[time-nuts] GPSDO control loops and correcting quantizationerror

[Poul-Henning Kamp]

In message <3A001267-52DE-4EE9-B6EE-6638FB270C06 at rtty.us>, Bob Camp writes:
>Hi
>
>By far the most common approach to optimizing these is the "measure
>it and see" approach.
>
>1) measure the noise out of the GPS ( must be done no matter what)
>2) measurer the noise of the specific OCXO (again must be done)
>3) *guess* at a cross over
>4) try it and measure the result.
>5) step and repeat 3 and 4 until exhaustion sets in

Indeed.

What I've done is to automate that, using the zero-crossing
frequency of the residual as input.

>If you simply try a dynamic tune approach, you never really get
>to an optimum point.

For the stuff I did, hitting the optimum point exactly from the
beginning, was not nearly as important as getting close to the
optimum point when circumstances changed.

But with that being said:  Even in the "ideal scientific" setting,
I think my approach is not only valid, I think it is one of the
most efficient ones, because you don't need a 3rd reference to
measure against.

If you have a 3rd (& better) reference, by all means use it, but
if all you have is a GPSDO, my method delivers better results than
I have seen from anything else.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
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