II Morrow Inc. 920 User Manual

Page 85

Using
Differential
GPS

In order to use DGPS, you must purchase a
marine DGPS receiver capable of transmitting
RTCM-104 differential GPS data at 9600 bits
per second. The data should conform to RS-232
specifications. Use the optional serial data cable
connected to the serial data port on the back of
the Apollo handheld GPS receiver for the
purpose of transferring this information. Make
connections as Section D describes. Follow
instructions provided with the DGPS receiver.
Once the DGPS data is transferred to the
handheld GPS receiver, position accuracy will
automatically be improved.

Where is
Differential
GPS Data
Available?

Contact the United States Coast Guard for
information on location of reference stations.
The DGPS system is not scheduled for
completion until 1996, so DGPS may not yet
be available in your area.

For more information on DGPS, refer to
RTCM Paper #134-89/SC 104-68, RTCM
Recommended

Standards

for

Differential

Navstar GPS Service available from the Radio
Technical Commission for Maritime Services,
PO Box 19087, Washington, D.C. 20036.

You may also contact the nearest office of the
United States Coast Guard.