GB522710A - Improvements in or relating to thermionic valve frequency changers - Google Patents

Abstract

522,710. Valve circuits for wireless reception; thermionic valves. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., and BELL, D. A. Dec. 13, 1938, No. 36361. [Classes 39 (i) and 40 (v)] The signal-to-noise ratio in a frequency changing value is increased by reducing the mean current flowing to the output anode to a valve only just sufficient to carry the intermediate frequency output current component. Electrons from cathode 1 are focused into a beam by the negative electrode 2 and the positive electrode 3 having a slit 4, and the beam is intensity-modulated at the frequency of the local oscillator 9, 10 by applying a controlling voltage to the electrode 2 or to-an additional grid (not shown) external to the electrode 3. The beam is deflected between the " split " anode 7, 8 by the signal voltage applied to deflector plates 5, 6, the part 7 of the anode being connected to the intermediatefrequency output circuit 13. The deflection control may be electro-magnetic. A bias is applied to the deflector plates from a potentiometer 15, or the anode parts are slightly displaced, so that in the absence of a signal practically all the electron beam falls on the idle anode 8, whilst on receipt of a signal the current flowing to anode 7 is proportional to the product of the signal and local-oscillator voltages. More than one electron beam may be used, all the beams being modulated in intensity by the local oscillator and being deflected by the signal.