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A. Two localizer antennas with dual rf output ports are installed in the nose radome. One antenna is mounted above and the other below the weather radar antenna. Both rf ports of the lower antenna and one rf port of the upper antenna are connected to the VOR/LOC antenna switches to provide localizer rf to the three VOR/ILS receivers.
6. VOR/LOC Antenna Switches
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A. Five antenna switches are installed behind the VOR/ILS receivers on shelves E1-2 and E1-3 of the main equipment center. The switches operate in the 108- to 118-MHz frequency range and select either the VOR antenna or the localizer antenna as an rf source for the associated VOR/ILS receiver. Switching is accomplished by one of two types of physically and functionally interchangeable switches. For one type, switching is accomplished by changing the characteristics of a tuned line network to match input and output impedances for signal transfer. For the other type, switching is done electromechanically via solenoid actuation of the switches.
7. Glide Slope Antennas
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A. On XA ALL EXCEPT LH 011-099; AF 152-154, 172-173, 191-194; MD 501-599 and GN 601-699, a total of six glide slope antennas are installed in the aft nose gear wheel well doors. Each door cavity houses one track antenna, two capture antennas, a hybrid antenna coupler and interconnecting coaxial cables. The track antenna is a tunable single element I-slot type installed in the door leading edge. The capture antennas are two element tunable antenna arrays installed in the outer side of each door parallel to the longitudinal axis. The hybrid within the door cavity provides impedance matching for combining the rf outputs of the two capture antennas. On LH 051-054; AF 152-154, 172-173, 191-194; GN ALL and MD ALL, a total of three glide slope antennas, two track and one dual capture, are installed. The track antennas are dual element nontunable I-slot type units located one each on the leading edge of the aft nose gear wheel well doors. The capture antenna, also a nontunable unit, is located in the nose radome. On LH 011-050, 055-099, a total of four glide slope antennas, two track and two dual capture, are installed. The track antennas are dual element nontunable I-slot type units located one each on the leading edge of the aft nose gear wheel well doors. The capture antennas, also nontunable units, are located in the nose radome.
8. Glide Slope Antenna Hybrids
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A. On XA ALL EXCEPT LH 011-099; AF 152-154, 172-173, 191-194; MD 501-599 and GN 601-699, two additional 4-port type hybrid antenna couplers are installed at station 400. The station 400 hybrids combine the rf output of the track and capture antennas to provide a single glide slope rf input for the receivers. On AF 152-154, 172-173, 191-194; GN ALL and MD ALL, one additional hybrid antenna coupler is installed at station 400. The hybrid couples the output of single glide slope antennas, either capture or track to VOR/ILS receivers No. 1 and No. 3.
EFFECTIVITY
AF 101-120, 123-154, CONFIG 1 172-173, 191-194; GN ALL; 07 Page 5 LH ALL AND MD ALL Sep 25/94
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9. Glide Slope Antenna Coaxial Relays (LH 011-099; AF 115-120, 123-154, 172-173,__________________________________ 191-194; GN ALL and MD ALL)
A. On LH 051-054; AF 115-120, 123-154; GN ALL and MD ALL, two coaxial relays are mounted on glide slope antenna switching panels P31 and P32. On LH 011-050, 055-099, three coaxial relays are installed.
B. On AF 115-120, 123-151, the coaxial relays disconnect the glide slope capture antennas from the glide slope antenna hybrids. This eliminates spurious capture antenna signals which cause loss of glide slope capture during high bank angles with the landing gear down. On LH 011-099; AF 152-154, 172-173, 191-194, GN ALL and MD ALL, The coaxial relays switch the VOR/ILS receiver glide slope rf signal input from the nose radome capture antenna(s) to the landing gear door track antennas when the landing gear is down (Fig. 8).
C. The coaxial relays are controlled by transistor switching logic in the primary and alternate landing gear logic units. The relays are energized to complete the glide slope capture antenna configuration when the landing gear are up and glide slope 28-volt dc power is available. When the landing gear are down, the relays are de-energized, to open the rf line between the capture antennas and the VOR/ILS receivers. This leaves the VOR/ILS receiver glide slope rf input connected to only the glide slope track antenna. On LH 011-050, 055-099, relay No. 3 is controlled by transistor switching logic in autopilot accessory box No. 3 and in the primary and alternate landing gear logic units.
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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1(149)
