Beautiful Pictures of Campfires

Saturday, 2 July 2011

Electromechanical television

Electromechanical television

The Nipkow disk. This schematic shows the circular paths traced by the holes, that may also be square for greater precision. The area of the disk outlined in black shows the region scanned.
The beginnings of mechanical television can be traced back to the discovery of the photoconductivity of the element selenium by Willoughby Smith in 1873, the invention of a scanning disk by Paul Gottlieb Nipkow in 1884 and John Logie Baird's demonstration of televised moving images in 1926.
As a 23-year-old German university student, Paul Nipkow proposed and patented the first electromechanical television system in 1884.[1] Although he never built a working model of the system, variations of Nipkow's spinning-disk "image rasterizer" for television became exceedingly common, and remained in use until 1939.[2] Constantin Perskyi had coined the word television in a paper read to the International Electricity Congress at the International World Fair in Paris on August 25, 1900. Perskyi's paper reviewed the existing electromechanical technologies, mentioning the work of Nipkow and others.[3]
However, it was not until 1907 that developments in amplification tube technology, by Lee DeForest and Arthur Korn among others, made the design practical.[4] The first demonstration of the instantaneous transmission of still silhouette images was by Georges Rignoux and A. Fournier in Paris in 1909, using a rotating mirror-drum as the scanner and a matrix of 64 selenium cells as the receiver.[5]

Electronic television

Electronic television

In 1908, Alan Archibald Campbell-Swinton, fellow of the Royal Society (UK), published a letter in the scientific journal Nature in which he described how "distant electric vision" could be achieved by using a cathode ray tube (or "Braun" tube, after its inventor, Karl Braun) as both a transmitting and receiving device,the first iteration of the electronic television method that would dominate the field until recently. He expanded on his vision in a speech given in London in 1911 and reported in The Times[17] and the Journal of the Röntgen Society. In a letter to Nature published in October 1926, Campbell-Swinton also announced the results of some "not very successful experiments" he had conducted with G. M. Minchin and J. C. M. Stanton. They had attempted to generate an electrical signal by projecting an image onto a selenium-coated metal plate that was simultaneously scanned by a cathode ray beam.These experiments were conducted before March 1914, when Minchin died,[22] but they were later repeated by two different teams in 1937, by H. Miller and J. W. Strange from EMI,[23] and by H. Iams and A. Rose from RCA.[24] Both teams succeeded in transmitting "very faint" images with the original Campbell-Swinton's selenium-coated plate. Although others had experimented with using a cathode ray tube as a receiver, the concept of using one as a transmitter was novel.[25] By the late 1920s, when electromechanical television was still being introduced, several inventors were already working separately on versions of all-electronic transmitting tubes, including Philo Farnsworth and Vladimir Zworykin in the United States, and Kálmán Tihanyi in Hungary.
On September 7, 1927, Farnsworth's Image Dissector camera tube transmitted its first image, a simple straight line, at his laboratory at 202 Green Street in San Francisco.[26][27] By September 3, 1928, Farnsworth had developed the system sufficiently to hold a demonstration for the press.[27] In 1929, the system was further improved by elimination of a motor generator, so that his television system now had no mechanical parts.[28] That year, Farnsworth transmitted the first live human images with his system, including a three and a half-inch image of his wife Elma ("Pem") with her eyes closed (possibly due to the bright lighting required).[29]

The problem of low sensitivity to light resulting in low electrical output from transmitting or "camera" tubes would be solved by Tihanyi beginning in 1924.[35] His solution was a camera tube that accumulated and stored electrical charges ("photoelectrons") within the tube throughout each scanning cycle. The device was first described in a patent application he filed in Hungary in March 1926 for a television system he dubbed "Radioskop".[36] After further refinements included in a 1928 patent application,[35] Tihanyi was awarded patents for the camera tube in both France and Great Britain in 1928, and applied for patents in the United States in June of the following year. Although his breakthrough would be incorporated into the design of RCA's "iconoscope" in 1931, the U.S. patent for Tihanyi's transmitting tube would not be granted until May 1939. The patent for his receiving tube had been granted the previous October. Both patents had been purchased by RCA prior to their approval.[37][38] The idea of charge & storage (with various and very different technological solutions) is still remained[39] as a basic requirement for all type of modern image sensors until this day.

