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 (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 similarly 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.

 (3)  
Bendix RNA-34A Receiver

 (a)  In glide slope operation, the 90-Hz/150-Hz signal output of the UHF receiver is fed through filters to the ILS multiplexer. The output of the multiplexer is fed through an analog-to-digital converter to the microprocessor. From this signal input, the microprocessor develops glide slope deviation voltages that are fed to the glide slope deviation displays in the flight instruments. As in VOR and LOC operation, the microprocessor monitors operation of the unit and produces a GS warning (flag) if a malfunction occurs.

 (4)  
KING RADIO KNR 6030 Receiver

 (a)  
The ILS transmission consists of two separate channels to provide for both vertical and horizontal displacement information with respect to the runway approach path. The glide slope transmission is in the UHF band and is comprised of two intersecting radiation lobes. The top lobe consists of an rf carrier modulated by a 90-Hz signal and the bottom lobe consists of a 150-Hz signal. The path where the 90-Hz and 150-Hz modulations are equal defines the glide slope. The localizer transmission is similar to the glide slope, except the rf carrier is in the VHF band and the 90-Hz and 150-Hz lobes are arranged differently. As viewed from an approach to the runway, the 150-Hz lobe is on the right and the 90-Hz lobe is on the left. The path where the 90-Hz and 150-Hz modulations are equal defines an extension of the runway centerline.

 (b)  
The glide slope signal is detected by the glide slope antenna and is fed into the UHF receiver. The demodulation signal is then passed to the ILS deviation board where the 90-Hz and the 150-Hz components are filtered out and rectified via active peak filters. The difference of the two rectified signals is taken and then filtered to a DC level to produce the GS deviation signal.

 EFFECTIVITY
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 (c)  
The rectified 90-Hz and 150-Hz signals, of similar polarity, are summed, filtered to a DC level, and compared to a reference voltage. A GS flag is generated when the two components fail to have enough signal strength to exceed the reference voltage.

 (d)  
The localizer signal is received by the VOR/LOC antenna and is fed to the VHF receiver. The demodulated signal is processed by the ILS deviation board in the same manner as the GS signal to produce the LOC deviation and LOC flag outputs.

 D. Functional Description, VOR/ILS Self-Test Operation
 (1)  
COLLINS 51RV-2B Receiver

 (a)  
Modulated rf test signals are generated within the VOR/ILS receiver by the VOR/ILS test generator. The test generator is activated by the test switches on the front panel of the receiver and on the VHF NAV control panel. A relay in the flight instruments accessory box provides dc ground for self-test modes.

 (b)  
The test signals 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.

 (2)  
Bendix RNA-34A and Collins 51RV-4( ) Receivers

 (a)  
VOR/ILS self-test provides the VOR and ILS self-test audio signals, 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 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)  
　
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