34-43-00
ALL ú ú 08 Page 25 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL
The master processor (MP) acts as the control computer for the RDR-4B R/T. It also produces the timing and control signals that control the operation of the modulator/transmitter, receiver, multipliers, and the weather, turbulence, and windshear digital processor (DSP) circuits. The MP control module decodes the ARINC 429 mode and range data from the control panel bus. The MP down loads this data to the DSP circuits when a mode change occurs.Timing signals activate the modulator/transmitter during the transmit period to produce the pulse-modulated X-band radar output between 9330 and 9360 MHz. This signal is routed through the circulator and waveguide to the radar antenna.During the receiver period, radar returns pass through the waveguide, circulator and the limiter to the preamplifier. The preamplifier provides amplification with low noise and narrow band pre-selection of the receiver signals. The receiver signals are mixed with the X-band local oscillator at the first mixer to produce the 211.68 to 212.76 MHz first i-f signal, which is sent to the receiver.The receiver operates with the digital slow agc and provides high-gain narrow-band amplification and converts the 212 MHz (nominal) first i-f signal to a 4.76 to 5.22 third i-f signal by mixing the incoming i-f signal with the second and third local oscillator frequencies. The receivers 5-MHz (nominal) i-f signal output is applied to an analog-to-digital (A/D) converter at the input of the DSP system.The analog-to-digital (A/D) converter serves as the front end for the DSP subsystem. The DSP subsystem includes the time module, frequency module, signal module, and range module. The A/D module converts the band-limited i-f signal from the receiver module to a digital data flow that is fed directly to the time-module. The time-domain processing in the time module performs functions on the incoming digitized signal from the A/D converter in the time and cross-range domain, and produces a time-domain output signal to the frequency module for further processing.The time module is the second module is the signal processing chain. It performs functions in the time and cross-range domains on the incoming digitized signal from the A/D converter module. The time domain signal is sent to the frequency module for further processing.
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34-43-00
ALL ú ú 12 Page 26 ú Feb 18/02
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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747-400
MAINTENANCE MANUAL
The frequency module provides range-doppler filtering only in the windshear mode of operation. This module is bypassed in other radar operating modes. Range-doppler filtering consists of analyzing time samples of the incoming radar returns for each range bin over several pulse repetition intervals. The random motion of the rain droplets causes a frequency shift in the receiver pulses which represents turbulence. For doppler processing, the spectrum width of the received frequency signals is computed. This width correlates with random motions of rain droplets caused by weather turbulence. The DSP circuitry examines small areas of storm cells with successive pairs of transmitted pulses for doppler frequency shifts, and then computes the auto-correlation between them. The system shifts to the interlaced high and low PRF pattern to acquire intensity as well as turbulence information when the turbulence mode is selected.The next module in the signal processing chain is the signal module. It performs functions on the incoming digitized signal from the weather or turbulence or windshear circuits. Sensitivity time control (STC) circuits reduce the brightness of the close-in return. Ground clutter suppression (GCS) circuits reduce the ground clutter from the display data. This processed signal is sent to the range module as weather and/or turbulence or predictve windshear data.Range processing is accomplished by the range module, which is a two-processor subsystem containing the hazard processor and range converter. The hazard processor DSP performs two parallel functions, depending on whether or not the system is in the windshear mode. The hazard processor performs these functions in all modes: ground tracking, azimuth compensation, and clutter-error compensation.The other function in the hazard DSP is operatonal for airplanes with predicitive windshear. It is used to determine the size and shape and range from the airplane of a windshear microburst. This is determined in an operational windshear mode by performing hazard factor compensation, hazard area determination and several other functions. The range converter DSP filters out the range requests from the control busses 1, 2 and processes the video data and then stores it in the video memory. This data is sent to the digital I/O circuits.The control bus data from the WXR control panel and EFIS control panel sends selected mode, and range to the digital I/O. In addition, antenna azimuth and elevation position from the microprocessor and antenna stabilization processor are sent to the digital I/O. The processed weather-intensity range bin data along with the control data is formated into a 1600-bit serial display data words over the ARINC 453 data bus. The 453 words are divided into two busses and sent from the digital I/O to the EHSIs for display of the weather radar data. 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(92)
