[time-nuts] How accurate are cheap radio controlled clocks?
Charles P. Steinmetz
charles_steinmetz at lavabit.com
Sat Jun 25 20:51:05 UTC 2011
>WWVB clocks look at the Time Code treansmitted by WWVB, not at the carrier
>which is used for precision timing.
The ones I have do not monitor WWVB constantly -- they do it once a
day in the middle of the night (signal permitting), at which time
they synch up and update an oscillator correction factor based on how
far they were off since the previous update. Mine seem to stay
within 500 mS over 24 hours compared to 1PPS "ticks" from a
Thunderbolt (subject to the resolution limits of using my eyes and
ears as the two measurement inputs and the comparator between my
ears), which is as close as the Lady Heather display clock on my system.
Perhaps some newer WWVB clocks monitor more often than that, or even
constantly, but I have not seen any that synch more often than once
every 24 hours. On one of mine, you can turn the WWVB Rx off. The
instructions indicate that the expected battery life goes up 12-fold
if you do, which may explain why they don't recalibrate more often.
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