My Stratum-0 Atomic Clock
coverclock.blogspot.com
coverclock.blogspot.com
I've looked at doing this a few times. I don't have references handy but there are cheaper atomic oscillators available now, under $1000. Still to expensive for me to justify it but one of these years I'll find one cheap.
I have a couple of GPSDOs here and it is fun to play them against each other, the differences in the short term can be substantial, but over anything more than a few days they are extremely accurate.
You're also not likely to be out of GPS for particularly long stretches of time.
Gravitational bias is a really fun one since you can easily demonstrate it & its' not immediately obvious. Take a quartz oscillator, and a reference oscillator. Measure the frequency of both. Turn the quartz oscillator on its side. The phase (and usually also frequency) will change: the physical quartz has inertia & gravitational mass, so changing its orientation changes how it oscillates. In one orientation the movement of the quartz atoms is perpendicular to the force of gravity, so both directions of oscillation are biased the same amount. In another orientation one the movement of the quartz atoms is parallel to the force of gravity, so the part of the crystal moving down accelerates a bit more than the part of the crystal moving up.
Indeed! And that short term stability of a (good) OCXO is most impressive, you can fairly easily outperform a GPSDO and with a little work and a lot of attention to supply voltage and other external influences you can even (short term) outperform an atomic clock. But aging is a thing, you'll need to re-calibrate almost every week if you care about that kind of precision. I have a bunch of different standards to compare with each other and the first time I got lucky with a very good OCXO I was wondering if I had made some kind of mistake, it was that stable.
That gravitational bias thing sounds very interesting, I knew it existed but did not realize you could trivially demonstrate it like that, I'll have to try this.
Thank you.
A signal distribution box used from eBay is a lot cheaper than a good outdoor GPS antenna!
Though if you have enough cable and enough antennas already, no harm in having a little array like in OP.
Those are not cheaper than an antenna! Although from the photo I'm not sure he bought the cheap antennas.
Speaking from experience deploying stratum-1. Not stratum-0, but the same GPS concerns.
Don't those splitters typically have an amplifier, so become a single point of failure?
If you're going through the trouble to have multiple time servers on your network, you probably want to make sure that an amplifier failure doesn't take them all down at the same time.
Also the splitter will pass through the dc-bias on the first port to power the antenna, -- so whatever is hooked there is another spof.
I've been testing it and it is noticeably better, but I haven't yet had time to set up an A/B test to get real numbers.
Too bad you couldn't hack the Americium module from a smoke detector and create a DIY atomic oscillator. Cesium seems to be preferred. (And I know nothing about this sort of thing.)
(EDIT: chatting with an LLM… I realize I had assumed that "atomic clocks" meant radioactive and so suggested Americium because it is easy to obtain. LLM schooled me and suggested "Rubidium oscillator modules" instead since they come up for a few hundred dollars or so on eBay. Still not the DIY approach I had hoped for—I think I am still channelling the old "Amateur Scientist" column from Scientific American from the day.)
And Americium is not as useful for a timing reference, as it's not as stable as Rubidium and a lot less safe to handle. Otherwise time nuts would hoard cheap smoke detectors :)
So now you have me going to eBay in search one but all it turns up are BM25CSAC carburetors! What are the magic keywords to use in my search?
The photo of the device on the article says "Jackson Labs" which seems to have been the previous name of "Viavi Solutions" and a review video [2] mentioned using Symmetricom atomic clock modules, which was acquired first by Microsemi (2013) and subsequently Microchip (2018)[3].
[1] https://www.viavisolutions.com/en-us/products/chip-scale-ato...
Judging by the misaligned capacitors(?) on the Viavi board, it is almost like the Viavi one is an early prototype, with the Jackson Labs one being an early production version and the Microchip one being the current production version. I have no idea how that would work out acquisition timeline wise.
But yeah, hardware companies are rather acquisition happy. When designing hardware it is very common to come across datasheets with an "X is now known as Y" cover page stapled onto it. Heck, every once in a while you'll even come across a datasheet which is obviously scanned-in, for a brand which hasn't existed in three decades - and the chip will still be in production!
[1] https://www.gpsworld.com/wirelesstimingnewssymmetricom-offer...
[2] https://www.si.edu/object/symmetricom-chip-scale-atomic-cloc...
[3] https://febo.com/pipermail/time-nuts_lists.febo.com/2021-Jan...
Americium is not a good atomic clock material---it doesn't have superior electronic transitions, and the nuclear transitions causing its radioactivity would get in the way.
Nuclear oscillations could also be used: there is a proposal to use a low-energy nuclear oscillation in Thorium; it would be more stable than electronic oscillations: https://en.wikipedia.org/wiki/Nuclear_clock
The distinction of what can or cannot be called 'radioactive' is somehow artificial: masers, atoms and nuclei all emit radiation, so they all are technically 'radioactive'. Conventionally, 'radioactive' radiation requires energies that cause ionization of common materials, usually quoted as above 10eV. The Thorium nuclear transition is actually below that, so technically it is not radioactive---but I'd still not want to sit next to such clock without some shielding, because even UV radiation with energies above 3eV is known to damage living tissue.