FreeDV Experiments: Blogger post
SV1AFN provides a nice implementation of the ADF4351 synthesiser. To test this board I used a 80 MHz LO with the SPI interface driven from a RPI. This software from F5OEO makes the exercise very easy.
Others have mentioned that it's important to use a clean 3.3V supply from this synth. Looking at the output signal (say at 430.1 MHz) gave these results when the synth was driven from the RPI 3.3V on the GPIO connector, compared to a clean supply.