RadioBanter - Printing wire list from EZNEC?

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Richard Harrison wrote:
Yuri Blanarovich, K3BU wrote:
"Have you figured out how to model loading coil of particular
inductance and physical size to reflect the real current drop across
it?"

Current drop across a coil is E/Z where Z is complex. If a reflection is
involved in the antenna, there are multiple Es involved, perhaps.

(the rest snipped)
Best regards, Richard Harrison, KB5WZI

Richard, there is no such thing as a "current drop."
73,
Tom Donaly, KA6RUH

Tom Donaly, KA6RUH wrote:
"Richard, there is no such thing as a "current drop."

This is where i came in almost a year ago. Yuri may havr posted Fig 9-22
from page 9-15 of the 1994 edition of ON4UN`s "Low-Band DXing". There
are base loading, center loading, and continuous loading examples of
short vertical antennas, and their current distributions. In every case,
the currents at the two ends of the coil are different.

The impedance of an antenna is a function of position along the antenna.
There is radiation from an antenna so not only is the impedance along an
antenna a variable, but the the transmit power level power level along
an antenna is a variable, too. These variables ensure a difference
between the current into and out of a loading coil.

Current is high where impedance is low, and current is high where power
is high.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
Tom Donaly, KA6RUH wrote:
"Richard, there is no such thing as a "current drop."

This is where i came in almost a year ago. Yuri may havr posted Fig 9-22
from page 9-15 of the 1994 edition of ON4UN`s "Low-Band DXing". There
are base loading, center loading, and continuous loading examples of
short vertical antennas, and their current distributions. In every case,
the currents at the two ends of the coil are different.

Unfortunately those diagrams are misleading. They draw a current profile
against a scale of electrical height, which makes it look as if there is
a significant change in current along the length of the coil.

The current profile can only be correctly drawn against a scale of
*physical* height. Then the error goes away, and the current is seen to
be uniform through the coil. What does change is the shape of the
current distribution above and below the coil.

All of ON4UN's math is good, and if you follow that instead of the
pictures, you will find that the current through the coil is always
assumed to be constant. In other words, he assumes an ideal inductor.
The text and math shown that ON4UN actually understands the situation
perfectly. I don't believe for a moment that he expected those diagrams
to be so fundamentally misinterpreted.

The impedance of an antenna is a function of position along the antenna.
There is radiation from an antenna so not only is the impedance along an
antenna a variable, but the the transmit power level power level along
an antenna is a variable, too. These variables ensure a difference
between the current into and out of a loading coil.

No: there is no change in current through a coil that is physically
tiny, and doesn't have any capacitive coupling with the rest of the
antenna. All the changes occur above and below the coil.

Any deviation from equal currents in and out has to be caused by the
physical size of any real coil being non-zero. Then, even a physically
small coil will behave like a very short section of helical monopole
antenna. It is radiating an EM field, so there must also be some
variation in current along its length. (The extreme case of a long coil
is the fully helical whip, where the antenna and the coil are one and
the same.)

There is also a lot of loose talk about "phase variation" due to an
ideal inductor. This is NOT a phase variation in the current from end to
end! What changes is the phase of the voltage between the input and the
output. At each end you are measuring the phase of the voltage,
*relative* to the phase of the current which does *not* change.

Now someone is going to come right back at me, talking about "real life"
this and "practical" that. But if someone does not understand how an
inductor is even *meant* to behave, all their practical knowledge is
built on sand - they may know lots of stuff, but they don't truly
understand it.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Now someone is going to come right back at me, talking about "real life"
this and "practical" that. But if someone does not understand how an
inductor is even *meant* to behave, all their practical knowledge is
built on sand - they may know lots of stuff, but they don't truly
understand it.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Here we go again!

Where have you been Ian? Applying DC current behaviour in the inductor to
standing wave RF current situation in the antenna, Eh?

In case you missed previous exchanges
http://www.k3bu.us/loadingcoils.htm

That is in practice and (right) theory. Cecil showed (hairpinned) model in
EZNEC. And that ain't no lie!

73 and keep your readers informed properly :-)

Yuri, K3BU.us
www.computeradio.us home of "Dream Radio One"

Yuri Blanarovich wrote:

Now someone is going to come right back at me, talking about "real life"
this and "practical" that. But if someone does not understand how an
inductor is even *meant* to behave, all their practical knowledge is
built on sand - they may know lots of stuff, but they don't truly
understand it.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Here we go again!

Where have you been Ian? Applying DC current behaviour in the inductor to
standing wave RF current situation in the antenna, Eh?

No.

Step 1: I am starting from the fundamental AC current behaviour of an
ideal inductor. The phases of the voltages at its opposite ends are
different; but at every given instant, the currents at its opposite ends
are equal and in phase.

2. I am expecting that ideal inductor to behave in exactly the same way
when used as a loading device in an antenna - which in fact it does,
because exactly the same laws of physics apply.

3. Then I'm in a good place to start to think how that behaviour will
change for a real inductor that has both physical size and capacitive
coupling to the rest of the antenna.

In case you missed previous exchanges
http://www.k3bu.us/loadingcoils.htm

That is in practice and (right) theory. Cecil showed (hairpinned) model in
EZNEC. And that ain't no lie!

73 and keep your readers informed properly :-)

Oh, I shall, I shall...

I'll begin by pointing out the obvious: an ideal inductor, a honkin'
great length of Airdux and a shorted parallel stub are three physically
different objects. Each one is a different kind of loading device, with
different effects when inserted into an antenna - and none of those
loading devices is the same as the length of real antenna that it's
claimed to "replace".

