I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these at http://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

Bill wrote:
I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these at http://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

Hi Bill,

I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth is
inverse to the length/diameter ratio, and a single wire has a bad L/D on the
lower frequency bands. A single-wire 125' dipole made from #14 (0.071" OD)
has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia = 8")
has a L/D of 190:1.

If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500 &
4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses
(24"x24"). I use #14ga 168-strand soft-drawn copper wire but smaller wire
could be used w/o much sacrifice in strength. A handy online calculator is
he http://www.smeter.net/antennas/dipcage2.php

A few photos of my home QTH antenna: http://tinyurl.com/2puwx5, the apex at
about 50' in a tree. A bunch of photos of my latest FD setup:
http://tinyurl.com/38v9wn, the apex at 35' on a homebrew tilt-up/rotatable
mast. I use a choke balun at the feedpoint. All parts came from Davis RF:
http://www.davisrf.com/ because they have good prices and stock my preferred
compression insulators.

Vy 73,
Bryan WA7PRC

I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth is
....[snip]....
has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia = 8")...

I'm curious why a 2-foot-square cage has an effective diameter of only 8"


If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500 &
4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses
(24"x24"). I use #14ga 168-strand soft-drawn copper wire ....

Doesn't soft-drawn copper stretch like mad?

--
--Myron A. Calhoun.
Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge
NRA Life Member & Certified Instructor for Rifle, Pistol, & Home Firearm Safety
Also Certified Instructor for the Kansas Concealed-Carry Handgun (CCH) license

Myron wrote:
I use 4 wire cage designs for 80m (as an inverted vee) because bandwidth
is
....[snip]....
has a L/D of over 20000:1 while a 4-wire 24"x24"cage (effective dia =
8")...

I'm curious why a 2-foot-square cage has an effective diameter of only 8"

It's apparent to me that it can't appear that large because it's 4 strands
of 14ga wire instead of a 24" diameter cylinder. I obtained the 8" figure
from the calculator program at: http://www.smeter.net/antennas/dipcage2.php.
I don't know how the effective diameter was calculated.

If cut for the middle of the band, VSWR is just a touch over 2:1 at 3.500
&
4.000 MHz. I make spreaders from 1/2" thinwall PVC tubing & crosses
(24"x24"). I use #14ga 168-strand soft-drawn copper wire ....

Doesn't soft-drawn copper stretch like mad?

I was told by the CSR at Davis RF that it's soft-drawn but I expect it's
hard-drawn -- an unscientific stretch test in my workshop appears to confirm
this. Over a 12 month period, a 12ga single-wire 80m dipole (with choke
balun & RG58 feedline) did not noticeably stretch. Also consider that in
my case, the cage dipole is in inverted vee form, so there's no concern
about wire stretch caused by the heavier LMR400 feedline & balun weight.
Also, it's 4 strands of 14ga wire instead of one, and the spreaders don't
add much weight.

--
--Myron A. Calhoun.

Bryan WA7PRC

On Sat, 15 Sep 2007 19:16:39 -0700, wrote:

I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these at http://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

Hello Bill,

I can understand that the coax dipoles you built are somewhat more broadbanded than a simple dipole. However,
I suspect that you are unaware of the reason for the broadbanding. Sorry to tell you, but it is achieved only
by the resistive losses in the coax, and not by the reactance obtained by the two sections of shorted coax, as
incorrectly stated in several published articles.

I have made extensive measurements and calculations that prove my statement above. I have reported these
measurements and calculations in both QST and in my book 'Reflections'. The QST reference appears in the
Technical Correspondence, September 1976 issue, and in Chapter 18 in Reflections. You can read Chapter 18 from
my web page at www.w2du.com.

On the other hand, realistic broadbanding, without the loss introduced by the resistances in the coaxial
dipole, can be obtained by the 'cage' dipole, using several parallel wires separated by spacers, as mentioned
other posts appearing in this thread.

Walt, W2DU

Hello Bill,

I can understand that the coax dipoles you built are somewhat more
broadbanded than a simple dipole. However,
I suspect that you are unaware of the reason for the broadbanding. Sorry
to tell you, but it is achieved only
by the resistive losses in the coax, and not by the reactance obtained by
the two sections of shorted coax, as
incorrectly stated in several published articles.

I have made extensive measurements and calculations that prove my
statement above. I have reported these
measurements and calculations in both QST and in my book 'Reflections'.
The QST reference appears in the
Technical Correspondence, September 1976 issue, and in Chapter 18 in
Reflections. You can read Chapter 18 from
my web page at www.w2du.com.

On the other hand, realistic broadbanding, without the loss introduced by
the resistances in the coaxial
dipole, can be obtained by the 'cage' dipole, using several parallel wires
separated by spacers, as mentioned
other posts appearing in this thread.

Walt, W2DU

Hi Walt et al,
I was going to point out the same flawed thinking. I believe Frank Witt also
published the analysis for the flawed reasoning of the bazooka stubs
correcting for the reactance of the dipole off resonance. He also published
coaxial stub designs that did work in QST and several of the ARRL compendia.
It is amazing to me that the bazooka is still used given the alternatives.
One sight where thay are sold claims more gain too!

