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New, less than stellar install, advice?


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28 replies to this topic

#21 OFFLINE   bbartilson

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Posted 09 September 2012 - 07:40 PM

Was snow ever a problem with your other dish?


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.

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#22 OFFLINE   trh

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Posted 09 September 2012 - 08:13 PM

For your sake, I hope not.

#23 OFFLINE   dielray

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Posted 10 September 2012 - 03:55 PM

It would be good to see what you find.

The receivers are doing more than reading bit error rates in the setup test.
We've had reports of dish alignment errors with good SAT screen numbers.

After the AIM tests, it "does seem" like the CNR is getting measured by the receivers.


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.

Edited by dielray, 11 September 2012 - 08:02 PM.

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My thoughts and opinions are my own, and do not necessarily represent those of DirecTV, my HSP, or anyone else.

#24 OFFLINE   bbartilson

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Posted 11 September 2012 - 01:16 AM

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 BIR) is passable.


Do you have any sense of how the signal strength numbers on a receiver correlate with your power level numbers?

#25 OFFLINE   dielray

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Posted 11 September 2012 - 04:12 AM

Do you have any sense of how the signal strength numbers on a receiver correlate with your power level numbers?


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.
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#26 OFFLINE   veryoldschool

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Posted 11 September 2012 - 08:31 AM

Do you have any sense of how the signal strength numbers on a receiver correlate with your power level numbers?


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.

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.
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#27 OFFLINE   HoTat2

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Posted 11 September 2012 - 10:37 AM

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.


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.

C/N = Satellite EIRP + Earth station G/T - Free Space Path Loss (+ other losses) - 228.6 (Boltzmann's Constant) - Noise bandwidth.



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:

#28 OFFLINE   veryoldschool

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Posted 11 September 2012 - 11:14 AM

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:

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:]
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#29 OFFLINE   Jodean

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Posted 19 September 2012 - 10:57 PM

"95 or 88" is coming from either a receiver's screen, or a non AIM meter, but isn't the best way to determine pass/fail for the IV test.

I did some testing with the AIM and attenuating the signal to the LNB.
The first thing to fail the IV test was SNR/CNR. Output power would pass long after the SNR failed.
The pass/fail values vary between SATs too.
101 would fail with a 10.5 dB SNR & pass with a 10.7 dB SNR, while 99 would pass with a 9+ dB SNR.
I ended up quite surprised by the results, as I'd expected the output power to have had more to due with the pass/fail than it did.


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.
Dish -- 722k, 722, 612, 512, 510

Directv -- HR34, HR24, 2 H25's, 2 H24's




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