VERY LOW FREQUENCY or VLF is the ITU designation for radio frequencies (RF) in the range of 3 to 30 kilohertz (kHz), corresponding to wavelengths from 100 to 10 kilometres, respectively. The band is also known as the MYRIAMETRE BAND or MYRIAMETRE WAVE as the wavelengths range from one to ten myriametres (an obsolete metric unit equal to 10 kilometres). Due to its limited bandwidth , audio (voice) transmission is highly impractical in this band, and therefore only low data rate coded signals are used. The VLF band is used for a few radio navigation services, government time radio stations (broadcasting time signals to set radio clocks ) and for secure military communication. Since VLF waves can penetrate at least 40 meters (120 ft) into saltwater, they are used for military communication with submarines . CONTENTS * 1 Propagation characteristics * 2 Antennas * 3 Applications * 4 VLF submarine communication methods * 5 PC-based VLF reception * 6 Amateur radio * 7 List of VLF transmissions * 8 See also * 9 References * 10 Further reading * 11 External links PROPAGATION CHARACTERISTICSBecause of their large wavelengths, VLF radio waves can diffract around large obstacles and so are not blocked by mountain ranges or the horizon, and can propagate as ground waves following the curvature of the Earth. The main mode of long distance propagation is an Earth-ionosphere waveguide
Earth-ionosphere waveguide mechanism
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VLF AUTOMOTIVE is a small American-based automotive company formed in January 2016. It follows VL AUTOMOTIVE, founded in 2012 by Bob Lutz and Gilbert Villarreal , and was renamed after Henrik Fisker joined the company. CONTENTS * 1 Company history * 2 Products * 2.1 VLF Destino * 2.2 VLF Force 1 * 2.3 Humvee C-Series * 3 References * 4 External links COMPANY HISTORYThe company was founded by designer "> * ^ A B Lavrinc, Damon (14 January 2013). " Fisker Karma Gets a 638-HP Corvette Heart Transplant". Wired. Retrieved 25 May 2013. * ^ Nunez, Alex (14 January 2013). "Destino: Bob Lutz\'s Corvette-powered Fisker Karma". Road & Track. Retrieved 25 May 2013. * ^ Smith, David (3 May 2013). "Fisker Woes Won’t Dash Destino Plans". Wards Auto. Retrieved 25 May 2013. * ^ "Detroit reveal for VL Destino convertible". Autocar. 14 January 2014. Retrieved 19 January 2014
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The HERTZ (symbol: Hz) is the derived unit of frequency in the International System of Units (SI) and is defined as one cycle per second . It is named for Heinrich Rudolf Hertz
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Hertz , the first person to provide conclusive proof of the existence of electromagnetic waves . Hertz
Hertz are commonly expressed in multiples : kilohertz (103 Hz, kHz), megahertz (106 Hz, MHz), gigahertz (109 Hz, GHz), and terahertz (1012 Hz, THz). Some of the unit's most common uses are in the description of sine waves and musical tones , particularly those used in radio - and audio-related applications. It is also used to describe the speeds at which computers and other electronics are driven. CONTENTS * 1 Definition * 2 History * 3 Applications * 3.1 Vibration * 3.2 Electromagnetic radiation * 3.3 Computers * 4 SI multiples * 5 See also * 6 Notes and references * 7 External links DEFINITIONThe hertz is equivalent to cycles per second , i.e., "1/second" or s 1 {displaystyle {text{s}}^{-1}}
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The METRE (international spelling ) or METER (American spelling ) (from the Greek noun μέτρον, "measure") is the base unit of length in the International System of Units
International System of Units (SI). The SI unit symbol is M. The metre is defined as the length of the path travelled by light in a vacuum in 1/299 792 458 seconds . The metre was originally defined in 1793 as one ten-millionth of the distance from the equator to the North Pole
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North Pole . In 1799, it was redefined in terms of a prototype metre bar (the actual bar used was changed in 1889). In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86 . In 1983, the current definition was adopted. The imperial inch is defined as 0.0254 metres (2.54 centimetres or 25.4 millimetres). One metre is about 3 3⁄8 inches longer than a yard , i.e. about 39 3⁄8 inches
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The RADIO SPECTRUM is the part of the electromagnetic spectrum from 3 Hz to 3000 GHz (3 THz ). Electromagnetic waves in this frequency range, called radio waves , are extremely widely used in modern technology, particularly in telecommunication . To prevent interference between different users, the generation and transmission of radio waves is strictly regulated by national laws, coordinated by an international body, the International Telecommunication
