Generally, radio waves refer to the extremely low frequency of 10KHz to the ultra-high frequency of 30GHz (Giga Hertz), because the radio frequency spectrum outside this range has very different characteristics. For example, light, X-ray, etc. In the above 10KHz to 30GHz, it is usually divided into seven regions. See the table below, where the high frequency of 3 ~ 30MHz is the short wave we are discussing.
broadcast
Broadcast frequency:
Long-wave AM radio = 148.5 kHz-283.5 kHz (LF)
Medium Wave AM Radio = 525 kHz-1710 kHz (MF)
Short-wave AM radio = 3 MHz-30 MHz (HF)
TV and FM radio frequency assignments vary by country. Since VHF and UHF frequencies are desirable for many uses in urban areas, some parts of the former television broadcast band have been reassigned to cellular phones and various land mobile communication systems in North America. TV band devices use channels without local radio stations, even within the allocation range dedicated to television.
The Apex band in the United States was a World War II allocation before VHF audio broadcasting; it was obsolete after the introduction of FM broadcasting. [2]
Air band
Airband refers to the VHF frequency of 118 to 137 MHz and is used for navigation and voice communications with aircraft. Transoceanic aircraft also carry high-frequency radio and satellite transceivers. [2]
Marine band applications
The greatest impetus for the development of radio was the need to communicate with ships far from the visual range. From the early days of broadcasting, large ocean-going vessels carried powerful long-wave and medium-wave transmitters. Although satellite systems have taken over some safety applications previously served by 500 kHz and other frequencies, high-frequency allocations are still specified for ships. 2182 kHz is a medium wave frequency for marine emergency communications.
Marine high-frequency radios are used for relatively short distance communications and onshore sites between coastal waters and ships. Radio channelization, different channels are used for different purposes; marine channel 16 is used for calls and emergency situations. [2]
Amateur radio frequency
The allocation of amateur radio frequencies varies across the world. Amateurs around the world usually have several frequency bands, usually the high-frequency part of the spectrum. The other frequency bands are allocated by countries or regions, only due to the different allocation of other services, especially in the VHF and UHF parts of the radio spectrum. [2]
Citizens band and personal broadcasting services
Citizen band radios are allocated in many countries, using channelized radios in the higher part of the spectrum (about 27 MHz). It is used for personal, small business and hobby purposes. Other frequency allocations are used for similar services in different regions, such as UHF CB allocations in Australia. There are a wide variety of personal radio services around the world, which usually emphasize short-range communications between individuals or small businesses, do not require a license, and typically use an FM transceiver of about 1 watt or less. [2]
Industry, science, medical
The ISM band was originally reserved for non-communication uses of RF energy, such as microwave ovens, high-frequency heating, and similar purposes. However, in recent years, the greatest use of these bands has been for short-range, low-power communication systems, as users do not have to hold a radio operator's license. Cordless phones, wireless computer networks, Bluetooth devices and garage door openers all use the ISM band. ISM equipment has no regulatory protection from interference from other users. [2]
Terrestrial band use
Frequency bands, especially those in the VHF and UHF bands, are allocated for communication between fixed base stations and land mobile on-board or portable transceivers. In the United States, these services are informally referred to as commercial band radios. See also professional mobile radio.
Police radio and other public safety services, such as fire departments and ambulances, are generally available in VHF and UHF sections. Relay systems are often used to make the most efficient use of a limited number of available frequencies.
The demand for mobile phone services has resulted in a large amount of radio spectrum being allocated to cellular frequencies. [2]
Radio control
Reliable radio control uses frequency bands dedicated to this purpose. Radio-controlled toys may use unlicensed spectrum in the 27 MHz or 49 MHz band, but more expensive aircraft, boats or ground vehicles use dedicated radio-controlled frequencies near 72 MHz to avoid interference for undocumented uses. The 21st century has begun to develop towards 2.4 GHz spread-spectrum RC control systems.
Licensed amateur radio operators use some 6-meter bands in North America. Industrial remote controls for cranes or railway locomotives use specified frequencies, which vary by region. [2]
radar
Radar is used in relatively high-power pulse transmitters and sensitive receivers, so the radar operates in frequency bands that do not need to be used for other purposes. Most radar bands are part of the microwave, although some important applications in meteorology use powerful transmitters in the UHF band. Radio waves are a type of electromagnetic radiation. The wavelength of the electromagnetic spectrum is longer than that of infrared light. Radio waves have frequencies up to 300 GHz, as low as 3 kHz, although some definitions describe waves of 1 GHz or above as microwaves, or include any lower frequency wave. The corresponding wavelength is 1 mm (0.039 in) at 300 GHz and 100 km (62 mi) at 3 kHz. Like all other electromagnetic waves, they travel at the speed of light. Naturally generated radio waves are generated by lightning or astronomical objects.
Artificially generated radio waves are used in fixed and mobile radio communications, broadcasting, radar and other navigation systems, communications satellites, computer networks and other applications. Radio waves are generated by a radio transmitter and received by a radio receiver. Radio waves of different frequencies have different propagation characteristics in the Earth's atmosphere; long waves can diffract around obstacles like mountains and follow the contour of the earth (ground waves). Shorter waves can be reflected away from the ionosphere and on the horizon ( Sky waves) return to Earth, while shorter wavelengths have less bending or diffraction, and a line of sight, so their propagation distance is limited to the horizon.
In order to prevent interference between different users, the artificial generation and use of radio waves is strictly regulated by the law. It is coordinated by an international organization called the International Telecommunication Union (ITU). Different uses. [2]
