Roy Lewallen wrote:
I haven't had the time to participate in this, but in a brief look, it
looks pretty silly. Of course EZNEC shows no current difference across a
load. The EZNEC model of a load has zero length, so the current at both
terminals has to be the same.

It appears that EZNEC also doesn't account for phase shifts across
a zero length coil.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Cecil Moore wrote in message ...
Mark Keith wrote:
As far as the reverse currents Cecil mentions, I'd have to ponder that
a while.

While you are pondering, here is a quote from _Antenna_Theory_, by Balanis.

"Standing wave antennas, such as the dipole, can be analyzed as traveling
wave antennas with waves propagating in opposite directions (forward and
backward) and represented by traveling wave currents 'If' and 'Ib' in
Figure 10.1(a)."

Standing wave antennas necessarily have standing waves caused by forward
waves and reflected waves. Analyze any coil subjected to forward current
and reflected current and you will be forced to agree that the current
at one end of the coil is not the same as the current at the other end
of the coil. W8JI is thinking lumped circuits when he should be thinking
distributed networks. The phase shift through the coil changes the
phase relationship between the forward current and reflected current, so
of course, their superposed value will be different at each end of the coil.

How much though? What would be an average ratio difference you would
be likely to see on a 8 ft center loaded whip? Or lets go one
better...What would be a likely "worse case" scenario? Will this vary
from antenna to antenna? I would think so. I've never said there would
not be a difference. I actually expect a small difference. But I still
don't think it would be a large amount. Will this change in value be
enough to cause large errors in modeling these antennas? It's already
obvious to me that any info I may gleen from these tests will have no
impact on the position of my loading coils, being I already use them
at the optimum heights. Or as close as physically possible anyway. So
any info gleaned from these tests would only be useful from a modeling
aspect. And I'm not in a position to really comment on that too much.
I don't design modeling engines. Is it your opinion that the modeling
we now see with these antennas and coils is quite flawed? It's obvious
Yuri seems to think so. Myself, I really don't know at this point.
I've never worried about it too much. I don't model shorter than 1/4
wave verticals. MK

I haven't had the time to participate in this, but in a brief look, it
looks pretty silly. Of course EZNEC shows no current difference across a
load. The EZNEC model of a load has zero length, so the current at both
terminals has to be the same. You will see a current change over the
length of a model of a conductor, because it does have length. The coil
in the web site pictures certainly has length, so why should you be
surprised to find a current change over its length?

W8JI used it as a "proof" that current in the loading coil is virtually the
same at both ends. We were not surprised, but W8JI was insisting that it is,
used Eznec to prove it (go see his web site) and ridiculed us.

Did the experimenter
perhaps do the same test with the meters placed the same distance apart
with just a conductor in between? Would there be some great revelation
in finding that the current was different at the two points?

Not to us, but see W8JI arguments speculating and "knowing" that current must
be the same.

I was intrigued by the claim that a toroid measured significantly
different from one end to the other. I wonder if the tester tried
reversing the meters to verify that he got the same reading in both
cases. If he did, I'd be interested in learning more details.

I believe he did use the same method, and W9UCW can answer that. Looks like you
are also not getting the main point of the argument. Appears that the rule is:
"loading inductance (whatever form) inserted in the radiating element exhibits
current magnitudes at its ends corresponding to the current in the length of
radiator in electrical degrees that it replaces." Replacing inductance with
piece of wire won't do the simulation, it has to have properties of inductor
(replacing radiator's segment in degrees, inductance). Toroid, loading stub,
and lumped inductors do the same thing.

Unfortunately, the main objective of the web site seems to be to insult
Tom, W8JI, rather than to be objective. So in my mind that leaves the
possibility open that the experimenter is more interested in finding
evidence that would disprove Tom than in presenting carefully measured
and objective data.

