AGC: why/why not and what is the current value?

[lanceberc]

By default AGC is turned off for RTL-style dongles when using AIS-catcher; why is that?

I spent a few days messing around with a range of gain values but it's a hard value to optimize when the targets are moving in and out of my receivable zone.

I turned AGC on and I think it's working but it's hard to tell - I don't see any AGC adjustment messages in the log. Is there a way to pull the current value out of AIS-catcher? I'm thinking of something like how readsb's current value shows up in graph1090.

[jvde-github]

I think the answer is that we are comparing different things.

The tuner AGC and RTLAGC should be on by default:

https://jvde-github.github.io/AIS-catcher-docs/configuration/input/rtlsdr/

Note that these are the gains on the RTL-SDR stick and we do not get feedback from the device what gains are used so cannot report in the log. My experience is that these settings work well in general so good for most users as a starting point.

graphs1090 and readsb work differently, they set the tuner gain in the software and adjust it with some algorithm. That is different and apparently works well for planes.

AIS is not pulse based modulation but constant amplitutde and less sensitive to precise gain settings so I think that is why the RTL-SDR internal approach works and as such I never felt a need to add an algorithm as in readsb.

Does that help?

[lanceberc]

Yes, that's much clearer. Thx!