digplanet beta 1: Athena
Share digplanet:


Applied sciences






















Radio Tower of NKR Leimen-Ochsenbach, Germany
This symbol denotes an NDB on an aeronautical chart. A hollow square superimposed on this symbol indicates a co-located DME installation.

A non-directional (radio) beacon (NDB) is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF omnidirectional range (VOR) and TACAN. NDB signals follow the curvature of the Earth, so they can be received at much greater distances at lower altitudes, a major advantage over VOR. However, NDB signals are also affected more by atmospheric conditions, mountainous terrain, coastal refraction and electrical storms, particularly at long range.

NDBs used for aviation are standardised by ICAO Annex 10 which specifies that NDBs be operated on a frequency between 190 kHz and 1750 kHz,[1] although normally all NDBs in North America operate between 190 kHz and 535 kHz.[1] 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. North American NDBs are categorized by power output, with low power rated at less than 50 watts, medium from 50 W to 2,000 W and high being over 2,000 W.[2]

Automatic direction finder equipment[edit]

NDB navigation consists of two parts — the automatic direction finder (or ADF) equipment on the aircraft that detects an NDB's signal, and the NDB transmitter. The ADF can also locate transmitters in the standard AM medium wave broadcast band (530 kHz to 1700 kHz at 10 kHz increments in the Americas, 531 kHz to 1602 kHz at 9 kHz increments in the rest of the world).

ADF equipment determines the direction to the NDB station relative to the aircraft. This may be displayed on a relative bearing indicator (RBI). This display looks like a compass card with a needle superimposed, except that the card is fixed with the 0 degree position corresponding to the centreline of the aircraft. In order to track toward an NDB (with no wind) the aircraft is flown so that the needle points to the 0 degree position, the aircraft will then fly directly to the NDB. Similarly, the aircraft will track directly away from the NDB if the needle is maintained on the 180 degree mark. With a crosswind, the needle must be maintained to the left or right of the 0 or 180 position by an amount corresponding to the drift due to the crosswind. (Aircraft Heading +/- ADF needle degrees off nose or tail = Bearing to or from NDB station).

The formula to determine the compass heading to an NDB station (in a no wind situation) is to take the relative bearing between the aircraft and the station, and add the magnetic heading of the aircraft; if the total is greater than 360 degrees, then 360 must be subtracted. This gives the magnetic bearing that must be flown: (RB + MH)%360 = MB.

When tracking to or from an NDB, it is also usual that the aircraft track on a specific bearing. To do this it is necessary to correlate the RBI reading with the compass heading. Having determined the drift, the aircraft must be flown so that the compass heading is the required bearing adjusted for drift at the same time as the RBI reading is 0 or 180 adjusted for drift. An NDB may also be used to locate a position along the aircraft track. When the needle reaches an RBI reading corresponding to the required bearing then the aircraft is at the position. However, using a separate RBI and compass, this requires considerable mental calculation to determine the appropriate relative bearing.

To simplify this task a compass card is added to the RBI to form a "Radio Magnetic Indicator" (RMI). The ADF needle is then referenced immediately to the aircraft heading, which reduces the necessity for mental calculation.

The principles of ADFs are not limited to NDB usage; such systems are also used to detect the locations of broadcast signals for many other purposes, such as finding emergency beacons.

Use of non-directional beacons[edit]


NDB transmitter at 49° 12.35' N, 2° 13.20' W. Callsign JW – 'Jersey West'. 329.0 kHz.

A bearing is a line passing through the station that points in a specific direction, such as 270 degrees (due West). NDB bearings provide a charted, consistent method for defining paths aircraft can fly. In this fashion, NDBs can, like VORs, define "airways" in the sky. Aircraft follow these pre-defined routes to complete a flight plan. Airways are numbered and standardized on charts; colored airways are used for low to medium frequency stations like the NDB and are charted in brown on sectional charts. Green and red airways are plotted east and west while amber and blue airways are plotted north and south. There is only one colored airway left in the continental United States. It is located off the coast of North Carolina and is called G13 or Green 13. Alaska is the only other state in the United States to make use of the colored airway systems.[3] Pilots follow these routes by tracking radials across various navigation stations, and turning at some. While most airways in the United States are based on VORs, NDB airways are common elsewhere, especially in the developing world and in lightly populated areas of developed countries, like the Canadian Arctic, since they can have a long range and are much less expensive to operate than VORs.

