A how-to on building a Raspberry Pi stratum 1 NTP server:
So this article is going to be my notes on how I built one using a cheap GPS module off eBay as the reference time source and a Raspberry Pi. (a 2B in this case, but hopefully the differences for newer models will be minor; if there are any, they’re probably around the behavior of the serial port since I think things changed on the Pi3 with bluetooth support?)
See the full post on The Life of Kenneth blog.