X-fs from WS (PLL)

I've built this circuit a few times, here's my recipe:

- ADF4001 PLL synthesizer from ADI
- 3rd order PLL filter with ~20Hz F1 frequency
- 12C508A PIC for configuring ADF4001, if there isn't a host controller around to do it.

Google for "Dean's Book", written by a National Semiconductor PLL designer. It's a great reference for designing this kind of stuff.