Radio: Béda antarrépisi
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'''Radio''' nyaeta [[wireless|pangiriman sinyal tanpa kabel]], ku cara numpangan atawa nga-[[modulasi]] [[radiasi elektromagnetik|gelombang elektromagnetik]] ku [[frekuensi|frekuensi-frekuensi]] handapeun [[cahaya]] katenjo. [[rambatan radio|Rambatan]] radiasi elektromagnetik dimungkinkeun ku cara ngaayun-ayun medan magnetic. Ieu gelombang henteu merlukeun midiyeum pikeung ngaliwat. Informasi dibawa sacara sistematik ku cara ngarobah ([[modulasi|numpangan]]) sababaraha sifat gelombang anu dipancarkeun, saperti amplitudo atawa frekuensina. Mangsa gelombang radio ngaliwatan konduktor elektrik, medan anu ngayun-ambing ngahasilkeun arus listrik bulak-balik dina konduktor. Arus listrik ieu bisa dideteksi jeung dirobah kana sinyal sora atawa sinyal liana [[demodulation|detected]] and transformed into sound or other signals that carry information.
Sanajan [[Nikola Tesla]] anu munggaran medarkeun yen komunikasi nir-kabel bisa dilaksanakeun, persisna dina taun 1893, [[Guglielmo Marconi]] asal Italia, ngarupakeun panimu anu munggaran ngembangkeun komunikasi radio. Manehna ngirim jeung narima sinyal radio munggaran di Italia dina taun 1895.<br>
Kecap 'radio' digunakeun pikeun ngagambarkeun ieu fenomena.
{{tarjamahkeun|Inggris}}
==Etimologi==
Originally, radio or radioteleography was called 'wireless telegraphy', which was shortened to 'wireless'. The prefix ''radio-'' in the sense of wireless transmission was first recorded in the word ''radioconductor'', coined by the French physicist [[Edouard Branly]] in 1897 and based on the verb ''to radiate'' (in Latin "radius" means "spoke of a wheel, beam of light, ray"). 'Radio' as a noun is said to have been coined by advertising expert [[Waldo Warren]] (White 1944). The word appears in a 1907 article by [[Lee de Forest]], was adopted by the [[United States Navy]] in 1912 and became common by the time of the first commercial broadcasts in the United States in the 1920s. (The noun 'broadcasting' itself came from an agricultural term, meaning 'scattering seeds'.) The term was then adopted by other languages in Europe and Asia, although British Commonwealth countries retained the term 'wireless' until the mid-20th century. In Japanese, the term 'wireless' is the basis for the term 'radio wave' although the term for the device that listens to radio waves is literally 'device for receiving sounds'.
In recent years the term 'wireless' has gained renewed popularity through the rapid growth of short range networking, e.g., [[WLAN]] ('Wireless Local Area Network'), [[WiFi]] and [[Bluetooth]] as well as mobile telephony, e.g., [[GSM]] and [[UMTS]]. Today, the term 'radio' often refers to the actual transceiver device or chip, whereas 'wireless' refers to the system and/or method used for radio communication. Hence one talks about radio transceivers and Radio Frequency Identification ([[RFID]]), but about wireless devices and wireless sensor networks.
== Invention ==
{{see|Invention of radio}}
Although invention was long attributed to [[Guglielmo Marconi]], the identity of the original [[invention of radio|inventor of radio]], at the time called [[wireless telegraphy]], is contentious[http://www.gutenberg.org/files/15207/15207-8.txt]. Development from a laboratory demonstration to commercial utility spanned several decades and required the efforts of many practitioners. The controversy over who invented the radio, with the benefit of hindsight, can be broken down as follows:
*In 1887, [[David E. Hughes]] transmitted Morse code by radio at and below the [[Super low frequency]] range (via a clockwork transmitter).
*In 1888, [[Heinrich Rudolf Hertz|Heinrich Hertz]] produced and measured the [[Ultra High Frequency]] range (via a [[sparkgap transmitter]]).
*In 1891, [[Nikola Tesla]] began wireless research. He developed means to reliably produce radio frequencies, publicly demonstrated the principles of radio, and transmitted long-distance signals.
*Between 1893 and 1894, [[Roberto Landell de Moura]], a Brazilian priest and scientist, conducted experiments. He did not publicise his achievement until 1900 but later obtained Brazilian patent.
*In 1894 in [[Kolkata]] (Calcutta), Sir [[Jagdish Chandra Bose|Jagdish Chandra Bose (J. C. Bose)]] invented the [[mercury (element)|mercury]] [[coherer]], together with the [[telephone]] receiver.
