Abstract
The theory of random signals, as applied by various workers to the phenomenon of random fading of pulses singly reflected from the ionosphere, is considered critically. It is shown that, contrary to the prevalent idea, the velocity distribution of fading is independent of the power spectrum of the returned wave. This invalidates the ordinarily accepted explanation of certain observed departures from theory. An alternative explanation of these departures is given, which explanation is quantitative in character and can therefore be experimentally verified. The influence of a steady signal superposed on the randomly fading wave, on the velocity distribution of fading is investigated. It is found that unlike the effect on the amplitude distribution, the effect in this case is very small, resulting only in a very slight increase in the velocity of fading. An alternative method of determining the autocorrelation function of the fading pattern (from which the power spectrum of the returned wave can be derived by inverse Fourier transform) is given. This provides an alternative method of determining the velocity of drift of ionospheric irregularities. The method of deriving the theoretical power spectrum returned by drifting ionospheric irregularities has been improved upon, yielding a form of the power spectrum which appears to be more in accordance with observations.