A Statistical Study of Selective Fading of 

 Super-High Frequency Radio Signals 



By R. L. KAYLOR 



(Manuscript received May 7, 1953) 



The results of two months of comprehensive frequency-sweep measure- 

 ments of selective fading in the hand between 3750 and 4190 mc ever a radio 

 relay path in Iowa are reported. An abridgement of the data, general 

 conclusions derived from the data and an example of the use of the data in 

 connection with frequency diversity measures for radio relay systems are 

 given. 



INTRODUCTION 



It is well known that, in the high-frequency range during fading con- 

 ditions, 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 kno^vn 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 trans- 

 mission. 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. 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 



^ 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. 



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