GB453858A - Noise suppression and tuning correction in radio receivers - Google Patents

Abstract

453,858. Valve circuits for wireless reception. MURPHY RADIO, Ltd., 62, Brook Street, Hanover Square, London, and BAKER, G. B., Murphy Radio Works, Welwyn Garden City. March 19, 1935, No. 8570. [Class 40 (v)] In a superheterodyne receiver having automatic correction of tuning and a muting system, the muting is removed by a voltage produced by the error detector which is inoperative as regards action on the tuning system during manual tuning. The error detector comprises two tuned circuits 10, 11, tuned above and below the intermediate frequency, coupled to the output of the I.F. stage 4 and feeding two diodes 12, 13, the load resistances 14, 15, of which are arranged in opposing sense in the suppressor grid biassing circuit, of the automatic tuning valve 16 acting as a variable reactance across the tuned circuit of the local oscillator 3. Muting bias is applied to the low frequency pentode 6 by resistances 21 and also by resistance 22 in the suppressor grid circuit. With the signal 6 is biassed to cut-off; during manual tuning the switch 23 is closed to prevent action of the automatic tuning, the switch being interlocked with the tuning knob. As a station is tuned in, energization of circuit 10 or 11 by a station of adequate strength causes a rectified p.d. across resistance 14 or 15 which diminishes the negative bias on the suppressor grid of 6 and removes the muting. The switch 23 is then opened and the final tuning is automatic. Specifications 407,057 and 443,423 are referred to.