# SNR/CNR to the receiver's reported "signal strength"



## slice1900 (Feb 14, 2013)

I messaged P Smith about this, but it may be of more general interest so I'm reopening this old thread since it deals with the information he found relating SNR/CNR to the receiver's reported "signal strength".

I did a little playing around to try to figure out the receiver's thresholds for SS for picture loss, by attenuating the signal. I re-configured a receiver (an H20-600 for this experiment) for legacy, and connected it to the 13v 22 KHz output of a PI6S, which was in turn connected to a SL5 LNB. I looked at the signal meter for 103ca tpn 23 (high frequency above 2100 MHz, so more easy to attenuate) and started adding splitters to attenuate the signal. The reason I went through the PI6S rather than directly to the SL5 was to insure that the voltage was strong (in case some may be "lost" in a long chain of splitters)

After creating a fairly long chain of splitters SS was down to 40. When I tuned to FX (channel 248, on 103ca tpn 23) I still had a perfect picture - though there was an infomercial on so it wasn't a particularly demanding program. By swapping around splitters for different types I managed to get down to SS 20, and observed pixellation and occasional loss of signal. It was not something I'd want to watch, but the picture was good enough that I could recognize people etc.

According to P Smith's data, a SS of 40 is a SNR of about 6, and SS 20 is a SNR of about 3.5. Now "my understanding" is that due to the advanced modulation and FEC rate Directv uses, the minimum SNR should be somewhere between 6 and 9 for Directv, and probably towards the higher end of that range for most HD channels.

So I have a few questions to pose. One, is this test valid at all? If there's some gain in the tuner, it would partially make up for the attenuation I added. If this gain is present when tuning a channel but not when viewing a transponder's signal strength, then my test is meaningless. Anyone know if that's the case?

If the test is valid, what does it mean? Let's say the minimum SNR required for the modulation/FEC on FX at the time I did this was 6, does that mean the minimum SNR is for _perfect reconstruction_, which is what I observed, and a lower SNR will still work, albeit with a lot of errors like I found with SS 20? Or is it possible the SNR the receiver converts into SS is a threshold value - that is, if it reports a SNR of 3.5 (SS 20) that means it is 3.5db above some minimum SNR value and the true SNR is higher than 3.5 db?

Other possible explanations I'm missing?


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## TomCat (Aug 31, 2002)

slice1900 said:


> But is that because of the dish itself? Seems like the LNB would be much more of a factor. Maybe the LNBs back in the AT9 days were better made, and the ones made for the Slimline cut a few corners to save a few bucks?
> 
> Doubling the dish area theoretically increases your S/N by 3 db, so the ~4-5% bigger AT-9 dish would probably only help S/N by 0.14 db or so. That hardly seems likely to account for a noticeable difference in signal strength.
> 
> Are you getting 100s on any 99c/103ca/103cb transponders? 100s on the 101/110/119 are no big deal, but AFAIK 100s on the HD sats are pretty rare.


Its not rare at my house.

The size of the reflector was engineered to work with the LNBF technology at the time to provide a standard illumination to the LNBF. But LNB technology has been improving yearly since the 80's. Newer dishes are smaller, and can be, because newer LNBFs have a lower noise temp and better amplification so are better, not worse. A slightly lower illumination level is OK when the noise temp is lower, because when it is that can yield the same SNR at the output.

That item is not something that DTV can tinker with; it is likely an outsourced item, and a closed system. But while better, new LNBFs are also likely less expensive. There would be no payoff to intervene in that to "save a few bucks".

The newer antenna systems all seem to perform slightly better than the older ones according to anecdotal reports, assuming proper alignment and equivalent weather. But some of that may be because when tested, the older systems may have deteriorated while new systems replacing them likely have not.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> So I have a few questions to pose. One, is this test valid at all?
> 
> If the test is valid, what does it mean?
> 
> Other possible explanations I'm missing?


I'm not going to say the test was "invalid", but not sure you were able to measure or decipher everything going on either.
The tuner chip is spec'd down to -70 dBm, but like any chip off a wafer, some are better than others.
An HD channel starts to show breakup in the teens. I think I was trying to watch one that was 13 and the forum has helped others with 17.
"Perhaps" the difference between these and your "test" is you were using a "fixed" attenuation verses weather related that may have been able to have the error correction "help".


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> I'm not going to say the test was "invalid", but not sure you were able to measure or decipher everything going on either.
> The tuner chip is spec'd down to -70 dBm, but like any chip off a wafer, some are better than others.
> An HD channel starts to show breakup in the teens. I think I was trying to watch one that was 13 and the forum has helped others with 17.
> "Perhaps" the difference between these and your "test" is you were using a "fixed" attenuation verses weather related that may have been able to have the error correction "help".


I didn't realize it was normal to be able to see some sort of a picture down as low as the teens. Ignoring my test and focusing on your real world examples, a SS in the teens would correspond to a SNR less than 3 based on P Smith's graph.

So is the tuner able to work with a SNR that low? I thought DVB-S2 QPSK 3/4 required 8 db or so, but maybe that's not correct. Or is the SNR that is used to calculate SS the "SNR above minimum", so that 0 means "no or negative margin" and even a SS of 1 means you've got something above that minimum level? Perhaps the SS in the teens you were able to watch, indicating a SNR of 2.5 db, is really 10.5 db - 2.5 db above that 8 db threshold value.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> I didn't realize it was normal to be able to see some sort of a picture down as low as the teens. Ignoring my test and focusing on your real world examples, a SS in the teens would correspond to a SNR less than 3 based on P Smith's graph.
> 
> So is the tuner able to work with a SNR that low? I thought DVB-S2 QPSK 3/4 required 8 db or so, but maybe that's not correct. Or is the SNR that is used to calculate SS the "SNR above minimum", so that 0 means "no or negative margin" and even a SS of 1 means you've got something above that minimum level? Perhaps the SS in the teens you were able to watch, indicating a SNR of 2.5 db, is really 10.5 db - 2.5 db above that 8 db threshold value.


First off it's CNR
The signal screens are showing more of a relative bit error rate than signal power/strength.
You should have seen this as you added attenuation.
"I think" a CNR of 8 dB would return a reading of 100%, "all things being equal", but I haven't measured/tested this.
You'd need to have a meter that can measure CNR, and when I had one on loan, my work was looking into rain fade, and characterizing LNBs.
CNR varied in my testing from 10ish to maybe 14+ and has nothing to do with frequency.


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> First off it's CNR
> The signal screens are showing more of a relative bit error rate than signal power/strength.
> You should have seen this as you added attenuation.
> "I think" a CNR of 8 dB would return a reading of 100%, "all things being equal", but I haven't measured/tested this.
> ...


P Smith's results from earlier in this thread show a CNR of 8 corresponding to a SS of 58. If you saw results from 10 to 14, why would believe 8 corresponds to a SS of 100? If that was true, at a receiver you should be seeing a reading of 100 on every transponder you tested. The range from 10ish to 14+ is 80s to upper 90s on P Smith's graph.

When you were doing your testing with the meter, did you ever test how low you could get the CNR and still get a picture? Or were you using the meter only, and not checking both the meter and a receiver's results at the same time? That's what I'm curious about, and if it is true that you can get a picture with a CNR of only 2 or 3 db, how that compares to seeing claims that DVB-S2 QPSK 3/4 requires like 8 db.


