Cebic found when comparing different style programs that some behaved
well in certain circumstance where others did not. Yet all antenna
programs
are based on the use of Maxwells equations where all programs should
have the same results, after all Maxwells equations are exact and not
fudged. One of the reasons is that since Maxwells laws are exact
radiators used must be resonant at repeatable points designated as a
period.
Fact is that most users use fractional wavelength designs, usually
a half wavelength, that is not resonant at repeatable points where
the area around the datum line of a sine wave is never equal when
generated around a tank circuit.
The reason for this is "voltage over shoot" which gets smaller
with every cycle but never disappears. Thus when programs are used
based on fractional wavelength radiators the results will never show
100% accountability and in fact efficiencies derived will be in the
order of 92%!
If the radiator is of a wavelength then one is not using a "fudge"
figure
in the calculations and then becomes possible to attain total
accountability with efficiency of 100%. regardles of what type program
is used.
If one is to use exact equations, as are Maxwell equations, then
one must also use measurements that are also exact and repeatable and
that is definitely not fractional wavelengths!
What one gains from this aproach is that any radiator of any shape,
size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is resonant at
exact and repeatable measurements.
If anybody can give pointers that refute the accuracy of the above I
would be very interested in hearing them

On Sat, 14 Nov 2009 22:23:05 -0800 (PST), Art Unwin
wrote:

Cebic found when comparing different style programs that some behaved
well in certain circumstance where others did not. Yet all antenna
programs
are based on the use of Maxwells equations where all programs should
have the same results, after all Maxwells equations are exact and not
fudged. One of the reasons is that since Maxwells laws are exact
radiators used must be resonant at repeatable points designated as a
period.
Fact is that most users use fractional wavelength designs, usually
a half wavelength, that is not resonant at repeatable points where
the area around the datum line of a sine wave is never equal when
generated around a tank circuit.
The reason for this is "voltage over shoot" which gets smaller
with every cycle but never disappears. Thus when programs are used
based on fractional wavelength radiators the results will never show
100% accountability and in fact efficiencies derived will be in the
order of 92%!
If the radiator is of a wavelength then one is not using a "fudge"
figure
in the calculations and then becomes possible to attain total
accountability with efficiency of 100%. regardles of what type program
is used.
If one is to use exact equations, as are Maxwell equations, then
one must also use measurements that are also exact and repeatable and
that is definitely not fractional wavelengths!
What one gains from this aproach is that any radiator of any shape,
size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is resonant at
exact and repeatable measurements.
If anybody can give pointers that refute the accuracy of the above I
would be very interested in hearing them


How do I simulate a sheet metal or other metal structure in NEC,
when the software only knows (infinitesimally thin) "wires"

w.

On Nov 15, 6:23*am, Art Unwin wrote:
Cebic found when comparing different style programs that some behaved
well in certain circumstance where others did not. Yet all antenna
programs
are based on the use of Maxwells equations where all programs should
have the same results, after all Maxwells equations are exact and not
fudged. One of the reasons is that since Maxwells laws are exact
radiators used must be resonant at repeatable points designated as a
period.
* *Fact is that most users use fractional wavelength designs, usually
a half wavelength, that is not resonant at repeatable points where
the area around the datum line of a sine wave is never equal when
generated around a tank circuit.
* * The reason for this is "voltage over shoot" which gets smaller
with every cycle but never disappears. Thus when programs are used
based on fractional wavelength radiators the results will never show
100% accountability and in fact efficiencies derived will be in the
order of 92%!
* If the radiator is of a wavelength then one is not using a "fudge"
figure
in the calculations and *then becomes possible to attain total
accountability with efficiency of 100%. regardles of what type program
is used.
* *If one is to use exact equations, as are Maxwell equations, then
one must also use measurements that are also exact and repeatable and
that is definitely not fractional wavelengths!
*What one gains from this aproach is that any radiator of any shape,
*size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is *resonant at
exact and repeatable measurements.
If anybody can give pointers that refute the accuracy of the above I
would be very interested in hearing them

the key is that while all the programs are based on maxwell's
equations, it is impossible to implement maxwell's equations with 100%
accuracy on a digital computer. this is true of any and all
simulation and modeling programs for electrical or mechanical design.
all such programs make approximations and take shortcuts to reduce
calculation time while maintaining some minimum level of accuracy and
precision. it is important to understand the assumptions and
simplifications that have been made in order to make proper use of the
programs. typical traps in antenna simulations are that they don't
like very small or very large length/diameter ratios... so using them
for extrement long or short wires or very fat or very thin wires may
produce results that aren't realistic. many of them also don't like
very small spacing between wires, this is where most optimizer
programs fall apart, they start moving wires close together and get
strange results like super gain or unrealizable narrow beam patterns,
often accompanied by a very low feedpoint impedance.

