Mark Furneaux | Building a GPS Time Reference for NTP on pfSense @TheUbuntuGuy | Uploaded May 2016 | Updated October 2024, 4 hours ago.
I go over one way to use a u-blox NEO 7M as a PPS source for NTP. You can use this on pfSense or any other networked PC with the right software. The pfSense config is for some reason missing from the video, but all that is necessary is to select the "U-blox" GPS type and the correct baud rate in Services/NTP/Serial GPS.

This is what the stability looked like after: imgur.com/dbOTsic

I have a second channel:
youtube.com/channel/UCN3Dgu6CVBcecDkc5DmIIqw