[time-nuts] FE-5680A heat sink

Rex rexa at sonic.net
Mon Jun 8 23:48:33 EDT 2009

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.

Several years back I bought a 5680A and mine came still mounted on the 
original (Lucent?) circuit board. There is a small amount of circuitry 
on one end, but most of the large board is just a solid plated area 
where the FE-5680A mounts. This is almost 100 in^2 plated on both sides, 
so an equivalent would be a sheet of aluminum about 7.25 x 13.5 inches. 
I'll let someone else translate that to an appropriate finned heatsink.

> 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.

I never saw that particular pdf article before. It looks interesting. 
The 5680A I got was a bit different from most and I never found a way to 
program mine. I'll have to revisit the unit and see if the header 
connector he used works. I though I looked at that, but it has been a 
long time. Worth another attempt, I guess.

-Rex, kk6mk

>> I'm puzzled.  I admit that I don't have a lot of experience with
>> Rb standards, but I do have a bit of experience with the HP-5065A
>> Rb standard.
>> In the 5065A, the entire physics package is enclosed in an oven.
>> Assuming that your Rb is the same, and I believe it is, your plan
>> to force the physics package to run at room temperature is just going
>> to make the oven work harder in its never ending quest to maintain
>> stable temperature.  If you monitor the current draw of the 5680A,
>> you will probably see that it goes up when you put a fan on it.
>> Sometimes, you just have to let electronics run hot.
>> What did the manufacturer suggest?
>> -Chuck Harris
>> Leigh L. Klotz, Jr WA5ZNU wrote:
>>> I've attached an SMA connector to my FE-5680A and built an external 
>>> linear power supply with a TO-3 7815.
>>> I ran the device today for about half an hour, and used an infrared 
>>> sensing thermometer to measure the external case temperature.
>>> It got up to 48 C externally in the physics package area.
>>> I put a muffin fan on top and it brought it down to 38C but I don't 
>>> think this is a good plan because I worry about the effects of the 
>>> fan's magnetic field on the Rubidium system.
>>> I found in my junk box a finned Aluminum heat sink that's exactly 
>>> the same size as the FE-5680A and plan to tap it around the edges 
>>> for 4-40 hardware to attach to the many screw holes.  Even so, this 
>>> heat sink will be on the bottom, so the FE-5680A will have to be 
>>> operated upside down for this to help.
>>> Has anybody got good thermal management solution for this device?  
>>> This is the one currently selling on eBay in the 25x88x125mm chassis.
>>> Thanks,
>>> Leigh.

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