"Roy Lewallen" wrote in message
...
Yuri Blanarovich wrote:

Oooops, carefull here.
As far as I know, nobody has claimed that inserted loading coil replaces
the "missing" degrees of the radiator in terms of providing magical
properties that would look like that "replaced" portion of the antenna,
or make the antenna act like 90 degree full size physical radiator.

Agreed, it's not quite stated as such. Here are some statements which were
made:

From your web page http://www.k3bu.us/loadingcoils.htm, in bold type:

"In summary:
The current in a typical loading coil in the shortened antennas drops
across the coil roughly corresponding to the segment of the radiator it
replaces."

By Cecil, on March 5, on this newsgroup:

"A loading coil thread is climaxing over on qrz.com. I have
used EZNEC to generate a graphic which shows a 3/4WL vertical
and a similar 1/2WL vertical with a ~1/4WL loading coil. The
loading coil is a wire helical coil containing (surprise)
roughly 1/4WL of wire. The coil does a good (not perfect)
job of replacing 1/4WL of wire. Many things can be gathered
from observation of the current reported by EZNEC for the
two antennas. The coil occupies roughly the same number
of degrees of the antenna as the wire it replaces. The
current at the top and bottom of the coil is roughly the
same as the current at the two ends of the wire it replaces.
Is the coil an exact replacement? Of course not."

What we are saying that the loading coil appears to replace "missing"
electrical degrees of the radiator in order to make it resonant, that is
back to 90 electrical degrees (has to be in order to resonant), which
rest of the existing "straight" radiator forces it to do (+/-).

It's getting muddier and muddier just what you mean by "replace". Nobody
has questioned that a loading coil makes the antenna resonant; that's its
purpose. But that's simply an impedance transformation property which can
be accomplished well away from the antenna by many different methods.


Roy,
the above are the attempts to illustrate and add some more to understanding
and reasoning why the current across (alonng) the loading coil, roughly half
way or 2/3 up the resonant quarter wave radiator is larger at the bottom and
drops about 40 - 60% at the top. While one side argues that it is (almost)
the same, we argue that it drops. That is the argument and not detours to
degrees, phasors, and rest of the mud that was rehashed here.

Radiation properties and efficiency of the loaded antenna is proportional
to the area under the current curve. It is obvious to anyone comparing
the area under the current curve of full size quarter wave radiator vs.
loaded radiator that there is huge difference in area under the curve and
performance, efficiency, which is known and been verified by numerous
measurements.
HOW the current curve is modified by different loadings and position
along the radiator is important in knowing how the current distribution
curve along the radiator is modified.

I agree with all this. I'm glad you've clarified this for the benefit of
posters like the one to whom my recent posting was directed.

The whole controversy is that "gurus" claim current doesn't drop across
the coil, while we say that it does, therefore making the area under
current curve above the coil smaller and effciency of loaded antenna
worse than they believe and insist on.

I don't think you'll have any trouble winning your arguments against your
imaginary "gurus", whomever and whatever they might be. Over two years ago
I made careful measurements which showed a current difference between the
top and bottom of a loading coil. Cecil posted an EZNEC model on his web
site showing a substantial difference. I've commented on it several times,
explaining the reason for the difference, and modifying the model to
illustrate the explanation.

If I remember correctly you inserted the coil at the base and I am not sure
if it was resonant quarter wave radiator. Can you describe the setup, length
and frequencies used? You should try to use quarter wave resonant radiator
with coil about 1/2 to 2/3 up the mast and tell us what the current values
are. W9UCW has pictures and data measured, we should try to emulate this
situation, that is the object of controversy. Cecil mentioned cases when
current can be the same, or lower at the top, or bottom, depending where the
same coil is placed in relation to the standing wave and current
distribution on the radiator. Are you denying that this is the case or
something wrong with W9UCW test setup and results?

