Ground-interference pattern of 16kHz radio waves during summer days

Results are presented from measurements of the signal strength made in an aircraft flying northwards from the 16kHz transmitter GBR, Rugby, England, on four days in June 1969, near the epoch of maximum, solar activity. The interference pattern due to the combination of ground and sky waves is found to change significantly with local time, whereas the change between different days at the same local time is small, even though the conditions of magnetic and solar activities have changed. This implies that, for the present observations, the influence of the Sun´s position was more marked than that of the magnetic or solar conditions. The pattern is similar to, but extends, those of Budden, Ratcliffe and Wilkes3 and of Weekes4, which were also made at solar maximum.