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)
Peak jitter threshold --- If the jitter value of at least one axis exceeds this threshold, the
ACU raises an 'model fault'. If this happens three consecutive times, the ACU resets the
models of both axes. Adaptive tracking will be possible not until 6 hours after this
happens.During adaptive tracking, the ACU evaluates for each axis a figure called jitter. The
jitter value describes standard deviation of the measured peak positions with respect to the
positions calculated from the (currently selected) model. The figure is also expressed as a
percentage of the antenna's beamwidth, low values indicate, that the model ideally describes
the antenna's path. High values indicate that's something wrong. The step track results may
be to noisy at low amplitudes or the model does not fit at all. This may be the case if a
satellite gets repositioned in the orbit.A typical threshold value is 20%, this will detect very
early that a model does not fit to describe the satellite's motion. If this value causes false
alarms too often, you may want to raise the threshold to 50%. Setting it to 0 switches the
threshold monitoring completely off.
8.4.4 Hardware Protective Mode (Spindle Save Mode)
The so called Spindle Save Mode will reduce the tracking cycles and will therefore increase the
life time of the jack screws and other drive components.
The idea behind this mode is, to used the model parameter from the adaptive tracking and
perform only a calculate positioning step between the required step track cycles to reduce the
movement of the drive components.
With the 'Spindle save mode parameter we can define how many positioning only cycles will be
done between the step track cycles.
Example: Tracking cycle Time = 30sec and Spindle Save Mode = 3, than a full steptrack will
perform every
(3+1) x 30 sec = 120sec
but we will still have 3 positioning cycles between to
keep the antenna on the satellite.
Since the quality of the model must be good for this type of operation, there exist an additional
parameter 'Spindle save threshold' which allow to define a limit. The parameter will look to the
peak jitter to qualify the model parameter, a value between 3 to 10% should deliver good results.
If the peak jitter above the limit the sat-nms ACU will perform normal steptrack at each cycle.
Program tracking is a tracking method which lets the antenna follow a path which usually has
been calculated by an extern software. This software produces a list of time stamp / antenna
pointing records. The list is copied to the ACU and the ACU is switched to PROGRAM track mode.
The ACU now moves the antenna following the path described in the file. This way of tracking has
a couple of advantages:
There is no beacon receiver needed.
Even very low elevation satellites may be tracked.
Also objects which are not in a geostationary orbit may be tracked for a couple of hours,
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