GB443956A - Improvements in and relating to radio receivers - Google Patents

Abstract

443,956. Valve circuits for wireless reception. FERRANTI, Ltd., HALL, A., and SEARBY, N. H., Hollinwood, Lancashire. Aug. 10, 1934, No. 23203. [Class 40 (v)] In a radio receiver having automatic control of volume, muting bias on the signal rectifier is removed when the signal strength exceeds a predetermined value by a device operated by the D.C. component derived from rectification of signal voltage, the selectivity of the AVC and muting circuits being capable of variation without affecting the selectivity of the receiver. The output from a high or intermediate frequency amplifier 1 is applied at 2 to the signal diode 25 of a double diode pentode 7 and at 4, 5 to an A..V.C. diode 6, from the load resistance 8 of which, A.V.C. potentials are applied through resistance 11 to preceding amplifier stages. The signal diode circuit 25 includes a filter resistance 23 and load resistances 22, 21, the rectified potentials being applied to the control grid of the low frequency pentode 7 from resistance 30. The control grid of a triode 14 acting as a muting impedance is connected to a tapping on the resistance 8 and its anode is connected to the junction of resistances 22, 21. The arrangement is such that with no signal, the impedance of the valve 14 is low and there is a large p.d. across resistance 21 ; the diode 25 is thus practically at earth potential, while its cathode 26 has a positive potential with respect to earth equal to the sum of the voltages across resistances 27 and 19 ; this is the delay voltage. The circuit 4, 5 is much more sharply tuned than circuit 2, so that when a station of the predetermined strength is tuned in, the rectified voltage across resistance 8 causes the grid of triode 14 to swing highly negative, its impedance becomes very great and the potential of its anode, and therefore that of the diode 25, becomes almost that of the cathode 26 ; the muting is thus removed. The valve 14 may be replaced by a relay, the winding of which constitutes resistance 8. Circuits 4, 5 may be coupled in any manner to any part of circuit 2 and the coupling between 4 and 5 may be variable to vary the frequency band of the muting control. Resistance 21 may be omitted and the anode of 14 is then connected to the junction of 22, 23.