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## P Smith (Jul 25, 2002)

if you could make same tests and pull logs from your DVR ... we will more confident in the CNR vs SS numbers in your tests

and reminder about CNR and modulation relation from http://www.advantechwireless.com/wp-content/uploads/DVB-S2-theory.pdf and R&S PDF:


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> When you were doing your testing with the meter, did you ever test how low you could get the CNR and still get a picture? Or were you using the meter only, and not checking both the meter and a receiver's results at the same time?


It wasn't my interest at the time to see what the picture was and I was monitoring where the meter lost lock, which I'd imagine is where the receiver would too.


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> It wasn't my interest at the time to see what the picture was and I was monitoring where the meter lost lock, which I'd imagine is where the receiver would too.


That seems logical that the meter would lose lock at about the same time as the receivers, as they probably have similar chipsets.

How far down did CNR drop before it lost lock? I seem to remember a picture you posted with the meter at the threshold of losing lock with a signal power in the low -40s dbm, but I don't recall the CNR value.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> That seems logical that the meter would lose lock at about the same time as the receivers, as they probably have similar chipsets.
> 
> How far down did CNR drop before it lost lock? I seem to remember a picture you posted with the meter at the threshold of losing lock with a signal power in the low -40s dbm, but I don't recall the CNR value.


It's been too long to remember, "but" the CNR isn't reported when it loses lock, so you'd need to check it at about -37 dBm.

What I did find was I could get the CNR to drop by 3 dB if I covered the LNB with 40 sheets of sandpaper, which was about 3/4" thick.
I have no way to know/measure how much attenuation the sandpaper had, but it would seem like it should be more than 3 dB "to me".


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> It's been too long to remember, "but" the CNR isn't reported when it loses lock, so you'd need to check it at about -37 dBm.
> 
> What I did find was I could get the CNR to drop by 3 dB if I covered the LNB with 40 sheets of sandpaper, which was about 3/4" thick.
> I have no way to know/measure how much attenuation the sandpaper had, but it would seem like it should be more than 3 dB "to me".


I was thinking in terms of what CNR looks right before / at the very threshold of losing lock. I guess that circles back to the question of how you cause a drop in CNR to reach that point. I suppose one way to accomplish this would be to tweak the dish aim until you lose lock, then move it back just enough to regain lock, and observe the CNR.

I wonder how much the 3 db CNR drop in your sandpaper test was due to attenuation and how much was due to the increased antenna noise caused by 3/4" of ~300K sandpaper in the path of the LNB?

I found a paper a while back that did calculations for rain fade in the Ka band, and the maximum (aside from solar outage) antenna noise temperature of ~300K during heavy rain worked out to an increase in overall system noise of just over 4 db. This was based on consumer DBS in Europe, which don't have exactly the same characteristics as Directv's LNB, but wouldn't be wildly dissimilar.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> I wonder how much the 3 db CNR drop in your sandpaper test was due to attenuation and how much was due to the increased antenna noise caused by 3/4" of ~300K sandpaper in the path of the LNB?


Without any sandpaper, the LNB was pointed at a reflector is bright sun, making it hard to believe the temp of the sand paper had any effect.
If it did, we'd all have problems between day and night and need to shade the dish, instead of only having them when the sun is behind the SAT.
The change in temp due to rain does make sense, as the same is true for a SAT pointed to earth verses a dish pointed to the sky.


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## P Smith (Jul 25, 2002)

perhaps he is using old fashion metrics [in Kelvin's degrees] instead of modern dB for noise figures


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## veryoldschool (Dec 10, 2006)

P Smith said:


> perhaps he is using old fashion metrics [in degrees] instead of modern dB for noise figures


Think it was kelvin [used in the KTB for noise]


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> Without any sandpaper, the LNB was pointed at a reflector is bright sun, making it hard to believe the temp of the sand paper had any effect.
> If it did, we'd all have problems between day and night and need to shade the dish, instead of only having them when the sun is behind the SAT.
> The change in temp due to rain does make sense, as the same is true for a SAT pointed to earth verses a dish pointed to the sky.


Except the reflector isn't reflecting the sun directly at the LNB, and that's what matters - during the equinox, the noise temperature increasing to ~ 6K is why we experience solar outages.

However, there is a very good example of why the sandpaper stack is probably mostly irrelevant as far as noise - the LNB cover. It is at ambient, and present in the signal path, but it does not increase noise to the same degree (no pun intended) as pointing the LNB at the ground or through miles of raindrops does. Is it because there isn't much of material, it isn't very dense, it is an insulator rather than a conductor? I don't know.

And yes, you're correct in your response to P Smith, the 'K' I was referring to is Kelvin, since it is noise _temperature_. Here's a little calculator I found which can run through some examples using the various components of noise temperature in a satellite receiver. http://www.satsig.net/noise.htm.


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## veryoldschool (Dec 10, 2006)

nice link, but maybe 3/4th of the info we don't have.


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## slice1900 (Feb 14, 2013)

Yes, it is only interesting as far as playing with the various dials and seeing the relative effect they have. Aside from the Slimline's antenna gain (should be about 40 db in the Ka band) we'll never know the correct values for the rest of those.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> Yes, it is only interesting as far as playing with the various dials and seeing the relative effect they have.


Thirty years ago we had to do it "long hand" :eek2:


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## P Smith (Jul 25, 2002)

veryoldschool said:


> Think it was kelvin [used in the KTB for noise]


I did omit a word "Kelvin" that time as it was obvious, since there was typed "300K"


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## samrs (May 30, 2004)

Serial:
AIM Version: 2.4 Build: 100
Db Version: 0025
Date: 04-02-2014, 12:36:44
Account:
Notes:
ODU: Slimline-3S (SWiM)
Multiswitch: None
Zip: 28328
Config: ODUo---oSPLo---oDECA---oIRD
Location: At ODU output
Options: All nationals
Sat/Tr Freq(MHz) Pwr(dBm) *SNR*(dB) SQ Offset(MHz) Lock Volts(V) Cur(mA) ODU SWiM
ssss/tt xxxx.xx -xxx.x xx.x xxx (-)x.xx xxx xx.x xxxx abcd x
99/1 274.00 -27.6 *14.2* 97 0.06 YES 21.0 400 SL3S 2
99/2 274.00 -27.4 *14.1* 97 0.06 YES 21.0 400 SL3S 2
99/3 314.00 -27.4 *13.6* 96 0.06 YES 21.0 400 SL3S 2
99/4 314.00 -27.5 *13.9* 96 0.05 YES 21.0 400 SL3S 2
99/5 354.00 -27.4 *13.7* 96 0.06 YES 21.0 400 SL3S 2
99/6 354.00 -27.6 *13.4* 95 0.05 YES 21.0 400 SL3S 2
99/7 394.00 -27.5 *13.7* 96 0.06 YES 21.0 400 SL3S 2
99/8 394.00 -27.4 *13.7* 96 -0.57 YES 21.0 400 SL3S 2
99/9 434.00 -27.4 *13.6* 96 0.06 YES 21.0 400 SL3S 2
99/10 434.00 -27.5 *13.6* 96 0.05 YES 21.0 400 SL3S 2
99/11 474.00 -27.6 *13.5* 96 0.05 YES 21.0 400 SL3S 2
99/12 474.00 -27.3 *13.6* 96 0.05 YES 21.0 400 SL3S 2
99/13 514.00 -27.2 *14.8* 98 0.05 YES 21.0 400 SL3S 2
99/14 514.00 -27.4 *14.4* 97 0.07 YES 21.0 400 SL3S 2

