Stands for Non-Directional Beacon. An aerial navigation facility which simply broadcasts its station identifier in
morse code. Two aerials (one in the front of the
aircraft and one in the
rear - or at least as differently-located as possible) receive the signal. The phase difference between the two signals is computed and displayed as a bearing from the station.
NDB stations, like
VOR stations, only provide
position line information. See also
DME.