6 BELL SYSTEM TECHNICAL JOURNAL 



subject to frequent interruption and the cable was regarded as an economi- 

 cally justified supplement to the radio services as they then were. 



Postponed temporarily because of general business depression, the cable 

 project was later postponed indefinitely because, in the face of improvements 

 in transatlantic radio communication, so expensive a cable to carry a single 

 conversation could no longer be justified. Today it seems improbable 

 that such a cable will ever be laid across the Atlantic. Fortunately, other 

 cable possibilities have in the meantime been developed which look more 

 attractive. Before going into these, however, let us review the develop- 

 ment of transatlantic radio telephony and estimate some of its future pos- 

 sibilities. 



The development of radio communication, even more strikingly than that 

 of wire communication, has been characterized by widening of its spectrum. 

 In fact, starting with Marconi's low-frequency transatlantic experiments 

 of 1901, the spectrum has widened until today it provides some thousands 

 of megacycles. Only a small portion of this range is, however, available 

 for transoceanic communication. There are utilized only two isolated 

 ranges each of which, by comparison with the total radio band, is compara- 

 tively narrow. The low-frequency or long-wave range is a band some tens 

 of kilocycles wide with a top of about 100 kilocycles. This low-frequency 

 portion of the spectrum was intensely cultivated during the first two 

 decades of the present century and by the close of that period had become 

 rather densely populated with radio transmissions. 



In the 1920's the band of frequencies useful for long distances was widened 

 several hundredfold by the discovery that long-distance transmission could 

 be carried on by short waves, that is, by frequencies in the range 3 to 30 

 megacycles. This discovery put transoceanic radio communication on its 

 present world-wide basis. Short waves not only contributed greatly to 

 the communication band width but contributed as well as to the demand 

 for service by reducing costs, since the apparatus required for short-wave 

 circuits proved to be less expensive than that for long waves. 



The transatlantic telephone like its telegraph predecessor started in the 

 relatively cramped long-wave band and then moved into the freer region 

 of the short-wave range. It was in 1915, 14 years after Marconi had 

 spanned the Atlantic by radio telegraph, that speech was first sent across 

 the oceans from Arlington, Virginia to Paris and to Honolulu. This achieve- 

 ment, somewhat beclouded by the events of the first World War, was the 

 result of a plan to talk across the ocean which was definitely undertaken by 

 Bell System engineers after they had successfully established wire telephone 

 communication across the North American continent. For its accomplish- 

 ment there were evolved the first high-power vacuum tubes and the first 

 master-oscillator, power-amplifier tube transmitter. This experiment was 



