GB514723A - Improvements in or relating to superheterodyne wireless receivers - Google Patents

Abstract

514,723. Automatic 'fine-tuning systems for radio receivers. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. March 14, 1938, No. 7871. Convention date, March 13, 1937. [Class 40 (v)] The automatic frequency control circuit of a superheterodyne receiver comprises a control valve having its output circuit coupled to the tuned circuit of the local oscillator, oscillations from which are also impressed, together with A.F.C. voltages, on each of the two grids of the control valve. In Fig. 1, the control valve 21, is of the double triode type, the anodes being connected in parallel to the oscillator tank circuit 5, while the control grid 24 is coupled to the junction of a resistance 26 and condenser 27 connected in series with condenser 28 across the tank circuit; control grid 25 is coupled to the earthed end of that network over condenser 30. The two grids are supplied with A.F.C. potentials from the two-circuit discriminator 11, 13, 14, 15, 16 coupled to the I.F. stage. Thus, the valve 21 has a push-pull input and parallel output for radio frequencies. In a modification, Fig. 2 (not shown), the valve 21 has its control grids fed in parallel from the tank circuit, to which the anode circuits are coupled in pushpull ; the discriminator is of the phasevariation type known per se. Specifications 487,687 and 489,094 are referred to. According to the Specification, as open to inspection under Sect. 91. the control valve is of the heptode type, the two grids being separated by a screen-grid, Fig. 3 (Cancelled, not shown). The control voltages are adjusted to compensate for the unequal control effect of the respective control grid. This subjectmatter does not appear in the Specification as accepted.