101/1 974.00 -28.7 *15.2* 99 0.37 YES 21.0 400 SL3S 2
101/2 988.58 -28.4 *15.9* 100 0.56 YES 21.0 400 SL3S 2
101/3 1003.16 -29.2 *15.1* 99 0.37 YES 21.0 400 SL3S 2
101/4 1017.74 -30.0 *12.8* 95 0.35 YES 21.0 400 SL3S 2
101/5 1032.32 -29.6 *15.3* 99 0.30 YES 21.0 400 SL3S 2
101/6 1046.90 -29.0 *16.9* 100 0.37 YES 21.0 400 SL3S 2
101/7 1061.48 -28.8 *14.0* 97 0.30 YES 21.0 400 SL3S 2
101/8 1076.06 -28.9 *17.0* 100 0.37 YES 21.0 400 SL3S 2
101/9 1090.64 -29.8 *15.3* 99 0.37 YES 21.0 400 SL3S 2
101/10 1105.22 -29.0 *16.3* 100 0.56 YES 21.0 400 SL3S 2
101/11 1119.80 -29.2 *15.7* 100 0.36 YES 21.0 400 SL3S 2
101/12 1134.38 -30.9 *11.2* 85 0.41 YES 21.0 400 SL3S 2
101/13 1148.96 -29.6 *15.2* 99 0.30 YES 21.0 400 SL3S 2
101/14 1163.54 -28.8 *17.3* 100 0.81 YES 21.0 400 SL3S 2
101/15 1178.12 -29.0 *14.8* 98 0.30 YES 21.0 400 SL3S 2
101/16 1192.70 -27.9 *17.0* 100 0.30 YES 21.0 400 SL3S 2
101/17 1207.28 -29.7 *15.4* 99 0.37 YES 21.0 400 SL3S 2
101/18 1221.86 -34.6 *11.7* 88 0.29 YES 21.0 400 SL3S 2
101/19 1236.44 -29.0 *15.6* 100 0.43 YES 21.0 400 SL3S 2
101/20 1251.02 -29.4 *12.0* 90 0.40 YES 21.0 400 SL3S 2
101/21 1265.60 -29.7 *15.5* 100 0.31 YES 21.0 400 SL3S 2
101/22 1280.18 -28.8 *17.2* 100 0.49 YES 21.0 400 SL3S 2
101/23 1294.76 -28.8 *15.8* 100 0.37 YES 21.0 400 SL3S 2
101/24 1309.34 -28.1 *17.5* 100 0.31 YES 21.0 400 SL3S 2
101/25 1323.92 -29.5 *15.3* 99 0.43 YES 21.0 400 SL3S 2
101/26 1338.50 -- -- -- -- NO 21.0 400 SL3S 2
101/27 1353.08 -29.1 *15.2* 99 0.43 YES 21.0 400 SL3S 2
101/28 1367.66 -28.0 *15.0* 99 0.34 YES 21.0 400 SL3S 2
101/29 1382.24 -29.7 *15.8* 100 0.30 YES 21.0 400 SL3S 2
101/30 1396.82 -29.5 *17.0* 100 0.18 YES 21.0 400 SL3S 2
101/31 1411.40 -27.5 *15.5* 100 0.36 YES 21.0 400 SL3S 2
101/32 1425.98 -27.8 *17.5* 100 0.31 YES 21.0 400 SL3S 2

103b/1 274.00 -27.2 *15.1* 99 0.35 YES 21.0 400 SL3S 2
103b/2 274.00 -27.2 *14.4* 97 0.35 YES 21.0 400 SL3S 2
103b/3 314.00 -27.4 *13.9* 96 0.35 YES 21.0 400 SL3S 2
103b/4 314.00 -27.5 *13.2* 95 0.34 YES 21.0 400 SL3S 2
103b/5 354.00 -27.4 *13.8* 96 0.35 YES 21.0 400 SL3S 2
103b/6 354.00 -27.3 *13.6* 96 0.35 YES 21.0 400 SL3S 2
103b/7 394.00 -27.6 *13.5* 96 0.35 YES 21.0 400 SL3S 2
103b/8 394.00 -27.4 *13.2* 95 0.35 YES 21.0 400 SL3S 2
103b/9 434.00 -27.3 *13.9* 96 0.35 YES 21.0 400 SL3S 2
103b/10 434.00 -27.5 *13.4* 95 0.35 YES 21.0 400 SL3S 2
103b/11 474.00 -27.4 *13.2 *95 0.35 YES 21.0 400 SL3S 2
103b/12 474.00 -27.3 *13.2* 95 0.34 YES 21.0 400 SL3S 2
103b/13 514.00 -26.9 *13.9* 96 0.36 YES 21.0 400 SL3S 2
103b/14 514.00 -26.9 *13.5* 96 0.36 YES 21.0 400 SL3S 2

103a/9 1840.00 -27.0 *14.6* 98 0.35 YES 21.0 400 SL3S 2
103a/10 1840.00 -27.5 *12.9* 95 0.35 YES 21.0 400 SL3S 2
103a/11 1880.00 -27.4 *14.0* 97 0.35 YES 21.0 400 SL3S 2
103a/12 1880.00 -27.4 *13.6* 96 0.35 YES 21.0 400 SL3S 2
103a/13 1920.00 -27.2 *14.0* 97 0.34 YES 21.0 400 SL3S 2
103a/14 1920.00 -27.5 *13.7* 96 0.34 YES 21.0 400 SL3S 2
103a/15 1960.00 -27.4 *13.6* 96 0.34 YES 21.0 400 SL3S 2
103a/16 1960.00 -27.2 *14.2* 97 0.34 YES 21.0 400 SL3S 2
103a/17 2000.00 -27.5 *14.1* 97 0.35 YES 21.0 400 SL3S 2
103a/18 2000.00 -27.4 *14.2* 97 0.35 YES 21.0 400 SL3S 2
103a/19 2040.00 -27.4 *14.5* 98 0.35 YES 21.0 400 SL3S 2
103a/20 2040.00 -27.2 *14.3* 97 0.35 YES 21.0 400 SL3S 2
103a/21 2080.00 -27.4 *14.3* 97 0.34 YES 21.0 400 SL3S 2
103a/22 2080.00 -27.4 *14.1* 97 0.35 YES 21.0 400 SL3S 2
103a/23 2120.00 -26.8 *15.4* 99 0.34 YES 21.0 400 SL3S 2
103a/24 2120.00 -26.9 *15.1* 99 0.34 YES 21.0 400 SL3S 2

Here are some numbers you can play with.

[Mod edit] highlighted CNR


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## slice1900 (Feb 14, 2013)

So this post by samrs brings up something I've always been curious about - why do different transponders from the same satellite have different SNR/CNR/SS values? All the transponders for 103ca are from D12, so they're coming from the exact same location in the sky. Do different transponders have slightly different footprints, do they start out from the uplink site with different power levels, do they have different modulation schemes, does it just have to do with the vagaries of no two LNBs being exactly alike across the frequency band?

Using what he posted as an example, why would 103ca tpn 10 be lower than the rest, and tpn 23 & 24 be higher than rest? For 101 the tpns from D9S are the ones I always seem to get 100 on, and the ones from D8 never quite manage 100. That makes some sense to me; perhaps D9S has a slightly more powerful signal, or is aimed a bit better for my location. But why should I see different readings amongst different transponders for 99c, 103ca and 103cb where all tpns from each are provided by single satellite?

