Not so obvious
 

It's quite obvious the current through a loading coil tapers. As a first
approximation it's because the voltage and current along it varies according
to a 'cosine' curve as they do along any other sort of continuous
transmission line.

V and I on either side of a coil can be opposite in phase as they pass
through it.

This occurs when the length of the coil passes through a 1/2-wavelength
point. 1/2-wave points can occur at any point along a coil depending on
where the coil starts and ends along the antenna. This helps to illustrate
the action of 'phase-reversing' coils between adjacent antennas lengths.

What I find so intriguing is what the 'taper proponents' intend to do with
the 'taper' data when at last they have it in the form of numbers? Of what
use is it? Into what are the numbers inserted? What is the next stage in
the proposed modelling process?
----
Reg, G4FGQ

What I find so intriguing is what the 'taper proponents' intend to do with
the 'taper' data when at last they have it in the form of numbers? Of what
use is it? Into what are the numbers inserted? What is the next stage in
the proposed modelling process?
----
Reg, G4FGQ



Efiiciency of the loaded radiator is roughly proportional to the area under the
current curve along the radiator.
1. Placement of the loading coil can drastically affect that. (Base loaded vs.
Top Hat loaded)
2. When using loaded elements in multielement designs, the current distribution
and magnitude along the elements needs to be accounted for optimum design and
performance. It affects the inter element coupling, current flow in the
segments of the elements and how the modeling programs "see" it. Try loaded 3
el. 80m beam or 4 square. Programs that can do optimization (YO, AO, 4NEC2)
would give better results if they can deal with real current distribution
closely modeled.
Now it is up to those program authors that neglected proper modeling of the
current in the loading coils to iclude this feature and make their softy wares
better and reflect reality mo betta.

Yuri, K3BU.us

On Sat, 7 Feb 2004 21:28:03 +0000 (UTC), "Reg Edwards"
wrote:

What I find so intriguing is what the 'taper proponents' intend to do with
the 'taper' data when at last they have it in the form of numbers?

That day never seems to arrive. Perhaps eh/cfa testing results are
clogging the queue.

Of what
use is it?

Bragging rights of the ****-ant stature.

Into what are the numbers inserted?

second only to preparation H for that application.

What is the next stage in
the proposed modelling process?

creating a new icon to worship.

C'Mon, Reg, you new those answers all along!

Reg Edwards wrote:
What I find so intriguing is what the 'taper proponents' intend to do with
the 'taper' data when at last they have it in the form of numbers? Of what
use is it?

As I said on the other newsgroup, Reg, it is useful for discrediting the
assertion of one of r.r.a.a's ex-gurus.

W8JI wrote:
If you look at HOW an inductor works, the current flowing in one terminal
ALWAYS equals the current flowing out the other terminal.

"ALWAYS" to me, means zero taper. What does it mean to you, Reg?
--
73, Cecil http://www.qsl.net/w5dxp



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Yuri Blanarovich wrote:
1. Placement of the loading coil can drastically affect that. (Base loaded vs.
Top Hat loaded)

BTW, Yuri, you and others may not be aware that my junk box top-loaded
mobile antenna equaled the best-of-the-best in one of the antenna
shoot-outs. The loading coil was just some cheap 1.75" dia coil stock
from my junk box. It wasn't anything like a bugcatcher and it cost
virtually nothing.

The bottom section was a 108" conductor curving toward the coil which was
***HORIZONTAL***. Yes, the coil was horizontal as was the top hat to which
it was attached. If I had known it was going to do that well, I could have
won by making the top hat a little bigger. Here is an ASCII diagram of that
antenna:
loading coil
- ////////////--Capacitive top hat
/
/
/
/
| Pickup
|
|
|
|
FP
--------GND------------------------------------------------------
So I discovered by accident what is being discussed now. Seems obvious that
the coil could be shorted and the top hat disconnected for higher frequencies.
--
73, Cecil http://www.qsl.net/w5dxp



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Reg Edwards wrote:

SNIP

What I find so intriguing is what the 'taper proponents' intend to do with
the 'taper' data when at last they have it in the form of numbers? Of what
use is it? Into what are the numbers inserted? What is the next stage in
the proposed modelling process?
----
Reg, G4FGQ


IMO: The next stage is designing the coil! A long thin coil [like a
Hamstick] requires a longer length of wire than a short 'fat' [note the
quotes] coil [like a bug catcher or a screwdriver].

The hamstick has a higher current taper than the screwdriver or bugcatcher.

The resultant integral of the current and length [in degrees]
[ampere*degrees] of the resulting antenna is higher with the short fat
coil than with a long thin coil. {This assumes the coils are located
approximately at the same location.}

Deacon Dave, W1MCE

Dave Shrader wrote:




IMO: The next stage is designing the coil! A long thin coil [like a
Hamstick] requires a longer length of wire than a short 'fat' [note the
quotes] coil [like a bug catcher or a screwdriver].

