Hi, I just read instructions on building a "helically wound" antenna
using a broom stick.
http://www.hard-core-dx.com/nordicdx.../bromstik.html

After reading this, I had an idea. I'm doing more google searches for
this type of configuration, but wanted to ask here as well to get some
opinions. What if I took two broom sticks, and wound each with about
68 feet of wire. Each stick making half of a dipole antenna. Then
attach 450 ohm ladder line (or 50 ohm coaxial). How would this behave
when connected to a tuner? Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

Jim

"James barrett" a écrit dans le message de news:
...
Hi, I just read instructions on building a "helically wound" antenna
using a broom stick.
http://www.hard-core-dx.com/nordicdx.../bromstik.html

After reading this, I had an idea. I'm doing more google searches for
this type of configuration, but wanted to ask here as well to get some
opinions. What if I took two broom sticks, and wound each with about
68 feet of wire. Each stick making half of a dipole antenna. Then
attach 450 ohm ladder line (or 50 ohm coaxial). How would this behave
when connected to a tuner? Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

Jim

HI,

Obviously, Like a short dipole !

Dan

On Fri, 30 Nov 2007 08:06:02 -0800 (PST), James barrett
wrote:

Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

Hi Jim,

At the right frequency, the right height, and at night it might act
like an aeronautical beacon. Or given the season, it might provide
sufficient light to be used as the star of Bethlehem decoration.

But if you want even more outlandish claims for performance (I like
the part of adding capacity hats to lower noise), add the google term
"Gaussian array." Good luck with making any sense of what passes for
construction hints (you will have to wade through a lot of window
dressing to find them first).

OK, now for some real technical content:

The first order of business is in the description for a tight wound
coil. The proximity of windings drives efficiency down. Open up the
windings. The short physical length of a radiator drives the
efficiency down. Extend the winding pitch further. The short
physical length of a radiator demands closer attention to matching
(lower efficiency again). Lengthen the radiator. Using the entire
length of a radiator to support a coil drives down the radiation
current (this is really a combination of the earlier problems, but it
is way cool to say it sucks again). Lengthen the radiator.

The advice is sufficient for a receiving antenna, hence the source of
Radio Habana Cuba's recommendation. It is especially poor for
transmitting, hence its absence in Radio Habana Cuba's transmitting
antenna farm. Those two clues should be sufficient.

73's
Richard Clark, KB7QHC

On Nov 30, 11:25 am, Richard Clark wrote:

The advice is sufficient for a receiving antenna, hence the source of
Radio Habana Cuba's recommendation. It is especially poor for
transmitting, hence its absence in Radio Habana Cuba's transmitting
antenna farm. Those two clues should be sufficient.


Good enough for me. Maybe I'll experiment with a 2 meter receiving
antenna just to compare it to a ground plane. I'll just stick with my
plans to put up a long dipole with no coils.

Jim

James barrett wrote:
Hi, I just read instructions on building a "helically wound" antenna
using a broom stick.
http://www.hard-core-dx.com/nordicdx.../bromstik.html

After reading this, I had an idea. I'm doing more google searches for
this type of configuration, but wanted to ask here as well to get some
opinions. What if I took two broom sticks, and wound each with about
68 feet of wire. Each stick making half of a dipole antenna. Then
attach 450 ohm ladder line (or 50 ohm coaxial). How would this behave
when connected to a tuner? Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

If you use the same amount of wire for the helix as you
would for the wire dipole, the resonant frequency will not
be the same.

Feedpoint impedance wise, you can get it to respond like a
1/2WL dipole probably with a lower feedpoint resistance.

Radiation wise, it will respond like a shortened antenna.
The currents on opposite sides of the coil are close to
180 degrees out of phase and, like a transmission line,
tend to cancel the fields. In addition, a broomstick is
not the best dielectric to use for your coil form.
--
73, Cecil http://www.w5dxp.com

"Cecil Moore" wrote in message
t...
James barrett wrote:
Hi, I just read instructions on building a "helically wound" antenna
using a broom stick.
http://www.hard-core-dx.com/nordicdx.../bromstik.html

After reading this, I had an idea. I'm doing more google searches for
this type of configuration, but wanted to ask here as well to get some
opinions. What if I took two broom sticks, and wound each with about
68 feet of wire. Each stick making half of a dipole antenna. Then
attach 450 ohm ladder line (or 50 ohm coaxial). How would this behave
when connected to a tuner? Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

If you use the same amount of wire for the helix as you
would for the wire dipole, the resonant frequency will not
be the same.

