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Radio

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Radio nyaéta pangiriman sinyal nirkabel, ku cara numpangkeun atawa nga-modulasi sinyal informasi kana gelombang éléktromagnétik dina jajaran frékuénsi handapeun frékuénsi cahaya katémbong. Rambatan gelombang éléktromagnétik dimungkinkeun ku cara ngaayunambing médan magnét. Ieu gelombang henteu merlukeun mediyeum pikeun ngaliwat. Informasi dibawa sacara sistematik ku cara ngarobah sababaraha sifat gelombang anu dipancarkeun, saperti amplitudo atawa frékuénsina. Mangsa gelombang radio ngaliwatan konduktor listrik, médan anu ngaayun-ambing ngahasilkeun arus listrik bulak-balik dina konduktor. Arus listrik ieu bisa didetéksi jeung dirobah jadi sinyal sora atawa sinyal liana.

Sanajan Nikola Tesla anu munggaran medar yén komunikasi nir-kabel bisa dilaksanakeun, persisna dina taun 1893, Guglielmo Marconi asal Italia, mangrupa panimu anu munggaran ngalakukeun komunikasi radio. Manéhna ngirim jeung narima sinyal radio munggaran di Italia dina taun 1895.

Radio

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Kecap radio asalna tina kecap radioteléografi anu disebut ogé 'wireless telegraphy', anu disingket 'wireless'. Préfiks radio- dina harti pangiriman sacara nirkabel munggaran dicutat dina kecap 'radioconductor, anu ditimukeun ku fisikawan Perancis Edouard Branly dina taun 1897 sarta dumasar kana kecap gawe to radiate (dina basa Laten "radius" hartina "pancaran cahaya, sinar").

'Radio' salaku kecap barang cenah ditimukeun ku ahli iklan Waldo Warren (White 1944). Kecap kasebut, anu muncul dina hiji artikel nu diterbitkeun ku Lee de Forest taun 1907, digunakeun ku Angkatan Laut Amérika Sarikat dina taun 1912 sarta jadi ilahar nepi ka waktu munggaran ayana siaran komérsial di Amérika Sérikat dina taun 1920-an. Istilah éta terus digunakeun dina basa-basa lian di Éropah jeung Asia, sanajan nagara-nagara Persemakmuran Inggris mertahankeun istilah 'wireless' nepi ka tengah abad ka-20.

Kiwari istilah 'wireless' meunangkeun deui popularitas alatan tumuwuhna jaringan télékomunikasi jarak pondok anu lumangsung gancang, contona WLAN ('Wireless Local Aréa Network'), WiFi jeung Bluetooth sarta telepon mobil, misalna GSM katut UMTS. Kiwari, istilah 'radio' mindeng nujul kana alat transceiver (alat pancar sakaligus panarima) atawa chip, sedengkeun 'wireless' nujul kana sistem jeung/atawa métode anu digunakeun pikeun komunikasi radio.

Panimuan

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Sanajan panimuan radio lila dikaitkeun jeung Guglielmo Marconi, jatidiri panimu radio anu mimiti, anu dina mangsa harita disebut wireless telegraphy, jadi bahan kontrovérsi [1]. Kamajuan ti mimiti percobaan di laboratorium nepi ka radio jadi barang kaperluan komérsial ngabutuhkeun waktu sabababaraha dasawarsa sarta merlukeun usaha ti para panalungtik. Kontrovérsi ngeunaan saha anu nimukeun radio, bisa kapanggih ku cara merhatikeun kronologi ditimukeunna radio saperti di handap ieu:

