Garmin GPSMAP 172C - Manual (Page 84)

Main Menu: Comm Tab
If ‘Garmin DGPS’ or ‘RTCM In/NMEA Out’ format is selected, additional fields are provided to
control a Garmin differential beacon receiver directly from your GPSMAP 172/172C. You may have the
unit automatically scan for the DGPS beacon signal or you can enter the beacon frequency and bit rate
on the unit and the information is used to tune the beacon receiver.
To have the unit automatically scan for a frequency:
1. With the unit set to ‘ Garmin DGPS’ or ‘RTCM In/NMEA Out’, use the ARROW KEYPAD to high-
light the “Beacon” field and press ENTER.
2. Highlight ‘Scan’ and press ENTER. The numbers in the ‘Frequency’ field changes as the unit scans
from 284 kHz to 325 kHz, 200 bit rate, then 100, at 6-second intervals.
To restart the scan:
1. Press MENU, highlight ‘Restart Scan’ and press ENTER. The “Status” field shows one of the
following:
• Tuning – unit is attempting to tune to the specified frequency and bit rate.
• Scanning – unit is automatically scanning through the frequencies and bit rates.
• Receiving – unit is receiving DGPS signal and ready for operation.
• Check Wiring – unit is not making connection with DGPS receiver.
When the unit is receiving a DGPS signal, the “SNR” (Signal to Noise Ratio) and “Distance” fields
shows data. The SNR range is 0dB to 30dB, with 30 being the best. The Distance may or may not show
data, depending upon the signal being broadcast from the DGPS site.
The DGPS beacon transmitters are operated by the U.S. Coast Guard (or similar government
agency in other countries), which is responsible for their accuracy and maintenance. For DGPS trans-
mitter problems or to find the most updated list of frequencies and coverage areas, contact your local
USCG, or see their web site at http://www.navcen.uscg.mil/.
You may also manually enter a
frequency and bit rate.
Status Field
SNR and Distance shows data
when signal is received.

Reference