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737-300/400/500MAINTENANCE MANUAL
4) Glide Slope Operation a) The UHF synthesizer produces the UHF glide slope highside injection frequency for the first mixer in the glide slope receiver. b) Frequency select information from the control panel is converted to binary-coded-decimal data in the 2x5 monitor. This data controls tuning of the preselector. c) The G/S UHF receiver operates similar to the VHF NAV receiver. The glide slope rf from the glide slope antenna is applied via preselector to the first mixer. The first IF is amplified and processed through a second conversion and applied to detector and AGC circuits. The audio output of the detector is applied to the glide slope instrumentation for deviation detection. d) The glide slope instrumentation produces glide slope deviation signals which are applied to the pilot's instruments. e) The glide slope flag outputs provide an indication of the glide slope instrumentation operational status as well as the validity of the incoming rf signals.
5) VOR/ILS Self-Test Operation a) VOR/ILS self-test provides the VOR and ILS self-test audio signals and timing sequence for control of the flags during self-test. A self-test is initiated by the test switch on the VHF NAV control panel with control provided by a preprogrammed Read-Only-Memory capable of generating VOR test, DN/R test, UP/L test and End test outputs. b) Modulated rf test signals, generated by the self-test oscillators, are applied to the input of the VHF and UHF receiver sections to simulate a VOR signal on any VOR channel or localizer and glide slope signals on any ILS channel. These signals provide an overall operational test for the VOR/ILS navigation system. c) Prior to self-test initiation control, logic will allow normal operation of the glide slope and VOR/localizer flags. When self-test is initiated the flags will remain in view for 3 |1 seconds, retract from view and 20 |5 seconds after initiating test, reappear and remain in view for as long as the self-test is actuated.
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737-300/400/500MAINTENANCE MANUAL
(2) VHF NAV Control Panel Schematic (Fig. 5)
(a)
The panel provides control of the VHF NAV and DME systems. Switches are provided to select automatic or manual frequency control, select the frequency during manual operation, and initiate self-test of the VHF NAV and DME systems.
(b)
Manual Tuning
1) When relay K1 is relaxed, tuning is performed manually and MANUAL is annunciated on the AUTO/MANUAL switch/indicator. The annunciator is illuminated by 28v dc form J1-46, and the return is through K1 to the airplane master dim circuit. K1 applies the frequency select common to the 2-out-of-5 encoder, enabling the switched output. The manual lines are connected through J1 to the VHF NAV receiver and to the DME interrogator. The manual frequency display is driven from the unswitched output of the encoder, and AUTO is blanked.
(c)
AUTO Tuning
1) The auto tune function is armed by 28v dc from J1-48. When the AUTO/MANUAL switch/indicator is pressed, the relay control is set, energizing K1. With K1 energized, AUTO is annunciated and the encoder enable is removed. The auto display is enabled by the display power and the frequency select common, switch by K1. Display power is applied to the bar solenoid and the bar is raised over the manual display. Auto frequency control is provided by the flight management system, which is connected in parallel with the panel output to the VHF NAV receiver and to the DME interrogator. The frequency is displayed by the AUTO display. Auto tuning is deselected by pressing the AUTO/MANUAL switch/indicator, resetting the relay control circuit, or when the auto tune arm discrete is removed from J1-48. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300 400 500 AMM 飞机维护手册 导航 NAVIGATION 2(160)
