The modulation signal may be an audio signal representing sound from a microphone, a video signal representing moving images from a video camera, or a digital signal consisting of a sequence of bits representing binary data from a computer. At the sending end, the information to be sent is converted by some type of transducer to a time-varying electrical signal called the modulation signal.
In radio communication systems, information is carried across space using radio waves. Radio communication Ĭomparison of AM and FM modulated radio waves The wide use of radio waves for telecommunication is mainly due to their desirable propagation properties stemming from their large wavelength. The other types of electromagnetic waves besides radio waves, infrared, visible light, ultraviolet, X-rays and gamma rays, can also carry information and be used for communication. Radio waves travel at the speed of light in a vacuum.
An omnidirectional antenna transmits or receives radio waves in all directions, while a directional antenna or high-gain antenna transmits radio waves in a beam in a particular direction, or receives waves from only one direction. Īs they travel farther from the transmitting antenna, radio waves spread out so their signal strength ( intensity in watts per square meter) decreases, so radio transmissions can only be received within a limited range of the transmitter, the distance depending on the transmitter power, the antenna radiation pattern, receiver sensitivity, noise level, and presence of obstructions between transmitter and receiver. They are generated artificially by time varying electric currents, consisting of electrons flowing back and forth in a metal conductor called an antenna. Radio waves are radiated by electric charges undergoing acceleration. The emission of radio waves is regulated by law, coordinated by the International Telecommunication Union (ITU), which allocates frequency bands in the radio spectrum for different uses. The first commercial radio broadcast was transmitted on Novemwhen the live returns of the Harding-Cox presidential election were broadcast by Westinghouse Electric and Manufacturing Company in Pittsburgh, under the call sign KDKA.
Transistor radio with bluex code#
In the mid 1890s, building on techniques physicists were using to study electromagnetic waves, Guglielmo Marconi developed the first apparatus for long-distance radio communication, sending a wireless Morse Code message to a source over a kilometer away in 1895, and the first transatlantic signal on December 12, 1901. The existence of radio waves was first proven by German physicist Heinrich Hertz on November 11, 1886. The noun radio is also used to mean a broadcast radio receiver. In wireless radio remote control devices like drones, garage door openers, and keyless entry systems, radio signals transmitted from a controller device control the actions of a remote device.Īpplications of radio waves that do not involve transmitting the waves significant distances, such as RF heating used in industrial processes and microwave ovens, and medical uses such as diathermy and MRI machines, are not usually called radio. In radio navigation systems such as GPS and VOR, a mobile receiver accepts radio signals from navigational radio beacons whose position is known, and by precisely measuring the arrival time of the radio waves the receiver can calculate its position on Earth. In radar, used to locate and track objects like aircraft, ships, spacecraft and missiles, a beam of radio waves emitted by a radar transmitter reflects off the target object, and the reflected waves reveal the object's location. In radio communication, used in radio and television broadcasting, cell phones, two-way radios, wireless networking, and satellite communication, among numerous other uses, radio waves are used to carry information across space from a transmitter to a receiver, by modulating the radio signal (impressing an information signal on the radio wave by varying some aspect of the wave) in the transmitter. A variety of radio antennas on Sandia Peak near Albuquerque, New Mexico, US
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