wrote:
That's not correct at all Richard. The coil in a TWT tube behaves
considerably different than a small inductor operted at a low
frequency.

A 75m bugcatcher coil is not a small inductor. You guys have
backed so far out of the basic real world argument that we can't
even see your coils anymore without a microscope. Of course,
microscopic coils have delays that can be ignored. 75m bugcatcher
coils are not microscopic. They are HUGE!

How you can argue that the magnitude of the current is the same
at both ends of the coil when 12 out of 13 of the measurements
showed they were different is magical thinking, divorced from
reality.

The only real argument against this seems to be from Cecil, and as I
understood it he thinks standing waves are what causes current to be
different at each end and somehow sets the phase difference between
ends of the inductor.

If you don't understand that fact of physics, you don't understand
the distributed network model at all. In a standing wave antenna,
there exist forward current and reflected current. Any model that
doesn't take that fact into account is doomed to failure.

800 posts later the same major group of people seem to agree, the same
one or two people seem to think something magical occurs in an antenna
making a regular lumped inductor behave like a self-resonant helice
with standing waves and all.

The magic is that current travels through coils faster than the speed
of light. That's what your lumped-circuit argument presupposes. It
also completely ignores reflected waves.

Doesn't it seem logical to use a model that includes reflected waves
when one installs a loading coil in a standing wave antenna?
--
73, Cecil http://www.qsl.net/w5dxp

you measured
You cannot have
You cannot use
you going
you made
you didn't
you think
What are dreams made of?

Cecil,

I guess I am a bit puzzled.

The bugcatcher example I sent you showed a phase shift of about 7
degrees at 4 MHz. The current at the top of the coil drops off to about
85% of the base current. I believe the delay computes to something
around 5 ns. That does not seem like a HUGE delay for a coil that
contains nearly 40 feet of wire.

I presume you can now duplicate and verify these results, since we have
not heard any contrary information. That coil is real close in design to
a genuine Texas Bugcatcher #680 from Henry Allen.

Absolutely no one around RRAA clings to a rigid lumped component model,
except your straw man. The distinction is that most people treat this
non-ideality as a perturbation. You seem to want to elevate it to the
status of realignment of the planets.

It has been explained over and over why real coils are not ideal. I am
sure you understand. I am not at all sure why you persist in carrying on
this rather pointless argument.

73,
Gene
W4SZ

Cecil Moore wrote:


A 75m bugcatcher coil is not a small inductor. You guys have
backed so far out of the basic real world argument that we can't
even see your coils anymore without a microscope. Of course,
microscopic coils have delays that can be ignored. 75m bugcatcher
coils are not microscopic. They are HUGE!

How you can argue that the magnitude of the current is the same
at both ends of the coil when 12 out of 13 of the measurements
showed they were different is magical thinking, divorced from
reality.

Gene Fuller wrote:
The bugcatcher example I sent you showed a phase shift of about 7
degrees at 4 MHz.

I've been waiting for you to come back with the facts that
contradict W8JI's measurements. Thanks once again.

The coil has about half the inductance of the 100 uH coil
measured by W8JI. He measured ~4 degrees in 100 uH. EZNEC
reports 8 degrees in 60 uH for an 8.5 foot antenna.

My wild ass guess was at least five times more accurate
than W8JI's measurements. Thanks for pointing that out.
--
73, Cecil http://www.qsl.net/w5dxp

Cecil,

I did not say anything about W8JI's measurements. He had a completely
different setup, and I had nothing to do with it.

You have a remarkable Teflon coating. I completely called your bluff on
the bugcatcher coil, and you simply ignore the result and slide away to
some other Don Quixote adventure. I am not really surprised, of course.

73,
Gene
W4SZ

Cecil Moore wrote:
Gene Fuller wrote:

The bugcatcher example I sent you showed a phase shift of about 7
degrees at 4 MHz.


I've been waiting for you to come back with the facts that
contradict W8JI's measurements. Thanks once again.

The coil has about half the inductance of the 100 uH coil
measured by W8JI. He measured ~4 degrees in 100 uH. EZNEC
reports 8 degrees in 60 uH for an 8.5 foot antenna.

My wild ass guess was at least five times more accurate
than W8JI's measurements. Thanks for pointing that out.

Richard Harrison wrote:
Tom, W8JI wrote:
"Many people vizualize current in a small loading inductor as starting
at one end and traveling through the conductor turn-by-turn.

That`s how the experts say the coul in a TWT works, and it is no
different from other coils.
. . .

I maintain that 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 believe that current traveling down a straight wire goes at nearly the
speed of light. I also believe that if you take that straight wire and
wind it into a helix with very widely spaced turns, it also travels down
the wire at nearly the speed of light. But if you wind a helix that's
short in terms of wavelength and with a reasonable length/diameter
ratio, the field from the current in each turn couples to all other
turns, which makes the propagation axially from one end to the other
close to the speed of light. That is, for the same length of wire, an
inductor with closely coupled turns has a much lower propagation delay
than one with the turns spread out in a loose helix.

