Cecil Moore wrote:
Ian White GM3SEK wrote:
1. The magnitude and phase of the current flowing into the loading
inductance are both the same as that of the current flowing out (this
a fundamental property of pure inductANCE).

That is a fundamental property of a pure inductance in a lumped
circuit analysis which assumes a DC current or a pure traveling-
wave current. It is NOT a fundamental property of a pure inductance
if the current you are talking about is a net standing wave
current. Your stated principle is simply false for a standing
wave environment. In a transmission line, it is easy to install
a coil that has zero current at one end and an amp of current
at the other end.


Be very careful here. We're talking about the effect of cutting the
physically shortened wire antenna, and inserting a loading device. This
therefore has to be a TWO-terminal device.


It simply doesn't apply in a standing wave environment - and a
75m bugcatcher loaded mobile antenna is a standing wave antenna.
Please take a look at my example and questionaire to understand
what is wrong with your above statement.

The measured current at the bottom of a loading coil is primarily
standing wave current. IT IS NOT FLOWING.

The measured current at the top of a loading coil is primarily
standing wave current. IT IS NOT FLOWING.

Since neither of these two currents are flowing, they don't
have to be equal. They just stand there.


I'm sorry, but those last three paragraphs are simply contradictions in
terms, which demonstrate their own illogicality.

Electrical current is defined as a net rate of transfer of electrons, so
by the very definition of the term there is literally no such thing as a
non-flowing current (except when the current is exactly zero and the
definition becomes moot).

I seriously wonder if you understand what a standing wave is. It is
simply a pattern of variation in current along the length of a
transmission line, which is stable in time.

If you pick any point along the transmission line or antenna wire,
there is a simple net current characterized by one amplitude and one
phase, relative to some other reference point. (In this whole discussion
we discount the normal cyclic sinusoidal variation of instantaneous RF
current which is happening everywhere in the system.)

In our minds, we may choose to explain the causes of the standing wave
by resolving the net physical current into conceptual forward and
reverse components; but the physical system doesn't know what you are
thinking. To be valid, your concept must do nothing more than explain
what's seen to be happening; it cannot seek to affect it.

At the point where you have to say that a measured (and therefore
measurable) current does not flow, your concept is in trouble.


If I present to you a black box with zero amps at one terminal
and one amp at the other terminal, what can we conclude? One
possibility is 1/4 wavelength of coiled up coax with an
infinite SWR. Please ponder that and apply it to your coil
assertion above.

Your length of coiled up coax is a FOUR-terminal device, like Richard's
transformer was. It isn't an applicable solution for this problem.


The currents that are doing the flowing are the underlying
current components, the forward current and the reflected
current and they are close to equal. Everything you say
about a coil is true for the forward current and the
reflected current. It is simply not true for the standing
wave current which is just a conceptual construct and not
a flowing phasor at all.

If you really want to accurately apply the principles you are
asserting, you must treat the forward current and reflected
current separately and then superpose the results.

It is entirely *your* responsibility to ensure that your postulated
forward and reflected currents obey the same circuit laws as the
physical net current. If you cannot do that, your concept fails.


Applying
your above principle to standing wave current is akin to
superposing power and that's a no-no.

I have never seen such a wide-spread blind spot.

Take the transmission line example.

---------------------------X----------------------------
Ifor=1.0amp -- --Iref=1.0amp

There's a black box at 'X'. Inside the black box is 1/4WL
of coiled up transmission line. The current measured at
left of the black box is zero amps. The current measured
at the right of the black box is 2 amps. That doesn't
violate any laws of physics.

The laws it violates are those of logic. Your black box is not allowed
to sometimes have two terminals and sometimes need four.

That obeys the laws of physics
for a transmission line with reflections. You are measuring
the currents at a current node and at a current loop. It's
absolutely no big deal.

Sorry, I just don't see it. But what I do see are the contradictions and
inconsistencies of logic that you are forced to resort to, in order to
arrive at the conclusion you've already decided upon. I think that
proves the exact opposite.



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

Ian White GM3SEK wrote:
Be very careful here. We're talking about the effect of cutting the
physically shortened wire antenna, and inserting a loading device. This
therefore has to be a TWO-terminal device.

