Telecommunication, often used in its plural form or abbreviated as telecom, is the transmission of information with an immediacy comparable to face-to-face communication. As such, slow communications technologies like postal mail and pneumatic tubes are excluded from the definition. Many transmission media have been used for telecommunications throughout history, from smoke signals, beacons, semaphore telegraphs, signal flags, and optical heliographstowires and empty space made to carry electromagnetic signals. These paths of transmission may be divided into communication channels for multiplexing, allowing for a single medium to transmit several concurrent communication sessions. Several methods of long-distance communication before the modern era used sounds like coded drumbeats, the blowing of horns, and whistles. Long-distance technologies invented during the 20th and 21st centuries generally use electric power, and include the telegraph, telephone, television, and radio.
Since the 1960s, the proliferation of digital technologies has meant that voice communications have gradually been supplemented by data. The physical limitations of metallic media prompted the development of optical fibre. The Internet, a technology independent of any given medium, has provided global access to services for individual users and further reduced location and time limitations on communications. (Full article...)
Carbon microphone from Western Electric telephone handset, around 1976.
The carbon microphone, also known as carbon button microphone, button microphone, or carbon transmitter, is a type of microphone, a transducer that converts sound to an electrical audio signal. It consists of two metal plates separated by granules of carbon. One plate is very thin and faces toward the speaking person, acting as a diaphragm. Sound waves striking the diaphragm cause it to vibrate, exerting a varying pressure on the granules, which in turn changes the electrical resistance between the plates. Higher pressure lowers the resistance as the granules are pushed closer together. A steady direct current is passed between the plates through the granules. The varying resistance results in a modulation of the current, creating a varying electric current that reproduces the varying pressure of the sound wave. In telephony, this undulating current is directly passed through the telephone wires to the central office. In public address systems it is amplified by an audio amplifier. The frequency response of most carbon microphones, however, is limited to a narrow range, and the device produces significant electrical noise.
Before the proliferation of vacuum tube amplifiers in the 1920s, carbon microphones were the only practical means of obtaining high-level audio signals. They were widely used in telephone systems until the 1980s, while other applications used different microphone designs much earlier. Their low cost, inherently high output and frequency response characteristic were well suited for telephony. For plain old telephone service (POTS), carbon-microphone based telephones can still be used without modification. Carbon microphones, usually modified telephone transmitters, were widely used in early AM radio broadcasting systems, but their limited frequency response, as well as a fairly high noise level, led to their abandonment in those applications by the late 1920s. They continued to be widely used for low-end public address, and military and amateur radio applications for some decades afterward. (Full article...)
Image 2Historical marker commemorating the first telephone central office in New York State (1878) (from History of the telephone)
Image 3Around 1920, radio broadcasting started to get popular. The Brox Sisters, a popular singing group, gathered around the radio at the time. (from History of radio)
Image 4AT&T magazine advertisement announcing commercial launch of Picturephone service. (from History of videotelephony)
Image 5Artist's conception: 21st-century videotelephony imagined in the early 20th century (1910) (from History of videotelephony)
Image 6Heinrich Rudolf Hertz (1856–1894) proved the existence of electromagnetic radiation. (from History of radio)
Image 14The Nipkow disk. This schematic shows the circular paths traced by the holes, which may also be square for greater precision. The area of the disk outlined in black shows the region scanned. (from History of television)
Image 19Actor portraying Alexander Graham Bell in a 1932 silent film. Shows Bell's second telephone transmitter (microphone), invented 1876 and first displayed at the Centennial Exposition, Philadelphia. (from History of the telephone)
Image 31Australian radio sets usually had the positions of radio stations marked on their dials. The illustration is a dial from a transistorised, mains-operated Calstan radio, circa 1960s. (Click image for a high resolution view, with readable callsigns.) (from History of broadcasting)
Image 32"Fiction becomes fact": Imaginary "Edison" combination videophone-television, conceptualized by George du Maurier and published in Punch magazine. The drawing also depicts then-contemporary speaking tubes, used by the parents in the foreground and their daughter on the viewing display (1878). (from History of videotelephony)
Image 34In the 1920s, the United States government publication, "Construction and Operation of a Simple Homemade Radio Receiving Outfit", showed how almost any person handy with simple tools could a build an effective crystal radio receiver. (from History of radio)
Image 35RCA 630-TS, the first mass-produced television set, which sold in 1946–1947 (from History of television)
Image 36An exposed view of the Picturephone's rear circuit board (courtesy: Richard Diehl) (from History of videotelephony)
Image 45Antonio Meucci, 1854, constructed telephone-like devices. (from History of the telephone)
Image 46The Marconi Company was formed in England in 1910. The photo shows a typical early scene, from 1906, with Marconi employee Donald Manson at right. (from History of broadcasting)
Image 50The "Kerbango Internet Radio" was the first stand-alone product that let users listen to Internet radio without a computer. (from History of broadcasting)
Image 73The British Broadcasting Corporation's landmark and iconic London headquarters, Broadcasting House, opened in 1932. At right is the 2005 eastern extension, the John Peel wing. (from History of broadcasting)
Paul Julius Gottlieb Nipkow (22 August 1860 – 24 August 1940) was a German technician and inventor. He invented the Nipkow disk, which laid the foundation of television, since his disk was a fundamental component in the first televisions. Hundreds of stations experimented with television broadcasting using his disk in the 1920s and 1930s, until it was superseded by all-electronic systems in the 1940s.
Nipkow has been called the "father of television", together with other early figures of television history like Karl Ferdinand Braun. (Full article...)
... that Nathan Safir, general manager of Texas radio station KCOR for 44 years, was credited with being a pioneer in Spanish-language broadcasting in the United States?
... that the limited radio airplay of "Get Together" in the US spawned a petition, outrage, and conspiracy theories among Madonna fans?
... that even though an FCC examiner recommended denial of an application for a radio station in Illinois after approving it twice, the commission granted it anyway?
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