Electromagnetic radiation travels via oscillating electromagnetic fields that pass through the air and the vacuum of space. It does not require a medium of transport. Information is carried by systematically changing (modulating) some property of the radiated waves, such as their amplitude or their frequency. When radio waves pass an electrical conductor, the oscillating fields induce an alternating current in the conductor.
The word 'radio' is used to describe this phenomenon, and television, radio, and cell phone transmissions are all classified as radio frequency emissions.
Modulation is the process where speech, music and the like are impressed onto the carrier wave of a transmission. Detection or demodulation is the reverse process which takes place in a receiver. The speech, music etc. is recovered and may then be amplified and applied to an ear piece or a loud speaker. The most common forms of modulation are Amplitude Modulation (AM) and Frequency Modulation (FM) both of which use different modulation and detection circuits. Cell phones, digital radio and digital television use more complex modulation and demodulation systems.
The simplest AM receiver is the Crystal Set or Crystal Radio. Demodulation is achieved by a semiconductor diode. One of the earliest forms of detection consisted of a thin copper wire in contact with a small chunk of Galena Rock. Adequate signals could be heard in headphones for up to 50 km with simple arrangements.
Old-Time Radio (OTR) and the Golden Age of Radio refer to a period of radio programming lasting from commercial radio's introduction in the early 1920s to its replacement in the late 1950s and early 1960s by television as the dominant home entertainment medium. During this period, when radio was dominant and the airwaves were filled with a variety of radio formats and genres, people regularly tuned in to their favorite radio programs. In fact, according to a 1947 C. E. Hooper survey, 82 out of 100 Americans were found to be radio listeners. The end of this period coincided with music radio becoming the dominant radio form and is often marked by the final CBS broadcasts of Suspense and Yours Truly, Johnny Dollar on September 30, 1962.
Radio content in the Golden Age of Radio had its origins in audio theatre. Audio theatre began in the 1880s and 1890s with audio recordings of musical acts and other vaudeville. These were sent to people by means of telephone and, later, through phonograph cylinders and discs. Visual elements, such as effects and sight gags, were adapted to have sound equivalents. In additions, visual objects and scenery were converted to have audio descriptions.
This photo shows an early 1930s wooden radio receiver in the classic "cathedral" shape, which was designed and built by Philco. Philco, at the time of this radio's construction, was the leading manufacturer of radios. Photo Credit: User:Gmaxwell
The station started at 7:00am on September 30, 1967, and succeeded the Light Programme, with some of the Light's music shows transferring to the newly-launched Radio 1. The first show however had actually started at 5.30am (on the Light programme) but continued on with Breakfast Special from Paul Hollingdale as Radio 1 split off.
The self-proclaimed "King of All Media" (a humorous reference to Michael Jackson's appellation "The King of Pop") has been dubbed a shock jock for his highly controversial use of scatological, sexual and racial humor. Stern has said that the show was never about shocking people, but primarily intended to offer his honest opinions on a gamut of issues (ranging from world affairs to problems among his own staff). Though controversial, he is one of the highest-paid radio personalities in the United States and the most fined personality in radio broadcast history.
RadioDecember 12, 2006 "...to create, expand, and maintain wikipedia articles related to radio, including radio propagation and reception, radio programming, radio personalities, and the business of radio." (Example: Mutual Broadcasting System)
Amateur RadioAugust 24, 2006 "...to improve Wikipedia's articles related to Amateur radio, maintain the amateur radio category and its sub-categories for clean organization, and to produce and maintain templates for Amateur radio-related topic identification." (Example: Amateur radio)
Radio StationsFebruary 15, 2005 "...to coordinate the activities of creating and maintaining articles about radio stations." (Example: KCBS-FM)
PodcastingJanuary 21, 2007 "...to make Wikipedia's knowledge of notable Podcast and podcast-related information as complete as possible." (Example: Podcast)