Yuri Blanarovich wrote:

W5DXP wrote:
There is forward current flowing into the bottom of the coil and out
the top. There is reflected current flowing into the top of the coil
and out the bottom. The net current is a standing current wave.

In view of the above, for practical putposes, trying to get maximum performance
out of the loaded radiator, it should be beneficial to have the same diameter
of whip above the coil, rather than tapering whip?

That doesn't help much. What helps is a humongous top hat which does
help to equalize the current at the bottom of the coil and the current
at the top of the coil.

One might deduct that if the current is diminishing towards the top, that the
diameter of the radiator (RF resistance) could be tapered also. But since the
RF current has to flow to the tip and then reflect and go back and interfere
with itself, we should make it uniform, where possible.
We are probably talking about fraction of a peanut, but for the purists and
sake of argument.

Nope, not a fraction of a peanut at all - more like 100% more radiated
power because of that humongous top hat. I'm considering a humongous top
hat for my pickup that runs the length of the truck and is mounted about
a foot above the cab - maybe 50 square feet in all. That would minimize
the size of the loading coil and ensure maximum current in the bottom
section. The maximum height above ground would be about seven feet, a
definite advantage for a mobile antenna around here.
--
73, Cecil http://www.qsl.net/w5dxp


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In view of the above, for practical putposes, trying to get maximum
performance
out of the loaded radiator, it should be beneficial to have the same
diameter
of whip above the coil, rather than tapering whip?

That doesn't help much. What helps is a humongous top hat which does
help to equalize the current at the bottom of the coil and the current
at the top of the coil.

I know about the effect of hat, but I am refering to straight whip loaded
radiator and whip above the coil only. Forget the hats and ties.

Again:
One might deduct that if the current is diminishing towards the top, that
the
diameter of the radiator (RF resistance) could be tapered also. But since
the
RF current has to flow to the tip and then reflect and go back and interfere
with itself, we should make it uniform, where possible. (?)

Yuri

Thanks for your comments Reg. The fact is my graph is produced in Excel
from data provided by a NEC 2 output file generated by few trivial lines of
NEC code. I cannot claim to have done anything requiring much thought. I
just considered, since so much discussion is centered on current
distribution, that some might be interested in the posted curves. So far
yours is the only response. I will probably delete the page in a day or so.
The loading inductor is 2.5" diameter, 6" long, with turns spaced at 0.5".
The NEC code is listed on the site, so anybody can copy to verify the
validity of my results -- or the validity of the code.

I have included a conductivity for copper (5.8001E7 S/m), and since the
ground is defined as perfect, this accounts for all losses within the model.
The program predicts the total radiated power as 95.918 W from 100 W input.
The input current is 2.3874 A RMS, and input impedance 17.545 Ohms. The
radiation resistance is therefore 16.829 Ohms. (Sorry for all the decimal
places, but they produce such nice round numbers). I was also puzzled by
the slight increase in current just under the loading coil, but suspect it
was caused by coupling between the lower conductor and the base of the coil.

I agree that some experimental data would be good. I have been planning for
some time to erect a 160 m vertical, so can see how the predicted results
compare. I have also used your software for modeling verticals, and it is
in very close to the results produced by NEC. The one problem with NEC 2
(Though not with NEC 4) is that it cannot model buried radials, but can get
very close to the ground.

I don't mind an occasional post on this news group, but not sure I can
contribute much. I do enjoy reading other people's posts though.

I sure could enjoy a glass of wine with cheese, but have nothing much in my
fridge -- except for some old Cheddar.

Regards,

Frank


"Reg Edwards" wrote in message
...

"Frank" wrote
As posted in a previous thread go to www.carolyns-creations.com/ve6cb to
view the (modeled) current distribution on an 84" monopole at 21.3 MHz.

====================================

Frank, I don't know, and it doesn't matter, how you produced the amperes
versus height graph which beautifully displayed itself with a single
mouse-click on my computer screen.

It displays the curve-shape which any properly educated electrical
engineer,
or amateur with any intuitive common sense, ought to expect. Thanks!

The many reams of heated arguments which have appeared on this newsgroup
have been a disgrace to the profession. Yes, I know its an amateur
mewsgroup
but the (aggressive?) contestents are mostly so-called professionals.

Clearly you have chosen an adequate mathematical demonstration model with
the ability to use it. Most likely without any thoughts about Terman or
theorem-writers Thevenin and Kirchoff, etc., who personally I have hardly
ever heard of.

If you have not already done so, may I suggest you include radiation
resistance in the model for slightly greater accuracy. It may remove the
small kink in your curve which occurs immediately at the bottom end of the
coil. I don't think it should be there. But further elaboration is hardly
worth the effort.

I also think its a good idea to base demonstration models (like actual
experimental measurements) on the lower frequencies. Try the 160 metre
band.
They are likely to be more accurate representations.

Frank, if you have the time to spare perhaps you should contribute to this
newsgroup more often. Improve its already good entertainment, even
educational if sometimes confusing, value!

By the way, I'm on Dourthe No.1, Bordeaux 2001, tonight. French politics
go
down very well with their excellent wine and British very mature Cheddar
cheese.

Hic!
----
Reg, G4FGQ

According to his website, he is still alive.

