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Old September 24th 06, 07:22 AM posted to rec.radio.amateur.antenna
Roy Lewallen Roy Lewallen is offline
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First recorded activity by RadioBanter: Jun 2006
Posts: 1,374
Default Use of lattice line to feed dipole

Mike Coslo wrote:

So is the lesson that Ladder line sucks, or is it that we shouldn't
wash our ladder line with soap and water? 8^)


Although I discovered it long ago, I keep getting surprised at how many
people require a binary answer to any question -- is it good or bad,
sucks or doesn't suck, good or evil. Sure makes it easy for our would-be
politicians and their 15 second sound bite solutions to complex issues.
Hopefully at least some readers will consider what Owen said, that the
knowledge we've gained by this can hopefully help in the intelligent use
of the line. Those needing a binary answer should look elsewhere; there
are plenty of gurus who are more than happy to categorically state
positive but simple answers to just about any question. I use a coin,
myself, but each to his own.

Wes' and my measurements, and Danny's observations, can't be directly
applied to other situations. What they're meant to, and do, illustrate,
is that significant loss *can* occur under some circumstances, and
people who assume that twinlead or window line loss will always be low
can be very much mistaken.


Has anyone run tests on what "real" (open) ladder line does when you
spray it with wetting agent and water?


I don't think any result would be very meaningful, except to show,
again, that significant loss could occur under some conditions (which
I'm confident is the case). Those lines are often run with a very high
SWR. The effect of conductivity and/or loss across the insulators would
depend very heavily on the position and size of the standing waves. For
example, if the SWR is high and the insulators happen to be at or near
the voltage peaks, even a small amount of loss would have a major
impact. But on a slightly different frequency, the antenna's impedance
will change and the standing wave will move. 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.

Roy Lewallen, W7EL