TRANSATLANTIC RADIO TELEPHONY 



141 



point that concerns the dip in the ratio occurring at night in London 

 between 12 midnight and 3 a. m. This dip is due to an increase in the 

 noise which occurs around 2 a. m. (A further reduction during this 



Transatlantic Radio Transmission Measurements 



Diurnal Variations of Si6nal to Noise Ratio 



Feb. 25- Apr 9, 1923. 

 Each circle is average of results of tests for that hour 



Fig. 12 



time, and one which extends the time of minimum ratio from sundown 

 on through the night until 2 a. m. is shown by the April measurements 

 which time has not permitted including in the curves). 



During each test period lists of disconnected words were spoken 

 over the systems. As an approximate and easily applied method of 

 indicating the talking efficiency of the circuit, note was made of the 

 percentage of the words which were correctly received. 



The curves of Figs. 13 and 14 show the manner in which the per- 

 centage of the words which were correctly received varies through 

 the 24 hours. Each point corresponds to the percentage of words cor- 

 rectly received during one unit test period. In many of these tests 

 the interference was noted to be caused by radio telegraph stations, 

 and the data in which the interference is of this character, in so far as 

 identified, are indicated by the triangular dots. It will be seen that 

 most of the poor receptions were due to this cause. Especially is 

 this true of tests at 12 noon at which time severe interference from 

 sources local in London was experienced. The circle points are the 



