[Discuss-gnuradio] [USRP2] Some problems by sending sinusoidal signals. :-(

[Costantini, Andrea]

Dear all,

the last discussion on sending and receiving the sinusoidal signal 
raised to me a lot of questions.
I am also having some problems with this basic example.

I have searched over the whole archive without founding an answer.
I know that such questions may not be appreciated by a list of expert 
people,
but I hope that some of you can enlight me on this problem.

I am using gnuradio 3.2SVN (downloaded on March 6th).
I have two USRP2 with XCVR2450 (last firmware version):
- USRP A: sends and receives a sinusoidal signal.
- USRP B: receives the sinusoidal signal from USRP A.

This is my setup for USRP A (USRP B is equal but without transmit path):
http://img168.imageshack.us/img168/8176/grcedit.png

The fft and the scope of the sending and receiving path in USRP A seem 
to be correct:
TX: http://img216.imageshack.us/img216/5880/txfftscopeusrp2.png
RX: http://img256.imageshack.us/img256/7669/rxsameusrp2.png

This is instead the output of fft and scope in USRP B:
http://img216.imageshack.us/img216/1213/rxdifferentusrp2.png

I really don't understand why I am seeing such a signal on USRP B.
It seems that the sinusoid here is centered on a frequency of ~ -115KHz.

Also note the amplitude of the sinusoid: in USRP B is larger than in 
USRP A, although A is actually the sender.

Waiting for your valuable inputs,

Best Regards,
Andrea Costantini