[time-nuts] Z3805A cooling requirements?

Bob Camp 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  
> supply.
> 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  
> plot.
> 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.
> bye,
> Said
> In a message dated 12/16/2012 18:11:02 Pacific Standard Time, lists at rtty.us 
> writes:
> Hi
> … 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.
> Bob
> On Dec  16, 2012, at 9:06 PM, Magnus Danielson <magnus at rubidium.dyndns.org> 
> wrote:
>> On 12/17/2012 02:47 AM, Bob Camp wrote:
>>> Hi
>>> 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.
>> Cheers,
>> Magnus
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