GB423773A - Improvements in or relating to radio and like modulated carrier wave receiving apparatus - Google Patents

Abstract

423,773. Valve circuits for wireless reception. MARCONI'S WIRELESS TELEGRAPH CO., Ltd., Electra House, Victoria Embankment, London.-(Assignees of George, R. W. ; Riverhead, Long Island, New York, U.S.A.) April 27, 1934, No. 12829. Convention date, April 27, 1933. [Class 40 (v)] In an ultra-high-frequency receiver the demodulator comprises a pair of valves whose input electrodes are energized in phase opposition and also co-phasally by energy 90‹ phase-shifted with respect to the component fed in phase opposition. The path energizing the valves in phase opposition comprises a high-frequency transformer with tuned primary and secondary windings with coupling and damping to give a flattened double peak response with a width equal to that of the band of frequencies to be demodulated. Fig. 1 shows an oscillating detector O of the Barkhausen-Kurtz type as described in Specification 394,267, and an intermediate frequency amplifier 1 .. 5 coupled by transformers with a flattened double hump characteristic produced by close coupling and damping shunt resistances. The tuning capacity for the primary of the transformer T1 is constituted by the high frequency byepass condenser 28 of the oscillating-detector O. The output is applied to the grids of the valves 6, 10 which are followed by push-pull detector 8, 9. The signal is fed in phase to the grids of the detectors through the valve 6 and is fed with a phase displacement of 90‹ relatively to the co-phasal feed differentially to the grids of the detectors through the valves 10, 7, the phase shifting line L1, L2, Fig. 1a, and the phase changing transformer PC. Metering, decoupling of the supply circuits and screening of the receiver elements are provided as shown. Frequency modulated signals are received by the push-pull transformer FT and amplitude modulated signals by the parallel transformer AT. The meters 21, 31 allow the valves to be statically balanced accurately and in operation facilitate tuning since incorrect phasing of the signals on the grids of the valves 8, 9 produces unbalance in the plate currents. The Specification gives vector diagrams and detector current characteristic curves. Secrecy may be obtained by transmitting one element of a signal as a frequency modulation and simultaneously another element of the signal as a keyed tone to give amplitude modulation, Fig. 8, (not shown). In a modification the phase displaced signals are fed to two separate grids in each of the detector valves, Fig. 1b, (not shown). Instead of applying the in-phase signals to the grids of the detector valves they may be applied to the cathodes either with direct coupling, Fig. 3, (not shown) or with capacitive coupling, Fig. 2, (not shown). The oscillating detector O may be replaced by any known form of first detector in a superheterodyne circuit and a large degree of intermediate frequency may not be needed, the first detector being coupled through phase shifting circuits and coupling valves to the demodulating valves.