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BELL SYSTEM TECHNICAL JOURNAL 



in the case of the so-called pole-pairs which straddle the pole and 

 whose wires are about 18 inches apart. (See Figure 9.) The con- 

 struction includes pins and glass insulators for supporting the wires. 



10'- 0" 



^, 4^ 4. 4- 4r^^^ M 4 ^^ -^ 



Figure 9 — Showing arrangement of wires on telephone pole line 



There are three gauges of wire in common use in the telephone 

 plant, having diameters of 104, 128 and 165 mils,* respectively. The 

 largest gauge, 165-mil pairs naturally afford the lowest attenuation 

 and have been generally used in connection with the application of 

 the longer systems. The pairs of this sized conductor are, however, 

 now fairly well used up for carrier purposes and new installations are 

 being made more often on the smaller diameter circuits. 



Typical attenuation curves for the three gauges of wire and the 

 extremes of weather conditions are given in Figure 10. It will be 

 noted that the wet weather attenuation may be as much as 40 per cent 

 higher than the dry weather attenuation. Also, these variations are 

 greater at the higher frequencies. 



It is interesting in this connection to consider the effect of the 

 possible variation in a practical case. Take, for example, a 165-mil 

 pair 200 miles long with a carrier channel frequency at 25 kilocycles. 

 This means a total attenuation of 20 TU in dry weather and 29 TU 

 in extremely wet weather, a variation of 9 TU or a current ratio of 

 about 3 to 1. In the case of a still longer line these possible variations 

 present rather startling figures. For example, in a 1,000-mile circuit 

 the variation would be five times the above or 45 TU, which would 



*The term " mil " as here used is equivalent to 0.001 inch. 



