Currently I have a coax fed trapped 75/40M dipole up between two
trees. The spacing of the trees (a bit over 110 feet) allows this
antenna with no extra length allowed, except for minimal support line and
insulator length.

I plan on replacing this dipole with 450 ohm ladder line feed doublet
so I can operate on more than just 75/40M, however a full 1/4 wave length
for 75 would be too long to fit between these trees.


My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ? Should it tune OK with a tuner such as the
new MFJ balanced tuner? Or, if I were to put either the old 40M traps,
or wind coils for the new dipole to shorten 75M resonance, would it then
tune OK on all bands from 75M down with balanced feed?

Ed K7AAT

A G5RV would fit and meet your needs for all band operation with a tuner.

"Ed" wrote in message
. 93.175...

Currently I have a coax fed trapped 75/40M dipole up between two
trees. The spacing of the trees (a bit over 110 feet) allows this
antenna with no extra length allowed, except for minimal support line and
insulator length.

I plan on replacing this dipole with 450 ohm ladder line feed doublet
so I can operate on more than just 75/40M, however a full 1/4 wave length
for 75 would be too long to fit between these trees.


My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ? Should it tune OK with a tuner such as the
new MFJ balanced tuner? Or, if I were to put either the old 40M traps,
or wind coils for the new dipole to shorten 75M resonance, would it then
tune OK on all bands from 75M down with balanced feed?

Ed K7AAT

I am running a 100 ft bowtie antenna ok with link coupled transmatch, fed
with 450 ohm twin lead and it tunes 75 thru 10 meters
Each side of center feedpoint has a pair of 50 ft wires, that are connected
at the ends with a piece of 6 ft wire.
"Ed" wrote in message
. 93.175...

Currently I have a coax fed trapped 75/40M dipole up between two
trees. The spacing of the trees (a bit over 110 feet) allows this
antenna with no extra length allowed, except for minimal support line and
insulator length.

I plan on replacing this dipole with 450 ohm ladder line feed doublet
so I can operate on more than just 75/40M, however a full 1/4 wave length
for 75 would be too long to fit between these trees.


My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ? Should it tune OK with a tuner such as the
new MFJ balanced tuner? Or, if I were to put either the old 40M traps,
or wind coils for the new dipole to shorten 75M resonance, would it then
tune OK on all bands from 75M down with balanced feed?

Ed K7AAT

On Sun, 16 Oct 2005 18:28:36 GMT, Ed
wrote:
I plan on replacing this dipole with 450 ohm ladder line feed doublet

Hi Ed,

The answers to your questions are found in the quote above.

If those bands on the old antenna were already resonant, and they
matched, then you didn't need 450 Ohm ladder line.

If you are going to use 450 Ohm ladder line on a generic doublet, it
stands to reason you won't be resonant much anywhere (or you don't
count on it) and you anticipate tuning and use this line for low loss.

The only thing left to be said is about the lobe structure at any
particular frequency. Long, long antennas at high frequency develop
sharp lobes and nulls. That being said, it is more a matter of where
you are pointed and where you want to be heard. The solution to that
is to use a fan tail design for the higher bands' sake.

Using a doublet, ladder line, and a tuner is classic - it works fine.

73's
Richard Clark, KB7QHC

"Ed" wrote in message
. 93.175...

Currently I have a coax fed trapped 75/40M dipole up between two
trees. The spacing of the trees (a bit over 110 feet) allows this
antenna with no extra length allowed, except for minimal support line and
insulator length.

I plan on replacing this dipole with 450 ohm ladder line feed doublet
so I can operate on more than just 75/40M, however a full 1/4 wave length
for 75 would be too long to fit between these trees.


My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ? Should it tune OK with a tuner such as the
new MFJ balanced tuner? Or, if I were to put either the old 40M traps,
or wind coils for the new dipole to shorten 75M resonance, would it then
tune OK on all bands from 75M down with balanced feed?

Ed K7AAT

If you are not satisified with the antenna you have then I would put up
about 130 feet of wire and feed it in the middle with the balanced feed. If
you can not get up the full 130 feet or so of wire, put it all up and let
the ends hang down. That is the support ropes could be attached 10 to 15
feet from each end and then you let whatever is left over hang down. Just
don't let the ends reach close enough to the ground where someone could
reach them. Shock and RF burns.

If you go to the 100 feet and feed it with open wire , you are trying to
make the antenna into a g5rv if you use whatever length of feedline the g5rv
calls for. Not really that good of an antenna for working all bands.

Ed wrote:
My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ?

Make it 102 ft. and you will have the G5RV length about which
virtually everything in the world is known. It works so well
on 75m that you should not be able to notice the difference.
How easy/hard it is to match will depend upon the feedline
length.
--
73, Cecil http://www.qsl.net/w5dxp

On Sun, 16 Oct 2005 18:28:36 GMT, Ed
wrote:



My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ? Should it tune OK with a tuner such as the
new MFJ balanced tuner? Or, if I were to put either the old 40M traps,
or wind coils for the new dipole to shorten 75M resonance, would it then
tune OK on all bands from 75M down with balanced feed?

Ed,

When you analyse the performance of a centre fed dipole antenna
system, you will find that for most practical dipoles, the challenge
is getting most of the power to the feed point, rather than the ohmic
losses in the radiator itself.

