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How does Roamio split signals?

Discussion in 'TiVo Roamio DVRs' started by kbmb, Oct 17, 2013.

  1. kbmb

    kbmb Active Member

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    Jun 22, 2004
    NH
    I'm curious....does anyone know the technology in how the Roamio is able to record 6 tuners at once? I'm assuming it isn't just splitting the signal internally right? Wouldn't that lead to a low quality signal? Or is it amping the signal internally?

    I'm curious because of my issue where I am seeing some channels, not all, start to have a lower signal and SNR in the diagnostics, while the rest remain 100%.

    Thanks for any info.

    -Kevin
     
  2. jmpage2

    jmpage2 New Member

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    You are thinking of this in traditional terms, that you need a "splitter" to split a single coax feed into six feeds.

    The TiVo has a digital cable m-card. This card can digitally decrypt six feeds from the coax line simultaneously. No splitting hokum needed.
     
  3. kbmb

    kbmb Active Member

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    Jun 22, 2004
    NH
    Cool thanks for the info. Kinda figured it would split them in a traditional sense.

    Do you think the Roamio amps the signal internally at all? The only reason I ask is, I get different readings of SNR from the Roamio vs. if I hook up my Comcast Moto DVR to the same line.

    -Kevin
     
  4. jmpage2

    jmpage2 New Member

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    Jan 20, 2004
    I doubt it has an amplifier. It's worth noting that there is a large variation in the sensitivity of tuners (even digital tuners) which would explain any tuner signal-level discrepancies you see between different boxes.
     
  5. kbmb

    kbmb Active Member

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    Jun 22, 2004
    NH

    Thanks for taking the time.

    Any idea why I would have a situation where yesterday I saw 2 channels have a lower signal (86%-93%) as opposed to the rest of the channels (all 100%), from within DVR diagnostics. I saw these channels get a lower signal throughout the day. I went downstairs to check the line to the Tivo (it's coming from a 4 port amp) and by just unplugging and replugging it back in (it was tight), the signal on those 2 channels went back to 100% and have stayed there all night?

    Any ideas why that would be?

    -Kevin
     
  6. jmpage2

    jmpage2 New Member

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    The first question I have is, what is the problem you are having that you are trying to solve?

    If you aren't seeing problems and are going OCD over the numbers on the screen, don't. There are a lot of reasons you might see that kind of variation such as how the software polls the different tuners, or the software itself and how it interacts with the m-card.

    If you're having a legitimate problem then maybe it's something that you should further investigate.
     
  7. kbmb

    kbmb Active Member

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    Jun 22, 2004
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    Ok you got me :D It is me being completely OCD about things.

    It all started back when I got the Roamio and I read reports of people showing high signal and SNR numbers. I decided to check mine and they were high, but I wasn't having any issues. Some people commented that too high a number and you can cause tuner issues over time (no idea if that's true). So I decided to test attenuating the signal. Long story short, what I saw when attenuating (with different levels) was that those certain channels, over the course of a week, would see their signal levels drop (they all started high). Because of the attenuation, there was times when it would drop so low I would get macro-blocking and the picture would degrade on those channels only.

    In the end I just went back to the amp and have not had any issues as I saw the signal levels go back to 100% and stay there for a while.

    It was only yesterday that I went into that screen to check when the last time the Tivo was rebooted and happened to notice that those 2 channels were suddenly not 100% anymore. I waited throughout the day and by night they had moved lower. That's when I went to check the line and replugged it and the signal levels came back, which of course puzzled me even more, since I was expecting the levels to be the same.

    Again, what's weird to me is it's not across the board....it's only certain channels that over time I have confirmed to have the issue.

    I like to tinker and try to understand how things work...and it usually gets me in trouble :eek:

    -Kevin
     
  8. HarperVision

    HarperVision TiVo's Italian Cuz!

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    Paradise...
    Yeah that's kind of true, but the signal in the cable line is still a modulated RF (radio frequency) signal, whether analog or digital, so you still have to have a tuner/demodulator involved to get the signals initially to IF (intermediate frequency), then demodulated to the baseband signal for use. Technically it IS a splitter in the traditional sense where it must send the RF signal to the 6 tuners within the TiVo or whatever tuner you happen to be using. The cablecard only authorizes viewing and maps channels for the signal, but the tuners need to demodulate said signals.
     
  9. kbmb

    kbmb Active Member

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    Interesting, any idea why a signal on certain channels would go down over time and by simply unplugging/replugging the cable would cause the signal to go back up?

    -Kevin
     
  10. HarperVision

    HarperVision TiVo's Italian Cuz!

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    Paradise...
    Only thing I can think of at the moment is there's usually an AGC (Automatic Gain Control) circuit involved which loops the signal back to the input stage so the system can attempt to maintain a contstant, regulated output. It senses the output signal and if it goes low, then the system boosts the output and if its high, it does the inverse. Maybe something isn't quite right in that circuit?
     
  11. HarperVision

    HarperVision TiVo's Italian Cuz!

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    Paradise...
    I've also heard of cable companies changing power levels on channels based on time of day and demand. (I.e. - stay home mommy channels daytime, popular primetime channels at night)
     
  12. kbmb

    kbmb Active Member

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    Jun 22, 2004
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    I thought maybe that's what could have been happening, which is why I was surprised when the signal level went back up after unplugging.

    I'm going to watch it....see when/if it happens again and leave it alone and see how low it goes.

    These two channels (Food and A&E) also were having problems on my Comcast box. Turns out that cable run had a loose connection, but what was interesting was that loose connection was only causing the bad signal on certain channels. When I had the Comcast guy out, he mentioned something like they were re-spectruming or re-signaling (can't remember the term) some channels and it was causing issues now where they weren't having issues before.

    -Kevin
     
  13. HarperVision

    HarperVision TiVo's Italian Cuz!

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    Paradise...
    A loose or bad connection can certainly only cause issues on certain frequencies as well. It depends on the frequency of the RF reflections that may occur by the connection. Think of it like a free flowing stream with no obstructions, but then a log is thrown in causing the flow to disburse every which way with the water reflecting off the shoreline and back into the stream, disrupting the nice even flow you once had.
     

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