GB481064A - Improvements in or relating to demodulating circuit arrangements for phase modulated waves - Google Patents

Abstract

481,064. Wireless receiving systems. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. May 5, 1937, No. 12849. Convention date, May 5, 1936. [Class 40 (v)] An oscillating detector is caused to respond correctly to phase-modulated signals by tuning its anode with a circuit of such low power factor that it will not respond at a rate higher than the lowest modulation frequency on the received wave. The received wave after passing through the amplifier RFA, frequency changer andassociated oscillator ID, LO, and intermediate frequency amplifier IFA is fed in push-pull from circuit 18 to coil 20 and the grids of the oscillators 10, 12, the grid circuits including grid leak, and condenser units 6, 8, The anodes of the valves are connected together by the radio frequency piezo-electric crystal 14 and through chokes RFC to the push-pull low frequency output transformer 24, and through resistances 26 to the high tension source. Valves 10, 12 due to internal coupling produce oscillations of a frequency determined by the piezo crystal which is substantially equal to the carrier frequency to be received, and which excite the control grids in phase displaced relationship with and also preferably in quadrature with the incoming waves. Due to the action of the grid leaks the anode currents become unbalanced as the phase of the voltages on the grids vary and a low frequency output is obtained from the transformer 24. The relative phase of carrier and local oscillations may be controlled by voltages appearing across resistances 26 and acting on the frequency-changing oscillator through the circuit PCC. Figs. 2 and 3 (not shown) illustrate alternative forms of the low power factor anode circuits, consisting respectively of a length of tubular transmission line acting as a parallel tuned circuit, and a magneto-striction oscillator.