Investigations of High-Frequency Echoes

A method of measurements of high accuracy has been developed for investigations of telegraph signals from high-frequency stations. Very exact time-interval measurements were obtained at echo signals on distant high-frequency transmitters within the frequency range between 10 and 20 Mc, presuming definite ionospheric conditions which are limited to a few hours daily. The time interval of a signal circulating completely around the earth manifests itself as a constant value of 0.13778 seconds. It seems to be quite independent from the radio frequency used, and further, from the daily and seasonal conditions; and no changes could be perceived during the course of three years. By the occurrence of the indirect signals which reach the recording place along the opposite great-circle path after a measurable time interval later than the direct signals, exact measurements have been possible on such high-frequency transmitters more than 1000 kilometers away. For these cases, the errors were ±25 kilometers from the true values of the geographical distances. A strange multiple-path phenomenon occurred on telegraph signals at less-distant stations regarding the principal signal, which is split into the signal which arrives first, the socalled direct signal, and into one or more retarded signals. It has been found and explained that no exact determination of distances is possible for transmitting stations which are less than about 1000 kilometers from the recording place.