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  #251   Report Post  
Old November 7th 03, 04:34 PM
Richard Harrison
 
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Yuri, K3BU wrote:
"Point by point please." to a list of 7 facts supporting his contention
that a non-uniform current exists in a 1/4-wave antenna with a loading
coil inserted at a spot from 50 to 70% of the radiator length, on Wed.
Nov. 5, 2003, 3:15 am (CST + 6).

1. Coil is warmer at bottom than top.

As power dissipation is proportional to the square of the current, it
shows that in a uniform structure heat is where the current is high.

2. Current indicators at the top and bottom of a loading coil show 40 to
60% difference in ends of the loading coil.

High accuracy may not be available, but the argument is between same
current or dissimilar currents at the ends of the coil. High accuracy is
not needed.

3. Let`s look at the RF choke.

It`s not what the coil is called. It`s position and size with respect to
wavelength.

4. W9UCW used a toroid and got the same results.

The results were based on phase delay, not coil radiation. Antenna
current in a coil results from overcoming an opposition. This impedance
is a vector sum of reactance and resistance. The reactance of the coil
is the same in both directions of energy travel. The impedance the
antenna presents at the ends of the coil is not the same in both
directions.

Any coil reactance produces a delay. Inductors used in telephone
circuits to block audio and pass d-c and low-frequency ringing current
are called "retardation coils". A delay time of the signal is called
"phase lag". These are appropriate names. Toroid coils cause phase lag
too.

5. Cecil explained the reflected wave situation and delay in the
coil---.

Cecil did it accurately and well.

6. ON4UN in his Low Band DXing book for years has shown and explained
the distribution of current in various configurations of loading
coils----etc.

ON4UN did it right and it has stood the test of time. Don`t hold your
breath waiting for revisions.

7. How could it be if the voltage (neon bulb test) is increasing along
the coil towards the top, current has to be decreasing.

Yes, unless the power is increasing in the same direction, and it`s not.
The neon shows high potential gradient points. In the driven
quarter-wave radiating element, loaded or unloaded, the maximum voltage
always seems to be at the tip end.

We know that as in a transmission line, in a standing-wave antenna,
reflection produces current maxima at voltage minima, and vice versa.

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

  #252   Report Post  
Old November 8th 03, 12:26 AM
Yuri Blanarovich
 
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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.
So far not a one "overthrow" of my 7 points, so I take it that we are on the
right track and hope that others get it too and help us to use it properly.

BTW I just found good source for liquid crystal strip thermometers, they have
them in the pet shops, they are used for aquarium temperature measurements cost
around $2. Cheap and easy way to verify the heat from current. I will get some
and run som visual tests on Hustlers.

73 Yuri
  #253   Report Post  
Old November 8th 03, 06:04 PM
Cecil Moore
 
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K7JEB wrote:
I will be happy to send out the .EZ file for this
to any interested parties. Splice together the
e-mail address below to contact me.


Good stuff, as usual, Jim. It comes as no surprise to me that a three
dimensional component with distributed resistance, distributed inductance,
and distributed capacitance changes the voltages and currents at each end
of the component. The changes are accentuated in a standing-wave environment.

And to improve on your model a tad, make the capacitive wires equal on
each side of the installation point, i.e. instead of a 2 foot wire sticking
out horizontally, make it one foot of wire sticking out in two opposite
directions. That will minimize radiation from those wires.
--
73, Cecil http://www.qsl.net/w5dxp



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  #254   Report Post  
Old November 8th 03, 10:19 PM
K7JEB
 
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Cecil, W5DXP, wrote:

And to improve on your model a tad, make the capacitive wires equal on
each side of the installation point, i.e. instead of a 2 foot wire sticking
out horizontally, make it one foot of wire sticking out in two opposite
directions. That will minimize radiation from those wires.


Good suggestion, Cecil. I had planned to make the capacitive
wires into little square-shaped contraptions having about the
same size as a turn of wire on the loading coil and then
duplicate them up and down in the Z direction. I may still
do this, but I wanted to publish the preliminary results as
soon as I saw an effect, however imperfectly perceived.

