[Discuss-gnuradio] self-interference with wbx

[Francois Quitin]

Dear List,

 

I am using a USRP-2 with a WBX daughterboard that is operating in full duplex mode. Both the Tx and Rx gain are cranked up to their maximum values (tx gain 25 dB, rx gain 30 dB). The Tx and Rx frequencies are about 70 MHz apart (Tx->964 MHz and Rx->892MHz).  I’m having a little trouble with the self-interference:

-          when the Tx chain is sending periodic packets (with 0s in between), this creates very high noise in my Rx chain (up to 0.01 on gnuradio companion scope)

-          when the Tx chain is sending a continuous pilot tone, there is no noise in my Rx chain (noise is lower than 0.0005 on gnuradio companion scope)

 

I would like that, when transmitting periodic packets, the noise would be as low as when transmitting a continuous pilot tone. I understand that periodic packets would create noise in a wider band than the periodic tone, but still, my Tx and Rx frequencies are very far apart. Is there some automatic gain in the USRP that is playing tricks here? If so, is there a way to solve this?

 

Any input is appreciated,

Thanks a lot,

 

Francois

 

PS: for our application, we had to turn the DUC cordic off. But even with the DUC cordic enabled, I still observe similar trends, so I don’ suppose that would matter. We also had to put the Clock source to “external” to avoid the automatic clock correction (but again, putting it to “Default” didn’t change a thing).