Re: GPSDO ubitx ?
If you are sticking with the Si5351 family for this and are ok with laying out a new board,
I'd use the $2 Si5351C in the QFN package. It has a refclk input that can work with
directly with the 10mhz reference clock often available from GPS modules.
The $1 Si5351A in the MSOP10 that we normally use can take a reference clock
in on one of the crystal pins, but spec sheet says it's only good for 25 to 27 mhz.
Reports are that it does work with a reference clock of 10mhz, but with
significantly more jitter.