Radio waves
98132
225697339
2008-07-14T23:23:55Z
Oli Filth
547762
Reverted 1 edit by [[Special:Contributions/76.0.201.40|76.0.201.40]]; Extremely niche. ([[WP:TW|TW]])
{{MWband}}
'''Radio waves''' are [[Electromagnetic radiation|electromagnetic waves]] occurring on the [[radio frequency]] portion of the [[electromagnetic spectrum]]. A common use is to transport [[information]] through the [[atmosphere]] or [[outer space]] without [[wire]]s. Radio waves are distinguished from other kinds of electromagnetic waves by their [[wavelength]], a relatively long wavelength in the electromagnetic [[spectrum]].
[[Image:RadioWaves.jpg|right|thumb|Diagram of the electric (E) and magnetic (H) fields of Radio Waves emanating from a radio transmitting antenna (small dark vertical line in the center). Radio waves are usually produced by electric current alternating at radio frequency flowing in a special purpose conductor, called an antenna. [[Antenna (radio)|Antenna]] dimensions must generally be comparable to wavelength to work efficiently. Very long waves are not practical because of the enormous antennas needed to produce them, although they are sometimes produced by lightning. Radio waves are also produced by [[radio astronomy|cosmic phenomena]] in deep space. Actually, any kind of reciprocating motion of electric charges or magnets can produce radio waves if it is fast enough. Although very impractical, even a person waving a charged stick very fast can produce faint radio waves.]]
==Propagation==
[[Image:3D Ionospheric Ray Example.gif|right|300px|thumb]]
Propagation is a term that describes the travel of electromagnetic waves, there being three main modes of propagation. The first is a straight line travel: the manner that radio waves travel through deep space (ignoring the slight deviations caused by gravity under the [[theory of relativity]]). A second way is [[skip (radio)|skip]], which is bouncing between the surface of the earth and the [[ionosphere]]. Frequencies between 3 MHz and 30 MHz are most reliable for this kind of propagation, called High Frequency (see image at right). The third way is to hug the surface of the earth as it curves around. Radio waves of very low frequency most often travel this way.
Radio signals can also enter two ionospheric layers of differing electron densities and duct between them. The image at the right illustrates this. Two radio signals of differing elevation angles are broadcast into the ionosphere, where they split into [[Birefringence#Mathematical_description|ordinary]] (red) and [[Birefringence#Mathematical_description|extraordinary]] (green) components. In this example, the ordinary component began ducting between the E and F ionospheric regions.
Although this mode of radio wave propagation is less common than the skip mode, it is nonetheless an important mode because it permits radio signals to travel significant distances with little [[attenuation]].
== Discovery and utilization==
[[Image:Atmospheric electromagnetic transmittance or opacity.jpg|thumb|300px|Rough plot of Earth's atmospheric transmittance (or opacity) to various wavelengths of electromagnetic radiation, including radio waves.]]
{{Main|invention of radio}}
Radio waves were first predicted by mathematical work done in 1865 by [[James Clerk Maxwell]]. Maxwell noticed wave-like properties of light and similarities in electrical and magnetic observations and proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887 [[Heinrich Hertz]] demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical use of radio waves to transfer information through space.
[[Nikola Tesla]] and [[Guglielmo Marconi]] are credited with inventing systems to allow radio waves to be used for communication.
==Radio portion of the electromagnetic spectrum==
Radio waves are divided up into bands by frequency (and corresponding [[wavelength]]) as shown in the radio [[frequency spectrum]] table below.
