1921U.S. Naval Compass Station provided radio compass bearings to vessels.Economy and Industry, Government and Public Service, Maritime & Fishing Industry, Transportation

A radio direction finder, also called a radio compass, is a radio receiver and directional antenna system used to determine the direction of the source of a signal. The antenna rotates and pinpoints the direction from which a radio signal is strongest. This is the direction of the broadcasting station, the position of which is already known. Using the directions and positions of several radio stations, a navigator can use triangulation to determine the position of his craft.

“Radio Direction Finder | Radio Navigation, Signal Detection, Wave Propagation | Britannica.” https://www.britannica.com/technology/radio-direction-finder.
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