Acu And Beacon Receiver - Calian SatService sat-nms ACU-19V User Manual

This method minimizes the impact of noise and measurement errors to the evaluated peak
position. The benefit is, that the size of depointing steps can be reduced to a very small value.
A tracking cycle consists of 2 .. 4 tests steps. With each step the antenna is moved a certain
angle increment, the beacon level is measured before and after the movement. The angle
increment is an adjustable value, expressed as a percentage of the antenna's 3dB beamwidth. A
typical value is 15% of the (half) beamwidth.
The diagram above shows the sequence of steps the tracking algorithm performs in one cycle on
one axis. It starts with a depointing step in one direction (A). If this step lets the signal level
decrease, the antenna makes a double step in the opposite direction. It the first step leads to a
better receive level, the tracking algorithm adds one or two steps in the same direction.
For a reliable tracking operation the step size have to be big enought to rech the maximum within
the 3dB bandwith within in the entered cycle time. This meas for an inclient satellite you need a
shorter cycle time than for a geostationary satellite.

8.3.2 ACU and Beacon Receiver

To perform a step track, the ACU requires the actually measured beacon level as a rate of the
received signal quality and therefore the closeness of the antenna pointing to the ideal value.
The sat-nms ACU is capable to be operated both with the sat-nms LBRX beacon receiver and
with third party beacon receiver products.
With a third party beacon receiver, the ACU reads the beacon level from an analog voltage input.
The beacon receiver therefore must provide a dB-linear output voltage, preferably in the range
0...10V. If the sat-nms beacon receiver is used, then the beacon level is sent from the beacon
receiver to the ACU via UDP packets on the LAN.
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