I don't see the same set of 103ca transponders as lowest/highest as samrs does, but I'm in a different location and of course it is a different LNB. Maybe just a tiny tweak in my dish's aim would change which ones are the strongest and weakest, but I'd still wonder why that should be when they're all from the same satellite and located no more than a few meters apart.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> So this post by samrs brings up something I've always been curious about - why do different transponders from the same satellite have different CNR values?


I'm sure there are a number of factors, but do you know what happens "in the SAT"?
Between the uplink and down link are a "whole bunch" of waveguide switches, traveling tubes, and the transponder(s).
By itself, the SAT signal path can account for the variations shown.


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## samrs (May 30, 2004)

^Your an engineer, read through this..http://en.wikipedia.org/wiki/Klystron


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## veryoldschool (Dec 10, 2006)

samrs said:


> ^Your an engineer, read through this..http://en.wikipedia.org/wiki/Klystron


This would be better http://en.wikipedia.org/wiki/Traveling_wave_tube
It is a bit strange that the link doesn't mention Watkins-Johnson who was a major supplier [and another company I worked for].

Having worked at Space Systems Loral [later] on the SATs before launch, I've left a few fingerprints on them :lol:


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## samrs (May 30, 2004)

Peanut Butter and Jelly...no doubt.


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## P Smith (Jul 25, 2002)

there is another factor: AIM's FW what convert SNR to SQ [SS} (are we sure CNR is equal SNR here ?)

no doubt in difference of signals between transponders, too many factors not to expect equal values (different TWTs, cabling, non linearity of LNBF, atmosphere condition, etc)


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## Stuart Sweet (Jun 19, 2006)

I've done a very similar test and found only one inescapable result: that there is only a very loose correlation between CNR and the receiver's reported signal strength. I have been told several things about this number, and the most credible is that it is derived from the CNR and the inverse BER. I can't reverse-engineer the formula but to answer your question from post #1, my experience has shown that there is not a concrete correlation between CNR and signal strength as reported so, yes it is a waste of time.


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## samrs (May 30, 2004)

Here are some more numbers you can look at an speculate about.

