46 BF.l.l. SYSTEM ir.CIIXIC.II. JOIKXAL 



this paper l>iil tlu-st- art- Kt^nirally will known am! tlicrefore require 

 no tietaiied description. 



1. Measirkmknts of Crosstalk 



In the circuit shown in Kig. 1 1. if a-c. power is supplied to a circuit 

 known as the "disturhinn" circuit and unlialances exist between this 

 circuit and a second known as the "disturbed" circuit, power will be 

 transferred from one circuit to the other causing crosstalk in the 

 second. A dehnite jwiwer transmission loss therefore takes place 

 between the two circuits which can be measured by a loop trans- 

 mission test similar to the elTicicncy tests described in the main body 

 of the pajK'r. An adjustable shunt called a "crosstalk meter" cali- 



C'oit Talk Uuijtr 



MeMv-em«flU of C/ots Talk 

 Fig. 11 — DiaKraiii SliowiiiK I'rincipK's of ("riisstalk Measurements 



lirated in either 77' or in irossialk units is subs(iluu<l tdr llie two 

 circuits. With the .same power supplied alternateK' to l)()lh the 

 "disturl)in(j" circuit and the meter and with the sending and recei\ing 

 end imiK-dance conditions as shown, the meter shunt is adjusted 

 until, in the o[>inion of the obser\er, the annoyance produced li\' the 

 tone in the recei\er is judged to be equal for the two conditions. 

 The reading of the shimt if there was no dist<jrtion of the line cross- 

 talk currents Wduld then give the \-olume of crosstalk which could 

 be e\|)ressed in Tl^ as 10 login Pr P, similar to loop transmission 

 testing. However, this relation only holds approximateK' in practise 

 since the line cro.ssialk measured is produced by various currents 

 having different phase relations and a certain amoimt of distortion 

 therefore occurs. The commercial form of crosstalk set now used is 

 equipiKil lo gi\e the approximate imiK-jiance relations rei|uired and 

 also pro\ides a feature for eliminating the effect of line noise except 

 in the case of one lyiK' of measurement which is made on long cable 

 circuits. lM»r practical reawins the results are generally expressed in 



.r..--i,.ll.: iii.ii- riiluT ih.UI 77'. 



