GB622763A - Improvements in or relating to push-pull mixing circuits - Google Patents

Abstract

622,763. Superheterodyne circuits. PHILIPS LAMPS, Ltd. March 31, 1947, No. 8633. Convention date, July 26, 1944. [Classes 40 (v) and 40 (vi)] [Also in Group XL (b)] In a superheterodyne mixing circuit in which signals are applied in push-pull to a pair of rectifiers over a Lecher wire system 2<1>, 2<11>, Fig. 1, local oscillations are applied in parallel by means of a coupling inductance 5 and condensers 6<1>, 6<11> in order to prevent radiation. The Lecher wires are earthed by a shorting bridge 4 at the remote end, the potential at the aerial due to local oscillations being reduced by connection of the cathodes of the rectifiers to earth over a high impedance 7 such as a choke. Radiation may be further reduced by earthing the inductance 5 at a tap having the same potential for local oscillations as the rectifier anodes. The choke 7 may then be omitted. The arrangement may be modified to comprise a pair of inductances each coupling the local oscillator to one of the rectifiers, in place of the inductance 5. The mixing valves may be triodes, the local oscillations being self-generated by utilizing the inter-electrode capacities and back-coupling the grids and anodes over inductances 9<1>, 9<11>, condensers 10<1>, 10<11>, and a common impedance 11. A path of high impedance is provided from the anodes to earth by high-frequency chokes 7<1>, 7<11>, over which the intermediate-frequency output is taken. Radiation may be further reduced by earthing a tap on the impedance 11 or by means of an artificial tap comprising condensers connected between earth and the respective grids and anodes (Fig. 3, not shown). The impedance 11 may be a cavity resonator for stabilizing the oscillator frequency (see Group XL (b)).