[time-nuts] GPSDO "accuracy"

[Dana Whitlow]

Not sure what you mean by "accuracy over a 10 sec interval".  If you mean
(in)correctness of frequency averaged over a given 10 sec interval, it's
more
like a few parts in 10^9.  But if you mean stability of frequency without
regard
for its correctness, you might see your 2 parts in 10^12 in at least some
intervals,
although that seems a bit tight to me.

The numbers I mention above are for a GPSDO using an OCXO with a
disciplining
time constant of just a few seconds, which is kind of a worst case
scenario.  However,
if your VCO is stable enough to be reigned in with a time constant of
hundreds of
seconds, you can do much better for stability and at least moderately
better for
absolute frequency accuracy.

If your primary interest is fixed in that 10 sec interval, a GPSDO with a
good OCXO is
likely to be the best way to go.  OTOH, if your interest evolves into
appreciably longer time
intervals, you'd likely do better with a GPS disciplined Rb oscillator,
where disciplining
time constants of several hours (or even longer) are feasible.  However,
many of the
usual Rb standards tend to have a hump in their phase and frequency
variations around
time intervals of a few seconds.

I hope this helps.

Dana


On Wed, Sep 9, 2020 at 6:40 PM donald collie <donaldbcollie at gmail.com>
wrote:

> Can any list member please tell me the "accuracy" that can be expected from
> a typical GPSDO
> over, say, a 10 second interval? I have several measuring instruments
> connected to my Trimbal GPSDO, and would like to know what to expect. At
> the moment I am guessing about 1 to 2 parts in 10^12.
>
> Thankyou,................................................................................Donald
> Brett Collie
>
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