steveeh131047 wrote:

Cecil: that's a VERY significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros paper it predicts an
axial Velocity Factor of 0.033. That would equate to a time delay of
24.7nS across the 10" long coil !!!!

Regards,
Steve G3TXQ

Hi Steve,

You're right. The numbers are amazingly close - almost as if his
'experimental apparatus' had calculated the result rather than measure it.

73, ac6xg

steveeh131047 wrote:

Cecil: that's a VERY significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros paper it predicts an
axial Velocity Factor of 0.033. That would equate to a time delay of
24.7nS across the 10" long coil !!!!

Regards,
Steve G3TXQ

Let's see how well the principles involved are understood.

What is the delay through a physically very small toroidal coil with the
same inductance as the solenoidal coil? Why?

Roy Lewallen, W7EL

On Apr 23, 2:29*pm, Roy Lewallen wrote:
* steveeh131047 wrote:
Cecil: that's a VERY significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros paper it predicts an
axial Velocity Factor of 0.033. That would equate to a time delay of
24.7nS across the 10" long coil !!!!

Regards,
Steve G3TXQ

Let's see how well the principles involved are understood.

What is the delay through a physically very small toroidal coil with the
same inductance as the solenoidal coil? Why?

Roy Lewallen, W7EL

A toroidal coil retains magnetism via hysteresis versus zero
hysteresis for a coil made of a diamagnetic material. A coil is in
equilibrium because all forces are accounted for
over one or more periods. A toroidal coil is not in equilibrium
because the energy that provides the hysterisis happens only once per
unit of time where as for equilibrium that same energy is provided for
every period and cancelled by same.
If a unit of energy is supplied to a radiator in equilibrium then the
unit of energy must be added to or increased to represent the
hysteresis lossesof the toroid The ratio of the original unit of
energy will represent the difference in time or delay required to
represent balance between the two. The above is based on a coil in the
medium of air and not magnetic core as the term "solenoid" suggests.
Roy doesn't see my posts either so somebody else has to pass this on.
Art

Roy Lewallen wrote:
steveeh131047 wrote:

Cecil: that's a VERY significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros paper it predicts an
axial Velocity Factor of 0.033. That would equate to a time delay of
24.7nS across the 10" long coil !!!!

Regards,
Steve G3TXQ

Let's see how well the principles involved are understood.

What is the delay through a physically very small toroidal coil with the
same inductance as the solenoidal coil? Why?
As in a coil wound on a toroidal magnetic core? or a air cored solenoid
bent in a circle?

Jim Lux wrote:
Roy Lewallen wrote:

Let's see how well the principles involved are understood.

What is the delay through a physically very small toroidal coil with
the same inductance as the solenoidal coil? Why?
As in a coil wound on a toroidal magnetic core? or a air cored solenoid
bent in a circle?

I'll say one wound on a magnetic core, simply to keep the size small,
the coupling tight, and the field confined. I don't, however, care how
long a piece of wire it's wound with.

Roy Lewallen, W7EL

On Apr 23, 2:32*pm, Roy Lewallen wrote:
Jim Lux wrote:
Roy Lewallen wrote:

Let's see how well the principles involved are understood.

What is the delay through a physically very small toroidal coil with
the same inductance as the solenoidal coil? Why?
As in a coil wound on a toroidal magnetic core? or a air cored solenoid
bent in a circle?

I'll say one wound on a magnetic core, simply to keep the size small,
the coupling tight, and the field confined. I don't, however, care how
long a piece of wire it's wound with.

Roy Lewallen, W7EL

There are some other configurations that I personally think are
interesting to ponder. You might never actually build one this way,
but you'll probably gain some insights considering it: an antenna,
say a nominally 1/4 wave vertical for 40 meters made from 4" diameter
aluminum tube (irrigation pipe) twenty feet long, resonated with a
loading coil placed inside the tube across a gap of two or three
inches in the pipe. Capacitance from the coil is almost entirely to
the pipe in this case, not to the world outside the pipe, so the
effect is capacitance in parallel with the coil, not as in a
transmission line where the capacitance is to ground. That's a
different situation than one where a coil with a diameter much larger
than the antenna conductor is used, where the coil has significant
capacitance to the outside world (e.g. to ground).

