Robert J Morton

Oscillators

L2 must have a reactance Z at the oscillator's operating frequency appropriate for the amplifier's output.

1. Maximise the Q of the inductor L
2. Varactor varies in capacitance between C1 and C2 according to the reverse voltage appled to it.
3. The bias capacitor Cb has a value such that Cb + C1 is the capacitance required to tune the oscillator to the low end of its range and Cb + C2 is the capacitance required to tune the oscillator to the high end of its frequency range.
4. C4 is to reduce the loading on the tuned circuit components. It may be as small as possible consistent with being able to provide sufficient drive to the succeeding buffer amplifier stage. Often the home constructor will often make C4 a trimmer.