Television

Since the 1940s television has become the window on the world for much of industrialized society. Anything the eye can see may be brought to television screens. What comes through the window, however, does not always please everyone. Newton Minow, Federal Communications Commission chairman under United States President John F. Kennedy, called television “a vast wasteland” because of what he considered the dismal quality of its programming. But if television has persisted in offering mindless entertainment, it has also frequently rewarded viewers with outstanding presentations in drama, documentary, and the arts.

Programming

In the late 1940s television began to make its presence felt, though the medium had existed for some years. World War II had temporarily halted its development, but once the war was over television sets were put on the market. The first mass television audience watched the broadcast of baseball's World Series in 1947. This event prompted people to go out to buy sets. And the selling of sets, in turn, prompted the networks to expand their programming.

There were originally four United States networks: the National Broadcasting Company (NBC), the Columbia Broadcasting System (CBS), the American Broadcasting Company (ABC), and the DuMont network. DuMont eventually failed. The remaining three networks have been supplemented by the Fox Broadcasting Company, Time Warner Inc.'s The WB, and United Paramount Network (UPN), as well as scores of cable stations. In addition, satellite transmissions of programs have increased. The stations of the Public Broadcasting Service (PBS) present generally noncommercial programming of a high quality.

The era of television as a modern entertainment form was launched on June 8, 1948, when Milton Berle's Texaco Star Theater arrived on the screen. This weekly comedy-variety show was soon followed by Your Show of Shows, which starred Sid Caesar and Imogene Coca. These shows attracted millions of viewers and made money for their sponsors, stations, and networks. The early years of television were a period of trial and error, of diversification, and of learning what the mass audience wanted.

Types of Shows

From the earliest days of mass broadcasting through the present time, audiences have wanted diversity in programming, and the networks have consistently complied. Some of the kinds of shows that proved popular over the years included the following:

Family situation comedies

These weekly series included The Honeymooners, I Love Lucy, The Adventures of Ozzie and Harriet, Father Knows Best, Maude, Family Ties, The Cosby Show, Frasier, 3rd Rock from the Sun, and Malcolm in the Middle. The earliest shows generally featured happy families and relatively safe, mainstream plots. However, with the first appearance of All in the Family on Jan. 21, 1971, television comedy underwent a permanent transformation to adult humor based on controversial subjects that had been previously banned.

Non–family situation comedies

Some of these programs had continuing stories; others did not. The best-known shows in this category included The Phil Silvers Show, Our Miss Brooks, Hogan's Heroes, The Mary Tyler Moore Show, Taxi, Cheers, Seinfeld, Friends, and Spin City.

Comedy-variety shows

Among these programs were some that made the successful transition from radio, with well-known performers such as Bob Hope, Eddie Cantor, Groucho Marx, George Burns and Gracie Allen, Red Skelton, and Jack Benny. The hosts of other comedy-variety shows were sometimes less well known to radio audiences, as in The Jackie Gleason Show, The Garry Moore Show, and Art Linkletter's People Are Funny. Several short-lived shows in the 1950s featured the innovative humor of Ernie Kovacs. Rowan and Martin's Laugh-In (1967–73) had much the same trendsetting impact on comedy-variety that All in the Family had on family comedies. Saturday Night Live, SCTV, and MADtv presented late-night sketch comedy, as did the popular British show Monty Python's Flying Circus.

Variety shows

These shows often included a good deal of comedy, as in the case of Arthur Godfrey's Talent Scouts, but they were often primarily showcases for performers of all kinds. One of the best of these programs was The Ed Sullivan Show, earlier called The Toast of the Town (1948–71). A later variety show was Hollywood Palace (1964–70).

Westerns

One of the first TV westerns was a direct carryover from radio. The Lone Ranger, which premiered on television in 1949, had already enjoyed a long run on radio, where broadcasts had begun in 1933. The radio series continued to broadcast until 1954, three years before the television version of the series would go off the air.

The longest-running Western in television history, however, was Gunsmoke. It came on the air on Sept. 10, 1955, and lasted until Sept. 1, 1975, after which it reappeared in reruns. Many other cowboy dramas followed its debut, including Have Gun, Will Travel; Rawhide; Maverick; Bonanza; and The Rifleman.

Police shows

Dragnet (1952–70) was the first major police show. Other notable ones were Naked City, The Untouchables, Hawaii Five-O, Starsky and Hutch, CHiPS, Police Story, Police Woman, Columbo, Kojak, Baretta, Cagney and Lacey, Hill Street Blues, Crime Story, Miami Vice, and NYPD Blue. Law & Order combined police and courtroom drama genres.

