wrote:
Hi Tom,

Well I don't know as much about antennas as I would like

I take your response to mean that you think only MoM can model a
"bugcatcher" coil accurately, and that you are dismissing the apparent
accuracy with which the Corum model predicts some coil performance
parameters?

I don't subscribe to the Corum-Moore "label". The genesis of the
transmission-line approach to coil analysis seems to go back a long
way from what I've read, and I don't think Cecil deserves or claims
any recognition for it. Besides the method might suddenly begin to
appear in all the text books - think how you'd feel then if it
included his name

Steve G3TXQ



On May 8, 10:44 pm, "Tom Donaly" wrote:
You know quite a bit about antennas, Steve, so you should know the
answer to the following:
1. Mathematically, what does MoM do?
2. Why would anyone use MoM if there were a set of symbolic equations
that would work just as well?
3. When are we going to see the Corum-Moore method in the textbooks?
73,
Tom Donaly, KA6RUH


Nothing would please me more than to see Cecil get his name as a
reference in some textbook. It would mean that there was a high
probability that he finally got it right, and that someone confirmed
his ideas experimentally. It would also give me a good laugh.

You know, you haven't shown that the Corum model accurately measures
the bugcatcher coil. You have stated - and I have no reason to
disbelieve you - that the Corum model agrees with EZNEC. If that's the
case, it's just as easy to use EZNEC, right or wrong. MoM is a method of
obtaining numerical solutions to integral equations. The only reason to
do that is if symbolic solutions are either too difficult or impossible
to puzzle out of those same integral equations. In other words, some
very deep thinkers decided that MoM would give results superior to
algebraic approximations and hand waving, so they applied it to antenna
analysis. I don't think it's perfect. It's certainly useful. If you
think Corum is good enough for your purposes, though, go for it.

You didn't answer my first two questions, above. That's o.k., they're
just something you should think about anyway. Besides, I didn't answer
yours concerning why we keep tearing the Corum-as-developed-by-Cecil
method down without offering an alternative. Perhaps there is no
alternative. Perhaps the best anyone can do is a numerical
approximation. Think about that.
73,
Tom Donaly, KA6RUH

Tom Ring wrote:
Art Unwin wrote:

Atta boy,
Keep using that slide rule from your school days, there is absolutely
no reason why you should change and update

Art

Your answers are just as wrong with a slide rule, an HP15C, Fortran IV
on a 360/65, C on a 64 bit AMD or anything else you can find.

And denigrating slide rules is silly. Most of the world that surrounds
you was calculated with a slide rule's resolution. When used properly
they give answers that are as accurate as is needed for engineering.

You obviously have no clue as to what it takes to do engineering
calculations.

Richard, if I used terms improperly, I ask forgiveness.

tom
K0TAR

There's no point in asking forgiveness from Richard. He's read _Through
the Looking Glass_:

"I don't know what you mean by 'glory,'" Alice said.
Humpty Dumpty smiled contemptuously. "Of course you
don't - till I tell you. I meant 'there's a nice knock-down
argument for you!'"
"But 'glory' doesn't mean 'a nice knock-down argument,'" Alice
objected.
"When I use a word," Humpty Dumpty said, in rather a scornful tone,
"it means just what I choose it to mean, neither more nor less."
"The question is," said Alice, "whether you _can_ make words mean
so many different things."
"The question is," said Humpty Dumpty, "which is to be master -- thats
all."

73,
Tom Donaly, KA6RUH

Tom,

I thought I'd quoted some numbers in the related "Dish reflector"
thread - apologies if I did not. Here are some mo

* I modelled a coil as a spiral in EZNEC (40T, diameter=6",
length=12", #14 copper wire)
* I added a 6ft "stinger" and found the frequency where the
combination was resonant: 3.79 MHz
* I checked the feedpoint impedance without the coil present: 0.46-
j2439
* That tells me the "lumped circuit equivalent" reactance of the coil
at 3.79 MHz is +j2439 ohms
* I found the frequency where the coil was resonant with no "stinger":
6.2 MHz

Now I look at what ON4AA's "Corum method" inductance calculator tells
me:

* "Lumped circuit equivalent" reactance at 3.79 MHz: +j2449
* Self-resonant frequency: 6.3 MHz

Unless I'm missing an option, if I want to predict the RF
characteristics of a "bugcatcher" it seems I have 3 choices:

* Use Wheeler's formula
* Build a helical model in EZNEC
* Use the Corum method

Wheeler's formula is inappropriate at frequencies close to a coil's
SRF.

