PrinciplesofTV
ThemethodofusingelectricityforTVinstantlytransmitsvisualimagesoftheevent.Similartomovies,televisionusesthevisualresidualeffectofthehumaneyetodisplayaframeofgradualstillimagestoformavisuallymovingimage.ThetransmittingendoftheTVsystemconvertseachminutepartofthesceneintoelectricalsignalsaccordingtobrightnessandchromaticity,andthentransmitstheminsequence.Atthereceivingend,thebrightnessandchromaofeachminutepartaredisplayedaccordingtothecorrespondinggeometricpositiontoreproducetheentireoriginalimage.TheTVsignalscanningsystemandchannelbandwidthofdifferentcountriesarenotexactlythesame.AccordingtotherecommendationsoftheInternationalRadioConsultativeCommittee(CCIR),theLatinalphabetisusedtodistinguishthem.
TVsignal
TheTVsignalissampled,transmittedandreproducedsequentiallyfrompointtosurfacebyscanning.TheTVscanningsystemofdifferentcountriesisdifferent.InChina,itis25framespersecondwith625linesperframe.Eachlineisscannedfromlefttoright,andeachframeisdividedintotwofieldsofoddandevenlinesfromtoptobottombyinterlacingtoreducethefeelingofflicker.Imageinformationistransmittedduringthescanningprocess,whenthescanningelectronbeamreturnsfromtheendofthepreviouslineforwardtothelineback-travelretracelinebeforethestartpointofthenextline,andaftereachfieldisscannedfromtoptobottom,itreturnstotheupperfieldback-travelreturn.Allsweeplinesshouldbeblanked.Duringthelineandfieldblankingperiod,thelineandfieldsynchronizationsignalistransmittedtosynchronizethescanningofreceivingandsending,soastoaccuratelyreproducetheoriginalimage.
TVcamera
TVcamerafocusesthelightimageofthesceneonthephotosensitive(orlightguide)targetsurfaceofthecameratube,andthephotoelectronexcitationorphotoconductivityateachpointofthetargetsurfaceThechangesvarywiththebrightnessofeachpointofthelightimage.Whenanelectronbeamisusedtoscanthetargetsurface,anelectricalsignalwhoseamplitudeisproportionaltothebrightnessofthelightimageofthesceneateachpointisgeneratedandtransmittedtotheTVreceivertomakethescanningelectronbeamofthekinescopescreenchangewiththestrengthoftheinputsignal.Whenscanningsynchronouslywiththesendingend,theoriginalimagesentwillappearonthescreenofthepicturetube.
TheprocessofTVsignaltransmissionanddistributiontakeslivebroadcastsinothercitiesasanexample,generallyfromcameras,TVcentersorOBtrucks,throughmicrowaverelaylines,transmitterstations,andfinallytouserTVreceivers.Inaddition,televisionbroadcastingsatellitesandcabletelevisionarealsoeffectivemeansfornationalandurbanregionaltelevisiontransmissionanddistribution,respectively.
TVsystem
TheTVsignalscanningsystemofvariouscountriesisnotexactlythesameasthechannelbandwidth.AccordingtotherecommendationsoftheInternationalRadioConsultativeCommittee(CCIR),theLatinalphabetisusedtodistinguish.Forexample,Mrepresents30framespersecond,526linesperframe,andthevideobandwidthis4.2MHz,plusthetotalhighfrequencybandwidthoftheresiduallowersidebandofFMaudioandAMvideois6MHz;DandKrepresent25framespersecond,625perframeOK,thevideobandwidthis6MHz,andthehighfrequencybandwidthis8MHz.ThefullTVsignalofthevideobasebandandtheaudiosignalarerespectivelymodulatedtotheVHForUHFfrequencybandforbroadcasttransmission.