Randy

Frank wrote -
I have also used your software for modeling verticals, and it is
in very close to the results produced by NEC. The one problem with NEC 2
(Though not with NEC 4) is that it cannot model buried radials, but can
get
very close to the ground.

================================

The only program I am reasonably familiar with is the several years old free
EZNEC. I don't know whether it has been updated or not and I make very
little use of it. Come to think of it, I don't make much use of my own
programs either.

Regarding shallow buried radials in conjunction with a vertical, have you
tried my recent program RADIALS2 ?

It is intended to demonstrate performance of the radials themselves in a
given ground rather than antenna performance. Which I suspect is the reverse
of NEC-4.

As you probably know, the effects of above-ground radials change very
rapidly as they get within a few inches of the ground surface. But once in
the ground they tend to remain static.

RADIALS2 uses an entirely different, unconventional form of performance
analysis. If other programs don't take soil permittivity into account at HF,
predictions must lose accuracy. Are the inputs and outputs of NEC-4 in a
form suitable for a direct comparison with my simple program?

But in view of the large uncertainties involving ground conditions, accuracy
is not worth making much of a song and dance about.
----
Reg, G4FGQ

"Frank" wrote -
I cannot claim to have done anything requiring much thought. I
just considered, since so much discussion is centered on current
distribution, that some might be interested in the posted curves. So far
yours is the only response.

==================================

That's because your graph embarasses that half of the contestants who insist
the coil's input and output currents are identical and so the less said
about it the better.

And it gratifies the exhausted sentiments of the other half who are
unwilling to grant you the credit for providing the convincing evidence
after all the hard work they have put into stating the bleeding obvious. And
still are.

(After John Cleese who joked about the value of the distinction of a
first-class university honours degree in stating the bleeding obvious.)

Neither was there was any response to my brief statement of 4 Facts except
yours. And for similar reasons. I did not expect any response. But after
all, any unsupported statement of mine (no Terman, no Kirchoff, no Kraus, no
Thevenin, no Balony) can hardly be construed as evidence of anything.

smileysmiley

----
Reg, G4FGQ

Frank wrote:
So far yours is the only response.

Hi Frank, your results look reasonable and thanks for your input.

I was also puzzled by
the slight increase in current just under the loading coil, but suspect it
was caused by coupling between the lower conductor and the base of the coil.

A number of us have reported the same thing. In my EZNEC octcoil.ez simulation,
(available from my web page below) the net current decreased by 2% from the feedpoint
to the coil and then in the first part of the bottom of the coil, it increased by 5%.
(Whoops, I almost said it "dropped" by 2% and "rose" by 5% which would have elicited
endless nitpicking. :-)

There is, no doubt, an impedance discontinuity at each end of the coil. The
net current standing-wave values at each end of the coil that differ from just
a straight wire are probably due to interference effects among the various
forward and reflected wave components. A conceptual idea of what is happening
might be the following solvable example (S-parameter analysis).

a1-- | --a2
--b1 | b2--

-----Z1-----+-----Z2-----+-----Z3-----open

bottom coil top
wire wire

The Z1 to Z2 impedance discontinuity will cause reflections in both directions.

b1 = s11*a1 + s12*a2 b2 = s21*a1 + s22*a2

The Z2 to Z3 impedance discontinuity will also cause reflections in both directions.

same equations as above with different parameters

The net current at the bottom and top of the coil cannot be expected to be the
same as in a straight piece of wire with no step functions in the impedance.
--
73, Cecil http://www.qsl.net/w5dxp


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On Sun, 07 Nov 2004 04:31:00 GMT, "Frank"
wrote:


Hi Frank,

|Thanks for your comments Reg. The fact is my graph is produced in Excel
|from data provided by a NEC 2 output file generated by few trivial lines of
|NEC code. I cannot claim to have done anything requiring much thought. I
|just considered, since so much discussion is centered on current
|distribution, that some might be interested in the posted curves. So far
|yours is the only response. I will probably delete the page in a day or so.
|The loading inductor is 2.5" diameter, 6" long, with turns spaced at 0.5".
|The NEC code is listed on the site, so anybody can copy to verify the
|validity of my results -- or the validity of the code.

I haven't run your code, but I did something similar, and announced
the results here, almost a year ago. Perhaps that explains the lack of
response.

http://www.qsl.net/n7ws/Loaded%20antennas.htm

or in downloadable form:

http://www.qsl.net/n7ws/Loaded_Antennas.pdf

the antenna files are he

http://www.qsl.net/n7ws/AntennaModels.zip

Regards,

Wes

Wes Stewart wrote:
I haven't run your code, but I did something similar, and announced
the results here, almost a year ago. Perhaps that explains the lack of
response.

http://www.qsl.net/n7ws/Loaded%20antennas.htm

Yet many keep insisting that the net currents at each end of a
loading coil are the same magnitude.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Wes Stewart wrote:

I haven't run your code, but I did something similar, and announced
the results here, almost a year ago. Perhaps that explains the lack of
response.

http://www.qsl.net/n7ws/Loaded%20antennas.htm


Yet many keep insisting that the net currents at each end of a
loading coil are the same magnitude.

No, "many" don't keep insisting anything of the sort. Those
interested should go to Tom Rauch's web site, read everything
he wrote on the subject, and come to their own conclusions as
to what "many" think.
73,
Tom Donaly, KA6RUH