Cecil Moore wrote:


The decrease (drop) in current across a loading coil installed in
a standing-wave antenna does NOT in any way violate Kirchhoff's current
law.

True.

One can imply from Kirchhoff's current law that there is no current
decrease (drop) across a point.

By 'point' I believe you are referring to what is commonly referred to
as a node. Kirchoff's current law stipulates that charge may not
accumulate at nodes. Therefore by definition, any feature of the system
where charge accumulation needs to be considered is not a node. This
makes sense since charge must accumulate on a surface (surface charge
density) (coul / meter squared) or in a dielectric volume (volume charge
density) (coul / meter cubed). Both concepts require some sort of
area or volume which is inconsistant with the notion of a node.

I don't know anyone who disagrees with
that so any argument is just a straw man. Kirchhoff never said the
current at one point in a network had to equal the current at another
point in the network.

The currents through two nodes connected in series, without branches, is
identical. I think that fact was established before Kirchoff but it's
certainly stipulated in circuit theory.

Many patches have been added to the DC circuit model to try to adapt
it to RF networks.

Many? Seems to me that the concept of electric displacement introduced
by Maxwell provides everything needed to extend DC theory all the way
through classical electromagnetics. What am I missing?

Some function after a fashion and some fail utterly.

Like what?

We all need to be able to recognize the difference. For EM waves, the
E-field and H-field are often affected in the same way.

Huh?

Saying that
the E-field voltage drops but the H-field current doesn't drop is
simply nonsense.

Saying the electric field voltage drops is nonsense. Voltage is the
scalar potential defined as the electric potential difference between
two points in space.

The electric field is vector field, characterized as having a field
strength in volts per meter dependant on spatial location, direction,
and perhaps time.

I don't understand what the term 'E-field voltage drop' could mean.
Same with 'H-field current drop'.

Likewise, saying that the H-field current flows and
the E-field voltage doesn't flow is nonsense.

H-field current flows?

The field H (amps per meter), is the so called magnemotive field. It
doesn't flow anymore than voltage flows through a resistor, and is
associated with the generation of magnetic flux. The magnetic flux
density, B, has the units of webers per meter squared and can be
integrated over an arbitrary surface to evaluate the total magnetic flux
passing through that surface. Magnetic flux is somewhat analogous to
current but H is not at all.

The E-field and H-field
are usually inseparable.

In the classical electromagnetic model, E & H are completely separable.
They are coupled via Faraday's law, and Maxwell's so called
displacement current. At steady state (DC) no coupling exists. When
one field quantity _varies_ in time, so will the other in accordance
with the curl equations. The coupling described by the time varying
part of the curl equations only involves the time varying components.

When determining the analysis method used to gather insight into a
physical system, one of the first considerations is to determine if the
time varying field components need to be considered, and if so, which
ones. For example, analysis of a 60 Hz power supply choke, or electric
motor, usually ignores the electric field in the air gap arising from
the time varying magnetic flux density. It's not important in the gap,
but is the driver of undesirable eddy currents in the core laminations.

bart
wb6hqk

Bart Rowlett wrote:
The currents through two nodes connected in series, without branches, is
identical. I think that fact was established before Kirchoff but it's
certainly stipulated in circuit theory.

Let's deal with concrete examples. Assume a lossless, unterminated
transmission line. Because of the standing waves, the net current
in that series loop varies from point. It is zero every 1/2WL and
in between those zero points, it is at a maximum. That's all I was
trying to say - that the series current in a distributed network
with standing waves is not constant because it no longer can be
considered a "circuit". It must be considered a network as it is
an appreciable portion of a wavelength. The phases of the forward
current and reflected current are rotating in opposite directions
which causes their superposition magnitude to vary from minimum
to maximum. The magnitudes of the forward and reflected traveling
wave currents can be constant while their phasor sum varies as a
standing wave sinusoid.

Most of the stuff in this posting is a diversion away from the original
argument which is: Does the current through a 75m bugcatcher vary from
end to end? Since the net current is the standing wave current in a
standing wave antenna, it is mostly standing wave current, not traveling
wave current. Kraus even suggests that we can consider the forward
current equal to the reflected current in a standing wave antenna
for purposes of conceptual discussion which means the net current
is not moving at all, i.e. not flowing into the bottom of the
coil and out the top as assumed by W8JI on his web page. Balanis
clearly states that a standing wave antenna can be analyzed based
on the forward current and the backward current.

Simulations with EZNEC using the helix option indicates that the net
current is not the same at each end of a bugcatcher coil. Essentially
the same result occurs using a series inductive stub.
--
73, Cecil http://www.qsl.net/w5dxp


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Balanis
clearly states that a standing wave antenna can be analyzed based
on the forward current and the backward current.

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

Who the heck is "Balony" Never heard of him or her.
----
Reg

Reg Edwards wrote:
Balanis
clearly states that a standing wave antenna can be analyzed based
on the forward current and the backward current.


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

Who the heck is "Balony" Never heard of him or her.
----
Reg



That's because you never read.
73,
Tom Donaly, KA6RUH

Reg Edwards wrote:

Balanis
clearly states that a standing wave antenna can be analyzed based
on the forward current and the backward current.

Who the heck is "Balony" Never heard of him or her.

:-) Balanis is my Arizona State University professor who directed
my thinking along these lines. He's the author of a textbook titled:
"Antenna Theory, Analysis and Design" that has come to be a later
reference than some of the Kraus, Jasik, Terman stuff. You can
obtain a copy of his book on Amazon.com for only $119. A web
search for "Constantine A. Balanis" turned up three pages of
lists of web pages.
--
73, Cecil http://www.qsl.net/w5dxp


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Bart Rowlett wrote:

Hi Bart. Good post, and good to see you here again.

