[time-nuts] Rubidium Frequency Standard FE-5680A

Steve . iteration69 at gmail.com
Wed Feb 22 06:41:33 UTC 2012

A few weeks ago I performed a thermal test while noting the power use of
the FE-5680A. My intentions were the least amount of power use possible. I
was able to get the total power consumption of the frequency standard below
6 watts and maintain lock. To do this I housed the standard in a make shift
thermal insulator using shipping bubble wrap, aluminum foil (as a radiation
shield), and a terry clothe. -- items I was able to find while at work.

The temperature leveled off around 67c and likewise the wattage < 6 watt.
The conditions were simply to start the standard with normal voltage /
current. Then when lock was achieved I set the power supply to voltage
control mode and slowly started to drop the voltage.I took 45 mins of
slowly dropping the voltage until i finally reached the minimal wattage.
Taking 100mv or so at a time, noting the current you can actually see the
heating characteristic of the standard. Wattage will will first drop as the
voltage is dropped, it will then increase due to increase of current
presumably in the heating circuitry, and then it will drop again and reach
an equilibrium. After the equilibrium is reached, I would again drop the
voltage.  The process continued until I lost lock, which I then increase
the voltage and again waited for equilibrium. Then after lock I began to
drop voltage again.

Below are the lowest V*A which I was able to demonstrate a maintained lock.
voltage: 9.96v
current: 543ma

I have a lousy video that I took while at work, which I just looked at to
remind myself exactly what it is that I had done. My video also reminds me
that the output of the standard became much more sinusoidal with thermal
insulation / lower power use than it is otherwise. In the video I remove
the make shift insulation to demonstrate how fast the standard will loose
lock without the additional thermal insulation while operating in this low
power mode.

If anyone is interested in the video, I suppose I could upload it to


On Wed, Feb 22, 2012 at 12:38 AM, Chris Albertson <albertson.chris at gmail.com
> wrote:

> On Tue, Feb 21, 2012 at 9:19 PM, Ken Kubick <kenkubick at hotmail.com> wrote:
> >
> > I just baught two FE-5680A Rubidium Frequency Standards.  Both units
> seem to work just fine.  The units I recieved are mounted to a PCB.  They
> both run real hot around 58 Deg. C.  Should I put them on heatsinks?  or is
> this normal?  The data sheet says the temperature range is -5 to +50 deg.
> C.  I don't want to put a heatsink on them if there is a heater inside that
> trys to keep them hot at 58 deg. C.
> If it has a Rubidium physics package inside then there is a heater
> that tries to keep it just over 100C.   The gas cell has to be hot to
> work.   If you use a heat sink, yes the heater has to work but if you
> cool if the electronic the unit will last longer.     That circuit
> board  served as the heat sink but there was a fan.  My FE5680 is
> screwed to a heat sink and inside an enclosure that used to hold disk
> drives. there is a temperature control fan and I hope this will
> stabilize the temperature inside the box, still have to tube this.
> I'm using a heat sink so that I can use a smaller fan.
> Chris Albertson
> Redondo Beach, California
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