My understanding of antenna modeling is that sharp corners or
connecting points should be avoided as they can create errors.
The question I ask is what constitutes a sharp angle ?
I am assuming that it is the capacitance at the connection is the
problem. If so
is the corner of a quad a problem or is a delta feed point on a dipole
a problem ?
I see many instances of quads being modeled and also " V" wire antennas
each without a correcting "gusset" at the corners. So when is an angle
termed to be sharp?
Regards
Art

On 25 Jan 2005 16:21:57 -0800, "art" wrote:

My understanding of antenna modeling is that sharp corners or
connecting points should be avoided as they can create errors.
The question I ask is what constitutes a sharp angle ?
I am assuming that it is the capacitance at the connection is the
problem. If so
is the corner of a quad a problem or is a delta feed point on a dipole
a problem ?
I see many instances of quads being modeled and also " V" wire antennas
each without a correcting "gusset" at the corners. So when is an angle
termed to be sharp?
Regards
Art

When it is at a current maximum. At a voltage maximum it's irrelevant.
Just my opinion.

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

What leads you to that opinion?
Art

On 25 Jan 2005 16:21:57 -0800, "art" wrote:
I am assuming that it is the capacitance at the connection is the
problem.

Hi Art,

Kinks (aka sharp bend) add inductance.

I see many instances of quads being modeled and also " V" wire antennas
each without a correcting "gusset" at the corners. So when is an angle
termed to be sharp?

It is not generally an issue because the greater bulk of the antenna
swamps out this small perturbation. It is the modeler that has the
problems. Consult your user's manual that cites considerations to be
taken for wires joining at an acute angle. Follow the rules offered.

73's
Richard Clark, KB7QHC

On Wed, 26 Jan 2005 01:11:19 GMT, (Robert
Lay) wrote:

On 25 Jan 2005 16:21:57 -0800, "art" wrote:

My understanding of antenna modeling is that sharp corners or
connecting points should be avoided as they can create errors.
The question I ask is what constitutes a sharp angle ?
I am assuming that it is the capacitance at the connection is the
problem. If so
is the corner of a quad a problem or is a delta feed point on a dipole
a problem ?
I see many instances of quads being modeled and also " V" wire antennas
each without a correcting "gusset" at the corners. So when is an angle
termed to be sharp?
Regards
Art

When it is at a current maximum. At a voltage maximum it's irrelevant.
Just my opinion.

Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html


On second thought, it's all irrelevant. The feed lines of a balance
feed attach at the center of the dipole. That's a right angle bend at
a current maximum. Must not be a problem - everybody does it - Hi!


Bob, W9DMK, Dahlgren, VA
Replace "nobody" with my callsign for e-mail
http://www.qsl.net/w9dmk
http://zaffora/f2o.org/W9DMK/W9dmk.html

lIif you look at lamina flow on any corner there is a change because
the cross sectional area changes rapidly.. My particular programm
suggests that the point of resonance changes because of this and thus
inserts a 'corrective' action.. What this action is I do not know..
In the past I have always cut corners with a conductive member so as
to cut the intersecting angle by half., but this does not appear to
be followed in demonstration articles.
After musing over this question for some time. and without further
knoweledge, I would discount any modeling results of a fractal type
antenna which is a worst case scenario.
of kinks and bends.and corresponding cross section changes.
Regards
Art

On 25 Jan 2005 21:18:27 -0800, "art" wrote:

I would discount any modeling results of a fractal type
antenna which is a worst case scenario.

Hi Art,

Worst case of what?

73's
Richard Clark, KB7QHC

Richard, what you are angling for you will not get.
Contribute to the subject or learn from the offerings of others.
Regards
Art


"Richard Clark" wrote in message
...
On 25 Jan 2005 21:18:27 -0800, "art" wrote:

I would discount any modeling results of a fractal type
antenna which is a worst case scenario.

Hi Art,

Worst case of what?

73's
Richard Clark, KB7QHC

Modeling of wires connected at an angle is a problem only with
MININEC-based programs such as AO or ELNEC, not with NEC-2 based
programs like EZNEC or most other modern programs.

The problem with wires connecting at an angle is that MININEC "cuts the
corner" -- it acts like a wire extends between about the middles of the
corner segments, rather than going clear to the corner as they should.
The problem gets less and less as the segment length gets shorter and
shorter near the junction (since the distance "cut" is less), or as the
angle gets more obtuse. There's no magic threshold where the problem
suddenly occurs (same reason). Its seriousness depends entirely on how
serious a small length error is -- it'll just shift the resonance
slightly of a single loop modeled with a moderate number of segments,
but it can seriously alter the pattern of a quad because of the
sensitivity of the parasitic element(s) to small wire length changes.

ELNEC had a way of correcting for this, called "segment length
tapering", where it would automatically convert a wire into a series of
wires with increasing segment lengths. That way you could have a very
short segment at the corner, but not have to use a large number of very
short segments for the whole antenna. That feature is still in EZNEC.
It's no longer needed for this purpose because NEC-2 doesn't have the
problem, but it's occasionally useful at other times.

You can find out more about this phenomenon in "MININEC: The Other Edge
of the Sword", in Feb. 1991 _QST_.

Roy Lewallen, W7EL

art wrote:
My understanding of antenna modeling is that sharp corners or
connecting points should be avoided as they can create errors.
The question I ask is what constitutes a sharp angle ?
I am assuming that it is the capacitance at the connection is the
problem. If so
is the corner of a quad a problem or is a delta feed point on a dipole
a problem ?
I see many instances of quads being modeled and also " V" wire antennas
each without a correcting "gusset" at the corners. So when is an angle
termed to be sharp?
Regards
Art

On Wed, 26 Jan 2005 06:03:21 GMT, "
wrote:

Richard, what you are angling for you will not get.

Hi Art,

I would discount any modeling results of a fractal type
antenna which is a worst case scenario.
Worst case of what?
A very simple question to your very un-informed statement. If you
will not explain what you mean, you demonstrate absolutely no care to
Contribute to the subject or learn from the offerings of others.
especially when you are simply throwing mud at a topic. Your kind of
badmouthing is not:
1 contributing to a subject;
2 learning;
3 nor an offering.

73's
Richard Clark, KB7QHC