Jim, K7JEB


  #255   Report Post  
Old November 9th 03, 12:28 AM
Art Unwin KB9MZ
 
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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




So far not a one "overthrow" of my 7 points, so I take it that we are on the
right track and hope that others get it too and help us to use it properly.

BTW I just found good source for liquid crystal strip thermometers, they have
them in the pet shops, they are used for aquarium temperature measurements cost
around $2. Cheap and easy way to verify the heat from current. I will get some
and run som visual tests on Hustlers.

73 Yuri



  #256   Report Post  
Old November 9th 03, 02:39 AM
Yuri Blanarovich
 
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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


I guess it is a sign of where "modern" technology and modeling is leading us -
to the imaginary paper world.

It just disturbs me that some of the "learned" people would not "lower"
themselves to the reality, question the facts and adjust their "knowledge" out
of the modeling world. As Cecil said, modeling supposed to model reality or
close to it, not the other way around. In view of this exercise I am going to
revise and investigate some of the topics I asked about here before. Looks like
the "advice" I got might not be based on reality.
I am sorry to see some of the "gurus" ridiculing and making snotty remarks,
rather than pausing and stepping back to have a closer look or question or
discuss it in a civil manner. Oh well, good thing it is only a hobby :-)

73 Yuri, K3BU
  #257   Report Post  
Old November 9th 03, 02:52 AM
Roy Lewallen
 
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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


  #258   Report Post  
Old November 9th 03, 04:31 AM
Roy Lewallen
 
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Here are some preliminary details about the inductor current measurement
I made.

My antenna isn't nearly as ideal as the one Yuri described. (But if my
results are different from the ones reported at the web site Yuri
referenced, I'll be eager to hear why.) It's about 33 feet high, and has
only 7 buried radials. The feedpoint impedance indicates a loss of about
25 ohms at 7 MHz, so I'd expect it to be a bit more at 3.8. It's bolted
to a galvanized fence line post which protrudes nearly four feet from
the ground, with spacing between the antenna and the post of about 1/4".
This mounting has only a minor effect on the feedpoint impedance at 7
MHz, which is the antenna's intended frequency of use. It's quite
profound at 3.8 MHz, though. The expected 370 or so ohms of capacitive
reactance is transformed to 185, while the feedpoint R is 35 ohms, not
far from the expected value. So the overall feedpoint Z is 35 - j185
ohms at 3.8 MHz, measured with a GR 1606A impedance meter. (I found that
my MFJ 269 was about right with the X, but measured R as zero --
apparently the combination of low frequency and large X is a problem for
it in resolving the R.) So I built an inductor with measured impedance
of 0.6 + j193 ohms. It's 26 turns on a T-106-6 toroid core. Q is a bit
over 300. This was placed in series at the antenna feedpoint.

For current measurements, I made two identical current probes. Each one
consists of 10 turns wound on an FT-37-73B ferrite core. The two leads
from the winding are twisted and wound in bifilar fashion on another
FT-37-73B core, 10 turns. This is then connected to an oscilloscope
input via a two-foot (approx.) piece of RG-58. A 50 ohm termination is
also at the scope input. This gives the probe a theoretical insertion
impedance of 0.5 ohm. While making the measurements, I moved, grabbed,
and re-oriented the coax cables, with no noticeable effect. This gave me
confidence that the outsides of the coax weren't carrying any
significant current.

One probe went to each channel of the scope. I left the two scope inputs
in the cal position, put both probes on the wire at the input end of the
inductor, and recorded the p-p values with the scope's digital
measurement feature. Then I reversed the order of the probes and
remeasured. I found a slight prejudice toward the probe closest to the
source -- 1.2% in one ordering, and 2.1% in the other. Averaging the two
channels, though, showed them to be the same within less than 1%. (Each
probe was always connected to the same scope channel, so this is a test
of the probe-scope channel combinations.)

