NationMaster - Encyclopedia: Direction finding

Direction finding (DF) refers to the establishment of the direction from which a received signal was transmitted. This can refer to radio or other forms of wireless communication. By combining the direction information from two or more suitably spaced receivers, the source of a transmission may be located in space via triangulation. This is called a cross-cut or fix. In radio terminology, a receiver is an electronic circuit that receives a radio signal from an antenna and decodes the signal for use as sound, pictures, navigational-position information, etc. ... Triangulation can be used to find the distance from the shore to the ship. ...

Direction finding often requires an antenna that is directional - that is, more sensitive in certain directions than in others. Many antenna designs exhibit this property. For example, a Yagi antenna has quite pronounced directionality, so the source of a transmission can be determined simply by pointing it in the direction where the maximum signal level is obtained. However, to establish direction to great accuracy requires much more sophisticated techniques. A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... A Yagi-Uda antenna. ...

A simple form of directional antenna is the loop aerial. This consists of an open loop of wire on an insulating former, or a metal ring that forms the antenna elements itself, where the diameter of the loop is a tenth of a wavelength or smaller at the target frequency. Such an antenna will be LEAST sensitive to signals that are normal to its face, and MOST responsive to those meeting edge-on, this due to the antenna sensing the difference between the volages induced either side of it at any instant because of the phase output of the transmitting beacon. Turning the loop face on, will not induce any current flow (think of the radio wave slipping through the loop), ( Simply by turning the antenna to obtain minimum signal will establish two possible directions that the signal could be emanating from). The NULL is used, as small angular deflections of the loop aerial near its null positions produce larger changes in current than similar angular changes near the loops max positions. For this reason, a null position of the loop aerial is used. To resolve the two direction possibilities, a sense antenna is used, the sense aerial has no directional properties but has the same sensitivety as the loop aerial. By adding the steady signal from the sense aerial to the alternating signal from the loop signal as it rotates, there is now only one position as the loop rotates 360 Degs at which there is zero current. This acts as a phase ref point, allowing the correct null point to be identified, thus removing the 180 Deg ambiguity. A dipole antenna exhibits similar properties, and is the basis for the Yagi antenna, which is familiar as the common VHF or UHF television aerial. For much higher frequencies still, parabolic antennas can be used, which are highly directional, focusing received signals from a very narrow angle to a receiving element at the centre. A wire is a single, usually cylindrical, elongated strand of drawn metal. ... // The Earths magnetic field, which is approximately a dipole. ... Very high frequency (VHF) is the radio frequency range from 30 MHz to 300 MHz. ... This article is about the radio frequency. ... It has been suggested that Analyzing the parabola be merged into this article or section. ...

More sophisticated techniques such as phased arrays are generally used for highly accurate direction finding such as that used in signals intelligence (SIGINT). A helicopter based DF system was designed by ESL Incorporated for the U.S. Government as early as 1972. A giant phased-array radar in Alaska In telecommunication, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and... SIGINT stands for SIGnals INTelligence, which is intelligence-gathering by interception of signals, whether by radio interception or other means. ... Robinson Helicopter Company (USA) R44, a four seat development of the R22 A helicopter is an aircraft which is lifted and propelled by one or more horizontal rotors, each having two or more rotor blades. ... ESL Incorporated is a high technology U.S. firm engaged in software design, systems analysis and hardware development for the strategic reconnaissance marketplace. ...

For the purpose of direction finding, large "Iron Horse" worldwide network of FLR-9 antennas was built during the Cold War. The AN/FLR-9 is a type of very large circular Wullenweber antenna array, built at many locations during the cold war to gather signals for western signals intelligence (SIGINT), . The world-wide network, known collectively as Iron Horse, could eavesdrop on HF communications from almost anywhere on the planet. ... The Cold War was the period of protracted conflict and competition between the United States and the Soviet Union and their allies from the late 1940s until the late 1980s. ...

