Certain Topics in Telegraph Transmission Theory

TLDR

Traditional transient analysis of telegraph signal distortion is well established for simple terminal conditions but becomes difficult for realistic, complex terminal apparatus. This paper seeks to solve the distortion problem for complex telegraph terminals by examining the system’s steady‑state characteristics. By expressing distortionless transmission criteria in terms of steady‑state parameters, the authors present a method that simplifies calculations for complex circuits, determine minimum frequency ranges for given signaling speeds, and compare single‑ and double‑sideband carrier telegraphy.

Abstract

The most obvious method for determining the distortion of telegraph signals is to calculate the transients of the telegraph system. This method has been treated by various writers, and solutions are available for telegraph lines with simple terminal conditions. It is well known that the extension of the same methods to more complicated terminal conditions, which represent the usual terminal apparatus, leads to great difficulties. The present paper attacks the same problem from the alternative standpoint of the steady-state characteristics of the system. This method has the advantage over the method of transients that the complication of the circuit which results from the use of terminal apparatus does not complicate the calculations materially. This method of treatment necessitates expressing the criteria of distortionless transmission in terms of the steady-state characteristics. Accordingly, a considerable portion of the paper describes and illustrates a method for making this translation. A discussion is given of the minimum frequency range required for transmission at a given speed of signaling. In the case of carrier telegraphy, this discussion includes a comparison of single-sideband and double-sideband transmission. A number of incidental topics is also discussed.