Television

In the United States, about 99 percent of households own at least one television set, and over 60 percent subscribe to cable television.

The device known as the television is actually a receiver that is the end point of a system that transmits pictures and sounds at a distance. The process starts with a television camera that converts all image information into electrical signals, which are delivered to homes and businesses through a television antenna, underground fiber optic cable, or satellite. The function of the receiver, or television set, is to unscramble the electrical signals, converting them into sounds and pictures.

Television is one of the greatest technological developments of all time. It did not happen overnight, but developed over a number of years, taking advantage of advances in the sciences and technologies of the time. Television has not only been a source of entertainment worldwide, but it has also linked people through their common experience of witnessing events that are happening in different parts of the world and beyond. For example, on July 20, 1969, about 720 million people all over the world watched on television as astronaut Neil Armstrong walked on the moon.

In the United States, about 99 percent of households own at least one television set. Over 60 percent subscribe to cable television. The average household watches approximately seven hours of television each day.

A group effort

No single person invented the television. Instead, it is the result of scientific research in various countries over several decades. In 1817, Baron Jöns Jakob Berzelius (1779–1848), a Swedish chemist, identified selenium as a chemical element. He found that selenium could conduct electricity and that this ability to conduct electricity varied with the amount of light hitting it. In 1878, Sir William Crookes (1832–1919), a British chemist and physicist, first mentioned cathode rays (beams of electrons in a glass vacuum tube). These scientific findings occurred separately and would take many years to be applied to the making of television.

In 1884, German engineer Paul Nipkow (1860–1940) built the first crude television with the help of a mechanical scanning disk. Small holes on the rotating disk picked up pieces of images and imprinted them on a light-sensitive selenium tube. A receiver then recreated the image pieces into a whole picture. Nipkow's mechanical invention, crude as it was, employed the scanning principle that would be used by future television cameras and receivers to record and recreate images for a television screen.

Television goes electronic

In 1911, while some scientists were trying to improve on Nipkow's mechanical scanning disk, Scottish electrical engineer Alan Archibald Campbell Swinton (1863–1930) discussed his idea of a "distant electric vision," using cathode rays. Although Swinton never built the electronic television that he so accurately described, other scientists brought into reality his idea of the television set as we know it today.

In 1897, German scientist Ferdinand Karl Braun (1850–1918) invented the cathode ray tube. Inside the glass tube, cathode rays could produce pictures by hitting the fluorescent (glowing) screen at the end of the tube. Boris Rosing of Russia demonstrated in 1907 that the cathode ray tube could serve as the receiver of a television system.

In England, John Logie Baird (1888–1946) experimented with Nipkow's scanning disk in the early 1920s. At around the same time, in the United States, Charles Francis Jenkins (1867–1934) was performing the same experiment. In 1926, Baird was the first to demonstrate the electrical transmission of images in motion.

The invention of television cameras during the 1920s further contributed to the development of television. Philo Farnsworth (1906–1971) of Idaho was only fifteen years old when he figured out the workings of an electronic television system. Farnsworth invented the image dissector tube, an electronic scanner. In 1927, he gave the first public demonstration of the electronic television by transmitting the image of a dollar sign. Along with another American, Allen B. Dumont (1901–1965), Farnsworth developed a pickup tube that became the home television set by 1939.

At the same time, Russian immigrant Vladimir Zworykin (1889–1982) invented an electronic camera tube called the iconoscope. Both television cameras invented by Farnsworth and Zworykin used a cathode ray tube as the television receiver for recreating the original images.

Color television

The earliest mention of color television was in a German patent in the early 1900s.

In 1928, John Logie Baird used Nipkow's mechanical scanning disk to demonstrate color television. A color television system developed by Hungarian-born American Peter Goldmark (1906–1977) in 1940 did not receive wide acceptance because it did not work in black-and-white television sets. It took almost twenty years for color television to be commercially available.

Raw Materials

The television is made up of four principal sets of parts: the exterior part or housing, the picture tube, the audio (sound) reception and stereo system, and the electronic components (parts). These electronics parts include cable and antenna input and output devices, a built-in antenna in most television sets, a remote control receiver, computer chips, and access buttons. The remote control, popularly called a "clicker," is an additional part of the television set.

