At this point the only clock in my life that doesn't auto set is the one on my stove, and that's because I abhor internet connected kitchen appliances.
In the 80s my uncle had digital clocks that used an antenna to tune into the atomic clock time signal that (was/is?) broadcast nationwide. I've long wished that it was incorporated into stoves, microwaves, essentially everything that isn't an internet device (yet... sigh)
Sadly I think the actual antenna and hardware were relatively large since it's a long wave signal, but maybe with SDR it'll all fit on the head of a pin these days.
I believe it was a longwave broadcast so probably WWVB which would apparently imply a 60mm antenna, but it was a standard old school "GE digital clock radio" form factor so size wasn't at a premium.
> Sadly I think the actual antenna and hardware were relatively large since it's a long wave signal, but maybe with SDR it'll all fit on the head of a pin these days.
Unfortunately there's no real way to cheat physics as far as shrinking a wavelength goes. With RF antennas about the best you can do is a major dimension 1/10th the frequency of interest.
There are many DCF77 receivers in Germany that are contained in a square box that's barely large enough for a AA battery; the rest of the square contains the motor/gears and the electronics/receiver (incl. a ferrite loopstick antenna).
Yeah, that's because it's receiving an extremely narrowband signal accumulated over a long window so it can suffer the trash efficiency I'm talking about.
