Tom, KA6RUH wrote:
"What makes you think the variation in current in two separate places of
a coil carrying A.C. is a "current drop"?"

You have a voltage deop, a temperature drop, or a drop in almost any
variable. Why not call a decline in current a current drop?

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
You have a voltage drop, a temperature drop, or a drop in almost any
variable. Why not call a decline in current a current drop?

Many examples exist for current drops in distributed networks. That's
one thing that makes circuit analysis invalid for distributed network
problems. The series current is NOT the same value everywhere in a
distributed network. Asserting that there is no such thing as "current
drop" in distributed networks simply indicates an invalid choice of
models.

How much current drop is there at 440 MHz in 100 feet of RG-58 between
the source and a 50 ohm load? Answer: A 20 dB power drop equates to a
40 dB current drop.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:

Many examples exist for current drops in distributed networks. That's
one thing that makes circuit analysis invalid for distributed network
problems. The series current is NOT the same value everywhere in a
distributed network. Asserting that there is no such thing as "current
drop" in distributed networks simply indicates an invalid choice of
models.

How much current drop is there at 440 MHz in 100 feet of RG-58 between
the source and a 50 ohm load? Answer: A 20 dB power drop equates to a
40 dB current drop.

Cecil,

You seem to like the "Roach Motel" theory of current flow. The electrons
check in, but they don't check out.

Here's a clue.

Conservation of charge is every bit as fundamental as conservation of
energy. Current does not just disappear. So what happens in your abused
RG-58 case?

Answer: this is not a simple series circuit.

At every point along the line the current splits between continuing down
the line and shunting to the other half of the transmission line. When
the line is lossless, the shunting is purely reactive, and no net
current flows. However, when there is loss in the line, there is a small
phase shift along with the attenuation, and net current is shunted.

The "circuit" model, as you like to call it, is every bit as valid as
the "distributed network" model. However, due to the distributed time
and space considerations in a transmission line, the "circuit" model is
mathematically intractable for many applications.

The physical reality remains the same even if we cannot easily do the math.

Oh, by the way, in a constant impedance environment the current change
corresponding to a power reduction of 20 dB is also 20 dB, not 40 dB.

73,
Gene
W4SZ

On Mon, 25 Oct 2004 15:10:22 GMT, Gene Fuller
wrote:

However, due to the distributed time
and space considerations in a transmission line, the "circuit" model is
mathematically intractable for many applications.

AKA Violation of Kirchhoff

Richard,

I am not sure why you think there is a violation of Kirchhoff.

The current law is unchanged. The analysis of the voltage law is much
more complicated, but not incorrect.

The situation is not really any different than the use of retarded
potentials for radiation. One must carefully keep track of the loop
voltages with consideration for time and space differences, but there is
no fundamental difference in the physics.

For distributed networks, the Kirchhoff voltage calculation is difficult
(intractable). It is not impossible, but it is unnecessary due to the
existence of the much more friendly transmission line formulations.

73,
Gene
W4SZ

Richard Clark wrote:
On Mon, 25 Oct 2004 15:10:22 GMT, Gene Fuller
wrote:


However, due to the distributed time
and space considerations in a transmission line, the "circuit" model is
mathematically intractable for many applications.


AKA Violation of Kirchhoff

On Mon, 25 Oct 2004 16:46:50 GMT, Gene Fuller
wrote:

I am not sure why you think there is a violation of Kirchhoff.

Hi Gene,

Kirchhoff does not allow for circuits of dimensions that are
appreciable size with respect to wavelength. Simple reason is that
you should then shrink down the unspecified lead length (for voltage
law) into the stray, equivalent and dimensionless components. This is
outrageously flaunted in this group, and then couched as examples of
modeling failure (when it is in fact modeler - the human component -
failure).

This is the "intractability" you speak of - the neglect of the proper
rendering of the network in dimensionless terms.

73's
Richard Clark, KB7QHC

Richard,

In simple terms Kirchhoff's loop law says that if we correctly add all
of the potential changes around a closed loop we do not end up with a
different potential than we had initially. (It does not say just how to
handle the computation.)

As you may know, there are some non-conservative systems in which this
behavior is not true. Traversing around a loop exhibits a spiral
behavior. The measured quantity continues to increase (or decrease) with
every pass around the loop. Kirchhoff's loop law says this sort of
spiral does not happen in an electrical circuit.

Computation is "intractable" for distributed RF networks, but the
principle is still valid.

73,
Gene
W4SZ

Richard Clark wrote:

On Mon, 25 Oct 2004 16:46:50 GMT, Gene Fuller
wrote:


I am not sure why you think there is a violation of Kirchhoff.


Hi Gene,

Kirchhoff does not allow for circuits of dimensions that are
appreciable size with respect to wavelength. Simple reason is that
you should then shrink down the unspecified lead length (for voltage
law) into the stray, equivalent and dimensionless components. This is
outrageously flaunted in this group, and then couched as examples of
modeling failure (when it is in fact modeler - the human component -
failure).

This is the "intractability" you speak of - the neglect of the proper
rendering of the network in dimensionless terms.

73's
Richard Clark, KB7QHC

Gene Fuller wrote:
Conservation of charge is every bit as fundamental as conservation of
energy. Current does not just disappear. So what happens in your abused
RG-58 case?

Answer: this is not a simple series circuit.

Thanks Gene, that is exactly my point. 17th century simple series
DC concepts don't work on RF distributed networks.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil,

I am glad you agree with me, but unfortunately my message was apparently
lost on you.

No one has ever discussed simple series DC concepts except you.
Kirchhoff laws do not require series circuits or DC.

The simple concepts work perfectly well, even on transmission lines.
However, setting up and solving problems is mathematically complex, so
everyone uses the transmission line formulations. There is no new
physics needed. The electrons and waves don't care about math models. (I
think I heard something from you along that line a few times.)

There is nothing wrong with the theory. It works perfectly well on "RF
distributed networks". What is wrong is calling a lossy transmission
line a "simple series circuit" and then misapplying the theory.

73,
Gene
W4SZ



Cecil Moore wrote:
Gene Fuller wrote:

Conservation of charge is every bit as fundamental as conservation of
energy. Current does not just disappear. So what happens in your
abused RG-58 case?

Answer: this is not a simple series circuit.


Thanks Gene, that is exactly my point. 17th century simple series
DC concepts don't work on RF distributed networks.

Gene Fuller wrote:
No one has ever discussed simple series DC concepts except you.

Don't you recognize "17th century DC concepts" as sarcasm?

What is wrong is calling a lossy transmission
line a "simple series circuit" and then misapplying the theory.

That's exactly my point, Gene. I think you missed it. What is
wrong is assuming a simple one-way series current flowing through
a point inductance in a *standing-wave* mobile antenna containing
a one foot by one foot 75m *bugcatcher* coil that occupies more
than 60 degrees of an electrical 1/4 wavelength.

The original argument originated over on eHam.net. Tom, W8JI
said there is no change in current from end to end in a loading
coil. Yuri disagreed. Everything else is a fallout from that
original argument.
--
73, Cecil http://www.qsl.net/w5dxp


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