Recent practical and theoretical investigations of the effect of signal distortion on the margins of operation of start‐stop telegraph receivers have led to the development of improved methods of testing and adjusting receivers, have enabled criteria of distortion tolerance to be set up for subscribers' and monitoring receivers and regenerative repeaters, and have made possible the application of more convenient and accurate standards of telegraph transmission. This paper describes the causes of distortion occurring both externally and internally to the receiver and the effects of such distortion on the operating margins. Methods of determining the internal distortion of a receiver are described and some of the more important considerations involved in establishing distortion tolerance criteria are discussed.

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A compact frequency‐shift carrier telegraph system is described which provides channels in the voice range and above the voice. The channel terminal unit incorporates arrangements for handling TWX supervisory signals and employs no electro‐magnetic relays.

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