Coils are transmission lines
 

ALL coils are distributed in space. They have a conductor. Therefore
they can be analysed in the same manner as transmission lines.

They ARE transmission lines, no matter what length. They can't help
it!

Program COILINE demonstrates how a simple coil-loaded vertical antenna
can be designed by using classical transmission line mathematics.

Enter length, diameter and number of turns on the coil, the length of
the top rod or whip or wire, and you can examine how the thing behaves
at any frequency. You can design anything from a bottom loaded long
wire to a helical for 160 metres.

Coils can vary between a few turns on an empty toilet roll tube to a 4
feet long, 1 inch diameter, plastic pipe wound with 1000 turns.

You can prune the whip to obtain resonance at a given frequency
without having to go out in the freezing cold back yard.

Discover the velocity factor, nano-seconds per meter, and other
numbers for your particular coil. All will be of interest to the
participants in the interminable civil war still raging on another
thread. Ammunition galore!

Download program COILINE from website below and run immediately. Only
47 kilo-bytes. Its quite entertaining.

By the way, it has just occurred to me, I forgot to include coil Q in
the results. But it hardly matters - there's little to be done with
the number even if you know it.
----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Coils are transmission lines
 

Reg Edwards wrote:
(snip)
By the way, it has just occurred to me, I forgot to include coil Q in
the results. But it hardly matters - there's little to be done with
the number even if you know it.

Thanks.

But what about comparing different ways of obtaining the same
inductance to find those with higher or lower Q?

Coils are transmission lines
 

Reg Edwards wrote:
Discover the velocity factor, nano-seconds per meter, and other
numbers for your particular coil.

Reg, would you care to share your formula for velocity factor?
--
73, Cecil http://www.qsl.net/w5dxp

Coils are transmission lines
 

But what about comparing different ways of obtaining the same
inductance to find those with higher or lower Q?

======================================

To double Q, whatever it is, just double length and diameter of the
coil, wind on a number of turns of much thicker wire for the same
inductance, and Bingo, Q is doubled. The value of Q is unecessary.

Efficiency and bandwidth can be deduced by calculating from the known
values of wire and radiation resistances. But I suppose Q, once
available, would be a short cut to crudely estimating bandwidth.
Additional information is needed.

The loss in the coil may not be the dominating factor. What matters is
the System Q. It can be considerably worse than coil Q.
----
Reg.

Coils are transmission lines
 

Reg, would you care to share your formula for velocity factor?
==========================================

Cec, can't you find it in your bibles?

Velocity = 1 / Sqrt( L * C) metres per second

where L and C are henrys and farads per metre.

What you really want to know is how to calculate L and C from coil
dimensions. But you won't find that from any bible.

As a special favour, I'll attach the source code for the program to an
e-mail. Read it with a non-proportional text editor such as Notepad.

In your discussions on the other thread you have mentioned a coil's
self-resonant frequency. In the source code you will also find a
formula for Fself. Which, again, cannot be found in any bible. It is
a fairly straightforward 2 or 3-line formula.

Fself is not used anywhere in the program. It is available solely out
of interest. It is fairly accurate. I have measured it on many coils
of all proportions and numbers of turns from 1 inch to 6 feet long
with 1500 turns.
----
Reg, G4FGQ

Coils are transmission lines
 

Reg Edwards wrote:
Velocity = 1 / Sqrt( L * C) metres per second

Well now, W7EL, a pretty smart fellow questioned that equation,
as I remember before a bottle of CA Sutter Home Cabernet Sauvignon,
circa 2001. (Not bad for a 5 year old red.)

Dr. Corum's equation is a mite more complicated involving
fractional powers of diameter, turns per inch, and wavelength
and it closely agreed with my self-resonant measurements.

If we work backwards from Dr. Corum's fairly accurate
VF, can we calculate the L and C of the coil?
--
73, Cecil http://www.qsl.net/w5dxp

Coils are transmission lines
 

Reg Edwards wrote:
Reg, would you care to share your formula for velocity factor?
==========================================

Cec, can't you find it in your bibles?

Velocity = 1 / Sqrt( L * C) metres per second

where L and C are henrys and farads per metre.

What you really want to know is how to calculate L and C from coil
dimensions. But you won't find that from any bible.

. . .

What seems to be getting lost in the discussion is that L is *series* L
per meter and C is *shunt* C per meter -- that is, the C to another
conductor(*). C is not the self-capacitance of the inductor.

(*) Conductors also have capacitance to free space, but I'm not at all
sure the transmission line equations for such things as velocity are
valid if this is used for C. The equation for the resonant length of a
wire in space is very complex and can't be solved in closed form, and
even approximate formulas are much more complex than those for
transmission lines. So while transmission lines and antennas -- or
radiating inductors -- share some characteristics, you can't blindly
apply the equations for one to the other and expect valid results.

