A New Single Channel Carrier Telephone System * 



By H. J. FISHER, M. L. ALMQUIST and R. H. MILLS 



The single channel carrier telephone system described in the 

 following paper is designated the Type H. It is characterized 

 by several new features, making it applicable not only to the needs 

 of telephone companies but also to those of railroads, power sys- 

 tems and oil companies. It replaces the Type D single channel 

 carrier system, more than 500 of which are now in operation in 

 the Bell System, and, in addition because of its lower cost is 

 applicable to shorter distances. It therefore marks another step 

 in extending the use of carrier. Reduction in size and provision 

 for operating on a-c supply simplify its installation, and its porta- 

 bility makes it well suited to provide emergency circuits. 



ON open-wire lines where the growth is not rapid, there is frequently 

 need for adding telephone circuits one at a time. When the 

 Type D single-channel carrier telephone system was developed a few 

 years ago it became possible to meet this need without stringing 

 additional wires. ^ 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 Type H, has recently been developed 

 and is now being applied. This new system offers improved per- 

 formance, and also, because of its lower cost, is applicable to pro- 

 viding service over shorter distances than were economical with the 

 earlier system. 



The Type 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.^ 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 24- 

 28, 1938. Published in Electrical Engineering, January 1938. 



1 " Carrier Telephone System for Short Toll Circuits," H. S. Black, M. L. Almquist 

 and L. M. Ilgenfritz, A. I. E. E. Transactions, Vol. 48, January 1929, pp. 117-140. 



2 "Carrier Telephone Systems — Application to Railroad Circuits," H. A. Affel, 

 Proceedings of the Association of American Railroads, Telephone and Telegraph Section, 

 October 1936, pp. 654-672. 



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