Non-Directional Beacon (NDB) is a ground-based, low frequency radio transmitter used as an instrument approach for airports and offshore platforms. The NDB transmits an omni-directional signal that is received by Automatic Direction Finder in a standard instrument onboard aircraft. NDB operates on a frequency between 190 to 1800 kHz. The main components of an NDB ground station are the Beacon transmitter, Antenna Tuning Unit and Antenna. Typically NDBs have output power from 25 to 125 watts for reception up to approximately 100 NM. Higher power systems from 500 to 1000 Watts are used for longer range applications.