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ú ú 05B Page 7 ú Jul 12/01
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A 737-300/400/500MAINTENANCE MANUAL
4. VOR/LOC Antenna
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A. The VOR/LOC antenna assembly is integral with the fin cap installed on top of the vertical stabilizer. The fin cap has metallic leading and trailing edge tips mounted on a fiberglass shell to provide an aerodynamic surface. The antenna consists of two balanced half loops with a hybrid coupler added for increased reliability under fault conditions. The hybrid coupler is composed of two quarter wavelength lines with the dual outputs to the receivers shunted by a 100-ohm resistor. In addition, an 18.5-inch tuning stub is connected to each half loop. A lighting diverter strip is embedded along the top centerline of the antenna assembly.
5. Glide Slope Antenna
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A. The glide slope antenna with dual output ports is a horizontally polarized unit installed above the weather radar antenna in the nose radome.
6. Glide Slope Antenna Director Bar
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A. The glide slope (G/S) antenna director bar is a passive element of the glide slope antenna used to alter the G/S radiation antenna patterns such that the navigation units have maximum glide slope sensitivity.
B. The bar consists of a 13-inch strip of aluminum foil, pressure sensitive tape, installed horizontally inside the nose radome approximately 22-inches forward of the aft edge of the nose radome top centerline.
7. Localizer Antenna
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A. A localizer antenna with dual rf output ports is installed in the nose radome below the weather radar antenna. The rf ports are connected to separate ILS relays to provide localizer rf to the navigation units.
8. ILS Relays
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A. Two coaxial relays are installed on shelf No. 4 of electronic equipment rack E3 in the main equipment center. The relays are energized by mode logic in the DFCS when the associated navigation unit is tuned to an ILS frequency. The logic requires that in ILS frequency be tuned; DFCS approach or VOR/LOC mode must be selected; and either VOR/LOC arm or VOR/LOC engage logic available in the associated DFCS flight computer. The relays, when energized, switch the navigation unit VOR/LOC rf input from the fin tip VOR/LOC antenna to the nose radome localizer antenna. The forward antenna selected ground signals to flight computers A and B of the DFCS are also routed through energized contacts of the relays.
9. VHF NAV Transfer Switch
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A. The VHF NAV transfer switch is part of the VHF NAV and compass transfer switching module installed on the pilots' overhead panel. The switch controls the associated VHF NAV transfer relays which enable either VOR/ILS system to feed both the captain's and first officer's flight instruments and the GPWS at the same time.
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ú ú 03B Page 8 ú Nov 15/87
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
10. VHF NAV Transfer Relays_______________________
A. Two stepping-type transfer relays are installed in rack E3-4. When the VHF NAV transfer switch is in the NORMAL position, the captain is on system No. 1 and the first officer is on system No. 2. Placing the VHF NAV transfer switch to BOTH ON 2 position momentarily energizes transfer relay No. 1 and the relay steps to the BOTH ON 2 position. Positioning the VHF NAV transfer switch back to the NORMAL position, again momentarily energizes transfer relay No. 1 and the relay steps back to the normal position. The first officer's transfer relay is controlled in the same manner as the captain's by positioning the VHF NAV transfer switch to BOTH ON 1.
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