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