Enter the characters you see below Sorry, we just need to make sure you’re not a robot. To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile can HF radio communicate with UHF or VHF radios?, or navigation devices, will be allocated in non-overlapping ranges of frequencies. Each of these bands has a traditional name.
These ITU radio bands are defined in the ITU Radio Regulations. 1 states that “the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table”. The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City, NJ in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942.
Frequency bands in the microwave range are designated by letters. This convention began around World War 2 with US military designations for frequencies used in radar, which was the first application of microwaves. The designation mm is also used to refer to the range from 30 to 300 GHz. Designations for television and FM radio broadcast frequencies vary between countries, see Television channel frequencies and FM broadcast band. Airband refers to VHF frequencies 118 to 137 MHz, used for navigation and voice communication with aircraft. Trans-oceanic aircraft also carry HF radio and satellite transceivers.
The greatest incentive for development of radio was the need to communicate with ships out of visual range of shore. From the very early days of radio, large oceangoing vessels carried powerful long-wave and medium-wave transmitters. Marine VHF radio is used in coastal waters and relatively short-range communication between vessels and to shore stations. Channel 16 is used for calling and emergencies.
Amateur radio frequency allocations vary around the world. Several bands are common for amateurs worldwide, usually in the HF part of the spectrum. It is used for personal, small business and hobby purposes. Other frequency allocations are used for similar services in different jurisdictions, for example UHF CB is allocated in Australia.
The ISM bands were initially reserved for non-communications uses of RF energy, such as microwave ovens, radio-frequency heating, and similar purposes. However, in recent years the largest use of these bands has been by short-range low-power communications systems, since users do not have to hold a radio operator’s license. Bands of frequencies, especially in the VHF and UHF parts of the spectrum, are allocated for communication between fixed base stations and land mobile vehicle-mounted or portable transceivers. Police radio and other public safety services such as fire departments and ambulances are generally found in the VHF and UHF parts of the spectrum.
Trunking systems are often used to make most efficient use of the limited number of frequencies available. The demand for mobile telephone service has led to large blocks of radio spectrum allocated to cellular frequencies. Reliable radio control uses bands dedicated to the purpose. Licensed amateur radio operators use portions of the 6-meter band in North America. Industrial remote control of cranes or railway locomotives use assigned frequencies that vary by area.
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Radar applications use relatively high power pulse transmitters and sensitive receivers, so radar is operated on bands not used for other purposes. Most radar bands are in the microwave part of the spectrum, although certain important applications for meteorology make use of powerful transmitters in the UHF band. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, communications satellites, computer networks and innumerable other applications. Radio waves are generated by radio transmitters and received by radio receivers. 3 000 GHz, propagated in space without artificial guide”. Article 1, Definitions of Radio Services, Article 1.
Competition and regulation in utility markets. The Post Office Electrical Engineers’ Journal. IEEE Std 521-2002 Standard Letter Designations for Radar-Frequency Bands. The Naval Institute Guide to World Naval Weapon Systems. Handbook of RF, Microwave, and Millimeter-Wave Components.
NOMENCLATURE OF THE FREQUENCY AND WAVELENTH BANDS USED IN RADIOCOMMUNCATION. 431: Nomenclature of the frequency and wavelength bands used in telecommunications. 1A, 6 December 1978: Performing Electronic Countermeasures in the United States and Canada, Attachment 1,ECM Frequency Authorizations. A reference to radio spectrum allocations. Radio spectrum: a vital resource in a wireless world” European Commission policy. Jump to navigation Jump to search This article is about science and technology. This article needs additional citations for verification.
The term “radio” is derived from the Latin word “radius”, meaning “spoke of a wheel, beam of light, ray”. The first use of radio- in conjunction with electromagnetic radiation appears to have been by French physicist Édouard Branly, who in 1890 developed a version of a coherer receiver he called a radio-conducteur. The use of “radio” as a standalone word dates back to at least December 30, 1904, when instructions issued by the British Post Office for transmitting telegrams specified that “The word ‘Radio’ is sent in the Service Instructions”. The switch to “radio” in place of “wireless” took place slowly and unevenly in the English-speaking world. In recent years the more general term “wireless” has gained renewed popularity, even for devices using electromagnetic radiation, through the rapid growth of short-range computer networking, e. Wi-Fi, and Bluetooth, as well as mobile telephony, e. Information such as sound is converted by a transducer such as a microphone to an electrical signal, which modulates a radio wave sent from a transmitter.
