Cable radio is radio broadcasting into homes and businesses via a cable. This can be a coaxial cable used for television, or a telephone line. It is generally used for the same reason as cable TV was in its early days when it was "community antenna television", in order to enhance the quality of over-the-air radio signals that are difficult to receive in an area. However, cable-only radio outlets also exist. It can be both FM or AM.
The use of cable radio varies from area to area - some cable TV systems don't include it at all, and others only have something approaching it on digital cable systems. Additionally, some stations may just transmit audio in the background while a public-access television cable TV channel is operating in between periods of video programming.
From the late 1970s to the late 1980s, before the advent of MTS Stereo television broadcasts, an additional cable decoder was offered to cable TV subscribers, which was connected to the FM antenna terminal of a radio receiver and broadcast audio simulcasts of television broadcasts on certain frequencies, but separately transmitted in FM stereo, along with traditional local radio stations at their specific frequencies, utilizing the cable system's own taller receiving antenna for maximum audio clarity. For instance, MTV's audio would be offered on a cable radio frequency, thus the video being played in monaural sound on cable would have its television audio muted, and the stereo audio instead heard through the radio receiver.
A related secondary meaning of the term is any automated music stream - the usual format of cable-only "stations".
United States
The first "commercial" cable radio station in the United States was CABL-FM 108 in California, on the Theta Cablevision system, serving West Los Angeles and surrounding areas. It went live on January 1, 1972, and was run by Brad Sobel, playing what he called "progressive top 40". CABL-FM 108 came into being after Sobel's original venture, K-POT, a bootleg FM station at 88.1 MHz, was silenced by the Federal Communications Commission (FCC) in November 1971. The illicit station ran for three days until it was shut down, and the event made the front page of the Los Angeles Times and the Los Angeles Herald-Examiner. Because Theta Cablevision charged extra for its FM hookups, CABL-FM 108's potential audience was between 4,700 and approximately 25,000 (based on information provided by Brad Sobel in an article in Billboard), out of Cablevision's approximately 100,000 subscriber households.
The first exclusively cablecasting community radio station was CPVR in Palos Verdes, California, a suburb of Los Angeles. CPVR 95.9 Cable FM radio was on the Times-Mirror cable system, and was started by a group of teenagers who initially practiced being disc jockeys in the homes of two of the founders. Since traditional broadcasting equipment was prohibitively expensive at the time, a young engineer named Tom Hewitt built much of the electronic hardware from scratch.
Mark Speer and Brad Gardner began the venture, which was run as a non-profit youth organization from a studio in the Golden Cove shopping center in Rancho Palos Verdes beginning in March 1972. Even though it was non-profit, it was not subject to the restrictions of terrestrial public radio stations, and thus was able to subsidize expenses by accepting commercial advertising.
Because the staff and audience were part of a highly desirable demographic (many of the DJs weren't even old enough to drive), advertisers of the day, such as concert promoter Pacific Presentations and local record stores eagerly bought ad time in order to reach such a prime demographic (males/females, 13-24) as CPVR had attracted during its history, further enabling CPVR to not only continue operations, but expand into larger studios.
Greg McClure (a.k.a. Isaac O. Zzyzx), Jim Sideris, Harv Laser, David Zislis, Richard Hower, Tony Fasola, Dave Chrenko (a.k.a. Johnny Ace), Kerry Doolin, Liane Benson, Lorraine Dechter, Clyde Stanton (a.k.a. Certified Clyde) and Kathy Bauer were some of the young disc jockeys who helped create the station's legendary style and sound. Unlike Cable 108, CPVR was not only on the FM dial, but was in stereo, and also appeared on the cable system's "barker" channel (Channel 3).
Although the station was only on the "cable" for about two years programming free-form rock and roll, CPVR often scooped its over-the-air competitors, breaking acts such as Bruce Springsteen and Queen, and often premiering landmark albums such as Pink Floyd's The Dark Side of the Moon and Procol Harum's Grand Hotel sometimes several weeks before the Los Angeles stations picked them up.