Non-Directional Beacon (NDB) (NDB)

A radio beacon that transmits essentially equally in all horizontal directions for direction-finding or identification.

A receiver with an automatic direction finder can determine the relative bearing of an NDB signal and combine it with heading to obtain a bearing to or from the beacon. Marine radiobeacons historically supported coastal navigation, while NDBs remain more familiar in aviation.

Bearings can be affected by coastlines, night effect, interference, thunderstorms, vessel structure and receiver limitations. Many maritime services have been withdrawn, so an NDB should be used only when current publications confirm that it is operational.