Yuri Blanarovich wrote:
Judging by description, I would guess that there wasn't much difference.

The feedpoint of the radiator alone is 35-j185. The impedance of the loading
toroid is 0.6+j193. Assuming perfect predictability, that gives the antenna
system a feedpoint impedance of 35.6+j8, i.e. it is *longer* than resonant.
That moves the current maximum point inside the toroid making the current
in and out even closer to equal. If a coil is installed at a current maximum
point or a current minimum point, the current in and out will be the same.
If a coil is installed at a place where the slope of the current envelope
is positive, the current will actually increase through the coil.
--
73, Cecil http://www.qsl.net/w5dxp



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Can I conclude from this that if I were to make a coil with more or less
inductance, then I would see a current difference between the ends of
the coil?

So tell you what. If you'll pull out your equations and calculate the
expected current difference, I'll replace the coil with one of 100 ohms
reactance and remeasure. How much current difference (magnitude andd
phase, of course) between the ends of a 100 ohm inductor at the base of
that same antenna?

Roy Lewallen, W7EL

Cecil Moore wrote:
Yuri Blanarovich wrote:

Judging by description, I would guess that there wasn't much difference.


The feedpoint of the radiator alone is 35-j185. The impedance of the
loading
toroid is 0.6+j193. Assuming perfect predictability, that gives the antenna
system a feedpoint impedance of 35.6+j8, i.e. it is *longer* than resonant.
That moves the current maximum point inside the toroid making the current
in and out even closer to equal. If a coil is installed at a current
maximum
point or a current minimum point, the current in and out will be the same.
If a coil is installed at a place where the slope of the current envelope
is positive, the current will actually increase through the coil.

Roy Lewallen wrote:
Can I conclude from this that if I were to make a coil with more or less
inductance, then I would see a current difference between the ends of
the coil?

So tell you what. If you'll pull out your equations and calculate the
expected current difference, I'll replace the coil with one of 100 ohms
reactance and remeasure. How much current difference (magnitude andd
phase, of course) between the ends of a 100 ohm inductor at the base of
that same antenna?

I know you are not that naive, Roy. I have said many times over the past
few days that if you locate a coil at a current maximum point, the current
will be approximately equal at each end. So what did you do? You locate
your coil at a current maximum point and I assume your measurements proved
me to be correct. As long as you install the coil at the base of the
antenna, the currents are guaranteed to be close to equal as I have
said any number of times.

If you place the coil at a location where the slope of the current is
maximum and positive, the current through the coil will *INCREASE*.

If you place the coil at a location where the slope of the current is
maximum and negative, the current through the coil will decrease. This
is typical of center-loaded mobile HF antennas.

Incidentally, Kraus engages in some of your alleged "pseudo-analysis"
in his book. He clearly shows the current drop through loading coils.
He even says a coil can be used to shift the current by 180 degrees.
Come to think of it, my 440 MHz mobile antenna has a coil in the center
that shifts the current by 180 degrees yielding considerable gain
from those two phased elements.
--
73, Cecil http://www.qsl.net/w5dxp



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Ah,

So now you're saying that any coil at the base of a short vertical
antenna, regardless of its value, will have equal currents at the input
and output?

Ok, suppose I make the measurement at, say, 10 MHz, where the coil is no
longer at the current maximum. Tell you what. I'll set up a 33 foot wire
vertical, to eliminate the difficulty of the mounting arrangement. I'll
furnish you the base impedance at 10 MHz, and even let you choose the
inductor value. Be sure and choose a value that will clearly illustrate
your point. Using the fine education you received from Balanis et al,
calculate the current into and out of the inductor (phase and
magnitude), and I'll set it up and measure it. Since it is a fair amount
of work on my part, though, I'd like to do a dry run first, using, say,
the base impedance predicted by EZNEC. Then, after you've shown us how
you make the calculations, I'll build the antenna and do the
measurement. I'd hate to go to the considerable trouble of setting it up
and find that you somehow aren't able to do the calculation.

Other predictions would be welcome, too, such as Yuri's, based on the
"missing antenna length" theory of inductor currents.

