(2)  
Set TONE (BFO) switch to OFF and select TEST mode. Check that loud and clear audio tone, of more than adequate level can be attained using GAIN controls on ADF control panel and pilots' audio selector panels, as required.

(3)  
Tune to a known station in the 190- to 1750-kHz range using left frequency selector to verify audio reception. Check that indicated tuned frequency, for clear and loud audio reception, is within 1 kHz of the station listed frequency. Check also that RMI pointers are stowed horizontally (90- or 270-degree relative bearing).

(4)  
Vary ADF control panel GAIN control from maximum to maximum. Check that audio output varies accordingly. Check also that audio output is available and adequate at each audio selector panel.

(5)  
Set mode selector switch to ADF. Check that narrow pointers on both RMI's indicate in-tolerance magnetic bearing to the selected station.

(6)  
Detune receiver to a clear channel. Check there is no audio noise and ADF narrow pointers are stowed horizontally in relation to lubber line.

(7)  
Repeat steps (3) thru (6) selecting two other stations in the 190- to 1750-kHz range.

(8)  
Set the pre-selected frequency readout to the same station in the 190 to 1750 kHz range. Set frequency transfer switch to select right frequency readout and repeat steps (1) thru (6) except use right frequency selector.

(9)  
Repeat steps (1) thru (8) for second ADF system. ADF system 2 drives wide pointers

(10)
Set mode selectors on ADF control panels to OFF, ADF, or ANT, as required, then remove electrical power if no longer required.

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D.  Test ADF System (Airplanes with single frequency indication)
(1)  
Press and hold TEST switch of ADF system 1. Check that the corresponding RMI pointers indicate 315 +5 degrees relative bearing (approaching north to be under lubber line), and that loud and clear audio tone (1020 Hz) is heard.

(2)  
Tune to a known station in the 190- to 1750-kHz range. Check that indicated tuned frequency, for clear and loud audio reception, is within 1 kHz of the listed station frequency. Check also that RMI pointers are stowed horizontally (90-or 270-degree relative bearing).

(3)  
Set GAIN control from maximum to minimum. Check that audio output varies accordingly. Check also that audio output is available and adequate at each audio selector panel.

(4)  
Set mode selector switch to ADF. Check that each RMI indicates correct magnetic bearing to the selected station.

(5)  
Detune receiver. Check that there is no audio noise and that ADF pointer is stowed horizontally (90- or 270-degree relative bearing).

(6)  
Repeat steps (2) thru (5) selecting two other stations in the 190- to 1750-kHz range.

(7)  
With ADF-2 selected on audio selector panels, repeat steps (1) thru (6) for ADF system 2. (ADF system 1 drives narrow pointers and ADF system 2 drives wide pointers).

(8)  
Set each mode selector switch to ADF.

(9)  
Press TEST switch on each ADF receiver. Check that TEST indicator rotates to 45 +5 degrees. Release TEST switch. Check that indicator returns to 0 degrees.

(10)
Set each mode selector switch to ADF, ANT, or OFF, as required.

(11)
Remove electrical power, if no longer required.

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AUTOMATIC DIRECTION FINDER LOOP ANTENNAS - REMOVAL/INSTALLATION
1.  Remove Antenna
A.  Remove loop antenna cover by removing mounting screws (Fig. 401).
B.  Support loop antenna assembly. Remove mounting screws.
C.  Lower loop antenna assembly.
D.  Disconnect antenna connector from quadrantal compensator assembly.
E.  Remove antenna assembly.
2.  Install Antenna
A.  Clean mating surfaces of antenna and airplane structure to provide an electrical bond.
B.  Apply a protective coating of corrosion preventive compound to mating surfaces of antenna and airplane structure (Ref 51-21-91 CP).
C.  Connect antenna connector to quadrantal compensator assembly.
D.  Position loop antenna and secure all but one of the mounting screws.
E.  Do an electrical bonding check between antenna and airplane structure per 20-22-01.
(1)  
Connect the ohmmeter or the resistance measuring bridge between the empty antenna mounting screw hole (antenna base plate) and the airplane skin.

(2)  
Make sure the resistance is not more than 0.1 ohm.
　
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