Roy Lewallen, W7EL

Coils are transmission lines
 

L and C are neither in series or in parallel with each other.

They are both DISTRIBUTED as in a transmission line.

To calculate the self-resonant frequency what we are looking for is an
equivalent shunt capacitance across the ends of the inductance.

Turn to turn capacitance is is a very small fraction of the total
capacitance. If there are 10 turns then there are 10 turn-to-turn
capacitances all in series. After a few turns there is very little
capacitance which can be considered to be across the coil.

Consider two halves of the coil. We have two large cylinders each of
half the length of the coil. Diameter of the cylinders is the same as
coil diameter. Nearly all the capacitance across the coil is that due
to the capacitance between the two touching cylinders (excluding their
facing surfaces).

The formula for VF is true for any transmission line with distributed
L and C. And a coil has distributed L and C.

Agreed, L and C are approximations for very short fat coils. But any
approximation is far better than none at all. All antennas have to be
pruned at their ends.
----
Reg.
"Roy Lewallen" wrote

Velocity = 1 / Sqrt( L * C) metres per second

where L and C are henrys and farads per metre.

What seems to be getting lost in the discussion is that L is
*series* L
per meter and C is *shunt* C per meter -- that is, the C to another
conductor(*). C is not the self-capacitance of the inductor.

(*) Conductors also have capacitance to free space, but I'm not at
all
sure the transmission line equations for such things as velocity are
valid if this is used for C. The equation for the resonant length of
a
wire in space is very complex and can't be solved in closed form,
and
even approximate formulas are much more complex than those for
transmission lines. So while transmission lines and antennas -- or
radiating inductors -- share some characteristics, you can't blindly
apply the equations for one to the other and expect valid results.

Roy Lewallen, W7EL

Coils are transmission lines
 

Of course I understand that both L and C are distributed. But the C in
the transmission line formula isn't a longitudinal C like the C across
an inductor; it's the (distributed, of course) shunt C between the two
conductors of the transmission line. I don't believe you can justify
claiming that the C across an inductor is even an approximation for the
C from the inductor to whatever you consider to be the other
transmission line conductor.

Roy Lewallen, W7EL

Reg Edwards wrote:
L and C are neither in series or in parallel with each other.

They are both DISTRIBUTED as in a transmission line.

To calculate the self-resonant frequency what we are looking for is an
equivalent shunt capacitance across the ends of the inductance.

Turn to turn capacitance is is a very small fraction of the total
capacitance. If there are 10 turns then there are 10 turn-to-turn
capacitances all in series. After a few turns there is very little
capacitance which can be considered to be across the coil.

Consider two halves of the coil. We have two large cylinders each of
half the length of the coil. Diameter of the cylinders is the same as
coil diameter. Nearly all the capacitance across the coil is that due
to the capacitance between the two touching cylinders (excluding their
facing surfaces).

The formula for VF is true for any transmission line with distributed
L and C. And a coil has distributed L and C.

Agreed, L and C are approximations for very short fat coils. But any
approximation is far better than none at all. All antennas have to be
pruned at their ends.
----
Reg.
"Roy Lewallen" wrote

Velocity = 1 / Sqrt( L * C) metres per second
where L and C are henrys and farads per metre.

What seems to be getting lost in the discussion is that L is
*series* L
per meter and C is *shunt* C per meter -- that is, the C to another
conductor(*). C is not the self-capacitance of the inductor.

(*) Conductors also have capacitance to free space, but I'm not at
all
sure the transmission line equations for such things as velocity are
valid if this is used for C. The equation for the resonant length of
a
wire in space is very complex and can't be solved in closed form,
and
even approximate formulas are much more complex than those for
transmission lines. So while transmission lines and antennas -- or
radiating inductors -- share some characteristics, you can't blindly
apply the equations for one to the other and expect valid results.

Roy Lewallen, W7EL

Coils are transmission lines
 

Roy Lewallen wrote:
Of course I understand that both L and C are distributed. But the C in
the transmission line formula isn't a longitudinal C like the C across
an inductor; it's the (distributed, of course) shunt C between the two
conductors of the transmission line. I don't believe you can justify
claiming that the C across an inductor is even an approximation for the
C from the inductor to whatever you consider to be the other
transmission line conductor.

Agreed. They are as different as a shunt element and a series element
in a pi filter.

Coils are transmission lines
 

I don't understand what you are trying to say. Express yourself, less
ambiguously, in fewer words.

Or perhaps you are nit-picking. I can't tell.

I have just explained that the resulting capacitance between adjacent
conductors in a coil is very small in comparison with the capacitance
of a large solid cylinder (of the same diameter as the coil) to the
rest of the world.

