Mike Coslo wrote:
Roy Lewallen wrote:

If most insulators are near voltage minima, you wouldn't likely
notice even quite a bit of loss. This effect would be most pronounced
at higher frequencies where the spacing between insulators might
become a sizable fraction of a wavelength, and not so pronounced at
lower frequencies or with more insulators. But the magnitude of the
SWR would still make a major difference.

I would assume then that the big difference is the continuous coating of
the PE then?
. . .

Classic ladder line and punched PE "window line" differ in several
fairly obvious ways, of course. First, the spacing of window line is
typically closer, so the leakage path is shorter. Second, the impedance
of window line is typically lower than window line, so the effect of
shunt Z on the impedance is less when the line is matched. But high SWR
could move the advantage either way, and for different load impedances
either type could have the higher SWR. Third, the fraction of the line
which is actually air-insulated is less with window line. Fourth, the
shape of the insulation is different -- flat with window line and
typically round for ladder line. This impacts the surface area involved
for potential leakage, and the way water might adhere. And finally, the
type of insulation is usually different -- PE for window line and
various materials for ladder line. (The coating of PE on the wires on
the sides of window line "windows" wouldn't make any significant
difference, except maybe to have some impact on how water would flow on
or off the insulating sections.)

Each of these will have some effect on the loss when wet, and different
effects as frequency and SWR change. As for the effect that I mentioned
where the loss could change quite dramatically with frequency or load
impedance depending on the position of the insulators relative to the
standing wave -- that won't happen at all if the insulation is solid,
and would be most pronounced when the insulators are distinct and
periodically spaced. So window line would fall somewhere in between.

Roy Lewallen, W7EL