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battery is present in the controller). If the current time corresponds to a portion of the satellite's
apparent motion for which there are valid entries in the track table, the controller switches over
to a memory track algorithm. When the memory track algorithm is controlling antenna
movement, the antenna smoothly tracks the satellite based on linear interpolation of the position
data stored in the track table.
If the satellite transponder goes down while the controller is step tracking, the controller enters a
search mode. Two search modes are supported: manual and automatic. In the manual search
mode the user is prompted to manually position the antenna on the satellite and hit a key to
continue tracking. With the automatic search mode, the controller periodically scans the antenna
looking for signal strength. The user can select manual or automatic search via the controller's
CONFIG mode.
For implementing the step track algorithm, the controller requires an analog voltage that varies
with received signal strength. The controller can accept voltages from 0 to 10 volts. The analog
voltage required for tracking can be obtained from a beacon receiver or from an AGC (automatic
gain control) or signal strength tuning meter output from an analog receiver or modem.
Setting Up a Single Axis Tracker
The following steps represent the ideal method to configure a single axis tracking system. In
practice, this method may not be practical because it requires that the installer initially configure
the tracker and then return to the site to readjust the mount. This procedure also assumes that the
antenna pointing angle and control axis tilt can be set independently.
1. Obtain ephemeris data on the satellite. This provides the azimuth bearing and elevation
angle to the satellite as a function of time.
Two common methods are employed to obtain satellite ephemeris. One employs the SDP4
algorithm using Two Line Element (TLE) parameters compiled by NORAD (North
American Air Defense) Command. See www.celestrak.com for a program that implements
the SDP4 algorithm and TLE data sets.
The other method is to use the IESS-412 software and parameters available from Intelsat
(www.intelsat.com). IESS-412 data is generally only available for Intelsat satellites. An
SDP4 program is also available from Research Concepts, Inc. Contact
support@researchconcepts.com for more information on this program.
Note that the third data field on the second line of a two-line element data set entry is the
inclination of the satellite's orbital plane with respect to the earth's equatorial plane. The
first data field on the second line of a two-line element set always contains '2'.
2. Use a geostationary satellite antenna pointing solution calculator to determine the satellite's
nominal azimuth and elevation pointing solution. Nominal position here refers to what the
az/el position of the satellite would be if it were geostationary. An antenna pointing
calculator (such as ANTENNA.EXE, available for download at
http://www.researchconcepts.com/antenna.htm) can provide this information given the
latitude/longitude of the earth station and the longitude of the satellite.
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