40 



BELL SYSTEM TECHNICAL JOURNAL 



over which the resistance is B. The coefficients of the resistance 

 expansion are readily shown to be 



ro = /35 + (1 - /3M, (11) 



r, = {B-A)'^^. (12) 



V 35 



0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 



P> 



Fig. 5 — Efficiency of a commutator modulator shown as a function of the pulse 

 fraction /3 with the ratio of the two commutator resistances as parameter. Here 

 the resistance terminations to signal and to sideband are optimum and the circuit 

 impedance is made high to unwanted components. Full line applies to double 

 sideband output, dashed line to single sideband output. 



The efficiency (with optimum termination) depends only on /3 and the 

 ratio AlB. The dashed curves on Fig. 5 show the variation of effi- 