  • Dina taun 1887, David E. Hughes mancarkeun kode Morse maké radio dina handapeun daérah Super low frequency.
  • Dina taun 1888, Heinrich Hertz ngahasilkeun sarta ngukur jajaran Ultra High Frequency.
  • Dina taun 1891, Nikola Tesla ngamimitian panalungtikan nirkabel. Manéhna nyieun alat anu bisa diandelkeun pikeun ngahasilkeun frékuénsi radio, mintonkeun ka balaréa prinsip-prinsip radio, sarta ngirimkeun sinyal ka jarak anu jauh.
  • Antara taun 1893 jeung 1894, Roberto Landell de Moura, urang Brazil, ngalakukeun percobaan. Manéhna henteu nerbitkeun hasilna nepi ka taun 1900 tapi tungtungna meunangkeun patén ti nagarana.
  • Dina taun 1894 di Kolkata (Calcutta), Sir Jagdish Chandra Bose (J. C. Bose) nimukeun coherer jeung panarima (receiver) telepon.
  • Alexander Stepanovich Popov, dina taun 1894, nyieun receiver radiona nu munggaran, anu ngandung hiji coherer tapi sabenerna coherer geus dipintonkeun saméméhna ku J.C. Bose. Popov. Popov satuluyna ngahadéan éta alat jadi hiji detéktor kilat sarta midangkeun dina Russian Physical and Chemical Society dina tanggal 7 Mei, 1895.
  • Dina taun 1894, Guglielmo Marconi macaan tulisan ngeunaan hasil gawé Hertz jeung Tesla dina perkara wireless telegraphy, sarta ngamimitian percobaanna sorangan.
  • Dina bulan Désémber 1901 Guglielmo Marconi ngagunakeun timuan J.C. Bose pikeun narima sinyal radio dina komunikasi transatlatik anu ngaliwatan jarak 2000 mil ti Poldhu, Inggris, ka St. Johns, Newfoundland. Marconi kasohor di sakuliah dunya lantara hasil anu dihontalna ieu. Henteu lila ti harita, Marconi narima patén, malah narima ogé panghargaan Nobel.
  • Dina awal taun 1900-an Reginald Fessenden [2] sarta Lee de Forest nimukeun modulasi amplitudo (AM) radio) anu ngamungkinkeun sinyal audio bisa dikirim ngaliwatan jomantara.
  • Dina taun 1935 Edwin H. Armstrong nimukeun modulasi frékuénsi (FM) radio, antukna sinyal audio anu dipancarkeun bisa nyingkahan listrik "statik," nyaéta interférensi tina alat-alat listrik katut gangguan atmosfir.
  • Dina taun 1943, Pangadilan Tinggi AS ngumumkeun yén gawé Marconi lain gawé asli jieunan manéhna, sarta kapamilikan patén dibikeun ka Nikola Tesla. Ngan, Tesla palastra teu lila saacan kaputusan kasebut dibéwarakeun.[1]

Sajarah

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Pikeun leuwih jéntré ngeunaan jejer ieu, mangga tingal Sajarah radio.
Tesla keur mintonkeun pangiriman informasi nirkabel dina kuliah ngeunaan frékuénsi luhur dina taun 1891. Saenggeus ngalakukeun risét anu sinambung, Tesla ngajelaskeun dasar-dasar ngeunaan radio dina taun 1893.

Dina taun 1893, di St. Louis, Missouri, Nikola Tesla nyieun alat pikeun percobaan listrik. Biantara di hareupeun Franklin Institute di Philadelphia sarta National Electric Light Association, manéhna ngajelaskeun, mintonkeun sarta ngawincik prinsip-prinsip gawé nirkabelna.

Dina taun 1894 Alexander Stepanovich Popov nyieun radio receiver, anu ngandung hiji coherer. Satuluyna manéhna nyampurnakeun éta alat jadi hiji detektor cahaya, anu dibébérkeun hareupeun Russian Physical and Chemical Society dina tanggal May 7, 1895.

Pintonan telegrafi nirkabel munggaran hareupeun balaréa lumangsung di ruang kuliah muséum Sajarah Alam Oxford University dina tanggal 14 Agustus 1894, anu dilaksanakeun ku Profésor Oliver Lodge jeung Alexander Muirhead. Dina éta pintonan, hiji sinyal radio dikirim ti gedong laboratorium Clarendon, sarta ditarima ku alat anu ditempatkeun di ruang kuliah dimaksud.

