Carrier current transmission, originally called wired wireless, employs guided low-power radio-frequency signals, which are transmitted along electrical conductors.
Carrier current transmission is used to send audio and telemetry to selected locations, and also for low-power broadcasting that covers a small geographical area, such as a college campus.
The most common form of carrier current uses longwave or medium wave AM radio signals that are sent through existing electrical wiring, although other conductors can be used, such as telephone lines.
Extensive systems can include multiple unit installations with linear amplifiers and splitters to increase the coupling points to a large electrical grid (whether a campus, a high-rise apartment or a community).
[1] By 1911, Major General George Owen Squier was conducting some of the earliest studies designed to put carrier current transmissions, which he called "wired wireless", to practical use.
The first commercial applications of carrier current technology included the setting up of long-distance telegraph, telemetry, and telephone communication by electrical companies over their high-voltage distribution lines.
[5] However, despite the power company's optimism that the system would eventually be installed nationally, the effort proved unable to compete with the free offerings provided by standard radio stations.
The Intercollegiate Broadcasting System (IBS) was formed in February 1940, to coordinate activities between twelve college carrier current stations and to solicit advertisers interested in sponsoring programs geared toward their student audiences.
[9] The innovation received a major publicity boost by a complimentary article that appeared in the May 24, 1941 issue of The Saturday Evening Post,[10] and eventually hundreds of college stations were established.
Responding to the growing phenomenon, a 1941 release issued by the U.S. Federal Communications Commission (FCC) stated that because of the stations' very limited ranges, it had "not promulgated any rule governing their operation.
Although college-based carrier current stations have existed for over 80 years, their numbers are steadily declining, becoming supplemented, or replaced, by other transmission methods, including low-power FM (LPFM), closed circuit over cable TV channels, and Internet streaming audio and video, along with simple PowerPoint presentations of college campus news and information being streamed using low-cost consumer televisions and monitors.