Hi,
yes, the result for multiple measurements (start ups of the system) at a
single frequency was different by multiples of 90°.
We did not investigated the problem any further, but I am quite sure
that gnuradio was not synchronizing the channels using the LO-sharing,
although it was selected. So do the test I described. If you see that he
is not using the LO-sharing, you know where to look further.
Keep in mind that it is not necessary to use LO-sharing to get a well
defined phase relation between the channels. Depending on your frequency
and bandwidth settings, it is possible to also achive this, as all LOs
are driven from a common 200 MHz reference clock.
Best regards,
Fabian
Am 03.04.2019 um 12:05 schrieb Piotr Krysik via USRP-users:
Hi Fabian,
W dniu 03.04.2019 o 11:05, Fabian Schwartau via USRP-users pisze:
Hi Piotr,
we once had a very similar issue. But we also saw this on the same
frequency when switching between frequencies. Can you try this as
well? Just switch forth and back between two frequencies and just plot
one of them?
I'm not sure I understand correctly what you mean. You mean that the
result for a given frequency was not stable in your case across many
measurements? In our case this situation was repeating, but the
application doing the recording was restarted for each measurement.
As far as I remember the issue was because we were not using the
LO-Sharing. We were able to get everything running by using a C++
application and not gnuradio (I can see you are using python - which
is basically the same). There was a bug in gnuradio/python causing
this issue.
You can try to remove one of the LO-sharing cables while doing a
measurement and see if the phase suddenly starts to do crazy things
(the signal should also be lost). If that is not the case, you are not
actually using LO-sharing.
Do you know what this bug was exactly? GNU Radio didn't configure
LO-Sharing the way it was specified?
--
Best Regards,
Piotr Krysik
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