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Discussion Starter · #1 ·
Thanks to Solid Signal for the use of a AIM, I've finally been able to look at an LNB in the detail I've wanted since I first came to this forum.

The whole story can be found here: http://forums.solidsignal.com/showthread.php/1371-The-ins-and-outs-of-an-LNB

The short story is dBm/dBµV doesn't mean anywhere near what I've been thinking for all of this time.

The LNB looks to be like this:



When I've always thought it was like this, where output levels are more related to input levels:



The difference is the LO/Mixer stage noise isn't being filtered out, so with no signal at the input the output power has been measured at -40 dBm to as high as -27 dBm.
The SNR/CNR is the only thing that matters.

I compared two LNBs and the output power had nothing to do with the SNR. Even when it was higher with one, the SNR was lower than with the other.



From the readings the AIM was able to make, this looks like the "ins & outs" of the LNBs.
 

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Discussion Starter · #3 ·
dsw2112 said:
Interesting info VOS. I would have thought the Input signal would be much more important.
The input is most important, but the output levels simply don't reflect the input levels as much as I've been thinking from all of my years of working with "things" like this.
They're built to a price and should work in the intended way, "but" their range for rainfade "could be" improved, for what might cost pennies.
 

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Interesting info VOS. I would have thought the Input signal would be much more important to the output.
Forgot a few words :lol:

Maybe there's a VOS LNB on the horizon :) I'm still waiting for the external DECA crossover though ;)
 

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veryoldschool said:
The input is most important, but the output levels simply don't reflect the input levels as much as I've been thinking from all of my years of working with "things" like this.
They're built to a price and should work in the intended way, "but" their range for rainfade "could be" improved, for what might cost pennies.
VOS:

I've got a Super Buddy and recently obtained a Turbo S2.
I think I've got several SL-3 and SL-5 LNB's and 2 or 3 different reflectors in various pieces.
The Allied Instrument meters give dBm and SNR outputs directly when tuning.
I'm not good with the electronics but can set up several experiments if you need more info.
May take a while to complete but love projects.
I'll need a spreadsheet of info you want and i can fill in the blanks.
PM me if you want to.

Doctor j
 

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Discussion Starter · #9 ·
doctor j said:
VOS:

I've got a Super Buddy and recently obtained a Turbo S2.
I think I've got several SL-3 and SL-5 LNB's and 2 or 3 different reflectors in various pieces.
The Allied Instrument meters give dBm and SNR outputs directly when tuning.
I'm not good with the electronics but can set up several experiments if you need more info.
May take a while to complete but love projects.
I'll need a spreadsheet of info you want and i can fill in the blanks.
PM me if you want to.

Doctor j
I've seen your work before, and sort of figured you might drop in here too. :lol:

It might be good to read the whole story in the solid signal link in the first post.

SNR is CNR, so the values will be the same dB.

Larger dishes might show better SNR. So that might be worth looking at.

dBm/dBµV outputs with zero [no] input will give some idea of the output amplifier gain of the LO/Mixer noise.

Now the difference of no input and the output power compared to the output power with an input signal, should be the SNR.
If the dish size is the same, then changes in the SNR between LNBs, should be from the gain of the Low Noise Amp [LNA] at the input of the LNB.

From the two samples I tested, the SNR varied 0.5-2.4 dB, but the output power varied as much as 15 dB.
With all of the TPs, it would take months :lol: to run the tests, so I streamlined my testing to 4 TPs from 99, 101, 103, as this gave two evens & two odds from each.

I could post a spreadsheet for you, but I've seen yours and you know how to yourself.
 

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VOS wrote on the SS forum:

... So what is the power on the lowest even/odd tps?

99-1 = -43.6 dBm
99-2 = -41.5 dBm [this one passed]
101-1 = -44.1 dBm
101-2 = -46.0 dBm
103a-9 = -46 dBm
103a-10 = -45 dBm
103b-1 = -41.9 dBm [doesn't look like it was part of the IV test]
103b-2 = -40.9 dBm [doesn't look like it was part of the IV test]
110-10 = -46 dBm
119- 23 = -46.6 dBm
119-22 = -47.4 dBm
Tp. 23 @ 119 is a spotbeam. Are you sure you didn't mean tp. 27 which is the only odd CONUS tp. @ 119?
 

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Discussion Starter · #11 ·
HoTat2 said:
VOS wrote on the SS forum:

Tp. 23 @ 119 is a spotbeam. Are you sure you didn't mean tp. 27 which is the only odd CONUS tp. @ 119?
I had to check and that was the TP I looked at after the IV test failed.
It was the first test I did with the AIM, so if it's a spot that doesn't point this way, it wasn't reflective of why 119 might have failed.

"The main point" is all other tests didn't look at 119, so the whole focus of this testing was the 99 - 101 - 103 a/b, as the SL3 is something everyone has, and 110 & 119 are sort of pointless.
 

