@Dianora @carstenfranke @ZenHeathen @Snowshadow @TimWardCam the concern about spoofing is why there's interest now in using ATSC 3.0 for this purpose

For more details look up the papers on Broadcast Positioning System (BPS) Using ATSC 3.0

Currently the USA is at ~70% population coverage for ATSC 3.0 signals. South Korea was leading this I think. It should be expanding around the world I think. There's already proof of hardware to use it as a clock source and positioning system.

I'm living in an area with coverage and I'd love to buy something that can do BPS and use it as an NTP clock source. I wonder if someone could build one with an SDR receiver? Or perhaps you'd need multiple?