[time-nuts] Hanging bridge question
EWKehren at aol.com
EWKehren at aol.com
Tue Mar 25 12:44:11 UTC 2014
The lowest cost solution is a DS chip in combination with a PIC. How ever
has any one thought about a fix by going to the source of the problem. The
TCXO. Use a DDS with internal multiplier like the AD9851 or AD 9913 and use
the sawtooth message from the GRS receiver and change the frequency. An
other alternative would be to use the sawtooth word to fine tune a TCXO or any
VCXO for that matter.
Bert Kehren
In a message dated 3/25/2014 7:28:11 A.M. Eastern Daylight Time,
phk at phk.freebsd.dk writes:
In message <6B362A4D-834A-4733-BED8-FCFEC0CCBA6C at rtty.us>, Bob Camp
writes:
I should add here, that you _can_ do a little bit better than the
sawtooth correction.
We know, or at least assume, that the GPS's internal clock is step-less
and slowly changing, so if you put a predictive filter on this stuff,
it can actually do a reasonable job at estimating which way the rounding
of the sawtooth correction went (since it is integral ns).
This reduces the random rounding error on the sawtooth correction
from +/- 0.5 ns to something like +/- 0.3 ns.
Totally not worth it, but a cool and educational project :-)
--
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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