AF 101-156; IB 405; CONFIG 1 LH 001-003; SN 301-302 03 Page 10 Apr 25/86
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(b)
Manual control of the loop attitude (that is the attitude of the rotor shaft in the goniometer) is given by the LOOP switch. This switch is spring-loaded to the center off position. When the function switch is set at LOOP, the gonio servomotor drives the goniometer rotor clockwise or counterclockwise according to whether the LOOP manual control switch is turned right or left of the center off position. Speed of rotation of the servomotor is increased progressively as the LOOP switch is turned further away from the center off position. When the function switch is set at ADF, operation of the LOOP manual control switch automatically overrides the ADF selection and the receiver is placed in the LOOP mode until the LOOP switch is restored to the center off position.
(c)
Frequency selection is controlled by three knobs set below an in-line digital frequency indicator. The left knob controls the selection of hundreds of Hz from 1 x 100 Hz to 17 x 100 Hz, the lower or center knob tens of Hz from 0 x 10 Hz to 9 x 10 Hz and the right-hand knob unit and half Hz from 0 Hz to 9.5 Hz.
(d)
The BFO control knob and the GAIN control knob are concentric. The BFO control knob operates an on/off switch and a potentiometer that controls the BFO note pitch. The GAIN control knob operates a potentiometer that controls audio gain on function ADF and rf gain on functions ANT and LOOP.
B. Controls
(1)
Prior to operating the ADF system, electrical power must be provided to the airplane (Ref 24-22-00, Electrical Power, Manual Control).
(2)
The master radio switches on the P5 pilots' overhead panel and the ADF 1 and ADF 2 circuit breakers (four total) on the P7 electronic circuit breaker panel must be closed.
(3)
For each ADF system, when the function switch is positioned from OFF to ADF and the receiver is tuned to receive a radio station, the appropriate ADF needle in each RMI should point toward the received station, confirming that the system is operating properly.
EFFECTIVITY
AF 101-156; IB 405; CONFIG 1 LH 001-003; SN 301-302 02 Page 11 Apr 25/86
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AUTOMATIC DIRECTION FINDER SYSTEM - DESCRIPTION AND OPERATION
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1. General (Fig. 1 and 2)
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A. The automatic direction finder system (ADF) is a navigational aid which receives radio signals from 190 to 1750 kilohertz and determines the direction to the station. Signal sources used are low frequency and standard broadcast radio stations. The system is used for either automatic or manual determination of bearing to a transmitting station, for flying radio ranges, and for reception of weather information and other broadcast programs.
B. Two separate and completely independent automatic direction finder systems are installed in the airplane. Each system consists of a receiver, sense antenna, sense antenna coupler, fixed loop antenna, quadrantal error corrector, and control panel.
C. Operation and mode selection of each automatic direction finder receiver is controlled from the flight deck. The receiver uses signals from both the sense and the fixed loop antennas to compute the bearing of the radio station being received. The bearing information is provided to flight instrument displays. Station audio is routed to the flight interphone system (23-51-00) for monitoring.
D. The direction finder system operates on 26 volts, 400 Hz and 28-volt dc power through circuit breakers on panel P7.
E. The 26v ac excitation power for the captain's or first officer's ADF pointer needle synchros is routed through the applicable ADF control panel where it is disconnected when the system is switched off (Fig. 2).
2. Loop Antenna (Fig. 1)
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A. The fixed loop antenna is a sealed, nonrotating, direction-sensitive rf pick-up device for the automatic direction finder system receiver. The antenna consists of two pairs of ferrite core coils, one pair oriented parallel to and the second pair oriented perpendicular to the fore and aft axis of the airplane. Both coil pairs are coupled to the system receiver through the quadrantal error corrector and loop antenna transmission cable.
B. Two antennas are mounted on the bottom centerline of the fuselage approximately at body stations 1005 (system No. 1) and 1068 (system No. 2). Each unit is flush-mounted from outside the airplane in an individual antenna cavity.
3. Quadrantal Error Corrector (Fig. 1)
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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 much of the pattern distortion (quadrantal error) from the incoming rf signals. The error corrector then couples the corrected rf signals into the loop antenna transmission cable.
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