318 



BELL SYSTEM TECHNICAL JOURNAL 



Components of Aa/AT computed by formula (15) are given in Fig. 18 

 It is evident that changes in R/L are responsible for most of the change in 

 attenuation since the small changes in attenuation introduced by ALC and 

 ARG tend to annul each other over most of the frequency range shown. 

 This is to be expected from the approximate high-frequency formula (12) 

 in which G/2C is much smaller than R/2L. 



\ 



40 50 60 70 



TEMP.-DEGREES FAHR. 



90 



100 



120 



Fig. 18— Components oi ^ = DB per °F. per mile = CiAR/L + CaAZC + CzARG vs. 

 temperature — 19 gauge pairs 



Phase Change and Velocity 



As pointed out above, merely changing the signs of the last parenthetical 

 expression in equations (10) and (11) gives corresponding formulas for phase 

 angle in radians. Fortunately, the phase change is nearly, though not 

 quite, linear with frequency (Fig. 19). The velocity, V = co//3, for 19-gauge 

 pairs is about 105,000 miles per second at 10 kc. and increases slowly to about 

 125,000 mps. at 100 kc. At high frequencies the internal inductance is 



