Tom Donaly wrote:
Finally, a modest question: if you have EZNEC, why would you
be wasting time with something inferior? The gold standard is the gold
standard.
Perhaps more the silver or electrum standard.
EZNEC doesn't do dielectric loading, for instance. (unless you get the
Nec4 engine from Roy)
And, it's a MoM code, so things not well represented by collections of
wires aren't necessarily modeled well.

Jim Lux wrote:
Tom Donaly wrote:
Finally, a modest question: if you have EZNEC, why would you
be wasting time with something inferior? The gold standard is the gold
standard.
Perhaps more the silver or electrum standard.
EZNEC doesn't do dielectric loading, for instance. (unless you get the
Nec4 engine from Roy)

All program types, including the demo, of EZNEC v. 4.0 and later do
dielectric loading similar to NEC-4. (The method came from sources other
than NEC-4.) Like the NEC-4 implementation, it's of limited accuracy and
usefulness -- it's really good only for thin wire insulation of moderate
permittivity.

And, it's a MoM code, so things not well represented by collections of
wires aren't necessarily modeled well.

Absolutely true. And it can't handle things like patch antennas or
antennas printed on a PCB.

Roy Lewallen, W7EL

Roy Lewallen wrote:
Jim Lux wrote:
Tom Donaly wrote:
Finally, a modest question: if you have EZNEC, why would you
be wasting time with something inferior? The gold standard is the gold
standard.
Perhaps more the silver or electrum standard.
EZNEC doesn't do dielectric loading, for instance. (unless you get the
Nec4 engine from Roy)

All program types, including the demo, of EZNEC v. 4.0 and later do
dielectric loading similar to NEC-4. (The method came from sources other
than NEC-4.) Like the NEC-4 implementation, it's of limited accuracy and
usefulness -- it's really good only for thin wire insulation of moderate
permittivity.

I stand corrected. Thanks.


And, it's a MoM code, so things not well represented by collections of
wires aren't necessarily modeled well.

Absolutely true. And it can't handle things like patch antennas or
antennas printed on a PCB.

NEC does OK at microstrip patches with air dielectric (or foam with very
low permittivity). I've used it to model an array of 9 patches and the
port to port coupling calculated by NEC and measured by a VNA were
pretty close (within measurement uncertainty).

It's pretty darn slow at this, though (lots and lots of wires in each
patch), I used lumped loads for the matching network model (capacitive
probe feed)

Jim Lux wrote:
Roy Lewallen wrote:

Absolutely true. And it can't handle things like patch antennas or
antennas printed on a PCB.

NEC does OK at microstrip patches with air dielectric (or foam with very
low permittivity). I've used it to model an array of 9 patches and the
port to port coupling calculated by NEC and measured by a VNA were
pretty close (within measurement uncertainty).

Yes, I meant patch antennas with common dielectrics, which are far more
common. It's of course the dielectric that NEC can't account for. I've
designed quite a few antennas on PCB material, but use a fudge factor
based on comparison between measured and EZNEC results of a simple
antenna near the same frequency. This gets me pretty close, but even
this approach wouldn't be adequate if field coupling through the
dielectric is significant.

It's pretty darn slow at this, though (lots and lots of wires in each
patch), I used lumped loads for the matching network model (capacitive
probe feed)

For large models, calculation time goes up as the cube of the number of
segments, so big models can get slow all right. However, EZNEC has
undergone a pretty dramatic speed improvement over time as various code
substitutions and updated compilers have been used, and it's much, much
faster than older NEC compilations. And some versions of NEC have been
similarly updated, so people using different NEC compilations can
experience pretty different calculation speeds.

Roy Lewallen, W7EL

On Apr 23, 8:43*pm, Roy Lewallen wrote:
Jim Lux wrote:
Roy Lewallen wrote:

Absolutely true. And it can't handle things like patch antennas or
antennas printed on a PCB.

NEC does OK at microstrip patches with air dielectric (or foam with very
low permittivity). *I've used it to model an array of 9 patches and the
port to port coupling calculated by NEC and measured by a VNA were
pretty close (within measurement uncertainty).

Yes, I meant patch antennas with common dielectrics, which are far more
common. It's of course the dielectric that NEC can't account for. I've
designed quite a few antennas on PCB material, but use a fudge factor
based on comparison between measured and EZNEC results of a simple
antenna near the same frequency. This gets me pretty close, but even
this approach wouldn't be adequate if field coupling through the
dielectric is significant.
Exactly. Maxwells law application is solely on the condition of all
forces be accounted for such that the summation is equal zero.
Omission of consideration of a force that is present prevents the
summation from equaling zero which means the creation of an error.
Very simple my dear Watson. This is tantamount to creating an abitrary
border where one omits recording the full amount of flux created.
Regards
Art

It's pretty darn slow at this, though (lots and lots of wires in each
patch), I used lumped loads for the matching network model (capacitive
probe feed)

For large models, calculation time goes up as the cube of the number of
segments, so big models can get slow all right. However, EZNEC has
undergone a pretty dramatic speed improvement over time as various code
substitutions and updated compilers have been used, and it's much, much
faster than older NEC compilations. And some versions of NEC have been
similarly updated, so people using different NEC compilations can
experience pretty different calculation speeds.

Roy Lewallen, W7EL

Jim Lux wrote:
Tom Donaly wrote:
Finally, a modest question: if you have EZNEC, why would you
be wasting time with something inferior? The gold standard is the gold
standard.
Perhaps more the silver or electrum standard.
EZNEC doesn't do dielectric loading, for instance. (unless you get the
Nec4 engine from Roy)
And, it's a MoM code, so things not well represented by collections of
wires aren't necessarily modeled well.

