THE FUTURE OF TRANSOCEAMC TELEPHONY 7 



thus, in a technical sense, the forerunner of modern radio telephony, 

 including broadcasting as well as transoceanic telephony. 



It required much study of radio transmission and many further improve- 

 ments in apparatus technique before speech could be projected across the 

 Atlantic with sufficient clarity and reliability to be truly serviceable. In 

 the long-wave range and for transatlantic distances, radio is seriously 

 limited in two respects: first, the level of noise is high, particularly in sum- 

 mer, due to the frequency of occurrence of thunderstorms in northern 

 latitudes; and second, the received signals become weak during the sunset 

 and sunrise periods. The ionized layers of the upper atmosphere upon 

 which long waves depend for their guidance around the earth are then 

 going through the transition from daylight to nighttime condition. The 

 development of the water-cooled high-power vacuum tube made possible 

 high -power amplifiers to deliver tens of kilowatts needed to lift the signal higher 

 above the level of atmospheric noise. The influence of static was further 

 reduced by the use of directive receiving antennas. Additional improvement 

 was provided by the technique of single-sideband transmission first used on 

 wires. These developments and others assured fairly reliable telephone 

 connections and in 1927 public service was opened jointly by the General 

 Post Office and the American Telephone and Telegraph Company. The 

 carrier frequency was 60 kc corresponding to a wave-length of 5000 meters. 



The opening of the first transatlantic short-wave telephone circuit in 

 1928 followed close on the heels of the long- wave circuit, and was followed 

 in turn by the establishment of additional short-wave circuits in 1929. 

 These were years of increasing disturbance in short-wave transmission and 

 about 1929 preparations were started on both sides of the Atlantic for a 

 second long-wave channel to diversify facilities and thus improve the con- 

 tinuity of the service. This work had not progressed very far, however, 

 before there came in sight opportunities for greatly improving short-wave 

 transmission. Accordingly, the project of the second long-wave circuit 

 was deferred and, upon the actual realization of the short-wave improve- 

 ments years later, was postponed indefinitely. More recently, experiments 

 have been conducted which have demonstrated the feasibility of transmit- 

 ting two channels at different frequencies using the same transmitting 

 equipment. This may lead ultimately to more economical provision of an 

 additional long-wave circuit. 



Short-wave radio has certain outstanding advantages over long waves 

 for transoceanic service; these are less attenuation, lower noise and a wider 

 frequency band in which to operate. The first two factors together with 

 the ability to obtain readily a high degree of antenna directivity, result 

 in considerable economies. In the case of a radio telephone connection 

 between the United States and England, the cost of short waves under 



