Polarization: FM & Television
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Polarization: FM & Television


This is a discussion on Polarization: FM & Television within the DTV | HDTV Reception and Antenna Discussion forums, part of the Over-the-Air (Antenna TV) category.

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  1. #1
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    Polarization: FM & Television

    Need some good backrounder on antenna and broadcast polarization.

    Like...

    What do most FM broadcasters use? And what percentage of stations use vertical, horizontal, both or other?

    Furthermore, do individual stations change the relative power to their vertical and horizontal antenna elements at different times of the day, like rush hour vs night time?

    Is there a handy website to find out information about local FM broadcasters practices with regards to polarization?

    Thanks.

    I know that all television broadasts are horizontal polarization.


  2. #2
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    Quote Originally Posted by EscapeVelocity View Post
    ...I know that all television broadasts are horizontal polarization.
    TV stations use horizontal, circular (elliptical) and some vertical polarization. You can look up individual TV station's polarization by entering the call letters at:
    http://www.fcc.gov/mb/video/tvq.html

    For FM:
    http://www.fcc.gov/mb/audio/fmq.html

  3. #3
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    Transmit polarity

    Quote Originally Posted by EscapeVelocity View Post
    Need some good backrounder on antenna and broadcast polarization.

    Like...

    What do most FM broadcasters use? And what percentage of stations use vertical, horizontal, both or other?

    Furthermore, do individual stations change the relative power to their vertical and horizontal antenna elements at different times of the day, like rush hour vs night time?

    Is there a handy website to find out information about local FM broadcasters practices with regards to polarization?

    Thanks.

    I know that all television broadasts are horizontal polarization.
    Virtually all FM is either circular or dual polarity because they hope to program to vehicle antennas (Vertical) and home antennas (Horizontal).
    Dual polarity requires twice the transmitter power for FM, and circular requires more transmitter power as well, but not quite as much as dual polarity, and of course, broadcasters want to avoid running more power than needed due to power costs.

    Polarity of TV antennas is normally horizontal, but circular polarity is sometimes used, but this requires more transmitter power as well. Circular polarization for TV is normally used in problematic or difficult reception areas where mountains and other objects can alter the polarity by reflection or refraction.

    Horizontal polarity has less atmospheric noise due to the fact that most natural and man made noise is usually vertically polarized, thus there is less natural horizontally polarized noise to deal with.

    The power levels for digital TV is always the same. You are required to run 90 to 100% of your assigned power levels at all times. Besides that, who is going to mount a vertically polarized antenna for channel 2 or 3 VHF. It would be as tall as a tower. LOL.
    Last edited by FOX TV; 10-26-2009 at 05:03 AM.
    WE ARE NOT SHEEPLE !!

 

 

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