Richard Harrison wrote:
There is a difference in impedance between the ends of a loading
coil so that the current at its ends are different.

Good point, Richard. Why isn't anyone arguing that the current on
each side of a loading coil in an antenna tuner is equal? It can
easily be proven to be different using a Smith Chart.

"For present purposes" we may declare anything so long as we don`t
define our purposes, but Fig 9-22 on page 9-15 of ON4UN`s "Low-Band
DXing" is significant and no one has said his pictures are wrong and
given reasons.

I haven't seen that book, but I have seen reproductions of his diagrams
on the net. The situation is not as simple as asserting that the coil
occupies the number of degrees not occupied by the vertical sections.
As usual, the facts lie somewhere in between the two rail arguments.

1. The currents at each end of the coil are not equal. (shoots down
rail #1 argument)

2. The current distribution over the entire loaded mobile antenna is
not a standing cosine wave. (shoots down rail #2 argument)

Since the coil is a different characteristic impedance than the vertical
sections, there exist reflections, both ways, from each end of the coil.
Taking four additional sets of reflections into account mathematically
is extremely difficult. That's probably why nobody has ever attempted it.

However, a bugcatcher antenna can be approximated by the following:

---600 ohm feedline---+---1600 ohm feedline---+---600 ohm feedline---open
bottom section loading coil top section

By modeling with EZNEC, I am attempting to ascertain the VF of the
loading coil. That's the only thing standing in the way of a
conventional analysis.
--
73, Cecil http://www.qsl.net/w5dxp


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Tom Donaly wrote:
So a shootout is your idea of a reliable antenna test.

Before you dismiss those efforts, I suggest you find out who was
involved in the design of the measurements. (Hint: It wasn't me)
--
73, Cecil http://www.qsl.net/w5dxp


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Richard Clark wrote:

Cecil Moore wrote:
magnitude of radiation is irrelevant

in an antenna forum, this is ludicrous.

Sorry, I thought the meaning was clear. The "magnitude of radiation is
irrelevant" to the argument which is confined to current through a loading
coil. You must be getting senile, Richard. You keep forgetting what the
argument is all about. I trust that's not a deliberate diversion. :-)
--
73, Cecil http://www.qsl.net/w5dxp


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Richard Clark wrote:

Cecil Moore wrote:

current across a loading coil installed in a standing-wave antenna does NOT in any way violate Kirchhoff's current
law.

There is no such law of a current into anything but a point (both
dimensionless and componentless).

My "point" exactly!!! A bugcatcher coil is NOT a point.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Tom Donaly wrote:

You'll find, though, that the difference between a
continuously loaded antenna and an antenna with the loading coil,
say, halfway up from the feedpoint won't amount to a hill of beans.


Wrong! Bragging rights after a 75m shootout are worth a lot more
than a hill of beans. A helical antenna has NEVER beaten a center-
loaded antenna in a 75m shootout. And in fact, my junk box *top-
loaded* antenna beat all the center-loaded bugcatchers in one of
the CA shootouts. The current below the coil is the highest current
in the average 75m mobile antenna. The longer that uninhibited
section is, the stronger the radiated signal, thus my success in
the shootout. My bottom section was about ten feet long, then a
horizontal coil and horizontal top hat. I'm going to refine that
configuration when I get time.

There's still no such thing as a "current drop."


The decrease (drop) in current across a loading coil installed in
a standing-wave antenna does NOT in any way violate Kirchhoff's current
law. One can imply from Kirchhoff's current law that there is no current
decrease (drop) across a point. I don't know anyone who disagrees with
that so any argument is just a straw man. Kirchhoff never said the
current at one point in a network had to equal the current at another
point in the network.

Many patches have been added to the DC circuit model to try to adapt
it to RF networks. Some function after a fashion and some fail utterly.
We all need to be able to recognize the difference. For EM waves, the
E-field and H-field are often affected in the same way. Saying that
the E-field voltage drops but the H-field current doesn't drop is
simply nonsense. Likewise, saying that the H-field current flows and
the E-field voltage doesn't flow is nonsense. The E-field and H-field
are usually inseparable.

Ahm still ignorin' you, Cecil. You don't actually read posts, you just
respond to what you think they ought to mean in order to be able to
say whatever you've just made up in your head.
73,
Tom Donaly, KA6RUH

Good point, Richard. Why isn't anyone arguing that the current on
each side of a loading coil in an antenna tuner is equal? It can
easily be proven to be different using a Smith Chart.


I mentioned way back too, question for Rauchians: How come we get RF current
drop across the RF choke, hmmm?
Or Are you going to argue that it is the same at both ends?
Extreme case but proves the point.
Get your "books" out, say it ain't so and look even more foolish.

I like the Hahastick :-) Yea, should have been Hamstick.

Yuri, K3BU.us
Viva Bush!

On Wed, 03 Nov 2004 13:39:57 -0600, Cecil Moore
wrote:
current across a loading coil installed in a standing-wave antenna does NOT in any way violate Kirchhoff's current
law.
There is no such law of a current into anything but a point (both
dimensionless and componentless).
My "point" exactly!!! A bugcatcher coil is NOT a point.
Hence, the first statement above was a troll.

On Wed, 03 Nov 2004 13:37:50 -0600, Cecil Moore
wrote:
The "magnitude of radiation is irrelevant" to the argument which is confined to current through a loading coil.
Which is a ludicrous observation in an antenna forum.

Tom Donaly wrote:
Ahm still ignorin' you, Cecil. You don't actually read posts, ...

Actually, I do read the posts and respond mostly to the old wives tales.
You and I probably agree on 99% of the physics. It's that other one per-
cent of physics based on old wives' shortcuts to which I object. Shortcuts
are NOT the laws of physics!!!

Hint: Every shortcut has a shortcoming.
--
73, Cecil http://www.qsl.net/w5dxp


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Yuri Blanarovich wrote:
Good point, Richard. Why isn't anyone arguing that the current on
each side of a loading coil in an antenna tuner is equal? It can
easily be proven to be different using a Smith Chart.



I mentioned way back too, question for Rauchians: How come we get RF current
drop across the RF choke, hmmm?
Or Are you going to argue that it is the same at both ends?
Extreme case but proves the point.
Get your "books" out, say it ain't so and look even more foolish.

I like the Hahastick :-) Yea, should have been Hamstick.

Yuri, K3BU.us
Viva Bush!




Since when has anyone claimed it's impossible to make a coil that
has a non-constant current distribution? You guys sure go out of
your way to pat yourselves on the back for proving something no
one has ever argued about. For those who really want to learn
about loading coils on small antennas, go to Tom
Rauch's web page and learn how a real engineer deals with
the problem.
73,
Tom Donaly, KA6RUH