Part III-Investigations of High-Frequency Echoes

Abstract

A high-frequency sky-wave propagation experiment, carried out on November 19, 1944 by the Institute of Physics, Luftkriegsakademie, Gatow, in co-operation with the Deutsche Reichspost, is described. Signals of duration of 10 to 12 msec were transmitted at 0.5-sec intervals from DLO, Rehmate (near Berlin) on 19,947 kc so that echoes which travelled repeatedly around the earth might be studied. The signals were simultaneously observed and recorded with a cathode-ray oscillograph on moving film at Randers, Denmark, 480 km, and at Gatow, 50 km, from the transmitter. The time intervals measured ranged from 0.1376 to 0.1384 sec between first and second circuits, and are shown graphically together with their individual amplitudes. Periodic fades of the echoes are correlated with multiple paths of propagation and the vertical motions of the ionospheric reflector. The high field intensity of repeated signals is evidence of strong focusing of the hf energy since the propagation seems to occur in a narrow great-circle beam