Cable FM

Cable radio or cable FM is a concept similar to that of cable television, bringing radio signals into homes and businesses via coaxial cable. It is generally used as cable TV was in its early days when it was "community antenna television", to enhance the quality of terrestrial radio signals that are difficult to receive in an area. However, cable-only radio outlets also exist.

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. In the late 1970s to the mid-to-late-1980s, before the advent of MTS Stereo television broadcasts, cable TV subscribers would tune in specific cable FM frequencies that simulcast the television broadcasts in stereo.

A related secondary meaning of the term is any automated music stream - the usual format of cable-only "stations".

The first "commercial" cable radio station in the United States was CABL-FM 108, on the Theta Cablevision system, serving West Los Angeles, California 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 Brad's original venture, K-POT, a bootleg FM station at 88.1 MHz was busted by the 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 Herald-Examiner. Because Theta Cablevision charged extra for their 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.

...
Wikipedia