Research Concepts RC2000C - Manual (Page 36)

28 RC2000C Az/El Tracking Antenna Controller Chapter 4 Inclined Orbit Satellites
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Figure 4.2 – Intelli-Search
4.3 Implementing the Tracking Algorithms
This section describes the information needed to implement the tracking algorithms. The purpose of
this section is to give the user insights into the operation of the controller and to prepare for the actual
entry of the setup information in the following sections.
4.3.1 Location Information
The Antenna Latitude, Antenna Longitude, and the Longitude of the inclined orbit satellite to be tracked
must be specified in order to determine the satellite's apparent motion. In most cases the satellite's
apparent motion as seen by the antenna mount is a skewed figure eight shape. This information is
needed to implement the controller's Intelli-Search algorithm.
4.3.2 Antenna Scale Factors
The azimuth and elevation scale factors refer to the mapping of antenna azimuth and elevation position
counts to antenna azimuth and elevation angles. The elevation scale factor is entered by the user. The
azimuth scale factor can either be specified by the user, or it can be derived from the position and
longitude data of adjacent geostationary satellites.
Scale factor information is entered into the controller via the Azim Constant and Elev Constant CONFIG
mode items. A non-zero value for the Elev Constant must be entered into the controller. If the Azim
Constant CONFIG mode item is initialized to a non-zero value, that value is used as the azimuth scale
factor. If the Azim Constant is initialized to a value of zero, the controller calculates the azimuth scale
factor based on the position and longitude data of geostationary satellites in the vicinity of the inclined
orbit satellite.
If the Azim Constant has a value of zero at least two geostationary satellites must be programmed into
memory (via SETUP mode) before a track may be initiated on an inclined orbit satellite. For this case it
is also very important that the proper longitude values be specified for geostationary satellites which are
programmed into the controller's memory. If a geostationary satellite is programmed into memory with
an incorrect longitude value (angle or direction), the controller will accurately position the antenna on
the geostationary satellite when it is recalled via AUTO mode, but may not track an inclined orbit
satellite properly which is located in the vicinity of the geostationary satellite. Verify the longitude
value of all satellites programmed into the controller via setup mode if the controller is using
geostationary satellites to determine the azimuth scale factor.
4.3.3 Antenna Radiation Pattern
The antenna radiation pattern specifies antenna receive power versus antenna pointing angle relative to
boresight. Boresight is the pointing angle associated with maximum received power from a given
satellite. The controller calculates the shape of the antenna's radiation pattern by knowing the Antenna
Size and the frequency Band (L, C or Ku) currently in use. Antenna Size data is entered via a CONFIG
mode prompt. The frequency Band data is specified in SETUP mode when the user initiates a track on
an inclined orbit satellite. Note that the controller also allows the user to specify a dual band inclined
orbit satellite. For this case the user is prompted to supply frequency band data on entry into TRACK
mode, and is allowed to change the Frequency Band via the TRACK mode menu.
Antenna radiation pattern information is necessary to allow the user to specify a maximum allowable
antenna pointing error (Max Track Error) in tenths of decibels (dB) rather than in elevation and azimuth
position counts. The Maximum Track Error is used to determine the step size and the frequency of
antenna movement in the STEP TRACK and PROGRAM TRACK sub-modes. In addition, antenna
radiation pattern information is used in SEARCH mode to determine the width of the parallelogram-
shaped search region, and the angle between successive sweeps.