Better yet, you can do the measurement yourself. As you can see from the
picture I just posted to my web site, the measurement ain't exactly
rocket science. I don't have much time to burn, but still shook loose
enough to set it up. Anybody with a two channel scope, a soldering iron,
and a signal generator or transmitter can do just what I've done. You
can too.

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

Can I conclude from this that if I were to make a coil with more or
less inductance, then I would see a current difference between the
ends of the coil?

So tell you what. If you'll pull out your equations and calculate the
expected current difference, I'll replace the coil with one of 100
ohms reactance and remeasure. How much current difference (magnitude
andd phase, of course) between the ends of a 100 ohm inductor at the
base of that same antenna?


I know you are not that naive, Roy. I have said many times over the past
few days that if you locate a coil at a current maximum point, the current
will be approximately equal at each end. So what did you do? You locate
your coil at a current maximum point and I assume your measurements proved
me to be correct. As long as you install the coil at the base of the
antenna, the currents are guaranteed to be close to equal as I have
said any number of times.

If you place the coil at a location where the slope of the current is
maximum and positive, the current through the coil will *INCREASE*.

If you place the coil at a location where the slope of the current is
maximum and negative, the current through the coil will decrease. This
is typical of center-loaded mobile HF antennas.

Incidentally, Kraus engages in some of your alleged "pseudo-analysis"
in his book. He clearly shows the current drop through loading coils.
He even says a coil can be used to shift the current by 180 degrees.
Come to think of it, my 440 MHz mobile antenna has a coil in the center
that shifts the current by 180 degrees yielding considerable gain
from those two phased elements.

Roy Lewallen wrote:
So now you're saying that any coil at the base of a short vertical
antenna, regardless of its value, will have equal currents at the input
and output?

No, I didn't say that. I wish you would read what I say. If the coil is
a low reactance (not many degrees) and the current maximum point is inside
the coil, the two currents will tend to be equal.

Ok, suppose I make the measurement at, say, 10 MHz, where the coil is no
longer at the current maximum. Tell you what. I'll set up a 33 foot wire
vertical, to eliminate the difficulty of the mounting arrangement. I'll
furnish you the base impedance at 10 MHz, and even let you choose the
inductor value. Be sure and choose a value that will clearly illustrate
your point. Using the fine education you received from Balanis et al,
calculate the current into and out of the inductor (phase and
magnitude), and I'll set it up and measure it. Since it is a fair amount
of work on my part, though, I'd like to do a dry run first, using, say,
the base impedance predicted by EZNEC. Then, after you've shown us how
you make the calculations, I'll build the antenna and do the
measurement. I'd hate to go to the considerable trouble of setting it up
and find that you somehow aren't able to do the calculation.

I can't do the calculation because I don't know the attenuation factor.
Do you think my inability to do the calculation proves anything about
what's happening in reality at the antenna? You guys need to turn loose
of the concept that what happens or doesn't happen on a piece of paper
dictates reality.

I can describe a base-loaded configuration that will demonstrate the
principle. Take a 75m bugcatcher coil, one of the 6"x6" models, and
choose a stinger that resonants the antenna in the 75m-80m band. Then
measure the in and out currents at a frequency a little below resonance.
--
73, Cecil http://www.qsl.net/w5dxp



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Cecil Moore wrote:
Roy Lewallen wrote:

So now you're saying that any coil at the base of a short vertical
antenna, regardless of its value, will have equal currents at the
input and output?


No, I didn't say that. I wish you would read what I say. If the coil is
a low reactance (not many degrees) and the current maximum point is inside
the coil, the two currents will tend to be equal.

I did read what you said. You said that it wouldn't exhibit a phase
shift if placed at a current maximum. The current at the base of a short
vertical antenna is at its maximum there. So now if you're saying that
it *won't* exhibit a phase shift if placed at the base of a short
antenna, let's try this. Suppose I remount my antenna to eliminate the
shunting effect of the mounting, and do my measurements at 3.8 MHz as
before. Suppose the base input Z is, say, 35 -j380. You choose any
inductor value you'd like, that will best illustrate your method, and
tell me what output to input current ratio to expect.

