Directional observations on H.F. transmissions over 2100 km

Using a wide-aperture spaced-loop direction-finder, measurements have been made of the direction of arrival of high-frequency radio waves propagated over 2100 km. Pulse transmissions were used for most of the experiments, and first- and second-order F-reflections could usually be identified at 11 Mc/s. The bearing fluctuations of these echoes included a lateral deviation component of approximately the magnitude expected from previous experiments at shorter distances. The rapid fluctuations were appreciably larger than they were at 700km, and this appears to be associated with an increased complexity of the individual pulses. This effect was very marked in the night-time observations on 5 Mc/s and resulted in a standard deviation of 1.5° for individual bearings in an hourly period. The corresponding figure for the 1F echo in the day-time on 11 Mc/s was only 0.6°. The results were unaffected by such changes in the transmitting aerial as were practicable, or by ionospheric or magnetic storms.