Video Artifacts

Transmitter

The transmitter forms the composite vision waveform, generates and amplifies the television RF channel, and feeds the antenna system.

A broadcast transmitter forms video, modulates a carrier, and raises it to RF powerNTSC and PAL use quadrature amplitude-modulated chroma, with PAL reversing one colour-difference component on alternate lines. SECAM instead sends frequency-modulated colour-difference components on alternate lines. Each family produces a composite baseband waveform containing sync, blanking, luminance, and encoded chrominance. The diagram illustrates the common negative-vision-modulation case; System L instead uses positive vision modulation. The shaped vision signal is power-amplified, combined with the separately generated sound carrier, filtered, and sent toward the antenna feed.PAL · NTSC · SECAMCOMPOSITE VIDEONEGATIVE VISION AM · COMMON CASESYSTEM L: POSITIVE VISION AMSAME ENVELOPE · MORE RF POWERVISIONSOUNDVSBMAIN SIDEBANDTIME DOMAINSCHEMATIC CHANNEL OCCUPANCY · NOT TO SCALE01020304BROADCAST VIDEO FORMATIONVISION AM + VSB SHAPINGRF POWER AMPLIFICATIONRF OUTPUT + SOUND COMBININGPICTURE COMPONENTS + TIMINGTO ANTENNA FEED

PAL, NTSC, and SECAM define composite colour encoding; the associated RF system defines vision-modulation polarity, channel spacing, and sound. The diagram shows the common negative-AM vision case, while System LA French 625-line analogue television transmission system using positive vision AM; it was commonly paired with SECAM colour. uses positive vision AM. These are functional zones: VSBVestigial-sideband transmission keeps one full AM sideband and only a remnant of the other to reduce channel bandwidth. shaping may occur in an exciter or an RF filter. Sound generation is not expanded here, but its carrier is combined in the RF output system.

  1. 01Broadcast video formationSync, blanking, bandwidth, and standard-specific colour encoding
  2. 02Vision modulation and VSB shapingAM polarity and depth, carrier accuracy, non-linearity and sideband response
    • Overmodulation
    • Vision-carrier frequency error
    • Differential gain
    • Differential phase
    • VSB amplitude-response error
    • VSB group-delay distortion
  3. 03RF amplificationPower gain, linearity and supply stability
    • RF gain compression
    • RF intermodulation products
    • RF-stage incidental AM and power-supply hum
  4. 04RF output systemOutput filtering, vision/sound combining, impedance match and antenna feed
    • Output-filter amplitude and group-delay error
    • Vision-to-sound power-ratio error
    • Feeder mismatch and high VSWR