The capacitance to the rest of the world includes electric lines of
force from one half of the cylinder to the other, especially from one
end to the other. The capacitance of the coil we are dealing with has
very little to do with coil turns.
----
Reg.


"John Popelish" wrote in message
...
Roy Lewallen wrote:
Of course I understand that both L and C are distributed. But the
C in
the transmission line formula isn't a longitudinal C like the C
across
an inductor; it's the (distributed, of course) shunt C between the
two
conductors of the transmission line. I don't believe you can
justify
claiming that the C across an inductor is even an approximation
for the
C from the inductor to whatever you consider to be the other
transmission line conductor.

Agreed. They are as different as a shunt element and a series
element
in a pi filter.

Coils are transmission lines
 

On Fri, 17 Mar 2006 01:12:38 +0000 (UTC), "Reg Edwards"
wrote:

What you really want to know is how to calculate L and C from coil
dimensions. But you won't find that from any bible.

An atheist is wholly unaware of what is to be found in a bible. Being
Buddhist myself, I got plenty.

Coils are transmission lines
 

Roy Lewallen wrote:
Of course I understand that both L and C are distributed. But the C in
the transmission line formula isn't a longitudinal C like the C across
an inductor; it's the (distributed, of course) shunt C between the two
conductors of the transmission line. I don't believe you can justify
claiming that the C across an inductor is even an approximation for the
C from the inductor to whatever you consider to be the other
transmission line conductor.

Roy Lewallen, W7EL

Hi Roy,

Any answer, even if just an educated guess, is better than giving no
answer at all. No matter how far off.

73 Tom

Coils are transmission lines
 

wrote:
Any answer, even if just an educated guess, is better than giving no
answer at all. No matter how far off.

An answer that is completely wrong is better than no answer at all?

Speaking of answers, here is a question to which you have, so far,
avoided giving an answer.

In the graphic at: http://www.qsl.net/w5dxp/3freq.gif , the currents
in the center graphic reported by EZNEC a

The current at the bottom of the coil is 0.17 amps with a phase angle
of -1.72 degrees.

The current at the top of the coil is 2.0 amps with a phase angle of
-179.6 degrees.

The current at the top of the coil is about 12 times the magnitude of
the current at the bottom of the coil.

The phase shift through the coil is about 178 degrees.

Once again, please explain those results. Thanks in advance.
--
73, Cecil, W5DXP

Coils are transmission lines
 

Cecil,

1. I have looked at that figure, and I suspect many others have as well.
There is no information given about dimensions or any other modeling
conditions, so it is difficult to say anything more than, "Yep, there's
a bunch of lines and numbers on that figure."

2. As I pointed out recently, a phase shift of 178 degrees is really a
phase shift of 2 degrees. It is a common, but unfortunate, convention
that the ordinary sign reversal of a sinusoidal function is deemed a
"phase shift" or "phase reversal". The only "phase" worth discussing is
the one that occurs inside the argument for the sinusoidal function.
That phase does not typically undergo sudden jumps or reversals.

73,
Gene
W4SZ

Cecil Moore wrote:


Speaking of answers, here is a question to which you have, so far,
avoided giving an answer.

In the graphic at: http://www.qsl.net/w5dxp/3freq.gif , the currents
in the center graphic reported by EZNEC a

The current at the bottom of the coil is 0.17 amps with a phase angle
of -1.72 degrees.

The current at the top of the coil is 2.0 amps with a phase angle of
-179.6 degrees.

The current at the top of the coil is about 12 times the magnitude of
the current at the bottom of the coil.

The phase shift through the coil is about 178 degrees.

Once again, please explain those results. Thanks in advance.
--
73, Cecil, W5DXP

Coils are transmission lines
 

"Gene Fuller" wrote:
1. I have looked at that figure, and I suspect many others have as well.
There is no information given about dimensions or any other modeling
conditions, so it is difficult to say anything more than, "Yep, there's
a bunch of lines and numbers on that figure."

The EZNEC file is available for the asking. Do you want a copy?
I will add the antenna specs to the bottom of the graphic.
--
73, Cecil, W5DXP

Coils are transmission lines
 

Gene Fuller wrote:
1. I have looked at that figure, and I suspect many others have as well.
There is no information given about dimensions or any other modeling
conditions, so it is difficult to say anything more than, "Yep, there's
a bunch of lines and numbers on that figure."

Information has been added to the graphic at:

http://www.qsl.net/w5dxp/test316.GIF

The associated EZNEC file can be downloaded from:

http://www.qsl.net/w5dxp/test316.EZ
--
73, Cecil http://www.qsl.net/w5dxp

Coils are transmission lines
 

Gene Fuller wrote:
1. I have looked at that figure, and I suspect many others have as well.
There is no information given about dimensions or any other modeling
conditions, so it is difficult to say anything more than, "Yep, there's
a bunch of lines and numbers on that figure."

