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

[Marcus D. Leech]

On 07/16/2013 04:31 PM, rmsrms1987 wrote:
> 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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You haven't described your flow-graph, nor how you "flip to a new file".

The USRP has *zero* idea about what you're doing with the samples once 
they leave the USRP.  It doesn't care.  So any anomalies with things like
  file recording are utterly independent of the USRP (modulo any 
overruns that might be caused by your flow-graph, in which case, you'll see
  phase-hits).



--
Marcus Leech
Principal Investigator
Shirleys Bay Radio Astronomy Consortium
http://www.sbrac.org