Radio systems used for communication have the following elements. With more than 100 years of development, each process is implemented by a wide range of methods, specialised for different communications purposes. This consists of a source of electrical energy, producing alternating current of a desired frequency of oscillation. Amplitude modulation of a carrier wave works by varying the strength of the transmitted signal in proportion to the information being sent. For example, changes in the signal strength can be used to reflect the sounds to be reproduced by a speaker, or to specify the light intensity of television pixels. Frequency modulation varies the frequency of the carrier. The instantaneous frequency of the carrier is directly proportional to the instantaneous value of the input signal.
FM has the “capture effect” whereby a receiver only receives the strongest signal, even when others are present. Angle modulation alters the instantaneous phase of the carrier wave to transmit a signal. Yagi-Uda antennas like these six are widely used at VHF and UHF frequencies. It is usually used with a radio transmitter or radio receiver. Once generated, electromagnetic waves travel through space either directly, or have their path altered by reflection, refraction or diffraction.
Electrical resonance of tuned circuits in radios allow individual stations to be selected. A resonant circuit will respond strongly to a particular frequency, and much less so to differing frequencies. This allows the radio receiver to discriminate between multiple signals differing in frequency. At the receiver, these currents are demodulated, which is conversion to a usable signal form by a detector sub-system.
Early radio systems relied entirely on the energy collected by an antenna to produce signals for the operator. Radio became more useful after the invention of electronic devices such as the vacuum tube and later the transistor, which made it possible to amplify weak signals. A radio communication system sends signals by radio. A radio communication system may send information only one way. For example, in broadcasting a single transmitter sends signals to many receivers. By using two radio frequencies, two stations may continuously and concurrently send and receive signals – this is called ” duplex” operation.
In 1864 James Clerk Maxwell showed mathematically that electromagnetic waves could propagate through free space. Early 20th century radio systems transmitted messages by continuous wave code only. Early attempts at developing a system of amplitude modulation for voice and music were demonstrated in 1900 and 1906, but had little success. Early uses were maritime, for sending telegraphic messages using Morse code between ships and land. The earliest users included the Japanese Navy scouting the Russian fleet during the Battle of Tsushima in 1905. Germany used radio communications for diplomatic messages once it discovered that its submarine cables had been tapped by the British. The United States passed on President Woodrow Wilson’s Fourteen Points to Germany via radio during the war.
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Today, radio takes many forms, including wireless networks and mobile communications of all types, as well as radio broadcasting. Bakelite radio at the Bakelite Museum, Orchard Mill, Williton, Somerset, UK. Transmissions are affected by static and interference because lightning and other sources of radio emissions on the same frequency add their amplitudes to the original transmitted amplitude. US Government during World War II. Bush House, old home of the BBC World Service.
FM broadcast radio sends music and voice with less noise than AM radio. It is often mistakenly thought that FM is higher fidelity than AM, but that is not true. AM is capable of the same audio bandwidth that FM employs. AM receivers typically use narrower filters in the receiver to recover the signal with less noise. During unusual upper atmospheric conditions, FM signals are occasionally reflected back towards the Earth by the ionosphere, resulting in long distance FM reception.
High power is useful in penetrating buildings, diffracting around hills, and refracting in the dense atmosphere near the horizon for some distance beyond the horizon. A few old, “grandfathered” stations do not conform to these power rules. FM subcarrier services are secondary signals transmitted in a “piggyback” fashion along with the main program. Special receivers are required to utilize these services.
