"Art Unwin" wrote in message
...


What diametric ratio must a fractional wave length radiator be to
allow contrary current flow thru it's center. ?
Diameter / wavelength = 1.0, 0.5, 0.1. 0.001, 0.0001,
0.00001,...?
Regards
Art

Art, Did you look at my link below? What does "diametric" mean?

Ansoft's (www.ansoft.com) "Maxwell" is a "Finite Element Modeling"
(FEM) program which, among other things, can accurately produce
a graphical representation of the current distribution in a cylindrical
conductor. See examples at:
http://www3.telus.net/nighttrainexpr...in%20depth.htm
These graphs are reproduced from an article in the November/December
issue of QEX magazine, pp20 - 29, by Rudy Severns, N6LF.

73,

Frank

On Jan 13, 3:02*pm, "Frank" wrote:
"Art Unwin" wrote in message

...



What diametric ratio must a fractional wave length radiator be to
allow contrary current flow thru it's center. ?
Diameter / wavelength = 1.0, * *0.5, *0.1. * * 0.001, * * *0.0001,
0.00001,...?
Regards
Art

Art, Did you look at my link below? *What does "diametric" mean?

Ansoft's (www.ansoft.com) "Maxwell" is a "Finite Element Modeling"
(FEM) program which, among other things, can accurately produce
a graphical representation of the current distribution in a cylindrical
conductor. *See examples at:http://www3.telus.net/nighttrainexpr...in%20depth.htm
These graphs are reproduced from an article in the November/December
issue of QEX magazine, pp20 - 29, by Rudy Severns, N6LF.

73,

Frank

No, but I will now. First I will look up the word "finite" and
"finite"
Just now going out for dinner
Re diametrics, I was referring to the ratio of diameter with respect
to wavelength
( I am assuming that skin depthg is not limitless.)
Best regards
Art

"Art Unwin" wrote in message
...

( I am assuming that skin depthg is not limitless.)

of course it is limitless, it is an exponential function so it never goes to
zero. the so called 'skin depth' is only the point where the current has
dropped to 1/e or about 37% of the surface value, still a significant
current.

Dave wrote:

"Art Unwin" wrote in message
...

( I am assuming that skin depthg is not limitless.)

of course it is limitless, it is an exponential function so it never
goes to zero. the so called 'skin depth' is only the point where the
current has dropped to 1/e or about 37% of the surface value, still a
significant current.

The plots at the link Frank provided show current going rather abruptly
to zero - even negative ("contrary"?) in some cases. I wouldn't presume
to know whether it is modeled correctly.

ac6xg

The plots at the link Frank provided show current going rather abruptly
to zero - even negative ("contrary"?) in some cases. I wouldn't presume
to know whether it is modeled correctly.

ac6xg

Having some expience of Ansoft's FEM modeling software I feel the
results are highly credible. Also Rudy Severns publishing list is pretty
impressive:
http://www.snubberdesign.com/Springt...terprises.html

73,

Frank (VE6CB)

On Jan 13, 10:19*pm, "Frank" wrote:
The plots at the link Frank provided show current going rather abruptly
to zero - even negative ("contrary"?) in some cases. *I wouldn't presume
to know whether it is modeled correctly.

ac6xg

Having some expience of Ansoft's FEM modeling software I feel the
results are highly credible. *Also Rudy Severns publishing list is pretty
impressive:http://www.snubberdesign.com/Springt...terprises.html

73,

Frank (VE6CB)

Frank, I am not saying he is not credible but he is part of the older
generation and there was not enough detail supplied to determine
whether I accept it on trust. When the antenna programs
throw out the yagi in favor of arrays or radiators in equilibrium form
should we throw it out in favor of conforming with the past? Yes,the
article is in line with what the older generation has lived with
but the new generation have more tools and information than the
present dying generation.
Problem with present day authors is up against the "publish or
perish" format regure references to prior papers in quantity to
provide legitamacy to any new papers, without which they will have a
hard time publishing. Greasing the wheels of fellow contributers or
white paper authors is much preferable to declaring those who judge
are in error. Frank, a lot of the theory of antennas is either based
on vanishingly thin radiators without regard to room required for eddy
field and in some cases with transmission lines where it is possible
to get three different current flows together with a closed circuit,
yet we are now protecting the idea of non closed circuits where the
current flow
is on top of each other. No wonder it is said over the last 100 years
that we don't fully understand radiation especially when it takes over
70 posts on how to make a cantenna from a panel of experts
Best regards
Art

Frank, I am not saying he is not credible but he is part of the older
generation and there was not enough detail supplied to determine
whether I accept it on trust. When the antenna programs
throw out the yagi in favor of arrays or radiators in equilibrium form
should we throw it out in favor of conforming with the past? Yes,the
article is in line with what the older generation has lived with
but the new generation have more tools and information than the
present dying generation.
Problem with present day authors is up against the "publish or
perish" format regure references to prior papers in quantity to
provide legitamacy to any new papers, without which they will have a
hard time publishing. Greasing the wheels of fellow contributers or
white paper authors is much preferable to declaring those who judge
are in error. Frank, a lot of the theory of antennas is either based
on vanishingly thin radiators without regard to room required for eddy
field and in some cases with transmission lines where it is possible
to get three different current flows together with a closed circuit,
yet we are now protecting the idea of non closed circuits where the
current flow
is on top of each other. No wonder it is said over the last 100 years
that we don't fully understand radiation especially when it takes over
70 posts on how to make a cantenna from a panel of experts
Best regards
Art

I would hardly call the tools used in this simulation "Older".
Ansoft produces some of the most sophisticated, and up to
date FEM software available. I have seen Ansoft's HFSS
accurately model current flow through PCB vias, around an end-
launch connector at 20 GHz. CST Microwave also
produces high end FEM software. All the models are
done in full 3 D, with actual physical dimensions. This
FEM software started to apear about 10 years ago and
costs in the range of $40,000 to $50,000, with a $10,000
per year maintenance fee.

