NDB – Non-Directional Beacon
What is NDB?
NDB is a navigational system consisting of an automatic direction finder (ADF) and a radio transmitting unit. The automatic direction finder equipment is typically installed aboard an aircraft, and detects the NDB signal sent by the NDB transmitter stationed at a known location. The ADF determines the direction to the NDB transmitter, which is indicated by a relative bearing indicator (RBI). An RBI can be described as a kind of compass, except that the pointer that aims on the magnetic north in a magnetic compass, is substituted with at pointer to the NDB station on an RBI.
Non-directional beacon supports better and more precise aircraft navigation. In addition to sending out a morse code identity of the location, an NDB may also broadcast weather and meteorological information, as well as surface and terminal information.
Pilots using ADF to track NDB’s may be subject to certain challenges. Fluctuations in signal strength may be a result of radio waves reflecting back from the ionosphere, especially around sunrise and sunset. This is often referred to as “night effect”. Also, the “terrain effect” may give erroneous readings as a result of mountains reflecting radio waves. In addition electrical, shoreline and bank effects may disturb readings.
These are challenges that may occur with all kinds of NDB equipment, however, pilots are well trained to try to compensate for these effects.