[Discuss-gnuradio] Loss of synchronization while creating new file

[rmsrms1987]

Hi Everyone,

I am having some issues with figuring out the cause of a loss of
synchronization using the USRP N210. I will be using the USRP as a
receiver for a radar system, but I am still in the calibration phase.
For calibration testing, I am interested in seeing the stability of the
baseband IQ data when applying a known pulsed RF signal with RF
frequency
matched to the frequency of the DDC.  The data collection program
developed through GNURadio libraries is to continuously run while
creating a new file after a specified amount of time, to avoid having
one massive file. Typically each file is set to 5 minutes, but for this
issue the number has been altered several times. The baseband IQ data
from a single inter pulse period is plotted every 5 seconds. To
synchronize the pulsed RF with the USRP, we are using an external 10 MHz
clock in addition to a PPS signal.

During testing, at first everything seemed to be working as it should,
because the baseband IQ plots were the same every 5 seconds a new plot
was  displayed.  The problem occurred after the completion of a file,
and the start of a new file.  The start of the new file caused the IQ
values to change, and these values remained until completion of the
file, where the problem will continue to the next file. I have tried
many different tests to understand this problem, but I have run out of
ideas. I was wondering, is something on the NCO is not being reset
during the closing and opening of a new file. Or, is there always going
to be some loss of synchronization during this change?  For a
visualization of the problem I have attached a couple pictures of the
phase for subsequent files. If anyone has any suggestions to solve this
problem it would be greatly appreciated.  Also if there is any other
information you need, please let me know.

Thank you very much,
Robert

<http://gnuradio.4.n7.nabble.com/file/n42517/file1.jpg> 
<http://gnuradio.4.n7.nabble.com/file/n42517/file2.jpg> 



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