Oscillator Experiment Interesting Results Part II 

I think it might be a common base with emiter feedback.

The comments are a month old yet the video is four minutes old? A glitch in the matrix? Oh, great series of videos. Thanks for sharing. I hope all is well with you. Have a great July 4th!

So this circuit works well on a breadboard only because of the parasitic capacitances between the metallic strips in the breadboard itself. To overcome parasitics you'd need to include higher capacitance in parallel. So your transformer needs a capacitor in parallel to a primary or a secondary. This will fix the problem of nonlinearities and will have a strong signal buildup. One more note regarding the transformer in the signal feedback path. Normally oscillators using a transformer are called Armstrong oscillators. However, they're normally connected along the negative feedback path. For an oscillator intended for RF applications, the best amplifier topology is common base and not using a transformer. Frequency selective circuits, the LC tank, should be between input and output directly. There are few techniques to connect a divider network to diminish the gain for wideband applications, some high gain for narrowband. RF is a wide field, and fun for those who have patience for replicating natural phenomenons to create special applications.

Thank you for the follow up. I found it interesting that the Collector signal looked quite clean, compared to the Emitter signal.

Becauseyou have nt makes capasitor betwen base and ground and betwen emeter and ground

Next step would be to wire it deadbug style with the wires as separated as possible to reduce capacitance. It should require the tuning cap to be stable at that point.

Thanks 😁 Yes, this is a common base oscillator. It would be interesting to put a capacitor across the variable resistor, which should provide higher AC gain and perhaps cause the waveforms of the collector and emitter to clip.