Art:

[snip]
"Art Unwin KB9MZ" wrote in message
m...
But Peter you said something about changing a model
What was that all about ?
Regards
Art
[snip]

What I meant is that there is the "real world" and its' behaviour as
evidenced by
experiment and measurement and then there are "models" , i.e. theories or
mathematical constructs which humans have devised to "imitate" or "model"
the
"real world".

When considering accuracy and precision whenrepresenting real experiments
and measurements models that attempt to reflect real world performance over
time have come in various stripes.

In the history of electro-dynamics there have been three major
models/theories
developed in three eras over the last couple of hundred years.

(I) Circuit-Theoretic Model Era (circa: 1750 - 1850):

The first model/theory of electro-dynamics was the "circuit-theoetic" model
which
used the circuit theory of Messers Kirchoff and Ohm, developed in the late
1700's and the early part of the 1800's . Kirchoff's Laws and Ohm's
Laws for DC circuits ultimately supported by Heaviside's operational
calculus in
the mid 1800's to reflect both DC and AC phenomena. [Heaviside invented the
terms reactance, and impedance, etc.] But experimentalists and the
"electricians"
of the day found that circuit theory models did not predict everything
exactly!

All that said, the circuit-theoretic electro-dynamic model is pretty simple
and
accessible to anyone with a modicum of mathematical background, say the
equivalent of high school algebra and complex numbers.

Sorry... but if you can't do simple algebra, deal with the square root of
minus
one, and manipulate complex numbers then circuit-theoretic models are not
your cup of tea.

Get off the train here and go into marketing or the social sciences!

:-)

Circuit theory does a pretty good job of predicting lots of things, but it
fails to predict
effects such as skin effect, proximity effect, radiation, etc...

And so the electro-dynamic model was eventually augmented by a newer model
which
was more accurate reflects reality more closely. The second stage of the
three eras of
electro-dynamic theories was the:

(II) Field-Theoretic Model Era (circa: 1840 - 1910):

The "field-theoretic" model was first formulated the famous Scottish
theoretical
physicist James Clerk Maxwell, and rendered in its' modern form by the
eccentric,
uneducated, self-taught English genius Oliver Heaviside. Heaviside wrote
down
Maxwell's extremely complex theory in the form of four simple vector
differential
equations as we now know them. Whilst previously it had taken the Cambridge
educated Maxwell 22 quaternion laced equations to write down the same simple
theory!

Heh, heh... Of course Heaviside, a denzien of the London slums, who never
went to school
beyond age 16, had the advantage of "simplicity-of-thought" over the
Cambridge educated
Maxwell.

All that said, the field-theoretic model is considerably more complicated
than the
circuit-theoretic model and is only accessible to those prepared to go
beyond high school
algebra and complex numbers into the calculus of vector differential
equations.

Sorry but if you are not prepared to go there, as the sixteen year old poor
boy from the
slums of mid 1800's London did, then field-theoretic modeling is not your
cup of tea, and
you need to go into marketing or the social sciences...

:-)

Field theory is more complicated than circuit theory but it does a pretty
good job of
predicting all that circuit theory predicts plus a lot of other things, such
as skin effect,
proximity effect, radiation, etc... but even field theory fails to predict
the photo-electric
effect, and other interactions of photonic energy and matter, etc...

And so the electro-dynamic model had to be expanded yet again, this third
(and final)
theory is called QED or Quantum Electrodynamics.

(III) Quantum-Theoretic Model Era a.k.a. QED (circa: 1900 - 2000)

The quantum-theoretic model was initiated by Einstein in the first decade of
the 1900's
to explain the photoelectric effect and was further developed by Pauli,
Dirac, Schrodinger,
Planck, and many others and ultimately "simplified", in the Oliver Heaviside
style, by
one Richard P. Feynman from the Bronx, NY who also dramatically exposed the
cause of the Challenger tragedy with a glass of ice water. For these
efforts "Albert"
was awarded the Nobel prize. One can only presume that the Nobel committee
did
not feel that the Theory of Relativity a.k.a the "Ultimate Theory of
Gravitation", was
worth the prize! Although they did award the prize to that Italian ham
radio operator
Guglielmo Marconi! What? :-)

Now the mathematics needed to access QED is considerably more complex than
that needed for circuit theory (Algebra and Complex Numbers), field theory
(Algebra
and Complex Numbers plus Vector Calculus and Vector Differential Equations).
Indeed to access QED models one needs to understand all of the
aforementioned
plus the mathematical Theory of Probability and the Theory of Groups, Rings
and Ideals.
If you are not prepared to go there, as that poor boy named "Richard" from
the Bronx
was, why then QED is not your cup of tea and you should get off the model
train now
and take up marketing or the social sciences...

:-)

It seems today that QED models encompass all prior models and fully explain
all
known electro-dynamic phenomena and that mankind does not require further
models to augment those at hand to predict electrodynamic reality.

I wonder?

All that said... this does not mean that QED has displaced field-theoretic
and
circuit-theoretic concepts and models. Indeed circuit-theroretic and
field-theoretic
models are more widely used today than ever before!

Indeed circuit-theoretic models and field-theoretic models are used daily by
Engineers
and scientists (Note the capitalization!) on a daily basis. [Engineers make
things
people need out of stuff they can get, while scientists... :-)]

Indeed the mathematics and mechanisms of QED and field-theory are much to
complicated and unecessary to make efficient modeling of phenomena that are
quite adequately described by circuit theory. Hence the very popular
SPICE computer programs, originally developed, with US Taxpayer
support, at UC Berkeley in California and widely available for free
download,
which are used everywhere today to design both discrete and integrated
electronic
circuits from modern Op-Amps to Pentium processors uses the century and
a half old circuit-theoretic models. For an excellent free version of SPICE
download
LTSpice from the Linear Technology Corp. web site at:

http://www.linear.com/software/

and run circuit-theoretic models to your heart's content, just don't use
SPICE codes
to design antennas or predict the skin effect! :-)

Oliver Heaviside would quickly recognize the SPICE program flow charts and
computer codes were he alive today!

But circuit theory is not complex enough to solve antenna and radiation
problems
or skin and proximity effects and so one needs access to models and computer
programs that solve the partial differential vector equations of the
Maxwell-Heaviside
field theory. Hence the very popular, US Taxpayer supported, NEC computer
program codes were developed at Lawrence Livermore Labs, also available as
free
downloads. Our own Roy Lewallen W7EL provides his EZNEC programs based upon
the free NEC codes for a modest fee.

Download Roy's free demo of EZNEC at:

http://www.eznec.com/index.shtml

and run field-theoretic models to your heart's content, just don't use it to
design
photoelectric sensors or Pentium processors! ;-)

Finally if you really need to go there...

There are plenty of QED computer programs available, also widely supported
by the US Taxpayers, just google...

An Engineer is a person who knows reality and knows her models, and she...
"knows whento hold them and when to fold them".

She uses them to design and build things that people need out of stuff that
she can get.

Don't forget to thank the, often vilified, US Taxpayers for their unwavering
support of
the development of all of the free computer program implementations of
circuit-theoretic,
field-theoretic and QED models with the computer programs called SPICE, NEC
and
other QED kinda stuff...

Happy Holidays, y'all!

--
Peter K1PO
Indialantic By-the-Sea, FL
Hey... "surf's up"!