All standard airways are plotted on aeronautical charts, such as U.S. sectional charts, issued by the National Oceanographic and Atmospheric Administration (NOAA).


NDBs have long been used by aircraft navigators, and previously mariners, to help obtain a fix of their geographic location on the surface of the Earth. Fixes are computed by extending lines through known navigational reference points until they intersect. For visual reference points, the angles of these lines can be determined by compass; the bearings of NDB radio signals are found using RDF equipment.

Airspace Fix Diagram

Plotting fixes in this manner allow crews to determine their position. This usage is important in situations where other navigational equipment, such as VORs with distance measuring equipment (DME), have failed. In marine navigation, NDBs may still be useful should GPS reception fail.

Determining distance from an NDB station[edit]

To determine the distance in relation to an NDB station in nautical miles, the pilot uses this simple method:

  1. Turns the aircraft so that the station is directly off one of the wingtips.
  2. Flies that heading, timing how long it takes to cross a specific number of NDB bearings.
  3. Uses the formula: Time to station = 60 x number of minutes flown / degrees of bearing change
  4. Uses the flight computer to calculate the distance the aircraft is from the station; time * speed = distance

NDB approaches[edit]

A runway equipped with NDB or VOR (or both) as the only navigation aid is called a non-precision approach runway; if it is equipped with ILS it is called a precision approach runway.

Instrument landing systems[edit]

NDBs are most commonly used as markers or "locators" for an instrument landing system (ILS) approach or standard approach. NDBs may designate the starting area for an ILS approach or a path to follow for a standard terminal arrival procedure, or STAR. In the United States, an NDB is often combined with the outer marker beacon in the ILS approach (called a locator outer marker, or LOM); in Canada, low-powered NDBs have replaced marker beacons entirely. Marker beacons on ILS approaches are now being phased out worldwide with DME ranges used instead to delineate the different segments of the approach. German Navy U-boats during World War II were equipped with a Telefunken Spez 2113S homing beacon. This transmitter could operate on 100 kHz to 1500 kHz with a power of 150 W. It was used to send the submarine's location to other submarines or aircraft, which were equipped with DF receivers and loop antennas.[4]


One of the wooden poles of NDB HDL at Plankstadt, Germany
Ferrite antenna for non-directional beacon (NDB), frequency 255 - 526.5 kHz

NDBs typically operate in the frequency range from 190 kHz to 535 kHz (although they are allocated frequencies from 190 to 1750 kHz) and transmit a carrier modulated by either 400 or 1020 Hz. NDBs can also be co-located with a DME in a similar installation for the ILS as the outer marker, only in this case, they function as the inner marker. NDB owners are mostly governmental agencies and airport authorities.

NDB radiators are vertically polarised. NDB antennas are usually too short for resonance at the frequency they operate – typically perhaps 20m length compared to a wavelength around 1000m. Therefore they require a suitable matching network that may consist of an inductor and a capacitor to "tune" the antenna. Vertical NDB antennas may also have a 'top hat', which is an umbrella-like structure designed to add loading at the end and improve its radiating efficiency. Usually a ground plane or counterpoise is connected underneath the antenna.

