direction finder, electronic device used to determine the position of a ship or aircraft. In a simple direction finder a radio receiver is equipped with a revolving directional antenna. The antenna receives the strongest radio signal when it is pointing directly at a transmitter. By determining the direction of two land-based transmitters, a navigator may plot his position by triangulation. Direction finders have been replaced in many applications with more accurate systems, such as radar and satellite navigation systems (see satellite, artificial).

automatic direction finder: see radio range.