c.tHKiiK ii:ii.riioxy ox high i"i.,.i<,i. ii\,^ \"-> 



aiirc i)f the liiu-. If tlic appari-nt inipt.'(laiui' of the line is plollcd 

 against the tcrniinatini; iniprdaiui-, in (I) tlic iiirvc will he hori- 

 zontal; in (,2) the curve will have a positive slope a|)|)roa(hinK ■♦•''° 

 anil in (3) the curve will have a negative slope of approximately 

 45°. Kach of these curves will intersect a 45° line drawn through the 

 origin at a (loint where the terminal inipeilance is ecjual to the surgj. 

 itn|X"dance of the line. This intersection can he determined with the 



FCEQUENCY IN OUAETte WAVE LENC.TH3 IM168 



Fig. 3 — Frfr|ucncy vs. .Attenuation and Frequency vs. Surge Impedance'as Measured 

 on the Tallulah Falls-Gainesville 110,000 Volt Power Line 



greatest ease and accuracy when the curve crosses the 45° line at 

 right angles or under condition (3), that is, when the determination 

 is made at a frequency corresponding to an odd quarter wave length. 

 To determine the surge impedance at a given frequency all that was 

 neccssiiry was to terminate the line at the distant end in an impedance 

 which it was anticipated w-ould he just helow the surge impedance 

 and measure by the substitution method the apparent impedance 

 of the line, and then to terminate the line at the distant end in an 

 impedance which would just exceed the surge impedance and deter- 

 mine the corresfKinding apparent imfwdance. The intersection of 

 a straight line through these points with the 45° line determined the 

 correct terminating impedance. In Fig. 2 is shown a determination 



