THERMIONIC VACUUM TUBES 



81 



it being presupposed (see Sec. 38) that E g is enough less than zero to 

 keep the grid negative at all times. If detection is accomplished by 

 means of a blocking condenser, the variation is as shown in Fig. 50, 

 no sharply defined maximum being present in the curve. 



Plate voltage 



Fig. 50 



Fig. 51 



The variations of detected current under heterodyne operation are 

 shown in Figs. 51 and 52 which refer respectively to detection with 

 and without a blocking condenser. The abscissa, eie 2 , gives the 

 product of the two high frequency amplitudes in the input. As is 

 to be expected when no grid condenser is used (see Equation 13), the 



Fig. 52 



variation of detected current with e\e% is very nearly linear provided 

 E g is sufficiently negative. Fig. 51 referring to detection with grid 

 condenser shows no linear relation however. The data for Figs. 51 

 and 52 are taken from Van der Bijl. 



44. Comparison of Tubes as Detectors. If a tube is available whose 

 detecting coefficient is known, other tubes may be calibrated in terms 



