwavepropagation10-12kmabovegroundTroposphereScatteringpropagationdistanceis100-500KMSuitablefrequencyis400-6000MHZ(d)ScatterpropagationOnereasonforthehighfrequency(radiofrequency)ofradiotransmissionisthatthehighfrequencyissuitableforantennaradiationandwirelesspropagation.Onlywhenthesizeoftheantennacanbecomparedwiththesignalwavelength,theradiationefficiencyoftheantennawillbehigher,sothatthesignalpowercanbetransmittedatalongerdistanceandthereceivingantennacaneffectivelyreceivethesignal.Theso-calledmodulationistousethemodulationsignaltocontroltheparametersofthehigh-frequencycarrier,sothatoneorseveralparameters(amplitude,frequencyorphase)ofthecarriersignalchangeaccordingtothelawofthemodulationsignal.Accordingtothedifferentmodulationparametersofthecarrier,themodulationisdividedintothreebasicmodes,namelyamplitudemodulation(amplitudemodulation),frequencymodulation(frequencymodulation),andphasemodulation(phasemodulation),whicharerespectivelyrepresentedbyAM,FM,andPM.Thereisalsoacombinedmodulationmethod.4.ModulationCharacteristics01RadiosignalcharacteristicsTheamplitudeofspectrallinereflectspeakvalueofaudiosignal,andthedistanceofspectrallinefromoriginoffrequencyaxisreflectsfrequencyofaudiosignal.01RadiosignalcharacteristicsAcousticwaveMicrophoneLowFrequencyACSignalLargeAmplitudeinSpectrumSmallAmplitudeinSpectrumBigsoundlowpitchSmallsoundlowpitchBigsound,highpitchHighfrequencyBigsoundlowpitchLowfrequencyUsuallytheactualaudiosignalisnotasingle-frequencysinewave,soitsspectrumisalsocomposedofmultiplelines,thewaveformofthe"ah..."soundsignalisshowninthefigure.01Radiosignalcharacteristics1.GenerationoftheRadioAge2.BriefHistoryofRadioCommunicationDevelopmentRFIDtechnologyisbasedontheuseofelectromagneticenergytoachieveAIDC.Electromagneticenergyisaformofenergyexistinginnature.Tracingbacktohistory,naturalmagnetswerediscoveredandusedinChinainBC.Magnetswereusedasguides.Inmoderntimes,moreandmorepeoplehavemadein-depthobservationofelectricity,magnetismandlightandstudiedthemathematicalbasis.In1895,Marconiinventedthemethodoftransmittingsignalsoverlongdistancesbyelectromagneticwaves.In1899,thefirstradiotelephonesystemwasbuiltinCollinsta,USA.In1906,FessendenestablishedthefirstradiotelephonetransmitterintheUnitedStates.In1919,Britainestablishedthefirstradiostationtobroadcastlanguageandmusicprograms.In1921,humanbeingsfirstachievedshort-wavetransoceanictransmission.In1925,Beldinventedthefirstpracticaltelevision.In1930,microwavecommunicationwasrealized;now,peoplecantransmitinformationsuchastext,sound,dataandimagetoalldirectionsthroughelectromagneticwaves.02Applicationofelectromagneticwaves3.ElectromagneticSpectrumThegenerationmechanismandapplicationfieldsofelectromagneticwavewavelengthsareoftenverydifferent.Therefore,varioustypesofelectromagneticwavesareoftenarrangedinarowaccordingtothewavelength,whichiscalledelectromagneticspectrum.Accordingtothewavelengthofelectromagneticwaves,theyarearrangedinorderfromsmalltolarge,suchasg-ray,X-ray,ultravioletlight,visiblelight(purple,sputum,blue,green,yellow,orange,red),infraredlight,radiowaves(microwave,ultrashortwave,shortwave,longwave).Becauseoftheirdifferentproperties,therearemanydifferentuses.02ApplicationofelectromagneticwavesRadiowaveisanelectromagneticwavegeneratedbytheoscillationoffreeelectronsinaradioantennaundertheactionofanelectromagneticfield,andhasawavelengthrangeof0.75×10-3to1×104m.Sincetheelectromagneticwavepropagationmodesandcharacteristicsofdifferentfrequencybandsaredifferent,theirusesarealsodifferent.Onethingthatneedsspecialattentioninradiofrequencyallocationistheinterferenceproblem.Therefore,