Not so, first I posted on eHam.net fact that current is different at the ends
of loading coil. To which W8JI rode in with his "answers" and ridiculed me in
public (I don't know the laws, didn't read the books, etc.) to which I
responded in kind, provided proof and defended my (and others) position.
Because this has happened about fifth time (he did it to others too) I simply
will not take the crap and bite back. He is parading as a knowitall guru and
pontificating with sometimes erroneous information. If anyone questions or
challenges that, he does his routine. If you read the trail from the start you
would get the picture. If he discussed the matters in a civil manner, there
would be no problem, we can exchange arguments, learn something and mainly give
a credit where is due. That's what professionals do. He first argues wrong,
then goes away for a while and then emerges with change as a guru or inventor.
That does not give hams good name and is poor example for those no-coders
coming into ham radio.
From the past postings, you could probably see that I can discuss the subjects
in a civil manner, but when someone who is wrong starts pulling out smart ass
remarks and ridicule, the gloves are off and I will defend the truth to the
end. It is not just proving Tom wrong, it is to set the record straight, to
bring aspect of antenna engineering to light (after 50 years of perpetuation of
wrong in some antenna books), to alert software designers to the problem so
they can accommodate the proper procedure or workarounds. I hope you can see
how inaccurate results will EZnec produce if you simply inserted 0 size
inductors in elements of 3 el. 80m shortened parasitic beam. Magnitudes and
current distribution will be off, producing skewed results. Optimizing programs
will be chasing wrong tail.

Again, I apologize for the tone, but I will not give in to the bully. If he
doesn't learn and shape up, I will be at his case, pointing out the wrongs that
he is disseminating (he has some more on his web site).

We were hoping that you were around, following the discussions, helping to
point where we are wrong, suggest workarounds or proper procedure for modeling
and we are willing to help with testing and verifications. Cecil brought some
insight from the theoretical side, I (and W9UCW?) can do measurements and all
this can bring greater understanding of the phenomena, rather than propagating
misconceptions and wrong ideas.
I found a lot more help and expertise on this NG than on eHam.net no-code flat
earth society, for which I am grateful.

Can we now look at the modeling problems? Seems that Cecil's way of
substituting the lumped inductance with loading stubs allows closer
approximation of configuration for the modeling programs. But this can still
distort the true picture. I would like to point out, that W6?? replaced loading
stubs in 3 el. 80m KLM beam with coils and the performance of the beam,
especially pattern improved tremendously. So it looks like loading wires and
radiation from them (folded along the element) upset the current distribution
and resulting deterioration of performance. (So much for nice, low loss
loading.) This was done, tested, measured and verified, no speculations. Is
there better way of modeling the case, can we use cosine of degree of
electrical length of wire that coil replaces?

Roy Lewallen, W7EL

Yuri, K3BU

On Sun, 02 Nov 2003 03:44:03 -0800, Roy Lewallen
wrote:

|I haven't had the time to participate in this, but in a brief look, it
|looks pretty silly. Of course EZNEC shows no current difference across a
|load. The EZNEC model of a load has zero length, so the current at both
|terminals has to be the same. You will see a current change over the
|length of a model of a conductor, because it does have length. The coil
|in the web site pictures certainly has length, so why should you be
|surprised to find a current change over its length? Did the experimenter
|perhaps do the same test with the meters placed the same distance apart
|with just a conductor in between? Would there be some great revelation
|in finding that the current was different at the two points?

I too have been lurking and while I didn't spend any time reading the
eham stuff what was going on here got me looking at a model of this
situation.

I used MultiNEC to invoke EZNEC for all calculations. I modeled a
shorter-than-quarter-wavelength vertical, loaded with an inductor, all
of this over perfect ground. Using MultiNEC, I used equations to
change the length of the radiator, the position of the inductor, keep
the segment length as short as guidelines allow and resonate the
result after each change.

Nothing I did solved this argument but I did make a couple of slightly
related observations. Unless I'm mistaken (always a distinct
possibility):

1) When the radiator is electrically very short and near resonant the
current does not follow the classic patterns shown in most of the ham
literature, i.e. nearly constant below the inductor and close to a
straight line taper above. The current actually peaks at the inductor;
in other words, the highest current point on the structure is at the
inductor.

Hanson's paper (Robert C. Hanson, "Optimum Inductive Loading of Short
Whip Antennas", IEEE Transactions On Vehicular Technology, Vol VT-24,
No. 2, May 1975, pp 21-29) shows this, although his graphs show a
steady decrease in current from the feedpoint to where the peaking
begins. I did not see that, but instead a steadly increasing current
from the feedpoint to the current peak.

