Extremely low frequency
From Wikipedia, the free encyclopedia
Frequency range
| 3 to 30 Hz |
|---|---|
Wavelength range
| 100,000 to 10,000 km, respectively |
| ITU radio bands | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||
| EU / NATO / US ECM radio bands | ||||||||||||
| IEEE radio bands | ||||||||||||
| Other TV and radio bands | ||||||||||||
Extremely low frequency (ELF) is the ITU designation[1] for electromagnetic radiation (radio waves) withfrequencies from 3 to 30 Hz, and corresponding wavelengths of 100,000 to 10,000 kilometers, respectively.[2][3] Inatmospheric science, an alternative definition is usually given, from 3 Hz to 3 kHz.[4][5] In the related magnetospherescience, 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 penetrateseawater, which makes them useful in communication with submarines. The US, Russia, and India are the only nations known to have constructed ELF communication facilities.[6][7][8][9][10][11][12][13] The U.S. facilities were used between 1985 and 2004 but are now decommissioned.[9] 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. The frequency of alternating current flowing in electric power grids, 50 or 60 Hz, also falls within the ELF band, making power grids an unintentional source of ELF radiation.
Contents
[hide]Alternate definitions[edit]
ELF is a subradio frequency.[14] Some medical peer reviewed journal articles refer to ELF in the context of "extremely low frequency (ELF) magnetic fields (MF)" with frequencies of 50 Hz[15] and 50–80 Hz.[16] United States Government agencies, such as NASA, describe ELF as non-ionizing radiation with frequencies between 0 and 300 Hz.[14] The World Health Organization (WHO) have used ELF to refer to the concept of "extremely low frequency (ELF) electric and magnetic fields (EMF)"[17] and have also referred to "ELF electric and magnetic fields in the frequency range >0 to 100,000 Hz (100 kHz)."[18] The WHO also stated that at frequencies between 0 and 300 Hz, "the wavelengths in air are very long (6000 km at 50 Hz and 5000 km at 60 Hz), and, in practical situations, the electric and magnetic fields act independently of one another and are measured separately."[17]
Propagation[edit]
Due to their extremely long wavelength, ELF waves can diffract around large obstacles, and so are not blocked by mountain ranges or the horizon and can travel around the curve of the Earth. ELF and VLF waves propagate long distances by an Earth-ionosphere waveguide mechanism.,[19][20] The Earth is surrounded by a layer of charged particles (ions) in the atmosphere at an altitude of about 60 km at the bottom of the ionosphere, called the D layer which reflects ELF waves. The space between the conductive Earth's surface and the conductive D layer acts as a parallel-plate waveguide which confines ELF waves, allowing them to propagate long distances without escaping into space. Since the height of the layer is much less than one wavelength at ELF frequencies, the only mode that can propagate is the TEM mode in vertical polarization, with the electric field vertical and the magnetic field horizontal. ELF waves have extremely low attenuation of 1 – 2 dB per 1000 km,[20] giving a single transmitter the potential to communicate worldwide.
ELF waves can also travel considerable distances through "lossy" media like earth and seawater, which would absorb higher frequency radio waves.
Schumann resonances[edit]
Main article: Schumann resonances
The attenuation of ELF waves is so low that they can travel completely around the Earth several times before decaying to negligible amplitude, and thus waves radiated from a source in opposite directions circumnavigating the Earth on a great circle path interfere with each other. At certain frequencies these return waves are in phase and add (reinforce), causingstanding waves. In other words, the closed spherical Earth-ionosphere cavity acts as a huge cavity resonator, enhancing ELF radiation at its resonant frequencies. These are called Schumann resonances after German physicist Winfried Otto Schumann who predicted them in 1952, and were detected in the 1950s. The fundamental Schumann resonance is at approximately 7.83 Hz, the frequency at which the wavelength equals the circumference of the Earth, and higher harmonics occur at 14.1, 20.3, 26.4, and 32.4 Hz, etc. Lightning strikes excite these resonances, causing the Earth-ionosphere cavity to "ring" like a bell, resulting in a peak in the noise spectrum at these frequencies, so the Schumann resonances can be used to monitor global thunderstorm activity.
Submarine communications[edit]
The United States Navy utilized extremely low frequencies (ELFs) as radio band and radio communications. The Submarine Integrated Antenna System (SIAS) was a research and development effort to communicate with submerged submarines.[21] The Soviet/Russian Navy also utilized ELFs for submarine communications system, ZEVS.[22] The Indian Navy has an operational ELF communication facility at the INS Kattabomman naval base to communicate with its Arihant class andAkula class submarines.[23][24]
Explanation[edit]
Because of its electrical conductivity, seawater shields submarines from most higher frequency radio waves, making radio communication with submerged submarines at ordinary frequencies impossible. 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 an antenna of the required size on a submarine (the antenna needs to be of an exceptional size in order to achieve successful communication). Generally, ELF signals were used to order a submarine to rise to a shallow depth where it could receive some other form of communication.
Difficulties of ELF communication[edit]
One of the difficulties posed when broadcasting in the ELF frequency range is antenna size, because the length of the antenna must be at least a substantial fraction of the length of the waves. Simply put, a 3 Hz (cycle per second) signal would have a wavelength equal to the distance EM waves travel through a given medium in one third of a second. Taking account of refractive index, ELF waves propagate slightly slower than the speed of light in a vacuum. As used in military applications, the wavelength is 299,792 km (186,282 mi) per second divided by 50–85 Hz, which equals around 3,500 to 6,000 km (2,200 to 3,700 mi) long. This is comparable to the Earth's diameter of around 12,742 km (7,918 mi). Because of this huge size requirement, to transmit internationally using ELF frequencies, the Earth itself forms a significant part of the antenna, and extremely long leads are necessary into the ground. Various means, such as electrical lengthening, are used to construct practical radio stations with smaller sizes.
