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Zenith has been a pioneer in the development of television since the 1930s, and has remained one of the largest selling TV brands ever since its first set hit the market in 1948. There have been many improvements made to television since its invention, but the basic principles of television have remained essentially the same since that time. And, while virtually every home in America has a TV set, few people have any idea how one works. The pictures you see on your TV are drawn by a beam of electrons fired out of a gun at the back of the set. When the beam hits chemicals (called phosphors) that are painted on the inside of the picture tube, the phosphors glow. But because they glow only for a fraction of a second, the beam has to immediately draw another picture. In fact, the beam draws a picture 30 times every second - which is so fast that, together, the pictures look like they're moving. But how does the TV know what to draw? The TV receives electrical signals, either through the air from broadcast stations, or over cable or from a VCR. Those signals are pulses of electrical energy that arrive in waves. Those waves can have many different shapes, and each shape can tell the TV something about what it's supposed to do. A TV uses two kinds of waves, AM (for Amplitude Modulation) and FM (for Frequency Modulation). As their names suggest, AM waves vary in strength but not how frequently they repeat, while FM waves vary in frequency but not their strength. Each TV channel uses multiple AM signals and one FM signal. And there are several channels broadcast at the same time. It's the job of the tuner in the TV set to filter out all channels except the one you want to watch. For example, if you want to watch channel 7, the tuner blocks out all the channels below 7, and all the channels above 7. The only one it lets through is channel 7, with its AM and FM signals. After the channel passes through the tuner, it travels through a series of filters that separate the FM waves from the AM waves, and then separates the multiple AM waves from each other. The FM signal, which is the same kind used to carry FM radio signals, carries the sound information, just like a radio. FM signals can carry multiple audio channels - in this case, two, for stereo sound. AM waves, which are the same kind used to carry AM radio signals, carry the picture information. The TV uses one AM wave to carry the basic picture information - what is needed to draw a black & white picture. In effect, it tells the electron gun how brightly to illuminate the screen at each point along a horizontal line. When it finishes drawing that line, it draws another and another, until it fills the screen with 525 lines. And when it finishes drawing a screen, it draws a second, and a third, and so on, at a rate of 30 pictures every second. (For more on this, see How a Picture Tube Works.) The TV "draws" pictures by synchronizing the electron guns (which shoot the beams that light the screen) with the yoke, a circle of magnets that deflect, or "pull," the electron beam left and right, and up and down, across the screen. Together, the guns and the yoke can draw pictures, by knowing what to draw and where to draw it. Another AM signal carries the color information - it tells the TV where to put the color. This signal actually consists of two signals on the same wave, separated by time. To use the example of music, the two waves are like whole notes. One wave arrives on a downbeat, while another, separate wave begins on a downbeat a quarter note later. Because the TV knows where the beat begins, it can tell the waves apart - when one wave's downbeat begins, the second one begins a quarter note later. This is called "multiplexing" and it allows more than one signal to be carried at one time, providing more information for the TV. On a color TV, black is produced when no colors are lit. White is produced when red, green and blue are lit together. If the TV lights only blue, the TV will, of course, produce blue. But if it lights red and green, the TV will produce yellow. If it lights blue and green, the TV produces cyan. In fact, using only red, green and blue, the TV can produce any color. Zenith has improved on these basic principles of television by designing special circuits to correct errors in the signals and help the TV draw better pictures, with truer, more vivid color, sharper lines and better sound. |