Detective programs

These “private eye” and mystery programs follow the exploits of one or two crime fighters not connected with a police force. One of the earliest was Martin Kane, Private Eye, which started in 1949. Magnum, P.I., was a later favorite. Murder, She Wrote, was an example of the amateur sleuth at work. PBS channels have regularly shown British whodunits on the series Mystery.

Adventure shows

This category encompasses action programming that does not easily fit into either the police or private eye format. One of the best early shows was The Wild, Wild West, which had the appearance of a Western but was otherwise nothing like the traditional cowboy drama. Other programs in this category included The A-Team, Knight Rider, and Walker, Texas Ranger.

Suspense programs

Similar to mystery shows, but often emphasizing horror, were the anthology series such as Boris Karloff's Thriller, Rod Serling's Twilight Zone, Alfred Hitchcock Presents, and The Outer Limits. In The X-Files, two FBI agents confront government conspiracy, extraterrestrials, and paranormal activity.

Lawyer shows

This category has two main types—those in which mysteries are solved and those that attempt to portray the workings of the court system. Among the former, Perry Mason was the most popular. Courtroom drama was highlighted on The Defenders, L.A. Law, and The Practice.

Spy programs

These shows, though involving a good deal of adventure and some mystery, focus on international intrigue, espionage, and sabotage of the James Bond type. One of the early and popular ones was I Led Three Lives. The Man from U.N.C.L.E. used much sophisticated weaponry and ingenious plotting, as did Mission: Impossible.

Soap operas

This type of program is an ongoing series of dramas with complex plots. Soaps were first popular on radio and daytime television, but on April 2, 1978, CBS introduced the first weekly prime-time soap, Dallas. It was soon followed by Knots Landing, a Dallas spin-off; Dynasty; Falcon Crest; and Melrose Place. Among the long-running daytime shows were As the World Turns, All My Children, The Guiding Light, Days of Our Lives, One Life to Live, The Edge of Night, General Hospital, The Bold and the Beautiful, and Port Charles.

Hospital shows

One of the earliest was The Doctor, but the most famous was Dr. Kildare, and the popularity of this program inspired others, including Marcus Welby, M.D., Ben Casey, St. Elsewhere, Chicago Hope, and E.R.

One of the best-received television shows in history almost falls into this category: M*A*S*H ran from 1972 until 1983. It combined a Korean War army hospital setting with drama, comedy, pathos, and a good deal of antiwar sentiment.

Dramatic productions

These were weekly series with the same casts, normally programs of social relevance, using different settings to get their messages across. Lou Grant was about a newspaper editor, while Quincy, M.E., featured a medical examiner who used forensic medicine to solve crimes. Set in the White House, The West Wing centered on the administration of a fictional president of the United States.

Some weekly programs, such as The Fugitive, incorporated elements of suspense and mystery, and over the years gained a cult status. The Avengers, The Saint, and The Prisoner were British shows in this category that were broadcast in the United States and gained a large audience there.

Besides the continuing dramatic series, there have been since the earliest years of television a number of shows that brought viewers essentially theatrical productions on a regular or intermittent basis. They included Actors Studio, Playhouse 90, Kraft Television Theatre, Great Performances, Hallmark Hall of Fame, and the British series Masterpiece Theatre.

Quiz and game shows

Programs in which contestants compete for prizes have been consistently popular, especially during daytime viewing hours. Shows such as Jeopardy offered money prizes, while Let's Make a Deal, The Price Is Right, and Wheel of Fortune gave products—such as cars, appliances, and furniture—or trips. The prime-time blockbuster Who Wants to Be a Millionaire premiered in the United States on Aug. 16, 1999, and revitalized the genre.

Talk shows

The style for talk shows was set by NBC's Today, which was introduced on Jan. 14, 1952. The first host was Dave Garroway, formerly of the variety show Garroway at Large (1949–51). ABC's Good Morning, America, another early-morning show, succeeded A.M. America in 1975. Popular daytime talk shows were hosted by Merv Griffin, Phil Donahue, Oprah Winfrey, Geraldo Rivera, and Jerry Springer.