I have added the information gathered in this thread and
others to my web page. Please click on my web page below
and scroll down to the bottom of the page.
--
73, Cecil http://www.qsl.net/w5dxp/current.htm

Coils are transmission lines
 

Cecil,

I downloaded your EZNEC file, and I played around for a while with both
the original and several variations.

There were no surprises for the fundamental frequency case. When I
modeled a real bugcatcher coil, or at least as real as those on the GLA
web site, the current at the top of the coil was 85% to 90% of the base
current. I think it is more typical that a bugcatcher coil is at least 4
turns per inch rather than the 2 turns per inch in your example. I also
attempted to model the coil tested by Tom, W8JI, and reported earlier in
this thread. This coil pushes EZNEC both in terms of the number of
segments and the short length of the segments, but in any case it
appears that his coil when placed in your antenna model has higher
current at the top than you reported.

I ignored the harmonic examples. Who ever said that a coil would be a
lumped inductor when it is operated above its self resonant frequency?
Even your new guru from Mount Olympus, Dr. Teslacoil, does not discuss
such things.

In summary, the world of RF electrical phenomena is still intact. I
don't believe I have anything more to add, and I plan to back to sleep.

73,
Gene
W4SZ

Cecil Moore wrote:
Gene Fuller wrote:

1. I have looked at that figure, and I suspect many others have as
well. There is no information given about dimensions or any other
modeling conditions, so it is difficult to say anything more than,
"Yep, there's a bunch of lines and numbers on that figure."


Information has been added to the graphic at:

http://www.qsl.net/w5dxp/test316.GIF

The associated EZNEC file can be downloaded from:

http://www.qsl.net/w5dxp/test316.EZ

Coils are transmission lines
 

Gene Fuller wrote:
I think it is more typical that a bugcatcher coil is at least 4
turns per inch rather than the 2 turns per inch in your example.

I tried 4 turns per inch. EZNEC didn't like it.

I ignored the harmonic examples. Who ever said that a coil would be a
lumped inductor when it is operated above its self resonant frequency?

Whoever said that a coil would be a lumped inductor at 60%
of its self resonant frequency? Did you say that?

Used at 5.89 MHz, self-resonant at 9.75 MHz, phase-reversing at
11.78 MHz. Sounds a lot like a slow wave transmission line to me.
5.89 is 60% of the self-resonant frequency. Dr. Corum says that
the lumped-circuit fails above a 15% value. 60% is far above 15%.

In summary, the world of RF electrical phenomena is still intact.

Of course, and more than that, I took its side in the argument.

When I reported measuring no phase shift up and down a dipole,
Tom, W8JI, said my measurements were wrong. But EZNEC says
the same thing as I.
--
73, Cecil http://www.qsl.net/w5dxp

Coils are transmission lines
 

Gene Fuller wrote:
I ignored the harmonic examples. Who ever said that a coil would be a
lumped inductor when it is operated above its self resonant frequency?

Oh, I forgot to ask you a technical question, Gene. Given that
at 11.78 MHz, the current at the bottom of the coil is 0.17 amps
and the current at the top is 2.0 amps, how do you explain those
values if the current is flowing up through the coil? The details
are at the bottom of the following web page.
--
73, Cecil http://www.qsl.net/w5dxp/current.htm

Coils are transmission lines
 

Cecil Moore wrote:
Gene Fuller wrote:

I ignored the harmonic examples. Who ever said that a coil would be a
lumped inductor when it is operated above its self resonant frequency?


Oh, I forgot to ask you a technical question, Gene. Given that
at 11.78 MHz, the current at the bottom of the coil is 0.17 amps
and the current at the top is 2.0 amps, how do you explain those
values if the current is flowing up through the coil? The details
are at the bottom of the following web page.

Cecil,

Why is this an issue? Is there someone other than your strawman who has
a problem with this concept? I don't recall anyone ever questioning such
matters. Only in your imagination does anyone deny the existence of
distributed, non-lumped components.

If there really is such a person, it might be better to address your
query to him or to her.

73,
Gene
W4SZ

Coils are transmission lines
 

Gene Fuller wrote:

Cecil Moore wrote:
Oh, I forgot to ask you a technical question, Gene. Given that
at 11.78 MHz, the current at the bottom of the coil is 0.17 amps
and the current at the top is 2.0 amps, how do you explain those
values if the current is flowing up through the coil? The details
are at the bottom of the following web page.

I don't recall anyone ever questioning such matters.

You seem to be trying to have it both ways. 0.17 amps
is not equal to 2.0 amps. 0 degrees is not equal to
180 degrees. How are those values possible in a lumped
inductor?
--
73, Cecil http://www.qsl.net/w5dxp