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THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1956 



Thus under dial operation there is a need for better trunk stability. 

 Therefore, a greater burden is placed on the plant forces to locate unsatis- 

 factory trunks so that proper maintenance action can be taken before 

 customers experience difficulty. 



EFFECT OF CARRIER OPERATION 



Carrier is the principal transmission instrumentality which makes it 

 possible to go ahead A\dth natiomvide dialing with assurance that people 

 can talk satisfactorily over the complex connections set up by the switch- 

 ing sj^stems. But it brings with it formidable problems of maintenance. 

 The high attenuation per mile of the hue conductors at carrier frequencies 

 increases the number of variable elements as well as the precision with 

 which they must be adjusted. The interrelation between the elements 

 adds to the complication. 



Table I illustrates this by giving some figures comparing 100 miles of a 

 voice-frequency cable trunk with 100 miles of a typical trunk on K car- 

 rier, which is \\idely used on cable facilities. The figures apply in both 

 cases to one direction of transmission. 



The ten-to-one ratio in the number of electron tubes represents a 

 greater chance of trouble developing in the carrier trunk due to aging or 

 failure of electron tubes. In the carrier trunks there are more automatic 

 adjustable features. For instance, in a typical K2 carrier system there are 

 five flat gain regulators and one twist regulator in one twist section of 

 approximately 100 miles, against a single regulator in a voice-frequency 

 trunk 100 miles long. These regulators are depended upon to keep the 

 loss variations to tolerable amounts. Any malfunction can have a serious 

 effect on trvmk loss. Furthermore, they must be adjusted to the desired 

 regulating range and therefore they are points at which maladjustments 

 may be made. 



The channels of any one carrier system or of a 12-channel group are 

 commonly routed by the circuit layout engineers to a number of terminal 



Table I 



Total Conductor Loss -db 



Gain Required to Reduce to Via Net Loss -db 



Percentage of Line Loss Represented by a 2 db Variation 



Number of Electron Tubes 



Number of Amplifiers 



Number of Automatic Regulators 



