On 10/25/10 12:50 PM, KD7HB wrote:

Just some thoughts for you. Good luck, and don't be afraid to try
different schemes.


300 ohm line is probably not the best choice if you want to use
non-coaxial feedline. Much better is real ladder line or window line.

And there are some serious misconceptions about window line too, so you
hav eto be careful of what you read.


Wes Stewart, N7WS wrote what is commonly cited as ladder line's fatal flaw:

http://users.triconet.org/wesandlinda/ladder_line.pdf

I suggest that you read it.


But the study in itself suffers from a fatal flaw. And it is actually
demonstrated in the article.

Stewart had difficulties in getting his ladder line completely wet. In
fact, the water created antibubbles on the surface of the line, and ran off.

Well now, how do we fix this? We apply wetting agent to the line, this
will cause the water to wet the entire surface, then measure the loss.

Anyone see the problem here? Last time I checked, there is no wetting
agent in rain. This is testing of artificially wetted window line,
nothing more, nothing less.

I have ladder line that has been up for 10 years now, and water still
beads up on it like it did when it was new. I'll not even add that it is
vertical, so there won't be as much water hitting it as when it comes
form a spray bottle - oh wait, I did mention it.....

The characteristics of polyethelene which is used to cover window line
in fact make it very difficult to be wetted. One might be able to
enforce wetting by sandblasting the line to roughen the surface, or oh
yeah, apply wetting agent.

That however makes the results of the experiment of equal value to
modifying coax in a detrimental way, then measuring some aspect, and
saying "all coax is like this". And why would ya do it anyway?

There are reasons to use ladder or window line, and there are reasons to
use coax. For example, at our club mountaintop station, we use
copperweld for the dipoles, properly hung on towers. There is a shrt run
of normal premium coax, just enough to lower the antennas for maintence
if needed, but the coax is switched to hardline coax for most of the run
into the shack. This is a good setup if you have lots of space, a goodly
number of towers, and monoband (or at least fan) antennas.

Now for the home QTH, I have some limited space, around a 100 feet. yet
I still want multi-band operation. So I'm looking at more limited choices.

Monoband dipoles are pretty much out of the question. Loaded multiband
dipoles? For all the ham bands? Maybe not so good. Fan dipoles? a pain,
and I'd have to start supporting the antenna on a messenger line.

So that ladder line or window line fed doublet is looking pretty darn
good about now. Rain or shine.

- 73 de Mike N3LI -