[Discuss-gnuradio] Problem with symmetric behavior

[Robert Miller]

Hello,

I created a flowgraph based upon the usrp_nbfm_ptt.py example.  I am
witnessing some weird, asymmetric behavior when running the graph.  The code
generates a tone from the user specified daughterboard and then plots the
spectrum via an fft from another user specified daughterboard.  I am using 2
RFX-1800 daughterboards with a single USRP to run the graph, however I
imagine it should work the same for any RFX board.  Here is the main issue:

Everything works fine when using Side B as the transmitter and Side A as the
Receiver.  When running with Side A as the transmitter and Side B as the
receiver, however, the fft display is really just noise (once in a while
there exist some spectral lines at odd frequencies).  As a note, I am fairly
certain that the mux's are being set correctly and that the boards are
tuning correctly.  To verify that the issue is not the hardware, I am
capable of running usrp_siggen.py and usrp_fft.py in both configurations
successfully.  (TXR A --> RXR B, TXR B --> RXR A).  Also, I have done the
tests in completely wired (with 60 dB of attenuation) and unwired
environments, with both yielding the same results.  Attached is the code
that I am running, can anyone point out something silly that I am doing that
is causing this problem?

http://www.nabble.com/file/p14642329/DualChannel.py DualChannel.py 

As an added note, I am getting a segmentation fault when I close the graph
by any means other than <Ctrl-C> from the command line.  I don't think this
is related to the above issue, and I don't get the seg fault when running
the original usrp_nbfm_ptt.py code.

Thanks!
Rob

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