[time-nuts] FE-5680A heat sink

Chuck Harris cfharris at erols.com
Mon Jun 8 23:38:31 EDT 2009

Hi Leigh,

I just looked at a manual for an EG&G Rb standard module, and their spec
is for -55C ambient to +68C baseplate.  They had another spec that said
MTBF >90,000 hours at 40C baseplate.  Your FEI unit probably has a similarly
worded spec.

To me this means that the ideal (expected) temperature for the baseplate is 40C.

If you are intending to operate your Rb block in a home environment, that
has conditioned air, you can assume that the ambient temperature will be
nominally 25C.  I would start from that point, simply attach the
block to the chassis, and measure the operating temperature of the baseplate.
If it is around 40C, great!  If it is much above 40C, you might want to add a

I wouldn't go out of my way to get below 40C.

You can calculate the heatsink size knowing only the ambient temperature,
and the power demand of the Rb block.  But for operation in a civilized
area, it is easier just to try a simple experiment.

-Chuck Harris

Leigh L. Klotz, Jr WA5ZNU wrote:
> Chuck,
> This device is a pull from a larger system, probably a cell site.  It's 
> clearly designed to be mounted on something, as it has lots and lots of 
> holes around the edge.  I suspect there's some thermal management that's 
> missing.  The FEI sheet gives "typical" data for the 0-50C range, though 
> presumably that's ambient temperature.
> I don't want to cool the physics package per se, but I do want to at 
> least approximate what kind of thermal solution ought to be supplied.
> Quite a few of these have been sold, and I've gotten good advice from 
> others on this list about calibration.  I'd hoped that someone would 
> have experience with the thermal management.
> So far I've seen 
> http://www.dd1us.de/Downloads/precise%20reference%20frequency%20rev%200_4.pdf 
> which shows (but doesn't describe) a heat sink on the bottom.
> Leigh.

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