Tom,
thank you for your explanations.
Such information helps the newer time-nuts as me to get easier in touch
to this fundamentals.
I did not know the reasons for these quasi perturbations which also I
could see on my own reference oscillators. Now I understand where they
come from...
--
with best Regards
Chris
Am 15.10.18 um 07:31 schrieb Tom Van Baak:
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.
Attached are:
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 TICC counter.
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.
/tvb
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