[time-nuts] Newbie question: GPSDO filtering principles

[Tom Van Baak]

> Hello all,
> 
>     The recent talk about the ideal GPSDO has reminded this newbie of a
> question I hope someone might be able to simply answer:  we have a couple
> of Rubidium GPSDOs which track in the long term, but their phase drifts
> by several hundreds of nanoseconds with an irregular, but roughly daily,
> pattern.  The units have a log output which shows the changes to the EFC
> DAC, and this changes usually after a period of 8192 seconds - sometimes
> longer, but rarely less.  I understand the need to average the GPS
> reading over this sort of period, but by only changing the EFC at this
> period leads to comparatively wild frequency swings - parts (plural!) in
> 10^11!

What make/model GPSDO is this? Is there a setup menu
where you can control the integration period or is it fixed
at 8192 always? Can you send a few lines of the log so we
can see the granularity of the DAC? When you say the
phase drifts, is this something the GPSDO reports by itself
or is this an external measurement made by you with some
counter and some other standard time reference?

/tvb