*[[Alexander Stepanovich Popov]], in 1894, built his first radio receiver, which contained a [[coherer]] but actually coherer was first demonstrated by J.C. Bose. Popov demonstrated the coherer, further refined as a lightning detector, to the Russian Physical and Chemical Society on [[May 7]], 1895.
*In 1894, [[Guglielmo Marconi]] read about Hertz's and Tesla's work on wireless telegraphy, and began his own experiments.
*In December of 1901 [[Guglielmo Marconi]] used J.C. Bose's inventions to receive the radio signal in his first transatlantic radio communication over a distance of 2000 miles from Poldhu, UK, to St. Johns, Newfoundland. Marconi was celebrated worldwide for this achievement. Soon after the patent was given to Marconi. He even received the Nobel Prize.
*In early 1900s [[Reginald Fessenden]] <small><sub>[http://www.invent.org/hall_of_fame/59.html]</sub></small> and [[Lee de Forest]] invented [[amplitude modulation|amplitude-modulated]] ([[AM radio|AM]]) radio) allowing an audio signal to be sent over the air.
*In 1935 [[Edwin Armstrong|Edwin H. Armstrong]] invented [[frequency modulation|frequency-modulated]] ([[FM radio|FM]]) radio, so that an audio signal can avoid "static," that is, interference from electrical equipment and atmospherics.
*In 1943, the U.S. Supreme Court acknowledged that Marconi's work wasn't original, and the patent ownership is given back to Nikola Tesla. However, Tesla died shortly before the decision was announced.<ref>[[List of Tesla patents]]</ref>
==History==
{{details|History of radio}}
[[Image:TeslaWirelessPower1891.png|thumb|333px|right|Tesla demonstrating wireless transmissions during his high frequency and potential lecture of 1891. After continued research, Tesla gave the fundamentals of radio in 1893.]]
In 1893, in [[St. Louis, Missouri|St. Louis]], [[Missouri]], [[Nikola Tesla]] made devices for his experiments with [[electricity]]. Addressing the ''[[Franklin Institute]]'' in [[Philadelphia]] and the ''[[National Electric Light Association]]'', he described and demonstrated in detail the principles of his wireless work. [http://www.ieee-virtual-museum.org/collection/people.php?taid=&id=1234597&lid=1] The descriptions contained all the elements that were later incorporated into radio systems before the development of the [[vacuum tube]]. He initially experimented with magnetic receivers, unlike the [[coherer]]s (detecting devices consisting of tubes filled with [[iron]] filings which had been invented by [[Temistocle Calzecchi-Onesti]] at Fermo in Italy in 1884) used by [[Guglielmo Marconi]] and other early experimenters. [http://www.teslasociety.com/teslarec.pdf].
In [[1894]] [[Alexander Stepanovich Popov]] built his first [[radio receiver]], which contained a [[coherer]]. Further refined as a [[lightning detector]], it was presented to the [[Russian Physical and Chemical Society]] on [[May 7]], [[1895]].
The first public demonstration of wireless telegraphy took place in the lecture theatre of the Oxford University Museum of Natural History on August 14, 1894, carried out by Professor [[Oliver Lodge]] and [[Alexander Muirhead]]. During the demonstration a radio signal was sent from the neighbouring Clarendon laboratory building, and received by apparatus in the lecture theatre.
In [[1896]], Marconi was awarded the [[United Kingdom|British]] [[patent]] 12039, ''Improvements in transmitting electrical impulses and signals and in apparatus there-for'', for radio. In 1897 he established the world's first radio station on the [[Isle of Wight]], [[England]]. Marconi opened the world's first "wireless" factory in Hall Street, [[Chelmsford, England]] in 1898, employing around 50 people.
