[time-nuts] frequency stabilty question

Tom Van Baak tvb at LeapSecond.com
Mon Aug 15 06:19:55 UTC 2011

> Does this mean the observations made were at the very begining
> and the very end of the 1 second time.


> If so what value about all the values in between? What happens
> if the oscillator deviated far worse than this during the interrim.

Oscillator behavior in between 1 second intervals is unknown. As
you say it could be much worse, or it could be much better. If you
need to know for sure, then you must re-run the measurement
and collect data at shorter intervals this time.

Specifically, if you make only one measurement per second you
can compute ADEV(1 second), or actually ADEV(N seconds).

By contrast, if you collect 100 measurements per second you
can compute ADEV(0.01 x N seconds). This allows you to see
how well the oscillator performs for intervals less than a second.

> Or does the measurement consist of making measurements
> every cycle during that 1 second and then entering all those
> values into a formula that accounts for them all??

If you had measurements every cycle it would be great. But not
all measurement systems can measure every cycle. In the real
world there are limitations on the rate of measurement. There
are also limitations on the resolution of each measurement.
With some instruments you can increase the rate but you then
loose resolution, or visa-versa.

These two limits dictate how short a tau you can plot and how low
an ADEV you can observe. I can provide examples if you wish.


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