radio
radio
[′rād·ē·ō]Radio
Communication between two or more points, employing electromagnetic waves as the transmission medium.
Radio waves transmitted continuously, with each cycle an exact duplicate of all others, indicate only that a carrier is present. The message must cause changes in the carrier which can be detected at a distant receiver. The method used for the transmission of the information is determined by the nature of the information which is to be transmitted as well as by the purpose of the communication system.
In code telegraphy the carrier is keyed on and off to form dots and dashes. The technique, often used in ship-to-shore and amateur communications, has been largely superseded in many other point-to-point services by more efficient methods.
In frequency-shift transmission the carrier frequency is shifted a fixed amount to correspond with telegraphic dots and dashes or with combinations of pulse signals identified with the characters on a typewriter. This technique is widely used in handling the large volume of public message traffic on long circuits, principally by the use of teletypewriters.
In amplitude modulation the amplitude of the earner is made to fluctuate, to conform to the fluctuations of a sound wave. This technique is used in AM broadcasting, television picture transmission, and many other services.
In frequency modulation the frequency of the carrier is made to fluctuate around an average axis, to correspond to the fluctuations of the modulating wave. This technique is used in FM broadcasting, television sound transmission, and microwave relaying.
In pulse transmission the carrier is transmitted in short pulses, which change in repetition rate, width, or amplitude, or in complex groups of pulses which vary from group to succeeding group in accordance with the message information. These forms of pulse transmission are identified as pulse-code, pulse-time, pulse-position, pulse-amplitude, pulse-width, or pulse-frequency modulation. Such techniques are complex and are employed principally in microwave relay systems.
In radar the carrier is normally transmitted as short pulses in a narrow beam, similar to that of a searchlight When a wave pulse strikes an object, such as an aircraft, energy is reflected back to the station, which measures the round-trip time and converts it to distance. A radar can display varying reflections in a maplike presentation on a cathode-ray tube. See Radar
Hundreds of thousands of radio transmitters exist, each requiring a carrier at some radio frequency. To prevent interference, different carrier frequencies are used for stations whose service areas overlap and receivers are built to select only the carrier signal of the desired station. Resonant electric circuits in the receiver are adjusted, or tuned, to accept one frequency and reject others.
All nations have a sovereign right to use freely any or all parts of the radio spectrum. But a growing list of international agreements and treaties divides the spectrum and specifies sharing among nations for their mutual benefit and protection. Each nation designates its own regulatory agency. In the United States all nongovernmental radio communications are regulated by the Federal Communications Commission (FCC).
radio
(1) The transmission of wireless signals (electromagnetic waves) over the air or through a hollow tube called a "waveguide." Although "radio" is often thought of as only AM and FM or sometimes two-way radio, all transmission systems that propagate signals through the air are some form of "radio," including TV, satellite, portable phones, cellphones and wireless LANs. See spectrum. |
| Electromagnetic Spectrum |
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| The radio portion of the entire spectrum of radiation is from 3 kHz to 300 GHz. This huge band of frequencies has been defined by the FCC in the U.S. and governmental bodies in other countries. |
(2) An electronic circuit that transmits and receives wireless signals (electromagnetic waves). The phrase "the device has four radios" means the unit has some combination of receivers and transceivers, which may reside on one or more chips. See transceiver.
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| A Four-Radio Chip From TI |
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| In addition to a cellular radio, modern smartphones have other radios. This single chip has four: two receivers (FM and GPS) and two transceivers (Wi-Fi and Bluetooth). (Image courtesy of Texas Instruments, Inc.) |
(3) A device that receives wireless audio signals (electromagnetic waves) such as an AM/FM radio or satellite radio. See Vintage Radio Museum.
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| For the Early Adopter! |
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| In 1925, listeners tuned three stages on this battery-operated Stewart Warner Model 325 to get a good signal. Once they got one, they logged the numbers so they could tune in quickly the next time. (Equipment courtesy of Vintage Radio and Communications Museum of Connecticut, www.vrcmct.org) |
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| A Double Thrill for Dad |
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| Not only was it a pleasure for John Coolidge to have his son Calvin accept the Republican nomination for U.S. president in Cleveland, Ohio in 1924, but to actually hear the speech was quite exciting. (Image courtesy of Vintage Radio and Communications Museum of Connecticut, www.vrcmct.org) |
Radio
a method of transmitting messages without wires over a distance by means of radio waves, invented by A. S. Popov in 1895. The term “radio” also refers to the scientific and technical field associated with the study of the physical phenomena that underlie this method (radio physics) and with the method’s use for communication (radio communication), sound broadcasting (radio broadcasting), the transmission of images (television), signaling, monitoring, and control (radio remote control), and the detection and location of various objects (radar).
In a limited sense, the term also signifies radio broadcasting, one of the greatest mass mediums for distributing political, cultural, educational, and general-interest information.
The term “radio” came into use in the second decade of the 20th century.
Radio
a monthly scientific journal of radio engineering for the general public, published by the Ministry of Communications and the DOSAAF (All-Union Voluntary Society for Cooperation With the Army, Air Force, and Navy) of the USSR.
Radio has been published since 1924 in Moscow, and the present title has been used since 1946 (up to 1931 the title was Radioliubitel’ [Radio Amateur], and from 1931 to 1941, Radiofront). The journal provides information on the most important advances in radio engineering, electronics, and communication; it serves the amateur-radio field and popularizes competitions for radio amateurs. Descriptions of commercial and amateur electronic instruments and equipment are contained in the journal, as are reference materials and the latest information on measuring techniques and household appliances. There is also advice on problems in radio engineering.
Radio has been awarded the Order of the Red Banner of Labor (1974). Circulation, 850,000 (1975).