SUBMARINE TELEGRAPH CABLES 439 



of the leads from battery to amplifier and the avoiding of loose switch 

 contacts. 



Results Obtained in Service 



The first two amplifiers built were put in operation on the New 

 York-Azores cable in September 1924, and after a few weeks' testing a 

 speed of 65 cycles per second or about 2,080 letters per minute in 

 cable code was demonstrated. In the fall of 1926 three additional 

 permalloy loaded cables were completed and equipped with vacuum 

 tube amplifiers. They are laid between New York and Bay Roberts, 

 Newfoundland, between Bay Roberts and Penzance, England, and 

 between Fayal, Azores, and F^mden, Germany. A speed of ninety 

 cycles has been demonstrated on the New York-Bay Roberts cable, 

 and the longer section from Bay Roberts to Penzance has worked at 

 eighty cycles. The adjustment of amplification and the flexibility of 

 the shaping networks is such that it has proved possible to remove an 

 amplifier adjusted for operation at about 40 cycles from the long 

 New York-Azores cable and readjust it for use on the short New York- 

 Bay Roberts cable at 20 cycles in about fifteen minutes. 



During the two and one half years of operation of amplifiers on the 

 New York-Azores cable the maintenance required has been almost 

 negligible and the rare cases of trouble have usually been found in 

 the external connections. The longest delay to traffic caused by the 

 amplifiers during this period was about two hours, and was due to the 

 disarrangement of some temporary wiring. The reliability of the 

 amplifiers is well attested by the fact that during the first two years 

 there was only one available at each station, and there was no difficulty 

 in keeping cable and amplifiers in continuous operation. 



In connection with maintenance the vacuum tube amplifiers have a 

 great advantage in that they do not require any delicate mechanical 

 adjustments, while the electricians responsible for the operation of 

 mechanical amplifiers must frequently spend hours at tasks requiring 

 the skill and patience of a watchmaker. 



It has been found possible to handle messages during thunder- 

 storms which prevented operation of the non-loaded cables and their 

 mechanical amplifiers for several hours. As an experiment the loaded 

 cable and amplifier were worked continuously through an unusually 

 severe thunderstorm during which stop watch observations of the 

 intervals between lightning flashes and thunder claps showed that 

 lightning had struck within a thousand feet of the cable terminal on 

 three occasions. Although the induced surges were frequently several 

 times as strong as the signals, the automatically limited output of the 



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