GB445273A - Improvements in and relating to wireless and like receivers - Google Patents

Abstract

445,273. Valve circuits for wireless reception. TRUEFITT, E. S. V., 115, Elgin Avenue, Maida Vale, and SPENCER, R. E., 8, Courtfield Gardens, West Ealing, both in London. Sept. 5, 1934, No. 25607. [Class 40 (v)] In a receiver in which inter-channel noise suppression is effected by causing a carrier frequency amplifier to pass grid current which, flowing through the load resistance of a detector diode, also disables the latter, the rectified signal voltage developed in said load resistance by signals of above a predetermined amplitude is amplified and then used to suppress the flow of said grid current. As shown, in the absence of signals of above a predetermined amplitude, the cathode 13 of the audio frequency amplifying triode 11 is positive relative to earth being connected through a resistance 22 to a point 23 on the plate current source which is negative relative to earth. The grid of the I.F. valve 8 is connected to the cathode 13 through its input tuned circuit 10 and resistances 19, 15, while its cathode is earthed through a switch 21. This causes grid current to flow to reduce its amplification and disable the diode detector 12, 13, the load resistance of which is the resistance 15. When a signal of above a predetermined amplitude is fed to the diode 12, 13, the D.C. potential together with an adjustable portion of the signal developed in the load resistance 15 is fed to the grid of the triode 11 from the potential divider 17, 18 shunted across the resistance 15. The anode current of triode 11 is thus reduced, its cathode 13 becomes more negative, the grid of valve 8 becomes negative, grid current ceases to flow, the blocking bias on the diode 12, 13 is removed and by a cumulative action the grid of valve 8 reaches its correct operating potential. Earlier valves such as 7 receive amplified volume control potentials from the cathode 13 through the diode 13, 24 which becomes conducting when the cathode reaches earth potential, the anode being earthed through a resistance 25. The muting action may be disabled by opening the switch 21 to include a biassing resistance 26 in the cathode circuit of valve 8. In a modification (Fig. 3, not shown), the resistance 19 is replaced by a choke and the switch 21 is replaced by a double pole switch which in the muting position includes a manually variable biassing control for the valve 8 which in the other position is controlled directly by the common A.V.C. source.