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From: Robert C. Colby (no email)
Date: Wed Aug 18 1999 - 08:11:45 EDT
FYI, I am sure that most of you are aware of this anyways, but this is
happening this weekend:
Important Information for GPS Users:
Contact Your Receiver Manufacturer Before Aug. 19
Users of the Global Positioning System (GPS) should contact
the manufacturers of their receivers before Aug. 19 to determine
if their systems could malfunction beginning on that date due
to conditions related to "End-of-Week" (EOW) rollover.
What is GPS?
GPS is a satellite-based system that allows consumers who
use electronic receivers to determine their location and receive
timing information. Recreational boaters and pilots, hikers,
campers, hunters, and fishermen are among the consumers
who rely on GPS receivers. The military and businesses also
use GPS.
End-of-the-Week Rollover
The GPS EOW rollover occurs every 1,024 weeks -- about
once every 20 years. The GPS system calculates time by counting
the number of weeks since Jan. 6, 1980 -- up to a maximum
of 1,024 weeks. At midnight between Aug. 21-22, 1999
Universal Time Coordinated (UTC) (which is 8:00 p.m. Eastern
Daylight Time) the GPS week "counter" will roll over to zero
weeks. The Department of Defense (DOD), which operates
the GPS satellites, says this will not create problems for the GPS
satellites or DOD's GPS ground control center, but it could
present a problem for consumers who use GPS receivers and
related applications. That's because after Aug. 21, 1999,
receivers that are not built to standards could process satellite
data incorrectly and display inaccurate information.
Changes on Aug. 19
On Thursday, Aug. 19, at 10:00 p.m. UTC (which is 6:00 p.m.
Eastern Daylight Time), new information tables will begin to be
uploaded to the GPS satellites. These tables, known as
almanacs, contain information that allow GPS receivers to predict
which satellites are in view at an estimated location and time.
These are used by the receiver to lock onto the correct satellites
and to continue proper operation as satellites fall below the
horizon and others rise into view. GPS receivers that are not fully
compliant with the current standards may experience GPS
receiver malfunctions when trying to use the new almanacs.
Possible Receiver Malfunctions
Consumers who depend on noncompliant GPS receivers for
geographic locations at sea, on land or in the air, may experience
one of the following problems with their receiver:
It will be unable to locate the satellites, resulting in
the receiver not working.
It will take more time than usual to locate the satellites.
It will appear to be working but display inaccurate positions,
times or dates.
Is This Related to Y2K?
"Year 2000," or Y2K, is a similar but distinctly different problem.
DOD has determined that the GPS satellites and its ground
control center will operate properly after Dec. 31, 1999. But
if consumer GPS receivers and applications are not Y2K-ready,
they could process satellite data incorrectly at that time.
What Should You Do?
If you use GPS, check with your receiver manufacturer to find
out if your receiver and applications are EOW rollover- and
Y2K-compliant. You may want to check the Coast Guard
Navigation Center's web site
http://www.navcen.uscg.mil/gps/geninfo/y2k/default.htm
where the Department of Transportation has posted a list
of receiver manufacturers and contacts. You also can call
the free Y2K consumer hotline (1-888-USA-4-Y2K) for
manufacturer contact information. You will need to tell the
manufacturer your receiver's model, serial number, and
the firmware version or release date displayed on the
startup screen.
Bob Colby
USCG Auxiliary
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