The first late-night entertainment show was Broadway Open House with Jerry Lester (1950–51). Elements of this show and of Today were combined in NBC's durable Tonight Show, beginning on Sept. 27, 1954. For more than two years Steve Allen was the host of the variety program. In July 1957 Jack Paar became host and began using more celebrity guests. He retired from the program in 1962, and, after a succession of temporary hosts, Johnny Carson was chosen to replace him. His first appearance on Tonight was on Oct. 2, 1962. Jay Leno succeeded Carson in May 1992. Other talk shows were hosted by Dick Cavett, David Frost, Mike Douglas, David Letterman, and Conan O'Brien.

“Reality” television

Following the lead of MTV's Real World, programs that featured nonactors in dramatic, supposedly unscripted situations proved very popular. Survivor, which premiered in the summer of 2000, sent 16 voluntary castaways to a secluded island to compete for 1 million dollars. The show won enormous ratings and spawned sequels and several imitators.

Sports events

In the United States the greatest number of viewers watch professional sports games, which include mostly football, baseball, basketball, and hockey events. On a worldwide basis, however, soccer (association football) has probably the largest audiences. In the United States, play-offs and championship games draw the most viewers, with the World Series and the Super Bowl being the greatest attractions.

Events such as tennis matches, golf tournaments, professional bowling, horse races, auto races, and professional wrestling also attract viewers. The Olympics are telecast every two years (with the Summer and Winter Games alternating), and there are similar competitions presented annually in such events as ice skating, skiing, and track and field on weekly programs such as Wide World of Sports. Local telecasts of high school events are shown in many states, and college events are broadcast both locally and nationally.

Newscasts

Local channels and national networks telecast news every day. Television proved a real advantage in bringing almost instant coverage of events from around the world. Among the stirring events it brought into homes were the hearings in which Senator Joseph R. McCarthy investigated the Army in 1954; the Vietnam War; the assassination and funeral of President Kennedy in 1963; the moon landing in 1969; the Congressional hearings on the Watergate affair in 1973–74; the takeover of the United States Embassy in Iran in 1979; the explosion of the space shuttle Challenger in 1986; live reports from the Persian Gulf War in 1991; and Floridians hand counting ballots after the United States presidential election in 2000.

Special programs and documentaries included 60 Minutes, See It Now, Meet the Press, and Face the Nation. Several television journalists set early standards for excellence in their programs, which the networks tried to maintain. Among them were Edward R. Murrow, Walter Cronkite, Chet Huntley, David Brinkley, and Lawrence Spivak.

Children's programs

Apart from the Saturday morning cartoon festivals, there were many nationally telecast shows that were both entertaining and educational. Among them were Captain Kangaroo, Mickey Mouse Club, Bozo, Howdy Doody, The Shari Lewis Show, Sesame Street, The Muppets, Barney & Friends, and Teletubbies.

Religious broadcasting

Nationally known religious figures such as Bishop Fulton J. Sheen, Billy Graham, and Norman Vincent Peale appeared regularly on television. There were also nationally telecast series such as Life Is Worth Living, Crossroads, and Lamp unto My Feet. Local stations brought their viewers weekly programs and special events. There was a religious network that broadcast programs daily on UHF channels.

Educational television

In the early years of television, educational shows were limited to early-morning broadcasting. In all major cities there are now educational channels that offer regular college or high school courses and other informational shows. PBS has how-to shows, such as Julia Child's and the Frugal Gourmet's cooking instruction, and the home-renovation show This Old House.

Motion pictures

Network and local television regularly feature movies that have run in the theaters and have since been sold for television viewing. There are also made-for-television films, including miniseries, or a program that takes two or more evenings to telecast. Shogun, based on the best-selling novel by James Clavell, was considered one of the best; however, the broadcast of Roots, based on Alex Haley's Pulitzer Prize-winning biography of his family's history, remains perhaps the most notable miniseries in television history. During its initial broadcast in 1977, the miniseries—broadcast over eight evenings—garnered the largest viewing audience ever, with 130 million viewers tuning in.

Others

Many programs do not fit easily into these categories—for example, Marlin Perkins' Wild Kingdom, the Jacques Cousteau specials, The Simpsons, Star Trek and its spin-offs, America's Most Wanted, Antiques Roadshow, and American Experience. There were also spectaculars, such as single telecasts of famous performers such as Maurice Chevalier, Fred Astaire, Judy Garland, Ethel Merman, and Barbra Streisand. There are numerous telecasts of musical or theatrical events not associated with a regular series. In addition, there are once-a-year programs such as various awards shows, Macy's Thanksgiving Day Parade, the Orange Bowl Parade, and the Tournament of Roses.

