[time-nuts] Z3805A cooling requirements?
SAIDJACK at aol.com
SAIDJACK at aol.com
Thu Dec 20 00:24:58 UTC 2012
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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