Disappearing HD Channels
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Thread: Disappearing HD Channels

  1. #1

    Question Disappearing HD Channels

    Some HD channels keep disappearing and reappearing later. One time picture quality is perfect (and the signal strength is strong and steady). Next time the picture keeps breaking up or the TV shows "no signal." It does not seem related to weather. It's not even consistent across the different channels where this happens. What's going on and is there anything I can do about it?

  2. #2
    A common reason for the intermittent disappearance and reappearance of DTV reception is caused by multipath, or marginal system bandwidth problems at those particular frequencies. Here are some things to check on your end:

    1. Coax: How old is the coax between the antenna, any splitters, and your TV? Coax, especially when exposed to sun or heat over time, will allow signal leakage or change impedance, which compromises bandwidth, specially for UHF DTV channels. For the same reasons, is your coax cable running through a closed window or door that has squashed it over time? Also, is that coax a good quality RG6, and NOT RG59? RG59 is not suitable for use with reliable OTA DTV reception, but may have been already in the house from previous cable or analog TV days.

    2. Splitters: If you use cable splitters for multiple TV's, make sure they are rated to 2Ghz and not from Radio Shack. Old splitters are rated to 470Mhz (down hill with a tail wind), and are not suitable for modern DTV use. Also terminate all unused spigots on the splitter with 75 ohm terminating resistors. Un-terminated connections will alter the bandwidth and impedance of all distribution points, making for marginal bandwidth and potential signal leakage.

    3. Height of antenna: Not always possible, but an outdoor antenna at least 30 feet off the ground, gives you the best opportunity for watching OTA DTV. Antennas in attics, not so good.

  3. #3
    Quote Originally Posted by Kelly A View Post
    A common reason for the intermittent disappearance and reappearance of DTV reception is caused by multipath, or marginal system bandwidth problems at those particular frequencies. Here are some things to check on your end:

    1. Coax: How old is the coax between the antenna, any splitters, and your TV? Coax, especially when exposed to sun or heat over time, will allow signal leakage or change impedance, which compromises bandwidth, specially for UHF DTV channels. For the same reasons, is your coax cable running through a closed window or door that has squashed it over time? Also, is that coax a good quality RG6, and NOT RG59? RG59 is not suitable for use with reliable OTA DTV reception, but may have been already in the house from previous cable or analog TV days.

    2. Splitters: If you use cable splitters for multiple TV's, make sure they are rated to 2Ghz and not from Radio Shack. Old splitters are rated to 470Mhz (down hill with a tail wind), and are not suitable for modern DTV use. Also terminate all unused spigots on the splitter with 75 ohm terminating resistors. Un-terminated connections will alter the bandwidth and impedance of all distribution points, making for marginal bandwidth and potential signal leakage.

    3. Height of antenna: Not always possible, but an outdoor antenna at least 30 feet off the ground, gives you the best opportunity for watching OTA DTV. Antennas in attics, not so good.
    Excellent advice! My personal experience has taught me three more important OTA tips:
    1. Get the best UHF aerial that you can logistically use for your particular situation and add a rotator.
    2.Get the most high gain rf amp that you can.
    3. MAKE SURE THAT THE RF AMPLIFIER FM TRAP (OR FILTER) IS "IN" OR "ON"! This is the most important step you can make. The only continuous signals in the VHF/UHF spectrum are generally the FM stations. A powerful FM station can easily swamp a high gain amp. Even if only a UHF antenna is used. Please do yourself a gigantic favor and use the FM trap!

  4. #4
    The antenna is a ClearStream 2V - roof mounted. In particular, I've got two channels that disappear and reappear (not necessarily at the same time).
    No rotor, although the antenna is aimed in the direction of one of the two stations in question. I'll try an RF amplifier. Thanks.

    But any idea what causes channels to disappear and reappear like this? Never happened with analog.

  5. #5
    Quote Originally Posted by Oscar Madison View Post
    The antenna is a ClearStream 2V - roof mounted. In particular, I've got two channels that disappear and reappear (not necessarily at the same time).
    No rotor, although the antenna is aimed in the direction of one of the two stations in question. I'll try an RF amplifier. Thanks.

    But any idea what causes channels to disappear and reappear like this? Never happened with analog.
    The set manufacturers squelch the signal at a level that they arbitrarily believe is too low for good reception. 19 million bits per second is easy to mess up and hard to reassemble. A good example is a scanner with the squelch set too high to receive the weak signals.
    I got surprisingly good reception with a 4 bay UHF panel hung from a window. I didn't even need a rotator. The problem for my situation was an airport a few miles away. Planes approaching and leaving would cause multiplex and the signal would cut in and out. Sometimes maddeningly often with very slow recovery to boot. A high gain yagi, high gain amplifier and a rotator fixed reception to within reason.
    Of course, YMMV.

    WOW! I just saw how much your antenna cost on Amazon! You can get much more for much less! I grabbed an Antennacraft 10G202 high gain amp and an Antennacraft MXU 59 high gain yagi together for that price! Please be kind to yourself and look around for a better deal!
    Last edited by xyz; 05-22-2016 at 05:32 PM.

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