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Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of light.
Radio waves
Radio waves are a form of electromagnetic radiation, created whenever a charged object (in normal radio transmission, an electron) accelerates with a frequency that lies in the radio frequency (RF) portion of the electromagnetic spectrum. In radio, this acceleration is caused by an alternating current in an antenna. Radio frequencies occupy the range from a few tens of hertz to a few hundred gigahertz.
| ELF - SLF - ULF/VF - VLF - LF/LW - MW - HF/SW - VHF - UHF - SHF - EHF Electromagnetic radio spectrum |
Electromagnetic spectrum and diagram of radio transmission of an audio signal.
Electromagnetic radiation travels (propagates) by means of oscillating electromagnetic fields that pass through the air and the vacuum of space equally well, and does not require a medium of transport (such as the aether). When radio waves pass an electrical conductor, the oscillating electric or magnetic field (depending on the shape of the conductor) induces an alternating current and voltage in the conductor. This can be transformed into audio or other signals that carry information. The word 'radio' is used to describe this phenomenon, and television, radio, radar, and cell phone transmissions are all classed as radio frequency emissions.
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United States :: North America
Radio :: Recreation
Football Uniforms Turn Up The Heat
Thu, 28 Aug 2008 00:01:00 -0400
Injury-inducing collisions aren't the only safety issues football coaches and trainers need to worry about, physiologists say. High temperatures and humidity can also take a serious toll on players wrapped up in pads and uniforms.
MLB Dips Its Toe Into World Of Instant Replays
Wed, 27 Aug 2008 16:49:00 -0400
On Thursday, for the first time ever, Major League Baseball will use a limited instant-replay system to review questionable homeruns. Buster Olney, of ESPN The Magazine, says this season's rash of bad calls led to the decision.
10-Year-Old's Fastball Gets Him Kicked Off League
Wed, 27 Aug 2008 16:16:00 -0400
Jericho Scott is only 10 years old, but he's already throwing a 40 mph fastball. His skill has resulted in him getting kicked out of his local league. Other teams say he's just too good and they don't want to play against him.
Reuters: Sports News
Venus and Safina hit top gear to reach round three
Thu, 28 Aug 2008 18:40:09 -0400
NEW YORK (Reuters) - The fading memory of her two title-winning runs at Flushing Meadows spurred Venus Williams to hit top gear at the U.S. Open on Thursday.
De La Hoya to fight Pacquiao in December
Thu, 28 Aug 2008 15:33:59 -0400
MIAMI (Reuters) - Ten-times world champion Oscar De La Hoya will fight WBC lightweight world champion Manny Pacquiao of the Philippines in December with the American refusing to call the bout his last.
Montgomerie down but not out of wild card chance
Thu, 28 Aug 2008 15:03:58 -0400
GLENEAGLES (Reuters) - Briton Colin Montgomerie clung to his Ryder Cup hopes on Thursday despite trailing Johnnie Walker Championship leader Gregory Havret by six shots after Thursday's opening round.
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