SOME ASPECTS OF NOISE INDUCTION 



473 



With an inductive exposure of the Umited dimensions available, it is 

 impracticable to secure results which can be related in a quantitative 

 sense to field conditions. Also, such effects as the shielding between 



E 





POWER LINE 



TRANSPOSITION 



SWITCHES 



E 





POWER LINE 

 TRANS- 



TRANSPOSITION 





T 



TO APPARATUS 



FOR 



UNBALANCING 



LINE 



TRANSPOSITION 



AMPLIFIER AND 

 ■^L OUDS PEAKER 



Fig. 1 — Schematic of demonstration circuit. 



the various telephone circuits on a multi-wire line, propagation effects, 

 etc., cannot be shown. Furthermore, the exposure is a great deal 

 more regular than those usually encountered in practice so that, for 

 example, a higher effectiveness of transpositions than is usual can be 

 secured. However, many of the fundamentals of the problem can be 

 illustrated qualitatively. 



Nature of Magnetic and Electric Induction 

 It is often desirable to consider effects of magnetic and electric 

 induction separately, particularly in the technical analyses of specific 

 problems. This is not only because the physical processes and the 

 effects of voltage and current induction are quite different but also 

 because the power circuit voltages and currents are often affected 

 differently by changes in conditions. "Electric induction" is a term 

 used to refer to induction due to the voltages on the power line, while 

 "magnetic induction" is used in connection with the inductive effects 

 of currents. 



Considering electric induction first, perhaps the simplest method of 

 visualizing the phenomenon, is by means of the capacitances involved 

 with a single power wire and a single telephone wire as shown in Fig. 2. 

 Neglecting the impedances outside the exposure (which are shown 

 dotted in Fig. 2) the voltage of the power wire to ground (£p) divides 

 over the capacitances Ctp and Cto in proportion to their impedances 



