l.UiCTRIC.M. i FSIS .1X1) lUI-.IK .II'I'IJCITIONS 



.\67 



Similarly llio unlialanre relatidiis priHluciin; crosslalk hrlwcrii itu' 

 phaiUoin and the ■■|)lark" side is 



Capacity vinhalame = 2 (G + C, - {C\ + G) + A (Cp - Cnxt)]- 



The factor 2 enters into the last two fornuila> since the difference 

 in ilirect capacities have about twice the effect on phantom to side 

 crosstalk as they do on side to side crosstalk. 



The capacity unbalances gi\'en above are measured on each cjuad 

 in every loading section and give a measure of the side to side and 

 phantom to side crosstalk due to capacity unbalance in the cable. 

 Such measurements are usually made at three points in every loading 

 section and the c|uads are spliced at these points in such a way that 

 the capacity unbalances in the two directions will tenfl to neutralize. 

 In this connection particular care is taken to neutralize the phantom 

 to side unbalances since these are usually higher. 



For making capacity unbalance tests a special portable bridge 

 known as the capacity unbalance test set was developed which has 

 been in general use since the introduction of quadded cables in the 

 telephone plant. Fig. 13 .shows the schematic circuit arrangement 

 of this bridge for measuring the capacity unbalance as indicated above 

 between sides of a quad. 



The two conductors of each side circuit of the quad are connected 

 to opposite cf)rnprs of the bridge, these being designated as "white 

 and "white mate" and "black" and "black mate." The diiect 

 capacities between these conductf)rs then become the arms of the 

 bridge. An oscillator is connected through a transformer to the 

 "white" and "white mate" terminals of the bridge and a \ariable 

 air condenser is connecte<l to these same terminals. .A telephone 

 receiver is connected through a transformer to the "black" and "black 

 mate" terminals. The variable air condenser is adjusted until a 

 minimum lone is observed in the receiver, this adjustment adding 

 capacity to one side or the other f)f the bridge. The variable con- 

 denser is calibrated to read the unbalances directlv in micro micro- 



