Problem with symmetric behavior

GNU Radio
1

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 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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2

Robert M. wrote:

Receiver. When running with Side A as the transmitter and Side B as the

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 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

Your problem is in the tuning I think:

class receive_path(gr.hier_block):
…
def set_freq(self, target_freq):

    r = self.u.tune(self.subdev._which, self.subdev, target_freq) #

← look here

Which should be:
class receive_path(gr.hier_block):
…
def set_freq(self, target_freq):

    r = self.u.tune(0, self.subdev, target_freq) # <-- look here

The first parameter is the channel you are tuning, which is always
channel 0 if you only receive one stream.
It is NOT subdev._which, which indicates on which side the daughterboard
is.

I hope this helps,

Martin

3

Martin,

Thanks a ton for your help. Tuning the reciever via:

r = self.u.tune(0, self.subdev, target_freq)

did the trick.

Much appreciated!
Rob

Martin D. wrote:

RFX-1800 daughterboards with a single USRP to run the graph, however I
tuning correctly. To verify that the issue is not the hardware, I am
As an added note, I am getting a segmentation fault when I close the
Your problem is in the tuning I think:
…

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http://www.nabble.com/Problem-with-symmetric-behavior-tp14642329p14681395.html
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