Roy, W7EL wrote:
"I maintain there`s no such group as "other coils", but that coils act
quite differently depending on their physical sizes and the amount of
coupling between turns."

I wrote:
"That`s how the experts say the coil in a TWT works, and is no different
from other coils."

All coils aren`t inside TWTs, but all coils do create inductance.

Bill Orr wrote this concerning the coil in a Traveling Wave Tube:
"Figure 25 is a simplified sketch of a basic helix-type TWT tube. Spaced
closely around the beam is a circuit, in this case a helix of tightly
wound wire, capable of propagating a slow wave. The r-f energy travels
along the wire at the velocity of light, because of the helical path,
the energy progresses along the length of the tube at a considerable
slower veloity than is determined primarily by the pitch of the helix."

Terman wrote this concerning the coil in a TWT:
"The beam is shot through a long, loosely wound helix, and is collected
by an electrode at anode potential as shown."

Lenkurt wrote:
"The RF signal travels as a surface wave around the turns of the helix,
toward the collector, at about the velocity of light. The forward or
axial velocity is slower, of course, because of the pitch and diameter
of the helix."

Orr`s example was a helix of tightly wound wire.

Terman`s example was a long, loosely wound helix, and Lenkurt did not
specify how tight or loosely the coil was wound. In all cases the coil
retarded the signal well below the velocity of light along the axis that
the electron beam traveled so that the beam could keep up with the
signal along the path. The beam needs to be speeded as well as slowed
for velocity modulation.

Point is that group velocity does not exceed the velocity of light even
in W8JI`s coil no matter how he makes it. There is no way to coerce
actual energy to exceed the velocity of light. It would turn into a
pumpkin or something.

Also, electric current follows the course of maximum potential
difference and that`s along the conductor supplying the electrons. The
wave impels electrons to move in the conductor.

Kraus wrote:
"The helical antenna, which is discussed in this chapter, may be
regarded as the connecting link between the linear antenna and the loop
antenna, discussed in preceeding chapters. The helical antenna is the
general form of antenna of which the linear and the loop are special
cases. Thus, a helix of fixed diameter collapses to a loop as spacing
approaches zero. On the other hand, a helix of fixed spacing between
turns straightens out into a linear conductor as the diameter approaches
zero.

This thread has been about a coil loaded whip. This is a standing wave
antenna. When the signal gets to the antenna tip it has no where else to
go but return over the path which brought it. The coil has an incident
wave impinging from the transmitter and an out-of-phase signal reflected
from its tip. These two waves have the same origin so they are locked in
step to make standing waves in both voltage and current. These determine
the ratios of voltage to current at each point along the signal route.
In this respect the coil behaves as a conductor in the antenna. It has
more opposition to the signals traversing it than a straight wire but
the volts and amps at each of its ends can obviously be very different.
Thus, current in one end of the coil can be very different from the
current at the other end of the same coil.

Best Regards, Richard Harrison, KB5WZI

From all that, I gather that your answer is "yes", that you do believe
that the current in a small inductor with close turn spacing (i.e., one
where the fields from the turns couple well) flows around and around
along the wire at near the speed of light, resulting in a delay from end
to end approximately equal to the wire length divided by the speed of light.

Or did I misinterpret what you said, and you don't believe this?

Roy Lewallen, W7EL

Richard Harrison wrote:
Roy, W7EL wrote:
"I maintain there`s no such group as "other coils", but that coils act
quite differently depending on their physical sizes and the amount of
coupling between turns."

I wrote:
"That`s how the experts say the coil in a TWT works, and is no different
from other coils."

All coils aren`t inside TWTs, but all coils do create inductance.
. . .

Rot, W7EL wrote:
"From all that, I gather your answer is Yes."

I believe the wave is guided by the wire in its path and takes no
shortcut along the axis of a coil.

Best regards, Richard Harrison, KB5WZI

It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a couple
of calibrated current probes, and a dual-channel scope, will you believe
the results? Or would you rather have someone else make the measurement
or do it yourself?

Roy Lewallen, W7EL

Richard Harrison wrote:
Rot, W7EL wrote:
"From all that, I gather your answer is Yes."

I believe the wave is guided by the wire in its path and takes no
shortcut along the axis of a coil.

Best regards, Richard Harrison, KB5WZI

Roy Lewallen wrote:

It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a couple
of calibrated current probes, and a dual-channel scope, will you believe
the results? Or would you rather have someone else make the measurement
or do it yourself?

You will, no doubt, chose a piece of Air-Dux so
small that all the flux is linked to every coil.

Instead of a small Air-Dux coil, use a 75m bugcatcher
coil mounted over a ground plane and see what you get.
--
73, Cecil http://www.qsl.net/w5dxp

Roy Lewallen wrote:
It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a couple
of calibrated current probes, and a dual-channel scope, will you believe
the results? Or would you rather have someone else make the measurement
or do it yourself?

