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 6)  TILT control - Tilts the antenna radiator up or down a maximum of 15 degrees from the zero reference position. Antenna tilt in + or - degrees is displayed in the upper RH corner of the EHSI. The tilt control can be adjusted up or down to provide a more accurate EHSI display of the weather conditions in front of the airplane.
 7)  STAB (stabilization) pushbutton - Allows selection of antenna stabilization from the inertial reference system. When the STAB pushbutton is off, the antenna sweep is centered on the zero boresight of the airplane. When the pushbutton switch is on, the weather radar system uses pitch and roll signals from the inertial reference system to stabilize the antenna sweep to earth horizontal.
 8)  GAIN control - R/T gain is controlled in the weather radar WX, WX+T and MAP modes by rotating the GAIN control through its ten detented positions. Counterclockwise rotation of the GAIN control decreases the gain. A VAR message is displayed on the EHSI anytime the GAIN control is in any detent position other than CAL. The VAR message appears to the left of the mode message in the upper right hand corner of the EHSI. (See Fig. 5). In the MAP mode the CAL position is the same value as two detent positions counterclockwise of the MAP position.
 (4)  Antenna Functions (Fig. 4)
 (a)  
The radar antenna is a split-axis type mount, having its elevation axis mounted on the scan axis. It is stabilized by a microprocessor-controlled digital servo loop located in the receiver-transmitter unit. The antenna can be manually tilted |15 degrees from the horizontal (zero-degrees) and is stabilized over a combined tilt, pitch, and roll input of |45 degrees.

 (b)  
The antenna unit consists of the antenna pedestal and the antenna planar array. The pedestal itself contains power supply, motor driver, receiver/monitor driver, incremental and zero monitors, and scan and elevation stepper motors.

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737-300/400/500MAINTENANCE MANUAL
 (c)  
The flat plate develops the required pencil beam radiation pattern by means of phase reinforcement/cancellation of energy from adjacent slots in the planar array.

 (d)  
The motor driver provides an interface with the power supply to pass the binary encoded scan and elevation drive signals from the R/T to the receiver/monitor driver, and the scan and elevation monitor signals from the receiver/monitor driver to the system R/T. The receiver/monitor driver buffers and translates the binary encoded scan and elevation drive signals to provide motor positioning control signals to the motor driver. It also buffers the incremental and zero monitor signals and provides a binary encoded output to the R/T for interpretation. When commanded by the receiver/monitor driver, the motor driver provides drive voltages to incrementally rotate the scan and elevation stepper motors to move the antenna |90 degrees in scan and |40 degrees in elevation in 0.25-degree steps.

 (e)  
Incremental monitors track the motor shaft rotation of the scan and elevation stepper motors from a zero reference point to provide constant monitoring for use by the system receiver-transmitter.

 (f)  
Zero monitors provide a reference synchronizing point for the scan and elevation stepper motors from which incremental changes in antenna position can be measured by the incremental monitors.

 (g)  
Scan and elevation toggle switches provide a manual means of disabling the input power to the scan and elevation stepper motors. When the pedestal cover is closed, the switches are tripped to ON position by the cover. This prevents the switches from being inadvertently left in OFF position and disabling the antenna drive.

 (5)  BEJ 061-112; Receiver/Transmitter Functions (Fig. 4)
 (a)  The R-T unit is a lightweight airborne unit consisting of transmitter, receiver, video processing circuitry, a central processing unit (CPU), input/output circuits, system monitoring circuitry, and power supply.
 EFFECTIVITYùùùùùùùùùùùùùùùùùùùùùùùùùùùùùù. AIRPLANES WITH EFIS ú

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 ú ú 15A Page 19 ú Mar 15/98

BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
　
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