TelecommunicationUnion (ITU). Different parts of the radio spectrum are allocated by the ITUfor different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio
RadioRegulations (RR). In some cases, parts of the radio spectrum are sold or licensed to operators of private radio transmission services (for example, cellular telephone operators or broadcast television stations). Ranges of allocated frequencies are often referred to by their provisioned use (for example, cellular spectrum or television spectrum)
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EXTREMELY LOW FREQUENCY (ELF) is the ITU designation for electromagnetic radiation (radio waves ) with frequencies from 3 to 30 Hz , and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively. In atmospheric science , an alternative definition is usually given, from 3 Hz to 3 kHz. In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3 Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU radio bands . ELF radio waves are generated by lightning and natural disturbances in Earth's magnetic field , so they are a subject of research by atmospheric scientists. Because of the difficulty of building antennas that can radiate such long waves, ELF frequencies have been used in only a very few human-made communication systems. ELF waves can penetrate seawater , which makes them useful in communication with submarines . The US, Russia, and India are the only nations known to have constructed ELF communication facilities. The U.S. facilities were used between 1985 and 2004 but are now decommissioned. ELF waves can also penetrate significant distances into earth or rock, and "through-the-earth " underground mine communication systems use frequencies of 300 to 3000 Hz
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SUPER LOW FREQUENCY (SLF) is electromagnetic waves (radio waves ) in the frequency range between 30 hertz and 300 hertz. They have corresponding wavelengths of 10,000 to 1,000 kilometers. This frequency range includes the frequencies of AC power grids (50 hertz and 60 hertz). Another conflicting designation which includes this frequency range is Extremely Low Frequency
Frequency(ELF), which in some contexts refers to all frequencies up to 300 hertz. Because of the extreme difficulty of building transmitters that can generate such long waves, frequencies in this range have been used in very few artificial communication systems. However, SLF waves can penetrate seawater to a depth of hundreds of meters. Therefore, in recent decades the U.S., Russian and Indian military have built huge radio transmitters using SLF frequencies to communicate with their submarines . The U.S. naval service is called Seafarer and operates at 76 hertz. It became operational in 1989 but was discontinued in 2004 due to advances in VLF communication systems. The Russian service is called ZEVS and operates at 82 hertz
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ULTRA LOW FREQUENCY (ULF) is the ITU designation for the frequency range of electromagnetic waves between 300 hertz and 3 kilohertz. In magnetosphere science and seismology , alternative definitions are usually given, including ranges from 1 mHz to 100 Hz, 1 mHz to 1 Hz, 10 mHz to 10 Hz. Frequencies above 3 Hz in atmosphere science are usually assigned to the ELF range. Many types of waves in the ULF frequency band can be observed in the magnetosphere and on the ground. These waves represent important physical processes in the near-Earth plasma environment. The speed of the ULF waves is often associated with the Alfvén velocitythat depends on the ambient magnetic field and plasma mass density. This band is used for communications in mines , as it can penetrate the earth. CONTENTS * 1 Earthquakes
Earthquakes * 2 Earth mode communications * 3 See also * 4 References * 5 External articles EARTHQUAKESSome monitoring stations have reported that earthquakes are sometimes preceded by a spike in ULF activity. A remarkable example of this occurred before the 1989 Loma Prieta earthquakein California
California, although a subsequent study indicates that this was little more than a sensor malfunction
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LOW FREQUENCY (LOW FREQ) or LF is the ITU designation for radio frequencies (RF) in the range of 30 kHz–300 kHz. As its wavelengths range from ten kilometres to one kilometre, respectively, it is also known as the KILOMETRE BAND or KILOMETRE WAVE. LF radio waves exhibit low signal attenuation , making them suitable for long-distance communications. In Europe and areas of Northern Africa and Asia, part of the LF spectrum is used for AM broadcasting as the "longwave " band. In the western hemisphere, its main use is for aircraft beacon, navigation ( LORAN
