[time-nuts] Z3805A cooling requirements?
lists at rtty.us
Thu Dec 20 00:48:11 UTC 2012
Ok, what happens if you keep the air gun in the exact same position and let it stabilize for an hour with no insulation around the OCXO ?
On Dec 19, 2012, at 7:24 PM, SAIDJACK at aol.com wrote:
> Hi Bob, et. al.,
> this discussion prompted my interest to see how a 10811-600160 unit that we
> have sitting here on the bench would react to airflow changes. I had a
> thin layer of anti-static shipping material around the unit, and I opened up
> one side of that layer and then pushed air into that side.
> The unit is from a 53132A counter, and has the 53132A OCXO PCB with voltage
> regulator attached to it, and is being fed from an external stable power
> Please see the frequency plot attached, I used an air gun to push air onto
> the unit for about 60 seconds or so. The unit had quite a large and
> immediate change in frequency, up to about 3.5E-011 and then down to -4E-011 at
> which point I captured the image (while it was still drifting negative). I
> did not wait until it settled back (will take probably 30 minutes or more I
> would guess), but it went quite a bit more negative after I captured the
> This airflow sensitivity is probably a combination of the circuitry on the
> support PCB, the OCXO, and the external power supply.
> The stability before the unit was exposed to the airflow was quite good as
> can be seen in the left half of the plot, and I think this illustrates how
> adding a bang-bang type airflow to these oscillators can worsen ADEV
> performance significantly, albeit we are talking 10's to 100's of parts per
> trillion here.. I would much rather see the unit perform as it did initially in
> my test setup without the airflow though.
> In a message dated 12/16/2012 18:11:02 Pacific Standard Time, lists at rtty.us
> … and what I'm trying to say also comes from the real world...
> If you start putting "stuff" on an OCXO, be careful about the case
> temperature and how the OCXO is spec'd. A few mm of dead air can make a good
> insulator. That can boost the case temp quite a bit.
> On Dec 16, 2012, at 9:06 PM, Magnus Danielson <magnus at rubidium.dyndns.org>
>> On 12/17/2012 02:47 AM, Bob Camp wrote:
>>> The gotcha here is that an un-cooled piece of gear will heat up and
> cool down as it's work load changes. There is no "magic bullet" that keeps
> the temperature constant with zero airflow in a normal design. Yes, I'm old
> enough to remember oil cooled computers. Still no constant temperature and
> you have turbulence.
>> I agree that there is no "silver bullet", but my point was that
> sometimes you kill one property when you apply a solution to another problem. I am
> very well aware of heating problems and cooling my components, as this is
> part of my real world. But rather than isolating the full box, I'm talking
> about the TCXO or OCXO. Just putting a small wind-shield over it changes
> things a lot at times.
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