The next great invention was the [[vacuum tube]] detector, invented by [[Westinghouse Electric Corporation|Westinghouse]] engineers. On [[Christmas Eve]], 1906, [[Reginald Fessenden]] used a synchronous rotary-spark transmitter for the first radio program broadcast, from [[Ocean Bluff-Brant Rock, Massachusetts|Brant Rock, Massachusetts]]. Ships at sea heard a broadcast that included Fessenden playing ''[[O Holy Night]]'' on the [[violin]] and reading a passage from the [[Bible]]. The first radio news program was broadcast [[August 31]], [[1920]] by station 8MK in [[Detroit, Michigan]]. The first college radio station began broadcasting on [[October 14]], 1920, from [[Union College]], [[Schenectady]], [[New York]] under the personal call letters of Wendell King, an African-American student at the school.[http://w2uc.union.edu/RADIO_web.htm] That month 2ADD, later renamed [[WRUC]] in 1940, aired what is believed to be the first public entertainment broadcast in the United States, a series of Thursday night concerts initially heard within a 100 mile radius and later for a 1,000 mile radius. In November 1920, it aired the first broadcast of a sporting event.[http://w2uc.union.edu/RADIO_web.htm],[http://2000.union.edu/N/DS/edition_display.php?e=677&s=2700] At 9 pm on August 27, 1920, Sociedad Radio Argentina aired a live performance of Richard Wagner's Parsifal opera from the Coliseo Theater in downtown Buenos Aires, only about twenty homes in the city had a receiver to tune in. Meanwhile, Regular entertainment broadcasts commenced in 1922 from the [[Guglielmo Marconi|Marconi]] Research Centre at [[Writtle]], near [[Chelmsford, England]].
One of the first developments in the early 20th century (1900-1959) was that [[aircraft]] used commercial AM radio stations for navigation. This continued until the early 1960s when [[VHF omnidirectional range|VOR]] systems finally became widespread (though AM stations are still marked on U.S. [[aviation]] charts). In the early 1930s, [[single sideband]] and [[frequency modulation]] were invented by amateur radio operators. By the end of the decade, they were established commercial modes. Radio was used to transmit pictures visible as [[television]] as early as the 1920s. Commercial television transmissions started in North America and Europe in the 1940s. In 1954, Regency introduced a pocket [[transistor]] radio, the [[Regency TR-1|TR-1]], powered by a "standard 22.5 V Battery".
In [[1960]], [[Sony]] introduced its first transistorized radio, small enough to fit in a vest pocket, and able to be powered by a small battery. It was durable, because there were no tubes to burn out. Over the next 20 years, transistors replaced tubes almost completely except for very high-power uses. By 1963 color television was being regularly transmitted commercially, and the first (radio) [[communication satellite]], TELSTAR, was launched. In the late 1960s, the U.S. long-distance telephone network began to convert to a digital network, employing [[digital radio]]s for many of its links. In the 1970s, [[LORAN]] became the premier radio navigation system. Soon, the U.S. Navy experimented with [[satellite navigation]], culminating in the invention and launch of the [[Global Positioning System|GPS]] constellation in 1987. In the early 1990s, [[amateur radio]] experimenters began to use personal computers with audio cards to process radio signals. In 1994, the U.S. Army and [[DARPA]] launched an aggressive, successful project to construct a [[software radio]] that could become a different radio on the fly by changing software. Digital transmissions began to be applied to broadcasting in the late 1990s.
==Uses of radio==
Early uses were maritime, for sending telegraphic messages using [[Morse code]] between ships and land. The earliest users included the Japanese Navy scouting the Russian fleet during the [[Battle of Tsushima]] in 1905. One of the most memorable uses of marine telegraphy was during the sinking of the [[RMS Titanic|RMS ''Titanic'']] in 1912, including communications between operators on the sinking ship and nearby vessels, and communications to shore stations listing the survivors. The first radio couldn't transmit sound or speech and was called the "wireless telegraph"
Radio was used to pass on orders and communications between armies and navies on both sides in [[World War I]]; Germany used radio communications for diplomatic messages once its submarine cables were cut by the British. The United States passed on President [[Woodrow Wilson|Woodrow Wilson's]] [[Fourteen Points]] to Germany via radio during the war. Broadcasting began from [[San Jose, California|San Jose]] in 1909[http://www.bayarearadio.org/schneider/kqw.shtml], and became feasible in the 1920s, with the widespread introduction of radio receivers, particularly in Europe and the United States. Besides broadcasting, point-to-point broadcasting, including telephone messages and relays of radio programs, became widespread in the 1920s and 1930s. Another use of radio in the pre-war years was the development of detecting and locating aircraft and ships by the use of [[radar]] (''RA''dio ''D''etection ''A''nd ''R''anging).
Today, radio takes many forms, including [[wireless network]]s and [[mobile communication]]s of all types, as well as radio [[broadcasting]]. Before the advent of [[television]], commercial radio broadcasts included not only news and music, but dramas, comedies, variety shows, and many other forms of entertainment. Radio was unique among methods of dramatic presentation in that it used only sound. For more, see [[radio programming]].
===Audio===
[[Image:Fisher 500 radio.jpg|right|thumb|A Fisher 500 AM/FM hi-fi receiver from 1959.]]
