[Radio Wrangler]

Take note of the word 'dirty'. The phase noise sideband level of an oscillator is related to the Q of the oscillator's resonator. Super-duper quality coils can give a Q of a few hundred, and the better varactor diodes will be a further limitation, typically halving that figure depending on the fixed/variable capacitive proportions. Mechanical tuning capacitors have much higher Q. At the other end of the Q range, some larger SMT parts can reach 100. small cheap SMT parts can be around 20.

Having set the scene, now for the punch line: R-C oscillators have effective resonator Q's below unity!

Add in a fair amount of drift with temperature.

These sorts of parts have uses in general electronics, but prove to be seriously limited in radio work.

They can be phase locked, and the loop used to rein-in the noise over the loop bandwidth, but they are always worse than L-C based designs.

Sorry for the cold water, but I thought I'd better point out the limitations as they particularly affect radio applications.

One really wild thing in the oscillator world are integrated MEMS oscillators with MHz range mechanical resonators. More like a crystal substitute than a VCO.

David