The US maintained two sites, in the Chequamegon-Nicolet National Forest, Wisconsin and in the Escanaba River State Forest, Michigan (originally named Project Sanguine, then downsized and rechristened Project ELF prior to construction), until they were dismantled, beginning in late September 2004. Both sites used longpower lines, so-called ground dipoles, as leads. These leads were in multiple strands ranging from 22.5 to 45 kilometres (14.0 to 28.0 mi) long. Because of the inefficiency of this method, considerable amounts of electrical power were required to operate the system.
Ecological impact[edit]
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 judgment was not accepted by everyone and, during the time that ELF was in use, some Wisconsin politicians such as Senators Herb Kohl, Russ Feingold and Congressman Dave Obey called for its closure. Similar concerns have, in the past, been raised about electromagnetic radiation and health.
Other uses[edit]
Transmitters in the 22 Hz range are also found in pipeline inspection gauges, also known as "PIGs". The signal is generated as an alternating magnetic field, the transmitter is mounted to or part of the PIG. The PIG is pushed through a pipeline, mostly made of metal. The ELF signal can be detected through the metal on the outside. It is needed to check if a PIG has passed a certain location and to locate a stuck PIG.
Some radio monitoring hobbyists record ELF signals using antennas ranging in size from eighteen inch active antennas up to several thousand feet in length taking advantage of fences, highway guard rails, and even decommissioned railroad tracks, and play them back at higher speeds to more easily observe natural low frequency fluctuations in the Earth's electromagnetic field. Increasing the playback speed increases the pitch, so that it can be brought into the audio frequencyrange for audibility.
Natural sources[edit]
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.[25] Though VLF signals were predominantly generated from lightning discharges, it was found that an observable ELF component (slow tail) followed the VLF component in almost all cases.[26] 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 of 14, 20, 26 and 32 Hz appear as peaks in the ELF spectrum and are called Schumann resonance.
ELF waves have also been tentatively identified on Saturn's moon Titan. Titan's surface is thought to be a poor reflector of ELF waves, so the waves may instead be reflecting off the liquid-ice boundary of a subsurface ocean of water and ammonia, the existence of which is predicted by some theoretical models. Titan's ionosphere is also more complex than Earth's, with the main ionosphere at an altitude of 1,200 km (750 mi) but with an additional layer of charged particles at 63 km (39 mi). This splits Titan's atmosphere into two separate resonating chambers. The source of natural ELF waves on Titan is unclear as there does not appear to be extensive lightning activity.[25]
Huge ELF radiation power outputs of 100,000 times the Sun's output in visible light may be radiated by magnetars. The pulsar in the Crab nebula radiates powers of this order at the frequency 30 hertz.[27] Radiation of this frequency is below the plasma frequency of the interstellar medium, thus this medium is opaque to it, and it cannot be observed from Earth.
Exposure[edit]
In electromagnetic therapy and electromagnetic radiation and health research, electromagnetic spectrum frequencies between 0 and 100 hertz are considered extremely low-frequency fields.[28] Since the late 1970s, questions have been raised whether exposure to ELF electric and magnetic fields (EMF) within this range of frequencies produces adverse health consequences.[18] In October 2005, WHO convened a Task Group of scientific experts to assess any risks to health that might exist from "exposure to ELF electric and magnetic fields in the frequency range >0 to 100,000 Hz (100 kHz) in regards to childhood leukaemia."[18] There are established biological effects from acute exposure at high levels (well above 100 µT) that are explained by recognized biophysical mechanisms[citation needed]. External ELF magnetic fields induce electric fields and currents in the body which, at very high field strengths, cause nerve and muscle stimulation and changes in nerve cell excitability in the central nervous system. Health effects related to short-term, high-level exposure have been established and form the basis of two international exposure limit guidelines (ICNIRP, 1998; IEEE, 2002). At present, these bodies consider the scientific evidence related to possible health effects from long-term, low-level exposure to ELF fields insufficient to justify lowering these quantitative exposure limits. The long-term, low-level exposure is evaluated as average exposure to residential power-frequency magnetic field above 0.3 to 0.4 µT, and it is estimated that only between 1% and 4% of children live in such conditions.[18] A common source of ELF fields in the United States is 60 Hz electric and magnetic fields from high-voltage electric power transmission lines and secondary distribution lines, such as those found in residential neighborhoods.[17][18][28]
In summary, when all of the studies are evaluated together, the evidence suggesting that EMFs may contribute to an increased risk of cancer is very weak.[29][30]Epidemiological studies suggest a possible association between long term occupational exposure to ELF and Alzheimer's disease.[31][32]
ELF effects on human nervous system[edit]
A study by Reilly in 1999 showed that the threshold for direct perception of exposure to ELF RF by human volunteer subjects started at around 2 to 5 kV/m at 60 Hz, with 10% of volunteers detecting the ELF exposure at this level. The percentage of detection increased to 50% of volunteers when the ELF level was raised from 7 to 20 kV/m. 5% of all test subjects considered the perception of ELF at these thresholds annoying.[33]
ELF at human perceivable kV/m levels was said to create an annoying tingling sensation in the areas of the body in contact with clothing, particularly the arms, due to the induction of a surface charge by the ELF. 7% of volunteers described the spark discharges as painful where the subject was well-insulated and touched a grounded object within a 5 kV/m field. 50% of volunteers described a similar spark discharge as painful in a 10 kV/m field.[34]
Patents[edit]
- 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[edit]
References[edit]
Notes[edit]
- ^ "Rec. ITU-R V.431-7, Nomenclature of the frequency and wavelength bands used in telecommunications" (PDF). ITU. Retrieved 20 February 2013.
