Digital signal dropouts

Discussion in 'TiVo Series3 HDTV DVRs' started by borabora, Sep 1, 2007.

  1. borabora

    borabora New Member

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    0
    Aug 30, 2007
    I am the new owner of a Tivo HD on Comcast cable. Still waiting for my cable cards. Previously I used analog tuners only but I have started watching clear qam broadcasts (including HD) using the new Tivo. Every so often, digital cable channels go grey and disappear completely. I have done some debugging and here is what I found:

    - Dropouts can last from seconds to minutes
    - During a dropout, Tivo reports zero signal strength.
    - Not all digital cable channels are affected simultaneously but all digital channels are affected once in a while.
    - Analog channels are not affected.
    - Things seem to get worse in the evening
    - Dropouts seem to get more frequent when splitters are in the cable path (but that may be coincidence).
    - I test rigged a PC-based Qam tuner (Fusion) and established that on the same cable drop, the second tuner drops the channel at the exact same time.

    Since the second tuner drops the signal at the same time it's reasonable to assume that the Tivo box is not at fault. When the cable card installation occurs, no doubt the signal will be perfect but I want the cable guy to look into it anyway.

    Given the symptoms, is this likely simply a signal quality issue (even though not all channels are affected simultaneously and Tivo indicates zero signal strength) or is it more likely that some device (repeater) in Comcast's signal chain has some type of problem?

    I know this is not strictly a Tivo topic but hope some the experts may have ideas what causes this...?

    Also, when dropouts are recorded then the dropout period is skipped and during playback there simply is some macro-blocking and of course "missing material." I wonder if others have the same problem and categorize it as the famous macro-blocking problem.

    Thanks for any advice!!!

    BoraBora
     
  2. jfh3

    jfh3 Active Member

    4,471
    2
    Apr 15, 2004
    Denver area
    Get your cable company to come out and measure the signal level coming into your Tivo HD box. It should be as close to +0 dBmv as possible. A good installer should be able to put a meter on it and check things. THIS IS VERY DIFFERENT FROM WHAT THE TIVO BOX ITSELF REPORTS.

    Three things that tell me you probably don't have a good signal - it gets worse at night (temperature change), you have the same problem on a non-Tivo box, and splitters are involved (which cause signal loss).

    Ideally, you would have a direct feed into the Tivo HD, without your own splitters/amps. If not, get the signal adjusted to compensate as required.

    As for any of this being related to the THD macroblocking problem, as long as you don't have your CableCARDs installed and are running at the current 8.17b2 level, it's far more likely to be a cable signal issue than anything to do with the Tivo box.
     
  3. borabora

    borabora New Member

    45
    0
    Aug 30, 2007
    Thanks for your reply. While I suspect that you are right, I am still mystified why the signal disappears and reappears so abruptly simultaneously when using two different tuners. I would expect a varyingly bad signal to generate uncorrectable errors that would manifest themselves in artifacts rather than complete dropouts. It's more like a component in the signal chain turns on and off (but you are right that does not correlate with the apparent effect of splitters).

    For what it's worth, Tivo reports a signal strength of 97-100 when a channel works (and zero when it doesn't).

    By the way, I know that the macro-blocking issue is generally related to cablecard issues. My point was that there may be Tivo users who only view recorded shows and see artifacts due to signal dropouts and interpret them as cablecard-related macro-blocking.
     
  4. jfh3

    jfh3 Active Member

    4,471
    2
    Apr 15, 2004
    Denver area
    Could be something as simple as a bad connection and/or the cable moving.

    Anyway, have your cable company check things out.

    Remember also that there can be artifacts BROADCAST in the cable signal itself, due to errors/compression, etc.
     

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