[[AM broadcasting|AM broadcast radio]] sends music and voice in the Medium Frequency (MF—0.300 MHz to 3 MHz) radio spectrum. AM radio uses [[amplitude modulation]], in which the amplitude of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone while the transmitted frequency remains unchanged. Transmissions are affected by static and interference because lightning and other sources of radio that are transmitting at the same frequency add their amplitudes to the original transmitted amplitude. The most wattage an AM radio station in the [[United States]] is allowed to use is 50,000 watts and the majority of stations that emit signals this powerful were grandfathered in; these include [[WGN (AM)]], [[WJR]], and [[CKLW]]. In 1986 [[KTNN]] received the last granted 50,000 watt license.
[[FM broadcasting|FM broadcast radio]] sends music and voice with higher fidelity than AM radio. In [[frequency modulation]], amplitude variation at the [[microphone]] causes the transmitter frequency to fluctuate. Because the audio signal modulates the frequency and not the amplitude, an FM signal is not subject to static and interference in the same way as AM signals. FM is transmitted in the Very High Frequency (VHF—30 MHz to 300 MHz) radio spectrum. <!-- FM requires more radio frequency spectrum than AM and there are more frequencies available at higher frequencies, so there can be more stations, each sending more information. --> VHF radio waves act more like light, traveling in straight lines, hence the reception range is generally limited to about 50-100 miles. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the [[ionosphere]], resulting in [[TV/FM DX|Long distance FM reception]]. FM receivers are subject to the [[capture effect]], which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. FM receivers are relatively immune to lightning and spark interference.
High power is useful in penetrating buildings, diffracting around hills, and refracting for some distance beyond the horizon. Consequently, 100,000 watt FM stations can regularly be heard up to 100 miles (160 km) away, and farther (e.g., 150 miles, 240 km) if there are no competing signals.
A few old "grandfathered" stations do not conform to these power rules. [[WBCT-FM]] (93.7) in [[Grand Rapids, Michigan|Grand Rapids]], [[Michigan]], runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. This huge power level does not usually help to increase range as much as one might expect, because [[VHF]] frequencies travel in nearly straight lines over the horizon and off into space. Nevertheless, when there were fewer FM stations competing, this station could be heard near Bloomington, Illinois, almost 300 miles (500 km) distant.
FM Sub-carrier services are secondary signals transmitted "[[piggyback]]" along with the main program. Special receivers are required to utilize these services. Analog channels may contain alternative programming, such as reading services for the blind, background music or stereo sound signals. In some extremely crowded metropolitan areas, the sub-channel program might be an alternate foreign language radio program for various ethnic groups. Sub-carriers can also transmit digital data, such as station identification, the current song's name, web addresses, or stock quotes. In some countries, FM radios automatically re-tune themselves to the same channel in a different district by using sub-bands.
Aviation voice radios use [[VHF radio|VHF]] AM. AM is used so that multiple stations on the same channel can be received. (Use of FM would result in stronger stations blocking out reception of weaker stations due to FM's [[capture effect]]). Aircraft fly high enough that their transmitters can be received hundreds of miles (or kilometres) away, even though they are using VHF.
Marine voice radios can use AM in the shortwave High Frequency (HF—3 MHz to 30 MHz) radio spectrum for very long ranges or [[Marine VHF radio|narrowband FM in the VHF spectrum]] for much shorter ranges. Government, police, fire and commercial voice services use narrowband FM on special frequencies. Fidelity is sacrificed to use a smaller range of radio frequencies, usually five [[hertz|kHz]] of deviation, rather than the 75 kHz used by FM broadcasts and 25 kHz used by TV sound.
Civil and military HF (high frequency) voice services use [[shortwave]] radio to contact ships at sea, aircraft and isolated settlements. Most use [[single sideband]] voice (SSB), which uses less bandwidth than AM. On an AM radio SSB sounds like ducks quacking. Viewed as a graph of frequency versus power, an AM signal shows power where the frequencies of the voice add and subtract with the main radio frequency. SSB cuts the bandwidth in half by suppressing the carrier and (usually) lower sideband. This also makes the transmitter about three times more powerful, because it doesn't need to transmit the unused carrier and sideband.
TETRA, [[Terrestrial Trunked Radio]] is a digital cell phone system for military, police and ambulances. Commercial services such as [[XM Radio|XM]], [[WorldSpace]] and [[Sirius Satellite Radio|Sirius]] offer encrypted digital [[Satellite radio]].
