Cecil Moore wrote:
Ian White GM3SEK wrote:
"Lumped inductance is often a good approximation to reality, so [most
models other than Cecil's] very sensibly use that as their
starting-point.

For the umpteenth time, Ian, I don't have a model developed
by me. The model I use is the distributed network model
invented before I was born. Dr. Corum merely expanded upon
that model
and I consider his concepts to be valid.

That last line makes it "your model" by adoption - and certainly "your
model" by advocacy.

Your lumped circuit model seems more like a religion
than a valid tool of science. Zero phase shift through
a real-world loading coil?

That wasn't what I said. What I did say - and you cut - was:

"Lumped inductance is often a good approximation to reality, so [most
models other than Cecil's] very sensibly use that as their
starting-point. Then they can progressively apply corrections for the
distributed properties of a real-life inductors. The smaller those
corrections are, the simpler the model becomes.

In practical terms, a lumped-inductance model will take you straight to
a buildable prototype."




--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:
In practical terms, a lumped-inductance model will take you straight to
a buildable prototype."

If you are a technician or a hobbyist, by all means
use the shortcuts. If you are an engineer or physicist,
to do so will lead your concepts astray.

Take the use of standing-wave current to try to measure
the delay through a 75m mobile loading coil. The results
of using the lumped-inductance model are off by a magnitude.
A 75m mobile loading coil is a distributed network that
is an appreciable percentage of a wavelength. As such, the
lumped inductance model is inadequate for analysis.

Here is a quote from my web page:

Many experiments and measurements have been made on loading
coils using net standing wave current. A lack of understanding
of the nature of standing wave current has resulted in some
strange and magical assertions about current through a loading
coil. The equation for standing wave current is of the form:

I(x,t) = Imax sin(kx) cos(wt)

For any point location 'x', it can be seen that the standing
wave current is not "flowing" in the ordinary sense of the word
but rather, is just oscillating in place at that fixed point.
EZNEC confirms that the phase of standing wave current is essentially
constant all up and down a typical HF mobile antenna and therefore
cannot be used to make a valid measurement of the phase shift (delay)
through a loading coil (or even through a wire.) The validity of that
statement is obvious if one understands the implications of the
standing wave current equation above. In fact, we can just as easily
write the standing wave current equation as:

I(x,t) = Imax sin(kx) cos(-wt)

We can reverse the direction of rotation of the standing wave
current phasor and still have the same value of current. Standing
wave current really doesn't have a direction of flow.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

I(x,t) = Imax sin(kx) cos(wt)

For any point location 'x', it can be seen that the standing
wave current is not "flowing" in the ordinary sense of the word
but rather, is just oscillating in place at that fixed point.

According to the equation you provide above, for any point location
'x', the phase of the current varies continuously with t. Presumably
that is what it means to just oscillate in place.

73, ac6xg

Jim Kelley wrote:
Cecil Moore wrote:

I(x,t) = Imax sin(kx) cos(wt)

For any point location 'x', it can be seen that the standing
wave current is not "flowing" in the ordinary sense of the word
but rather, is just oscillating in place at that fixed point.

According to the equation you provide above, for any point location 'x',
the phase of the current varies continuously with t. Presumably that is
what it means to just oscillate in place.

Of course, that's what it means. It doesn't move right or left.
I(x,t) = Imax sin(kx) cos(-wt) would be just as accurate a
description. One cannot even tell which way the standing-wave
phasor is rotating. This equates to putting the source
on either end of a lossless stub without anything changing.
Standing-wave current phase is unchanging up and down a lossless
stub. Standing-wave current phase changes hardly at all up and
down a stub with losses or a wire 1/2WL dipole. That current
cannot be used to obtain a valid delay through a wire or a coil.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Jim Kelley wrote:

Cecil Moore wrote:

I(x,t) = Imax sin(kx) cos(wt)

Standing-wave current phase changes hardly at all up and
down a stub with losses or a wire 1/2WL dipole.

That is correct to the same extent that t in the equation above
"changes hardly at all" with time.

73, ac6xg

Jim Kelley wrote:
Cecil Moore wrote:
Jim Kelley wrote:

Cecil Moore wrote:

I(x,t) = Imax sin(kx) cos(wt)

Standing-wave current phase changes hardly at all up and
down a stub with losses or a wire 1/2WL dipole.

That is correct to the same extent that t in the equation above "changes
hardly at all" with time.

t changes hardly at all referenced to the source current
phase which is what we are talking about. Please don't
try to feign ignorance of that fact. What I don't get is
why people like you have to distort the technical facts.
What do you possibly have to gain through distortion and
diversion?
--
73, Cecil http://www.w5dxp.com

Jim Kelley wrote:
Cecil Moore wrote:
Jim Kelley wrote:

Cecil Moore wrote:

I(x,t) = Imax sin(kx) cos(wt)

Standing-wave current phase changes hardly at all up and
down a stub with losses or a wire 1/2WL dipole.

That is correct to the same extent that t in the equation above "changes
hardly at all" with time.

The phase is referenced to the source phase, as it is in EZNEC,
but you already knew that and just want to perform your usual
diversions away from the technical facts.

I have said at least a dozen times that the current phase
I am talking about is the same as EZNEC reports. If you don't
like what EZNEC reports, take it up with Roy.

For those who don't understand Jim's diversion above, EZNEC
sets t=zero as a reference and then reports the phase. Jim
knows that and is just trying to hoodwink the uninitiatated.
His motives for such remain a mystery.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:

Jim Kelley wrote:

Cecil Moore wrote:

Jim Kelley wrote:

Cecil Moore wrote:

I(x,t) = Imax sin(kx) cos(wt)


Standing-wave current phase changes hardly at all up and
down a stub with losses or a wire 1/2WL dipole.


That is correct to the same extent that t in the equation above
"changes hardly at all" with time.


The phase is referenced to the source phase, as it is in EZNEC,
but you already knew that and just want to perform your usual
diversions away from the technical facts.

Actually, I'm trying to figure out what technical meaning there is to
be obtained from your repeated observation "Standing-wave current
phase changes hardly at all up and down a stub with losses or a wire
1/2WL dipole." The phase of the standing wave varies with position
from one perspective, and with time from another, and with amplitude
from yet another. If you hold t fixed, then amplitude and position
remain variable. This is a revelation?

I have said at least a dozen times that the current phase
I am talking about is the same as EZNEC reports. If you don't
like what EZNEC reports, take it up with Roy.

One should be careful not to invite comparisons to a craftsman holding
his tools responsible for poor craftsmanship. ;-)

73, ac6xg