Dina taun 1896, Marconi dibéré patent 12039 ku Inggris, Improvements in transmitting electrical impulses and signals and in apparatus there-for. Dina taun 1897 manéhna ngadegkeun stasiun radio munggaran di dunya di Isle of Wight, Inggris. Marconi muka pabrik "nirkabel" munggaran di dunya di Hall Street, Chelmsford, Inggris dina taun 1898, anu ngagawékeun kira-kira 50 urang.

Panimuan hébat satuluyna nyaéta detéktor bungbung hapa, anu katimu ku para insinyur Westinghouse. Dina tanggal 25 Désémber 1906, Reginald Fessenden ngagunakeun synchronous rotary-spark transmitter pikeun siaran program radiona munggaran, ti Brant Rock, Massachusetts. Kapal-kapal di laut ngadéngé siaran Fessenden anu ngamaénkeun biola. Program warta berita radio munggaran disiarkeun dina 31 Agustus, 1920 ku stasiun 8MK di Detroit, Michigan. Stasiun radio kampus munggaran mitembeyan siaran dina tanggal 14 Oktober, 1920, ti Union College, Schenectady, New York.[3] Archived 2008-05-15 di Wayback Machine. Dina bulan anu sarua, stasiun radio 2ADD, anu satuluyna dingaranan WRUC dina taun 1940, nyiarkeun siaran hiburan munggaran di Amérika Sarikat. Dina bulan Nopémber 1920, éta stasiun nyiarkeun kagiatan olah raga.[4] Archived 2008-05-15 di Wayback Machine,[5] Archived 2009-01-25 di Wayback Machine Dina jam 9 isuk-isuk tanggal 27 Agustus 1920, Sociedad Radio Argentina nyiarkeun langsung pintonan opera ti Coliseo Theater di puseur kota Buenos Aires; duapuluh imah di éta kota boga alat panarima radio pikeun nangkep siaran kasebut. Sedengkeun siaran hiburan regulér dimimitian dina taun 1922 ti Pusat Risét boga Marconi di Writtle, deukeut Chelmsford, Inggris.

Artikel ieu keur dikeureuyeuh, ditarjamahkeun tina basa Inggris.
Bantuanna didagoan pikeun narjamahkeun.

One of the first developments in the éarly 20th century (1900-1959) was that aircraft used commercial AM radio stations for navigation. This continued until the éarly 1960s when VOR systems finally became widespréad (though AM stations are still marked on U.S. aviation charts). In the éarly 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 éarly as the 1920s. Commercial television transmissions started in North America and Europe in the 1940s. In 1954, Regency introduced a pocket transistor radio, the 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 yéars, 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 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 éarly 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.

Kagunaan radio

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Radio munggaran digunakeun pikeun kaperluan maritim, nyaéta pikeun ngirim pesen telegraf anu maké kode Morse antara kapal laut jeung kapal laut sarta antara kapal laut jeung daratan. Para pamaké munggaran di antarana Angkatan Laut Jepang pikeun nyilidik armada Rusia dina paperangan di Tsushima dina taun 1905. Kagunaan telegraf maritim anu paling diinget nyaéta waktu teuleumna RMS Titanic dina taun 1912, di antarana pikeun komunikasi antara para operator dina kapal nu titeuleum jeung kapal-kapal anu padeukeut sarta pikeun komunikasi jeung stasiun-stasiun di basisir pikeun ngémbarkeun anu salamet. Radio nu munggaran acan bisa mancarkeun sora atawa ucapan sarta disebut "wireless telegraph" atawa telegraf nirkabel.

Radio digunakeun pikeun ngirimkeun paréntah sarta komunikasi antara angkatan darat jeung angkatan laut dina Perang Dunia I; Jérman ngagunakeun komunikasi radio pikeun pesen diplomatik mangsa sakali waktu kabel lautna dipegatkeun ku Inggris. Amérika Sarikat ngirimkeun opat welas paringetan ti présidén Woodrow Wilson's ka Jérman ngagunakeun radio dina perang kasebut. Siaran radio mitembeyan ti San Jose dina taun 1909 [6] Archived 2010-10-17 di Wayback Machine, sarta jadi ilahar dina taun 1920-an, mangsa sumebarna alat panarima radio (radio receiver), hususna di Éropah jeung Amérika Sarikat. Sagigireun ti éta, siaran titik-ka-titik, kaasup pesen telepon sarta rélay program-program radio, sumebar dina taun 1920-an jeung 1930-an. Kagunaan lainna radio dina taun-taun saacan perang nyaéta hadirna kapal udara sarta kapal laut nu mampu ngadetéksi sarna manggihan kapal musuh maké radar (RAdio Detection And Ranging).

