VOA慢速英语2018--July 23, 2003: History of Radio（在线收听）

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VOICE ONE:

This is Steve Ember.

VOICE TWO:

And this is Faith Lapidus with the VOA Special English program EXPLORATIONS. You are listening to our program today on a radio. Almost no communication would exist in the world without the electromagnetic waves that make radio possible. Today we explain the history of radio and tell how it works.

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VOICE ONE:

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. Mister Maxwell was not able to prove his idea. Other scientists could not prove it either until German scientist Heinrich Hertz tried an experiment in eighteen-eighty-seven.

VOICE TWO:

Mister 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. This receiver was placed several meters from the other device.

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

VOICE ONE:

Later, Mister Hertz demonstrated the experiment to his students in a classroom. One of the students asked what use might be made of this discovery. But Mister 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 every kind of 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.

VOICE TWO:

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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.

Mister 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.

Mister 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.

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VOICE ONE:

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

Ships at sea needed the device. Before Mister 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.

All of Mister Marconi’s radios communicated using Morse code. It sounds like this. What you will hear are three letters. V-O-A. We will repeat, or send, each group of three letters two times.

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An expert with Morse code could send and receive thirty or forty words a minute. Mister Marconi’s radio greatly increased the speed of communications.

VOICE TWO:

On December twenty-fourth, nineteen-oh-six, radio operators on ships in the Atlantic Ocean near the American coast began hearing strange things. At first it was violin music. Then they heard a human voice. The voice said “Have a Merry Christmas.”

That voice belonged to a man named Reginald Fessenden. He had been working on producing a device that could transmit the human voice or music using radio. He decided to try it for the first time on December twenty-fourth. It was the first time a human voice had been heard on radio.

VOICE ONE:

Improvements in radio technology now came more quickly. Large companies became interested. Broadcasting equipment and radio receivers were improved.

Fourteen years after Mister Fessenden’s voice was heard by radio operators at sea, the first real radio broadcast was transmitted. It came from the city of Pittsburgh, Pennsylvania.

The radio program was transmitted on radio station K-D-K-A on the evening of November second, nineteen-twenty. The man speaking on the radio was Leo Rosenberg. He was announcing the early results of the presidential election between James Cox and Warren Harding.

Within a year, the little radio station employed the world’s first full-time radio announcer. His name was Harold Arlin. K-D-K-A in Pittsburgh is still a successful radio station today. Oh, and Mister Harding won the presidential election!

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VOICE TWO:

Those first K-D-K-A broadcasts led to the success of the radio industry. People began buying the first radios. Other companies decided radio could make a profit. Only four years after the first K-D-K-A broadcast, there were six-hundred radio stations in the United States. Radio stations also began to broadcast in other countries.

Radio stations began selling “air time” as a way to pay their workers and to pay for needed equipment. A few minutes of air time were sold to different companies so they could tell about their products to the radio station’s listeners. This method of supporting radio and later television is still used today.

VOICE ONE:

Radio changed the way people thought and lived. It permitted almost everyone to hear news about important events at the same time. Political candidates could be heard by millions of listeners. The same songs were heard across the country.

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The work by British scientist James Maxwell and German scientist Heinrich Hertz led to the development of modern communications technology. This includes television broadcasts, satellite use, cellular telephones, radio-controlled toys, and much more.

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VOICE TWO:

Now we will explain electromagnetic waves. We will begin with Mister Hertz’s experiment. You can also try this experiment. It is very easy to do. 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.

VOICE ONE:

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.

Most radio frequencies around the world are named after Heinrich Hertz. For example, one popular radio station in Washington, D-C broadcasts on six-hundred-thirty kilohertz. This is called a medium wave. The kilo means thousand. The hertz means cycles or waves per second.

VOICE TWO:

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. Mega means a million. 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.

Short wave can be heard for very long distances, but sometimes the signal is not clear. However, radio technology continues to improve. Today, V-O-A broadcasts to satellites in space that send the signal back to stations on the ground that transmit programs with a clear signal.

It is even possible today to use a computer to link with thousands of radio stations around the world. We think Mister Hertz would be very proud of the little device he thought would never be of any use.

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VOICE ONE:

This program was written by Paul Thompson. It was produced by Mario Ritter. This is Steve Ember.

VOICE TWO:

And this is Faith Lapidus. Join us again next week for another EXPLORATIONS program in Special English on the Voice of America.