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98-429: The AN/FLR-9 Operation and Service Manual describes the array as follows: The antenna array is composed of three concentric rings of antenna elements. Each ring of elements receives RF signals for an assigned portion of the 1.5 to 30-MHz radio spectrum. The outer ring normally covers the 2 to 6-MHz range (band A), but also provides reduced coverage down to 1.5 MHz. The center ring covers the 6 to 18-MHz range (band B) and

196-624: A common center point. A movable switch could connect opposite pairs of these wires to form a dipole, and by rotating the switch the operator could hunt for the strongest signal. The US Navy overcame this problem, to a point, by mounting antennas on ships and sailing in circles. Such systems were unwieldily and impractical for many uses. A key improvement in the RDF concept was introduced by Ettore Bellini and Alessandro Tosi in 1909 (U.S. Patent 943,960). Their system used two such antennas, typically triangular loops, arranged at right angles. The signals from

294-530: A directional antenna is used which 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 by pointing it in the direction where the maximum signal level is obtained. Since the directional characteristics can be very broad, large antennas may be used to improve precision, or null techniques used to improve angular resolution. A simple form of directional antenna

392-503: A directional antenna pattern, then the amplitude may be included in the comparison. Typically, the correlative interferometer DF system consists of more than five antenna elements. These are scanned one after the other via a specific switching matrix. In a multi-channel DF system n antenna elements are combined with m receiver channels to improve the DF-system performance. Radio direction finding , radio direction finder , or RDF ,

490-497: A discipline overlapping with ES, is the related process of analyzing and identifying intercepted transmissions from sources such as radio communication, mobile phones , radar , or microwave communication . SIGINT is broken into two categories: electronic intelligence ( ELINT ) and communications intelligence ( COMINT ). Analysis parameters measured in signals of these categories can include frequency , bandwidth , modulation , and polarization . The distinction between SIGINT and ES

588-441: A few tens of kilometres. For aircraft, where the horizon at altitude may extend to hundreds of kilometres, higher frequencies can be used, allowing much smaller antennas. An automatic direction finder, often capable of being tuned to commercial AM radio transmitters, is a feature of almost all modern aircraft. For the military, RDF systems are a key component of signals intelligence systems and methodologies. The ability to locate

686-639: A fleet of mobile DF vehicles around the UK. If a transmitter was identified by the fixed DF stations or voluntary interceptors, the mobile units were sent to the area to home in on the source. The mobile units were HF Adcock systems. By 1941 only a couple of illicit transmitters had been identified in the UK; these were German agents that had been "turned" and were transmitting under MI5 control. Many illicit transmissions had been logged emanating from German agents in occupied and neutral countries in Europe. The traffic became

784-437: A known wave angle (reference data set). For this, at least three antenna elements (with omnidirectional reception characteristics) must form a non-collinear basis. The comparison is made for different azimuth and elevation values of the reference data set. The bearing result is obtained from a correlative and stochastic evaluation for which the correlation coefficient is at a maximum. If the direction finding antenna elements have

882-510: A landfall. In the United States, commercial AM radio stations were required to broadcast their station identifier once per hour for use by pilots and mariners as an aid to navigation. In the 1950s, aviation NDBs were augmented by the VOR system, in which the direction to the beacon can be extracted from the signal itself, hence the distinction with non-directional beacons. Use of marine NDBs

980-459: A measure used to protect against an electronic enemy attack (EA) or to protect against friendly forces who unintentionally deploy the equivalent of an electronic attack on friendly forces. (sometimes called EW fratricide ). The effectiveness of electronic protection (EP) level is the ability to counter an electronic attack (EA). Flares are often used to distract infrared homing missiles into missing their target. The use of flare rejection logic in

1078-399: A multiple channel receiver system. One form of radio direction finding works by comparing the signal strength of a directional antenna pointing in different directions. At first, this system was used by land and marine-based radio operators, using a simple rotatable loop antenna linked to a degree indicator. This system was later adopted for both ships and aircraft, and was widely used in

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1176-524: A number of radio DF units located at civil and military airports and certain HM Coastguard stations. These stations can obtain a "fix" of the aircraft and transmit it by radio to the pilot. Radio transmitters for air and sea navigation are known as beacons and are the radio equivalent to a lighthouse . The transmitter sends a Morse Code transmission on a Long wave (150 – 400 kHz) or Medium wave (520 – 1720 kHz) frequency incorporating

1274-465: A number of small antennas fixed to a circular card, with all of the processing performed by software. Early British radar sets were also referred to as RDF, which was a deception tactic. However, the terminology was not inaccurate; the Chain Home systems used separate omnidirectional broadcasters and large RDF receivers to determine the location of the targets. In one type of direction finding,

