TRANSOCEANIC TELEPHONE SERVICE 267 



dotted curve shows the variation in the horizontal component of the 

 earth's field. The heavy solid line follows the daily averages of the 

 short-wave received signal field. It is apparent that the disturbance 

 took two days to reach its peak and the recovery to normal took nearly 

 a week. The heavy dotted line shows received field on long waves (60 

 kilocycles) and indicates that transmission was improved slightly at the 

 same time the short waves were suffering high attenuation. 



The experience with transatlantic telephone service on short waves 

 covers a period of nearly three years, there having been available a one- 

 way channel from the United States to England used as an emergency 

 facility for the first year and a half, a two-way circuit for the next year, 

 and two circuits since June, 1929. It is only in this later period, how- 

 ever, that a circuit has been available operating regularly with the 

 amounts of transmitter power and antenna directivity which have been 

 mentioned. 



The performance of the two one-way channels forming this circuit is 

 charted in Fig. 3. The charts are plotted between hours of the day 

 and days in the year so that each unit block represents one hour of 

 service time. The solid black areas are time in which commercial 

 operation could be carried on. The dotted strips are uncommercial 

 time. The blank areas are for time in which, for one reason or another, 

 the circuit was not operating and no data were obtained. Perhaps the 

 most outstanding feature of these charts is the tendency of the lost time 

 to fall in strips over a period of two or three days. These strips coin- 

 cide approximately for both directions of transmission. The principal 

 ones are about July 10 and 15 and August 2 and 17. These are charac- 

 teristic of the interruptions accompanying magnetic disturbances of the 

 kind which occur at irregular intervals of a few days to several weeks. 

 They are, of course, not as severe as the disturbance illustrated in Fig. 2. 



It is apparent that for these three summer months this new circuit 

 gave a good account of itself and furnished commercial transmission 

 for something like 80 per cent of the time that service was demanded of 

 it. In these same months the long-wave system suffered its greatest 

 difficulty from static, and we have concretely illustrated the mutual 

 support which the two types of facilities give each other. 



It should not be inferred from these data that the short-wave trans- 

 atlantic radio links furnish 80 per cent of the time talking circuits as 

 stable and noise free as good wire lines. Under good conditions they 

 do provide facilities which compare favorably with good wire facilities. 

 On the other hand they may at times be maintained in service and 

 graded "commercial" under conditions of noise or other transmission 

 defects for which wire lines would be turned down for correction, since 



