(3)  
Install and tighten the last mounting screw.

F.  Hold antenna cover in place and install the screws.
G.  Perform operational check of system (Ref 34-57-0 A/T).
502 
Oct 20/91  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-57-11 Page 401 

H25612
34-57-11 ADF Loop Antenna Installation

ADF SENSE ANTENNA COUPLERS - REMOVAL/INSTALLATION
1. General (Fig. 1)
A.  Each sense antenna coupler assembly (assy) is removed from the airplane independently of the other.
2.  Remove Coupler Assy
A.  Gain access to the coupler assy located at the aft outboard corner of the main wheel well.
B.  Remove cable connector or connectors from inboard end of coupler assy.
C.  Support coupler and remove four mounting screws.
CAUTION: DO NOT PULL COUPLER. WIRE TERMINATIONS MAY BE DAMAGED.
D.  Disconnect antenna lead from stud on aft face of coupler assy.
E.  Remove coupler assy.
3.  Install Coupler Assy
A.  Connect antenna lead to coupler assy.
B.  Locate coupler and install four mounting screws.
C.  Install cable connector or connectors on coupler assy.
D.  Test ADF system (Ref 34-57-( ), Adjustment/Test).
517 
Aug 15/79  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-57-21 Page 401 

H61896 H61899
ADF Sense Antenna Coupler Installation  517 
34-57-21  Figure 401 (Sheet 1)  Aug 15/79 
Page 402 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

517  ADF Sense Antenna Coupler Installation 
Aug 15/79  Figure 401 (Sheet 2)  34-57-21 
Page 403 
BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

ADF SENSE ANTENNA - REMOVAL/INSTALLATION
1.  General
A.  The ADF sense antenna is flame-sprayed on the reinforced wing body fairing. The metal coating of the fairing is used as the antenna element, and is not removable from the fairing.
B.  To remove or replace the wing body fairing, refer to 53-51-21, Aft Wing-to-Body Fairing -Removal/Installation.
500 
Jun 20/88  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  34-57-31 Page 401 

OMEGA NAVIGATION SYSTEM - DESCRIPTION AND OPERATION
1. General
A.  The OMEGA Navigation System (ONS) is a fully automatic, computerized navigation system which determines aircraft position changes by utilizing very low frequency radio signals (VLF). The radio signals are provided by 8 OMEGA transmitters located throughout the world to provide reliable signal reception from several stations regardless of airplane position. The system navigation data is displayed on the control display unit (CDU) and steering signals are available for the autopilot system. Navigation data is sent to the CAPT and F/O HSI's and the Performance Data Computer System.
B.  One system is installed in the airplane (Fig. 1). The system consists of: A Receiver Processor Unit (RPU) located in main electronic equipment rack; a Control Display Unit (CDU) located on the cockpit aisle stand; on GJ B-2501 thru B-2505, an antenna coupler which is connected to the ADF sense antenna located in the left main landing gear wheel well or on GJ ALL EXCEPT B-2501 thru B2505, an H-FIELD antenna/coupler unit located on the tip of the left stabilizer. The system also utilizes a true airspeed (TAS) signal from the CADC, compass heading from an RMI, and an air ground discrete signal from the landing gear accessory module. System electrical power is obtained from 115 vac electronic bus No. 1.
2.  Basic OMEGA Principles
A.  The OMEGA stations are located to provide reliable world wide coverage (Fig. 2). Each transmitter has three output frequencies which are radiated individually for a specified duration. The stations are synchronized to universal time with the transmitting sequence repeated every 10 seconds. Taking station A, for example, the transmitter radiates a 10.2-kHz signal for 0.9 second, then no radiation for 0.2 second, then radiates 13.6 kHz for 1.0 second, 0.2 second pause, then radiates 11.3 kHz for 1.1 seconds. The next transmission starts when the 10-second sequence is completed. Each transmitter transmits the same frequencies in the same sequence, however, the duration of transmission is resequenced for each station. This duration difference is used by the OMEGA receiver to identify the various stations.
B.  The principle frequency used for system computation is 10.2 kHz. The wave length for 10.2 kHz is approximately 16 nautical miles (nm). Two stations at the same frequency will provide points of 0-degree phase difference at each half wavelength or 8 nm. These half wavelengths of 0-degree phase difference from hyperbolic lines which form lanes (Fig. 3). By using three or more stations, a series of intersecting lanes are formed which permit the OMEGA system to locate its position within the various lanes. When the OMEGA system present position has been established within the lanes (. 4 nm), the computer measures the respective phase changes and translates this information into present position.
　
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