1372-456: A ring and use electronic switching to rapidly select dipoles to feed into the receiver. The resulting signal is processed and produces an audio tone. The phase of that audio tone, compared to the antenna rotation, depends on the direction of the signal. Doppler RDF systems have widely replaced the huff-duff system for location of fleeting signals. The various procedures for radio direction finding to determine position at sea are no longer part of

1470-598: A small loop's null. For much higher frequencies still, such as millimeter waves and microwaves , parabolic antennas or "dish" antennas can be used. Dish antennas are highly directional, with the parabolic shape directing received signals from a very narrow angle into a small receiving element mounted at the focus of the parabola. More sophisticated techniques such as phased arrays are generally used for highly accurate direction finding systems. The modern systems are called goniometers by analogy to WW II directional circuits used to measure direction by comparing

1568-430: A suitable oscilloscope, and he presented his new system in 1926. In spite of the system being presented publicly, and its measurements widely reported in the UK, its impact on the art of RDF seems to be strangely subdued. Development was limited until the mid-1930s, when the various British forces began widespread development and deployment of these " high-frequency direction finding ", or "huff-duff" systems. To avoid RDF,

1666-460: A valuable source of intelligence, so the control of RSS was subsequently passed to MI6 who were responsible for secret intelligence originating from outside the UK. The direction finding and interception operation increased in volume and importance until 1945. Electronic warfare Electromagnetic warfare or electronic warfare ( EW ) is warfare involving the use of the electromagnetic spectrum (EM spectrum) or directed energy to control

1764-489: A wider electronic warfare suite. Several distinct generations of RDF systems have been used over time, following new developments in electronics. Early systems used mechanically rotated antennas that compared signal strengths from different directions, and several electronic versions of the same concept followed. Modern systems use the comparison of phase or doppler techniques which are generally simpler to automate. Modern pseudo-Doppler direction finder systems consist of

1862-755: Is a practice range that provides training for personnel operating in electronic warfare. There are two examples of such ranges in Europe : one at RAF Spadeadam in the northwest county of Cumbria , England, and the Multinational Aircrew Electronic Warfare Tactics Facility Polygone range on the border between Germany and France. EWTRs are equipped with ground-based equipment to simulate electronic warfare threats that aircrew might encounter on missions. Other EW training and tactics ranges are available for ground and naval forces as well. Antifragile EW

1960-624: Is a step beyond standard EP, occurring when a communications link being jammed actually increases in capability as a result of a jamming attack, although this is only possible under certain circumstances such as reactive forms of jamming. Electronic warfare support (ES) is a subdivision of EW involving actions taken by an operational commander or operator to detect, intercept, identify, locate, and/or localize sources of intended and unintended radiated electromagnetic (EM) energy. These Electronic Support Measures (ESM) aim to enable immediate threat recognition focuses on serving military service needs even in

2058-485: Is a suite of countermeasure systems fitted primarily to aircraft for the purpose of protecting the host from weapons fire and can include, among others: directional infrared countermeasures ( DIRCM , flare systems and other forms of infrared countermeasures for protection against infrared missiles; chaff (protection against radar-guided missiles); and DRFM decoy systems (protection against radar-targeted anti-aircraft weapons). An electronic warfare tactics range (EWTR)

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2156-901: Is addressing the other NATO defense lines of development. Primary EW activities have been developed over time to exploit the opportunities and vulnerabilities that are inherent in the physics of EM energy . Activities used in EW include electro-optical, infrared and radio frequency countermeasures; EM compatibility and deception; radio jamming , radar jamming and deception and electronic counter-countermeasures (or anti-jamming); electronic masking, probing, reconnaissance, and intelligence; electronic security; EW reprogramming; emission control; spectrum management; and wartime reserve modes. Electronic warfare consists of three major subdivisions: electronic attack (EA), electronic protection (EP), and electronic warfare support (ES). Electronic attack (EA), also known as electronic countermeasures (ECM), involves

2254-513: Is an element of information warfare; more specifically, it is an element of offensive and defensive counterinformation. NATO has a different and arguably more encompassing and comprehensive approach to EW. A military committee conceptual document from 2007, MCM_0142 Nov 2007 Military Committee Transformation Concept for Future NATO Electronic Warfare , recognised the EME as an operational maneuver space and warfighting environment/domain. In NATO, EW