Serial:
AIM Version: 2.4 Build: 100
Db Version: 0025
Date: 04-04-2014, 16:16:13
Account: Sam's Crib
Notes:
ODU: Slimline-3
Multiswitch: Standalone SWiM
Zip: 28328
Config: ODUo---oSWiMo---oSPLo---oDECA---oIRD
Location: At ODU output
Options: All nationals with spots
Sat/Tr Freq(MHz) Pwr(dBm) SNR(dB) SQ Offset(MHz) Lock Volts(V) Cur(mA) ODU SWiM
ssss/tt xxxx.xx -xxx.x xx.x xxx (-)x.xx xxx xx.x xxxx abcd x
99/1 274.00 -26.2 13.6 96 -0.79 YES 13.1 80 SL3 0
99/2 274.00 -25.5 13.8 96 -0.78 YES 18.2 80 SL3 0
99/3 314.00 -25.3 13.3 95 -0.79 YES 13.1 80 SL3 0
99/4 314.00 -25.2 13.7 96 -0.78 YES 18.2 80 SL3 0
99/5 354.00 -27.4 13.2 95 -0.79 YES 13.1 80 SL3 0
99/6 354.00 -27.6 13.2 95 -0.78 YES 18.2 80 SL3 0
99/7 394.00 -28.1 13.4 95 -0.79 YES 13.1 90 SL3 0
99/8 394.00 -28.2 13.6 96 -0.16 YES 18.2 80 SL3 0
99/9 434.00 -28.2 13.1 95 -0.79 YES 13.1 90 SL3 0
99/10 434.00 -28.6 13.1 95 -0.79 YES 18.2 80 SL3 0
99/11 474.00 -28.4 13.3 95 -0.79 YES 13.1 80 SL3 0
99/12 474.00 -28.4 13.5 96 -0.79 YES 18.2 80 SL3 0
99/13 514.00 -28.7 14.2 97 -0.79 YES 13.1 90 SL3 0
99/14 514.00 -28.8 14.0 97 -0.80 YES 18.2 90 SL3 0
99/15 554.00 -29.3 14.4 97 -0.79 YES 13.1 90 SL3 0
99/16 554.00 -27.7 14.8 98 -0.79 YES 18.2 90 SL3 0
99/17 598.00 -32.5 11.1 85 -0.80 YES 13.1 90 SL3 0
99/18 598.00 -33.5 10.0 78 -0.80 YES 18.2 90 SL3 0
99/19 642.00 -- -- -- -- NO 13.1 90 SL3 0
99/20 642.00 -27.5 15.1 99 -0.80 YES 18.2 90 SL3 0
99/21 682.00 -27.1 14.0 97 -0.81 YES 13.1 90 SL3 0
99/22 682.00 -28.3 14.5 98 -0.80 YES 18.2 90 SL3 0
99/23 726.00 -28.8 15.0 99 -0.78 YES 13.1 90 SL3 0
99/24 726.00 -30.8 14.8 98 -0.79 YES 18.2 90 SL3 0
101/1 974.00 -27.3 14.4 97 -0.14 YES 13.1 90 SL3 0
101/2 988.58 -24.2 15.0 99 -0.22 YES 18.2 90 SL3 0
101/3 1003.16 -26.5 13.3 95 -0.17 YES 13.1 90 SL3 0
101/4 1017.74 -21.9 14.7 98 -0.17 YES 18.2 90 SL3 0
101/5 1032.32 -26.6 12.6 94 -0.08 YES 13.1 90 SL3 0
101/6 1046.90 -23.1 15.9 100 -0.16 YES 18.2 90 SL3 0
101/7 1061.48 -26.5 12.3 92 -0.12 YES 13.1 90 SL3 0
101/8 1076.06 -23.0 15.8 100 -0.20 YES 18.2 90 SL3 0
101/9 1090.64 -27.1 13.2 95 -0.15 YES 13.1 90 SL3 0
101/10 1105.22 -23.7 15.4 99 -0.36 YES 18.2 90 SL3 0
101/11 1119.80 -25.6 14.1 97 -0.19 YES 13.1 90 SL3 0
101/12 1134.38 -24.5 13.0 95 -0.18 YES 18.2 80 SL3 0
101/13 1148.96 -26.3 13.5 96 -0.10 YES 13.1 90 SL3 0
101/14 1163.54 -23.1 16.7 100 -0.18 YES 18.2 90 SL3 0
101/15 1178.12 -25.5 13.6 96 -0.13 YES 13.1 90 SL3 0
101/16 1192.70 -23.0 16.7 100 -0.09 YES 18.2 90 SL3 0
101/17 1207.28 -25.9 14.4 97 -0.17 YES 13.1 90 SL3 0
101/18 1221.86 -32.0 7.3 58 -0.11 YES 18.2 80 SL3 0
101/19 1236.44 -24.9 15.0 99 -0.21 YES 13.1 90 SL3 0
101/20 1251.02 -22.6 13.4 95 -0.20 YES 18.2 90 SL3 0
101/21 1265.60 -26.2 14.4 97 -0.12 YES 13.1 90 SL3 0
101/22 1280.18 -23.2 17.0 100 -0.32 YES 18.2 90 SL3 0
101/23 1294.76 -25.4 14.5 98 -0.15 YES 13.1 90 SL3 0
101/24 1309.34 -23.8 17.4 100 -0.11 YES 18.2 90 SL3 0
101/25 1323.92 -25.8 14.5 98 -0.19 YES 13.1 90 SL3 0
101/26 1338.50 -- -- -- -- NO 18.2 90 SL3 0
101/27 1353.08 -26.3 14.8 98 -0.22 YES 13.1 90 SL3 0
101/28 1367.66 -25.5 13.1 95 -0.14 YES 18.2 90 SL3 0
101/29 1382.24 -26.8 14.7 98 -0.13 YES 13.1 90 SL3 0
101/30 1396.82 -23.9 17.1 100 0.04 YES 18.2 90 SL3 0
101/31 1411.40 -25.2 14.2 97 -0.16 YES 13.1 90 SL3 0
101/32 1425.98 -23.6 17.6 100 -0.12 YES 18.2 90 SL3 0
103b/1 274.00 -27.6 14.0 97 -0.77 YES 13.1 90 SL3 0
103b/2 274.00 -29.0 14.0 97 -0.77 YES 18.2 90 SL3 0
103b/3 314.00 -28.7 13.1 95 -0.78 YES 13.1 90 SL3 0
103b/4 314.00 -29.7 12.5 93 -0.77 YES 18.2 90 SL3 0
103b/5 354.00 -30.4 13.0 95 -0.78 YES 13.1 90 SL3 0
103b/6 354.00 -31.1 13.1 95 -0.77 YES 18.2 90 SL3 0
103b/7 394.00 -30.4 12.8 95 -0.78 YES 13.1 90 SL3 0
103b/8 394.00 -30.8 12.5 93 -0.77 YES 18.2 90 SL3 0
103b/9 434.00 -30.0 13.3 95 -0.78 YES 13.1 90 SL3 0
103b/10 434.00 -29.4 13.1 95 -0.77 YES 18.2 90 SL3 0
103b/11 474.00 -29.8 12.7 94 -0.78 YES 13.1 90 SL3 0
103b/12 474.00 -28.4 12.9 95 -0.77 YES 18.2 90 SL3 0
103b/13 514.00 -27.5 13.4 95 -0.78 YES 13.1 90 SL3 0
103b/14 514.00 -27.5 13.4 95 -0.78 YES 18.2 80 SL3 0
103b/15 554.00 -- -- -- -- NO 13.1 90 SL3 0
103b/16 554.00 -- -- -- -- NO 18.2 90 SL3 0
103b/17 598.00 -- -- -- -- NO 13.1 90 SL3 0
103b/18 598.00 -- -- -- -- NO 18.2 90 SL3 0
103b/19 642.00 -33.9 6.8 53 -0.78 YES 13.1 90 SL3 0
103b/20 642.00 -- -- -- -- NO 18.2 90 SL3 0
103b/21 682.00 -26.8 14.5 98 -0.78 YES 13.1 90 SL3 0
103b/22 682.00 -27.4 13.2 95 -0.77 YES 18.2 90 SL3 0
103b/23 726.00 -- -- -- -- NO 13.1 90 SL3 0
103b/24 726.00 -37.3 3.2 21 -0.78 YES 18.2 90 SL3 0
103a/1 1691.67 -- -- -- -- NO 13.1 90 SL3 0
103a/2 1691.67 -23.4 9.1 73 -0.80 YES 18.2 90 SL3 0
103a/3 1754.17 -- -- -- -- NO 13.1 90 SL3 0
103a/4 1754.17 -21.3 13.5 96 -0.79 YES 18.2 90 SL3 0
103a/5 1800.67 -- -- -- -- NO 13.1 90 SL3 0
103a/6 1800.67 -27.4 9.8 77 -0.80 YES 18.2 90 SL3 0
103a/9 1840.00 -27.3 14.2 97 -0.79 YES 13.1 90 SL3 0
103a/10 1840.00 -28.1 12.6 94 -0.79 YES 18.2 90 SL3 0
103a/11 1880.00 -27.7 13.9 96 -0.79 YES 13.1 90 SL3 0
103a/12 1880.00 -28.9 12.7 94 -0.79 YES 18.2 90 SL3 0
103a/13 1920.00 -27.5 13.4 95 -0.79 YES 13.1 90 SL3 0
103a/14 1920.00 -28.9 12.8 95 -0.79 YES 18.2 90 SL3 0
103a/15 1960.00 -28.4 13.4 95 -0.79 YES 13.1 90 SL3 0
103a/16 1960.00 -29.3 13.5 96 -0.79 YES 18.2 90 SL3 0
103a/17 2000.00 -26.9 13.4 95 -0.79 YES 13.1 90 SL3 0
103a/18 2000.00 -28.8 13.2 95 -0.79 YES 18.2 80 SL3 0
103a/19 2040.00 -28.1 13.9 96 -0.79 YES 13.1 90 SL3 0
103a/20 2040.00 -29.0 13.6 96 -0.80 YES 18.2 90 SL3 0
103a/21 2080.00 -27.8 13.6 96 -0.80 YES 13.1 90 SL3 0
103a/22 2080.00 -28.9 13.0 95 -0.80 YES 18.2 90 SL3 0
103a/23 2120.00 -29.2 14.5 98 -0.79 YES 13.1 90 SL3 0
103a/24 2120.00 -29.7 14.1 97 -0.79 YES 18.2 90 SL3 0


Behind the HR20-100.

