Hi Murat
The value of the rectifier smoothing capacitor isn't too critical. The time constant for 10nF and 28k is 280us. The time between cycles at 1MHz is 1us so there will be adequate smoothing over the frequencies it's designed for.
I put a x10 probe on my PCB this evening and, with 12W in at 14MHz I measured 20mV of ripple on TP1 and 10mV at the ADC input. I think this is perfectly acceptable.
The numbers varied very slightly as I moved the probe earth around the PCB, so the levels you're seeing may be due to your layout.
--
Mike G8GYW
