Electronics > Metrology

Low cost <1 ppb 10 MHz OXCOs on ebay

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There are a slew of references based on the CTI OSC5A2B02 10MHz 5V Square Wave OCXO Crystal Oscillator very cheap (~$20 USD).  After placing in an enclosures to protect against drafts, the two I am testing are holding <0.1 ppb day to day stability once trimmed to the thermal environment.  Bare modules are less than $3, though I don't yet know what I'm going to get.

The one shown  lacks fiber fill to damp airflow and is very stable lying flat, but shifts frequency quite a bit if placed long edge vertical.  Lay it flat again and it's back where it was.  Another filled with cotton balls doesn't care about orientation.

This one will get a mat of fiber insulation and a temperature controller.  The dramatic change in frequency from convection makes keeping a copy of this pointless except as an example of what not to do.

The yellow trace is one of Leo Bodnar's GPSDOs.  The other trace is the OXCO output.  I attached the two screen dumps so you can calculate the frequency difference independently of my 5386A.  I know from experience that when the error is <0.01 Hz I can't possibly get it better.

One of the great virtues of packaging them in a box is the ability to use it with any T&M kit that takes an external 10 MHz reference via a backpanel  port.

Have Fun!

I see the boards, but I don't see any bare oscillators. I wonder what these came from? Cell sites?

I wanted a rude username:

They tend to be "gently reworked" off various PCBs as you can see in this photo from an AliExpress listing. The thought of saw-induced vibrations in such a precision part gives me the screaming abdabs.

I have bare boards for these low cost OCXOs here: : https://www.ebay.com/itm/155419526549 if anyone is interested.

Also re-did the 53131A OCXO module (which was originally from the HP design/schematics) but changed out the expensive and sometimes hard to get AD7243ARZ DAC with a less expensive 5V DAC.


 Limited to a 10 s gate, the 5386A is  really not  much more accurate than ~0.1 Hz.  So for serious study I need to develop an appropriate instrument by feeding a GPSDO clock to the timer inputs of a fast MCU dev board.

At the moment I'm leaning towards putting aluminum plates thermally bonded to Peltier devices with old CPU  heat sinks and fans attached for precise temperature control.  The optimal temperature is just high enough to keep the OXCO oven from turning on, avoiding generating  transient thermal events generated by the OXCO heater.

I rather fear I am among the lost as I'm about to see if the fabled <$150 rubidium standards exist.

Pray for my salvation and that I shall be delivered from the debauchery of becoming a Time-Nut. ;-)

BTW this is the board design I bought though possibly not this vendor.



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