Bravo on the LMR400. I have a length of it that I will replace my LMR240 with sometime soon. Have to shuffle the tickets in my “Job Jar” so I can get to it.
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Okay, so last week I was getting great results out of the receiver, as I described. Thursday my receiver picked up over 2,500 aircraft and 264,000 messages. Friday looked like it was going to be a little bit lighter, but then around noon reception dropped by more than half.
I installed and ran @wiedehopf’s gain optimizer and it seems to indicate that my setup works best at -10. Occasionally it drops to 49.6, but then the next cycle or two it immediately kicks back up to -10. I now have it running overnight. My understanding is that this is a ridiculously high gain setting. And I’m still receiving only half of what I was getting last week. Basically, I could put the whip antenna in the basement window back on this thing and I’d get similar results to what I have with the 1090Mhz antenna that’s 16-ish feet above the ground.
We have had some weather that reduced our VFR traffic starting Friday morning, but that cleared up yesterday and there has been no improvement in results.
I’m open to suggestions on what to do next.
install graphs1090 as advised before 
and determine what your setup is doing, in a good situation you would have around 5% strong messages.
When you have the data availble much can be said on basis of the screenshots, now everybody is poking in the dark
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I installed graphs1090 last week before this started. I’ll get some screenshots when I get home.
The great thing about LMR400 is you don’t need a pole – just lift the antenna up using the coax 
(I’m joking, it’s stiff coax for anyone who’s not used it)
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That is funny. Point taken. Leave it in the sun awhile before trying to uncoil it.
Isn’t using LMR400 for ADS-B receiver like using a cannon to kill a fly?
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True enough but for some it’s not about needing it but wanting it, so you do it and gather some enjoyment from it because you can. Sometimes it’s the little things that make us the happiest and it turns out to be worth it.
I needed at least 35 feet from the receiver, and I want to add 8 to 10 feet to the mast height; for that distance I decided to go with low-loss cable compared to the LMR240 that I had been using (and which wasn’t working anymore).
I forgot to get screen shots last night after putting my son to bed–at 42, I don’t have the energy to keep up with an 18 month old boy! I’ll try to remember them tonight.
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Apparently graphs1090 just… stopped… collecting data on Friday evening. Not sure what’s going on there, but here’s what I have. I’ve tried to restart graphs1090 but nothing, so I’ll reinstall it and hope it works.
You’ll note the sudden and drop around 12:00 on Friday.
Based on the partial information I see two things:
- Your weakest signals are quite high ( -22,8 dB)
- your noise figure is at 11,1%
Most likely you are too high on the gain but that should be visible when you have a longer duration of the graphs.
Wondering where your actual gain is running during this 1090 graphs recording period. Also, your results relative to the window whip antenna and the 1090 antenna at 16 feet in the air is concerning. I found that I had no control of my gain setting until I changed the “Adaptive Dynamic Range” setting to “No” in the Piaware-config file. Without that ADR setting in place, any attempt to change the gain setting would reset to the max auto setting of 49.6.
I did change the ADR setting to “no” last night and reset the auto gain script to run starting at a gain of 20.7. It bumped everything back up to -10.
I think this evening when I get home I’ll add lower gain values to the script and try it again from a gain of maybe 10.0 (positive, not negative) and see where it goes from there.
Graphs1090 won’t restart for some reason, so I think I’m going to have to uninstall and reinstall and try again. It was getting toward bedtime last night, anyway, and so maybe the auto gain script wasn’t getting enough data to operate effectively.
I’m sure there are plenty of other opinions, but I would suggest you hard set your gain to a number and move completely away from the auto gain scenario.
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That is exactly what I do.
(1) Disable auto gain setting.
(2) Manually set gain to a value max (49.6 dB) to start with.
(3) Wait for 24 hrs, then check graphs for % of signal > -3 dBFS. If it is higher than 10%, I reduce gain setting to say 42, and leave it running for anther 24 hrs.
(4) After 24 hrs, check %signals > -3 dBFS, and increase or decrease gain setting accordingly.
(5) Repeat this till I get optimum results.
To make it easy to manually set / change gain, I have installed an add-on in Skyaware map, through which I can adjust gain without using CLI Terminal or PuTTY.
https://github.com/abcd567a/set-gain/blob/master/README.md
Set-gain drop-down embeded in Skyaware map
Click on Screenshot to See Larger Size
Thank you for the pointer to the set-gain drop down embedded in the Skyaware map. I will work on installing that here and I appreciate your efforts with that tool.
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I have turned off the dump1090-fa autogain setting and turned on @wiedehopf’s gain optimization script. That’s the one that kept bumping it upwards. I’m going to try it again today when there’s more traffic and see if I get better results.
I ran a different script that seemed to suggest that 20.7 or 22.9 were better options. That’s why I started the gain optimization script at that level. I’ll try to paste those results when I get home if they’re still on the screen, as well.
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I have successfully installed your tool and have a new browser window up with Skyaware that now has the “Current gain / Set gain” functionality in the top title bar. Thanks again.
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Heh, I have a Uputronics preamp screwed directly into the bottom of the FA antenna with a SMA-N adapter, and then 1m of LMR400 connecting that to the Pro Stick+.
I now use the approach detailed in this blog post. It has let me find the optimum gain for the range of the receiver within minutes. You can add RSSI to the SkyAware table and click the column to sort by it. This works well for the Pro Stick family shipset at least.
Here’s the results from the gain check I did last night.
===Totals===
Gain, Messages, Positions, Aircraft
49.6 9583 2112 62
48.0 8719 1833 62
44.5 8949 1972 61
43.9 7599 1536 64
43.4 7541 1493 65
42.1 7689 1454 65
40.2 7302 1432 62
38.6 7619 1472 65
37.2 8115 1648 60
36.4 8238 1663 56
33.8 7212 1490 55
32.8 8112 1617 58
29.7 8336 1752 60
28.0 7974 1650 63
25.4 8414 1685 60
22.9 9262 1985 59
20.7 9351 2148 58