Invention process
Maxwell first clarified the theoretical basis of electromagnetic wave propagation in his paper "The Dynamic Theory of Electromagnetic Fields" submitted to the Royal Society. These works were completed between 1861 and 1865.
In 1864, British scientist Maxwell established a complete electromagnetic wave theory based on summarizing previous studies of electromagnetic phenomena. He concluded that electromagnetic waves exist and deduced that electromagnetic waves and light have the same propagation speed. In 1887, German physicist Hertz experimentally confirmed the existence of electromagnetic waves. After that, people conducted many experiments, which not only proved that light is a kind of electromagnetic wave, but also discovered more forms of electromagnetic waves. Their essence is exactly the same, but the wavelength and frequency are very different.
Heinrich Rudolf Hertz first verified Maxwell's theory experimentally between 1886 and 1888. He demonstrated that radio radiation has all the properties of a wave and discovered that the equations of the electromagnetic field can be expressed in terms of partial differential equations, often called wave equations.
In 1893, Nikola Tesla publicly demonstrated wireless communications for the first time in St. Louis, Missouri, USA. In lectures to the Franklin Institute in Philadelphia and to the National Electric Light Association, he described and demonstrated the basic principles of radio communications. The instrument he built contained all the basic elements of radio systems that preceded the invention of the vacuum tube. Nikola Tesla patented radio technology in the United States in 1897. However, the U.S. Patent Office revoked his patent in 1904 and instead granted Marconi a patent for his invention of radio. This move may have been the result of the influence of Marconi's financial backers in the United States, including Thomas Edison and Andrew Carnegie.
On Christmas Eve in 1906, Reginald Fessenden used the heterodyne method to achieve the first radio broadcast in history in Massachusetts, USA. Fessenden broadcast himself playing "Silent Night" on violin and reciting excerpts from the Bible. The Marconi Research Center in Chelmsford, England, launched the world's first regularly broadcast radio entertainment program in 1922.
Guglielmo Marconi (also translated as Guglielmo Marconi) holds what is generally regarded as the world's first patent for radio technology, British Patent No. 12039 , "Improvements in electrical pulse and signal transmission technology and the required equipment." In fact, Marconi only improved radio.
In 1909, Marconi and Karl Ferdinand Braun won the Nobel Prize in Physics "for their contribution to the invention of wireless telegraphy".
In 1943, shortly after Nikola Tesla's death, the U.S. Supreme Court reaffirmed the validity of Nikola Tesla's patent and declared Marconi's radio patent invalid. The U.S. Supreme Court recognized that Nikola Tesla's invention preceded Marconi's patent, granting his patent priority on key radio technology. Some believe this decision was made for financial reasons so that the U.S. government during World War II could avoid paying royalties to the Marconi Company.
In 1898, Marconi opened the world's first radio factory in Hall Street, Chelmsford, England, employing about 50 people.
Radio has gone through various stages of development, from tubes to transistors, to integrated circuits, from shortwave to ultra-shortwave, to microwaves, from analog to digital, from fixed use to mobile use. Radio technology has Become an important pillar of modern information society.
There is also Russian inventor Popov. Russians believe that he also invented radio in 1895.
The birth of radio more than 90 years ago, three weak and short signals "beep, beep, beep" were transmitted across the Atlantic Ocean 2,500 kilometers across the airwaves, announcing the birth of radio to the world.
It was December 12, 1901, and we set up camp to wait.
At Marconi on Signal Hill in Newfoundland, located in the southeastern corner of Canada, a receiving antenna was set up using balloons and kites, and finally received signals from Poldhu in the southwest corner of the United Kingdom. A high-power transmitting station transmits the "S" character in the International Morse Code. This was the first radio communication across the Atlantic Ocean in history. This experiment showed the world that radio was no longer a novelty limited to the laboratory, but a practical communication medium. This news caused a sensation around the world, aroused strong interest among radio enthusiasts, and promoted the vigorous development of the amateur radio movement.
Although Marconi's test results were quite exciting, most people at the time believed that radio behaved like light waves. After being launched, it would definitely move in a straight line. From the United Kingdom to Canada, no matter what, it would be impossible to complete a straight line. Radio communications (because the earth's surface is curved), scientific theories at the time even proved that radio waves launched from the UK must drive directly into space. How could they reach Canada? However, judging from the experimental records of Marconi's use of crude radio equipment to conquer long-distance communications, the signal can reach as far as 700 miles during the day and as far as more than 2,000 miles at night. These experimental data make the previous theory impossible. The inevitable result that was deduced began to waver.
At the same time, Mr. KENNELLY and Mr. HEAVISIDE put forward the same view respectively: there is an electron layer in the earth's atmosphere, which can refract radio waves back to the earth like a mirror without causing Straight into space, due to this refracted and returned signal, distant stations can communicate with each other. This electron layer that acts like a mirror on radio waves is called the KENNELLY HEAVISIDE layer, but today it is generally called the ionosphere (lonosphre). The reason why shortwave is so developed is due to the ionosphere.
Since 1925, many scientists have begun to explore the ionosphere. By transmitting radio pulse signals to the ionosphere, and then from the refracted echo (Echo) of the ionosphere, they can After understanding the natural phenomena of the ionosphere, the result is: the ionosphere above the earth is like a big umbrella covering the earth, and it changes with the changes of day or night or season. At the same time, it is found that certain frequencies can penetrate Passing through the ionosphere, some frequencies return to the surface at different angles. Although the ionosphere has been unveiled and a certain degree of understanding has been achieved, international shortwave communications have developed greatly. However, in the past sixty years, In the past, scientists have not missed any opportunity to continue studying the ionosphere. Even rocket launches, artificial satellite tests, and recent space shuttle flights have designed certain experiments in the hope of further understanding the ionosphere, with the help of ultra-high-speed computers. , through the hypothetical model, it is finally hoped that the ionospheric conditions in the next few days can be predicted like meteorology.
The history of radio development is, to a large extent, the history of people’s research and application of various bands. The first one to be used is the long-wavelength band, because the long-wavelength induced current on the earth's surface is small, the radio wave energy loss is small, and it can bypass obstacles. However, long-wave antenna equipment is bulky, expensive, and has small communication capacity, which prompts people to seek new communication bands. In the 1920s, amateur radio operators discovered that shortwave waves could travel great distances. The theory of the ionosphere appeared in 1931. The ionosphere is like the mirror Hertz said. It is best suited for reflecting short waves. Shortwave radios are economical and lightweight and are widely used in telecommunications and broadcasting. However, the ionosphere is affected by meteorology, solar activity and human activities, which reduces communication quality and reliability. In addition, short-wave band capacity cannot meet the growing needs. The shortwave band is 3MHz ~ 30MHz. If each shortwave station occupies a 4KHz frequency band, it can only accommodate a few thousand radio stations. Each country can only be allocated a very limited number of radio stations, and the TV station (8MHz) cannot be squeezed in. Since the 1940s, microwave technology has been developed in the world.
Microwaves are close to the frequency of light. They propagate in straight lines and can pass through the ionosphere without being reflected. Therefore, microwaves need to be reflected by relay stations or communication satellites before propagating to a predetermined distance.