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What is GPS?
GETTING STARTED
The Global Positioning System (GPS) is a system of 24 satellites which circle the
earth twice a day in a very precise orbit and transmit information to earth. The GPS
III must continuously “see” at least three of these satellites to calculate your position
and track your movement. At times, additional satellites may be needed to determine
a position.
By using an almanac (a timetable of satellite numbers and their orbits) stored in
the receiver’s memory, the GPS III can determine the distance and position of any
GPS satellite and use this information to compute your position.
Your GPS receiver can only see satellites above the horizon, so it needs to know
what satellites to look for at any given time. To use this almanac data, your GPS
needs to either be told its general location (“initialized”) or given the opportunity to
find itself. Once you initialize the unit to a position, it will typically compute a fix
within a few minutes. We’ll show you how to initialize your new GPS III on page 5.
Initialization is only necessary under the following conditions:
• The first time you use your receiver (new from the factory).
• After the receiver has been moved over 500 miles (with the power off) from
the last time you used it.
• If the receiver’s memory has been cleared and all internally stored data has
been lost.
Because the GPS III relies on satellite signals to provide you with navigation
guidance, the receiver needs to have an unobstructed, clear view of the sky for best
performance. In a nutshell, the GPS receiver’s view of the sky will generally deter-
mine how fast you get a position fix—or if you get a fix at all. GPS signals are rela-
tively weak and do not travel through rocks, buildings, people, metal, or heavy tree
cover, so remember to keep a clear view of the sky at all times for best performance.
Hold the receiver at a
comfortable height with the
antenna pointing up.
When new (or if a position
cannot be determined after 10
minutes), the GPS III will
prompt you to initialize the
receiver. The unit needs a
starting position to determine
which satellites are in view.
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GPS III A 7/21/98 8:51 AM Page 4