Title | Radio |
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Caption | Classic radio receiver dial |
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Radio is the transmission of signals by modulation of electromagnetic waves with frequencies below those of visible light. 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 receivers to tune in this radio program. Meanwhile, regular entertainment broadcasts commenced in 1922 from the Marconi Research Centre at Writtle, England.
In 1943 the United States Supreme Court upheld Tesla's patent for radio, number 645,576 (1897), with the supreme court's justification that claim 16 in Marconi's related patent, number 763,772 (1904), contained nothing new not having been published earlier and registered by Tesla, Lodge, and others. After years of patent battles by Marconi's company, the United States Supreme Court, in the 1943 case "Marconi Wireless Telegraph co. of America v. United States", held regarding the priority of engineering advances concerning the invention of radio that "[but] it is now held that in the important advance upon his basic patent Marconi did nothing that had not already been seen and disclosed". The decision effectively awarded priority of the invention of radio to Tesla and his 1893 presentation in St. Louis. Although Marconi claimed that he had no knowledge of prior art taken from Tesla's patents, the supreme court considered his claim false. In addition to the June 21, 1943 ruling made by the supreme court, the United States Court of Claims also invalidated the fundamental Marconi patent earlier, in 1935. This case defined radio by the statement: "A radio communication system requires two tuned circuits each at the transmitter and receiver, all four tuned to the same frequency." Because Tesla's 1897 patent for radio was intended for general transmission of energy, the court determined that Tesla's patent clearly was the first to disclose a system which could be used for wireless communication of intelligible messages (such as human voice and music) and used the four-circuit tuned combination.
.]] One of the first developments in the early 20th century was that aircraft used commercial AM radio stations for navigation. This continued until the early 1960s when 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, the Regency company introduced a pocket transistor radio, the TR-1, powered by a "standard 22.5 V Battery".
In 1960, the Sony company introduced its first transistorized radio. It was small enough to fit in a vest pocket, and able to be powered by a small battery. It was durable, because it had no vacuum tubes to burn out. Over the next 20 years, transistors replaced tubes almost completely except for very high-power transmitter uses. By 1963, color television was being regularly broadcast commercially (though not all broadcasts or programs were in color), 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 radios 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 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-defined radio that can be programmed to be virtually any radio by changing its software program. 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 in 1912, including communications between operators on the sinking ship and nearby vessels, and communications to shore stations listing the survivors.
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 it discovered that its submarine cables had been tapped by the British. The United States passed on President Woodrow Wilson's Fourteen Points to Germany via radio during the war. Broadcasting began from San Jose, California in 1909, 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 detection and locating of aircraft and ships by the use of radar (RAdio Detection And Ranging).
Today, radio takes many forms, including wireless networks and mobile communications 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 (the era from 1930 to the mid-1950s is commonly called radio's "Golden Age"). Radio was unique among methods of dramatic presentation in that it used only sound. For more, see radio programming.
Audio
receiver from 1959.]] 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 emissions on the same frequency add their amplitudes to the original transmitted amplitude. In the early part of the 20th century, American AM radio stations broadcast with powers as high as 500 kW, and some could be heard worldwide; these stations' transmitters were commandeered for military use by the US Government during World War II. Currently, the maximum broadcast power for a civilian AM radio station in the
United States and Canada is 50 kW, and the majority of stations that emit signals this powerful were grandfathered in (see
List of 50kw AM radio stations in the USA). In 1986
KTNN received the last granted 50,000 watt license. These 50 kW stations are generally called "
clear channel" stations (not to be confused with
Clear Channel Communications), because within
North America each of these stations has exclusive use of its broadcast frequency throughout part or all of the broadcast day.
, home of the BBC World Service.]]
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. Due to its need for a wider bandwidth, FM is transmitted in the Very High Frequency (VHF, 30 MHz to 300 MHz) radio spectrum. 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 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 in the dense atmosphere near the horizon 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, USA, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. Such a 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, USA, almost 300 miles (500 km) away.
FM subcarrier services are secondary signals transmitted in a "piggyback" fashion 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 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 single sideband voice (SSB) in the shortwave High Frequency (HF—3 MHz to 30 MHz) radio spectrum for very long ranges or narrowband FM in the VHF spectrum for much shorter ranges. Narrowband FM sacrifices fidelity to make more channels available within the radio spectrum, by using a smaller range of radio frequencies, usually with five kHz of deviation, versus the 75 kHz used by commercial FM broadcasts, and 25 kHz used for TV sound.
Government, police, fire and commercial voice services also use narrowband FM on special frequencies. Early police radios used AM receivers to receive one-way dispatches.
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, or the adults in a Charlie Brown cartoon. 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 one of the sidebands. 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, WorldSpace and Sirius offer encrypted digital Satellite radio.
Telephony
Mobile phones transmit to a local
cell site (transmitter/receiver) that ultimately connects to the 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 digital material from a radio broadcast (such as a song) to a mobile phone.
Satellite phones use satellites rather than cell towers to communicate.
