VII.

Television's History

The scientific principles on which television is based were discovered in the course of basic research. Only much later were these concepts applied to television as it is known today. The first practical television system began operating in the 1940s.

In 1873 the Scottish scientist James Clerk Maxwell predicted the existence of the electromagnetic waves that make it possible to transmit ordinary television broadcasts. Also in 1873 the English scientist Willoughby Smith and his assistant Joseph May noticed that the electrical conductivity of the element selenium changes when light falls on it. This property, known as photoconductivity, is used in the vidicon television camera tube. In 1888 the German physicist Wilhelm Hallwachs noticed that certain substances emit electrons when exposed to light. This effect, called photoemission, was applied to the image-orthicon television camera tube.

Although several methods of changing light into electric current were discovered, it was some time before the methods were applied to the construction of a television system. The main problem was that the currents produced were weak and no effective method of amplifying them was known. Then, in 1906, the American engineer Lee De Forest patented the triode vacuum tube. By 1920 the tube had been improved to the point where it could be used to amplify electric currents for television.

A.

Nipkow Disk

Some of the earliest work on television began in 1884, when the German engineer Paul Nipkow designed the first true television mechanism. In front of a brightly lit picture, he placed a scanning disk (called a Nipkow disk) with a spiral pattern of holes punched in it. As the disk revolved, the first hole would cross the picture at the top. The second hole passed across the picture a little lower down, the third hole lower still, and so on. In effect, he designed a disk with its own form of scanning. With each complete revolution of the disk, all parts of the picture would be briefly exposed in turn. The disk revolved quickly, accomplishing the scanning within one-fifteenth of a second. Similar disks rotated in the camera and receiver. Light passing through these disks created crude television images.

Nipkow's mechanical scanner was used from 1923 to 1925 in experimental television systems developed in the United States by the inventor Charles F. Jenkins, and in England by the inventor John L. Baird. The pictures were crude but recognizable. The receiver also used a Nipkow disk placed in front of a lamp whose brightness was controlled by the signal from the light-sensitive tube behind the disk in the transmitter. In 1926 Baird demonstrated a system that used a 30-hole Nipkow disk.

B.

Electronic Television

Simultaneous to the development of a mechanical scanning method, an electronic method of scanning was conceived in 1908 by the English inventor A. A. Campbell-Swinton. He proposed using a screen to collect a charge whose pattern would correspond to the scene, and an electron gun to neutralize this charge and create a varying electric current. This concept was used by the Russian-born American physicist Vladimir Kosma Zworykin in his iconoscope camera tube of the 1920s. A similar arrangement was later used in the image-orthicon tube.

The American inventor and engineer Philo Taylor Farnsworth also devised an electronic television system in the 1920s. He called his television camera, which converted each element of an image into an electrical signal, an image dissector. Farnsworth continued to improve his system in the 1930s, but his project lost its financial backing at the beginning of World War II (1939-1945). Many aspects of Farnsworth's image dissector were also used in Zworykin's more successful iconoscope camera.

Cathode rays, or beams of electrons in evacuated glass tubes, were first noted by the British chemist and physicist Sir William Crookes in 1878. By 1908 Campbell-Swinton and a Russian, Boris Rosing, had independently suggested that a cathode-ray tube (CRT) be used to reproduce the television picture on a phosphor-coated screen. The CRT was developed for use in television during the 1930s by the American electrical engineer Allen B. DuMont. DuMont's method of picture reproduction is essentially the same as the one used today.

The first home television receiver was demonstrated in Schenectady, New York, on January 13, 1928, by the American inventor Ernst F. W. Alexanderson. The images on the 76-mm (3-in) screen were poor and unsteady, but the set could be used in the home. A number of these receivers were built by the General Electric Company (GE) and distributed in Schenectady. On May 10, 1928, station WGY began regular broadcasting to this area.

C.

Public Broadcasting

The first public broadcasting of television programs took place in London in 1936. Broadcasts from two competing firms were shown. Marconi-EMI produced a 405-line frame at 25 frames per second, and Baird Television produced a 240-line picture at 25 frames per second. In early 1937 the Marconi system, clearly superior, was chosen as the standard. In 1941 the United States adopted a 525-line, 30-image-per-second standard.

