We could mount an si5351 the Adafruit si5351 breakout board to the back
of the uBitx:
https://www.qrp-labs.com/synth.html
https://www.adafruit.com/product/2045
https://www.etherkit.com/rf-modules/si5351a-breakout-board.html

I'm thinking some duct tape on the back for insulation,
then solder wires from breakout grounds to uBitx groundplane securing it
mechanically.
Steal the old clk0,1,2 lines going into the uBtix for use as i2c SDA,
SCL lines.

Hans of qrp-labs.com is active in this forum.
Nik is successfully using that Adafruit board on his Raduino replacement:
https://groups.io/g/BITX20/message/41676
And we were initially using the Etherkit si5351 library on the Bitx40.
All good choices.

Jerry, KE7ER


On Mon, Apr 9, 2018 at 06:56 pm, Vince Vielhaber wrote:

Another solution would be to separate the Si5351 from the raduino.
Put it on its own board that plugs into the uB. Pins 10-16 pass thru
to another connector. Another connector connects the I2C to the
raduino. Then you can put the UNO part of the raduino (or use
something else entirely) wherever you want where the Xtal won't be
an issue. That also gives more options for boxes and mounting.

I have it partially finished in KiCAD but other things have gotten
in the way so it's on hold. I tried to get Mike Hagen to do it but
he didn't seem interested.