A non-directional beacon (NDB) or non-directional radio beacon is a radio transmitter consisting of a Beacon transmitter, Antenna Tuning Unit, and Antenna at a known, ground-based location operating within MF or LF bandwidth that does not include directional information, transmits signals containing code elements used to identify an area/station with equal power in all directions as the standard equipment used to assist and navigate ships or aircraft in marine and aviation applications. Non-directional beacons (NDB) or non-directional radio beacons are widely used at airports, ports, or offshore platforms.

Non-directional beacon (NDB) or non-directional radio beacon on land works by sending an Omni-directional signal to an antenna installed on a ship/aircraft, then an Automatic Direction Finder (ADF) receives the signal and uses it to determine the direction of the aircraft or berth and displays its position.

Non-directional Beacon (NDB) stations are distinguished by their signal coverage.

An automatic direction finder, (ADF) is a navigational instrument that automatically and continuously displays the relative bearing of a ship or aircraft to the appropriate radio station used as a navigational aid.

The reliability of Non-Directional Beacons (NDB) and their low cost and proven have been installed for decades without interruption, therefore that they are still widely used for airports, offshore platforms, or used as helicopter landing instruments.