United States

United States

Television antenna on a rooftop
The first regularly scheduled television service in the United States began on July 2, 1928. The Federal Radio Commission authorized C.F. Jenkins to broadcast from experimental station W3XK in Wheaton Maryland, a suburb of Washington, D.C. For at least the first eighteen months, 48-line silhouette images from motion picture film were broadcast, although beginning in the summer of 1929 he occasionally broadcast in halftones.[76][77]
Hugo Gernsback's New York City radio station began a regular, if limited, schedule of live television broadcasts on August 14, 1928, using 48-line images. Working with only one transmitter, the station alternated radio broadcasts with silent television images of the station's call sign, faces in motion, and wind-up toys in motion.[78][79] Speaking later that month, Gernsback downplayed the broadcasts, intended for amateur experimenters. "In six months we may have television for the public, but so far we have not got it."[80] Gernsback also published Television, the world's first magazine about the medium.
General Electric's experimental station in Schenectady, New York, on the air sporadically since January 13, 1928, was able to broadcast reflected-light, 48-line images via shortwave as far as Los Angeles, and by September was making four television broadcasts weekly. It is considered to be the direct predecessor of current television station WRGB. The Queen's Messenger, a one-act play broadcast on September 11, 1928, was the world's first live drama on television.[81]
Radio giant RCA began daily experimental television broadcasts in New York City in March 1929 over station W2XBS. The 60-line transmissions consisted of pictures, signs, and views of persons and objects.[82] Experimental broadcasts continued to 1931.[83]

Germany

Germany

Electromechanical broadcasts began in Germany in 1929, but were without sound until 1934. Network electronic service started on March 22, 1935, on 180 lines using telecine transmission of film, intermediate film system, or cameras using the Nipkow Disk. Transmissions using cameras based on the iconoscope began on January 15, 1936. The Berlin Summer Olympic Games were televised, using both all-electronic iconoscope-based cameras and intermediate film cameras, to Berlin and Hamburg in August 1936. Twenty-eight public television rooms were opened for anybody who did not own a television set. The Germans had a 441-line system on the air in February 1937, and during World War II brought it to France, where they broadcast from the Eiffel Tower.
The American Armed Forces Radio Network at the end of World War II, wishing to provide US TV programming to the occupation forces in Germany, used US TV receivers made to operate at 525 lines and 60 fields. US broadcast equipment was modified; they changed the vertical frequency to 50 Hz in accordance to the European mains frequency standard to avoid power line wiggles, changed the horizontal frequency from 15,750 Hz to 15,625 Hz a 0.5 microsecond change in the length of a line. With this signal, US TV receivers with only an adjustment to the vertical hold control had a 625 line (= 576 visual lines + 49 lines of non-visual synch and burst data), 50 field scan, which became the German standard. This AFN system, however, was not the later PAL standard native to Germany, as the displays themselves were not capable of displaying any more than the standard NTSC 486 visual lines, which effectively were even only 243 visible lines due to display-internal deinterlacing by means of alternatively discarding one field and applying line doubling on the result. Additionally, it still took until the 1960s for the PAL-specific YUV color system to be invented by Walter Bruch, with PAL operating at 576 visual lines.

