> My favorite idea was to use circular or square duct; loosely assemble
> and install in-place the entire 70-foot length or at least long
> sections of the duct/shield (which in my situation could be mostly
> straight with only one 90-degree bend) with just a pulling rope
> inside; make spacers from hollow, thin-shell, stiff plastic spheres
> having outside diameters just slightly smaller than the inside
> diameter of the duct, drilling holes through each sphere
> symmetrically about its center for the wires; thread the wires
> through the spheres with a large "needle"; fasten the spheres to the
> wires somehow (hot glue?); pull the resulting "string of beads"
> through the duct; peek and as necessary reach through the (so far
> loose) joints of the duct to check and if necessary reposition the
> hollow spherical spacers; and seal the seams of the duct with wide,
> adhesive, metal-foil tape (such the strong aluminum-foil tape that I
> found in the HVAC section of a Home Depot).
>
> There's no reason why you'd have to assemble the entire duct and then
> pull the entire line through it. You could make short sections of
> line, each with spacers and wire conductors inside; then you could
> join the sections, soldering the wires together and pulling them taut
> as you went.
I have been kicking around the idea of making my own air dielectric
coax using 2 or 3 inch irrigation tubing for the outer conductor. I
had just about exactly the same idea with the balls. I had been looking
at plastic playground balls (like they have at McDonalds). There
are also balls made to float on tanks of liquid to prevent evaporation.
For the center conductor, I was going to use PVC pipe coated with
the aluminum foil tape you mentioned. Originally, the idea is that
this would cost very little since I have lots of used irrigation tubing
laying around. But then I realized that it is too dirty on the inside
and too banged up to use for coax, so I would have to buy new tubing
for a buck or two a foot. The project has gone back on hold for now.
Rick N6RK
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