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Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of light.

Radio waves

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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

Other types of electromagnetic radiation, with frequencies above the RF range, are infrared, visible light, ultraviolet, X-rays and gamma rays. Since the energy of an individual photon of radio frequency is too low to remove an electron from an atom, radio waves are classified as non-ionizing radiation.
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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Radio - Twitter Search

RT @KENARD: Dj's bring your 10min mix to WGCI by Noon on 1/11, to be a guest mixer on the radio w/ Dj Phantom, Tim (cont) http://tl.gd/1iqfj
jaicrenshaw (Jai Crenshaw) Tue, 05 Jan 2010 19:18:32 -0000
RT @KENARD: Dj's bring your 10min mix to WGCI by Noon on 1/11, to be a guest mixer on the radio w/ Dj Phantom, Tim (cont) http://tl.gd/1iqfj
Check this video out -- Arsonal @ Redikalis Radio http://www.youtube.com/watch?v=pAktSmwju_M check us out 3HM (Ray SwaG)
RAYSWAGG5 (TERRENCE ) Tue, 05 Jan 2010 19:18:31 -0000
Check this video out -- Arsonal @ Redikalis Radio http://www.youtube.com/watch?v=pAktSmwju_M check us out 3HM (Ray SwaG)
This nigga just touched my radio -_-
MrLyphe (Dave Gachelin) Tue, 05 Jan 2010 19:18:29 -0000
This nigga just touched my radio -_-
Key to a succesful workout: put your pandora radio on lil jon n jump on the treadmill
ShaaySmif (Shaina Smith) Tue, 05 Jan 2010 19:18:28 -0000
Key to a succesful workout: put your pandora radio on lil jon n jump on the treadmill
Geoff Bodine live tonight on RacersReunion (((RADIO))) on RacersReunion.com. 7 PM ET
RacersReunion1 (Jeff Gilder) Tue, 05 Jan 2010 19:18:28 -0000
Geoff Bodine live tonight on RacersReunion (((RADIO))) on RacersReunion.com. 7 PM ET
Pongo la radio..y Mcfly...me escojono yo sola jajajaja
art_music (Virginia ) Tue, 05 Jan 2010 19:18:28 -0000
Pongo la radio..y Mcfly...me escojono yo sola jajajaja

 

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Bright Path Video: KPFA - KPFA, is one of the most important outlets of progressive broadcasting. Events to save KPFA in streaming video and Real Audio. [Requires free RealPlayer]
Meta Description: [ brightpathvideo, progressive video, progressive web site, streaming media, web writing, john parulis. ]

Creative Radio - An eGroups e-mail discussion groups for those interested in using radio to promote health and development around the world.
Meta Description: [ creative-radio: Creative-Radio media making a difference ]

Flashpoints - Progressive interview and discussion program out of KPFA community radio, Berkeley, CA

Grassroots Radio Conference - Information about an annual gathering of grassroots radio stations. The 1999 gathering was Aug. 20-23 in Bar Harbor, Maine.

500 Radio For Peace International - International broadcast organization dedicated to peace and economic and social justice. Includes access to RealAudio programming.

Radio Volta - Breaking independent news, culture and free form music, offered by Philadelphia Indy Media.
Meta Description: [ Radio Volta, named after historic Philly anarchist Voltairine de Cleyre, is a project of the Philadelphia Independent Media Center. We are a community, listener-supported, volunteer-driven station bringing you breaking independent news, culture and freeform music. Radio Volta germinated as W... ]

Your Call - Progressive news, intelligent talk and alternative viewpoints. Broadcasts worldwide via the internet and on the Boulder/Denver, Colorado airwaves at KWAB 1490 AM.