EZNEC and the Corum method give very close results. The Corum formulas
are not difficult to use; even if they were, there is an on-line
calculator which removes the need for any maths. So it seems to me the
Corum formulas would be the more convenient tool to use, at least for
a "first look".

73,
Steve G3TXQ


On May 9, 7:06*am, "Tom Donaly" wrote:

You know, you haven't shown that the Corum model accurately measures
the bugcatcher coil. You have stated - and I have no reason to
disbelieve you - that the Corum model agrees with EZNEC. If that's the
case, it's just as easy to use EZNEC, right or wrong. MoM is a method of
obtaining numerical solutions to integral equations. The only reason to
do that is if symbolic solutions are either too difficult or impossible
to puzzle out of those same integral equations. In other words, some
very deep thinkers decided that MoM would give results superior to
algebraic approximations and hand waving, so they applied it to antenna
analysis. I don't think it's perfect. It's certainly useful. If you
think Corum is good enough for your purposes, though, go for it.

Tom Donaly wrote:
3. When are we going to see the Corum-Moore method in the textbooks?

"Transmission Lines and Networks", by Johnson
copyright 1950

"Fields and Waves in Modern Radio", Ramo and Whinnery,
Copyright 1944, 1953 - my fields and wave textbook
in ~1957 at Texas A&M.

The fundamentals of everything I have presented have
been in that textbook for 65 years and I'm sure it
was not the first textbook on the subject.

"Reflection and Transmission at a Discontinuity"

Equations for traveling waves vs standing waves

"Energy Theorems for Transmission Lines"

"The Idealized Helix and Other Slow-Wave Structures"

Separate forward and reflected Poynting vectors
whose ratio is rho^2

"Quarter-wave coating for Eliminating Reflections"

"Elimination of Reflections from Dielectric Slabs"

"Scattering and Transmission Coefficients"

"Directional Couplers"

Add "Antennas ..." by Kraus and Balanis
Add "Optics ..." by Hecht and Born and Wolf
Add "Traveling Wave Engineering", by Moore
Add "Reflections", by Walter Maxwell

One cannot blame one's ignorance on a lack of
textbooks.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

wrote:
... I don't think Cecil deserves or claims any recognition for it.

I've been accused of inventing theories while at the
same time being accused of quoting others too much.

All I have ever done is borrow some technical water
from the experts who came before me to use in wearing
away some of the mythical stones presented as technical
facts by the misinformed on this newsgroup and others.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Jim Kelley wrote:
I have no particular knowledge
or opinion on Cecil's EZNEC files, other than his rather odd take
standing wave current phase shift - whatever that is.

It's not my take, Jim, it is EZNEC's take. EZNEC
reports current on a standing-wave antenna that
closely matches the standing wave equations for
current whose phase cannot be used to measure
delay through a wire or through a loading coil.

Both w7el and w8ji used the current
on a standing wave antenna to measure phase shift
and predictably, there was negligible phase shift.
They erroneously attributed the lack of phase
shift with a lack of delay, i.e. they assumed the
proof - a well known logical fallacy.

There is no relationship between phase shift and
delay in the current on standing wave antennas
either through the wire or through a loading coil.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

On May 9, 7:48*am, Cecil Moore wrote:
Jim Kelley wrote:
I have no particular knowledge
or opinion on Cecil's EZNEC files, other than his rather odd take
standing wave current phase shift - whatever that is.

It's not my take, Jim, it is EZNEC's take. EZNEC
reports current on a standing-wave antenna that
closely matches the standing wave equations for
current whose phase cannot be used to measure
delay through a wire or through a loading coil.

Both w7el and w8ji used the current
on a standing wave antenna to measure phase shift
and predictably, there was negligible phase shift.
They erroneously attributed the lack of phase
shift with a lack of delay, i.e. they assumed the
proof - a well known logical fallacy.

