ADF System Component Location  5C8 
34-57-01  Figure 1 (Sheet 3)  Jun 20/88 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

5C8  ADF System Simplified Block Diagram 
Jun 20/88  Figure 2  34-57-01 
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BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details. 

3.  Quadrantal Error Corrector (Fig. 1)
A.  The airplane wings and fuselage interact with the field of an incoming rf signal to distort the reception pattern. The quadrantal error corrector compensates the loop antenna signal through fixed attenuators which remove this pattern distortion (quadrantal error) from the incoming rf signals. The error corrector then couples the corrected rf signals into the loop antenna transmission cable.
B.  The quadrantal error correctors are mounted directly on top of their respective loop antenna assemblies inside the loop antenna mounting cavities. Removal as individual units is possible only after the loop antennas have been removed.
4.  Loop Antenna Transmission Cable (Fig. 1)
A.  The corrected loop antenna rf output is transmitted from the loop antenna cavity to the receiver in the aft center equipment center by the loop antenna transmission cable. This cable consists of a bundle of four twisted coaxial transmission lines in a sheathed cover.
5.  Sense Antenna (Fig. 1)
A.  Two ADF sense antennas are installed on the airplane, one on the right wing-body fairing and the second on the left wing-body fairing. The antennas are located aft of the aft wheel well bulkhead at station 766. The metal coats of the fairings are used as the antenna elements.
B.  The sense antennas provide a nondirectional reception pattern and high signal strength to the receivers.
6.  Sense Antenna Input Coupler
A.  An input coupler is used in each of the ADF systems to match the capacitance of the sense antenna to the capacitance of the transmission line between the antenna and the receiver. The coupler contains the necessary circuits to provide optimum performance. The total capacitance of the sense antenna, coupler, and line, as seen by the receiver input, is approximately 3000 pF. On airplanes with an OMEGA navigation system installed, an Omega coupler is added between ADF sense antenna No. 1 and the ADF coupler. Received rf is divided in the Omega coupler and directed to the Omega navigation system through an amplifier and to the ADF coupler through an amplifier and on to the ADF system. Power for the Omega amplifier is from the Omega system via the signal cable. Power for the ADF amplifier is from the ADF control panel via a separate cable (Ref 34-59-00, Description and Operation).
B.  The input couplers are mounted near their respective sense antenna at station 727, waterline 160 and buttock line 45 (Fig. 1).
5C8 
34-57-01 Page 6  BOEING PROPRIETARY - Copyright . - Unpublished Work - See title page for details.  Jun 20/88 

7.  Receiver (Fig. 1)
A.  The receiver is a transistorized, superheterodyne radio receiver that processes amplitude-modulated, rf signals within the frequency range of 190 to 1750 kHz, and produces a synchro output representing relative compass bearing to the rf transmitter site. It also produces an audio output from any modulation on the received rf signal for use in the flight interphone system.
B.  Both receivers are mounted on the rack in the aft center fuselage equipment center.
8.  Control Panel (Fig. 1)
A.  The ADF control panel remotely controls receiver band switching, tuning and operational modes by passive, electrical means. It is manually operated and provides the operator with visual indications of selected mode and frequency.
B.  On airplanes with single frequency indication, the control panel provides a frequency selection capability with a set of concentric frequency selection knobs and a frequency indicating dial. The panel also has a mode select switch, a BFO (TONE/OFF) switch and a TEST switch. On airplanes with dual frequency indications, the control panel provides a dual frequency capability with two sets of concentric frequency selection knobs, two frequency indicating dials, and a frequency transfer (XFR) switch. The panel also has a mode select switch and a BFO (TONE/OFF) switch. The frequency transfer (XFR) switch selects one of the two preselected frequencies and illuminates the dial that indicates the operating frequency.
C.  On airplanes with single frequency indication, power for the ADF receiver and the operating mode is controlled by the mode select switch. The BFO (TONE/OFF) switch is a two-position toggle. The TEST switch is a momentary contact pushbutton switch. On airplanes with dual frequency indications, power for the ADF receiver and the operating mode is controlled by the mode select switch. This switch also has a TEST position that is a momentary contact position. The BFO (TONE/OFF) switch is a two-position toggle.
　
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