Performance characteristics of high-frequency radiotelegraph circuits

Operational data from several important long-distance radiotelegraph circuits have been analysed and the results discussed in relation to variations in solar and magnetic activity. It is shown that the lowest operational efficiency on radio circuits need not necessarily occur at the same time as the lowest level of solar activity. For example, in 1952 the performance of many difficult radio circuits deteriorated considerably, coincident with a peak of magnetic activity, but subsequently recovered although solar activity continued to fall. On certain circuits there is a pronounced seasonal asymmetry of performance in the two directions of the route; to confirm that this is due to propagation effects, data from different organizations operating on substantially the same radio path are compared-particular reference being made to the United Kingdom-South Africa and the United Kingdom-Australia circuits. Suggestions are put forward as to the possible reasons for this asymmetry with season, and consideration is given to effects such as ionospheric propagation, atmospheric noise and the path taken by the ray. Mention is also made of other propagation phenomena, such as echo signals, maximum latitude of ray path and M reflections, which have a bearing on the operation of radiotelegraph circuits. For the purposes of the paper all references to seasons relate to the northern hemisphere.