GB642549A - Method of injecting local oscillator signal into mixer - Google Patents

Abstract

642,549. Superheterodyne circuits. STANDARD TELEPHONES & CABLES, Ltd. Dec. 19, 1947, No. 33622. Convention date, Dec. 24, 1946. [Class 40 (v)] A signal mixer comprises a resonant circuit, a source of input signals, a source of local oscillator signals of relatively greater intensity, means for coupling the input signal source to the resonant circuit, and means for coupling the local oscillator signal source to the resonant circuit including a resistance having a value such that the amount of input signal energy injected into the local oscillator is negligible. As shown, the resonant coupling circuit is in the form of coaxial cylinders 9, 10, short circuited at one end, and connected by condensers 11 to the grid of a mixer valve 2. Condensers 13 tune the arrangement to the mid-frequency of the input signals from a source 3 which is coupled by concentric line 6, 7 connected to the resonator at a point which is distant from the valve 2 by a quarter wavelength at the input frequency. A local oscillator 4 is connected by lines 14, 15 to the resonator at a point distant from the valve 2 by a quarter wavelength at the local oscillator frequency. A resistance 18 is inserted of sufficient value to prevent an appreciable amount of input signal energy being lost in oscillator 4. Lines 14, 15 have such lengths as to match oscillator 4 to the load. Also, feeder 6, 7 is made threequarter wavelengths long at the local oscillator frequency so as to prevent any substantial injection of power from the local oscillator into the input signal circuits.