NEW YORK-CHICAGO CABLE S3 



Telegraph 



In the section between Philadelphia and Pittsburgh practically all 

 of the existing long aerial wire circuits are composited, that is, they 

 are arranged for simultaneous telephone and telegraph operation. 

 The telegraph circuits thus obtained are generally used in furnishing 

 what is sometimes called "leased wire" service. The ground return 

 system providing either full duplex or single-line operation is used 

 and the line currents average about 75 milliamperes. This grounded 

 telegraph system cannot be used where simultaneous telephone and 

 telegraph service is desired on loaded cible circuits of the length 

 involved in this cable, and as a part of the work of carrying out the 

 comprehensive toll cable plans of the Bell system, a new telegraph 

 system had to be developed. It was found preferable to use a metallic 

 return circuit and to limit the line current to a value between 3 and 5 

 milliamperes in order to prevent serious interference to the telephone 

 circuits due to the "flutter effect, "^ Morse thump, and mutual inter- 

 ference between telegraph circuits. Morse thump results when the 

 composite sets, that is, the apparatus used for separating the tele- 

 phone and telegraph currents, do not completely prevent the latter 

 from entering the telephone circuit, thus causing interference. The 

 telegraph repeaters are located at about 100-mile intervals on the 

 No. 19 circuits and at somewhat less frequent intervals on No. 16 

 circuits. The telegraph apparatus is of course located in the same 

 buildings that are used to house the telephone repeaters, and on the 

 Philadelphia-Pittsburgh cable telegraph repeaters will be located 

 initially at Philadelphia, Harrisburg, Bedford and Pittsburgh. 



Test Boards 



All of the conductors in the cables are carried into stations located 

 at about 50-mile intervals and apparatus is provided in these stations 

 for making regular tests to ascertain the condition of the cable and to 

 locate trouble quickly. At these offices the different kinds of operat- 

 ing apparatus are also connected to the cable conductors; examples 

 of this apparatus are phantom repeating coils, composite sets to per- 

 mit simultaneous telephone and telegraph operation, telegraph 

 repeaters, telephone repeaters and associated balancing equipment, 

 signaling apparatus, and where required, the switchboards necessary 

 for making the telephone connections involved in furnishing service. 

 It is necessary that this apparatus which is installed in large quantities 



'Paper by Martin and Fondiller in Journal of A. I. E. E., February, 1921. 