Inadditiontoincludingthescansandchannelsthatarethesameasthoseofblack-and-whiteTV,whicharedistinguishedbyLatinletters,differentcolorTVsystemsareformedaccordingtothedifferentencodinganddecodingmethodsofthethreeprimarycolorsignalsatthetransmittingandreceivingends..Thebroadcastcolortelevisionsystemrequirescompatibilitywithblack-and-whiteTV,thatis,black-and-whiteTVsetscanreceivecolorTVbroadcasts,andcolorTVscanalsoreceiveblack-and-whiteTVbroadcasts,butalltheyreceiveareblack-and-whiteimagesandaccompanyingaudio.Tothisend,colorTVsarebasedontheprincipleofmixingacertainproportionofthethreeprimarycolorsintheadditivecolormixingmethodintovariouscolorsincludingwhitelight.Atthesametime,inordertobecompatibleandcompressthetransmissionband,red(R)andgreen(G)aregenerallyused.Thethreeprimarycolorsignalsofblue(B)andblue(B)composethebrightnesssignal(Y)andthetwocolordifferencesignals(BY)and(RY)ofblueandred.Thebrightnesssignalcanbeusedtotransmitblackandwhiteimages,andthecombinationofthecolordifferencesignalandthebrightnesssignalcanrestoreThreeprimarycolorsignalsofred,greenandblue.Therefore,compatiblecolorTVsnotonlytransmitthesamebrightnesssignalandaudiosignalasblack-and-whiteTVs,butalsotransmitchrominancesignalsatthesametimeinthesamevideofrequencyband.Thechrominancesignaliscomposedoftwocolordifferencesignalsmodulatingthecolorsubcarriersatthehighfrequencyendofthevideofrequencyband.Inordertopreventthemodulationofthecolordifferencesignalfrombeingoverloaded,theblueandreddifferencesignals(BY)and(RY)arecompressedandcompressed.ThefollowingblueandreddifferencesignalsarerepresentedbyUandV.
NTSCisacompatiblecolortelevisionsystemofficiallybroadcastintheUnitedStatesin1954,andisalsousedinCanada,Japanandothercountries.NTSCistheabbreviationofNationalTelevisionSystemCommittee(NationalTelevisionSystemCommittee).Thissystemisbasedonthehumaneye’sweakestabilitytodistinguishcolordetailsbetweenblueandmagenta,andthestrongestabilitytodistinguishcolordetailsbetweenredandyellow.ItusesthecolordifferencesignalQandredbetweenblueandmagenta.ThecolordifferencesignalIbetween,andyellowreplacestheblueandreddifferencesignalsUandV.UseQandIcolordifferencesignalstoperformquadraturebalanceamplitudemodulationontwoco-frequencycolorsub-carrierswithinitialphaseanglesof33°and123°tofacilitatedecoding,separationandsuppressionofsub-carriers.Themodulatedtwocolor-differencesignalsaremixedtoformChrominancesignal.Inordertoperformsynchronousdetectiononthechrominancesignalatthereceivingend,itisnecessarytousethehorizontalblankingperiodatthetransmittingendtosendanexcellentsynchronizationsignal.Thissystemischaracterizedbysimpledecodingcircuitandlowcost.
ThePALsystemwasdevelopedbytheFederalRepublicofGermanyin1963toreducethephasesensitivityoftheNTSCsystem.Itwasofficiallybroadcastin1967andisalsousedincountriessuchastheUnitedKingdomandChina.PAListheabbreviationofPhaseAlternationLine.ThissystemusesUandVcolordifferencesignalstoperformquadraturebalanceamplitudemodulationontwoco-frequencycolorsubcarrierswithinitialphasesof0°and90°,andinvertthecolordifferencesignalsoftheVcomponentlinebyline.Inthisway,thephasedeviationofthechrominancesignalisaveragedbetweenadjacentrowstobecancelled.Thecharacteristicofthissystemisthatitisnotverysensitivetophasedeviation,andislessaffectedbytheappearanceofghostingcolorsduetomultipathreceptionduringtransmission.
TheSECAMsystemwasofficiallybroadcastinFrancein1967.ItisalsoacompatiblecolortelevisionsystemdevelopedtoimprovethephasesensitivityoftheNTSCsystem.ItisalsousedintheSovietUnionandsomeEasternEuropeancountries..SECAMistheabbreviationofSéquentialCouleuràMémoire(SéquentialCouleuràMémoire).Whentheluminanceandchrominancesignalsaretransmittedatthesametime,thesendertransmitstheredandbluedifferencesignalslinebyline.However,whendecodingatthereceivingend,itisnecessarytohaveboththebrightnessandredandbluedifferencesignalstorestorethered,green,andblueprimarycolorsignals.Therefore,thedelaylineisusedinthereceivingdecodertostoreoneofthereceivedcolordifferencesignalsforoneline.,Andthenwiththereceivedbrightnessofthenextline(whichhasbeendelayedbyonelineatthesender)andanothercolordifferencesignaltoformthreesignalsfordecoding.Thechrominancesignalisformedbyfrequencymodulationofthetwocolordifferencesignalsofredandbluerespectivelytotwocolorsubcarrierswithacertainfrequencyinterval.Thecharacteristicofthissystemisthatitislessaffectedbythemultipathreceptioninthetransmission.
