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advantage in London of the large noise values which night there had 

 brought on. Conversely, the high signal to noise ratio, obtaining at 

 about sunrise in London, appears to be due to the fact that as the 

 termination of the night belt, moving westward, intervenes between 

 England and the source of atmospherics to the east, the noise level 

 drops rapidly and has reached low values by the time sunrise arrives 

 in London. At this time, however, darkness still extends to the west 



Transatlantic Radio Transmission measurements 



Fig. 11 



and the transmission efficiency from America is at its maximum. It 

 is, therefore, due to this interplay between these two factors, signal 

 strength and noise strength, controlled very largely by the transition 

 periods between day and night, that the signal to static ratio varies 

 diurnally in the manner pictured in Figs. 11 and 12. 



Concerning seasonal variation, shown by a comparison of Figs. 

 11 and 12, the following can be said: The dimunition in signal-to- 

 noise ratio in the second test period as compared with the first is 

 caused by the fact that the signal strength has decreased and at the 

 same time the noise has somewhat increased. There is just one other 