Some academic research has centered on the use of software-defined radios to perform the DF operations using receiveres with one or more separate channels in conjunction with multiple antenna arrays. A software-defined radio (SDR) system is a radio communication system which uses software for the modulation and demodulation of radio signals. ...

1 Single Channel DF
- 1.1 Pseudo-Doppler DF Technique
- 1.2 Watson-Watt w/ Adcock Antenna Array
2 Usage
3 See also
4 Related Links

Single Channel DF

Single-channel DF refers to the use of a multi-antenna array with a single channel radio receiver. This approach to DF obviously offers some advantages and drawbacks. Since it only uses one receiver, mobility and lower power consumption are obvious benefits but without the ability to look at each antenna simultaneously (which would be the case is one were to use multiple receivers) more complex operations need to occur at the antenna in order to present the signal to the receiver.

The two main categories that a single channel DF algorithm falls into are amplitude comparison and phase comparison. Some algorithms can be hybrids of the two.

Pseudo-Doppler DF Technique

The pseudo-doppler technique is a phase based DF method that produces a bearing estimate on the received signal by measuring the doppler shift induced on the signal by sampling around the elements of a circular array. The original method used a single antenna that physically moved in a circle but the modern approach uses a multi-antenna circular array with each antenna sampled in succession. The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ...

Watson-Watt w/ Adcock Antenna Array

The Watson-Watt technique uses two Adcock antenna pairs to perform an amplitude comparison on the incoming signal. An Adcock antenna pair is a pair of monopole or dipole antennas that takes the vector difference of the received signal at each antenna so that there is only one output from the pair of antennas. Two of these pairs are co-located but perpendicularly oriented to produce what can be referred to as the N-S (North-South) and E-W (East-West) signals that will then be passed to the receiver. In the receiver, the bearing angle can then be computed by taking the arctangent of the ratio of the N-S to E-W signal. In mathematics, the trigonometric functions are functions of an angle, important when studying triangles and modeling periodic phenomena. ...

Usage

Radio direction finder, or RDF, is a term used to describe a navigational device for finding the direction to a radio transmitter source. RDF was once the primary form of aircraft navigation, and strings of beacons were used to form "airways" from airport to airport. In the 1950s, these systems were generally being replaced by the VOR system, in which the angle to the beacon can be measured from the signal itself, with no moving parts. Since the signal being broadcast in the RDF system is non-directional, these older beacons were referred to as non-directional beacons, or NDB in the aviation world. Today, all such systems are being generally removed in favour of the GPS system. In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ... This page discusses Beacons, fires designed to attract attention. ... D-VOR (Doppler VOR) ground station, co-located with DME. VOR, short for VHF Omni-directional Radio Range, is a type of radio navigation system for aircraft. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... A non-directional beacon (NDB) is a radio broadcast station in a known location, used as an aviation or marine navigational aid. ... Aviation refers to flying using aircraft, machines designed by humans for atmospheric flight. ... Over fifty GPS satellites such as this NAVSTAR have been launched since 1978. ...

Disaster response

There are many forms of radio transmitters designed to transmit as a beacon in the event of an emergency, which are widely deployed on civil aircraft. Modern emergency beacons transmit a unique identification signal that can aid in finding the exact location of the transmitter. In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ... Emergency position-indicating Radio beacons (EPIRB), Emergency Locator Transmitters (ELT) and Personal Locator Beacons, are tracking transmitters that operate as part of the Cospas-Sarsat Satellite System [1]. When activated, the beacons send out a distress signal that allows the beacon to be located by the satellite system and search... An Airbus A380, currently the worlds largest airliner An aircraft is any vehicle or craft capable of atmospheric flight. ...

