(b)  
The VOR instrumentation circuits consist of the primary instrumentation channel, manual instrumentation circuits which are connected in series to the primary channel to provide fail-safe operation, and a monitor instrumentation channel identical to the primary channel. The output signal from the audio amplifier is supplied to both channels simultaneously.

 (c)  
The primary channel provides automatic VOR operation. The output from the FM detector is phase-compared to the signal in the 30-Hz A channels. The phase difference information controls a servosystem which positions resolvers in both the primary and monitor channels of the instrumentation section. This servosystem also positions the shaft of the differential synchro. At servosystem null, the shaft position, modified by a voltage level input from the compass bearing is displayed on the RMI as VOR bearing information.

 (d)  
The manual instrumentation circuits provide VOR/LOC deviation information and to/from data to the HSI. The course setting which is selected by the pilot is mechanically coupled to the course resolver. The stator of the course resolver has a 400-Hz reference voltage applied from the resolver in the VOR/ILS receiver whose rotor is positioned by the motor shaft which controls the VOR bearing outputs.

 (e)  
The difference between the course selected and the VOR bearing set by the motor shaft results in an induced voltage which is supplied to the two discriminators. The discriminators convert the resolver output to analog signals representing VOR deviation from the selected course.

 (2)  COLLINS 51RV4/4( ) Receiver
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 (a)  
Frequency select information from the control panel is converted to binary-coded-decimal data in the 2x5 monitor. This data controls tuning of the preselectors. The synthesizer provides the required injection 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 receiver section), which provide receiver signals to the VOR and localizer instrumentation sections, digital instrumentation section, and drives an audio amplifier in the RMI driver section to provide an audio input to the flight interphone system (23-51-00).

 (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 statuses as well as the validity of the incoming rf signal.

 (d)  
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.

 (e)  
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 (Fig. 2). The RMI analog signal is derived from a 16-bit digital word from the Digital Instrumentation section.

 (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.

 (g)  
Self-test oscillator and modulator provides modulated rf carrier in self-test mode of operation. Since the synthesizer also tunes with a self-test input, the receiver does not need to be tuned off channel to receive the self-test input. The self-test input provides an end-to-end test of the receiver, since the self-test rf input is injected in the first preselector.

 (3)  Bendix RNA-34A Receiver
 (a)  Frequency select information from the control panel is processed in the microprocessor. These signals are used to control operation of the synthesizer which provides the required injection frequencies and tuning voltages for the VHF tuner. For VOR operation, navigation signals selected by the tuner are processed into a composite NAV signal. This composite signal is fed to VOR signal processing circuits and to an audio amplifier. The audio output is provided to the flight interphone system (23-51-00).
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 (b)  The VOR signal processing separates the 30-Hz variable and 30-Hz reference-phase signals from the composite signal. The two 30-Hz analog signals are then converted to digital signals which are compared in the microprocessor to determine the phase difference which represents the bearing to the VOR station. The bearing to the VOR station is supplied in sin 0/cos 0 format; in digital format; relative bearing to the RMI
　
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