On Tue, 27 Apr 2004 19:25:49 GMT, zeno wrote:

Thinking about getting through walls with ladder line:

Hi Bill,

This is bordering on too much thinking. ;-)

1. Would it be better to have the wires proceed continuously
to the tuner, without having to make connections at feed
through insulators?

As a generalization, sure. As an instance, it will probably never
matter. The real question is how can you goof to make it matter?

Obviously by making poor connections [You don't plan to do that do
you? You aren't typically shoddy are you? Let's put that nightmare
to one side.] There will no doubt be fifteen postings pointing out
how lightning "may" melt the connections (and this, of course,
presumes many improbabilities equal in likelihood to lightning
striking).

but I want to anticipate any arcing etc.
and the inevitable moisture in the air during rainy season
etc.
which introduces:

2. How should I be conceptualizing the type of RF energy in
these lines? I assume that these wires will carry something
more like "high voltage" than the usual type of electrical
energy in domestic AC lines. How far away should these ladder
line wires actually be away from everything as they go
through the wall?

Far enough. Flash-over, arcing, and such all derive from the geometry
of the gap, barometric pressure, humidity, and such. However, just
dredge up a common circumstance of the ordinary Spark Plug and observe
the several KV it takes to leap maybe an inch?

You have to work very hard to make it happen - why would it be easier
through chance?

However, this doesn't answer the question so much as offer
perspective. Keep the ladder line as far away from anything (fill in
the blank) as it is wide. If you want, double that value for a safety
factor of two. If it won't arc across the lines, it sure won't jump
to the wall out of caprice.

SWR is a manifestation of literal Standing Waves that in turn exhibit
voltage peaks and current peaks distributed along the line between the
line leads. If you are so lucky as to have a balanced load (which
thus offers a minimum of common mode potentials), it stands to reason
you've confined your risk. Bringing nearby conductive elements into
the scheme introduces both an unbalance with a corresponding rise of
common modality. Would you hold a nail between the conductors?
Recent suggestions that little matters over the short haul mock your
sensibility to this question. Sparks occur at site dislocalities and
drawing down wide spaced, paired lines to fit through a small hole are
classic spark generators (anyone every see a jacob's ladder?). Same
thing goes for the impedance bump of a dielectric (your wall)
introduced between them coming through separate holes. In short,
jeopardy either way.

Which scenario offers more path resistance? There is no better
determiner of success. Your ceramics were made to answer that.
Basically, (and on the basis of what you have written thus far) trust
your instincts and then test.

The question is simply: how much potential resides between the two
leads at any site dislocality? Change the frequency and you have to
answer that question again. Are those holes bridging (AKA shorting) a
voltage maxima, or voltage minima of the Standing Wave? If you know
that answer, then apply that knowledge to every half wave interval
along the line all the way to (and including) the antenna and ask: is
there something nearby each or any of those points that will catch a
spark and render a flame?

73's
Richard Clark, KB7QHC