John Smith wrote:

...
If you can't participate, if you think I am am an idiot, if you think I
am a moron ... could you do it politely until I give you reason to do
differently ... indeed, I may feel threaten my "moronic brains" and
respond ... please don't take insult, just reassure me I am not wrong ...

Regards,
JS

Look, that got "corrupted" in my frustration, I am not a writer, I just
attempt to bring my skills up to speed to participate here ...

Let me change all that:

If I can't think here ... If I can use this as a "note pad" ... If I can
speculate here ... If I can't search for others here, if I can't use
other as a "backboard" here ...

.... then let it all be damned ... I am an idiot ... and let's look over
your past, present and future questions, speculations, advances, etc. ...

Regards,
JS

John Smith wrote:

...
Regards,
JS

Geesh, can = can't in a lot of that. Those with a brain will know ...
those without will point it out ... don't think it necessary ... PLEASE!

I am taking a break from all this ... I need to ... :-)

Regards,
JS

On Thu, 02 Oct 2008 15:10:05 -0700, John Smith
wrote:

Geesh, can = can't in a lot of that. Those with a brain will know ...
those without will point it out

It took 3 posts to point it out, but you managed....

... don't think it necessary ... PLEASE!

Not in the least necessary from any perspective; but I can see why
some modeling would be impossible to confirm against the data offered.
Afterall, if the prognosis of, say, netzheimers were based on a ±0.1dB
DNA error, then all bets are off in proving sanity.

Knowledge may give weight, but accomplishments
give lustre, and many more people see than weigh.
Lord Chesterfield

73's
Richard Clark, KB7QHC

John Smith wrote:
I don't believe the above is correct.

Proof that NEC cannot model everything is at:

http://www.w5dxp.com/SUPRGAIN.EZ

Would you believe a vertical with
24 dBi omnidirectional gain?
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein

Richard Clark wrote:

...
Not in the least necessary from any perspective; but I can see why
some modeling would be impossible to confirm against the data offered.
Afterall, if the prognosis of, say, netzheimers were based on a ±0.1dB
DNA error, then all bets are off in proving sanity.

Knowledge may give weight, but accomplishments
give lustre, and many more people see than weigh.
Lord Chesterfield

73's
Richard Clark, KB7QHC

LOL!

Thanks Richard!

I will place a grain (or two, or more) of salt upon the joint of the
thumb with wrist (and, thinking fondly of you, as reason enough), swag
down the shot of Tequila and touch tongue to the joint ... but for now,
more important things beckon me ...

Ahh yes, if only for a night ... I suppose you will be here tomorrow ...
may your dreams be filled with the such of mine ... here is too our
further "exploits" :-)

Regards,
JS

Cecil Moore wrote:

...
Would you believe a vertical with
24 dBi omnidirectional gain?

Cecil:

With the "truth" we have maintained before us, and especially here,
another shot of Ta-Kill-Ya (or, Tequila), I'd believe anything you would
state!--await my returned "brain" tomorrow--please? ROFLOL

Regards my friend,
JS

John Smith wrote:
--await my returned "brain" tomorrow--please? ROFLOL

Good luck on that one. :-)
--
73, Cecil http://www.w5dxp.com
"According to the general theory of relativity,
space without ether is unthinkable." Albert Einstein

Cecil Moore wrote:
John Smith wrote:
I don't believe the above is correct.

Proof that NEC cannot model everything is at:

http://www.w5dxp.com/SUPRGAIN.EZ

Would you believe a vertical with
24 dBi omnidirectional gain?

Got a regular NEC deck or text description (can't read the EZ-NEC file..)

Jim Lux wrote:
Cecil Moore wrote:
John Smith wrote:
I don't believe the above is correct.

Proof that NEC cannot model everything is at:

http://www.w5dxp.com/SUPRGAIN.EZ

Would you believe a vertical with
24 dBi omnidirectional gain?

Got a regular NEC deck or text description (can't read the EZ-NEC file..)

Although NEC can't model everything (for example, it can't model a patch
antenna containing dielectric), this model is not at all proof of that.
All it shows is that models can be carelessly or intentionally
constructed in such a way as to cause NEC to malfunction. An experienced
EZNEC or NEC modeler would immediately run an Average Gain test and seen
that the reported gain is about 16.7 dB too high due to numerical
problems. If desired, this can be subtracted from the reported gain to
give the gain that's much closer to reality.

