television transmission and reception of still or moving images by means of electrical signals, especially by means of electromagnetic radiation using the techniques of radio and by fiberoptic and coaxial cables. Television has become a major industry, especially in the industrialized nations, and a major medium of communication and source of home entertainment. Television is put to varied use in industry, e.g., for surveillance in places inaccessible to or dangerous for human beings; in science, e.g., in tissue microscopy (see microscope ); and in education.

Evolution of the Scanning Process

The idea of "seeing by telegraph" engrossed many inventors after the discovery in 1873 of variation in the electrical conductivity of selenium when exposed to light. Selenium cells were used in early television devices; the results were unsatisfactory, however, chiefly because the response of selenium to light-intensity variations was not rapid enough. Moreover, until the development of the electron tube there was no way of sufficiently amplifying the weak output signals. These limitations precluded the success of a television method for which Paul Nipkow in Germany received (1884) a patent.

His system employed a selenium photocell and a scanning disk; it embodied the essential features of later successful devices. A scanning disk has a single row of holes arranged so that they spiral inward toward the center from a point near the edge. The disk revolves in front of a light-sensitive plate on which a lens forms an image; each hole passes across, or "scans," a narrow, ring-shaped sector of the image. Thus the holes trace contiguous concentric sectors, so that in one revolution of the disk the entire image is scanned. When the light-sensitive cell is connected in an electric circuit, the variations in light cause corresponding fluctuations in the electric current. The image can be reproduced by a receiver whose luminous area is scanned by a similar disk synchronized with the disk of the transmitter.

Although selenium cells proved inadequate, the development of the phototube (see photoelectric cell ) made the mechanical disk-scanning method practicable. In 1926, J. L. Baird in England and C. F. Jenkins in the United States successfully demonstrated television systems using mechanical scanning disks. While research remained at producing pictures made up of 60 to 100 scanned lines, mechanical systems were competitive. These were soon superseded, however, by electronic scanning methods; a television system employing electronic scanning was patented by V. K. Zworykin in 1928. The 1930s saw the laboratory perfection of television equipment that began to reach the market in 1945 after World War II.

The modern scanning process, which is the essence of television accomplishment, operates as do the eyes in reading a page of printed matter, i.e., line by line. A complex circuit of horizontal and vertical deflection coils controls this movement and causes the electronic beam to scan the back of a mosaic of photoelectric cells in a 525-line zigzag 30 times each second. (The 525-line 30-frame-per-second system is used in the United States, Japan, and elsewhere; many other countries use similar but incompatible systems.) Because of persistence of vision only about 30 pictures need be transmitted each second to give the effect of motion. The development of interlaced scanning results in alternate lines being scanned each 1/60 sec, the remaining lines being covered in the next 1/60 sec.

Development of the Television Camera and Receiver

V. K. Zworykin's iconoscope (1923) was the first successful camera tube in wide use. Its functioning involved many fundamental principles common to all television image pickup devices. The face of the iconoscope consisted of a thin sheet of mica upon which thousands of microscopic globules of a photosensitive silver-cesium compound had been deposited. Backed with a metallic conductor, this expanse of mica became a mosaic of tiny photoelectric cells and capacitors. The differing light intensities of various points of a scene caused the cells of the mosaic to emit varying quantities of electrons, leaving the cells with positive charges proportionate to the number of electrons lost. An electron gun, or "scanner," passed its beam across the cells. As it did so, the charge was released, causing an electrical signal to appear on the back of the mosaic, which was connected externally to an amplifier. The strength of the signal was proportional to the amount of charge released. The iconoscope provided good resolution, but required very high light levels and needed constant manual correction.

The orthicon and image-orthicon camera tubes improved on the iconoscope. They used light-sensitive granules deposited on an insulator and low-velocity scanning. These could be used with lower light levels than required by the iconoscope, and did not require the constant manual manipulation. The vidicon was the first successful television camera tube to use a photoconductive surface to derive a video signal.

Solid state imaging devices were first demonstrated in the 1960s. Today's solid-state television cameras use semiconductor charge-coupled devices or CCDs. Each element in a CCD stores a charge that is determined by the illumination incident on it. At the end of the exposure interval, the charge is transferred to a storage register and the CCD is freed up for the next exposure. The charges in the storage register are transferred to the output stage serially during that time. Although almost all consumer video cameras and camcorders use CCD imagers, camera tubes are still common in professional applications.

