Abstract
This report presents the results of field strength measurements on horizontally polarized u.h.f. transmissions at 560 Mc/s over the North Sea at distances from 123 miles (198 km) up to 591 miles (950 km). These measurements extended over a period of two years and have been used in the preparation of field strength/distance curves for various percentages of the overall time. Measurements of site variation factor made within 1 mile (1.6. km) of the Happisburgh site indicates that the difference between the field strengths received at the Happisburgh site and the average site in the area depends upon the degree of abnormal propagation present.
The results are compared with earlier measurements at 187 Mc/s made over similar transmission paths and with measurements at 495 and 560 Mc/s made over land paths. It is revealed that signals are propagated over sea paths with considerably less attenuation in Band IV than in Band III. In Band IV there is less attenuation over sea paths than over land paths.
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