8.4.3 Adaptive Tracking Parameters

The behaviour of the adaptive is adjustable with a couple of parameters. First, adaptive tracking also is a step track algorithm. The parameters described in chapter '8.3.4 Steptrack Parameters' therefore apply to the adaptive tracking as well. The parameters concerning the adaptive tracking in particular are discussed in the table below. All parameter described here are to be set at the Tracking page.

• AZMaximummodeltype ELMaximummodeltype --- 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.
• Levelthreshold --- If the beacon level falls below this threshold value, the ACU does not perform a step track cycle. If the level falls below the threshold during the steptrack cycle, the cycle gets aborted.If the ADAPTIVE tracking is enabled and there is enough data in the tracking memory, the ACU computes a mathematical model from the stored data and predicts the antenna pointing position from the extrapolation of the model. 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)
• Peakjitterthreshold --- 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.