Feedpoint impedance wise, you can get it to respond like a
1/2WL dipole probably with a lower feedpoint resistance.

Radiation wise, it will respond like a shortened antenna.
The currents on opposite sides of the coil are close to
180 degrees out of phase and, like a transmission line,
tend to cancel the fields. In addition, a broomstick is
not the best dielectric to use for your coil form.
--
73, Cecil http://www.w5dxp.com

Helically wound antennas used to be more common some years ago. An outfit in
CT used to sell HF beams that had elements slightly more than 1/2 normal
length. More common were CB mobile antennas, which are probably still made.
I have a CB vertical bought for RC use that is about 18 inches tall.
Supposedly a shortened helically wound antenna has a wider bandwidth than a
lumped inductor antenna of the same length.

Tam/WB2TT

"Tam/WB2TT" wrote in
:

about 18 inches tall. Supposedly a shortened helically wound antenna
has a wider bandwidth than a lumped inductor antenna of the same
length.

Probably mostly due to the higher loss of the loading system. Better
bandwidth, poorer efficiency.

Owen

"Owen Duffy" wrote in message
...
"Tam/WB2TT" wrote in
:

about 18 inches tall. Supposedly a shortened helically wound antenna
has a wider bandwidth than a lumped inductor antenna of the same
length.

Probably mostly due to the higher loss of the loading system. Better
bandwidth, poorer efficiency.

Owen

I don't think so.

Tam

"James barrett" wrote in message
...
Hi, I just read instructions on building a "helically wound" antenna
using a broom stick.
http://www.hard-core-dx.com/nordicdx.../bromstik.html

After reading this, I had an idea. I'm doing more google searches for
this type of configuration, but wanted to ask here as well to get some
opinions. What if I took two broom sticks, and wound each with about
68 feet of wire. Each stick making half of a dipole antenna. Then
attach 450 ohm ladder line (or 50 ohm coaxial). How would this behave
when connected to a tuner? Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

Jim

Sounds a lot like the Slinky antenna,
From what I've heard, using 2 slinkies (one on each side) will make a
40-meter dipole, and 2 on each side makes a 75-meter dipole (or was that a
20 and 40)?? But they used bamboo fishing poles as support instead of
broomsticks.

People have an extremely strong tendency to simplify the mass of
incoming data into simply digested and understood binary categories: Is
it good, or is it evil? Does the antenna work, or doesn't it? And here
the binary choice is between a 136 foot dipole and a shorter dipole.

The answer here, as it is to so may binary questions, is that it behaves
in some ways like one, some ways like the other, and some ways like neither.

The helically wound antenna can be made resonant. A 136 foot dipole is
resonant, but a shorter dipole isn't, unless loaded.

It will be inefficient, which is also usually characteristic of a short
dipole and not a 136 foot one. A short dipole with a properly designed
matching network could be made to be more efficient than the helically
wound antenna.

The input resistance at resonance will be between that of a 136 foot
dipole and a straight dipole the length of the helical antenna, unless
the loss is exceptionally high.

The bandwidth will be between that of a 136 foot dipole and one the
length of the helical antenna, unless the loss is exceptionally high.

The pattern will be more like that of a short dipole than that of a 136
foot dipole, although you wouldn't be able to tell the difference. It
would even be hard to measure using professional equipment.

Roy Lewallen, W7EL

James barrett wrote:
Hi, I just read instructions on building a "helically wound" antenna
using a broom stick.
http://www.hard-core-dx.com/nordicdx.../bromstik.html

After reading this, I had an idea. I'm doing more google searches for
this type of configuration, but wanted to ask here as well to get some
opinions. What if I took two broom sticks, and wound each with about
68 feet of wire. Each stick making half of a dipole antenna. Then
attach 450 ohm ladder line (or 50 ohm coaxial). How would this behave
when connected to a tuner? Would it behave like a 136 foot dipole, or
would it behave like a shorter dipole?

Jim