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[[image]] REGULATIONS [[image]]

FLIGHT


Section 3251 
ADF AND LOOP RECEIVERS

A. Navigation with Radio Loop Equipment

1. Methods of Elimination of the 180° Ambiguity

a. Definition of Null and 180° Ambiguity

(1) When the plane of the loop type antenna is parallel to a line drawn to a station, a maximum signal is heard. If the loop is turned so that its plane lies perpendicular to a line to the station, a minimum signal is heard. This minimum signal is called the aurul [[aural]] null. With the radio equipment turned to compass and making use of the aurul [[aural]] null, 180° ambiguity may be present. This term means that the station may be either at the fore or aft end of the needle.

b. Elimination of 180° Ambiguity

(1) To determine the exact direction of the station without turning the equipment to ADF,  a definite procedure is required. After orienting aircraft so that station is on a wing tip null, continue on byro [[gyro]] heading for several minutes and again tune in the station for null. If the needle must be turned to the right or clockwise in order to obtain the null, the station is to the right. If the needle must be turned to the left to obtain a null, the station is on the left. REMEMBER: Clockwise, station right; Counterclockwise, station left.

(2) Instead of turning the needle, the ship may be turned several minutes after receiving the null. If the loop antenna is kept in a fixed position and the ship is turned to the right, a null is received if the station is to the right. If a null is received when turning the ship to the left, the station is to the left of the ship.

2. Determining a Fix with 2 or More Lines of Position

a. Use of the Radio Equipment

(1) A particularly valuable aid to the loop equipment is the rotatable dial on the azimuth indicator. If the aircraft has a fixed dial, all bearings would have to be measured in relation to the heading or the nose of the ship. With the rotatable azimuth, the azimuth is turned to the compass heading of the ship. The north point of the azimuth will now poin [[point]] to magnetic north and all other points will naturally point to their respective magnetic directions. This is assuming, of course, that there is little magnetic compass.

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Flight