NDB (Non-Directional Beacon, Non-Directional Radio Transmitter) is a radio broadcasting station located at a specific area, providing air or sea navigation support. Each NDB ground station is identified by a one, two or three letter morse code.
NDB – Ground stations are classified according to their power output and usage:
The L ground station has a power of less than 50 watts.
The M ground station has a power from 50 watts to 2000 watts.
The H ground station has a power of 2000 watts or higher.
Navigation with radio waves is still widely used. It is generally used when specialized navigation equipment is not available on board or on the ground. Hence NDBs are often associated with Non-Precision Approach procedures.
The cost of installation and maintenance of ground stations is relatively low. In addition to serving as stand-alone primary instrument approaches at airports, NDBs are also used as Locator Outer Markers (LOM) for Instrument Landing Systems (ILS). Outer Markers designate the starting area of an ILs approach or flight path to follow for a standard terminal arrival or STAR procedure.
Ground stations transmit between the 200 and 450 kHz frequency bands. The signal is not transmitted in the line of sight (LOS (live of sight)) of VHF (very high frequency) or UHF (ultra high frequency). But on the earth, it curves, following the shape of the earth. This allows reception at great distances at low altitudes. The transmitter need not to be designed for navigation. It can be a radio or television station, a communication station, or any other broadcasting system.
NDB Ground Station Use
In aviation, an aircraft may follow an orientation towards a ground station or in the opposite direction from the ground station. Ground station orientations provide planned, reliable routes through which aircraft can fly. Aircraft complete the flight plan by following these predetermined routes.
A non-directional beacon (NDB) is a radio beacon operating in the MF or LF band-widths. NDBs transmit a signal of equal strength in all directions. The signal contains a coded element which is used for station identification (normally 1-3 letters in Morse Code).
Aircraft equipped with Automatic Direction Finding (ADF) on board use bearings from NDBs for navigation purposes.