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Re: ATM Re: GPS time receiver (was Atomic Clock via SNTP)


The whole topic of using a GPS as a very accurate time reference is quite
interesting, and luckily, there is quite a bit of good information out there.

Probably one of the more useful sites to go to is the Tuscon Amateur Packet
Radio site, www.tapr.org.   In particular, they have a page dedicated toward
GPS and related experimentation, and you can order OEM GPS units through them.
If what you are after is a good clock synchronized with atomic references
with very high accuracy, the TAC-2 kit they offer is a good way to go.  Tom
Clark developped this kit to serve as a very accurate clock to serve the
needs of scientists and amateur radio hobbyists alike, and it works very
well.  It requires a GPS with an accurate 1 pps output capability.  Note
that normal NMEA signals are NOT sufficient, the accuracy in such timing is
probably no better than a few milliseconds.  Several OEM GPS units that are
suggested are the Garmin GPS-20, Motorola Oncore, and Trimble SK-8.  You can
order the Motorola and Garmin units directly from TAPR.  Clark claims that
properly setup, the clocks can be accurate to better than 50ns RMS, and
biases reduced to less than 20ns.

If you don't need clocks that accurate, there is a clock put out by Oregon
Scientific called the Time Machine Radio Controlled clock.  It is a simple
digital clock that synchronizes with the radio signals WWVB.  I have no idea
what time accuracy it actually holds, but its second indicators are in lock
step to the WWV signals I tune into on my shortwave.  The MSRP is listed as
$99, but I got mine from Fry's Electronics for about $30.  (I've also heard
that Radio Shack carries this clock). 

Various webpointers:

http://www.tapr.org/gps/index.html
http://www.tapr.org/tapr/html/tac2.html
http://www.oregonscientific.com/timefram.html

Mark

-- 
Mark T. VandeWettering                  Telescope Information (and more) 
Email: <markv@pixar.com>                http://www.idle.com/~markv/
No Code International Member #1173