[time-nuts] EFC info on Trimble 34310-T OXCO

Bob Camp kb8tq at n1k.org
Sun Aug 24 20:48:26 EDT 2014


Hi

Keep in mind that the OCXO is likely (if it’s a modern part) optimized for TC at it’s normal thermal gain. The gain and set point are adjusted for a flat curve. If you bump either the gain or the set point you rotate the curve.

Bob

On Aug 24, 2014, at 8:36 PM, EWKehren at aol.com wrote:

> Charles
> I use double bobble pack inside the Alu channel and I always start out by  
> monitoring the OCXO and make sure it is at least 10 C below the spec range. 
> The  tbolt is center located and I use a combination of rubber mounts but 
> suspended  that they sell for hard drives and squares of double bubble pack. 
> Vibration and  thermal.
> Bert Kehren
> 
> 
> In a message dated 8/24/2014 8:26:02 P.M. Eastern Daylight Time,  
> csteinmetz at yandex.com writes:
> 
> Bert  wrote:
> 
>> As I said before am waiting for the small spheres and will  see what 
> happens.
> 
> Monitor carefully, as I suspect the spheres will pack  too tightly 
> leaving too little airspace.  You could easily burn down  an OCXO if 
> this proves to be the case and the oven control loop goes  
> unstable.  I'd put a thermal sensor on the OCXO itself for  testing.
> 
> Even if it doesn't burn down, you could find that the oven  
> performance is degraded by (i) instability or quasi-instability of 
> the  oven controller, or (ii) too much thermal resistance (remember, 
> you want  to add as little thermal resistance as possible).
> 
> On the other hand,  mounting the OCXO as centrally as possible inside 
> the outer enclosure on  thermally non-conducting standoffs (teflon or 
> nylon), with at least an  inch of air on all six sides, has proven to 
> work extremely  well.
> 
> When I described using packing peanuts (or similar) to break up  the 
> airflow, it was in the context of having already mounted the OCXO as  
> centrally as possible inside the outer enclosure on thermally  
> non-conducting standoffs with at least an inch of air on all six  
> sides.  And as I said, I have not found the additional step necessary  
> once you have done this.  It may even be  counterproductive.
> 
> Best  regards,
> 
> Charles
> 
> 
> 
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