Sorry for the double posting, but I just thought of an experiment
that will settle everything.

Take W8JI's 100 uH coil. Keep the spacing between coil 1 and
coil 100 the same at one foot. Get rid of all the other coils
leaving only coil 1 and coil 100 separated by one foot of air.
Use coil 1 as the primary coil and measure the coupling from
coil 1 to coil 100. If it is 100%, you will have made believers
out of everyone and we can stop this silly argument.

The lumped circuit theory says that all the flux in coil 1
links to coil 100 one foot away just as if they were
both tightly wrapped around a toroid.

So there's the challenge. Simply prove that 2" dia coils one
foot apart in air transfer all the energy from one coil to
the other. Piece of cake.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil Moore wrote:
Roy Lewallen wrote:

It'll be easy enough to show that's false. If I set up a simple
measurement with a piece of Air-Dux in series with a resistor, a
couple of calibrated current probes, and a dual-channel scope, will
you believe the results? Or would you rather have someone else make
the measurement or do it yourself?


Sorry for the double posting, but I just thought of an experiment
that will settle everything.

Take W8JI's 100 uH coil. Keep the spacing between coil 1 and
coil 100 the same at one foot. Get rid of all the other coils
leaving only coil 1 and coil 100 separated by one foot of air.
Use coil 1 as the primary coil and measure the coupling from
coil 1 to coil 100. If it is 100%, you will have made believers
out of everyone and we can stop this silly argument.

The lumped circuit theory says that all the flux in coil 1
links to coil 100 one foot away just as if they were
both tightly wrapped around a toroid.

So there's the challenge. Simply prove that 2" dia coils one
foot apart in air transfer all the energy from one coil to
the other. Piece of cake.

What lumped circuit theory? It's a simplification and everyone
knows it. Don't set up any more straw men than you have to, Cecil.
73,
Tom Donaly, KA6RUH

Tom Donaly wrote:
Cecil Moore wrote:
So there's the challenge. Simply prove that 2" dia coils one
foot apart in air transfer all the energy from one coil to
the other. Piece of cake.

What lumped circuit theory? It's a simplification and everyone
knows it. Don't set up any more straw men than you have to, Cecil.

It's not a straw man if someone actually believes it. We
have a 2" dia. x 12" long coil. That's a length to diameter
ratio of 6/1. There's no way coil 1 links all its flux to
coil 100. Yet the *measured* delay through that coil was
3 nS. EZNEC says the delay through a better linked 70 uH
coil is 6.22 nS.

Have you noticed that the coils having instantaneous
propagation times have been getting smaller and smaller
and more conceptual rather than real?
--
73, Cecil http://www.qsl.net/w5dxp

Tom Donaly wrote:

What lumped circuit theory? It's a simplification and everyone
knows it. Don't set up any more straw men than you have to, Cecil.

It's a simplification of any real-life coil - but loading by
pure-and-simple lumped inductance is also a vital test case.

This form of loading is the simplest imaginable. If a theory about the
behaviour of loaded antennas fails to give correct results for this very
simplest test case, it cannot be valid... and all the further
elaborations about real-life coils will not be valid either.

Cecil's theory does work for this test case, because it requires that
basic electrical properties like current and inductance switch into a
different kind of behaviour in what he calls a "standing wave
environment". But it is an absolutely basic fact that the physical world
does NOT change its behaviour according to the way we choose to think
about it. If any theory requires that, it's an absolute proof that such
theory is false.


For the avoidance of doubt (as they say in Scottish legal documents):
It certainly IS possible to analyse and predict the behaviour of
coil-loaded antennas in terms of travelling and standing waves. My
objection is specifically against Cecil's method, which is provably
incorrect.



(Away now to the GMDX Convention, so no replies till Monday.)


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Richard Harrison wrote:

Rot, W7EL wrote:
"From all that, I gather your answer is Yes."

I believe the wave is guided by the wire in its path and takes no
shortcut along the axis of a coil.

If 100% of the flux from each and every coil physically linked
100% of each and every other coil, the current would indeed skip
from one end of the coil to the other without interference. That
is the basic presupposition of the lumped-circuit model.

Quoting Dr. Corum:
"Lumped element circuit theory assumes that there are no wave
interference phenomena present, ...", i.e. no superposition
of forward and reflected waves, i.e. no standing waves.

Continuing the quote:
"This is manifested by two phenomena: 1. The current distribution
function is spatially uniform across each element. 2. The spatial
phase delay between circuit extremities is zero."

One has to imagine that W8JI's 2" dia x 12" length 100 uH coil
links 100% of the flux in coil number 1 with coil number 100
a foot away and vice versa. That's quite an imagination but W8JI
did measure a 3 nS delay, virtually instantaneous, so it must
be true.
--
73, Cecil http://www.qsl.net/w5dxp