246 BELL SYSTEM TECHNICAL JOURNAL 



important central station linked with a continental wire network from 

 which it is desired to establish connections with a number of smaller 

 outlying points. This possibility is not as simple as it may appear, 

 however, because there enter the problems of directive antennas, of 

 shifting frequencies if widely different distances are involved, and of 

 not permitting the return transmission to be materially weaker than 

 the outgoing transmission which means the use of relatively powerful 

 stations at the outlying points. In general, these short-wave stations 

 represent rather large investments and in working out interconnecting 

 arrangements of this kind it is important to fit together the schedules 

 at the various stations so as to minimize lost circuit time and to avoid 

 leaving stations in idleness. 



North Atlantic Facilities 



Of the four circuits which now exist across the North Atlantic, as 

 indicated in Fig. 2, one is the long-wave circuit, with which the service 

 was originally started, and three are short-wave circuits. The dashed 

 line, shown in the figure, between New York and London indicates an 

 additional long-wave circuit which is planned. There is also indicated 

 in the figure the ship-to-shore telephone service on the North Atlantic 

 which connects with the land line network on either side. 



The transatlantic long-wave system has already been the subject 

 of technical papers ^ and need not be described in detail. It operates 

 on a single side-band carrier suppression system in a frequency band 

 centering at 60 kc. The single side-band system is used to minimize 

 the frequency space occupied. The single band is used alternately for 

 transmission in the two directions by means of voice actuated switch- 

 ing devices at the New York and London terminals. For the purpose 

 of minimizing the principal limitation of long waves, that of "static," 

 the receiving stations are located as far north as is reasonably possible 

 and use is made of directive receiving antennas. 



The three short-wave circuits which have been provided on the 

 North Atlantic route add materially to the trafiic capacity but are 

 erratic in their behavior and their usefulness is dependent, in a large 

 measure, upon being operated in combination with the more stable 

 long-wave circuit. All three short-wave circuits are affected similarly 

 by the adverse conditions accompanying magnetic storms, whereas 

 long- wave transmission is not materially affected by these conditions 

 except at night.^ The second long-wave circuit is planned to provide 

 a more balanced combination of facilities as well as to add to the total 



1 See attached bibliography. 



- Bibliography 6, 14, 15. 



