814 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1953 



power supply resistance are the resistance component and the line and 

 power separation filter capacity to ground make up the shunt capacity. 

 If the circuit were used in this form the primary current at each repeater 

 would be different since it would be the vector sum of the current in 

 the succeeding section and the current in the shunt capacitance. This 

 is undesirable as the objective is to make all power supplies alike. A 

 familiar solution is applied to this problem by inserting an inductive 

 reactance in series with the line. A value of this reactance is chosen for 

 each repeater to compensate for the current through the effective shunt 

 capacitance and thus make the currents through each of the power 

 supplies as nearly aHke as possible. 



To simplify the loading adjustment in the L3 system a continuously 

 variable loading inductor was developed. This arrangement allows more 

 accurate adjustment of loading without the complications of changing 

 wiring taps in a high voltage circuit. The design of such an inductor 

 presented formidable obstacles as a large range of variation was de- 

 sired (20-120 mh), and relatively high currents and voltages were in- 

 volved. The device used consists of the two inductors which may be 

 rotated with respect to each other, so that the coupling between their 

 magnetic circuits varies ideally between zero and 100 per cent. One in- 

 ductor is inserted in each side of the power circuit and a net result is 

 obtained which is equivalent to varying each inductor. 



3.24 Physical Description 



The type of auxiliary repeater generally used is shown in Fig. 17. 

 It consists of a 6-foot cable duct framework upon which the component 

 panels are mounted. It is completely wired in the factory. The lower 

 third of the bay contains the power supply equipment while the upper 

 part contains two transmission panels. One panel is provided for each 

 direction of transmission and all of the transmission components of the 

 circuit are found on these panels. The demountable units, amplifier, 

 regulator, and pilot alarm unit are interconnected with plugs and jacks, 

 so that they may be removed for maintenance. The other units are 

 interconnected by screw-type terminals and cable as it is expected that 

 they seldom will require maintenance. 



Other types of repeaters will be available to meet special conditions 

 such as manholes where sealed apparatus cases will be required to pre- 

 vent damage due to water submersion, or telephone offices where stand- 

 ard ll'-6" frameworks are usually desired. 



