Current through coils
 

Roy Lewallen wrote:

It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a couple
of calibrated current probes, and a dual-channel scope, will you believe
the results? Or would you rather have someone else make the measurement
or do it yourself?

You will, no doubt, chose a piece of Air-Dux so
small that all the flux is linked to every coil.

Instead of a small Air-Dux coil, use a 75m bugcatcher
coil mounted over a ground plane and see what you get.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

To nobody in particular.

If the propagation time along a coil is equal to the time taken for
the current to travel along the length of wire in the coil at the
velocity of light, then, at a given frequency, if a half-wavelength of
wire is wound into a coil it should become self-resonant at that
frequency.

But it isn't. The coil resonates at a different frequency which
depends on the length and diameter of the coil as well as on the
length of wire.

Just make a coil, measure its resonant frequency, then measure the
length of wire it contains. There will be no direct relationship
between resonant frequency and length of wire.

The same experiment can be carried out using pencil and paper.

The resonant frequency will be directly related to wire length only
when the coil is stretched out straight. And only then.
----
Reg.

Current through coils
 

Roy Lewallen wrote:
It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a couple
of calibrated current probes, and a dual-channel scope, will you believe
the results? Or would you rather have someone else make the measurement
or do it yourself?

Sorry for the double posting, but I just thought of an experiment
that will settle everything.

Take W8JI's 100 uH coil. Keep the spacing between coil 1 and
coil 100 the same at one foot. Get rid of all the other coils
leaving only coil 1 and coil 100 separated by one foot of air.
Use coil 1 as the primary coil and measure the coupling from
coil 1 to coil 100. If it is 100%, you will have made believers
out of everyone and we can stop this silly argument.

The lumped circuit theory says that all the flux in coil 1
links to coil 100 one foot away just as if they were
both tightly wrapped around a toroid.

So there's the challenge. Simply prove that 2" dia coils one
foot apart in air transfer all the energy from one coil to
the other. Piece of cake.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

On Sat, 1 Apr 2006 00:59:10 +0100, "Reg Edwards"
wrote:

To nobody in particular.

To nobody in reply.

If the propagation time along a coil

which has been described as a transmission line

is equal to the time taken for
the current to travel along the length of wire in the coil at the
velocity of light, then, at a given frequency,

um, yes.

if a half-wavelength of wire is wound into a coil

which has been described as a transmission line

it should become self-resonant at that frequency.
But it isn't.

Maybe it is - within ±59% (after fudging the Vf)

Cecil's theories allows for so many possibilities ;-)

Current through coils
 

Reg Edwards wrote:
The coil resonates at a different frequency which
depends on the length and diameter of the coil as well as on the
length of wire.

Yes, that's why inductive loading is more efficient than
linear loading. The inductor has the advantage of adjacent
wire flux coupling. However, the farther away in space that
a particular coil is located from a reference coil, the lower
the coupling. I just issued a challenge to anyone to prove that
the coupling between 2" dia coils separated by one foot of
air is 100%. If anyone can do that, I will admit I am wrong.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Richard Clark wrote:
Cecil's theories allows for so many possibilities ;-)

I would have loved to have invented the distributed network
model, but it was proven valid and in widespread use long
before I was born. But apparently, it has been forgotten
in the past half-century. The results are otherwise intelligent
engineers trying to use an unchanging standing wave phase to
measure the phase shift through a loading coil in a standing wave
antenna system, not realizing that the phase of the standing wave
current cannot even be used to measure the phase shift in
a piece of wire (since it is virtually unchanging).
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Reg Edwards wrote:
To nobody in particular.

If the propagation time along a coil is equal to the time taken for
the current to travel along the length of wire in the coil at the
velocity of light, then, at a given frequency, if a half-wavelength of
wire is wound into a coil it should become self-resonant at that
frequency.

But it isn't. The coil resonates at a different frequency which
depends on the length and diameter of the coil as well as on the
length of wire.

Just make a coil, measure its resonant frequency, then measure the
length of wire it contains. There will be no direct relationship
between resonant frequency and length of wire.


Thanks Reg, but I'm sure most people already understand that. I think
those who have been following this thread and who don't understand that
are beyond help.

As a matter of fact if we all just go back to the very first post you
made, we'll see nothing has changed from what you initially said.

I'm sure the 800-post thread will continue another 800 posts. People
must be bored.

73 Tom

Current through coils
 

wrote:
I'm sure the 800-post thread will continue another 800 posts. People
must be bored.

Actually, they are wondering how you are going to prove 100%
coupling between coil 1 and coil 100 in your 100uH coil such
that the result was 3 nS of delay over that one foot length.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Cecil, W5DXP wrote:
"Actually, they are wondering how you are going to prove 100% coupling
between coil #1 and #100 in your 100 uH coil such that the result was 1
nS delay over that one foot length."

Yes. I think turn-to-turn capacitance doesn`t amount to much and won`t
bypass the coil as you have 100 small capacitors in series, so their sum
approaches zero.

The speed of the wave is almost 984 feet per microsecond. At 75 meters
(4 MHz), 1/4-wave is about 60 feet, and this corresponds to 90-degrees.
The delay corresponding to the time required to establish current in the
coil to induce voltage seems trivial to me. Almost instantaneous
transmission between the first and last coil turns should be possible
were they tightly coupled.

But, I think Cecil is on to something. I`ve played with antique radios
using front panel adjustment to control distance between two coils on
the same axis to control their mutual impedance. You only had a couple
inches of adjustment which was enough to seriously decouple the coils.
12-inch separation would surely have almost completely decoupled them.
This much separation was not available as I`m sure it is unnecessary.

Best regards, Richard Harrison, KB5WZI

Current through coils
 

Richard Harrison wrote:
. . . Almost instantaneous
transmission between the first and last coil turns should be possible
were they tightly coupled.
. . .

Oops, wait a minute. Just a couple of hours ago you said the current
would have to wind its way around each turn, following the wire from one
end to the other, and that it would take nearly the wire length divided
by the speed of light. Have you changed your mind about how inductors work?

Roy Lewallen, W7EL