[time-nuts] Re: CTI OSC5A2B02 OXCO testing

[Forrest Christian (List Account)]

The way I would approach it as a beginner is with a 10mhz to 1hz picdiv and
a timestamping counter like a tapr ticc.  Both of

Feed the ticc's reference clock with your 10mhz reference.   Then run the
10mhz out of the ocxo into the picdiv which will result in 1hz output.
 Then run this 1hz into one of the ticc channels.

That way you'll get a high accuracy timestamp of each 10,000,000th pulse.
 If they are exactly 1 second apart you're right on 10mhz.   This last
statement is oversimplified and ignores all sorts of potential errors such
as accuracy of the clock source and other sources of measurement noise but
is good enough to get you started down the time nuts path.

Note that by logging each timestamp you can then feed that into timelab or
another other similar tool and get some detailed statistical analysis of
the ocxo over various time periods.

One other method which may use hardware you already have is to feed your 10
mhz reference clock into one channel on a 2 or more channel oscilloscope
and the ocxo output into the second channel.   Trigger off of the first
channel and watch how much the signal on the second channel drifts.  If
they are both on the same frequency there will be no relative drift.   If
they are different they will drift and the rate will increase the further
apart they are.   There is math you can do to determine how off if you can
time how long it takes a single cycle to drift.  Note that it doesn't take
much of a difference for this method to not be usable as you quickly get
drift rates which exceed what a human can interpret on the screen.

Note that all of the above is just to get you started.   Like I implied
there is a lot of details I left out or oversimplified, but that should get
you started.

On Fri, Jun 2, 2023, 9:55 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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