“After This Brief Message”

In the United States especially, television is a commercial enterprise. This means it must make money to pay for all aspects of programming. To do this, television networks and stations sell time to companies who want to advertise their products. The advertisements are called commercials. In the early years of television, the sponsors bought the programs and were able to dictate policy. By 1960, however, the networks and stations had taken control of their programming, and they simply sold advertising time to the sponsors.

The cost of television programming, particularly in prime time (evenings from 8 to 11 PM Eastern Standard Time), is very large. Making an hour-long episode of a drama program, for example, often costs more than 1 million dollars. Conversely, programs that air during daytime hours are much less expensive. The cost of a commercial spot varies greatly, and advertising time during a program that commands many viewers is generally more expensive. At the start of the 21st century, a 30-second time slot during a special event such as the Super Bowl cost more than 2 million dollars.

The Name of the Game Is Ratings

How long commercially sponsored programs stay on the air is a matter of their popularity. No sponsor wants to pay for advertising time if large audiences are not watching to see the commercials. To survive on the air a show must command a 30 percent audience share with reasonable consistency.

The leading ratings organizations in the United States are Nielsen Media Research and Arbitron. The most widely accepted ratings have been those conducted by Nielsen. AGB Television Research also provided ratings data during the 1980s.

Nielsen collects and publishes two sets of statistics: one for network broadcasting and the other for local broadcasts. To collect data, Nielsen had used an Audimeter attached to television sets in 1,200 households. The device registered how long a set was turned on and to which channel it was tuned. Additional data, called the National Audience Composition, was gathered from 2,000 households that kept a log of their viewing habits. The purpose of the ratings method was to give an accurate picture of the share of households that watched specific programs.

In 1987 Nielsen and AGB Television Research each initiated the use of “people meters,” supposedly a more accurate device for registering viewing habits. Each member of a selected household is required to punch an assigned personal viewing button on a box attached to the television or on a remote-control device, which then feeds the viewing information to a central computer. The information indicates the number of viewers and associates detailed data collected on the viewers—such as age, sex, income level, and ethnic background. These data are highly valued by advertisers.

Arbitron traditionally used telephone and personal interviews to gather data. The company subsequently began using people meters as well.

History of Telecasting

Through a series of technical developments in Great Britain, Europe, the Soviet Union, and the United States, television reached a state of technical feasibility by 1931. The first notable outside broadcast by the British Broadcasting Corporation (BBC) was the procession of the coronation of King George VI from Hyde Park Corner in November 1937. A portable transmitter mounted on a special vehicle was used. Several thousand viewers saw the transmission.

Television developments were slower in the United States. It was not until April 30, 1939, at the opening of the New York World's Fair, that a public demonstration was made by the National Broadcasting Company. The Columbia Broadcasting System and the DuMont network began telecasting in 1939 and 1940, respectively, and by mid-1940 there were 23 television stations in the United States.

World War II brought nearly all television activity to an end, but the trend resurged after the war. By 1949 there were 1 million receivers in use; the 10-million mark was passed in 1951 and the 50-million mark eight years later. In England, BBC television service was resumed in June 1946; by 1949 there were 126,567 television licenses, and by 1950 there were 343,882, equal in proportion to 1 million in the United States. Other nations did not begin television broadcasting on anything resembling a wide scale until the 1950s.

Technology

Any television signal starts with the transformation of an image into an electronic code by a television camera. The conventional television camera uses a device called an image orthicon tube. A lens focuses the image on a transparent plate inside the tube. The inner surface of the plate has a metallic coating. When it is struck by light, this coating gives up electrons. Each point or element on the coating thus acts somewhat like the rods and cones in the retina of the eye. The number of electrons given up depends upon the strength of the light hitting the element.

These released electrons are drawn to a thin glass target plate by the force of the anode, which bears a positive charge. The target plate is at first neutral; but, as electrons strike the near side, they knock off other electrons by a process called secondary emission. A fine-mesh screen draws off these displaced electrons, leaving a positive charge on the target plate. The glass is thin enough for the positive charge to exert force through the plate. The positive-charge pattern is an electrostatic equivalent of the image. A strongly charged point is a bright spot on the image; a weak charge is a spot of shadow.

A scanning beam of electrons starts from a negatively charged cathode, called an electron gun, at the base of the tube. The beam is just strong enough to come near the target plate before a positive charge on the electron multiplier turns it and draws it back as a return beam. At the turn, however, enough electrons fly off to neutralize each positive charge. The scanning beam moves from left to right down the plate, depositing electrons at each positive charge. The leftover electrons then return along the beam. The ever-changing number of electrons amounts to varying pulses of negative charge in the beam.

