Ionospheric Demodulation of Radio Waves at Vertical Incidence

Abstract

In a previous communication, Aitchison and Goodwin (1955) have described an investigation carried out at the University of Adelaide on the demodulation of radio waves at vertical incidence. At a frequency of 1550 kc/s, which is close to the local gyro frequency of approximately 1600 kc/s at the height of the E layer of the ionosphere, marked reductions in the modulation depth were observed on the sky wave. The experimental results tabulated in the previous communication suggested that the effect was greatest at a modulation frequency of the order of 800-1500 cis. From subsequent measurements it is apparent that, in the case of F-Iayer reflection the demodulation was greatest at a modulation frequency of, very approximately, 1 kc/s; in the case of E-Iayer reflection, the degree of demodulation did not vary markedly with change of modulation frequency.