FullTVsignalThecompositesignalofthetransmissionimageintheTVvideobaseband.ThefullTVsignalofblack-and-whiteTVincludes:line(horizontal)andfield(vertical)scanningsynchronizationandblankingsignalsduringthescanningbackwardtravelperiod,andtheblackandwhiteluminancesignalduringthescanningforwardtraveltime.Amongthem,thesynchronizationsignalsynchronizesthescanningofthereceivingandsendingtoensurethestablereproductionofthereceivedimage;theblankingsignalisusedtoeliminatetheinterferenceoftheflybackbrightline;theblackandwhitebrightnesssignalisusedfortheblackandwhiteorcolorTVtoreceivetheblackandwhiteTVimage.
Etymology
In1934,SunMingjingworkedasYangJianchu’sassistantattheSchoolofScience,NanjingCentralUniversity,anddevelopedChina’sfirstsetofcamera-capable,transmission,ReceivedandbroadcastedTVprincipleprototype.YangJianchuidentified"TV"asthecorrespondingnameoftelevisioninChinese.
In1939,SunMingjingofficiallylisted"TV"asthethirteenthcourseofJinlingUniversity,and"TV"officiallybecameaChineseuniversitycourse.
Systemstructure
Signalsystem
TheTVsignalsystemincludesthreeparts:thepublicsignalchannel,thesoundchannelandthefinalstagecircuitofthevideoamplifier.TheirmainfunctionsareAmplifyandprocessthereceivedhigh-frequencytelevisionsignal(includingimagesignalandaudiosignal),andfinallyreproducetheimageonthefluorescentscreen,andrestoretheaudiointhespeaker.Itiscomposedofhigh-frequencyamplifier,mixerandlocaloscillator.
Thefunctionofthehigh-frequencyamplifieristoselectandamplifythehigh-frequencyTVprogramsignalreceivedbythehigh-ratedtuner,andobtaintheimagemiddle-frequencysignalandtheaudiointermediate-frequencysignalthroughthemixingprocess.
Theroleoftheacousticsurfaceoftheintermediatefrequency(firstintermediatefrequency)signalistoformtheamplitude-frequencycharacteristicsoftheimage.
Theroleofpre-amplifier:amplifythesmallsignal(20dBamplifyasmallamount)tocompensateforthesignallossofthesurfaceacousticfilter.
Thesurfacefilterrealizestheimpedancematchingbetweenthehigh-pricedtunerandtheimageamplifier.
ACC(automaticgaincontrol)circuit:Bycontrollingthegainofthemid-ampandhigh-amplificationcircuits,theamplitudeofthevideosignalvoltageoftheAGCandANCoutputbythedetectorisbasicallystable;
ANC(Automaticnoisesuppression)circuit:toreducetheinfluenceandinterferenceoftheexternalnoisesignaloftheTVontheTV.
Scanningsystem
TheTVscanningsystemincludesasynchronizationcircuit,alinescanningcircuit,afieldscanningcircuit,apicturetubeanditspowersupplycircuit.Themainfunctionofthescanningsystemistoformanormalgratingonthephosphorscreenofthepicturetube.
TheamplitudeseparationcircuittakesadvantageofthehighestamplitudeofthesyncsignalinallTVsignals,takesoutthecompositesyncsignalandtheintegrationcircuitusesthefeaturethatthewidthoftheverticalsyncsignalismuchsmallerthanthewidthofthehorizontalsyncsignaltosynchronizetheverticalThesignalisseparatedfromthecompositesynchronizationsignaltocontrolthefieldscanningcircuittoachieveTVfieldscanningsynchronization.
TheseparationmethodoftheintegralcircuitisalsocalledthewidthseparationAFCcircuit.ThefunctionoftheAFCcircuitistoautomaticallyrealizethelinesynchronization.Theprincipleistotakethehorizontalsynchronizationsignaloutofthecompositesynchronizationsignal,compareitwiththehorizontalfrequencysawtoothplatingsignalfedbackfromthelineoutputstageofthemachine,andthenoutputtheerrorcontrolvoltagetoadjustthefrequencyandphaseofthehorizontalscanningtorealizethehorizontalTVsynchronizationcircuit.
Powersupplycircuit
ThefunctionoftheTVpowersupplycircuitistotransform(step-down)the220VACvoltageprovidedbytheTV,andthenrectify,filterandstabilizeittomeettherequirementsThestableDCvoltageissuppliedtoeachpartofthecircuit.
Developmenthistory
Birthprocess
Christmas1883
TheGermanelectricalengineerNipkovusedhisinvented"NipThe"KoffDisk"usedamechanicalscanningmethodtoconductthefirstexperimentoftransmittingimages.Eachpicturehas24lines,andtheimageisquiteblurry.