2352-795: Is considered to be warfare in the EME. NATO has adopted simplified language which parallels those used in other warfighting environments like maritime, land, and air/space. For example, an electronic attack (EA) is offensive use of EM energy, electronic defense (ED), and electronic surveillance (ES). The use of the traditional NATO EW terms, electronic countermeasures (ECM), electronic protective measures (EPM), and electronic support measures (ESM) has been retained as they contribute to and support electronic attack (EA), electronic defense (ED) and electronic surveillance (ES). Besides EW, other EM operations include intelligence, surveillance, target acquisition and reconnaissance (ISTAR), and signals intelligence (SIGINT). Subsequently, NATO has issued EW policy and doctrine and

2450-454: Is determined by the controller of the collection assets, the information provided, and the intended purpose of the information. Electronic warfare support is conducted by assets under the operational control of a commander to provide tactical information, specifically threat prioritization, recognition, location, targeting, and avoidance. However, the same assets and resources that are tasked with ES can simultaneously collect information that meets

2548-457: Is known as radio direction finding or sometimes simply direction finding ( DF ). Using two or more measurements from different locations, the location of an unknown transmitter can be determined; alternately, using two or more measurements of known transmitters, the location of a vehicle can be determined. RDF is widely used as a radio navigation system, especially with boats and aircraft. RDF systems can be used with any radio source, although

2646-517: Is now only one position as the loop rotates 360° at which there is zero current. This acts as a phase reference point, allowing the correct null point to be identified, removing the 180° ambiguity. A dipole antenna exhibits similar properties, as a small loop, although its null direction is not as "sharp". The Yagi-Uda antenna is familiar as the common VHF or UHF television aerial. A Yagi antenna uses multiple dipole elements, which include "reflector" and "director" dipole elements. The "reflector"

2744-428: Is often stated was a deception. In fact, the Chain Home systems used large RDF receivers to determine directions. Later radar systems generally used a single antenna for broadcast and reception, and determined direction from the direction the antenna was facing. The earliest experiments in RDF were carried out in 1888 when Heinrich Hertz discovered the directionality of an open loop of wire used as an antenna. When

2842-409: Is the loop aerial . This consists of an open loop of wire on an insulating frame, or a metal ring that forms the antenna's loop element itself; often 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 perpendicular to its face and most responsive to those arriving edge-on. This is caused by the phase of

2940-452: Is the longest dipole element and blocks nearly all the signal coming from behind it, hence a Yagi has no front vs. back directional ambiguity: The maximum signal only occurs when the narrowest end of the Yagi is aimed in the direction from which the radio waves are arriving. With a sufficient number of shorter "director" elements, a Yagi's maximum direction can be made to approach the sharpness of

3038-446: Is the use of radio waves to determine the direction to a radio source. The source may be a cooperating radio transmitter or may be an inadvertant source, a naturally-occurring radio source, or an illicit or enemy system. Radio direction finding differs from radar in that only the direction is determined by any one receiver; a radar system usually also gives a distance to the object of interest, as well as direction. By triangulation ,

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3136-693: The Bayraktar TB2 had a life expectancy of about six flights. By summer 2022, only some one-third of Ukrainian UAV missions could be said to have been successful, as EW had contributed to Ukraine losing 90% of the thousands of drones it had at the beginning of the invasion. Russian EW capacity to disrupt GPS signals is credited with the reduction in the success of Ukrainian usage of HIMARS and JDAM bombs. The failure of GPS guidance forces these weapons, in particular JDAMS, to use inertial navigation system which reduces accuracy from around 5 metres (15 ft) down to around 27 metres (90 ft). Ukraine

3234-531: The Euphrates River , modeled after a North Korean reactor and supposedly financed with Iranian assistance. Some reports say Israeli EW systems deactivated all of Syria's air defense systems for the entire period of the raid. In December 2010, the Russian Army deployed their first land-based multifunctional electronic warfare system known as Borisoglebsk 2 , developed by Sozvezdie . Development of

3332-526: The aviation world. 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. Due to relatively low purchase, maintenance and calibration cost, NDBs are still used to mark locations of smaller aerodromes and important helicopter landing sites. Similar beacons located in coastal areas are also used for maritime radio navigation, as almost every ship

3430-451: The ionosphere . The RDF station might now receive the same signal from two or more locations, especially during the day, which caused serious problems trying to determine the location. This led to the 1919 introduction of the Adcock antenna (UK Patent 130,490), which consisted of four separate monopole antennas instead of two loops, eliminating the horizontal components and thus filtering out

3528-411: The sky waves being reflected down from the ionosphere. Adcock antennas were widely used with Bellini–Tosi detectors from the 1920s on. The US Army Air Corps in 1931 tested a primitive radio compass that used commercial stations as the beacon. A major improvement in the RDF technique was introduced by Robert Watson-Watt as part of his experiments to locate lightning strikes as a method to indicate

