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

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

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

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

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

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

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.

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.

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

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