LORAN), information, and weather systems. A number of time signal broadcasts are also broadcast in this band. CONTENTS * 1 Propagation * 2 Uses * 2.1 Standard time signals * 2.2 Military * 2.3 Experimental and amateur * 2.4 Meteorological information broadcasts * 2.5 Radio
Radionavigation signals * 2.6 Radio
Radiobroadcasting * 2.7 Other applications * 3 Antennas * 4 See also * 5 References * 6 Further reading PROPAGATION Atmospheric radio noise increases with decreasing frequency. At the LF band and below, it is far above the thermal noise floor in receiver circuits
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MEDIUM FREQUENCY (MF) is the ITU designation for radio frequencies (RF) in the range of 300 kilohertz (kHz) to 3 megahertz (MHz). Part of this band is the medium wave (MW) AM broadcast band. The MF band is also known as the HECTOMETER BAND or HECTOMETER WAVE as the wavelengths range from ten to one hectometer (1,000 to 100 m). Frequencies immediately below MF are denoted low frequency (LF), while the first band of higher frequencies is known as high frequency (HF). MF is mostly used for AM radio
AM radio broadcasting , navigational radio beacons , maritime ship-to-shore communication, and transoceanic air traffic control . CONTENTS * 1 Uses and applications * 2 Propagation * 3 Antennas * 4 See also * 5 References * 6 Further reading * 7 External links USES AND APPLICATIONS Mast radiator of a commercial MF AM broadcasting station, Chapel Hill, North Carolina, USA A major use of these frequencies is AM broadcasting ; AM radio stations are allocated frequencies in the medium wave broadcast band from 526.5 kHz to 1606.5 kHz in Europe; in North America this extends from 525 kHz to 1705 kHz Some countries also allow broadcasting in the 120-meter band from 2300 to 2495 kHz; these frequencies are mostly used in tropical areas. Although these are medium frequencies, 120 meters is generally treated as one of the shortwave bands
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HIGH FREQUENCY (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the DECAMETER BAND or DECAMETER WAVE as its wavelengths range from one to ten decameters (ten to one hundred metres). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio . Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave " propagation – these frequencies are suitable for long-distance communication across intercontinental distances. The band is used by international shortwave broadcasting stations (2.31–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses. CONTENTS * 1 Propagation characteristics * 2 Uses * 3 Antennas * 4 See also * 5 References * 6 Further reading * 7 External links PROPAGATION CHARACTERISTICS _ A modern Icom M700Pro_ two-way radio for marine HF radio communications
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VERY HIGH FREQUENCY (VHF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves ) from 30 to 300 Megahertz (MHz), with corresponding wavelengths of ten to one meters. Frequencies immediately below VHF are denoted high frequency (HF), and the next higher frequencies are known as ultra high frequency (UHF). Common uses for VHF are FM radio
FM radio broadcasting, television broadcasting, two way land mobile radio systems (emergency, business, private use and military), long range data communication up to several tens of kilometres with radio modems , amateur radio , and marine communications . Air traffic control communications and air navigation systems (e.g. VOR "> "Rabbit-ears" VHF television antenna (the small loop is a separate UHF
UHF antenna). For analog TV, VHF transmission range is a function of transmitter power, receiver sensitivity, and distance to the horizon, since VHF signals propagate under normal conditions as a near line-of-sight phenomenon. The distance to the radio horizon is slightly extended over the geometric line of sight to the horizon, as radio waves are weakly bent back toward the Earth by the atmosphere
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ULTRA HIGH FREQUENCY (UHF) is the ITU designation for radio frequencies in the range between 300 MHz and 3 GHz, also known as the DECIMETRE BAND as the wavelengths range from one meter to one decimeter . Radio waves with frequencies above the UHF band fall into the SHF (super-high frequency ) or microwave frequency range. Lower frequency signals fall into the VHF (very high frequency ) or lower bands. UHF radio waves propagate mainly by line of sight ; they are blocked by hills and large buildings although the transmission through building walls is strong enough for indoor reception. They are used for television broadcasting , cell phones , satellite communication including GPS , personal radio services including Wi-Fi and Bluetooth , walkie-talkies , cordless phones , and numerous other applications. The IEEE defines the UHF radar band as frequencies between 300 MHz and 1 GHz. Two other IEEE radar bands overlap the ITU UHF band: the L band between 1 and 2 GHz and the S band between 2 and 4 GHz. _ UHF television antenna on a residence. This type of antenna, called a Yagi-Uda antenna , is widely used at UHF frequencies. Another antenna type common at UHF; a reflective array TV antenna consisting of two high-bandwidth "bow tie" dipoles in front of a flat reflector screen