3626-406: The 1930s and 1940s. On pre- World War II aircraft, RDF antennas are easy to identify as the circular loops mounted above or below the fuselage. Later loop antenna designs were enclosed in an aerodynamic, teardrop-shaped fairing. In ships and small boats, RDF receivers first employed large metal loop antennas, similar to aircraft, but usually mounted atop a portable battery-powered receiver. In use,

3724-521: The 1960s, many of these radios were actually made by Japanese electronics manufacturers, such as Panasonic , Fuji Onkyo , and Koden Electronics Co., Ltd. In aircraft equipment, Bendix and Sperry-Rand were two of the larger manufacturers of RDF radios and navigation instruments. Single-channel DF uses a multi-antenna array with a single channel radio receiver. This approach to DF offers some advantages and drawbacks. Since it only uses one receiver, mobility and lower power consumption are benefits. Without

3822-554: The 20th century a feature of most aircraft, but is being phased out. For the military, RDF is a key tool of signals intelligence . The ability to locate the position of an enemy transmitter has been invaluable since World War I, and played a key role in World War II's Battle of the Atlantic . It is estimated that the UK's advanced " huff-duff " systems were directly or indirectly responsible for 24% of all U-boats sunk during

3920-573: The FLR-9 at San Vito began, and it was totally deconstructed by the end of that month. Although the markings of where the array stood remain in the ground, the structure is completely gone. Demolition of the FLR-9 at Misawa began in October 2014. A decommissioning ceremony for the last active FLR-9, at Joint Base Elmendorf-Richardson , was held on May 25, 2016. Direction finding Direction finding ( DF ), or radio direction finding ( RDF ),

4018-577: The Germans had developed a method of broadcasting short messages under 30 seconds, less than the 60 seconds that a trained Bellini-Tosi operator would need to determine the direction. However, this was useless against huff-duff systems, which located the signal with reasonable accuracy in seconds. The Germans did not become aware of this problem until the middle of the war, and did not take any serious steps to address it until 1944. By that time huff-duff had helped in about one-quarter of all successful attacks on

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4116-580: The Japanese communications link by attempting to transmit a stronger radio signal over the Shinano Maru's signal, hoping to distort the Japanese signal at the receiving end. Russian Admiral Zinovy Rozhestvensky refused the advice and denied the Ural permission to electronically jam the enemy, which in those circumstances might have proved invaluable. The intelligence the Japanese gained ultimately led to

4214-455: 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. The basic principle of the correlative interferometer consists in comparing the measured phase differences with the phase differences obtained for a DF antenna system of known configuration at

4312-433: The RDF operator would first tune the receiver to the correct frequency, then manually turn the loop, either listening or watching an S meter to determine the direction of the null (the direction at which a given signal is weakest) of a long wave (LW) or medium wave (AM) broadcast beacon or station (listening for the null is easier than listening for a peak signal, and normally produces a more accurate result). This null

4410-506: The Swedish newspaper Svenska Dagbladet said its initial usage caused concern within NATO. A Russian blog described Borisoglebsk-2 thus: The 'Borisoglebsk-2', when compared to its predecessors, has better technical characteristics: wider frequency bandwidth for conducting radar collection and jamming, faster scanning times of the frequency spectrum, and higher precision when identifying

4508-659: The U-boat fleet. Several developments in electronics during and after the Second World War led to greatly improved methods of comparing the phase of signals. In addition, the phase-locked loop (PLL) allowed for easy tuning in of signals, which would not drift. Improved vacuum tubes and the introduction of the transistor allowed much higher frequencies to be used economically, which led to widespread use of VHF and UHF signals. All of these changes led to new methods of RDF, and its much more widespread use. In particular,

4606-412: The UK was installing sufficient DF stations to cover the entire area to receive skywave signals reflected back from the ionised layers in the upper atmosphere. Even with the expanded network, some areas were not adequately covered and for this reason up to 1700 voluntary interceptors (radio amateurs) were recruited to detect illicit transmissions by ground wave . In addition to the fixed stations, RSS ran

4704-454: The UK, and Search and Rescue helicopters have direction finding receivers for marine VHF signals and the 121.5 MHz homing signals incorporated in EPIRB and PLB beacons, although modern GPS-EPIRBS and AIS beacons are slowly making these redundant. A radio direction finder ( RDF ) is a device for finding the direction, or bearing , to a radio source. The act of measuring the direction

