On Thu, 14 Aug 2003 21:13:49 -0700, W7TI wrote:

Has anyone ever made their own hardline? I'm thinking 1/2 inch copper
water pipe with a center conductor supported by some plastic discs
spaced every so often. You might not get it exactly to 50 ohms but I'd
think the loss would be so low it wouldn't really matter.

Wellll....

The stuff isn't that difficult to make.
Making it correctly is something else.

OTOH, with half inch I think you will find the loss is not as low as
you have been thinking.

With half inch connectors are fairly simple to make.
Splices are also relatively easy to make if you have a lathe.
The commercial stuff uses gasketed brass rings with at least 4 screws
through the flanges to hole the sections together. The center
conductor can be joined using a threaded fitting, or just soldered
with the outer conductor slid back.

BUT as to the practicality of using hard line...
You need the proper spacing for the spacers
Breakdown voltage is less than for coax cable the same size with foam
or solid dielectric.
Copper oxide will become a problem unless the feed line is "purged"
with dry Nitrogen.

Typically the coax is *almost* air tight. It is purged with a very
low flow and pressure of dry Nitrogen. IF the flow increases and or
the pressure drops you know three is a problem.

Don't purge it and it *will* develop problems sooner or later. If you
live in a hot dry climate this might not be much of a problem.

IF you make your own, it will probably still cost twice as much as
good coax.

IF you are looking at saving money, or coming up with a good "low
loss" cable try (as others have already suggested) the 75 ohm TV hard
line. It's usually free, works great, you can easily find 1/2 inch
and 3/4 inch. I understand 1 inch is also available.

It's relatively easy to make connectors for the 1/2 inch and 3/4 inch.
I'd think the same approach used for the 3/4 inch would work for the 1
inch.

The only drawbacks are the difficulty of making short radius turns,
care in handling it, and the 1/2 inch is relatively fragile. The 3/4
inch and up is pretty rugged but still requires care in making bends
or it will easily "kink" which pretty much renders that piece useless.

Roger Halstead (K8RI EN73 & ARRL Life Member)
www.rogerhalstead.com
N833R World's oldest Debonair? (S# CD-2)

Comments?