Dale W4OP

On 15 Sep, 19:16, wrote:
I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these athttp://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

BILL
The best way of using coax with antennas is by stripping the PVC and
soaking the braid
in polyurothane so the clock wise windings are insulated from the
counter wound windings
By shorting one end of the braiding you can feed the other end i.e.
the two different windings
2where the actual span is somewhat less than a 1/2 wave ( calculate
the true wire length)
The same can be accomplished by using somewhat less than a full wave
length folded back on itself
and directly feed the ends. This arrangement takes the fragility away
from the span by not feeding at the center
as well as using the center wire of the coax for mechanical strength.
This method comes in quite usefull when the need is for a 160 meter
antenna where you can wind the coax cross wise fashion so the ends for
feeding finish together.
This comes out at around 60 turns on a 2 foot former. This method
gives more gain over 1/2 wave designs in a similar way that a quad or
loop of one wavelength exceeds others. You can also use a single wire
instead of coax for cheapness if you wish but ofcourse you like coax
but this way you can join scraps of coax and solder them together
without bothering with individual strands. This method by the way does
not require a ground plane so you may leave the barrel on the ground
or place it on top of the tower for rotation purposes. You can have a
lot of fun with this antenna if you can also rotate the axis of the
barrel by useing two rotators or a combination satelite version.
Note thatusing a full wave length antenna you achieve tha same
gains( ~ 3db) that a quad obtains over the standard fractional WL
length radiator(~2db when using single wire). Feed impedance is around
50/60 ohms resistive and is quite broad banded. The above is based
around Gausswian formulae that also conforms with Maxwellian laws so
you can use suitable modeling programs such as AO to derive all
specifications. The above is subject to possible U.S. patents
acceptance at this time
Enjoy
Regards
Art
KB9MZ....XG

On Sat, 22 Sep 2007 08:14:58 -0700, art wrote:

On 15 Sep, 19:16, wrote:
I have built several coaxial dipole antennas in the past with great
success. What I like about this antenna is it is broadbanded. If you
design it using the center of the band of your interest, for the most
part you can cover the entire band without retuning. The problem I
have always had with this is the antenna is somewhat fragile. I have
used plexiglass squares to secure the center of the antenna and taped
nylon fishing line to the legs for more strengh. Any one with more
ideas? These are mostly useful in the HF range. You can find the info
on designing these athttp://www.amateurradios.info and other places
on the net.

73's
Bill w5grx

BILL
The best way of using coax with antennas is by stripping the PVC and
soaking the braid
in polyurothane so the clock wise windings are insulated from the
counter wound windings
By shorting one end of the braiding you can feed the other end i.e.
the two different windings
2where the actual span is somewhat less than a 1/2 wave ( calculate
the true wire length)
The same can be accomplished by using somewhat less than a full wave
length folded back on itself
and directly feed the ends. This arrangement takes the fragility away
from the span by not feeding at the center
as well as using the center wire of the coax for mechanical strength.
This method comes in quite usefull when the need is for a 160 meter
antenna where you can wind the coax cross wise fashion so the ends for
feeding finish together.
This comes out at around 60 turns on a 2 foot former. This method
gives more gain over 1/2 wave designs in a similar way that a quad or
loop of one wavelength exceeds others. You can also use a single wire
instead of coax for cheapness if you wish but ofcourse you like coax
but this way you can join scraps of coax and solder them together
without bothering with individual strands. This method by the way does
not require a ground plane so you may leave the barrel on the ground
or place it on top of the tower for rotation purposes. You can have a
lot of fun with this antenna if you can also rotate the axis of the
barrel by useing two rotators or a combination satelite version.
Note thatusing a full wave length antenna you achieve tha same
gains( ~ 3db) that a quad obtains over the standard fractional WL
length radiator(~2db when using single wire). Feed impedance is around
50/60 ohms resistive and is quite broad banded. The above is based
around Gausswian formulae that also conforms with Maxwellian laws so
you can use suitable modeling programs such as AO to derive all
specifications. The above is subject to possible U.S. patents
acceptance at this time
Enjoy
Regards
Art
KB9MZ....XG

Art, I'm curious concerning what kind of mind-enhancing substance you were on when you wrote the above post.
As far as I can tell, this post concerns the coaxial dipole. However, I don't discern any relationship between
your post and the coaxial dipole.

What does "60 turns on a 2 foot former" have to do with the coaxial dipole?

And what is the "barrell" that you can leave on the ground or put on the top of the tower for rotation
purposes? Rotation of an 80-meter dipole with a barrell on the top of the tower? Art, you have been smoking
too much liquid polyurethane in your Gaussian pipe.

Walt, W2DU

On Mon, 24 Sep 2007 14:43:54 -0400, "Jimmie D" wrote:


"Walter Maxwell" wrote in message
.. .
On Sat, 22 Sep 2007 08:14:58 -0700, art wrote:

Art, I'm curious concerning what kind of mind-enhancing substance you were
on when you wrote the above post.
As far as I can tell, this post concerns the coaxial dipole. However, I
don't discern any relationship between
your post and the coaxial dipole.

What does "60 turns on a 2 foot former" have to do with the coaxial
dipole?

And what is the "barrell" that you can leave on the ground or put on the
top of the tower for rotation
purposes? Rotation of an 80-meter dipole with a barrell on the top of the
tower? Art, you have been smoking
too much liquid polyurethane in your Gaussian pipe.

Walt, W2DU


ROTFLMAO

Jimmie

Jimmie, will you please translate 'ROTFLMAO' ? My dimwitted brain can't figure out what you mean.

Walt, W2DU

Walter Maxwell wrote:
Jimmie, will you please translate 'ROTFLMAO' ?

Hey Walt, if you don't want to be an OF, you
need to QSY to the following web page: :-)

http://www.gaarde.org/acronyms/%5C
--
73, Cecil http://www.w5dxp.com