Tom's experiment
 

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

Tom's experiment
 

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

Tom's experiment
 

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

Tom's experiment
 

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

Tom's experiment
 

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's experiment
 

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's experiment
 

"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

Tom's experiment
 

Owen Duffy wrote:
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.

Something I observed and reported more than 2 years ago
in a heated exchange over on QRZ.com.

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.

Something I observed and reported.

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.

Something I observed and reported. I got "ploinked" by W7EL
for that observation, among others - like energy actually
existing in reflected waves. Wonder if W7EL will now "ploink"
you?

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

No, but it is a surprise that Tom attempts to disguise and
rationalize that measured phase change as the *delay* through
a 100 turn coil. If his measurements were correct, I could
speed up my computer bus by installing coils in series with
the data lines. :-)
--
73, Cecil http://www.w5dxp.com

Tom's experiment
 

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

Tom's experiment
 

Tom Donaly wrote:
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, ...

No, W8JI has to prove himself right since the onus of
proof is upon him for asserting the 3 ns delay through a
100 turn coil. If the delay through that 100T coil is not
3 ns, then my two-year-old assertion that the 3 ns delay
is impossible turns out to be true.

We had this out two years ago over on QRZ.com. Tom is incapable
of mistakes and therefore is incapable of changing his mind.
The same holds true for other gurus on this newsgroup.

(P.S. By now, you, and everyone else, should know that Cecil never
argues in good faith, ...

P.S. By now everyone should know that Tom Donaly attempts
to get readers to believe Big Lies about me. He and the
rest of the guru gang are more interested in saving
face than in technical facts. The 3 ns delay through a
100T coil is just one example. Reflected EM waves with
measurable voltages but zero energy content is another.
--
73, Cecil http://www.w5dxp.com

Tom's experiment
 

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

Tom's experiment
 

"AI4QJ" wrote in
:

I ran W8JI through the corum calculator. I got a super-well tuned
calculation of several coil parameters that I assume to be correct for
now, and surprise, phase angle is still close to 90 degrees (what else
could it be?). The beta axial propagation factor is 2.122 rad/m. I am
trying to figure out the significance of that; it looks like a
velocity factor correction relative to a traveling wave in a vacuum???

You have to view the helix as a transmission line.

The phase change along the transmission line representation of the helix
is 2.1 rad/m, so along 0.254m, there is a phase change of 0.53 rad or 30°
in waves travelling along the line.

To help get your mind into gear, solve this problem:

You have 4.124m of RG58C/U, the far end is s/c, what is the apparent
inductance at 4MHz looking into the line.

Did you get 1.1uH?

What is the electrical length of the line?

What is Beta?

Now apply the same thinking to the helix transmission line equivalent.

Owen

Tom's experiment
 

"AI4QJ" wrote in
:


"Owen Duffy" wrote in message
...
"AI4QJ" wrote in
:

I ran W8JI through the corum calculator. I got a super-well tuned
calculation of several coil parameters that I assume to be correct
for now, and surprise, phase angle is still close to 90 degrees
(what else could it be?). The beta axial propagation factor is 2.122
rad/m. I am trying to figure out the significance of that; it looks
like a velocity factor correction relative to a traveling wave in a
vacuum???

You have to view the helix as a transmission line.

The phase change along the transmission line representation of the
helix is 2.1 rad/m, so along 0.254m, there is a phase change of 0.53
rad or 30° in waves travelling along the line.

To help get your mind into gear, solve this problem:

You have 4.124m of RG58C/U, the far end is s/c, what is the apparent
inductance at 4MHz looking into the line.

Did you get 1.1uH?

I got 1.025uH using 250nH/m.

Well, it is about the right answer, but could be for the wrong reasons.

The line is 30° in length, and Zo is 50, so Xl is about 50*tan(30), then
work out L from there. Is that how you did it?



What is the electrical length of the line?

Electrical length at 4 MHz = 49.5 m assuming polyethylene dielectric.

VF=0.66, so the electrical length is 4.124/0.66m or 6.248m. That is
6.248/75 wl, or 30° (which you needed above).


What is Beta?

