A STUDY OF TRANSATLANTIC RADIO PROPAGATION MODES AT 41.5 MC/S

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Abstract
Both great-circle and off-path propagation modes have been investigated on a transatlantic path. Measurements of signal strength and azimuthal bearing were made at Ottawa, Canada, on the 41.5-Mc/s BBC TV sound channel transmissions during the winter months of 1957–58. The predominant signal was found to be a ground (land or sea) sidescatter signal arriving about 35° to the south of the great circle path. The presence of this signal can be explained qualitatively by ground-level focusing near the intersection of the receiver and transmitter skip distances.A secondary off-path signal, arriving about 7° to the north of the great circle path, was observed. This signal may be ionospheric sidescatter from irregularities in the auroral zone. It is suggested that the ionospheric sidescatter is analogous to ground sidescatter since focusing is not restricted to ground level.It is shown that the method using the two-hop geometric great circle path is superior to the 2000-km control-point method for predicting monthly median transatlantic maximum usable frequencies during winter daytime when low to moderate transmitted power is used.

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