(b)
The modulator generates a 100-Hz signal which is converted to a square wave and then applied to a triangular wave generator. The triangular wave frequency modulates an oscillator signal in the transmitter. The resultant signal is amplified and frequency multiplied to produce the nominal 4.3 GHz transmitter output signal.
EFFECTIVITY
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(c)
The transmit signal is applied through the transmit circulator to the transmit antenna. The signal from the antenna is radiated to the earth and reflected back to the receive antenna. The transmit and receive circulators transfer any reverse direction power to high loss loads to provide protection (isolation) for receiver-transmitter circuits.
(d)
The ground return signal from the receive antenna is coupled through the receive circulator to the stripline mixer. A sample of the transmitted signal is also applied to the mixer. The mixer processes the instantaneous transmit and receive signal frequencies to produce an output difference frequency which is proportional to airplane altitude above the terrain. This signal is applied to the preamplifier and tracking filter circuits.
(e)
The preamplifier and tracking filter adjusts the signal gain and filters the signal to improve the systems signal tracking capabilities. The output is applied to the pointer stow circuit which provides an on scale altitude signal to the time domain filter. This filter processes the signal to remove double bounce signals and provides signal tracking.
(f)
The output from the time domain filters is applied to the dual frequency counter and operational amplifier circuits. Pulse outputs from the frequency counters are converted to dc altitude signals by the operational amplifier. The amplifiers provide the dc altitude signals used to drive the height indicator and to provide altitude data to other systems on the airplane. The autopilot/flight director system uses the altitude signal to facilitate gain programming of the glide slope and localizer deviation signals during approach modes. The auto throttle system uses the altitude signal to enable speed control during the low altitude flare maneuver.
(g)
The dc altitude signals are also applied to the receiver-transmitter altitude fixed-trip circuits. Each trip circuit consists of an adjustment potentiometer, altitude detector, dc amplifier, and a switch which drives a relay. The dc altitude input voltage is compared to a reference voltage (altitude trip setting). If the input voltage exceeds the reference voltage, the trip relay remains de-energized. When the input voltage is less than the reference voltage, the trip relay is energized. The output from each altitude trip circuit is a ground signal to using equipment.
(2) Altitude Indication (Round Dial Height Indicators)
(a) In round dial height indicators, the positive dc altitude voltage from the receiver-transmitter and a dc feedback voltage from the isolation amplifier are applied to the differential preamplifier. The dc feedback voltage represents the position of the altitude pointer, and the dc altitude voltage represents airplane altitude.
EFFECTIVITY
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RECEIVER TRANSMITTER
LRRA-1 and LRRA-2 System SchematicFigure 3 (Sheet 1)
EFFECTIVITY
CONFIG 4
LH ALL
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ADI
LRRA 1 or 2 System Schematic
Figure 3 (Sheet 2)
EFFECTIVITY CONFIG 4 LH ALL
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RECEIVER TRANSMITTER
LRRA-3 System Schematic Figure 3 (Sheet 3)
EFFECTIVITY
CONFIG 4
LH 004-099
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LRRA-3 System Schematic
Figure 3 (Sheet 4)
EFFECTIVITY CONFIG 4LH 004-099
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RECEIVER TRANSMITTER NC
LRRA 1 or 2 System Schematic
Figure 3 (Sheet 5)
EFFECTIVITY
CONFIG 4
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IB 405
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ADI
LRRA 1 or 2 System Schematic
Figure 3 (Sheet 6)
EFFECTIVITY CONFIG 4 IB 405
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(b)
When the two voltages applied to the differential preamplifier are not equal in value, a difference voltage is produced and applied to the servo-amplifier. The servo-amplifier drives the motor which repositions the feedback potentiometer (and altitude pointer) until the voltages are equal. When the two voltages are equal, the altitude pointer indicates the correct airplane altitude.
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本文链接地址：747飞机维护手册AMM CHAPTER 34 - NAVIGATION 第34章导航2(70)
