On Tue, 15 Feb 2005 21:44:34 -0600, me wrote:

After many years of experimenting with coax fed wire antennas I am
taking my first plunge at open wire line.

To get into shack, I need to go through exterior steel siding,
exterior wood siding & plywood, a layer of insulation, then interior
sheetrock and wood paneling. Assume I need about 4-6" of safe
feedthrough so that standoffs can be mounted on the walls oustide
and inside the shack.

I generally run 100 to 1500W output...at full legal limit probably
3KV on the feedline...am not crazy about the idea of setting my house
on fire due to HV arc over.

Am looking for the old style porcelain feedthrough isnulators, but so
far have not found same.

Local Home Depot has thin PVC tubing (as in sink/toilet stems), vinyl
tubing, welding rod tubes, etc. What are the dielectric properties of
these, and the high voltage breakdown voltage...???

Seems like glass, porcelain, or ceramic tubing would be best
feedthrough insulator, but where to find?

Are any modern day materials found in Lowes or Home Depot safe from
arcing and also efficient for RF?

Dear Dan,

It seems that many take the approach of using a pair of coax lines
hooked up as a balanced coax pair as the answer to that problem. If
you are worried about the impedance discontinuity, it's a short
section and will not be a problem. If you are worried about whether or
not the coax can handle it, RG-8 is good enough and RG-17 is better.
If you want to combine a little bit of protection against near strikes
while you're at it, run through the wall low to the ground and close
to the biggest, best earthing system you can put together, and then
connect the shields of the coax to a short hunk of heavy wire to that
earthing system.

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html