UNITS

SHIRLEY GRIFFITH: Our story begins in Britain in eighteen seventy-three. A scientist named James Maxwell wrote a mathematical theory about a kind of energy. He called this energy electromagnetic waves.

His theory said this kind of energy could pass unseen through the air. James Maxwell was not able to prove his idea. Other scientists could not prove it either until German scientist Heinrich Hertz tried an experiment around eighteen eighty-seven.

STEVE EMBER: Hertz’s experiment sounds very simple. He used two pieces of metal placed close together. He used electricity to make a spark jump between the two pieces of metal. He also built a simple receiver made of wire that was turned many times in a circle or looped. At the ends of the loop were small pieces of metal separated by a tiny amount of space. The receiver was placed several meters from the other device.

Heinrich Hertz proved that James Maxwell’s idea was correct. Electromagnetic waves or energy passed through the air from one device to the other.

SHIRLEY GRIFFITH: Later, Hertz demonstrated the experiment to his students in a classroom. One of the students asked what use might be made of this discovery. But Hertz thought his discovery was of no use. He said it was interesting but had no value.

He was wrong. His experiment was the very beginning of the electronic communications we use today. In recognition of his work, the unit of frequency of a radio wave, one cycle per second, is named the hertz.

STEVE EMBER: Radio waves became known to scientists as Hertzian Waves. But the experiment was still of no use until Guglielmo Marconi improved on the device that created Hertzian Waves. He began his experiments in Italy in eighteen ninety-four.

Marconi was soon able to transmit sound across a distance of several kilometers. He tried to interest Italian government officials in his discovery, but they were not interested.

Marconi traveled to Britain. His invention was well received there. In eighteen ninety-seven, he established the Wireless Telegraph and Signal Company. The company opened the world’s first radio factory in Chelmsford, England in eighteen ninety-eight.

Very quickly, people began sending and receiving radio messages across long distances using equipment made by Marconi’s company.

Ships at sea needed the device. Before Marconi’s invention, they had no communication until they arrived in port. With radio, ships could call for help if they had trouble. They could send and receive information.

STEVE EMBER: Now we will explain electromagnetic waves. We will begin with Heinrich Hertz’s experiment. You can also try this experiment. First, move the controls on your radio to an area where no station is being received.

Now, you will need a common nine-volt battery and a metal piece of money. Hold the battery near the radio and hit the top of the battery with the coin. You should hear a clicking noise on the radio.

Your coin and battery are a very simple radio transmitter. This radio will not transmit very far. However, if you know a little of Morse code, you could communicate with this device.

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.