GB493622A - Improvements in or relating to frequency converter circuits - Google Patents

Abstract

493,622. Valve circuits for wireless reception. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. April 13, 1937, No. 10510. Convention date, April 13, 1936. [Class 40 (v)] In an electron coupled frequency changer a path is provided between the signal grid and local oscillator for applying to the signal grid out of phase local oscillations to reduce the effect of second and higher order demodulation products causing interference. Fig. 3 shows a valve 1 with the signal applied to the control grid 6 adjacent the cathode and the local oscillation applied to the grid 7 and also through condenser 10 and to the grid 6. In a modification, Fig. 2 (not shown), the signal is applied to the grid 7 and the local oscillation to the grid 6 adjacent the cathode and also to the grid 7. The auxiliary coupling of the local oscillator may be magnetic, Fig. 4 (not shown), or by a condenser common to the signal and oscillator tuned circuit, Fig. 5 (not shown), or by magnetic coupling to the cathode lead, Fig. 6 (not shown). Fig. 7 shows a separate local oscillator coupled to the grid 7 and through a phase inverting valve 21 to the grid 6 to which the signal is applied. The cancellation voltage for the second and higher order demodulation products is varied by the application of automatic volume control to the frequency changer. This variation is compensated by varying the mutual conductance of the phase inverter 21 in the opposite sense by grid bias control through resistance 23 from the potentiometer 25, 26 in the screen circuit of the valve 1. In a modification, Fig. 8 (not shown), the automatic gain control voltage is applied to both signal and oscillator grids, when, if the oscillator grid draws little current the two grids will vary in the same sense but at different rates, the grid next to the cathode to which the signal is applied varying less than the grid to which the local oscillation is applied. Specification 454,996 is referred to.