The television housing is made of injection-molded plastic. In injection molding, liquid plastic is forced into a mold with the help of high pressure. The plastic takes on the shape of the mold as it cools. Some television sets may have exterior wooden cabinets. The audio reception and stereo systems are made of metal and plastic.

The picture tube materials consist of glass and a coating made of the chemical phosphor, which glows when hit by light. Other picture tube materials include electronic attachments around and at the rear of the tube. Brackets and braces hold the picture tube inside the housing.

The antenna and most of the input-output connections are made of metal. Some of the input-output connections are coated with plastic or special metals to improve the quality of the connection or to insulate it. (The insulation material prevents the escape of heat, electricity, or sound.) The chips (also called microchips) are made of silicon, metal, and solder (a metal that is heated and used to join metals).

Design

Different types of engineers are responsible for designing a television set. These include electronics, audio, video, plastics, and fiber optics engineers. The engineering team may design a bigger television set patterned after an existing model. They may also design new features, including an improved picture, better sound system, or a remote control that can work with other devices, such as a DVD player.

The team members discuss ideas about the new features, redrawing plans as they develop new ideas about the design. After the engineers receive initial approval for manufacturing the set, they make a prototype, or a model, after which the other sets will be patterned. A prototype is important for testing out the design, appearance, and functions of the set. Having a prototype also enables the production engineers to determine the production processes, machining (the cutting, shaping, and finishing by machine), tools, robots, and changes to existing factory production lines.

When the prototype passes a series of strict tests and is finally approved for manufacture by management, the engineers draw detailed plans and produce specifications for the design and production of the model. Specifications include the type of materials needed, their sizes, and workmanship involved in the manufacturing process.

Raw materials and components that are manufactured by other persons are ordered. The production line is constructed and tested. Finally, the components that would go into the new television sets are put together in the assembly line.

The Manufacturing Process

Housing

1 Television housings are mostly made of plastic. Using a process called injection molding, high pressure is applied to liquid plastic to force it into molds. The plastic is allowed to cool and harden. The formed solid plastics are released from the molds, trimmed, and cleaned. They are then assembled to make up the television housing. The molds are designed so that brackets and supports for the various parts of the television set are part of the housing.

Picture tube

2 The television picture tube, also called a cathode ray tube (CRT), is shaped like a funnel. The widest part of the funnel is a slightly curved plate made of glass. The glass is the television screen on which pictures are viewed. A dark tint may be added to the glass plate to improve color. The inside of the screen is covered with tiny dots of phosphors, or chemicals that glow when hit by electrons. The phosphor dots come in the primary colors red, green, and blue.

3 Immediately behind the phosphor layer is a thin metal shadow mask with thousands of small holes. Some shadow masks are made of iron. The better-quality shadow masks are made of a mixture of nickel and iron called Invar that lets the picture tube operate at a higher temperature. Higher temperatures result in brighter pictures.

4 The narrow end of the color picture tube contains three electron guns. Their job is to shoot electron beams at the phosphors, with each gun responsible for a specific color. The shadow mask makes sure the electron guns each shoot at one color of phosphors in a process called scanning (see sidebar on page 272). When hit by electrons, the phosphors light up, creating the pictures on the television screen.

After the electron guns are placed inside the picture tube, air is removed from the tube to prevent it from interfering with the movement of the electrons. Then, the end of the tube is closed off with a fitted electrical plug that will be placed near the back of the set.

5 A deflection yoke, consisting of two electromagnetic coils, is fitted around the neck of the picture tube. The electromagnetic coils cause pulses of high voltage to guide the direction and speed of the electron beams as they scan the television screen.

Audio system

6 The speakers, which go into the housing, are typically made by another company that works closely with the television manufacturer. They are made according to certain characteristics specified by the manufacturer. Wiring, electronic sound controls, and integrated circuitry are assembled in the television set as it travels along the assembly line. An integrated circuit, also called a chip or microchip, is a tiny piece of silicon on which electronic parts and their interconnections are imprinted.