"Publish or perish" is usually applied to university positions.
It is doubtfull that too many people are able to pubish in
the Proceedings of the IEEE, or one of the IEEE Society
Transactions.

Frank, I am not saying he is not credible but he is part of the older
generation and there was not enough detail supplied to determine
whether I accept it on trust. When the antenna programs
throw out the yagi in favor of arrays or radiators in equilibrium form
should we throw it out in favor of conforming with the past? Yes,the
article is in line with what the older generation has lived with
but the new generation have more tools and information than the
present dying generation.
Problem with present day authors is up against the "publish or
perish" format regure references to prior papers in quantity to
provide legitamacy to any new papers, without which they will have a
hard time publishing. Greasing the wheels of fellow contributers or
white paper authors is much preferable to declaring those who judge
are in error. Frank, a lot of the theory of antennas is either based
on vanishingly thin radiators without regard to room required for eddy
field and in some cases with transmission lines where it is possible
to get three different current flows together with a closed circuit,
yet we are now protecting the idea of non closed circuits where the
current flow
is on top of each other. No wonder it is said over the last 100 years
that we don't fully understand radiation especially when it takes over
70 posts on how to make a cantenna from a panel of experts
Best regards
Art

This is so amusing. Those who don't appreciate knowledge thus far, probably
don't know it. Those who are desperately hoping for a revolution might just
have a ulterior motive or agenda.

It is interesting to note though, that it takes a lot of PhD's to design
something so that impoverished people (often children) can have a bowl of
rice every day to build the technology. Also, the environmental disaster
that is created by throwing away "gadgets" every 6 months to implement the
latest technology. I wonder if the Liberal academic establishment is in
touch with the environmental disaster they are creating so that we can all
be enslaved to the global neural network.

The cantenna posts are amusing, in that no one even brought up the
transition from the connector to the resistor element, or adequate thermal
conductivity between the oil and the outside air. The biggest problems
revolves around these issues. Starting with how long must the transition be
to allow adequate oil convection flow. The answer to all this can be found
with the high power Bird loads that have a smaller oil area but use large
radiating fins, or better yet, A chip resistor array directly mounted to a
large fin area.

Jim Kelley wrote:
Dave wrote:
"Art Unwin" wrote in message
...

( I am assuming that skin depthg is not limitless.)
of course it is limitless, it is an exponential function so it never
goes to zero. the so called 'skin depth' is only the point where the
current has dropped to 1/e or about 37% of the surface value, still a
significant current.

The plots at the link Frank provided show current going rather abruptly
to zero - even negative ("contrary"?) in some cases. I wouldn't
presume to know whether it is modeled correctly.


Decrease of RF current with depth below the surface of a conductor is
only a true exponential if the available conductor depth is infinite.
In the modeled situations where there is 'competition' from a skin
effect on the opposite side of the conductor, the solution is a Bessel
function which does pass through zero and reverse direction at certain
depths.

In other words, the model is behaving as expected.

Programs such as NEC and Maxwell are not released until they have gone
through a very detailed process of checking and validation. The first
step is to check against special cases that can be independently solved
by analytical methods (in other words, pure math). The work isn't
complete until all the results agree within close margins, and the
reasons for any differences are fully understood.

By the time we amateurs come to hear about these programs, they have
already been thoroughly validated by developers and professional users.
That doesn't make them immune from further criticism... but only by
people who have done the work to earn that right.


--

73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek

On Jan 14, 2:46*am, Ian White GM3SEK wrote:
Jim Kelley wrote:
Dave wrote:
*"Art Unwin" wrote in message
...

( I am assuming that skin depthg is not limitless.)
*of course it is limitless, it is an exponential function so it never
goes to zero. *the so called 'skin depth' is only the point where the
current has dropped to 1/e or about 37% of the surface value, still a
significant current.

The plots at the link Frank provided show current going rather abruptly
to zero - even negative ("contrary"?) in some cases. *I wouldn't
presume to know whether it is modeled correctly.

Decrease of RF current with depth below the surface of a conductor is
only a true exponential if the available conductor depth is infinite.
In the modeled situations where there is 'competition' from a skin
effect on the opposite side of the conductor, the solution is a Bessel
function which does pass through zero and reverse direction at certain
depths.

In other words, the model is behaving as expected.

Programs such as NEC and Maxwell are not released until they have gone
through a very detailed process of checking and validation. The first
step is to check against *special cases that can be independently solved
by analytical methods (in other words, pure math). The work isn't
complete until all the results agree within close margins, and the
reasons for any differences are fully understood.

By the time we amateurs come to hear about these programs, they have
already been thoroughly validated by developers and professional users.
That doesn't make them immune from further criticism... but only by
people who have done the work to earn that right.

--

73 from Ian GM3SEKhttp://www.ifwtech.co.uk/g3sek

So the developers know why the programs in the final analysis
gyrate towards radiators and arrays in equilibrium?
Do you know what that reason is?
Present thinking, I thought, suggest that the skin depth is quite thin
when used
for non destructive testing of materials. Is that also known by the
developers?
If the providing current is on the surface of a radiator then why does
the resulting eddy current
penetrate to the limits? Seems a sort of scrambled assumptions at play
here!