Welcome to You Ask Andy

Betsy Blanchard, age 13, of Indianapolis, Indiana, for her question:

Why does radio work on different channels?

When you want to change programs on the radio, you turn a dial. Your radio switches to another channel or band of radio frequencies, and tunes in another show. It is so easy to do, and yet, behind that flip of the dial lies the whole story of the magic of radio:

The story begins with a miracle of math called the electromagnetic spectrum: This is a band of assorted wave lengths of energy, ranging from very short at one end to very long at the other end. A very small part of the electromagnetic spectrum consists of the rainbow colored wave lengths that we see as visible light. The shortest colored waves are the blues and 'shorter still are the invisible rays of ultraviolet.  Xrays are shorter than ultraviolet and gamma rays have still shorter wave lengths.

The longest waves of visible electromagnetic energy are at the red end of the rainbow spectrum. Next comes longer waves of invisible infrared, and after that comes a wide band of still longer waves of radio energy. Like all electromagnetic energy, radio energy travels at the speed of light. Its beams must travel in straight lines  they cannot bend or god around corners. A radio station uses these straight, speedy beams to carry its broadcasts. It sends them fanning out from the station in all directions. To them it adds the electrical impulses of the actual broadcast, to be carried far and wide as the long waves speed silently and invisibly in all directions.

A radio set is a receiver made to pick up the carrier waves and translate their coded impulses back into sounds thatyour ears can hear. The band of different radio wave lengths is very wide and a station could broadcast on any one of many frequencies. But at the receiving end, this would mean chaos. You must be able to choose the program you want to' hear. Your channel selector must be able to tune in to tae channel at a time or you will receive a jumble of sounds from several stations.

To avoid tangles and jangles of this kind, the Federal Communications Commission of our government has set up a radio traffic system. Anyone wishing to broadcast must ask permission. If permission is granted, the broadcaster is allotted a small slot in the radio section of the electromagnetic spectrum. He can send code bearing carrier waves with a certain number and nobody else may use or interfere with his number.

The number refers to kilocycles, the alternating wave lengths of radio. Each kilocycle equals 1,000 pulses of radio energy per second. Most commercial radio broadcasts are within a range of 550 to 1500 kilocycles. Within this range, each station has its own range of 10 kilocycles and no

one else can broadcast on this frequency. This is its channel. This is .... the band of radio wave lengths your channel selector tunes in when you turn the dial to the right station.

Other people, of course, besides commercial stations use radio. These broadcasters 8re allotted their own wave lengths outside the range of commercial stations. Police cars and taxi cabs use shorter radio frequencies. Chances are, your set is not made to pick up these radio waves. You need a special short wave radio set to pick up and translate their messages into sounds. Many boys and girls and people of all ages make a hobby of short wave radio. There are a quarter of a million amateur radio operators in America. All of them spend hours of fascinating fun. And many have saved lives by picking up distress signals' from foundering ships and relaying the news to the proper rescue squads.

 

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