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Double Tvision

Discussion in 'Beginner Electronics' started by Robin Graham, Sep 9, 2004.

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  1. Robin Graham

    Robin Graham Guest

    A friend's TV has a ghost image. She lives in the New Forest and tells me
    that all TVs in the area are the same because of poor reception. She has a
    booster in the aerial system.

    Is the ghost image due to poor reception or actually something else (which
    is my feeling)? What else can be done about it? I can't believe in this day
    and age that someone should have to put up with a ghost image.

    Rob Graham
  2. Dana Raymond

    Dana Raymond Guest

    What you are describing is called "Multipath Distortion". Thats where an
    antenna system picks up a TV picture as well as a slightly delayed, weaker
    signal coming from reflections of the TV signal off of buildings. The ghost
    will be to the right of the main image and will usually be faint.

    NTSC TV broadcasts the picture with AM modulation, so the ghost is added
    into the picture. Audio is FM radio, and the TV will lock into the stronger
    TV signal - thats why ghosting only affects the image and not the sound.

    Now, if this only happens on one particular station, or other stations also
    have it but look different, then it probably really is multipath distortion.
    However, if it occurs on all TV stations and looks the same, then I would
    suspect a problem with the amplifier or cabling. If a cable is improperly
    terminated (bad cable, connectors, etc.) then you can get those reflections
    in the cable itself.

    Assuming that she has her own antenna, amplifier, and cabling, and the
    ghosting is the same on her neighbour's TV, then its definately Multipath

    The only solution: Get a highly direction TV antenna and an antenna rotator
    (available at Radio Shack!) and she can rotate the antenna to point directly
    at the transmitting antenna, reducing or eliminating the ghosting.

    BTW Ghosting and antenna rotators were common in the days when everyone had
    their own antenna. Cable systems started out at the community level and used
    seperate antennas pointing to each TV transmitter, and a combining power
    amplifier for distribution to the local community. The advantage was
    stronger TV signals with much less noise.

    We have been spoiled!
  3. Robin Graham

    Robin Graham Guest

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