The influence of wave-propagation on the planning of short-wave communication

This paper deals with the path from transmitter to receiver as it affects communication on frequencies of 2¿30 Mc/s, and describes the war-time practice of the Interscrvices Ionosphere Bureau (I.S.I.B.). In this band the chief factor is the ionosphere. Methods of exploration of the ionosphere are discussed, especially with regard to obtaining data applicable to communications. Mention is made of the great expansion in the number of ionosphere observatories during the war, and on the basis of this new knowledge, methods of predicting ionosphere characteristics are described, with examples. From a communication point of view, a transmission path via the ionosphere behaves as a band-pass filter introducing noise and distortion as well as attenuation, and modern methods of calculating the frequency limits and the properties in the pass-band are given, with typical examples. Predictions are made for mean values, and deviations from the mean are also considered, including the effects of magnetic storms. The war-time service of prediction of magnetic storms, given by the authors from I.S.I.B., is described in outline. Attention is directed to some of the main points in need of further elucidation, such as attenuation and noise, and the method of production of the ionosphere.