Introduce The Main Applications Of Some Radio Technologies
Radio is the electromagnetic wave that is propagated in all free spaces (including air and vacuum), which is one of the finite frequency bands with an upper frequency at 300GHz (gigahertz) and the lower limit frequency is less uniform in various RF specifications, common with 3KHz ~ 300GHz (ITU-International Telecommunication Union), 9KHz ~ 300GHz, 10KHz ~ 300GHz.
Radio technology is the technology that propagates signals through radio waves. The principle of radio technology is that changes in the current in the conductor will produce radio waves. With this phenomenon, the information can be loaded on the radio wave by modulation. When the radio waves spread through the space to reach the receiver, radio waves caused by changes in the electromagnetic field will produce current in the conductor. Through the demodulation of information from the current changes in the extraction, to achieve the purpose of information transmission.
The earliest use of radio in the sailing, the use of Morse telegraph in the ship and land transfer information. Radio has a variety of applications, including wireless data networks, a variety of mobile communications and radio and so on.
The following are the main applications of some radio technologies:
Wireless communication in the modern communication occupies an extremely important position, almost any field using wireless communications, including commercial, meteorological, financial, military, industrial, civilian and so on. We can from the communication system, modulation, multiple access and other aspects of the wireless communication system can see a wide range of types. FM, LSB, USB, ISB, FSK, PSK, MSK, GMSK, QAM and other multiple access methods, such as AM, FM, LSB, USB, ISB, FSK, PSK, MSK, GMSK, QAM, etc. (TDMA), frequency division multiple access (FDMA), and code division multiple access (CDMA).
* The earliest form of sound broadcasting is the nautical radio telegraph. It uses a switch to control the transmission of a continuous wave, thereby generating an intermittent sound signal at the receiver, i.e., the Morse code.
* AM broadcasts can spread music and sound. AM broadcast using amplitude modulation technology, that is, the greater the volume received at the microphone, the radio is also the greater the energy emitted. Such signals are susceptible to interference such as lightning or other sources of interference.
* FM radio can spread music and sound more than fidelity broadcasts. For frequency modulation, the higher the volume received at the microphone, the higher the frequency of the transmitted signal. FM radio work in very high frequency (Very High Frequency, VHF). The higher the band, the greater the frequency bandwidth it has, and thus can accommodate more radio stations. At the same time, the shorter the wavelength of the radio waves spread closer to the light wave propagation characteristics.
* FM radio sideband can be used to spread digital signals such as station identification, program name introduction, website, stock market information. In some countries, when moved to a new area, the FM radio can automatically automatically find the original channel based on the sideband information.
* Nautical and aeronautical use of voice stations using VHF AM technology. This allows the use of light antennas on airplanes and ships.
* Government, fire, police and commercial use of radio stations are usually used in special frequency band narrowband FM technology. These applications typically use 5KHz of bandwidth. Relative to the FM radio or television sound 16KHz bandwidth, fidelity had to make sacrifices.
* Civil or military high frequency voice services use shortwave for communication between ships, airplanes or isolated locations. In most cases, single-sideband technology is used, which saves half the frequency band relative to AM technology and makes more efficient use of transmit power.
* Terrestrial Trunked Radio (TETRA) is a digital trunking telephone system designed for special departments such as military, police, and first aid.
* Cellular phones or mobile phones are the most commonly used wireless communication methods. The cell phone coverage area is usually divided into multiple cells. Each cell is covered by a base station transmitter. Theoretically, the shape of the cell is a honeycomb hexagon, which is also the source of the cell phone name. Currently widely used mobile phone system standards include: GSM, CDMA and TDMA and LTE. 3G mobile communication services provided by operators, the leading standards for UMTS and CDMA2000, operators of 4G mobile communications services TD-LTE and FDD-LTE.
* Satellite phones exist in two forms: INMARSAT and Iridium systems. Both systems provide global coverage services. INMARSAT uses geostationary satellites that require directional high gain antennas. Iridium is a low-orbiting satellite system that uses mobile phone antennas directly
* The usual analog TV signal uses the image amplitude modulation, audio frequency modulation and synthesis in the same signal transmission.
* Digital TV using MPEG-2 image compression technology, which only need to simulate half of the bandwidth of the TV signal.