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747-400 MAINTENANCE MANUAL
 VOR NAVIGATION SYSTEM - DESCRIPTION AND OPERATION
_________________________________________________
 1.  General_______
 A.  The VOR (VHF omnidirectional range) navigation system is a navigational aid that determines absolute bearing with respect to a ground station. The system receives rf signal data from the ground station and converts it into bearing data. This data is then sent to interfacing systems for display and navigational use.
 B.  The VOR navigation system consist of two independent systems designated as left and right VOR. Each system consist of a VOR receiver, VOR/LOC antenna and a VOR/LOC rf power divider. Component location is shown in Fig. 1.
 C.  The VOR receivers are normally tuned automatically by the Flight Management Computers (FMC) or they can be tuned manually through the FMCs using the CDU keyboard.
 D.  VOR bearing, deviation, system source annunciation, TO/FROM annuciation, tuned frequency/identifier and flag warning is displayed on the captain's and first officer's Navigation Displays (ND). VOR audio ground station identification is supplied to the cockpit speakers and headsets. VOR digital data is also supplied to the flight management computers (FMC) and the Central Maintence Computers (CMC).
 2.  VOR/MKR Receiver________________
 A.  Two VOR/MKR receivers are used to process VOR signals from the ground stations. Each VOR/MKR receiver provides reception of VOR signals in the frequency range of 108.00 to 117.95 MHz with 50 kHz channel spacing. The frequency range of 108.00 to 111.95 MHz is shared with the ILS. VOR frequencies are the even numbered tenths with the ILS using the odd numbered tenths. The frequency range from 112.00 to 117.95 MHz are all VOR frequencies. The receivers processes the VOR signals to provide bearing and station identification in digital data format. It also provides audio signals to the flight interphone system for station identification.
 B.  Each receiver has built-in test equipment (BITE) which automatically performs self-test procedures as part of an internal program. In addition, a system self-test may be manually initiated by the front panel TEST button. The results of the self-test show on the front panel of the receiver.
 C.  The receiver also contains the circuits for the marker beacon system (Ref 34-32-00).
 D.  The left and right VOR/MKR receivers are located in the E2 electronics equipment rack in the main equipment center.
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747-400 MAINTENANCE MANUAL
PILOTS' LIGHTSHIELD
SEE H
PILOTS'
PILOTS' CENTER OVERHEAD
INSTRUMENT PANEL PANEL SEE A

SEE G FIRST OFFICER'S INSTRUMENT PANEL
CAPTAIN'S INSTRUMENT PANEL SEE B C
SEEB F
AFT ELECTRONIC CONTROL PANEL 
SEE  D  E 
FORWARD ELECTRONIC CONTROL PANEL SEE EB  MAIN EQUIPMENT CENTER RACK E2 LEFT VOR/MKR RECEIVER E2-2 RIGHT VOR/MKR RECEIVER E2-3 
SEE  I 

VOR/LOC ANTENNA
VOR Navigation System Component Location
Figure 1 (Sheet 1)

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MAINTENANCE MANUAL

IRS MODE SELECT UNIT

SOURCE SELECT SWITCHES NAVIGATION DISPLAY (ND)

B 
C
VOR Navigation System Component Location Figure 1 (Sheet 2)

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747-400
　
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