Computing stuff tied to the physical world

More accurate 10 MHz

In Hardware on Jan 22, 2012 at 00:01

To follow up on yesterday’s post, here’s a similar TCXO oscillator which is considerably more accurate:

DSC 2862

It’s a 10.000 MHz unit which has been calibrated and claims a 0.1 ppm accuracy. That’s 10 MHz ± 1 Hz, i.e. 7 digits. Here’s the output signal, which appears to be AC coupled:


Not bad for a low-cost unit. I got it from the RFcandy shop. Current consumption is 0.94 mA @ 5V.

Once you start looking into this stuff, all sorts of things pop up on the web. There’s a group of amateurs who call themselves Time-Nuts (terrific name!) and who aim to keep track of time as accurately as they can – with pretty amazing results. In a comment yesterday, John Beale pointed me to a web page with info about the Rubidium clocks now available cheaply on eBay.

I found this page most entertaining, summarizing the history of accurate time-keeping in a few slides.

  1. Hmm – I’d expect crystal ageing would soon (relatively!) make that initial calibration precision invalid. Some doubt about the TXCO tag here, though there are enough components there to have some analog circuit “pulling” the crystal along the inverse of the temperature curve. Depending on the repeatability of RTC chip, I suspect it also can be calibrated to a similar accuracy.

    Good price point though compared to getting to the next level of precision with a GPS shield.

    • Funny you mention GPS – I’ve just been looking at a nice GPS-controlled project (PDF). Got a little GPS unit lying around here, so who knows – maybe one day I’ll try that. I’m also tempted to get one of those Rb units, just for the heck of it (“an atomic clock at home!”).

      But I have to admit that although this stuff is addictive, I don’t really see a need for this. All I know after seeing the above scope screenshot, is that either that TCXO or my scope is off by a few Hz…

      There are too many time sinks in this world!

  2. GPS module/dongle prices are certainly attractive – could all be done in firmware by manipulating the TCO ageing register. I suspect an external antenna is required though to get away from the board emissions – those GPS signals are truly tiny.

    Time sink? True, but fascinating.

    A man with one clock thinks he knows the correct time, with two clocks, he knows he doesn’t

  3. Really looking forward to where this goes… most projects have a time/clock related need/implication…. toss in a GPS location component with wireless comm’s…. and one can hardly restrain their anticipation…. ;) thanks for your continued efforts JCW

  4. I think a TCXO is the only real battery-powered timing source (maybe augmented by occasional corrections from GPS, network, etc.) You can get cheap OCXO parts (see my project here, ) but that will run 6xAA batteries flat in about 24 hours. And, of course a Rb reference is 12 watts or so after warmup. Many of the “time-nut” crowd have a GPSDO called a “Thunderbolt”, formerly available as cheap surplus, although the supply has recently dried up.

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