The controversy is in the explanation of the difference. It simply doesn't
require Cecil's theories. I've never been able to tell exactly what your
theory is, if you indeed have one.


The controversy is about the claims that the current at the ends of the
typical loading coil is the same or different in range of 40 -60% drop. Its
not my theory, it is the reality that we are trying to bring forth and
correct misconceptions that are obviously floating around since 1953. My
approximation and explanation (latest) I mentioned is in one of my posts in
reply to W8JI "arguments" (to do with impedances).

Again, when applied in modeling programs, wrong assumption will produce
erroneous results, which will be magnified in multielement antenna
designs.
So the "gurus" basically ignore behavior of coil in the standing wave
environment along the loaded radiator, where the current drops from max
at base to zero at the tip, but coil would magicaly resist that, because,
bla, bla, bla.... (see their "reasons")

Would you name these "gurus" so we can read their postings and see what
you're talking about?

Mostly the "equal current camp".

So while everyone knows (?) that standing wave current drops acros
(along) the wire (all the antenna books show that), but it is
"impossible" to drop along the coiled wire (real inductance - coil,
loading stub). Reality and measurments prove that, but according to them
"it can't be so".

I am already gathering necessary hardware to do more experiments,
measurements to show what is really happening, and will prepare articles
how to model and apply it to antenna design.
I would challenge the "unbelievers" to join me and repeat the tests, to
see wasaaaap.

You'll be surprised when everyone agrees that there's a current difference
between the top and bottom of the coil. Unless your "gurus" show up,
whomever they are.

I've already made a test and posted the results, over a year ago. When it
failed to show a current difference anywhere near the number of degrees it
"replaced", your complaint was that I was using an inductor which was too
small physically. So obviously your theory works only on certain size
inductors. Once you or Cecil has the theory fully worked out, it should be
able to not only tell us what the current difference between top and
bottom should be, but also how physically large an inductor must be before
the theory works. And why it doesn't work for physically small inductors.

I have not verified it, but W9UCW claims using ferite inductor and got very
similar results. I believe your test, you used coil near the base. I will
run test with different inductors from bugcatcher type, "no good" Hustler,
to ferite and in different positions.

Those of us stuck with old fashioned conventional theory can explain the
drop for small as well as large coils, so you folks have a bit of catching
up to do.

Looks like the size of the coil has small effect on current variation
(unless high resistance). Position of the coil in relation to current
distribution along the radiator would cause equal (special case), less on
the top of coil or more, depending where on the standing wave curve coils is
located. In our case we are arguing about 2/3 up the resonant radiator.

I think a lot of the experimental work can be done by modeling. I'd be
interested in hearing of any cases where measured results differ
significantly from EZNEC results. Incidentally, your web page is a bit
outdated in that respect, apparently being written before EZNEC v. 4.0 was
available with its automated helix creation feature.

Now with solenoid generation in EZNEC 4.0 it helps to get away from the
lumped inductance and it shows that there is current drop, reflecting
situations in question. Also the loading stub produces similar results.
Cecil showed the cases and with different positions along the current curve,
demonstrated in EZNEC huge differences in current at the ends of the coil.
But this is getting strangely ignored and instead we get all kinds of
"reasons" why it can't be.
I am sorry I dropped out of this due to AOL dropping NG, and I thought that
reality would be understood by now. Only when Cecil told me that subject
flared up again and nothing changed, I rejoined the discussions. I think
really at this point, it is beating the dead horse. I will do the tests and
write it up. I will try to corellate the tests with modeling in EZNEC. If
someone denies the reality, that's their choice. I will post the progress on
my web page.
I can't stomach W8JI "exchanges" any more. No answer to questions or
following the points, just twist and jive.

Roy Lewallen, W7EL

I didn't look it up, but is there way in EZNEC to know or calculate the
inductance of modeled solenoid? Or better, specify the inductance and let
the EZNEC "make" the coil of prescribed diameter and TPI?

73, Yuri Blanarovich, K3BU