[time-nuts] Re: Does cm accurate GPS via RTK give more accurate time?

[Pavel Kořenský]

Hello,

this is my mistake. I thought about something and wrote something other.
Of course, my GPSDO is based on rubidium clock, not cesium. I do not 
know what I was thinking when I wrote the message. Probably dreaming 
about my own private cesium or H-maser frequency standard.

Best regards
PavelK

Dne 28.04.2025 v 21:58 Poul-Henning Kamp napsal(a):
> --------
> Pavel Kořenský via time-nuts writes:
>
>
>> I'm currently using this module in my prototype GPSDO based on a cesium
>> clock, [...]
>>
>> Now, regarding how to measure which clock is "better": that's a tough
>> question. If you have only two clocks, you can't really tell which one
>> is more accurate — you need a third, better reference.  […]
> But that is not really what you want to know, is it ?
>
> What you want to know is that your PLL has the right time-constant,
> so that you derive maximum benefit from both your two sources.
>
> This is what Dave Mills called "The Allan Intercept"
>
> When your PLL tracks near the Allan Intercept, the error output of
> the phase detector will have a flat-ish frequency spectrum.
>
> If your PLL is too loose, the spectrum will slope up towards higher
> frequencies, if it is too stiff, lower frequencies will dominate.
>
> But be aware that with a Cs-VCO, the signal is in constant peril
> from rounding and truncation in floating point math.
>