On Tue, 14 Jun 2005 14:29:16 -0700, Wes Stewart
wrote:

No problem. The guys that really deserve the thanks are the geniuses
1: who developed the NEC engine, 2: Roy, W7EL, (among others) who put
a pretty face on it, and 3: Dan Maguire, AC6LA, who did the Excel
stuff.

And the absolutely amazing thing is, they give away their work! Is
this a great country or what?

Regards,

Wes N7WS


Thanks for the help, Wes. I will be looking for that additional
thread. One of these days I'll get rich and famous and I can budget
the cost of EZNEC and get the full copy. 20 elements is just not
quite what I need for an antenna I am toying with in my mind.

BTW, how closely does the program get the measurements for antennas?
If I plot a dipole and EZNEC says the length should be 45 feet, will I
need to trim the antenna to a different length or will it be within an
inch or two?



--
73 for now
Buck
N4PGW

Buck wrote:

Thanks for the help, Wes. I will be looking for that additional
thread. One of these days I'll get rich and famous and I can budget
the cost of EZNEC and get the full copy. 20 elements is just not
quite what I need for an antenna I am toying with in my mind.

BTW, how closely does the program get the measurements for antennas?
If I plot a dipole and EZNEC says the length should be 45 feet, will I
need to trim the antenna to a different length or will it be within an
inch or two?


I sure encourage Wes and anyone else to post his experience with
agreement or disagreement between modeling and measurement. But I've
gotten a pretty good overview from the comments I've gotten in 15 years
of selling EZNEC and its predecessor. These include reports from a
spectrum of users ranging from amateurs who've measured what they can
with the tools they have available, to professional users who have
exceptionally good measurement equipment and access to high quality test
ranges.

With quite a handful of caveats, below, the program gives very accurate
results(*). Here are the caveats.

First, the antenna has to be just like the model. By "just like", I mean
that anything materially affecting the antenna has to be in the model.
Radiating feedlines are one of the most common elements overlooked by
amateurs. I've also seen cases where the test meter itself is large and
close enough to the antenna to change its impedance very significantly,
and correspondence wasn't achieved until the meter was added to the
model. Also, most people don't appreciate how much effect another
antenna (or other resonant conductor) can have, even when surprisingly
far away.

Next are a handful of modeling traps. These include but aren't limited
to making sure the model is within modeling guidelines (segmentation,
choice of ground type, etc.), that the NEC engine isn't having any
particular difficulty (average gain close to 1), and the model doesn't
contain any features which are known to cause an error (e.g., connected
wires of different diameters, particularly in a parsitic element).
Serious geometry errors such as connecting a wire end to a segment
midpoint on another wire appeared quite frequently in files sent to me
by users, which prompted me to expend the considerable effort to develop
a comprehensive geometry check for the EZNEC v. 4.0 release. But many
errors can still be made. It takes a fair amount of care, knowledge, and
experience to gain a high degree of confidence that all these conditions
are met.

Then, even when the model is correct, most people don't know just how
difficult it is to make good measurements. Measurements made through
feedline are subject to a host of errors including failure to account
for the effect of even a small amount of loss, and line impedance that's
different from its specification -- a very common situation.
Measurements made without feedline often suffer from the effects of
common mode current and the close proximity of the person making the
measurements. And so forth.

All that being said, it's really not hard to make a very decent model of
a simple antenna -- or even a fairly complex one. But there are too many
things I can't know about your modeling ability, how well you've
suppressed feedline current in the real antenna, and how you'll be
deciding that the antenna "works" to know if it'll come out within an
inch or two.

Based on past experience, some number of the readers will interpret what
I've written to mean that it's impossible to make a good model, or that
modeling doesn't give accurate results. Neither is true at all. But a
careless model and casual measurement probably won't match very well,
either.

So my advice is to cut the antenna a bit long. Only after *you* have
built and measured a few can you gain (or not gain) confidence in the
ability of *your* models to match *your* measurements.

(*) I can't and don't take credit for the accuracy of the program.
That's solely due to its NEC calculating engine which was developed by
others. I will take blame for any EZNEC results which differ from those
given by NEC. Those would be bugs, and I'd appreciate very much if
anyone seeing a difference would contact me so I can track it down and
fix it.

