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BELL SYSTEM TECHNICAL JOURNAL 



larger percentage modulation in the opposite phase. When the modulation 

 frequency exceeds a few hundred cycles the lamps are unable to follow the 

 individual cycles and the output wave is identical in form to the input. At 

 intermediate modulating frequencies the transmission of a modulated wave 



Fig. 17 — D-C characteristics of a lamp bridge. 



0(1,0) 

 Fig. 18 — Envelope transmission of a modulated wave through a lamp bridge. 



Fig. 19 — Envelope transmission of a modulated wave through two similar tuned circuits 



of selectivity Q. 



involves a phase shift. The behavior of a typical lamp bridge is presented 

 in Fig. 18. 



If the Q of the grid and plate circuits are both relatively high the filter 

 circuit may be taken as equivalent to two separate tuned circuits. The 

 transmission of each is given by Fig. 9. The combined transmission of the 

 pair is given in polar form in Fig. 19. Because two tuned circuits are 



