The trend in the design of telephone transmitters and receivers

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 reduction 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.