Antenna Theory
 

wrote in message
ups.com...
Ah, the perennial cry of the pseudoscientist. I am misunderstood! My
idea will change the WORLD.

But then, you offer no real evidence. You're basically giving a
supernatural explanation for the operation of the antenna. The RF
current flow is a ghost.. it's a haunted antenna. What measurements do
you have to show that your grounding system does what you say?

A very, very inefficient antenna can get you good signal reports.
You're trying to get people to send you cash for your haunted antenna,
so you won't do real measurements. You don't really know how much
power is being radiated by this antenna, and never will we, unless we
send you money.

Dan


Sounds like the junk ads you see on TV where the real profit is in the
shipping and handling.

Antenna Theory
 

Felix wrote:
Cecil Moore Wrote:
Richard Fry wrote:-

Felix Meyer, HB9ABX
Felix

Felix- your confusion is based on the fact that no one will believe you
without a basis for a real comparison of your antenna with a reference
antenna, done by another person, with publication of the results and a
description of the method.
NO qso "data" will do this. In that regard, you are just another
pusher of an EH or CFA antenna.
If you are serious, you will let some independent expert make one to
your description, and test it properly. (That's what shot down the EH)
In regard to the inability of such programs as EZNEC to properly
evaluate your antenna, I have not seen a well described antenna that
could not be evaluated honestly by a person aware of antenna theory and
the modelling programs.
Good luck-Bill

Antenna Theory
 

Bill wrote:
I have not seen a well described antenna that
could not be evaluated honestly by a person aware of antenna theory and
the modelling programs.

The Lentine (sp?) antenna, consisting of different lengths
of radiating transmission stubs proved impossible for me
to model with EZNEC.
--
73, Cecil http://www.w5dxp.com

Antenna Theory
 

Cecil Moore wrote:
Bill wrote:
I have not seen a well described antenna that
could not be evaluated honestly by a person aware of antenna theory and
the modelling programs.

The Lentine (sp?) antenna, consisting of different lengths
of radiating transmission stubs proved impossible for me
to model with EZNEC.
--
73, Cecil http://www.w5dxp.com

Cecil- Obviously, you fit the qualifications I mentioned, and- just as
obviously, I did not know of that example. I need to do some homework.
Thanks-Bill

Antenna Theory
 

EZNEC can model radiating transmission line stubs made from either
parallel wires or coax. To do it, parallel wire lines have to be modeled
as wires, not with the non-radiating transmission line model. Radiating
coax is modeled with a combination of a non-radiating transmission line
model for the inside, and a wire to represent the radiating outside of
the coax. This technique is described in the EZNEC manual and
illustrated with the DipTL.EZ example file included with EZNEC.

There are some types of antennas which aren't possible to model with
NEC-based programs. An example is a patch antenna on a dielectric
substrate -- NEC and EZNEC have no way to model the dielectric.
Likewise, a "loopstick" antenna -- a solenoid wound on a ferrite rod --
isn't possible because of the ferrite and possibly because of the
exceptionally small dimensions (for one used at AM broadcast frequencies).

But most often when you see an antenna inventor or seller claim that his
antenna "can't be modeled" by NEC, EZNEC, or other programs, it just
means that modeling fails to show the extraordinary performance he
claims for it. That's simply a failure of the program to include the
effects of magical properties and wishful thinking in its calculations.
I've come to regard such claims as a red flag indicating a probable
exaggeration of antenna performance.

Roy Lewallen, W7EL

Bill wrote:
Cecil Moore wrote:
Bill wrote:
I have not seen a well described antenna that
could not be evaluated honestly by a person aware of antenna theory and
the modelling programs.
The Lentine (sp?) antenna, consisting of different lengths
of radiating transmission stubs proved impossible for me
to model with EZNEC.
--
73, Cecil http://www.w5dxp.com

Cecil- Obviously, you fit the qualifications I mentioned, and- just as
obviously, I did not know of that example. I need to do some homework.
Thanks-Bill

Antenna Theory
 

Roy Lewallen wrote:
But most often when you see an antenna inventor or seller claim that his
antenna "can't be modeled" by NEC, EZNEC, or other programs, it just
means that modeling fails to show the extraordinary performance he
claims for it. That's simply a failure of the program to include the
effects of magical properties and wishful thinking in its calculations.
I've come to regard such claims as a red flag indicating a probable
exaggeration of antenna performance.

I wish I could remember the correct spelling for the antenna
I tried to model. Something like "Lentine". It is a dipole
of sorts made from shorted and open sections of balanced
transmission line. I tried modeling it with wires in EZNEC
and got all sorts of errors. It looked something like this:

+--------+--------+--------FP--------+--------+--------+
+------ +------ +------ ------+ ------+ ------+

Anyone remember the correct spelling for that antenna?
--
73, Cecil http://www.w5dxp.com

Antenna Theory
 

Cecil Moore wrote:
Roy Lewallen wrote:
But most often when you see an antenna inventor or seller claim that
his antenna "can't be modeled" by NEC, EZNEC, or other programs, it
just means that modeling fails to show the extraordinary performance
he claims for it. That's simply a failure of the program to include
the effects of magical properties and wishful thinking in its
calculations. I've come to regard such claims as a red flag
indicating a probable exaggeration of antenna performance.

