Studies of experimental techniques for sounding the ionosphere at low and very low radio wave frequencies

Abstract

Phase measurements of waves reflecting from the lower regions of the ionosphere using frequencies in the range 15 to 100 kc/s furnish a new method of investigating the effects of solar activity on radio communication. In an effort to explore this method of measurement the Ionospheric Research Project of the California Institute of Technology constructed a complete 50-kc/s station in the Mojave desert with the transmitter near Randsburg and the receiver near Victorville. This paper describes the equipment requirements of the station, and a paper by R.S. Macmillan (Cf. Ref. 1) will present the theoretical aspects of the data that were obtained. A crystal-controlled transmitter was used to drive a half-wave resonant dipole, which at 50 kc/s was 8600 feet long. The antenna pattern was such that radiated power was directed upward to the inosphere and thence back to the receiving site by means of reflection. The necessary reference signal was sent to the receiving site by means of a very-high-frequency, frequency-modulated transmitter. A double superheterodyne receiver received the 50-kc/s signal and converted it to 1.61 kc/s. This output was then compared by means of a phase meter with a 1.61-kc/s reference, derived from the 50 kc/s reference signal. The output of the phase meter was filtered (bandwidth=1 c/s) and then recorded. A commercial field-strength meter (bandwidth= 350 c/s) was used in conjuction with this receiver to obtain the amplitude of the reflected wave.