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(1)
The VOR/ILS navigation system provides VOR/LOC data via the VOR antenna when the AP/FD NAV mode select switch is placed in either the INS, HEADING or VOR/LOC position, the appropriate frequency is selected on the VHF NAV control panel, and 28-volt dc power is supplied to the VOR/ILS receiver.
(2)
The systems receive 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. Frequency selection is accomplished electronically using the two-out-of-five binary-coded-decimal system.
B. Functional Description, VOR/LOC Mode Operation (Fig. 2)
(1)
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).
(2)
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.
(3)
The VOR/LOC flag provides an indication of VOR AND LOCALIZER operational statuses as well as the validity of the incoming rf signal.
(4)
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.
(5)
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.
(6)
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.
EFFECTIVITY
AF 121, 122, 155-171, CONFIG 3 174-190, 195-199; 02 Page 8 VM ALL Sep 25/94
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VOR/ILS RECEIVER VOR/ILS Receiver Block Diagram Figure 2
EFFECTIVITY
CONFIG 3
AF 121,122,155-171,174-190,
799 Page 9/10
195-199;
34-31-00
Sep 25/94
VM ALL
T34011
(7)
The digital phase detector provides phase detection of the 30-Hz reference and variable signals and outputs a digital word indicating bearing to the VOR ground station. This signal is applied to the microprocessor. The processor also uses airplane magnetic heading and omni bearing set (OBS) data from the HDG and OBS synchro to digital processors to compute the course deviation, VOR bearing and to/from outputs for the flight instrument displays and the autopilot flight control system (AFCS). A monitoring function of the microprocessor assures that all inputs are valid prior to accepting them for computation. If an invalid signal appears at the processor or in the receiver channel, the flag circuits will output a flag condition and the associated warning flag will appear in the flight instrument display(s).
(8)
The localizer receiver is the same as the VOR receiver with the detected output filtered in 90-Hz and 150-Hz bandpass filters. The localizer deviation and flag outputs are provided to the AFCS and the flight instrument displays.
C. Functional Description, Glide Slope Mode Operation
(1)
The GS UHF receiver operates similarly to the VHF NAV receiver. The glide slope rf from the glide slope antenna is applied via a bandpass filter 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 deviation channel of the ILS circuits.
(2)
The GS deviation channel produces glide slope deviation signals which are applied to the flight instrument displays. ILS deviation output are also compared in the flag monitoring circuits which during ILS operation produce the VOR/LOC and GS super (S) flag signals. These flag signals bias the localizer and glide slope warning flags in the flight instrument displays out-of-view. If a fault occurs the super flag voltage is interrupted and the associated flight instrument warning flag will appear.
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