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Subject: Re: Radio Synchronized Clock
From: Dan Allen (danallen46@XXX.XXX)
Date: Thu Feb 28 2002 - 12:52:36 EST
I found at nice stainless-steel cased wall clock at Ikea for $15 a year or two ago (they don't have them any more, alas), and it is
radio synchronized. They change at midnight and have a button on the back for the 4 main US time zones. They automatically change
for Daylight Savings time. The signal that they use is NOT WWV but WWVB at 60 kHz.
More info on WWVB can be found at:
http://www.boulder.nist.gov/timefreq/stations/wwvb.htm
WWVB barely covers North America and it depends upon the time of day:
http://www.boulder.nist.gov/timefreq/stations/wwvbcoverage.htm
I think there may be other radio stations similar to WWVB. I would expect that if there are similar stations broadcasting in the
same format and frequency that my $15 clock would work world-wide, but with the time zones being off (not a major problem).
-----Original Message-----
From: Navigation Mailing List
[mailto:NAVIGATION-L@XXX.XXX]On Behalf Of Jared Sherman
Sent: Thursday, February 28, 2002 9:05 AM
To: NAVIGATION-L@XXX.XXX
Subject: Re: Radio Synchronized Clock
Dov-
This (correcting a quartz count) was implemented around 1980 in a totally sealed diving watch which I think came out under the name
"Pulsar" before the new company of that name. It was a hermetically sealed watch, solar cells for the 'face' and an LED display on
the 'shoulder' of the face. Besides the time set buttons it also offered a calibration/adjustment mode, since there was no way to
open the watch for internal adjustment.
Since then watch accuracy has improved, typically better than +-15 seconds a month which is well beyond what the mass market pays
atttention to. I don't see any market incentive for a manufacturer to do better, unless you buy the Casio GPS watch which will put
the accuracy of 16 atomic clocks on your wrist--without your need to manually adjust it.<G>
I've been told the radio watches use a power conservation algorithm. They only turn on the receiver circuit near midnight (when the
WWV signal should be propogating, etc. at its best) and try to correct themselves once every 24 hours. If they miss the correction,
then they become more agressive about turning on and seeking it. This may vary with manufacturers of course...but in any case the
watch would only need to see "sky" once daily, since the typical quartz accuracy of +-15 sec/month means it will still be within 1/2
second of "right" for the rest of the day.
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