Bob Ammerman wrote:
> Don't lock to the 1PPS signal, lock to the carrier. WWVB carrier is
> _very_ accurate.

It is very accurate when it leaves the transmitter because it is derived
from the NIST atomic clock in Boulder.  However, there is significant phase
noise as the signal takes different paths thru the atmosphere and off the
ionisphere.  If you're close enough so that you get mostly ground wave, this
won't be too bad.  Here in New England 2000 miles from the transmitter we
only get skips.  The long term accuracy is still good, but "long term" is
now several hours to a day.

This sounds like a good PIC project.  Create a highly accurate local
oscillator by phase locking it to the WWVB carrier frequency.  Due to the
very long phase lock loop time constant required, this would need to be done
digitally.

I was thinking of making a WWVB receiver and PIC real time clock that would
be a "NTP server in a box".  Maybe adding a high accuracy frequency output
would be a nice additional feature.


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