Gene Fuller wrote:
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.

Yep, you're right. All I was (mistakenly) thinking about was the 10
vs 20 multiplier. Mea culpa. 20 lashes with a wet noodle for me.
--
73, Cecil http://www.qsl.net/w5dxp


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Richard Harrison wrote:

Tom Donaly, KA6RUH wrote:
"I know there are people in the past who have attempted to characterize
antennas as transmission lines."

True. You can include Terman among them.

Kraus also.
--
73, Cecil http://www.qsl.net/w5dxp


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Ian Jackson wrote:

Cecil Moore writes:
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.

Uh? Are you really REALLY sure? Do you want to change your mind?

Yep, already did. My bad. Mea culpa. 20 more lashes with a wet noodle.
--
73, Cecil http://www.qsl.net/w5dxp


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Tom Donaly wrote:
... it doesn't mean that
Cecil knows what he's talking about when he espouses the theories
he made up in his head out there in the hot Texas sun.

Tom, I think I get it now. Here is what I have learned from you.

1. Even though the only difference in the voltage and current equations
for a transmission line is one constant (the variable terms yield
exactly the same relative magnitude, phase, and attenuation
for the voltage wave and the current wave) and the decrease in the
voltage and current between the source and the load is exactly the
same percentage:

While the voltage reaching the load suffers a 10% drop, the current
does not suffer a drop. The current only suffers a 10% decrease.

2. While the voltage wave and current wave are traveling exactly the
same path in the same phase at the same speed from the source to the
load:

The current wave flows to the load but the voltage wave does not
flow to the load. The voltage wave only travels to the load.

Did I get it right?
--
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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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

Cecil,

I am fully aware of the "original argument". To confess my bias, I agree
with Tom D. and Tom R. There is no "current drop" ever, and there is no
current change in an ideal inductor. W8JI explains in some detail why
real coils show different currents at each end.

My response was aimed at your little demo circuit. Let me share one of
my own.


----------------------------------------------------
+ | | |
------------ ----------- -----------
| | | Ra | | Rb |
| 1 V DC | | 100 Ohm | | 100 Ohm |
| 20 mA | | 10 mA | | 10 mA |
------------ ----------- -----------
- | | |
----------------------------------------------------


The source provides 20 mA, but Rb passes only 10 mA. Would you call this
a "current drop"? Most people would say that the total current has
simply divided into multiple paths.

Your RG-58 transmission line example is no different. The current from
the source is not lost or "dropped". It simply finds other paths in
addition to the "load" to return back to the source. Antennas and
loading coils exhibit the same phenomenon.

The error is in considering the transmission line as simply two
non-interacting conductors that somehow magically enforce a fixed
impedance, Zo. If the conductors did not interact there would be no
fixed impedance; it would not be a transmission line.

Your reference to simple DC analysis ignores the interaction between the
transmission line conductors. If you modeled the problem correctly you
would need to account for the leakage current. There would be no
"current drop" and no mystery.

The laws of electromagnetics do not change in any fundamental way until
relativistic and/or quantum considerations come into the picture. There
are "different horses for different courses", and there are different
"computationally preferred" approaches to different electromagnetic
configurations. Often there is best choice for practical reasons, but
that does not make the more difficult computation wrong.

73,
Gene
W4SZ


Cecil Moore wrote:
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.

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:

Cecil,

I am fully aware of the "original argument". To confess my bias, I agree
with Tom D. and Tom R. There is no "current drop" ever, and there is no
current change in an ideal inductor. W8JI explains in some detail why
real coils show different currents at each end.

So do I, Gene. Have you looked at my web page? A standing-wave antenna
contains standing waves. The forward and reflected currents superpose.
If there is any phase shift at all through a 75m bugcatcher coil, the
current at the bottom and at the top will NOT be equal even if the
forward current through the coil is constant and the reflected current
through the coil is constant. If you disagree with me and agree with
Tom, you are saying there is zero phase shift through a one foot by
one foot bugcatcher coil. Do you really want to assert that?

How can there possibly be a current drop across a dimensionless point?
The fact is, a dimensionless point inductance does NOT and can NOT exist
in reality. So are more interested in playing games in your mind than
you are in the real world? The argument is about real world 75m bugcatcher
coils, not ideal inductances that exist only in someone's wet dream.

Your example is a circuit, not a distributed network, and is therefore
irrelevant to this discussion. Distributed networks behave different
enough from lumped circuits that the lumped circuit shortcuts just
don't work on distributed networks. Why you and Tom want to force your
lumped constant concepts unquestioned upon the field of distributed
network problems is beyond me.

Your RG-58 transmission line example is no different. The current from
the source is not lost or "dropped". It simply finds other paths in
addition to the "load" to return back to the source. Antennas and
loading coils exhibit the same phenomenon.

Some of the power radiated from an antenna does NOT return to the source.
It may even escape to outer space. Power lost from the system causes
a current drop. In fact, it is hard to separate the H-field from the
E-field for RF. I am amazed how you guys have been seduced by your math
models. Reality is supposed to dictate math models, not vise versa.
--
73, Cecil http://www.qsl.net/w5dxp


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