H.F. propagationߞits present and future use for communication purposes

In the present congested conditions of the h.f. band the planning of frequency allocation demands improved accuracy of prediction of both maximum and minimum frequencies usable on any radio circuit. Such improvement involves greater accuracy in the prediction of ionospheric critical frequencies and m.u.f. factors. An extension of knowledge of the paths taken by the waves in travelling from transmitter to receiver is important both for prediction purposes and also for facilitating the design of aerials. Current work on these problems, especially that at the Radio Research Station, is reviewed. The effects of ionospheric ioegularities, such as storms, in degrading the accuracy of predictions is noted, and new results on irregularities in trans-equatorial propagation are described. Recent work on the study of lateral deviation of h.f. signals and on the application of the back-scatter technique to the determination of optimum signalling frequencies and to the study of the distribution of sporadic-E ionization is summarized.