GB413402A - Improvements in or relating to modulated carrier wave receivers - Google Patents

Abstract

413,402. Valve circuits for wireless reception. TELEFUNKEN GES. FUR DRAHTLOSE TELEGRAPHIE, 12, Hallesches Ufer, Berlin. Feb. 8, 1933, No. 3903. Convention date, Feb. 8, 1932. Addition to 393,415. [Class 40 (v).] A detector, arranged to give constant rectified signal despite changes in radio-frequency input, comprises a grid-leak rectifying valve having a plate-current grid-voltage characteristic of approximately logarithmic form convex towards the zero plate current line. The curve I of Fig. 2<a> shows the logarithmic curve, grid voltage E being measured horizontally, and plate current J vertically. The theoretical curve rises asymptotically to the ordinate V but in practice the characteristic curve bends off as shown at II. On the assumption that a grid-leak rectifier biasses itself to an extent equal to the amplitude of the incoming carrier, the Specification shows mathematically that the rectified signal is independent of the strength of the incoming carrier, but is dependent solely on its depth of modulation. Volume control on the occurrence of fading is thus automatic. The actual valve characteristic may with advantage lie in the position III below the theoretical curve I, as this counterbalances the tendency for the grid to assume positive voltage during positive peaks of input. The valve should be a screen-grid or pentode valve of high internal resistance compared with its external resistance, and with an amplification factor greater than 20. The inner grid mesh may differ in different sections, as described in the parent Specification.