- ^ NASA "Extremely Low Frequency" Check
|url=value (help). ANL Glossary. Retrieved 28 September 2013. - ^ "Extremely low frequency". ANL Glossary. Retrieved 9 August 2011.
- ^ Liemohn, Michael W. and A. A. CHAN, "Unraveling the Causes of Radiation Belt Enhancements". EOS, TRANSACTIONS, AMERICAN GEOPHYSICAL UNION, Volume 88, Number 42, 16 October 2007, pages 427-440. Republished by NASA and accessed online, 8 February 2010. Adobe File, page 2.
- ^ Barr, R.; Jones, D. Llanwyn; Rodger, C. J. (2000). "ELF and VLF radio waves".Journal of Atmospheric and Solar-Terrestrial Physics. 62 (17-18): 1689–1718.Bibcode:2000JASTP..62.1689B. doi:10.1016/S1364-6826(00)00121-8.
- ^ Wolkoff, E. A.; W. A. Kraimer (May 1993). "Pattern Measurements of U.S. Navy ELF Antennas" (PDF). ELF/VLF/LF Radio Propagation and Systems Aspects. Belgium: AGARD Conference proceedings 28 Sept. – 2 Oct. 1992, NATO. pp. 26.1–26.10. Retrieved 17 February 2012.
- ^ Coe, Lewis (2006). Wireless Radio: A brief history. USA: McFarland. pp. 143–144. ISBN 0786426624.
- ^ a b Sterling, Christopher H. (2008). Military communications: from ancient times to the 21st century. ABC-CLIO. pp. 431–432. ISBN 1851097325.
- ^ Bashkuev, Yu. B.; V. B. Khaptanov; A. V. Khankharaev (December 2003)."Analysis of Propagation Conditions of ELF Radio Waves on the "Zeus"–Transbaikalia Path". Radiophysics and Quantum Electronics. Plenum. 46 (12): 909–917. Bibcode:2003R&QE...46..909B.doi:10.1023/B:RAQE.0000029585.02723.11. Retrieved 17 February 2012.
- ^ Jacobsen, Trond (2001). "ZEVS, The Russian 82 Hz ELF Transmitter". Radio Waves Below 22 kHz. Renato Romero webpage. Retrieved 17 February 2012.External link in
|work=(help) - ^ Hardy, James (28 February 2013). "India makes headway with ELF site construction". IHS Jane's Defence Weekly. Archived from the original on 23 February 2014. Retrieved 23 February 2014.
- ^ "Navy gets new facility to communicate with nuclear submarines prowling underwater". The Times of India. 31 July 2014.
- ^ a b NASA.gov, page 8. ">0 to 300 Hz ... Extremely low frequency (ELF)"Archived 21 July 2011 at the Wayback Machine.
- ^ Legros, A; Beuter, A (2006). "Individual subject sensitivity to extremely low frequency magnetic field". Neurotoxicology. 27 (4): 534–46.doi:10.1016/j.neuro.2006.02.007. PMID 16620992.
- ^ ESTECIO, Marcos Roberto Higino and SILVA, Ana Elizabete. Alterações cromossômicas causadas pela radiação dos monitores de vídeo de computadores. Rev. Saúde Pública [online]. 2002, vol.36, n.3, pp. 330-336. ISSN 0034-8910. Republished by docguide.com. Accessed 8 February 2010.
- ^ a b c "Electromagnetic Fields and Public HealthL - Extremely Low Frequency (ELF)". Fact Sheet N205. November 1998. World Health Organization. Accessed 12 February 2010. "ELF fields are defined as those having frequencies up to 300 Hz. ... the electric and magnetic fields act independently of one another and are measured separately."
- ^ a b c d e "Electromagnetic fields and public health". Fact Sheet No. 322, June 2007. World Health Organization, Accessed 7 February 2010.
- ^ Barr, R.; Jones, D. Llanwyn; Rodger, C.J. (June 14, 2000). "ELF and VLF radio waves" (PDF). Journal of Atmospheric and Solar-Terrestrial Physics. Pergamon.62: 1689–1718. doi:10.1016/s1364-6826(00)00121-8. Retrieved 2012-02-23., p.1692, on VLF Group website, Stanford Univ.
- ^ a b Jursa, Adolph S., Ed. (1985). Handbook of Geophysics and the Space Environment, 4th Ed. (PDF). Air Force Geophysics Laboratory, U.S. Air Force. pp. 10.25–10.27.
- ^ "U.S. Navy: Vision...Presence...Power." SENSORS - Subsurface Sensors. US Navy. Accessed 7 February 2010.
- ^ http://www.vlf.it/zevs/zevs.htm ZEVS, the Russian 82 Hz ELF transmitter
- ^ "Navy gets new facility to communicate with nuclear submarines prowling underwater". The Times of India. 31 July 2014.
- ^ http://www.janes.com/article/11147/india-makes-headway-with-elf-site-construction
- ^ a b "Titan's Mysterious Radio Wave". Jet Propulsion Laboratory. 1 June 2007. Retrieved 2007-06-02. Republished as "Casini - Unlocking Saturn's Secrets - Titan's mysterious radio wave". 22 November 2007. NASA. Accessed 7 February 2010.
