304 JOURNAL OF THE WASHINGTON ACADSMY OF SCIENCES VOL. 11, NO. 13 



contemplate their use with any degree of confidence. When a multi- 

 plicity of electron tubes is used the storage battery equipment pre- 

 sents a serious problem to the field party. Either the battery must 

 be of large capacity or provision must be made for frequent charging. 

 If, therefore, any radio receiver-recorder is to be available for service 

 in the field, keeping the number of tubes down to a minimum is an 

 important consideration. 



The nucleus of our receiver-recorder is the regenerative circuit shown 

 in figure 1. It consists of a capacity Ci and inductance Li in the grid 

 circuit of the electron tube, the inductance Li being coupled to the in- 

 ductance Li in the plate circuit of the tube. In order that the circuit 



may be regenerative the coupling must 

 be of such sign that a rise in plate cur- 

 rent results in a rise in the grid pot- 

 ential. The potentiometer P serves 

 to adjust the mean grid potential over 

 a suitable potential range, both nega- 

 tive and positive. 



Such a circuit is capable of acting as a 

 generator of electrical oscillations. The 

 frequency is determined in the main by 

 the inductance capacity combination 



If, by adjusting the potentiometer P, 

 Fig. 1. Regenerative circuit. t^g gj-id potential is gradually made 

 more and more negative, the oscillations are stopped. Upon grad- 

 ually raising the potential it will be found that there is a critical 

 grid potential at which the oscillations set in. This grid potential is 

 characteristic for the circuit used. 



Figure 2 shows a plate current-grid potential, characteristic of a 

 typical receiver type electron tube. If the grid be at a mean potential 

 corresponding to the point Cr and an alternating e.m.f. be applied to 

 it, the increase of plate current during the positive half of the cycle will 

 be greater than the decrease during the negative half. This is due 

 to the curvature of the characteristic. Thus the mean value of the 

 plate current is increased by the periodic e.m.f. on the grid. If C^ is 

 the critical point on the characteristic at which the circuit becomes 

 self -oscillatory, the amplitude of the periodic component of the grid 

 potential builds up ; Hkewise the amplitude of the periodic plate cur- 



