Non-directional beacon
A ground-based radio beacon providing bearing information for navigation.
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A non-directional beacon (NDB) is a radio beacon that transmits a signal without directional information, used as an aviation or marine navigational aid. It is notable for its ability to follow the curvature of the Earth, allowing reception at greater distances and lower altitudes than VOR, though its signals are more affected by atmospheric conditions, mountainous terrain, coastal refraction, and electrical storms.
Quick Facts
- Frequency range
- 190 kHz to 1750 kHz (ICAO); 190 kHz to 535 kHz (North America)
- Power classifications
- Low (<50 W)
- Medium (50 W to 2000 W)
- High (>2000 W)
- First instrument approach
- May 9, 1932
- Developer
- United States Army Air Corps Captain Albert Francis Hegenberger
- Types
- En route NDBs
- Approach NDBs
- Localizer beacons
- Locator beacons
Facts from the source article.
Lore & Background
The non-directional beacon system was developed by United States Army Air Corps Captain Albert Francis Hegenberger and was used to fly the world's first instrument approach on May 9, 1932. NDBs are standardized by the International Civil Aviation Organization (ICAO) Annex 10, which specifies operation on frequencies between 190 kHz and 1750 kHz, though North American NDBs normally operate between 190 kHz and 535 kHz. Each NDB is identified by a one, two, or three-letter Morse code callsign; in Canada, privately owned NDB identifiers consist of one letter and one number.
NDBs in North America are classified by power output: low (less than 50 watts), medium (50 W to 2000 W), and high (more than 2000 W). There are four types of NDBs in aeronautical navigation service: en route NDBs (used to mark airways), approach NDBs, localizer beacons, and locator beacons—the last two used in conjunction with an instrument landing system (ILS). NDB signals follow the curvature of the Earth, providing a major advantage over VOR at lower altitudes and greater distances, but they are more affected by atmospheric conditions, mountainous terrain, coastal refraction, and electrical storms, particularly at long range.
Reader's Guide
NDB navigation consists of two parts: the automatic direction finder (ADF) equipment on the aircraft and the NDB transmitter. The ADF determines the bearing to the NDB station using a combination of directional and non-directional antennas, displaying this bearing on a relative bearing indicator (RBI) or, when combined with a compass card, a radio magnetic indicator (RMI). The RMI reduces mental calculation by referencing the ADF needle directly to the aircraft's magnetic heading, and many RMIs can also display VOR information, allowing aircraft to fly Victor routes while using NDBs for triangulation.
NDBs define airways, particularly colored airways (green, red, amber, blue) charted on sectional charts, which are used for low to medium frequency stations. As of September 2022, only one colored airway remains in the continental United States (G13 off the coast of North Carolina), while Alaska and other regions, especially the developing world and lightly populated areas like the Canadian Arctic, continue to use NDB airways due to their long range and lower operating cost compared to VORs. NDBs are also used to obtain geographic fixes by intersecting bearings, important when other navigational equipment fails, and in marine navigation when GPS reception fails. A runway equipped with NDB or VOR as the only navigation aid is called a non-precision approach runway; NDBs are commonly used as locators for ILS approaches, such as the locator outer marker (LOM) in the United States.
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Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Non-directional beacon (CC BY-SA 4.0).
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