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From: Sisler, Clyde <Clyde.Sisler_at_wang.com>
subject: [Paddlewise] GPS 1024 rollover problem
Date: Thu, 11 Mar 1999 13:39:58 -0500
Has anyone else heard of this problem?  The April/99 issue of Soundings, a
boating newspaper, indicates older units 'may' go haywire on August 21,
1999.

GPS satellites apparently broadcast time in GPS week numbers which range
from 0 to 1023.  The GPS week started January 6, 1980 and will roll back to
0 on August 21.  Problems could range from date not showing improperly, to
searching for satellites where they were in 1980, to displaying grossly
erroneous information.

Newer(?) models are supposed to handle the rollover.  They're still testing
to determine the impact on older models.

The suggestion is to check out your manufacturer's web site or call their
technical support for current information.

And yes, August 21 is on a weekend (Saturday).

Clyde Sisler
http://csisler.com


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From: Sisler, Clyde <Clyde.Sisler_at_wang.com>
subject: RE: [Paddlewise] GPS 1024 rollover problem
Date: Thu, 11 Mar 1999 14:33:25 -0500
Garmin says no problemo on y2k or 1024 with older models.
http://www.garmin.com/faqs/1.html


Clyde Sisler
http://csisler.com
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From: <WILAX_at_aol.com>
subject: Re: [Paddlewise] GPS 1024 rollover problem
Date: Thu, 11 Mar 1999 19:48:09 EST
The GPS system will suffer it's version during the WRNO date (August '99).
The week number rollover is well defined on the Trimble Navigation website
www.trimble.com    they have a section devoted to Y2K and WRNO.
Most likely, a receiver that is not WRNO compliant will suddenly stop
navigating at the rollover time.  It will then go into a "cold search" start.
This means the rx has no idea where it is, what time it is or what it should
be searching for (its internal almanac is blank).  It will take 20 minutes to
a couple of hours for the rx to re-acquire and start giving position fixes
(depends on the manufacturer). 
Think of yourself being placed somewhere on the surface of the earth and not
knowing time/date/hemisphere then trying to figure out (from the stars) where
you are.  That's what the rx is doing...it will take a bit of time. 
After fixing again, it will, most likely, navigate properly with the exception
that date information will be wrong.
Many manufacturers have firmware versions that are Y2K WRNO compliant so be
sure your updated.
The issue is very "manufacturer specific".  The only way to know about your
particular navigator is to check with the manufacturer.  One observation is
that "handhelds" have only been financially attractive to kayakers in the last
5 years.  Most  GPS units built in the last 5 years are compliant.  The units
built in 90, 91 and all the "desert storm surplus" stuff out there is probably
not compliant.

Tom    
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