[time-nuts] Re: CTI OSC5A2B02 OXCO testing

[Bob Camp]

Hi

By far the biggest issue with any small OCXO is the “stable temperature”
part of things. Any sort of draft is going to be a really big deal. HVAC cuts
in … problem. Door to the lab opens and closes ….problem. Folks move around
in the lab … problem. Dog wags tail ..

I would spend some time coming up with some sort of enclosure that at the
very least keeps the drafts at bay. You don’t want things buried under a big
blanket, the OCXO’s will overheat. Enclosures build of water bottles are indeed
an option. Monitoring the temperature inside the enclosure is a very good idea.

Simply shorting the EFC to ground is a quick and simple way to handle that side
of things. They will be off frequency. The long term data still should be representative
of the part. Having them at a range of frequencies just might help with various cross 
talk issues.

Keeping any of this stable while plugging the parts into some sort of board is a
challenge. Soldering them into a board is great, un-soldering them may well 
damage them. How this impacts things depends a lot on a whole lot of details. 

Switching wise, kill the signal at the oscillator. Don’t let it head over to a switch. It’s
a CMOS output device. A gate will do that pretty well. You need some sort of
buffer anyway. These parts will not drive a chunk of coax cable. 

If you are looking for aging, a reading an hour should be adequate. If you are trying
for ADEV, then you only want to look at one device at a time. One part in the fixture,
all the rest on the other side of the room …..

As noted in other messages, a cute way to do this is to divide all the OCXO’s to 1 pps
and then look at time drift. Log the time offset once an hour. Anything that gives you
a nanosecond-ish reading is plenty good enough.

Fun !!!

Bob 

> On Jun 2, 2023, at 7:14 PM, Reginald Beardsley via time-nuts <time-nuts at lists.febo.com> wrote:
> 
> Hi,
> 
> I've tried to avoid time-nutting for a long time, but I have lost the battle.
> 
> I bought 10 bare CTI modules on ebay for $2.93 each which I wish to test over a long period of time.  I can set up 2-4 GHz SMA relay switching, GPSDO reference etc.  Question is, what to read the frequency with.  My 5386A with a GPSDO isn't precise enough.
> 
> I don't know anything about it yet, but nanoPFA  FW on a nanoVNA  H4 looks attractive.  Are there other instruments/methods to consider?  I have a crazy mid 90's lab, so a bit more is not an issue other than where to put it.
> 
> All I'm looking for is a pebble tossed in the right direction.  Current plan is an LM399 reference with emitter followers driving Vref on the OXCOs, very stiff PSU and a fairly stable temperature.
> 
> Thanks,
> Reg
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