Gene Fuller wrote:
Have you actually read and understood that article? Corum mentions
several times that everything he reduces to the simple formulas applies
only to quarter-wave resonance conditions.

Yes, a mobile 75m bugcatcher antenna is quarter-wave resonant.
It is clear that you have not taken time to understand the
paper. Figure 2 looks just like a loading-coil, stinger, and
top hat which is 1/4WL resonant. Note that the coil is conceptually
replaced with a length of transmission line and that's exactly
how mobile loaded antennas work. Here are the conditions:

At the feedpoint is a piece of transmission line with a Z0 of
4000 ohms and a VF of 0.02 - physical length to be determined.

Attached to that is a piece of transmission line with a Z0 of
400 ohms and a VF of 1.0. This element is 8 feet long.

The frequency of operation is 4.0 MHz. What physical length
of the 4000 ohm line will cause 1/4WL resonance?

If you can solve that problem, you will understand how loaded
mobile antennas work. Hint: the delay through the 4000 ohm
section is NOT 3 nS.

Look at the author's highlight between equations 31 and 32. Look at the
discussion near equation 47. Look at the discussion following equation
60. Read the entire discussion in section 5.

I have done that, Gene. A 75m bugcatcher coil falls within
the specified test conditions and thus the VF equation should
be within ten percent accuracy.

Note that he does not say the characteristic impedance is a constant
that can be deduced from resonance conditions and then applied to
operating conditions. In fact, he says exactly the opposite.

Yes, and I have never stated otherwise. The approach that works
is to take a 1/4WL self-resonant coil and use only a percentage
*at the same frequency*. The VF and Z0 will remain approximately
the same as long as we don't change frequencies.

Here is what can be done. Take a 75m bugcatcher coil and extend
the number of turns until it is self-resonant at 4 MHz indicating
that the coil is 90 degrees long. Measure the VF of the coil at
the 4 MHz self-resonant frequency. Remove those extra turns and
calculate the new electrical length. Hint: That electrical length
will be nowhere near a 3 nS delay (technically impossible).

"It is worth noting that, for a helical anisotropic wave guide, the
effective characteristic impedance is not merely a function of the
geometrical configuration of the conductors (as it would be for lossless
TEM coaxial cables and twin-lead transmission lines), but it is also a
function of the excitation frequency."

That's true - Z0 and VF change with frequency. The solution is
to measure or calculate the Z0 and VF at the chosen frequency
of operation. Problem solved!

I am suspicious of anyone's motives who says he believes in
an impossible 3 nS delay through a huge loading coil while
dismissing an IEEE white paper that suggests otherwise.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Gene Fuller wrote:
Have you actually read and understood that article? Corum mentions
several times that everything he reduces to the simple formulas
applies only to quarter-wave resonance conditions.

Yes, a mobile 75m bugcatcher antenna is quarter-wave resonant.
It is clear that you have not taken time to understand the
paper. Figure 2 looks just like a loading-coil, stinger, and
top hat which is 1/4WL resonant. Note that the coil is conceptually
replaced with a length of transmission line and that's exactly
how mobile loaded antennas work. Here are the conditions:

At the feedpoint is a piece of transmission line with a Z0 of
4000 ohms and a VF of 0.02 - physical length to be determined.

Attached to that is a piece of transmission line with a Z0 of
400 ohms and a VF of 1.0. This element is 8 feet long.

The frequency of operation is 4.0 MHz. What physical length
of the 4000 ohm line will cause 1/4WL resonance?

If you can solve that problem, you will understand how loaded
mobile antennas work. Hint: the delay through the 4000 ohm
section is NOT 3 nS.

Look at the author's highlight between equations 31 and 32. Look at
the discussion near equation 47. Look at the discussion following
equation 60. Read the entire discussion in section 5.

I have done that, Gene. A 75m bugcatcher coil falls within
the specified test conditions and thus the VF equation should
be within ten percent accuracy.