Nothing is perfect, but which is better, EZNEC or the Cecil-Corum method
of modeling antennas?
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
Jim Lux wrote:
Tom Donaly wrote:
Finally, a modest question: if you have EZNEC, why would you
be wasting time with something inferior? The gold standard is the gold
standard.
Perhaps more the silver or electrum standard.
EZNEC doesn't do dielectric loading, for instance. (unless you get the
Nec4 engine from Roy)
And, it's a MoM code, so things not well represented by collections of
wires aren't necessarily modeled well.

Nothing is perfect, but which is better, EZNEC or the Cecil-Corum method
of modeling antennas?

Depends on what your modeling needs are. NEC and it's ilk are more
generalized, but take more computational effort. The Corums have an
analytical approximation that is reasonably good for a certain class of
configurations, although I have to say that for the original Corum
application of Tesla Coils, a lumped approximation gets you almost as
close, at much less work, considering the usual construction tolerances
in a tesla coil. Modern Tesla Coil modeling is typically done with
either a lumped model or a FEM code that assumes it's axially symmetric
and often an assumed voltage distribution. The assumed distribution the
result of a combination of more detailed analytical modeling and some
experimental measurements on real coils, and speeds up the computation
drastically, while not adversely affecting the accuracy of the results
(that is, the changes are less than a few percent, comparable to
construction tolerances on these things).



73,
Tom Donaly, KA6RUH

On Apr 23, 7:49*pm, Jim Lux wrote:
Tom Donaly wrote:
Jim Lux wrote:
Tom Donaly wrote:
Finally, a modest question: if you have EZNEC, why would you
be wasting time with something inferior? The gold standard is the gold
standard.
Perhaps more the silver or electrum standard.
EZNEC doesn't do dielectric loading, for instance. (unless you get the
Nec4 engine from Roy)
And, it's a MoM code, so things not well represented by collections of
wires aren't necessarily modeled well.

Nothing is perfect, but which is better, EZNEC or the Cecil-Corum method
of modeling antennas?

Depends on what your modeling needs are. *NEC and it's ilk are more
generalized, but take more computational effort. *The Corums have an
analytical approximation that is reasonably good for a certain class of
configurations, although I have to say that for the original Corum
application of Tesla Coils, a lumped approximation gets you almost as
close, at much less work, considering the usual construction tolerances
in a tesla coil. *Modern Tesla Coil modeling is typically done with
either a lumped model or a FEM code that assumes it's axially symmetric
and often an assumed voltage distribution. The assumed distribution the
result of a combination of more detailed analytical modeling and some
experimental measurements on real coils, and speeds up the computation
drastically, while not adversely affecting the accuracy of the results
(that is, the changes are less than a few percent, comparable to
construction tolerances on these things).

73,
Tom Donaly, KA6RUH

You are correct in pointing out that a Tesla coil is a lumped
inductance. A "preponderance" of a lumped load disqualifies the use of
Maxwell's statements
The only metrics he supplied to justify the presence of equilibrium
were distributed loads and no more.
Regards
Art

Tom Donaly wrote:
Nothing is perfect, but which is better, EZNEC or the Cecil-Corum method
of modeling antennas?

EZNEC and the Cecil-Corum method are in agreement.
How would you measure the delay through a wire
or through a coil using the following current
reported by EZNEC through a 90 degree monopole?

EZNEC+ ver. 4.0
thin-wire 1/4WL vertical 4/23/2009 8:01:44 PM
--------------- CURRENT DATA ---------------
Frequency = 7.29 MHz
Wire No. 1:
Segment Conn Magnitude (A.) Phase (Deg.)
1 Ground 1 0.00
2 .97651 -0.42
3 .93005 -0.83
4 .86159 -1.19
5 .77258 -1.50
6 .66485 -1.78
7 .54059 -2.04
8 .40213 -2.28
9 .25161 -2.50
10 Open .08883 -2.71

Exactly how does one use a current that changes phase
by 2.71 degrees in 90 degrees of antenna to obtain
the delay through anything?

Your silence on this subject speaks volumes.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On Apr 23, 8:04*pm, Cecil Moore wrote:
Tom Donaly wrote:
Nothing is perfect, but which is better, EZNEC or the Cecil-Corum method
of modeling antennas?

EZNEC and the Cecil-Corum method are in agreement.
Correct but the solution is in error as equilibrium demands that the
radiator is in equilibrium ie equal to a period or multiples there of.
Both of the above determined that resonance alone without reference
to the period was a reflection of equilibrium.
This may account for Krauss's error in determiming gain via Maxwells
law by determining a half wave was in equilibrium and thus determined
gain was approx
3db more than that was actually attainable. Later measurements mad by
others show that Kraus over estimated the gain by 100 % the equivalent
of 3db or the doubling of gain or energy expenditure.This error is
actually a reflection of pitch of windings which is a fraction of the
possible generated electric field for maximum efficiency.

Lesson
One must account for all actual vectors used within a boundary for
equilibrium
where the addition of all vectors finish at the starting point of the
period. The idea that a coil does not radiate is fallacious since the
charge is still accelerating but to a lesser extent than when current
moves along a straight wire. The total velocity factor is the average
velocity of that of a slow wave plus the velocity without the addition
of lumped loads ie straight radiator addition.This being equal to the
total length of wire
required with tha absence of lumped loading ie straight.
Regards
Art




--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com