I've tried to output various frequencies from Raspberry Pi Pico, In MicroPython, changed the machine frequency (this automatically programs the PLL), then divided by 2 or more using PIO, to avoid any glitches caused by the running software.
I don't have a good spectrum analyzer, so can not really measure the phase noise. No obvious problems with the signal.
This is not a true synthesizer like Si5351A, mainly because the PLL phase detector requires 5MHz or more. The step between the possible frequencies is in the range of 50..100kHz, with all whole MHz numbers and many x.xMHz numbers covered.
Unfortunately, this is far from the resolution required for WSPR or FT8 signal output. Still an easily programmable crystal replacement for $4 sounds good to me.
73, Mike AF7KR