iftwostationsoperateinthesamearea(S)andthesametimeperiod(T)withthesamefrequency(F)orveryclosefrequency,interferencewillinevitablyoccur.3.ElectromagneticSpectrum02ApplicationofelectromagneticwavesG-rayisanelectromagneticwaveemittedbyradioactivematerial.Itswavelengthislessthan2x10-10m.Itisakindofphotonflowwithgreatenergy.Inmedicaltreatment,g-raycanbeusedasa"surgicalknife"(calledgknife)toremovetumors.Ithasagoodtherapeuticeffect.X-rayisanelectromagneticwaveproducedbyX-raytube.Itswavelengthrangeis10-15-10-7m.X-rayhasdifferentpenetratingpowerfordifferentdensitiesofsubstances.Itisoftenusedinmedicalexamination.Inairportsafetyinspection,X-rayisalsocommonlyusedforluggagefluoroscopy.Ultravioletray:Whenthephotoelectriccurrentpassesthroughtheionizedgasbetweenthetwoelectrodes,itproducesultravioletrays,whosewavelengthis4*10-8~4*10-7m.Sunlightcontainsultravioletrays,whichcanstimulatefluorescence.Fluorescentlampisakindoflampthatusesultravioletraysinsidethetubetostimulatethephosphorcoatedontheinnerwallofthetubeandemitsasimilarspectrumofsunlight.Ultravioletradiationisalsocommonlyusedinmedicalsterilizationandanti-counterfeitingtechnology.3.ElectromagneticSpectrum02ApplicationofelectromagneticwavesVisiblelightisanelectromagneticwavethatcaninducehumanvisualsensation.Itswavelengthrangeis0.4×10-6～0.8×10-6m.Solarenergyemitsvisiblelight,whichiscomposedofsevencolors(red,orange,yellow,green,blue,indigo,purple)indifferentproportion.Infraredrayisanelectromagneticwaveemittedbyaburningobject.Itswavelengthrangeis0.8×10-6～1×10-3m.Itwillcausethetemperatureoftheobjecttorise.Infraredelectromagneticwavecanformthermalimagingonaspecificinfraredsensitivefilm.Microwaveisaveryshortwavelengthradiowavecommonlyusedinradarequipment.Itswavelengthrangeis1×10-3～1m.Becauseofthegoodorientationofmicrowave,thetimeoftransmittingandreflectingwaveisoftenusedtocalculatethepositionoftarget.Microwaveovenisakindofdevicethatcooksfoodwiththethermaleffectofmicrowave.Radiowaveisanelectromagneticwavegeneratedbytheoscillationoffreeelectronsintheradioantennaundertheactionofelectromagneticfield.Itswavelengthrangeis0.75×10-3～1×104m.3.ElectromagneticSpectrum02ApplicationofelectromagneticwavesFigure4ElectromagneticspectrumrangeforvariouscommunicationmediaRadiowaveMicrowaveInfraredVisiblelightUltravioletrayX-rayγ-rayDoublelineCoaxialwireRadio(AM)Radio(FM)TVchannelGroundmicrowavecommunicationSatellitecommunicationOpticalfiber02Applicationofelectromagneticwaves1.TermsRelatedtoElectromagneticWaves(1)TheRelationbetweenElectricField,MagneticFieldandPropagationDirectionTheelectricfieldvectorandmagneticfieldvectorofspaceelectromagneticwaveatanypointinspacearealwaysperpendiculartoeachotherandperpendiculartothepropagationdirection.Thiskindofelectromagneticwaveiscalledtransverseelectromagneticwave.Itspropagationdirectioncanbedeterminedbytheright-handrule.RightHandRule:Extendyourrighthand,pointyourfourfingersinthedirectionofelectricfield,bendyourfourfingersinthedirectionofmagneticfield,andthenpointyourthumbinthedirectionofelectromagneticwavepropagation.VariablemagneticfieldDirectionofpropagationVariableelectricfield02Applicationofelectromagneticwaves(2)PhaseAngleofElectromagneticWaveInthewayofelectromagneticwavepropagation,theelectricfieldintensityisdifferentatthesametimeinawavelengthrange.Theinstantaneousstateoftheintensity,directionandchangingtrendofthefieldatacertainpointiscalledthephaseoftheelectromagneticwave.Thephaseofelectromagneticwaveisusuallyexpressedbyangle,whichiscalledphaseangle.ItisusuallyexpressedbyΦ.Thephasedifferenceofthedistancebetweenwavelengthλis360o.Figure4.4-5Phaseangleofelectromagneticwave02Applicationofelectromagneticwaves(3)WavefrontThesurfacecomposedofpointswiththesamephaseinelectromagneticwaveiscalledwavefront.Thewavefrontofelectromagneticwaveissphericalwave.Farfromtheantenna,thewavefrontcanbeseenasaplane.