Broadcast3164.pptx

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1、Broadcast BasicsWeek 13ICS 620BROADCAST BASICSICS 620Week 13IntroductionVideo Basics(Analog Systems)Transmission Systems Wireless(terrestrial)Wired(cable television)Digital Video(Two Weeks)Video StandardsStandards and PrincipalsPersistence of VisionThe rapid presentation of frames of video informati

2、on to give you the illusion of smooth motion.Frequency StandardsFrame Frequency16 Frames per Second(fps)Black and White24 fps SOFContinuity of ActionProblem of FlickerThe gross alteration of light and darkFrequency StandardsField FrequencyFrame Frequency x 2Continuity of IlluminationFilm Vs.VideoFil

3、m-Project a complete picture Video-Scan,line by line,at a high rate of speed-6 million bits per secondHow do we describe a picture?A picture element(“pel”or“pixel”)one at a timeFor each pel we need to somehow describe:Brightness(luminance)Hue(phase,“tint”)Saturation(color intensity,“chroma”)Vertical

4、 ResolutionThe picture quality associated with the number of dots(pixels)used to construct the picture.367,000 dots on 525 rows(vertical)Film vs.NTSC SpecsAspect RatioCamera TubesEarly Camera TubesImage OrthiconElectronic Scan(Camera Pickup Tube)Video SignalElectron BeamTargetLensObjectScanningProgr

5、essiveInterlace/OffsetInterlace ExampleNTSC:525 lines,30 frames/sec,60 fields/secPicture TubePicture TubePicture TubeScanning a Focused ImageProgressive ScanningInterlace ScanningSync PulsesDifferences Between Horizontal and Vertical Synch PulsesRate DurationVertical59.94/sec 1:3Horizontal 15,734.26

6、4/sec 3:1Waveform Sketch of a Video SignalA simple video waveformOne LineWaveform of Sync PulsesIRE Measurement ScaleVertical Blanking Interval(VBI)Lines 1-21 of each field Vertical Interval Test Signal(VITS)Vertical Interval Reference Signal(VIRS)Lines 1-9V-sync and Equalizing PulsesLines 12-14SMPT

7、E Time CodeLines 17-19VITS and VIRSLine 20Network Source Code(field 1)Line 21 Closed captioning(field 1)Kell FactorThe Ratio of effective resolution to the theoretical resolution is known as the Kell Factor.Vertical Resolution SummaryMax Lines/Frame=525Lost for Vertical Blanking=42(21 lines per fiel

8、d)Visible=525-42=483Kell Factor=72.5%Effective Resolution=350 linesHorizontal Resolution Summary(4.2 MHz Video Bandwidth)=4.2 cycles per microsecondx 52 microseconds(active scan)x 2 pixels per cycle=436 pixels per lineTelevision Transmission Picture Information Blanking pulses Sync pulses Audio info

9、rmationWhat about Color?Component Nature of ColorRGBVideo Color PaletteColor TelevisionR=RedG=GreenB=Blue B+G=CyanG+R=YellowB+R=MagentaNTSC Color BarsBlock Diagram of Color CameraGamma G A measurement of contrast,gamma correction is required because the brightness output of a camera does not corresp

10、ond to the brightness recognition of the human eye.Composite ColorY=Luminance SignalY=30%red+59%green+11%blueC=Chrominance SignalC=I Q MatrixColor MatrixSaturation=Amplitude of the I and Q signalsHue=Phase developed by the difference in amplitude between the I and Q signalsTransmitter TubeColor TV T

11、ransmitterTV Frequency Allocations 2-4VHF-Lo 54 MHz-72 MHz 5-6VHF-Lo 76 MHz-88 MHz 7 13VHF-Hi174 MHz 216 MHz14 59UHF470 MHz 746 MHzNOTE:Natural breaks occur between channels 4 and 5;channels 6 and 7;and channels 13 and 14.Each channel is 6 MHz wide.NTSC Bandpass Characteristics(Black and White)Color

12、 TV SignalNTSC Bandpass Characteristics(Color)Color TV SignalWorldwide StandardsNational Television System Committee-NTSC(1953)Phase Alternation Line-PAL(1967)Sequentiel Couleur Avec Memoire-SECAM(1967)World TV StandardsWorld TV StandardsPrincipal TV SystemsFM Stereo TransmitterTransmitter Output Ma

13、in Channel(L+R)Stereo Channel(L-R)19 kHz Pilot Sub-carrierStereo MultiplexingL+R Signal(Main Channel)L-R Signal(Stereo Channel)19 kHz Pilot Subcarrier(FM)The Math(L+R)+(L-R)=2 L(L+R)+(-L+R)=2 RFM Stereo ReceiverTelevision StereoMulti-channel Television Sound(MTS)Used to provide Stereo on conventiona

14、l NTSC TV broadcast(TV has been FM mono for most of its history)Television Transmission SystemsOver-the AirTerrestrial BroadcastingAntenna SystemsRadio Energy in Space300 million meters per secondE=MC2Speed of LightSpectrumWavelengthLambda(meters)Velocity(300,000,000 meters/sec.)Frequency(Hz)=v/fTV

15、StationWTHR-TVWTHR-TVCh.13(210-216 MHz)WAVELENGTH IN:A.MetersB.MilesC.FeetWTHR Television-Channel 13Indianapolis,Indiana Channel 13(210-216 MHz)316 kw visual 63.2 kw aural 980t/1,039gTelevision Factbook47 CFR 73.603Wavelength ExampleWTHR TelevisionMeters:Lambda=300/211.25=1.46 metersMiles:Lambda=.18

16、6/211.25=.00088 milesFeet:1 meter=3.28 feetLambda=1.46 meters x 3.28=4.79 feetAM StationWhat is the height of this AM station antenna tower operating at 540 kHz,in meters and feet?PropagationRadiation Patterns(Contours)AM-Tower as the AntennaFM/TV-Antenna on TowerTV PropagationTV Propagation MapFM P

17、ropagation MapKFMD-FM DenverAM TowerSide viewTop viewAM Directional TowersAM Directional PropagationIrregular Geographical PatternsRefractionReflectionAbsorptionInterferenceWhy Directional Arrays?Co-ChannelAdjacent ChannelOtherTypes of WavesDirect Waves(FM/TV)Ground Waves(AM)RadialsSwampy Soil vs.Sa

18、ndy TerrainSky Waves(AM at night)Types of WavesDirect WavesThe primary path of the direct wave is from the transmitting antenna to the receiving antenna.So,the receiving antenna must be located within the radio horizon of the transmitting antenna.Because direct waves are refracted slightly,even when

19、 propagated through the troposphere,the radio horizon is actually about one-third farther than the line-of-sight or natural horizon.Direct WavesGround WavesThe Earth has one refractive index and the atmosphere has another,thus constituting an interface that supports surface wave transmission.These refractive indices are subject to spatial and temporal changes.Ground WavesSky WavesSky waves,often called ionospheric waves,are radiated in an upward direction and returned to Earth at some distant location because of refraction.Sky WavesQuestionsandAnswers