Part II-Investigations of High-Frequency Echoes

Oscillographic high-speed records of high-frequency telegraph signals (10 to 20 Mc) which show periodic variations in the field strength are investigated in this paper. A movement of the ionospheric reflector is considered as the cause of Doppler shifts, which are measured within the amplitudes of interfering radio waves between two consecutive minima. The long-distance propagation which usually occurs over multiple paths in the transmission, indicates shifts of 0.1 to 0.5 cps; 2.4 cps were measured at the interference of direct and indirect signal of VIS, Sydney, Australia, on 16,450 kc. Routes passing the auroral zones are characterized by the occurrence of "cleft signals" with shifts between 5 and 30 cps.