[IRCA] Plastic potting compound

["Craig Healy" <bubba@xxxxxxxxxxxxxxxxxxxx>]

Before I went on vacation, I wanted to seal some transformer boxes I built.
These particular ones are 3db splitters, 50 ohm.  One is a 0 degree
configuration, the other a 180 degree.  Both are built in small Hammond cast
aluminum boxes and are BNC in/out.

What I used was a clear epoxy type plastic sold at a craft supplier.  This
is used for things like putting dollar bills in a block of plexiglass type
material.

I measured a box and found it took 4 ounces of fluid to fill it.  So, I
mixed four oz. of the plastic resin in a small disposable drinking cup.  Per
the instructions, I put 22 drops of catalyst in it.  When poured in the
splitter box, it flowed nicely around all the parts without any air bubbles
left.  It filled the box almost to the top.

I let it cure while I was on vacation.  In a week it turned into something
that looked just like plexiglass.  The toroid and wiring was clearly
visible, and the box looks to be sealed from any water getting in.  Of
course, the BNC connectors aren't waterproof, but..  I also have found that
using anti-sieze compound on the box lid screws helps.  They can be
tightened more than dry, and don't snap from galling.  Permatex makes a good
product and can be found at any auto supply house.

There was no appreciable heat generated during the curing process, and
shrinkage was barely noticeable, if at all.  I'm quite pleased with the
results.  It has made it extremely rugged, and essentially waterproof.  I
will certainly do this again, if I need to seal something.  If I *really*
need a waterproof box, I'd use type N connectors, or possibly high end Type
F if I were to use RG-6.  Those can be waterproofed quite well.

I have a picture of one of the units and the plastic stuff used:

http://www.am-dx.com/Graphics/sealed_box.jpg

Craig Healy
Providence, RI

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