Dgps: How It Works - Garmin 23 Owner's Manual And Reference Manual

Reference
DGPS:
How It Works
The Main Menu Page on the
GPS III/III+/12Map/
Navtalk. Select 'Setup' to
make the desired interface
settings.
From the Interface Page,
select 'RTCM/NMEA' to
properly interface with the
GBR 23.
14
Satellites received by the shipboard GPS receiver, but
not by the GPS receiver at the beacon transmitter site, will
not have corresponding corrections. When four or more
satellites received by the shipboard GPS receiver have
corresponding corrections, the result is a highly accurate
position reading. The more satellites with corrections, the
more accurate the position.
The GBR 23 receives RTCM-SC-104 format signals
from ground based DGPS Beacon Stations operating in
the 283.5 kHz to 325.0 kHz frequency band, with MSK
modulation and data rates of 25,50,100, or 200 bits per
second. These stations are typically operated by
government agencies such as the U.S. Coast Guard.
Generally, the closest DGPS station will provide the
most accurate correction data. Individual stations vary
and the user may wish to verify the suitability of the
signal for the intended application with the station
operator. The station power is normally set to provide a
usable range somewhere near 300 km. Other factors such
as local interference, lightning, time of day and season, if
the path to the station is over ground or water, and
antenna selection or installation affect the usable signal
range.
DGPS BEACON
SIGNAL IN
GBR 23 H-FIELD
BEACON RECEIVER
CORRECTION
(RTCM SC-104)
Figure 5: Shipboard DGPS System
GPS SIGNAL IN
GPS
RECEIVER
DATA
GA-29 GPS
ANTENNA