I've recently used insights from this article to implement a sample rate step size 128 times smaller than previously supported in HackRF:

https://www.pa3fwm.nl/technotes/tn42a-si5351-programming.html

This means that sample rates around 20 Msps can be adjusted in steps of about 0.015 Hz. The precision is even better at lower sample rates.

I highly recommend reading it if you use #Si5351 in any projects. #Si5351A #Si5351B #Si5351C

Understanding and enhancing Si5351 programming