There is no relationship between phase shift and
delay in the current on standing wave antennas
either through the wire or through a loading coil.
--
73, Cecil, IEEE, OOTC, *http://www.w5dxp.com

Cecil
I believe Steve has vindicated you in your struggle
so you should feel good. I would avoid the tactics if I were you when
attempts are made to reserect this debate.Corum are acknowledged
experts with respect to coils and tho not as absolute as Maxwells
equations one should feel confident with respect to their works so I
feel you have finally made your point.
Well done
Art

On May 9, 1:40*am, wrote:
Tom,

I thought I'd quoted some numbers in the related "Dish reflector"
thread - apologies if I did not. Here are some mo

* I modelled a coil as a spiral in EZNEC (40T, diameter=6",
length=12", #14 copper wire)
* I added a 6ft "stinger" and found the frequency where the
combination was resonant: 3.79 MHz
* I checked the feedpoint impedance without the coil present: 0.46-
j2439
* That tells me the "lumped circuit equivalent" reactance of the coil
at 3.79 MHz is +j2439 ohms
* I found the frequency where the coil was resonant with no "stinger":
6.2 MHz

Now I look at what ON4AA's "Corum method" inductance calculator tells
me:

* "Lumped circuit equivalent" reactance at 3.79 MHz: +j2449
* Self-resonant frequency: 6.3 MHz

Unless I'm missing an option, if I want to predict the RF
characteristics of a "bugcatcher" it seems I have *3 choices:

* Use Wheeler's formula
* Build a helical model in EZNEC
* Use the Corum method

Wheeler's formula is inappropriate at frequencies close to a coil's
SRF.

EZNEC and the Corum method give very close results. The Corum formulas
are not difficult to use; even if they were, there is an on-line
calculator which removes the need for any maths. So it seems to me the
Corum formulas would be the more convenient tool to use, at least for
a "first look".

73,
Steve G3TXQ

On May 9, 7:06*am, "Tom Donaly" wrote:



You know, you haven't shown that the Corum model accurately measures
the bugcatcher coil. You have stated - and I have no reason to
disbelieve you - that the Corum model agrees with EZNEC. If that's the
case, it's just as easy to use EZNEC, right or wrong. MoM is a method of
obtaining numerical solutions to integral equations. The only reason to
do that is if symbolic solutions are either too difficult or impossible
to puzzle out of those same integral equations. In other words, some
very deep thinkers decided that MoM would give results superior to
algebraic approximations and hand waving, so they applied it to antenna
analysis. I don't think it's perfect. It's certainly useful. If you
think Corum is good enough for your purposes, though, go for it.



Steve, this is fine for a base loading coil, but I'd suggest you try
your experiment with a loading coil well up the antenna, where the
coil is significantly larger diameter than the straight conductor in
which it's placed. The same size coil you described (though
presumably a different number of turns), placed at least half way up
something like a 15 or 20 foot long thin wire, should illustrate the
point. Is the EZNEC model then in such good agreement with placing a
reactive load at that point in the antenna, where the reactance is
from ON4AA's online calculator?

If I trusted NEC to handle large steps in conductor diameter
accurately, I'd suggest putting a segment in the antenna description
to represent the length and diameter of the coil, with the calculated
reactance placed as a load in that segment. As I understand it,
though, NEC has trouble with large diameter steps.

Cheers,
Tom

K7ITM wrote:
Steve, this is fine for a base loading coil, but I'd suggest you try
your experiment with a loading coil well up the antenna, where the
coil is significantly larger diameter than the straight conductor in
which it's placed. The same size coil you described (though
presumably a different number of turns), placed at least half way up
something like a 15 or 20 foot long thin wire, should illustrate the
point. Is the EZNEC model then in such good agreement with placing a
reactive load at that point in the antenna, where the reactance is
from ON4AA's online calculator?

The key to understanding this question and its logical
answer lies in the phase shift that occurs at impedance
discontinuities.

