Simplified 48-channel carrier telephone system

THE SINGLE-SIDEBAND suppressed carrier method of deriving multiple communication channels from a common transmission medium is now almost 40 years old. The first systems to provide good telephone circuits by this method came into widespread use in 1927, followed by large scale installation of 3-channel systems about 1933. By 1938 12-channel systems had been applied to trunkline telephony, and soon thereafter equipment was available to provide really large numbers of channels over a coaxial cable. Current developments include the application of radio relay to the telephone plant and carrier systems designed for simplification of application and reduction of equipment cost.