Too bad you couldn't hack the Americium module from a smoke detector and create a DIY atomic oscillator. Cesium seems to be preferred. (And I know nothing about this sort of thing.)
(EDIT: chatting with an LLM… I realize I had assumed that "atomic clocks" meant radioactive and so suggested Americium because it is easy to obtain. LLM schooled me and suggested "Rubidium oscillator modules" instead since they come up for a few hundred dollars or so on eBay. Still not the DIY approach I had hoped for—I think I am still channelling the old "Amateur Scientist" column from Scientific American from the day.)
And Americium is not as useful for a timing reference, as it's not as stable as Rubidium and a lot less safe to handle. Otherwise time nuts would hoard cheap smoke detectors :)
A signal distribution box used from eBay is a lot cheaper than a good outdoor GPS antenna!
Though if you have enough cable and enough antennas already, no harm in having a little array like in OP.
mzs•50m ago