CE-1008
(3)
When the system is energized and ready for operation, the POLARIZATION MODE select switch on
the Control Indicator may be set to the desired mode; for example, RHC +45 The motor then starts and runs until it
.
reaches the right-hand 45-degree position. At this time, the normally closed contacts on the RH switch, S3, open and
then the normally open contacts close. Also in the circuit is an index switch which physically supports the feed element
in the unit. Due to the fine action of this switch, its contacts remain closed until the polarizer reaches a precise position,
at which time its closed contacts open and its open contacts close, resulting in two important functions: connecting a
resistive load across the motor, providing an effective electromagnetic braking action to the motor, and at the same time
reversing the polarity of the 28-volts DC which was received through the reversing switch contacts. This leaves the
circuit in a ready condition for the next actuation.
B.
SCHEMATIC DIAGRAM AND PARTS LIST - Figure 5-4 is the schematic diagram for the polarization unit.
The parts list is contained in Table 5-5.
6.
ELECTROMECHANICAL LINEAR ACTUATOR (See Figure 5-5)
A.
GENERAL DESCRIPTION AND THEORY OF OPERATION - The electromechanical linear actuator consists
essentially of a reversible DC motor geared to a movable shaft, two electrical limit switches, and a position indicator
potentiometer. The DC drive motor is controlled by a DPDT BEAM INCREASE BEAM DECREASE switch on the
Antenna Position Control Indicator which, when operated, applies 28-volts DC to one or the other fields of the motor,
causing the geared shaft to extend or retract, depending upon the direction of rotation of the drive motor. The length of
the actuator in its fully retracted position is 17. 375 inches and in its fully extended position 29.375 inches. Mechanical
stops are provided at these points. Two electrical limit switches are provided which limit extension and retraction of the
actuator shaft to 29.250 and 17.500 inches, respectively. The position indicating potentiometer, which is also geared to
the actuator drive motor, provides a voltage which is proportional to amount of extension of the actuator shaft to drive the
BEAM WIDTH meter on the Antenna Position Control Indicator.
(1)
The electromechanical actuator is installed between the dipole feed and the polarization unit. The
primary purpose of this unit is to provide remotely selectable actuation of the linear movement of the dipole feed relative
to the focal point of the reflector. The primary effect of defocusing the antenna feed toward the reflector from the focal
point is to increase the phase error across the reflector, broadening the main lobe by several degrees and reducing the
gain of the antenna.
B.
ADJUSTMENTS - The only adjustment possible on the electromechanical linear actuator is the position
indicator potentiometer. This potentiometer should be adjusted as follows:
5-15
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