A New Single Channel Carrier Telephone System

N open-wire lines where the growth is not rapid, there is frequently need for adding telephone circuits one at a time. When the T y p e D single-channel carrier telephone system was developed a few years ago it became possible to meet this need without stringing additional wires. 1 More than 500 of these systems have been placed in service in the Bell System plant. A new single-channel carrier telephone system, known as the T y p e H, has recently been developed and is now being applied. This new system offers improved performance, and also, because of its lower cost, is applicable to providing service over shorter distances than were economical with the earlier system. The T y p e H system, which is characterized by a number of new features and special developments, is applicable not only to the needs of telephone companies but also to those of railroads, power systems, and oil companies. 2 In the first place it is designed to operate either on alternating current or on direct-current plate and filament supply. A repeater is available to extend the range of operation. Through the use of specially designed but simple filters the system can be employed on circuits which are equipped with bridged telephone * Presented at Winter Convention of A. I. E. E., New York, N. Y., January 2428, 1938. Published in Electrical Engineering, January 1938. 1 " Carrier Telephone Svstem for Short Toll Circuits," H. S. Black, M. L. Almquist and L. M. Ilgenfritz, A. J. E. E. Transactions, Vol. 48, January 1929, pp.