GB407057A - Improvements in or relating to selective receivers for wave signals - Google Patents

Abstract

407,057. Valve circuits for wireless reception. ROBINSON, J., and BRITISH RADIOSTAT CORPORATION, Ltd., 24, Throgmorton Street, London. Sept. 9, 1932, No. 25221. [Class 40 (v).] In a highly selective receiver the tuning is automatically controlled by means responsive to changes in the frequency of the incoming signals. Fig. 3 shows an arrangement in which energy from the intermediate frequency amplifier 38 is used to control the frequency of the oscillator 37 in a supersonic heterodyne circuit. Piezo-electric crystals 55, 56 are tuned above and below the intermediate frequency used and control detectors 57, 58 which control polarized armature 65 and the operation of relay 63. Relay 63 is adapted to apply prohibitive bias to the amplifier 70 when the signal is below a predetermined amount so that weak signals are suppressed. Fig. 1 shows an arrangement in which the transfer from the tuned circuit 15 to the following valve 17 is through a piezo-electric crystal 16, the resonant frequency of which is adjusted by varying the electrode spacing a balanced condition of the system being maintained by a simultaneous variation of the capacity 21. The control is effected by variation ot the energy applied to valve 25 which is shunted by a piezo-electric crystal 22, tuned to a frequency differing slightly from the signal so that the carrier frequency falls on one of the major sloping portions of the crevasse and decrease of carrier frequency will vary the amount of energy shunted by the piezo-electric crystal in one direction while an increase of this frequency will produce an opposite variation in the amount of energy shunted by the crystal. In a modification (Fig. 2, not shown) the resonantor in the frequency controlling circuit is a tuning fork and the control of the tuning of the receiver is effected by movement of an iron core in a tuning inductance. Fig. 4 shows a modification of the arrangement in Fig. 1 in which the control adjusts a tuning condenser and part of the energy at carrier frequency in the control circuit is applied to the tuned circuit 73 to diminish the percentage modulation so that an improvement in selectivity is produced consequent on the demodulation of weaker signals by stronger signals in the detector 39. In a further modification (Fig. 5, not shown) a pair of piezo-electric crystals are energized in opposite phase by the signals, the crystals are tuned above and below the signal respectively. A supersonic heterodyne circuit is used and part of the output from the crystals is used to control the tuning of the oscillator while the other part of the output is applied to a pair of valves in push-pull. The parallel output from these valves is fed to the succeeding detector of the receiver. Specifications 296,678, [Class 40 (v)], 344,034, 344,869, and 355,339 are referred to.