Serial:
AIM Version: 2.4 Build: 100
Db Version: 0025
Date: 04-04-2014, 16:33:28
Account: Sam's Crib
ODU: Slimline-3
Multiswitch: Standalone SWiM
Zip: 28328
Config: ODUo---oSWiMo---oSPLo---oDECA---oIRD
Location: At IRD input
Options: All nationals
Sat/Tr Freq(MHz) Pwr(dBm) SNR(dB) SQ Offset(MHz) Lock Volts(V) Cur(mA) ODU SWiM
ssss/tt xxxx.xx -xxx.x xx.x xxx (-)x.xx xxx xx.x xxxx abcd x
99/1 274.00 -45.5 13.3 95 0.65 YES 13.0 170 SL3 6
99/2 274.00 -45.4 13.5 96 0.64 YES 13.0 160 SL3 6
99/3 314.00 -45.7 13.1 95 0.65 YES 13.0 210 SL3 6
99/4 314.00 -45.6 13.5 96 0.64 YES 12.9 270 SL3 6
99/5 354.00 -46.0 12.8 95 0.64 YES 13.0 260 SL3 6
99/6 354.00 -45.9 12.8 95 0.64 YES 13.0 250 SL3 6
99/7 394.00 -45.7 13.2 95 0.64 YES 13.0 250 SL3 6
99/8 394.00 -45.8 13.4 95 0.01 YES 13.0 250 SL3 6
99/9 434.00 -45.9 12.8 95 0.64 YES 12.9 260 SL3 6
99/10 434.00 -46.1 12.9 95 0.63 YES 12.9 250 SL3 6
99/11 474.00 -45.8 13.0 95 0.64 YES 13.0 250 SL3 6
99/12 474.00 -45.6 13.2 95 0.63 YES 12.9 250 SL3 6
99/13 514.00 -45.8 13.8 96 0.63 YES 13.0 250 SL3 6
99/14 514.00 -46.1 13.6 96 0.65 YES 12.9 260 SL3 6
101/1 974.00 -46.7 14.3 97 -0.05 YES 13.0 260 SL3 6
101/2 988.58 -47.5 14.4 97 0.02 YES 13.0 250 SL3 6
101/3 1003.16 -47.2 13.4 95 -0.05 YES 12.9 250 SL3 6
101/4 1017.74 -46.8 14.3 97 -0.07 YES 13.0 250 SL3 6
101/5 1032.32 -47.8 12.6 94 -0.12 YES 12.9 260 SL3 6
101/6 1046.90 -47.7 15.6 100 -0.05 YES 12.9 250 SL3 6
101/7 1061.48 -47.4 12.5 93 -0.12 YES 13.0 250 SL3 6
101/8 1076.06 -47.4 15.4 99 -0.36 YES 12.9 260 SL3 6
101/9 1090.64 -48.1 13.1 95 -0.05 YES 12.9 250 SL3 6
101/10 1105.22 -47.9 15.0 99 0.13 YES 13.0 250 SL3 6
101/11 1119.80 -47.6 14.0 97 -0.06 YES 13.0 260 SL3 6
101/12 1134.38 -47.9 12.9 95 -0.02 YES 12.9 250 SL3 6
101/13 1148.96 -48.0 13.4 95 -0.12 YES 13.0 260 SL3 6
101/14 1163.54 -47.2 16.1 100 -0.06 YES 12.9 260 SL3 6
101/15 1178.12 -47.3 13.3 95 -0.12 YES 13.0 250 SL3 6
101/16 1192.70 -46.4 16.2 100 -0.12 YES 13.0 260 SL3 6
101/17 1207.28 -47.9 14.1 97 -0.06 YES 13.0 260 SL3 6
101/18 1221.86 -54.6 6.8 53 -0.14 YES 13.0 250 SL3 6
101/19 1236.44 -47.3 14.6 98 0.76 YES 13.0 250 SL3 6
101/20 1251.02 -46.6 13.2 95 -0.02 YES 13.0 260 SL3 6
101/21 1265.60 -48.0 14.2 97 -0.13 YES 13.0 250 SL3 6
101/22 1280.18 -47.6 16.4 100 0.06 YES 13.0 260 SL3 6
101/23 1294.76 -47.2 14.4 97 -0.07 YES 13.0 260 SL3 6
101/24 1309.34 -46.3 16.9 100 -0.12 YES 13.0 250 SL3 6
101/25 1323.92 -47.9 14.4 97 -0.07 YES 13.0 260 SL3 6
101/26 1338.50 -- -- -- -- NO 13.0 260 SL3 6
101/27 1353.08 -47.5 14.6 98 0.02 YES 13.0 260 SL3 6
101/28 1367.66 -46.7 12.8 95 -0.10 YES 13.0 250 SL3 6
101/29 1382.24 -47.8 14.5 98 -0.13 YES 13.0 250 SL3 6
101/30 1396.82 -47.5 16.5 100 0.13 YES 13.0 260 SL3 6
101/31 1411.40 -45.7 14.0 97 -0.07 YES 13.0 260 SL3 6
101/32 1425.98 -46.0 16.9 100 -0.13 YES 13.0 250 SL3 6
103b/1 274.00 -45.1 13.7 96 0.64 YES 13.0 250 SL3 6
103b/2 274.00 -45.3 13.6 96 0.64 YES 13.0 260 SL3 6
103b/3 314.00 -45.8 12.8 95 0.65 YES 13.0 250 SL3 6
103b/4 314.00 -45.8 12.3 92 0.64 YES 13.0 260 SL3 6
103b/5 354.00 -45.8 12.9 95 0.64 YES 13.0 260 SL3 6
103b/6 354.00 -45.7 13.0 95 0.64 YES 13.0 260 SL3 6
103b/7 394.00 -45.9 12.5 93 0.64 YES 13.0 260 SL3 6
103b/8 394.00 -46.0 12.2 91 0.64 YES 13.0 260 SL3 6
103b/9 434.00 -45.8 13.1 95 0.64 YES 13.0 260 SL3 6
103b/10 434.00 -45.9 12.9 95 0.63 YES 13.0 260 SL3 6
103b/11 474.00 -46.3 12.5 93 0.64 YES 13.0 250 SL3 6
103b/12 474.00 -45.8 12.6 94 0.63 YES 13.0 260 SL3 6
103b/13 514.00 -44.9 13.1 95 0.64 YES 13.0 250 SL3 6
103b/14 514.00 -45.2 13.0 95 0.64 YES 13.0 260 SL3 6
103a/9 1840.00 -45.2 13.7 96 0.57 YES 13.0 260 SL3 6
103a/10 1840.00 -45.8 12.0 90 0.57 YES 13.0 260 SL3 6
103a/11 1880.00 -45.8 13.4 95 0.57 YES 13.0 260 SL3 6
103a/12 1880.00 -45.8 12.1 91 0.58 YES 13.0 260 SL3 6
103a/13 1920.00 -45.7 12.9 95 0.57 YES 13.0 260 SL3 6
103a/14 1920.00 -45.9 12.0 90 0.57 YES 13.0 260 SL3 6
103a/15 1960.00 -45.7 13.0 95 0.57 YES 13.0 260 SL3 6
103a/16 1960.00 -45.7 12.6 94 0.57 YES 13.0 260 SL3 6
103a/17 2000.00 -45.8 12.9 95 0.56 YES 13.0 260 SL3 6
103a/18 2000.00 -45.9 12.3 92 0.56 YES 13.0 260 SL3 6
103a/19 2040.00 -45.7 13.5 96 0.57 YES 13.0 260 SL3 6
103a/20 2040.00 -45.7 12.8 95 0.57 YES 13.0 260 SL3 6
103a/21 2080.00 -45.8 13.1 95 0.56 YES 13.0 260 SL3 6
103a/22 2080.00 -45.8 12.4 92 0.56 YES 13.0 260 SL3 6
103a/23 2120.00 -44.9 13.9 96 0.56 YES 13.0 250 SL3 6
103a/24 2120.00 -44.9 13.3 95 0.56 YES 13.0 260 SL3 6


----------



## slice1900 (Feb 14, 2013)

Stuart Sweet said:


> I've done a very similar test and found only one inescapable result: that there is only a very loose correlation between CNR and the receiver's reported signal strength. I have been told several things about this number, and the most credible is that it is derived from the CNR and the inverse BER. I can't reverse-engineer the formula but to answer your question from post #1, my experience has shown that there is not a concrete correlation between CNR and signal strength as reported so, yes it is a waste of time.


Stuart, could you elaborate on the test you did, and what your results were? What method did you use to reduce CNR, and how low did you get it before the receiver could no longer maintain a perfect/any picture?

When you found only a loose correlation between CNR and SS, were you testing across transponders/satellites? I would probably agree with you that raw CNR is not used, but rather than adding BER as a second factor I think SS may be calculated from Eb/N0 (see http://en.wikipedia.org/wiki/Eb/N0) which is basically CNR adjusted to be independent of modulation and transponder bandwidth. Thus the 0-100 scale would mean the same thing across all satellites. A CNR x on a Ku satellite isn't going to mean the same thing as the same CNR x on a Ka satellite, when they're using different modulation and have different transponder bandwidths, so if you tested across Ku and Ka, I could well imagine you would conclude there isn't a strong relationship between CNR and SS.