The first regular television broadcasts began in the United States in 1939, but after two years they were suspended until shortly after the end of World War II in 1945. A television broadcasting boom began just after the war in 1946, and the industry grew rapidly. The development of color television had always lagged a few steps behind that of black-and-white (monochrome) television. At first, this was because color television was technically more complex. Later, however, the growth of color television was delayed because it had to be compatible with monochrome—that is, color television would have to use the same channels as monochrome television and be receivable in black and white on monochrome sets.

D.

Color Television

It was realized as early as 1904 that color television was possible using the three primary colors of light: red, green, and blue. In 1928 Baird demonstrated color television using a Nipkow disk in which three sets of openings scanned the scene. A fairly refined color television system was introduced in New York City in 1940 by the Hungarian-born American inventor Peter Goldmark. In 1951 public broadcasting of color television was begun using Goldmark's system. However, the system was incompatible with monochrome television, and the experiment was dropped at the end of the year. Compatible color television was perfected in 1953, and public broadcasting in color was revived a year later.

Other developments that improved the quality of television were larger screens and better technology for broadcasting and transmitting television signals. Early television screens were either 18 or 25 cm (7 or 10 in) diagonally across. Television screens now come in a range of sizes. Those that use built-in cathode-ray tubes (CRTs) measure as large as 89 or 100 cm (35 or 40 in) diagonally. Projection televisions (PTVs), first introduced in the 1970s, now come with screens as large as 2 m (7 ft) diagonally. The most common are rear-projection sets in which three CRTs beam their combined light indirectly to a screen via an assembly of lenses and mirrors. Another type of PTV is the front-projection set, which is set up like a motion picture projector to project light across a room to a separate screen that can be as large as a wall in a home allows. Newer types of PTVs use liquid-crystal display (LCD) technology or an array of micro mirrors, also known as a digital light processor (DLP), instead of cathode-ray tubes. Manufacturers have also developed very small, portable television sets with screens that are 7.6 cm (3 in) diagonally across.

E.

Television in Space

Television evolved from an entertainment medium to a scientific medium during the exploration of outer space. Knowing that broadcast signals could be sent from transmitters in space, the National Aeronautics and Space Administration (NASA) began developing satellites with television cameras. Unmanned spacecraft of the Ranger and Surveyor series relayed thousands of close-up pictures of the moon's surface back to earth for scientific analysis and preparation for lunar landings. The successful U.S. manned landing on the moon in July 1969 was documented with live black-and-white broadcasts made from the surface of the moon. NASA's use of television helped in the development of photosensitive camera lenses and more-sophisticated transmitters that could send images from a quarter-million miles away.

Since 1960 television cameras have also been used extensively on orbiting weather satellites. Video cameras trained on Earth record pictures of cloud cover and weather patterns during the day, and infrared cameras (cameras that record light waves radiated at infrared wavelengths) detect surface temperatures. The ten Television Infrared Observation Satellites (TIROS) launched by NASA paved the way for the operational satellites of the Environmental Science Services Administration (ESSA), which in 1970 became a part of the National Oceanic and Atmospheric Administration (NOAA). The pictures returned from these satellites aid not only weather prediction but also understanding of global weather systems. High-resolution cameras mounted in Landsat satellites have been successfully used to provide surveys of crop, mineral, and marine resources.

F.

Home Recording

In time, the process of watching images on a television screen made people interested in either producing their own images or watching programming at their leisure, rather than during standard broadcasting times. It became apparent that programming on videotape—which had been in use since the 1950s—could be adapted for use by the same people who were buying televisions. Affordable videocassette recorders (VCRs) were introduced in the 1970s and in the 1980s became almost as common as television sets.

During the late 1990s and early 2000s the digital video disc (DVD) player had the most successful product launch in consumer electronics history. According to the Consumer Electronics Association (CEA), which represents manufacturers and retailers of audio and video products, 30 million DVD players were sold in the United States in a record five-year period from 1997 to 2001. It took compact disc (CD) players 8 years and VCRs 13 years to achieve that 30-million milestone. The same size as a CD, a DVD can store enough data to hold a full-length motion picture with a resolution twice that of a videocassette. The DVD player also offered the digital surround-sound quality experienced in a state-of-the-art movie theater. Beginning in 2001 some DVD players also offered home recording capability.

G.

