What progress has radio technology made?

1820, Danish physicist Oster found that when the current passes through a metal wire, the magnetic needle placed near it will deflect. Then, Faraday, an apprentice British physicist, clearly pointed out that Oster's experiment proved that "electricity produces magnetism". He also discovered the phenomenon that a wire moves in a magnetic field to generate current through arduous experiments, which is called "electromagnetic induction".

Maxwell, a famous scientist, further expressed the research results of Faraday and others with mathematical formulas and extended the theory of electromagnetic induction to space. He thinks that there will be a changing electric field around the changing magnetic field, and there will be a changing magnetic field around the changing electric field. If you push it away layer by layer like water waves, you can spread the alternating electromagnetic field far away. As a result, Maxwell became the first person in human history to predict the existence of electromagnetic waves.

But the existence of electromagnetic waves is proved by Hertz. 1887 One day, Hertz was doing an experiment in a dark room. He applied high voltage to two closely spaced metal balls, followed by a crackling spark discharge. At this time, an unopened ring appeared behind him. When Hertz narrowed the opening of the ring to a certain extent, he saw sparks passing through the gap. Through this experiment, he came to the conclusion that electromagnetic energy can travel through space. The discovery of Hertz has opened up an infinitely broad prospect for human beings to use electromagnetic waves.

Hertz first confirmed the existence of electromagnetic waves by flashing sparks, but he flatly denied the possibility of using electromagnetic waves to communicate. However, the flash of Hertz electric spark lit the way for two young foreign inventors. 1895, Russian youth popov and Italian youth Marconi invented the wireless telegraph respectively and bravely broke into the "forbidden zone" defined by Hertz. On May 6th, 2008, Marconi successfully conducted radio communication in Bristol Strait.

Since Marconi invented the wireless telegraph in 1895, scientists began to study the use of electromagnetic waves to transmit voice information. 1896, the French inventor Leiblang (1857~ 1923) put forward the idea of using electromagnetic waves to spread sound, and modulated high-frequency electromagnetic waves with sound signals. The birth of the electron tube created conditions for the invention of radio broadcasting.

After Marconi invented the wireless telegraph, it attracted the attention of all countries in the world. The Meteorological Bureau of USDA decided to transmit weather forecast by wireless telegraph to serve agricultural production. 1900, the bureau hired Fessenden, a professor of physics at the University of Pittsburgh, to do the experiment of radio transmission of meteorological information. Professor Fessenden wants to use electromagnetic waves to spread sound in his experiments. He began to experiment with radio broadcasting according to the principle of amplitude modulation proposed by Leiblang. By 190 1, the experiment had achieved initial results. After five years of research, he invented the world's first radio station. This radio station is located in Massachusetts, and its transmitting antenna is a wireless telegraph antenna borrowed from the National Electric Signal Company of the United States, with a height of 128 meters. Powered by alternator, the power is 65,438+0 kW. On Christmas Eve, 65,438+0,906, voice and music were tested for the first time and successfully broadcast.

The transmitting and receiving principle of radio broadcasting is: the sound information such as language and music passes through the audio signal output by the audio amplifier and the high-frequency oscillation signal generated by the audio oscillator, and then becomes a high-frequency amplitude-modulated oscillation signal through the modulator, and then is sent to the antenna of the transmitting station through the high-frequency amplifier to emit electromagnetic waves into the air. After receiving this electromagnetic wave, the radio first becomes a high-frequency current. However, this current is very weak. Need to amplify, and then use the detector to detect, detect the audio current. After audio amplification, it is sent to the speaker to become the original language and music sound.