[time-nuts] Predicting clock stability from thevariouscharacterizationmethods

Dr Bruce Griffiths bruce.griffiths at xtra.co.nz
Fri Dec 1 18:24:50 EST 2006


Tom Van Baak wrote:
> Brooke,
>
> Maybe this helps. The clock prediction into the future
> is based on the past history and the current point. If
> the measured ADEV for a clock is, say 1e-13, for a
> measurement interval of 1 day (tau), then the prediction,
> within one standard deviation, is that you'll be within
> 1e-13 tomorrow. 1e-13 at one day is about 9 ns. I think
> this is right. Can someone double check?
>
> It shouldn't matter what your divider does -- 9 ns of
> time error is 9 ns regardless if it's the zero-crossing
> of a 5 MHz RF output of the leading edge of a 1PPS
> signal.
>
> A divider postpones cycle wrapping but doesn't affect
> clock accuracy or stability (other than the obvious
> introduction of passive & active component noise in
> the signal path).
>
> /tvb
>
> ----- Original Message -----
> From: Brooke Clarke
> To: Tom Van Baak ; Discussion of precise time and frequency measurement
> Sent: Thursday, November 30, 2006 13:31
> Subject: Re: [time-nuts] Predicting clock stability from
> thevariouscharacterizationmethods
>
> Hi Tom:
>
> Is there a way to use the Allan plot to predict the variation in a reading?
> For example if you use the plot comparing the 1 PPS from a GPS receiver to a
> good Cesium frequency standard, then:
> (1) what size of variation would you expect if the Cesium standard was
> divided down to 1 kHz and that was compared to the GPS 1 PPS, or
> (2) what size of variation would you expect if the Cesium standard was
> divided down to 1 Pulse/1,000 seconds?
>
> Have Fun,
>
> Brooke Clarke
>
>
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>
>   
Tom

Surely the time standard deviation should be:

TDEV = TAU*MODADEV(TAU)/SQRT(3) ??

At least this appears to be so in the link you gave:

http://www.wriley.com/paper2ht.htm

Bruce



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