{| class="wikitable"
|-
! Band name
! [[Abbreviation|Abbr]]
! [[International Telecommunication Union|ITU]] band
! Frequency<BR />and<BR />Wavelength in air
! Example uses
|-
|
|align="center"|
|align="center"|
|align="center" style="white-space: nowrap;"| < 3 [[Hertz|Hz]]<BR />> 100,000 [[kilometer|km]]
|align="center"|
|-
| [[Extremely low frequency]]
|align="center"| ELF
|align="center"| 1
|align="center" style="white-space: nowrap;"| 3–30 [[Hertz|Hz]]<BR />100,000 km – 10,000 km
|align="center"|[[Communication with submarines]]
|-
| [[Super low frequency]]
|align="center"| SLF
|align="center"| 2
|align="center" style="white-space: nowrap;"| 30–300 [[Hertz|Hz]]<BR />10,000 km – 1000 km
|align="center"| [[Communication with submarines]]
|-
| [[Ultra low frequency]]
|align="center"| ULF
|align="center"| 3
|align="center" style="white-space: nowrap;"| 300–3000 [[Hertz|Hz]]<BR />1000 km – 100 km
|align="center"| Communication within mines
|-
| [[Very low frequency]]
|align="center"| VLF
|align="center"| 4
|align="center" style="white-space: nowrap;"| 3–30 [[Kilohertz|kHz]]<BR />100 km – 10 km
|align="center"| Submarine communication, [[Avalanche#Beacons|avalanche beacons]], wireless [[heart rate monitor]]s, [[geophysics]]
|-
| [[Low frequency]]
|align="center"| LF
|align="center"| 5
|align="center" style="white-space: nowrap;"| 30–300 [[Kilohertz|kHz]]<BR />10 km – 1 km
|align="center"| [[Radio navigation|Navigation]], [[radio clock|time signals]], AM [[longwave]] broadcasting
|-
| [[Medium frequency]]
|align="center"| MF
|align="center"| 6
|align="center" style="white-space: nowrap;"| 300–3000 [[Kilohertz|kHz]]<BR />1 km – 100 [[m]]
|align="center"| [[AM radio|AM]] (Medium-wave) broadcasts
|-
| [[High frequency]]
|align="center"| HF
|align="center"| 7
|align="center" style="white-space: nowrap;"| 3–30 [[Megahertz|MHz]]<BR />100 m – 10 m
|align="center"| [[Shortwave]] broadcasts, [[amateur radio]] and over-the-horizon aviation communications
|-
| [[Very high frequency]]
|align="center"| VHF
|align="center"| 8
|align="center" style="white-space: nowrap;"| 30–300 [[Megahertz|MHz]]<BR />10 m – 1 m
|align="center"| [[FM radio|FM]], [[television]] broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications
|-
| [[Ultra high frequency]]
|align="center"| UHF
|align="center"| 9
|align="center" style="white-space: nowrap;"| 300–3000 [[Megahertz|MHz]]<BR />1 m – 100 [[millimeter|mm]]
|align="center"| [[television]] broadcasts, [[microwave]] ovens, [[mobile phone]]s, [[wireless LAN]], [[Bluetooth]], [[GPS]] and Two-Way Radios such as FRS and GMRS Radios
|-
| [[Super high frequency]]
|align="center"| SHF
|align="center"| 10
|align="center" style="white-space: nowrap;"| 3–30 [[Gigahertz|GHz]]<BR />100 mm – 10 mm
|align="center"| [[microwave]] devices, [[wireless LAN]], most modern [[Radar]]s
|-
| [[Extremely high frequency]]
|align="center"| EHF
|align="center"| 11
|align="center" style="white-space: nowrap;"| 30–300 [[Gigahertz|GHz]]<BR />10 mm – 1 mm
|align="center"| [[Radio astronomy]], high-speed [[microwave radio relay]]
|-
|
|align="center"|
|align="center"|
|align="center" style="white-space: nowrap;"| Above 300 [[Gigahertz|GHz]]<BR />< 1 mm
|align="center"|
|}
===Notes===
* Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of [[electromagnetic radiation]], until the atmosphere becomes transparent again in the so-called [[infrared]] and optical window frequency ranges.
* The ELF, SLF, ULF, and VLF bands overlap the AF ([[audio frequency]]) spectrum, which is approximately 20–20,000 Hz. However, sounds are transmitted by atmospheric compression and expansion, and not by electromagnetic energy.
* The SHF and EHF bands are sometimes not considered to be a part of the [[radio spectrum]], forming their own [[microwave|microwave spectrum]].
== Named frequency bands ==
===General===
Broadcast Frequencies:
*Longwave AM Radio = 148.5 - 283.5 kHz (LF)
*Mediumwave AM Radio = 530 kHz - 1710 kHz (MF)
*TV Band I (Channels 2 - 6) = 54 MHz - 88 MHz (VHF)
*FM Radio Band II = 88 MHz - 108 MHz (VHF)
*TV Band III (Channels 7 - 13) = 174 MHz - 216 MHz (VHF)
*TV Bands IV & V (Channels 14 - 69) = 470 MHz - 806 MHz (UHF) [http://etvcookbook.org/extra/frequency.html]
For more information see the NTIA frequency allocation chart: http://www.ntia.doc.gov/osmhome/allochrt.html
=== Amateur radio frequencies ===
The range of allowed frequencies vary between countries. These are just some of the more common bands, often collectively termed [[shortwave]]. The article [[amateur radio]] contains another list.
{| class="wikitable"
|- bgcolor="#CCCCCC"
! Band !! Frequency range
|-
| 160 m || 1.8 to 2.0 MHz
|-
| 80 m || 3.5 to 4.0 MHz
|-
| 60 m || 5.3 to 5.4 MHz
|-
| 40 m || 7 to 7.3 MHz
|-
| 30 m || 10.1 to 10.15 MHz
|-
| 20 m || 14 to 14.35 MHz
|-
| 15 m || 21 to 21.45 MHz
|-
| 12 m || 24.89 to 24.99 MHz
|-
| 10 m || 28.0 to 29.7 MHz
|-
| 6 m || 50 to 54 MHz
|-
| 2 m || 144 to 148 MHz
|-
| 70 cm|| 430 to 440 MHz
|-
| 33 cm|| 902 to 928 MHz
|-
| 23 cm|| 1240 to 1300 MHz
|}
=== IEEE US ===
{| class="wikitable"
|- bgcolor="#CCCCCC"
! Band !! Frequency range !! Origin of name
|-
| [[HF band]] || 3 to 30 MHz || '''H'''igh '''F'''requency
|-
| [[VHF band]] || 30 to 300 MHz || '''V'''ery '''H'''igh '''F'''requency
|-
| [[UHF band]] || 300 to 3000 MHz || '''U'''ltra '''H'''igh '''F'''requency
Frequencies from 216 to 450 MHz were sometimes called P-band: '''P'''revious, since early [[United Kingdom|British]] [[Radar]] used this band but later switched to higher frequencies.
