set trasmissione radio
Radio is the transmission of signals by modulation of with below those of . Information is carried by systematically changing some property of the radiated waves, such as , , , or pulse width. [ Originally, radio or radiotelegraphy was called , which was shortened to wireless by the British. The prefix radio- in the sense of wireless transmission, was first recorded in the word radioconductor , coined by the French physicist in 1897 and based on the verb to radiate in Latin radius means spoke of a wheel, beam of light, ray . This word also appears in a 1907 article by , was adopted by the 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 widely . In recent years the term wireless has gained renewed popularity through the rapid growth of short-range computer networking, e.g., , , and , as well as mobile telephony, e.g., and . 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 , but about wireless devices and wireless sensor networks. [ Radio systems used for will have the following elements. Each system contains a . The transmitter sends the modulated electrical energy to a tuned ; The electromagnetic wave is intercepted by a tuned receiving ; At the receiver, these currents are , which is conversion to a usable signal form by a sub-system. Radio became more useful after the invention of devices such as the and later the , which made it possible to amplify weak signals. Today radio systems are used for applications from children's toys to the control of , as well as for , and many other applications. [ Radio frequencies occupy the range from a few tens of to three hundred gigahertz, although commercially important uses of radio use only a small part of this spectrum. Other types of electromagnetic radiation, with frequencies above the RF range, are , , visible , , and . Since the energy of an individual of radio frequency is too low to remove an from an , radio waves are classified as . [ [ The meaning and usage of the word radio has developed in parallel with developments within the field and can be seen to have three distinct phases: electromagnetic waves and experimentation; Many individuals—inventors, engineers, developers, businessmen - contributed to produce the modern idea of radio and thus the origins and 'invention' are multiple and controversial. Early radio could not transmit sound or speech and was called the . Experiments, later patented, were undertaken by and his employees of . In 1895 built his first radio receiver, which contained a . In 1895 created a wireless system capable of transmitting a signal at long distances 1.5 mi./ 2.4 km . [ Marconi achieved greater range thanks to the layout of his apparatus and creation of the first effective radio receiver. Following his experiments, Marconi deduced that transmission range is proportional to the square of the antenna height Marconi's law . [ [ In 1896, Marconi was awarded the British patent 12039, Improvements in transmitting electrical impulses and signals and in apparatus there-for , for radio. In 1897, he established a radio station on the , England. Marconi opened his wireless factory in Hall Street, , England in 1898, employing around 50 people. Although Marconi has long been credited with inventing the radio, in 1943, maybe for political reasons related to Marconi suing the U.S. over Patent infringement during WWI, the U.S. Supreme Court upheld Tesla's radio patent number 645,576. 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 . Meanwhile, regular entertainment broadcasts commenced in 1922 from the Marconi Research Centre at , . This continued until the early 1960s when systems finally became widespread though AM stations are still marked on U.S. aviation charts . In 1954, the Regency company introduced a pocket radio, the , powered by a standard 22.5 V Battery . By 1963, color television was being regularly broadcast commercially though not all broadcasts or programs were in color , and the first radio , , was launched. Soon, the U.S. Navy experimented with , culminating in the invention and launch of the constellation in 1987. [ Early uses were maritime, for sending telegraphic messages using between ships and land. Radio was used to pass on orders and communications between armies and navies on both sides in ; Another use of radio in the pre-war years was the development of detection and locating of aircraft and ships by the use of RA dio D etection A nd R anging . Today, radio takes many forms, including and of all types, as well as radio . Before the advent of , 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 . [ AM radio uses , 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. Currently, the maximum broadcast power for a civilian AM radio station in the and Canada is 50 kW, and the majority of stations that emit signals this powerful were grandfathered in see . These 50 kW stations are generally called stations not to be confused with , because within each of these stations has exclusive use of its broadcast frequency throughout part or all of the broadcast day. In , amplitude variation at the causes the transmitter frequency to fluctuate. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the , resulting in . FM receivers are subject to the , which causes the radio to only receive the strongest signal when multiple signals appear on the same frequency. 