LEAD-COVERED PAPER-INSULATED TELEPHONE CABLE 435 



The elements of a typical cable route are illustrated in the New 

 York to Pittsburgh cable chart shown in Hg. 3. A Pittsburgh call 

 originating at a subscriber's station, for example, in Yonkers, New 

 York, passes through the toll board of the local telephone exchange to 

 the toll center located at Walker Street, New York City. At this 

 point the connections are completed for the call to Pittsburgh through 

 the toll cable circuits and repeater stations between the two cities. 



The speech currents as they travel along this circuit diminish in 

 intensity. Loading coils placed along the cable circuit at regular 

 intervals reduce these losses to a considerable degree but even with 



1 VER. '■., 



WEST VIRGINIA 



Fig. 3 — Typical cable route. 



these it is necessary to supply amplifiers (repeaters) ^^ ^ at intervals of 

 approximately fifty miles to boost the energy level. 



The amount of amplification required for intelligible speech varies 

 with the resistance of the cable conductors which changes with the 

 temperature. In order to regulate the amount of the amplification to 

 compensate for these variations, what is known as a pilot wire regulator 

 is installed at certain repeater points which automatically adjusts the 

 gain of the repeaters to correct for the changing line losses. 



Difficulty is also experienced on long toll lines due to the voice 

 currents being reflected back to the speaker. To prevent this, a 

 device is provided which automatically short circuits one side of the 



^A. I. E. E. Transactions (1919), Vol. XXXVIII, Part 2, "Telephone Repeaters," 

 by Bancroft Gherardi and Frank B. Jewett. . . 



^A I E.E. Transactions (1923), Vol. XLII, "Telephone Transmission over Long 

 Cable Circuits," by A. B. Clark. Bell. Sys. Tech. Jour., Jan., 1923. 



