RESEARCH CONCEPTS RC2000C Manual page 77

RC2000C Az/El Tracking Antenna Controller
changed after the satellite was programmed into non-volatile memory. Note that not all
versions of the software support polarization control.
When controllers which support polarization control are used on systems which do not have
polarization control present make sure that the Rotating Feed Present CONFIG mode item is
set to 0. When the Rotating Feed Present CONFIG mode item is set to zero the controller
assumes that a Polarotor is present in the system. A Polarotor is controlled in an open loop
fashion - there is no position feedback from the Polarotor so the controller cannot tell whether it
is actually connected to a Polarotor device or not. Even if a polarization control device is not
present a valid horizontal and vertical polarization position must be programmed into memory
for each satellite. If a polarization control device is not present for a given installation, when
SETUP Mode is used to program a satellite into memory make sure that polarization limits are
not displayed when the horizontal and vertical polarizations are specified. If necessary, use the
POL CCW and POL CW keys to 'jog' the Polarotor away from the limits.
DISABLING RUNAWAY ERRORS
The controller has a provision to only allow the accumulation of position counts when the
antenna has been commanded to move, or movement has just ceased (as defined by the Az/El
Fast Deadband and Az/El Slow Deadband CONFIG mode items). This has the effect of
disabling RUNAWAY errors. It is generally not recommended to disable the runaway error. If
necessary, it can be accomplished by setting the Az/El Fast Deadband CONFIG mode item to a
value that ends in '01', i.e. 2001, 2301, etc.
THE PROGRAM TRACK TABLE HAS GAPS EVEN THOUGH THE SATELLITE TRANSPONDER HAS
NOT POWERED DOWN
In the STEP TRACK sub-mode, the controller periodically peaks the antenna. Two events can
trigger a peaking operation. The antenna will peakup at the sidereal times corresponding to
entries in the track table and store the peak azimuth and elevation antenna positions. A
peaking operation will also occur whenever the controller calculates that the antenna pointing
error could exceed the error specified by the Max Track Error CONFIG mode item because of
the satellite's apparent motion. The controller determines this time interval by knowing the
satellite's inclination (specified when the track is initiated via SETUP Mode) and the antenna
beamwidth (calculated by having information on the antenna size and frequency band).
Since the track table has 48 entries and a sidereal day is 23 hours, 56 minutes and 4 seconds
long, a track table-inspired peakup will occur roughly every 30 minutes. A problem can arise if
a Max Track Error inspired peakup is in progress when the track table peakup should occur -
the controller will not perform the track table peakup, and no azimuth and elevation position
data will be stored in the track table. This causes gaps in the track table data (which may be
examined via the TRACK MENU - VIEW function). To prevent this from occurring, the
controller will not initiate a Max Track Error peakup within 120 seconds prior to a sidereal time
that corresponds to a track table entry. The 120 seconds is referred to as the Peakup Holdoff
Interval.
The user can change the Peakup Holdoff Interval by manipulating the value of the Az/El Slow
Deadband CONFIG mode item. If the Az/El Slow Deadband CONFIG mode item is a multiple
of 50, the default value of 120 seconds is used as the Peakup Holdoff Interval. The user can
select any Peakup Holdoff Interval (up to 500 seconds) by selecting a Peakup Holdoff Interval
that is not a multiple of 50.
The relationship between these two items is illustrated by way of an example:
Az/El Slow Deadband = 818 milliseconds
818 divided by 50 equals 16 with a remainder of 18. For this case the Peakup Holdoff Interval
will be (18 * 10) or 180 seconds.
The Peakup Holdoff Interval should be longer than the worst case time that it takes to perform a
peaking operation. The worst case peakup time will correspond to the portion of the satellite's
apparent motion when the satellite is passing through the earth's equatorial plane.
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