Operation of this defocusing process is controlled by the BEAM INCREASE-BEAM DECREASE switch, S7, on the
Control Indicator. Switch S7 is a DPDT switch which applies 28-volts DC to one of the fields of a reversible actuator
motor in the electromechanical linear actuator on the antenna. This drives a shaft on the actuator which extends or
retracts, depending upon the positioning of S7, the feed on the antenna. Reversing the position of switch S7 reverses
the direction of shaft movement.
(1) BEAM WIDTH meter M2 on the Control Indicator, which is essentially a 0- to 50-millimeter graduated
from 0 to 100, indicates the position of the antenna feed as a percentage of increase relative to the focal point of the
antenna. The position of the pointer on the meter is controlled by a position-indicating potentiometer on the
electromechanical linear actuator which is mechanically ganged to the actuator drive motor and adjusting resistors R4
and R6 on the Control Indicator. The normal focal point of the antenna is obtained when the actuator is completely
retracted; in this position, the indicating potentiometer is at its further clockwise point and the beam width meter on the
Control Indicator indicates zero. As the beam width is defocused, the position-indicating potentiometer rotates in a
counterclockwise direction, increasing the current flow through the beam width meter and thus the position of the pointer.
Maximum defocusing is obtained when the beam width meter is at 100.
(1) BLOWER AND CONTROL CIRCUITS (See Figure 1-8) - The radome-platform blower and control
circuits consist of the RADOME POWER circuit breaker, CB1, and the BLOWER switch, S2, on the Antenna Control
Power Supply and blower B1, relay K1 and pressure switch S1 in the radome-platform. When the RADOME POWER
circuit breaker is operated to the ON position, three-phase AC power is made available to the open contacts of relay K1.
When the BLOWER switch is placed to the ON position, relay K1 is energized, allowing the blower to operate.
(2) PRESSURE SAFETY SWITCHES AND INDICATOR CIRCUITS (See Figure 1-9) - The radome-platform
pressure safety switch circuits consist of pressure switch S1 in the junction box in the radome-platform, which is in series
with the SAFE-RUN switch on the antenna pedestal. This provides two interlocks for the azimuth drive circuit and if
either one is inoperative, the antenna will not drive in azimuth or elevation. The pressure switch closes when radome
pressure falls below 6 inches of water (approximately 0.22 PSI). Indicator light DS2 on the junction box in the radome-
platform indicates when the pressure switch is closed if antenna system power is available in the pedestal. Another
indicator light, DS1, also on the junction box, indicates when the pressure switch is open or when any one of the SAFE-
RUN switches is in the SAFE position. When pressure switch S1 is operated, +28-volts DC is applied to the PRESSURE
SAFE indicator light on the Antenna Control Power Supply.
Revised January 22, 1968