[time-nuts] Characterising frequency standards
Tom Van Baak
tvb at LeapSecond.com
Tue Apr 7 20:16:14 UTC 2009
Steve,
You've asked a couple of questions. Let me start with this.
It is true that if one were only interested in the performance
of a pendulum (or quartz or atomic) clock for averaging times
of one day that all you would need is a series of time error
(aka phase) measurements made about the same time once
a day (doesn't have to be that exact). After one week, you'd
have 7 error measurements (=6 frequency =5 stability points)
and this is adequate to calculate the ADEV for tau 1 day.
This alone allows you to rank your clock among all the other
pendulum clocks out there. Note also you get time error and
rate error from these few data points too.
As another example, suppose you have a nice HP 10811A
oscillator and want to measure its drift rate. In this case you
could spend just 100 seconds and measure its frequency
once a day, or even once every couple of days. Do this for
a month and you'd have several dozen points. If you plot
these frequency measurements you will likely see that they
approximately fall on a line; the slope of the is the frequency
drift rate of the 10811. The general shape of the points, or
the fit of the line is a rough indication of how consistent the
drift rate is or if it's increasing or decreasing.
Neither of these examples require a lot of data. Both of these
are real-world examples.
OK so far?
/tvb
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