Leica MX400 Operating Instructions Manual page 22

Keypad & Display Description
Because of the limited range of the beacon transmitters, typically
150 to 400km, the corrections generated by the reference station are
always valid for users who can receive the correction signals and
maintain a 5 meter or better accuracy figure. Just like the satellite
segment which maintains in-orbit spare satellites, most beacon
stations operate two live running GPS reference stations. One
reference station normally broadcasts into the air for you to receive,
the other GPS receiver normally broadcasts into a dummy load,
through a secondary transmitter. That means there is always a back-
up or standby beacon transmitter and reference station ready to
transmit should the primary fail. Each reference station is normally
assigned a unique ID number (i.e. Pt. Loma, San Diego operates
IDs 262 and 263), so you can always tell if you are on the primary
or back-up system. In addition to the standby back-up system,
virtually all beacon stations are connected to an integrity monitor
receiver and computer. The integrity monitor is normally placed at
a remote location from the transmitter site to monitor the signal
strength of the transmitter, as well as the accuracy of the corrections
being transmitted. If the accuracy of the corrections falls outside a
predetermined radius (usually 5 meters), the computer automati-
cally generates a warning message. The warning message is then
sent to the reference station, either by radio or landline, and the
warning message is broadcast to the user community. Some
agencies have opted to install the integrity monitor at the same
location as the transmitter. Some agencies have also created central
monitoring systems which monitor multiple beacon transmitter
stations to ensure network integrity. Operators maintaining the
beacon station equipment may also create their own unique mes-
sages to broadcast planned outages or other important information.
When a message is received, you will be notified with an alarm
indication. You can then view the received message in the DGPS3
screen.
Version 3.3
Operator's Manual
9