93.7 in , , USA, runs 320,000 watts ERP, and can increase to 500,000 watts ERP by the terms of its original license. [ services are secondary signals transmitted in a piggyback fashion along with the main program. Use of FM would result in stronger stations blocking out reception of weaker stations due to FM's . Marine voice radios can use voice SSB in the shortwave High Frequency HF—3 MHz to 30 MHz radio spectrum for very long ranges or 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 of deviation, versus the 75 kHz used by commercial FM broadcasts, and 25 kHz used for TV sound. Most use voice SSB , which uses less bandwidth than AM. Commercial services such as , and offer encrypted digital . [ transmit to a local transmitter/receiver that ultimately connects to the public switched telephone network through an optic fiber or microwave radio and other network elements. [ sends the picture as AM and the sound as AM or FM, with the sound carrier a fixed frequency 4.5 MHz in the system away from the video carrier. Digital television uses modulation in North America under the digital television standard , and modulation elsewhere in the world using the standard . Although many current and future codecs can be sent in the , as of 2006 most systems use a standard-definition format almost identical to : video in and MP2 audio. [ All systems use satellites with precision clocks. In some cases they used marine radiolocation beacons, which share a range of frequencies just above AM radio with amateur radio operators. systems also used time-of-flight radio signals, but from radio stations on the ground. Very High Frequency Omnidirectional Range , systems used by aircraft , have an antenna array that transmits two signals simultaneously. When the VOR station is collocated with DME , the aircraft can determine its bearing and range from the station, thus providing a fix from only one ground station. [ Radio Detection And Ranging detects objects at a distance by bouncing radio waves off them. [ Most new radio systems are digital, see also: , , . The oldest form of digital broadcast was spark gap , used by pioneers such as Marconi. The next advance was continuous wave , or CW , in which a pure radio frequency, produced by a was switched on and off by a key. CW is still used, these days primarily by operators hams . Strictly, on-off keying of a carrier should be known as Interrupted Continuous Wave or ICW or OOK . Microwave dishes on satellites, telephone exchanges and TV stations usually use QAM . Communication systems that limit themselves to a fixed narrowband frequency range are vulnerable to . , most cell phones, and the 802.11b version of 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 . Modern COFDM systems use a small computer to make and decode the signal with , which is more flexible and far less expensive than older systems that implemented separate electronic channels. COFDM is used for , some , , , and many other local area network, digital TV and radio standards. [ 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. Induction are used for melting metal for , and for cooking. [ , also known as ham radio , is a hobby in which enthusiasts are licensed to communicate on a number of bands in the non-commercially and for their own enjoyment. Radio amateurs use a variety of modes, including nostalgic ones like and experimental ones like . Several forms of radio were pioneered by radio amateurs and later became commercially important including , SSB , , digital packet radio and satellite repeaters. [ Unlicensed, government-authorized personal radio services such as in , the , and , and and in North America exist to provide simple, usually short range communication for individuals and small groups, without the overhead of licensing. [ use radio waves to transmit control data to a remote object as in some early forms of , some early TV remotes and a range of model boats, and airplanes. [ [ L. de Forest, article in Electrical World 22 June 1270/1 1907 , early use of word radio . - 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. Tesla - Man Out of Time . The Continuous Wave: Technology and the American Radio, 1900-1932 Princeton University Press, 1985 . The History of Broadcasting in the United Kingdom Oxford University Press, 1961 . Father of Radio: The Autobiography of Lee de Forest 1950 . 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 . , . Lewis, Tom, Empire of the Air: The Men Who Made Radio , 1st ed., New York : E. Invention and Innovation in the Radio Industry The Macmillan Company, 1949 . FCC: The Ups and Downs of Radio-TV Regulation Iowa State University Press, 1990 . A Social History of British Broadcasting, Volume One, 1922-1939 Basil Blackwell, 1991 . The American Radio Industry and Its Latin American Activities, 1900-1939 University of Illinois Press, 1990 . Electronic Media, A Guide to Trends in Broadcasting and Newer Technologies 1920-1983 Praeger, 1984 . The American Radio University of Chicago Press, 1947 . Rohde, Jerry Whitaker Communications Receivers, Third Edition , McGraw Hill, New York, NY, 2001, . [ at the Essay by , The Atlantic Monthly, January 1998. - Archives Center, National Museum of American History, Smithsonian Institution NTIA .
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