Re: [Discuss-gnuradio] Problems when receiving after transmit

[Johnathan Corgan]

Dan Halperin wrote:
> Just-powered on USRP rev 4.2 with RFX2400 rev 2-6-2006. Current SVN.
> 
> usrp_rx_cfile.py -f 2.485G -d 8 -s pre.dat
> usrp_siggen.py -i 16 -f 2.485G
> usrp_rx_cfile.py -f 2.485G -d 8 -s post.dat
> 
> In the first set of data, the noise level is what I'd expect and
> everything works hunky-dory. After the siggen, however, it all goes
> haywire, the noise floor becomes huge even though an adjacent USRP sees
> nothing.

I wonder if somehow the USRP transmitter is getting left powered up.
The mixer would be getting random noise and upconverting it to your
passband.  This would feed through from the blocked side of the TX/RX
switch (about 30dB of attenuation) into the receiver.

You'd have to measure the logic level at the mixer chip enable pin to be
sure.

If this is the case, I have a suspicion about the cause.

-- 
Johnathan Corgan
Corgan Enterprises LLC
http://corganenterprises.com