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VOA慢速英语2010年-EXPLORATIONS - The Story of Radio

时间:2011-01-03 03:14来源:互联网 提供网友:hp2786   字体: [ ]
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STEVE EMBER: And I’m Steve Ember with EXPLORATIONS in VOA Special English. Today we tell about the history of radio and the latest technology.

(MUSIC)

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.

A group of radio listeners in Washington DC in the 1920s

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.

Guglielmo Marconi

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 Wireless1 Telegraph and Signal Company. The company opened the world’s first radio factory in Chelmsford, England in eighteen ninety-eight.

(MUSIC)

SHIRLEY GRIFFITH: 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.

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

STEVE EMBER: 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 decided2 to try it for the first time on December twenty-fourth. It was the first time a human voice had been heard on radio.

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

Fourteen years after Reginald 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 KDKA 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.

STEVE EMBER: Those first KDKA 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 KDKA 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.

SHIRLEY GRIFFITH: 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.

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, cellular3 telephones, radio-controlled toys and much more.

(MUSIC)

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 interfere4 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 amplitude5 modulation6. 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.

Radio personality Howard Stern in New York City during his first show on Sirius Satellite Radio in 2006

In the United States, people who want satellite radio programs can buy the services of the company Sirius XM. The company provides listeners with programs about music, news, sports, weather, politics and much more. Many of these programs do not include commercial advertising7. People can use these satellite radio services in their cars, homes or on portable devices. More and more radio stations are also broadcasting using digital radio technology.

STEVE EMBER: The Internet is also adding to the expansion of radio programming. Radio stations around the world can put their programs on the Internet for listeners everywhere to hear. The website Pandora began its Music Genome Project to create a database of song descriptions. Pandora’s Internet radio is able to predict what songs listeners will like based on their earlier musical choices. Listeners can create their own personalized radio programming with this and other forms of Internet radio.

We think Heinrich Hertz would look at all these developments and be very proud of the device he made that he thought would never be of any use.

(MUSIC)

SHIRLEY GRIFFITH: This program was written by Paul Thompson. It was produced by Dana Demange. I’m Shirley Griffith.

STEVE EMBER: And I’m Steve Ember. Our programs are online with transcripts8 and MP3 files at voaspecialenglish.com. And you can find us on Twitter, Facebook and YouTube at VOA Learning English. Join us again next week for EXPLORATIONS in VOA Special English.


点击收听单词发音收听单词发音  

1 wireless Rfwww     
adj.无线的;n.无线电
参考例句:
  • There are a lot of wireless links in a radio.收音机里有许多无线电线路。
  • Wireless messages tell us that the ship was sinking.无线电报告知我们那艘船正在下沉。
2 decided lvqzZd     
adj.决定了的,坚决的;明显的,明确的
参考例句:
  • This gave them a decided advantage over their opponents.这使他们比对手具有明显的优势。
  • There is a decided difference between British and Chinese way of greeting.英国人和中国人打招呼的方式有很明显的区别。
3 cellular aU1yo     
adj.移动的;细胞的,由细胞组成的
参考例句:
  • She has a cellular telephone in her car.她的汽车里有一部无线通讯电话机。
  • Many people use cellular materials as sensitive elements in hygrometers.很多人用蜂窝状的材料作为测量温度的传感元件。
4 interfere b5lx0     
v.(in)干涉,干预;(with)妨碍,打扰
参考例句:
  • If we interfere, it may do more harm than good.如果我们干预的话,可能弊多利少。
  • When others interfere in the affair,it always makes troubles. 别人一卷入这一事件,棘手的事情就来了。
5 amplitude nLdyJ     
n.广大;充足;振幅
参考例句:
  • The amplitude of the vibration determines the loudness of the sound.振动幅度的大小决定声音的大小。
  • The amplitude at the driven end is fixed by the driving mechanism.由于驱动机构的作用,使驱动端的振幅保持不变。
6 modulation mEixk     
n.调制
参考例句:
  • The soft modulation of her voice soothed the infant. 她柔和的声调使婴儿安静了。
  • Frequency modulation does not allow static to creep in. 频率调制不允许静电干扰混入。
7 advertising 1zjzi3     
n.广告业;广告活动 a.广告的;广告业务的
参考例句:
  • Can you give me any advice on getting into advertising? 你能指点我如何涉足广告业吗?
  • The advertising campaign is aimed primarily at young people. 这个广告宣传运动主要是针对年轻人的。
8 transcripts 525c0b10bb61e5ddfdd47d7faa92db26     
n.抄本( transcript的名词复数 );转写本;文字本;副本
参考例句:
  • Like mRNA, both tRNA and rRNA are transcripts of chromosomal DNA. tRNA及rRNA同mRNA一样,都是染色体DNA的转录产物。 来自辞典例句
  • You can't take the transfer students'exam without your transcripts. 没有成绩证明书,你就不能参加转学考试。 来自辞典例句
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TAG标签:   VOA慢速英语  expansion
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