Note that he does not say the characteristic impedance is a constant
that can be deduced from resonance conditions and then applied to
operating conditions. In fact, he says exactly the opposite.

Yes, and I have never stated otherwise. The approach that works
is to take a 1/4WL self-resonant coil and use only a percentage
*at the same frequency*. The VF and Z0 will remain approximately
the same as long as we don't change frequencies.

Here is what can be done. Take a 75m bugcatcher coil and extend
the number of turns until it is self-resonant at 4 MHz indicating
that the coil is 90 degrees long. Measure the VF of the coil at
the 4 MHz self-resonant frequency. Remove those extra turns and
calculate the new electrical length. Hint: That electrical length
will be nowhere near a 3 nS delay (technically impossible).

"It is worth noting that, for a helical anisotropic wave guide, the
effective characteristic impedance is not merely a function of the
geometrical configuration of the conductors (as it would be for
lossless TEM coaxial cables and twin-lead transmission lines), but it
is also a function of the excitation frequency."

That's true - Z0 and VF change with frequency. The solution is
to measure or calculate the Z0 and VF at the chosen frequency
of operation. Problem solved!

I am suspicious of anyone's motives who says he believes in
an impossible 3 nS delay through a huge loading coil while
dismissing an IEEE white paper that suggests otherwise.


Cecil,

First, this is NOT an IEEE white paper. It appears to be a simple
conference proceedings paper.

Second, your analysis is utter rot! Are you suggesting that if the coil
can be made resonant at some frequency, and then you cut it in half,
that it still behaves the same?

Corum does not say anything like that, and you shouldn't either.

Shame on you!

73,
Gene
W4SZ

Gene Fuller wrote:
Second, your analysis is utter rot! Are you suggesting that if the coil
can be made resonant at some frequency, and then you cut it in half,
that it still behaves the same?

No, it behaves approximately like half of the original
coil tending to have approximately the same Z0 and VF as
the original coil. The phase shift through the coil will
tend to be approximately 1/2 of the original phase shift -
not exact because of end effects.

Let's say we have a 1/4WL helical antenna with an obvious
phase shift of 90 degrees. If we cut that helical in half,
it is likely to have a phase shift of approximately 45
degrees, nowhere near the 4.5 degrees that W8JI has
"measured".

If we add a stinger to the above half-coil, we will have
a base-loaded antenna. The phase shift will be relatively
close to 45 degrees at the same frequency. The stinger
contributes another few degrees. The impedance discontinuity
between the coil and stinger contributes the rest of the
90 degrees of electrical length.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Gene Fuller wrote:
Second, your analysis is utter rot! Are you suggesting that if the
coil can be made resonant at some frequency, and then you cut it in
half, that it still behaves the same?

No, it behaves approximately like half of the original
coil tending to have approximately the same Z0 and VF as
the original coil. The phase shift through the coil will
tend to be approximately 1/2 of the original phase shift -
not exact because of end effects.

Let's say we have a 1/4WL helical antenna with an obvious
phase shift of 90 degrees. If we cut that helical in half,
it is likely to have a phase shift of approximately 45
degrees, nowhere near the 4.5 degrees that W8JI has
"measured".

If we add a stinger to the above half-coil, we will have
a base-loaded antenna. The phase shift will be relatively
close to 45 degrees at the same frequency. The stinger
contributes another few degrees. The impedance discontinuity
between the coil and stinger contributes the rest of the
90 degrees of electrical length.

"Utter rot" is a pretty good description of this. Your problem is
that you've become so enamored of your little reflection theory that
you insist that only a set of transmission lines 90 degrees in total
length can resonate. Too bad your education isn't complete or you'd know
this isn't so.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
Your problem is
that you've become so enamored of your little reflection theory that
you insist that only a set of transmission lines 90 degrees in total
length can resonate. Too bad your education isn't complete or you'd know
this isn't so.

