Clapp oscillator

LC oscillators use a transistor (or vacuum tube or other gain element) and a positive feedback network.

Although the Clapp circuit is used as a variable frequency oscillator (VFO) by making C0 a variable capacitor, Vackář states that the Clapp oscillator "can only be used for operation on fixed frequencies or at the most over narrow bands (max.

"[5] The problem is that under typical conditions, the Clapp oscillator's loop gain varies as f  −3, so wide ranges will overdrive the amplifier.

Therefore the amplifier input, the gate, is connected to the high impedance top of the LC circuit C0, C1, C2, L1 and the amplifier output, the source, is connected to the low impedance tap of the LC circuit.

A smaller value of C3 gives less harmonic distortion, but requires a larger load resistor.