86 



BELL SYSTEM TECHNICAL JOURNAL 



system used 16-gauge pairs.) Because the conductors are small and 

 closely spaced, with paper and air dielectric, the attenuation of a 

 non-loaded 19-gauge pair at the frequencies involved is inherently 

 high, as will be seen from Fig. 4. Because of the high attenuation, 

 the repeaters must be placed much closer together than is necessary 

 for voice-frequency cable circuits. Fortunately this effect is partly 

 offset by the fact that it is possible, as discussed later, to use higher 

 gains in the carrier repeaters. 



The cable pairs exhibit the rise in attenuation with frequency which 

 is familiar in most transmission circuits. This effect is brought about 

 largely by the increase in conductor resistance, due to skin effect, and 



3.0 



2.5 



r, 2.0 



Z 1.5 



q 1.0 



0.5 



10 15 20 25 30 35 40 45 50 55 60 



FREQUENCY IN KILOCYCLES PER SECOND 



Fig. 4 — Attenuation of 19-gauge non-loaded cable pair. 



65 70 



the increasing dielectric losses. More important than this, however, 

 is the fact that the resistance of the wires and the other "constants" 

 of the cable pair undergo variations with temperature, which in turn 

 affect the attenuation. The magnitude of the result for a representa- 

 tive non-loaded 19-gauge cable pair is illustrated by the curves of Fig. 

 4, which show, respectively, the attenuation for an average tempera- 

 ture, assumed to be 55° F., and for 0° F. and 110° F. The latter 

 values, often taken as the extremes of annual variation for an aerial 

 cable, are in fact frequently exceeded. One reason for this is that 

 when the sun is shining directly on an aerial cable, it may assume a 

 temperature from 15° to 25° above that of the ambient air. The 



