Triggered by a video on EEVblog of a Rubidium frequency standard and its teardown, I decided to get one myself. These things are available from eBay for around €40 these days, as recalls from cellphone towers, apparently:
It’s about the size of a hard drive, it’s completely closed, and there really is nothing to it – connect power, wait a few minutes for things to stabilize, and out comes a 10 MHz signal – a perfect black box:
There’s a capacitor in the output circuit, so the resulting signal is AC-coupled and hence centered around 0V and 1.5 V peak-to-peak. There’s also a 1 pulse-per-second (PPS) output signal, with a 1 µs pulse (at first I thought it didn’t work, but the pulse is really there).
The big deal about such a Rubidium-based atomic clock is its accuracy. More on this tomorrow…