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Non Directional Beacon (NDB) System


Non-Directional Beacon (NDB) transmitters are ground-based, radio transmitters operate in MW band between 190-1250 KHz and 1600-1800 KHz.

A NDB normally would be installed along side of landing strips of airports or in a location closed to a helipad. The main function of NDB is to transmit an omni-directional location signal (beacon) with an assigned identification code. Pilots of approaching airplanes or helicopters receive the transmitted signal using a MW receiver called Automatic Direction Finder (ADF) to located the destination airport or helipad. The ADF determines the relative NDB direction to the aircraft. The ADF needs to be tuned on NDB frequency to indicate the heading to the land station. The ADF or Automatic Direction Finder simply consists of a needle which points toward the NDB.

NDBs signal should be normally transmitted on an uninterrupted 24/7 basis. An audible Morse Code call sign of one or more letters or numbers is used to identify the NDB being received. This code helps the pilots confirm that they are tuned to the right frequency.

NDB’s used for aviation are standardized by ICAO, the International Civil Aviation Organization, Annex 10 which specifies that NDB be operated on a frequency between 190 to 1800 kHz. According to ICAO a Non Directional Beacon System should be operational in every registered airport. Also Offshore NDBs were first introduced during early years of petroleum exploration and have become standard equipment on offshore platforms and drill ships to provide highly reliable navigation for helicopter pilots and ADF-equipped crew boats as they support crews on drilling and production platforms

A Non Directional Beacon (NDB) station normally consists of three main components:

• NDB Transmitter
• Antenna Tuning Unit (ATU)
• Antenna

In some applications Remote Control Units (RCUs) and Monitoring Receiver would be also used to control and monitor NDB operations from a remote location. The range of the beacon will depend on the type of antenna used, the location of the installation; the RF power supplied to the antenna, and the operating frequency and ground conductivity. Effective coverage also varies according to the time of day and the season of the year. Correct installation of a NDB system is a key factor in system efficiency. Antenna tuning and matching to the transmitter to keep the VSWR at the lowest possible level close to 1 is essential in any NDB system installation.


An installed NDB systems may have limited Signal because of several factors including:

• Interference Effect
• Thunderstorm Effect
• Mountain Effect
• Night Effect
• Coastal Refractions

TASHKOO engineers are skilled and trained and have experiences to design different components of a NDB station based on customer requirements and environmental situations. This would guarantee system performance and reliability for the system life cycle. NDB systems typically provide decades of uninterrupted service.


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