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Re: [Discuss-gnuradio] Question about metadata filesink

From: Ellie White
Subject: Re: [Discuss-gnuradio] Question about metadata filesink
Date: Wed, 10 Jul 2019 16:19:11 -0400

Hi Marcus,

Thanks for getting back to me! I really appreciate your suggestion --
why didn't I think of that! I have done similar calculations before to
determine the amount of time from the beginning of a run, but for a
much less precise application.

This brings me to another question, though -- I notice that when I
read the metadata header, the time ("Seconds" field) always says zero
when I get the file from the TCP client flowgraph, but when I save a
metadata header file on the machine that the Ettus is connected to, it
gives me some fractional answer (always different, never zero). Not
sure why that is, or what time standard the UHD is using (this is the
one I have, by the way:
https://files.ettus.com/manual/page_usrp1.html)? Maybe the Ettus just
needs to be connected to an external clock source -- the final system
will have a 10 MHz clock source connected, but the temporary system
that is set up now doesn't have an external clock. If you have any
thoughts on this, I would be interested to hear them.

Thanks again, and have a good afternoon!


On Wed, Jul 10, 2019 at 3:07 PM Marcus D Leech <address@hidden> wrote:
> The thing to note is that the UHD sends a time stamp only on start of 
> streaming and whenever there’s an overrun.
> You can know the time of any given sample by knowing the sample rate and 
> offset from the beginning.
> In your case you will have to throw in some more factors to account for FFT 
> size and decimation etc.
> More later when I get to a real computer.
> Sent from my iPhone
> > On Jul 10, 2019, at 2:54 PM, Ellie White <address@hidden> wrote:
> >
> > Hello!
> >
> > I am working on a radio astronomy project with the Green Bank
> > Observatory / NRAO Central Development Lab this summer, utilizing GNU
> > Radio and an Ettus Research SDR, and I've got a question regarding how
> > to collect metadata information from a filesink.
> >
> > I have attached the flowgraph I am using to this email. The project
> > requires that I use two computers in tandem for data collection -- one
> > is connected to the Ettus -- it is the TCP server, and sends an
> > interleaved data stream to the TCP client flowgraph (attached) on the
> > machine which will be storing the data. As you can see, I am saving
> > integrated spectra to a file. My question is simply, how do I retrieve
> > a time stamp corresponding to each spectra using the metadata time
> > sink? I have been fiddling with this all afternoon attempting to get
> > it to work properly, and I have been able to save data to a file, read
> > out spectra (using attached Python program), and display header
> > information using the command gr_read_file_metadata in the terminal,
> > but this is just showing me a timestamp for the beginning of the data
> > collection run, rather than showing me timestamps for each spectrum
> > which is saved to file, and I am not sure how to implement this.
> >
> > Any advice would be much appreciated! If I can provide any more info
> > about my system or what steps I have tried, please let me know. Thank
> > you so much for your time -- have a good afternoon!
> >
> > Best,
> > Ellie
> > <ettus-filesink.grc>
> > <dataGraphing.py>
> > _______________________________________________
> > Discuss-gnuradio mailing list
> > address@hidden
> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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