It's also worth considering that the charge distribution on an antenna
is dynamic, so it's probably not a good idea to try to analyze the
antenna as if there was the same capacitance to ground from the coil
as there would be if the charge distribution on the antenna wire were
static (that is, the DC case, or at a frequency that's a tiny fraction
of the lowest natural resonance of the antenna system).

Analyzing exactly how even a simple wire antenna works in detail is
far from trivial, and when you add in a coil that has significant
physical size, it further complicates things. If you use a simplified
model, it can be useful to gain insights into what's going on, but
don't expect the details to be correct. Be wary about gaining
insights that aren't actually true.

Cheers,
Tom

On Apr 23, 6:59*pm, K7ITM wrote:
On Apr 23, 2:32*pm, Roy Lewallen wrote:

Jim Lux wrote:
Roy Lewallen wrote:

Let's see how well the principles involved are understood.

What is the delay through a physically very small toroidal coil with
the same inductance as the solenoidal coil? Why?
As in a coil wound on a toroidal magnetic core? or a air cored solenoid
bent in a circle?

I'll say one wound on a magnetic core, simply to keep the size small,
the coupling tight, and the field confined. I don't, however, care how
long a piece of wire it's wound with.

Roy Lewallen, W7EL

There are some other configurations that I personally think are
interesting to ponder. *You might never actually build one this way,
but you'll probably gain some insights considering it: *an antenna,
say a nominally 1/4 wave vertical for 40 meters made from 4" diameter
aluminum tube (irrigation pipe) twenty feet long, resonated with a
loading coil placed inside the tube across a gap of two or three
inches in the pipe. *Capacitance from the coil is almost entirely to
the pipe in this case, not to the world outside the pipe, so the
effect is capacitance in parallel with the coil, not as in a
transmission line where the capacitance is to ground. *That's a
different situation than one where a coil with a diameter much larger
than the antenna conductor is used, where the coil has significant
capacitance to the outside world (e.g. to ground).

It's also worth considering that the charge distribution on an antenna
is dynamic, so it's probably not a good idea to try to analyze the
antenna as if there was the same capacitance to ground from the coil
as there would be if the charge distribution on the antenna wire were
static (that is, the DC case, or at a frequency that's a tiny fraction
of the lowest natural resonance of the antenna system).

Analyzing exactly how even a simple wire antenna works in detail is
far from trivial, and when you add in a coil that has significant
physical size, it further complicates things. *If you use a simplified
model, it can be useful to gain insights into what's going on, but
don't expect the details to be correct. *Be wary about gaining
insights that aren't actually true.

Cheers,
Tom

Tom you are correct in not making a descision on the basis of one
observation but consideration of all the observable facts. The analogy
of this is only with the use of alln segtments of a jigsaw puzzle can
there be confidance of the ensuing picture.
Roy stated that his conclusion was only based on one observable and
where his statement said he did not care beyond that single observable
which matched a predetermined picture. An accurate production of the
ensuing picture comes about only with a matching relationship between
all the parts of the jigsaw and certainly not based on the visual of
one. Your last sentence speaks volumes regarding Roy;'s responce
Regards
Art

K7ITM wrote:
On Apr 23, 2:32 pm, Roy Lewallen wrote:
Jim Lux wrote:
Roy Lewallen wrote:
Let's see how well the principles involved are understood.
What is the delay through a physically very small toroidal coil with
the same inductance as the solenoidal coil? Why?
As in a coil wound on a toroidal magnetic core? or a air cored solenoid
bent in a circle?
I'll say one wound on a magnetic core, simply to keep the size small,
the coupling tight, and the field confined. I don't, however, care how
long a piece of wire it's wound with.

