[time-nuts] Phase noise from Allan Deviation ?

[Tom McDermott]

Hi Iain,

I'll publish a flowgraph soon.  I built a Out-Of-Tree module to decimate
the output
down to one sample per reading to keep the output file small for even long
runs.
On the order of about 48000:! decimation.  Strange thing is - it works when
the
QT Time Sink is enabled, but gives very wrong outputs when the QT Time Sink
is Disabled (the only change).

So I suspect my custom OOT is doing something wrong, but not sure why
enabling/disabling the scope display changes the gnuradio behavior so much.
I'd like to get more to the bottom of this before publishing the code.

Have done some short runs throwing 48,000 samples/sec to the output file,
then post
processing that in Python, and it gives the same results as my OOT module
when the
QT GUI is showing.  Very strange, but the data file is much too verbose:
700 Megabytes/hour.

-- Tom, N5EG



On Mon, Dec 14, 2015 at 1:15 AM, Iain Young <iain at g7iii.net> wrote:

> Hi Tom,
>
> On 14/12/15 03:15, You wrote:
>
> I've constructed a homebrew setup to measure time intervals using a
>> software defined radio.  Basically a single-channel downconversion to
>> about one hertz, then count samples from the SDR clock to time stamp
>> the zero crossings.  This is done in gnuradio and saved to a file for
>> post processing. The resolution is theoretically good, but the accuracy
>> is unknown.
>>
>
> Very interesting. Would you consider making your flowgraph available ?
>
> I have done similar things with just thresholding and looking for the
> start of second (or minute) marker of various distant radio clocks, and
> then graphing how far apart they were, as well as feeding NTP.
>
>
> 73s
>
> Iain
>
>
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