A resistance, the jagged schematic symbol that we use in basic circuit
analysis, can be and often is used as a simple model of a resistor. But
anyone who has ever done any electronic design or analysis quickly
discovers that this model is adequately accurate only under some limited
group of conditions -- for example, it's a lousy model of a leaded
resistor at 10 GHz --, and any calculations made using it will be far
from measurement of a real resistor (assuming the measurements are
capably made). Like the resistance and all other models, NEC also has
limitations and boundaries over which it's valid. And it can be
misapplied to produce just as egregiously bad results as using a
resistance to model a leaded resistor at 10 GHz. In this case, the model
violates at least one NEC rule by spacing two 40-foot #14 wires 1/2 wire
diameter (0.032") apart. (NEC guidelines specify that parallel wires
should be at least several wire diameters apart.) It would be a great
challenge to actually construct this antenna. But, even at that, the NEC
results are probably not bad once the average gain correction is made.

Here's the model in .NEC format for those who don't have EZNEC. I've
changed the current source to a voltage source which simplifies the
model without making any difference in results.

CM 40m triangular loop
CE
GW 1,31,.003048,0.,3.048,.003048,0.,12.192,8.138E-4
GW 2,53,0.,0.,12.192,0.,16.4592,12.192,8.138E-4
GW 3,61,0.,16.4592,12.192,0.,0.,3.048,8.138E-4
GW 4,31,0.,0.,3.048,0.,0.,12.192,8.138E-4
GE 1
LD 5,1,0,0,5.7471E+7,1.
LD 5,2,0,0,5.7471E+7,1.
LD 5,3,0,0,5.7471E+7,1.
LD 5,4,0,0,5.7471E+7,1.
FR 0,1,0,0,7.
GN 2,0,0,0,13.,.005
EX 0,1,16,0,1.414214,0.
RP 0,181,1,1000,90.,0.,-1.,0.,0.
EN

Roy Lewallen, W7EL

Jim Lux wrote:

I doubt that any antenna an amateur is likely to build has some physics
not adequately modeled by the math in NEC. Exactly what might be these
discrepancies in equations, formulae and assumptions? Considering that
NEC has had decades of validation against actual measurements and a lot
of really, really smart people looking at how it works, I'd be kind of
surprised.

However, I can also easily believe that an amateur (or professional)
could build an antenna that has measured performance different than
expected from their NEC model of that antenna. The differences would
lie, most likely, in these areas:
1) Inaccuracies in the model itself. Things like earth properties (NEC
assumes uniform dielectric, it isn't) are an important source of error
for antennas close to the ground. Most amateur models do not include a
very good model of the surroundings (supports, trees, feedlines, etc.)

2) Inaccuracies in the measurements or not measuring the right things. A
good example is using NEC to get feedpoint characteristics, then
measuring at the rig, and not properly accounting for the transmission
line, particularly if the feedpoint Z is reactive.

In the professional antenna world, if someone models an antenna, then
builds it and tests it on the range, and the measurements differ from
what the model predicted, the usual assumption is that what was built
differed from what was modeled, or the measurements were off.

A lot of people are aware that some knowledge and skill is necessary in
order to construct a good model which will give accurate results. What's
not so widely appreciated is how difficult it is to make decent
measurements of even such seemingly simple things as impedance, let
alone gain and pattern.

Some years ago I was at what was then NOSC (Naval Ocean Systems Center)
in San Diego, where they had the very best equipment to do full 3D
pattern measurements of antennas mounted on carefully constructed and
accurate scale models of U.S. Navy ships. They were also modeling the
antennas and ship structures with NEC-4. One of the engineers confided
to me that they'd learned that when the measurement disagreed with the
model result, the model result was probably better. Of course, these
people were very highly skilled in using the modeling software and how
to avoid and detect its limitations. But they were also very highly
skilled in making the best possible measurements.

A claim by an antenna manufacturer or creator that an antenna "can't be
modeled by NEC" very often means that NEC's accurate results don't back
up the manufacturer's or creator's inflated claims. If the claim
includes a statement that some alleged physical rule or phenomenon
("critical coupling" comes to mind) isn't "accounted for" by NEC, you
can be certain that the disparity is due to inflated claims rather than
a shortcoming of NEC. There are, of course, some antennas that truly
can't be modeled with NEC, for example a patch antenna with dielectric
between the patch and ground plane. But those of NEC's limitations that
aren't apparent from the basic program structure have been pretty well
discovered and documented in the 30 years or so it's been in use.

Antennas are being designed every day with NEC and EZNEC which provide
critical communications functions for military and government agencies,
aerospace companies, space agencies, domestic and international
broadcasters, scientific researchers, and many others. Many of those
antennas have been carefully measured and verified before being put into
service, and countless of them are in current use. I personally have
designed a number of antennas with EZNEC, tested physical prototypes at
a professional range, and seen them put into daily service performing
critical functions as designed.

Roy Lewallen, W7EL