Cecil Moore wrote:

If you want to know the velocity factor of a piece of
transmission line, the easiest thing to do is find
its first self-resonant frequency. A little math
will yield the VF which allows prediction of the
phase shift through any reasonable length of
tranmission line.

If you want to know the velocity factor of a coil,
the easiest thing to do is find its first self-
resonant frequency. A little math will yield the
VF of the coil which allows prediction of the
phase shift through any reasonable length of coil.

If the inductor in question does not take much advantage of mutual
induction across its length nor has much capacitance across its length
(say, a straight conductor, strung with ferrite toroids), then I can
see the similarity with a transmission line. But as the inductor
approaches a lumped inductance with significant inter winding
capacitance and mutual inductance coupling the current across a
significant part of its winding length, I see on reason to assume the
transmission line method (delay independent of frequency) strictly
applies. It might, but it would take more than you saying so to
assure me that it is a fact.

In other words, transmission line concepts like uniform inductance per
length and uniform capacitance per length get rather muddled in a real
inductor.

John Popelish wrote:

If the inductor in question does not take much advantage of mutual
induction across its length nor has much capacitance across its length
(say, a straight conductor, strung with ferrite toroids), then I can see
the similarity with a transmission line. But as the inductor approaches
a lumped inductance with significant inter winding capacitance and
mutual inductance coupling the current across a significant part of its
winding length, I see on reason to assume the transmission line method
(delay independent of frequency) strictly applies. It might, but it
would take more than you saying so to assure me that it is a fact.

In other words, transmission line concepts like uniform inductance per
length and uniform capacitance per length get rather muddled in a real
inductor.

Tom W8JI posted a good description and summary of inductor operation a
little while ago, but it looks like it could bear repeating, perhaps
with a slightly different slant.

In a transmission line, a field at one end of the line requires time to
propagate to the other end of the line. As the EM fields propagate, they
induce voltages and currents further down the line, which create their
own EM fields, and so forth. These propagating fields and the currents
and voltages they produce make the whole concept of traveling voltage
and current waves useful and meaningful.

But in a tightly wound inductor, a field created by the current in one
turn is coupled almost instantly to all the other turns (presuming that
the coil is physically very small in terms of wavelength). Consequently,
output current appears very quickly following the application of input
current. The propagation time is nowhere near the time it would take for
the current to work its way along the wire turn by turn.

Once again it's necessary to point out that I'm speaking here of an
inductor which has very good coupling between turns and minimal field
leakage or radiation, for example a toroid. If you make an air wound
inductor and slowly stretch it out until it's nothing more than a
straight wire, it'll begin by resembling the toroid -- more or less,
depending on how well coupled the turns are and how much its field
interacts with the outside world -- then slowly change its
characteristics to resemble a straight wire. There's no magic transition
point. So by choosing the inductor, you can observe behavior anywhere
along this continuum.

Roy Lewallen, W7EL

Roy Lewallen wrote:
But in a tightly wound inductor, a field created by the current in one
turn is coupled almost instantly to all the other turns ...

"All the other turns"? Here's what Jim Lux, W6RMK, had to say
about that:

"For inductance the signficant thing is that the magnetic field
of one segment pretty much links to the adjacent segments, and
less so for the rest."

Less to the 3rd, less than that to the 4th, even less than that
to the 5th. What do you think it might be by the time it gets
to the 80th turn on Tom's coil? Seems that we can assume that
the linkage between coil #1 and coil #80 is negligible.

Once again it's necessary to point out that I'm speaking here of an
inductor which has very good coupling between turns and minimal field
leakage or radiation, ...

So was W6RMK.

There's no magic transition point.

Indeed there isn't. I repeat, in case your didn't understand -
indeed there isn't. So you can discard your magic lumped-
circuit model for a system containing reflections.
--
73, Cecil http://www.qsl.net/w5dxp

John Popelish wrote:
... I see no reason to assume the transmission line method
(delay independent of frequency) strictly applies. It might, but it
would take more than you saying so to assure me that it is a fact.

Assume the environment of the coil is fixed like the variable
stinger measurement I reported earlier. Besides the frequency
term, the phase constant depends upon L, C, R, and G as does
the Z0 equation. Why would the L, C, R, and G change appreciably
over a relatively narrow frequency range as in my bugcatcher coil
measurements going from 6.7 MHz to 3.0 MHz?

And I didn't mean to imply that the delay is "independent" of
frequency, just that it is not nearly as frequency dependent
as Tom's measurements would suggest. If Tom made his measurements
from 1 MHz to 16 MHz, what do you think the curve would look like?

Freq 1 2 4 8 16 MHz
Delay ___ ___ 3 ___ 16 nS

That looks non-linear to me. How about you?
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
John Popelish wrote:

... I see no reason to assume the transmission line method (delay
independent of frequency) strictly applies. It might, but it would
take more than you saying so to assure me that it is a fact.


Assume the environment of the coil is fixed like the variable
stinger measurement I reported earlier. Besides the frequency
term, the phase constant depends upon L, C, R, and G as does
the Z0 equation. Why would the L, C, R, and G change appreciably
over a relatively narrow frequency range as in my bugcatcher coil
measurements going from 6.7 MHz to 3.0 MHz?

