I've seen some Hartley oscillators both with and without the R/C combination in the feedback loop. What is their theoretical purpose? I've tried both with and without the inserted R/C combo with around those values, but can't determine any worthwhile differences. The frequency is around 1 MHz and Vcc for Q1 is 9 volts. The output is into an NPN B-E junction. What might the R/C components do?

Thank you.

 

I've seen some Hartley oscillators both with and without the R/C combination in the feedback loop. What is their theoretical purpose? I've tried both with and without the inserted R/C combo with around those values, but can't determine any worthwhile differences. The frequency is around 1 MHz and Vcc for Q1 is 9 volts. The output is into an NPN B-E junction. What might the R/C components do?

Thank you.

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The Barkhausen condition is a necessary condition for oscillation. It has two parts a gain part and a phase shift part. It is not a sufficient condition for oscillation. Most oscillators need some additional factors to start like initial conditions, noise, or other deviations of components from ideality.
https://en.wikipedia.org/wiki/Barkhausen_stability_criterion

 

The Barkhausen condition is a necessary condition for oscillation. It has two parts a gain part and a phase shift part. It is not a sufficient condition for oscillation. Most oscillators need some additional factors to start like initial conditions, noise, or other deviations of components from ideality.
https://en.wikipedia.org/wiki/Barkhausen_stability_criterion

Yes, indeed... but what do the 270 ohm and 10 nF capacitor do? It operates equally well (as far as I can tell) without these components.

 

Those components make circuit operation more reliable across a wider range of circuit and device parameters.

The 270 ohm resistor is a DC bias "feedback" resistor for the FET current though the coil while the 10nf cap is a high frequency feedback bypass for that bias resistor to the coil.
https://www.wikiwand.com/en/Hartley_oscillator