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I have a severe problem problem here, I don’t know where to put it exactly, I am having severe problems in isolating analogue GND from the digital ground in pcb design for a critical RF application. I have tried numerous filters using high quality inductors and capacitors, strictly speaking as long as I don’t have a good GND free of noises from crystals of the digital circuitry, filtering would be of no use. When we monitor the circuit on spectrum analyzer, we see first and second harmonics of these crystal frequencies with -50dbm of power which are deadly in our application. How could we get rid of these unwanted harmonics? How should I design digital and analogue grounds? Do the commands from the microcontroller carry these harmonics to the RF board? If so, what’s the solution? After all I can’t filter digital commands before applying them to the target board, because if I do so, there would be no commands. Help me brother.