Electronic parts

7 After the picture tube and the audio system are assembled in the set, other electronic parts are added to the rear of the set. The antenna, cable jacks, other input and output jacks, and the electronics for receiving remote control signals are prepared as subassemblies on another assembly line or by specialty contractors hired from outside the company. These electronic components are added to the set, and the housing is closed.

Quality Control

Like other precision products, the television requires strict quality control during manufacture. Inspections, laboratory testing, and field testing are constantly conducted during the development of prototypes. The manufacturer has to be sure the resulting product is not only technologically sound but also safe for use in homes and businesses.

The Future

Researchers continue to find new ways to improve on television sets. The high-definition television (HDTV) system that we have today is a digital television system. The conventional television system transmits signals using radio waves. During transmission, these waves could get distorted, for example, by bad weather. The television set, unable to distinguish between distorted and good-quality waves, converts all the radio waves it receives into pictures. Therefore, the resulting images may not all be of good quality.

Digital television, on the other hand, while also using radio waves, assigns a code to the radio waves. When it comes time to recreate the picture, the television set obtains information from the code on how to display the image. HDTV offers clearer and sharper images with its 1,125-line picture. Compared to the traditional 525-line picture, HDTV offers a far better picture because more lines are scanned by the television camera and receiver. This means more details of the images are included.

In the future, digital television could also allow the viewer to choose camera angles while watching a concert or a sports event. The viewer could also communicate with the host of a live program and edit movies on screen.

Flat-panel television screens, such as liquid-crystal display (LCD) and plasma screens, are being perfected to achieve the kind of picture and sound seen in movie theaters. They are also seen as replacements for the present bulky television sets made of cathode ray tubes. The flat screens are not only lightweight but are also energy-efficient. However, unless these state-of-the art technologies become affordable, it will be a while before consumers convert to flat-screen televisions.

antenna:

A device used in television to send and receive electromagnetic waves, or waves of electrical and magnetic force brought about by the vibration of electrons.

cable television:

The transmission of television programs from television stations to home television sets through fiber optic cable or metal cable.

cathode ray tube (CRT):

A vacuum tube whose front part makes up the television screen. In the tube, images are formed by electrons striking the phosphor-coated screen.

chip:

Also called microchip, a very small piece of silicon that carries interconnected electronic components.

electron:

A small particle within an atom that carries a negative charge, which is the basic charge of electricity.

fiber optic cable:

A bundle of hair-thin glass fibers that carry information as beams of light.

fluorescent:

Giving off light when exposed to electric current.

persistence of vision:

A physical phenomenon in which the retina of the eye holds on to an image for a fraction of a second longer after it has seen the image. The brain, which works with the eye, puts these still images together so that the eye perceives them as a single movement.

phosphor:

A chemical that glows when struck by light.

satellite:

An object that is put into space and used to receive and send television signals over long distances.

scan:

To move electrons over a surface in order to transmit an image.

shadow mask:

A metal sheet with thousands of small holes. It is found behind the phosphor layer of the color picture tube and through which three electron guns at the other end of the tube shoot electron beams. The shadow mask ensures that each gun shoots at the specific phosphor color.

silicon:

A nonmetallic material widely used in microchips because of its ability to conduct electricity.

For More Information

Books

Graham, Ian. Communications. Austin, TX: Steck-Vaughn Company, 2001.

Graham, Ian. Radio and Television. Austin, TX: Steck-Vaughn Company, 2001.

Parker, Steve, Peter Lafferty, and Steve Setford. How Things Work. New York, NY: Barnes & Noble Books, 2001.

Periodicals

Brown-Kenyon, Paul I., Alan Miles, and John S. Rose,. "Unscrambling Digital TV." McKinsey Quarterly. (2000): pp.71-81.

Kubey, Robert, and Mihaly Csikszentmihalyi. "Television Addiction." Scientific American. (February 2000).

Web Sites

Early Television Foundation. http://www.earlytelevision.org (accessed on July 22, 2002).

"The Revolution of Television." Technical Press. http://www.tvhandbook.com/History/History_TV.htm (accessed on July 22, 2002).