Using Dgps To Determine Position - NorthStar 961 Reference Manual

Chapter 5 - Understanding Position Coordinates

Using DGPS to determine position

Using DGPS to
increase repeatable
accuracy
DGPS-in-use
indicator
DGPS status screen
Page 5-4
which affect accuracy. HDOP can range from an ideal value of
slightly less than one up to a poor value of 10 or more; any
value less than two indicates excellent performance.
For a higher level of repeatable accuracy than basic GPS, you'll
want to use differential GPS, or DGPS.
The 961XD/962XD includes an internal differential receiver,
and uses DGPS whenever signals are available. To use DGPS
with a 961X/962X, you must add an internal differential
receiver (call your authorized Northstar dealer for details).
With good DGPS corrections, your 961/962 should provide
better than four-meter accuracy (repeatable and absolute) 95
percent of the time, SOG readings accurate to 0.1 knot, and
COG measurements accurate to about 0.5 degree. For more
information about GPS, see "Using GPS to determine position"
starting on page 5-2.
When using DGPS as your navigation source, your position
coordinates may actually exceed the accuracy of some charts.
The DGPS indicator appears as the word DGPS in the upper
left-hand corner of the CHART screen. When this indicator is
displayed, it means you're using DGPS's higher level of
accuracy for received data. When you require this additional
accuracy, check for the presence of this indicator, since its
absence means DGPS isn't in use.
To display more information about received DGPS corrections,
press the STAR key until you reach the SERVICE MENU
screen, then press the GPS STATUS key. The GPS SATELLITE
STATUS screen appears, showing the DGPS differential
transmitter now in use. The lower half of the screen shows the
beacon's name, and the transmitter's frequency and baud rate.
The beacon name may sometimes be unknown, but the
system will work properly without it.
NOTE:
961/962 Operations and Reference Manual, Rev. A