A Statistical Study of Selective Fading of Super-High Frequency Radio Signals

It is well known that, in the high-frequency range during fading conditions, radio signals on different frequencies may exhibit at any instant radically different behavior. This may be true even though they are in the same frequency band and exhibit the same statistical behavior, when observed over a longer period of time. It is also known that h-f fading may be frequency selective enough within the narrow limits of a single radio channel to cause severe distortion of modulated signals. It has been established that the cause of these phenomena is multipath transmission. This knowledge, which is of long standing in the high-frequency range, raised questions concerning the prevalence of similar phenomena in the super-high-frequency range about which relatively little has been known until recently. During recent years studies of super-high-frequency propagation and fading have been made which have been previously reported.1 In these tests a frequency-sweep method was used to determine how the loss of a particular radio path varied with frequency at a given instant; and short-pulse methods were used to determine the path length differences which were involved when multipath transmission occurred. These are 1 A. B. Crawford and W. C. Jakes, Jr., Selective Fading of Microwaves, and 0. E. DeLange, Propagation Studies at Microwave Frequencies by Means of Very Short Pulses, Bell System Tech J., 31, Jan., 1952.