most reputable programs like NEC have been validated very diligently
over many years and their accuracy is well documented... as are the
restrictions and assumptions that apply, but you have to read ALL the
documentation, not just the quick start guide. Other programs like
mininec, ao, yo, yagimax, and others make even more simplifications
and therefore added restrictions so they can run on a desktop
relatively quickly. unfortunately they don't always document the
limitations as well as the professional level products. after all the
professionals have millions of dollars riding on the accuracy of
designs, hams have only pennies, so it just doesn't pay to write lots
of documentation or do lots of testing that won't be read for ham
users.

so, while all the programs must be based on the same equations, the
results they generate, especially in the fringe cases, may be vastly
different. remember two maxims... 'garbage in - garbage out', and
'you get what you pay for'.

On Nov 15, 12:23*am, Art Unwin wrote:

*What one gains from this aproach is that any radiator of any shape,
*size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is *resonant at
exact and repeatable measurements.

"Figures in the order or 100%" of what?

All radiators of all sizes and shapes will radiate on the order of
100% of all the r-f energy that can be coupled into them through their
input terminals, whether or not those conductor sizes/shapes are
naturally resonant at the applied frequency.

But the fact remains that natural resonance does not occur in
electrically small radiators -- while their radiation resistance is
very small, and their feedpoint is very reactive. These realities
make it very difficult to supply r-f power to such a radiator without
relatively high losses.

As a consequence, the efficiency of the transmitter SYSTEM
(transmitter + radiator + matching network, + r-f ground loss in the
case of monopoles) can be very low.

To illustrate, the link below leads to a calculation of the
performance of a 3-meter monopole system on 1500 kHz. Due to the low
radiation resistance and system losses, and even though the short
monopole itself is nearly 100% efficient at radiating the power across
its feedpoint, that radiator receives only about 0.37% of the power
available from the transmitter. So the system efficiency is very
poor.

Such an electrically short radiator (no matter what its shape) is not
very useful compared to a naturally resonant 1/4-wave monopole or 1/2-
wave dipole -- both of which can radiate nearly 100% of the available
power.

The calculations in the link below were made using standard equations,
in a spreadsheet format to make it easy to follow and confirm.
Properly constructed/used NEC models will verify the spreadsheet
calculation, and the statements about the dipoles mentioned above.

There is no cause to distrust NEC when it is properly understood and
properly used.

http://i62.photobucket.com/albums/h8...5on1500kHz.gif

RF

On Nov 15, 1:16*am, Helmut Wabnig hwabnig@ .- --- -. dotat wrote:
On Sat, 14 Nov 2009 22:23:05 -0800 (PST), Art Unwin



wrote:
Cebic found when comparing different style programs that some behaved
well in certain circumstance where others did not. Yet all antenna
programs
are based on the use of Maxwells equations where all programs should
have the same results, after all Maxwells equations are exact and not
fudged. One of the reasons is that since Maxwells laws are exact
radiators used must be resonant at repeatable points designated as a
period.
* Fact is that most users use fractional wavelength designs, usually
a half wavelength, that is not resonant at repeatable points where
the area around the datum line of a sine wave is never equal when
generated around a tank circuit.
* *The reason for this is "voltage over shoot" which gets smaller
with every cycle but never disappears. Thus when programs are used
based on fractional wavelength radiators the results will never show
100% accountability and in fact efficiencies derived will be in the
order of 92%!
*If the radiator is of a wavelength then one is not using a "fudge"
figure
in the calculations and *then becomes possible to attain total
accountability with efficiency of 100%. regardles of what type program
is used.
* If one is to use exact equations, as are Maxwell equations, then
one must also use measurements that are also exact and repeatable and
that is definitely not fractional wavelengths!
What one gains from this aproach is that any radiator of any shape,
size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is *resonant at
exact and repeatable measurements.
If anybody can give pointers that refute the accuracy of the above I
would be very interested in hearing them

How do I simulate a sheet metal or other metal structure in NEC,
when the software only knows (infinitesimally thin) "wires"

w.

