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Radio Definition, History, & Facts

Passive tags, the most common type, have a chip powered by the radio energy received from the reader, rectified by a diode, and can be as small as a grain of rice. They are incorporated in products, clothes, railroad cars, library books, airline baggage tags and are implanted under the skin in pets and livestock and even people. Privacy concerns have been addressed with tags that use encrypted signals and authenticate the reader before responding. Passive tags use 125–134 kHz, 13, 900 MHz and 2.4 and 5 GHz ISM bands and have a short range. Active tags, powered by a battery, are larger but can transmit a stronger signal, giving them a range of hundreds of meters.

A few stations experimented with telephone lines to allow two or more outlets to carry (or “network”) an occasional presidential address or sporting event. Magazines, books, and even movies featured or included references to Radio broadcasting. Radio-controlled models – a popular hobby is playing with radio-controlled model boats, cars, airplanes, and helicopters which are controlled by radio signals from a handheld console with a joystick. Most recent transmitters use the 2.4 GHz ISM band with multiple control channels modulated with PWM, PCM or FSK. Ground-penetrating radar – a specialized radar instrument that is rolled along the ground surface in a cart and transmits a beam of radio waves into the ground, producing an image of subsurface objects. Since radio waves cannot penetrate very far into earth, the depth of GPR is limited to about 50 feet.

The program is then received not via AM/FM or HD Radio, but via the Internet, which is why this reception channel is also called Internet radio or web radio. The selection of radio stations is therefore much greater than with classic radio. The easiest way to listen to the radio on your mobile phone is via a radio app. Most radio apps are free and easily available in the respective app stores for iOS and Android.

The radio spectrum, the total range of radio frequencies that can be used for communication in a given area, is a limited resource. Each radio transmission occupies a portion of the total bandwidth available. Radio bandwidth is regarded as an economic good which has a monetary cost and is in increasing demand. In some parts of the radio spectrum, the right to use a frequency band or even a single radio channel is bought and sold for millions of dollars.

Concerns about interference with military wireless transmissions, however, led to a shutdown until 1922, when government-authorized stations appeared, including the first London-based outlet. The first Mexican radio station aired in the capital city in 1921, though many in the country had first heard broadcasts from Cuba or Puerto Rico. By that point, stations had also appeared in Australia , New Zealand , and Denmark . See History of radio, Invention of radio, Timeline of radio, History of broadcastingOn November 11, 1886, propagation of an electromagnetic wave was first observed by German physicist Heinrich Hertz. His discovery was followed up by other scientist, trying to discern the nature of radio waves.