Wildlife tracking

Location of radio-tagged animals by triangulation is a widely applied research technique for studying the movement of animals. The technique was first used in the early 1960s, when the technology used in radio transmitters and batteries made them small enough to attach to wild animals, and is now widely deployed for a variety of wildlife studies. Most tracking of wild animals that have been affixed with radio transmitter equipment is done by a field researcher using a handheld radio direction finding device. When the researcher wants to locate a particular animal, the location of the animal can be triangulated by determining the direction to the transmitter from several locations. Triangulation can be used to find the distance from the shore to the ship. ... Phyla Subregnum Parazoa Porifera Subregnum Eumetazoa Placozoa Orthonectida Rhombozoa Radiata (unranked) Ctenophora Cnidaria Bilateria (unranked) Acoelomorpha Myxozoa Superphylum Deuterostomia Chordata Hemichordata Echinodermata Chaetognatha Xenoturbellida Superphylum Ecdysozoa Kinorhyncha Loricifera Priapulida Nematoda Nematomorpha Onychophora Tardigrada Arthropoda Superphylum Platyzoa Platyhelminthes Gastrotricha Rotifera Acanthocephala Gnathostomulida Micrognathozoa Cycliophora Superphylum Lophotrochozoa Sipuncula Nemertea Phoronida Ectoprocta Bryozoa... In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ... This does not cite its references or sources. ... Wild, in zoology or botany, is a rough if problematic antonym to domesticated: see wildlife. ...

Reconnaissance

Phased arrays and other advanced antenna techniques are utilized to track launches of rocket systems and their resulting trajectories. These systems can be used for defensive purposes and also to gain intelligence on operation of missiles belonging to other nations. These same techniques are used for detection and tracking of conventional aircraft. A giant phased-array radar in Alaska In telecommunication, a phased array is a group of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and... A Yagi-Uda beam antenna Short Wave Curtain Antenna (Moosbrunn, Austria) A building rooftop supporting numerous dish and sectored mobile telecommunications antennas (Doncaster, Victoria, Australia) An antenna or aerial is an arrangement of aerial electrical conductors designed to transmit or receive radio waves which is a class of electromagnetic waves. ... A Redstone rocket, part of the Mercury program The traditional definition of a rocket is a vehicle, missile or aircraft which obtains thrust by the reaction to the ejection of fast moving fluid from within a rocket engine. ... Exocet missile in flight A missile (see also pronunciation differences) is a projectile propelled as a weapon at a target. ... An Airbus A380, currently the worlds largest airliner An aircraft is any vehicle or craft capable of atmospheric flight. ...

Sport

Events hosted by groups and organizations that involve the use of radio direction finding skills to locate transmitters at unknown locations have been popular since the end of World War II. Many of these events were first promoted in order to practice the use of radio direction finding techniques for disaster response and civil defense purposes, or to practice locating the source of radio frequency interference. The most popular form of the sport, worldwide, is known as Amateur Radio Direction Finding or by its international acronym ARDF. Another form of the activity, known as "transmitter hunting", "mobile T-hunting," or "fox hunting" takes place in a larger geographic area, such as the metropolitan area of a large city, and most participants travel in motor vehicles while attempting to locate one or more radio transmitters with radio direction finding techniques. Combatants Major Allied powers: United Kingdom Soviet Union United States Republic of China and others Major Axis powers: Nazi Germany Italy Japan and others Commanders Winston Churchill Joseph Stalin Franklin Roosevelt Harry Truman Chiang Kai-Shek Adolf Hitler Benito Mussolini Hideki Tojo Casualties Military dead: 17,000,000 Civilian dead... The UK organisation for the provision of Disaster Response by Radio amateurs is called RAYNET. More information on RAYNET and the services it provides can be found at http://www. ... The old United States civil defense logo. ... Radio Frequency Interference (RFI) is electromagnetic radiation which is emitted by electrical circuits carrying rapidly changing signals, as a by-product of their normal operation, and which causes unwanted signals (interference or noise) to be induced in other circuits. ... A German competitor on a two-meter ARDF course. ... Transmitter hunting is an activity wherein participants use radio direction finding techniques to locate one or more radio transmitters hidden within a designated search area. ... In communications and information processing, a transmitter (sometimes abbreviated XMTR) is an object (source) which sends information to an observer (receiver). ...

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