RC4500 Antenna Controller Chapter 5 MODES – In Depth Descriptions
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conclude that the smallest value of Max Track Error leads to the tightest track. When the value of this
parameter is reduced to a point where the peakup azimuth or elevation step sizes approach the value of
the mechanical hysteresis (slop) of the antenna mount, the controller can not peakup properly. This can
lead to PEAK LIMIT errors, or the antenna peaking itself off of the antenna.
Here is the mechanism which can lead to this undesirable result:
1. The Max Track Error parameter is set to a 'low' value which results in an elevation peakup step
size of just one position count.
2. When a peakup occurs, the controller measures the signal strength at the current antenna
position, and then moves the antenna up or down in elevation in an attempt to find the strongest satellite
signal. After recording the signal strength at the starting position, the controller moves the antenna up in
elevation by one position count.
3. Due to mechanical hysteresis, the antenna's pointing angle does not change even though the
antenna's elevation actuator has moved one position count.
4. Thermal noise in the receiver's AGC circuit or changing atmospheric conditions result in the
controller measuring a stronger AGC input at the 'new' antenna position.
5. Since a stronger signal was measured whent the antenna moved up, the controller concludes that
the satellite has moved up. The controller will record the signal strength at the current antenna position,
and again move up by one position count. At the new position, the controller will measure the signal
strength again to determine if the signal is stronger at the new position than at the starting position. This
process will continue until a weaker signal strength is recorded. When that occurs, the controller will back
up one step and conclude that it has found the elevation peak.
6. A problem occurs if the controller makes the wrong decision at step 4. Any time the controller
step size is comparable in magnitude to the antenna's mechanical hysteresis, a problem WILL eventually
occur.
For most antennas the Max Track Error should not be made smaller than 5 (0.5 dB).
HOLDOFF: SET PEAKUP HOLDOFF TIME<1 - 999 SECONDS>
The peakup_holdoff_interval configuration item specifies the number of seconds before a track table entry
point (basepoint) that the controller will disable a normal periodic peakup operation. The reason for this
holding off of a non-track-table-entry peakup is to avoid a situation where a scheduled peakup takes too
long and the time that a track table entry is to be updated is passed by.
The peaking holdoff interval should be longer thatn 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 (i.e. moving fastest).
TIME: SIGNAL SAMPLE TIME <2-99 SECONDS>
The track_sample_time item specifies the number of seconds that will be spent sampling signal strength
following each peakup move. A longer time will allow a better chance to distinguish at which position the
higher average signal strength was present but will also make total peakup actions proportionately longer.
LOG: <0>DISABLE <1>ENABLE TRACK DATA LOGGING
Contact the factory if track logging is required.
The RC4000 may be setup to output a stream of data in ASCII format that can be read/recorded through
HyperTerminal or similar programs. The track data that is output at regular time intervals and is also
output each time a new command is carried out during the tracking process.
The track log is output through a serial port that may or may not be accessible from existing user interface
panel connectors.
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