Simrad MX575D User Manual

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Operation | HS80/MX575C/MX575D User Manual
Operation
GPS overview
When referring to the four D/GPS compass models, namely: HS80, HS80A, MX575C and
MX575D this manual uses the general term “smart GPS compass”. Specific model number
will be called when describing a particular feature or operation that is unique to that model.
The HS80/HS80A compass GPS compass models are GPS only receiver, while the MX575C/
MX575D models are GPS + GLONASS receivers.
When the smart GPS compass is powered for the first time, it performs a ‘cold start’ that
involves acquiring the available GPS satellites in view and the land-based beacon DGPS
service for the MX575C/MX575D. External source of RTCM SC-104 differential corrections can
also be used in lieu of the built-in beacon receiver. If you use an external source of correction
data, it must support an eight data bit, no parity, one stop bit configuration (8-N-1).
GPS operation
The GPS receiver is always operating, regardless of the DGPS operation mode. The following
sections describe general operation of the Smart GPS compass’s internal GPS receiver.
¼ Note: Differential source and status have no impact on heading, pitch, or roll. They only have
an impact on positioning and heave.
GLONASS overview
The GLONASS receiver technology is only available in the HS80A and the MX575D models.
GLONASS is a global satellite navigation system developed by the Soviet Union, providing
real-time position and velocity determination for military and civilian users. The GLONASS
satellites are located in orbits at 25,510 km altitude with a 64.8 degree inclination. GLONASS’
orbit makes it especially suited for use in high latitudes (north or south), where getting a
GPS signal can be problematic. The constellation operates in three orbital planes, with 8
evenly spaced satellites on each plane. A fully operational constellation with global coverage
consists of 24 satellites. To get a position fix the receiver must be in the range of at least four
satellites.
Combining the GPS and GLONASS system provides the following advantages:
• Better signal acquisition times
• Better position and time accuracy
• Reduces the physical blocking of signal in urban cities where tall buildings are the norms.
• Better satellite geometry resulting in better HDOP
Automatic tracking
The Smart GPS compass receiver automatically searches for GPS (and GLONASS) satellites,
acquires the signals, and manages the navigation information required for positioning and
tracking.
Receiver performance
The Smart GPS compass works by finding four or more GPS satellites in the visible sky. It uses
information from these satellites to compute a position within 4.0 m. Since there is some
error in the GPS data calculations, the Smart GPS compass also tracks a differential correction.
The Smart GPS compass uses these corrections to improve its position accuracy to better
than 1.0 m.
The two main aspects of GPS receiver performance are:
1. Satellite acquisition, and
2. Positioning and heading calculation.
When the Smart GPS compass is properly positioned, the satellites transmit coded
information to the antennas on a specific frequency. This allows the receiver to calculate a
range to each satellite from both antennas. GPS/GLONASS is essentially a timing system. The
ranges are calculated by timing how long it takes for the signal to reach the antenna. The
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Simrad MX575D Specifications

General

Brand	Simrad
Model	MX575D
Category	Marine GPS System
Language	English