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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

Before there was Radio, there was 99.9fm #watching
TaiyouSun (Aditya Nandode) Tue, 05 Jan 2010 19:12:35 -0000
Before there was Radio, there was 99.9fm #watching
RT @DrumMajorsATL: Shout out 2 the dj's. got us playing on the radio in germany. wow. god is good>> that's wuts up!!
bookoobread (Teneal D. ) Tue, 05 Jan 2010 19:12:35 -0000
RT @DrumMajorsATL: Shout out 2 the dj's. got us playing on the radio in germany. wow. god is good>> that's wuts up!!
New Year Resolutions interview Jan 5th on internet talk radio show Adrenaline Living Talk Show! at 10amCST http://tinyurl.com/yd58wcj
mikkiwilliams (Mikki) Tue, 05 Jan 2010 19:12:34 -0000
New Year Resolutions interview Jan 5th on internet talk radio show Adrenaline Living Talk Show! at 10amCST http://tinyurl.com/yd58wcj
Iyaz-Solo only on bay area radio
Tharenusi (Tharen Usi) Tue, 05 Jan 2010 19:12:33 -0000
Iyaz-Solo only on bay area radio
High Velocity Radio intrvw w/ Bonnie Buol Ruszczyk / BBR Marketing now posted: http://bit.ly/5XUsJm
stonepayton (Stone Payton) Tue, 05 Jan 2010 19:12:31 -0000
High Velocity Radio intrvw w/ Bonnie Buol Ruszczyk / BBR Marketing now posted: http://bit.ly/5XUsJm
@richardpbacon Good luck in your new radio slot on Five - anything exciting lined up?
DerbyFreelancer (Rob Lane) Tue, 05 Jan 2010 19:12:26 -0000
@richardpbacon Good luck in your new radio slot on Five - anything exciting lined up?

 

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Africa Meets Africa - Progressive one-hour weekly radio magazine showcasing Africa and the Diaspora, from WPFW in Washington DC. Offers online listening, playlists, events and forums.
Meta Description: [ Progressive source for cutting-edge, positive and action-oriented news, information and features on Africa and Africans....... ]

BBC World Service - Network Africa - Offers twice-daily programme audio live and on demand, plus list of topics, Africa schedules and frequencies (SW and FM).

BBC World Service - Radio Schedules for Africa - Online listening plus day-by-day broadcast programme schedules with radio stations and frequencies by country, city and language. Includes links to BBC Africa programmes, in depth reports, publications and TV schedules.
Meta Description: [ International news, analysis and information from the BBC World Service. In-depth news and sport with audio, video and forums. BBC World Service reports in English and 32 other languages. ]

Channel Africa: Broadcasting via the internet - Links to African Internet broadcasting: Chinyanja, English, French, Portuguese, Silozi, Swahili.

Rainbow Radio Online - African music station broadcasting 24 hours per day and on the web. Offers programmes, news, DJ and MC profiles, special events and chat room.

Talking Africa - Weekly program broadcasting from the UK -- recent programs in sound file format.
Meta Description: [ A portal for news, information, exchange of opinions and experiences - from the Talking Africa radio show at the Africa Centre, London. ]

TotallyRadio - Afrobase - Weekly program focused on African-based music provides audio archives, show information and playlists.
Meta Description: [ totallyradio is an internet radio station broadcasting specialist music free to all and available on-demand with new shows every day. Join our Listeners' Club, support the independent music scene and get access to our huge archive and exclusive shows for members with improved features and higher ... ]