APPLYING CARRIER TELEPHONE SYSTEMS 561 



ground construction adjacent to a repeater station differ on the two 

 cables, it is preferable to have pairs in the cable having the longer 

 section of underground connected to repeater inputs. With these and 

 other factors in mind, tentative directions of transmission were assigned 

 to the cable conductors and computations of expected noise currents 

 made and checked with computations which assumed the directions 

 reversed. The total overall noise currents computed to be 1.25 db 

 better when assuming the directions of transmission finally selected 

 for the New York-Charlotte project than when assuming these direc- 

 tions reversed. This was largely due to the fact that south of Peters- 

 burg, where but one cable had existed, a small cable was added to 

 permit carrier operation. Pairs in this cable, because of its small size, 

 are more susceptible to static induction directly into the cable than 

 pairs in larger cables. The effect, therefore, of the greater contribu- 

 tion to overall noise currents, which this small cable tends to cause, 

 was reduced by selecting the directions of transmission so as to take 

 advantage of the increased shielding resulting from underground con- 

 struction adjacent to repeaters. Tables 5 and 6 show the final noise 

 level computations for the 1000-cycle point of channel 12 (57 kc on 

 the line) of a New York-Charlotte system. It will be noted that the 

 longer repeater sections contribute a great deal of noise as compared 

 to average or shorter sections. Noise measurements which have been 

 made indicate that noise conditions compare favorably with those 

 which it was calculated might be expected. 



Non-Regulating Repeater Points 



Examination of the carrier repeater sections on the New York- 

 Charlotte route showed seven to be unusually short and involving all 

 underground cable construction. The usual plan would have been to 

 provide flat gain regulation at each carrier repeater point, but since 

 these seven sections averaged but 14.8 miles in length and the theoreti- 

 cal transmission variation might be but ± 1.42 db, it was obvious 

 that the regulators having a normal range of ± 7.15 db would be 

 required to operate only over a small part of their range. However, 

 the real limitation is not the regulating mechanism but the lower levels 

 to which the line currents without regulated gain would drop during 

 periods of high cable temperature with corresponding impairments in 

 noise levels. In this layout, omission of regulation at one station 

 increases the noise level about the same as lengthening the following 

 repeater section about ^ of a mile. Omission of two successive regu- 

 lators is approximately equivalent to increasing the second repeater 

 section about % of a mile and the third about 1| miles. Repeater 