Kiwari, radio boga rupa-rupa wangunan, di antarana nyaéta sagala rupa jaringan nirkabel sarta komunikasi mobil katut siaran radio. Saacan ditimukeunna televisi, radio komérsial nyiarkeun lain waé warta jeung musik, tapi ogé drama, komedi, variety shows, jeung wangun hiburan lianna.

Audio

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Receiver hi-fi AM/FM Fisher 500 ti mangsa taun 1959.

Radio siaran AM ngirimkeun musik jeung ucapan dina spékrum gelombang radio Frékuénsi Sedeng (MF—0.300 MHz nepi ka 3 MHz). Radio AM ngagunakeun modulasi amplitudo, di mana amplitudo sinyal pamawa dirobah proporsional jeung amplitudo sora anu katangkep (di-trandusi) ku mikropon sedengkeun frékuénsina tetep henteu dirobah. Pangiriman sinyal cara kieu keuna ku gangguan listrik statik jeung interférensi lantaran kilat sarta sumber gangguan lianna anu mancar dina frékuénsi anu sarua ngarobah amplitudo sinyal anu dipancarkeun. Ukuran daya paling gedé anu dimeunangkeun pikeun stasiun radio AM di Amérika Sarikat nyaéta 50,000 watts sarta lolobana stasiun anu mancar sakuat ieu geus karolot; stasiun-stasiun ieu di antarana WGN (AM), WJR, sarta CKLW. Dina taun 1986 KTNN mangrupa stasiun pamungkas anu narima idin operasi dina 50,000 watt.

Radio siaran FM ngirimkeun musik jeung ucapan kalayan kehandalan (fidelity) anu leuwih hadé ti batan radio AM. Dina modulasi frékuénsi, parobahan amplitudo dina mikropon nyababkeun frékuénsi transmitter fluktuasi. Lantaran sinyal audio ngamodulasi frékuénsi lain amplitudo, mangka sinyal FM henteu keuna ku gangguan statik sarta interférensi saperti halna sinyal AM. FM dipancarkeun dina spéktrum gelombang radio Frékuénsi Luhur Pisan atawa Very High Frequency (VHF—30 MHz nepi ka 300 MHz). Gelombang radio VHF watekna leuwih mirupa cahaya, ngarambat dina garis anu lempeng, antukna jarak panarimaan kawates antara 50-100 mil. Dina kondisi atmosfir bagian luhur anu henteu biasa, sinyal FM kadang dipantulkeun balik ka bumi ku ionosfir, ngakibatkeun jarak pancar FM anu jauh. Receiver FM keuna ku capture effect, anu nyababkeun radio ngan narima sinyal anu paling kuat mangsa aya leuwih ti hiji sinyal anu datang dina frékuénsi nu sarua. Receiver FM relatif kebal tina gangguan kilat jeung interférensi.

Daya nu gedé boga mangfaat pikeun nembus wangunan, nyebar sabudeureun pasir-pasir, sarta mengkol dina luhureun horizon. Akibatna, stasiun-stasiun FM nu dayana 100,000 watt bisa sacara régulér kadéngé sajauh 100 mil (160 km), malah bisa leuwih jauh deui (nyaéta 150 mil, 240 km) lamun euwueh sinyal lianna dina frékuénsi nu sarua.

Stasiun FM anu dijalankeun maké daya 320,000 watts ERP nepi ka 500,000 watts ERP henteu ngabantu pikeun manjangkeun jarak pancar sabab frékuénsi VHF ngarambat ampir mirupa garis lempeng dina luhureun horizon sarta nembus ka angkasa luar.