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It took a whole lot of reading to find out why you were doing all this reporting. The first of the two reasons you listed didn't really make sense to me, but the second make a lot of sense (that is, "to characterize/define the LNB output to know what determines a good setup"). One other motivation for all these details is LNB performance verification. That is to say, you can take several readings to determine whether or not an old, used LNB is still good.

It seems as though you are using the only meter (the AIM) that can properly decode the 99 and 103 Ka signals to provide an IRD number like you'd see on the receivers which is what they use to pass the IV test. The AI Turbo S2 can't show any signal strengths off 99 or 103 for reasons that I think are legal rather than technical. I do believe that you can see the 99 and 103 S/N ratio with the AI Turbo S2 using a Ka/Ku (non SWiM) LNB, but I tried twice to peak in a dish using the S/N ratio, and both times it failed to pass IV. I had to go back out and repeak/dither the dish to get 99 and 103 above 85 signal strength. You mention that S/N ratio is the most important element of an installation, but it doesn't matter much in practice if an installer can't use it to pass the IV test.

It may just be me, as I only tried twice to peak in using the S/N on 99 and 103. I don't have an AIM (yet). I really hate dithering, and I hate even more not knowing what my signals are at the dish during the first trip out. Lately, either the LNBs or the reflectors (or both) we've been getting are just terrible, and guys have been swapping out 3 or 4 brand new LNBs in a day, and using up 2 or 3 dishes, just to try to pass IV. It makes for a WHOLE LOT of trips to the dish when you can't see what the signals are out there. I really want to invest in an AIM to overcome this, but it's hard when the pay just keeps dropping and dropping (I should start advertising for commercial work, but that's another topic).
 

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Discussion Starter · #13 ·
ZandarKoad said:
It took a whole lot of reading to find out why .
The IRD has nothing to do with a pass/fail of IV at the dish. I didn't ever enter an IRD for my testing.
What I found using the AIM was the SNR would cause the IV failure long before the power level was too low.
A 10.5 dB SNR would fail on the 101 IV test, if it was the lowest.
There is so much noise power that is coming out of the LNB, that it makes power readings almost pointless.
The difference between the noise power and the SNR is all.

Dithering showed a one turn either way from a centered alignment of the 99 and the SNR clearly showed the drop, though small.
 

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Discussion Starter · #14 ·
With an LNB not mounted to a dish, and sitting on my dinning table pointed at the ceiling, its output power was:

99
odd -37 dBm
even -34 dBm
101
odd -38 dBm
even -40 dBm
103a
odd -27 dBm
even -30 dBm
103b
odd -34 dBm
even -38 dBm.

SNR was zero.

Mounted and aligned:

|WNC dBm|SNR dB|Calamp||gain diff dB|SNR diff dB
99-1|-30.4|11.0|-27.0|9.1|+3.4|-1.9
-2|-24.3|12|-31.2|9.9|-6.|-2.1
-3|-30.3|11|-26.4|9.2|+3.9|-1.8
-4|-23.5|11.7|-30.2|10.2|-6.7|-1.5
101-1||12.8||12.2||-0.6
-2||13||12.2||-0.8
-3||12.3||11.8||-0.5
-4||14.6||14.1||-0.5
103a-9|-20.4|11.1|-32.5|9.6|-12.1|-1.5
-10|-26.5|10.9|-31.4|10.3|-4.9|-0.6
-11|-19.3|12.3|-30.3|10.7|-11|-1.6
-12|-25.9|11.5|-30.5|11|-4.6|-0.5
103b-1|-21.9|11.8|-31.7|11.3|-9.8|-0.5
-2|-26.7|12.3|-29.7|9.9|-3|-2.4
-3|-21.9|11.5|-31.1|10.6|-9.2|-0.9
-4|-27.1|11.3|-29.3|10|-2.2|-1.3

If you review these readings, you'll find the SNR comes from the first stage amp, and the final output power comes from the second stage amp, which is amplifying the noise of the LO & mixer.
 

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"ZandarKoad" said:
It took a whole lot of reading to find out why you were doing all this reporting. The first of the two reasons you listed didn't really make sense to me, but the second make a lot of sense (that is, "to characterize/define the LNB output to know what determines a good setup"). One other motivation for all these details is LNB performance verification. That is to say, you can take several readings to determine whether or not an old, used LNB is still good.

It seems as though you are using the only meter (the AIM) that can properly decode the 99 and 103 Ka signals to provide an IRD number like you'd see on the receivers which is what they use to pass the IV test. The AI Turbo S2 can't show any signal strengths off 99 or 103 for reasons that I think are legal rather than technical. I do believe that you can see the 99 and 103 S/N ratio with the AI Turbo S2 using a Ka/Ku (non SWiM) LNB, but I tried twice to peak in a dish using the S/N ratio, and both times it failed to pass IV. I had to go back out and repeak/dither the dish to get 99 and 103 above 85 signal strength. You mention that S/N ratio is the most important element of an installation, but it doesn't matter much in practice if an installer can't use it to pass the IV test.