Yes, I realize that. Do you realize that the characteristic
impedance of a single #14 wire 30 feet above ground is 600
ohms? That pesky ground return path raises its ugly head once
again. It's impossible to install a two-terminal system 30
feet above *ground* and have it remain a two-terminal system.
It's only a two-terminal system in your mind.

Electrical current is defined as a net rate of transfer of electrons, so
by the very definition of the term there is literally no such thing as a
non-flowing current (except when the current is exactly zero and the
definition becomes moot).

You have hit the nail squarely on the head without realizing it.
A non-flowing current doesn't exist in reality but that is exactly
what you are measuring when you measure standing-wave current.
The only things that exist in reality are the forward and reflected
current. So you guys are basing your high and mighty concepts on
something that doesn't even exist in reality. No wonder you are
confused. You are measuring two currents flowing in opposite
directions at the same time and don't realize it.

I seriously wonder if you understand what a standing wave is. It is
simply a pattern of variation in current along the length of a
transmission line, which is stable in time.

Nope, that's not what it is. For example, a current standing
wave on a particular transmission line is the sum of one amp
flowing in one direction and one amp flowing in the opposite
direction. Exactly what is the net charge flow when identical
currents are flowing in opposite directions? Let's see now,
this is a really tough one. One amp flowing in one direction
minus one amp flowing in the opposite direction. What could
the result possibly be? :-) Hint: think DC to see what the
net charge flow would be.

If you pick any point along the transmission line or antenna wire, there
is a simple net current characterized by one amplitude and one phase,
relative to some other reference point. (In this whole discussion we
discount the normal cyclic sinusoidal variation of instantaneous RF
current which is happening everywhere in the system.)

I suggest you review traveling wave phasors which rotate at omega
(2*pi*f). A standing wave 'phasor' doesn't rotate at all so a standing
wave current is not moving. I'm not even sure it is technically valid
to call a standing wave current a "phasor" since it doesn't even possess
a frequency characteristic. Please think about a perfectly stationary,
non-revolving 'phasor' and then comment. Wouldn't a non-revolving
phasor be DC?

To be valid, your concept must do nothing more than explain
what's seen to be happening; it cannot seek to affect it.

The same thing applies to your concepts. So what do your concepts
say about a phasor with an omega(2*pi*f) equal to zero as is the
case for standing waves? Are standing waves really DC? Do they
exist at all anywhere besides the human mind?

At the point where you have to say that a measured (and therefore
measurable) current does not flow, your concept is in trouble.

Sorry, I have absolutely no idea what that means. Surely you have
measured zero current at a standing wave current minimum where the
forward current equals one amp and the reflected current equals
one amp. Is that zero amps in the act of flowing?

Your length of coiled up coax is a FOUR-terminal device, like Richard's
transformer was. It isn't an applicable solution for this problem.

If you include that pesky ground under antennas, it is. My electronics
equation book contains a formula for the characteristic impedance
of a single wire transmission line over ground. Is that invalid?
Doesn't that sound very much like a dipole wire in the air?

The laws it violates are those of logic. Your black box is not allowed
to sometimes have two terminals and sometimes need four.

An antenna system installed on this earth is always a four terminal
system whether you like it or not. Haven't you ever seen those diagrams
of the current return to ground from an antenna system?
--
73, Cecil http://www.qsl.net/w5dxp

Ian White GM3SEK wrote:
Electrical current is defined as a net rate of transfer of electrons, so
by the very definition of the term there is literally no such thing as a
non-flowing current ...

I'm sorry, I forgot to provide a reference for your
non-existant non-flowing current. On page 464 of
"Antennas for All Applications", by Kraus and Marhefka,
3rd edition, it shows the current on a 1/2WL dipole along
with its phase. The phase is *fixed* at zero degrees over
the entire 1/2 wavelength. So what does an RF current
with a fixed phase of zero degrees really mean? It means
that the 'phasor', if it is indeed a phasor, doesn't
flow. How could an RF current with a fixed phase of zero
degrees manage to flow? e^wt would be zero.
--
73, Cecil http://www.qsl.net/w5dxp