[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

John wrote:

>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.

Best regards,


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