CSI Wireless ABX-3, Справочное руководство

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ABX-3 / MBX-3 Reference Manual 39
4.3.1.1 Global Search
When powered for the first time in ABS mode, the MBX-3 initiates a
Global Search, examining each available DGPS beacon frequency, and
recording Signal Strength (SS) measurements in units of dB
µ
V/m to
the Global Search Table. The receiver uses these measured values to
compute an average SS, and noise floor, and to sort the frequencies in
descending order of SS. The two channels cooperatively examine the
frequencies with the highest SS measurements, above the computed
noise floor, to determine the station providing the strongest RTCM
signal. The receiver's primary channel locks to the first identified
DGPS broadcast, while the second channel continues searching in the
background for superior beacon signals. If no signal is available, the
MBX-3 will initiate a fresh Global Search, continuing this cycle until it
finds a valid beacon.
4.3.1.2 Background Search
During the Background Search, the second channel examines all
frequencies at both the 100 and 200 bps MSK bit rates to identify
beacons possessing superior signal quality. If a DGPS broadcast is
identified that exhibits a 2 dB greater signal strength than that of the
primary station, the receiver will automatically switch to this beacon.
No loss of lock occurs on the primary station during the background
scan.
The MBX-3 stores the current primary beacon in memory so that it is
available upon subsequent power-up. You may force a new Global
Search at any time using the proprietary NMEA 0183 command defined
in Section 5.7.2.1.
4.3.2 Manual Mode
In Manual tune mode, you may select a specific frequency and bit rate
for the receiver to tune to, or simply specify the frequency, allowing the
MBX-3 to identify the correct MSK bit rate on its own. This mode of
operation is most useful when working in an area where you know the