Principle of radio technology
Radio refers to electromagnetic waves propagating in free space (including air and vacuum), and radio technology is a technology that propagates signals through radio waves. The principle of radio technology is based on the theory of electromagnetic waves, which states that a change in the strength of the current in a conductor produces radio waves. Using this phenomenon, information can be loaded onto the radio waves through modulation. When the radio wave travels through space and reaches the receiving end, the change in the electromagnetic field caused by the wave in turn generates a current in the conductor. By demodulating the information to be extracted from the current changes, the purpose of information transfer is achieved.
Radio frequency
Radio waves contain a rapidly vibrating magnetic field. The rate of vibration is the frequency of the wave, measured in hertz (Hz). 1 hertz is equal to one vibration per second. One kilohertz (kHz) is equal to 1,000 hertz. Different frequency bands are used to transmit different kinds of information.
Radio bands
Radio is classified by wavelength and frequency:
Long-wave: wavelength >1000 meters, frequency below 300KHz;
Medium-wave: wavelength 100m~1000m, frequency 300KHz~3000KHz;
Short-wave: wavelength 100m~10m, frequency 3MHz~30MHz;
Ultra-short wave: wavelength 1m~10m, frequency 30MHz~300MHz, also known as very high frequency (VHF) wave, meter wave;
Microwave: wavelength 1m~0.1mm, frequency 300MHz~3THz.
Applications
The earliest application of radio is in navigation, which uses the Morse telegraph to transmit information between ships and land. Radio has many applications, including wireless data networks, various mobile communications, and radio broadcasting.
The following are some of the major applications of radio technology:
Broadcasting
Amplitude Modulation (AM) broadcasting allows the transmission of music and sound. AM broadcasting uses amplitude modulation techniques, which means that the louder the volume received at the microphone, the more energy the station transmits. Such signals are susceptible to interference from sources such as lightning or other sources of interference. FM broadcasting can transmit music and sound with a higher degree of fidelity than AM broadcasting. For frequency modulation, the higher the volume received at the microphone, the higher the corresponding frequency of the transmitted signal. The higher the FM broadcast band, the greater the frequency bandwidth it has, thus allowing more stations to be accommodated. At the same time, the shorter the wavelength, the closer the propagation of radio waves is to the linear propagation of light waves. The sidebands of FM broadcasting can be used to transmit digital signals such as station logos, program synopses, web addresses, stock market information, etc.
Television
The usual analog signal combines image AM and accompanying FM in the same signal. Digital TV uses MPEG-2 image compression, which requires about half the bandwidth of an analog signal.
Telephone
Cellular or cellular telephones are the most common form of wireless communication today. Cellular telephone coverage is usually divided into zones, each covered by a base station transmitter; usually each zone is shaped like a honeycomb hexagon, which is where cellular telephony gets its name. Currently widely used cellular telephone modes include GSM, CDMA, and TDMA.
Data transmission
Digital microwave transmission equipment, satellites, etc. usually use quadrature amplitude modulation.QAM modulation utilizes both signal amplitude and phase loading information. This allows a larger amount of data to be transmitted over the same bandwidth.
Bluetooth
Bluetooth is a short-range wireless communication technology. It can support communication or data transfer between portable computers, cellular phones, and other mobile devices.
Recognition
The use of active or passive radio devices can recognize or indicate the identity of the object.RFID, that is, radio frequency identification, commonly known as electronic tags.RFID radio frequency identification is a kind of non-contact automatic diagnosis technology, it through the radio frequency signal automatic diagnosis of the target and obtain the relevant data, the recognition of the work without human intervention, can be worked in a variety of harsh environments.RFID technology Widely used in logistics, retail, warehousing, transportation, anti-counterfeiting, security, medical and military and other fields.
Amateur radio
Amateur radio refers to radio communications involving radio enthusiasts. Amateur radio stations have access to many open frequency bands across the spectrum. Many of the technologies used by hobbyists, some of which later became commercially available, such as FM, upper-sideband AM, digital packet radio, and satellite signal transponders, were first applied by amateurs.
Navigation
Almost all satellite navigation systems use satellites equipped with precise clocks. Navigation satellites broadcast their position and timing information, and receivers receive signals from multiple navigation satellites simultaneously. The receiver measures the travel time of the waves to determine its distance from each satellite and then calculates its precise position.
Radar
Estimates the distance to a target by measuring the delay of reflected radio waves, and senses the surface type of the target by the polarization and frequency of the reflected waves.
Heating
A microwave oven uses high-powered microwaves to heat food.
Biological applications
A new technology that enables wireless remote control of insects.
Power
Radio waves can generate weak electrostatic and magnetic forces. It can be used to immobilize objects in microgravity conditions.
Aerospace power
One program proposes that pressure generated by high-intensity microwave radiation could be used to power interplanetary probes.
Astronomy applications
The physical structure and chemical properties of celestial bodies can be studied using radio wave signals emitted by cosmic objects received through radio astronomy telescopes. This discipline is called radio astronomy.