[time-nuts] Hanging bridge question

Bob Camp lists at rtty.us
Tue Mar 25 07:40:24 EDT 2014


Most of the more modern receivers don’t stop at one ns resolution on the correction. You can go well below the ns level with them. If you are doing it in software, it’s pretty much free.


On Mar 25, 2014, at 7:27 AM, Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:

> 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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