A
non-directional (radio) beacon (
NDB) is a
radio transmitter at a known location, used as an aviation or marine
navigational aid. As the name implies, the signal transmitted does not include
inherent directional information, in contrast to other navigational aids such as
low frequency radio range,
VHF omnidirectional range (VOR) and
TACAN. NDB signals
follow the curvature of the Earth, so they can be received at much greater distances at lower altitudes, a major advantage over VOR. However, NDB signals are also affected more by atmospheric conditions, mountainous terrain, coastal refraction and electrical storms, particularly at long range.