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About GPS Navigation
About GPS Navigation
Operator's Manual
Version 7.5
This GPS receiver is a precision navigation instrument utilizing the
latest technology available today to provide optimum performance
. from the GPS satellite and Beacon land signals received. As with all
other forms of radio signals, the ultimate navigation result is depen-
dent upon the quality of these signals. Radio signals may, on occa-
sion; be distorted, jammed, or otherwise incorrect. As a result, your
positionaccuracy may occasionally be less than that which can nor-
mally be expected.
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The Navstar Global Positioning System, commonly referred to as GPS,
is a satellite navigation system developed by the V.S. Department of
Defense to provide both military and civilian users with highly accu-
rate, worldwide, three dimensional navigation and time. By receiving
signals from orbiting GPS satellites, authorized users are able to con-
tinuously navigate with an accuracy on the order of 16 meters or bet-
ter, while civilian users are limited to accuracy's of approximately 30
meters 2D RMS.
A technique referred to as Differential GPS (DGPS), allows users to
obtain maximum accuracy from the GPS system. DGPS requires the use
oftwo GPS receivers. One receiver, known as theRe/erence Station, is
placed at a surveyed location, the coordinates of which are precisely
known. The purpose ofthe differential GPS system is to use the refer-
ence station to measure the errors in the GPS signals and to compute
corrections to remove the errors. The corrections are then communi-
cated in real-time to the navigators, where they are combined with the
satellite signals received by the navigators, thereby improving their
navigation or positioning. The geographic validity of these correc-
tions decreases with distance from the reference station, but the cor-
rections are valid for navigators hundreds ofkilometers fromthe refer-
ence station.
Marine radio beacons operating in the 283.5 to 325.0 KHz frequency
range are in widespread use for direction finding in coastal navigation.
Because the beacon system has been in place and widely used for
many years, it provides an effective means for the transmission of
DGPS signals. Depending on their local environment and power out-
put, their signals may be usable to several hundred miles. Marine bea-
cons provide an economical means of obtaining DGPS accuracy for
coastal navigators. GPS receivers with built-in beacon receivers are
designed to provide low cost reception of DGPS corrections broad-
cast (normally free of charge) by coastal authorities.
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