Welcome to You Ask Andy

Billy Fullerton, age 12, of Fredericton, N.fi., for his question:

How do pictures get on TV?

To most of us, TV is an everyday event. Yet it is but a few years old. A hundred years ago, TV would have seemed like a miracle from Aladdin's Lamp. This miracle could not become real until certain forces of nature were discovered and tamed. We had to discover electricity and tame its mighty power. Radio had to be discovered and put to work. The science of electronics had to be developed. Complex gadgets had to be invented to put these mighty forces to work. TV draws on our knowledge of electricity., radio, electronics, light and other mysteries, solved in the modern Age of Science.

Three factors operate together in television. One is the drama enacted in the studio, one is the copy of these events on your TV screen. The other is a powerful electromagnetic force which carries the show on invisible waves from the studio to home.

The carrier waves are sent out from the broadcasting station. They are electromagnetic or radio waves and they fan out from their powerhouse in all directions. These radio waves have been known for a long time. In TV, the trick was to make them carry a series of pictures. When you remember that they are invisible, this seems impossible. But the problem was solved. The pictures could be carried as electrical impulses. The scene is the studio is translated into electrical impulses and these impulses affect the radio waves which carry them. The TV set picks up the carrier waves an. notes the electrical impulses. It translates these impulses back into pictures.

The translating job is done with scanners. One scanner works in the studio. It scans the scene before it in rows from left to right, from top to bottom. Look at a newspaper picture under a magnifying glass. You will. see that it is built up from rows of small dots. A patch of heavy dots makes a dark patch, pale dots make light areas. The TV scanner also build up a picture of dark and light dots.

The light, bright dots produce strong electrical impulses. The dark  dots produce weak impulses. The scanner covers the scene before it much as you read a page but much faster. It builds up an entire picture 30 times every second. The pictures follow each other in rapid succession like a moving picture film. Our eyes are fooled into thinking we see a continuous performance. Actually, we are seeing 30 slightly different pictures every second.

The scanner in the studio feeds its series of electrical impulses into the powerful carrier waves. Instead of black and white dots, the radio waves carry a fast series of strong and weak impulses. They fan out in all directions seeking TV sets to tune in on them. You choose a program by tuning in on the special wave length used by this or that TV broadcasting station.

Your TV set picks up the electrical impulses carried by the radio waves. It translates them back into dots of light. This job is done by a wonderful electron gun which fires a stream of electrons at high speed. These electrons bombard the inside of your TV screen.

The inside of the picture screen is painted with fluorescent paint of another substance which is sensitive to light. The gun aims its series of electrons at the screen. The inside of the screen glows with light when struck by electron bullets. The gun scans the screen from right to left, from top to bottom. The screen is covered 30 times a second to match the scanner in the studio.

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