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Interpreting SWM Signal Strengths

Discussion in 'DIRECTV Installation/MDU Discussion' started by jpitlick, Jan 16, 2009.

  1. jpitlick

    jpitlick Icon

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    How do I interpret the signal strength screen under sat signals for SWM? Most of the numbers are in the 90-100 range. Some are 0. Are the 0s channels assigned to the connected receivers? If so, I have two HR2xs and and H21, but I do not see five 0s. The most I ever see on one receiver is three 0s. Or are those 0s the other two receivers? Thanks.
     
  2. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Zeros do seem to be "other" [active] tuners.
    I have played a bit with this and this is what I've seen:
    If I have only one receiver connected, I have no zeros, which I also get if I put each receiver in the setup menu and look at the SWM screen on each.
    As each receiver returns to "normal" [exit setup] a zero will show up on the receiver screen I'm monitoring.
    Now, if a receiver starts to record, while I'm monitoring, another zero shows up.
    "In theory" with three DVR and a non recorder, you should be able to get six zeros to show on the non recorder, but since each SWM is 100 MHz wide, two receivers tuned to different channels, could still be using the same SWM channel. I have gotten five zeros. :hurah:
     
  3. jpitlick

    jpitlick Icon

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    Makes sense. Thanks for the info.
     
  4. rudeney

    rudeney Hall Of Fame

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    I have to respectfully disagree with VOS on this. I believe the transponder signal strengths shown on the SWM screen are the strengths of the transponders that are mapped or routed to the nine SWM channels (remember, it has eight tuner-selectable channels, plus one channel that is always locked onto the transponder feeding guide and system data). If it showed 0's for the channels in use, then a SWM with eight tuners using eight unique transponders would show all zeros, and that isn't what I've observed.

    I believe the reason VOS may be seeing the zeros appear as recordings kick in is because that tuner is using a transponder that is already on one of the SWM channels. The SWM doesn't seem to duplicate the same transponder on two different channels.

    My guess is that the SWM continually "publishes" a map of which transponder is routed to which of the nine channels. The tuners continually "publish" requests for the specific transponders they need. The SWM evaluates those requests and routes the needed transponders to its channels. If the same transponder is being requested by two or more tuners, it only routes it onto a single channel and then those tuners share that SWM channel. This seems to be the case as it's possible to "overload" the SWM with more than eight tuners and as long as they need eight or fewer unique transponders, the system works fine. As soon as a 9th unique transponder is requested, one tuner gets a 771 SFSS error (and which one is the unlucky loser seems to be random).

    So, it's possible to have eight tuners needing feeds from fewer than eight unique transponders, so the SWM might have empty channels, shown as zero strength. If all eight tuners are requesting unique transponders, there should be no zeros. The problem is, you may never be able to observe this. For you quantum physics fans, it's sort of like the Heisenberg Uncertainty Principle - the moment you put a SWM-attached receiver into signal strength mode, it changes what it is requesting from the SWM and thus your observation changes what is observed.
     
  5. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Haven't we "been here before"? Last time you "blamed" my H21, so this time I'm using my HR21.
    All receivers tuned to 202 and then put each into setup SWM screen. No zeros.
    Moved a HR20 out of setup [back to CNN], now have two zeros on my HR21.
    Moved my second HR20 out of setup [back to CNN], now have four zeros.
    Moved my H21 out of setup [back to CNN], now have five zeros.
    So each "zero" is directly related to how many tuners are active.

    Please repeat these steps with your system and post your results.
     
  6. LameLefty

    LameLefty I used to be a rocket scientist

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    Middle...
    In this corner, we have Rudeney!

    And in this corner we have VOS!

    (crowd cheers)

    DING! DING! DING!

    Fight! :D

    Anyway, to the original poster, as we can see there is some uncertainty out there about this. Since there is still no documentation from Directv showing what the signal strength tests for the SWM actually represent, people have experimented on their own to try to figure it out. :p
     
  7. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    More "data" always helps. :D

    "Ding" round.... :lol:
     
  8. joe diamond

    joe diamond Hall Of Fame

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    Wouldn't you think a tech manual would solve all this? It looks like the HSPs are siting on the books. I tried to get some info the other day and was told it is for installers only........well, ok?

    Anybody know how to access a little recent info or is it necessary to go buy a blue shirt?

    Joe
     
  9. rudeney

    rudeney Hall Of Fame

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    LOL! OK, maybe I will have some time tomorrow to do some testing.
     

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