In1908
KembelSwinton,EnglandandRoschenkofffromRussiaputforwardtheprincipleofelectronicscanning,whichlaidthetheoreticalfoundationfortelevisiontechnology.
1923
Oneoftheinventorsoftelevision,theSoviet-AmericanZwarikin(alsotranslatedasVeratimirSforodin)inventedtheelectrostaticstoragecameratube.In1923,inventedtheelectronicscanningpicturetube,whichwasthepioneeroftelevisionphotography.
In1925
BritishJohnRockyBairdcarriedoutnewresearchworkbasedonthe"NipkovDisc"andinventedamechanicalscanningTVcameraandreceiver.Atthattime,theresolutionofthepicturewasonly30lines,thescannercouldonlyscanthescanningarea5timespersecond,andthepictureitselfwasonly2incheshighandoneinchwide.PerformedtothepublicinasmallshopinLondon.
In1926
Oneoftheinventorsoftelevision,Baird,gaveabroadcastandreceptionperformancetotheBritishpress.
1927—1929
BairdconductedthefirstelectromechanicalTVtrialbroadcastviatelephonecable;thefirstshortwaveTVtrial;theBritishBroadcastingCorporationbegantobroadcastTVprogramscontinuouslyforalongtime.
1930
RealizethesimultaneousbroadcastingofTVimagesandsound.
1931
ThefilmwasputontheTVscreenforthefirsttime.PeoplewatchedthelivebroadcastofthefamousBritishlocaljockeyclubontelevisioninLondon.AmericanFerroFarnsworth,oneoftheinventorsoftelevision,inventedatubetelevisiondevicethatcanproject25imagespersecond.
In1936
TheBritishBroadcastingCorporationadoptedBaird'selectromechanicaltelevisionbroadcasting,andforthefirsttimebroadcastedtelevisionimageswithhighdefinitionandenteredthepracticalstage.
In1939
AmericanRadioCorporationbeganbroadcastingall-electronictelevision.SwissPhilipinventedthefirstblack-and-whiteTVprojector.
1940
U.S.Guermadevelopedanelectromechanicalcolortelevisionsystem.
December17,1949
ThefirsttelevisioncablelaidbetweenLondonandSudenCalfelterwasputintouse.
1951
AmericanH.Loweinventedathree-gunshadowmaskcolorpicturetube,andLorenzinventedasingle-shotcolorpicturetube.
In1954
TheTexasInstrumentsCorporationoftheUnitedStatesdevelopedthefirstall-transistortelevisionreceiver.
1966
AmericanRadioCorporationdevelopedintegratedcircuittelevisions.Threeyearslater,acolortelevisionreceiverwithanelectronictuningdevicewasproduced.
In1972
JapandevelopedacolorTVprojector.
1973
Digitaltechnologywasusedintelevisionbroadcasting,andexperimentsprovedthatdigitaltelevisioncanbeusedforsatellitecommunications.
1976
TheUKcompletedthestudyofthe"TVLibrary"system.Userscandirectlychecknews,books,newspapersormagazinesontheTV.
1977
ThefirstbatchofportableTVsetsweredevelopedintheUK.
1979
Theworld'sfirst"cableTV"wasopenedinLondon.ItwasinventedbytheBritishPostOffice.Itcantransmittheinformationinthecomputerthroughtheordinarytelephonelineanddisplayitontheuser'sTVscreen.
In1981
JapanSonyCorporationdevelopedapocketblackandwhiteTVwitha2.5-inchLCDscreenandbattery-powered.
In1984
Japan'sPanasonicCorporationlaunched"UniversalTV."Thesystem’spictureis3.6meterswideand4.62metershigh,whichisequivalentto210inches.Itcanbeplacedonasmalltruckandplayedinsmallstreetsandsquareswhereneeded.Thesystemusesthe"high-brightnesscolorluminoustube"exclusivelydevelopedbyPanasonic,whichcangetcolorfulandbrightimagesoutdoorseveninthedaytime.
March17,1985
AttheTsukubaScienceWorldExpoheldinJapan,theultra-smallcolorTVwallbuiltbySonywasunveiled.Itislocatedonthecentralsquare,40meterslong,25metershigh,withanareaof1,000squaremeters,andtheentirebuildingisashighasa14-storybuilding.Itisquitea1857-inchcolorTV.Theultra-smallscreenconsistsof36smallluminousscreens,eachweighing1tonand1.8metersthick,with4linesand9workstotaling450,000colorluminouselements.Throughthecamerainstalledonthetop,variousactivitiesonthevenuecanbedisplayedatanytime,andvariousadvertisingvideosofSonycanbeplayed.
