Huge increase on "bad" messages > -3dBFS after gain adjustment from 49.6 to max

[biekerc]

The slightly longer version…

@obj

Manual gain settings range from 0 to around 49dB. Larger numbers mean more amplification.

AGC is fairly confusing in the context of ADS-B, the AGC actually doesn’t work well with the type of signal that ADS-B is using, so the feedback loop ramps up to maximum gain and stays there. Due to an unfortunate (fortunate?) quirk of how the rtlsdr libraries configure the tuner, in AGC mode the maximum total gain is actually a little higher than the maximum gain you can set in manual mode.

So think of “-10” as effectively being “a bit more than 49dB”. (Yeah, it’s confusing)

If you’re right by the runway then you probably will want to set a lower manual gain, not AGC, maybe try 30dB as a starting point.

We did not have this discussion for a long time, but I still had this reply bookmarked…