Anyway, that speculation aside, I'm not sure I see how CNR and BER can vary independently to any great degree under normal circumstances. How can BER increase while CNR is held constant, or vice versa, unless the bit error rate is changing prior to the signal downlink? (i.e. due to issues in the uplink, or modulation errors at the source) That is, what might be the source of increased BER on the downlink that would not also decrease CNR? If they don't vary independently except in rare circumstances, even if BER is a factor in calculating SS it may be a factor you can ignore 99% of the time.

I find it hard to discount P Smith's findings without seeing something equally as compelling as the diagnostic logs he located in the DVR showing SS and SNR, and the relationship his graph demonstrated. Even if that relationship isn't exact (i.e. if it doesn't actually use the SNR value reported as the method or sole method of generating SS) it must be quite close, at least across his sample. Otherwise the graph he produced would be a scatter plot. I wonder if he would have had much more scattered results if he'd tuned some SD channels during the period the log was generated, since those SNR values would not correlate to SS in the same way as the HD channels. Likewise if some HD channels use QPSK and others use 8PSK.


----------



## veryoldschool (Dec 10, 2006)

Sorting through the logs [and not yet all of them] preliminary results look to be:
100% = CNR 15.5 or greater
99% = 15.0-15.4
98% = 14.5-14.9
97% = 14.0-14.4
96% = 13.5-13.9
95% = 12.8-13.4
94% = 12.6-12.7
93% = 12.5
91% = 12.1-12.2
90% = 12.0
88% = 11.7 
85% = 11.1-11.2
78% = 10.0 
77% = 9.8
73% = 9.1
58% = 7.3
53% = 6.8
21% = 3.2


----------



## P Smith (Jul 25, 2002)

veryoldschool said:


> Sorting through the logs [and not yet all of them] preliminary results look to be:
> 100% = CNR 15.5 or greater
> 99% = 15.0-15.4
> 98% = 14.5-14.9
> ...


Did you pull DVR's log ? Or it's about AIM's output?

Edit: looks like your values matching that curve by DVR's logs.

[sharedmedia=core:attachments:22926]


----------



## veryoldschool (Dec 10, 2006)

P Smith said:


> Did you pull DVR's log ? Or it's about AIM's output?


I'm working with the AIM logs.


----------



## P Smith (Jul 25, 2002)

veryoldschool said:


> I'm working with the AIM logs.


does AIM reporting BER ?


----------



## veryoldschool (Dec 10, 2006)

P Smith said:


> does AIM reporting BER ?


No.


----------



## slice1900 (Feb 14, 2013)

P Smith said:


> does AIM reporting BER ?


Solid Signal has an outdated version of the AIM manual from 2010 at http://manuals.solidsignal.com/DIRECTV_AIM_Manual.pdf. I say outdated, because it doesn't mention CNR at all (nor BER) Not sure if there is a newer manual available somewhere, a quick google couldn't find one.

Interestingly, the manual shows rather than CNR it reports Es/N0, which is closely related to Eb/N0 (differs in being energy per symbol as opposed to energy per bit) Not only that, but if you look on page 46, Es/N0 is shown as one of the four checks that must pass for IV, along with LNB Offset, Signal Power and Lock Status. It is also shown as being reported for a transponder survey, not CNR or SNR.

VOS has results from an AIM that reported CNR, and samrs has posted results from an AIM (I think that's a transponder survey?) that shows SNR. So if the AIM used to report Es/N0 and now reports CNR or maybe SNR, was Es/N0 renamed with a firmware update at some point to reduce confusion?


----------



## veryoldschool (Dec 10, 2006)

slice1900 said:


> VOS has results from an AIM that reported CNR, and samrs has posted results from an AIM (I think that's a transponder survey?) that shows SNR.
> confusion?


The AIM I used showed SNR, but "the folks a DirecTV" gave me a lot of crap for using SNR as it was really CNR, which is true.
My reply was for them to fix their own damn meter then. :lol:


----------



## samrs (May 30, 2004)

> VOS has results from an AIM that reported CNR, and samrs has posted results from an AIM (I think that's a transponder survey?) that shows SNR. So if the AIM used to report Es/N0 and now reports CNR or maybe SNR, was Es/N0 renamed with a firmware update at some point to reduce confusion?


You can pause in one room, move to the next and pick up where you left off.

Likely a lot of hands stirring the pot.

I was trained CNR.


----------



## P Smith (Jul 25, 2002)

is AIM and DTV receivers using same tuner/demod chips ?


----------



## veryoldschool (Dec 10, 2006)

P Smith said:


> is AIM and DTV receivers using same tuner/demod chips ?


:shrug:


----------



## slice1900 (Feb 14, 2013)

veryoldschool said:


> The AIM I used showed SNR, but "the folks a DirecTV" gave me a lot of crap for using SNR as it was really CNR, which is true.
> My reply was for them to fix their own damn meter then. :lol:


OK, so it never displayed anything labeled "CNR", but originally displayed Es/N0 and now displays something labeled "SNR". Given the AIM based IV pass/fail on Es/N0 back in 2010, I have a hunch that they just changed the name, as "SNR" is a more familiar term, but the underlying measurement is likely the same. In addition, one would assume receiver's IV test would be done in the same way as the AIM's, so it is probably based off Es/N0 as well. I wouldn't be at all surprised if what P Smith found labeled as "SNR" is really Es/N0.

When I scanned the AIM manual, I noticed the instructions for dithering show peaking on signal power in dBm, versus Es/N0. Do the instructions still say to peak on signal power rather than (what is now called) SNR? I would think you'd want to maximize signal to noise, not power - though perhaps it ends up being pretty much the same thing in practice.


----------



## P Smith (Jul 25, 2002)

damn !
I know for sure BCM450x reporting SNR ... some of DTV have it (almost all e* IRD running it)


----------



## P Smith (Jul 25, 2002)

Perhaps I must keep the "CNR" labeling on my chart seen the name in logs ... just BCM4505 reporting SNR made me think there was mistake. Perhaps not.


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## peds48 (Jan 11, 2008)

slice1900 said:


> Do the instructions still say to peak on signal power rather than (what is now called) SNR?


Yes. you peak on signal power


----------



## slice1900 (Feb 14, 2013)

peds48 said:


> Yes. you peak on signal power


If you peaked on "SNR", would you get the same result, or is the peak SNR not always at the same point where you get peak power?


----------



## P Smith (Jul 25, 2002)

SNR is more important parameter then RF level in same condition


----------



## peds48 (Jan 11, 2008)

slice1900 said:


> If you peaked on "SNR", would you get the same result, or is the peak SNR not always at the same point where you get peak power?


SNR is not not part of the peaking process "screen"


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## slice1900 (Feb 14, 2013)

peds48 said:


> SNR is not not part of the peaking process "screen"


I understand that, and I realize that when you're working for Directv you have to do installs how they say, but it is _possible_ to peak for SNR - with a little bit more work watching the meter as you do the fine adjustments. If it doesn't show SNR on the "peaking screen" there's no reason you'd have to use that screen, is there?

What all does peaking involve? As I understand it, it keeps track of the highest signal power for you, and provides the "turns calculator". Anything else? I suppose it must disable the AGC in a SWM LNB, otherwise there would be no "peak" power to find. Curious how that works, as I think the AGC on the ASWM chip may only amplify, and never attenuate. Maybe it uses a fixed amplification to overcome the "insertion loss" in/through the RF5201.