For total accuracy you MUST take account of voltage overshoot which is
neglected, so that
something other than a "period:" of a cycle will provide repeatability
of the half wave intersection with respect to resistance.
Note, "infinitesimally" is not "finite", Maxwell's equation are of
finite metrics and not close enough as in horse shoes!

On Nov 15, 6:18*am, Dave wrote:
On Nov 15, 6:23*am, Art Unwin wrote:



Cebic found when comparing different style programs that some behaved
well in certain circumstance where others did not. Yet all antenna
programs
are based on the use of Maxwells equations where all programs should
have the same results, after all Maxwells equations are exact and not
fudged. One of the reasons is that since Maxwells laws are exact
radiators used must be resonant at repeatable points designated as a
period.
* *Fact is that most users use fractional wavelength designs, usually
a half wavelength, that is not resonant at repeatable points where
the area around the datum line of a sine wave is never equal when
generated around a tank circuit.
* * The reason for this is "voltage over shoot" which gets smaller
with every cycle but never disappears. Thus when programs are used
based on fractional wavelength radiators the results will never show
100% accountability and in fact efficiencies derived will be in the
order of 92%!
* If the radiator is of a wavelength then one is not using a "fudge"
figure
in the calculations and *then becomes possible to attain total
accountability with efficiency of 100%. regardles of what type program
is used.
* *If one is to use exact equations, as are Maxwell equations, then
one must also use measurements that are also exact and repeatable and
that is definitely not fractional wavelengths!
*What one gains from this aproach is that any radiator of any shape,
*size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is *resonant at
exact and repeatable measurements.
If anybody can give pointers that refute the accuracy of the above I
would be very interested in hearing them

the key is that while all the programs are based on maxwell's
equations, it is impossible to implement maxwell's equations with 100%
accuracy on a digital computer. *this is true of any and all
simulation and modeling programs for electrical or mechanical design.
all such programs make approximations and take shortcuts to reduce
calculation time while maintaining some minimum level of accuracy and
precision. *it is important to understand the assumptions and
simplifications that have been made in order to make proper use of the
programs. *typical traps in antenna simulations are that they don't
like very small or very large length/diameter ratios... so using them
for extrement long or short wires or very fat or very thin wires may
produce results that aren't realistic. *many of them also don't like
very small spacing between wires, this is where most optimizer
programs fall apart, they start moving wires close together and get
strange results like super gain or unrealizable narrow beam patterns,
often accompanied by a very low feedpoint impedance.

most reputable programs like NEC have been validated very diligently
over many years and their accuracy is well documented... as are the
restrictions and assumptions that apply, but you have to read ALL the
documentation, not just the quick start guide. *Other programs like
mininec, ao, yo, yagimax, and others make even more simplifications
and therefore added restrictions so they can run on a desktop
relatively quickly. *unfortunately they don't always document the
limitations as well as the professional level products. *after all the
professionals have millions of dollars riding on the accuracy of
designs, hams have only pennies, so it just doesn't pay to write lots
of documentation or do lots of testing that won't be read for ham
users.

so, while all the programs must be based on the same equations, the
results they generate, especially in the fringe cases, may be vastly
different. *remember two maxims... 'garbage in - garbage out', and
'you get what you pay for'.

Exactly.
If one uses a "period" of a cycle or a full wave instead of fractional
wavelengths
Maxwell's equations can be used in antenna programs to achieve 100%
accountability
or efficiency Where as the fudge figure of fractional wavelengths can
only achieve efficiencies in the lower 90s unless voltage over shoot
is accounted for.
Programs with optimizers recognize over shoot by providing radiators
that are all multiples of a wavelength and resonant so that the array
is also resonant as a whole.

On Nov 15, 6:47*am, Richard Fry wrote:
On Nov 15, 12:23*am, Art Unwin wrote:

*What one gains from this aproach is that any radiator of any shape,
*size or elevation can provide figures in the order of 100% as long as
the radiator is a multiple of a wavelength where it is *resonant at
exact and repeatable measurements.

"Figures in the order or 100%" of what?

All radiators of all sizes and shapes will radiate on the order of
100% of all the r-f energy that can be coupled into them through their
input terminals, whether or not those conductor sizes/shapes are
naturally resonant at the applied frequency.

