The NDB, or Non Directional Beacon, has been in use in one form or another for almost a century.
It was first conceived in the late 19th century, when German scientist Heinrich Rudolf Hertz discovered that the direction of a radio source could be determined with a looped antenna. By the 1930s this technology evolved into modern Automatic Direction Finding equipment or ADF. These more modern systems were extremely simple to use; the NDB station acted like a lighthouse that the ADF would point to when tuned to the station frequency.
NDB stations were placed strategically all over the world. With the use of two stations pilots could triangulate their position. They are most commonly found at airports or just outside them, placed so that pilots can use them to easily line up with the desired runway.
Cheap and simple to maintain but limited in range and precision, the NDB was supplemented in marine and aviation use by longer range LORAN systems and starting in the 1950s pilots could use even more precise and useful TACAN and VOR / DME systems which could more accurately determine one’s position relative to any VOR beacon.
With the advent of satellite based GPS systems, NDB stations are being taken off-line in many regions in favor of GPS based navigation. Of all the NDB stations around Winnipeg, half have been taken out of service. Soon, ground based VOR systems may see the same fate.
While NDB systems are being retired, their positions are still commonly used in takeoff and landing procedures.