GB186138A - Improvements in and relating to thermionic signal receiving systems - Google Patents

Abstract

186,138. British Thomson - Houston Co., Ltd., (General Electric Co.). June 20, 1921. Thermionic amplifiers and detectors.-In a thermionic signal receiving system of the type described in Specification 117,283, signalling potentials are simultaneously impressed upon the anode 3 and the third or plate electrode 4; the cathode grid circuit 2 - - 5 and the cathodethird electrode circuit 2 - - 4 have negative resistance characteristics; and the cathode-grid circuit is tuned to a frequency slightly different from that of the received signals. The negative resistance characteristics are given to the cathode-grid and cathode-third electrode circuits by adjusting the potentials applied to the grid 5 and to the third electrode 4 at the points 8 and 7, Fig. 1, in the common battery 6. The resultant tendency of the cathode-third electrode circuit to self-oscillation is eliminated because the transformer secondary 10 is common both to this circuit and to the cathode-anode circuit, and because a change of current in one circuit is accompanied by a corresponding but opposite change in the other circuit. A tuned circuit 11, 12 is included in the other self-oscillatory circuit, whereby potential variations differing from the signal frequency may be applied to the grid 5 so as to secure audible beat effects. Fig. 3 shows a family of characteristic curves showing the relation between third electrode potential and current for different values of grid voltage. The point 7, Fig. 1, is normally chosen so as to coincide with the point C, Fig. 3. The effect of signal potentials impressed upon the transformer 10 will then be to vary the third electrode potential between the points C and E. The corresponding variations of grid potential, if synchronous with the applied signals, would result in a half-wave rectification of the signals in the cathode-third electrode circuit, but, if the circuit 11, 12 is suitably tuned, a beat effect will be obtained which will give an audible note in the telephones 14. Owing to the fact that any current-change in the cathode-third electrode circuit is accompanied by an equal but opposite change in the cathode-anode circuit, the current though the secondary of the transformers 10 will be substantially independent of the signalling potential. For the same reason, the telephones 14 may equally be placed in the anode-cathode circuit, as in Fig. 2, wherein the different batteries are shown separately, and a positive resistance 17 is inserted in the cathode-third electrode circuit in order to increase amplification. Specification 184,875 also is referred to.