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Operation |
HS80/MX575C User Manual
Beacon operation
Many marine authorities, such as the U.S. coast guard, have installed networks of radio beacon
stations that broadcast DGPS corrections to users of this system. With the increasing utility of
these networks for terrestrial applications, there is an increasing trend toward densification
of these networks inland. The dual channel beacon receiver in the MX575C can operate in
manual or automatic tuning mode, or, using database mode, will select the closest station
in compliance with IEC 61108-4 standards. The MX575C is configured to receive DGPS
corrections from beacon stations by default.
HS80/MX575C overview
The HS80/MX575C provides accurate and reliable heading and position information at
high update rates. To accomplish this task, the HS80/MX575C uses a high performance GPS
receiver and two antennas for GPS signal processing. One antenna is designated as the
primary GPS antenna and the other is the secondary GPS antenna. Positions computed by the
HS80/MX575C are referenced to the phase center of the primary GPS antenna. Heading data
references the vector formed from the primary GPS antenna phase center to the secondary
GPS antenna phase center.
The heading arrow located on the bottom of the HS80/MX575C enclosure defines system
orientation. The arrow points in the direction the heading measurement is computed (when
the antenna is installed parallel to the fore-aft line of the vessel). The secondary antenna is
directly above the arrow.
Fixed baseline moving base station RTK
The HS80/MX575C’s internal GPS receiver uses both the L1 GPS C/A code and carrier phase
data to compute the location of the secondary GPS antenna in relation to the primary GPS
antenna with a very high sub-centimeter level of precision. The technique of computing
the location of the secondary GPS antenna with respect to the primary antenna, when the
primary antenna is moving, is often referred to as moving base station Real Time Kinematic
(or moving base station RTK).
Generally, RTK technology is very sophisticated and requires a significant number of possible
solutions to be analyzed where various combinations of integer numbers of L1 wavelengths
to each satellite intersect within a certain search volume. The integer number of wavelengths
is often referred to as the “ambiguity” as they are initially ambiguous at the start of the RTK
solution.
The HS80/MX575C restricts the RTK solution. It does this knowing that the secondary GPS
antenna is 50 cm from the primary GPS antenna. This is called a fixed baseline and it defines
the search volume of the secondary antenna as the surface of a sphere with radius 50 cm
centered on the location of the primary antenna (see Figure 3-1).
Primary Antenna
50 cm
Baseline
Figure 3-1: Secondary antenna’s search volume
¼
Note:
The HS80/MX575C moving base station algorithm only uses GPS to calculate heading.
Differential corrections are not used in this calculation and will not affect heading accuracy.
Summary of Contents for HS80/MX575C
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