Roy Lewallen, W7EL

There are some other configurations that I personally think are
interesting to ponder. You might never actually build one this way,
but you'll probably gain some insights considering it: an antenna,
say a nominally 1/4 wave vertical for 40 meters made from 4" diameter
aluminum tube (irrigation pipe) twenty feet long, resonated with a
loading coil placed inside the tube across a gap of two or three
inches in the pipe. Capacitance from the coil is almost entirely to
the pipe in this case, not to the world outside the pipe, so the
effect is capacitance in parallel with the coil, not as in a
transmission line where the capacitance is to ground. That's a
different situation than one where a coil with a diameter much larger
than the antenna conductor is used, where the coil has significant
capacitance to the outside world (e.g. to ground).

It's also worth considering that the charge distribution on an antenna
is dynamic, so it's probably not a good idea to try to analyze the
antenna as if there was the same capacitance to ground from the coil
as there would be if the charge distribution on the antenna wire were
static (that is, the DC case, or at a frequency that's a tiny fraction
of the lowest natural resonance of the antenna system).

Analyzing exactly how even a simple wire antenna works in detail is
far from trivial, and when you add in a coil that has significant
physical size, it further complicates things. If you use a simplified
model, it can be useful to gain insights into what's going on, but
don't expect the details to be correct. Be wary about gaining
insights that aren't actually true.

Cheers,
Tom

I didn't do exactly as you say, Tom, but I did take a homemade coil
(140mm long, 155mm in diameter) and wrapped it with a sheet of .005 inch
copper foil separated by a couple of strips of double sided foam tape.
It acted more like a transmission line than the bare coil, but it had
some peculiarities that made its behavior puzzling to say the least.
73,
Tom Donaly, KA6RUH

Roy Lewallen wrote:
What is the delay through a physically very small toroidal coil with the
same inductance as the solenoidal coil? Why?

A toroidal coil cannot be modeled using the Dr. Corum
formulas. But I will take a stab at the answer.

In a physically very small toroidal coil, all the
turns are tightly coupled, i.e. the flux caused by
one coil links all of the other windings so the
delay should be quite small. In any case, one
cannot use a current with unchanging phase (referenced
to the source phase) to calculate the delay through
anything. The only phase information left in a
standing wave is in the magnitude. If the current
magnitude at the bottom of the coil is 1.0, the phase
shift is the ARCCOSine of the current magnitude at
the top of the coil for a base-loaded resonant
antenna. Actual phase measurements on the current
in standing-wave antennas is meaningless. We already
know it hardly changes at all with length. EZNEC
confirms that statement.

In an air-core solenoidal coil, like the one w8ji
used, the flux linkage tends to be associated with
adjacent turns so all the flux does not link all
the coils. Tom's coil was 100 turns, 10 TPI, 2"
diameter. The first turn was 10 inches away from
the last turn. The delay through that coil calculates
out to be about 25 nS.

If we setup a 2" transmit coil and a 2" receive
coil 10 inches away in air, the energy transfer
efficiency would be very small. I don't have a
formula for such but I assume one (or more) exists.

Bottom line: There are now formulas for calculating
the Z0 and VF of large air-core loading coils which
are known to be in the family of *slow-wave* devices.

I doubt that a toroidal coil is in the family of
slow-wave devices.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com

Jim Kelley wrote:
steveeh131047 wrote:
Cecil: that's a VERY significant result. If I feed the dimensions of
W8JI's coil into Equation 32 in the Corum Bros paper it predicts an
axial Velocity Factor of 0.033. That would equate to a time delay of
24.7nS across the 10" long coil !!!!

You're right. The numbers are amazingly close - almost as if his
'experimental apparatus' had calculated the result rather than measure it.

Why do you say "approximately 25 nS" and 24.7 nS are
amazingly close? "Approximately 25 nS" might include
an unknown measurement inaccuracy.
--
73, Cecil, IEEE, OOTC, http://www.w5dxp.com