Beta = 0.08 rad/m for 75m

Beta=2*pi/75 rad/m or .083 rad/m... so I will pay 0.08.



Now apply the same thinking to the helix transmission line
equivalent.

Thanks Owen.

Tom's experiment
 

Owen Duffy wrote:
You have to view the helix as a transmission line.

At a fixed frequency, it has L and distributed C and
some losses, just like a transmission line. A coil
can be conceptually replaced with a transmission line
of the equivalent Z0 and VF if one is mindful of the
boundary conditions for the model.
--
73, Cecil http://www.w5dxp.com

Tom's experiment
 

Owen Duffy wrote:
'You have to view the helix as a transmission line."

B. Whitfield Griffith, Jr. treats "Transmission Lines for Special
Impedances" starting on page 293 of "Radio-Elewctronic Transmission
Fundamentals". On page 295 he gives Zo = sq. rt. L/C. Also, velocity of
phase propagation is given as: v = 1/sq.rt.LC.

Best regards, Richard Harrison, KB5WZI

Tom's experiment
 

Owen Duffy wrote in
:

....
You have to view the helix as a transmission line.

I mightn't have spelled this out fully.

A 15m straight length of wire could be viewed as a transmission line.

Coiling the wire into the form that Tom measured changes the transmission
line characteristics. Corum's paper and his references deal with
development of parameters for the new transmission line.

Corum argues that solving this new transmission line is a better method
of determining the inductance of the coil that other methods. That
probably understates it a bit, because he represents that his method is a
better way of estimating self resonance, better than the notion of a
lumped parasitic capacitance to deal with distributed capacitance
(another transmission line attribute).

Estimating inductance has been a challenge over a long time.

Corum's method with some extensions is incorporated in the online
calculator to which I gave a link. I have used this calculator to a
limited extent, and it has reconciled well with measured values. My
observations don't prove that it is accurate, but they haven't proved it
grossly inaccurate, and so far, it seems a good estimator for the types
of problems I have solved.

I must admit that I haven't tried solving inductance using David Knights
approach, it may well work and looks to be a degree simpler, but it
doesn't seem to deal with the distributed capacitance /self resonance
issue. One of my to-do jobs is to knock up a calculator and compare both
solutions to some measured values... which is something of a problem for
me because I mainly depend on others for quality measurements.

This issue has held up further work on bootstrap coax traps
(http://www.vk1od.net/coaxtrap/index.htm) . After a lot of work modelling
one of my correspondent's traps, he didn't want the analysis published
because it disagreed with his QEX article. A later QEX article supports
my model. Ah, that's ham radio!

I see people quoting the late Reggie's tools, but unfortunately he did
not expose the underlying algorithms to most of them, so they are a bit
of an unknown quantity in that respect.

I digressed a bit there, but estimating inductance remains a great
interest for RF practitioners.

Owen

Tom's experiment
 

"AI4QJ" wrote in
:


"Owen Duffy" wrote in message
...

You have 4.124m of RG58C/U, the far end is s/c, what is the
apparent inductance at 4MHz looking into the line.

Did you get 1.1uH?

I got 1.025uH using 250nH/m.

Well, it is about the right answer, but could be for the wrong
reasons.

Well, I used a manufacturers' spec.. The same manufacturer I think
used 53 Ohms for Zo. I like your method better although mfr's spec. is
probably accurate over a very wide frequency band.

RG58C/U would usually be 50 ohms Zo.

You cannot use the inductance/metre figure in the general case. If you
approached it that way, though your answer is close, the method is
inaccurate for all but very short lines. Compare the results of both
methods on 16.496m s/c stub of the same line at 4MHz, your method gives
4uH, bit the correct answer is that it is not inductive, it looks like a
capacitive reactance around 86 ohms.

The next dimension is the loss or equivalent series R of the impedance
looking into the stub. The maths is a bit uglier, and is implemented in
the calculator at http://www.vk1od.net/tl/tllc.php . Playing with the
calculator will reveal why transmission line elements don't necessarily
make good reactors.

This concepts above will be explained in any decent transmission line
text. Some of these concepts are the reason you are having difficulty in
understanding Corum's transmission line representation of the coil.

Owen

Tom's experiment
 

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