[time-nuts] Cheap jitter measurements

Gary E. Miller gem at rellim.com
Tue Apr 24 23:45:08 EDT 2018


Time-nuts!

I went ahead and bought the TAPR-TICC, it is a very impressive
instrument.  For this setup it is combined with a Jackson Labs
GPSTLXO as the 10MHz reference.  The JL is a GPS disciplined temperature
compensated crystal oscillator.

The first setup uses the TAPR-TICC in Period mode, outputting the PPS
period individually for channel A and channel B.

Channel A is the PPS of a plain u-blox NEO-M8N.  Channel B is the
PPS of the JL GPSTLXO.

Simple to get the cycle times from the USB serial port.

Then I grabbed a copy of the easy to use Python Allantools.
    https://github.com/aewallin/allantools

A little coding later and there are nice plots.  They were compared to
the output of tvb's adev.c program.  Results are similar.

Results are attached.  gps.png is the plain NEO-M8N.  GPSTLXO is the
JL part.

gps.png looks as expected.  GPSTLXO.png shows the quality of the JL part,
but does have some odd divots in the plot.  Maybe artifacts of using the
PPS derived from the reference 10MHz?  Or an artifact of the 10e6 divider?

There are adev's of Rb standards here: http://www.ke5fx.com/rb.htm

My guess is that the oadev at 1s would be about 50x better with
a Rubidium?  But similar at 10k seconds?

Comments?

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  Tel:+1 541 382 8588

	    Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin
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