Mixing stage with oscillator frequency coupling via reactance - has FET and capacitance diode between secondary circuit of input band filter and mixer input

摘要

The mixer is formed by a F.e.t. in a stage with a capacitively coupled oscillator. The stage is provided with coupling of the oscillator frequency, via a reactance element, and is intended for a receiver input circuit which can be tuned in a greater frequency range. A capacitive diode is between the secondary circuit of the input band filters and the mixer input. Across a resistor, a tuning voltage is supplied to the diode, while an inductance is incorporated between the oscillator output and the mixer input. The oscillator circuit is pref. tunable by voltage dependent capacitive diodes, for which the tuning voltage serves simultaneously as the control voltage. This mixing stage enables improved coupling of lower oscillator frequencies. When using a f.e.t. the high input capacity restricts considerably the tuning range, while at lower circuit capacities the amplification is highly increased by the high ohmic character of the circuit.