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SUPER HIGH FREQUENCY (SHF) is the ITU designation for radio frequencies (RF) in the range between 3 GHz and 30 GHz. This band of frequencies is also known as the CENTIMETRE BAND or CENTIMETRE WAVE as the wavelengths range from one to ten centimetres. These frequencies fall within the microwave band, so radio waves with these frequencies are called microwaves. The small wavelength of microwaves allows them to be directed in narrow beams by aperture antennas such as parabolic dishes , so they are used for point-to-point communication and data links and for radar . This frequency range is used for most radar transmitters, wireless LANs , satellite communication , microwave radio relay links, and numerous short range terrestrial data links. Wireless USBtechnology is anticipated to use approximately one-third of this spectrum. Frequencies in the SHF range are often referred to by their IEEE radar band designations: S , C , X , Ku , K , or Ka band, or by similar NATO or EU designations. CONTENTS * 1 Propagation * 2 Antennas * 2.1 Waveguide * 3 Advantages * 4 See also * 5 References * 6 External links PROPAGATION A variety of parabolic antennas on a communications tower in Australia for point-to-point microwave communication links. Some have white plastic radomes over their apertures to protect against rain. X-band(8 - 12 GHz) marine radar antenna on a ship
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EXTREMELY HIGH FREQUENCY (EHF) is the International Telecommunications Union (ITU) designation for the band of radio frequencies in the electromagnetic spectrum from 30 to 300 gigahertz . It lies between the super high frequency band, and the far infrared band which is also referred to as the terahertz gap . Radio waves in this band have wavelengths from ten to one millimetre, giving it the name MILLIMETRE BAND or MILLIMETRE WAVE, sometimes abbreviated MMW or mmW. Millimetre-length electromagnetic waves were first investigated in the 1890s by Indian scientist Jagadish Chandra Bose
Jagadish Chandra Bose. Compared to lower bands, radio waves in this band have high atmospheric attenuation ; they are absorbed by the gases in the atmosphere. Therefore, they have a short range and can only be used for terrestrial communication over about a kilometer. Absorption by humidity in the atmosphere is significant except in desert environments, and attenuation by rain (rain fade ) is a serious problem even over short distances. However the short propagation range allows smaller frequency reuse distances than lower frequencies. The short wavelength allows modest size antennas to have a small beam width, further increasing frequency reuse potential
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TERAHERTZ RADIATION – also known as SUBMILLIMETER RADIATION, TERAHERTZ WAVES, TREMENDOUSLY HIGH FREQUENCY, T-RAYS, T-WAVES, T-LIGHT, T-LUX or THZ – consists of electromagnetic waves within the ITU -designated band of frequencies from 0.3 to 3 terahertz (THz; 1 THz = 1012 Hz ). Wavelengths of radiation in the terahertz band correspondingly range from 1 mm to 0.1 mm (or 100 μm ). Because terahertz radiation begins at a wavelength of one millimeter and proceeds into shorter wavelengths, it is sometimes known as the _submillimeter band_, and its radiation as _submillimeter waves_, especially in astronomy. Terahertz radiation
Terahertz radiationoccupies a middle ground between microwaves and infrared light waves known as the terahertz gap , where technology for its generation and manipulation is in its infancy. It represents the region in the electromagnetic spectrum where the frequency of electromagnetic radiation becomes too high to be measured digitally via electronic counters , so must be measured by proxy using the properties of wavelength and energy . Similarly, the generation and modulation of coherent electromagnetic signals in this frequency range ceases to be possible by the conventional electronic devices used to generate radio waves and microwaves, requiring the development of new devices and techniques
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