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