Cecil:

Here is the crux of my fruitless attempts to use EZNEC...
With EZNEC, when I plug in the value of my gamma rod and -jxr, along with
all other elements, EZNEC spits out an error! (something about too short a
loop seems to bother EZNEC, but this short loop IS working!)
However, I am looking at a REAL and functional antenna which appears to be
well matched and receiving well.
So, I end up throwing up my hands and just using the antenna and going about
with the "cut-and-try" method! (probably just my inability to use the app)

Regards,
John
--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"John Smith" wrote in message
...
Cecil:

One element I do not understand in EZNEC is: say I end up with 225 ohms
inductive reactance in the gamma rod(just an example figure, use any you
please), how do I inform EZNEC I am inserting a 225 ohm capactive
reactance,
at the feedpoint to offset it?
Or, I am all wet in considering this?

Regards,
John

--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"John Smith" wrote in message
...
Cecil:

Your work with EZNEC is greatly appreciated here.
Your configuration is for a horz ant and I am working with a
vertical--conversion is trivial.
"A picture is worth a thousand words..." has real significance here.
I am sure an analysis of your file will provide me with insight into the
workings of EZNEC and accelerate my learning curve!

THANKS!,
John

--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"Cecil Moore" wrote in message
...
Cecil Moore wrote:
John Smith wrote:
I cannot find a configuration on the gamma which brings the swr under
that figure...

As Richard H. said, find the point where the feedpoint
resistance is 50 + jXL ohms. That must occur somewhere.
Then tune out the reactance with a series capacitor.

I've used EZNEC to model a gamma-fed 33' 20m dipole at
40' made out of 0.5" aluminum tubing. With a gamma element
three feet long 6" below the 33' element and a series
Xc=122 ohms, it indicates a feedpoint impedance of
49+j0.3 ohms. The EZNEC file can be downloaded by
clicking on the link below.
--
73, Cecil http://www.qsl.net/w5dxp/GAM20DIP.EZ


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John Smith wrote:
"However, I am looking at a REAL and functional antenna which appears to
be well matched and receiving well."

Congratulationns!

In a previous posting, I quoted Dr. Arnold King who wrote prior to 1945:
"The accurate calculation of the (antenna) input impedance at AB of the
modified antenna as a function of the impedance (presented to the
matching section) and the (wire) lengths AC and BD has not been
accomplished."

If it were easy to calculate, they would have done it. They had
excellent marhematicians prior to 1945, too. The implication is that you
find the match by trial. John proved he could do it.

Best regards, Richard Harrison, KB5WZI

John Smith wrote:

Cecil:

Here is the crux of my fruitless attempts to use EZNEC...
With EZNEC, when I plug in the value of my gamma rod and -jxr, along with
all other elements, EZNEC spits out an error! (something about too short a
loop seems to bother EZNEC, but this short loop IS working!)
However, I am looking at a REAL and functional antenna which appears to be
well matched and receiving well.
So, I end up throwing up my hands and just using the antenna and going about
with the "cut-and-try" method! (probably just my inability to use the app)

Or maybe not. EZNEC apparently won't properly model
the Lattin antenna. www.g3ycc.karoo.net/lattin.htm

Somewhere I have a .ez file that shows 20 dBi omni-
directional gain from an inverted-L antenna. Now that's
what you need. :-)

And you taught me something today. I didn't know one
can attach .ez files to a newsgroup posting.
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil Moore wrote:

Or maybe not. EZNEC apparently won't properly model
the Lattin antenna. www.g3ycc.karoo.net/lattin.htm
. . .

I took a look at it, and sure enough, it can't. The antenna is
constructed from tubular 300 ohm twinlead, and EZNEC has no way to
account for the dielectric between conductors. In that antenna, it looks
like the velocity factor of the differential mode field between
conductors would be important to its operation, and without the ability
to model the dielectric between conductors, EZNEC wouldn't get the
velocity factor right.

When I see a claim that EZNEC can't model a particular antenna, I often
find that the reason for the claim is that the antenna's inventor or
seller has dreamed up some magical property to explain the impossibly
good performance he's claiming for the antenna. EZNEC models the antenna
just fine, it just doesn't model the magical property and validate the
claims -- that is, it shows how the antenna really works, not how the
huckster claims it works. But there are, certainly, some kinds of
antennas which it really can't model properly for one reason or another.
The Lattin antenna is one of those.

Roy Lewallen, W7EL

On Thu, 07 Apr 2005 10:05:04 -0700, Roy Lewallen
wrote:

But there are, certainly, some kinds of
antennas which it really can't model properly for one reason or another.
The Lattin antenna is one of those.

Hi Roy,

Having model dozens of variations of this antenna, as well as what was
described in the patent - I cannot think of one reason why it should
work except through haphazard luck. Certainly the offered "theories"
are no more credible than those for other antennas that defy modeling
such as the single or double bazooka, the eh, the cfa.

This antenna has many reports of its confounding expectation and then
in the same breath those who are confounded expressing their sincere
belief it works. It's one of those situations where the builder can't
get it to sing, but has a brother-in-law who knows this fellow who
lives next door to one who can, but who took it down ten years ago
because it was so hard to tune.

Perhaps you could widen your customer base if you added a "belief
scale" to the available control settings for EZNEC. It could range
from "agnostic" to "I believe in miracles."

73's
Richard Clark, KB7QHC