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Encyclopedia > Extremely low frequency
Extremely low frequency (ELF)
Frequency: 3 Hz to 30 Hz

Wavelength: 100 000 km to 10 000 km

Extremely low frequency (ELF) is the band of radio frequencies from 3 to 30 Hz. ELF was used by the US Navy and Soviet/Russian Navy to communicate with submerged submarines. A band is a small section of the spectrum of radio communication frequencies, in which channels are usually used or set aside for the same purpose. ... Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... MHZ redirects here. ... Motto: (Out Of Many, One) (traditional) In God We Trust (1956 to date) Anthem: The Star-Spangled Banner Capital Washington D.C. Largest city New York City None at federal level (English de facto) Government Federal constitutional republic  - President George Walker Bush (R)  - Vice President Dick Cheney (R) Independence from... The Soviet Navy (Russian: Военно-морской флот СССР, Voyenno-morskoy flot SSSR, literally Naval military forces of the USSR) was the naval arm of the Soviet armed forces. ... The Russian Navy or VMF (Russian: Военно-Морской Флот (ВМФ) - Voyenno- Morskoy Flot (VMF) or Military Maritime Fleet) is the naval arm of the Russian armed forces. ... Copy of the original phone of Alexander Graham Bell at the Musée des Arts et Métiers in Paris Telecommunication is the transmission of signals over a distance for the purpose of communication. ... USS Virginia, a Virginia-class nuclear attack (SSN) submarine Alvin in 1978, a year after first exploring hydrothermal vents. ...

Contents

Explanation

1982 aerial view of the Clam Lake, Wisconsin ELF facility.
1982 aerial view of the Clam Lake, Wisconsin ELF facility.

Because of the electrical conductivity of salt water, submarines are shielded from most electromagnetic communications. Signals in the ELF frequency range, however, can penetrate much deeper. Two factors limit the usefulness of ELF communications channels; the low data transmission rate of a few characters per minute, and to a lesser extent the one-way nature due to the impracticality of installing a huge transmitter on a submarine. Generally ELF signals were used to order a submarine to rise to a shallow depth where it could receive some other form of communication. Image File history File links Download high-resolution version (3000x2400, 2711 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Extremely low frequency Communication with submarines ... Image File history File links Download high-resolution version (3000x2400, 2711 KB) File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Extremely low frequency Communication with submarines ... Electrical conductivity or specific conductivity is a measure of a materials ability to conduct an electric current. ... For other uses, see Salt (disambiguation). ... Impact from a water drop causes an upward rebound jet surrounded by circular capillary waves. ...


Difficulties of ELF communication

One of the difficulties posed when broadcasting in the ELF frequency range is antenna size. This is because the antenna must be at least a substantial fraction of the size (in at least one dimension) of the wavelength of the frequency of EM waves you wish to create. Simply put, a 1 Hz (cycle per second) signal would have a wavelength equal to the distance EM waves travel through your chosen medium in 1 second. For ELF, this is very slightly slower than the speed of light (in a vacuum). Though ELF is defined as 3-30Hz the Russian and American Navies actually used aprox. 50-85 Hz. Therefore, for this purpose the antenna needs to be ~299 792 (kilometers per second) divided by 50-85, which is 3,450km to 5,996 km long. The earth's diameter varies from 12,715 km (pole to pole) to 12,756 km (equatorial). A yagi antenna Most simply, an antenna is an electronic component designed to send or receive radio waves. ... MHZ redirects here. ... A line showing the speed of light on a scale model of Earth and the Moon, about 1. ...


