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

Poul-Henning Kamp phk at phk.freebsd.dk
Thu Aug 23 18:35:28 EDT 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
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Never attribute to malice what can adequately be explained by incompetence.




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