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 first sources used were discrete radio stars. With the advent of satellite transmissions at altitudes varying from 300 km to several Earth radii, various areas of the globe were studied. In years of high solar flux, observations from polar and equatorial regions will experience deep fading at frequencies ranging from 150 MHz to 1600 MHz. 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 users and users of proposed systems such as IRIDIUM is discussed