Why this circuit oscilates?

[kodiak]

Hello guys! I have been searching for some oscilators and I found this circuit. It's based on the Collpits oscilator, and it definetely works, but I would like to understand why this circuit produces oscilations (and pretty accurate sines, actually)! Could you guys give me some help to understand it? Thank you!

 

[Warpspeed]

https://en.wikipedia.org/wiki/Colpitts_oscillator

 

[Audioguru]

The Wikipedia explanation is too complicated.
The transistor amplifies its own noise which is tuned by the LC to one frequency. C2 couples the output signal at the collector to the emitter which is the input when the transistor is a common base amplifier. Then the signal goes around and around oscillating.

 

[D.A.(Tony)Stewart]

Common base amplifiers are non-inverting and this one uses a capacitance divider feedback to the emitter for positive feedback at LC tank resonance with 0 deg phase shift.

Thus oscillation is sustained when the loop has gain at resonance by ratio of Collector to emitter impedance at resonance.

The Bias resistors control the dc current operating point to improve gain.

Due to saturation effects of reducing gain softly, the signal remains mostly sinusoidal.