Hey there!
Boy, it's been a long time since I touched that code. It's very "hacked together", and needs some love!
I'd recommend trying psk31_rx.grc with this video[1]. If you have youtube-dl, you can save it to a wav file.
For the TX side, I didn't really get that flushed out properly. The audio sink doesn't like it when you stop sending samples to it, and I couldn't figure out a tidy way to clean things up.
In the mean time, look at the vector source in psk31_tx.grc. \x80 is the "preamble" byte, and everything else is just plain ASCII.
That should get you up and running! Maybe if I have some time later, I can get a transmitter block up and running with the osmocom sink. It's just a simple AM transmitter.
- Tim