[time-nuts] Is this a cesium frequency standard?

Poul-Henning Kamp phk at phk.freebsd.dk
Thu Aug 23 22:35:28 UTC 2012

In message <33222. at mymail.acsalaska.net>, "R
ichard H McCorkle" writes:

>See the chart TVB produced to see the PRS10 hump in published data.

I have measured similar data when the PRS10 is fed a 1PPS from a GPS
without sawtooth correction.

The PRS10 has a 1/256 exponential average filter which can get rid of
most of that noise, and I suspect Tom didn't enable it for that

But even with that filter, the "hanging bridges" leak through at all
relevant timeconstants of the PRS10's internal PLL.

I tried converting the "negative saw-tooth" and injecting it into
the PRS10 via the serial port, but the results were at best very
mixed.  In the end I used the PRS10 to timestamp the 1PPS, pulled
the measurement out via the serial port, and implemented my own
neg-saw corrected PLL in software, which injected the correction
back into the PRS10 via the serial port.

When you do that, you get much better results, at 2Hz and elsewhere.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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