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Television - Operation Of The Cathode Ray Tube, High Definition Television, Cable Television - Television of the future

plasma digital system image

The invention of the cathode ray tube in 1897 by Ferdinand Braun quickly made possible the technology that we call television. Indeed, by 1907, the cathode ray tube was supplying television images. Within 50 years, television had become a dominant form of entertainment and an important way to acquire information. This remains true today, as the average American spends between two and five hours each day watching television.

The name television means distance seeing. Television, or TV, is the technology used to transmit pictures with sound using radio frequency and microwave signals or closed-circuit connections. Television operates on two principles that underlie how the human brain perceives the visual world. First, if an image is divided into a group of very small colored dots (called pixels), the brain is able to reassemble the individual dots to produce a meaningful image. Second, if a moving image is divided into a series of pictures, with each picture displaying a successive part of the overall sequence, the brain can put all the images together to form a single flowing image. The technology of the television (as well as computers) utilizes these two features of the brain to present images. The dominant basis of the technology is still the cathode ray tube.


Plasma television

Plasma television has been available commercially since the late 1990s. It is currently expensive, and as so is not yet popular. As with other technologies, however, refinements over time will drive down the price into the affordable range for many people. Plasma televisions do not have a cathode ray tube. Thus, the screen can be very thin. Typically televisions screens are about 6 in (15 cm) thick. This allows the screen to be hung from a wall.

In a plasma television, fluorescent lights are present instead of phosphors. Red, green, and blue fluorescent lights enable a spectrum of colors to be produced, in much the same way as with conventional television. Each fluorescent light contains a gas called plasma. Plasma consists of electrically charged atoms (ions) and electrons (negative in charge). When an electrical signal encounters plasma, the added energy starts a process where the particles bump into one another. This bumping releases a form of energy called a photon. The release of ultraviolet photons causes a reaction with phosphor material, which then glows.


ATV

ATV stands for advanced television, the television system expected to replace the current system in the United States. Television technology is rapidly moving toward the ATV digital system planned to replace the aging analog process. ATV is a digital-television system, where the aspects that produce the image are processed as computer-like data. Digitally processed TV offers several tremendous advantages over analog TV methods. In addition to sharper pictures with less noise, a digital system can be much more frugal in the use of spectrum space.

Most TV frames are filled with information that has not changed from the previous frame. A digital TV system can update only the information that has changed since the last frame. The resulting picture looks to be as normal as the pictures seen for years, but many more images can be transmitted within the same band of frequencies.

TV audiences have been viewing images processed digitally in this way for years, but the final product has been converted to a wasteful analog signal before it leaves the television transmitter. Satellite relays have relayed TV as digitally compressed signals to maximize the utilization of the expensive transponder equipment in orbit. The small satellite "dishes" offered for home reception receive digitally-encoded television signals.

ATV will not be compatible with current analog receivers, but it will be phased in gradually in a carefullyconsidered plan that will allow older analog receivers to retire gracefully over time.

Resources

Other

Ovadia, Schlomo. Broadband Cable TV Access Networks: From Technologies to Applications. Upper Saddle River, NJ: Prentice Hall, 2001.

Thomas, Jeffrey L., and Francis M. Edgington. Digital Basis for Cable Television Systems. Upper Saddle River, NJ: Prentice Hall, 1999.


Donald Beaty

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Chrominance

—Color information added to a video signal.

Coaxial cable

—A concentric cable, in which the inner conductor is shielded from the outer conductor; used to carry complex signals.

Compact disc

—Digital recording with extraordinary fidelity.

Field

—Half a TV frame, a top to bottom sweep of alternate lines.

Frame

—Full TV frame composed of two interlaced fields.

Parallax

—Shift in apparent alignment of objects at different distances.

Phosphor

—Chemical that gives off colored light when struck by electron.

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