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RC3000 Antenna Controller Chapter 1 Introduction
15
1.3.9 System Performance
The performance achieved by the RC3000 in locating and tracking satellites is dependent on the
mechanical tolerances of the mount, the correctness of the installation and the accuracy of the various
sensors.
The largest source of error for the system is due to errors in determining the truck's magnetic heading.
Errors in heading primarily affect the accuracy of the antenna's calculated azimuth position. The flux gate
determines the magnetic heading by measuring the direction of the magnetic field at the sensor tower.
Problems arise because the earth's magnetic field can be distorted by ferrous metals (such as steel and
iron; aluminum is a non-ferrous metal) and man-made magnetic fields. These man-made fields can be
generated by electric motors, generators, and transformers, as well as those "worked into" the coach
body during manufacturing.
For the flux gate sensor, there are two unique categories of objects that distort the magnetic field in the
vicinity of the truck. Some of the distortion is due to objects and electrical devices on the truck itself. This
component of the distortion can be largely compensated for during system calibration.
The other component of the distortion is due to large metal objects and man-made magnetic fields around
the site where the truck is being operated. This component of the distortion varies as the truck moves
from one location to another, and it affects the accuracy of the calculated azimuth position. Environments
which typically produce the largest errors include railroad yards, areas around electrical substations, and
sites near structures containing large amounts of steel or iron, such as bridges or large buildings.
To date, the largest known azimuth error due to these interactions is less than 10 degrees. To help
alleviate this azimuth error, the Auto Peak feature scans an azimuth range about the target azimuth and
seeks the strongest signal. This feature is explained in full in section 3.2.2.3.
The RC3000 uses a 10 bit analog to digital converter for measuring voltages from azimuth, elevation and
polarization potentiometers as well as measuring signal strength inputs. In most cases this provides
adequate resolution but should be considered. For example, if the azimuth axis has 360 degrees of
travel, the resolution achieved is 360 / 1024 (approximately 0.35 degrees). This example highlights why
pulse or resolver sensors are used to make precise movements for inclined orbit tracking. The optional
resolver interface uses a 16 bit resolver to digital converter. This allows resolution of 0.0055 ( 360 /
65536) degrees.