ULTRA-SHORT WAVE PROPAGATION 



131 



distance field that would result from radiation in free space." The 

 field strength is more nearly inversely proportional to the second than 

 to the first power of the distance as may be seen by comparison with 

 the light dashed line in Fig. 3. 



In addition to the measurements taken on the ground, measurements 

 on the highest frequency, 80 mc, were made with the receiver in an 

 airplane." The results are discussed later in connection with Fig. 11. 



The effect of altitude was determined at two distances, 77 and 142 

 kilometers, using the Deal transmitter at 69 and 17 mc. The results 



.?so 



10 40 







10 20 



DISTANCE- KILOMETERS 



Fig. 3 — Field strength as a function of distance for transmission over salt water 



from Cliff wood Beach. 



are shown in Figs. 4 and 5. The increase of signal with elevation was 

 much greater on the higher frequency than on the lower frequency. 

 It is interesting to note, however, that if the field were plotted against 

 altitude in wave-lengths the slopes would be approximately the same for 

 the two frequencies. Significance should not be attached to the ratio 

 of the field obtained on one frequency to that obtained on the other. 



Transmission Over Land 

 The transmitters located at Deal were employed for studying the 

 propagation of waves of 17, 34 and 69 mc. over various types of 

 terrain. The transmission paths are shown by the lines radiating from 

 Deal on the map of Fig. 2. Three types of paths are represented. 

 The best for ultra-short wave work was found to be that with the other 

 terminal on high ground, such as is found to the northwest. Another 

 type, not so favorable to the transmission of ultra-short waves, but 

 typical of flat country, could be studied by locating the receiving 



" In free space, the field produced by a given current in a doublet is one half 

 as great as that produced by the same current and doublet when located at and 

 perpendicular to the surface of a perfect conductor. 



'•* These measurements were possible through the cooperation of Mr. F. M. Ryan. 