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 réading services for the blind, background music or steréo sound signals. In some extremely crowded metropolitan aréas, 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 wéaker 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 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 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 séa, 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, WorldSpace and Sirius offer encrypted digital Satellite radio.

Telephony

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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 néars the edge of the cell site's radio coverage aréa, 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.

Satellite phones use satellites rather than cell towers to communicate. They come in two types: INMARSAT and Iridium. Both types provide world-wide coverage. INMARSAT uses géosynchronous satellites, with aimed high-gain antennas on the vehicles. Iridium uses 66 Low éarth Orbit satellites as the cells.

Video

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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 vidéo carrier. Analog television also uses a vestigial sideband on the vidéo 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 vidéo 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 vidéo 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.

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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 éach 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 néar cities. In some cases they used marine radiolocation béacons, 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 simultanéously. A directional signal rotates like a lighthouse at a fixed rate. When the directional signal is facing north, an omnidirectional signal pulses. By méasuring the difference in phase of these two signals, an aircraft can determine its béaring or radial from the station, thus establishing a line of position. An aircraft can get réadings 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 béaring 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 méasuring equipment, VOR/DME and VORTAC stations are identical in navigation potential to civil aircraft.

Radar

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Radar (Radio Detection And Ranging) detects objects at a distance by bouncing radio waves off them. The delay caused by the echo méasures the distance. The direction of the béam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide aréa two to four times per minute. They use very short waves that reflect from éarth 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 héavy storms, as well as land and vehicles. Some can superimpose sonar data and map data from GPS position.

Séarch radars scan a wide aréa with pulses of short radio waves. They usually scan the aréa two to four times a minute. Sometimes séarch radars use the doppler effect to separate moving vehicles from clutter. Targeting radars use the same principle as séarch radar but scan a much smaller aréa far more often, usually several times a second or more. Wéather radars resemble séarch radars, but use radio waves with circular polarization and a wavelength to reflect from water droplets. Some wéather radar use the doppler to méasure wind speeds.

Data (digital radio)

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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 énérgizing 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, créating 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 créate 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 wéather 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 repéat. 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 spréad spectrum begin in the 1980s. Bluetooth, most cell phones, and the 802.11b version of Wi-Fi éach use various forms of spréad spectrum.

Systems that need reliability, or that share their frequency with other services, may use "coded orthogonal frequency-division multiplexing" or COFDM. COFDM bréaks a digital signal into as many as several hundred slower subchannels. The digital signal is often sent as QAM on the subchannels. modérn COFDM systems use a small computer to maké 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 phones, Digital Radio Mondiale, Eureka 147, and many other local aréa network, digital TV and radio standards.

Heating

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Radio-frequency energy generated for héating 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 héat 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 séaling of blood vessels. Induction furnaces are used for melting metal for casting.

Amateur radio service

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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 gréat 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 repéaters. Some amateur frequencies may be disrupted by power-line internet service.

Unlicensed radio services

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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 overhéad 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 maké any money, while the Pirate station could not exist without adverts, payolas, etc.

Radio control (RC)

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Radio remote controls use radio waves to transmit control data to a remote object as in some éarly forms of guided missile, some éarly TV remotes and a range of modél 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.[7] He was awarded U.S. patent No. 613,809 for a "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles." [8]

The electromagnetic spectrum

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Radio waves are a form of electromagnetic radiation, créated whenever a charged object (in normal radio transmission, an electron) accelerates 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 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.[2] Other types of electromagnetic radiation, with frequencies above the RF range, are microwave, infrared, visible light, ultraviolet, X-rays and gamma rays. 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

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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 microwaves, and the technique has been demonstrated. (See Microwave power transmission). These schemes include, for example, solar power stations in orbit béaming energy down to terrestrial users.

See also

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Catetan

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  1. ↑ List of Tesla patents
  2. ↑ The Electromagnetic Spectrum, University of Tennessee, Dept. of Physics and Astronomy

Rujukan

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Bacaan salajengna

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  • 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).

Sumber utama

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  • De Forest, Lee. Father of Radio: The Autobiography of Lee de Forest (1950).

Tumbu luar

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