(4)PropagationVelocityofElectromagneticWaveThepropagationspeedofelectromagneticwaveinvacuumisequaltothespeedoflightc.Thepropagationspeedofelectromagneticwaveinairisslightlylessthanthatoflight,butitcanbeapproximatelyconsideredtobeequaltothespeedoflight.(5)PolarizationofWavesWhenelectromagneticwavepropagatesinspace,itselectricfieldvectorvariesaccordingtocertainrules,whichiscalledpolarizationofelectromagneticwave.Theelectricfielddirectionofelectromagneticwaveiscalleditspolarizationdirection.Polarizationwaveofelectromagneticwaveincludeslinearpolarizationandcircularpolarizationwave,horizontalpolarizationandverticalpolarizationwave,etc.02Applicationofelectromagneticwaves3.TheWayofElectromagneticWavePropagationRadiowavecanbedividedintoskywave,groundwaveandspacewave.(1)GroundWavePropagationRadiowavesbelowtheHFband(<3MHz)propagatealongtheearth'ssurface(orseasurface)tothereceivingpoint,sotheyarealsocalledgroundwaves(surfacewaves).Mediumandlongwavesaremainlypropagatedbygroundwaves.Groundwave02Applicationofelectromagneticwaves(2)SkyWavePropagationTheradiowave(shortwave)workinginHFband(3MHz-30MHz)iscalledskywave.Skywavestravelinstraightlines,notalongtheearth'ssurface.Reflectionsandrefractionsoccurwhenskywavesreachtheionosphereataltitudesof60to200miles.TheionospherecanreflectskywaveshundredsofmilesawayfromEarth.Itcanrealizelong-distancetransmissionofradiosignals.02ApplicationofelectromagneticwavesIonosphereHFfrequencybandWhentheelectromagneticwaveenterstheionosphere,itwillcausetherefractionoftheelectromagneticwavebecausetheelectrondensityoftheionosphereisnotuniform.Theresultofcontinuousrefractionmaycauseelectromagneticwavestoreturntothegroundorpenetratetheionosphereintoouterspace.Thedegreeofionosphericrefractionofelectromagneticwavesisrelatedtothefrequencyofelectromagneticwaves,theelectrondensityoftheionosphereandtheincidentangle.Generallyspeaking,thehigherthefrequency,theharderitistorefract.Thehighertheelectrondensityandincidentangle,theeasiertheelectromagneticwaveistorefractbacktotheground.Thehigherthedensityoftheionosphere,thegreatertheattenuationoftheionospheretotheelectromagneticwave.Therefore,thedaytimeattenuationofshortwavepropagatedbyionosphericrefractionislarger.02ApplicationofelectromagneticwavesIonosphereHFfrequencyband(3)SpaceWave(DirectWave)PropagationBecauseofthehighfrequency,theelectromagneticwavewithworkingfrequencyabove30MHz(VHF,UHFband)willpenetratetheionospherewithoutreflecting,andthetransmissionlossalongthegroundislarge.Therefore,itcanonlypropagateinastraightlinepath,whichiscalleddirectwave.Alsoknownasline-of-sightpropagation.Television,satelliteandothercommunicationsignalsadoptthismodeoftransmission.IonosphereVHFUHFfrequencybandLine-of-sightregion02ApplicationofelectromagneticwavesBecausethepropagationmodesandcharacteristicsofelectromagneticwavesindifferentfrequencybandsaredifferent,theirusesarealsodifferent.Onethingthatneedsspecialattentioninradiofrequencyallocationisinterference.Becausetheelectromagneticwavepropagatesaccordingtothecharacteristicsofitsfrequencyband,thereisnolawtorestrictit.Therefore,iftworadiostationsoperateatthesamefrequency(F)orverysimilarfrequencyinthesamearea(S)andthesametimeperiod(T),itwillinevitablycauseinterference.Becausetheavailablerangeofmodernradiofrequenciesislimited,theycannotbeoccupiedindisorderandneedtobecarefullyplannedandutilized.Soinforeig