NEGATIVE IMPEDANCE TELEl'lloXK HIlI'KATKRS 



1077 



that the line and network impodances do not have to be coiitiolled over 

 an extended freciuency band. The conversion f>;ain is hmited by rechicing 

 l3 to a small value at low freciuencies by capacitors (^ and C'., of I'^ig. Ki 

 in the plate-to-grid coupling network, and at high frefiuencies by the 

 small capacitors (\ and ('2 across the grid resistors 7^5 and R& respectively. 



'I'he conversion ratio is affected by small losses inherent in the elec- 

 tron tube and transformer. These are balanced out by a fixed resistor 

 R9 connected in series with the gain adjusting network to increase the 

 amount of positive feedback. 



The final negative series impedance presented to the line is equal to 

 approximately —O.IZn over the frequency band of 300 to 3,500 cycles. 

 The impedance Z.v is determined by the configuration of the gain-ad- 

 justing network comprising several inductors, capacitors, and resistors. 

 These components may be arranged in any form to obtain the desired 

 negati^'e impedance, which in turn, introduces the gain and frequency 

 shaping characteristic desired for each type of line facility. 



The E2 repeater employs a Western Electric 407A twdn-triode elec- 

 tron tube of the 9-pin miniature type. The tube heater circuit can be 

 operated from 24- or 48-volt office battery. The heater current is 100 

 milliamperes for 20-volt operation, 50 milliamperes for 40 volt opera- 

 tion and the plate current is 1 1 milliamperes. 



^M-^ 17.8/1 



j( ^AV 



Fig. 17 — Sclioinatic circuit of E3 repeater. 



