On Mon, Nov 16, 2020 at 05:27 AM, Rafael Diniz wrote:

Did anybody managed to add a GPS to external referente the SI 5351?

Might be a round about way to do it. Depending on available pins.

In the time that the Nano processor is not doing much, let the Nano
read the 1 PPS pulses from a GPS to get a counter value that would
represent how far off the 16mhz CPU clock is. 

Then, once and a while, let the SI5351 generate a couple of mhz signal
(extra unused SI5351 output) that is fed into an input of the Nano.
Count that frequency, also.

Then calculate a correction factor for the SI5351 values needed to
program it to the correct frequency.

Just a rough idea. Haven't kept track if any extra pins are still
available on the Nano recently.

Tom, wb6b