Because of this huge size requirement, and in order to transmit internationally using ELF frequencies, the earth itself must be used as an antenna, with extremely long leads going into the ground. The US maintained two sites, in the Chequamegon-Nicolet National Forest, Wisconsin and the Escanaba State Forest, Michigan (originally named Project Sanguine, then downsized and rechristened Project ELF prior to construction), until dismantling them began in late September 2004. Both sites used long power lines, such called ground dipoles, as leads. These leads were in multiple strands ranging from 22.5 to 45 kilometers long. Because of the inefficiency of this method, considerable amounts of electrical power were required to operate the system. Welcome sign The Chequamegon-Nicolet National Forest is a 1,519,800 acre (6,150 km²) U.S. National Forest in northern Wisconsin in the United States. ... Official language(s) None Capital Madison Largest city Milwaukee Area  Ranked 23rd  - Total 65,498 sq mi (169,790 km²)  - Width 260 miles (420 km)  - Length 310 miles (500 km)  - % water 17  - Latitude 42°30N to 47°3N  - Longitude 86°49W to 92°54W Population  Ranked... Official language(s) None (English, de-facto) Capital Lansing Largest city Detroit Area  Ranked 11th  - Total 97,990 sq mi (253,793 km²)  - Width 239 miles (385 km)  - Length 491 miles (790 km)  - % water 41. ... Year 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Power Line is a neoconservative blog run by three lawyers: John H. Hinderaker (Hindrocket), Scott W. Johnson (The Big Trunk) and Paul Mirengoff (Deacon). Power Line covers political and social issues from a conservative viewpoint. ... A Ground dipole (alt: Ground antenna) is a special type of antenna which consists of two electrodes positioned in the ground. ... A kilometer (Commonwealth spelling: kilometre), symbol: km is a unit of length in the metric system equal to 1,000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... Transmission lines in Lund, Sweden Electric power, often known as power or electricity, involves the production and delivery of electrical energy in sufficient quantities to operate domestic appliances, office equipment, industrial machinery and provide sufficient energy for both domestic and commercial lighting, heating, cooking and industrial processes. ...


Ecological impact of ELF signals

There have been some concerns over the possible ecological impact of ELF signals. In 1984 a federal judge halted construction requiring more environmental and health studies. This judgment was overruled by a federal appeals court on the basis that the US Navy claimed to have spent over 25 million dollars studying the effects of the electromagnetic fields with results indicating that they were similar to the effect produced by standard power distribution lines. The judgement was not accepted by everyone and during the time ELF was in use, some Wisconsin politicians such as Herb Kohl, Russ Feingold and Dave Obey called for its closure. This article or section does not cite any references or sources. ... The United States Navy (USN) is the branch of the United States armed forces responsible for naval operations. ... This article refers to Sen. ... Russell Dana Russ Feingold (born March 2, 1953) is an American politician from the U.S. state of Wisconsin. ... David Ross Dave Obey (pronounced Obie) (born October 3, 1938) is an American politician. ...


It is also discussed the association between ELF, SLF, etc. electromagnetic radiation and health. Electromagnetic radiation can be classified into ionizing radiation and non-ionizing radiation, based on whether it is capable of ionizing atoms and breaking chemical bonds. ...


Other uses

Transmitters in the 20 Hz range are also found in pipeline inspection gauges, also known as "pigs". The transmitted signal is often used to track the pig should it become stuck in the pipeline. A pig used in natural gas pipelines A Pipeline inspection gauge or pig in the pipeline industry is a tool that is sent down a pipeline and propelled by the pressure of the product in the pipeline itself. ...


Some radio hams record ELF (or even lower) signals from very large homemade antennas, and play them back at higher speeds in order to catch the natural fluctuations in the Earth's electromagnetic field. Increasing the speed of the magnetic tape increases the pitch, so that it is brought into the audio frequency range. Amateur radio station with modern solid-state transceiver featuring LCD display and DSP capabilities Amateur radio, often called ham radio, is a hobby that uses various types of radio broadcasting equipment to communicate with other radio amateurs for public service, recreation and self-training. ... In telecommunication, signalling (or signaling) has the following meanings: The use of signals for controlling communications. ... This article does not cite any references or sources. ... This article is about Earth as a planet. ... The electromagnetic field is a physical field that is produced by electrically charged objects and which affects the behaviour of charged objects in the vicinity of the field. ... Compact audio cassette Magnetic tape is a non-volatile storage medium consisting of a magnetic coating on a thin plastic strip. ... Pitch is the perceived fundamental frequency of a sound. ... An audio frequency (abbreviation: AF) is any frequency from about 20 hertz to about 20 kilohertz, which is the approximate range of sound frequencies that is audible to humans. ...


Natural ELF waves

Naturally-occurring ELF waves are present on Earth, resonating in the region between ionosphere and surface. They are initiated by lightning strikes that make electrons in the atmosphere oscillate[1]. The fundamental mode of the Earth-ionosphere cavity has the wavelength equal to the circumference of the Earth, which gives a resonance frequency of 7.8 Hz. This frequency (and higher resonance modes: 14, 20, 26 and 32 Hz) appear as peaks in the ELF spectrum and are called Schumann_resonance. Relationship of the atmosphere and ionosphere The ionosphere is the uppermost part of the atmosphere, distinguished because it is ionized by solar radiation. ... This article needs additional references or sources for verification. ... The Schumann resonance is a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earths electromagnetic field spectrum. ...


