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RC4000 ACU Boardset
Chapter 4
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STEP 4. Clockwise and Counterclockwise Limits.
Discrete Limit Switches. Some mounts may mechanize polarization clockwise and counterclockwise
limits via actual limit switches. If this is the case, move the polarization axis through its range of motion
and verify that the CW and CCW limit indications appear in the MANUAL screen. After confirming these
indications move on to the next step.
Polarizaiton Electrical Limits. Other mounts may not have polarization limit switches. In this case, the
RC4000 allows for the CW and CCW limits to be set based on the polarization potentiometer voltage.
The position of these limits is defined in the MAINTENANCE – POL CALIBRATION screen (3.3.1.2.4)
under the CW and CCW entries.
To set the polarization clockwise limit, go to MANUAL mode and jog the antenna in polarization to the
desired polarization clockwise limit. If the controller indicates that the polarization clockwise limit is
reached before the antenna reaches the desired position for that limit, the POL CALIBRATION – CW
entry may have to be adjusted to allow the antenna to move. Adjust CW by the number of degrees
needed. To verify that the CW has been adjusted properly, verify that the antenna cannot move
clockwise in azimuth but can move counter-clockwise.
A similar procedure is used to set the polarization counter-clockwise limit. A default limit will be set in
software based upon specific antenna types.
STEP 5. Polarization Scale Factor.
NOTE: in most cases the default polarization scale factor for a mount will be correct and should
not be changed. Perform this substep only if Appendix B suggests that the polarization scale
factor for your mount should be characterized.
To calculate the polarization scale factor, move the feed between two known physical polarization
positions and note the difference in the sensed polarization voltage between the two locations
Example: at +90 degree reference position the polarization voltage is 3.86. At the –90 degree reference
position the polarization voltage is 1.14. The polarization scale factor is calculated as:
180 degrees / (3.86 –1.14) = 66.16 degrees / volt.
66.16 would be entered as the scale factor.
STEP 6. Polarization Reference Orientation Definition.
The orientation achieved by placing the polarization axis in the reference position must be specified as
horizontal or vertical. This choice will depend on whether the operator wants to refer to the receive or the
transmit port when commanding the controller to move polarization to the horizontal or vertical position.
The RC4000 uses this definition when automatically calculating the polarization angle for single port
feeds.
STEP 7. Additional Polarization Settings.
Polarization Offset. This item describes any difference between the electrical and physical position of
the polarization axis. In almost all cases the polarization offset will be 0.0. Offset might not be able to be
characterized until final calibration.
Default Horizontal and Vertical Positions. Preset locations for polarization horizontal and vertical
positions (3.2.1) are entered for use in the MANUAL mode.
Automatic Polarization Movement. Automatic movement of the polarization axis as part of the
LOCATE function may be enabled/disabled by the AUTO configuration item.
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