1985
BritishTelecom(BT)launchedanintegrateddigitalcommunicationnetwork.Itprovidesuserswithvoice,fasttransmissionchart,fax,slowscanTVterminalandsoon.November25,1991
Japan’sSonyCorporation’shigh-definitionTVbegantrialbroadcasting:itsscanninglineswere1,125,andtheimagequalitywasimprovedby100%;theaspectratioofthescreenwaschangedfromthetraditional9:12to9:16.Theviewer’ssenseofpresenceisenhanced;theviewingangleoftheflatcamerahasbeenexpandedfrom10degreesto30degrees,andthemaphasamoresenseofdepth;the“pixels”oftheTVsurfaceimagehaveincreasedfrom280,000to1.27millionunitsofinformationinonefellswoopIncreasedbynearly4times...Therefore,thedistancetowatchhigh-definitionTVisnot7timesofthepreviousscreenheightbut3times,andtheaccompanyingsoundisrealistic,using4-channelhigh-fidelitystereo,whichisfullofappeal.
1995
Japan’sSonyCorporationlaunchedanultra-miniaturecolorTVreceiver(ie,palm-typecolorTV),whichisassmallasapalmandweighs280grams.Ithasaspeakerandaheadphonejack.TheLCDscreenisabout5.5cm.Thepicturelookssmall,buttheimageisclear.Itsmostobviousfeatureis:thehumanbodyisusedasanantennatoobtaintheviewingeffect,andthetwoleadsareusedwhenwatchingTV.Putitaroundyourneck,youcangettheeffectofanoutdoorantenna.
1996
Japan’sSonyintroducedthe"wall-mounted"TVtothemarket:itslengthis60cm,widthis38cm,anditsthicknessisonly3.7cm,anditsweightisonly1.7kg,justlikeoneAmural.
DevelopmentofChina
September2,1958
mycountry’sfirstTVsetwassuccessfullymanufactured,andblack-and-whiteTVbegantobebroadcast,andcorrespondingTVsetswereestablishedindustry.
In1973,colorTVwaspiloted.
OnAugust10,2019,HuaweireleasedtheHonorSmartScreen.
Patentapplication
Bairdapplication
Withtheinventionofthetelephonein1875andthedevelopmentofradioandfilmtechnology,manyscientificandtechnicalpersonnelbegantostudyimagetransmissiontechnology,thinkingApplyingthelatestscientificandtechnologicalachievements,photoelectricconversionofstillormovingscenesandimagesiscarriedout,andelectricalsignalsaresentoutsothatthepicturescanbereproducedinotherplacesinrealtime.TheBritishengineerJ.L.Baird(JohnLogieBaird)whofirstinventedandrealizedsuchaTVsystem.BairdappliedtotheBritishPatentOfficeforthetitle"Systemfortransmittingimages,portraitsandscenesthroughwiredorradiowavecommunication"onJuly26,1923,andwasauthorizedonOctober9,1924.ThepatentnumberisGB222604..Thesystemisnotsomuchelectronicasitismechanical.ItisbasedonPaulNiphow,aRussian-GermanfromBerlin,Germany.TheGermanpatentDE30105named"ElectronicTelescope"in1884,the"ElectronicTelescope"consistsoftwoidenticalrotatingdisks,oneonthetransmitterandtheotheronthereceiver.Eachdiskhas24squareholesandaphotoelectrictubeforimagetransmission.Itisbasedontheconceptofmovingimages,thatis,whenaseriesofstillimageschangefastenough,itwillproducetheeffectofmovingpicturesvisually.However,duetotechnicalreasons,thepatenthasnotbeenimplemented.