Analog channels may contain alternative programming, such as reading services for the blind, background music or stereo sound signals. Aviation voice radios use Aircraft band VHF AM. AM is used so that multiple stations on the same channel can be received. Aircraft fly high enough that their transmitters can be received hundreds of miles away, even though they are using VHF. FM in the VHF spectrum for much shorter ranges. Government, police, fire and commercial voice services also use narrowband FM on special frequencies. Early police radios used AM receivers to receive one-way dispatches.
TETRA, Terrestrial Trunked Radio is a digital cell phone system for military, police and ambulances. When the mobile phone nears the edge of the cell site’s radio coverage area, the central computer switches the phone to a new cell. Analog television also uses a vestigial sideband on the video carrier to reduce the bandwidth required. All satellite navigation systems use satellites with precision clocks. The satellite transmits its position, and the time of the transmission. Radio direction-finding is the oldest form of radio navigation. Before 1960 navigators used movable loop antennas to locate commercial AM stations near cities.
In some cases they used marine radiolocation beacons, which share a range of frequencies just above AM radio with amateur radio operators. A directional signal rotates like a lighthouse at a fixed rate. When the directional signal is facing north, an omnidirectional signal pulses. The military operates a similar system of navaids, called TACANs, which are often built into VOR stations.
The delay caused by the echo measures the distance. The direction of the beam determines the direction of the reflection. The polarization and frequency of the return can sense the type of surface. Navigational radars scan a wide area two to four times per minute. They use very short waves that reflect from earth and stone. General purpose radars generally use navigational radar frequencies, but modulate and polarize the pulse so the receiver can determine the type of surface of the reflector. The best general-purpose radars distinguish the rain of heavy storms, as well as land and vehicles.
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Some can superimpose sonar data and map data from GPS position. Search radars scan a wide area with pulses of short radio waves. They usually scan the area two to four times a minute. Sometimes search radars use the Doppler effect to separate moving vehicles from clutter. Targeting radars use the same principle as search radar but scan a much smaller area far more often, usually several times a second or more. Most new radio systems are digital, including Digital TV, satellite radio, and Digital Audio Broadcasting. They send a bit as one of two tones using frequency-shift keying.
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Groups of five or seven bits become a character printed by a teleprinter. Aircraft use a 1200 Baud radioteletype service over VHF to send their ID, altitude and position, and get gate and connecting-flight data. QAM sends data by changing both the phase and the amplitude of the radio signal. Communication systems that limit themselves to a fixed narrowband frequency range are vulnerable to jamming. A variety of jamming-resistant spread spectrum techniques were initially developed for military use, most famously for Global Positioning System satellite transmissions. Systems that need reliability, or that share their frequency with other services, may use “coded orthogonal frequency-division multiplexing” or COFDM. COFDM breaks a digital signal into as many as several hundred slower subchannels.
The digital signal is often sent as QAM on the subchannels. COFDM resists fading and ghosting because the narrow-channel QAM signals can be sent slowly. Radio-frequency energy generated for heating of objects is generally not intended to radiate outside of the generating equipment, to prevent interference with other radio signals. Microwave ovens use intense radio waves to heat food.
Diathermy equipment is used in surgery for sealing of blood vessels. Amateur radio, also known as “ham radio”, is a hobby in which enthusiasts are licensed to communicate on a number of bands in the radio frequency spectrum non-commercially and for their own experiments. They may also provide emergency and service assistance in exceptional circumstances. Radio amateurs use a variety of modes, including efficient ones like Morse code and experimental ones like Low-Frequency Experimental Radio.
Wi-Fi also operates in unlicensed radio bands and is very widely used to network computers. Free radio stations, sometimes called pirate radio or “clandestine” stations, are unauthorized, unlicensed, illegal broadcasting stations. These are often low power transmitters operated on sporadic schedules by hobbyists, community activists, or political and cultural dissidents. Radio remote controls use radio waves to transmit control data to a remote object as in some early forms of guided missile, some early TV remotes and a range of model boats, cars and airplanes. In Madison Square Garden, at the Electrical Exhibition of 1898, Nikola Tesla successfully demonstrated a radio-controlled boat.