TEl.EPllOXr. rR.lXSMISSlOX M.IIM r.X.IXCIi 49 



express impedance in terms of its resistance component and ecjuivalent 

 inductance or capacit>'. In ineasurini; an im|)edance li.i\inj{ inductive 

 reactance at any fre(iuenc\ , /, for example, a l)alance ni\es R = Rx 

 and L=Lx. At tlie fre(iueni-\- /, the etTecti\e resistance is given 

 direcll\- 1)V tlie \alue of R and the re. ut, nice li\- the rilalinn, 1 ir f L_ 



(a) Otreci Current Peftr«tar>ce 



Null M«ih«d of Meac< 



(b) Impedance having rnducCive Pedctence 

 -ing Peftisiance.Peactance and Impedance 



Fig. 14 — Diagrams Showing Principles of N'uU Metliotis for Measuring Resistance, 

 Reactance and Inipcilance 



Tlie impedance is tiic \ectorial sliih of these two or v i?- + (2 ir/L)-. 

 In maintenance work invoi\ing; impedance measurements as will be 

 noted in the next testing method descrilied, the effective resistance 

 component and the eqiii\aleiU indtictaiue are generally used directly 

 without combining. 



5. M E.XSCREMENTS OF LiNE IMPEDANCE AND LOCATION OI- Im PEDANCE 



Irregularities 



Fig. 1.5 shows a telephone circuit connected to a bridge and termi- 

 nated at its distant end in characteristic impedance. If the circuit 

 has approximately uniform impedance throughout its length the 

 resistance and equivalent inductance curves of this impedance within 

 a range of frequencies will be fairly smooth as indicated by .4 and C 

 of the figure. The curves are not perfectly smooth since it is not 

 practicable to construct the line for perfect impedance uniformity. 

 If at some point in the circuit an irregularity is [jresent such as an 

 omitted loading coil, an inserted length of line of different construc- 

 tion, etc., which changes the impedance, this will produce a periodic 

 change in the resistance and inductance cur\'es A and C such as 

 shown by Curve B. Curve C will be changed in the same way as 

 Curve -4 but for simplification this is not shown on the diagram. 



The change in impedance in the circuit reflects some of the current 

 sent out back to the sending end where it adds to or subtracts from 



