Non-Directional Beacon (NDB)

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What is the Definition of Non-Directional Beacon (NDB)?

A Non-Directional Beacon (NDB) is a ground-based radio transmitter that emits signals in all directions, providing bearing information for aircraft navigation. Operating in the low to medium frequency range (190 kHz to 1750 kHz), NDBs allow pilots to determine their direction relative to the station using an Automatic Direction Finder (ADF).

Unlike VOR (VHF Omnidirectional Range) systems, NDBs do not provide azimuth information but are still widely used for en-route navigation, approach procedures, and backup navigation. They remain an essential part of air traffic control infrastructure, especially in remote areas or as supplementary navigation aids alongside GPS and other modern systems.

Key Components of Non-Directional Beacon

  • Transmitter – The core component that continuously emits radio signals in all directions.
  • Omnidirectional Antenna – Radiates signals uniformly, allowing aircraft to receive bearings from any direction.
  • Frequency Range – Operates within 190 kHz to 1750 kHz in the low to medium frequency bands.
  • Automatic Direction Finder (ADF) – The onboard aircraft instrument used to interpret NDB signals and determine bearing.
  • Station Identifier – A unique Morse code identifier that helps pilots verify the correct NDB station.
  • Ground Infrastructure – Includes power supply, antenna supports, and shielding to maintain signal integrity.
  • Signal Modulation – Uses amplitude modulation (AM) to transmit continuous wave signals.
  • Coverage Area – Varies depending on power output, terrain, and atmospheric conditions, typically ranging from 15 to 100 nautical miles.
  • Weather Resistance – Designed to operate reliably in various environmental conditions, including storms and electromagnetic interference.
  • Backup Navigation Role – Serves as an alternative navigation aid in case of GPS or VOR system failures.

What are the Applications of Non-Directional Beacon (NDB)?