3 antennas modeled with EZNEC
 

Thanks to Wes, n7ws, I found out how easy it is to model a helical coil
with EZNEC. The following three antennas were modeled using the same
coil, 4.5 turns, 12 inch diameter, 10.8 inches long, using approximately
14 feet of wire. The antennas are similar. The frequencies are different
to illustrate three different arguments. EZNEC zero-impedance loads were
placed directly below and directly above the coil to ascertain the currents.
The accompanying .ez files can be downloaded and run on EZNEC if desired.

1. The first antenna is a simple center-loaded 1/4WL monopole. The
lengths of wire above and below the coil are approximately the same
as the length of wire used in the coil. This one illustrates the
current taper through the loading coil. Calculations indicate that
the coil occupies approximately 20% of the electrical length of the
antenna.

http://www.qsl.net/w5dxp/octcoil1.gif
http://www.qsl.net/w5dxp/octcoil1.ez

2. The second antenna is electrically 3/4 wavelength long. This one
illustrates how the current at the top of the loading coil can be
greater than the current at the bottom of the loading coil.

http://www.qsl.net/w5dxp/octcoil2.gif
http://www.qsl.net/w5dxp/octcoil2.ez

3. The third antenna illustrates the phase-reversing coil described
by Kraus in _Antennas_For_All_Applications_, 3rd edition. It is similar
in concept to the Diamond NR72B when used on 70 cm. The current at the
bottom of the coil is 180 degrees different in phase from the current at
the top of the coil which means - for 1/2 of the RF cycle, current is
flowing into both ends of the coil at the same time. For the other 1/2
cycle, current is flowing out of both ends of the coil at the same time.

http://www.qsl.net/w5dxp/octcoil3.gif
http://www.qsl.net/w5dxp/octcoil3.ez

It appears to me that EZNEC handles the segmented wire coils in a manner
related to the real world.
--
73, Cecil http://www.qsl.net/w5dxp



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Welcome back from the dark side Cecil...

"Cecil Moore" wrote in message
...
Thanks to Wes, n7ws, I found out how easy it is to model a helical coil
! =-----

It appears to me that EZNEC handles the segmented wire coils in a manner
related to the real world.
--
73, Cecil http://www.qsl.net/w5dxp



Eggscellent!!!
Thanks for putting up with the flat earth society.

Yuri, C6AYB

Cecil wrote,

Thanks to Wes, n7ws, I found out how easy it is to model a helical coil
with EZNEC. The following three antennas were modeled using the same
coil, 4.5 turns, 12 inch diameter, 10.8 inches long, using approximately
14 feet of wire. The antennas are similar. The frequencies are different
to illustrate three different arguments. EZNEC zero-impedance loads were
placed directly below and directly above the coil to ascertain the currents.
The accompanying .ez files can be downloaded and run on EZNEC if desired.


It certainly is interesting how a person who, only a short time ago was railing

against "the math model," suddenly gets religion when he thinks it agrees with
him. EZNEC not only uses math to reach its conclusions, that's *all* it uses,
plus
a few assumptions about how current is distributed over antenna segments.
Glad you've joined the fold, brother Moore.
73,
Tom Donaly, KA6RUH

Tdonaly wrote:
Cecil wrote,

Thanks to Wes, n7ws, I found out how easy it is to model a helical coil
with EZNEC. The following three antennas were modeled using the same
coil, 4.5 turns, 12 inch diameter, 10.8 inches long, using approximately
14 feet of wire. The antennas are similar. The frequencies are different
to illustrate three different arguments. EZNEC zero-impedance loads were
placed directly below and directly above the coil to ascertain the currents.
The accompanying .ez files can be downloaded and run on EZNEC if desired.

It certainly is interesting how a person who, only a short time ago was railing
against "the math model," suddenly gets religion when he thinks it agrees with
him.

It is certainly interesting that you choose to mount an ad hominem attack
instead of providing an iota of technical content.

I do not rail against all math models, just the ones that don't match
reality. I require my math models to give the correct answer. Others
obviously have lower standards for math models than I do.

One rock plus one rock equals two rocks is a math model with which I
fully agree. Coils with zero capacitance is a math model with which
I disagree.

Now please tell us why lumped inductive reactances don't agree with
wire segment coils, stubs, or reality.
--
73, Cecil http://www.qsl.net/w5dxp



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On Fri, 06 Feb 2004 06:12:43 -0600, Cecil Moore
wrote:
Now please tell us why lumped inductive reactances don't agree with
wire segment coils, stubs, or reality.
Operator error.

It's like trying to measure Ohms without turning on the meter's
current source. There's a lot of institutionalized ignorance in these
threads.

Richard Clark wrote:

wrote:

Now please tell us why lumped inductive reactances don't agree with
wire segment coils, stubs, or reality.

Operator error.

Yep, the error is in the operator's choice of a model
that doesn't match reality.
--
73, Cecil, W5DXP

On Fri, 06 Feb 2004 13:32:40 -0600, Cecil Moore
wrote:
Yep, the error is in the operator's choice of a model
that doesn't match reality.
Institutionalized here for the sake of argument.

Cecil wrote,
(snip)

I do not rail against all math models, just the ones that don't match
reality. I require my math models to give the correct answer.

(snip)

That's code. It means "I do not rail against all math models, just the
ones that don't agree with me. I require my math models to give the
answer I've already made up in my head."
73,
Tom Donaly, KA6RUH

Cecil Moore wrote in message

2. The second antenna is electrically 3/4 wavelength long. This one
illustrates how the current at the top of the loading coil can be
greater than the current at the bottom of the loading coil.

http://www.qsl.net/w5dxp/octcoil2.gif
http://www.qsl.net/w5dxp/octcoil2.ez

Why the 3/4 wave example? This is NOT what I had in mind. What I would
like to see, is you take a 8 ft mobile whip for 80m. Start with a
center load. Note the current taper. Then place the coil below the
midpoint level. Note the current taper. Then place the coil above the
midpoint level. Note the current taper.
You should be able to find a configuration that provides max current
at the top of the coil, if what you claim is true. I want to see max
current at the top of the coil in the SHORT loaded 8ft mobile whip for
80m. Not a funky overly tall 3/4 wave antenna. I'd try it myself, but
I only have the demo of eznec and don't have the segment capability.
Then if you can see this happen in the model, I'd like to see it
confirmed in the real world. If this occurs, then I might start to
think what you claim holds some water. I'll reserve further comment
until you can try this simple test. MK