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BELL SYSTEM TECHNICAL JOURNAL 



These interfering effects are subject to considerable variations from 

 channel to channel in an irregular manner depending on repeater 

 spacing, phase relations between the carrier sources, etc., so that the 

 characteristics given in Figs. 13 and 14 must be interpreted as indicating 

 average values and trends rather than specific amounts. 



The erratic character of the results due to such fortuitous circum- 

 stances is particularly noticeable in spacing interference measurements 

 made as a function of channel frequency, or in those relating to parasitic 

 currents produced by steady currents in the remaining channels of the 

 system. The general effect of repeater load on spacing interference 

 is illustrated for a particular channel in Fig. 15. This refers to the case 

 where the interference is caused by non-synchronized signals on the 

 remaining channels. 



12 14 16 18 20 22 24 26 28 30 32 3 



SIGNAL-TO-INTERFERENCE RATIO IN DECIBELS 



Fig. 16 — Increase in signal distortion caused by spacing interference. 



As far as the toll line itself is concerned, noise from other circuits is 

 an almost negligible factor in the distortion of signals. It is of a 

 highly fortuitous character and shows no definite trend with frequency 

 except perhaps as it may be somewhat greater in the effective voice 

 range, as modified, however, by variations in cross-talk efficiency with 

 frequency. 



The effect of spacing interference on telegraph distortion is given in 

 Fig. 16, which shows that a residual current as small as 30 db below 

 signaling begins to degrade transmission. 



