Cecil Moore wrote:
Joe Bloe wrote:

However, I did
get a two bits of good information, a closer explanation of the effect
of a fat conductor antenna, and a web-site with a calculator for just
such a thing.


You can probably arrive at the same correct technical
conclusions by downloading the free demo version of
EZNEC and selecting the diameter of the conductor.

No doubt, Cecil. Of course this wasn't where the conversation started
at. I haven't tried EZNEC to model a cage antenna, will it do it? Or do
you just make the wires really thick? And how does really thick wire
compare to a cage of the same relative diameter?

- 73 de Mike KB3EIA -

On Thu, 17 Aug 2006 21:33:17 -0400, Mike Coslo
wrote:

how does really thick wire
compare to a cage of the same relative diameter?

Hi Mike,

Close, but no cigar. Actually, the degree of closeness depends on how
well the cage represents the solid. That degree is a function of the
number of wires that form the skeletal shape. Four is pretty lousy,
120 would be outstanding. Then there is something in the middle:

http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
offers an example that may be suitable. This is a 4 meter tall
antenna that tunes all frequencies from 20M through 10M.

73's
Richard Clark, KB7QHC

http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
offers an example that may be suitable. This is a 4 meter tall
antenna that tunes all frequencies from 20M through 10M.

73's
Richard Clark, KB7QHC

What is the diameter of the antenna design?

buck
n4pgw

--
73 for now
Buck
N4PGW

On Fri, 18 Aug 2006 03:07:06 -0400, Buck wrote:
http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
offers an example that may be suitable. This is a 4 meter tall
antenna that tunes all frequencies from 20M through 10M.

What is the diameter of the antenna design?

Hi Buck,

Download the EZNEC file for a specific answer, by dead reckoning (look
at the picture) it is around 2 meters in diameter. Plus or minus.

....pretty thick wire.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Thu, 17 Aug 2006 21:33:17 -0400, Mike Coslo
wrote:

how does really thick wire
compare to a cage of the same relative diameter?

Hi Mike,

Close, but no cigar. Actually, the degree of closeness depends on how
well the cage represents the solid. That degree is a function of the
number of wires that form the skeletal shape. Four is pretty lousy,
120 would be outstanding. Then there is something in the middle:

http://home.comcast.net/~kb7qhc/ante.../Cage/cage.htm
offers an example that may be suitable. This is a 4 meter tall
antenna that tunes all frequencies from 20M through 10M.

A single fat wire can be a reasonable approximation to a cage provided
that the diameter is very small compared to a wavelength. (The NEC
recommendation is around 0.02 wavelength maximum diameter, which you can
find in the EZNEC manual in the Building The Model/Modeling The Antenna
Structure/About Wires topic.) For a cage of only a few parallel wires,
you can use an equivalent diameter as follows, where d = the wire
diameter and s = ctr-ctr wire spacing, everything in the same units:

2 wires - Equiv. dia. = 1.414 * sqrt(d * s)
3 wires in a triangle - Equiv. dia. = 1.587 * cube root(d * s^2)
4 wires in a square - Equiv. dia. = 1.834 * fourth root(d * s^3)
N wires equally spaced on a circle with radius r -
Equiv. dia. = 2 * r * Nth root((N * d) / (2 * r))

-- derived from equations in Fundamentals of Coupled Lines and Multiwire
Antennas, by Hidenari Uchida (Sasaki, 1967).

I've made myself a note to include this in a future EZNEC manual update.

For cages larger than about 0.02 wavelength diameter, you should model
the individual wires.

Roy Lewallen, W7EL

Mike Coslo wrote:
Cecil Moore wrote:
You can probably arrive at the same correct technical
conclusions by downloading the free demo version of
EZNEC and selecting the diameter of the conductor.

No doubt, Cecil. Of course this wasn't where the conversation
started at. I haven't tried EZNEC to model a cage antenna, will it do
it? Or do you just make the wires really thick? And how does really
thick wire compare to a cage of the same relative diameter?