But the fact remains that natural resonance does not occur in
electrically small radiators -- while their radiation resistance is
very small, and their feedpoint is very reactive. *These realities
make it very difficult to supply r-f power to such a radiator without
relatively high losses.

As a consequence, the efficiency of the transmitter SYSTEM
(transmitter + radiator + matching network, + r-f ground loss in the
case of monopoles) can be very low.

To illustrate, the link below leads to a calculation of the
performance of a 3-meter monopole system on 1500 kHz. *Due to the low
radiation resistance and system losses, and even though the short
monopole itself is nearly 100% efficient at radiating the power across
its feedpoint, that radiator receives only about 0.37% of the power
available from the transmitter. *So the system efficiency is very
poor.

Such an electrically short radiator (no matter what its shape) is not
very useful compared to a naturally resonant 1/4-wave monopole or 1/2-
wave dipole -- both of which can radiate nearly

The use of the term "nearly" does not imply total accuracy.
To use Maxwell's equations for accuracy one cannot introduce metrics
that are not absolute.
1/4 or 1/2 wave radiators cannot supplant the "period" of a wave form
and thus introduce inaccuracies. The use of different algarithums in
programing accentuate or minimise the effect of these inaccuracies
thus providing different results. Same goes for close spaced wires
where the use of "near" accurate capacitances by avoidance of all
other proximety effects again take away from the accuracy of Maxwell's
equations. An accurate measurement of resonance of a mesh as I have
shown on my web page need not be dissed because of the presence of a
computer program.


100% of the available
power.

The calculations in the link below were made using standard equations,
in a spreadsheet format to make it easy to follow and confirm.
Properly constructed/used NEC models will verify the spreadsheet
calculation, and the statements about the dipoles mentioned above.

There is no cause to distrust NEC when it is properly understood and
properly used.

http://i62.photobucket.com/albums/h8...5on1500kHz.gif

RF

Helmut Wabnig wrote:
How do I simulate a sheet metal or other metal structure in NEC,
when the software only knows (infinitesimally thin) "wires"

One creates a mesh using wires. The openings in the
mesh must be small compared to a wavelength. Here's
how I modeled my pickup - don't know how accurate
it might be.

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

On Nov 15, 11:40*am, Cecil Moore wrote:
Helmut Wabnig wrote:
How do I simulate a sheet metal or other metal structure in NEC,
when the software only knows (infinitesimally thin) "wires"

One creates a mesh using wires. The openings in the
mesh must be small compared to a wavelength. Here's
how I modeled my pickup - don't know how accurate
it might be.

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

Correct Cecil, note that you are refering to a wavelength and not a
fractional WL
This is the foundation of a Faraday cage which is the very essence of
a passive radiator. In a mesh the current applied is straight but
broken up into segments
so that the displacement current is also broken up by encircling the
holes. The holes consist of a capacitor or a field that when
intersected by the initial current field produces acceleration to
applied particles while within the confines of the intersection. This
mechanism provides the maximum acceleration possible within the
Universe per Einstein where the particle achieves the same properties
as that exhibited by light and other non visible phenomina such as x
rays etc

Art Unwin wrote:

What one gains from this aproach is that any radiator
of any shape, size or elevation can provide figures in
the order of 100% as long as the radiator is a multiple
of a wavelength where it is resonant at exact and
repeatable measurements.

then Art wrote:

The use of the term "nearly" does not imply total accuracy.

Note that your use of the phrase "in the order of" does not
imply total accuracy, either -- even for radiators meeting
your criteria.

To use Maxwell's equations for accuracy one cannot introduce
metrics that are not absolute. 1/4 or 1/2 wave radiators cannot
supplant the "period" of a wave form and thus introduce
inaccuracies.

Apparently you believe that only full-wave radiators are
"perfect" (exactly 100% efficient).

However a full-wave, center-fed dipole has a radiation resistance of
about 2,000 ohms, and a feedpoint reactance exceeding 1,000 ohms
(capacitive). That impedance would present a very high VSWR to a
normal transmitter unless some kind of matching network was used.

Even if there was no matching or transmission line loss (or r-f ground
loss in the case of a monopole), that full-wave radiator still would
not be 100% efficient because of the ohmic losses encountered by the r-
f current flowing along the radiating structure (NOT the radiation
resistance).

RF