Digital Television

Digital television uses technology that records, transmits, and decodes a signal in digital form—that is, as a series of ones and zeros. This process produces much clearer picture and sound quality than analog systems, similar to the difference between a compact disc recording (using digital technology) and an audiotape or long-playing record. It also permits additional features to be embedded in signals including program and consumer information as well as interactivities. Early digital equipment included digital television receivers that converted analog signals into digital code. The analog signal was first sampled and stored as a digital code, then processed, and finally retrieved. ATSC digital tuners designed to decode purely digital signals are now standard on new televisions.

There are three types of broadcast digital television (DTV), each with progressively better picture and sound quality: standard-definition TV (SDTV), enhanced-definition TV (EDTV), and high-definition TV (HDTV).

The high-definition television (HDTV) system was developed in the 1980s. It uses 1,080 lines and a wide-screen format, providing a significantly clearer picture than the traditional 525- and 625-line television screens. Each line in HDTV also contains more information than normal formats. HDTV is transmitted using digital technology. Because it takes a huge amount of coded information to represent a visual image—engineers believe HDTV will need about 30 million bits (ones and zeros of the digital code) each second—data-compression techniques have been developed to reduce the number of bits that need to be transmitted. With these techniques, digital systems need to continuously transmit codes only for a scene in which images are changing; the systems can compress the recurring codes for images that remain the same (such as the background) into a single code. Digital technology is being developed that will offer sharper pictures on wider screens, and HDTV with cinema-quality images.

A fully digital system was demonstrated in the United States in the 1990s. A common world standard for digital television, the MPEG-2, was agreed on in April 1993 at a meeting of engineers representing manufacturers and broadcasters from 18 countries. Because HDTV receivers initially cost much more than regular television sets, and broadcasts of HDTV and regular television are incompatible, the transition from one format to the next could take many years. The method endorsed by the U.S. Congress and the FCC to ease this transition is to give existing television networks a second band of frequencies on which to broadcast, allowing networks to broadcast in both formats at the same time. Engineers are also working on making HDTV compatible with computers and telecommunications equipment so that HDTV technology may be applied to other systems besides home television, such as medical devices, security systems, and computer-aided manufacturing (CAM).

The Congress of the United States has mandated that all over-the-air television broadcasting become digital, although the date for the end of all analog broadcasting has been changed a number of times. After the conversion date (now set as February 2009), viewers with analog televisions will need special converter boxes to watch over-the-air broadcasts.

H.

Flat Panel Display

In addition to getting clearer, televisions are also getting thinner. Flat panel displays, some just a few centimeters thick, offer an alternative to bulky cathode ray tube televisions. Even the largest flat panel display televisions are thin enough to be hung on the wall like a painting. Many flat panel TVs use liquid-crystal display (LCD) screens that make use of a special substance that changes properties when a small electric current is applied to it. LCD technology has already been used extensively in laptop computers. LCD television screens are flat, use very little electricity, and work well for small, portable television sets. LCD has not been as successful, however, for larger television screens.

Flat panel TVs made from gas-plasma displays can be much larger. In gas-plasma displays, a small electric current stimulates an inert gas sandwiched between glass panels, including one coated with phosphors that emit light in various colors. While just 8 cm (3 in) thick, plasma screens can be more than 150 cm (60 in) diagonally.

I.

Computer and Internet Integration

As online computer systems become more popular, televisions and computers are increasingly integrated. Such technologies combine the capabilities of personal computers, television, DVD players, and in some cases telephones, and greatly expand the kinds of services that can be provided. For example, computer-like hard drives in set-top recorders automatically store a TV program as it is being received so that the consumer can pause live TV, replay a scene, or skip ahead. For programs that consumers want to record for future viewing, a hard drive makes it possible to store a number of shows. Some set-top devices offer Internet access through a dial-up modem or broadband connection. Others allow the consumer to browse the World Wide Web on their TV screen. When a device has both a hard drive and a broadband connection, consumers may be able to download a specific program, opening the way for true video on demand.

Personal computers have also taken on television-like functions. Webcasting includes the broadcasting of video content over the World Wide Web. Television programs and other types of video media can be viewed from Web sites. Streaming allows a live video signal to be played as it is sent over the Internet in small packets of data. Archived programs can be viewed on-demand or downloaded to a computer. Small, handheld portable media devices with video capability can also play television programs or other video as downloaded podcasts. Some devices can also receive television broadcasts and wireless Internet.

Consumers may eventually need only one main system or device, known as an information appliance, which they could use for entertainment, communication, shopping, and banking in the convenience of their home.