Systems

For the viewer, scanning is the most crucial element of picture transmission. The total number of lines in the scanning pattern of the system chosen is the variable that determines how sharp and how detailed the television image appears.

The television system that has been used in the Western Hemisphere (and adopted by Japan) is known as NTSC, for the National Television Systems Committee that developed it as a compatible method of color-picture transmission that would not make existing black-and-white sets obsolete. Public broadcasting of NTSC began in the United States in 1954. Modifications in NTSC produced the PAL (phase alternation line) color system, which was chosen by Great Britain and West Germany in 1967. Also that year the higher-definition SECAM (système électronique couleur avec mémoire) was introduced in France and the Soviet Union.

In all these systems, the scanning pattern is a series of parallel straight lines that progress from left to right in sequence from the top to the bottom of the picture frame. The target plate has an uneven number of lines of positive-charge elements. Guided by deflection coils, the scanning beam neutralizes the even-numbered lines on its first trip down the plate, the odd-numbered on its second. Each set of lines is called a field; the two together are called a frame. The number of pictures transmitted per second (25 or 30) is governed by the prevailing electric-power frequency (50- or 60-hertz power).

The NTSC color system uses 525 vertical scanning lines to produce about 130,000 picture elements of maximum detail per frame. PAL operates at 625 lines for 210,000 picture elements per frame. SECAM has up to 819 scanning lines, with 440,000 picture elements.

Unlike the NTSC, PAL, and SECAM analog systems, whose signals use a continuously variable element to represent the program information, DTV (digital television) delivers the information as bits of binary data, as does a computer (see computer). With DTV, broadcasters can transmit more information. They can use the extra capacity to telecast as many as six standard-definition programs simultaneously; or to broadcast one program with superior image resolution and sound quality; or they can use a mixture of the two approaches. HDTV (high-definition television) is a type of DTV that transmits a signal of more than 1,000 scanning lines to achieve a very sharp picture.

Cameras

In color television cameras, light is collected by the lens and focused on a series of mirrors. In the center are two dichroic mirrors, which are made of special optical glass that reflects one color but transmits other colors. The first mirror reflects red light but lets blue and green pass through. The second mirror reflects blue but lets green pass. Three images, one in each primary color, are created. The images are focused on the faces of camera tubes by reflecting mirrors and a lens system. Color filters assure that the color quality of each primary has the exact value for the system. An electron beam in each camera tube scans the image pattern that has been formed on the tube screen, and a primary-color signal is produced. The three primary-color signals are then processed for transmission or recording.

Instead of the orthicon tube, some television cameras use a solid-state device called a CCD (charge-coupled device), which is more rugged and lighter. When light strikes the top layer of a CCD element, which is part of a square array of many such elements, electrons are emitted. These electrons are trapped in a positively charged lower layer. After the image is exposed, electric impulses move the bunches of electrons stored at each element one by one to a collector at the end of each line of elements.

Video recording

Once the signal has left the camera, generally the next step is to record it on tape. Live television, in which the signal is broadcast directly at the time it is being recorded, was originally the only kind of program broadcast. With the development of videotape in the 1960s, however, live broadcasts became increasingly rare.

Videotape recording eliminates some problems of live broadcasting, where mistakes cannot be edited or reshot. High-quality images from distant points can be recorded without delays from processing, as conventional film requires. With the development of satellite communications, news events taped around the world can be transmitted to central stations for later use.

The use of videotape has also expanded the reach of television for deaf viewers through CC (closed-captioned) broadcasts, in which dialogue becomes visible on a margin of the screen of a television receiver that is equipped with a decoder. With letterboxing, contrasting dark bands are added at the top and bottom of the screened image so that a commercial film can be shown in its full range, without segments cropped from the sides. Most videodiscs now feature the process, and the letterbox is also used to make subtitles more visible.

After a more compact form of videotape recorder—called the VCR (videocassette recorder)—was developed, television programs could be distributed on videocassettes without having been broadcast at all. The distribution of commercial motion pictures on videotape for private home viewing developed in the early 1980s. Later, commercial television broadcasts were also sold in videocassette form. In addition, VCRs allowed viewers to record programs from their television receivers in order to watch them at a later time or to keep them in a permanent tape file for repeated viewing.

