Adjusting gain

Dear all, what is the easiest way to figure out the correct amount of gain. My setup is:

raspi3 with flightaware 7.2 image.=> the orange dongle (R820T2 SDR + RF Amp v1.1) => ADS-B SAW filtered preamp 1090 MHz => 6 meters (19,6 ft) cable => ADS-B 1090 antenna.

piaware-config:

For a receiver type of ‘rtlsdr’, these control dongle settings

rtlsdr-device-index 0
rtlsdr-gain 49,6

rtlsdr-gain -10

rtlsdr-ppm 0

Thanks a lot!

Marcus

I would start with installing Graphs1090:

Let it running for 24 hrs and see what the percentage of strong messages is.
If it is higher then 5% reduce the gain.

Sometimes it can’t be lowered due to environment circumstances but that is totally dependant on your local environment.
Max gain for the orange dongle is indeed 49,6.

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There is some code around that will periodically check the gain level and adjust it for you. Look around for autogain1090 on GitHub. I have been running it for a while but I’d have to check my notes to see how it is installed. It runs each afternoon and checks the percentage of messages that are over -3dB.

You might want to have a read of this thread: Thoughts on optimizing gain

It’s long, but has a lot of discussion about gain and various ways to measure your receivers performance.

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First question: What is YOUR major interest (it makes a difference to the “best” gain setting).
You may be interested in:

  • Range - the greatest distance you can get
  • Planes - the max number of planes you can spot
  • Message count - number of messages per plane per day
  • Uninterrupted local reception
  • other?

Without explaining why, raising your gain to maximise range usually results in close aircraft overloading the receiver causing distorted/un-decodable messages.
Dropping the gain so you don’t lose local positions will usually cost you max. range.

It’s your station, so you get to optimise it to suit your interests.

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