For a base-loading coil, there is only one impedance
discontinuity in the system, a hi-Z0 coil to a low-Z0
stinger. That single discontinuity provides a positive
phase shift at the '+' junction of the coil and stinger.

coil stinger
FP//////////+-------------------

When a straight shaft section is installed under the
coil, it introduces one additional impedance discontinuity
at 'x' in addition to the '+' top of coil to stinger
discontinuity.

base coil stinger
FP-------x////////////+---------

Because the impedance discontinuity between the base
section is a low-Z0 to hi-Z0 transition, the phase shift
is negative, i.e. the antenna *loses electrical degrees*
at that junction.

Therefore, more turns must be added to the inductor
to supply the number of negative degrees lost at the
base section to coil impedance discontinuity.

This might best be illustrated with pieces of transmission
line. Please reference my web page at:

http://www.w5dxp.com/shrtstub.htm

The following concepts apply to the above antennas but
may be easier to understand using transmission lines.

Here is a dual-Z0 stub that is physically 44.4 degrees
long but is 90 degrees (1/4WL) long electrically, i.e.
it is functionally a 1/4WL open-circuit stub.

---22.2 deg 300 ohm line---+---22.2 deg 50 ohm line---

The Z0=300 ohm to Z0=50 ohm transition provides for
+45.6 degrees of phase shift. This is akin to the base-
loaded antenna above.

Here is a dual-Z0 stub with 11.1 degrees (half) of
the 50 ohm line moved to the left. (The words are
abbreviated because of space on the line.)

--11.1 deg 50--+--22.2 deg 300--+--11.1 deg 50--

Who can tell me how long electrically is this stub
using the identical feedlines from the above example?

This reconfigured stub with half of the 50 ohm feedline
moved to the bottom is now electrically only ~80.6 degrees
long. What has happened? The new impedance discontinuity
from the base section at the bottom of the coil has cost
us electrical degrees by providing a *negative phase shift*.

How do we solve the problem? Add some length (degrees) to
the Z0=300 ohm section. If we make the 300 ohm section
38.5 degrees long, the stub will be electrically 90 degrees
long once again.

This is conceptually the same problem we encounter when
we move the loading coil from the base location to the
center location. When we move the coil up the shaft, we
introduce a negative phase shift at the bottom of the
coil. Therefore, we must increase the number of turns
to make the loading coil electrically longer.

Incidentally, w8ji knows about the coil to stinger
positive phase shift and describes it on his web page.
He apparently doesn't know about the opposite negative
phase shift at the bottom of the coil where the shaft
attaches.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Cecil Moore wrote:
"One cannot blame one`s ignorance on a lack of textbooks."

True. The most reliable in my opinion is Terman`s 1955 opus "Electronic
and Radio Engineering".

Terman agrees with Cecil.

On page 854 Terman writes:
"The laws governing such radiation are obtained by using Maxwell`s
equations to express the fields associated with the wire; when this is
done there is found to be a component, termed the radiation field,
having a strength that varies inversely with distance."

Terman then gives the formula for the electric field strength in terms
of distance from the elementary doublets in the wire that make up the
antennna to a distant observing point P, and angle of the direction of
point P with respect to a plane perpendicular to the axis of the
elementary doublet. The strength of the radiated field is distributed in
space in accordance with the doughnut pattern for a thin wire which is
short compared with wavelength and has a figure-of-8 cross section.
Illustrations are provided on page 865. On page 866 Terman illustrates
current distribution on an antenna open circuited at both ends and made
up of elementary doublets. On page 867 Terman says:
"A wire antenna is a circuit with distributed constants; hence the
current distribution in a wire antenna that results from the application
of a localized voltage follows the principles discussed in Chap. 4
(Transmission Lines), and depends upon the antenna length, measured in
wavelengths; the terminations at the ends of the antenna wire; and the
losses in the system. The current distribution is also affected by the
ratio of the wire length to diameter in situations where the wire is
unusually thick. Under most circumstances the losses are sufficiently
low and the ratio of wire length to diameter sufficiently great so that
to a first approximation very closely the current distribution can be
taken as that for a line with zero losses; it then has the
characteristics discussed in 4-5.

Best regards, Richard Harrison. KB5WZI