Other information transmitted by an NDB[edit]

Apart from Morse Code Identity of either 400 Hz or 1020 Hz, the NDB may broadcast:

  • Automatic Terminal Information Service or ATIS
  • Automatic Weather Information Service, or AWIS, or, in an emergency i.e. Air-Ground-Air Communication failure, an Air Traffic Controller using a Press-To-Talk (PTT) function, may modulate the carrier with voice. The pilot uses their ADF receiver to hear instructions from the Tower.
  • Automated Weather Observation System or AWOS
  • Automated Surface Observation System or ASOS
  • Meteorological Information Broadcast or VOLMET
  • Transcribed Weather Broadcast or TWEB
  • PIP monitoring. If an NDB has a problem, e.g. lower than normal power output, failure of mains power or standby transmitter is in operation, the NDB may be programmed to transmit an extra 'PIP' (a Morse dot), to alert pilots and others that the beacon may be unreliable for navigation.

Common adverse effects[edit]

Navigation using an ADF to track NDBs is subject to several common effects:

  • Night effect: radio waves reflected back by the ionosphere can cause signal strength fluctuations 30 to 60 nautical miles (54 to 108 km) from the transmitter, especially just before sunrise and just after sunset (more common on frequencies above 350 kHz)
  • Terrain effect: high terrain like mountains and cliffs can reflect radio waves, giving erroneous readings; magnetic deposits can also cause erroneous readings
  • Electrical effect: electrical storms, and sometimes also electrical interference (from a ground-based source or from a source within the aircraft) can cause the ADF needle to deflect towards the electrical source
  • Shoreline effect: low-frequency radio waves will refract or bend near a shoreline, especially if they are close to parallel to it
  • Bank effect: when the aircraft is banked, the needle reading will be offset

While pilots study these effects during initial training, trying to compensate for them in flight is very difficult; instead, pilots generally simply choose a heading that seems to average out any fluctuations.

Radio-navigation aids must keep a certain degree of accuracy, given by international standards, FAA, ICAO, etc.; to assure this is the case, Flight inspection organizations periodically check critical parameters with properly equipped aircraft to calibrate and certify NDB precision.

Monitoring NDBs[edit]

A PFC QSL card from an NDB

Besides their use in aircraft navigation, NDBs are also popular with long-distance radio enthusiasts ("DXers"). Because NDBs are generally low-power (usually 25 watts, some can be up to 5 kW), they normally cannot be heard over long distances, but favorable conditions in the ionosphere can allow NDB signals to travel much farther than normal. Because of this, radio DXers interested in picking up distant signals enjoy listening to faraway NDBs. Also, since the band allocated to NDBs is free of broadcast stations and their associated interference, and because most NDBs do little more than transmit their Morse Code callsign, they are very easy to identify, making NDB monitoring an active niche within the DXing hobby.

In North America, the NDB band is from 190 to 435 kHz and from 510 to 530 kHz. In Europe, there is a longwave broadcasting band from 150 to 280 kHz, so the European NDB band is from 280 kHz to 530 kHz with a gap between 495 and 505 kHz because 500 kHz was the international maritime distress (emergency) frequency.

The beacons that are between 510 kHz and 530 kHz can sometimes be heard on AM radios that can tune below the beginning of the AM broadcast band. (For example, the "HEH" beacon in Newark, Ohio at 524 kHz is within the bandwidth of most AM radios, the "OS" beacon in Columbus, Ohio at 515 kHz and the "YWA" beacon in Petawawa, Ontario, Canada at 516 kHz can also be heard on some AM radios). Some beacons can also be heard on 530 kHz, although from the adjacent frequencies such as "LYQ" at 529 kHz in Manchester, Tennessee but for the most part, reception of NDBs requires a radio receiver that can receive frequencies below 530 kHz (the longwave band). A NDB in Miramichi, New Brunswick once operated at 530 kHz as "F9" but had later moved to 520 kHz. Most so-called "shortwave" radios also include mediumwave and longwave, and they can usually receive all frequencies from 150 kHz to 30 MHz, which makes them ideal for listening to NDBs. Whilst this type of receiver is adequate for reception of local beacons, specialized techniques (receiver preselectors, noise limiters and filters) are required for the reception of very weak signals from remote beacons.[5]

The best time to hear NDBs that are very far away (i.e. that are "DX") is the last three hours before sunrise. Reception of NDBs is also usually best during the fall and winter because during the spring and summer, there is more atmospheric noise on the LF and MF bands.

