alt Hacker NewsI think people have a wrong idea of what a modern atomic clock looks like. These are readily available commercially, Microchip for example will happily sell you hydrogen, cesium or rubidium atomic clocks. Hydrogen masers are rather unwieldy, but you can get a rubidium clock in a 1U format and cesium ones are not much bigger. I think their cesium freq standards are formerly a HP business they acquired.
Example: https://www.microchip.com/en-us/products/clock-and-timing/co...
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It is also important to realize that an atomic clock will only give you a steady pulse. It will count seconds for you, and do so very accurately, but that is not the same as knowing what time it is.
If you get a rubidium clock for your garage, you can sync it up with GPS to get an accurate-enough clock for your hobby NTP project, but large research institutions and their expensive contraptions are more elaborate to set up.
Sure, but F2 is a bit more accurate: "As of February 2016 the IT-CsF2 cesium fountain clock started reporting a uB of 1.7 × 10−16 in the BIPM reports of evaluation of primary frequency standards." ( from https://web.archive.org/web/20220121090046/ftp://ftp2.bipm.o... )
woah hold on a sec. that's not how these clocks are actually used though.
It's a huge huge huge misconception that you can just plunk down an "atomic clock", discipline an NTP server with it and get perfect wallclock time out of it forever. That is just not how it works. Two hydrogen masers sitting next to each other will drift. Two globally distributed networks of hydrogen masers will drift. They cannot NOT drift. The universe just be that way.
UTC is by definition a consensus; there is no clock in the entire world that one could say is exactly tracking it.
Google probably has the gear and the global distribution that they could probably keep pretty close over 30-60 days, but they are assuredly not trying to keep their own independent time standard. Their goal is to keep events correlated on their own network, and for that they just need good internal distribution and consensus, and they are at the point where doing that internally makes sense. But this is the same problem on any size network.
Honestly for just NTP, I've never really seen evidence that anything better than a good GPS disciplined TCXO even matters. The reason they offer these oscillators in such devices is because they usually do additional duties like running PtP or distributing a local 10mhz reference where their specific performance characteristics are more useful. Rubidium, for instance, is very stable at short timescales but has awful long term stability.