GB556724A - Frequency modulation receivers - Google Patents

Abstract

556,724. Frequency modulation. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 17, 1942, No. 8324. Convention date, June 17, 1941. [Class 40 (v)] Demodulation of a frequency-modulated carrier wave is effected by applying it to an electron discharge tube or tubes which is thus caused to generate pulses at a frequency equal to, or an integral faction of, the received frequency and substantially independent of variations in amplitude, the pulses being used to discharge a condenser, the charging current of which passes through an output impedance, giving an output current which varies with the pulse frequency. In a reciprocally-coupled valve arrangement, Fig. 2, the output from a frequency changer 2 is applied to the first valve 90 and the anode resistance of the second valve 92 is in parallel with a condenser 98 and an audio-transformer 103 feeding the audio amplifier 54. In Fig. 4, the I.F. output from 2 is applied in push-pull to the grids of a pair of valves which have an inductance 68 in their common anode circuit. Current in this coil is cut off only when both valves are blocked as the I.F. voltage passes through zero, and the voltage pulses, arising at the anodes are delivered through a condenser 66 to the grid of a triode valve 118, shunted by a condenser 121. The anode circuit includes a resistance 123 and the transformer 103 feeding the AF stage 54. In Fig. 1 the I.F. output is applied in push-pull to the first and second grids of a pentode valve 74, one or the other of which blocks the anode current except as the I.F. voltage passes through zero. On each such occasion, the condenser 86 which has been charged through the AF transformer coil 85, discharges through the valve. Circuits of the blocking oscillator type may be used for generating pulses at the intermediate frequency, the pulses being applied to the grid of a valve which shunts the condenser, Figs. 3 and 5 (not shown). The Specification as open to inspection under Sect. 91 also describes the circuit shown in Fig. 1 (Cancelled) in which the output from 2 is applied in push-pull to the outer grids of a pair of valves 14, 25 which have their anodes reciprocally coupled to the inner grids. The pulses produced in the anode circuits are passed through a transformer 42 and double rectifier 50 to charge a condenser 52 across which an audio amplifier 54 is connected. In an alternative arrangement, the valve anodes are connected to each other and through a condenser to a single rectifier, Fig. 2 (Cancelled) (not shown). This subject-matter does not appear in the Specification as accepted.