location and function of the test points and adjustments on the Antenna Position Control Indicator are contained in Table
scan generator circuit card, potentiometers R2, R3, and R4 on the Control Indicator, and a 6. 3-volt AC transformer on
the Antenna Position Power Supply. These components control the antenna for sector scanning. The scan generator
circuit card contains the circuitry which senses the antenna position as indicated by antenna position potentiometer R4,
amplifies the positioning voltage and allows reversing the direction of rotation of the azimuth servo drive while the
antenna is scanning.
a. Antenna position potentiometer R4 is coupled by magnetic clutch L3 to the shaft which rotates R4. Rotation of R4
varies a voltage representing the antenna position. When the clutch is deenergized, the wiper of R4 is centered by a
spring. With the clutch deenergized, the antenna is pointed ill the. direction to be scanned. To scan, the clutch is
energized and as the antenna turns, the voltage on the wiper of R4 is proportional to antenna position. Twenty-four volts
DC is applied to one side of R4 and to a two-to-one voltage divider formed by resistors R6, R11, R9 and R12. These
resistors form a bridge circuit on the scan generator circuit card. Sector width potentiometer R3 is connected between
the wiper of R4 and the center of the divider. A different: al amplifier on the scan generator circuit card, consisting of
transistors Q2 and Q3, senses the voltage difference between the voltage divider and the wiper of R3. Transistors Q1
and Q4 comprise two emitter-follower amplifiers which act as buffers for the differential amplifier formed by transistors
Q2 and Q3 against the loading of the differential amplifier formed by transistors Q5 and Q6.
b. Approximately 0. 15-volt difference between the bases of Q2 and Q3 drives the collectors of Q5 and Q6 to either
set or reset a flip-flop formed by transistors Q7 and Q8. When sector width potentiometer R3 is turned fully
counterclockwise, only a few degrees of movement of R4 is sufficient to develop the 0. 15-volt difference between the
bases of Q2 and Q3. When the wiper of R3 is rotated clockwise, it requires proportionately larger angles of rotation of
R4 to develop the 0. 15-volt difference between the bases of Q2 and Q3. Therefore, with R3 rotated fully
counterclockwise, the angle scanned will be small; that is, approximately 10 degrees. With the R3 rotated almost fully
clockwise, the width of the angle scanned is approximately +270 degrees.
Revised January 22, 1968