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ú ú 12 Page 402 ú Jul 15/98
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500
MAINTENANCE MANUAL
COAXIAL CABLE
ELECTRONIC EQUIPMENT RACK E3
SEE A
RF ATTENUATOR M1437
ILS TRANSFER RELAY
RF ATTENUATOR M1436
SHELF NO. 4
A
RF Attenuator Installation
Figure 401
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ú ú 11 Page 403 ú Mar 15/91
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
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737-300/400/500MAINTENANCE MANUAL
MARKER BEACON SYSTEM - DESCRIPTION AND OPERATION
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General (Fig. 1, 2, and 3)
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A. The marker beacon system provides visual and aural indications when the airplane flies over ground based marker beacon transmitters. The ground stations transmit narrow beams of RF signals modulated with either 400, 1300, or 3000 Hz audio. The signals turn on appropriate lights as the airplane passes over the transmitters. This confirms specific positions during point to point navigation. It also gives positive indication of distance from the runway during a landing approach.
B. The marker beacon system consists of a receiver, an antenna, two indicator light assemblies and a HIGH/LOW sensitivity switch.
C. Marker beacon stations all transmit a 75 MHz RF signal modulated with either a 400, 1300 or 3000 Hz audio. This audio is keyed and a light is pulsed (dots and/or dashes) to provide identification. Markers are generally used on final approach to the runway. The outer marker is located approximately four miles from the runway end. When the aircraft passes over this marker, the blue light on the forward instrument panels turns on and a tone (400 Hz) keyed as continuous dashes is heard on the interphone. The middle marker turns on the amber light on the panels and a 1300 Hz tone is keyed as alternate dots and dashes. This marker is located approximately five tenths of a mile from the runway end. The inner marker, located approximately one tenth of a mile from the runway end, turns on the white light on the panels and 3000 Hz tone is keyed as continious dots.
D. The back course marker located at the opposite end of the runway from the inner marker also has a 3000 Hz tone and turns on the white light but the tone is keyed as continuous paired dots. By monitoring the lights and tone the flight crew is able to mark progress on final approach to the runway. When the markers are used as airways identifiers, the 3000 Hz tone is used and the white light on the panels turns on when the airplane passes over the beacon. The tone is keyed with a Morse code identifier. The specific code is obtained from the airway charts. The keyed codes for final approach markers is as stated previously unless otherwise altered on a airport area charts.
Receiver
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A. The receiver is a single conversion crystal-controlled superheterodyne operating at a fixed frequency of 75 MHz. Sensitivity of the receiver is variable and controlled by a switch located on the captain's instrument panel. Audio filters tuned to 400, 1300, and 3000 Hz separate the three modulated tones used by the beacons. The receiver, which contains an integral power supply, is installed on the electronic equipment rack (E2-4).
Antenna
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A. The marker beacon antenna is shaped like a canoe hull and is flush mounted on the bottom centerline of the fuselage. It receives the 75 MHz marker beacon signal and provides it to the receiver on a 52 ohm coaxial cable.
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34-35-00
ALL ú ú 02 Page 1 ú Feb 25/85
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
A
737-300/400/500MAINTENANCE MANUAL
FIRST OFFICER'S INSTRUMENT PANEL SEE A
CAPTAIN'S INSTRUMENT PANEL SEEA B
ELECTRONIC EQUIP
MARKER BEACON SHELF E2-4
ANTENNA MARKER BEACON
SEE D RECEIVER
SEE C
51Z-4 COLLINS
MARKER
HIGH
TEST SWITCH
(OPTIONAL)
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