GB402637A - Improvements in or relating to thermionic oscillation generators - Google Patents

Abstract

402,637. Valve generating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.- (Assignees of Goddard, De W. R. ; Riverhead, Long Island, New York, U.S.A.) March 9, 1933, No. 7208. Convention date, March 14, 1932. [Class 40 (v).] A generator adapted to produce oscillations at either of two frequencies comprises a thermionic valve 2 associated with two resonant circuits, e.g. containing piezo-electric crystals A, B, in such a manner that the voltage applied to the valve electrodes determines which of the resonant circuits shall control the frequency. The valve 2 is a four-electrode valve, the plate and electrode 8 deriving their voltage from a potentiometer 14. When switch 24 contacts with contact a, the electrode 8 acts as a screen grid and the crystal A, coupling the plate and control grid, determines the frequency. When the switch 24 contacts with contact b, the electrode 8 is at a higher potential than the plate anc acts as an anode, the crystal B, coupling the electrode 8 and the control grid, controlling the frequency. In this latter case, the oscillations are transferred to the output circuit by the crystal A and by inherent coupling between the plate and the electrode 8. The oscillations may be fed to a buffer amplifier 28 or frequency multiplier and modulated by variations in voltage applied to the electrode 34 of a valve 30. Code signalling may be achieved by switching from contact a to contact b and secret signalling may be attained by a periodic change in frequency, so that two receivers, one tuned to each frequency, will give the total signal after combining their outputs.