thanks to a friend who has prepared an exploitable tetrapol-kit on kali and raspberry 4 I ca play with.
The hings are complex for my old brain to undertand the sources :)

I got some unencrypted communications and I am very happy.
   ( unfortunately I can't use my SDRPlay receivers RSP1A and RSP2) 

 
I get oftenly a lot sync_fail or broken frames. The RF signals are very good and strong.
I try to change rf gain values, sure about the ppm correction of the key.

Do you have another idea or tune something to prevent the losses ? 

Anyway, warm thanks and big applause to the coders !

I wish to all a very good christmas and happy new year 2021.

JPhi