TRAKSACTIONS OF SECTION A. 



149 



1. A Wireless Method of Measuring e/m. 

 By R. Whiddinoton, M.A., D.Sc.^ 



It is well known that if inductance capacity circuits of low resistance be 

 associated with a three electrode thermionic valve in the manner shown in 

 fig. 1, oscillations may be set up in the anode circuit having a period 2 irv/LC 

 (very nearly), providing that 



(1) The resistance R of the anode circuit is small. 



(2) The ' resistance ' p of the valve is great. 



(3) The mutual induction M between the grid and anode coils is only 

 just great enough to maintain the oscillations, a condition approximately 



realized -wlien M > 



\Q * =«)• 



In the arrangement of fig. 1, which represents a typical oscillation circuit, 

 the ionic flow within the valve pulsates at a frequency determined by the 

 values of the inductance and capacity associated with the anode circuit. 



This method of producing oscillations has been very largely used for many 

 purposes, particularly in wireless telegraphy and telephony, and in modern 

 practice is usually employed in conjunction with ' hard ' valves — that is to 



Fig. 1. 



say, valves from which gas and vapour have been removed to such a degree 

 that ionisation by collision is negligible. 



The arrangement of fig. 1 can be used equally successfully, however, and 

 usually more efficiently with ' soft ' valves — that is to say, valves containing 

 small quantities of gas or vapour so that ionisation by collision can occur. 



It is the object of this short paper to show that in the case of soft valves 

 a simpler scheme than the one just outlined — and, moreover, one involving 

 entirely different principles — can be used to produce oscillations. This new 

 arrangement is represented in fig. 2. 



There are in this arrangement no capacity inductance circuits, as in fig. 1, 

 but simply a non-inductive potentiometer device in the grid circuit and a 

 constant source of high potential in the anode circuit. 



It is found in practice that quite strong oscillations can be produced, of 

 a frequency dependent almost altogether on the grid potential and geometrical 

 dimensions of the valve electrodes. 



It will be convenient at this stage to outline a simple theory which explains 

 broadly the observed phenomena. 



1 See Radio Bevieto, Nov. 1919. 



1919. 



