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BELL SYSTEM TECHNICAL JOURNAL 



In this case the current in the line leading toward the source is in- 

 creased; that is, the reflected wave is of opposite phase to that reflected 

 by an impedance in series with the line. 



Fig. 11 — ^The shunt booster. 



If Zb is made a negative impedance with shunt characteristics and 

 greater in magnitude than Zo/2, the current through Zh reverses in 

 sign, the wave transmitted toward the receiver increases, the transmis- 



Fig. 12 — Echoes caused by boosters and 21-type repeaters 



sion loss becoming a gain and the reflected wave reverses in sign, thus 

 reducing or reversing the current in the line leading toward the source. 

 The relation between the magnitude of the echo and the gain is the 



