12. Relays and Switches
___________________
 A.  Switching from VOR to ILS, selection of VOR/ILS data from receiver 1, 2 or 3, and selection of radio (VOR/ILS) or INS navigation data at the captain's and first officer's instrument panel is accomplished by the
 following switches and relays:
 ITEM
____
(1)  
AP/FD NAV mode select switch

(2)  
Captain's VOR/ILS-INS transfer switch and RADIO/INS relay

(3)  
First officer's VOR/ILS-INS transfer switch and RADIO/INS relay

 (4)  
Captain's VOR/ILS transfer switch and VOR/ILS A and B transfer relays

(5)  
VOR/LOC antenna switch 1

(6)  
VOR/LOC antenna switch 2

(7)  
VOR/LOC antenna switch 3

(8)  
VOR/LOC antenna switch 4

EFFECTIVITYFUNCTION
VOR to localizer antenna transferoccurs after localizer capture and the NAV mode select switch is in ILS or LAND position.Enables the captain to select coursepresentation from either the VOR/ILSnavigation system or from the INSSame as captain's
Enable the selection of either VOR/ILSreceiver 1 or 3 as the radio nav signalsource for the AP/FD system and the captain's flight instrument displays or selection of either VOR/ILS receiver 2 or 3 as the radio nav signal source for the AP/FD system and the first officer's flight instrument displaysSelects rf from either the VOR antenna or the lower localizer antenna for VOR/ILS receiver 1Selects rf from either the VOR antenna or the lower localizer antenna for VOR/ILS receiver 2Selects rf from either the VOR antenna or the upper localizer antenna for VOR/ILS receiver 3Switches rf from the VOR antenna to VOR/ILS receiver 1 or 3
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 (9)  VOR/LOC antenna switch 5 Switches rf from the VOR antenna to VOR/ILS receiver 2 or 3.
 13. ILS Buffer Amplifiers (LH 011-099)
_____________________
 A.  Two ILS buffer amplifiers are installed in flight instrument relay panel P73.
 B.  The amplifiers isolate the ILS deviation and flag warning outputs circuits of the auxiliary (3rd) VOR/ILS receiver from a fault in these circuits of the No. 1 or the No. 2 VOR/ILS navigation systems. If a fault occurs, and either the captain or the first officer select the 3rd receiver, the amplifiers prevent the fault from damaging the 3rd receiver or the ILS deviation and warning input circuits to channel C of the fail-operative AP/FD system.
 14. Operation
_________
 A.  Functional Description, VOR/ILS Operation
 (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 volts 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)  
BENDIX RNA-26C Receiver, VOR Operation

 (2)  
The VHF receiver section receives either VOR or Localizer rf from the antennas via antenna switching. The frequency of the local oscillators is controlled by tuning logic which is driven by 2-of-5 frequency select code signals from the frequency select switches in the VHF NAV control panel.

 (3)  
The IF is detected and applied via an audio amplifier to the flight interphone system to permit monitoring of the VOR/LOC audio signal. The output of the detector is also applied to the VOR and localizer circuits.

 (a)  The 9960-Hz frequency modulated VOR reference phase signal is fed from the detector to the 9960-Hz limiter detector, the output of which is the 30-Hz reference phase signal used to drive the phase shifting resolver. The resolver output is connected to a phasing network such that the output phase is a function of the angular position of the resolver, but of a constant amplitude. This signal is coupled to the 30-Hz reference phase amplifier. After amplification the reference signal provides one of the inputs to the automatic VOR phase detector.
 EFFECTIVITY

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 (b)  
A second output from the receiver detector is fed, after passing the VOR check switch, to the 30-Hz variable phase amplifier. The amplified 30-Hz variable phase signal is connected as the second input to the VOR phase detector. A portion of both the reference and variable phase signals is sampled and fed to the flag logic circuits.
　
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