ELECTRON TUBE PERFORMANCE 



325 



In a rectifier, the effect of fourth-order modulation is to destroy the square 

 law of the rectifier. The error is 



,2 



he ~'Ag 



(0 



This correction is valid for the case of frequency doublers. 

 Two-Frequency Input 



In a detector the fourth-order modulation produces an overloading efifect; 

 the modulator gain is then a function of the input 



G = ^ + |/? + |i) 



(0 



TYPE 6SK7 

 PLATE VOLTS 250 

 SCREEN VOLTS 100 



I^AeJ^Ae 



- GRID VOLTAGE, e 



Fig. 4 — g-e characteristic with second, third and fourth order modulation present. 

 D = f(CB - 2FH); Ag = CB - 2D; S = AD 



A? 

 Neglecting ^ D in comparison with -^ , the error in linearity is 



8Gc . D 



(0 



There will be also a cross-loading effect for an interfering signal R cos rl. 



,2 



^f = 2D[- 



(0 



In a heterodyne oscillator fourth-order modulation will produce a second 

 harmonic at the output. 



H2 = 20 log ^ -f- 20 log ^ + 20 log ^ - 10. 