In the television receiver, the original image is reconstructed essentially by reversing the operation of the video camera. The final image is typically displayed on the face of a cathode-ray tube , where an electron beam scans the fluorescent face, called the "screen," line for line with the pickup scanning. The fluorescent deposit on the tube's inside face glows when hit by the electrons, and the visual image is reproduced. Liquid crystal displays have also been used, mainly on small, portable sets; they are also finding increasing use as light valves on large-screen projectors. Although LCD technology is advancing rapidly, video projectors that use electron tubes can still produce better pictures. Other devices in the receiver extract the crucial synchronization information from the signal and demodulate (separate the information signal from the carrier wave) it.

Development of Color Television

Several systems of color television have been developed. In the first color system approved by the Federal Communications Commission (FCC), a motor-driven disk with segments in three primary colors—red, blue, and green—rotated behind the camera lens, filtering the light from the subject so that the colors could pass through in succession. The receiving unit of this system formed monochrome (black-and-white) images through the usual cathode-ray tube, but a color wheel, identical with that affixed to the camera and synchronized with it, transformed the images back to their original appearance. This method is said to be "field-sequential" because the monochrome image is "painted" first in one color, then another, and finally in the third, in rapid enough succession so that the individual colors are blended by the retentive capacities of the eye, giving the viewer the impression of a full colored image. This system, developed by the Columbia Broadcasting System (CBS), was established in 1950 as standard for the United States by the FCC. However, it was not "compatible," i.e., from the same signal a good picture could not be obtained on standard black-and-white sets, so it found scant public acceptance.

Another system, a simultaneous compatible system, was developed by the Radio Corporation of America (RCA). In 1953 the FCC reversed its 1950 ruling and revised the standards for acceptable color television systems. The RCA system met the new standards (the CBS system did not) and was well received by the public. This system is based on an "element-sequential" system. Light from the subject is broken up into its three color components, which are simultaneously scanned by three pickups. However, the signals corresponding to the red, green, and blue portions of the scanned elements are combined electronically so that the required 4.1-MHz bandwidth can be used. In the receiver the three color signals are separated for display. The elements, or dots, on the picture tube screen are each subdivided into areas of red, green, and blue phosphor. Beams from three electron guns, modulated by the three color signals, scan the elements together in such a way that the beam from the gun using a given color signal strikes the phosphor of the same color. Provision is made electronically for forming proper gray tones in black-and-white receivers. The FCC allowed stereo audio for television in 1984.

Broadcast, Cable, and Satellite Television Transmission

Television programs may be transmitted either "live" or from a recording. The principle means of recording television programs for future use is videotape recording. Videotape recording is similar to conventional tape recording (see tape recorder ) except that, because of the wide frequency range—4.2 megahertz (MHz)—occupied by a video signal, the effective speed at which the tape passes the head is kept very high. The sound is recorded along with the video signal on the same tape.

When a television program is broadcast, the varying electrical signals are then amplified and used to modulate a carrier wave (see modulation ); the modulated carrier is usually fed to an antenna, where it is converted to electromagnetic waves and broadcast over a large region. The waves are sensed by antennas connected to television receivers. The range of waves suitable for radio and television transmission is divided into channels, which are assigned to broadcast companies or services. In the United States the Federal Communications Commission (FCC) has assigned 12 television channels between 54 and 216 MHz in the very-high-frequency (VHF) range and 56 channels between 470 and 806 MHz in the ultra-high-frequency (UHF) range (see radio frequency ).

Most television viewers in the United States no longer receive signals by using antennas; instead, they receive programming via cable television. Cable delivery of television started as a way to improve reception. A single, well-placed community antenna received the broadcast signals and distributed them over coaxial or fiber-optic cables to areas that otherwise would not be able to receive them. Today, cable television is popular because of the wide variety of programming it can deliver. Many systems now provide more than 100 channels of programming. Typically, a cable television company receives signals relayed from a communications satellite and sends those signals to its subscribers. The first transatlantic television broadcast was accomplished by such a satellite, called Telstar, on July 10, 1962. Some television viewers use small satellite dishes to receive signals directly from satellites. Most satellite-delivered signals are scrambled and require a special decoder to receive them clearly.

See also broadcasting .

Television Technology Innovations

The next great advance in television will be the adoption of a high-definition television (HDTV) system. Non-experimental analog HDTV broadcasting began in Japan in 1991. In 1994 the FCC approved a U.S. standard for an all-digital system, to be used by all commercial broadcast stations by mid-2002. Although it was hoped that the transition to digital broadcasting would be largely completed by 2006, less than a third of all stations had begun transmitting digital signals by the mid-2002 deadline.

