[time-nuts] PRS10 MDEV

Tom Van Baak tvb at LeapSecond.com
Mon Oct 15 01:31:07 EDT 2018


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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