The Trend in the Design of Telephone Transmitters 



and Receivers ' 



By W. H. MARTIN and W. F. DAVIDSON 2 



This is a report of the Joint Subcommittee on Development and Research, 

 National Electric Light Association and Bell Telephone System. It was 

 prepared by the Chairmen, respectively for the Bell System and the 

 N.E.L.A., of the Project Committee assigned to this study. 



The report reviews the history and present trend of the design of telephone 

 transmitters and receivers, particularly from the standpoint of their response 

 frequency characteristics, and discusses the possibility of obtaining a re- 

 duction in the effect of line noise by shifting their points of maximum 

 response. It is concluded that no advantage from this standpoint is 

 indicated inasmuch as it has been found that the distribution with frequency 

 of the extraneous energy on telephone toll lines is approximately uniform 

 over the more important portion of the frequency range. It is further 

 stated that the present trend in improvement of the response characteristics 

 of transmitters and receivers is in the direction of reducing the difference 

 between their maximum and average response. 



IN the beginnings of the telephone, the outstanding marvel was that 

 the devices used as transmitters and receivers could perform the 

 necessary conversions between speech sound waves and electrical 

 waves. In the application of these devices, however, it was early 

 appreciated that the range and cost of telephone circuits were directly 



1 Editor's Note: In this issue of the Bell System Technical Journal there are two 

 papers and one report dealing with various phases of the inductive coordination 

 problem, which have had their origin in the work of the Joint Subcommittee on 

 Development and Research of the National Electric Light Association and the Bell 

 Telephone System. 



This organization is one of the subcommittees of the Joint General Committee of 

 the N.E.L.A. and Bell Telephone System, which has for its general objective the 

 working out of methods of procedure whereby problems involving the physical 

 relations between the plants of the electric supply companies and the telephone 

 companies may be handled cooperatively on mutually satisfactory bases. The 

 questions involved are largely of an engineering character, and to carry on that phase 

 of the work the Engineering Subcommittee of the Joint General Committee was 

 appointed. The Engineering Subcommittee has recommended certain broad 

 principles of cooperation as well as the adoption of more detailed principles and 

 practices, which were accepted by the Joint General Committee and published in 

 1922. 



As a result of further recommendations by the Engineering Subcommittee the 

 Joint Subcommittee on Development and Research was organized. It is charged 

 with the conduct of technical investigations, the accumulation of data, and the 

 development of engineering methods for use in the solution of problems of coordi- 

 nation. Its work is organized under a number of subordinate committees known as 

 "Project Committees," each of which is assigned a certain range of subjects for 

 study. 



The first volume of Engineering Reports of the Joint Subcommittee on Develop- 

 ment and Research, containing a considerable part of the technical information thus 

 far developed by the subcommittee has recently been published (April, 1930). 

 ^N. E. L. A. Bulletin, Aug., 1930. 



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