The most noticeable difference between the current system and the HDTV system is the aspect ratio of the picture. While the ratio of the width of a current TV picture to its height is 4:3, the HDTV system has a ratio of 16:9, about the same as the screen used in a typical motion-picture theater. HDTV also provides higher picture resolution and high quality audio. Each frame of video consists of 720 or 1,125 horizontally scanned lines instead of the current 525. Furthermore, the lines are scanned sequentially, not interlaced as they are now.

The wide availability of television has raised concerns about the amount of time children spend watching TV, as well as the increasingly violent and graphic sexual content of TV programming. Starting in 1999 the FCC required TV set manufacturers to install "V-Chip" technology that allows parents to block the viewing of specific programs; that same year the television industry adopted a voluntary ratings system to indicate the content of each program.

Various interactive television systems have been tested or proposed. An interactive system could be used for instant public-opinion polls or for home shopping. Many cable television systems use an interactive system for instant ordering of "pay-per-view" programming. Others systems poll their subscribers' equipment to compile information on program preferences. Several competing commercial systems have connected televisions to the Internet .

Bibliography

See D. G. Fink and D. M. Lutyens, The Physics of Television (1960); M. S. Kiver, Television Simplified (7th ed. 1973); R. Armes, On Video (1988); K. B. Benson and J. C. Whitaker, Television and Audio Handbook (1990); K. B. Benson, Television Engineering Handbook (1992); D. E. Fisher and M. J. Fisher, Tube (1996).

Television. Experiments in the radio transmission of visual images had been conducted for several decades before manufacturers offered the first television receivers for sale in 1939. Consumer indifference and World War II, however, kept demand slight until 1948 when, soon after the beginning of regular network telecasts, TV sales took off. In 1949, 2.3 percent of homes had televisions; by 1962, 90 percent did. Despite the relatively high costs of the first sets, Americans purchased televisions regardless of income. And television quickly emerged as the most popular mass medium, with more Americans spending more time watching TV than consuming any other mass medium. Television's initial popularity owed much to its convenience. For the post–World War II family, television, compared to moviegoing, was cost‐efficient entertainment; parents and children could be entertained at home, without traveling to a theater or buying tickets.

The 1950s: Rise of the Networks.

Most TV stations—over 90 percent in the 1950s and early 1960s—signed exclusive “affiliation” agreements with networks. In exchange for compensation, an affiliate agreed to carry network programming at specified hours (usually in the evening). As a result, the networks determined evening viewing, when most Americans watched television.

Two networks, Columbia Broadcasting System (CBS) and the National Broadcasting Company (NBC), initially dominated. Their large lead in radio gave them clear advantages, including show‐business expertise and goodwill with their radio affiliates, many of which acquired TV licenses. Then, too, the number of TV channels was limited to twelve on the very high frequency (VHF) transmitting band. The Federal Communications Commission (FCC) encouraged rival commercial and noncommercial networks by awarding channels 14 through 81 in the ultra high frequency (UHF) beginning in 1952. In most markets, however, UHF could not compete with VHF outlets. By early 1956, 60 of 159 UHF channels had left the air. UHF's stark disadvantages seriously undercut educational television as well as the third commercial network, the American Broadcasting Company (ABC), which disproportionately relied on UHF channels for affiliates.

Advertisers played a powerful role in early programming. With some advertisers holding back from entering television, the position of those who did was strengthened. Typically sponsoring entire programs, they often insisted on changes in individual productions. In one instance a tobacco company ordered that the Russian villains in a Cold War drama not be shown smoking cigarettes. Commercials were frequently integrated into shows. In the middle of a program, the leads would suddenly praise (or be shown using) the sponsor's product. Yet some of TV's earliest underwriters championed more diverse programming by sponsoring dramatic and news series targeting smaller, more educated audiences. As viewership increasing and advertising rates rose in the late 1950s and early 1960s, however, advertisers abandoned sole sponsorships, preferring instead to spread their investment, and the networks asserted near total control over programming and scheduling.

The earliest programming appealed to a wide range of tastes. Because the first stations were established in the largest cities, popular shows tended to reflect a big‐city sensibility. This included comedy variety hours, notably one starring Milton Berle, as well as original dramas. Nearly all were aired live. As television reached smaller communities in the South and West, however, the appeal of such shows faded. Viewers preferred filmed series with a regular cast of characters who were uniformly white, usually middle class, and living in smaller cities or towns. The dominant characters were almost always male.

The 1960s and 1970s: New Technologies and New Challenges.

