Research Concepts RC2000C - Manual (Page 33)

RC2000C Az/El Tracking Antenna Controller Chapter 4 Inclined Orbit Satellites 25
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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 the antenna pointing error based on the following data: the apparent
motion of the satellite (determined by the Inclination of the satellite’s orbital plane), the antenna's
beamwidth (determined by the Antenna Size and the satellite frequency Band), and the length of time
since the last peakup. To determine the peakup interval the controller assumes that the satellite is
always moving at its maximum velocity as seen by the antenna. The maximum velocity occurs when
the satellite is passing through the earth’s equatorial plane. When the controller determines that in
length of time since the last peakup occurred the satellite could have moved so far as to allow the
antenna pointing error to exceed the Max Track Error specified by the user, a 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 that 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 4.4.5 -
Tracking Problems. 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.