===Telephony===
[[Mobile phone]]s transmit to a local [[cell site]] (transmitter/receiver) that ultimately connects to the public switched telephone network ([[Public switched telephone network|PSTN]]) through an optic fiber or microwave radio and other network elements. When the mobile phone nears the edge of the cell site's radio coverage area, the central computer switches the phone to a new cell. Cell phones originally used FM, but now most use various digital modulation schemes. Recent developments in Sweden (such as DROPme) allow for the instant downloading of digitial material from a radio broadcast (such as a song) to a mobile phone. <br /><br />Satellite phones use satellites rather than cell towers to communicate. They come in two types: [[Inmarsat|INMARSAT]] and [[Iridium (satellite)|Iridium]]. Both types provide world-wide coverage. INMARSAT uses geosynchronous satellites, with aimed high-gain antennas on the vehicles. Iridium uses 66 Low Earth Orbit satellites as the cells.
===Video===
[[Television]] sends the picture as AM and the sound as FM, with the sound carrier a fixed frequency (4.5 MHz in the [[NTSC]] system) away from the video carrier. Analog television also uses a [[vestigial sideband]] on the video carrier to reduce the bandwidth required.
Digital television uses [[8VSB]] modulation in North America (under the [[ATSC]] digital television standard), and [[COFDM]] modulation elsewhere in the world (using the [[DVB-T]] standard). A [[Reed-Solomon error correction]] code adds redundant correction codes and allows reliable reception during moderate data loss. Although many current and future codecs can be sent in the MPEG-2 [[transport stream]] [[container format]], as of 2006 most systems use a standard-definition format almost identical to [[DVD]]: [[MPEG-2]] video in [[Anamorphic widescreen]] and [[MPEG-1 Audio Layer II|MPEG layer 2]] (''MP2'') audio. [[High-definition television]] is possible simply by using a higher-resolution picture, but [[H.264/MPEG-4 AVC|H.264/AVC]] is being considered as a replacement video codec in some regions for its improved compression. With the compression and improved modulation involved, a single "channel" can contain a high-definition program and several standard-definition programs.
===Navigation===
All [[satellite navigation]] systems use satellites with precision clocks. The satellite transmits its position, and the time of the transmission. The receiver listens to four satellites, and can figure its position as being on a line that is tangent to a spherical shell around each satellite, determined by the time-of-flight of the radio signals from the satellite. A computer in the receiver does the math.
Radio direction-finding is the oldest form of radio navigation. Before 1960 navigators used movable loop antennas to locate commercial AM stations near cities. In some cases they used marine radiolocation beacons, which share a range of frequencies just above AM radio with amateur radio operators. [[Loran]] systems also used time-of-flight radio signals, but from radio stations on the ground. [[VHF omnidirectional range|VOR]] (Very High Frequency Omnidirectional Range), systems (used by aircraft), have an antenna array that transmits two signals simultaneously. A directional signal rotates like a lighthouse at a fixed rate. When the directional signal is facing north, an omnidirectional signal pulses. By measuring the difference in phase of these two signals, an aircraft can determine its bearing or radial from the station, thus establishing a line of position. An aircraft can get readings from two VORs and locate its position at the intersection of the two radials, known as a "fix." When the VOR station is collocated with DME ([[Distance Measuring Equipment]]), the aircraft can determine its bearing and range from the station, thus providing a fix from only one ground station. Such stations are called VOR/DMEs. The military operates a similar system of navaids, called TACANs, which are often built into VOR stations. Such stations are called VORTACs. Because TACANs include distance measuring equipment, VOR/DME and VORTAC stations are identical in navigation potential to civil aircraft.
===Radar===
[[Radar]] (Radio Detection And Ranging) detects objects at a distance by bouncing radio waves off them. The delay caused by the echo measures the distance. The direction of the beam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide area two to four times per minute. They use very short waves that reflect from earth and stone. They are common on commercial ships and long-distance commercial aircraft
General purpose radars generally use navigational radar frequencies, but modulate and polarize the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms, as well as land and vehicles. Some can superimpose sonar data and map data from [[Global Positioning System|GPS]] position.
Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. Sometimes search radars use the [[doppler effect]] to separate moving vehicles from clutter. Targeting radars use the same principle as search radar but scan a much smaller area far more often, usually several times a second or more. Weather radars resemble search radars, but use radio waves with circular polarization and a wavelength to reflect from water droplets. Some weather radar use the [[Doppler effect|doppler]] to measure wind speeds.
