NorthStar Navigation Explorer 660 - Manual (Page 29)

Northstar Explorer 660 Installation and Operation Manual 29
GPS worldwide navigation
The US Government operates the GPS system.
Twenty-four satellites orbit the earth and
broadcast position and time signals. The positions
of these satellites are constantly changing. The
GPS receiver analyses the signals from the closest
satellites and calculates exactly where it is on
earth. This is called the GPS position.
The accuracy of the GPS position is typically
better than 10 m (33 ft) for 95% of the time. A
GPS antenna can receive signals from the GPS
satellites when it is almost anywhere on earth.
DGPS
A DGPS system uses correction signals to remove
some of the errors in the GPS position. The
Explorer 660 can use one of two types of DGPS
system:
WAAS and EGNOS DGPS
WAAS and EGNOS are two satellite based DGPS
systems. The correction signals are broadcast
by satellites and are received by the Explorer
660’s standard GPS antenna. The accuracy of the
corrected GPS position is typically better than 5 m
(16 ft) for 95% of the time.
WAAS covers all of the USA and most of
Canada. EGNOS will cover most of Western
Europe when it becomes operational.
Differential
beacon DGPS
Differential beacons are land based radio
transmitters that broadcast correction signals
that can be received by a special receiver
on the boat. Differential beacons are usually
only installed near ports and important
waterways, and each beacon has a limited
range. The accuracy of the corrected GPS
position is typically better than 2 to 5 m (6 to
16 ft).
7 Satellites
GPS antennas
The Explorer 660 must be used with an external
GPS antenna:
• Normally, use the GPS antenna supplied.
• Fit an optional differential beacon DGPS
antenna to give enhanced accuracy within
range of land based differential beacons
in areas where WAAS or EGNOS are not
available. Such a DGPS antenna has both a
GPS receiver and a beacon receiver, and it
automatically applies the beacon correction
to the GPS position.
• The Explorer 660 can use GPS satellite data
from a optional compatible instrument or
antenna connected by NavBus or NMEA (see
section 16-6). In this case, the Explorer 660
does not need its own antenna.
To configure the Explorer 660 for different
antenna options, see section 15-4. For more
information, contact your Northstar dealer.
Startup
Each time a GPS receiver is turned on, it normally
takes about 50 seconds before it outputs the first
position. Under some circumstances it will take
up to two minutes or longer.