A DVD (digital videodisc or digital versatile disc) can store more data than a videotape can and provides a higher-resolution picture and better audio quality. VCRs typically yield a picture with about 240 lines of horizontal resolution, compared to about 500 lines for DVD players. DVRs (digital video recorders) save programs directly onto a hard drive and thereby eliminate the need for a tape or disc. They also offer additional features such as the ability to watch one program while recording another.

VCRs have also advanced the process of making home movies. Consumers use camcorders—small television cameras with built-in video recorders—to make movies that can be shown on their own television sets. Digital circuitry enables users to create graphics, titles, and captions. (See also electricity, “Magnetic Fields.”)

Transmission

• Light from a scene being televised live is broken into three primary colors—red, blue, and …

After a television program has been recorded, the next step is to broadcast it. For transmission the video signal is impressed on a radio carrier wave, and the audio signal is impressed on another wave. These are sent out together on high-frequency radio waves that occupy a band, or channel, 6 megacycles (6 million Hertz, or cycles per second) wide. High frequencies are used partly because the lower frequencies are already taken by standard radio and also because high frequencies are fairly free from static. Television is broadcast on the VHF (very high frequency) and UHF (ultrahigh frequency) bands.

High-frequency radio waves do not follow the Earth's curvature as do lower frequencies. Since they travel in straight lines when broadcast into the atmosphere, telecasting antennas can only serve receivers between the antenna and the horizon. For further transmission, the waves are beamed from point to point by relay stations and from satellites or are carried by coaxial cables. Such transmissions can carry other signals besides television—telephone and telegraph messages, for example.

To transmit color signals, which today are virtually all television signals, the colors are divided into three characteristics. The first is brightness, or luminance—the total of intensities of all wavelengths in a light beam. The optical effect to which the eye responds, luminance is independent of color.

In color telecasting the luminance signal is a composite of the brightness from the three color camera tubes. Each primary color (red, green, and blue) contributes a definite percentage of the total intensity. This percentage corresponds to the percentage of each of these colors in a beam of white light. In effect, the luminance signal is the same as that produced in a black-and-white camera tube.

Hue is the second color characteristic that must be transmitted. It specifies that an object is basically red, blue, or green or a mixture of any two of them. Hue is determined by the dominant wavelength. If all light is of the red wavelength, the hue is saturated red. The third characteristic is chroma—the degree to which a primary color is diluted with white. Chroma makes the difference between red and pink.

The hue and chroma information is combined on a single carrier wave that becomes the chrominance signal. The luminance and chrominance signals are in turn combined and transmitted together. Synchronizing signals accompany the color video signal on the standard television bandwidth.

Television broadcasting became more accessible and more variable with the development of cable television networks. CATV (community antenna television) systems distribute television signals from a central receiver to individual home sets in areas where reception is poor. They also provide many additional channels that can be aimed at specialized audiences. These channels are also used by services that offer pay-TV, pay-cable, subscription TV, and closed-circuit TV.

Another breakthrough was the use of communications satellites to relay television signals. This allowed live, worldwide coverage of special events such as the Olympic Games. It also allowed many nations whose populations were too dispersed or too poor to have conventional television stations to receive broadcasts from a satellite. Since the satellites are located in orbits some 22,200 miles (35,700 kilometers) above the equator, a single satellite can have direct line-of-sight contact with an entire country.

Although the antennas needed in order to receive satellite television signals were initially quite large—dishes 33 feet (10 meters) across—the dish size shrank as satellite transmitting power grew, and DSB (direct satellite broadcast) was possible. DSB consumers with small dishes on their roofs can receive broadcasts from satellites.

Reception

• Electromagnetic waves are received by an antenna and converted back into electric currents. The …

In conventional broadcasting a receiving antenna captures the broadcast wave and carries the signal to the television receiver. Such antennas are made in various shapes and sizes, but most are a combination of dipoles that actually catch the wave and reflectors that reflect waves into the dipole. The dipole may be straight or folded. Inside the receiver the video and audio signals are separated by special electronic circuits. The audio signal is amplified and converted into sound in the speaker.

After amplification the video signal passes into the picture tube, a cathode-ray tube that is the heart of the television receiver. (The tube was originally trademarked as the Kinescope, and this name was given to the type of motion picture that was used to preserve early television shows.)

Action begins as the cathode produces a stream of electrons. The picture information of the video signal goes into a grid that regulates the strength of the stream. The synchronizing pulses go to the deflection plates, or coils surrounding the neck of the tube; these make the beam follow the same path as the scanning beam in the camera tube. One or more anodes speed the passage of electrons in the beam. The face of the picture tube is coated with a phosphorescent material that gives off light when struck by the electron beam. Thus, as the beam scans the face, or screen, it re-creates a picture of the original image.