===Data (digital radio)===
Most new radio systems are digital, see also: [[Digital TV]], [[Satellite Radio]], [[Digital Audio Broadcasting]]. The oldest form of digital broadcast was spark gap [[telegraphy]], used by pioneers such as Marconi. By pressing the key, the operator could send messages in [[Morse code]] by energizing a rotating commutating spark gap. The rotating commutator produced a tone in the receiver, where a simple spark gap would produce a hiss, indistinguishable from static. Spark gap transmitters are now illegal, because their transmissions span several hundred megahertz. This is very wasteful of both radio frequencies and power.
The next advance was continuous wave [[telegraphy]], or CW ([[Continuous Wave]]), in which a pure radio frequency, produced by a [[vacuum tube]] [[electronic oscillator]] was switched on and off by a key. A receiver with a local oscillator would "[[heterodyne]]" with the pure radio frequency, creating a whistle-like audio tone. CW uses less than 100 Hz of bandwidth. CW is still used, these days primarily by [[amateur radio]] operators (hams). Strictly, on-off keying of a carrier should be known as "Interrupted Continuous Wave" or ICW or [[on-off keying]] (OOK).
[[radioteletype|Radio teletype]]s usually operate on short-wave (HF) and are much loved by the military because they create written information without a skilled operator. They send a bit as one of two tones. Groups of five or seven bits become a character printed by a teletype. From about 1925 to 1975, radio teletype was how most commercial messages were sent to less developed countries. These are still used by the military and weather services.
Aircraft use a 1200 Baud radioteletype service over VHF to send their ID, altitude and position, and get gate and connecting-flight data. Microwave dishes on satellites, telephone exchanges and TV stations usually use [[quadrature amplitude modulation]] (QAM). QAM sends data by changing both the phase and the amplitude of the radio signal. Engineers like QAM because it packs the most bits into a radio signal when given an exclusive (non-shared) fixed narrowband frequency range. Usually the bits are sent in "frames" that repeat. A special bit pattern is used to locate the beginning of a frame.
Communication systems that limit themselves to a fixed narrowband frequency range are vulnerable to [[jamming]].
A variety of jamming-resistant [[spread spectrum]] techniques were initially developed for military use, most famously for [[Global Positioning System]] satellite transmissions.
Commercial use of spread spectrum begin in the 1980s.
[[Bluetooth]], most cell phones, and the 802.11b version of Wi-Fi each use various forms of spread spectrum.
Systems that need reliability, or that share their frequency with other services, may use "coded orthogonal frequency-division multiplexing" or [[COFDM]]. COFDM breaks a digital signal into as many as several hundred slower subchannels. The digital signal is often sent as QAM on the subchannels. Modern COFDM systems use a small computer to make and decode the signal with [[digital signal processing]], which is more flexible and far less expensive than older systems that implemented separate electronic channels. COFDM resists fading and ghosting because the narrow-channel QAM signals can be sent slowly. An adaptive system, or one that sends error-correction codes can also resist interference, because most interference can affect only a few of the QAM channels. COFDM is used for [[WiFi]], some [[cell phone]]s, [[Digital Radio Mondiale]], [[Eureka 147]], and many other local area network, digital TV and radio standards.
===Heating===
Radio-frequency energy generated for heating of objects is generally not intended to radiate outside of the generating equipment, to prevent interference with other radio signals. [[Microwave oven]]s use intense radio waves to heat food. (Note: It is a common misconception that the radio waves are tuned to the resonant frequency of water molecules. The microwave frequencies used are actually about a factor of ten below the resonant frequency.) [[Diathermy]] equipment is used in surgery for sealing of blood vessels. Induction [[furnace]]s are used for melting metal for [[casting]].
===Amateur radio service===
[[Amateur radio]] is a hobby in which enthusiasts purchase or build their own equipment and use radio for their own enjoyment. They may also provide an emergency and public-service radio service. This has been of great use, saving lives in many instances. Radio amateurs are licensed to use frequencies in a large number of narrow bands throughout the radio spectrum. They use all forms of encoding, including obsolete and experimental ones. Several forms of radio were pioneered by radio amateurs and later became commercially important including [[FM]], single-sideband (SSB), AM, digital packet radio and satellite repeaters. Some amateur frequencies may be disrupted by power-line internet service.
===Unlicensed radio services===
Personal radio services such as [[Citizens' Band Radio]], [[Family Radio Service]], [[Multi-Use Radio Service]] and others exist in North America to provide simple, (usually) short range communication for individuals and small groups, without the overhead of licensing. Similar services exist in other parts of the world. These radio services involve the use of handheld units.
The commonest form of unlicensed radio is known as Free or Pirate radio, the main differences being that a Free radio station does not advertise or make any money, while the Pirate station could not exist without adverts, payolas, etc.
