Table of Contents
Advertisement
Software version 3.18 upgrades
This section describes several software enhancements made in
upgrading software version 3.12 to software version 3.18.
WAAS differential capability
The Northstar 941X uses a high-performance GPS receiver as its
primary source of position data. Position, COG, and SOG are
calculated directly from the received GPS satellites, along with
the time, the date, and an estimate of the unit's accuracy. In
contrast, the Northstar 941XD uses an internal differential
receiver to obtain position corrections from Coast Guard
radiobeacons. (The Coast Guard radiobeacon system consists of
non-directional, short-range beacons installed at lighthouses and
other coastal locations; their range is usually 10 to 175 nautical
miles, and their corrections in most cases improve GPS position
fixes to an accuracy of 1 to 3 meters.)
With software version 3.18 and higher, however, the 941 can
receive differential corrections to GPS signals from Wide Area
Augmentation System (WAAS) satellites. As with Coast Guard
radiobeacons, WAAS satellites use surveyed reference stations to
monitor GPS signals from each visible satellite, determine if
errors exist, and develop corrections.
However, unlike Coast Guard radiobeacons or other land-based
transmitters on other frequencies, WAAS uses a network of
geostationary communication satellite transponders, which
remain in fixed positions at approximately twice the distance
from the earth's surface as the orbiting GPS satellites, and
transmit on the same frequency as GPS. These satellite-based
transmissions provide consistent position corrections over a
much greater contiguous geographical area than the
radiobeacons. WAAS differential corrections maintain a position
accuracy of better than 3 meters 2dRMS, without the signal
interference problems periodically experienced with low-
frequency, shore-based radiobeacon differential signals.
With software version 3.18 and higher, the 941 will be able to
receive WAAS differential corrections by interfacing it to the
external Northstar 2201 WAAS Pod. Available in the future, the
– 18 –
Addendum P/N GM210
032101
Advertisement
Table of Contents
