7.4. Radio Direction Finder

A radio direction finder (RDF) is a device for finding the direction, or bearing, to a radio source. Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately, using two or more measurements of known transmitters, the location of a vehicle can be determined. RDF is widely used as a radio navigation system, especially with boats and aircraft [67].

In 1955, Hemphill investigated a magnetic radio compass antenna that the magnetic energy was picked up by the collector bars and conducted as magnetic energy to the small pickup coil in the center. Since the antenna was placed on the surface of the aircraft, it did not cause any additional drag [26].