The Bell System Technical Journal 



July, 1933 

 Carrier in Cable * 



By A. B. CLARK and B. W. KENDALL 



In order to meet future demands for high-grade and economical circuits 

 in cables, considerable carrier development work has been done which has 

 included an extensive experimental installation on a 25-mile loop of under- 

 ground cable. Sufficient pairs were provided in the cable and repeaters were 

 installed to set up nine carrier telephone circuits 850 miles long. Tests on 

 these circuits showed the quality of transmission to be satisfactory, while 

 the methods and devices adopted to prevent interference between them 

 were found to be adequate. The trial has, therefore, demonstrated that the 

 obtaining of large numbers of carrier telephone circuits from cable is a 

 practicable proposition. 



This paper is largely devoted to a description of the trial installation 

 and an account of the experimental work which has been done in this connec- 

 tion. Due to present business conditions, it is expected that this method 

 will not have immediate commercial application. 



This work is part of a general investigation of transmission systems 

 which are characterized by the fact that each electrical path transmits a 

 broad band of frequencies. Such systems offer important possibilities of 

 economy particularly for routes carrying heavy traffic. The conducting 

 circuit is non-loaded so that the velocity of transmission is much higher 

 than present voice-frequency loaded cable circuits. This is particularly 

 important for very long circuits where transmission delays tend to introduce 

 serious difficulties. 



ATRIAL installation was recently made in which, for the first 

 time, carrier methods were applied to wires contained wholly in 

 overland cable for the purpose of deriving a number of telephone 

 circuits from each pair of wires. The trial centered at Morristown, 

 New Jersey. A 25-mile length of underground cable was installed in 

 the regular ducts on the New York-Chicago route in such a manner 

 that both ends terminated in the Long Lines repeater station at 

 Morristown. The cable contained 68 No. 16 A.W.G. (L3 millimeter 

 diameter) non-loaded pairs on which the carrier was applied. Sufifi- 

 cient repeaters and auxiliary equipment were provided at Morristown 

 so that these 68 pairs could be connected together with repeaters at 

 25-mile intervals to form the equivalent of an 850-mile four-wire 

 circuit. 



From this 850-mile four-wire circuit nine carrier telephone circuits 

 were derived, using frequencies between 4 and 40 kilocycles. The 

 diagram of Fig. 1 shows the system simulated by the experimental 

 setup. 



* Presented at Summer Convention of A.I.E.E., Chicago, Illinois, June 30, 1933. 

 Published in Electrical Engineering, July, 1933. 



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