===Radio control (RC)===
[[Radio control|Radio remote controls]] use radio waves to transmit control data to a remote object as in some early forms of [[guided missile]], some early TV remotes and a range of model boats, [[Radio-controlled car|cars]] and airplanes. Large industrial remote-controlled equipment such as [[crane (machine)|crane]]s and switching [[locomotive]]s now usually use digital radio techniques to ensure safety and reliability.
In [[Madison Square Garden]], at the Electrical Exhibition of 1898, Nikola Tesla successfully demonstrated a radio-controlled boat.[http://www.pbs.org/tesla/ins/lab_remotec.html] He was awarded U.S. patent No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles." [http://www.pbs.org/tesla/res/613809.html]
==The electromagnetic spectrum==
Radio waves are a form of electromagnetic radiation, created whenever a [[electric charge|charged]] object (in normal radio transmission, an [[electron]]) [[accelerate]]s with a frequency that lies in the [[radio frequency]] (RF) portion of the [[electromagnetic spectrum]]. In radio, this acceleration is caused by an [[alternating current]] in an [[antenna (radio)|antenna]]. Radio frequencies occupy the range from a few tens of [[hertz]] to three hundred gigahertz, although commercially important uses of radio use only a small part of this spectrum.<ref>''The Electromagnetic Spectrum'', University of Tennessee, Dept. of Physics and Astronomy</ref> Other types of electromagnetic radiation, with frequencies above the RF range, are [[microwave]], [[infrared]], visible [[light]], [[ultraviolet]], [[X-ray]]s and [[gamma ray]]s. Since the energy of an individual [[photon]] of radio frequency is too low to remove an [[electron]] from an [[atom]], radio waves are classified as [[non-ionizing radiation]].
===Other===
[[Energy autarkic radio technology]] consists of a small radio transmitter powered by environmental energy (push of a button, temperature differences, light, vibrations, etc.). A number of schemes have been proposed for [[Wireless energy transfer]]. Various plans included transmitting power using [[microwave]]s, and the technique has been demonstrated. (See [[Microwave power transmission]]). These schemes include, for example, [[solar energy|solar power]] [[Solar power satellite|stations]] in orbit beaming energy down to terrestrial users.
==See also==
{{col-begin}}
{{col-break}}
* [[Amateur radio]]
* [[Antique radio]]
* [[Army No. 11 Wireless Set]]
* [[Batteryless radio]]
* [[Community radio]]
* [[Crystal radio receiver]]
* [[Dead air]]
* [[Federal Communications Commission]] (United States)
* [[Hertz]]
* [[Hospital radio]]
* [[Hot and cool media]]
* [[International broadcasting]]
* [[Internet radio]] and [[Internet radio device]]
* [[Invention of radio]]
*'''Lists'''
** [[Radio network]]
** [[List of Internet stations]]
** [[List of radio broadcasters who also do podcasting]]
* [[Longwave]]
* [[Mediumwave]]
{{col-break}}
* [[Music radio]]
* [[Near Vertical Incidence Skywave]]
* [[Old-time radio]]
* [[Pirate radio]]
* [[Radio astronomy]]
* [[Radio documentary]]
* [[Radio commercial]]
* [[Radio programming]]
* [[Radio propagation]] and [[ionosphere]]
* [[Radio software]]
* [[Receiver (radio)]]
* [[Satellite radio]]
* [[Shortwave]]
* [[Software radio]]
* [[TV/FM DX|Long-distance FM reception (FM DX)]]
* [[Transistor radio]]
* [[Tuner (radio)]]
* [[Types of radio emissions]]
* [[VFO]]
{{col-end}}
==Notes==
{{reflist}}
*[http://www.124radiostation.com Online Radio Station] 124radiostation online radio station as review says it is the "most easiest" to use website to listen songs.
==References==
* [http://pagina.vizzavi.pt/~nc22723a/radio.htm ''A História da Rádio em Datas (1819-1997)'' (in Portuguese) - notes on etymology]
* Leigh White, ''Buck Fuller and the Dymaxion World'' (refers to Waldo Warren as the inventor of the word ''radio''), in: The Saturday Evening Post, [[14 October]] 1944, cited in: Joachim Krausse and Claude Lichtenstein (eds.), ''Your Private Sky'', Lars Müller Publishers, Baden/Switzerland, 1999, page 132. ISBN 3-907044-88-6
* L. de Forest, article in Electrical World [[22 June]] 1270/1 (1907), early use of word "radio".
* http://web.mit.edu/varun_ag/www/bose.html - It contains a proof that Sir Jagadish Chandra Bose invented the Mercury Coherer which was later used by Guglielmo Marconi and along with other patents.
