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Many receivers watching same channel = reduced signal strength??

Discussion in 'DIRECTV Installation/MDU Discussion' started by slice1900, Feb 26, 2013.

  1. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    In this case the 2-way splitter adds about 5 dB of loss. A WB68 wouldn't have this loss, but adds a failure point.
    The WB616 was discontinued several years ago, so anything around is either used or old stock. Now the WB616 is powered, so why not do what everyone else is for more than two SWiM-16s and use an amp before the splitters?

    This might be of some use: http://forums.solidsignal.com/showthread.php/336-WHITE-PAPER-More-than-16-tuners-in-the-home
     
  2. P Smith

    P Smith Mr. FixAnything

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    Seems to me you should look inside AIM design and dig into its capability to lock.
    LNBF wouldn't "lock".

    I would give you a link to a company who is doing design of chips using in the LNBF, but afraid you could find it by yourself.
     
  3. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Well if nothing else you can throw insults, but hey, you haven't done/seen what I have so....
     
  4. P Smith

    P Smith Mr. FixAnything

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    :shrug:
    It's not an insult, but friendly attempt to find the "lock" parameter where is it belong.
     
  5. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    "OK" if the LO is 3 MHz off, the receiver is going to have a hard time finding which channel it should be getting.
    We've seen this with the [defective] SWiMs in cold weather and someone even posted a video for the receiver wandering between two channels.

    One of my tests was off the legacy ports of the SWiM-16, which have a good 10 dB of loss, so the AIM was locked @ -42 dBm, but failed the LNB test because of low power, while it had a good CNR.
    This same test at the LNB loses lock @ -39 dBm, as the CNR has dropped too far.
    Without having an SA and picking apart the LNB, "It would seem" the LNB locks the LO to a signal from the TP, so when the LO is off, like this one showing a 3 MHz offset, the receiver gets the correct frequency.

    A PLL needs a reference and it seems to be in the TP signal.
     
  6. HoTat2

    HoTat2 Hall Of Fame

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    Los...
    OK, so again to clarify;

    The 1 and 3 MHz refer to the "unlocked" LO frequency error on the two legacy LNBs tested?

    And since a Ka/Ku LNB has three LOs these figures were measurements on just one satellite transponder and band you selected for the test which you do not recall at the moment?
     
  7. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    I'm not sure the AIM gives the offset when it isn't locked.

    I dug through my notes and here's two legacy & one SWiM LNB

    99
    3.14 MHz & 1.07 MHz [SWiM] 3.31 MHz

    101
    0.64 MHz & 0.25 MHz [SWiM] 0.71 MHz

    103a
    2.31 MHz & 1.45 MHz [SWiM] 2.63 MHz

    103b
    2.40 MHz & 1.53 MHz [SWiM] 2.71 MHz
     
  8. HoTat2

    HoTat2 Hall Of Fame

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    Los...
    That's what I thought at first, but then your recent statement to P. Smith here;

    Confused me since if the LO on the LNB you're using is 3 MHz from where it should be when its locked shouldn't you be experiencing the problem you describe above? :confused:

    While I'm certainly familiar with the age-old receiver superhetrodyne principle, I guess I'm missing something basic here.
     
  9. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    During my testing with the AIM, I was more focused on signal levels and simulating rainfade.

    With my second cup of coffee in hand :)lol:), "Lock" being related to CNR, it may be the AIM reporting it has min CNR, much like a menu in my TV.

    LO offset may merely be the difference between the signal from the TP and the LO.
    103a & 103b are using the same LO, but the offset [above] varies 80-90 KHz.

    The tuner may be where the offset is sorted out, but if its too great, the tuner drifts to the adjacent channel.
     
  10. Nick

    Nick Retired, part-time PITA DBSTalk Club

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    As a young engineer at a small-town radio station, I was once asked by our advertising sales mgr, "How many radios in the county will our 5kw signal feed?"