They have also been tentatively identified on Saturn's moon Titan. Titan's surface is thought to be a poor reflector of ELF waves, so they may be reflecting instead off of the liquid-ice boundary of a subsurface ocean of water and ammonia predicted by some theoretical models. Titan's ionosphere is also more complex than Earth's, with the main ionosphere at an altitude of 1200 km but with an additional layer of charged particles at 63 km. This splits Titan's atmosphere to some extent into two separate resonating chambers. The source of natural ELF waves on Titan is unclear as there doesn't appear to be extensive lightning activity.[1] Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ... A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. ... Titan (, from Ancient Greek Τῑτάν) or Saturn VI is the largest moon of Saturn and the second largest moon in the solar system,[4] after Jupiters moon Ganymede. ...


Patents

  • Tanner, R. L., U.S. Patent 3,215,937 , "Extremely low-frequency antenna". 1965.
  • Hansell, Clarence W., U.S. Patent 2,389,432 , "Communication system by pulses through the Earth".
  • Altshuler, U.S. Patent 4,051,479 , ELF vertical dipole antenna suspended from aircraft

See also

Because electromagnetic radiation such as normal radio communication cannot travel through thick conductors such as salt water, communication with submarines when they are submerged is a difficult technological task which requires specific techniques and devices. ... Legend γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultra high frequency VHF = Very high frequency HF = High... The Schumann resonance is a set of spectrum peaks in the extremely low frequency (ELF) portion of the Earths electromagnetic field spectrum. ... TACAMO is a US military term literally meaning Take Charge and Move Out. TACAMO actually refers to a system of survivable communications links designed to be used in nuclear war to maintain communications between the decision-makers (the National Command Authority) and the triad of strategic nuclear weapon delivery systems. ... This list contains acronyms, initialisms and pseudo-blends. ... The skin effect is the tendency of an alternating electric current (AC) to distribute itself within a conductor so that the current density near the surface of the conductor is greater than that at its core. ... A Ground dipole (alt: Ground antenna) is a special type of antenna which consists of two electrodes positioned in the ground. ...

References

  1. ^ a b "Titan's Mysterious Radio Wave", Jet Propulsion Laboratory, June 01, 2007. Retrieved on 2007-06-02. 

Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era. ... is the 153rd day of the year (154th in leap years) in the Gregorian calendar. ...

External links

Radio spectrum
ELF SLF ULF VLF LF MF HF VHF UHF SHF EHF
3 Hz 30 Hz 300 Hz 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz
30 Hz 300 Hz 3 kHz 30 kHz 300 kHz 3 MHz 30 MHz 300 MHz 3 GHz 30 GHz 300 GHz


The International Agency for Research on Cancer (IARC, or CIRC in its French acronym) is an intergovernmental agency forming part of the World Health Organisation of the United Nations. ... Logo of the GreenFacts website GreenFacts, formerly the GreenFacts Foundation, is an international non-profit organization founded in 2001 in Brussels, Belgium. ... Radio frequency, or RF, refers to that portion of the electromagnetic spectrum in which electromagnetic waves can be generated by alternating current fed to an antenna. ... Super Low Frequency (SLF) is the frequency range between 30 hertz and 300 hertz. ... Ultra Low Frequency (ULF) is the frequency range between 300 hertz and 3000 hertz. ... Very low frequency or VLF refers to radio frequencies (RF) in the range of 3 to 30 kHz. ... Low Frequency or LF refers to Radio Frequencies (RF) in the range of 30–300 kHz. ... Mediumwave radio transmissions (sometimes called Medium frequency or MF) are those between the frequencies of 300 kHz and 3000 kHz. ... High frequency (HF) radio frequencies are between 3 and 30 MHz. ... Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). ... This article is about the radio frequency. ... Microwave Slang for small waves, like at a beach, often used by surfers. ... Extremely high frequency is the highest radio frequency band. ...


  Results from FactBites:
 
Kids.Net.Au - Encyclopedia > Extremely Low Frequencies (192 words)
ELF is used by the US Navy to communicate with submerged submarines.
The low transmission rate of most ELF communications limits their use as communications channels; generally an ELF signal serves to request that a submarine surface and initiate some other form of contact.
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size.
  More results at FactBites »

 
 

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