K7JEB wrote:
Consider using an UNBALANCED, open-wire line. It would consist
of three wires fairly close together with uniform spacing
between them. The center wire is "hot" and the outer two
are "ground".

Hi Jim, what would be the range of Z0's possible with this configuration?
--
TNX & 73, Cecil http://www.qsl.net/w5dxp



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I originally wrote:
Consider using an UNBALANCED, open-wire line. It would consist
of three wires fairly close together with uniform spacing
between them. The center wire is "hot" and the outer two
are "ground".

Cecil, W5DXP asks:
Hi Jim, what would be the range of Z0's possible with this
configuration?

Jasik has a formula for this type of line:

Zo = (207/sqrt(epsilon))*(log(1.59*(Dist/dia)))

where Zo is in ohms, epsilon is relative dielectric constant
of surroundings (=1.0 in this case), sqrt is the square root
function, log is the base-10 logarithm function, Dist is the
distance between the center wire and one of the outside wires
and dia is the diameter of the wires used, Dist and dia being
in the same units.

Setting dia=0.116 inches (#10 AWG stranded wire) and varying
Dist gives:

Dist = 1.0 inch ............ Zo = 235 ohms
Dist = 2.0 inches .......... Zo = 297 ohms
Dist = 4 inches .......... Zo = 360 ohms
Dist = 10 inches .......... Zo = 442 ohms

The trade-off would be between the desireable high impedance
from wide spacing and leakage suppression from close spacing.
Dist=4 inches looks about right.

Although I haven't tried it, my guess is that common electric-
fence hardware would be adequate for supports and insulation,
but the conductors should be copper (and #10 gauge). Stacking
the conductors vertically should simplify the mechanical aspects
and possibly partially suppress sky-wave leakage from the line.

Jim, K7JEB
Glendale, AZ

Balance woun't be the problem, Doug. The problem is that over that long a
run, the feedline will radiate, and become a major part of the antenna
system. The other problem is keeping the feedline far enough away from
eveyerything else along that run, that could interact with it.

For such a long run with a feeder at ground-level, you might want to
investigate low-loss coax...

- Mike KI6PR
El Rancho R.F., CA

"DOUGLAS SNOWDEN" wrote
I am planning on putting up a ground mounted vertical for 40 and 80
meters.
Somewhere between 70-90 ft tall
and insulated from the ground. The antenna will be about 275 ft from the
shack. My question: is it advisable to feed a vertical with open wire
feeder? I am thinking it would work ok either directly or through a balun
on one or each end of the feedline, but how does one keep the RF from the
radiator from unbalancing the line? Or would it just tend to hit both
sides
of the line and not upset the balance?

Doug, N4IJ

Mikey wrote:
Balance woun't be the problem, Doug. The problem is that over that long a
run, the feedline will radiate, and become a major part of the antenna
system.

The reason that the feedline radiates *is* unbalanced currents.
If the currents can be balanced, the feedline will not radiate
appreciably assuming good engineering practices are followed.
--
73, Cecil, W5DXP

I saw an ariticle from a British ham that fed a vertical with open wire line,
mounted on his roof. Ground mounted might be problematic due to the fact that
the feedline could not be brought away at a preferred angle. Would be an
interesting experiment though!

73s,

Evan

Thanks for all the feedback. As for running 275 ft of RG58, I would not do
that, but would try something like 9913 or LMR400, etc. The only reason I
am considering open wire feeders is to get ever watt to the antenna, and
save the cost of good coax. As for the comment that the feedline would be
part of the antenna at that long of a run, that was part of the original
post, and my worrying about the antenna intself unbalancing the feedline.
The way I understand it, the feedline should not radiate or be part of the
antenna if it is balanced. At least I know others are doing this with
success. I don't know if I would want to go to the trouble of making a three
wire open wire feeder.
As for the interaction of other things with the feeline, there is nothing
except open field for the distance.


Doug N4IJ



"K9SQG" wrote in message
...
I saw an ariticle from a British ham that fed a vertical with open wire
line,
mounted on his roof. Ground mounted might be problematic due to the fact
that
the feedline could not be brought away at a preferred angle. Would be an
interesting experiment though!

73s,

Evan

Doug, N4IJ, wrote:

... As for the comment that the feedline would be
part of the antenna at that long of a run, that
was part of the original post, and my worrying
about the antenna intself unbalancing the feedline.
The way I understand it, the feedline should not
radiate or be part of the antenna if it is balanced.

I think that given the length of your run (275 ft) and
the use of close-spaced commercial "window line", any
common-mode problems on the line would sort themselves
out before they got back to your shack. Giving the
line a relatively tight twist (1 twist/6 inches) might
help too.

Given that you intend to drive a relatively non-directional
antenna, I don't think feedline radiation will be a big
problem system-wise if it is 1/10 the total radiated power.
(ie: suppressed 10 dB).

Nobody wants to take me up on the unbalanced ladder-line.
Oh, well!

Jim, K7JEB
Glendale, AZ

K7JEB wrote:
Nobody wants to take me up on the unbalanced ladder-line.
Oh, well!

Hi Jim,
I'm thinking it has a distinct advantage over balanced ladder-
line. It appears to me that it can be formed into a helix
where the outside insulated wires are touching without suffering
the ill effects of balanced ladder-line. This is interesting to
me because I vary the length of the ladder-line to achieve
a match. Now if it could only be coiled up in a box like
coax.
--
73, Cecil http://www.qsl.net/w5dxp



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