Warning: this post contains extreme nerdiness
Back in the early eighties, I built myself an atomic clock.
OK, not strictly true: I built a digital clock that was linked to a time signal generated by an atomic clock housed in the National Physics Laboratory in Teddington. This time signal was then broadcast from Rugby at a Very Low Frequency. The clock picked up this VLF, then demodulated and decoded it in order to display the precise time. It worked well, and I added more bits to it so that it eventually displayed the time in hours, minutes and seconds, the date DDMMYY, the day of the week and a GMT/BST indication (that I never did manage to get working). Even an alarm function (some, but mainly not all, my own design, I hasten to add).
I was quite pleased with it, because in those days, I never had access to frequency counters and oscilloscopes and such, so there was much trial, error and AGC gain measuring to be done in order to get it working. The RF side of things – picking up the actual signal from Rugby – was always only just working, but was OK as long as you didn’t move the thing around too much. As we only live 30 miles or so from the radio station (MSF) in Rugby, reception was never too much of a problem.
But then, the other day, I read this. Cumbria? Jeez! Would it pick up from GBZ in Cumbria? It should (at that frequency), but the way it was cobbled together, I wasn’t sure. So today, I climbed up into the loft (where the clock currently lives) and sure enough, discovered it was dead:
Arse! It may be held together with Blu-Tack and string (that’s actually true: it is inside), but for over 20 years it has worked fine.
So, I dug out my DVM and started tweaking the AGC. It should only take a few seconds.
Of course, a second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.
As you well know.
Anyway, twenty minutes later:
Eagle-eyed amongst you may notice that the date is exactly correct… if you add 20 years. Yup, it wasn’t Y2K compliant, and when 1999 ticked over into 2000, my clock jumped back to 1980. I did plan to sort it out, but seven years later, I wonder if it’s worth the bother. Anyway, I think it adds a sort of olde-worlde charm to it!