LEAD-COVERED PAPER-INSULATED TELEPHONE CABLE 467 



returns to the lower end of the scale, See Fig. 35. The high resistance 

 in series with the grid of the third or rectifier tube prevents the over- 

 loading of the milliammeter when a large input voltage is impressed on 

 the indicator circuit. 



Toll cable in addition to the above receives a capacitance unbalance 



CWM' 



C4 



:cb 



Cbm 



C3 



C2 



Ci 



GROUND 



AGROUND UNBALANCE = (C2 + C4) - (c | + C3) 



I ||ll- GROUND 



cbm 



'GROUND 

 Fig. 37 — Side-to-side capacitance unbalances. 



test which is indicative of the cross-talk existing between circuits. 

 These tests are made with a special shielded bridge mentioned above, 

 which measures the capacitance unbalance between side and phantom 

 and side circuits of "quads" (Figs. 36 and 37). These bridges are also 

 provided with visual balance indicators as described above. 



After the cable has successfully met all electrical requirements both 



