GB476486A - Improvements in or relating to radio receiving apparatus and the like - Google Patents

Abstract

476,486. Valve circuits for wireless reception. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. June 2, 1936, No. 15398. Convention date, May 31, 1935. [Class 40 (v)] The selectivity of a tuned circuit is varied by variation of the mutual conductance of a pentode valve connected in shunt therewith, a portion of the signal voltage across the tuned circuit being applied to the grid of the valve to produce an opposing voltage. As shown, the tuned primary 41, 43 of an I.F. transformer 21 coupling valves 11, 19 is shunted by the anodecathode path of a pentode 47, to the grid 56 of which is applied signal voltages from the high potential end of the circuit 41, 43 through condenser 81. The steady potential of the grid 56 is controlled through resistance 59 either by manual adjustment of the slider 71 on potential divider 29 or automatically in accordance with signal strength by an A.V.C. voltage from terminal 65. The transformer 21 is so designed that an increase in the damping of the primary 41 results in an overall increase of selectivity of the transformer. In a second embodiment, Fig. 2 (not shown), the controlled circuit is an aerial circuit and selectivity is reduced when the grid of the control valve is made more positive.