Range for OTA HD reception

Discussion in 'DirecTV TiVo Powered PVRs & Receivers' started by AWAHOO, Jan 24, 2006.

  1. greywolf

    greywolf New Member

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    Apr 9, 2004
    Evanston IL
    In very strong signal areas, a variable attenuator may be needed. Do not used an amplified antenna.
     
  2. newsposter

    newsposter Poster of News

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    Aug 18, 2002
    SE PA
    try a paperclip out the coax jack just to see if that's big enough :) just kiddin
     
  3. Arcady

    Arcady Stargate Fan

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    Oct 14, 2004
    Philadelphia...
    Well, I received the HD tivo today. I plugged in an old set of rabbit ears (which has one "ear" that is half broken off) and I get signals in the 90's.

    Thanks for the help.
     
  4. greywolf

    greywolf New Member

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    Apr 9, 2004
    Evanston IL
    Mechanical attenuation. Clever.
     
  5. newsposter

    newsposter Poster of News

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    Sounds like a good idea for a patent.
     
  6. TyroneShoes

    TyroneShoes HD evangelist

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    Sep 6, 2004
    It's totally quantifiable, and measurable. ATSC 8VSB signals will unlock when the S/N ratio dips below 15 dB. IOW, if the background noise is at -29 dBmV at a point of reception (a common level for residential reception areas), a received signal will unlock at measured carrier level of -14 dBmV, which is the ratio of that signal being 15 dB above the noise floor. That's a theoretical number of course. In reality there can be dynamically changing environmental issues that can make it less than accurate, or maybe not exactly a hard cutoff at that ratio at every point in time.

    And that's a lot lower than NTSC. As long as there is signal lock, the ATSC picture will be perfect. In comparison, NTSC analog signals need to be a minimum of 43 dB above the noise floor to provide even acceptable PQ, although complete loss of sync lock won't happen until much lower (but the PQ suffers greatly).

    This also takes only signal levels into account. Interference can also cause a ATSC signal to unlock, because interference, even multipath interference, can be considered "noise". And if the ratio of such interference (that also can't be rejected by the tuner) with respect to the desired signal dips low enough, that can also thwart signal lock.

    S/N is not a measurement that the HR10 can make, but many TV sets can. Most Sonys have a S/N ratio measurement. As one example, my Sony reported a s/n ratio of 19 dB on the channel that was the worst for me, and which gave me occasional breakup (while all others were about 27-30 and did not break up).

    In theory that should have been good enough, and usually it was, but what I think that meant was that while the reading was usually pretty steady at 19, occasionally there was some impulse noise or other interference that would crest above the noise floor and briefly bring that ratio down below 15 dB, causing the signal to unlock briefly, and causing brief pixellation. Once I added an amp the S/N ratio on that worst channel went to 26 dB, and I have seen no problems since, probably because even with impulse noise disturbances, the S/N ratio still remains constanly at some point above 15 dB.

    ATSC provides for what they call "quasi-error-free" reception. In a real world hostile environment, even under perfect conditions you will see a brief breakup on the average of once every 24 hours or so. But this degrades exponentially, to once an hour for less than average conditions, then to about once a minute for poor conditions, to regular breakup in bad conditions. Most reception scenarios fall somewhere in between optimal and "less than optimal" once everything that can be done to improve reception has been done, so it is common to see a single breakup of a ATSC signal every few hours or so for many viewers.

    Sorry...gotta cut down on the Red Bulls :D
     
  7. newsposter

    newsposter Poster of News

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    Aug 18, 2002
    SE PA
    Well if you want that in english (big grin), I've found on the HDtivo any steady digital signal of 60 and above will produce a recordable picture with minimal to no pixels. Of course when you have a signal that low, even a tad of multipath kills the pic. That's why you gotta get the signal as high as possible so when the trees blow, you are only going from 85-65 not 60 down to 40 :)
     

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