The simplest use of radio waves in navigation is radio direction finding, in which a medium frequency radio signal is broadcast from a station at a known location. This signal is omnidirectional, but a directional antenna on a vessel is used to determine the bearing of the station. This constitutes an LOP, which can be crossed with another LOP to determine a fix.

Once used extensively throughout the world, radiobeacons have been discontinued in the U.S. and many other areas. They are now chiefly used as homing devices by local fishermen, and very little of the ocean's surface is covered by any radiobeacon signal. Because of its limited range, limited availability, and inherent errors, radio direction finding is of limited usefulness to the professional navigator.

In the past, when radiobeacon stations were powerful and common enough for routine ocean navigation, correction of radio bearings was necessary to obtain the most accurate LOP's. The correction process accounted for the fact that, while radio bearings travel along great circles, they are most often plotted on Mercator charts. The relatively short range of those stations remaining hasmade this process obsolete. Once comprising a major part of NIMA Pub. 117, Radio Navigational Aids, radiobeacons are now listed in the back of each volume of the geographically appropriate List of Lights.

A Radio Direction Finding Station is one which the mariner can contact via radio and request a bearing. Most of these stations are for emergency use only, and a fee may be involved. These stations and procedures for use are listed in NIMA Pub. 117, Radio Navigational Aids.

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