Somehow I'm getting the image here of engineers sitting at their
computers, proposing lofty but unsupportable theories and modeling
idealized but impossible circuits, while the tinkerers -- REAL MEN --
with grease under their fingernails, wrenches in hand, are designing and
producing the practical items that REALLY WORK.

Lemme tell 'ya. Those generators that make your power, those turbine
blades that spin them. Those jet engines and airframes that get you
across the country with nearly unbelievable reliability and safety. The
little HTs you yak on. The signal generators, spectrum analyzers,
oscilloscopes you use to make measurements. The marvelous ICs that do
everything from running your microwave oven to being the guts of your
PC. Those weren't designed by technicians or back room tinkerers. Those
were designed by engineers who know and understand basic principles and
how to apply them. Nearly anything designed in the last couple of
decades has been extensively modeled before the first metal is cut, the
first wire soldered, the first circuit board or IC produced. And when
the extensively modeled airplane is built, it flies. The IC and circuit
board work. They work by the thousands or hundred of thousands, despite
tolerances, component variations, and temperature changes. Because they
were modeled and they were understood. Not because somebody made one
sorta work once on a workbench by experimenting. People who reject
modeling as "paper stuff" and decry established theory have simply
crippled themselves. It's their choice, but there's no reason to be
proud of it.

Part of the everyday work of an engineer involves making measurements of
one sort or another. And it's when the results are surprising that
you'll see the difference between someone who has a solid background in
fundamentals and the person who doesn't. The former will work to resolve
the surprising measurement results with known and trusted theory. The
latter will question the theory, not having a solid background to build
on. I've seen technicians quickly reject Ohm's law on the basis of a
single careless measurement. From then on, that person has lost the
ability to rely on a powerful principle, and can never be quite sure
what kind of relationship to expect among voltage, current, and
resistance. A person who does understand the principles will search for
what errors or shortcomings have been made in the measurement process,
or what simplifications have been made that aren't valid, will resolve
them, and will learn from them. Let me give just one example from my own
experience -- there've been scores like it over the years. Years ago, I
was measuring the input impedance of a simple antenna (folded dipole, as
I recall) through a one wavelength piece of coax. Assuming that the
measured impedance was the same as at the antenna, the results were very
different than modeling had shown. Some people, it seems, would have
immediately posted the results on the web, challenging the modeling and
transmission line theory, loudly and forcefully demanding that everyone
who doesn't believe the results should immediately go out and make
measurements. After all, that's proof, is it not, that the modeling is
bunk and transmission line theory is bunk.

Well, the reason for the strange results turned out to be coax loss. A
bit of analysis (based on known principles) shows that even a small
amount of transmission line loss will skew the measured Z toward the
line's Z0. The effect is surprisingly strong when the impedance to be
measured is quite different from the line's Z0, as it was in this case.
Another thing I learned was that the coax I was using, a small diameter
75 ohm cable, was extraordinarily lossy at the low frequency of 7 MHz
where I was making the measurements. I determined this to be due to the
small center conductor, made of strands of tiny Copperweld wire. The
copper coating was thick in terms of percentage, but thin in terms of
skin depths at the low frequency because of the very small strand
diameter. So current was flowing in the steel cores. I ended up learning
two important things from the episode, which I've applied ever since to
similar problems, and other ones too. If I were someone who was quick to
throw out conventional theory or modeling results, I never would have
learned from it, and I wouldn't be able to depend on either modeling or
transmission line theory.

Now, getting to the issue at hand. Those of us who studied and
understood basic circuit analysis know that a vanishingly small inductor
or any other two-terminal component must have equal currents in and out.
When measurements show results that differ from this, it means -- to we
who understand and believe the principles -- that either there's
something we don't know about the measurement method that's skewing the
results, or the approximation of a vanishingly small component isn't
valid. Of course a lengthy inductor in an antenna isn't vanishingly
small, and it also couples strongly to the antenna above and below it.
So no one who understands basic principles would be the least bit
surprised to find different currents at the inductor ends. However, the
statement that significant current differences were found at the ends of
an apparently small toroid aroused my curiosity. Either there's a
peculiarity in the measurement, or there's a sneak current path, such as
stray capacitance, accounting for the current imbalance.