- ^ Tepley, Lee R. "A Comparison of Sferics as Observed in the Very Low Frequency and Extremely Low Frequency Bands". Stanford Research Institute Menlo Park, California. 10 August 1959. 64(12), 2315–2329. Summary republished by American Geophysical Union. Accessed 13 February 2010
- ^ http://www.cv.nrao.edu/course/astr534/Pulsars.html
- ^ a b Cleary, Stephen F. "Electromagnetic Field: A Danger?". The New Book of Knowledge - Medicine And Health. 1990. 164-74. ISBN 0-7172-8244-9.
- ^ GC.ca
- ^ "Expertise de l'Afsset sur les effets sanitaires des champs électromagnétiques d'extrêmement basses fréquences" (in French). 6 April 2010. Retrieved 23 April2010.
- ^ García AM, Sisternas A, Hoyos SP (April 2008). "Occupational exposure to extremely low frequency electric and magnetic fields and Alzheimer disease: a meta-analysis". International Journal of Epidemiology. 37 (2): 329–40.doi:10.1093/ije/dym295. PMID 18245151.
- ^ Scientific Committee on Emerging; Newly Identified Health Risks-SCENIHR (January 2009). "Health Effects of Exposure to EMF" (PDF). Brussels: Directorate General for Health&Consumers; European Commission: 4–5. Retrieved2010-04-27.
- ^ Reilly, JP (1999). "Comments concerning "Guidelines for limiting exposure to time-varying elec- tric, magnetic and electromagnetic fields (up to 300 GHz)".".Health Phys. 76 (3): 314–315.
- ^ Extremely Low Frequency Fields Environmental Health Criteria Monograph No.238, chapter 5, page 121, WHO
General information[edit]
- Non-ionizing radiation, Part 1: Static and Extremely Low-Frequency (ELF) Electric and Magnetic Fields (2002) by the IARC. (Non-Ionizing Radiation)
Radio spectrum
From Wikipedia, the free encyclopedia
(Redirected from ITU radio bands)
ITU radio bands
1 (ELF) 2 (SLF) 3 (ULF) 4 (VLF) 5 (LF) 6 (MF) 7 (HF) 8 (VHF) 9 (UHF) 10 (SHF) 11 (EHF) 12 (THF)
EU / NATO / US ECM radio bands
IEEE radio bands
Other TV and radio bands
Part of a series on Antennas 
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 intelecommunication. 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 Union(ITU).[1]
Different parts of the radio spectrum are appointed by the ITU for different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio Regulations (RR).[2] 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).[3]
From Wikipedia, the free encyclopedia
(Redirected from ITU radio bands)
| ITU radio bands | ||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| ||||||||||||
| EU / NATO / US ECM radio bands | ||||||||||||
| IEEE radio bands | ||||||||||||
| Other TV and radio bands | ||||||||||||
| Part of a series on |
| Antennas |
|---|
 |
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 intelecommunication. 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 Union(ITU).[1]
Different parts of the radio spectrum are appointed by the ITU for different radio transmission technologies and applications; some 40 radiocommunication services are defined in the ITU's Radio Regulations (RR).[2] 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).[3]
Contents
By frequency[edit]
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.
Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges.
To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies.
Each of these bands has a basic bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility oftransmitters and receivers. See detail of bands:http://www.ntia.doc.gov/files/ntia/Spectrum_Use_Summary_Master-06212010.pdf
As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10n) metres, with corresponding frequency of 3×108-n hertz, and each covering a decade of frequency or wavelength. Each of these bands has a traditional name. For example, the term high frequency (HF) designates the wavelength range from 100 to 10 metres, corresponding to a frequency range of 3 MHz to 30 MHz. This is just a naming convention and is not related to allocation; the ITU further divides each band into subbands allocated to different uses.
Band name Abbreviation ITU band Frequency
and
wavelength in air Example uses Extremely low frequency ELF 1 3–30 Hz
100,000 km – 10,000 km Communication with submarines Super low frequency SLF 2 30–300 Hz
10,000 km – 1000 km Communication with submarines Ultra low frequency ULF 3 300–3000 Hz
1000 km – 100 km Submarine communication, communication within mines Very low frequency VLF 4 3–30 kHz
100 km – 10 km Navigation, time signals, submarine communication, wireless heart rate monitors,geophysics Low frequency LF 5 30–300 kHz
10 km – 1 km Navigation, clock time signals, AM longwave broadcasting (Europe and parts of Asia), RFID,amateur radio Medium frequency MF 6 300–3000 kHz
1 km – 100 m AM (medium-wave) broadcasts, amateur radio, avalanche beacons High frequency HF 7 3–30 MHz
100 m – 10 m Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFID, over-the-horizon radar, automatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio communications, marine and mobile radio telephony Very high frequency VHF 8 30–300 MHz
10 m – 1 m FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications, land mobile and maritime mobile communications, amateur radio, weather radio Ultra high frequency UHF 9 300–3000 MHz
1 m – 100 mm Television broadcasts, microwave oven, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS and two-way radios such as land mobile, FRS and GMRS radios, amateur radio, satellite radio Super high frequency SHF 10 3–30 GHz
100 mm – 10 mm Radio astronomy, microwave devices/communications, wireless LAN, most modern radars,communications satellites, cable and satellite television broadcasting, DBS, amateur radio,satellite radio Extremely high frequency EHF 11 30–300 GHz
10 mm – 1 mm Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weapon, millimeter wave scanner Terahertz orTremendously high frequency THz or THF 12 300–3000 GHz
1 mm – 100 μm Experimental medical imaging to replace X-rays, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/communications,remote sensing, amateur radio
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.
Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges.
To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies.