The flaw in your viewpoint is that you are expecting a loading device to
"replace" too many of the properties of a genuine piece of antenna. It
actually replaces very few of them, and each different loading device
does it in a different way.

Cecil's stub behaves exactly as expected - for a stub. But a shorted
transmission line is not an inductor - it has some of the properties of
an inductor, but not all of them. In particular, the currents at its two
terminals can be unequal, because a stub can carry common-mode current
and radiate and EM field, which an inductor cannot. Therefore the stub
example is irrelevant to a discussion that is trying to compare various
inductors.

The same is true of different types of inductors. The ideal inductor and
the Airdux are both loading devices - they do not completely replace the
missing piece of the antenna. They replace it in one respect only
(making the feedpoint reactance equal to zero) but all other things
about the loaded antenna are *different* from the full-sized antenna. In
particular, the current and voltage distributions above and below the
load are different from full size, and so of course is the feedpoint
resistance.

I cannot explain every detail of Barry Boothe's measurements, but I know
for certain that the true explanation is the one that obeys all the laws
of physics and circuit theory, down to the last detail.

What you have, Yuri, is an "explanation" that uses those laws in some
parts, but twists or ignores them in others. That cannot possibly be
correct.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Roy Lewallen wrote in message
...
Chuck wrote:
. . .
That said, I take exception with your
statement regarding the
bi-directionality of the simulated
coaxial transmission lines in available
NEC(n) engines. Their simulations are
uni-directional - from the input to the
load, but not in reverse.

That is patently false, and can be easily demonstrated. The transmission
line model in NEC (and EZNEC) is a linear network which is completely
bidirectional.

Roy,

Linear, yes... bi-directional? Not as I see
it... and leaves one wondering why NEC3
is available only to government entities
and contractors...

To confirm your claim, please post a
demonstration that confirms energy in the
load is flowing into the input.

Also, please repost your reply to my post
with the header "another lie..." as it did not
show up in my newsreader.

Thanks,

Chuck, WA7RAI

I cannot explain every detail of Barry Boothe's measurements, but I know
for certain that the true explanation is the one that obeys all the laws
of physics and circuit theory, down to the last detail.

What you have, Yuri, is an "explanation" that uses those laws in some
parts, but twists or ignores them in others. That cannot possibly be
correct.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

You can't explain reality, but you have good arguments to support your
"theory".
Now you can plug in solenoid/helix into EZNEC 4.08 and see for yourself
what'sup (See my other recent post). We are not claiming that hairpin is exact
replacement for lumped inductor, but some properties when inserted into
modeling program illustrate better what is really happening (current is NOT
equal at both ends of the coil).
Take the fricken RF ammeters and stick'em in the coil's ends, you have
excellent current probe on your web site. As you can see from W9UCW
measurements and my recent example of 10m loaded vertical that there is
significant difference in the current across the loading coil (not equal) and
lower you go on frequency when antenna gets short relative to wavelength used,
the more pronounced the effect is.

Significance? As ON4UN points out, efficiency is proportional to the area under
the current curve, that is important for loaded antenna designers, and if they
understood this, we would not have the flood of "magical" wrongly loaded,
shortened antennas (like Vincent/UoRI "patented" crap).

Yuri, K3BU.us
just another "dumb" ham

Ian White, G3SEK wrote:
"The phases of the voltages at its (ideal inductor) ends are different,
but at every given instant, the currents at its opposite ends are equal
and in phase."

When an inductor is placed in a too short standing-wave antenna to
correct its power factor, the volts, amps, and impedance at every point
on the antenna result from superposition. In general, they vary from end
to end. The impedance at any point results from a wave traveling from
the feedpoint and a reflected wave from the open-circuit at the tip of
the antenna. The reflected wave travels back toward the feedpoint. These
waves combine to produce a standing-wave pattern on the antenna much as
would be produced on a transmission line.

In a standing-wave antenna, such as Yuri has used as an example, of a
coil loaded vertical, the impedance is high and the current is
insignificant at the open-circuit antenna tip. The impedance is low and
the current is high back 90-degrees from the antenna tip.

One end of the standing-wave, coil-loaded antenna is fed by its
capacitance to the outside world. The other end is fed by its connection
to the generator. There is no inherent balance in the feed to the
antenna or a loading coil contained within the antenna.

A balanced feed to an ideal coil may result in the same current into and
out, but an unbalanced feed to a coil will likely result in different
currents in and out.

Certainly the same power in and out of a coil will produce differing
volts and amps to comply with differing impedances at the input and
output.

The extreme example comes from continuous loading. The entire antenna is
a solenoid or coil of wire. The impedance at the tip is very high. At
its feedpoint, the impedance is low. The current in the coil tapers from
one end to the other. Adding conductors to either or both ends of the
coil changes the current but does not usually eliminate current taper in
the coil.

Best regards, Richard Harrison, KB5WZI

Sorry, Chuck, I can't thing of one reason why I should accommodate you.

Roy Lewallen, W7EL

Chuck wrote:

Roy,

Linear, yes... bi-directional? Not as I see
it... and leaves one wondering why NEC3
is available only to government entities
and contractors...

To confirm your claim, please post a
demonstration that confirms energy in the
load is flowing into the input.

Also, please repost your reply to my post
with the header "another lie..." as it did not
show up in my newsreader.

Thanks,

Chuck, WA7RAI