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

[Eric Blossom]

On Tue, Mar 17, 2009 at 12:32:57PM +0100, Costantini, Andrea wrote:
> 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 RX picture doesn't look right to me.  There should be a single
peak.  Possible causes include pushing the transmitter into a
nonlinear region, overdriving the receiver input, having the gain set
too high, or seeing transmitter underruns.

Try setting the Signal Source amplitude to 0.1 instead of 1.0 and see
if that doesn't clean it up.

> 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

Eric