It has been proposed that a helix can be represented by a transmission
line with certain parameters including Beta (the phase part of the
complex propagation constant), and solution of the transmission line
gives meaningful numbers for the inductance and self resonance of the
helix.

Some seem to state that the behavior of a physically short loading coil
demands the above transmission line solution for adequate accuracy, and
that the electrical length of the transmission line (Beta*CoilLength)
simply replaces the equivalent physical length of straight conductor and
so shortens the "quarter wave resonant" antenna.

Tom has described an experiment
(http://www.w8ji.com/inductor_current_time_delay.htm) where he has
measured the S21 delay of a 10" (254mm) long coil typical of a loading
coil for an 80m antenna. He hasn't described how the measurement is
actually made.

If the coil is represented as a transmission line with the load end
shorted to ground (as in the style of a helical resonator) it is much
shorter than a quarter wave transmission line.

Tom did not describe any form of directional coupler that would
effectively isolate and measure the forward and reflected waves at each
of the measurement points. Such a thing would be a considerable challenge
since Zo of the equivalent line varies with frequency and he sweeps from
0.3 to 30MHz in his measurement.

If a simple current probe was used to sample the magnitude and phase of
the current at each end of the coil, the samples are each of the sum of
the forward and reflected current components at each point.

It is the nature of a low loss transmission line less than an electrical
quarter wave and terminated in a short circuit, that the phase of the
(net) current at all points on the line is almost uniform.

Is it any surprise that Tom's measurement of delay indicates an apparent
phase change much smaller than the value of Beta*CoilLength?

Owen

On Sun, 02 Dec 2007 02:47:38 GMT, Owen Duffy wrote:


It has been proposed that a helix can be represented by a transmission
line with certain parameters including Beta (the phase part of the
complex propagation constant), and solution of the transmission line
gives meaningful numbers for the inductance and self resonance of the
helix.

Some seem to state that the behavior of a physically short loading coil
demands the above transmission line solution for adequate accuracy, and
that the electrical length of the transmission line (Beta*CoilLength)
simply replaces the equivalent physical length of straight conductor and
so shortens the "quarter wave resonant" antenna.

Tom has described an experiment
(http://www.w8ji.com/inductor_current_time_delay.htm) where he has
measured the S21 delay of a 10" (254mm) long coil typical of a loading
coil for an 80m antenna. He hasn't described how the measurement is
actually made.

If the coil is represented as a transmission line with the load end
shorted to ground (as in the style of a helical resonator) it is much
shorter than a quarter wave transmission line.

Tom did not describe any form of directional coupler that would
effectively isolate and measure the forward and reflected waves at each
of the measurement points. Such a thing would be a considerable challenge
since Zo of the equivalent line varies with frequency and he sweeps from
0.3 to 30MHz in his measurement.

If a simple current probe was used to sample the magnitude and phase of
the current at each end of the coil, the samples are each of the sum of
the forward and reflected current components at each point.

It is the nature of a low loss transmission line less than an electrical
quarter wave and terminated in a short circuit, that the phase of the
(net) current at all points on the line is almost uniform.

Is it any surprise that Tom's measurement of delay indicates an apparent
phase change much smaller than the value of Beta*CoilLength?

Owen

Hi Owen,

All very fine points, and it certainly brings together all the
cautions, objections, and observations of shortfalls and omissions
mentioned by several writers. I would add that some few (e.g Cecil)
may only read the last paragraph as vindication of their proof of a
concept that bares scant relation to the point offered.

73's
Richard Clark, KB7QHC

Richard Clark wrote in
:

....
mentioned by several writers. I would add that some few (e.g Cecil)
may only read the last paragraph as vindication of their proof of a
concept that bares scant relation to the point offered.

To do so would be to misunderstand my post.

Simply, I doubt that Tom's experiment, as far as described, was likely to
reveal the value of Beta, except were resonance was observed (which implies
90° one way phase change along the equivalent line). The test setup was
unlikely to reveal the true undisturbed resonance of the helix alone, there
would be better configurations.

To my mind, Tom's experiment doesn't prove Cecil et al wrong, but that
should not be taken in any way to imply support for their proposition.

Owen

On Sun, 02 Dec 2007 03:56:01 GMT, Owen Duffy wrote:

To my mind, Tom's experiment doesn't prove Cecil et al wrong, but that
should not be taken in any way to imply support for their proposition.

Hi Owen,

To my mind, I don't know what Tom's experiment does prove. It lacks
too much to be even called data.

73's
Richard Clark, KB7QHC

Richard Clark wrote:
On Sun, 02 Dec 2007 03:56:01 GMT, Owen Duffy wrote:

To my mind, Tom's experiment doesn't prove Cecil et al wrong, but that
should not be taken in any way to imply support for their proposition.