Ok, suppose I make the measurement at, say, 10 MHz, where the coil is
no longer at the current maximum. Tell you what. I'll set up a 33 foot
wire vertical, to eliminate the difficulty of the mounting
arrangement. I'll furnish you the base impedance at 10 MHz, and even
let you choose the inductor value. Be sure and choose a value that
will clearly illustrate your point. Using the fine education you
received from Balanis et al, calculate the current into and out of the
inductor (phase and magnitude), and I'll set it up and measure it.
Since it is a fair amount of work on my part, though, I'd like to do a
dry run first, using, say, the base impedance predicted by EZNEC.
Then, after you've shown us how you make the calculations, I'll build
the antenna and do the measurement. I'd hate to go to the considerable
trouble of setting it up and find that you somehow aren't able to do
the calculation.


I can't do the calculation because I don't know the attenuation factor.

What "attenuation factor" is it you need? Is it something that can be
measured? If not, how about an equation or prediction with the
"attenuation factor" as a variable? We can estimate a probable range of
values, then see if the measurement results are within them.

Do you think my inability to do the calculation proves anything about
what's happening in reality at the antenna? You guys need to turn loose
of the concept that what happens or doesn't happen on a piece of paper
dictates reality.

I hope to demonstrate what constitutes reality by theoretical analysis
and by measurement. Where I come from, that counts much more than
arm-waving, insulting, and vague explanations. Ultimately, each of the
readers of these exchanges will decide what to believe, and I'm sure you
will have convinced some.

I can describe a base-loaded configuration that will demonstrate the
principle. Take a 75m bugcatcher coil, one of the 6"x6" models, and
choose a stinger that resonants the antenna in the 75m-80m band. Then
measure the in and out currents at a frequency a little below resonance.

I have no disagreement that a "bugcatcher" coil, or any coil of
physically significant size, will exhibit a phase shift and magnitude
change of current from one end to the other. Where we disagree is that
you believe that a physically very small inductor will also exhibit
this. I don't. I'm proposing a test which will show, with reasonable
certainty, which viewpoint is correct. I fully expect every test I make
to bring forth a flurry of objections. So I'm giving you the opportunity
to choose the inductor which will best illustrate your point of view. I
want to limit the parameters of the test to conditions I think I can
measure with reasonable accuracy. With the equipment I've got, that
pretty much limits me to doing measurements at the antenna base. But I
think (although I'm still not sure) that you're now saying that there
should be a substantial current difference between the input and output
of a small inductor at the base of an antenna, if the antenna and
inductor are properly chosen. So, you choose. And if you won't make the
measurement, I will.

Roy Lewallen, W7EL

Roy Lewallen wrote:
I did read what you said. You said that it wouldn't exhibit a phase
shift if placed at a current maximum.

I'm sorry, there is a misunderstanding that is my fault. When I say
"current is the same.", I'm implying magnitude only. That's a
convention left over from my college days and may not be a
convention any longer. If I said anything at all about phase, I
used the word, "phase", in my posting. So I will stop omitting
the word, "magnitude", when I am talking about magnitude.

So do a system reset on what you think I said. There is always a
phase shift through a real-world inductor. Whether it can be
measured accurately is another matter. When I said: "If the
current maximum point is located in the middle of a coil, the
current (implied magnitude) in and out of a coil will be equal.",
I was implying current magnitude only. I didn't imply or say anything
about phase unless I used the word, "phase" in the sentence.

I also have not said anything about the phase of the currents into
and out of your toroidal inductance except to say it replaces
approximately 18 degrees of antenna.

The current at the base of a short
vertical antenna is at its maximum there. So now if you're saying that
it *won't* exhibit a phase shift if placed at the base of a short
antenna, let's try this.

As you can see above, I never said anything like that.

Suppose I remount my antenna to eliminate the
shunting effect of the mounting, and do my measurements at 3.8 MHz as
before. Suppose the base input Z is, say, 35 -j380. You choose any
inductor value you'd like, that will best illustrate your method, and
tell me what output to input current ratio to expect.

I am still leery about your ability to separate small phase shifts
from noise. We need to make the inductor large enough to ensure
the phase shift measurements are above the noise level.