----------



## peds48 (Jan 11, 2008)

slice1900 said:


> I understand that, and I realize that when you're working for Directv you have to do installs how they say, but it is _possible_ to peak for SNR - with a little bit more work watching the meter as you do the fine adjustments. If it doesn't show SNR on the "peaking screen" there's no reason you'd have to use that screen, is there?
> 
> What all does peaking involve? As I understand it, it keeps track of the highest signal power for you, and provides the "turns calculator". Anything else? I suppose it must disable the AGC in a SWM LNB, otherwise there would be no "peak" power to find. Curious how that works, as I think the AGC on the ASWM chip may only amplify, and never attenuate. Maybe it uses a fixed amplification to overcome the "insertion loss" in/through the RF5201.


I can go to the satellite tune screen and see the CSR signal power and all the stuff posted by samrs.

Sent from my SM-N900V using Tapatalk


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> Curious how that works, as I think the AGC on the ASWM chip may* only amplify, and never attenuate*. Maybe it uses a fixed amplification to overcome the "insertion loss" in/through the RF5201.


Check the logs. It does both.


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> Check the logs. It does both.


I'm not so sure. In a SWM 8 / SWM LNB each input is split 3 ways to the 3 RF5201s, and then split 4 ways in the 6x4 multiswitch inside each RF5201. Perhaps that 6x4 has buffer amps like the WB68 so there's essentially no insertion loss, but that wouldn't make a whole lot of sense when there are two amplifiers (an AGC amp followed by a programmable gain amp) for each of the three SWM channel outputs of the RF5201, and the one legacy output of the RF5201 is also amplified.

If we assume for the moment buffer amps aren't used in the 6x4, there's a ~7 db loss through the 3 way split, and another ~8 db loss through the 6x4, for a total of ~15 db. Since the SWM's rated AGC range is for inputs from -15 dbm to -45 dbm to output at -30 dbm, given 15 db of loss at the input there's no need to ever attenuate, only to amplify with a range from 0-30 db. This would simplify the design by eliminating buffer amps in the 6x4 switch as well as removing the requirement for the AGC to be able to attenuate the input.

If you do the math for the SWM16, which has an additional ~4 db loss to split the inputs between the two SWM8 "halves" inside, the loss to the legacy ports would be around 19 db if there was no amplification anywhere. It has been reported that the loss is actually a bit over 10 db, which is what you'd expect if the 6x4 multiswitch was lossless, but if that's the case, then the amp on the legacy port output in the RF5201 is providing zero gain.

I'm assuming that amp is there for a reason, but it is possible it isn't powered in the SWM16 - because I do wonder why the amp wasn't designed to be capable of making up all the loss, allowing lossless cascading as appears to be the case with the SWM32. Perhaps the amp is inactive in the SWM16, but is enabled in the SWM32. There's no way to know for certain.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> I'm not so sure.


"says the armchair quarterback"
If you actually got into the game, you'd find how it's played.

Once again I'm having difficulty with answering a question, only to find "I'm not so sure".

At some point "I don't care".


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## slice1900 (Feb 14, 2013)

If I was sure I'd say so. I don't understand why you like to criticize so much when I admit that I'm not sure. I respect those who are willing to admit to the limits of their knowledge much more so than those who claim to speak from a position of authority but can't back it up when it comes down to it.

If you're sure the AGC itself attenuates the signal, what "logs" were you referring to? Unless your logs show the signal levels at each stage inside the SWM, all they demonstrate is that the input level to the SWM may be higher than the output level, which is already known.

If you "don't care" that's fine, but why bother to question my original statement that I prefaced with "I think"? All that says is "I think" one thing and "you think" something else, but never of us knows for sure. As you say, the point is academic, except to one who is curious how the ASWM operates internally.

For those who are, here's a block diagram and pinout of the RF5401


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> If I was sure I'd say so. I don't understand why you like to criticize so much when I admit that I'm not sure. I respect those who are willing to admit to the limits of their knowledge much more so than those who claim to speak from a position of authority but can't back it up when it comes down to it.
> 
> If you're sure the AGC itself attenuates the signal, what "logs" were you referring to? Unless your logs show the signal levels at each stage inside the SWM, all they demonstrate is that the input level to the SWM may be higher than the output level, which is already known.
> 
> If you "don't care" that's fine, but why bother to question my original statement that I prefaced with "I think"? All that says is "I think" one thing and "you think" something else, but never of us knows for sure. As you say, the point is academic, except to one who is curious how the ASWM operates internally.


"Let's see....."
One side reads papers but doesn't understand what they read. One might ask how much schooling/experience they've had in this field.
The other side has been involved in testing and the engineers at DirecTV, which along with their own experience, "just might" give them an idea of how it works.

Why don't you take apart a SWiM and test it?
This way "you'll know".


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> "Let's see....."
> One side reads papers but doesn't understand what they read. One might ask how much schooling/experience they've had in this field.
> The other side has been involved in testing and the engineers at DirecTV, which along with their own experience, "just might" give them an idea of how it works.
> 
> ...


Well, if I had the test equipment to do so, I could pry open a SWM and probe the signal level at the AGC +/- inputs and compare with the signal level at the FDM +/- outputs. Then I'd know.

Or one can resort to "appeal to authority" and state that because he was involved in testing with Directv's engineers and has experience in the field he automatically knows the internals of the RF5201. Do you even know who designed it? If you think it was Entropic, you'd be wrong.


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## peds48 (Jan 11, 2008)

slice1900 said:


> If you think it was Entropic, you'd be wrong.


well you gave out the answer..... !rolling


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> Or one can....


Accept that SWiM [all but the -32] attenuates from -15 dBm and amplifies to -45 dBm for the output of -30.


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## slice1900 (Feb 14, 2013)

veryoldschool said:


> Accept that SWiM [all but the -32] attenuates from -15 dBm and amplifies to -45 dBm for the output of -30.


I never suggested otherwise, and if you think I did perhaps my wording was not clear. The question I posed was whether the AGC amp in the RF5201 (shown as 430 in Figure 11) ever does any attenuation or only amplifies in a 0-30 db range.

We know the SWM will attenuate an input of -15 dbm to a -30 dbm output. But if there's a 15 db loss between the SWM's input and the AGC amp's input as I believe to be the case, then that AGC amp never attenuates as the losses prior to reaching it (from the 3 way split between RF5201s followed by a 4 way split in the 6x4 switch) would have already done so.

At the other extreme, with an input to the SWM of -45 dbm, the AGC amp would receive an input of -60 dbm and amplify it by 30 db to reach the nominal -30 dbm output.

I'm curious, it sounds like you're suggesting the SWM-32 has a different AGC range? I know one important difference between it and the SWM16 is is that it has legacy outputs that are about level with its inputs, but wasn't aware it had a different AGC range.


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## veryoldschool (Dec 10, 2006)

slice1900 said:


> I'm curious, it sounds like you're suggesting the SWM-32 has a different AGC range? I know one important difference between it and the SWM16 is is that it has legacy outputs that are about level with its inputs, but wasn't aware it had a different AGC range.


I'm not sure it matters to anyone else here on the forum as to what goes on inside a SWiM.
How it functions "from the outside" is, and how do I get it to work for me the best it can.
I don't need to know how to refine gasoline to use it in my car.
Input and output signals of a SWiM are what we need to know and deal with.
The SWiM-32 has a lower input level maximum. This suggests there is an amp that would compress at the input levels of the others.


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