GB369100A - Improvements in or relating to modulation systems for electric oscillations - Google Patents

Abstract

369,100. Wireless transmitting systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Marconi House, Strand, London.-(Assignees of Roberts, W. van B. ; 155, Hodge Road, Princeton, New Jersey, U.S.A.) June 22, 1931, No. 18023. Convention date, July 10, 1930. [Class 40 (v).] Frequency or phase modulation of a carrier wave is effected by passing the wave through a circuit whose L.C. value is half that necessary for resonance, and by applying the signal as variations of resistance either across the condenser, or in series with the inductance, of the tuned circuit. As shown in Fig. 1, a constant voltage of carrier frequency is applied at the terminals 8 of a circuit comprising an inductance 6 in series with a condenser 4 shunted by a variable modulating resistance 2. As the resistance 2 is varied the current through the circuit remains constant, but the phase varies. The circuit 4, 6 may be interposed in an amplifier chain, and the resistance 2 may be the plate-filament path of a valve which has its grid voltage varied by a microphone or other signal producer, Fig. 2 (not shown). The phasemodulated output may be taken by a coil coupled to the coil 6 and may be amplified and passed through a current-limiter before proceeding to the radiating aerial. In a modification shown in Fig. 3, a screen-grid carrier wave amplifier 10 giving a constant output current has in its plate circuit a condenser 4 shunted by a coil 6 in series with a microphone 30 or other variable resistance, the L.C. value of 4 and 6 being half that necessary for resonance with the carrier. Phase-modulated output is taken through a condenser 32 to an amplifier and limiter 34 and thence to the aerial.