See also[edit]


  1. ^ a b "U.S. FAA Aeronautical Information Manual Chapter 1. Section 1. 1-1-2". Retrieved 2008-04-27. 
  2. ^ "ADF (Automatic Direction Finder)". Navigation Systems – Level 3. ALLSTAR Network. May 4, 2008. Retrieved 17 October 2010. 
  3. ^ "FAA Aeronautical Information Manual, 5-3-4. Airways and Route Systems". 
  4. ^ Robert Connolly (December 2010). "Beacon Updates and Frequencies to Try". Radio User 5 (12): 48. ISSN 1748-8117. 
  5. ^ Remington, S., KH6SR (1987–1989). "On the Art of NDB DXing". The Longwave Club of America. Retrieved 2008-01-06. [dead link]

Further reading[edit]

  • International Civil Aviation Organization (2000). Annex 10 — Aeronautical Telecommunications, Vol. I (Radio Navigation Aids) (5th ed.).
  • U.S. Federal Aviation Administration (2004). Aeronautical Information Manual, § 1-1-2.[1]
  • Remington, S., KH6SR (1987–1989). "On the Art of NDB DXing". The Longwave Club of America. Retrieved 2008-01-06. [dead link]
  • Appleyard, S.F.; Linford, R.S. and Yarwood, P.J. (1988). Marine Electronic Navigation (2nd Edition). Routledge & Kegan Paul. pp. 68–69. ISBN 0-7102-1271-2. 
  • Godfrey Manning (December 2007). "Sky High: ADF and NDBs". Radio User (PW Publishing Ltd) 2 (12): 25. ISSN 1748-8117. 
  • Godfrey Manning (January 2008). "Sky High: NDB/ADF". Radio User (PW Publishing Ltd) 3 (1): 24–25. ISSN 1748-8117. 
  • Richard Gosnell (April 2008). "An Introduction to Non Directional Beacons". Radio User (PW Publishing Ltd) 3 (4): 28–29. ISSN 1748-8117. 
  • Robert Connolly (August 2009). "NDB DXing – Understanding the basics". Radio User (PW Publishing Ltd) 4 (8): 40–42. ISSN 1748-8117. 
  • Instrument Procedures Handbook FAA-H-8261-1A. FAA. 2007. pp. 5–60. 

External links[edit]

Original courtesy of Wikipedia: http://en.wikipedia.org/wiki/Non-directional_beacon — Please support Wikipedia.
This page uses Creative Commons Licensed content from Wikipedia. A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia.
2230 videos foundNext > 

Nondirectional Radio Beacon (NDB)

In this tutorial, I am going to go over the basics of NDB's, the associated aircraft and ground based systems, how to use them, and their limitations.

Navigation Using NDB

Using the ADF and NDB together to navigate can seem like a difficult subject, especially when you start reading about it. But, this video explains everything in just a few minutes.

Non-Directional Beacon

The function and purpose of NDB. How it works ? The uses of NDB. Please do like and subscribe our video.-- Created using PowToon -- Free sign up at http://www.powtoon.com/join -- Create animated.

Meet my Non-Directional Beacon (NDB)

This is a Spilsbury-Tindall LWX-100A Mediumwave NDB Transmitter originally intended as a navigational aid to aircraft. Its frequency is 530 kHz, generated by a crystal-controlled carrier oscillator...

Ferrite antenna for Non-directional beacon (NDB) Air navigation

BAZ Spezialantennen, Germany presents: One of the largest ferrite of the world. Dimensions: length 100 cm, diameter of the ferrite 10 cm, weight 16 kg. This ferrite antenna was made for receiving...

Aprenda os procedimentos de uma IAL NDB 2.mpg

Radiofarol (muitas vezes referido pela sigla NDB, de Non-Directional Beacon) é uma estação transmissora especializada, instalada numa posição geográfica fixa e precisamente conhecida,...

