What do you mean by optimum length since open-wire feedline has minimal
loss? When I moved into this property last July, I just strung the longest
wire that would fit into the lot, and reeled out the amount of feedline that
would reach between the tuner and my shack on the second floor. I can not
make the feedline appreciably shorter, and if I made it longer I would have
to figure out how to support the additional feedline. I estimate the
feedline has a length of 70 feet.

John, N9JG

"Cecil Moore" wrote in message
et...
John, N9JG wrote:
My antenna is similar to yours, but slightly longer. I have a 110 feet
dipole running between my chimney and a tree at the back of the lot. The
dipole is at a height of 30 feet and is fed with open-wire. I use an
antenna tuner and the antenna works fairly well on all bands 80 through
10 meters.

Your dipole is 8 feet longer than the G5RV length which
is a positive for 80m operation. For your favorite bands,
there is probably an optimum length of feedline. EZNEC
allows one to model different lengths of feedline. I
wrote a compiled BASIC DOS program that will estimate
the optimum lengths of feedline at:

http://www.w5dxp.com/imax.exe
--
73, Cecil http://www.w5dxp.com

John, N9JG wrote:
What do you mean by optimum length since open-wire feedline has minimal
loss?

By "optimum length", I mean the length where you can
switch your antenna tuner into bypass mode and obtain
a 50 ohm SWR of less than ~1.6:1. For any dipole that
is 1/2WL on the lowest frequency of operation, that
will be at an SWR current maximum point making the
antenna plus tuned feeder system resonant without a tuner.

On 20m, for example, if one can vary the ladder-line
length by plus or minus 15 feet, one can always locate
the SWR current maximum point and usually bypass the
antenna tuner. I have a 20m 1/2WL dipole that I use
on 20m, 17m, 15m, 12m, 10m, and 6m without a conventional
antenna tuner by simply varying the length of the
300 ohm ladder-line.
--
73, Cecil http://www.w5dxp.com

Thanks for the explanation. What you have described would be more convenient
from an operating standpoint since I would have one less thing to tune
during a QSY.

"Cecil Moore" wrote in message
t...
John, N9JG wrote:
What do you mean by optimum length since open-wire feedline has minimal
loss?

By "optimum length", I mean the length where you can
switch your antenna tuner into bypass mode and obtain
a 50 ohm SWR of less than ~1.6:1. For any dipole that
is 1/2WL on the lowest frequency of operation, that
will be at an SWR current maximum point making the
antenna plus tuned feeder system resonant without a tuner.

On 20m, for example, if one can vary the ladder-line
length by plus or minus 15 feet, one can always locate
the SWR current maximum point and usually bypass the
antenna tuner. I have a 20m 1/2WL dipole that I use
on 20m, 17m, 15m, 12m, 10m, and 6m without a conventional
antenna tuner by simply varying the length of the
300 ohm ladder-line.
--
73, Cecil http://www.w5dxp.com

"John, N9JG" wrote in
et:

Thanks for the explanation. What you have described would be more
convenient from an operating standpoint since I would have one less
thing to tune during a QSY.

You might have misunderstood Cecil. I think he is describing a system where
the "optimal length" may be different on each band, so whilst you don't
tune an ATU, you tune the feeder length.

Cecil will confirm or deny... Owen

Owen Duffy wrote:
"John, N9JG" wrote in
et:

Thanks for the explanation. What you have described would be more
convenient from an operating standpoint since I would have one less
thing to tune during a QSY.

You might have misunderstood Cecil. I think he is describing a system where
the "optimal length" may be different on each band, so whilst you don't
tune an ATU, you tune the feeder length.

Throwing a couple of knife switches is certainly an easier
and faster QSY than rotating a coil switch and twisting
two interacting capacitor knobs.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
t...
Owen Duffy wrote:
"John, N9JG" wrote in
et:
Thanks for the explanation. What you have described would be more
convenient from an operating standpoint since I would have one less
thing to tune during a QSY.

You might have misunderstood Cecil. I think he is describing a system
where the "optimal length" may be different on each band, so whilst you
don't tune an ATU, you tune the feeder length.

Throwing a couple of knife switches is certainly an easier
and faster QSY than rotating a coil switch and twisting
two interacting capacitor knobs.
--
73, Cecil http://www.w5dxp.com

Cecil, I was thinking of trying your no= tune antenna and the 16 ft piece
may not be doable at my QTH, I have to keep it all hidden behind the bushes.
Could this piece be replaced with a circuit using lumped LC values.

Jimmie

On Thu, 19 Apr 2007 12:24:52 -0400, "Jimmie D"
wrote:

Cecil, I was thinking of trying your no= tune antenna and the 16 ft piece
may not be doable at my QTH, I have to keep it all hidden behind the bushes.
Could this piece be replaced with a circuit using lumped LC values.

Hi Jimmie,

I've been doing it with a binary switched coax matcher for 15 years.
It occupies about half a cubic foot and tunes in increments of 1, 2,
4, 8, and 16 feet.

73's
Richard Clark, KB7QHC

Jimmie D wrote:
Cecil, I was thinking of trying your no= tune antenna and the 16 ft piece
may not be doable at my QTH, I have to keep it all hidden behind the bushes.
Could this piece be replaced with a circuit using lumped LC values.

That would work at one frequency but not others. What I do with
the 16 foot length is coil it into a spiral of 4 turns. The
diameter of the spiral is about 16 inches and the overall
length of the spiral is about 24 inches. That should fit
"behind the bushes". I use a piece of fiberglass rod to
which to tiewrap the coils.

There's nothing magic about the 16 foot length. It is only
necessary if you need to vary your length from 0 to 31 feet.
In actual practice with my 130 foot dipole, I only needed
to vary the length from 0 to 23 feet so I made the "16 ft"
section just another 8 foot section. The 16 foot section
was required from 3.5-3.6 MHz and I never use those frequencies.
That's why I could get away with replacing the 16 ft section
with another 8 ft section.
--
73, Cecil, w5dxp.com