Figure 2-3.
Mixer circuit.
b. Component Functions. Capacitor C1 and the primary of transformer T1 form a
parallel resonant circuit for the RF signal, which is coupled through the
transformer to the base circuit of Q1. Capacitor C2 and the primary of transformer
T2 form a parallel resonant circuit for the oscillator frequency, which is coupled
through the transformer to the emitter circuit of mixer Q1. Resistor R1 provides
emitter-base bias, and resistor R3 is a voltage-dropping resistor. Capacitor C4 is
a bypass capacitor.
Resistor R2 is the emitter-swamping resistor.
Capacitor C5
and the primary of transformer T3 form a parallel resonant circuit for the
intermediate frequency which is coupled through the transformer to the following
stage.
2-4.
CONVERTER
a. Operation. A schematic diagram of a converter stage is shown in figure 2-4.
The radio frequency injected into the base circuit and the oscillator frequency
generated by converter Q1 are heterodyned in the converter. The parallel resonant
circuit, consisting of capacitor C3 and the primary of transformer T3, selects the
desired intermediate frequency. The intermediate frequency is then coupled through
transformer T3 to the following stage.
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