Use the PLL mode of LMX2571 (fpd=4.8M), use an external VCO to oscillate, and the output frequency is between 130~180MHz. Every 3M frequency, similar to (150, 153, 156M) phase noise will fluctuate up and down. Change the phase detection frequency (fpd=6.4M), the frequency will jitter every 2M phase noise. The peripheral hardware circuit has been checked and there is no problem. why is that?