I wish I could remember the correct spelling for the antenna
I tried to model. Something like "Lentine". It is a dipole
of sorts made from shorted and open sections of balanced
transmission line. I tried modeling it with wires in EZNEC
and got all sorts of errors. It looked something like this:

+--------+--------+--------FP--------+--------+--------+
+------ +------ +------ ------+ ------+ ------+

Anyone remember the correct spelling for that antenna?

Google for "Lattin antenna". (Too many "lentils", Cecil :-)

One of the first hits is http://www.g3ycc.karoo.net/lattin.htm which
shows a good sketch. The antenna is made from sections of 300-ohm ribbon
or tubular feeder, configured as a string of quarter-wave stubs that
progressively make the dipole shorter as the frequency increases.

The modeling challenge is that the ribbon operates in two different
modes at the same time: a radiating common mode with a velocity factor
of say 0.95; and a non-radiating "stub" mode with a VF of about 0.8. The
problem is to model both modes simultaneously, for the whole string of
stubs, without changing the physical dimensions of the real antenna. I'm
not sure if NEC can do this, but maybe Roy can comment?


--
73 from Ian GM3SEK
http://www.ifwtech.co.uk/g3sek

Antenna Theory
 

On Tue, 3 Oct 2006 08:43:07 +0100, Ian White GM3SEK
wrote:

The modeling challenge is that the ribbon operates in two different
modes at the same time: a radiating common mode with a velocity factor
of say 0.95; and a non-radiating "stub" mode with a VF of about 0.8.

Hi Ian,

This "two different modes" is the magic mode factor that has not been
designed into EZNEC.

One need only look at the Lattin designs that "work" to discover they
violate the precepts of "how" they work.

Then note those that "should" work result in those don't work.

The bottom line is fairly obvious, but there are those who can 'splain
how its done (see magic mode factor).

73's
Richard Clark, KB7QHC

Antenna Theory
 

In article , Ian White GM3SEK
wrote:

Google for "Lattin antenna". (Too many "lentils", Cecil :-)

One of the first hits is http://www.g3ycc.karoo.net/lattin.htm which
shows a good sketch. The antenna is made from sections of 300-ohm ribbon
or tubular feeder, configured as a string of quarter-wave stubs that
progressively make the dipole shorter as the frequency increases.

The modeling challenge is that the ribbon operates in two different
modes at the same time: a radiating common mode with a velocity factor
of say 0.95; and a non-radiating "stub" mode with a VF of about 0.8. The
problem is to model both modes simultaneously, for the whole string of
stubs, without changing the physical dimensions of the real antenna. I'm
not sure if NEC can do this, but maybe Roy can comment?

Hello, and Roy will probably want to weigh in here. What I can say is
that if you can create a wire model of the antenna consisting of
interconnected segments (ideally about 1/20 wavelength each) then NEC will
find the currents in each by considering all the interactions (conductive,
capacitive, inductive) between the segments. NEC doesn't care about the
geometry or "modes" of the antenna - it just sees a bunch of
interconnected segments distributed in 3-D space. There is no magic here
as NEC is merely applying text-book electromagnetic theory (you wouldn't
want to tackle this with just pencil and paper).

Once the individual segment currents are found (the time-consuming part)
It is relatively straight-forward for NEC to find the radiation pattern
shape, antenna gain and driving point(s) impedances. As with any
modelling program the trick is to make sure the wire segment model
adequately represents the actual/planned structure. Besides segment
length, there are a few other rules imposed by NEC that must also be
adhered to in order to obtain the correct results.

Roy is absolutely right in a previous post that an antenna vendor is most
likely blowing smoke by proclaiming that his/her antenna can't be modelled
by a method-of-moments program like NEC. (My favorite antenna "myth
busters" using NEC are Drs. John Belrose and Gerald Burke). Sincerely, and
73s from N4GGO,

John Wood (Code 5550) e-mail:
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375-5337

Antenna Theory
 

J. B. Wood wrote:
One of the first hits is http://www.g3ycc.karoo.net/lattin.htm which
shows a good sketch. The antenna is made from sections of 300-ohm ribbon
or tubular feeder, configured as a string of quarter-wave stubs that
progressively make the dipole shorter as the frequency increases.

The modeling challenge is that the ribbon operates in two different
modes at the same time: a radiating common mode with a velocity factor
of say 0.95; and a non-radiating "stub" mode with a VF of about 0.8. The
problem is to model both modes simultaneously, for the whole string of
stubs, without changing the physical dimensions of the real antenna. I'm
not sure if NEC can do this, but maybe Roy can comment?

Hello, and Roy will probably want to weigh in here. What I can say is
that if you can create a wire model of the antenna consisting of
interconnected segments (ideally about 1/20 wavelength each) then NEC
will find the currents in each by considering all the interactions
(conductive, capacitive, inductive) between the segments. NEC doesn't
care about the geometry or "modes" of the antenna - it just sees a
bunch of interconnected segments distributed in 3-D space. There is no
magic here as NEC is merely applying text-book electromagnetic theory

That isn't a complete model of this particular antenna. The missing part
is the velocity factor of the twin-lead when acting as a stub, which
means that the electrical length of the stub is different from the
physical length. Which of those two lengths would you use in the NEC
model?

The answer is easy for a single-band model; but it's not so easy to
create one NEC model that will be valid for all the bands this antenna
is designed to cover.


--
73 from Ian GM3SEK

http://www.ifwtech.co.uk/g3sek