1904 Fleming invents the vacuum diode British engineer Sir John Ambrose Fleming invents the two-electrode radio rectifier; or vacuum diode, which he calls an oscillation valve. Based on Edison's lightbulbs, the valve reliably detects radio waves. Transcontinental telephone service becomes possible with Lee De Forest's 1907 patent of the triode, or three-element vacuum tube, which electronically amplifies signals. 1906 Christmas Eve 1906 program On Christmas Eve 1906 engineering professor Reginald Fessenden transmits a voice and music program in Massachusetts that is picked up as far away as Virginia. 1906 Audion Expanding on Fleming’s invention, American entrepreneur Lee De Forest puts a third wire, or grid, into a vacuum tube, creating a sensitive receiver. He calls his invention the "Audion." In later experiments he feeds the Audion output back into its grid and finds that this regenerative circuit can transmit signals. 1912 Radio signal amplifier devised Columbia University electrical engineering student Edwin Howard Armstrong devises a regenerative circuit for the triode that amplifies radio signals. By pushing the current to the highest level of amplification, he also discovers the key to continuous-wave transmission, which becomes the basis for amplitude modulation (AM) radio. In a long patent suit with Lee De Forest, whose three-element Audion was the basis for Armstrong’s work, the courts eventually decide in favor of De Forest, but the scientific community credits Armstrong as the inventor of the regenerative circuit.
1917 Superheterodyne circuit While serving in the U.S. Army Signal Corps during World War I, Edwin Howard Armstrong invents the superheterodyne circuit, an eight-tube receiver that dramatically improves the reception of radio signals by reducing static and increasing selectivity and amplification. He files for a patent the following year. 1917 Superheterodyne circuit While serving in the U.S. Army Signal Corps during World War I, Edwin Howard Armstrong invents the superheterodyne circuit, an eight-tube receiver that dramatically improves the reception of radio signals by reducing static and increasing selectivity and amplification. He files for a patent the following year. 1920 First scheduled commercial radio programmer Station KDKA in Pittsburgh becomes radio’s first scheduled commercial programmer with its broadcast of the Harding-Cox presidential election returns, transmitted at 100 watts from a wooden shack atop the Westinghouse Company’s East Pittsburgh plant. Throughout the broadcast KDKA intersperses the election returns and occasional music with a message: "Will anyone hearing this broadcast please communicate with us, as we are anxious to know how far the broadcast is reaching and how it is being received?" 1925 Televisor Scottish inventor John Logie Baird successfully transmits the first recognizable image—the head of a ventriloquist’s dummy—at a London department store, using a device he calls a Televisor. A mechanical system based on the spinning disk scanner developed in the 1880s by German scientist Paul Nipkow, it requires synchronization of the transmitter and receiver disks. The Televisor images, composed of 30 lines flashing 10 times per second, are so hard to watch they give viewers a headache. Charles F. Jenkins pioneers his mechanical wireless television system, radiovision, with a public transmission sent from a navy radio station across the Anacostia River to his office in downtown Washington, D.C. Jenkins’s radiovisor is a multitube radio set with a special scanning-drum attachment for receiving pictures—cloudy 40- to 48-line images projected on a six-inch-square mirror. Jenkins’s system, like Baird’s, broadcasts and receives sound and visual images separately. Three years later the Federal Radio Commission grants Charles Jenkins Laboratories the first license for an experimental television station. 1927 All-electronic television system Using his all-electronic television system, 21-year-old Utah farm boy and electronic prodigy Philo T. Farnsworth transmits images of a piece of glass painted black, with a center line scratched into the paint. The glass is positioned between a blindingly bright carbon arc lamp and Farnsworth’s "image dissector" cathode-ray camera tube. As viewers in the next room watch a cathode-ray tube receiver, someone turns the glass slide 90 degrees—and the line moves. The use of cathode-ray tubes to transmit and receive pictures—a concept first promoted by British lighting engineer A. Campbell Swinton—is the death knell for the mechanical rotating-disk scanner system.
1928 Televisor system produces images in crude color John Logie Baird demonstrates, with the aid of two ventriloquist’s dummies, that his Televisor system can produce images in crude color by covering three sets of holes in his mechanical scanning disks with gels of the three primary colors. The results, as reported in 1929 following an experimental BBC broadcast, appear "as a soft-tone photograph illuminated by a reddish-orange light." 1928 Televisor system produces images in crude color John Logie Baird demonstrates, with the aid of two ventriloquist’s dummies, that his Televisor system can produce images in crude color by covering three sets of holes in his mechanical scanning disks with gels of the three primary colors. The results, as reported in 1929 following an experimental BBC broadcast, appear "as a soft-tone photograph illuminated by a reddish-orange light." 1929 Television camera and a cathode-ray tube receiver Vladimir Zworykin, who came to the United States from Russia in 1919, demonstrates the newest version of his iconoscope, a cathode-ray-based television camera that scans images electronically, and a cathode-ray tube receiver called the kinescope. The iconoscope, first developed in 1923, is similar to Philo Farnsworth’s "image dissector" camera tube invention, fueling the growing rivalry between the two inventors for the eventual title of "father of modern television."
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