Direction finding

radio direction findingradio direction-findingdirection-findingRDFDFAutomatic Radio Direction FinderD/F loopDF radioDF-ingdirection find
Direction finding (DF), or radio direction finding (RDF), is the measurement of the direction from which a received signal was transmitted.wikipedia
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Radar

radar stationradarsradar system
This can refer to radio or other forms of wireless communication, including radar signals detection and monitoring (ELINT/ESM).
Through his lightning experiments, Watson-Watt became an expert on the use of radio direction finding before turning his inquiry to shortwave transmission.

Chain Home

Daventry Experimentearly warning Chain Home radar system
In fact, the Chain Home systems used large RDF receivers to determine directions.
From the earliest days of radio technology, signals had been used for navigation using the radio direction finding (RDF) technique.

Loop antenna

loopstick antennasloop aerialloopstick antenna
A simple form of directional antenna is the loop aerial.
Due to this directional pattern they are used for radio direction finding (RDF), to locate the position of a transmitter.

Robert Watson-Watt

Robert Watson WattRobert WattRobert Alexander Watson-Watt
The Watson-Watt technique uses two Adcock antenna pairs to perform an amplitude comparison on the incoming signal.
Sir Robert Alexander Watson-Watt, KCB, FRS, FRAeS (13 April 1892 – 5 December 1973) was a British pioneer of radio direction finding and radar technology.

Signals intelligence

SIGINTELINTelectronic intelligence
For the military, RDF is a key tool of signals intelligence.
Traffic analysis is the discipline of drawing patterns from information flow among a set of senders and receivers, whether those senders and receivers are designated by location determined through direction finding, by addressee and sender identifications in the message, or even MASINT techniques for "fingerprinting" transmitters or operators.

Triangulation

triangulatetriangulatedtriangulating
By combining the direction information from two or more suitably spaced receivers (or a single mobile receiver), the source of a transmission may be located via triangulation.

Radio

radio communicationradio communicationswireless
This can refer to radio or other forms of wireless communication, including radar signals detection and monitoring (ELINT/ESM).

VHF omnidirectional range

VORDVORVHF omni-directional range
Starting in the 1950s, these beacons were generally replaced by the VOR system, in which the bearing to the navigational aid is measured from the signal itself; therefore no specialized antenna with moving parts is required.
The intersection of radials from two different VOR stations can be used to fix the position of the aircraft, as in earlier radio direction finding (RDF) systems.

Radio direction finder

automatic direction finderdirection finderradio compass
An automatic direction finder, which could be tuned to radio beacons called non-directional beacons or commercial AM radio broadcasters, was until recently, a feature of most aircraft, but is now being phased out
Pseudo-doppler radio direction finder systems use a series of small dipole antennas arranged in a ring and use electronic switching to rapidly select dipoles to feed into the receiver.

Non-directional beacon

NDBNDB approachnon-directional beacon (NDB)
An automatic direction finder, which could be tuned to radio beacons called non-directional beacons or commercial AM radio broadcasters, was until recently, a feature of most aircraft, but is now being phased out

Amateur radio direction finding

ARDFfox huntingfoxhunts
The most popular form of the sport, worldwide, is known as Amateur Radio Direction Finding or by its international abbreviation ARDF.
Amateur radio direction finding (ARDF, also known as radio orienteering, radio fox hunting and radiosport) is an amateur racing sport that combines radio direction finding with the map and compass skills of orienteering.

Transmitter hunting

foxhuntTransmitter Hunts
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.
Transmitter hunting (also known as T-hunting, fox hunting, bunny hunting, and bunny chasing), is an activity wherein participants use radio direction finding techniques to locate one or more radio transmitters hidden within a designated search area.

MUSIC (algorithm)

MUltiple SIgnal ClassificationMUSICMUSIC (Multiple Signal Classification)
MUSIC (MUltiple SIgnal Classification) is an algorithm used for frequency estimation and radio direction finding.

Amplitude-comparison monopulse

amplitude monopulseamplitude comparison
Amplitude-comparison monopulse refers to a common direction finding technique.

Avalanche transceiver

avalanche beaconavalanche beaconsavalanche transceivers
Avalanche transceivers operate on a standard 457 kHz, and are designed to help locate people and equipment buried by avalanches.
Following an avalanche, and if the holder of the transceiver is safe and has not themselves been caught by the avalanche, they may switch the transceiver from transmit into receive mode, allowing use as a radio direction finding device to search for signals coming from other skiers' transceiver who may be trapped.

Radio beacon

Electric beaconradio beaconsbeacon
Radio beacons transmit a radio signal which is picked up by radio direction finding systems on ships, aircraft and vehicles to determine the direction to the beacon.

Yagi–Uda antenna

Yagi antennaYagi-Uda antennaYagi
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.

Captain-class frigate

Captain-classCaptain class frigateCaptain class
The Royal Navy also deployed direction finding equipment on ships tasked to anti-submarine warfare in order to try to locate German submarines, e.g. Captain class frigates were fitted with a medium frequency direction finding antenna (MF/DF) (the antenna was fitted in front of the bridge) and high frequency direction finding (HF/DF, "Huffduff") Type FH 4 antenna (the antenna was fitted on top of the mainmast).
A medium frequency direction finding antenna (MF/DF) was fitted in front of the bridge and a high-frequency direction finding (HF/DF, "Huffduff") Type FH 4 antenna was fitted on top of the mainmast; furthermore, a radio-receiving set tuned to the frequencies used for ship-to-ship communication by German U-boats and E-boats was fitted and a German-speaking rating carried.

Wullenweber

Circularly Disposed Antenna ArrayCDAAElephant Cage
It is a large circular antenna array used for radio direction finding.

MI8

Radio Security ServiceRSS
The work was undertaken by the Radio Security Service (RSS also MI8).
RSS also established a series of Radio Direction Finding stations, in the far corners of the British Isles, to identify the locations of the intercepted transmissions.

Emergency position-indicating radiobeacon station

EPIRBemergency locator transmitterEmergency Position-Indicating Radio Beacon
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.
SAR authorities have no way of knowing whether a 121.5 MHz/243.0 MHz signal is actually a distress signal until they physically deploy to the location and home in on the source (and sound) of the transmission.

Phase-comparison monopulse

Phase interferometrymonopulsephase
Phase-comparison monopulse (also called phase-interferometry) describes a technique that can be used in radar and direction finding applications to accurately estimate the direction of arrival of a signal from the phase difference of the signal measured on two (or more) separated antennas.

AN/FRD-10

AN/FRD-10A(V)Classic BullseyePUSHER
The AN/FRD-10 Circularly Disposed Antenna Array (CDAA) was a United States Navy circular "Wullenweber" antenna array, built at a number of locations during the cold war for high frequency radio direction finding (HF/DF) and signals intelligence.

Geolocation

geo-locationgeolocateGeoIP
This is in contrast to earlier radiolocation technologies, for example Direction Finding where a line of bearing to a transmitter is achieved as part of the process.