By the late 1950s, network programming had been standardized. Most series were produced in Southern California in assembly‐line fashion, by the old film studios or companies utilizing studio facilities and talent. Reruns of popular series, “syndicated” to TV stations across the countries for fees, and later to cable channels, proved popular and immensely profitable.

The development of videotape in the late 1950s profoundly affected the industry. Until then, the networks had to telecast programs live, across four continental time zones, meaning that a dramatic program aired at 9 PM eastern time was telecast at 6 PM on the West Coast. (Affiliates could carry poor quality “kinescope” recordings, in which motion‐picture cameras photographed the images on television picture tubes.) At first, the networks used videotaping largely for time‐shifting, to telecast programs later in the Mountain and Pacific time zones. Over time, however, most productions were taped to correct any flaws in a telecast and at the insistence of performers, most of whom preferred not to appear live. Videotape's greatest impact may have been on TV news. Film was expensive and could take hours to develop and edit. Videotape, by comparison, provided quick and cost‐efficient TV reporting.

By the late 1960s, television technology changed in another important way. Since the 1950s, the Radio Corporation of America (RCA) and other TV manufacturers had been promoting color television. But consumers were put off by the comparatively high cost. As late as 1965, less than 6 percent of all homes had color receivers. As prices fell, however, more families purchased color TVs, and by 1972 just over half of all households owned them.

News programs appeared on TV from the beginning, but they had almost always lost money, and the networks offered them mainly to placate federal overseers. Resources normally went into fifteen‐minute newscasts in the early and late evenings. Gradually, though, TV news gained respect and larger audiences. In 1963, CBS and NBC expanded their nightly newscasts to thirty minutes; ABC followed in 1967. In November 1963, the networks canceled all entertainment programming for four days to cover the assassination and funeral of President John F. Kennedy. By then most critics agreed that TV news had demonstrated its potential and maturity, and surveys suggested that, for the first time, Americans ranked TV as their main source of information. More important to the networks, advertising on the evening newscasts had become a vital revenue source. Debates between the major party presidential candidates, introduced in 1960, became a quadrennial ritual beginning in 1976.

The Vietnam War constituted the networks' greatest journalistic challenge in the 1960s. Contrary to a common misperception, TV coverage up to 1968 was, with very few exceptions, supportive of America's intervention and dismissive of the budding antiwar movement. Fearful of upsetting viewers, the networks rarely showed actual combat or bloodshed. To cut costs, the networks did not use satellites to transmit signals to New York, electing instead to fly film, which could take several days. Although the respected CBS news anchor Walter Cronkite (1916– ), who declared the war a stalemate early in 1968, has been credited with helping to end U.S. escalation, most studies suggest that President Lyndon B. Johnson and his advisers were already war weary. Nevertheless, the networks and some writers popularized myths that TV made Vietnam “the living‐room war” and that Cronkite forced peace on the government. More likely, the more critical coverage beginning in 1968 prevented Johnson's successor, Richard M. Nixon, from seriously escalating the fighting.

All told, the influence of network news ought not be overstated. The nightly newscasts never had audiences comparable to the entertainment shows that followed, and local newscasts normally had larger followings. Indeed, local stations in the 1960s had begun pouring resources into their newscasts, which proved their most profitable programming. In time, the drive for profits diluted most local stations' news agenda. Light features and sensational crimes were highlighted to boost ratings.

The 1960s similarly marked the marriage of sports and television. TV had carried certain sporting events, notably wrestling and boxing, from the beginning. But in the 1960s, more mobile cameras afforded viewers better angles, while instant replays of controversial calls by referees gave viewers twenty‐twenty hindsight. Although every sports league coveted television, none matched the National Football League in making its game a television ritual. ABC's Wide World of Sports, meanwhile, introduced Americans to a broad array of sporting events year round. ABC also pioneered in turning the Olympic Games into television spectacles.

Although economics normally shaped television broadcast fare, the FCC in the 1960s took modest steps to change the industry, promoting increased competition by improving UHF reception and fostering noncommercial, educational television stations (ETV), many of which were on the upper frequency. Empowered by Congress to set standards for TV receivers, the commission ruled that all TVs sold after 1 April 1964 must be able to receive both UHF and VHF signals. Over time, this greatly expanded the total audience for the upper‐frequency channels. In 1967, with the Public Broadcasting Act, Congress created the Public Broadcasting System (PBS), which displaced the old ETV network. Although chronically underfunded, PBS provided alternatives in cultural and news programming that the commercial networks had largely abandoned.