Estações NDB "Non-Directional Beacon" com Degen 1103

Log de algumas estações de Radiofarol não-direcional feita no dia 29/07/2014 no município de Ouro Preto MG. Receptor Degen DE1103, antena Ferrite + tecsun AN 200.

Charts lesen - aber richtig! Teil 5: NDB - Non Directional Beacon

In dieser Reihe von Tutorials erklären wir euch den richtigen Umgang mit Charts, was ihr alles daraus lesen könnt und wann sie zum Einsatz kommen. In diesem Video erklären wir euch das Anfliegen.

Non-Directional Beacon NDB NAGOYA 「KC」360kHz

Homer beacon NDB NAGOYA 「KC」360kHz Non-Directional Beacon 指向性無線標識 NDB 名古屋 Kentec BCL-1 Nixie Tube Frequency Counter.

Radio Escuta Farol NDB Brasil Non-Directional Beacon

Radiofarol (muitas vezes referido pela sigla NDB, de Non-Directional Beacon) é uma estação transmissora especializada, instalada numa posição geográfica fixa e precisamente conhecida,...

2230 videos foundNext > 

41 news items

Alaska Public Radio Network
Mon, 08 Dec 2014 12:48:53 -0800

The Federal Aviation Administration is conducting a study on a navigational beacon at the Nome Airport, with the intention of decommissioning the technology. The beacon – dubbed the “Gold” non-directional beacon, in a nod to Nome's gold rush past – is ...
The Island.lk (subscription)
Sun, 14 Dec 2014 12:15:00 -0800

An aeroplane crashed somewhere in the vicinity of Hokandara on Friday, making attempts to land at Ratmalana. First let us address the sadness at an aviator and his crew losing their lives in an accident that is shrouded in mystery. The blame game has ...

The Island.lk (subscription)

The Island.lk (subscription)
Sun, 08 Feb 2015 12:03:45 -0800

There is no radio landing aids available at Ratmalana airport other than a basic NDB (Non Directional Beacon) which is a navigational aid rather than a landing aid. It is highly dangerous and unwise to do a visual landing without any radio landing aid ...
The Island.lk (subscription)
Sun, 07 Dec 2014 12:28:46 -0800

Approach Control acknowledged this message and cleared the aircraft to 2,000ft with instructions to report 'Kilo Alpha Tango' (Katunayake Non-Directional Beacon) or 'airfield in sight'. This message was acknowledged by the aircraft. There was no ...

Airports International Magazine

Airports International Magazine
Thu, 03 Jul 2014 01:37:30 -0700

Control Tower / Airfield Lighting and Navigational Aids including: communication control system, ground receivers, master clock, information management system (2008), telephone system, met wind systems & barometer, glide path, non-directional beacon, ...
Mon, 12 May 2014 06:20:52 -0700

... pilots to climb to a safe altitude while continuing to fly through the valley – roughly along the Inn river – before turning around and following the same flightpath in the opposite direction to a holding area overhead the Rattenberg non ...
The Western Nebraska observer
Wed, 02 Apr 2014 15:52:10 -0700

"Early ELTs, which most civilian aircraft have, is a non-directional beacon which means that it's an omni directional beacon. It sends out a signal all over the place just like AM or FM radio does. So you have to have the device, make a circle, find ...
Air Cargo News.com
Mon, 03 Mar 2014 12:03:45 -0800

With its 2,048 meter runway equipped with ILS (Instrument Landing System) and DVOR/NDB (Doppler Very High Frequency Omni-Directional / Non-Directional Beacon) equipment, UTH can accommodate any aircraft up to 747 types (as a matter of fact, UTH ...

Oops, we seem to be having trouble contacting Twitter

Support Wikipedia

A portion of the proceeds from advertising on Digplanet goes to supporting Wikipedia. Please add your support for Wikipedia!

Searchlight Group

Digplanet also receives support from Searchlight Group. Visit Searchlight