It may just be me, as I only tried twice to peak in using the S/N on 99 and 103. I don't have an AIM (yet). I really hate dithering, and I hate even more not knowing what my signals are at the dish during the first trip out. Lately, either the LNBs or the reflectors (or both) we've been getting are just terrible, and guys have been swapping out 3 or 4 brand new LNBs in a day, and using up 2 or 3 dishes, just to try to pass IV. It makes for a WHOLE LOT of trips to the dish when you can't see what the signals are out there. I really want to invest in an AIM to overcome this, but it's hard when the pay just keeps dropping and dropping (I should start advertising for commercial work, but that's another topic).
Basically what was found here is the length of lines or number of splits does not influence rain fade provided they are within operating levels.

SNR/CNR is what the receivers use for IV, they just set it to a 100 point scale.

I'm not familiar with the meter you are using. The AIM has its pluses and minuses. It's the best meter for DirecTV installations. It is slow to boot up. It's not very stable and is prone to crashing.

What LNBs do you have now? We've been getting the new R3 WNCs (-01). They vary greatly in signal levels. To pass IV on the worst ones I must not remove the LNB after fine tuning, and must dither on the 103. Dithering on the 101 usually brings the 103 1 point below IV values. Dithering the 101 brings the 99 higher than with the 103 however. Is it the 103 even you normally fail? I realize you can't dither the 103 with your meter, but perhaps a 1/4 turn either way on the knobs could get you to pass. Go to 103(ca) TP 16 on the receivers signal meter and adjust until it's fluctuating into 89.
 

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Discussion Starter · #16 ·
dielray said:
The AIM has its pluses and minuses. It's the best meter for DirecTV installations. It is slow to boot up. It's not very stable and is prone to crashing.
Slow to boot was something I noticed.
Stability [or instability] and crashing I didn't find, in the few days I used it.
Eating up the battery charge I sure noticed.
How often does yours crash or show stability problems?
 

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dielray, are you on the latest firmware? I don't see an issue with crashing, although I use it less than most installers would.
 

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"Stuart Sweet" said:
dielray, are you on the latest firmware? I don't see an issue with crashing, although I use it less than most installers would.
Yes, I'm on the current firmware. I came from the birdog which always just turned on and worked. The AIM works most of the time, it crashes maybe once a week.
 

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veryoldschool said:
With an LNB not mounted to a dish, and sitting on my dinning table pointed at the ceiling, its output power was:

If you review these readings, you'll find the SNR comes from the first stage amp, and the final output power comes from the second stage amp, which is amplifying the noise of the LO & mixer.
But isn't this LNB behavior what one would expect and is similar to that of analog LNBs receiving FM TV of the previous era?

Like all FM receivers the very high gain of the LNB IF amplifier generates lots of noise at the output under no signal conditions. Then when a signal of sufficient strength is received it actually "quiets" the noise output level to a point where the demodulated TV signal is of an acceptable quality.

The demodulated output would be measured as Video p-p/noise ratio for analog and of course BER for digital.

Those minimum C/N ratio readings you list are analogous to the "quieting sensitivity" of an FM receiver.
 

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Discussion Starter · #20 ·
HoTat2 said:
But isn't this LNB behavior what one would expect and is similar to that of analog LNBs receiving FM TV of the previous era?

Like all FM receivers the very high gain of the LNB IF amplifier generates lots of noise at the output under no signal conditions. Then when a signal of sufficient strength is received it actually "quiets" the noise output level to a point where the demodulated TV signal is of an acceptable quality.

The demodulated output would be measured as Video p-p/noise ratio for analog and of course BER for digital.

Those minimum C/N ratio readings you list are analogous to the "quieting sensitivity" of an FM receiver.
I don't see the similarity that you're trying to draw here.
The LNB is a [down] converter.
The first stage has an LNA to set/keep the noise figure low.
I wish I could measure the attenuation of 40 sheets of 100 grit sandpaper, which is what I used to attenuate the signal to the LNB.
This caused "only" a 3 dB drop of the output from the 101 SAT. Output & SNR dropped equally as I added sheets of sandpaper to the stack that ended up being 3/4" thick.
I find it hard to believe that this only attenuated the Ku input by half.
I suspect there is a log amp after the LNA.
The thermal noise [static] at this stage, with a 500 MHz bandwidth will be in the range of -85 dBm.
The unlocked output in this state measured from -40 to -27 dBm.
The noise may drop to some degree when the LO locks, but not 40+ dB.
 
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