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

No we are saying the same thing two different ways. Let's first talk about
the matching section. For example a G5RV may be modified by adjusting the
feedline length from about 22 to 38 feet. From the end of the matching
section you can run any practical length of coax.

If you had the top of your G5RV mounted at 100 feet, those length might not
be practical. Adding an additional 1/2 wave length, or multiple thereof
would allow the mechanism that switches in lengths of matching sections to
be at ground level.

For example my 132 foot dipole uses 90 feet of fixed 450 ohm ladderline to
the relay box. It is matched at 4035 and I then add sections to lower the
frequency. 3.5 MHz requires an additional 39 feet.

On 7.3 the first Imax point is at 29.5 feet and adding an additional 1/2
wave brings us to 90.3 feet. We could just as easily used 151, 211, 272,
333 etc. Feet.

Where is the matching section? The first or the last 29.5 feet on the 90.3
feet? I think you could say that the first section matches the antenna
impendence to somewhere around 50 Ohms and the 1/2 wave simply repeats it.
Or you could say the first 1/2 wave section repeats the antenna impendence
and the last 23 feet matches it. Potato, Patata, they both make the same
fries.


"Buck" wrote in message
...
On Thu, 9 Jun 2005 00:27:26 -0400, "Fred W4JLE"

Fred, I believe that you and Cecil are 180 degrees out of phase. Did
someone make a type-O?

--
73 for now
Buck
N4PGW

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

[snip]

1. Open EZNEC and open the file "BYdipole.ez".

2. Go to "Setups" (at the top of the window) and select "Frequency
Sweep."

3. When the pane opens, select "On" and type in 14.35 for the "Stop
Frequency" and .05 for the "Frequency Step."

4. Under output. check the box "Microsmith Files" and for file name
type "g5rv" and hit Ok.

5. Go to the "Wires" menu and change the Y value for End 1 to -51.
Change the Y value for End 2 to 51.

6. Do a "Save As" and type "g5rv".

7. Perform a Freq Swp. (Bottom left button).


A little mea culpa. The above sequence fails to identify the
segmentation error in this model. I'm so used to using Multinec to
interface to EZNEC that I forgot that when using EZNEC directly this
error isn't trapped.

EZNEC's automatic segmentation check doesn't run when changing wire
lengths. It will allow the change that I made that results in too few
segments in the new length. The minimum number should be 13, with
more the merrier. With this simple structure, however, the error is
small and the other results are generally acceptable.

Let me answer each question below

"Buck" wrote in message
...
On Thu, 9 Jun 2005 16:30:18 -0400, "Fred W4JLE"
wrote:

Given an antenna that has 50 Ohms +J0, feed it with 50 ohm line and the
swr
for the system is 1:1, substitute a 1/2 wave of 450 ohm line and the
antenna
and the rig are both at 50 ohms. The SWR on the feedline is 450/50 or
9:1.

Exactly correct, actually you can replace it with 1/2 electrical wave length
of anything including lampcord. That being said you should not use lamp cord
before someone has a cow.



Ok, just to reiterate so I know I understand (and you can see if I
don't), If I feed a 20 meter dipole cut for my favorite frequency, I
can feed the radio with exactly 1/2 wave of 450 ohm feedline and it
will match the radio? Of course, coax will make a better match (with
less loss?)

No coax won't make a better match, a match is a match. The loss is lower on
the ladder line. The use of ladder line for a dipole designed for and used
on a single band probably doesent make a lot of sense. If you want to run an
80 meter dipole on all bands it is a must (sans a tuner). Look at it this
way 450 Ohms divided by 50 Ohms = 9 an 18:1 SWR at 450 ohms is only 2:1 at
50 ohms.

Now, if I understand, the principle of the 130 foot dipole matching
the rig is based on the length of 450 ohm twin-lead. The twin lead is
always 1/2 WL long.

NO SEE MY OTHER REPLY

The coax and rig are 50 ohms, but according to
the smith chart, the impedance of the various frequencies range from
20 to 100 ohms. This would make me wonder why I don't get the same
impedances at my rig, or at least at my feed point of 50 ohm coax.


Thanks


--
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.