You Can Phreak Atomic Clocks

You don’t hear much about them anymore, as computers and smartphones all get their time from networks, but consumer atomic clocks used to be a big deal. Despite what I thought as a child, those weren’t actually atomic clocks at all, but rather receivers for a national broadcast of the time from an actual atomic clock. And as Jeff Geerling points out in his newest video, you can phreak that signal.

For our younger readers: phreaking was an early form of telecommunications hacking. A classic example was phreaking public payphones using toy whistles to mimic the pitch of signaling tones in order to make free long-distance calls. At the time, long-distance calls were expensive, so you can see the motivation.

Geerling explains how you can do something similar for atomic clock receivers by phreaking the signal broadcast. There is free, open-source software called Time Station Emulator you can use to do exactly that. You can even access that from a browser, then broadcast the signal from a tablet or smartphone by using sound to induce the proper frequency in an antenna — the physics there were beyond Geerling and are beyond me, too.

If you have a suitable atomic clock, you use that signal to control its timing. To see the signal for himself, Geerling set up an SDR (Software-Defined Radio) receiver to examine the frequencies in detail.

Is there any practical utility here? Not that I can see, beyond some potential for pranking people that use very timing-sensitive equipment. But even if it isn’t useful, it is incredibly interesting.