Then I moved one probe to the output side of the inductor, and measured
input and output current. And I reversed the probe positions on inductor
input and output. The ratio of output to input current in the two tests
differed by only 1.4%.

When I encounter an astrologist, they invariably ask what "sign" I "am",
then proceed to tell me how my personality meets their expectations. So
what I do instead is to have them tell *me* what "sign" I "am" *first*
-- which they should easily be able to do, based on my personality.
Well, they don't find that to be fair, for some reason (although I
certainly find it amusing). And so, I doubt if the following challenge
will be regarded to be fair, for much the same reason. Those with
alternative rules for solving circuit problems are challenged to predict
what the ratio of output current to input current will be. I'm
particularly targeting Cecil, and others who have bandied about a lot of
pseudo-analysis about electrical length, reflections, and the like. And,
Richard (Harrison), who said something like "an inductor without phase
shift is like". . . I don't recall. . .hot dog without ketchup or
something. Pull out your theories, and calculate it, like any competent
engineer should be able to do. For cryin' out loud, it's a simple series
circuit (except for Cecil, where it's some kind of distributed thing).

First post your answers, then I'll post the result of my measurements.

Roy Lewallen, W7EL

  #259   Report Post  
Old November 9th 03, 05:38 AM
Cecil Moore
 
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Roy Lewallen wrote:
Pull out your theories, and calculate it, like any competent
engineer should be able to do. For cryin' out loud, it's a simple series
circuit (except for Cecil, where it's some kind of distributed thing).

First post your answers, then I'll post the result of my measurements.


What is the value of the distributed capacitance between each two
turns on the toroid? That distributed capacitance is what makes a
75m mobile loading coil act like a transmission line.

Question: Why didn't you use a 75m bugcatcher coil for the experiment?
--
73, Cecil http://www.qsl.net/w5dxp



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  #260   Report Post  
Old November 9th 03, 06:22 AM
Cecil Moore
 
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Roy Lewallen wrote:
I'm
particularly targeting Cecil, and others who have bandied about a lot of
pseudo-analysis about electrical length, reflections, and the like.


Balanis would be surprised to know that you consider the material that
he teaches in his classes at ASU to be pseudo-analysis. Some of the
stuff I have posted is in Balanis' book, _Antenna_Theory_ which you
haven't read. In particular, he says: "Standing wave antennas, such
as the dipole, can be analyzed as traveling wave antennas with waves
propagating in opposite directions (forwards and backwards) as represented
by traveling wave currents If and Ib in Figure 10.1(a)."

I'm just wondering how you can be so sure that what I have offered is pseudo-
analysis and which of the following statements you disagree with. Please
be specific.

1. The feedpoint impedance of a typical traveling wave antenna is in the
hundreds of ohms since there are no reflected waves.

2. The feedpoint impedance of a standing wave antenna is the result of
superposition of forward and reflected waves (which cause the observable
standing waves).

3. At the feedpoint of a 1/2WL resonant dipole, the forward current, reflected
current, and forward voltage are all in phase. The reflected voltage is 180
degrees out of phase. This results in a purely resistive low-voltage/high-current
ratio for the feedpoint impedance.

4. The above relationship is true for any dipole, 1/2WL or physically shorter,
that has a purely resistive feedpoint impedance. (No resistive loading)

5. The phases of the signals at the feedpoint are known. The phases of the signals
at the open tips of the dipole are known. Any loading used in order to increase
the electrical length to 1/2WL must maintain those known phase conditions in
order to achieve a purely resistive feedpoint impedance.

On page 18, in Figure 1.15, Balanis shows how a 1/2WL dipole is achieved by
flaring out the last ~1/4WL of an unterminated transmission line. He says:
"As the section of the transmission line begins to flare, it can be assumed
that the current distribution is essentially unaltered in form in each of
the wires."
--
73, Cecil http://www.qsl.net/w5dxp



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