USRP N200 with SBX Daughterboard Full-Duplex

[Mario45]

Hello NI-Community

I'm kind of new to the USRP and Gnu Radio Companion thing and also at my limits with ideas. I have a USRP N200 with a SBX Daughterbaord. I am using the UHD Version 4.4 and on Windows 10. 

My Goal is to send a Testsignal with the Tx/Rx port and Receive it with the Rx2 Port. When I test sending and receiving separately, they work fine. But if I test both together, I get nothing but nonsense on the Rx2 port. What does not work together? How do I have to set it up, so that the Ports work fine?

I also get these Error-Messages:

"[ERROR] [USRP2] Control packet attempt 2, sequence number 328:
RuntimeError: no control response, possible packet loss
[ERROR] [UHD] An unexpected exception was caught in a task loop.The task loop will now exit, things may not work.RuntimeError: link dead: timeout waiting for control packet ACK
Uusrp_sink :error: In the last 4341 ms, 1 underflows occurred."

And nothing that I do helps.

I already tried:

- Changing the UHD-Version.

- Updating every Software that I use.

- Tried diffrent combination with the "Sync" and "ClockSource"- Parameter.

- I thought it probably has to do with the sample rate and changed that as well.

but nothing helped. Maybe you guys can help me 🙂

The Project that 'm working on is attached.

[Mario45 · Accepted solution]

I am very pleased to announce that I have found my mistake.
I can't say what in the hardware is causing the problem (if anyone knows, I'd be very interested), but the effect was solveable with the software. The SBX Daughterbaord has the possibility to set a gain of up to 31.5dB on the Tx port. But when you do this, it seems to override the Rx port, which then blocks. So you can simply set the gain of the Tx port to 1 in the software and both ports will work perfectly.

A small tip: The data sheet for the SBX daughterboard from Ettus states that it is not possible to transmit and receive on the same frequency (in my case this was unfortunately absolutely necessary), but in my practical test it worked.