[NLRS] Efratom Lpro 101 Rubidium Standard

[tosca005 at umn.edu]

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