4802-450: The ability to compare the phase of signals led to phase-comparison RDF, which is perhaps the most widely used technique today. In this system the loop antenna is replaced with a single square-shaped ferrite core , with loops wound around two perpendicular sides. Signals from the loops are sent into a phase comparison circuit, whose output phase directly indicates the direction of the signal. By sending this to any manner of display, and locking

4900-400: The ability to look at each antenna simultaneously (which would be the case if one were to use multiple receivers, also known as N-channel DF) 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

4998-429: The aircraft's radio set. Bellini–Tosi direction finders were widespread from the 1920s into the 1950s. Early RDF systems were useful largely for long wave signals. These signals are able to travel very long distances, which made them useful for long-range navigation. However, when the same technique was being applied to higher frequencies, unexpected difficulties arose due to the reflection of high frequency signals from

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5096-494: The antenna was aligned so it pointed at the signal it produced maximum gain, and produced zero signal when face on. This meant there was always an ambiguity in the location of the signal: it would produce the same output if the signal was in front or back of the antenna. Later experimenters also used dipole antennas , which worked in the opposite sense, reaching maximum gain at right angles and zero when aligned. RDF systems using mechanically swung loop or dipole antennas were common by

5194-471: The antennas were sent into coils wrapped around a wooden frame about the size of a pop can , where the signals were re-created in the area between the coils. A separate loop antenna located in this area could then be used to hunt for the direction, without moving the main antennas. This made RDF so much more practical that it was soon being used for navigation on a wide scale, often as the first form of aerial navigation available, with ground stations homing in on

5292-464: The battle, although many were defeated by Vietnamese ECCM. In 2007, an Israeli attack on a suspected Syrian nuclear site during Operation Outside the Box (or Operation Orchard ) used electronic warfare systems to disrupt Syrian air defenses while Israeli jets crossed much of Syria, bombed their targets, and returned to Israel undeterred. The target was a suspected nuclear reactor under construction near

5390-557: The case of anti-radiation weapons, this often includes missiles or bombs that can home in on a specific signal (radio or radar) and follow that path directly to impact, thus destroying the system broadcasting. In November 2021, Israel Aerospace Industries announced a new electronic warfare system named Scorpius that can disrupt radar and communications from ships, UAVs , and missiles simultaneously and at varying distances. On 8 September 2024, Russian drones entered both Romanian and Latvian airspace. Romania scrambled two F-16s to monitor

5488-584: The collection requirements for more strategic intelligence. The earliest documented use of EW was during the Second Boer War of 1899–1902. The British Army, when trying to relieve Ladysmith, under siege by the Boers , used a searchlight to "bounce" Morse code signals off the clouds. The Boers immediately spotted this and used one of their own searchlights in an attempt to jam the British signals. This

5586-450: The correct bearing and allowed the navigator to avoid plotting a bearing 180 degrees opposite the actual heading. The U.S. Navy RDF model SE 995 which used a sense antenna was in use during World War I. After World War II, there were many small and large firms making direction finding equipment for mariners, including Apelco , Aqua Guide, Bendix , Gladding (and its marine division, Pearce-Simpson), Ray Jefferson, Raytheon , and Sperry . By

5684-723: The decisive Battle of Tsushima , where the Russian Navy lost all its battleships and most of its cruisers and destroyers. These losses effectively ended the Russo-Japanese War in Japan's favor. During World War II , the Allies and Axis Powers both extensively used EW, or what Winston Churchill referred to as the " Battle of the Beams ": as navigational radars were used to guide bombers to their targets and back to their base,

5782-529: The differences in two or more matched reference antennas' received signals, used in old signals intelligence (SIGINT). A modern helicopter -mounted direction finding system was designed by ESL Incorporated for the U.S. Government as early as 1972. Time difference of arrival techniques compare the arrival time of a radio wave at two or more different antennas and deduce the direction of arrival from this timing information. This method can use mechanically simple non-moving omnidirectional antenna elements fed into

5880-509: The direction of thunderstorms for sailors and airmen. He had long worked with conventional RDF systems, but these were difficult to use with the fleeting signals from the lightning. He had early on suggested the use of an oscilloscope to display these near instantly, but was unable to find one while working at the Met Office . When the office was moved, his new location at a radio research station provided him with both an Adcock antenna and

5978-820: The drone's progress, it landed "in an uninhabited area" near Periprava , according to the Romanian Ministry of Defence. The drone that entered Latvian airspace from Belarus crashed near Rezekne . This comes as the ISW noted increased success in Ukrainian Electronic Warfare against Russian drones that resulted in "several Russian Shahed drones (that) recently failed to reach their intended targets for unknown reasons." Two Kh-58s also reportedly failed to reach their targets. Electronic protection (EP), also known as an electronic protective measure (EPM) or electronic counter-countermeasure (ECCM) are

