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Understanding signal strength

Discussion in 'DIRECTV Installation/MDU Discussion' started by seadan, Jun 28, 2012.

  1. seadan

    seadan Mentor

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    I've got a situation that I'm having trouble understanding, and wanted to run it by the experts here to see if you can help me out!

    Setup: Slimline-3 dish with SWM LNB, 3 HD DVRs
    Installed in October 2009, and been running smoothly ever since...until the past couple months.

    In April, I was getting bad pixelation on many stations, and the signal meter was showing most transponders in the 50-60 range. I finally requested a dish realignment, and that fixed up my pixelation issues, and the signal meters have jumped up to the 90s for all active transponders on my receivers. The SWM signal strength is typically showing as 98-99.

    In May, my HR22 started having issues showing picture at all (black screen), and I was getting tuner 2 failures in the system test. It was also taking a really long time to boot out of the blue screens (5+ minutes). The tech came out, and determined the receiver was bad (it couldn't download new software?) and swapped it out for an HR24 that so far has been working just fine.

    In June, another one of my receivers (HR21) had twice over three days gotten into a state where the picture was just black, but the receiver (DTV) UI worked (similar to what happened to my HR22, but I wasn't getting any tuner error messages). No searching for satellite messages or anything like that. When I tried to run the receiver self test, it basically hung at 9%. After rebooting--which took an extraordinary amount of time, maybe 10+ minutes--everything eventually was back to normal and the system test reported no errors. I requested a service call, and when the technician came and diagnosed the problem--to make a long story short--he said there's too much loss on the line and that all of the cabling inside the house would need to be replaced. Now, this is despite the fact that I'm still seeing all transponders in the 90s in the signal meter, and SWM in the 98-99 range.

    Some more details here...the tech hooked his meter up at a few different points in my setup, and when he ran some tests it came back with all 'X's in the boxes instead of checkmarks (I don't know exactly which test this is on his meter), meaning there was too much loss on the line. He determined the signal strength to be the following:

    • At the ground block (right off the dish): -26dbm
    • At the comm closet, where the line comes in and prior to being split to the receivers (4-way splitter): -32dbm
    • At the wall plate where the receivers are (we tested two and they were both the same): -47dbm

    The house was built in 2006 and I believe the wiring is RG6 copper clad steel, but I have to confirm. The numbers above are what was on his meter, but honestly I'm not certain what measurement they were for. The comm closet is located on the 3rd floor, and from there the lines run straight to where the receivers are located.

    So...here are the questions I'd like to understand:
    1. Are the signal numbers reported by the tech normal/reasonable or are they out of line?
    2. If indeed I do have so much signal loss, how come my receivers seem content to register in the high 90s for satellite and SWM strength in their UI?
    3. Are the issues I've experienced with my receivers common, and is there some other cause (software/bad hw?) that might explain it?

    I find it odd that my system has been working near perfectly for 2.5 years even with a poorly aligned dish, and now all of a sudden my home wiring is bad and needs to be replaced. Am I just lucky and on the bubble of acceptable signal strength? Or is there more to it?

    Thanks for reading this far! Hopefully I've included all the details you need but if not, please let me know.
     
  2. P Smith

    P Smith Mr. FixAnything

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    Looks reasonable as sat tuner could go down to -60, but I would check that last -15 dBm drop. For 4-way I would expect a loss -8 dB.

    Your DVR shows a values of SNR (converted to the 100 scale) not the levels.

    Definitely HW problem(s) could be the reason.
     
  3. Alebob911

    Alebob911 Hall Of Fame

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    Since everything worked fine for years, I would be looking for hardware problems with the 21 since you said the 24 is working just fine. I do believe they may have run the SWM compatibility test on your lines?? That would check all the SWM channel levels I believe. If your 24 is working just fine, then I would press for a replacement for your 21. I'm sure others will provide more info but I think this is a good start.
     
  4. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    His meter looks to be off by about 5 dB, as the SWiM output is normally in the -30/-31 dBm range.
    It would be nice to know what frequency he was measuring too, as there is more loss at the high end than the low.

    The SWiM to receiver loss margin maxes at about 30 dB, which "at first" looks like you're within, "but" if the meter is off by 5 dB "and" he was measuring the lowest frequency, "Then" -47 dBm -5 dB [meter error] - 9 dB [coax/splitter roll off at the high end] becomes -61 dBm which is right at the receiver minimum level.

    As posted, the receiver displays a percentage from the signal to noise ratio, but this isn't a true power level, which the meter is reading.
    You could have a marginal power level that most of the time is just within the SNR range and give good numbers.

    "Frankly" I just can't yet tell whether you have too much loss or not.
     
  5. texasbrit

    texasbrit Well-Known Member

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    Aren't you adding in the splitter losses twice? The -47dBm already includes the losses in the four-way, plus the cable, so even if the meter were 5dBm incorrect, that still gives -52dBm at the receiver, less any loss in the cable from the wallplate to the receiver which (hopefully) will be small.
     
  6. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    No, I was accounting for the differences in loss between 950 and 1790 MHz.
    "If" the power was -47 dBm @ 950 MHz, "then" @ 1790 MHz, it would be close to -56 dBm, and if the meter is off my 5 dB...