Not only that, the peaking is almost independent of inductor Q.
"Almost" meaning that my model shows that the current is actually
slightly higher in a lower Q inductor.

2) The structure Q, defined as the change in reactance with respect
to frequency, is independent of inductor Q.

3) For a give length radiator, gain is unaffected by where the
inductor is located along the length of the radiator and by inductor
Q.

If 3 is correct then I can remove the inductor from the radiator
without effecting the gain and place it before the feedpoint to
resonate the structure. Once out of the radiator, the current through
the inductor is constant. Just like it is in the antenna if it has
zero length.

By now you're all saying, "Huh?" But remember, this is for an antenna
over perfect (zero loss) ground.

So instead of worrying about perfecting our antennas, we should be
trying to perfect ground and/or zero length loading coils.

|
|I was intrigued by the claim that a toroid measured significantly
|different from one end to the other. I wonder if the tester tried
|reversing the meters to verify that he got the same reading in both
|cases. If he did, I'd be interested in learning more details.

Considering that *anything* inserted in the structure upsets the
current distribution, as Roy says above, why wouldn't the answer be
different. Even the toroid, or the distance between the insertion
points, have *some* length.
|
|Unfortunately, the main objective of the web site seems to be to insult
|Tom, W8JI, rather than to be objective. So in my mind that leaves the
|possibility open that the experimenter is more interested in finding
|evidence that would disprove Tom than in presenting carefully measured
|and objective data.

Eureka!


Wes Stewart N7WS

Mike,
the differences in current are in order of 40 - 60%, that is significant.
The lower the band, the shorter the antenna, the bigger the effect, the more
important where the coil is. It will vary from antenna to antenna, depending on
the coil "shortening" factor. If the coil is closer to the feedpoint, the
current difference is lees, but efficiency suffers most. As you move coil up
the radiator, turns increase, current difference increases and effciency goes
up. If you replace (part of) coil with top loading, current differences
decrease (0 difference at 0 deg. long coil) and your efficiency goes up.
Efficiency or radiated power of loaded antenna is roughly proportional to the
area under the corresponding current curve of the remaining (straight)
radiator. Coil "eats" part of the radiator and its current carrying (radiating)
capabilities, this is why the current will be significantly different at the
ends of the coil. I hope this illustrates the situation?

As Cecil showed, modeling is not accounting for the effect and now that Roy is
on, we hope to sort things out and come up with ways to best implement the
phenomena in modeling programs. Right now, it appears that the best way to
approximate the effect is to use loading stubs of the same inductance as
intended coil.

Barry and Cecil agreed to cooperate on the article describing in detail (and in
civil manner :-) this subject and we hope that Roy will join us adding the
modeling aspect to it.

Yuri, K3BU/m

NM5K:

NO , I didn't see the pictures. Like I said, they didn't load on that
site. All the pix load except his.


Then you are missing a lot.
I don't know what the problem with eHam.net site is, I uploaded all the
pictures the same way, some showed, some not. This is why I posted link to my
page
http://www.k3bu.us/loadingcoils.htm
which has the pictures, also RIGHT drawings from ON4UN book, latest modeling of
W5DXP stub loaded G5RV and some selected comments explaining the phenomena.
Check it out.

Again, put on the fricken Hustler 80m resonator, feed it 100W and feel it!
No meters, no hokus pokus, just "naked" antenna.

What would that mean? The hustler coil is known to be flawed, and
makes a poor coil to be tested in this manner. The effects of it's
metal end caps, and overall design problems are fairly well known. I
refuse to use such a lousy coil. You can feed my homebrew coil 100w
all day long, and you won't feel anything except the finger on the
mike button hand start to go numb from holding the key down.


Another "very well known fact" from W8JI's teachings? Metal caps are at both
ends, top would feel the same then, it doesn't. Hustler coil is "lousy" because
uses aluminum wire to achieve "match" through some loss and that is additional
loss. But from the point of view as inductor, it is uniformly wound solenoid,
same wire and diameter, so according to I2R law, the heat developed in it is
proportional to the square of current. If there is more heat at the bottom,
then irrefutably there is more current flowing at the bottom.

