No, it is not possible to have a stable DC output from a variable frequency input without some form of frequency stabilization or conversion. This is because DC, by definition, has a constant voltage with no variation over time. However, a variable frequency input would cause the output voltage to fluctuate, resulting in an unstable DC output.
To convert a variable frequency input to a stable DC output, a rectifier circuit can be used. A rectifier circuit converts an AC input to a DC output by allowing current to flow in only one direction. However, the output voltage of the rectifier circuit will still be affected by the input frequency, and may fluctuate if the frequency varies.
To stabilize the output voltage of a rectifier circuit, a smoothing capacitor can be used. The capacitor will charge and discharge to smooth out the voltage fluctuations caused by the variable frequency input. However, this method may not be sufficient for highly variable input frequencies, and additional frequency stabilization or conversion techniques may be required