1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

New, less than stellar install, advice?

Discussion in 'DIRECTV Installation/MDU Discussion' started by bbartilson, Sep 7, 2012.

  1. bbartilson

    bbartilson Cool Member

    18
    0
    Sep 7, 2012
    Actually, no, snow was not ever a problem. But I think that's because I could get to it easily if it were a problem.

    Given that this one is too high to reach, it's likely to be pasted all winter.
     
  2. trh

    trh This Space for Sale

    5,626
    275
    Nov 2, 2007
    NE FL
    For your sake, I hope not.
     
  3. dielray

    dielray Legend

    234
    1
    Aug 5, 2009
    Here's what I found. An AIM set to the IRD location fails power level around -60dBm. The receivers IV test will pass at least around -62 dBm when the SNR(and thus BER) is passable.
     
  4. bbartilson

    bbartilson Cool Member

    18
    0
    Sep 7, 2012
    Do you have any sense of how the signal strength numbers on a receiver correlate with your power level numbers?
     
  5. dielray

    dielray Legend

    234
    1
    Aug 5, 2009
    They don't, except that at a certain point the power level becomes too low for the receivers, and thus drop those numbers. Power level is how "loud" the signal is, the receivers numbers are how "clear" the signal is.
     
  6. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

    42,683
    348
    Dec 9, 2006
    There is so much noise [power] coming out of the LNB, that power levels are almost meaningless. Signal to noise [or carrier to noise] ratio is everything.
    An LNB not even mounted to a dish has measured -30 dBm.
    The receiver signal screens are related to bit error rates, which are related to the SNR/CNR, and not power levels. If power level had any affect, receivers on shorter coax would read higher than those on long coax.
    When the levels drop so low that the SNR/CNR is reduced, then the receiver will show a drop.

    The AIM will fail for power at the LNB when the levels are around -40 dBm, and the SNR is good.
    Programing the AIM to measure at the receiver, lowers this level to -60 dBm, as this is very close to the minimum the receiver needs to have a good SNB/CNR.

    "Rainfade" drops the SNR/CNR at the LNB, so the AIM is very critical of the SNR to pass the IV test. This is to ensure the alignment is done well.
     
  7. HoTat2

    HoTat2 Hall Of Fame

    7,261
    179
    Nov 16, 2005
    Los...
    One of the hard parts of understanding this non-linear relationship between received power level and SNR/CNR is that its not reflected (or at least from what I can see) in the classic C/N equation for satellite transmission whether analog or digital.



    This equation has all linear terms so changing any of ones affecting power level (or any others for that matter) make it appear the C/N will vary in the same proportion. :confused:
     
  8. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

    42,683
    348
    Dec 9, 2006
    As I've tried to explain before, the equation works all the way to the LNA output stage. The LO and final amplifier stages are where the noise power comes from.

    This is much like a test amp someone made for me. It had three stages, with the second having the filtering.
    Its output was too noisy to make the measurements I needed.
    "Everyone knows" the noise figure is related to the input, but in this case the noise came from the third stage amp. Changing the chip to a low noise amp solved this, and the designer's comment was "we should have filtered the third stage more". [well DUH :lol:]
     
  9. Jodean

    Jodean Icon

    769
    10
    Jul 17, 2010
    not real sure what the receiver measures or is supposed to.....

    I do know that if a certain transponder is 84, it will not pass, if its 85 it will pass, so i just assume it actually uses the numbers on the signal screen. That may or may not be in correlation with actual signal level, but ive encountered this 84 not passing thing a few times, wait for the cloud to pass to get the 85, then it passes.
     

Share This Page