50 



/?/■/-/. SrSTHM ll-CHXIC.IL JOlKX.iL 



the st'iulinv; lurrfiit cit'iK-iulinn on llu- phase relations of ilie iwn cur- 

 rents at any particular fre(|iiency. Since imix-dance equals E I its 

 value changes as the \alue of / changes. This is made use of in line 

 impedance measuring work to gi\e a location of inipedaiue irregu- 

 larities which mav exist somewhere in the line. 



C*co»l under Tert 



3 





Null >MU<ed or Uwurinf I 



•-^cy of MvMufMf C*rf«nl 



B lmp«d»nc« md LOCM.04 l«wp«d»f>e« trrequlai 



l-'ig. IS — Diagram and Imix^danrc Curves Showing Principles of Line Impedance 

 .Measurements by Null Method and Location of Impedance Irregularities 



Referring to Fig. 1'), let d cqua\ the distance in miles to an im- 

 IH'dance irregularity and /, one frequency at which the resistance 

 comiMinent of the impedance is a maximum. The next maximum 

 |)oint will occur at a frequency /: such that as the frequency has 

 been increased, one complete wa\e length is added in the distance 

 lra\eletl by the reflectetl current. Maximum points at /.i, A, etc., 

 occur in the s;ime way as the frequency is increased. Considering 

 the two values /i and /j let 



r =vel<K'it\- of ciurcnl in miles per second 

 11*1= wave length at fre(|ucncy/i 

 M'; = wave length at frequency /j 

 .V = number of \va\i- lengths in distance Iraxeied 

 li\ icllti i( d I urrcni or 2 d. 