The electric field is vector field, characterized as having a field
strength in volts per meter dependant on spatial location, direction,
and perhaps time.

I don't understand what the term 'E-field voltage drop' could mean. Same
with 'H-field current drop'.

I think I understand what you both are saying. In the case of a
standing wave, the 'current drop' Cecil refers to (as I understand it)
is simply the current differential between two positions
Iz2 - Iz1, where I(z)=Imax(cos(wt + phi(z)), the amplitude of the
standing wave current as a function of position z. Phi being the kind
of phase which for a traveling wave varies with time at a given point,
and in this case varies with position along the standing wave. The
distinction being that Phi is not the phase of current with respect to
voltage.

The other point of disconnect between the parties hereabouts relates to
the occasional lack of distinction between the 'flow' of electrons, and
the propagational 'flow' of an EM wave.

73, Jim AC6XG

Likewise, saying that the H-field current flows and
the E-field voltage doesn't flow is nonsense.


H-field current flows?

The field H (amps per meter), is the so called magnemotive field. It
doesn't flow anymore than voltage flows through a resistor, and is
associated with the generation of magnetic flux. The magnetic flux
density, B, has the units of webers per meter squared and can be
integrated over an arbitrary surface to evaluate the total magnetic flux
passing through that surface. Magnetic flux is somewhat analogous to
current but H is not at all.

The E-field and H-field

are usually inseparable.


In the classical electromagnetic model, E & H are completely separable.
They are coupled via Faraday's law, and Maxwell's so called
displacement current. At steady state (DC) no coupling exists. When
one field quantity _varies_ in time, so will the other in accordance
with the curl equations. The coupling described by the time varying
part of the curl equations only involves the time varying components.

When determining the analysis method used to gather insight into a
physical system, one of the first considerations is to determine if the
time varying field components need to be considered, and if so, which
ones. For example, analysis of a 60 Hz power supply choke, or electric
motor, usually ignores the electric field in the air gap arising from
the time varying magnetic flux density. It's not important in the gap,
but is the driver of undesirable eddy currents in the core laminations.

bart
wb6hqk

Jim Kelley wrote:

Bart Rowlett wrote:
I don't understand what the term 'E-field voltage drop' could mean.
Same with 'H-field current drop'.

I think I understand what you both are saying. In the case of a
standing wave, the 'current drop' Cecil refers to (as I understand it)
is simply the current differential between two positions
Iz2 - Iz1, where I(z)=Imax(cos(wt + phi(z)), the amplitude of the
standing wave current as a function of position z.

Here's more what I had in mind. In a source/transmission line/
load configuration, where the loss in the transmission line is 3dB,
the load voltage and load current decrease by the same percentage.
Saying that the voltage wave dropped but the current wave didn't
drop seems a little strange to me. Also, saying the current wave
flowed but the voltage wave didn't, seems a little strange.

The signal attenuated by the transmission line has the identical
equations for voltage and current except for the 'Z0' constant. Does
that Z0 term have the power to cause the current wave to flow and
the voltage wave not to flow? Does the current wave leave the
voltage wave behind in the transmission line dust? Since RF waves
always move at the speed of light, exactly where does the voltage
wave reside when it is not moving at the speed of light and how does
it magically arrive at the load at the same time as the current wave
if it doesn't flow at the speed of light along with the current wave?
(For the humor impaired, this is pure unadulterated humor.)

Doesn't "drop" and "decrease" mean the same thing? Webster's says
they are synonyms. How can a voltage wave drop in magnitude but a
current wave cannot drop in magnitude even if it is defined as
having a constant relationship (Z0) to the voltage wave?

Doesn't "flow" and "travel" mean the same thing? How does the
voltage traveling wave get to the load without flowing? Seems if
the voltage traveling wave didn't flow along with the current
traveling wave, it would never get to the load. But, they tell me
that logic doesn't matter anymore and quantum physics rules. There's
no such thing as reflected energy anymore and only a mush of energy
ever exists. Never mind the ghosting on your TV. That is all in your
mind. Oh yeah, ghosting TV's never reach steady-state. Never mind that
radar couldn't work without reflected energy. Oh yeah, radar never
achieves steady-state. Now I understand completely!

In the classical electromagnetic model, E & H are completely
separable.

I got to wondering exactly how Bart goes about separating the E-
field from H-field in the light from the Sun before it gets to
Earth. :-) But I'm only a lowly grasshopper, trying to grok the
deep thoughts of the gurus. (As always, in good humor)
--
73, Cecil, W5DXP

"Jim Kelley" wrote in message
...
snip
The other point of disconnect between the parties hereabouts relates to
the occasional lack of distinction between the 'flow' of electrons, and
the propagational 'flow' of an EM wave.

73, Jim AC6XG
snip

You got that right, bubba.
73
H.
NQ5H

H. Adam Stevens, NQ5H wrote:
"Jim Kelley" wrote:
The other point of disconnect between the parties hereabouts relates to
the occasional lack of distinction between the 'flow' of electrons, and
the propagational 'flow' of an EM wave.

You got that right, bubba.

So does a current wave flow or not? This is not a trivial question
and tends to distinguish between the problems one can solve with
a DC circuit model Vs the more complicated distributed network model
where current waves and voltage waves share a lot of common characteristics.
--
73, Cecil, w5dxp