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CONFIGURATION AND OPERATION
perform a new Global Search, thus rebuilding the table. This situation
will not occur in areas of continuous coverage as the goal of ABS is to
provide a continuous source of differential corrections. It will happen
only if the receiver is moved to a new location un-powered, that does not
have the same beacon coverage, or if it is out of range of the three beacons in this table.
You may force a Global Search, if desired, by selecting the ERASE
AUTO menu item in Level 4 of the software menu tree. For this function
to be executed, place the receiver in Manual Tune mode prior to selecting ERASE AUTO.
3.7.1 ABS Operational Mode
During the background search, alternate beacons are identified, and
stored in an Automatic Beacon Table. The VDO DGPS-Receiver remains locked to the primary frequency until it determines that it should
tune to an alternate frequency with a higher signal strength.
When in the ABS operational mode, the VDO DGPS-Receiver maintains
its lock on the primary beacon, and periodically scans other frequencies,
to track other stations that have come into range of the receiver. The
switching period is dependent upon the quality of the primary beacon
signal. The temporary release of lock from the primary beacon will contribute approximately a 10 second correction latency to the last received
RTCM message. Latencies of less than 10 seconds contribute positioning errors of less than 1 meter.
3.7.2 Menu Tree
Figure 3-2 (next page) provides the layout of the VDO DGPS-Receiver
Software Menu Tree.
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