Overview
2.9.3 Steptrack
Steptrack mode provides automatic periodic positioning of the antenna for maximum
receive signal strength as measured at the ACU tracking signal input. The 7200 ACU
utilizes the General Dynamics Adaptive Steptrack (AST) algorithm to perform the
function of conventional steptrack peak signal optimization, eliminating the random
"guessing" errors associated with predetermined fixed scan patterns. AST employs
alternate AZ and EL peaking operations based upon a mathematical relationship
between the changes in receive signal level and angular antenna position. For each
axis, an initial fixed-size step is taken; signal strength levels before and after the step
are used to determine the magnitude and direction of the corrective (peaking) step
required. Once the peak position is determined, flags are set, indicating the direction
of travel of the satellite so that the initial step for the next peaking operation will tend
to move the antenna along the satellite ephemeris. This feature greatly reduces the
errors introduced by the "wrong" guess made during significant portions of the daily
satellite drift by algorithms that consistently make initial steps in a given direction.
Steptrack peaking operations are performed at user-definable time intervals, or when
the receive signal level falls below a user-settable threshold. Steptracking parameters,
including tracking signal frequency, cycle time, track threshold, etc., are established
for each target, allowing maximum versatility for the system. (Refer to Section
5.8.2.4.1)
2.9.4 Star Tracking
Automatic Star tracking is provided as an aid in performing antenna gain calculations
by the radio star method. Such measurements require consistent, accurate
positioning along the path of a star with relatively high velocity. This can be done by
manual positioning, but automatic pointing yields more accurate tests, performed in
less time. Based upon site location coordinates, automatic pointing for stars including
Cassiopeia A, Taurus, and Orion is supported.
2.9.5 Intelsat 11-element Track
In this IESS-412 mode, the antenna is moved according to pointing data generated
using the Intelsat Eleven Parameter Model. The ACU accepts element sets as
distributed by Intelsat, as well as local site data, and calculates the corresponding
predicted AZ and EL positions along the ephemeris. The antenna is then moved to
the predicted positions with sufficient frequency to maintain pointing within a user-
selectable deadband around the theoretical values. The data for a given target is
maintained in a dedicated database for that target and is continually updated to
provide appropriate positioning anytime the target is accessed (within time of validity
constraints).
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