Step_Track - RESEARCH CONCEPTS RC2000C Manual

26 RC2000C Polar Tracking Antenna Controller
track table has been established for a satellite, the controller will remain in the PROGRAM_TRACK
submode.
The SEARCH submode is active when the satellite signal is lost and track table data is not available. In
this submode the controller performs a search for the satellite in the region where it calculates the
satellite will be found, based on its knowledge of the satellite's apparent motion. If the satellite is found
while the controller is performing a search, the STEP_TRACK submode will receive control. If the
satellite is not found while performing the search, the controller will wait Search Retry Interval minutes
and perform another search. If while waiting for the Search Retry Interval to expire, the sidereal time
advances to a time for which valid track table data is available, the PROGRAM_TRACK mode will
become active.
The automatic search may be disabled via the Search Enable CONFIG mode item. If the automatic
search is disabled, the user is simply prompted to position the antenna on the satellite and hit the ENTER
key.
The TRACK_ERROR submode becomes active whenever an error occurs. Some of the errors which can
occur are: antenna jammed, antenna limit reached while tracking, antenna runaway, track table data
corrupted, system CONFIG data corrupted, or a peak limit error has occurred (while peaking the antenna
the controller had to move too far - possibly peaking on an adjacent satellite). Errors are described in
Chapter 7.
4.2.1

STEP_TRACK

In the STEP_TRACK submode, the controller will periodically jog the antenna in elevation and then
azimuth to peak up the antenna's received signal strength. This step_track operation will be referred to
as a peakup. The STEP_TRACK submode is active whenever there is no track table information
available for the current sidereal time and a satellite signal is present.
When STEP_TRACK mode is active, two events can trigger a step_track operation. The first is when the
current sidereal time reaches a value that corresponds to one of the 48 track table entries. The second is
when the controller calculates that the antenna pointing error exceeds the value specified by the user.
The Max Track Error CONFIG mode item allows the user to specify the maximum tracking error in tenths
of a dB.
The controller constantly calculates this error based on the following data: the apparent motion of the
satellite (determined by the inclination), the antenna's beamwidth and radiation pattern (determined by
the antenna size and the satellite frequency band), and the length of time since the last peakup. When
the controller determines that the length of time since the last peakup has allowed the satellite to move
away from the boresight of the antenna further than allowed by the max track error, a new peakup will be
initiated.
The size of the azimuth and elevation movements (or step sizes) for the step_track operation is also
determined by the max track error value. The step size corresponds to the angular movement of the
antenna which would change the received signal strength by max track error tenths of a dB. It is
calculated based on the antenna's beamwidth and radiation pattern.
Reducing the Max Track Error value results in more frequent step_track operations with smaller step
sizes. There are limits to how small the max track error may be. This is discussed in section 4.4.4.
Step_track operations will occur more frequently for satellites with larger orbital inclination values, or with
larger antenna sizes. For a given antenna size and satellite inclination, step track operations will occur
more frequently for Ku band transponders than for C band transponders. (The user is prompted to enter
satellite band data during setup.) For hybrid satellites (both C and Ku band), the TRACK menu system
allows the user to switch bands.
The STEP_TRACK submode will pass control to these TRACK mode submodes on the following
conditions:
PROGRAM_TRACK..receives control when the current sidereal time equals a time for which
track table data is available.
SEARCH..receives control if the satellite signal is lost.
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Chapter 4 Inclined Orbit Satellite