Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
What voltages did they present to the O'scope?

Sorry, I don't remember and can't find my
lab notebook at the moment.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Tom Donaly wrote:
Wrong. In the first place, you obviously don't know the criterion for
resonance. In the second place you just assume the number
90 without any reason. In the third place, the number 37
has only your assumption for the necessity of a 90 degree
phase shift to justify its existence. As I wrote before, this
is pretty poor shooting for a professional symbol slinger.

Tom, you obviously don't know what you are talking
about or how to do the analysis and are now just waving
your hands in emotional frustration.

The criterion for resonance is a 90 degree phase shift
end-to-end in the stub. MicroSmith and antenna analyzer
measurements verify the shortened stub is resonant at
the design frequency with the 100 ohm section of 10
degrees and the 600 ohm section a tad longer than 43
degrees. I have been designing these shortened dual-Z0
stubs for at least 20 years.

The larger question is: Why don't you know how to
verify or disprove my figures? Is this subject beyond
your engineering comprehension level?
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
Perhaps there is just no reason why the "phase shifts" should add
to 90. That would make the problem go away.

But there is every reason why the phase shifts *must*
add up to 90 degrees (or 270 or 450 or ...).

The only way you can get zero ohms looking into an
open stub is if the phase shift end-to-end is 90
degrees (or 270 or 450 or ...). The reflected current
must arrive back at the feedpoint in phase with
the forward current for the stub to be 1/4WL resonant.

In a typical loaded mobile antenna, the only way
to get a resistive feedpoint impedance is if the
antenna is electrically 90 degrees long.

Take a 1/4WL straight monopole wire. It is
electrically 90 degrees long. Put one turn of
loading in it. Is it still electrically 90 degrees
long or not? Proceed until the antenna is all
coil, i.e. self-resonant. Is it still electrically
90 degrees long or not?
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

On Dec 6, 8:59 am, Cecil Moore wrote:
Keith Dysart wrote:
Perhaps there is just no reason why the "phase shifts" should add
to 90. That would make the problem go away.

But there is every reason why the phase shifts *must*
add up to 90 degrees (or 270 or 450 or ...).

The only way you can get zero ohms looking into an
open stub is if the phase shift end-to-end is 90
degrees (or 270 or 450 or ...). The reflected current
must arrive back at the feedpoint in phase with
the forward current for the stub to be 1/4WL resonant.

In a typical loaded mobile antenna, the only way
to get a resistive feedpoint impedance is if the
antenna is electrically 90 degrees long.

Take a 1/4WL straight monopole wire. It is
electrically 90 degrees long. Put one turn of
loading in it. Is it still electrically 90 degrees
long or not? Proceed until the antenna is all
coil, i.e. self-resonant. Is it still electrically
90 degrees long or not?

You are good at building scenarios that align with
your hypotheseses. To test your hypothesis for
correctness you need to examine the scenarios
that may not align rather than those that do.

And you already have one. You have needed to
invent a phase shift occuring at an impedance
discontinuity to explain the missing "electrical
length".

You should also consider a shortened monopole
where lumped elements are used to tune out
the reactance.

Also consider a lengthened monople where
either distributed or lumped elements are used
to tune it.

You should consider a pure lumped element
circuit that presents the same impedance.
Identify the locations that sum to a 90 degree
"electrical length".

Lastly, for real fun, find the 90 degree
"electrical length" in a crystal.

....Keith

Loading Coils; was : Vincent antenna
 

On Thu, 06 Dec 2007 13:00:06 GMT, Cecil Moore
wrote:

Richard Clark wrote:
What voltages did they present to the O'scope?

Sorry, I don't remember and can't find my
lab notebook at the moment.
What was used as the phase reference?

Loading Coils; was : Vincent antenna
 

On Thu, 06 Dec 2007 13:00:06 GMT, Cecil Moore
wrote:

Richard Clark wrote:
What voltages did they present to the O'scope?

Sorry, I don't remember and can't find my
lab notebook at the moment.
How much power was applied to the network?

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:

Keith Dysart wrote:

Perhaps there is just no reason why the "phase shifts" should add
to 90. That would make the problem go away.


But there is every reason why the phase shifts *must*
add up to 90 degrees (or 270 or 450 or ...).

That's true only if you assume the desired feedpoint impedance must be
the lowest possible value. And I think, as you have pointed out on
more than one occasion, the current maximum is not usually located at
the feedpoint, where it would otherwise be if the current minimum is
located 90 degrees away.

73 jk

Loading Coils; was : Vincent antenna
 

Cecil Moore wrote:
Tom Donaly wrote:
Wrong. In the first place, you obviously don't know the criterion for
resonance. In the second place you just assume the number
90 without any reason. In the third place, the number 37
has only your assumption for the necessity of a 90 degree
phase shift to justify its existence. As I wrote before, this
is pretty poor shooting for a professional symbol slinger.

Tom, you obviously don't know what you are talking
about or how to do the analysis and are now just waving
your hands in emotional frustration.

The criterion for resonance is a 90 degree phase shift
end-to-end in the stub. MicroSmith and antenna analyzer
measurements verify the shortened stub is resonant at
the design frequency with the 100 ohm section of 10
degrees and the 600 ohm section a tad longer than 43
degrees. I have been designing these shortened dual-Z0
stubs for at least 20 years.

The larger question is: Why don't you know how to
verify or disprove my figures? Is this subject beyond
your engineering comprehension level?

I'm not an engineer, so I don't have an engineering
comprehension level. Secondly, you must have figured
this out with the aid of a Smith chart or you'd know
exactly how many degrees you need for your 600 ohm line.
Finally, if you don't know how to prove your own figures,
how do you expect me to be able to do it?
Do you know how to figure the other zeros in this line? Are
they the same as they would be in a quarter wave line with
identical Zo's?
73,
Tom Donaly, KA6RUH

Loading Coils; was : Vincent antenna
 

Keith Dysart wrote:
You should also consider a shortened monopole
where lumped elements are used to tune out
the reactance.

Please feel free to pursue that line of
development if you are so inclined.

Since lumped elements do not exist in reality,
they are outside of the scope of real-world
75m mobile loading coils that I am trying to
cover here. I am not proposing a theory of
everything nor do I intend to waste my time
with such. But be my guest.

The ARRL Antenna Book equations for a small loop
are "wrong" for a large loop. Moral: Recognize
the limitations of the model being used.

Lastly, for real fun, find the 90 degree
"electrical length" in a crystal.

Even Einstein's theory of relativity has its
limitations. It is a diversion to try to
require every model to cover every real and
imagined possibility.
--
73, Cecil http://www.w5dxp.com

Loading Coils; was : Vincent antenna
 

Richard Clark wrote:
What was used as the phase reference?

Channel 1 was used for the phase reference for
Channel 2. The time-phase difference between the
two signals at zero-crossing was the the delay
through the coil measured using traveling-wave
current.
--
73, Cecil http://www.w5dxp.com