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6076-418: The electromagnetic spectrum. The electromagnetic spectrum portion of the information environment is referred to as the electromagnetic environment (EME). The recognized need for military forces to have unimpeded access to and use of the electromagnetic environment creates vulnerabilities and opportunities for electronic warfare in support of military operations. Within the information operations construct, EW

6174-529: The first application of EW in WWII was to interfere with the navigational radars. Chaff was also introduced during WWII to confuse and defeat tracking radar systems. As battlefield communication and radar technology improved, so did electronic warfare, which played a major role in several military operations during the Vietnam War . Aircraft on bombing runs and air-to-air missions often relied on EW to survive

6272-416: The ground, and thereby provided excellent great circle route ground wave propagation that pointed directly to the transmitter. Methods of performing RDF on longwave signals was a major area of research during the 1900s and 1910s. Antennas are generally sensitive to signals only when they have a length that is a significant portion of the wavelength, or larger. Most antennas are at least 1 ⁄ 4 of

6370-530: The guidance (seeker head) of an infrared homing missile to counter an adversary's use of flares is an example of EP. While defensive EA actions (jamming) and EP (defeating jamming) both protect personnel, facilities, capabilities, and equipment, EP protects from the effects of EA (friendly and/or adversary). Other examples of EP include spread spectrum technologies, the use of restricted frequency lists, emissions control ( EMCON ), and low observability (stealth) technology. Electronic warfare self-protection (EWSP)

6468-401: The horizon", which is valuable for ships when the line-of-sight may be only a few tens of kilometres. For aerial use, where the horizon may extend to hundreds of kilometres, higher frequencies can be used, allowing the use of much smaller antennas. An automatic direction finder , which could be tuned to radio beacons called non-directional beacons or commercial AM radio broadcasters, was in

6566-545: The incoming signal. The popular Watson-Watt method uses an array of two orthogonal coils (magnetic dipoles) in the horizontal plane, often completed with an omnidirectional vertically polarized electric dipole to resolve 180° ambiguities. The Adcock antenna array uses 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 each pair of antennas. Two of these pairs are co-located but perpendicularly oriented to produce what can be referred to as

6664-539: The inner ring covers the 18 to 30-MHz range (band C). Band A contains 48 sleeve monopole elements spaced 78.4 feet (23.9 m) apart (7.5 degrees). Band B contains 96 sleeve monopole elements spaced 37.5 feet (11.43 m) apart (3.75 degrees). Band C contains 48 antenna elements mounted on wooden structures placed in a circle around the central building. Bands A and B elements are vertically polarized. Band C elements consist of two horizontally polarized dipole antenna subelements electrically tied together, and positioned one above

6762-413: The intersecting bearings, the navigator could locate the relative position of his ship or aircraft. Later, RDF sets were equipped with rotatable ferrite loopstick antennas, which made the sets more portable and less bulky. Some were later partially automated by means of a motorized antenna (ADF). A key breakthrough was the introduction of a secondary vertical whip or 'sense' antenna that substantiated

6860-527: The location and source of radar emissions, and increased capacity for suppression. During the first two days of the 2022 Russian invasion of Ukraine , Russian EW disrupted Ukraine's air defense radars and communications, severely disrupting Ukrainian ground-based air defense systems. Russian jamming was so effective it interfered with their own communications, so efforts were scaled back. This led to Ukrainian SAMs regaining much of their effectiveness, which began inflicting significant losses on Russian aircraft by

6958-817: The location of a radio source can be determined by measuring its direction from two or more locations. Radio direction finding is used in radio navigation for ships and aircraft, to locate emergency transmitters for search and rescue , for tracking wildlife, and to locate illegal or interfering transmitters. During the Second World War, radio direction finding was used by both sides to locate and direct aircraft, surface ships, and submarines. RDF systems can be used with any radio source, although very long wavelengths (low frequencies) require very large antennas, and are generally used only on ground-based systems. These wavelengths are nevertheless used for marine radio navigation as they can travel very long distances "over

7056-520: The location of the station and its transmitter, which can reduce the accuracy of the 'fix' when approaching the broadcast city. A second factor is that some AM radio stations are omnidirectional during the day, and switch to a reduced power, directional signal at night. RDF was once the primary form of aircraft and marine navigation. Strings of beacons formed "airways" from airport to airport, while marine NDBs and commercial AM broadcast stations provided navigational assistance to small watercraft approaching

