1920] Thermionic Valve in Wireless Telegraphy & Telephony 109 



then picks them up and the valve rectifies the groups into uni- 

 directional gushes of electricity. These passing through the telephone 

 give rise to a steady musical sound. By radiating short or long 

 collections of groups of waves, the sound in the telephone can be cut 

 up into short or long periods, which make the dot and dash signals 

 of the Morse alphabet. 



In the other system, called the continuous wave (C.W.) system, 

 the waves are sent out in an unbroken stream, except in so far as 

 this stream is cut up into short and long periods to make the Morse 

 signals. The method by which these continuous waves are detected 

 will be explained presently. 



Some time after the introduction of this oscillation valve I found 

 that another method of employing it as a detector was as follows : — 



a J 



Fig. 4. — Change of Slope op Characteristic Curve. 



If we connect the plate of the valve with the negative terminal 

 of the filament heating battery, and insert in that circuit a battery 

 for creating a thermionic current, we can delineate a characteristic 

 curve, as already described, by varying the electromotive force 

 (E.M.F.) of the plate circuit battery. That curve has generally 

 some places in it at which the slope changes rather quickly. If 

 we adjust the E.M.F. of the plate battery to work at that point, 

 and then by means of a transformer superimpose a feeble oscilla- 

 tory E.M.F. derived from a wireless receiving aerial, the thermionic 

 current will oscillate from one value to another, and it is easy to 

 see from the concave form of the characteristic curve that the 

 mean value of this varying thermionic current is greater than the 

 value of the steady thermionic current when the oscillations are 

 not superimposed on the steady or battery voltage (Fig. 4). This 



