Weather Radar System Block Diagram
Figure 2
EFFECTIVITYAF 101-120,123-156,158,159,
CONFIG 2 172-182,185-199; SN 301-350;799 Page 5 IB 405; GN ALL; MD ALL; VM ALL Sep 25/94
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G. Antenna stabilization circuits in the R/T consist of operational and servo amplifiers. The amplifiers use discrete silicon semiconductors and integrated circuits. Stabilization self-test circuits are provided.
H. The power supply is solid-state, including the warmup time delay circuits. The power supply and all control circuits use silicon-controlled rectifiers, reducing the number of relays required.
4. R/T Mount
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A. On Passenger Airplanes, The R/T mount consists of a dual mounting shelf for the R/Ts, mating quick-disconnect electrical and waveguide fittings, a rotary waveguide switch, dummy load and rf feeder waveguides between the switch and R/Ts. Two holdown clamps secure each R/T to the R/T mount.
B. On Freighter Airplanes, Two single R/T mounts consist of a mounting shelf for each R/T, mating quick-disconnect electrical and waveguide fittings, and waveguide switch with dummy load. Rf feeder waveguides are connected between the R/T mounts and the waveguide switch and another waveguide goes forwad from the waveguide switch to the antenna.
5. Waveguide
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A. On Passenger Airplanes, The X-band waveguide connects the selected R/T from the waveguide switch to the antenna. A flexible waveguide selection is connected to the waveguide switch and then rigid sections extend forward and pass through the pressure seal into the nose radome area. In unpressurized nose radome rigid waveguide sections are connected to a final flexible waveguide section that connects to a top-mounted waveguide flange on the antenna.
B. On Freighter Airplanes, Flexible waveguide sections are installed between both R/T mounts to the waveguide switch. From the waveguide switch rigid sections extend forward and pass through the pressure seal into the nose radome area. In the unpressurized nose radome rigid waveguide sections are connected to a final flexible waveguide section that connects to a top-mounted waveguide flange on the antenna.
6. Indicator
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A. The indicators are self-contained and require no power from the R/T units except for control signals, thereby enhancing reliability and assisting in fault isolation. Silicon solid-state devices are used exclusively in the sweep and video circuits. An electronic resolved-sweep deflection system is employed.
B. The indicator has a 5-inch display storage cathode ray tube which provide for direct viewing under all ambient light conditions. Controls allow for viewing directly ahead or choosing left or right offset displays. An erase control allows the display to be erased rapidly and completely.
C. A variable-density polarized filter on the indicator allows the display brightness to be attenuated in low ambient light conditions, and no electronic brightness control is required. At maximum attenuation, the display assumes a dark red color for night viewing.
7. Antenna
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EFFECTIVITY AF 101-120, 123-156, 158,
159, 172-182, 185-199; SN 301-350; IB 405; GN ALL; CONFIG MD ALL; VM ALL 02 Page 6
Sep 25/94
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A. The antenna is mounted by its roll axis on the airplane bulkhead behind the nose radome. The azimuth axis in turn mounts to the roll axis, and the elevation axis mounts on the azimuth axis. This provides a split-axis system in which control signals from the inertial navigation system (INS) can control roll separate from elevation and azimuth. Azimuth is controlled by the scanning rate of the weather radar system, and elevation is controlled by the combination of INS pitch stabilization signals and tilt angles set at the weather radar control panel.
B. The antenna drive system is fully redundant, including the azimuth drive motor and primary gear train, sweep resolvers, roll and elevation motors and their primary gear trains, elevation resolvers, azimuth resolvers, tilt resolvers, and power supply. The electronic portion of the antenna stablization circuits is located in the respective R/T units.
C. The antenna feed and reflector normally provide a pencil beam. Selecting the ground mapping mode causes the feed to mechanically rotate 90 degrees and bring a horizontally polarized spoiler into action.
D. On AF 101-116; GN ALL; and MD ALL; VM ALL, a flat plate radiator antenna is installed. Operation of the antenna is the same as conventional parabolic dish antenna except that no feed horn is required and shaping of the radiated pattern to fan beam in the MAP mode is accomplished by phasing elements in the flat plate radiator.
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