I have no disagreement that a "bugcatcher" coil, or any coil of
physically significant size, will exhibit a phase shift and magnitude
change of current from one end to the other.

Huh?????? I thought that was what the argument was all about. What
triggered this whole discussion was W8JI's alleged assertion that
a loading coil like a bugcatcher doesn't affect the current at all.

Where we disagree is that
you believe that a physically very small inductor will also exhibit
this. I don't.

The effect of a very small inductor may be too small to measure in
the presence of strong fields and noise. Ask yourself, at exactly
what value of inductor does the phase shift completely disappear?
+j1? +j10? +j100? +j1000? What is the crossover point from some
phase shift to zero phase shift? Can you measure a phase shift of
0.1 degree at HF? Zero phase implies faster than light propagation
through the coil.
--
73, Cecil, W5DXP

"Roy Lewallen" wrote in message
...
I did read what you said. You said that it wouldn't exhibit a phase
shift if placed at a current maximum. The current at the base of a short
vertical antenna is at its maximum there. So now if you're saying that
it *won't* exhibit a phase shift if placed at the base of a short
antenna, let's try this.

Naturally, the inductance of the coil and the resistance of the circuit
determine how much of a phase shift there will be. But the amount of
resulting change in current magnitude will depend on where on the cosine
curve this shift occurs. A 10 degree phase shift from 40 to 50 degrees
generates almost an order of magnitude greater change in current that it
does shifting from 0 to 10 degrees. Obviously, the closer the center of
the coil is to zero (or 180) degrees, the smaller the resulting differential
in current across the coil.

73, Jim AC6XG

Roy, W7EL wrote:
"Other predictions would be welcome, too, such as Yuri`s based on the
"missing antenna length" theory of inductor current."

It`s desirable to resonate a standing-wave antenna to reduce impediment
to antenna current.

In the 19th edition of the ARRL Antenna Book, there is a section on
"Base Loading and Center Loading" beginning on page 16-4.

First point is that current is not uniform in a ground mounted whip
because the bottom section of the whip is closest to the ground, and so
has more capacitance to the ground.

Next point is that raising the coil up in the whip improves current
distribution. The high voltage which boosts capacitive current is moved
farther away from the earth or ground plane. Lower voltage below the
coil has less capacitive current between the earth and whip than before
the coil was boosted. Current below the coil is now almost uniform.

Table 1 gives coil values for base loading and center loading an 8-ft
whip in amateur bands between 1.8 and 29 MHz.

There is a CD-ROM attached to the rear cover of the ARRL Antenna Book
which includes a program, MOBILE.EXE, for optimization of coil
placement.


There is much practical information in this Antenna Book section. I`d
speculate it was tried and proved useful before it was included in the
Antenna Book. Has anyone found faults?

Best regards, Richard Harrison, KB5WZI

Hopefully your skills extend beyond looking up values in books, to being
able to do actual calculations. Given the measured antenna impedance I
reported and the inductor I used, what should we expect as the ratio
(magnitude and phase) of output to input current at the two inductor leads?

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"Other predictions would be welcome, too, such as Yuri`s based on the
"missing antenna length" theory of inductor current."

It`s desirable to resonate a standing-wave antenna to reduce impediment
to antenna current.

In the 19th edition of the ARRL Antenna Book, there is a section on
"Base Loading and Center Loading" beginning on page 16-4.

First point is that current is not uniform in a ground mounted whip
because the bottom section of the whip is closest to the ground, and so
has more capacitance to the ground.

Next point is that raising the coil up in the whip improves current
distribution. The high voltage which boosts capacitive current is moved
farther away from the earth or ground plane. Lower voltage below the
coil has less capacitive current between the earth and whip than before
the coil was boosted. Current below the coil is now almost uniform.

Table 1 gives coil values for base loading and center loading an 8-ft
whip in amateur bands between 1.8 and 29 MHz.

There is a CD-ROM attached to the rear cover of the ARRL Antenna Book
which includes a program, MOBILE.EXE, for optimization of coil
placement.


There is much practical information in this Antenna Book section. I`d
speculate it was tried and proved useful before it was included in the
Antenna Book. Has anyone found faults?

Best regards, Richard Harrison, KB5WZI