Transoceanic Telephone Service — Short-Wave 



Transmission 



By RALPH BOWN i 



The discussion relates to the transmission problems involved in short-wave 

 radiotelephony over long distances and the transmission bases for design of 

 the systems used in commercial transatlantic service. Choice of operating 

 frequencies, amounts of transmitter power, directive transmitting and re- 

 ceiving antennas, automatic gain controls in receivers, and voice-operated 

 switching devices are all factors which may be invoked to aid in solving these 

 problems. The way in which they have been applied in the transatlantic 

 systems and the results which have been obtained are set forth briefly. 



TRUNK circuits between London and New York which furnish 

 telephone service between these two cities and also permit suc- 

 cessful conversation by means of toll wire extensions between the 

 United States and Europe more generally are being carried over both 

 long waves and short waves. It is the purpose of this paper to consider 

 the transmission side of the new short-wave circuits which the American 

 Telephone and Telegraph Company and the British General Post Office 

 have made available for this service. In doing this we shall proceed 

 from the more general considerations, relating to wave-lengths and 

 communication channels, through a discussion of the principles govern- 

 ing the general design of the system, into a brief summary of practical 

 performance results. 



The frequency range so far developed for commercial radio use is 

 roughly 20 to 30 million cycles wide, extending from about 10 kilocycles 

 to perhaps 25,000 kilocycles per second. There are two parts of this 

 whole spectrum suitable for transoceanic radiotelephony — the long- 

 wave range which is relatively narrow, extending roughly from 40 

 kilocycles to 100 kilocycles, and the short-wave range which in its 

 entirety is much broader, extending from about 6000 kilocycles to 

 25,000 kilocycles. 



It is evident that the long-wave region, including perhaps only 50 

 kilocycles, offers opportunity for development of relatively few tele- 

 phone channels, particularly in view of the fact that it is in use by a 

 number of telegraph stations. Also it must be borne in mind that for 

 telephony these waves are suitable for only moderate distances of the 

 order of 3000 miles and for routes in the temperate zones where static 



1 Presented at the Winter Convention of the A. I. E. E., New York, N. Y., Jan. 

 1930. 



258 



