[NLRS] Efratom Lpro 101 Rubidium Standard

[Jim Hermanek]

Another observation.....

I packaged a Datum LPRO reference about a year
ago using a 24 v supply and an 1/8th inch aluminium plate as a heat
spreader....  monitoring the "air" temperature beneath the LPRO
showed a fairly rapid rise from room ambient to around 100 F within
45 minutes...  I had originally a 2 inch ventillation hole immediately
beneath the spreader and another at the top of the enclosure thinking
naturual convection would move enough air for cooling....

Not comfortable with the rise, I then added
a small  cooling fan as it was a cleaner/simple approach rather than lower
the supply voltage as suggested elsewhere....

Seems to work well....

73's  Jim   K0KFC


----- Original Message ----- 
From: <tosca005 at umn.edu>
To: "NLRS Reflector" <nlrs at mailman.qth.net>; "Roadrunners Microwave Group" 
<rmg at k5rmg.com>
Sent: Saturday, November 17, 2012 4:49 PM
Subject: [NLRS] Efratom Lpro 101 Rubidium Standard


>
>
> I am in the process of building up a rubidium standard into a die-cast
> aluminum box. The box will contain an Efratom Lpro 101 rubidium standard,
> power supply (24vdc direct input or 12vdc->24vdc voltage doubler boost
> regulator), a Down East Microwave 10-4 (four-port filter/splitter for the
> 10 MHz output), the rubidium oscillator lock signal -> LED circuit, and
> some voltage monitoring using digital panel meter LED blocks.
>
> I am puzzled about meeting the heat sinking requirements. Plan A was to
> simply drill 6 holes through the bottom of the aluminum box in the
> positions of the 6 mounting screw holes of the Lpro101, and bolt the
> Lpro101 to the inside bottom of the box (which will become the top of the
> box during operation, as I will put rubber feet on the "lid" and flip the
> whole assembly over to make that the base. One web site that discussed
> building up a standard like this claimed that this would be more than
> satisfactory at carrying away the excess heat of the rubidium
> lamp/oscillator. Then at the last meeting of the Roadrunners Microwave
> Group, one of the members (sorry, I'm bad with names and callsigns, I'll
> need a few repetitions to remember everyone) brought his homebrewed 10 MHz
> standard which also used the Lpro 101 but he added a heat sink on the wall
> of the box that the rubidium standard was bolted to. I didn't get a chance
> to discuss it with him in depth. But I got to thinking if a heat sink is
> really needed, I need to have excellent flatness on the inside of the
> aluminum box and heat sink compound between the Lpro101 and the box, plus
> between the box and the heat sink.
>
> Is this really necessary? Do I need to have the inside of the aluminum box
> milled to extreme flatness? (I am sure that without some work, it is not
> terribly flat now.) The outside of the aluminum box looks "flat enough" to
> me, but not the inside.
>
> Anyone with any insight on this that they'd like to share?
>
> John P. Toscano, W0JT/5
> EL09ro October-May
> EN34js May-September
>
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