Hi Owen,

To my mind, I don't know what Tom's experiment does prove. It lacks
too much to be even called data.

73's
Richard Clark, KB7QHC

It doesn't matter what it lacks or doesn't lack. There is no experiment
that anyone can do that will satisfy Cecil that he's wrong, but there
are an infinity of vague, disconnected references and twisted
interpretations that he will seize upon to prove he's right.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
It doesn't matter what it lacks or doesn't lack. There is no experiment
that anyone can do that will satisfy Cecil that he's wrong, but there
are an infinity of vague, disconnected references and twisted
interpretations that he will seize upon to prove he's right.

Tom, you seem to me to be emotionally about eight years
old and incapable of anything except ad hominem attacks.
Technically speaking, please put up or shut up.
--
73, Cecil http://www.w5dxp.com

Owen Duffy wrote in
:

....
Simply, I doubt that Tom's experiment, as far as described, was likely
to reveal the value of Beta, except were resonance was observed (which
implies 90° one way phase change along the equivalent line). The test
setup was unlikely to reveal the true undisturbed resonance of the
helix alone, there would be better configurations.

In thinking a little more about this, and thinking aloud, there is no
reason to think that the blip on Tom's delay measurement at around 16MHz
was for a mode of resonance where the one way phase change would be 90°, it
may well have been the next higher mode.

Owen

Richard Clark wrote:
I would add that some few (e.g Cecil)
may only read the last paragraph as vindication of their proof of a
concept that bares scant relation to the point offered.

Those grapes were probably sour anyway.
--
73, Cecil http://www.w5dxp.com

Owen Duffy wrote:
It has been proposed that a helix can be represented by a transmission
line with certain parameters including Beta (the phase part of the
complex propagation constant), and solution of the transmission line
gives meaningful numbers for the inductance and self resonance of the
helix.

Some seem to state that the behavior of a physically short loading coil
demands the above transmission line solution for adequate accuracy, and
that the electrical length of the transmission line (Beta*CoilLength)
simply replaces the equivalent physical length of straight conductor and
so shortens the "quarter wave resonant" antenna.

Tom has described an experiment
(http://www.w8ji.com/inductor_current_time_delay.htm) where he has
measured the S21 delay of a 10" (254mm) long coil typical of a loading
coil for an 80m antenna. He hasn't described how the measurement is
actually made.

If the coil is represented as a transmission line with the load end
shorted to ground (as in the style of a helical resonator) it is much
shorter than a quarter wave transmission line.

Tom did not describe any form of directional coupler that would
effectively isolate and measure the forward and reflected waves at each
of the measurement points. Such a thing would be a considerable challenge
since Zo of the equivalent line varies with frequency and he sweeps from
0.3 to 30MHz in his measurement.

If a simple current probe was used to sample the magnitude and phase of
the current at each end of the coil, the samples are each of the sum of
the forward and reflected current components at each point.

It is the nature of a low loss transmission line less than an electrical
quarter wave and terminated in a short circuit, that the phase of the
(net) current at all points on the line is almost uniform.

Is it any surprise that Tom's measurement of delay indicates an apparent
phase change much smaller than the value of Beta*CoilLength?

Owen

I suggest you email Tom and ask him about his experiment. It doesn't
matter, though. Cecil will always argue, that, because Tom is wrong,
he, Cecil, must be right. In point of fact, Tom doesn't have to prove
Cecil wrong, Cecil has to prove himself right, which he can't possibly
do because he refuses to use either mathematics or experiment to bolster
his claims. He expects us to believe what is, basically, a philosophical
fantasy masquerading as theory. Again, get in touch with Tom. He may not
correspond with you, but then again, he may. Trying to second guess an
experiment from a web page is a difficult proposition.
73,
Tom Donaly, KA6RUH
(P.S. By now, you, and everyone else, should know that Cecil never
argues in good faith, so there's little point in bothering your head
about his theories. Dealing with Cecil should only done for
entertainment, and then in small quantities. A little of his fantasmic
fulminations go a long way.)

"Tom Donaly" wrote in
. net:

....
... Again, get in touch with
Tom. He may not correspond with you, but then again, he may. Trying to
second guess an experiment from a web page is a difficult proposition.

Tom,

Yes it is difficult, and hence my heavily qualified comments.

I have written to Tom R a few times raising issues of understanding of
other of his web articles, but don't usually get a response so I don't tend
to waste the time now. He is probably just a busy fellow without time for
such.

Having some hundreds of articles published on my own web site, I have an
understanding of the nature of incoming traffic commenting on articles, but
my view is one must read and respond to them all, it is a part of
publishing info in such a way.

Owen