GB403709A - Improvements relating to the reduction of interference in thermionic valve circuits - Google Patents

Abstract

403,709. Valve circuits for wireless reception. ELECTRIC & MUSICAL INDUSTRIES, Ltd., Hayes, Middlesex, and WILLANS, P. W., 18, Park Hill Road, Hampstead, London. May 26, 1932, No. 15010. [Class 40 (v).] In a wireless receiver a circuit tuned to an unwanted frequency is arranged in the common anode and control grid circuits of a valve. The circuit may be tuned by a condenser ganged to the tuning condenser and in a superheterodyne receiver may be employed in the intermediate frequency stages or to prevent second channel interference or to prevent interference due to harmonics generated by the oscillator, in which case the circuit may comprise a low pass filter. The Figure shows a superheterodyne receiver in which the circuit 36, 37 is resonant at the frequency of second channel interference and the circuit 16<1> 17<1> may be resonant at this frequency or at a frequency at which interference arises due to other causes. The circuit 16<1> 17<1> may be fixed tuned or be replaced by a low pass filter to remove harmonics of the intermediate frequency or interference due to harmonics from the oscillator. The Provisional Specification describes the application to a receiver operating over two wave-bands to prevent the shorter wave-band signals from breaking through and producing interference on the longer wave band by means of a circuit thrown into and out of operation by the wave range switch. The Provisional Specification also describes the application of the invention to a beat frequency oscillator for producing audio frequencies in which interference due to oscillator harmonics or harmonics produced by the non-linearity of the detector is avoided. According to the Provisional Specification the feed back may take place to the grid circuit of a preceding valve instead of between the anode and grid circuits of the same valve.