The Bell System Technical Journal 



Vol XIV July, 1935 No. 3 



Further Results of a Study of Ultra-Short- Wave 

 Transmission Phenomena * 



By C. R. ENGLUND, A. B. CRAWFORD and W. W. MUMFORD 



Earlier published work has shown that, while the chief features of 

 ultra-short-wave transmission over "air line" ranges are calculable from 

 optical theory, there are deviations from this theory at the greater distances 

 where a bending around the earth occurs. In this paper the results of a 

 further study of these phenomena are given. It is shown that transmission 

 to regions beyond the optical range is determined by conditions which are 

 not constant and which, in fact, can produce great signal strength changes. 

 The variable percentage of water vapor normally present in the atmosphere 

 is suggested as a possible cause. The explanation seems, therefore, to 

 involve a combination of diffraction and refraction, this latter variable with 

 time, and at times predominant. 



T N a recently published paper ^ results obtained at the Holmdel 

 -■- Laboratory during a survey of ultra-short-wave transmission 

 phenomena have been given. In this report it was shown that, while 

 the chief features of ultra-short-wave transmission over "air line" 

 ranges are calculable from optical theory, there are deviations from 

 this theory at the greater distances where a diffraction around the 

 earth occurs. The results of a further study of these diffraction 

 phenomena form the data of this paper. 



It is probable that a diffraction around the earth will be distorted 

 by major topographical irregularities, at or near the area of grazing 

 incidence for the waves, and hence that the ocean surface is preferable 

 for a study of this kind. It hardly seems likely that the ocean contour 

 can be rough enough to give results differing markedly from those for 

 a smooth water surface. 



An obvious experimental setup, therefore, is to locate a transmitter 



at or very near the ocean shore and to record the transmitter field as 



a mobile receiver is carried towards or away from this transmitter, on 



paths that go well below the horizon. The receiver can be carried 



* Presented at April 1935 meeting of Union Radio Scientifique Internationale, 

 Washington, D.C. 



^Proc. I. R. E. 21, 464, 1933. 



369 



