automatic direction finder

Also found in: Acronyms.

automatic direction finder:

see radio rangeradio range,
geographically fixed radio transmitter that radiates coded signals in all directions to enable aircraft and ships to determine their bearings. An aircraft or ship can determine its line of position and drift if it knows its bearing relative to the radio transmitter
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The Columbia Electronic Encyclopedia™ Copyright © 2013, Columbia University Press. Licensed from Columbia University Press. All rights reserved.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Automatic Direction Finder


an aircraft radio direction finder for the automatic location of a bearing on transmitting ground stations. It usually consists of a receiver-indicator device coupled with a tracking system and two antennas—a directional loop and a nondirectional single wire antenna.

The signals from the radio station on which a bearing is being taken are received by both antennas and combined: the signal from the loop is switched with the frequency of a reference generator, producing an amplitude-modulated voltage at the receiver input. By comparing the voltages at the outputs of the receiver and the reference generator, an error signal is produced and then fed to the tracking system. The tracking system automatically rotates the loop to the position of minimum signal, which coincides with the bearing of the radio station. Sensors detect the angle of rotation of the loop and transmit it to an indicator with a pointer showing the relative angle of the radio station, that is, the angle between the longitudinal axis of the aircraft and the direction to the radio station.

Automatic direction finders generally operate with non-directional radio beacons, less often with other types, such as radio broadcast stations. Such devices make it possible to guide aircraft to the vicinity of an airfield, make a landing approach, and solve other navigational problems.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

automatic direction finder

[¦ȯd·ə¦mad·ik di′rek·shən ‚fīnd·ər]
A direction finder that without manual manipulation indicates the direction of arrival of a radio signal. Abbreviated ADF. Also known as radio compass.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

automatic direction finder (ADF)

automatic direction finder (ADF)click for a larger image
Equipment to determine the direction from which an electromagnetic signal is being generated. It can either be airborne or ground-based equipment. It operates in medium or low frequencies, consists of basically a loop aerial, and gives the null position of the transmitter. To remove 180° ambiguity, a sense aerial is used. The commonest air-interpreted ADF is the one that utilizes a ground-based transmitting station called an NDB (nondirectional beacon).
An Illustrated Dictionary of Aviation Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved
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