Once you do get measurement down to nanoseconds, you quickly realize how 'bad' so many clocks you thought were good actually are. Lots of GPS modules with massive sawtooth behavior. Over a day they may be within tens of ns. But over a minute, a lot worse!

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jacquesm 5 hours ago | parent [-]

Yes, but over a decade they are ridiculously precise.

And that's precisely the problem: when you need very short term stability that nicely couples into longer term stability you have your work cut out for you.

Another downside of this kind of project is that to collect the data you are always looking at a minimum of 24 hours or so of sample time and at high enough rates that really adds up. Suddenly you need media that are never going to hiccup during long sequential writes and it turns out that's not a simple problem either. Before long you'll be messing around with the buffering deep inside of GNU Radio (which is amazing piece of software by the way).

But: when it finally works it is extremely satisfying. To see a clock driving a frequency counter and a non-derived clock that lists 9 zeros with a 100 second sampling window is pretty cool.

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bradknowles 4 hours ago | parent [-]

Yup. I’ve known the guys at Meinberg since around 2003, when I started helping out with the NTP Public Support Project for NTP.org.

They are very well aware of both the short-term and long-term effects that they have to compensate for. And getting that both smooth and accurate down to the nanosecond level is particularly hard.

They are not the only vendor of Stratum-1 NTP time servers (on the AWS EC2-Chronos team, we called them Primary Time Appliances), but I think they are one of the best. If not the best. And a friend and former co-worker of mine from EC2-Chronos is now working there.

	▲	jacquesm 2 hours ago \| parent [-]
		Fascinating stuff all this. I just had a very practical problem to solve so my interest was purely accidental but I have deep respect for the people that make such an outwardly simple thing the focus of their career to the point that they can contribute in a meaningful way to the field itself. Half the world (or more) does not recognize the degree to which we casually rely on incredibly precise timekeeping and how much of an achievement it is. More so because it is so invisible. What I've also found is that everybody in this domain is incredibly friendly and willing to share advice and knowledge.