==Further reading==
* Aitkin Hugh G. J. ''The Continuous Wave: Technology and the American Radio, 1900-1932'' (Princeton University Press, 1985).
* Briggs Asa. ''The History of Broadcasting in the United Kingdom'' (Oxford University Press, 1961).
* Ewbank Henry and Lawton Sherman P. ''Broadcasting: Radio and Television'' (Harper & Brothers, 1952).
* Fisher, Marc ''Something In The Air: Radio, Rock, and the Revolution That Shaped A Generation'' (Random House, 2007).
* Maclaurin W. Rupert. ''Invention and Innovation in the Radio Industry'' (The Macmillan Company, 1949).
* Ray William B. ''FCC: The Ups and Downs of Radio-TV Regulation'' (Iowa State University Press, 1990).
* Scannell, Paddy, and Cardiff, David. ''A Social History of British Broadcasting, Volume One, 1922-1939'' (Basil Blackwell, 1991).
* Schwoch James. ''The American Radio Industry and Its Latin American Activities, 1900-1939'' (University of Illinois Press, 1990).
* Sterling Christopher H. ''Electronic Media, A Guide to Trends in Broadcasting and Newer Technologies 1920-1983'' (Praeger, 1984).
* White Llewellyn. ''The American Radio'' (University of Chicago Press, 1947).
===Primary sources===
* De Forest, Lee. ''Father of Radio: The Autobiography of Lee de Forest'' (1950).
==External links==
{{commonscat|Radio}}
{{wiktionary|radio}}
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your station is notable enough to be included, it will be added by someone else. -->
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*[http://www.commandline.net/Radio%20Frequency%20Chart1.htm Radio Frequency Chart]
* Horzepa, Stan, "''[http://www.arrl.org/news/features/2003/10/10/1/ Surfin': Who Invented Radio]?''". Arrl.org. [[10 October]] [[2003]].
* [http://www.radiomerkezi.com Online Radio]
* IAteacher: [http://www.iateacher.com/Lesson%206/L6P1-Title.htm Interactive Explanation of Radio Receiver Construction]
* U.S. Supreme Court, "''[http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&vol=320&invol=1 Marconi Wireless Telegraph co. of America v. United States]''". 320 U.S. 1. Nos. 369, 373. Argued [[9 April]]-12, 1943. Decided [[21 June]] [[1943]].
* [http://xroads.virginia.edu/~1930s2/Radio/day/radio.html 'A Day In Radio' from The University of Virginia's Department of American Studies]
*[http://www.locutoramariana.es.tl Radio Announcer]
* [http://web.archive.org/web/20060427024057/http://history.acusd.edu/gen/recording/radio.html Steven Schoenherr's History of Radio]
* [http://www.oldradio.com The Broadcast Archive - Radio History on the Web!]
* [http://invention.smithsonian.org/resources/fa_clark_index.aspx George H. Clark Radioana Collection, ca. 1880 - 1950] - Archives Center, National Museum of American History, Smithsonian Institution
* [http://members.aol.com/djadamson/arp.html A gallery of Antiques from the 1920s to the 1960s]
* [http://earlyradiohistory.us United States Early Radio History]
* [http://dmoz.org/Arts/Radio/ Open Directory Project - Radio]
* [http://www.rfzone.org/free-rf-ebooks/ Books about Radios and RF field; schematics for radio transmitters and receivers]
* [http://www.allstar.fiu.edu/aero/VOR.htm VOR Basic Information]
* [http://electronics.howstuffworks.com/radio.htm How Stuff Works - Radio]
* [http://members.aol.com/jeff560/canada.html Early Canadian Radio Station Lists]
* [http://www.broadcasting-history.ca Canadian Communications Foundation - The History on Canadian Broadcasting].
* [http://earlyradiohistory.us United States Early Radio History]
* [http://www.vk2bv.org/museum Historic Radios from Around the World at Kurrajong Radio Museum, Australia]
* [http://www.bdxc.org.uk The British DX Club]
* [http://www.worldofradio.com/ www.worldofradio.com] Glen Houser's World Of Radio
* [http://www.radiotoday.co.uk/ Radio Today] Daily News and Information about radio
* [http://www.cbaa.org.au/ Community Broadcasting Association of Australia]
* [http://www.cbonline.org.au/ Community Broadcasting Online (Australia)]
* [http://www.gbcghana.com/ Radio Broadcasting from Ghana West Africa]
* [http://www.podseek.net/ Internet Radio Broadcasting Directory]
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