Hi electroRF,
I think, RCinFLA has given you a very good and detailed description of the whole system.
In this context, he also has mentioned loop stability which is, of course, a very important aspect that deserves some specific investigations.
However, as far as the "dirty" signal is concerned, I think - as already mentioned in my previuos post - it is simply a result of bad filtering after signal detection.
Why are you surprised? Why do you expect a clean dc signal representing the output power?
There is no signal detection process that really can give you a "clean" and undistorted dc signal because each filter can provide for unwanted frequency components a finite attenuation only.
And - in your case - it seems that the filter is badly designed or you must select a higher filter order.
Therefore my question: Is the frequency of the "dirty" components identical to the output frequency?
W.