7154-539: The maritime safety system GMDSS , which has been in force since 1999. The striking cross frame antenna with attached auxiliary antenna can only be found on the signal masts of some older ships because they do not interfere there and dismantling would be too expensive. Modern positioning methods such as GPS, DGPS, radar and the now-outdated Loran C have radio direction finding methods that are imprecise for today's needs. Radio direction finding networks also no longer exist. However rescue vessels, such as RNLI lifeboats in

7252-431: The most tactical, rugged, and extreme environments. This is often referred to as simply reconnaissance, although today, more common terms are intelligence, surveillance and reconnaissance ( ISR ) or intelligence, surveillance, target acquisition, and reconnaissance ( ISTAR ). The purpose is to provide immediate recognition, prioritization, and targeting of threats to battlefield commanders. Signals intelligence (SIGINT),

7350-414: The offensive use of electromagnetic energy weapons, directed energy weapons, or anti-radiation weapons to attack personnel, facilities, or equipment with the intent of degrading, neutralizing, or destroying enemy combat capability including human life. In the case of electromagnetic energy, this action is most commonly referred to as "jamming" and can be performed on communications systems or radar systems. In

7448-540: The other. The array is centered on a ground screen 1,443 feet (439.8 m) in diameter. The arrangement permits accurate direction finding of signals from up to 4000 nautical miles (7408 km) away. FLR-9s were constructed at the following places: Advances in technology have made the FLR-9 obsolete. In 1997, the FLR-9 at the former Clark AB in the Philippines was converted into a 35,000-seat fabric-covered amphitheatre . In early May 2002, systematic dismantling of

7546-500: The position of an enemy transmitter has been invaluable since World War I , and it played a key role in World War II 's Battle of the Atlantic . It is estimated that the UK's advanced " huff-duff " systems were directly or indirectly responsible for 24% of all U-boats sunk during the war. Modern systems often use phased array antennas to allow rapid beam forming for highly accurate results. These are generally integrated into

7644-402: The radio waves could be arriving. This is called a null in the signal, and it is used instead of the strongest signal direction, because small angular deflections of the loop aerial away from its null positions produce much more abrupt changes in received current than similar directional changes around the loop's strongest signal orientation. Since the null direction gives a clearer indication of

7742-473: The received signal: The difference in electrical phase along the rim of the loop at any instant causes a difference in the voltages induced on either side of the loop. Turning the plane of the loop to "face" the signal so that the arriving phases are identical around the entire rim will not induce any current flow in the loop. So simply turning the antenna to produce a minimum in the desired signal will establish two possible directions (front and back) from which

7840-426: The signal direction – the null is "sharper" than the max – with loop aerial the null direction is used to locate a signal source. A "sense antenna" is used to resolve the two direction possibilities; the sense aerial is a non-directional antenna configured to have the same sensitivity 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

7938-401: The signal using PLL, the direction to the broadcaster can be continuously displayed. Operation consists solely of tuning in the station, and is so automatic that these systems are normally referred to as automatic direction finder . Other systems have been developed where more accuracy is required. Pseudo-doppler radio direction finder systems use a series of small dipole antennas arranged in

8036-402: The size of the receiver antennas are a function of the wavelength of the signal; very long wavelengths (low frequencies) require very large antennas, and are generally used only on ground-based systems. These wavelengths are nevertheless very useful for marine navigation as they can travel very long distances and "over the horizon", which is valuable for ships when the line-of-sight may be only

8134-528: The spectrum, attack an enemy, or impede enemy operations. The purpose of electromagnetic warfare is to deny the opponent the advantage of—and ensure friendly unimpeded access to—the EM spectrum . Electromagnetic warfare can be applied from air , sea , land , or space by crewed and uncrewed systems, and can target communication , radar , or other military and civilian assets. Military operations are executed in an information environment increasingly complicated by

8232-658: The start of March 2022. Rapid Russian advances at the start of the war prevented EW troops from properly supporting the advancing troops, but by late March and April 2022, extensive jamming infrastructure had been deployed. EW complexes were set up in Donbas in concentrations of up to 10 complexes per 13 mi (21 km) of frontage. Electronic suppression of GPS and radio signals caused heavy losses of Ukrainian UAVs, depriving them of intelligence and precise artillery fire spotting. Small quadcopters had an average life expectancy of around three flights, and larger fixed-wing UAVs like

8330-650: The station's identifier that is used to confirm the station and its operational status. Since these radio signals are broadcast in all directions (omnidirectional) during the day, the signal itself does not include direction information, and these beacons are therefore referred to as non-directional beacons , or NDBs . As the commercial medium wave broadcast band lies within the frequency capability of most RDF units, these stations and their transmitters can also be used for navigational fixes. While these commercial radio stations can be useful due to their high power and location near major cities, there may be several miles between

