Table of Contents
Advertisement
RC2000C Polar Tracking Antenna Controller
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 following sections.
4.3.1
Location Information and Antenna Mount Type
The antenna latitude and longitude, the longitude of the inclined orbit satellite to be tracked, and the type
of polar mount (either motorized declination or motorized latitude angle) determine the shape of the
satellite's apparent motion as seen by the antenna mount. This information is needed to implement the
Search algorithm and to determine step sizes for the step track 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 CONFIG mode item is set to zero, it is very important that the proper longitude value
be specified for geostationary satellites which are programmed into the controller's memory. If it is
programmed 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 size of the
antenna and the frequency band (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 in 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
STEP TRACK mode and to determine the frequency of antenna movement in program track mode. 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.
4.3.4
Real Time Clock
The controller contains a real time clock (powered by the same lithium battery that powers the controller's
non-volatile memory) which is used to calculate the sidereal time. The period of the satellite's motion is
one sidereal day. The controller maintains a track table which contains the satellite's azimuth and
elevation positions as a function of sidereal time. The controller uses the time and date maintained by
the real time clock to calculate the sidereal time. The user specifies the Time and Date via CONFIG
mode prompts.
Research Concepts, Inc. • 5420 Martindale Road • Shawnee, Kansas 66218-9680 • USA
Chapter 4
Inclined Orbit Satellites
www.researchconcepts.com
29
Advertisement
Table of Contents
Troubleshooting