Do I infer from your comments that you believe that the current
continues to flow along the wire at about the speed of light, so that if
the wire length stays the same, the propagation delay along the widely
spaced helix is the same as for the short one with close spaced turns?
That is, that both these cases fall into what you categorize as "other
coils", which act the same as the helix in a TWT?

Roy Lewallen, W7EL

Gene Fuller wrote:
Cecil,

I guess I am a bit puzzled.

The bugcatcher example I sent you showed a phase shift of about 7
degrees at 4 MHz. The current at the top of the coil drops off to about
85% of the base current. I believe the delay computes to something
around 5 ns. That does not seem like a HUGE delay for a coil that
contains nearly 40 feet of wire.

I presume you can now duplicate and verify these results, since we have
not heard any contrary information. That coil is real close in design to
a genuine Texas Bugcatcher #680 from Henry Allen.

Absolutely no one around RRAA clings to a rigid lumped component model,
except your straw man. The distinction is that most people treat this
non-ideality as a perturbation. You seem to want to elevate it to the
status of realignment of the planets.

It has been explained over and over why real coils are not ideal. I am
sure you understand. I am not at all sure why you persist in carrying on
this rather pointless argument.

Actually Gene if you look at:

http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

your EZNEC model's current agrees with similar coils in antennas I
measured.

I expect Cecil will ignore what you sent him, or announce it supports
his conclusions by editing the data.

73 Tom

Gene Fuller wrote:
I completely called your bluff on
the bugcatcher coil, and you simply ignore the result and slide away to
some other Don Quixote adventure.

The EZNEC simulation is just one more data point in a large set
of data points that are already widely scattered. EZNEC does not
have magic or God-like properties to override reality especially
when your design results in pages and pages of segmentation
guideline violations. The jury is still out on the question.

You guys have a habit of declaring victory when you score your
first point after trailing 10-0. When only one coil out of a
dozen tests showed the current at each end of the toroidal
coil to be the same, W8JI declared that was proof that all
coils have the same current at each end.

If you will check my postings, you will see that I said
the delay through a coil is what it is and we usually don't
know what it is. But we do know it is NOT instantaneous and
we know it is unlikely to be the 3 nS measured by W8JI.

I was surprised to see EZNEC report the delay as 20% less than
my lower estimate of 10 degrees. But that 8 degrees is 100%
higher than W8JI's measured values.

And there's your pesky posting about standing wave currents.

The only "phase" remaining is the cos (kz) term, which is really an amplitude
description, not a phase.

If we assume the 1.013 amp at the bottom of the coil occurs when
the forward and reflected currents are in phase, then the 0.7628
amps at the top of the coil would have the currents 82 degrees
out of phase, i.e. a 41 degree phase shift through the coil.
That is, of course, only a rough estimate, but enough different
from the 8 degrees to suspect something is wrong with my suggested
traveling wave antenna.
--
73, Cecil http://www.qsl.net/w5dxp

wrote:
Actually Gene if you look at:
http://www.w8ji.com/mobile_antenna_c...ts_at_w8ji.htm

your EZNEC model's current agrees with similar coils in antennas I
measured.

I still don't understand how you can continue to assert that there are
equal currents at each end of a loading coil when half of your own
measurements show a current at the top of the coil that is 73-79% lower
than the current at the bottom of the coil.

And I have shown that those currents depend upon where the coil is
placed in the standing wave system:

http://www.qsl.net/w5dxp/current.htm
http://www.qsl.net/w5dxp/1WLDIP.GIF

I expect Cecil will ignore what you sent him, or announce it supports
his conclusions by editing the data.

Please see my posting answering Gene. The 8 degree delay value is
20% less than my lowest estimate. The 8 degree delay value for the
~70 uH coil is 100% higher than your measured value of 3 nS for
a 100 uH coil. The EZNEC value is also suspicious in the face of
pages and pages of segmentation violations errors reported by EZNEC.

Gene Fuller wrote:
The only "phase" remaining is the cos (kz) term, which is really
an amplitude description, not a phase.

The phase information in a standing wave is in its amplitude and can
be used to estimate the difference in phase angles between the
forward and reflected currents.

If the current at the top of the coil is 75% of the current at the
bottom of the coil, it means that the forward and reflected current
phasors are approximately 82 degrees out of phase with each other,
i.e. there is roughly a 41 degree phase shift through the coil. That
comes from your own measurements.

The latest EZNEC results are just one more data point on a plot
already containing many scattered data points.
--
73, Cecil http://www.qsl.net/w5dxp

Roy Lewallen wrote:
I maintain that 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.

What's wrong with grouping coils that act quite differently
into a set called "other coils"?

But if you wind a helix that's
short in terms of wavelength and with a reasonable length/diameter
ratio, the field from the current in each turn couples to all other
turns, which makes the propagation axially from one end to the other
close to the speed of light.

This is easily proven not to be true by self-resonance testing.
My 75m bugcatcher is self-resonant on my GMC pickup at about
6.6 MHz. If the signal were "propagating axially from one end to
the other close to the speed of light", the self-resonant frequency
would be close to 1 GHz.
--
73, Cecil http://www.qsl.net/w5dxp