I have a rack of gear down at a datacenter down in California, where I’ve got a single internet connection. It’s quite reliable and performs well, but I wanted a backup means to reach my equipment in the case of an outage, or in the potential case of a router misconfig that breaks external connectivity.
I had an extra 1U rackmount case from the PoE PDU project, and with the LTE modems I’ve been using for the Cellular Webcams, it seemed very reasonable to put something together and have an inexpensive Out of Band connection to my remote installation.
At the same time, I had plenty of room in the case for another Raspberry Pi, and another person who has gear in the same facility noted that *some* GPS signal was available inside, though perhaps not great, so I searched for a reasonably high gain GPS antenna, and decided to add a NTP Stratum 1 time server as well.
I designed a couple of very basic custom PCBs, one to combine the two power supplies to provide redundancy, and the GPS board for the Stratum 1 Pi. Added a basic character LCD I had laying around in the junk pile to provide visible status.