Theabove-mentionedBairdpatentsuggestsamethodandsystemfortransmittingimages,portraitsandscenes.Eachareaofthesceneissuccessivelyprojectedonthephotosensitiveelement,andthereceiverusesthecurrentcausedbythephotosensitiveelement.Thechangelightsupaseriesofsmalllightssettothescreen,andthechangingilluminanceofthesesmalllightsonthescreenformsareproductionoftheoriginalpicture.Theinventionwillbefurtherdescribedbelowwithreferencetothedrawingsandembodiments:thesceneortargetAtobetransmittedisfocusedonarotatingdiskDthroughalensBtoformanimageC,andthediskDispiercedwithaseriesofsmallholesarrangedinaspiralline.ImageCcanbe1inchx1inch,andthediameteroftheholeonthediskcanbe1/18inch(or1/32inch).Theseholesaredistributedabout1inchcircumferentially.Thesecondholeis1/18inch(or1/32inch)closertothecenterthanthefirsthole,andthethirdholeis1/18inchclosertothecenterthanthesecondhole.Inch(or1/32inch),andsoonuntilthe18thhole(or32ndhole),sothatwhenthediskDrotates,eachpartofthepicturetobeconveyedpassesthrougha1/18inchoneafteranother.Inchholes(or1/32inchholes).ThereisaphotosensitiveelementEatthebackofthedisc.DifferentlightisappliedtothephotosensitiveelementthroughtheperforationM,whichcausesachangeinthecurrentflowingfromthebatteryFthroughthephotosensitiveelement,andthechangingcurrentisreducedthroughathermionicvacuumtube,etc.,throughawireorThecomponentsaretransportedtothereceiver.ThereceiverisequippedwithanarmGthatrotatesincompletesynchronizationwiththediskDofthetransmitter.TheendofthearmhasabrushandcommunicateswithaseriesofcontactsH,andeachcontactisconnectedtoasmalllight.,AndtheselightsarearrangedinrowsandcolumnstoformascreenK.Eachholescansastripofthepicture,andthestripisreproducedbyacolumnoflightsonthereceivingscreen,sothateachholehasitscorrespondingcolumnoflightscorrespondingtoit.Manylightscanbeused,andthemorelightsthebetterthepicture.Ifthecorrespondingmomentaryholefacesthebrightpartofthepicture,thelightwillbeverybright;ifthemomentaryholefacestheblackpartofthepicture,thelightwillbedim;thedifferentbrightnessofthelightonthescreenreproducesthepicture,thusforminganimage.
Bairdwasbornin1888.HestudiedatLatchfieldHighSchool,RoyalCollegeofTechnologyandGlasgowElementarySchool,butdroppedoutofschoolduetotheoutbreakoftheFirstWorldWar.Hewasanunsuccessfulbusinessman.Whenhestartedhisresearchwork,hewasverypoorandhadnofunds.Hehadtousewasteitemssuchasteaboxes,biscuitboxes,wires,wax,etc.,tomakeexperimentaldevicesbyhimself.Eventherotatingdiscsweremadeofcards.Madeofcardboard,thepictureis30linesfromthetoptothebottom,anditistransmitted10timespersecond.
In1924,hesuccessfullylaunchedasmallpictureoftheMalteseCrosswithinafewmeters.OnOctober2,1925,hefinallysucceededinmakingthefaceoftheyoungworkerWilliamTaynton(WillianTaynton)appearonthetelevision.Hesignedacontractwithadepartmentstoreforremunerationfortelevisiontransmissionperformance,andcontinuedtoimprovethesystem.
In1928,Bairdbegantoofficiallybroadcastitstelevisionsystem,andbegantoresearchandexperimentwithcolortelevision.
In1929,theBritishBroadcastingCorporation(BBC)signedalicensecontractwithBairdtousehisinventiontobroadcasttelevisiononatrialbasis.
In1936,theBBCusedradiotorealizetimedtelevisionbroadcastingforthefirsttimeintheworld.However,Baird'sTVadoptsthelimitationsofthemechanicaltechnicalroute.Despitehissmallefforts,thequalityofthetransmittedimageshasalwaysbeenproblematic.Thescanningaccuracyislimitedbytherotationspeed,theimageclarityisnotenough,andtheflickeringimagescauseheadachesfortheaudience.Itwasveryactiveinthisfieldatthattime.WhenBairdwasengagedintheresearchofTVsystemsbasedontheprincipleofmechanicalscanning,Americaninventorswereconductingresearchonelectronicscanning,tryingtoadoptanothertechnologicalroute—electronicTVsystems.
Zwolkin
Russian-AmericanengineerVladimirK.Zwolkin(VladimirEworykin)JappliedforonDecember29,1923,onDecember1938TheUS2141059patent,whichwasapprovedandpublishedonlyonthe20th,inventedtheCRTandcameratubetechnologyandtheTVsystem,layingthefoundationfortheelectronicTVsystem.AlthoughtheelectronicTVsystemwasnotperfectatthebeginning,theeffectwasnotasgoodasthemechanicalone,but,ThankstotheeffortsofZwolkin,AmericanWirelessCompanyandBritishEMICompany,thetechnologyhasmaderapidprogress.Forexample,thescanninglinewas48linesin1929and343linesin1935.
AlthoughZvolkin'spicturetubemakesTVpractical,itcannotmakeTVbroadcasteasyorperfect."Photoelectriccameratube"-asitisoftenmentionedbyTVcrews-canproduceclear,clearimages,butisnotverysensitivetolight.Inbrightdaylight,everythingisnormal,butinastudio,ahugeamountoflightisneeded—morethantheamountoflightrequiredbythefilmindustry.Theheatlevelexceeds100degreesFahrenheit,andactorsandactressesneedmakeup(includingthickeyeshadowboxesandlipgloss)tooffsetthedazzlinglightemittedbytheoldarclamps.Zvolkinandhisteamhavetoremedythis!