Here is the shocker:
When W9UCW bunch was measuring various coils, they also compared that perfect
coil as you and I have (heavy wire, proper form factor, good connections) to
"lousy" Webster Banspanner sliding coil (aka cheap screwdriver) they found
negligible difference in measured signal strength. They rechecked everything
scratched their heads, but that was it. So another myth about the quality of
coil (resistance of course applies, but is minuscule) importance. Now when we
look at it from the point of view of effect of the coil on the efficiency of
antenna, it is explanatory. Coil replaces portion of radiator that is not there
anymore, so the significance of its quality is not as important as the position
of the coil on the radiator (area under current curve). Of course the ohmic
losses are a factor, but that is minuscule (ohms or two) versus reduction in
current flowing in remaining radiator. I like and have big fat coils, but looks
like they can be optimized better, perhaps heavier wire in first few turns,
slimmer construction, less wind load, but placed higher up on the mast. So
there is another one you don't have to believe, I sure was surprised.
Measure it!!!


Yep, it sure is. I sure as hell won't have anything shoved down my
throat. I'm sorry, but you all haven't convinced me yet that your
measurements are any more accurate than the one I quoted on that same
web page. And the one I quoted did give a fairly good description of
how he went about it. The guy I quoted said he saw constant current
across the coil. How do you explain that? Should I automatically
dismiss his findings just because you all have a web page and a bunch
of pictures? How do I know who did the more accurate test? I DON'T!!!

I am not a salesman, I will not try to convince you of anything. I can
elaborate and answer some questions and it is up to you to believe it or not.
You can believe engineers with education, their experience and results, or you
can believe some "technical impostor" as K7GCO phrased it.

You could see almost constant current across the coil if the coil is at the
base of quarter wave radiator, has heavy windings and is replacing relatively
short electrical length of the radiator. Did he mention what coil, where was
the coil placed? We have methods and pictures of W9UCW tests on various bands
at different positions, we have yet to get objections or pointed out errors in
his setup. We don't know much about the other one. W8JI said that he measured
thousands of loading coils, modeled them and found no difference. He is
obviously lying. He has yet to tell us about ONE measurement I asked him to do.
You believe what you want. As I mentioned we will write concise article on the
subject and you can take it from there or stick with Rauchians.

I sure enjoyed this exercise, learned from it a thing or two and I am looking
forward to implement some of the stuff (measure it too) in the design of new
loaded mobile and low band antennas. As they say on FreeRepublic.com, this is
series and hugh :-)

Yuri, K3BU

N7WS:

I used MultiNEC to invoke EZNEC for all calculations. I modeled a
shorter-than-quarter-wavelength vertical, loaded with an inductor, all
of this over perfect ground.

How did you model inductor, as physical zero length inductance?
Did you try substituting (coil) inductor with equal inductance loading stub?
Did you try one of the situations (band, antenna/coil size) that W9UCW
describes in his measurements?
He used almost "perfect" ground of 60 radials for measurement. Results will be
offest by some amount due to varying ground conditions (at very low angles),
but in the same way and this is not the subject of the argument.

The current actually peaks at the inductor;
in other words, the highest current point on the structure is at the
inductor.

That's what W8JI calculated in EZnec, does it make sense? Like 2+2 is 4.5? Why
would inductor "suck" the current up? We should then use "those" inductors to
suck the current all the way to the top of the whip - perfect antenna?
Cecil, can you 'splain that?

3) For a give length radiator, gain is unaffected by where the
inductor is located along the length of the radiator and by inductor
Q.

(If the inductor is zero length?)
This should be huge screaming flag that there is something drastically wrong
with your whole approach. Look at any mobile shootout results and you will see
10 - 20 dB differences, ask Cecil, he wittnessed them.

Looks like we exhausted reasoning, facts, measurements, found what we wanted,
unless there is breakthrough in capturing the effect in modeling software we
are at the end of the rope.
Yea, Eureka!
Thanks!

Yuri, K3BU/m

Mark Keith wrote:
The guy I quoted said he saw constant current
across the coil. How do you explain that?

Constant current across the coil is one of the possiblities.
Increasing current across the coil is one of the possibilities.
Decreasing current across the coil is one of the possibilities.
It all depends upon where the coil is inserted in the antenna.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----