Heterodyne receiver tunable over wide band - has inductive coupling between oscillator circuit and mixer stage

摘要

In a radio receiver, the oscillatory circuit is turnable over a wide frequency band and is coupled to a mixer stage in which an FET serves as a mixer transistor. In a known circuit of this type, the input capacity of the FET is varied in accordance with the amplitude of the input signal, and this variation reacts on the oscillator, causing a change of oscillator frequency, which in turn causes undesired frequency modulation and rhythmic variation of the IF. This defect is avoided by providing an inductive coupling between the oscillatory circuit and the mixer stage. The coupling inductance is pref. connected to the live end of the oscillatory circuit.