Experiments in very low-frequency radio propagation

Abstract

In an effort to extend experimentally determined data on the characteristics of very low-frequency radio waves, a vlf transmitting station (8.4 kc) was established at Shaver Lake, California. The establishment of this station permitted controlled experiments in long distance propagation, ionospheric vertical sounding measurements, and attempts at the generation of round trip gyroelectric-echoes. The long distance measurements indicated that at vlf, the ground or surface wave radiated by the antenna, can be detected at great distances. The ionospheric vertical incidence measurements showed rapid fading of the received signal around local sunrise and sunset. Propagation in the presence of the ionosphere is considered in the theoretical form of propagation in a homogeneous gyroelectric medium. The results of this analysis are tabulated in graphical form so that the dispersive qualities of the medium can be readily examined. With the aid of these results, an examination of the natural phenomena of whistlers is presented in order to determine the feasibility of generating gyroelectric-echoes. Reflection and transmission coefficients are presented for vertical incidence in order to ascertain the order of magnitude of such an echo. Experiments thus far performed have not yielded echoes but with modifications in the transmitting and receiving equipment, echoes may be detected. A complete description of the experimental equipment used is given along with a proposal for a more sophisticated receiving system.