50 years of radio-scintillation observations

The author attempts a brief summary of the history of ionospheric fading from sources beyond the upper atmosphere. The concentration is on the early studies of scintillation. The first sources used as transmitters were radio stars with varying diameters. With the advent of satellite transmissions at altitudes varying from 300 km to several Earth radii, fading was studied as a function of various regions of the globe. In years of high solar flux, transionospheric propagation through polar and equatorial regions has experience deep fading at frequencies ranging from 54 MHz to 4 GHz. Fading of radio signals from satellites still plays a role in evaluating operational and proposed system effectiveness. The relevance of these studies to Global Positioning System reception and users of proposed systems at L band is discussed.