The principle of radio technology is that the change of current intensity in conductor will produce radio waves. Using this phenomenon, information can be loaded on radio waves by modulation. When radio waves propagate through space and reach the receiving end, the electromagnetic field changes caused by radio waves will generate current in the conductor. Through demodulation, information is extracted from the current change to achieve the purpose of information transmission.
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find
Maxwell expounded the theoretical basis of electromagnetic wave propagation for the first time in his paper "Theory of Electromagnetic Field Dynamics" submitted to the Royal Society. His work was completed between 186 1 and 1865.
Heinrich rudolf hertz first verified Maxwell's theory through experiments from 1886 to 1888. He proved that radio radiation has all the characteristics of waves, and found that the electromagnetic field equation can be expressed by partial differential equation, which is usually called wave equation.
1906 On Christmas Eve, Reginald Fessenden realized the first radio broadcast in history by heterodyne method in Massachusetts, USA. Fissenden played clips of himself playing Silent Night and reciting the Bible with the violin. Marconi Research Center in chelmsford, England, launched the world's first formal broadcast entertainment program at 1922!
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invent
There is still controversy about who invented the radio station.
1893, nikola tesla publicly demonstrated radio communication for the first time in St. Louis, Missouri, USA. He described and demonstrated the basic principles of radio communication in the reports of Franklin College in Philadelphia and the National Electric Light Association. The instrument he made contains all the basic components of the radio system before the invention of the electron tube.
Guillermo Marconi holds the British patent number, which is widely regarded as the world's first patent on radio technology. 12039, "improvement of electric pulse and signal transmission technology and required equipment".
Nikola tesla 1897 obtained the patent of American radio technology. However, in 1904, the US Patent Office revoked its patent right and granted Marconi a patent for inventing radio instead. This move may be influenced by Marconi's economic supporters in the United States, including Edison and andrew carnegie. 1909, Marconi and karl ferdinand braun won the Nobel Prize in Physics for their contribution to the invention of wireless telegraph.
1943, shortly after Tesla's death, the US Supreme Court re-affirmed Tesla's patent. This decision admitted that his invention had been completed before Marconi's patent. Some people think that this decision is obviously for economic reasons. In this way, the US government in World War II can avoid paying Marconi patent royalties.
1898, Marconi opened the world's first radio factory in Hall Street, chelmsford, England, with about 50 employees.
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The use of radio
Radio was first used in navigation, using Morse telegraph to transmit information between ships and land. Nowadays, radio has many applications, including wireless data network, various mobile communications and radio broadcasting.
The following are the main applications of some radio technologies:
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connect
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sound
* The earliest form of sound broadcasting was wireless telegraph at sea. It uses a switch to control whether to emit continuous waves, so as to generate intermittent sound signals at the receiving end, that is, Morse code.
* AM broadcasting can spread music and sound. AM broadcasting adopts amplitude modulation technology, that is, the greater the volume received by the microphone, the greater the energy emitted by the radio station. This signal is susceptible to interference such as lightning or other interference sources.
* Compared with AM broadcasting, FM broadcasting can spread music and sound with higher fidelity. For frequency modulation, the greater the volume received by the microphone, the higher the frequency of the transmitted signal. FM broadcasting works at a very high frequency (VHF). The higher the frequency band, the wider the frequency bandwidth it has, so it can accommodate more radio stations. At the same time, the shorter the wavelength, the closer the propagation of radio waves is to the linear propagation of light waves.
* The sideband of FM broadcasting can be used to spread digital signals, such as logo, program name introduction, website, stock market information, etc. In some countries, FM radio can automatically find the original channel according to the sideband information after moving to a new area.
VHF AM technology is applied to voice stations used in navigation and aviation. This makes it possible to use light antennas on airplanes and ships.
* Government, fire fighting, police and commercial radio stations usually use narrowband FM technology on dedicated frequency bands. These applications usually use a bandwidth of 5KHz. Compared with the 16KHz bandwidth of FM radio or TV sound, fidelity is sacrificed.
:: Civil or military high-frequency voice services use short waves to communicate between ships, planes or isolated locations. In most cases, single sideband technology is used, which can save half of the frequency band and use the transmission power more effectively compared with amplitude modulation technology.
* Terrestial Trunked Radio (TETRA) is a digital trunked telephone system designed for special departments such as military, police and first aid.