Attheendof1936andearly1937,twosystems,EMI’selectronictelevisionsystemandBaird’smechanicaltelevisionsystem,weresetupinAlexandraPalaceinthenorthofLondon,England.Useitinturntocomparewhichofthetwosystemsisbetter.Thefirst-classelectronicvarietytechnology.Threemonthslater,theBBCtoldBairdtoshutdownhissystem.Theelectronictelevisionsystemhasbecomethemainstreamtelevisionsystem.BairddiedinSussex,Englandin1946.Bexhill(Sussex).
Controversialevent
TVisnotaninventionofanyone.Itistheresultofasmallgroupofpeopleindifferenthistoricalperiodsandcountries.Asearlyasthenineteenthcentury,peoplebegantodiscussandexploremethodsoftransformingimagesintoelectronicsignals.In1900,theterm"Television"hadalreadyappeared.
Peopleusuallyregardtheimageofthepuppets"scanned"inanexperimentconductedbytheScotsmanJohnLogieBairdinLondononOctober2,1925asasignofthebirthoftelevision.,Heisknownasthe"fatheroftelevision."However,thisviewiscontroversial.
Because,alsointhatyear,theAmericanVladimirZworykinshowedhisTVsystemtohisbossatWestinghouse.
Althoughthetimeisthesame,thetelevisionsystemsofJohnLogieBairdandVladimirZworykinareslightlydifferent.Historically,thetelevisionsystemofJohnLogieBaird(JohnLogieBaird)wascalledamechanicaltelevision,whiletheSforogen'ssystemwascalledanelectronictelevision.Thisdifferenceismainlyduetothedifferentprinciplesoftransmissionandreception.
Thedevelopmentoftelevisioniscomplicated.Manypeopleweredoingthesameresearchatalmostthesametime.
AmericanRCAlaunchedblackandwhitetelevisionsin1939,setthenationalcolortelevisionstandardin1953andlaunchedRCAcolortelevisionsin1954.
Classification
Fromtheuseeffectandappearance,itcanberoughlydividedinto5categories:flat-screenTV(plasma,LCDandsomeultra-thinwall-mountedDLPrearprojection),CRTpicturetubeTV(pureFlatCRT,ultraflatCRT,ultra-thinCRT,etc.),rearprojectionTV(CRTrearprojection,DLPrearprojection,LCOSrearprojection,LCDrearprojection),projectionTV,3DTV.
FullChinesename | Chinesealias | Englishname | Englishabbreviation | Runthenetwork | Terminal |
---|---|---|---|---|---|
WebTelevision | WebTelevision | WebTV | Internet | Computer | |
DigitalTelevision | DigitalTelevision | DTV | Satellitetransmission | TV | |
Internet TV | Interactive InternetTV | Protocol | IPTV | Broadbandnetwork | TV Computer |
MobileTV | CarTV | Wirelesscommunicationnetwork Wirelesstransmission | Mobilephone Displayscreen | ||
OutdoorTV | StoreTV | WirelessTransmission HardDiskUDisk DVD | Displayscreen |
Suggestion
ThecloserthepersonistotheTV,Thelesstheirritationis,themorelikelyitistocauseeyefatigue.Therefore,theplacementoftheTVshouldbebasedontheprincipleofadaptingtothephysiologicalrequirementsoftheeye.
Thebestpositionisthatthepersonis2.5-8metersawayfromtheTV,anditsheightisslightlylowerthantheeyelevel.Whentheheightistoohigh,itiseasytocausefatiguewhenyoulookup.Whenitistoolow,itiseasytofatiguebecauseyouneedtolookdown.Ofcourse,youshouldalsopayattentionnottoplacetheTVtooobliquely,otherwise,tiltingyourheadwillnotonlycausetheimagetobeunclear,butalsomorelikelytocauseeyefatigue.
WhenwatchingTV,youshouldtakeashortbreakfornomorethan60minutesatatime,preferablywithyoureyesclosed.Someonehasdoneasurvey,ifyouwatchTVformorethan4hourswithouttakingabreak,youcanlosetwolinesofvision(0.2).WatchingTVforalongtimeisnotonlyeasytomakethechild'sbodyweakandobese,butalsoeasytoformmyopia.Ifthechildisalreadysufferingfrommyopia,itisbestnottowatchTVformorethanhalfanhouratatime,andrestfor10minutes.
