High-speed recording of radio-telegraph signals

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The paper first describes the systems in most general use, and gives a brief definition of modulation requirements for telegraph services. The various sources of distortion are described; these are fading, noise, and interference from other stations, but chiefly phase distortion due to propagation over more than one route between transmitter and receiver. The on-and-off character of morse signalling enhances the difficulties which come from most sources of distortion. There follows a description of the general characteristics required in radio receivers designed for the purposes under discussion, including a description of two types of receiver in current use. This is followed by a consideration of special requirements of the recording units into which the receivers' work, with a description of a typical unit. In the discussion of both the receiver and the recording unit the special measures provided to offset the three types of distortion previously mentioned are discussed in some detail. At first sight it may appear extraordinary that the simple business of rectifying a signal and passing the resulting direct current through an ordinary telegraph relay can become so complex as the paper suggests. It is almost wholly owing to the combined effects of the three types of distortion discussed that many of the complexities have arisen. Experience has shown that the necessity of continuing high-speed working during abnormal conditions demands the comparatively complicated solution described. Diversity reception is discussed in some detail, with particular reference to the special problems of combining the automatic gain-control (a.g.c.) systems and the receiver outputs. Recording by undulator is chiefly considered in the paper as a whole, but the discussion on the effects of distortion, and the counter-measures taken, is even more applicable to machine-printing systems, since the latter have less margins of tolerance in operation. The paper concludes with an indication of the trend of development towards different methods of signalling, which may reduce difficulties of reception and recording in comparison with the old on-and-off methods of conveying intelligence.