Carrier current

Carrier current is a method of low power AM radio transmission that uses AC electrical wiring to propagate a medium frequency AM signal to a relatively small area, such as a building or a group of buildings. In the United States, carrier current stations do not require a broadcasting license from the FCC, as long as the emissions adhere to the Part 15 Rules for unlicensed transmissions.

Predecessor

In the 1920s, Wired Radio's subscription music service was delivered over electrical power lines, and billed for on the customer's electric bill. As AM broadcasting improved and grew, its business model, in which content is supported by advertising rather than subscriber fees, destroyed the home market for this service. In 1934, its owner created the Muzak company, focused on the business market.

Application

Carrier current broadcasting has been used by many types of facilities that need to transmit radio to a small area. Carrier current is most often associated with college radio and high school radio, but was formerly used for hospital radio stations and at military bases, sports stadiums, convention halls, mental and penal institutions, trailer parks, summer camps, office buildings, and drive-in movie theaters. Many college stations that went on to obtain broadcasting licenses started out as carrier current stations because of the low cost and relative ease of starting up such a radio station.