GB524193A - Improvements in radio receivers comprising means for suppressing aperiodic disturbances - Google Patents

Abstract

524,193. Wireless receiving systems. PHILIPS LAMPS, Ltd. June 21, 1939, No. 18142. Convention date, June 24, 1938. [Class 40 (v)] A receiver incorporating means for suppressing a periodic disturbance comprises a highfrequency mixing valve 12 which supplies intermediate-frequency oscillations through a band-pass filter 13 to an intermediate-frequency amplifying valve 14. This supplies a lowfrequency amplifying valve 29 which is connected by a switch 10 to a final amplifying valve 38 to which is connected a loud-speaker 6. The anode circuit of valve 14 includes an oscillating circuit 15 of an intermediate-frequency bandpass filter 17, which is connected through condensers 18, 23 and 24 to the diode-anode 19 and cathode 25 of valve 29. The D.C. voltage set up by detection across a resistance 20 is supplied to the control grids of valves 12 and 14 and serves for automatic volume control. The oscillating circuit 16 of filter 17 is connected to diode anode 26 of valve 29 through a circuit including a resistance 28 to the cathode 25. The low-frequency voltages set up by detection across resistance 28 are supplied through a slide contact 30 to control grid' 32 of valve 29. A cathode ray tuning indicator (not shown) is also supplied from resistance 28 through resistance 33 and condenser 34. The band-pass filter 13 is connected to a valve 41 essentially similar to valve 14 and the output voltage of which is substantially constant since that control grids of both valves are interco nnected. The anode of valve 41 is connected through a band stop filter 7 to the anode 51 of a duo-diode 53, the anode 49 of which is connected to the anode of valve 14. The anode 51 is connected to the control grid 60 of an amplifying valve 61 in the anode circuit of which is included the relay 9 controlling switch 10. Under normal conditions diode 51, 52 does not rectify and control grid 60 is at earth potential. An aperiodic disturbance whose amplitude exceeds that of the high side-band frequencies will surpass the threshold voltage across resistance 54 and be rectified by diode 51, 52. Thus anode 51 and hence grid 60 acquires a negative potential causing a decrease in the anode current through relay 9, to render the lowfrequency amplifier temporarily inoperative. An arrangement is also described Fig. 3 (not shown) in which a second duo-diode is interposed between valves 53 and 61 whereby the threshold value above which disturbance elimination takes place is dependent on the side-band frequencies which correspond to the high modulation frequencies and is limited by the carrier wave of the desired signal.