Tropospheric Effects in Short and Medium Radio Wave Propagation

IN a recent letter, Mr. D. W. Heightman 1 has given some interesting evidence for tropospheric influences on radio wave propagation in the short- and medium-wave bands. Some measurements made in July 1945 on wave-lengths in the range 60–300 metres confirm the existence of such influences. During the course of a programme of ionospheric eclipse observations conducted by the Radio Division of the National Physical Laboratory, at Loth (Sutherland), it was found that echo signals of appreciable amplitude appeared at ranges of 45 km. and 65 km. These signals could be identified as reflexions from mountains and were observed at all frequencies in the range 1–5 Mc./s. Amplitude measurements made each day over a period of a week established the following points.