SHIRLEY GRIFFITH: Electromagnetic energy travels almost like an ocean wave – up and down, up and down. It also travels at the speed of light – two hundred ninety-nine million seven hundred ninety-two thousand four hundred fifty-eight meters each second.
Scientists have learned how to separate radio waves into different lengths called frequencies. This permits many radio stations to broadcast at the same time and not interfere with each other.
STEVE EMBER: You may be hearing our broadcast on what is called short wave. These are frequencies between three thousand and thirty thousand kilohertz. They are often called megahertz. One megahertz is the same as one thousand kilohertz.
Short wave is good for broadcasting very long distances. The short wave signals bounce off the ionosphere that surrounds the Earth, back to the ground and then back to the ionosphere.
The first radio broadcasts were made using amplitude modulation. AM radio can be sent over larger distances, but the quality of the sound is not as good as a later kind of radio signal processing, called frequency modulation. FM radio stations transmit in a range of frequencies between eighty-eight and one hundred eight megahertz. AM radio is between five hundred thirty-five and seventeen hundred kilohertz.
SHIRLEY GRIFFITH: Radio technology continues to improve. Today, VOA broadcasts to satellites in space that send the signal back to stations on the ground that transmit programs with a clear signal.
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2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25
2013-11-25