Each of these bands has a basic bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility oftransmitters and receivers. See detail of bands:http://www.ntia.doc.gov/files/ntia/Spectrum_Use_Summary_Master-06212010.pdf
As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10n) metres, with corresponding frequency of 3×108-n hertz, and each covering a decade of frequency or wavelength. Each of these bands has a traditional name. For example, the term high frequency (HF) designates the wavelength range from 100 to 10 metres, corresponding to a frequency range of 3 MHz to 30 MHz. This is just a naming convention and is not related to allocation; the ITU further divides each band into subbands allocated to different uses.
| Band name | Abbreviation | ITU band | Frequency and wavelength in air | Example uses |
|---|---|---|---|---|
| Extremely low frequency | ELF | 1 | 3–30 Hz 100,000 km – 10,000 km | Communication with submarines |
| Super low frequency | SLF | 2 | 30–300 Hz 10,000 km – 1000 km | Communication with submarines |
| Ultra low frequency | ULF | 3 | 300–3000 Hz 1000 km – 100 km | Submarine communication, communication within mines |
| Very low frequency | VLF | 4 | 3–30 kHz 100 km – 10 km | Navigation, time signals, submarine communication, wireless heart rate monitors,geophysics |
| Low frequency | LF | 5 | 30–300 kHz 10 km – 1 km | Navigation, clock time signals, AM longwave broadcasting (Europe and parts of Asia), RFID,amateur radio |
| Medium frequency | MF | 6 | 300–3000 kHz 1 km – 100 m | AM (medium-wave) broadcasts, amateur radio, avalanche beacons |
| High frequency | HF | 7 | 3–30 MHz 100 m – 10 m | Shortwave broadcasts, citizens' band radio, amateur radio and over-the-horizon aviation communications, RFID, over-the-horizon radar, automatic link establishment (ALE) / near-vertical incidence skywave (NVIS) radio communications, marine and mobile radio telephony |
| Very high frequency | VHF | 8 | 30–300 MHz 10 m – 1 m | FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications, land mobile and maritime mobile communications, amateur radio, weather radio |
| Ultra high frequency | UHF | 9 | 300–3000 MHz 1 m – 100 mm | Television broadcasts, microwave oven, microwave devices/communications, radio astronomy, mobile phones, wireless LAN, Bluetooth, ZigBee, GPS and two-way radios such as land mobile, FRS and GMRS radios, amateur radio, satellite radio |
| Super high frequency | SHF | 10 | 3–30 GHz 100 mm – 10 mm | Radio astronomy, microwave devices/communications, wireless LAN, most modern radars,communications satellites, cable and satellite television broadcasting, DBS, amateur radio,satellite radio |
| Extremely high frequency | EHF | 11 | 30–300 GHz 10 mm – 1 mm | Radio astronomy, high-frequency microwave radio relay, microwave remote sensing, amateur radio, directed-energy weapon, millimeter wave scanner |
| Terahertz orTremendously high frequency | THz or THF | 12 | 300–3000 GHz 1 mm – 100 μm | Experimental medical imaging to replace X-rays, ultrafast molecular dynamics, condensed-matter physics, terahertz time-domain spectroscopy, terahertz computing/communications,remote sensing, amateur radio |
ITU[edit]
The ITU radio bands are designations defined in the ITU Radio Regulations. Article 2, provision No. 2.1 states that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table[4]".
The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B.C. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942. (For example, the approximate geometric mean of Band 7 is 10 MHz, or 107 Hz.)[5]
Table of ITU Radio Bands
Band Number Symbols Frequency Range Wavelength Range† 4 VLF 3 to 30 kHz 10 to 100 km 5 LF 30 to 300 kHz 1 to 10 km 6 MF 300 to 3000 kHz 100 to 1000 m 7 HF 3 to 30 MHz 10 to 100 m 8 VHF 30 to 300 MHz 1 to 10 m 9 UHF 300 to 3000 MHz 10 to 100 cm 10 SHF 3 to 30 GHz 1 to 10 cm 11 EHF 30 to 300 GHz 1 to 10 mm 12 THF 300 to 3000 GHz 0.1 to 1 mm
† This column does not form part of the table in Provision No. 2.1 of the Radio Regulations
The ITU radio bands are designations defined in the ITU Radio Regulations. Article 2, provision No. 2.1 states that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table[4]".
