Some Results of a Study of Ultra-Short-Wave 

 Transmission Phenomena * 



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



The results of a series of transmission experiments made in the range 3.7 

 to 4.7 meters and over distances up to 125 miles are reported. These obser- 

 vations were chiefly confined to the region reached by the directly trans- 

 mitted radiation and are found in good agreement with the assumption 

 that such transmission consists mainly of a directly transmitted radiation 

 plus the reflection components which would be expected from the earth's 

 contour. The residual field not thus explained consists of a more or less pro- 

 nounced difi'raction pattern due to the irregularities of the earth's surface. 

 A hill-to-hill transmission has three demonstrable reflection surfaces. 



Quantitative checks on hill-to-hill transmission have been obtained and 

 it has been found that a field intensity of -iO microvolts per meter gives very 

 good transmission. Static is ordinarily entirely absent and no Heaviside 

 layer reflections have been observed. 



The almost universal standing wave diffraction patterns have been 

 studied and sample records are given. The methods of measuring field 

 intensity which we have used are described in an appendix. No long range 

 transmissions, such as harmonics of distant (greater than 500 miles) short- 

 wave stations would yield, have been observed. 



Introduction 



THIS paper details the results of certain studies which have been 

 made on phenomena connected with the transmission of ultra- 

 short waves during the past few years. The work was carried on 

 coincidently with that described in the companion paper by Schelleng, 

 Burrows, and Ferrell.^ It deals in particular with the establishment of 

 the presence of various ground reflections which must be taken into 

 account in computing ultra-short-wave transmission and with the local 

 disturbances due to both stationary and moving near-by objects. 



Apparatus 



The transmitting apparatus used by us possessed little novelty; 



one type of generator has already been described in an earlier paper,^ 



a second type consisted of a pair of 75-watt tubes operated "push-pull " 



and fed by a constant-current modulating system of orthodox type. 



This latter apparatus served permanently as station W2XM at our 



Holmdel laboratory, and was ordinarily modulated with the output 



from a broadcast receiver. We first employed superregenerative re- 



* Published in Proc. I. R. E., March, 1933. 



I Schelleng, Burrows, and Ferrell, "Ultra-short-wave propagation," this issue of 

 Bell Sys. Tech. Jour. 



^Bell Sys. Tech. Jour., vol. 7, p. 404; July (1928). 



197 