In the case of color reception, the receiver separates the chrominance signal from the luminance signal. The color information is then decoded. When it is recombined with the brightness information, a series of color signals is produced. These are then applied to the tricolor picture tube to form a color image.

The tricolor picture tube is a complicated, delicate vacuum tube. In its neck are three electron guns, or cathode-ray guns—one for each primary color—spaced 120 degrees apart around a central axis. Facing the guns is the shadow mask, a metal plate containing an orderly arrangement of tiny holes. There are approximately 200,000 holes in the shadow mask. Each hole is 0.009 inch (0.023 centimeter) in diameter. The distance between the centers of two holes is only 0.023 inch (0.058 centimeter). A metal-coated phosphor-dot plate immediately behind the shadow mask is composed of about 600,000 phosphor dots arranged in triangular groups called trios. Each trio contains a red phosphor dot, a blue phosphor dot, and a green phosphor dot.

• Electron beams representing the three colors pass through a shadow mask before striking colored …

The electron beams from the three cathode-ray guns continuously scan the phosphor-dot plate. The guns are tilted so that the three beams converge at a hole in the shadow mask. This hole is located in front of the phosphor-dot trio that is being scanned at that instant. Each beam passes through the hole at a specific angle. This arrangement permits its electrons to strike phosphor dots of only one color. As each phosphor dot is struck by a beam, it glows in a color corresponding to one of the primary colors in the original image. Each of the three sets of glowing dots produces an independent image in one of the primary colors. The three images blend together because of the very close spacing of the dots. As a result, the eyes see a compound image in full color.

History of Television Technology

The chain of events leading to television began in 1817, when a Swedish chemist named Jöns Jakob Berzelius discovered the chemical element selenium. Later it was found that the amount of electrical current that selenium could carry depended on the amount of light that struck it. (This property of certain conducting materials is called photoconductivity.)

The discovery led a U.S. inventor, G.R. Carey, to make the first crude television system using photoelectric cells. In 1875 he constructed a bank of photoelectric cells with many of them side by side. Each cell was connected by a wire to a corresponding electric lightbulb in a bank, or panel. As an object was focused through a lens onto the bank of photoelectric cells, each cell controlled the amount of electricity it passed on to its corresponding lightbulb. Crude outlines of the object projected onto the photoelectric cells then showed in the lights on the bank of bulbs.

Carey's apparatus needed a great number of wires, photoelectric cells, and lightbulbs. The amount of detail or clarity with which the original picture could be reproduced was quite limited. Because this device preceded radio broadcast technology, wires connected the picture-taking end and the receiving end.

In an effort to simplify Carey's apparatus, Paul Nipkow in 1884 invented what is known as the scanning disk. It is a round, flat disk with holes arranged in spiral fashion on its surface—that is, the first hole is placed fairly close to the center of the disk, and the others are spaced progressively closer to the edge.

In this early television system, a scanning disk at the sending end was placed between the object to be televised and a photoelectric cell. The disk was whirled around by a motor, causing strips of the object to be exposed to the photoelectric cell through the holes in the disk. The current that the cell gave off corresponded to the amount of light reflected from the object through each hole in the disk. This changing current was transmitted by wire to an electric lightbulb. A second scanning disk was placed between the lightbulb and the person observing the picture. Both the sending and the receiving disks revolved at the same speed and exposed corresponding holes at the same time. As the disks whirled, a person watching at the receiver could see, through the holes, a series of lines of light, varying in brightness according to the lights and shadows that made up the picture at the sending end. Because the eye has the ability to keep impressions for short periods of time, the viewer could see a picture of the original object.

The Nipkow scanning disk simplified the television system. Only one photoelectric cell and one lamp were needed. However, the pictures still were not very clear, mostly because of the limited number of holes that could be punched into a disk and the speed at which the disk could be rotated.

Additions and improvements accelerated in the 20th century. The first practical transmissions over wire were accomplished in 1923 by John L. Baird in England and C.F. Jenkins in the United States. Also in the 1920s Vladimir Zworykin and Philo Farnsworth made great advances in developing devices to serve as television cameras. Zworykin invented the iconoscope, and Farnsworth developed an image-dissector tube. Through 1935 either one or the other was used in television cameras as the light-sensitive device to pick up the images. Later the dissector was used largely in industrial television, and the iconoscope was limited to film work.

