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Old November 10th 03, 03:08 PM
Cecil Moore
 
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Roy Lewallen wrote:
and Cecil's, that the output current should equal the
current, both in phase and magnitude.


Hold the presses! That was a rounded off ballpark value.
You haven't told us what the feedpoint impedance is yet
so an accurate estimate is impossible so far. Is the
feedpoint impedance 35.6+j8? Is that the impedance into
which you are shoving one amp?
--
73, Cecil http://www.qsl.net/w5dxp



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Old November 10th 03, 03:25 PM
Cecil Moore
 
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Roy Lewallen wrote:
That's the problem. The more times I read what you've posted, the more
confused I've gotten.


Use EZNEC to display the current distribution for a 102 ft center-fed
dipole on 20m. Assume the origin is the feedpoint. Turn the current
phase on. You have 270 degrees of a cosine wave for the current to the
right of the feedpoint. You have a current maximum at zero degrees and
180 degrees. The current magnitude decreases to zero in the first 90
degrees. The current magnitude increases to a maximum negative value
in the second 90 degrees. The current magnitude decreases to zero in
the third 90 degrees. Where one locates a loading coil and how many
degrees it replaces will determine the magnitude and phase of the
current into the coil and the current out of the coil. There are
three possibilities.

You have a unique talent for turning an honest effort at being truthful
and accurate into an insult, as you did with Ian.


Roy, honest efforts are not always valid and the truth sometimes hurts.

This is precisely why I've given you the opportunity to choose the
inductor for the 10 MHz test. You choose it so that it will best
illustrate what you say is true. Shucks, I even encourage you to do the
experiments yourself.


I have some 1.5" diameter, 6 tpi stock. Get a one foot stinger and use
enough of that kind of stock to resonate on 10 MHz. I guarantee the
current will be different into and out of the coil.
--
73, Cecil http://www.qsl.net/w5dxp



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Old November 10th 03, 03:30 PM
Cecil Moore
 
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Roy Lewallen wrote:
What I'm looking for now, however, is your recommendation for a test
which will clearly show the current ratio you claim will happen, of such
a magnitude that the result will be clear even in the presence of a few
percent error.


Assuming the test is on 10 MHz, use a one foot stinger and enough 1.5"
diameter, 6 tpi air-core stock to resonate the vertical on 10 MHz. I
guarantee there is a difference in current in and out of the coil.
--
73, Cecil http://www.qsl.net/w5dxp



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Old November 10th 03, 03:40 PM
Richard Harrison
 
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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

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Old November 10th 03, 04:49 PM
Cecil Moore
 
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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



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Old November 10th 03, 08:06 PM
Jim Kelley
 
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"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



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Old November 10th 03, 08:20 PM
Roy Lewallen
 
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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


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Old November 10th 03, 08:21 PM
Roy Lewallen
 
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So, you've retracted your prediction. What's your new one, then?

Roy Lewallen, W7EL

Cecil Moore wrote:
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


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Old November 10th 03, 08:31 PM
Roy Lewallen
 
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The feedpoint impedance without the inductor was 35 - j185. The inductor
was 0.6 + j192. Sorry, I had left it up to you to add the two together,
to get 35.6 + j7 ohms.

It would be nice to have something better than a ballpark value, since I
think I can get the ratio of output to input to within a couple of
percent or so, and resolve two or three degrees of phase shift. Anything
more precise than that, though, I won't be able to resolve anyway. Which
is why the next test might be better, since you'll be choosing the
inductor size to make the shift very apparent. Won't you?

So what's your new, more precise prediction of the output:input current
ratio (magnitude and phase) for the system I did measure?

Incidentally, I've now also made a measurement using the same system on
the bench, substituting a series RC with the same Z as the antenna
feedpoint for the antenna. You've stated that you expect to see a
difference between this setup and the antenna (the former being "lumped"
and the latter "distributed"). Do you, Yuri? How about you, Richard? If
so, what should I be seeing for the ratio of output:input current in the
lumped setup?

Roy Lewallen, W7EL

Cecil Moore wrote:
Roy Lewallen wrote:

and Cecil's, that the output current should equal the current, both in
phase and magnitude.



Hold the presses! That was a rounded off ballpark value.
You haven't told us what the feedpoint impedance is yet
so an accurate estimate is impossible so far. Is the
feedpoint impedance 35.6+j8? Is that the impedance into
which you are shoving one amp?


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Old November 10th 03, 08:38 PM
Cecil Moore
 
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Roy Lewallen wrote:
So, you've retracted your prediction. What's your new one, then?


No, you misunderstood my prediction. I cannot make an accurate
prediction until you tell us the feedpoint impedance of the
antenna including the coil. Is it 34.6+j8 or what? You have
told us the feedpoint impedance of the antenna without the
coil and the impedance of the coil but we still don't have
an accurate measurement for the feedpoint impedance of the
antenna including the coil. Did you measure it? If not, any
estimate is not going to be very accurate.
--
73, Cecil, W5DXP

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