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Old December 4th 03, 04:22 PM
Richard Harrison
 
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Mike, W4EF wrote:
"What I am getting at is that both camps may be wrong."

One of the arguments is that current into one end of a loading coil
equals current out of the other end of the coil. That is not required of
an antenna loading coil in the middle of an antenna. Recall the diagram
of a center loaded short vertical whip from ON4UN`s Fig 9-22 that Yuri
Blanarovich posted early in the dispute. 45-degrees of the 90-degree
total antenna length is replaced by the loading coil. Current tapers
cosinusoidally from 1A at the drivepoint to 0A at the tip.

Cosine of 22.5-degrees = 0.924
Cosine of 67.5-degrees = 0.383

Roy sarcastically referred to "Yuri`s Cosine law". Yuri is right.
Current into the bottom of the coil is 0.924 A, and into the top of the
coil it is 0.383 A. Roy disappeared from the argument.
Yuri seems to have tired of the dispute too.

On page 86, King, Mimno, and Wing say:
"It is fundamentally incorrect to treat a centerdriven antenna as though
it were the bent-open ends of a two-wire line."

This is true for a whip as a continuation of a coax line too. The
antenna should radiate and the line should not. The difference between
an antenna and a transmission line is fundamental. Consider the
equivalent circuit of the balanced line. It is made from distributed
series-connected inductors with distributed capacitors shunted across
the inductor junctions. The two line conductors are closely coupled and
enforce balance in the line. The close equal and opposite currents
discourage radiation from the line.

Attach a non-radiating balanced load across the feedline. The currents
into both terminals of the load must be the same. There is much looser
coupling between the two sides of a dipole than between the wires of a
transmission line.

In a transmission line feeding a mismatched load, the reflected energy
"sees" Zo as does the incident energy traveling the line. Zo is enforced
in both directions by the inductance and capacitance distributed
uniformly in the line.

Due to energy escape in an antenna, incident and reflected energy can
"see" differing impedances on either end of a loading coil. The coil
doesn`t enjoy the type of enforced balanced feed imposed by a balanced
transmission. The feed at its ends is asymmetrical.

Best regards, Richard Harrison, KB5WZI

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Old December 4th 03, 08:16 PM
Richard Harrison
 
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Richard Clark wrote:
"The only points of interest are found in the data and the limits of
error that surround it."

Richard Clark is among other things an expert in measurements. Others
may find other points of interest in things which don`t intrest Richard.

For me, a simple go or no-go scale may be good enough. Regardless of
precision, the ultimate decision often must boil doewn to a simple yes
or no.

If my recollection is right, Yuri presented a photo of a loading coil in
action which had functioning r-f thermoammeters, one at each coil end.
Their readings were significantly different. This may not be conclusive,
but were I to see it often in various applications, I`d likely be
persuaded that currents are likely different at opposite ends of an
antenna loading coil sited in the middle of an antenna conductor.

Best regards, Richard Harrison, KB5WZI

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Old December 4th 03, 08:23 PM
Cecil Moore
 
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Richard Clark wrote:
This happened more from the basis of others forcing arguments upon
them, and then proving those straw men wrong;


The original question was pretty clear: For a real-world mobile
loading coil, does the current vary from end to end? And if it
does vary from end to end, does that violate Kirchhoff's laws?
--
73, Cecil, W5DXP

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Old December 4th 03, 08:34 PM
Cecil Moore
 
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Richard Harrison wrote:
Due to energy escape in an antenna, incident and reflected energy can
"see" differing impedances on either end of a loading coil. The coil
doesn`t enjoy the type of enforced balanced feed imposed by a balanced
transmission. The feed at its ends is asymmetrical.


If two series coils are installed in a balanced feedline with reflections,
the net currents through the coils will also change from end to end.
--
73, Cecil, W5DXP



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Old December 4th 03, 09:36 PM
Jim Kelley
 
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Richard Clark wrote:
As for go/no-go sieves, mine is does it make more than a dB
difference? In this case, barely 0.5dB.


So as a metrologist, plus or minus a dB is good enough? Do you use the
number 3 for Pi? That's only .02 dB off.

73, Jim AC6XG
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Old December 4th 03, 09:59 PM
Cecil Moore
 
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Jim Kelley wrote:
Do you use the
number 3 for Pi? That's only .02 dB off.


Heck, Pi is only 0.63 dB higher than e so they are
virtually interchangeable.

Some state (Tennessee?) once tried to pass a state law
requiring Pi to equal 3.00.
--
73, Cecil, W5DXP

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Old December 4th 03, 10:18 PM
Mark Keith
 
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Cecil Moore wrote in message ...
Michael Tope wrote:
What I am getting at, is that both camps may be
wrong. The answer may lie somewhere in between
these two extremes ...


As I understood it, there is an extreme on only one side. One side
says the current through a loading coil doesn't change. The other
side says that the current through a loading coil does change.


The current through the coil is not the issue as far as my "camp" is
concerned.
I can see where the current could taper across the coil in certain
setups.
The issue as far as I'm concerned is: does this taper drastically
cause error in modeling compared to lumped elements? I don't think it
does to any great degree, and others data, including Richard Clarks,
and also W4RNL, seem to concur. Or at least as far as I can see. The
taper of the current through the coil is of no great concern to me.
The claim that this variation of current across the coil causes
drastic modeling error is what I have problems with. To me, it's
trying to explain a problem that doesn't really exist, with something
that really doesn't matter that much as far as that problem is
concerned. No one yet has shown any examples of large modeling errors
that is due to this tapering of current. And THATS what the real issue
is. Or at least as Yuri tells it. MK
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Old December 4th 03, 11:06 PM
Richard Clark
 
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On Thu, 04 Dec 2003 13:36:24 -0800, Jim Kelley
wrote:

Richard Clark wrote:
As for go/no-go sieves, mine is does it make more than a dB
difference? In this case, barely 0.5dB.


So as a metrologist, plus or minus a dB is good enough? Do you use the
number 3 for Pi? That's only .02 dB off.

73, Jim AC6XG


Hi Jim,

Error is a fact of life. My sieve of "does it make more than a dB
difference" is not a statement of error however.

A simple example of error is found in
That's only .02 dB off.


73's
Richard Clark, KB7QHC
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