The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B.C. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942. (For example, the approximate geometric mean of Band 7 is 10 MHz, or 107 Hz.)[5]
| Band Number | Symbols | Frequency Range | Wavelength Range† |
|---|---|---|---|
| 4 | VLF | 3 to 30 kHz | 10 to 100 km |
| 5 | LF | 30 to 300 kHz | 1 to 10 km |
| 6 | MF | 300 to 3000 kHz | 100 to 1000 m |
| 7 | HF | 3 to 30 MHz | 10 to 100 m |
| 8 | VHF | 30 to 300 MHz | 1 to 10 m |
| 9 | UHF | 300 to 3000 MHz | 10 to 100 cm |
| 10 | SHF | 3 to 30 GHz | 1 to 10 cm |
| 11 | EHF | 30 to 300 GHz | 1 to 10 mm |
| 12 | THF | 300 to 3000 GHz | 0.1 to 1 mm |
† This column does not form part of the table in Provision No. 2.1 of the Radio Regulations
IEEE[edit]
Radar-frequency bands according to IEEE standard[6]
Band
designation Frequency range
[citation needed]HF 0.003 to 0.03 GHz High Frequency[7] VHF 0.03 to 0.3 GHz Very High Frequency[7] UHF 0.3 to 1 GHz Ultra High Frequency[7] L 1 to 2 GHz Long wave S 2 to 4 GHz Short wave C 4 to 8 GHz Compromise between S and X X 8 to 12 GHz Used in WW II for fire control, X for cross (as in crosshair). Exotic.[8] Ku 12 to 18 GHz Kurz-under K 18 to 27 GHz Kurz (German for "short") Ka 27 to 40 GHz Kurz-above V 40 to 75 GHz W 75 to 110 GHz W follows V in the alphabet mm or G 110 to 300 GHz[note 1] Millimeter[6]
| Band designation | Frequency range | [citation needed] |
|---|---|---|
| HF | 0.003 to 0.03 GHz | High Frequency[7] |
| VHF | 0.03 to 0.3 GHz | Very High Frequency[7] |
| UHF | 0.3 to 1 GHz | Ultra High Frequency[7] |
| L | 1 to 2 GHz | Long wave |
| S | 2 to 4 GHz | Short wave |
| C | 4 to 8 GHz | Compromise between S and X |
| X | 8 to 12 GHz | Used in WW II for fire control, X for cross (as in crosshair). Exotic.[8] |
| Ku | 12 to 18 GHz | Kurz-under |
| K | 18 to 27 GHz | Kurz (German for "short") |
| Ka | 27 to 40 GHz | Kurz-above |
| V | 40 to 75 GHz | |
| W | 75 to 110 GHz | W follows V in the alphabet |
| mm or G | 110 to 300 GHz[note 1] | Millimeter[6] |
EU, NATO, US ECM frequency designations[edit]
NATO LETTER BAND DESIGNATION[9][8][10] BROADCASTING
BAND
DESIGNATION NEW NOMENCLATURE OLD NOMENCLATURE BAND FREQUENCY (MHz) BAND FREQUENCY (MHz) A 0 – 250 I 100 – 150 Band I
47 – 68 MHz (TV) Band II
87.5 – 108 MHz (FM) G 150 – 225 Band III
174 – 230 MHz (TV) B 250 – 500 P 225 – 390 C 500 – 1 000 L 390 – 1 550 Band IV
470 – 582 MHz (TV) Band V
582 – 862 MHz (TV) D 1 000 – 2 000 S 1 550 – 3 900 E 2 000 – 3 000 F 3 000 – 4 000 G 4 000 – 6 000 C 3 900 – 6 200 H 6 000 – 8 000 X 6 200 – 10 900 I 8 000 – 10 000 J 10 000 – 20 000 Ku 10 900 – 20 000 K 20 000 – 40 000 Ka 20 000 – 36 000 L 40 000 – 60 000 Q 36 000 – 46 000 V 46 000 – 56 000 M 60 000 – 100 000 W 56 000 – 100 000 US- MILITARY / SACLANT N 100 000 – 200 000 O 100 000 – 200 000
| NATO LETTER BAND DESIGNATION[9][8][10] | BROADCASTING BAND DESIGNATION | ||||||
|---|---|---|---|---|---|---|---|
| NEW NOMENCLATURE | OLD NOMENCLATURE | ||||||
| BAND | FREQUENCY (MHz) | BAND | FREQUENCY (MHz) | ||||
| A | 0 – 250 | I | 100 – 150 | Band I 47 – 68 MHz (TV) | |||
| Band II 87.5 – 108 MHz (FM) | |||||||
| G | 150 – 225 | Band III 174 – 230 MHz (TV) | |||||
| B | 250 – 500 | P | 225 – 390 | ||||
| C | 500 – 1 000 | L | 390 – 1 550 | Band IV 470 – 582 MHz (TV) | |||
| Band V 582 – 862 MHz (TV) | |||||||
| D | 1 000 – 2 000 | S | 1 550 – 3 900 | ||||
| E | 2 000 – 3 000 | ||||||
| F | 3 000 – 4 000 | ||||||
| G | 4 000 – 6 000 | C | 3 900 – 6 200 | ||||
| H | 6 000 – 8 000 | X | 6 200 – 10 900 | ||||
| I | 8 000 – 10 000 | ||||||
| J | 10 000 – 20 000 | Ku | 10 900 – 20 000 | ||||
| K | 20 000 – 40 000 | Ka | 20 000 – 36 000 | ||||
| L | 40 000 – 60 000 | Q | 36 000 – 46 000 | ||||
| V | 46 000 – 56 000 | ||||||
| M | 60 000 – 100 000 | W | 56 000 – 100 000 | ||||
| US- MILITARY / SACLANT | |||||||
| N | 100 000 – 200 000 | ||||||
| O | 100 000 – 200 000 | ||||||
Waveguide frequency bands[edit]
Band Frequency range [11] R band 1.70 to 2.60 GHz D band 2.20 to 3.30 GHz S band 2.60 to 3.95 GHz E band 3.30 to 4.90 GHz G band 3.95 to 5.85 GHz F band 4.90 to 7.05 GHz C band 5.85 to 8.20 GHz H band 7.05 to 10.10 GHz X band 8.2 to 12.4 GHz Ku band 12.4 to 18.0 GHz K band 18.0 to 26.5 GHz Ka band 26.5 to 40.0 GHz Q band 33 to 50 GHz U band 40 to 60 GHz V band 40 to 75 GHz E band 60 to 90 GHz W band 75 to 110 GHz F band 90 to 140 GHz D band 110 to 170 GHz Y band 325 to 500 GHz
| Band | Frequency range [11] |
|---|---|
| R band | 1.70 to 2.60 GHz |
| D band | 2.20 to 3.30 GHz |
| S band | 2.60 to 3.95 GHz |
| E band | 3.30 to 4.90 GHz |
| G band | 3.95 to 5.85 GHz |
| F band | 4.90 to 7.05 GHz |
| C band | 5.85 to 8.20 GHz |
| H band | 7.05 to 10.10 GHz |
| X band | 8.2 to 12.4 GHz |
| Ku band | 12.4 to 18.0 GHz |
