GB448762A - Improvements in or relating to thermionic oscillators - Google Patents

Abstract

448,762. Valve modulating circuits. NAAMLOOZE VENNOOTSCHAP PHILIPS' GLOEILAMPENFABRIEKEN, Emmasingel, Eindhoven, Holland. Nov. 25, 1935, No. 32641. Convention date, Dec. 17, 1934. [Class 40 (v)] In a thermionic oscillator of the kind in which the frequency depends on the transit time of an electron, and tends to vary with the modulating-voltage applied to its electrodes, e.g. a magnetron or Barkhausen-Kurz oscillator, the modulation voltage is broken up into intermittent pulses at a medium frequency, the length of each pulse being dependent on the momentary value of the modulating-voltage. This avoids frequency changes, and overcomes other difficulties due to the valve ceasing to oscillate. Fig. 2 shows a magnetron oscillator 1 with its anode voltages supplied by a source 2 through a resistance or choke 3. A valve 4 has its plate-filament path in shunt to the oscillator, 1 and its grid voltage is supplied by the microphone 6 in series with a generator 5 giving a frequency higher than the highest modulation frequency. The effect of combining the microphonic voltage 7 with the voltage of the generator 5 is shown in the curve 8 of Fig. 3. The horizontal line 9 represents the grid voltage at and above which the valve 4 is conductive, and the heavy-line intercepts of the curve 8 on this line represent the periods during which valve 4 is conductive, the lengths of these periods being variable in dependence on the modulating-voltage 7. Whilst the valve 4 is conductive only a low voltage reaches the oscillator anodes, so that oscillation is feeble or ceases. During the non-conductive periods of the valve 4, the oscillator operates at a constant amplitude.