Inaddition,theroomshouldmaintainacertainbrightnesswhenwatchingTV.Thatistosay,thecontrastbetweenthebrightnessoftheTVandthebrightnessoftheroomaroundtheroomshouldnotbeverydifferent,otherwiseitwilleasilycauseeyefatigue,andwillalsopromotetheformationanddevelopmentofmyopia.Therefore,alow-intensitylampshouldbekeptindoors,anditsbrightnessshouldbesuitabletobeabletoreadthewritingofthebook.
Related
Screensize
ThescreensizeoftheTVisaparameterthatmeasuresthesmallestpossibledisplayscreenoftheTV.ItismeasuredbythediagonaloftheTVscreen.Thelengthofthe
,theunitisusuallyinches.
ThesizeoftheLCDTVscreenisthesizemarkedinthestrictproductmanual,becausetheLCDscreenisnotcoveredbytheframe.
Individualproductssoldinthemarkethavefalsedimensions,whicharemainlymanifestedas1-2cmlessthanthemarkedstandardsize,thatis,lessthan1inchofdistance.
Internetinteraction
TVisareal-timemedia,unlessitisrecorded,itcannotbereviewedorwatchedrepeatedly.However,thenetworkmediahasobviousadvantagesinthisregard.IthasprintmediathatcanbeviewedatanytimeIthasovercometheshortcomingsofpoortimeliness,lackofclassificationandlimitedspace,andhasbecomeafleetingdatabaseofTVprogramsandaclassifiedinformationlibrary.
InteractionisanimportantmeansthatTVmediahasbeenexploringtostrengthentheconnectionbetweenthespreaderandtheaudienceandunderstandtheaudience’sresponse.Thedevelopmentofnetworktechnologyhasallowedpeopletohaveadeeperunderstandingofthewordinteraction,andithasbeenwrittenintothelifeoftheaudienceandthemedia.ThecombinationofTVandtheInternetisthebestmarriage.ThenetworkabsorbsthecontentofTV,andTVusesthenetworkplatformtotrulyoptimizethetransmissioneffect.
SetTopBox
ForSetTopBox(SetTopBox),thereisnostandarddefinition.Broadlyspeaking,anynetworkterminaldeviceconnectedtoaTVcanbecalledasettopbox.Fromanalogchannelsupplementsandanalogchanneldecodersbasedoncabletelevisionnetworksinthepast,to"Villas"Internetset-topboxesthatconnecttelephonelineswithTVsets,andintegratedreceiverdecoders(IRDs)fordigitalsatellites(IRD),Digitalterrestrialset-topboxesandcableTVdigitalset-topboxescanallbecalledset-topboxes.Inanarrowsense,ifyouonlytalkaboutdigitaldevices,set-topboxescanbedividedintoInternetset-topboxes,digitalsatelliteset-topboxes(DVB-S),digitalterrestrialset-topboxes(DVB-T),andcableTVdigitalset-topboxes(DVB-C)accordingtotheirmainfunctions.AndthelatestIPTVset-topboxes.
DigitalTVset-topboxisoneoftheinformationappliances,itisakindofconsumerelectronicsthatallowsuserstowatchdigitalTVprogramsonexistinganalogTVs,andconductinteractivedigitalentertainment,educationandcommercializationactivities.product.
Internetvideo
IPTVisaninteractiveInternetTV.Itisakindofinfrastructurethatutilizesabroadbandnetwork.)”isthemainterminaldevice,providinguserswithnewtechnologiesthatprovideuserswithavarietyofinteractivedigitalmediapersonalizedservicessuchasvideo-on-demand,Internetaccess,ande-mailgames.NetworkTVsoftwarebasedontheP2Pprinciple,butdifferentfromotherP2PnetworkTVs,theserver-sidefunctionisopen,allowinguserstoaddprogramsbythemselves,andprogramsfoundontheInternetcanalsobeadded.BasedontheP2Pprinciple,programscanalsobeadded.
Teletext
Teletextisasubsidiaryserviceoftelevisionbroadcasting.TeletextisananalogTVsystem.TheTVscreendisplays25framesofTVsignalspersecond,with625linesperframe.Eachlinesweepsfromthelefttotherightofthescreen,andeachframeisdividedintotwofieldsandsweepsfromthetoptothebottomofthescreen.Ofthe625linesineachframe,only575linesareactuallydisplayedonthescreen,andtheother50linesarereversetravelandcannotbeseen.Inadditiontotransmittingtestsignals,thereverseprocesscanalsobeusedtotransmitadditionaldatainformation,includinggraphicsandtext.Atthereceivingend,viewerscanuseadedicatedteletextdecodertoviewthetransmittedinformationonthescreen.