Then how come wall clocks based on WWVB work so well anywhere in CONUS?

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Then how come wall clocks based on WWVB work so well anywhere in CONUS?

They don't -- there are plenty of places in the U.S. where it takes a fair
amount of experimentation to get them to sync at all. Most of them 'listen'
in the wee hours of the morning when propagation tends to be better too. And
finally, even if they do only manage to sync up 'once in a while' (say every
week or two), they still perform much better than a typical wall clock.

wrote:
Then how come wall clocks based on WWVB work so well anywhere in CONUS?

To my knowledge they don't use the WWVB carrier as a frequency reference,
like this DDS scheme appears to do.

--
If John McCain gets the 2008 Republican Presidential nomination,
my vote for President will be a write-in for Jiang Zemin.

clifto writes:

wrote:
Then how come wall clocks based on WWVB work so well anywhere in CONUS?

To my knowledge they don't use the WWVB carrier as a frequency reference,
like this DDS scheme appears to do.

Tracking the carrier would require the clock receiver to be on all the
time. All the clocks I have, including my DCF77 unit, read the time
code and set the clock. If the signal is weak, they keep trying for 5
minutes or so. The most common is every 4 hours. They then free run
from an on-board crystal between sets.

With the upgrade to WWVB, there is at least one period in the whole
US were the code can be recovered. This is a lot easier than
recovering the carrier. Clocks only display seconds, and sometimes
only minutes, so gettting the code right is pretty easy. When you
first set up a clock or change the battery, it might take a diurnal
period to get the time set.

Over the years I have noticed misreads-- 1 minute off, or 1 hour
off-- which are corrected at next read period.

Steve.

--
Steven D. Swift, , http://www.novatech-instr.com
NOVATECH INSTRUMENTS, INC. P.O. Box 55997
206.301.8986, fax 206.363.4367 Seattle, Washington 98155 USA