The hamstick has a higher current taper than the screwdriver or bugcatcher.

The resultant integral of the current and length [in degrees]
[ampere*degrees] of the resulting antenna is higher with the short fat
coil than with a long thin coil. {This assumes the coils are located
approximately at the same location.}

Deacon Dave, W1MCE

Additional note. 75 inches of wire versus 40 inches of wire at 14 MHz is
only a 1.1 degree difference.

"Yuri Blanarovich" wrote -

Efiiciency of the loaded radiator is roughly proportional to the area
under the
current curve along the radiator.
1. Placement of the loading coil can drastically affect that. (Base loaded
vs.
Top Hat loaded)
=========================

Typically, shifting the loading coil from the bottom of the antenna to its
most efficient location is about 1.5 dB at 7 MHz. Replacing a loading coil
at its most efficient location with a large top hat increases efficiency by
14 percent. Hardly drastic!

But Yuri's objective is not to find the optimum location of the coil along
the antenna. Every twopenny designer knows that THAT point exists.
Especially they who use rules of thumb. And there's nothing wrong with that.

The objective is to assist the coil designer to design coils by telling him
HOW to make use of the EXTRA knowledge of current distribution along the
antenna.

At present, it seems everybody assumes coil current has a uniform
distribution. Nothing wrong with that of course. Especially if everybody
makes the SAME assumption.

It is unwise to use "roughly" and "drastically" in the same context. After
all, it hasn't yet been discovered in which way the taper should go in order
to improve efficiency. (Yes, I know, you can't shift the taper.)

So that how is it proposed to alter the taper. Or to take advantage of it
by altering wire diameter, ie., by putting the lowest wire diameter in the
places where the smallest current flows. And vice-versa.

IF there is success in improving efficiency by, say, 1 percent, as a result
of increasing design and precision engineering costs, plus patenting costs,
plus testing and certification costs, plus manufacturing costs, by 5 or 10
times, would customers be prepared to buy it.

How accurate are (A-B) tests results expected to be? Within limits of
0.01%, 0.1%, 1% or 10% ?

You'll be lucky to obtain an accuracy of antenna power measurements within
+/- 20%, or within +/- 0.8 dB. This means you would be unable to GUARANTEE
to your customers an improvement in performance better (or worse?) than
about +/- 1 dB.

But an improvement of such a relatively large amount, by tinkering with
coils, I venture to say is impossible. So whatever improvement it is
expected to achieve it will be not be possible to honestly demonstrate it.
There is the possibility of an antenna actually being worse than measured.

But the $64,000 Question is whether customers will be prepared to pay for
another 0.5 dB or less gain, which may or may not exist. It would be like
searching for non-existent W.M.D.

On the other hand, it can be confident expected not to measure an antenna
gain worse than about 1 percent of what it actually is. But how do you
assess the difference between two antennas on the basis of back-to-front
ratio over an angle of 360 degrees in the presence of such small
differences.

It is suggested the next questions to ask are "What is the expected change
in improvement" and "How accurately can the expectation be measured".
Economics cannot be avoided.
----
Reg, G4FGQ

"ALWAYS" to me, means zero taper. What does it mean to you, Reg?
--
73, Cecil http://www.qsl.net/w5dxp

==============================

There's no such thing as a perfect coil. All coils have stray capacitance
and resistance. Consequently, it's exeedingly unlikely the current at one
end is equal to the current flowing at the other end. The current flows out
of the coil via the stray capacitance to its enironment. So we don't just
have I1+I2 - we have I1+I2+I3 to contend with, where I3 is distributed
along the length of the coil.

Not that anybody in his right mind would ever wish to know the magnitude of
the taper of the current or volts. Seems to be an invention of the denizens
of this newsgroup, most of whom seem to have lost theirs.

Now, Cecil, you understand this as well as I do. Cease pulling my leg. So
don't expect me to waste any more of my time discussing it. ;o)
----
Reg, G4FGQ

Reg Edwards wrote:
It is suggested the next questions to ask are "What is the expected change
in improvement" and "How accurately can the expectation be measured".

Obviously, a sour grapes or sweet lemons situation, depending upon
which side of the argument you are on. Reg, to settle the original
argument, is this statement true?

"If you look at HOW an inductor works, the current flowing in one
terminal ALWAYS equals the current flowing out the other terminal."

A simple "yes" or "no" will settle the original argument and hopefully
end the argument. W8JI's own measurements proved his statement to be
false.
--
73, Cecil http://www.qsl.net/w5dxp



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