Some Recent Developments in Long Distance Cables 

 in the United States of America 



By A. B. CLARK 



THE transmission history of long distance circuits, and particularly 

 long distance cable circuits, has been one of continually improving 

 standards. It has also been one of continual reduction of circuit costs. 

 These have resulted largely from new developments to which have 

 been added economies resulting from heavy growth and improved 

 engineering. 



To put it another way, present-day circuits are capable of trans- 

 mitting a kilocycle of frequency range more cheaply than those of 

 earlier days. As the cost per kilocycle of band width has been reduced, 

 part of the cost reduction has naturally been used in furnishing tele- 

 phone customers wider-band and generally better telephone circuits. 



The accompanying chart is of interest in comparing the transmission 

 frequency characteristics of what were considered good telephone cir- 

 cuits some time ago with what are considered good telephone circuits 

 today and what are proposed for the future. At the left of the chart 

 are shown various types of circuits which have been in use or proposed 

 for New York-San Francisco service, a distance of a little over 3,000 

 miles. The original loaded transcontinental line, which remained in 

 service from January 25, 1915, until April, 1920, when it was unloaded, 

 gave a band width of only about 900 cycles.* The non-loaded circuit 

 was better, giving about 1,800 cycles. The modern carrier telephone 

 circuit is better still, giving about 2,700 cycles. The extra-light loaded 

 type of cable circuit (H-44, which has been the standard loading system 

 for long distance use for some time) will give a band even wider, 

 extending up to at least 3,000 cycles. 



At the right of the chart are shown typical characteristics for New 

 York-Washington (about 225 miles) two-wire cable circuits with 

 various loadings. The now obsolete heavy-loaded system, H-245, gave 

 an effective range of 1,400 cycles, the medium-heavy loaded or H-174 

 gave 1,900 cycles while a new system which is being considered, called 

 B-88, will give about 2,700 cycles. (At the present time H-174 two- 



* The limiting frequencies are taken as those at which the loss is 10 db greater 

 than the loss at 1,000 cycles. 



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