GB496154A - Improvements in or relating to frequency mixing circuit arrangements - Google Patents

Abstract

496,154. Valve circuits ; thermionic valves. MARCONI'S WIRELESS TELEGRAPH CO., Ltd. Sept. 2, 1937, No. 24030. Convention date, Dec. 1, 1936. [Classes 39 (i) and 40 (v)] A radio frequency mixing circuit for producing a sum or difference frequency comprises two valves fed in phase quadrature so that any interfering frequency is balanced out for the output. Fig. 1 shows pentagrid frequency changing valves V1, V2. Thesignalis applied to grids 4, 9 in quadrature and local oscillations to the grids 1, 6 in quadrature and the output at the intermediate frequency is taken from the anodes in parallel. Elimination of interference is effected by adjusting the relative outputs of the valves V1, V2 by adjustment of resistances 15 .. 18 or of the bias applied at the points 13, 14. Phase quadrature voltages from the input may alternatively be obtained by wholly aperiodic circuits, Figs. 3a, 3b (not shown), or by a tuned circuit with a resistance between the inductance and earth, Fig. 4 (not shown). Fig. 5 shows an arrangement with a push-pull output in which reaction is obtained from a coil 19 in the cathode return circuit to compensate for the damping produced by resistance 15. The local oscillator may be connected to the valves in push-pull in which case the outputs are combined in phase quadrature, Fig. 6 (not shown). The resistance in the phase splitting signal input circuit may be altered with wavelength by using a variable resistance gangcontrolled with the tuning, Fig. 7 (not shown). Alternatively the phase splitting resistance may be gang-controlled with a resistance controlling the amplification of the triode portion of the valve V2, Fig. 8, and so the tuning of the circuit L2, C2. A copper oxide second detector may be employed and the valves V1, V2 may be combined in a single envelope. Fig. 9a shows a valve construction for a triodedouble-hexode with the oscillator grid LOG connected to both the grids of both the hexodes. In a modification the local oscillator grid is connected to the grid of only one of the hexodes, Fig. 9b (not shown). The arrangement may be used for single sideband modulation in transmission or for the reception of a single sideband, the carrier being supplied by a driven oscillator. The loss to the desired signal by the balancing process may be obviated by using an intermediate frequency equal to the sum of the signal and local oscillator frequency.