Being curious, I made some measurements of my own of a loading inductor
at the base of an antenna. The details of the test are a bit lengthy,
and this posting is already long, so I'll post it separately.

I feel kind of sorry for people who are quick to abandon established
principles each time a casual measurement -- or even a careful one --
seems to contradict them. They're pretty much doomed to randomly trying
this or that, without ever having the hope of understanding what they're
doing. It's just the sort of thing that gives rise to astrology and
phrenology, as ways to try to understand the mysteries around us. I
greatly prefer science, but each to his own. It is true that a person
with marginal math skills might not be able to discover, let alone
quantitatively prove, that coax loss was the culprit in the example I
gave above. Without some background in math, as well as basic
principles, it's not really possible to understand things on a very
fundamental level. So a person without math skills is pretty much
limited to general, rather than specific, understanding.

As a footnote, I was a technician for quite a few years, first self
taught, and later going through the Air Force radar technician school. I
worked as a broadcast engineer, and repaired various equipment from
radios, TVs, and telephone answering machines to heavy ground military
radar. (I was, incidentally, regarded as being a very good technician.
One reason was that I did firmly believe in the basic principles as I
was able to understand them, and applied them whenever possible.) But I
was often frustrated because I kept encountering things I didn't
understand as fully as I wanted, which is why I ended up working my way
(with a little help from Uncle) through engineering school. It gave me
the theoretical and mathematical tools to understand a whole lot more
about how things work, and on a much deeper level. I use modeling
extensively, as do nearly all my fellow engineers, and I've been able to
consistently design quality electronic equipment in a wide variety of
categories -- by understanding and applying basic principles. Far from
converting me to the effete theoretician I'm seeing caricatured here,
the education and engineering experience has added immeasurably to my
ability to understand this fascinating field.

Roy Lewallen, W7EL

Art Unwin KB9MZ wrote:
oSaddam (Yuri Blanarovich) wrote in message ...

Yuri shouldn`t bemoan lack of response to his Antenna Group 7. It only
shows there is not much to contradict.

Best regards, Richard Harrison, KB5WZI




Hi Richard,
thanks very much for the positive reinforcement. Seems that those who get their
hands dirty from antenna grease know a thing or two, those who model their
world on the computer know their paper stuff.


Yuri you make a very good point there. Those skilled in the
arts have often used gimmicks or quasi ruses in their studies
especialy in the use of mathematics where one can show on paper that
one plus one equals three
but cannot prove it factually. Engineers also use imaginary things in
the search of knoweledge where those that use their hands have to deal
with the real world. For many inductance is pure but imaginary as is
capacitance, each of these in the real world is a network but
engineers with the help of Laplace
have learned to deal with the real world with altered equations yet
use the same name such as inductance which in the real world there is
no such thing.
The fact that you used an imaginary term such as inductance instead of
a network unfortunately placed you in their camp in the world of
imagination.
An example with respect to your subject is for you to ask them to
provide you with an inductance of unlimited Q which in the imaginary
world that they frequent is no big deal, where in the real world you
are finding that Q beyond a 1000 is nigh impossible. Since speach
itself cannot resolve factual things to the satisfaction of all then
their will be no resolution.
All this reminds me of a problem I had years ago when I reffered to
capacitive coupling where its inherrent inductive component can be
used for matching purposes.
Now you tell me how you can convince experts that a capacitor is a
network
and thus has a usefull inductance component when they see for
mathematical reasons that the word capacitance refers to an imaginary
term to describe
what cannot be in the real world?
However Yuri your experimenting supplies an advantage over the experts
in that
it is in the real world that true invention has its value.
Art