In a message dated 8/28/01 9:43:14 AM Pacific Daylight Time, 2@vc.net
writes: <<
>
>Guys,
>Reviewing the wireman's "Loss Graph for Matched Transmission Lines"
chart,
>and I noticed #12AWG Twin Open Wire, as having the lowest loss by a long
>way. I guess I have never seen Open Wire as shown on a chart before to
>reinforce just how low the loss really is.
>Being a novice antenna guru, I have a few questions:
>
>How far away from the ground does this stuff need to be?
// My guess is that it should be >5-times the wire-spacing.
>What are the drawbacks of using it?
>
It won't work as advertised when fed from an unbalanced tuner with a 1 to
1 balun at the output. However, a Balanced L-network antenna tuner is
not hard to construct. An article was published in the February, 1990
*QST*. The manuscript for the balanced tuner article is available on my
Web site.
>I have a remote dipole that this stuff might be just the ticket for a long
>run. I have always used coax, except for some plastic windowed ladder
>line, which always worked nicely, but according to the chart has more loss
>that the Twin Open Wire.
// Yea, verily. . . Homebrewed #12-solid-Cu open wire line has low
loss - even with over the top SWR, so the antenna it feeds works for
multiband use. However, open wire feedline needs to be guyed with 2
Dacron cords to keep it from flailing around in strong winds.
>
>My guess is that this is the 6" spaced feedline I have seen before. I
>would make this and wonder what people use for the spacers, what spacing is
>required, etc.
// The above article also describes a simple way of constructing
open-wire feedline using commonly available materials and tools.
good luck, Eric
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
>>
Very good advice Rich.
Inadditon to the tuners mentioned, the Johnson Match Box does a great job.
Using my "magic length" of open wire feedline reduce reactance values as it's
a 1/2 wave or multiple on all bands. It's 135' and 123' for 450 ohm Ladder
line. QST always says "any length" which is just plain stupid and why many
have problems getting a match by some tuners and/or arcing.
When I grid dip a length of feedline that I use frequently, I short both
ends and tie both ends to a tree or other support with a rope. I find that
at about 4' above ground there is no affect of the ground on the resonant
frequency. The closer it is the resonant frequency changes. Try it and you
will see. The resonant frequencies will repeat all the way to 10M real
close. I grid dip it when installed also and modify as necessary. I run it
through walls and floors with no problem with hollow insulator tubes. I use
3.562 MHz as a base frequency if used on 80M. It will be a 1/2 multiple at
7.125, 10.688, 14.25, 17.812, 21.375, 24.937, & 28.5 MHz. Insulators about
3' apart give about a .98 VF. The higher the number of insulators the lower
the VF. It's measurable. Well made it will last you a life time. k7gco
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