| K band | 18.0 to 26.5 GHz |
| Ka band | 26.5 to 40.0 GHz |
| Q band | 33 to 50 GHz |
| U band | 40 to 60 GHz |
| V band | 40 to 75 GHz |
| E band | 60 to 90 GHz |
| W band | 75 to 110 GHz |
| F band | 90 to 140 GHz |
| D band | 110 to 170 GHz |
| Y band | 325 to 500 GHz |
Comparison of radio band designation standards[edit]
Frequency IEEE[6] EU,
NATO,
US ECM ITU no. abbr. A 3 Hz 1 ELF 30 Hz 2 SLF 300 Hz 3 ULF 3 kHz 4 VLF 30 kHz 5 LF 300 kHz 6 MF 3 MHz HF 7 HF 30 MHz VHF 8 VHF 250 MHz B 300 MHz UHF 9 UHF 500 MHz C 1 GHz L D 2 GHz S E 3 GHz F 10 SHF 4 GHz C G 6 GHz H 8 GHz X I 10 GHz J 12 GHz Ku 18 GHz K 20 GHz K 27 GHz Ka 30 GHz 11 EHF 40 GHz V L 60 GHz M 75 GHz W 100 GHz 110 GHz mm 300 GHz 12 THF 3 THz
| Frequency | IEEE[6] | EU, NATO, US ECM | ITU | ||
|---|---|---|---|---|---|
| no. | abbr. | ||||
| A | |||||
| 3 Hz | 1 | ELF | |||
| 30 Hz | 2 | SLF | |||
| 300 Hz | 3 | ULF | |||
| 3 kHz | 4 | VLF | |||
| 30 kHz | 5 | LF | |||
| 300 kHz | 6 | MF | |||
| 3 MHz | HF | 7 | HF | ||
| 30 MHz | VHF | 8 | VHF | ||
| 250 MHz | B | ||||
| 300 MHz | UHF | 9 | UHF | ||
| 500 MHz | C | ||||
| 1 GHz | L | D | |||
| 2 GHz | S | E | |||
| 3 GHz | F | 10 | SHF | ||
| 4 GHz | C | G | |||
| 6 GHz | H | ||||
| 8 GHz | X | I | |||
| 10 GHz | J | ||||
| 12 GHz | Ku | ||||
| 18 GHz | K | ||||
| 20 GHz | K | ||||
| 27 GHz | Ka | ||||
| 30 GHz | 11 | EHF | |||
| 40 GHz | V | L | |||
| 60 GHz | M | ||||
| 75 GHz | W | ||||
| 100 GHz | |||||
| 110 GHz | mm | ||||
| 300 GHz | 12 | THF | |||
| 3 THz | |||||
By application [edit]
Broadcasting[edit]
Broadcast frequencies:
- Longwave AM Radio = 148.5 kHz – 283.5 kHz (LF)
- Mediumwave AM Radio = 530 kHz – 1710 kHz (MF)
- Shortwave AM Radio = 3 MHz – 30 MHz (HF)
Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band. Since VHF and UHF frequencies are desirable for many uses in urban areas, in North America some parts of the former television broadcasting band have been reassigned tocellular phone and various land mobile communications systems. Even within the allocation still dedicated to television, TV-band devices use channels without local broadcasters.
The Apex band in the United States was a pre-WWII allocation for VHF audio broadcasting; it was made obsolete after the introduction of FM broadcasting.
Broadcast frequencies:
- Longwave AM Radio = 148.5 kHz – 283.5 kHz (LF)
- Mediumwave AM Radio = 530 kHz – 1710 kHz (MF)
- Shortwave AM Radio = 3 MHz – 30 MHz (HF)
Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band. Since VHF and UHF frequencies are desirable for many uses in urban areas, in North America some parts of the former television broadcasting band have been reassigned tocellular phone and various land mobile communications systems. Even within the allocation still dedicated to television, TV-band devices use channels without local broadcasters.
The Apex band in the United States was a pre-WWII allocation for VHF audio broadcasting; it was made obsolete after the introduction of FM broadcasting.
Air band[edit]
Marine band[edit]
The greatest incentive for development of radio was the need to communicate with ships out of visual range of shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-wave transmitters. High-frequency allocations are still designated for ships, although satellite systems have taken over some of the safety applications previously served by 500 kHz and other frequencies. 2182 kHz is a medium-wave frequency still used for marine emergency communication.
Marine VHF radio is used in coastal waters and relatively short-range communication between vessels and to shore stations. Radios are channelized, with different channels used for different purposes; marine Channel 16 is used for calling and emergencies.
The greatest incentive for development of radio was the need to communicate with ships out of visual range of shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-wave transmitters. High-frequency allocations are still designated for ships, although satellite systems have taken over some of the safety applications previously served by 500 kHz and other frequencies. 2182 kHz is a medium-wave frequency still used for marine emergency communication.
Marine VHF radio is used in coastal waters and relatively short-range communication between vessels and to shore stations. Radios are channelized, with different channels used for different purposes; marine Channel 16 is used for calling and emergencies.
Amateur radio frequencies[edit]
Amateur radio frequency allocations vary around the world. Several bands are common for amateurs worldwide, usually in the HF part of the spectrum. Other bands are national or regional allocations only due to differing allocations for other services, especially in the VHF and UHF parts of the radio spectrum.
