(g)
The antenna TILT control, calibrated in 1-degree increments, allows 0 to 15-degree UP or down (DN) tilt control of the radar antenna when MANual operation is selected.
(h)
The GAIN control is used to adjust the gain of the receiver in all modes. The control may be adjusted between minimum and maximum (MAX) gain or set to automatic (AUTO) for optimum operation.
(6) Antenna Functions
(a) The Radar Antenna is an X-band, line-of-sight antenna, stabilized by a microprocessor-controlled digital servo loop circuits located in the receiver-transmitter unit. The antenna is stabilized in roll up to |40 degrees and stabilized in pitch up to |25 degrees. The antenna can be manually tilted |15 degrees from the horizontal (zero-degree) and is stabilized over a combined tilt, pitch, and roll input of |45 degrees.
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(b)
The planar array develops the required pencil beam radiation pattern by means of phase reinforcement/cancellation of energy from adjacent slots in the planar array.
(c)
Pitch and roll information from the inertial reference system, tilt information from the manually set tilt control or automatic input from the EGPWS , azimuth angle information from the azimuth (scan) synchro transmitter, and elevation angle information from the elevation synchro transmitter, are processed by the stabilization microprocessor circuitry in the R-T to produce a control phase voltage for the elevation drive motor. The elevation drive motor repositions the antenna to maintain line-of-sight.
(d)
The elevation drive motor, is a two-phase servomotor which operates with a reference phase voltage of 115 volts, 400 Hz supplied to one winding and a 400-Hz control phase voltage of varying amplitude applied to the other winding. The reference phase voltage is applied at all times while the control phase is applied only when needed to reposition the antenna planar array in elevation as ordered by the stabilization microprocessor circuitry in the R-T unit. The control voltage is an error voltage supplied by the microprocessor circuitry. The elevation motor repositions the antenna in elevation until the phase of the error voltage induced in the control winding reaches a null. The speed at which this correction is performed is dependent on the error voltage amplitude.
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(e) The R-T unit also supplied the azimuth motor drive signal which drives the antenna through the oscillating 180 degrees of azimuth (scan). Controlled by the microprocessor circuitry in the R-T unit, the 115-volt drive signal is applied to one of the dual windings in the azimuth motor. The motor rotation drives the gear train, which in turn drives the antenna to one side of the straight ahead zero-degree heading. The azimuth synchro continuously transmits the antenna angle position to the microprocessor circuitry. When the antenna reaches the 85-degree position, the microprocessor through triac switching removes the 115-volt drive signal from the azimuth motor. The antenna continues to coast in the direction of its movement until the microprocessor circuitry determines the antenna has reached 90 degrees, at which time the 115-volt drive signal is applied to the other of the dual windings in the azimuth motor to drive the azimuth motor in the reverse direction. The antenna therefore is driven in the reverse direction, from the 90-degree angle position through the straight-ahead, zero-degree position and toward the 90-degree angle position of the opposite side. The microprocessor circuitry again removes the 115 volts from the azimuth motor when the antenna position has reached 85 degrees and the antenna coasts to the 90-degree angle position. The microprocessor circuitry applies the 115-volt drive signal to the motor winding which initiates reverse rotation each time the antenna position angle is 90 degrees, causing the antenna to constantly scan the 180-degree sector straight ahead. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：747-400 AMM 飞机维护手册 导航 NAVIGATION 2(91)
