A Possible Interpretation of the Fast Regular Fading observed on Satellite Transmissions

Abstract

Frihagen and Tröim¹ have already observed a deep and nearly sinusoidal type of fading on fast amplitude records at 108 Mc/s. The effect only lasted for a few periods and a time delay between similar features on records taken at two spaced aerials indicated that it was introduced in the ionosphere. They proposed that this phenomenon was caused by diffraction at a single ‘blob’ in the ionosphere and that it is similar to that which was observed in radio-star scintillation by Wild and Roberts². Apparently the same kind of amplitude variations were observed on several occasions at Kiruna (67.8° N., 20.4° E.) (ref. 3) on records of Transit IV A at 54 Mc/s which showed intense scintillation. The phenomenon was usually more persistent than that observed by Frihagen and Tröim and often lasted up to a hundred periods. The fading periods varied between 50 and 500 msec, but there was a predominance of periods of about 100 msec. Fig. 1 gives an example of persistent regular fading lasting about 10 sec. Some cases of the phenomenon of short duration (about 1 sec) which exhibit monotonically increasing (or decreasing) amplitude and period may be explained by diffraction at single ‘blob’ in the ionosphere. However, it is difficult to explain long lasting, regular fading in this way.