By the time the dipole is long enough to obtain acceptable performance
from a practical feed system, the loss in the radiator itself is
typically less than 0.5dB (unless you contrive do something pretty
silly).

It turns out that it becomes quite challenging to implement an
efficient feed system (especially over a wide frequency range) where
the dipole is less than about 35% of a wavelength at the lowest
frequency.

Now, the 100' you nominate is so close to the length of a G5RV that
you could draw some information from analyes of the G5RV. I wrote one
that focusses on the performance of common distortions of G5RV's
design and examines particularly the feed system performance, which I
suggest to you is the most significant influence on antenna system
efficiency in this case. Unlike many other analyses of the G5RV, this
does not just consider ham band performance, it models performance
every 100KHz from 1MHz to 30MHz, so you can see a continuous view of
the behaviour. The article is at http://www.vk1od.net/G5RV/ .

But you weren't asking about a G5RV were you. Look at Figure 10 and
the "Classic tune feeder" topic which is a 30m dipole fed with 23m of
ideal 600 ohm open wire feeder. (Ladder line won't perform quite that
well, especially when wet). That topic is directly relevant to your
proposal.

Nothing in the feed system affects the pattern (in three dimensions),
that is determined by the length of the dipole, and its environment.

Owen
--

On Sun, 16 Oct 2005 21:20:22 GMT, Owen Duffy wrote:

On Sun, 16 Oct 2005 18:28:36 GMT, Ed
wrote:



My QUESTION(s): How effective would a balanced fed dipole of about
100 feet length be on 75M ? Should it tune OK with a tuner such as the
new MFJ balanced tuner? Or, if I were to put either the old 40M traps,
or wind coils for the new dipole to shorten 75M resonance, would it then
tune OK on all bands from 75M down with balanced feed?

Ed,

When you analyse the performance of a centre fed dipole antenna
system, you will find that for most practical dipoles, the challenge
is getting most of the power to the feed point, rather than the ohmic
losses in the radiator itself.

By the time the dipole is long enough to obtain acceptable performance
from a practical feed system, the loss in the radiator itself is
typically less than 0.5dB (unless you contrive do something pretty
silly).

It turns out that it becomes quite challenging to implement an
efficient feed system (especially over a wide frequency range) where
the dipole is less than about 35% of a wavelength at the lowest
frequency.

Now, the 100' you nominate is so close to the length of a G5RV that
you could draw some information from analyes of the G5RV. I wrote one
that focusses on the performance of common distortions of G5RV's
design and examines particularly the feed system performance, which I
suggest to you is the most significant influence on antenna system
efficiency in this case. Unlike many other analyses of the G5RV, this
does not just consider ham band performance, it models performance
every 100KHz from 1MHz to 30MHz, so you can see a continuous view of
the behaviour. The article is at http://www.vk1od.net/G5RV/ .

But you weren't asking about a G5RV were you. Look at Figure 10 and
the "Classic tune feeder" topic which is a 30m dipole fed with 23m of
ideal 600 ohm open wire feeder. (Ladder line won't perform quite that
well, especially when wet). That topic is directly relevant to your
proposal.

Nothing in the feed system affects the pattern (in three dimensions),
that is determined by the length of the dipole, and its environment.


Hmmm.

Duffy (http://www.vk1od.net/G5RV/) says, see Cebik
(http://www.cebik.com/wire/g5rv.html)

Cebik (http://www.cebik.com/wire/g5rv2.html) says, see Duffy
(http://www.vk1od.net/G5RV/)


I'm going around in circles. :-)

On Sun, 16 Oct 2005 16:21:31 -0700, Wes Stewart
wrote:


Hmmm.

Duffy (http://www.vk1od.net/G5RV/) says, see Cebik
(http://www.cebik.com/wire/g5rv.html)

Cebik (http://www.cebik.com/wire/g5rv2.html) says, see Duffy
(http://www.vk1od.net/G5RV/)


I'm going around in circles. :-)

Wes,

A bit of mutual citation, bit obvious isn't it when there isn't some
indirection like a few intermediate authors / articles!

Nevertheless, LB Cebik deals more with patterns, and I deal more with
the feed system, and of course the big picture means considering them
both. I happily link to LB for people to read some useful info on the
other aspect. Is that too cosy for you?

More importantly, if you found any faults with my analysis, let me
know?

Owen
--

Ed wrote:
My QUESTION(s): How effective would a balanced fed dipole of
about
100 feet length be on 75M ?

Make it 102 ft. and you will have the G5RV length about which
virtually everything in the world is known. It works so well
on 75m that you should not be able to notice the difference.
How easy/hard it is to match will depend upon the feedline
length.


Thank you, Cecil. Very few here responded to my questions the way I
had hoped, although there was some very good info in those responces.

I had wondered what the effect of inductance in the dipole legs would
have on a balanced fed antenna. It now appears that to get decent
results on 75M I don't need to do that, anyway.

I had not thought much about adding dropping wires to the ends of my
dipole legs, as one fellow suggested, because the trees are so conical
shaped that their lower branches would likely be in the way of the
vertical wires coming down off the ends.

I guess I need to research the G5RV antenna. Someone else here
posted a nice URL to a site on it and I will be perusing it more.

Cecil, I definitely can make my dipole 102 feet accross the top. I
am guesstimating that I will need approximately 35 or 40 feet of feedline
from the shack to the feedpoint. Do you see any issues with that?

Ed K7AAT