Service manual

RC2000 Service Manual Chapter 1 Introduction 2
Research Concepts, Inc; 10679 Widmer; Lenexa, Kansas; USA 66215 WWW.RESEARCHCONCEPTS.COM
5. The Adapti-Drive variable speed control system allows the user to specify the desired slow speed
for each axis. The Adapti-Drive system will then adjust the actuator voltage (via a pulse width
modulation scheme) to maintain the speed selected by the user. This alleviates the problem of
poor speed regulation with varying direction along a given axis associated with constant voltage
slow speed systems.
6. The RC2000A and RC2000C are equipped with an RS-422 communications port. This allows the
controller to interface with a PC. The communication protocol used is compatible with the popular
SA-Bus protocol. Two IBM PC compatible programs are included with the controller. The optional
AUTOPILOT software package allows a single PC to control multiple antenna positioners and
satellite receivers. An optional RS-232 to RS-422 interface converter, designated RC1KADP, is
available to convert the RS-232 interface (which is standard on PC's) over to the RS-422 interface
required for the SA-Bus protocol.
1.2 Tracking Inclined Orbit Satellites
To understand the operation of our controller, it is necessary to review the characteristics of inclined
orbits. Satellites are allowed to drift into an inclined orbit to save satellite station-keeping propellant.
East-West station-keeping maneuvers must be performed to keep the satellite in its assigned orbital
position. North-South station-keeping is performed to keep the satellite in the earth's equatorial plane.
Natural forces tend to cause the satellite's orbital plane to tilt, or become inclined to the earth's
equatorial plane. By suspending North-South station-keeping maneuvers (while continuing East-West
station-keeping), a significant propellant savings can result. Typically, for a geostationary satellite, 90
percent of the total propellant usage is due to North-South station-keeping maneuvers.
A satellite in an inclined orbit has certain known characteristics (to a close approximation). The
inclination of the satellite's orbital plane relative to the earth's equatorial plane increases at a rate of
between 0.6 and 0.9 degrees per year. The rate varies from year to year. The apparent motion of the
satellite is periodic with time; the period is approximately 23 hours, 56 minutes, 4 seconds. The
apparent motion of the satellite about a nominal position as viewed from the center of the earth is in a
figure eight pattern, as described by the following equations:
Height of the figure eight (North-South) : 2 * i degrees
Width of the figure eight (East-West) : (i * i) / 115 degrees
where i is the inclination of the satellite's orbital plane to the earth's equatorial plane in degrees
Examination of the equations shows that the figure eight is much taller than it is wide. For example, a
5-degree inclination results in an apparent East-West position variation of 0.217 degrees. The
apparent motion of the satellite is practically a straight line oriented in a North-South direction. This
knowledge of the satellite's period and apparent motion is exploited by our tracking antenna controllers.
1.3 RC2000B/C Tracking Algorithm
The tracking algorithm used by the RC2000B/C antenna controllers can be divided into 3 distinct parts -
STEP_TRACK, PROGRAM_TRACK, and SEARCH. The process will be described in chronological
order as seen by a user initiating a track on a satellite for the first time. To initiate the track process the
user jogs the antenna to the satellite and verifies the identity of the satellite. The system then enters
STEP_TRACK mode.
In STEP_TRACK mode the controller periodically peaks the receiver's AGC signal strength by jogging
the antenna. The time and position are recorded in a track table maintained in the controller's non-
volatile memory. The interval between peakups is determined by antenna size, the frequency, and a
user-specified maximum allowable error (in dB). STEP_TRACK mode is active until a time is reached
that corresponds to a segment of the satellite's motion which has previously been stored in the track
table. When this occurs, PROGRAM_TRACK is activated.
In PROGRAM_TRACK mode the controller smoothly moves the antenna to the positions stored (or
derived from) entries in the track table. The time between movements is determined by the same
factors which govern the time between peakup operations in STEP_TRACK mode. In particular, the
user can specify the maximum allowable error between the antenna's actual position and the position
specified by the track table. By increasing the maximum allowable error, antenna movements can be
performed less frequently, thus avoiding unnecessary wear on the antenna actuators. In