[time-nuts] Using Allan Plots, was(LPRO-101 with Brooks Shera's GPS locking circuit)

[Poul-Henning Kamp]

In message <000601c72289$5f9a7350$03b2fea9 at athlon>, "Ulrich Bangert" writes:

>Having these specs at hand you don't need to make a single measurement
>to determine the TIC's Allan plot: It will be a straight line starting
>at 2E-11 @ 1 s and having a slope of -1.

Not quite.

2E-11 is the spec, the counter is likely to do better.

>If you are eager for making a
>measurement of your own: Let the SR620 make time interval measurments on
>pps signals that are derived from its own timebase.

Wrong.

This is will not give a random sampling over the internal noisespectrum,
and the number is likely to be different from the applicable jitter
value for the specific counter.

Instead feed in any stable frequency (an ocxo is best) different
from the clock on the SR620 to both start and stop inputs and measure
the time interval between them.

The jitter on that measurement is the number you really want to
know.


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