GB880541A - Improvements in or relating to mixing curcuits for high frequency oscillations - Google Patents

Abstract

880,541. Valve frequency changing circuits. PHILIPS ELECTRICAL INDUSTRIES Ltd. April 21, 1960 [April 24, 1959], No. 14026/60. Class 40(6). In a high-frequency frequency changing circuit the input to a self-oscillating mixer 9 comprises a bandpass filter formed of two coupled circuits 40, 5 each tuned to the signal frequency and comprising an inner conductor 3, 7 respectively and a conductive envelope 17, timing being performed by means of condensers 4, 12 respectively situated between the inner conductors and the conductive envelopes. Coupling is by means of an aperture 16 in the wall common to the two envelopes. The oscillator circuit comprises a similar arrangement of inner conductor 11 and condenser 13, the rotors of the condensers being carried by a common shaft 14 provided with earthing members 15. The arrangement is preceded by a grounded grid R.F. stage 2 the input transformer 1 of which is broadly resonant over the frequency band. The bandpass filter is coupled to the cathode of the mixer 9 by means of a lead 8 coupled to the circuit 5; according to the invention this lead extends through the common wall and forms a coupling loop 18 coupled to the circuit 40. In this way the amount of local oscillations reaching the circuit 40 via the coupling aperture 16 is counterbalanced by that reaching it via the coupling loop 18, so preventing the radiation of local oscillations.