[time-nuts] Transmitting a time sync signal - what's the trick?
Hal Murray
hmurray at megapathdsl.net
Wed Feb 27 04:27:46 UTC 2008
> What's the trick though? If I send a signal to say "it is 12:33:45",
> by the time that the signal has got there (at a mere 4800bps) and been
> interpreted, it won't be any more.
The bit rate isn't the problem. You can easily correct for any constant
delay.
The problem is noise/jitter. Do you have a central controller scheduling
things or do you have etherent/aloha type collisions and retransmissions and
such to add to the noise?
You can filter out most of the jitter if the receiver has a good local clock. Just average over several/many samples and maybe discard the outliers.
If you are trying to keep good time on a typical computer, the first step is to calibrate the local crystal.
There is lots of info here: http://www.ntp.org/
(It may be hard to find exactly what you are looking for.)
--
These are my opinions, not necessarily my employer's. I hate spam.
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