8428-529: The system started in 2004 and evaluation testing successfully completed in December 2010. The Borisoglebsk-2 uses four different types of jamming stations on a single system. The Borisoglebsk-2 system is mounted on nine MT-LB armored vehicles and is intended to suppress mobile satellite communications and satellite-based navigation signals. This EW system is developed to conduct electronic reconnaissance and suppression of radio-frequency sources. In August 2015,

8526-505: The turn of the 20th century. Prominent examples were patented by John Stone Stone in 1902 (U.S. Patent 716,134) and Lee de Forest in 1904 (U.S. Patent 771,819), among many other examples. By the early 1900s, many experimenters were looking for ways to use this concept for locating the position of a transmitter. Early radio systems generally used medium wave and longwave signals. Longwave in particular had good long-distance transmission characteristics due to their limited interaction with

8624-501: The two. 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 Watson-Watt technique uses two antenna pairs to perform an amplitude comparison on

8722-498: The war. Modern systems often used phased array antennas to allow rapid beamforming for highly accurate results, and are part of a larger electronic warfare suite. Early radio direction finders used mechanically rotated antennas that compared signal strengths, and several electronic versions of the same concept followed. Modern systems use the comparison of phase or doppler techniques which are generally simpler to automate. Early British radar sets were referred to as RDF, which

8820-462: The wavelength, more commonly 1 ⁄ 2 – the half-wave dipole is a very common design. For longwave use, this resulted in loop antennas tens of feet on a side, often with more than one loop connected together to improve the signal. Another solution to this problem was developed by the Marconi company in 1905. This consisted of a number of horizontal wires or rods arranged to point outward from

8918-464: Was equipped with a direction finder (Appleyard 1988). Very few maritime radio navigation beacons remain active today (2008) as ships have abandoned navigation via RDF in favor of GPS navigation. In the United Kingdom a radio direction finding service is available on 121.5 MHz and 243.0 MHz to aircraft pilots who are in distress or are experiencing difficulties. The service is based on

9016-551: Was expended on identifying secret transmitters in the United Kingdom (UK) by direction finding. The work was undertaken by the Radio Security Service (RSS also MI8). Initially three U Adcock HF DF stations were set up in 1939 by the General Post Office. With the declaration of war, MI5 and RSS developed this into a larger network. One of the problems with providing coverage of an area the size of

9114-762: Was graphically described by Winston Churchill in his book London to Ladysmith via Pretoria . During the Russo-Japanese War of 1904–1905 the Japanese auxiliary cruiser Shinano Maru had located the Russian Baltic Fleet in Tsushima Strait , and was communicating the fleet's location by radio signals to the Imperial Japanese Fleet HQ. The captain of the Russian warship Ural requested permission to disrupt

9212-480: Was in widespread use on front lines to impair small battlefield UAV activity, with Russia installing video feedback and control jammers on high-value equipment like tanks and artillery. By 11 March 2024, Ukraine reported it had destroyed a Russian Palantin EW system in Zaporizhzhia Oblast, which "suppress satellite radio navigation along the entire line of contact and in most parts of Ukraine, replacing

9310-580: Was largely supplanted in North America by the development of LORAN in the 1970s. Today many NDBs have been decommissioned in favor of faster and far more accurate GPS navigational systems. However the low cost of ADF and RDF systems, and the continued existence of AM broadcast stations (as well as navigational beacons in countries outside North America) has allowed these devices to continue to function, primarily for use in small boats, as an adjunct or backup to GPS. In World War II considerable effort

9408-490: Was losing some 10,000 drones a month due to Russian electronic warfare, according to a 19 May 2023 report by the Royal United Services Institute . This was an average of 300 drones a day. Russia has established EW posts about every 10 kilometres (6 mi) of the front, being some 6 kilometres (4 mi) back from the front line. In October 2023, The Economist reported that electronic warfare

9506-401: Was once the primary aviation navigational aid. ( Range and Direction Finding was the abbreviation used to describe the predecessor to radar . ) Beacons were used to mark "airways" intersections and to define departure and approach procedures. Since the signal transmitted contains no information about bearing or distance, these beacons are referred to as non-directional beacons , or NDB in

9604-455: Was symmetrical, and thus identified both the correct degree heading marked on the radio's compass rose as well as its 180-degree opposite. While this information provided a baseline from the station to the ship or aircraft, the navigator still needed to know beforehand if he was to the east or west of the station in order to avoid plotting a course 180-degrees in the wrong direction. By taking bearings to two or more broadcast stations and plotting

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