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SNR presence with not plugged it

Discussion in 'TiVo Roamio DVRs' started by dlongnecker, Feb 19, 2014.

  1. L David Matheny

    L David Matheny Active Member

    1,589
    1
    Jan 29, 2011
    SE Ohio
    My 4-tuner Roamio sometimes has trouble with a local PBS channel that has severe multipath problems. Right now DVR Diagnostics show something like:

    Signal Strength: 50%
    Signal Lock: Yes
    Program Lock: Yes
    ...
    SNR: 20dB
    RS Uncorrected: 2164260735
    RS Corrected: 0

    Uncorrected errors are not incrementing (much), and reception is fine. But earlier today I saw a V53 error and diagnostics something like:

    Signal Strength: -
    Signal Lock: No
    Program Lock: Yes
    ...
    SNR: 19dB
    RS Uncorrected: 2160000000 [millions less, but I don't remember]
    RS Corrected: 0

    And even with no (useable) signal, the uncorrected errors were climbing wildly. It appears that if the signal goes away, some of the other items just don't get updated, but errors are still counted even though they're meaningless. It doesn't make sense to say that there is no (useable) signal and synchronization with the transmitter has been lost, but yet the unit is locked onto a transport stream and able to count errors and calculate a SNR.

    IOW, if you disconnect your cable, any SNR shown is just a bogus artifact. And I will mention again that I have never seen the Roamio show any count of corrected errors. TiVo needs to clean up their software.
     
  2. nooneuknow

    nooneuknow TiVo User Since 2007

    3,554
    0
    Feb 5, 2011
    Cox Cable...
    I've found that most of the time, if a Tuning Adapter is involved, that corrected and uncorrected stay at zero in DVR Diags, but can be found under Tuning Adapter Diags.

    It's usually oddball situations, like you describe, where the uncorrected just keeps going forever, and everything else is also wonky in DVR Diags.

    I'm guessing that since a TA takes over tuning all channels, not just SDV, that it either makes sense that the cablecard entries in DVR diags are usually always at zero corrected/uncorrected (and is technically correct), or it could just be TiVo being lazy in carrying over the values. Perhaps it isn't as easy as one might think to carry over the values...

    Could you please educate me on what "multipath problems" are? It sounds like something I should know about.

    I'll probably find it with google, but I'd appreciate it in your own context.
     
  3. andyf

    andyf Active Member

    1,176
    2
    Feb 23, 2000
    Houston,...
    MultiPath is where the source signal (transmitter) bounces off objects (such as high rise buildings etc) such that the receiver (your antenna) receives multiple signals but off phase which can cause ghosting (in analog TVs) or interference.

    I'll let the experts explain better.
     
  4. L David Matheny

    L David Matheny Active Member

    1,589
    1
    Jan 29, 2011
    SE Ohio
    I think cable tuning is done by the cablecard, with the tuning adapter translating channel numbers so that the cablecard tunes the right physical channel and shows the right virtual channel number. In any case, I'm OTA only, so of course I have neither. If the tuner/demodulator chipset in my 4-tuner Roamio is operating correctly, I would think that there surely should be some correctable errors, yet none are ever shown in DVR Diagnostics, so maybe the TiVo isn't reading some chipset register correctly. And even if the chipset makes the mistake of continuing to count uncorrectable errors when no data is passing through it, the TiVo software should know to ignore those errors as meaningless.

    The multipath I was referring to is multipath interference, which can cause intermittent fading of broadcast signals, leading to signal strength fluctuation and digital dropouts. It can be static (from nearby buildings, bridges, hills, etc) or dynamic (from passing planes or trucks, moving tree branches, etc). Modern digital tuner/demodulator chipsets use digital signal processing to recognize and cancel out multipath signals within limits, but if the reflected signals are too strong or the delay is too great, the capabilities of the chipset can be overwhelmed. I'm no expert, but you can Google it for more. I believe some of my signals suffer from much static multipath, but little dynamic multipath.
     

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