The photoelectric cells in the iconoscope are microscopic in size and are on a plate called a mosaic. This mosaic is about 3 by 4 inches (8 by 10 centimeters) and contains thousands of tiny photoelectric cells, each insulated from the others. Magnified, the mosaic resembles the thousands of squares on graph paper. When a light image made up of blacks, grays, and whites is focused upon this mosaic plate, each cell takes on an electrical charge. The size of the charge depends on the amount of light striking it. To change these electrical charges back into light energy to make a picture, it is necessary to scan all the charges and make them form a new light image at some distant receiving point. In the neck of the iconoscope a stream of electrons is shot onto the mosaic plate and is made to scan the plate by magnetic or other means. This electron eye moves from left to right and from top to bottom. The stream of electrons reaches each photoelectric cell and causes the release of the charges stored in it in definite scanning order. This continuous stream of differing electric charges is then amplified and passed on to a radio transmitter.

Unlike the iconoscope, which is a storage device, the image dissector projects the picture onto a light-sensitive surface, from which electrons are released in proportion to the strength of the light, thus forming an electron image. These slow-moving electrons are speeded by a voltage difference between the light-sensitive screen and a coating on the far end of the tube. The amplified charges are passed on to a transmitter.

By 1945 both of these camera pickup tubes had been replaced by the image orthicon tube—the device that brought television into the mass market. The development of videotape two decades later shaped modern video, which integrates live, live-on-tape, edited-tape, and rerun broadcasts with film conversions and prerecorded commercials and title sequences.

An era of frantic manufacturing competition and increasing consumer demand, the 1980s brought enormous improvements in video equipment. The development of sets equipped with MTS (multichannel TV sound) spurred high-fidelity transmission: by 1988 all the major U.S. networks were scheduling their regular broadcasts in stereo. With MTS capability, there is an extra channel for SAP (second audio program), which broadcasters may use for bilingual transmission or some other sound track. Closed-captioned broadcasts also increased.

The manufacture of higher-definition VCRs increased the public's appetite for theater-quality broadcasts. IDTV (improved-definition television) enhanced the picture performance of standard broadcast signals through a noninterlaced scanning system. On June 3, 1989, Japan initiated the world's first broadcast of HDTV (high-definition television) programs; the first image to appear on giant screens across Japan was the Statue of Liberty and New York Harbor. The first HDTV broadcast in the United States showed the lift-off of the space shuttle Discovery with John Glenn aboard, on Oct. 29, 1998. Conversion from the NTSC analog system to DTV was gradual, however: only 24 stations carried the shuttle broadcast in HDTV, and only a small percentage of viewers owned digital television sets, which were initially quite expensive. The Federal Communications Commission determined that the two systems would be used side by side during the transition period, until at least 2006, at which point analog transmissions would cease.

Beginning in the 1990s, broadcasters teamed with cable television, computer, and telecommunications companies to develop ITV (interactive television). ITV systems let people interact with television programs and other viewers—for example, to play along with a game show, voice an opinion, or get more information about a news story. Television–personal computer hybrids such as WebTV allowed users to connect to the World Wide Web through their television sets.

Direct-view television sets have tubes generally from 5 to 38 inches (measured diagonally), and rear-projection televisions are popular in 40- to 70-inch sizes. Even larger televisions are available, including front-projection sets, which are far more expensive and thus much less common. Flat-tube sets reduce glare and picture distortion, and extremely thin models can be hung on a wall. Sets with a PIP (picture-in-picture) function can display more than one channel at a time. Personal, handheld televisions feature screens only a couple of inches big.

Additional references about television

Abramson, Albert. The History of Television, 1880–1941 (McFarland, 1987).

Allman, Paul. Exploring Careers in Video and Digital Video (Rosen, 2001).

Blum, R.A., and Lindheim, R.D. Primetime: Network Television Programming (Focal Press, 1987).

Cheney, G.A. Television in American Society (Watts, 1983).

Gross, Lynne. New Television Technologies (Brown, 1990).

Hartwig, Robert. Basic TV Technology, 3rd ed. (Focal Press, 2000).

Lambert, Mark. TV and Video Technology (Watts, 1990).

Newcomb, Horace, ed.Encyclopedia of Television, 3 vols. (Fitzroy Dearborn, 1997).

Postman, Neil. Amusing Ourselves to Death (Methuen, 1987).

Winn, Marie. The Plug-In Drug, rev. ed. (Penguin, 1985).

article taken from britannica encylopedia