After yesterday’s intro of my “get your own atomic clock”, which is really just doodling, here’s the next step:
The clock, and the PCB panel it came attached to, has been placed in an all-plastic enclosure along with a little 15V @ 1.7A switching power supply. This thing needs quite a bit of power and actually gets quite hot. Nevertheless, I expect that placing it inside this relatively small plastic enclosure will not be a problem because much of the heat seems to be generated simply to keep the Rubidium “physics package” inside at a certain fixed temperature. For that same reason, I suspect that the heat sink on which this clock is mounted is not so much meant to draw heat away, but to maintain a stable temperature and improve stability.
Speaking of stability… here are the specs of this unit from eBay:
To get an idea: 10 to the power -11 frequency stability is less than 0.3 milliseconds per year error!
This particular unit (they are not all identical, even when called “FE-5680A”) also needs a 5V logic supply.
I haven’t yet decided how to bring out various signals, so I’ll hook up the 50Ω BNC connector on the back first and wait with the rest. Also needed: a LED power-on light, LED indicators for the “output valid” and “1 pulse-per-second” signals (via a one-shot to extend the 1 µs second pulse), and a 7805 regulator. Here’s the front – so far:
I don’t intend to keep this energy-drain running at all times, but it’ll be there at the flick of a switch to generate a stable 10 MHz signal when needed. One of the things you can do with it is calibrate other clocks, and compare their accuracy + drift over time and temperature.
Geeky stuff. For a lot more info about precise time and frequency tracking, see the Time Nuts web site.
Tomorrow, I’ll describe some of the trade-offs w.r.t. time for JeeNodes and wireless sensors.