replicating FB architecture?

Patrick 201905-ntpsec at
Tue Mar 31 04:59:16 UTC 2020

On 2020-03-29 23:07, Hal Murray wrote:
>  You haven't said anything about how good a clock you want.  Dig out the spec
> sheets and compare the drift rate of a chip scale clock with its high end
> brothers.

I need to be able to drift less than 50 ms over 3 months.

> If you want good time but don't like the cost of high end Cesium clocks, the
> telco industry uses Rubidium clocks at roughly the same cost as the chip scale
> clocks.  They are not as good as the high end Cesium clocks, but much longer
> lifetime which turns into much much lower cost per year.

Am reading further on this. Thanks!

> If you are using GPS, one interesting parameter is what happens when your GPS
> stops working for whatever reason.  The usual technology is GPSDO - GPS
> disciplined oscillator.  The oscillator part is typically a good ovenized
> crystal.  While GPS is working, you adjust the crystal to have the desired
> frequency.  That corrects for crystal aging.  When GPS stops, you switch to
> "holdover" mode.  The aging on the crystal (and everything else like
> temperature) is low enough that you can repair it before it drifts out of spec
> relative to your requirements.

For less than 50 ms drift over 3 months, it looks like an OCXO will
likely hit the max drift wall:

msecs = 86400 * 1000 * 90
maxdrift = 50
maxdrift / msecs


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