Obviously, I am not talking about *physical* length.
The "90 degrees" is the total *electrical* length.
Please tell us how you get resonance out of a stub
that is *electrically* 45 degrees long? No resistive
or reactive components are allowed. Here's your
chance to nail me to the wall.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Tom Donaly wrote:
Your problem is
that you've become so enamored of your little reflection theory that
you insist that only a set of transmission lines 90 degrees in total
length can resonate. Too bad your education isn't complete or you'd know
this isn't so.

Obviously, I am not talking about *physical* length.
The "90 degrees" is the total *electrical* length.
Please tell us how you get resonance out of a stub
that is *electrically* 45 degrees long? No resistive
or reactive components are allowed. Here's your
chance to nail me to the wall.

And, if the total electrical length isn't 90 degrees, you
add a few degrees to the loading coil to make it come out right.
Very ingenious.
73,
Tom Donaly, KA6RUH

On 29 Nov, 14:52, "Tom Donaly" wrote:
Cecil Moore wrote:
Tom Donaly wrote:
Your problem is
that you've become so enamored of your little reflection theory that
you insist that only a set of transmission lines 90 degrees in total
length can resonate. Too bad your education isn't complete or you'd know
this isn't so.

Obviously, I am not talking about *physical* length.
The "90 degrees" is the total *electrical* length.
Please tell us how you get resonance out of a stub
that is *electrically* 45 degrees long? No resistive
or reactive components are allowed. Here's your
chance to nail me to the wall.

And, if the total electrical length isn't 90 degrees, you
add a few degrees to the loading coil to make it come out right.
Very ingenious.
73,
Tom Donaly, KA6RUH

I feel that many are disregarding the basics with respect to antennas!
It is one thing to say that an antenna is resonant which amateurs
are interested in for matching purposes. This is totally different
from being resonant AND in equilibrium which is demanded by Maxwell,
Newton and others when in the pursuit of the sciences
Art Unwin KB9MZ....xg

Tom Donaly wrote:
And, if the total electrical length isn't 90 degrees, you
add a few degrees to the loading coil to make it come out right.
Very ingenious.

Adding or subtracting loading-coil degrees is what
happens while one is tuning a screwdriver antenna.
At resonance, the screwdriver is electrically very
close to 90 degrees in length.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Gene Fuller wrote:
Second, your analysis is utter rot! Are you suggesting that if the
coil can be made resonant at some frequency, and then you cut it in
half, that it still behaves the same?

No, it behaves approximately like half of the original
coil tending to have approximately the same Z0 and VF as
the original coil. The phase shift through the coil will
tend to be approximately 1/2 of the original phase shift -
not exact because of end effects.

Let's say we have a 1/4WL helical antenna with an obvious
phase shift of 90 degrees. If we cut that helical in half,
it is likely to have a phase shift of approximately 45
degrees, nowhere near the 4.5 degrees that W8JI has
"measured".

If we add a stinger to the above half-coil, we will have
a base-loaded antenna. The phase shift will be relatively
close to 45 degrees at the same frequency. The stinger
contributes another few degrees. The impedance discontinuity
between the coil and stinger contributes the rest of the
90 degrees of electrical length.

Cecil,

It appears you missed the primary message of the Corum article. He is
completely denying the simple concept you wrote above. He argues that
there is a very special effect near resonance. You cannot simply cut the
coil in half and expect the same behavior.

Frankly, I have little interest in Tesla coils, and I don't know or care
if Corum is right or wrong. I do believe, however, that it is a bit
careless for you to pick and choose equations from the article, ignore
the caveats, and then go ahead and misuse those equations.

73,
Gene
W4SZ

Gene Fuller wrote:
It appears you missed the primary message of the Corum article.

I'm afraid you missed the point. As long as the frequency
is kept constant, the VF and Z0 of coil stock will be
relatively constant - why wouldn't it be? W8JI missed
the 4 MHz delay through that coil by at least a magnitude.
It is impossible for that delay to be 3 nS. The measured
delay through my 75m bugcatcher coil is 25 nS.
--
73, Cecil http://www.w5dxp.com