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    Re: Radio Synchronized Clock
    From: Dan Allen
    Date: 2002 Feb 28, 09:52 -0800

    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{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Jared Sherman
    Sent: Thursday, February 28, 2002 9:05 AM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    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.
    
     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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