Prolonged space-wave fadeouts in tropospheric propagation

This paper contains the r esults of studies performed during the last several years on t he short-term variability of t ropospheric signals received over within-the-horizon paths in Colorado and California. Signal variations of the type observed over such paths have been t ermed "prolonged space-wavE' fadeouts." They are analyzed as a function of carrier frequency, path characteristics, and meteorological parameters. The study also includes an evaluation of fadeouts observed over a path using a mountain peak as a diffracting knife-edge obstacle between transmitter and receiver. Principal results show a stronger diurnal trend of fadeout incidence in continental climates than in ma ritirne climates. A significant dependence of t he fadeout characteristics on the refractive index structu re has been observed in maritime climates. In general , fadeouts tend to be more frequent but of shorter duration for higher frequenci es. There are also indications that the occurrence of fadeout is well co rrelated on vertically spaced antennas. Thus, conventional space divers ity t echniques may not be effective to in crease the reliability of systems operating over within-the-horizon paths.