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Comment by JKCalhoun | Hacker News Reader

No mention of the cost of the CSAC GPSDO (only that it's "not cheap").

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.)

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The clocks need precise oscillations to measure time: the mechanical clocks used pendulums and springs; the maser clocks used precise microwave cavities; the atomic clocks that are dominating today use oscillations of electrons in selected atoms.

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.

Typically high hundreds / low thousands for a used GPSDO with a CSAC.

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 :)

I have 2 Rb GPSDOs and a few more OCXO ones, but had never heard of CSAC modules and thought that the inevitable next step would be an HP 5061A Cs clock or later model.

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?

Search for "rubidium clock" or "gpsdo rubidium" and you'll start whittling it down more. It's much harder to find just the CSAC part, unless you're building clocks commercially.

Americium is also chemically different and may not be as practical as cesium and rubidium to ionize and trap.

Words of wisdom (from a time nut).

Spinthariscope https://xkcd.com/2568/

He seems to be using a GPS-2700[0], which has a price tag of about $5500 / €4700. I reckon you can find a better price if you get very lucky on the second-hand market, though.

[0]: https://www.microchip.com/en-us/product/GPS-2700

It strikes me as strange that the article links to [1] which appears to be the same board, absent the "Viavi" logo on the main RF can, as the Microchip product you linked. I couldn't tell with a brief look if the Viavi product is offering something like software, configuration, tuning, etc. on top of GPS-2700 product.

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...

[2] https://www.youtube.com/watch?v=CogN630jUSs

[3] https://en.wikipedia.org/wiki/Symmetricom

There are some subtle differences. The Jackson Labs and Microchip boards both have a diagonal "swoosh" and a "do not touch" icon on the metal clock casing, a u-blox branded GPS receiver, and partially-filled mounting holes. The Viavi board has a blank clock casing, unbranded GPS receiver, and fully drilled-out mounting holes. But yes, all three are using a virtually-identical PCB.

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!

I did dig into this a bit more the other day and learned that the "main RF can" is the cesium oscillator module. The history there was pretty interesting! The early ones I found were the Symmetricom Quantum SA.45s[1,2] which included a pretty entertaining thread here[3]. There were several levels of quality and function in the family of products which have been discontinued in favor of the MAC-SA55[4], and I wish I could find where I saw that recommendation... It's a rubidium, instead of cesium oscillator, not that I know enough about these things to concluded one should be better than the other but my impression was cesium was higher precision.

[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...

[4] https://www.microchip.com/en-us/product/mac-sa55

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