Operational Notes on Non-Directional Beacons (NDB) and Associated Automatic Direction Finding (ADF) 1. Introduction These notes are a reproduction of a booklet originally 1-1 published by the Civil Aviation Authority 1. Introduction The non-directional beacon and its associated automatic direction finding equipment is. Non-Directional Beacons (NDBs) are today (c.2017) still the most common type of radio beacon found in Australia because of their simplicity and relative cheapness. NDBs are essentially a simple radio transmitter which radiates a signal equally in every direction (hence 'non-directional').

Non Directional Beacon Ndb
Non Directional Beacon List

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.

Non-Directional Beacon (NDB) Systems Interface is a leading supplier and installer of Non-Directional-Radio Beacons ( NDB s) around the world. NDB s have continued to provide a fundamental and reliable means of aircraft navigation despite the arrival of GNSS and modern ground based systems.

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]

2Use of non-directional beacons
3Technical

Automatic direction finder equipment

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 AMmedium 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 or bearing to the NDB station relative to the aircraft by using a combination of directional and non-directional antennae to sense the direction in which the combined signal is strongest. This bearing 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's current track (such as a radial path from a second NDB or a VOR). 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 driven by the aircraft's magnetic compass is added to the RBI to form a 'Radio Magnetic Indicator' (RMI). The ADF needle is then referenced immediately to the aircraft's magnetic heading, which reduces the necessity for mental calculation. Many RMIs used for aviation also allow the device to display information from a second radio tuned to a VOR station; the aircraft can then fly directly between VOR stations (so-called 'Victor' routes) while using the NDBs to triangulate their position along the radial, without the need for the VOR station to have a co-located DME. This display, along with the 'Omni Bearing Indicator' for VOR/ILS information, was one of the primary radionavigation instruments prior to the introduction of the Horizontal Situation Indicator and subsequent digital displays used in glass cockpits.

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

Airways

File:JW NDB transmitter 329.0kHz.jpg

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 CanadianArctic, 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).

Fixes

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.

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

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

Turns the aircraft so that the station is directly off

Non Directional Beacon Installation