Roy Lewallen, W7EL

Thanks for the reply and comments.

I have been enjoying my time playing around with the program. I have
notice that an antenna cut, trimmed and tuned at one location often
has a different dip in another.

As for the program, I would like to order the full version of eznec,
but I can't possibly budget that in right now. Is there a similar
program available without the 20 segment limit? I am thinking I saw
one many months ago when I first tried playing with this one.

Thanks,

--
73 for now
Buck
N4PGW

Buck wrote:
Thanks for the reply and comments.

I have been enjoying my time playing around with the program. I have
notice that an antenna cut, trimmed and tuned at one location often
has a different dip in another.

As for the program, I would like to order the full version of eznec,
but I can't possibly budget that in right now. Is there a similar
program available without the 20 segment limit? I am thinking I saw
one many months ago when I first tried playing with this one.

Thanks,

EZNEC-ARRL, a type of EZNEC v. 3.0, is included with the 20th Edition of
the ARRL Antenna Book. It has a 500 segment limit when analyzing any of
the several hundred EZNEC models included with the Antenna Book. You can
modify any of those models and retain the 500 segment limit. However, if
you save a modified model and open it again, the program will revert to
the 20 segments of the demo version, since the saved file isn't one of
the special ARRL files which relieve the segment limit. (Incidentally,
all those several hundred models are recognized by standard EZNEC
programs as ordinary EZNEC files, for those of you who have the standard
program.)

There are several other programs available which have higher segment
limits that are free. A web search and/or recommendations from other
people should lead you to some of them. NEC-2 itself is free and
available on the web, although you'll probably find it relatively
difficult to use.

Roy Lewallen, W7EL

On Wed, 15 Jun 2005 11:49:43 -0700, Roy Lewallen
wrote:

Buck wrote:
Thanks for the reply and comments.

I have been enjoying my time playing around with the program. I have
notice that an antenna cut, trimmed and tuned at one location often
has a different dip in another.

As for the program, I would like to order the full version of eznec,
but I can't possibly budget that in right now. Is there a similar
program available without the 20 segment limit? I am thinking I saw
one many months ago when I first tried playing with this one.

Thanks,

EZNEC-ARRL, a type of EZNEC v. 3.0, is included with the 20th Edition of
the ARRL Antenna Book. It has a 500 segment limit when analyzing any of
the several hundred EZNEC models included with the Antenna Book. You can
modify any of those models and retain the 500 segment limit. However, if
you save a modified model and open it again, the program will revert to
the 20 segments of the demo version, since the saved file isn't one of
the special ARRL files which relieve the segment limit. (Incidentally,
all those several hundred models are recognized by standard EZNEC
programs as ordinary EZNEC files, for those of you who have the standard
program.)

There are several other programs available which have higher segment
limits that are free. A web search and/or recommendations from other
people should lead you to some of them. NEC-2 itself is free and
available on the web, although you'll probably find it relatively
difficult to use.

Roy Lewallen, W7EL


Thanks, I reinstalled it. I had to uninstall everything and then
install ARRL first before it would work. Now, however, I have a
problem placing the folders where I want them. Is there a way to do
this?

I just finished experimenting with the ARRL version. I was able to
modify any file as long as I don't save or quit, i can get about as
elaborate as I want by hand entering all the data.



--
73 for now
Buck
N4PGW

Buck wrote:

Thanks, I reinstalled it. I had to uninstall everything and then
install ARRL first before it would work. Now, however, I have a
problem placing the folders where I want them. Is there a way to do
this?
. . .

Click Help, then Contents. This opens the EZNEC manual. Click the Index
tab (key icon), then type "folders" (without the quotation marks) into
the text box, or scroll down until you see "Folders".

You'll find the answers to most of your questions in the manual.

Roy Lewallen, W7EL

Buck wrote:

As for the program, I would like to order the full version of eznec,
but I can't possibly budget that in right now. Is there a similar
program available without the 20 segment limit? I am thinking I saw
one many months ago when I first tried playing with this one.

You could try 4nec2 at www.wyger.nl/usr/4nec2. If you are familiar with
EZnec, you should not have too much difficulties using 4nec2. However
both programs have their pros and contras

Success,
Arie.