INTERFERENCE ON SUBM.IRINE TELEGRAPH CABLES 405 



the signal frcciucncx-.' It is e\i(lcnt, that correspoiulini; to the niiiii- 

 muni amplitude at which signals are just leyil)le throui^h interference, 

 there is, for a gi\en \alue of sending \oltage, a niaxiniuni speed of sig- 

 nalling which cannot be exceeded, without danger of serious mutilation 

 of the signal. If In' an>' means the magnitude of the extraneous inter- 

 ference can be diminished, signals of smaller amplitude can be em- 

 ployed and the speed of operation consequently increiised. 



~5 6 7 9 3 10 11 12 13 14 15 

 FREQUENCY -CYCLES PER SECOND 



The present paper will be devoted to a description of the manner in 

 which extraneous interference is picked up by submarine cables, with 

 a discussion of the influence of various factors such as depth of water, 

 cable structure and operating conditions. There will also be described 

 a method of reducing interference by a modification of the cable struct- 

 ure. This method has been remarkably successful in the case of the 

 New York-Azores continuously loaded cable,- and has helped to make 

 available the great gain in operating speed due to continuous loading, 

 which is the outstanding feature of this cable installation. 



The disturbances encountered on submarine cables are due mainly 

 to induction from extraneous electromagnetic fields in the sea water, 



* The signal frequency is defined as the fundamental frequency involved in a suc- 

 cession of alternately positive and negative unit impulses. 



2 Buckley, O. E., Journal A. I. E. E., Vol. XLIV, p. 821, August 1925, Bell System 

 Technical Journal, Vol. IV, No. 3, July 1925. 



