Needs better rtl-sdr support

[andrewfer000]

There are a few issues with the RTL-SDR support for this application (Ubuntu 20.04, Java 11)

1. Audio does not work at all
2. Can't set gain or use automatic gain. (agc)
3. Barley works even when radio signal is perfectly clear and RDS works on other programs like sdr-j-fm

I can't tell if this project is still active. But if these three issues are fixed then this program would be epic.

[mvglasow]

I am listening to a local radio station with RDS Surveyor and a RTL-SDR on 20.04 as I write these lines, so audio works in general. What behavior are you getting? Just silence or some kind of noise/garbage? Does anything happen if you click the audio button?

It’s been more than five years since I wrote that driver and I admit radio signals are not really my strongest suit—I stopped when I had a feature-complete driver capable of receiving RDS data. The code itself is mostly copy-and-pasted from various rtl-sdr tools, as well as some (since abandoned) code from redsea for the RDS demodulation.

So far I have not encountered any of the issues you are describing. I also have a Si4703 tuner stick, and quality is comparable on both. I do not remember encountering any situations where one device was struggling as you describe while the other got a clear signal—so it is kind of hard for me to reproduce what you describe.

If you happen to have an idea for implementing gain control, then a pull request would certainly be welcome.