[Discuss-gnuradio] USRP2 missing Quadrature samples

[Leslie Choong]

Hi Everyone, I've been working with Thomas Schmid's old 802.1.54
demodulation code. I've got it running well on the original USRP and
have been trying to get the code to work with the USRP2. I basically
just changed out the source block and yet could not properly
demodulate a packet.

To investigate I used gr-utils/src/python/usrp2_rx_cfile.py to capture
incoming data and then plotted it using gr_plot_fft.py. I noticed 2
things:
1. The first block of data read by the plotter seems to always display
a strange dead signal, but all the other blocks have some In-phase
data.
2. More importantly, I am not seeing any quadrature component in the
IQ-plot (besides the noise at the beginning).

I compared this to data from the USRP using usrp_rx_cfile.py and
gr_plot_fft.py and am able to see IQ data.

Is there a reason for this? A hardware issue? or a Setup issue? I am
using the SVN revision 10306.

I've posted the plots here:
http://www.cs.ucla.edu/~septikus/usrp.html

Thanks for any help you can provide!
-Leslie