[time-nuts] Phase noise from Allan Deviation ?

Tom McDermott tom.n5eg at gmail.com
Sun Dec 13 22:15:57 EST 2015


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.

The result produces ADEV vs. Tau charts with reasonably sane looking
results.
The 'unknown' is a Rubidium oscillator locked to CDMA pilot (TS2700),
and the internal crystal oscillator in the SDR radio as the reference.
Thus, ADEV probably is mostly measuring that internal crystal rather than
the TS2700.  Later on a GPSDO will be tried as the reference clock to
see if the Adev results are better.

It brings up a question:  Is it possible to estimate the phase noise of that
internal crystal from the ADEV measurements?  There are a bunch of
papers that go the other way:  from Phase Noise to Adev.   Searching
brings up only one paper that goes from ADEV to Phase Noise but it's text
does not seem to be readily available.  It apparently models the oscillator
as a couple of well known error models.

-- Tom, N5EG



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