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

Excellent idea...I can envision a couple N or UHF connectors on either
side of the wall, and the entry point is indeed near the ground system
so that too is feasible. Thanks for the tip...there are others coming
in but this sounds very feasible and relatively easy!
73
Dan
K0DAN

On Wed, 16 Feb 2005 04:31:15 GMT, (Robert
Lay) wrote:

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

On Wed, 16 Feb 2005 09:31:54 -0600, me wrote:

Excellent idea...I can envision a couple N or UHF connectors on either
side of the wall, and the entry point is indeed near the ground system
so that too is feasible. Thanks for the tip...there are others coming
in but this sounds very feasible and relatively easy!

No, sorry, that is not what I had in mind and should have cleared that
up right at the outset.

I never use coax connectors in this situation, although I suppose you
could. I simply connect balanced line to the innter conductors of the
coax's on each side of the balanced coax segment. If you want a quick
disconnect, I use a pair of the General Radio type Banana plugs just
inside the shack. They are convenient for several reasons.
1) they seem to be able to stand the power level.

2) the spacing on the wire connectors is exactly right for 450 ohm
window line, and

3)they are hermaphroditic - i.e., they plug into one another either
way.


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