The Bell System Technical Journal 



April, 1933 



Ultra-Short Wave Propagation * 



By J. C. SCHELLENG, C. R. BURROWS and E. B. FERRELL 



Part I of this paper first describes a method of measuring attenuation 

 and field strength in the ultra-short wave range. A resume of some of the 

 quantitative experiments carried out in the range between 17 mc. (17 meters) 

 and 80 mc, (3.75 m.) and with distances up to 100 km. is then given. Two 

 cases are included: (1) "Optical" paths over sea-water and (2) "Non- 

 optical" paths over level and hilly country. An outstanding result is 

 that the absolute values of the fields measured were always less than the 

 inverse distance value. Over sea-water, the fields decreased as the fre- 

 quency increased from 34 mc. (8.7 m.) to 80 mc. (3.75 m.) while the opposite 

 trend was found over land. As a rule, the signals received were very 

 steady, but some evidence of slow fading was obtained for certain cases 

 when the attenuation was much greater than that for free space. 



Part II gives a discussion of reflection, diffraction and refraction as 

 applied to ultra-short wave transmission. It is shown, (1) that regular 

 reflection is of importance even in the case of fairly rough terrain, (2) that 

 diffraction considerations are of prime importance in the case of non-optical 

 paths, and (3) that refraction by the lower atmosphere can be taken into 

 account by assuming a fictitious radius of the earth. This radius is ordi- 

 narily equal to about 4/3 the actual radius. 



The experiments over sea-water are found to be consistent with the 

 simple assumption of a direct and a reflected wave except for distances so 

 great that the curvature of the earth requires a more fundamental solution. 

 It is shown that the trend with frequency to be expected in the results for 

 a non-optical path over land is the same as that actually observed, and 

 that in one specific case, which is particularly amenable to calculation, 

 the absolute values also check reasonably well. It is found both from 

 experiment and from theory that non-optical paths do not suffer from so 

 great a disadvantage as has usually been supposed. 



Several trends with respect to frequency are pointed out, two of which, 

 the "conductivity" and the "diffraction" trends, give decreased efficiency 

 with increased frequency, and another of which, the "negative reflection" 

 trend, gives increased efficiency with increased frequency under the con- 

 ditions usually encountered. 



The existence of optimum frequencies is pointed out, and it is emphasized 

 that they depend on the topography of the particular paths, and that 

 different paths may therefore have widely different optimum frequencies. 

 Thus, among the particular cases mentioned, the lowest optimum values 

 vary from frequencies which are well below the ultra-high frequency range 

 up to 1200 mc. (25 cm.). For other paths the lowest optimum frequency 

 may be still higher. 



Introduction 



WITH the extension of the radio frequency spectrum to higher and 

 higher frequencies have come new problems, both of experi- 

 ment and of theory, which require quantitative study for solution. 



* Presented at New York Mtg. of I. R. E., Nov. 2, 1932. Published in Proc. 

 I. R. E., March, 1933. 



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