The Bell System Technical Journal 



Vol. XXX January, ig§i No. i 



Copyright, 1951, American Telephone and Telegraph Company 



The Type N-1 Carrier Telephone System: 

 Objectives and Transmission Features 



By R. S. CARUTHERS 



{Manuscript Received Oct. 17, 1950) 



The Nl Carrier System is a 12-channel, double-sideband system for single 

 cable application. It provides low loss, stable, high velocity service for toll and 

 exchange circuits in the range from 15 or 20 miles to 200 miles. Units and sub- 

 assemblies are miniaturized and arranged on a plug-in basis. Emphasis has 

 been placed on reduction in cost of components, as well as simpUfication of 

 manufacturing methods, engineering, installation and maintenance. Economy 

 is achieved by many novel features, principal among which is a built-in low 

 cost compandor. By compressing and expanding the volume range of speech, 

 the compandor permits much higher tolerance of noise and crosstalk, thereby 

 substantially lowering the cost of both line and terminal facilities. Other impor- 

 tant features are self-contained dialing and supervisory signaling, an individual 

 channel regulator, and automatic equalization through the use of "frequency 

 frogging," or interchange of high- and low-frequency groups at each repeater. 



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Introduction and General Technical Description 



HE N-1 Carrier System is the most recent addition to the alphabetic 

 list of carrier telephone systems which began in 1918 with the A 

 system. This and many other systems produced since then have passed 

 into obscurity. Others like the C, H, J, K, and L Systems* carry the majority 

 of telephone traffic for distances exceeding 100 miles. Even though carrier 

 has been the backbone of all the longer-haul telephone service in the country, 

 these systems, and in particular the terminals, have been too expensive for 

 short-haul use. This has prevented tapping the great mass of circuits owned 

 largely by the Associated Companies and extending into nearly every city 

 and town. The M system, developed primarily for power line use, has 

 found limited appUcation in this field. 



The objective in the design of the N system has been to provide a single 

 cable carrier facility which, without special cable treatment, will be eco- 

 nomical for distances as short as 15 to 20 miles and which will be technically 

 satisfactory in performance for a nominal maximum of 200 miles. Relaxa- 



* See Ust of references at end of article. 



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