Hemisphere GPS MBX-4, User Manual

Page: 46 / 94

MBX-4 User Guide
37
Tune Modes
The MBX-4 may be operated in either Automatic or Manual Tune Mode.
In Automatic Beacon Search (ABS) Mode, the receiver identifies and
tunes to the station providing the strongest DGPS signal. In Manual
Mode, you specify the frequency to which the receiver will tune.
Refer to Figure 3-4 on page 37, and the “Configuring the Receiver”
section on page 51 to switch between Automatic and Manual Tune
modes using the display and keypad.
Automatic Beacon Search (ABS) Mode
The MBX-4 receiver operates in Automatic Beacon Search (ABS) mode
by default, selecting and tuning to the most appropriate beacon without
operator intervention. The MBX-4 uses its two independent channels to
identify and lock to DGPS beacons without interrupting the continuous
flow of RTCM data to your GPS receiver.
ABS mode is ideal for navigation applications over considerable areas,
eliminating the need for operator intervention when travelling from one
beacon coverage zone to another.
Global Search - When powered for the first time in ABS mode, the
MBX-4 initiates a Global Search, examining each available DGPS
beacon frequency, and recording Signal Strength (SS) measurements in
units of dBmV/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-4 will initiate a fresh Global
Search, continuing this cycle until it finds a valid beacon.