Steve, I've played around quite a bit with ways to make inexpensive
connectors for 1/2 inch Heliax, and here is my suggestion for a splice.
The inner conductor of 1/2 Heliax is 0.190 inch in diameter and made
from copper plated aluminum. 7/32 inch thinwall brass tubing makes an
excellent slip fit over the Heliax center conductor to make a solderable
For the shield, rigid copper tubing for plumbing applications comes in
three wall thicknesses ... types K, L, and M (type M has the thinnest
wall). Type L copper tubing is commonly available at all building
supply stores (including Home Depot, Lowes, etc) and makes a nice fit
over the corrugated copper shield of 1/2 Heliax with just a very slight
amount of deformation of the copper shield ... you can twist the
plumbing over the shield with your bare hands. You could make a splice
from one piece of tubing by sliding it down the Heliax before splicing
the center conductor, and then sliding the 1/2 inch plumbing back over
the joint and carefully soldering both ends with a propane torch. I try
to use a long enough piece that the solder joint is well back from the
exposed foam. Or you can use two pieces of 1/2 inch plumbing and join
them at the middle with a normal plumbing solderable sleeve coupling.
Either way, if you are careful with the heat and use non-corrosive flux
you should be able to make a water-tight joint.
I've never tried it, but you could even backfill the finished splice by
pre-drilling two small holes (one at each end of the 1/2 copper tube)
and squirting polyurethane foam in one hole until it comes out the
other. That might help improve high voltage performance.
If you also want to try making your own connectors for the ends of 1/2
inch Heliax, check out the 7/16 by 3/8 brass plumbing adapter made by
Watts and sold by Home Depot ... the designator is A-200 and it has a
green stripe across top of the bag. A light touch with a file will
allow the male end to be soldered inside of 1/2 inch Type L copper
tubing, and the female end has exactly the right threads to accept a UHF
barrel. For the center conductor, you need to transition from the 7/32
brass thinwall tubing over the center conductor of the Heliax to 3/16
and then to 5/32, the latter being the right diameter to make a nice
surrogate pin to go through the plumbing fitting and into the UHF barrel.
ACE Hardware's online outlet store carries a really wide selection of
brass tubing (made by K&S Engineering) at much better prices than I
could find anywhere else. I bought several feet of it ... if you need
just a couple of inches, let me know and I'll send some to you.
One of these days I'll take some pictures of my experiments and upload
them to my web site.
Steve London wrote:
> Anyone have some good tricks for splicing Andrew LDF4 1/2" Heliax ?
> This would be for HF use, only - not worried about a small impedance bump.
> Steve, N2IC
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