Electronics Handbook/Devices/Oscillator/Active Oscillator/Variable Frequency Oscillator or VFO/Colpitt Oscillator
Configuration edit
Oscillation frequency edit
The ideal frequency of oscillation for the circuits in Figures 1 and 2 are given by the equation:
where the series combination of C1 and C2 creates the effective capacitance of the LC tank.
Real circuits will oscillate at a slightly lower frequency due to junction capacitances of the transistor and possibly other stray capacitances.