Amateur radio frequency allocations vary around the world. Several bands are common for amateurs worldwide, usually in the HF part of the spectrum. Other bands are national or regional allocations only due to differing allocations for other services, especially in the VHF and UHF parts of the radio spectrum.
Citizens' band and personal radio services[edit]
Citizens' band radio is allocated in many countries, using channelized radios in the upper HF part of the spectrum (around 27 MHz). It is used for personal, small business and hobby purposes. Other frequency allocations are used for similar services in different jurisdictions, for example UHF CB is allocated in Australia. A wide range of personal radio services exist around the world, usually emphasizing short-range communication between individuals or for small businesses, simplified or no license requirements, and usually FM transceivers using around 1 watt or less.
Citizens' band radio is allocated in many countries, using channelized radios in the upper HF part of the spectrum (around 27 MHz). It is used for personal, small business and hobby purposes. Other frequency allocations are used for similar services in different jurisdictions, for example UHF CB is allocated in Australia. A wide range of personal radio services exist around the world, usually emphasizing short-range communication between individuals or for small businesses, simplified or no license requirements, and usually FM transceivers using around 1 watt or less.
Industrial, scientific, medical[edit]
The ISM bands were initially reserved for non-communications uses of RF energy, such as microwave ovens, radio-frequency heating, and similar purposes. However, in recent years the largest use of these bands has been by short-range low-power communications systems, since users do not have to hold a radio operator's license. Cordless telephones, wireless computer networks, Bluetooth devices, and garage door openers all use the ISM bands. ISM devices do not have regulatory protection against interference from other users of the band.
The ISM bands were initially reserved for non-communications uses of RF energy, such as microwave ovens, radio-frequency heating, and similar purposes. However, in recent years the largest use of these bands has been by short-range low-power communications systems, since users do not have to hold a radio operator's license. Cordless telephones, wireless computer networks, Bluetooth devices, and garage door openers all use the ISM bands. ISM devices do not have regulatory protection against interference from other users of the band.
Land mobile bands[edit]
Bands of frequencies, especially in the VHF and UHF parts of the spectrum, are allocated for communication between fixed base stations and land mobile vehicle-mounted or portable transceivers. In the United States these services are informally known as business band radio. See also Professional mobile radio.
Police radio and other public safety services such as fire departments and ambulances are generally found in the VHF and UHF parts of the spectrum. Trunkingsystems are often used to make most efficient use of the limited number of frequencies available.
The demand for mobile telephone service has led to large blocks of radio spectrum allocated to cellular frequencies.
Bands of frequencies, especially in the VHF and UHF parts of the spectrum, are allocated for communication between fixed base stations and land mobile vehicle-mounted or portable transceivers. In the United States these services are informally known as business band radio. See also Professional mobile radio.
Police radio and other public safety services such as fire departments and ambulances are generally found in the VHF and UHF parts of the spectrum. Trunkingsystems are often used to make most efficient use of the limited number of frequencies available.
The demand for mobile telephone service has led to large blocks of radio spectrum allocated to cellular frequencies.
Radio control[edit]
Reliable radio control uses bands dedicated to the purpose. Radio-controlled toys may use portions of unlicensed spectrum in the 27 MHz or 49 MHz bands, but more costly aircraft, boat, or land vehicle models use dedicated radio control frequencies near 72 MHz to avoid interference by unlicensed uses. The 21st century has seen a move to 2.4 gigahertz spread spectrum RC control systems.
Licensed amateur radio operators use portions of the 6-meter band in North America. Industrial remote control of cranes or railway locomotives use assigned frequencies that vary by area.
Reliable radio control uses bands dedicated to the purpose. Radio-controlled toys may use portions of unlicensed spectrum in the 27 MHz or 49 MHz bands, but more costly aircraft, boat, or land vehicle models use dedicated radio control frequencies near 72 MHz to avoid interference by unlicensed uses. The 21st century has seen a move to 2.4 gigahertz spread spectrum RC control systems.
Licensed amateur radio operators use portions of the 6-meter band in North America. Industrial remote control of cranes or railway locomotives use assigned frequencies that vary by area.
Radar[edit]
Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on bands not used for other purposes. Most radar bands are in the microwave part of the spectrum, although certain important applications for meteorology make use of powerful transmitters in the UHF band. Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, or include waves of any lower frequency. At 300 GHz, the corresponding wavelength is 1 mm (0.039 in), and at 3 kHz is 100 km (62 mi). Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are generated by lightning, or by astronomical objects.
Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, computer networks and innumerable other applications. Radio waves are generated by radio transmitters and received by radio receivers. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.
To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union (ITU), which defines radio waves as "electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide".[1] The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses
Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on bands not used for other purposes. Most radar bands are in the microwave part of the spectrum, although certain important applications for meteorology make use of powerful transmitters in the UHF band. Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies as high as 300 GHz to as low as 3 kHz, though some definitions describe waves above 1 or 3 GHz as microwaves, or include waves of any lower frequency. At 300 GHz, the corresponding wavelength is 1 mm (0.039 in), and at 3 kHz is 100 km (62 mi). Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are generated by lightning, or by astronomical objects.
Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, computer networks and innumerable other applications. Radio waves are generated by radio transmitters and received by radio receivers. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves), shorter waves can reflect off the ionosphere and return to earth beyond the horizon (skywaves), while much shorter wavelengths bend or diffract very little and travel on a line of sight, so their propagation distances are limited to the visual horizon.
To prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by law, coordinated by an international body called the International Telecommunications Union (ITU), which defines radio waves as "electromagnetic waves of frequencies arbitrarily lower than 3 000 GHz, propagated in space without artificial guide".[1] The radio spectrum is divided into a number of radio bands on the basis of frequency, allocated to different uses
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