CHARACTERISTICS OF TOLL TELEPHONE CABLES 



319 



small and, if the inductance L is expressed in abhenries and capacitance C 

 in abstat-microfarads, then V = 1/LC = l/k, where k is the dielectric 

 constant'^ 



Impedance 

 The characteristic impedance is 



V: 



R + jcoL 

 G + j(^C 



(16) 



which has a large reactive component at low frequencies as shown by the 

 curves of Fig. 20, based on the same reel-length measurements as the curves 



10 



35 



40 



45 



15 20 25 30 



FREQUENCY- KILOCYCLES 

 Fig. 19 — Phase; radians per mile — 16 gauge pairs 36°F. 



for 2?, L, G and C in Figs. 3 to 11. In actual long cables the curves are 

 irregular with frequency as a consequence of small irregularities along the 

 line^^. (See, for example. Fig. 26.) There are also small variations with 

 temperature; for the resistance component about ±1.5 per cent from the 

 average for the temperature range zero to 120° F. at 10 kc, and about ± 1 

 per cent at 100 kc. The reactive component varies ± 10 per cent at 10 kc. 

 over the same temperature range*. 



" G. H. Livens, "The Theory of Electricity," p. 456 and p. 539. 



* K. Simizu and I. Miyamoto, "Effect of Temperature on the Non-Loaded Carrier 

 Cable, Nippon Elec. Comm. Eng., May 1939, p. 596-599. Give similar data on the 

 variation of parameters and attenuation for spiral-four cable at frequencies 0-30 kc. and 

 temperatures 0-50°C. They do not specify the length measured but state that the wire 

 diameter was 1.5 mm. From their d-c. resistance data the length appears to have been 

 about 160 feet. 