|-
| [[L band]] || 1 to 2 GHz || '''L'''ong wave
|-
| [[S band]] || 2 to 4 GHz || '''S'''hort wave
|-
| [[C band]] || 4 to 8 GHz || '''C'''ompromise between S and X
|-
| [[X band]] || 8 to 12 GHz || Used in [[World War II|WW II]] for [[fire-control system|fire control]], X for cross (as in [[crosshair]])
|-
| [[Ku band|K<sub>u</sub> band]] || 12 to 18 GHz || '''K'''urz-'''u'''nder
|-
| [[K band]] || 18 to 26 GHz || [[German language|German]] '''K'''urz (short)
|-
| [[Ka band|K<sub>a</sub> band]] || 26 to 40 GHz || '''K'''urz-'''a'''bove
|-
| [[V band]] || 40 to 75 GHz
|-
| [[W band]] || 75 to 111 GHz || '''W''' follows V in the [[alphabet]] <!-- guessed -->
|}
=== EU, NATO, US ECM frequency designations ===
{| class="wikitable"
|- bgcolor=#CCCCCC"
! Band !! Frequency range
|-
| [[A band (radio)|A band]] || 0 to 0.25 GHz
|-
| [[B band]] || 0.25 to 0.5 GHz
|-
| [[C band]] || 0.5 to 1.0 GHz
|-
| [[D band]] || 1 to 2 GHz
|-
| [[E band]] || 2 to 3 GHz
|-
| [[F band]] || 3 to 4 GHz
|-
| [[G band]] || 4 to 6 GHz
|-
| [[H band]] || 6 to 8 GHz
|-
| [[I band]] || 8 to 10 GHz
|-
| [[J band]] || 10 to 20 GHz
|-
| [[K band]] || 20 to 40 GHz
|-
| [[L band]] || 40 to 60 GHz
|-
| [[M band]] || 60 to 100 GHz
|}
</blockquote>
=== [[Waveguide]] frequency bands ===
{| class="wikitable"
|- bgcolor=#CCCCCC"
! Band !! Frequency range <ref>[http://www.microwaves101.com/encyclopedia/waveguidedimensions.cfm www.microwaves101.com "Waveguide frequency bands and interior dimensions"]</ref>
|-
| [[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]] || 15.0 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]] || 50 to 75 GHz
|-
| [[W band]] || 75 to 110 GHz
|-
| [[Y band]] || 325 to 500 GHz
|}
</blockquote>
== References ==
{{reflist}}
*ITU-R Recommendation V.431: [http://www.itu.int/rec/R-REC-V.431/en Nomenclature of the frequency and wavelength bands used in telecommunications]. [[International Telecommunication Union]], Geneva.
*IEEE Standard 521-2002: Standard Letter Designations for Radar-Frequency Bands
*AFR 55-44/AR 105-86/OPNAVINST 3430.9A/MCO 3430.1, 27 October 1964 superseded by AFR 55-44/AR 105-86/OPNAVINST 3430.1A/MCO 3430.1A, 6 December 1978: Performing Electronic Countermeasures in the United States and Canada, Attachment 1,ECM Frequency Authorizations.
== See also ==
{{Wiktionary}}
{{Portal|Radio|Radio icon.png}}
*[[Radio propagation]]
*[[Frequency allocation]]
*[[Radio astronomy]]
*[[Radio electronics]]
== References ==
*[[PBS]], Tesla - Master of Lightning - http://www.pbs.org/tesla/ll/ll_whoradio.html
*[[James Clerk Maxwell]], "[[A Dynamical Theory of the Electromagnetic Field]]", ''Philosophical Transactions of the Royal Society of London'' '''155''', 459-512 (1865).
*[http://historical.library.cornell.edu/cgi-bin/cul.cdl/docviewer?did=cdl334&view=50&frames=0&seq=5[[Heinrich Hertz]], "Electric waves: being researches on the propagation of electric action with finite velocity through space"]. Cornell University Library Historical Monographs Collection. {Reprinted by} [http://www.amazon.com/dp/1429740361/ Cornell University Library Digital Collections]
{{Radio spectrum}}
{{EMSpectrum}}
[[Category:Radio technology|Radio waves]]
[[Category:Waves|Radio waves]]
[[Category:Electromagnetic spectrum|Radio waves]]
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