LINE CURRENT REGULATION 635 



from adding resistance at points (1) or (3) respectively, will move 

 the maximum point on the curve further to the right. This can best 

 be illustrated by the following example : 



With a line of 1500 ohms resistance, the resistance required in each 

 bridge arm for maximum received current is about 750 ohms, so that 

 the normal 500 ohm bridge arms as shown by Fig. 1 are short of the 

 maximum by 250 ohms. If the line current be reduced to the desired 

 value of .070 ampere by adding resistance at points (3) about 250 

 ohms will be required at each station. This will make the resistance 

 between the duplex sets, corresponding to T in equation (11), 1500 + 

 500 = 2000, for which the value of the bridge arms for maximum 

 received current is about 855 ohms. The operating point on the 

 curve is, therefore, 355 ohms on the left hand side of the maximum, 

 as compared wdth 250 ohms before the resistances were added. The 

 change in the maximum due to adding resistance at points (1) takes 

 place in the same general way though not in exactly the same degree. 



Fig. 4 shows how the line and received current are affected by the 

 resistances in each location with a 1,000 ohm line. From these curves 

 it will be noted that location (2) for the resistances results in a gain 

 of about 25.6 per cent, in received current strength as against location 

 (1) and as compared to location (3) the gain in received current 

 amounts to about 45.6 per cent. 



As the ratio of the bridge arms is not changed by adding the line 

 current regulating resistance in equal amounts at points (2) that 

 arrangement should introduce no difBculties in maintaining a balance 

 between the line and artificial line. Furthermore, arrangement (2) 

 should not increase disturbances due to small extraneous currents 

 in the line. 



