mode is selected. If the tracking mode is set to 'STEP', the ACU leaves the antenna where it
is if the beacon level drops below the limit.Adjusting the threshold level that adaptive tracking
is switched as expected must be done carefully and may require some iterations, specially if
the beacon is received with a low C/N. A good starting value for the threshold is 10 dB below
the nominal receive level or 2 dB above the noise floor the beacon receiver sees with a
depointed antenna, whatever value is higher.To turn off the monitoring of the beacon level
(this in fact inhibits the adaptive tracking), simply set the threshold the a very low value (e.g.
-99 dBm)
AZ Maximum model type / EL Maximum model type --- These settings let you limit the
adaptive model to a simpler one, the ACU would choose by itself. The maximum model type
can be set individually for each axis. Normally you will set both axes to 'LARGE', which
leaves the model selection fully to the ACU's internal selection algorithms.In cases where the
ACU seems to be too 'optimistic' about the quality of the step track results, the maximum
model on one or both axes may be limited to a more simple and more noise-resistant model.
Specially inclined orbit satellites which are located close to the longitude of the antenna's
geodetic location may require this limitation for the azimuth axis. With such a satellite, the
elevation may move several degrees while the azimuth shows almost no motion.
Measurement delay --- During a steptrack cycle, the ACU positions the antenna to a
certain offset and then measures the level. Between the moment when the antenna reached
commanded position and the beacon level measurement the ACU waits some time to let the
beacon level settle. The optimal delay value depends on the beacon receiver's averaging /
post detector filter setting and is a quite critical for the steptrack performance.If the delay is
too short, the beacon voltage does not reach its final value, the steptrack does not properly
recognize if the signal goes better or worse after a test step. If the delay is too long, the
impact of fluctuation to the measured level grows and may cover the small level difference
caused by the test step. With the sat-nms LBRX beacon receiver, best results are achieved
if the receiver is set to 0.5 Hz post detector filter bandwidth and a measurement delay of
1500 msec.
Recovery delay --- After the ACU has done the tracking steps for the elevation axis, it waits
some time before it starts tracking the azimuth axis. This is to let the beacon level settle after
the final position has been found. A typical value for this parameter is 4000 msec.
Level averaging --- When measuring the beacon level, the ACU takes a number of
samples and averages them. The standard value of 5 samples normally should not be
changed. Larger values will slow down the ACU execution cycle.
Retry after motor fault --- When the ACU encounters a motor fault during steptrack, the
tracking cycle gets aborted and the ACU shows a fault. This parameter tells the ACU how to
proceed after this, with the next tracking cycle:
NEVER --- The ACU will not try to move the antenna again. This will stop tracking until
an operator will have checked the antenna motor and re-started the tracking.
FOREVER --- The ACU try to move the antenna again with the next tracking cycle. If the
antenna is really blocked, the ACU will try to move the antenna every tracking cycle.
This increases the probability to keep the antenna following the satellite - even if the
antenna motors show sporadic faults. But this also increases the risk to crash motors
and/or spindles of the antenna.
ONCE --- This mode offers a compromise between preserving the motors and trying to
keep the antenna following the satellite. The mode ONCE allows the ACU to do exactly
one retry after a motor fault, if this fils as well the ACU stops tracking
Smoothing interval --- This parameter controls the smoothing function. Setting it to zero
disables smoothing. Smoothing lets the ACU point the antenna to positions evaluated from a
simple model calculated from the step track peaks of the recent few hours. A detailed
description of this function you find at chapter
'8.3.3 Smoothing'
(C) 2022, SatService GmbH
www.satnms.com
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