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).