A SUBMARINE TELEPHONE CABLE WITH SUBMERGED REPEATERS 83 



vana the gain with reduced feed back of the individual repeaters can be 

 measured by scanning the test frequency region with an oscillator and detec- 

 tor at Key West. An indication of incipient decay of gain of any repeater is 

 thus given. 



The power for the repeaters is supplied over the cable conductor from Key 

 West. A positive potential of about 250 volts is applied to one cable and 

 — 250 volts to the other, with a loop connection between the two cables at 

 Havana to complete the d-c. circuit. This neutral point is also connected to 

 ground. The current in the cable conductors is at present maintained at 0.23 

 ampere. A view of the rectifying and control equipment for one of the polari- 

 ties is given in Fig. 13. Precautions are taken against interruption of the 

 power supply to the cable, and sensitive controls are provided to maintain 

 the current constant in spite of earth currents and to guard against excessive 

 currents or potentials in the cable system in case of trouble in the power 

 supply or in the cable itself. 



Laying the Cables 



The laying of the cables was completed without undue incident by the 

 Cable Ship LORD KELVIN. The task was one of unusual difficulty since 

 modifications had to be made in the cable laying gear, some of them untried, 

 and it was particularly desirable that the prescribed lengths and courses be 

 realized. 



Modifications were made in the cable laying gear in order to obtain an 

 additional margin of safety in laying repeaters. As was previously indicated, 

 the repeater is capable of bending without harm on a diameter of approxi- 

 mately 72 inches; and the existing cable drum, approximately 68 inches in di- 

 ameter, would have been adequate. It was felt desirable, however, to build 

 the drum on the LORD KELVIN out to an 85-inch diameter to match the 

 diameter of the bow sheaves. The dynamometer sheaves and the sheave lead- 

 ing the cable off from the brake drum presented more of a problem. The lead 

 off sheave was replaced by a ring sheave, 85 inches in diameter, supported 

 on wheel bearings. The frame supporting these bearings was hinged at one 

 end and the pressure on the other end of the frame, due to the tension of the 

 cable passing over the sheave, offered a ready means for measuring this ten- 

 sion. For this purpose a resistance pressure cell was employed with a recorder, 

 which not only gave a continuous record of tension but also relayed the sig- 

 nals to a vertical indicator on deck for the guidance of the brake operator, 

 and to a smaller indicator on the bridge. This arrangement is shown in Fig. 

 14. It is felt that it has much to recommend it over the conventional dyna- 

 mometer from the standpoints of sensitivity and quickness of response. 



It was important to measure the transmission characteristics of the re- 



