Carrier Systems on Long Distance Telephone Lines

TWO previous papers before the American Institute of Electrical Engineers discussed the activities of the Bell System in the development of multiplex telephone and telegraph systems using carrier current methods. The present paper describes developments which have resulted in improvements in the carrier telephone art during the past few years. A new, so-called type " C " system is described in detail, together with suitable repeaters and pilot channel apparatus for insuring the stability of operation; the line problems are considered and typical installations pictured. The growth of the application of carrier telephone systems and their increasingly important part in providing long distance telephone service on open-wire lines are shown. INTRODUCTION A T the 1921 Midwinter Convention of the American Institute of Electrical Engineers, Messrs. Colpitts and Blackwell presented a paper entitled "Carrier Current Telephony and Telegraphy." This described the development work of the Bell System and the resulting commercial types of multiplex telephone and telegraph systems using carrier current methods. The paper also gave a brief historical summary and included a theoretical discussion of the methods involved.