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From: | Ellie White |
Subject: | Re: [Discuss-gnuradio] Question about metadata filesink |
Date: | Thu, 25 Jul 2019 12:46:39 -0400 |
On 07/10/2019 04:19 PM, Ellie White wrote:
> 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!
Also, other random questions:
What type of USRP (There are a plethora these days!)
What type of computer is direct-connected to the USRP?
Can you share the flow-graph for the computer that is direct-connected
to the USRP?
> Best,
> Ellie
>
>
> 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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