(d)

(e)

(f)

(g)

A
737-300/400/500MAINTENANCE MANUAL
The source of the RF transmission is in the R/T unit driver, where a 777.77 and 777.88 MHz signals are generated and applied to the power amplifier. In the power amplifier, the signal is amplified and split into two separate signals. The multiplier frequency multiplies the signals from the power amplifier in two stages and recombines them to obtain the 125 watt 9333.24 transmitter output signal.The duplexer couples the transmitter output signal to the waveguide. The duplexer is monitored by power monitor circuits that develop a loop error signal to correct for output frequency variation and noise. The output signal is transmitted through the waveguide and then radiated out the flat plate antenna.The reflected signal is received by the antenna during the interval between transmission pulses, and applied through the duplexer to the receiver circuits of the RT. The limiter protects the receiver from power pulses, allowing low power received signals to the mixer.The mixer uses a frequency source oscillator to develop the first IF frequency. The first IF amplifier provides a 25 dB gain. The second IF is mixed with frequency source oscillator signals to attain a 13.888 MHz signal. The second IF amplifier gain is controlled by the automatic gain control (AGC) and sensitivity time control (STC) circuits in the azimuth filter.The reflected signal is routed through the duplexer, limiter and the receiver section, and sent to the range filter. The range filter produces digital range samples and applies them to the azimuth filter and the ground clutter processor.The range filter is a low pass filter that also digitizes the signal. The low pass function improves the signal-to-noise ratio of the IF signal. The digitized signal is sent to the azimuth filter, which filters and encodes the signal. The encoded signal is sent to the input/output circuits, and formatted into a 1536-bit data word. A 64-bit control word is added to the data word and sent to the indicator, in serial form to the EHSIs.
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BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
 (h)

(i)

(j)

(k)

A
737-300/400/500MAINTENANCE MANUAL
The azimuth scan filter filters the range samples over multiple PRF samples and averages the returns for each range. It also develops STC and AGC gain control signals for the receiver. Display data is extracted from the returns, filtered, and routed to the displays.The ground clutter processor determines whether ground clutter is present. If present, a discrete is sent to the signal encoder which removes the ground targets from the display. The grouond clutter circuit starts operation when the IDENT (IDNT) switch on the WXR control panel is selected.Control word No. 1, from the weather radar control panel, sends mode, tilt, gain, and system stabilization data to the receiver transmitter. Control word No. 2, from the EFIS control panels send range data to the receiver/transmitter and to the L and R EFIS symbol generator. The words are processed in the R/T a control word generator and sent to the central processing unit (CPU). The CPU uses the control words to configure the operating parameters of the system. The CPU incorporates a microprocessor to perform its various internal functions. The receiver/transmitter utilizes time sharing techniques which allow independent range selection on the two EFIS control panels. The data for each display is collected by using the proper pulse width, PRF rate, band width and STC curve for each range selected by time sharing the antenna and receiver/transmitter between the EHSI displays. Each EHSI display is updated every 4 seconds. The microprocessor executes its control program, which consists of seven major control routines, 180 times a second.The seven major control routines are: 1) Attitude routine providing pitch and roll parameters for
 the stabilization routine. 2) Stabilization routine providing elevation position to the
 elevation maintenance routine. 3) Scan maintenance routine providing antenna scan drive. 4) Elevation maintenance routine providing antenna elevation
 drive.

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