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A 737-300/400/500MAINTENANCE MANUAL
(FIG. 14)(FIG. 13)
(FIG. 13)
(FIG. 14)

(FIG. 12)(FIG. 9 AND 13)

(FIG. 12)

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A
737-300/400/500MAINTENANCE MANUAL
 C.  Functional Description
 (1) VOR/ILS Navigation Unit Schematic (Fig. 4)
 (a) Collins 51RV-4( ) Navigation Unit
 1)  The navigation unit power is supplied from three sources, two 28v dc and one 26v ac. VOR/LOC DC powers the power supply and arms the ILS mode relay. G/S DC powers the glide slope receiver and 26v ac is used for VOR operation.
 2)  The navigation unit receives VOR/LOC signals in the frequency range of 108.00 to 117.95 MHz. This provides 160 VOR channels and 40 localizer channels with channel spacing of 50 kHz. Glide slope signals are in the frequency range of 329.15 to 335.00 MHz with 40 channels spaced at 150 kHz.
 3)  VOR/LOC Operation

 a)  Frequency select informaiton from the control panel is converted to binary-coded-decimal data in the 2x5 monitor. This data controls tuning of the preselectors. The sythesizer provides the required injecion frequencies and tuning voltages for the first mixer in the VHF NAV receiver section. Navigation signals are selected by a tuned rf filter controlled by the tuning voltages from the VHF synthesizer. The signals are processed, gain stabilized, and fed to a detector (all within the receive section), which provide receiver signals to the VOR and localizer instrumentaion sections, digital instrumentation section, and drives an audio amplifier in the RMI driver section to provide an audio input to the airplane audio integrating system.
 b)  VOR/LOC instrumentation provides localizer deviation, the switching between VOR and LOC deviation output, the monitor and flag output, and the to/from flag output.
 c)  The VOR/LOC flag provides an indication of VOR and localizer operational status as well as the validity of the incoming rf signal.
 d)  The RMI driver consists of a microcomputer, digital-to-analog converters, summing amplifiers, a synchro to sine/cosine converter, and the RMI X and Y drivers. The RMI analog signal is derived from a 16-bit digital word from the Digital Instrumentation section.
 e)  Digital instrumentation processes the VOR audio signal from the VOR/LOC receiver into a digital bearing word. The digital bearing word contains the relative bearing of the selected VOR radial.
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 4)
5)

A
737-300/400/500MAINTENANCE MANUAL
 f)  Park Control produces a voltage that is sent to the microcomputer. When an ILS frequency is selected, the computer output parks the RMI needle at the right wing point.
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.
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.
　
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