Frequency Regulation in RF Oscillator

Sajed, the frequency of 39 MHz is correct. That is where the reactance of 0.75 uH and 22 pF are equal.

I ran an LTSPICE simulation and it outputs the same waveform that you show.

yes!
thanks. I thought wrong! I think 2 capacitors are series and equal capacity is 11 pF !!

Sounds like you have confusion regarding "Impedance" and "Reactance" (judging by the following statement "...Impedance of inductor and capacitor when circuit oscillate should be equal"). The Reactance of the inductor and the capacitor, at resonate frequency, is equal in magnitude. The impedance is purely resistive because the inductive reactance and the capacitive reactance have a 180 degree phase difference, thus they cancel, leaving only the resistive component.

Reactance is the AC resistance of either a capacitor or an inductor. Impedance is the vector sum of Capacitive Reactance, Inductive Reactance and DC Resistance. _Impedance_ is not the same thing as _Reactance_. They can have the same value, in cases where there is only resistance or only capacitance or only inductance in a circuit (or device), but ONLY in those cases (and, technically, there is no such circuit). And, having the same value, doesn't make then conceptually the same. It's very important for you to learn this distinction (or change this habit of referring to _reactance_ as _impedance_).

Hi everybody,
There is a problem in tuning circuit in feed back of a Common Emitter Colpitt Oscillator!

In theorem and mathematics Reactance of inductor and capacitor when circuit oscillate should be equal ,but Simulator software (such as multiSim ) reported that other setting for them!
*which of them can ensure me?*

Thanks. and I correct it!

While both C2 and C3 help determine the resonant frequency there are other capacitances in the circuit. The BJT collector capacitance is in parallel with C3 while the BJT base capacitance is in parallel with C2.