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Old April 10th 06, 06:31 AM posted to rec.radio.amateur.antenna
 
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Default Current across the antenna loading coil - from scratch

Yuri Blanarovich wrote:

Just take 40m shorted vertical, make it resonant with DECENT coil like he
has about 2/3 up the mast, stick the RF ammeters at both ends and give us
the readings. You have the pictures, you should be able to replicate the
setup.


What is it you are after?

I already posted, years ago, measurements at:

http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

Then you tell us that the current is the same at both ends, show us the
pictures and describe your setup, meters, frequency and results.


I think what is happening here is you are getting angry and not paying
attention to what people are saying. I've already said it is possible
to have different currents at each end of a loading coil.

What I disagree with you about is you seem to attribute that difference
to some magical property related to the distribution of current based
on electrical degrees the loading coil replaces or standing waves, and
that is very simply and clearly wrong.

Current cannot "drop" or be "dropped". It can be divided between paths,
but it cannot vanish into thin air. The mechanism that allows current
to change in an antenna is displacement current, and it comes from
capacitance.

The only thing wrong with Barry's setup is he uses large meters
compared to the size of the coil, and they are invasive. The meter
requires cutting the leads and adding a fairly large bulk into the
system. I'd never use thermocoupler meters to measure high impedance
systems, magnetic-field coupling systems can be smaller, have less
distributed capacitance, and don't require rerouting leads. Current
transformer systems are also more accurate and can have much better
resolution, and can even be used to determine phase.

Let's not let the measurement method overshadow the real disagreement,
however.

The real disagreement is you seem to be saying the missing area of
antenna replaced by the inductor and standing wave patterns of current
distribution in the antenna are what causes the loading coil to behave
as it does. Barry also proposed that, if I am not mistaken.

That is not true.

The single thing that allows an inductor to have a current difference
and phase shift in current along the coil or at each terminal is the
capacitance of the coil to the outside world. That is why we would have
to be very careful NOT to disturb the coil by mounting other large
measurement devices on the coil.

This goes for the rest of the "gurus" that insist on the same.


The "gurus" you despise go back to Maxwell, who described displacement
current:

http://maxwell.byu.edu/~spencerr/websumm122/node72.html

The term displacement current is not an invention of those you call
"gurus". It is part of physics dating way back to the 19th century.
THAT is why so many people are trying to tell you about displacement
currents, it isn't to make you feel bad.

You have to include displacement currents in any model, or you cannot
have a current taper along the length of a conductor.

Then model the loading coil as a solenoid or loading stub of same inductance
in EZNEC and show us what you get. Cecil did it, and the silence is
deafening!!! Can you explain what is "wrong" with Cecil's examples?


Sure. His explanation of what is happening and the fact he picked a
very special conditions just to satisfy a twisted theory. Roy showed in
his models why Cecil's conclusions were wrong. Practical measurements
will show the same thing.

The ONLY thing that allows a conductor to have current taper along its
length is displacment current. That is a function of the capacitance
from that conductor to the world around that conductor compared to the
impedance presented by the system beyond that point. It is NOT
determined by standing waves. It is not determined by "missing length
replaxed by coil".

Looks like Belrose should get another pHDuuhh for starting all this
misconception and misinformation in ham literature. Pathetic is that some of
the "gurus" that should know better, are on the same bandwagon to la-la
land.


I'm not sure what motivates you to attack everyone, but at least you
universally seem to hate almost everyone. Jack Belrose is a great guy
and has contributed a great deal with his work. If you finmd something
wrong with what he is saying, tell us what it is. Don't attack the
person, point out the error.

Stop crap and twist and dance, answer the freakin questions or say nothing.
We are not idiots


I suppose everyone has a right to their own opinions on that topic.
I've done my best to answer the questions. I hope this post helps
clarify things. Calm down, there is no need to get upset.

Did this help answer your questions?

73 Tom