GB378998A - Improvements in or relating to oscillation generating and modulating arrangements suitable for use in wireless signalling - Google Patents

Abstract

378,998. Valve generating and modulating circuits. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Hansell, C. W. ; Port Jefferson, Long Island, New York, U.S.A.) June 1, 1931, No. 15992. Convention date, June 25, 1930. [Class 40 (v).] Frequency modulation is effected by providing two valve generators with their different frequencies determined by long-line frequency control, the two oscillators feeding a common circuit which causes them to adopt a common frequency, and the modulating currents being utilized to vary this common frequency by changing the relative intensity of oscillation cf the generators. As shown in Fig. 1, the natural frequencies of the generators 10, 12 are determined by the Lecher-wire control circuits 22, 24, and they feed a common output circuit 118. The relative intensity of the oscillations is varied by varying the grid voltage of the valves 10, 12 in phase opposition, by means of the push-pull transformer 8<1> fed by the microphone 2 or other signal producers 4, 6. The frequency-modulated output in the coil 118 feeds a carrier-suppression modulator 30, 32 supplied by a generator 34 of higher frequency, and the side bands are fed through a filter 34<1> and limiter 36 to the aerial. Alternatively, the frequency-modulated wave may be fed direct to the aerial. Inductive back coupling may be employed between the plate and grid circuits of the valves 10, 12. In the modification shown in Fig. 3, screen-grid oscillators 10<11>, 12<11> are employed, with separate tuned grid circuits 40, and a common output circuit 46. Back coupling is effected by means of long lines 22<1>, 24<1> in the form of coils, the lengths of which are an odd number of half wavelengths at their respective desired frequencies. Signal voltages are applied from the microphone amplifier 62 in phase opposition to the two grids. In a further modification, Fig. 4 (not shown), push-pull amplifiers are used in the low-frequency circuits, and the tuned output circuit 46 is connected in the grid circuit of a further amplifier, the plate circuit of which is back-coupled through longline coils such as 22<1>, 24<1> to the tuned grid circuits of the respective oscillators. The longline coils are in this case of a length equal to an even number of half wavelengths of the desired oscillation. The modulating voltages are applied in phase opposition to the screen grids of the oscillator valves. Specification 369,009 is referred to.