NEGATIVE IMPEDANCES AND THE TWIN 21-TYFE REPEATER 491 

 from which 



and from (7), 

 Hence if 



M = R, + R,+ 



r = -Rn 



R,Ro 



R, + Ro < M <Ri+ R2 + 



R,Ro 

 R, 



(10) 



(11) 

 (12) 



the impedance r is a negative resistance greater in magnitude than Ro but 

 the system cannot sing because the ampUfier cannot maintain or increase 



Fig. 5 — Curves illustrating properties of shunt negative resistances. 



