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