[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 <33222.206.174.114.110.1345760897.squirrel at mymail.acsalaska.net>, "R
ichard H McCorkle" writes:
>See the chart TVB produced to see the PRS10 hump in published data.
>http://www.leapsecond.com/museum/prs10/
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
measurement.
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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