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Old April 2nd 06, 06:24 PM posted to rec.radio.amateur.antenna
 
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Default Coils and Transmission Lines.


Yuri Blanarovich wrote:
More astonishing than that, Until the "gurus" put their finger on the coil,
or aquarium thermometer, or RF ammeter, or infrared scope and see that the
loading coil (in a typical quarter wave resonant whip) is heating up at the
bottom, being the reality that defies their "scientwific theories why it
shouldn't" - they will keep committing the same mental blunders over and
over.


Yuri,

No one I have seen has every said one tuern can't get hotter than
another turn in a loading coil.

For example, I can take a piece of airdux and short a single turn
anywhere in the coil. That turn and the turns around it will get very
hot, often even melting the form and discoloring the wire, even with
modest power applied in a resoant circuit.

I had my 75 watt Novice rig melt miniductor in certain spots way back
in the very early 60's.

The problem is wild theories are created from small grains of truth or
factoids. It is the wild theories that people question.

In an effort to support the wild claims, there seems to be an effort to
dismiss anything but the wild theories. Here is how it goes:

1.) My Hustler antenna loading coil (known to be a poor electrical
design) melted the heatshrink at the bottom

2.) This must be becuase there is only high current at the bottom of
every loading coil.

3.) This must be because the standing waves on the antenna all wind up
in the loading coil.

4.) This must mean all loading coils act just like they are the x
degrees of antenna they replace.

5.) This is why, no matter what we do with loading coil Q, efficiency
doesn't change much.

6.) We will write a IEEE paper about this astounding fact, since all
the texbooks about loading coils or inductors in general must be wrong

7.) Anyone who point out it is imperfections in the design of the
system that cause this must be wrong, since I saw the coil get hot

8.) Anyone who disagrees with me must think himself a guru, and be
incapable of learning or understanding how things work

9.) I know all this because the bottom of the coil gets hot in my
antenna

What's next? There is less current in a wire (coil) where wire (coil)
gets
hotter?
Thermometers don't lie, meters don't lie, even EZNEC shows it! So wasaaaaap?


It's all been explained over and over again.

If the termination impedance of the coil is very high compared to
shunting impedances inside the coil to the outside world, a coil can
have phase shift in current at each terminal and it can have uneven
current distribution.

This is not caused by standing waves or "electrical degrees" the coil
replaces, but rather by the displacement currents which can provide a
path for the through currents.

Reg actually explained this very well, as has Roy, Tom D, Gene, Tom
ITM, Ian, and a half dozen others.

The reason you keep beating your head against the wall is you want to
think the conclusions you formed were correct.

If I wanted to design a loading coil that has virtually 100% current
taper, I could. If I wanted to design one with virtually no taper, I
could. I could actually have an antenna of a fixed height and by making
various styles of loading coils go anywhere from nearly uniform
distribution at each end of the coil to some significant taper.

The problem is Cecil attributes it all to standing waves, and not to
the inductor's design. You seem to be doing the same.

Since we won't agree with your wrong theories, you then conclude we are
saying step one is wrong and you never saw what you saw. Step one is
fine. Step two is where everything you say falls apart.

73 Tom

 
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