We are not talking about L, C, R, or any other inherent property
changing with frequency. We are talking about the delay of a current
wave in a single direction (anybody have a pair of directional coupler
current probes?) through a complex component that has several
different mechanisms that contribute to the total current passing
through it. It is the vector sum (superposition) of those current
components that is in question. Over a narrow frequency range, it is
conceivable to me, that the phase (delay) of that sum might shift,
dramatically, though any component of that sum might change its
magnitude only slightly (no faster than in proportion to the
frequency), and the phase of that component might change not at all.

And I didn't mean to imply that the delay is "independent" of
frequency, just that it is not nearly as frequency dependent
as Tom's measurements would suggest. If Tom made his measurements
from 1 MHz to 16 MHz, what do you think the curve would look like?

Freq 1 2 4 8 16 MHz
Delay ___ ___ 3 ___ 16 nS

That looks non-linear to me. How about you?

Definitely nonlinear, just like impedance is very nonlinear as the
frequency passes through any resonance. This is why I am suspicious
of a measurement made at resonance, being extrapolated to non resonant
conditions.

John Popelish wrote:
We are not talking about L, C, R, or any other inherent property
changing with frequency.

The velocity factor of the coil is based on those quantities
and can be calculated.

The velocity factor of a transmission line is based on those
quantities and can be calculated.

Freq 1 2 4 8 16 MHz
Delay ___ ___ 3 ___ 16 nS

That looks non-linear to me. How about you?

Definitely nonlinear, just like impedance is very nonlinear as the
frequency passes through any resonance.

Care to fill in the blanks above?

This is why I am suspicious of
a measurement made at resonance, being extrapolated to non resonant
conditions.

Self-resonance is simply where the round trip delay through
the coil puts the forward and reflected voltages and the forward
and reflected currents either at zero degrees or 180 degrees.

That's what happens at an open-ended 1/4WL stub.

That's also what happens at the feedpoint of a resonant
standing wave antenna like a 75m mobile bugcatcher antenna.
Resonant mobile antennas are "self-resonant antenna systems".
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
John Popelish wrote:
We are not talking about L, C, R, or any other inherent property
changing with frequency.

The velocity factor of the coil is based on those quantities
and can be calculated.

I am not familiar with the velocity factor of coils.

The velocity factor of a transmission line is based on those
quantities and can be calculated.

Not quite. The velocity factor in transmission lines is based on
ratios:
capacitance per length, and inductance per length.

Where do you get the equivalent length numbers when dealing with semi
lumped inductors?

Freq 1 2 4 8 16 MHz
Delay ___ ___ 3 ___ 16 nS

That looks non-linear to me. How about you?

Definitely nonlinear, just like impedance is very nonlinear as the
frequency passes through any resonance.

Care to fill in the blanks above?
(snip)

My guesses at those numbers without a well tested method are as useful
as yours.

wrote:
The velocity factor of a transmission line is based on those
quantities and can be calculated.

Not quite. The velocity factor in transmission lines is based on
ratios: capacitance per length, and inductance per length.

There exist formulas for calculating the Z0 and VF of
helical transmission lines. I'll bet Reg can do it.
A coil has a capacitance per length and inductance
per length.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
John Popelish wrote:

We are not talking about L, C, R, or any other inherent property
changing with frequency.


The velocity factor of the coil is based on those quantities
and can be calculated.



What's the formula, Cecil? Also, what is the dominant mode
of a single wire, loading-coil transmission line: TE, TM,
TEM, or what? If not TEM, how do you calculate the cutoff
frequency? If I terminate one of these things in the
right impedance will it act like an infinite transmission line?
Given your loading coil terminated in a given impedance, what is
the expression for the impedance looking into it? I suppose you also
have something that will tell us how to find your coil's characteristic
impedance; o.k., out with it. All this bluster and threatening rhetoric
aren't advancing the acceptance of your crackpot theory one inch, Cecil.
I don't see anything wrong with at least attempting to characterize a
loading coil as a transmission line as long as the attempt is done
dispassionately with real theory and an acceptance of the possibility
of failure as part of the effort. Desperately thinking up excuses for
an idea you made up in your head, and becoming emotionally distraught
when people don't buy those excuses, is a waste of your time and
everyone else's.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
What's the formula, Cecil?

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf equation (32)

The velocity factor can also be measured from the self-
resonant frequency at 1/4WL. VF = 0.25(1/f)

I suppose you also
have something that will tell us how to find your coil's characteristic
impedance; o.k., out with it.

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf equation (43)

The characteristic impedance can also be measured at
1/2 the self-resonant frequency at 1/8WL. For a lossless
case, the impedance is j1.0, normalized to the
characteristic impedance so |Z0| = |XL|.
For a Q = 300 coil, that should have some ballpark accuracy.

We don't need extreme accuracy here. We just need enough to
indicate a trend that the velocity factor of a well-designed
coil doesn't increase by a factor of 5 when going from 16
MHz to 4 MHz.

In "Antennas for All Applications", Kraus gives us the phase
of the standing wave current on standing wave antennas like
a 1/2WL dipole and mobile antennas. 3rd edition, Figure 14-2.
It clearly shows that the phase of the standing wave is virtually
constant tip-to-tip for a 1/2WL dipole. It is constant whether
a coil is present or not. There is no reason to keep measuring
that phase shift over and over, ad infinitum. There is virtually
no phase shift unless the dipole is longer than 1/2WL and then
it abruptly shifts phase by 180 degrees.

I agree with Kraus and concede that the current phase shift in
the midst of standing waves is at or near zero. There is no
need to keep providing measurement results and references.
--
73, Cecil http://www.qsl.net/w5dxp