United Kingdom

United Kingdom

The first British television broadcast was made by Baird Television's electromechanical system over the BBC radio transmitter in September 1929. Baird provided a limited amount of programming five days a week by 1930. During this time, Southampton earned the distinction of broadcasting the first-ever live television interview, which featured Peggy O'Neil, an actress and singer from Buffalo, New York.[93] On August 22, 1932, BBC launched its own regular service using Baird's 30-line electromechanical system, continuing until September 11, 1935. On November 2, 1936 the BBC began broadcasting a dual-system service, alternating between Marconi-EMI's 405-line standard and Baird's improved 240-line standard, from Alexandra Palace in London, making the BBC Television Service (now BBC One) the world's first regular high-definition television service. The government, on advice from a special advisory committee, decided that Marconi-EMI's electronic system gave the superior picture, and the Baird system was dropped in February 1937. TV broadcasts in London were on the air an average of four hours daily from 1936 to 1939. There were 12,000 to 15,000 receivers. Some sets in restaurants or bars might have 100 viewers for sport events (Dunlap, p56).The outbreak of the Second World War caused the BBC service to be suspended on September 1, 1939, resuming from Alexandra Palace on June 7, 1946. At the end of 1947 there were 54,000 licensed television receivers, compared with 44,000 television sets in the United States at that time.[92]
The first transatlantic television signal was sent in 1928 from London to New York by the Baird Television Development Company/Cinema Television, although this signal was not broadcast to the public. The first live satellite signal to Britain from the United States was broadcast via the Telstar satellite on July 23, 1962.
The first live broadcast from the European continent was made on August 27, 1950.

Technological innovations

Technological innovations

The first live national television broadcast in the U.S. took place on September 4, 1951 when President Harry Truman's speech at the Japanese Peace Treaty Conference in San Francisco, California was transmitted over AT&T's transcontinental cable and microwave radio relay system to broadcast stations in local markets.[94][95][96]
The first live coast-to-coast commercial television broadcast in the U.S. took place on November 18, 1951 during the premiere of CBS's See It Now, which showed a split-screen view of the Brooklyn Bridge in New York City and the Golden Gate Bridge in San Francisco. In 1958, the CBC completed the longest television network in the world, from Sydney, Nova Scotia to Victoria, British Columbia. Reportedly, the first continuous live broadcast of a "breaking" news story in the world was conducted by the CBC during the Springhill Mining Disaster, which began on October 23 of that year.
The development of cable and satellite television in the 1970s allowed for more channels and encouraged businessmen to target programming toward specific audiences. It also enabled the rise of subscription television channels, such as Home Box Office (HBO) and Showtime in the U.S., and Sky Television in the U.K.

Television sets

Television sets

In television's electromechanical era, commercially made television sets were sold from 1928 to 1934 in the United Kingdom,[97] United States, and the Soviet Union.[98] The earliest commercially made sets sold by Baird in the UK in 1928 were radios with the addition of a television device consisting of a neon tube behind a mechanically spinning disk (the Nipkow disk) with a spiral of apertures that produced a red postage-stamp size image, enlarged to twice that size by a magnifying glass. The Baird "Televisor" was also available without the radio. The Televisor sold in 1930–1933 is considered the first mass-produced set, selling about a thousand units.[99]
Typical 1950s United States television set
The first commercially made electronic television sets with cathode ray tubes were manufactured by Telefunken in Germany in 1934,[100][101] followed by other makers in France (1936),[102] Britain (1936),[103] and America (1938).[104][105] The cheapest of the pre-World War II factory-made American sets, a 1938 image-only model with a 3-inch (8 cm) screen, cost US$125, the equivalent of US$1,863 in 2007. The most expensive model with a 12-inch (30 cm) screen was $445 ($6,633).[106]
An estimated 19,000 electronic television sets were manufactured in Britain, and about 1,600 in Germany, before World War II. About 7,000–8,000 electronic sets were made in the U.S.[107] before the War Production Board halted manufacture in April 1942, production resuming in August 1945.
Television usage in the United States skyrocketed after World War II with the lifting of the manufacturing freeze, war-related technological advances, the gradual expansion of the television networks westward, the drop in set prices caused by mass production, increased leisure time, and additional disposable income. In 1947, Motorola introduced the VT-71 television for $189.95, the first television set to be sold for under $200, finally making television affordable for millions of Americans. While only 0.5% of U.S. households had a television set in 1946, 55.7% had one in 1954, and 90% by 1962.[108] In Britain, there were 15,000 television households in 1947, 1.4 million in 1952, and 15.1 million by 1968.