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telephone
* Mobile phone or mobile phone is the most widely used wireless communication method at present. The coverage area of a cellular phone is usually divided into multiple cells. Each cell is covered by a base station transmitter. Theoretically, the shape of the cell phone battery is a honeycomb hexagon, which is also the source of the cell phone name. At present, the widely used mobile phone system standards include GSM, CDMA and TDMA. Some operators have started to provide the next generation 3G mobile communication services, and the leading standards are UMTS and CDMA2000.
* There are two types of satellite phones: Inmarsat and Iridium system. Both systems provide global coverage services. INMARSAT uses geosynchronous satellites and needs directional high-gain antennas. Iridium is a low-orbit satellite system, which directly uses mobile phone antenna.
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TV
* Usually, analog TV signals are transmitted in the same signal through amplitude modulation, audio modulation and synthesis.
* Digital TV adopts MPEG-2 image compression technology, which only needs about half the bandwidth of analog TV signal.
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Emergency radio communication service
* Emergency position indicating radio beacon, emergency positioning transmitter or personal positioning beacon is a small radio transmitter, which is used for positioning or measuring by satellite in an emergency. Its function is to provide rescuers with the exact location of the target, so as to provide timely rescue.
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data transmission
* Digital microwave transmission equipment, satellites, etc. Quadrature amplitude modulation (QAM) is usually used. QAM modulation uses the amplitude and phase of the signal to load information. In this way, more data can be transmitted on the same bandwidth.
* IEEE 802. 1 1 is the current wireless LAN standard. Using 2GHz or 5GHz frequency band, the data transmission rate is 1 1 Mbps or 54 Mbps.
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identify
* Active and passive radios can be used to identify and indicate the identity of objects.
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other
* Amateur radio is radio communication in which radio enthusiasts participate. Amateur radio stations can use many open frequency bands in the whole spectrum. Fans use different coding methods and techniques. Some later commercial technologies, such as frequency modulation, single sideband amplitude modulation, digital packet radio and satellite signal transponder, were first applied by amateurs.
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navigate by water/air
All satellite navigation systems use satellites with precise clocks. Navigation satellites broadcast their position and time information. The receiver simultaneously receives signals from multiple navigation satellites. The receiver measures the propagation time of the radio wave to obtain its distance to each satellite, and then calculates its precise position.
* Roland system also uses the propagation time of radio waves for positioning, but its transmitting stations are all located on land.
* VOR system is usually used for flight positioning. It uses two transmitters. A directional transmitter always transmits and rotates at a fixed rate like a beacon. When the directional transmitter faces north, another omni-directional transmitter will transmit pulses. The aircraft can receive the signals of two VOR stations, so as to determine its position by calculating the intersection of the two beams.
* Radio positioning is the earliest form of radio navigation. Radio direction finding uses a movable loop antenna to find the direction of a radio station.
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radar
* Radar calculates the distance of the target by measuring the delay of reflected radio waves. And the surface type of the target is caused by the polarization and frequency of the reflected wave.
* Navigation radar uses ultrashort wave to scan the target area. Generally, the scanning frequency is two to four times per minute, and the terrain is determined by reflected waves. This technology is usually used in merchant ships and long-haul commercial aircraft.
* Multi-purpose radar usually uses the frequency band of navigation radar. However, the pulse it emits is modulated and polarized to determine the surface type of the reflector. Excellent multi-purpose radar can distinguish rainstorm, land and vehicles.
* Search radar uses short-wave pulses to scan the target area, usually 2-4 times per minute. Some search radars use Doppler effect to distinguish moving objects from background.
* The homing radar adopts a similar principle to the search radar, but it can scan a small area quickly and repeatedly, usually up to several times per second.
* Weather radar is similar to search radar, but uses circularly polarized waves and wavelengths that are easily reflected by water droplets. Some weather radars also use Doppler effect to measure wind speed.
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hot
* Microwave ovens use high-power microwaves to heat food. (Note: A common misunderstanding is that the frequency used by microwave ovens is the * * * vibration frequency of water molecules. In fact, the frequency used is about one tenth of the vibration frequency of water molecules. )
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motive power
* Radio waves will produce weak electrostatic and magnetic forces. Under microgravity conditions, this can be used to fix the position of objects.
:: Aerospace power: It has been proposed that the pressure generated by high-intensity microwave radiation can be used as the power for interstellar probes.
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astronomy
* The physical and chemical properties of celestial bodies can be studied through the radio wave signals sent by cosmic celestial bodies received by radio astronomical telescopes. This subject is called radio astronomy.