In the 1960s and 1970s, most Americans most of the time watched network programming, and network TV became more diverse. African Americans began appearing and even starring in some programs. In series like The Mary Tyler Moore Show and Charlie's Angels, women played prominent roles. The main character in the most popular sitcom of the 1970s, All in the Family, was a working‐class bigot.

Ever eager to fill their schedules, the networks in the late 1960s began producing made‐for‐TV movies. This partly reflected the growing sexual explicitness of theatrical releases as well as Hollywood's over‐attention to younger moviegoers. Although most made‐for‐TV movies were forgettable, some had enormous impact. ABC's Roots (1977), a panoramic history of an African American family, based on a book by Alex Haley, helped to move the network for the first time into first‐place in ratings and revenues. More often, TV movies consciously appealed to women viewers, who had gained more control over viewing, particularly in homes having second TVs.

The 1970s also brought important shifts in television news. Despite pressure from the Nixon administration, CBS aggressively reported on the Watergate scandals; NBC and ABC belatedly did so as well. CBS News also scored a ratings coup in the late 1970s and 1980s with its top‐rated 60 Minutes, an hour‐long collection of features and interviews dubbed a TV news magazine.” For the first time, a news program successfully competed for audiences in evening prime time. Only after many misfires did imitations by ABC and NBC enjoy comparable success with the news magazine, which was much less expensive to produce than the typical hour‐long entertainment series. Meanwhile, early morning news programs—NBC's Today and ABC's Good Morning, America —became immensely profitable.

The 1980s and Beyond: Fragmentation of Audience, Consolidation of Ownership.

Still, the three‐network hold over television came undone in the 1980s. Non‐network or independent channels, often airing reruns of network shows, became serious competitors in many larger markets. Between 1979 and 1987, the proportion of stations affiliated with a network dropped from 86 to 61 percent. The Fox network, founded in 1986, lured younger viewers and advertisers. Two more networks, WB and UPN, commenced operations in the early 1990s.

The spread of cable television further undermined the networks. First introduced in the 1950s to improve reception for viewers in mountainous areas, cable burgeoned in the late 1970s and 1980s as Americans started subscribing to increase their programming choices. In many areas, subscribing to cable meant access to as many as thirty‐two channels. By the mid‐1990s, just over 60 percent of all homes had cable. Channels specializing in sports, the arts, religion, and other special‐interest areas added to cable's allure, as did the programming on “superstations” like Atlanta's WTBS and Chicago's WGN. With so many choices, the networks' viewership fell. Between the 1976–1977 and 1996–1997 TV seasons, the combined network share of evening prime time had dropped by a third, from 93 percent of the audience to 62 percent.

The proliferation of cable prompted a number of responses from the networks. To hold viewers, they tolerated increased sexual explicitness and violence. Spurred by Fox's appeal to younger viewers, they paid more attention to the demographic composition of audiences. Series popular with older viewers were frequently dumped in favor of sitcoms targeting younger adults.

Meanwhile, the networks and many stations underwent changes in ownership. Stations owned by individuals all but vanished in favor of group ownership. This trend was hurried along by the relaxation of long‐time FCC rules on multiple ownership. In 1985–1986, new proprietors acquired all three networks. A station group, Capital Cities, purchased ABC; General Electric purchased NBC's parent company, RCA; and Laurence Tisch assumed controlling interest in CBS. Two of the networks were purchased again in 1995, when Westinghouse secured CBS and Disney bought ABC. Four years later, Viacom bought CBS.

Despite such concentration in ownership, the larger development at the end of the twentieth century was the fragmentation of the once gargantuan television audience. Although a few programs, notably the annual NFL Super Bowl and ABC's Who Wants to be a Millionaire? had high ratings, the audiences for most TV series dwindled drastically. The new world of choices, combined with greater internet use, was fragmenting society and, by distracting citizens from informational programming, weakening civic bonds.
See also Advertising; Consumerism; Fifties, The; Foreign Relations: The Cultural Dimension; Internet and World Wide Web; Journalism; Mass Marketing; Multinational Enterprises; Murrow, Edward R.; Popular Culture; Public Broadcasting; Sarnoff, David; Satellite Communication; Sixties, The; Televangelism.

Bibliography

Daniel Hallin , The “Uncensored War”: The Media and Vietnam, 1986.
Christopher H. Sterling and and John Kittross , Stay Tuned: A Concise History of American Broadcasting, 2d ed., 1990.
James L. Baughman , Republic of Mass Culture: Journalism, Filmmaking and Broadcasting in America since 1941, 2d ed., 1997.

James L. Baughman