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DUMP1090 gain setting.

Posted: Mon Oct 27, 2014 10:17 am
by watsonm
Coming late to the party.

Apologies if you folk have already found this out but the dump1090 setting for auto-gain was found to be a misprint in the help according to the software developer.

I have recently set it to the "corrected" value with good results on my installation

Suggest you try --gain -10

Obviously "Your mileage may vary" .... :-)

Mike

Re: DUMP1090 gain setting.

Posted: Mon Oct 27, 2014 4:37 pm
by sashimi3
Yes our mileage may certainly vary :-)

Changing it to 10 from 48 cuts my tracked airplane count from 60-80 to something like 6

d

Re: DUMP1090 gain setting.

Posted: Mon Oct 27, 2014 5:40 pm
by jonfear
The -10 (Minus 10) is important. if you use 1o then something very strange happens. I use the autogain on all my RPi's and it works well

Jon

Re: DUMP1090 gain setting.

Posted: Mon Oct 27, 2014 6:52 pm
by sashimi3
Hmmm. ok missed that "-" :-)

Made that change. What would be the expected outcome?

d

Re: DUMP1090 gain setting.

Posted: Mon Oct 27, 2014 8:02 pm
by jonfear
In my case, I had the gain pretty much sorted so about 5NM extra and less false positives!

Jon

Re: DUMP1090 gain setting.

Posted: Tue Oct 28, 2014 9:22 am
by T-EGJA1
On a related note, can anyone explain the difference (if any) between the settings "--gain -10" and --enable-agc" ?
dump1090 --help merely gives:
--gain <db> Set gain (default: max gain. Use -10 for auto-gain)
--enable-agc Enable the Automatic Gain Control (default: off)

Re: DUMP1090 gain setting.

Posted: Wed Oct 29, 2014 3:41 pm
by T-EGJA1
Further to my previous post above, I've been doing some research and suspect that the two gain switches in dump1090 may relate to the 'RTL AGC' and 'Tuner AGC' options in SDR#, i.e. '--enable-agc' = 'RTL AGC' and '--gain -10' = 'Tuner AGC' (the latter in SDR#, when un-checked, can be manually set to a specific gain value) ........... can anyone confirm whether this is the case, or not?

From my research, consensus seems to suggest that (at least for SDR#), the preferred setting is to enable RTL AGC and disable Tuner AGC, manually setting a gain value that strikes a balance between a strong signal and low noise. To this end, I've been running SDR# tuned to 1090 Mhz and watching the ADS-B pulses in the 'waterfall' display, while adjusting the gain settings. So far, the best result seems to be with RTL AGC enabled, Tuner AGC disabled and RF Gain set to 40.2 dB. The next step is to transfer these settings to dump1090, i.e. "dump1090 --enable-agc --gain 40.2 etc. " and compare the polar plot with that from previous settings. I'll report back as to whether there's any difference after running the test for 24 hours or so.

Re: DUMP1090 gain setting.

Posted: Tue Nov 04, 2014 12:03 am
by T-EGJA1
Testing various settings over the past couple of days, the optimum settings (for my set-up) are "--enable-agc" (RTL Automatic Gain Control ON) and the "--gain " omitted, i.e. using default max 'Tuner' gain.

Setting both "--enable-agc" and "--gain -10" results in noticeably fewer contacts and reduced range, presumably as a result of overloading or drowning the signal in noise.

Your mileage may vary.