    Now something I might try is to have the receiver on the longest run use the lower frequencies, by powering everything down [pulling power cords]. Then power the SWiM up and go to the receiver on the longest coax run and power it up first, which should have it use the lower SWiM channels. Then power up the receivers on the shorter coax.

    This isn't the best way to build a system, but if the problem receiver works, then it does point to too much loss, and if it still has problems, it isn't a loss problem.
     
  7. texasbrit

    texasbrit Well-Known Member

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    good point, since he did not say at which frequency he was measuring the signal....

    The losses seem to imply a total of at least 220ft+ of RG6 cable in total, including 110ft from the dish to the splitter..If dish to splitter is not 110ft, then where's the 6dB of loss coming from?
    If your proposed test shows that the problem is indeed roll-off at the higher frequencies, then if one of the receivers is much further away, it might be worth investigating reconfiguring with two-way splitters instead of four way. It would mean probably mean running one of the DVRs "through" the power inserter which is not recommended (but seems to work oK for most) but would double the signal strength to the furthest receiver without affecting the other two.
    If it is indeeed 110 ft from the dish to the splitter, using RG11 instead of RG6 might be enough to solve the problem. Or even using a Sonora inline amp.

    But as you point out, suggested solutions are no good unless you can pinpoint the source of the problem!!
     
  8. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    "A good install" is when everything works in the "worst case".
     
  9. seadan

    seadan Mentor

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    Thanks for all the insight! To clarify some additional points:

    - I don't know which frequency the tech was reading the signal on. I recall he booted up his meter and ran through some test procedure. The test procedure had a 4x2 grid of boxes (for the 3 sats plus SWM on one axis, and even/odd on the other, I think?) and showed either a check or an X. From there, he cycled to another screen which showed the dBm measurement--not sure if that's helpful at all.

    - It shouldn't be a 110ft run of coax from dish to the closet. We have a 3 story house with 9-10' ceilings, and the wire runs from the ground (dish it mounted about 8 feet up) to the third floor, which is on the opposite side of the house (maybe another 20')--so it should be around half of that is my guess?

    - The problem receiver is not on the longest run, and I haven't had these issues with that receiver (yet...knock on wood). Not sure if that affects your test protocol, but I may give that a shot anyways to see if it changes anything.

    - The power inserter is plugged in at the closet, into one of the ports on the splitter. Would moving its location help boot power? Or is there an inline amp that would help as well?
     
  10. dielray

    dielray Legend

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    Unless both AIMs I've used have also been off, I regularly see values around -26 dB with SWM LNBs at the ODU. WNCs can approach -22 dBm on a clear day.
     
  11. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Once again, you add good information.

    The SWM8 is spec'd @ -30/-31 dBm by Sonora and they do the same for the LNB:

    1Capture.PNG

    The AIM has an adjustment mode, correct?
    I believe this locks the internal AGC and so this might be why.

    The AGC range is "supposed to be" from -15 dBm to -45 dBm, for a constant -30 dBm output.
     
  12. dielray

    dielray Legend

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    Yes, the AIM can put the LNB into peaking mode. The AIM also has a sat tune function where the LNB acts normally. I see values above -30 dBm there as well. On a very short run, it is possible to over power the receiver. DirecTV has even instructed techs to put an 8way behind the receiver in that situation. Interestingly, setting the AIM's location to in between a SWM multiswitch and the splitter causes the AIM to warn "A splitter may be necessary".
     
  13. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    I'm told I'll get a couple of days next week to work with an AIM, so I may get to know some things better.
    I've got a SWiM-16 system that I want to wring out and see what's what.
     
  14. cypherx

    cypherx Hall Of Fame

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    This is a very interesting thread. I suppose there is no secret diagnostic screen or mode you could put the receiver in to get power level? That's good to know your signals screen could look good but the reality is the signal could still be marginal or low.

    I'm always amazed at how "low" the signal can be to work on satellite and it still functions properly. On a cable line you wouldn't even get a picture at -60 dB yet alone -20dB. This technology is amazing. Super sensitive tuning?
     
  15. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    a 10 dB CNR will give great results.
     
  16. P Smith

    P Smith Mr. FixAnything

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    I will tell you one secret ;) : 5.9 dB SNR at some Ka sats give no errors in stream.
     
  17. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    yeah I was lazy, as I've heard something like 8 is closer to the min.
     
  18. P Smith

    P Smith Mr. FixAnything

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    That would be normal, while 10+ is best.
    It was just an example how low it could be. Definitely it wouldn't be good for long run, especially not in CA with best weather for receiving Ka signals.
     
  19. HoTat2

    HoTat2 Hall Of Fame

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    Los...
    First, to be more precise, since you mention "1790 MHz" on the high end aren't you referring to the SWiM center frequencies of 974-1790 MHz?

    And is that just a typical figure you have discovered through measurement?

    An average 9 dB roll-off from the lowest SWiM frequency of 974 MHz to 1790 MHz at the highest?
     
  20. veryoldschool

    veryoldschool Lifetime Achiever Staff Member Super Moderator DBSTalk Club

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    Remember I'm pulling most of this out of my head, as I hate to keep pulling up the SWiM training pdf.

    Cable loss comes from here: http://www.net-comber.com/cable-loss.html
     

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