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BELL SYSTEM TECHNICAL JOURNAL 



As might be expected, temperature has a great deal to do with the value 

 of G. Variations with temperature shown by the curves in Fig. 11 may be 

 expressed for small temperature ranges by the equation 



G = Gi [1 + kit - h)] (8) 



where Gi is the value of G at the temperature h and k is the temperature 

 coefficient of leakage conductance. Curves of k based on measurements on 

 a 61-pair, 16-gauge cable are given in Fig. 12 in the neighborhood of 70 

 degrees Fahrenheit. It will be noticed that k is negative below 1203 kc. 

 but at high frequencies the coefficient increases rapidly from its minimum 

 value reached at about 500 kc. 



o 



o 



-6 

 8 



6 8 10 



20 



40 60 



100 



200 



600 1000 2000 



FREQUENCY- KILOCYCLES 



Fig. 12 — Conductance-temperature coefficient; micromhos per mi. per 1°F. 

 16 AWG 61-pair paper insulated cable at 70°F. 



It was mentioned above that moisture in the cable has a pronounced effect 

 on the conductance. To drive out excess moisture during manufacture the 

 reels of paper covered cable (or cores) are placed in vacuum driers and then 

 stored in a room maintained at about 110° F. and at a relative humidity of 

 1/2 of 1 per cent or less until the cables are covered with their lead-antimony 

 sheaths. The lead presses are adjacent to the ovens and the cable is fed 

 through the wall directly into the press so that it emerges at the opposite 

 side covered with the sheath. This procedure minimizes the amount of 

 moisture entering the paper of the cables after they have been dried. The 

 practical measure of the moisture content and the effectiveness of the drying 



13 C. D. Hart, "Recent Developments in the Process of Manufacturing Lead-Covered 

 Telephone Cable," B.S.T.J., VII (1928) pp. 321-342. 