    To which I replied, "As many as will fit in the county." :scratch:
     
  11. HoTat2

    HoTat2 Hall Of Fame

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    Los...
    Sorry for the belated response to this VOS;

    According to the AIM manual I just d/l'ed, it describes "Lock" not specifically as minimum CNR but in a pinup notation as:

    But I feel this may be an inaccurate reference for what is really CNR since that would mean, ... what a -60 to -65 dbm level achieves a "Lock" on the meter? :confused:

    Agreed, as the manual "effectively" describes this for the meaning of "offset" simply as;

    So does this mean though that the legacy LNB you choose to currently use on the dish was a trade-off of a higher freq. error (~3 MHz) and a slightly lower power output for a better CNR (or noise figure)?

    Hey, and BTW, using the AIM figures for "SNR" (CNR) vs. the relative 0-100 scale signal levels on the meter in various examples quoted in the manual always equates out to .13 db per point.

    Do you think the AIM's same 0-100 scale is equivalent to the receiver's (IRD) 0-100 signal strength screen? :)

    So say a "100" on the Tp. SS screen reading means (at least a min.) of a 13 db CNR? :D

    Be nice to attach more of a definitive meaning to these common receiver SS readings than merely relative points on a scale of 0-100.
     
  12. P Smith

    P Smith Mr. FixAnything

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    Anyhow, the"lock" is not a parameter of LNBF, but a feature of AIM ( having demod chip).
     
  13. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    "lots of questions" :lol:

    The AIM is a good meter, but what I don't like about it is DirecTV seems to have put "the intelligence" in the meter and its menus, instead of the user.

    Of the 2 legacy LNBs I tested, there were three variations:

    1. CNR/SNR
    2. LO offset
    3. output power
    My first impression was to go with the higher output power, which also was the one with less offset.
    After attenuating the input signals, the one with the better CNR was my choice.

    As for the SS on the receiver screen, mine drop about 10 points on some SATs between the output of a legacy LNB and the output of a SWiM.
    This has always been the case, be it with a SWM8, SWiM LNB, or SWiM-16.
    My current readings are:
    101-119 mid 90s
    99c 80-91
    103ca 80-92
    103cb 82-90

    These 80s were 90s at the LNB
     
  14. slice1900

    slice1900 Well-Known Member

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    All this talk about AIM finally made me curious enough to download the AIM manual for a quick look. You ain't kidding about trying to put the intelligence in the meter instead of the installer - the "turns calculator" is all about not trusting the installer to be able to divide by two! :hurah: :lol:

    Why do you think the outputs of the LNB are dropping at the output of a SWM8/16? Could that be the AGC attenuating signals higher than -30dbm to reach its output target? If you try your experiment again in crappier conditions when your readings are lower at the LNB, I wonder if you'd see the same decrease?

    I'm sure the frequency conversion from the frequency off the LNB output to a SWM "channel" frequency is not a noiseless process, perhaps that added noise could be the reason for the decrease you're observing?
     
  15. HoTat2

    HoTat2 Hall Of Fame

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    Los...
    What I'm curious of though is that to use this example, whatever the cause of the 10 point drop, assuming the same levels which register 0-100 on the AIM's scale are also used on the receiver's SS screen, does that mean a 10 (point) x .13 db or 1.3 db reduction in CNR?

    Or approx. a 26% loss in the CNR at the receiver compared to the LNB?
     
  16. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    And I'm afraid I've got nothing to help you with, as it isn't clear what the SS is really reading. :shrug:

    It may be bit error rates, or something related to CNR [but I doubt it] and it definitely has nothing to do with power levels [or they'd be different between long and short coax runs].
     
  17. P Smith

    P Smith Mr. FixAnything

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    The answer is known, I posted how the number taken from SNR values, what sat NIM reporting to SW.
     
  18. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    I wish I still had access to the AIM, as my notes for this aren't as detailed as I would like, "but" they do have some CNR values before and after the SWiM, from the same SAT & TPs, which are either the same or .1 dB less, which doesn't account for a 10 point drop.
     

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