Radio is an electromagnetic wave with a relatively long wavelength. To understand the working principle of a radio transmitter, we must start with a character named Faraday.
Faraday
British scientist Faraday was the first to discover the phenomenon of electromagnetic induction. When a conductor cuts magnetic induction lines in a magnetic field, or when the magnetic field in a conductive coil changes, electric current is generated in the circuit. According to this law, Faraday invented the generator, and then various appliances emerged like mushrooms after rain. The most typical example is the invention of light bulbs, telephones, wired telegrams, electric motors, and other appliances, and people entered the era of electrical appliances.
But why does the magnetic field generate current in these situations? Faraday did not think clearly. Because Faraday's family was poor when he was young, and he dropped out of elementary school after only two years. His great achievements in later years were achieved through his love for science and his spirit of hard work and research. Therefore, Faraday was not very strong in mathematics and always liked to express physical laws in a visual way, but found it difficult to explain his great discoveries in mathematical language.
At this moment, another great figure, Maxwell, appeared.
Maxwell was forty years younger than Faraday, and when he graduated from Cambridge University at the age of 23, he read Faraday's scientific papers. He was attracted by Faraday's profound thinking and was determined to use mathematics to make up for his shortcomings. One year later, he published his first paper on electromagnetics and had in-depth discussions with Faraday.
Faraday was a great scientist and also a person of noble character, who was particularly concerned about young scholars. He said to Maxwell, "Don't just limit yourself to explaining my viewpoint mathematically, but innovate.". Encouraged by the older generation of scientific giants, Maxwell ultimately successfully proposed the Maxwell equations, becoming the greatest physicist between Newton and Einstein.
Maxwell pointed out that a changing electric field can generate a magnetic field, and a changing magnetic field can also generate an electric field. What's even more magical is that oscillating electric and magnetic fields can excite each other, propagate towards the distance, and form a substance similar to waves, named electromagnetic waves.
Maxwell calculated the speed of electromagnetic waves, which happened to be the same as the speed of light. Therefore, Maxwell boldly predicted that light is a type of electromagnetic wave.
Unfortunately, he did not personally confirm his prediction of electromagnetic waves. In 1879, Maxwell passed away in Cambridge at the age of only 48. And in that year, the greatest scientist of the last century, Einstein, happened to be born.
hertz
The baton of science passed to German scientist Heinrich Rudolf Hertz.
Connect the battery, inductor, and capacitor in one circuit, and connect two copper bars that are very close together at both ends of the circuit. If the switch in the circuit is closed and then opened, oscillating current will be generated in the circuit under the action of inductance. Moreover, the oscillation frequency of this current is very high, ranging from millions to tens of millions of times per second. At this time, the air between the two copper rods will be broken down, forming sparks and emitting electromagnetic waves.
Hertz also placed a similar device on the other end, but without a battery. Hertz carefully adjusted the receiving device and found that at a certain moment, when there was a spark between the two copper bars of the transmitting device, there was also a spark between the two copper bars of the receiving device. This indicates that the natural frequencies of the two devices are the same, and there is an electrical resonance phenomenon similar to mechanical resonance. This phenomenon indicates that a wave has propagated from the transmitting device to the receiving device.
Hertz carefully studied the wavelength, frequency, and other information of this wave, and concluded that the speed of this wave is equal to the speed of light, which is completely consistent with Maxwell's prediction. At this point, electromagnetic waves have been thoroughly confirmed by people.
The Hertz experiment not only confirmed Maxwell's electromagnetic theory, but also found a way for the development of radio, television, and radar. The mobile phones that we cannot live without today are also transmitted through electromagnetic waves.
There are many benefits to using radio to transmit signals, such as vacuum not being able to propagate mechanical waves. While shouting in space is inaudible to others, electromagnetic waves can be transmitted in a vacuum. Therefore, astronauts on the moon need to use radio communication even if they are further away. The wireless signal transmission speed is very fast. If we shout a sentence from New York, even if it spreads unobstructed, it will take nine hours for people in Beijing to hear it. But the speed of radio propagation is the speed of light, and it can almost spread all over the world in an instant. Moreover, electrical signals are easier to amplify and process than mechanical signals. Since the day electromagnetic waves were discovered, people have been studying how to use radio for communication.
Wireless telegraphy
When electromagnetic waves were discovered, people had already invented wired telegraphy. However, this method faces many problems such as laying wires, maintenance and upkeep, and people urgently need to transmit information through wireless means. Therefore, wireless telegraphy has been put on the agenda by many scientists and businessmen. Antenna factory
There are three scientists who have contributed to the invention of wireless telegraphy: Serbian American scientist Nikolat Sla, Italian scientist Marconi, and Russian scientist Popov.
In 1893, Nikola Tesla first publicly demonstrated wireless communication in St. Louis, Missouri, and obtained a patent for wireless technology in the United States in 1897. However, the United States Patent Office revoked its patent rights in 1904. This move is said to be due to Tesla's obsession with his dream of transmitting electricity wirelessly for the benefit of humanity, while ignoring the urgent need for wireless telegraphy among capitalists such as Thomas Edison, Andrew Carnegie, and Morgan. They then threw an olive branch at a new scientist, who was Italian Marconi.
In 1901, Marconi successfully transmitted radio messages across the Atlantic from England to Newfoundland, Canada. In 1909, radio first came into play. A steamship was destroyed in a collision and sank to the bottom of the sea. Due to the function of radio, most of the crew members were rescued. In the same year, Marconi was awarded the Nobel Prize, and he was known as the father of radio.
Almost at the same time, Russian scientist Popov also invented the radio device - the radio. He also installed an antenna on the radio, which was the first antenna of humanity. In 1896, Popov officially conducted a radio transmission of a piece of information called "Heinrich Hertz" at the annual meeting of the Russian Physical and Chemical Association to show respect for Hertz.
Who was the first to invent radio, different countries have different opinions. Even in a country, the saying is constantly changing. For example, although the United States revoked Tesla's patent in 1904 and granted it to Marconi, decades later in 1943, the US Supreme Court revoked Marconi's patent and still ruled that Tesla was the inventor of radio. Anyway, they are all great scientists who have provided infinite convenience to our world.