Garmin 125 GPS Receiver User Manual


 
DGPS Interface
The last two format settings allow the differential-
ready GPS 125 Sounder to accept RTCM DGPS correc-
tions in RTCM 104 version 2.0 format. Using DGPS
corrections will improve receiver accuracy to 5-10
meters, regardless of errors induced by the government’s
Selective Availability (SA) program. The RTCM/NONE
format will allow connection to any manually tuned
beacon receiver by using the proper output interface.
The baud rate is selectable from the GPS 125 Sounder.
The RTCM/NMEA selection controls the GARMIN
GBR-21 differential beacon receiver. Once a RTCM set-
ting has been selected, the GPS 125 Sounder will either
automatically try to tune the last frequency and bit rate
you selected or will switch to the default frequency of
304.0 kHz with a bit rate of 100 bps if no previous bea-
con has been tuned. You may also enter your own fre-
quency and bit rate if desired.
To enter a DGPS beacon frequency:
1. Highlight the ‘FREQ’ field and press
F
.
2. Enter the desired frequency and press
F
.
3. Highlight the ‘RATE’ field and press
F
.
4. Use
U
and
D
to select the desired transmit rate.
5. Press the
F
key to confirm your entry.
When the GPS 125 Sounder is receiving DGPS cor-
rections from the GBR-21, the ‘BEACON RECVR’ sec-
tion of the I/O setup page will display the beacon fre-
quency and signal strength, as well as the distance from
the transmitter to the beacon receiver. At the bottom of
the beacon receiver field, a status message will keep you
informed of DGPS activity:
• A ‘Tuning’ message will be displayed while a bea-
con signal is being tuned.
• Once the beacon signal has been tuned, a
‘Receiving’ message will be displayed.
• If a beacon signal is tuned and no corrections are
being received, a ‘No Data’ message will be dis-
played.
• If a beacon signal cannot be tuned, a ‘No Status’
message will be displayed.
DGPS Interface
REFERENCE
50
The selectable baud rate is
available for all RTCM
interface options.
Once a RTCM option is
selected, you must manual-
ly tune the beacon receiver
from the frequency field.
125 Man Rev B 7/23/98 11:48 AM Page 50