You can use the free demo version to model a large diameter
radiator with up to 20 segments. For the actual multi-wire
cage antenna, one would need to spring for the non-free
version which is, IMO, the best bargain in ham radio
antenna simulation software. Why ask questions here when
the answer is available to any individual who springs for
EZNEC?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
Mike Coslo wrote:
Cecil Moore wrote:
You can probably arrive at the same correct technical
conclusions by downloading the free demo version of
EZNEC and selecting the diameter of the conductor.

No doubt, Cecil. Of course this wasn't where the conversation
started at. I haven't tried EZNEC to model a cage antenna, will it do
it? Or do you just make the wires really thick? And how does really
thick wire compare to a cage of the same relative diameter?

You can use the free demo version to model a large diameter
radiator with up to 20 segments. For the actual multi-wire
cage antenna, one would need to spring for the non-free
version which is, IMO, the best bargain in ham radio
antenna simulation software.

No doubt, it is great software.



Why ask questions here when
the answer is available to any individual who springs for
EZNEC?


First thing is that Mr Bloe didn't start the thread off as what the
bandwidth of a cage dipole was. The bandwidth question came later. So
while it is good advice to send someone to EZNEC, it is kind of
presuming the person already knows the answer to their question when you
expect them to *not ask the question* in the first place.

I find the topic interesting, and certainly the feedback I've gotten
from Richard and Roy have been very illuminating. So I encourage more on
the topic.

Sure beats those 2000 post threads we seem to get in here! I'd sooner
see topics such as this than you and W8JI sharpening your claws on each
other......hehe

- 73 de Mike KB3EIA -

On Fri, 18 Aug 2006 11:43:34 -0400, Michael Coslo
wrote:

I find the topic interesting, and certainly the feedback I've gotten
from Richard and Roy have been very illuminating. So I encourage more on
the topic.


Hi Mike,

Going further, as you encouraged, you can observe the caged concept
applied to the Discone antenna at:
http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm

This also shows how well 16 wires approximate a solid, and further, it
also shows how the geometry of the apex angle affects the matching
characteristics. This is shown in 7 Smith charts where that angle
varies from 20° to 90°.

Upon close examination, it appears I report the wrong interval of
frequency sweep as every 0.5 MHz. Certainly the range covers 1 to 30
MHz for them all, but it would appear that I shift to every 0.25 MHz
for 50° through 90°.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Fri, 18 Aug 2006 11:43:34 -0400, Michael Coslo
wrote:

I find the topic interesting, and certainly the feedback I've gotten
from Richard and Roy have been very illuminating. So I encourage more on
the topic.


Hi Mike,

Going further, as you encouraged, you can observe the caged concept
applied to the Discone antenna at:
http://www.qsl.net/kb7qhc/antenna/Discone/discone.htm

Fascinating, and thank you! The discone and the Smith charts for it are
a great graphic tool. I note that your webpage is also featured in
Wikipedia.


This also shows how well 16 wires approximate a solid, and further, it
also shows how the geometry of the apex angle affects the matching
characteristics. This is shown in 7 Smith charts where that angle
varies from 20° to 90°.


Upon close examination, it appears I report the wrong interval of
frequency sweep as every 0.5 MHz. Certainly the range covers 1 to 30
MHz for them all, but it would appear that I shift to every 0.25 MHz
for 50° through 90°.

- 73 de Mike KB3EIA -

It takes a month of Sundays for an expert to enter and interpret the
input/output data of a cage dipole using an Eznec-type program.

The basic characteristics of a cage dipole can be displayed, in
practical terms, in a few seconds by downloading program DIPCAGE2 from
website below.

Vary length and diameter, number and gauge of wires in cage, etc., and
observe how resonant length, bandwidth and SWR change.

Program DIPCAGE2. Its about 1/2-way down the list. Been there for
years!
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........