Video
Television sends the picture as AM and the sound as AM or 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 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 layer 2 (MP2) audio. High-definition television is possible simply by using a higher-resolution picture, but 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. 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 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 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).
Radio teletypes 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. receivers.]] 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 began 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 Wi-Fi, some cell phones, 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 ovens use intense radio waves to heat food.
Diathermy equipment is used in surgery for sealing of blood vessels. Induction
furnaces are used for melting metal for
casting, and
induction hobs for cooking.
Amateur radio service
with multiple receivers and transceivers]]
Amateur radio, also known as "ham radio", is a hobby in which enthusiasts are licensed to communicate on a number of bands in the
radio frequency spectrum non-commercially and for their own enjoyment. They may also provide emergency and public service assistance. This has been very beneficial in emergencies, saving lives in many instances. Radio amateurs use a variety of modes, including nostalgic ones like
Morse code and experimental ones like
Low-Frequency Experimental Radio. 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
Unlicensed, government-authorized personal radio services such as
Citizens' band radio in
Australia, the
USA, and
Europe, and
Family Radio Service and
Multi-Use Radio Service in North America exist 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.
Free radio stations, sometimes called pirate radio or "clandestine" stations, are unauthorized, unlicensed, illegal broadcasting stations. These are often low power transmitters operated on sporadic schedules by hobbyists, community activists, or political and cultural dissidents. Some pirate stations operating offshore in parts of Europe and the United Kingdom more closely resembled legal stations, maintaining regular schedules, using high power, and selling commercial advertising time.
Radio control (R C)
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,
cars and airplanes. Large industrial remote-controlled equipment such as
cranes and switching
locomotives 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. He was awarded U.S. patent No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles."
See also
References
;General information
A História da Rádio em Datas (1819-1997) (in Portuguese) - notes on etymology">A História da Rádio em Datas (1819-1997) (in Portuguese) - notes on etymology 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. ;Footnotes
Further reading
Hugh G. J. Aitkin: The Continuous Wave: Technology and the American Radio, 1900-1932 (Princeton University Press, 1985). Asa Briggs: The History of Broadcasting in the United Kingdom (Oxford University Press, 1961). John Dunning: On the Air. The Encyclopedia of Old-Time Radio. New York; Oxford: Oxford University Press, 1998. ISBN 0-19-507678-8 Henry Ewbank and Sherman P. Lawton: Broadcasting: Radio and Television (Harper & Brothers, 1952). Marc Fisher: Something In The Air: Radio, Rock, and the Revolution That Shaped A Generation (Random House, 2007). Leland I. Anderson (ed.), "John Stone Stone, Nikola Tesla's Priority in Radio and Continuous-Wave Radiofrequency Apparatus". The Antique Wireless Review, Vol. 1. 1986. 24 pages, illustrated. Tom Lewis: Empire of the Air: The Men Who Made Radio, 1st ed., New York : E. Burlingame Books, 1991. ISBN 0060182156. "" (1992) by Ken Burns was a PBS documentary based on the book. W. Rupert Maclaurin: Invention and Innovation in the Radio Industry (The Macmillan Company, 1949). William B. Ray: FCC: The Ups and Downs of Radio-TV Regulation (Iowa State University Press, 1990). Alexander Russo: Points on the Dial: Golden Age Radio Beyond the Networks (Duke University Press; 2010) 278 pages; discusses regional and local radio as forms that "complicate" the image of the medium as a national unifier from the 1920s to the 1950s. 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). Christopher H. Sterling with Michael C. Keith (ed.): Encyclopedia of Radio. New York; London: Fitzroy Dearborn, 2004 (three vols.) Llewellyn White: The American Radio (University of Chicago Press, 1947). Ulrich L. Rohde, Jerry Whitaker: Communications Receivers, Third Edition, McGraw Hill, New York, NY, 2001, ISBN 0-07-136121-9.
External links
;General
"It's Radi-O! Essay by Richard Rubin, The Atlantic Monthly, January 1998. ;History
U.S. Supreme Court, "Marconi Wireless Telegraph co. of America v. United States". 320 U.S. 1. Nos. 369, 373. Argued 9–12 April 1943. Decided 21 June 1943. Horzepa, Stan, "Surfin': Who Invented Radio?" Arrl.org. 10 October 2003. Steven Schoenherr's History of Radio The Broadcast Archive - Radio History on the Web! Canadian Communications Foundation - The History on Canadian Broadcasting. United States Early Radio History Historic Radios from Around the World at Kurrajong Radio Museum, Australia Early Canadian Radio Station Lists United States Early Radio History ;Antiques
George H. Clark Radioana Collection, ca. 1880 - 1950 - Archives Center, National Museum of American History, Smithsonian Institution A gallery of Antiques from the 1920s to the 1960s ;Technical
Radio Frequency Chart National Telecommunications and Information Administration (NTIA). IAteacher: Interactive Explanation of Radio Receiver Construction How Stuff Works - Radio VOR Basic Information Dr. Phil's Receiver Designs Single-Triode and Single-Transistor Regenerative Radio Designs ;DX
The British DX Club World of Radio Glenn Hauser's internationally known DX radio show
Category:British inventions