Radiocommunication on Frequencies exceeding Predicted Values

An analysis is made of a large number of cases in which communication has been effected on frequencies 1¿6 Mc/s in excess of the monthly mean values predicted from normal-incidence ionospheric data. The analysis indicates that during the winter period, and particularly at the equinox periods March and September, the variability in F2-region characteristics will explain many of the apparent anomalies. The remaining cases show no marked disagreement with the conclusion that reflections from the abnormal E-region are responsible for the received signals. An analysis of observations on 30-Mc/s signals made in Japan over the four-year period 1935¿39 indicates conclusively that single-hop transmissions on frequencies considerably in excess of F2-region maximum usable frequencies are due to reflections from the abnormal E-region.