ELECTRON TUBE PERFORMANCE 319 



In general, the level of the undesirable fundamental will be higher than 

 the harmonic by 



7/2 = 20 log /-" = log ^^-^ + 12. 

 lip r 



For the maximum current case this reduces to 

 Hi = 20 log — + 18. 



The Modulator 

 When two inputs P cos pt and Q cos ql are applied to the grid, the output is 



^ = ^0 + 1 X^ (^' + Q^) + \ ^ (^' cos 2pt + (f coilqO 

 4 Ae 4 Ac t x^ _ i y 



+ ^ ^ ^Q cos (/, + 5)/ + i ^ PQ cos (/> - q)l 



The last two terms represent the sidebands. 



In the case of a detector the available supply of the carrier voltage Q is 



Ae 

 copious. Putting ^ = y the well known result is obtained 



Ip+g = I^g = lAgP. 

 The conversion transconductance is 



To formulate filtering requirements the signal and carrier leaks must be 

 found. 

 The signal leak is 



The carrier leak is 



20 log ^ =20 log ^ + 12. 

 ^p±g Ag 



Iq ^r. , G . ^^ , Ae 



20 log y-^ = 20 log - + 20 log ^ + 6. 



■i p±g ^t" r^ 



In the design of a heterodyne oscillator a generous supply of both input 



voltages is easily available and maximum output current is desirable This 



Ae 

 occurs when F = Q = — . Then 

 4 



Ip-9 = -^AgAe. 



