[time-nuts] PRS10 MDEV
CBURFORD1 at austin.rr.com
Mon Oct 15 11:12:28 EDT 2018
I suspect now after your review that the effect is thermally drive,
specifically my HVAC. My PRS10 is in a free air environment suspect to
the wall thermostat.
I'm sure I could parallel the RFS measurements with Lady Heather and
find a correlation between RFS case temp and the MDEV.
Thanks Tom for the analysis.
-----------------------------------------From: "Tom Van Baak"
To: "Discussion of precise time and frequency measurement"
Sent: Monday October 15 2018 12:31:07AM
Subject: Re: [time-nuts] PRS10 MDEV
When I see an ADEV or MDEV plot that looks unusual I like to check
the phase or frequency plots for clues. Thanks for your .TIM file.
Burford-6h-adev.png -- TimeLab 'a' command. This is a straight line
with slope -1; what you expect for a self-test. Note the ADEV at tau 1
second is right about 7e-11, 70 p/s, which is typical noise for the
Burford-6h-mdev.png -- TimeLab 'm' command. As you observed this has,
a plateau. Sort of unexpected given you weren't using a GPSDO.
Burford-6h-phase.png -- TimeLab 'p' command. Phase difference plot.
Notice all those bumps.
Burford-6h-phase-100s.png -- TimeLab 'g100' command. Phase difference
plot with 100 second averaging makes the variations stand out much
clearer. Can you guess what that is?
So the smoking gun is that you have quasi-periodic perturbations in
phase on the order of about 100 ps. The shape looks thermal to me. Do
you have a thermostatically controlled heater in the room or house? I
suspect this is causing your MDEV plateau.
If so, you've accidentally done a nice experiment -- which is to
establish your measurement noise floor and to examine the
environmental conditions of your work bench. Ah, the annoying joys of
working with precise time!
Again, assuming it is due to thermal effects, you can now find out if
it's your TICC or your cables or your PRS10. Since TimeLab will
display plots in real-time a heat gun or cold spray may help you
isolate the culprit quickly.
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