An experimental test of reciprocal transmission over two long-distance high-frequency radio circuits

Tests have been carried out under carefully controlled conditions to see whether the attenuation of high-frequency signals sent over a given long-distance radio path differs according to the direction of transmission. The results obtained both across the North Atlantic and between Australia and the United Kingdom show that at times the loss in both directions is substantially the same, and that at other times the loss difference can rise to values of the order of 5 or 10 dB. Usually the loss differences were such that signals outwards from the United Kingdom suffered the greater attenuation, but without further evidence it would be unwise to assume that this tendency is permanent.