RadioBanter - Current through coils

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Current through coils

Cecil Moore wrote:
"Gene Fuller" wrote:

Phase is gone. Kaput. Vanished. Cannot be recovered. Never to be seen
again.

So how can a signal, devoid of phase, be used to measure the phase
shift through a loading coil?

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

How can one make a phase measurement using only the amplitude
of a signal?
--
73, Cecil, W5DXP

Cecil,

The phase is uniformly zero, so the phase shift is also zero.

Your messages seem to imply that there is some sort of characteristic
"phase shift" in a loading coil. Ain't so.

In the example of a standing wave antenna the phase shift is zero, both
experimentally and theoretically. (Approximate. Real world conditions
might cause small non-zero shifts.)

If you place this same loading coil in a traveling wave antenna you can
undoubtedly measure some sort of phase shift. (Exact amount left as an
exercise for the student.)

Bottom line: Any characteristic, such as phase, that explicitly depends
on the wave nature of a signal needs to be referenced to that condition,
not some arbitrary setup.

73,
Gene
W4SZ

Current through coils

Gene Fuller wrote:

Cecil,

The phase is uniformly zero, so the phase shift is also zero.

Your messages seem to imply that there is some sort of characteristic
"phase shift" in a loading coil. Ain't so.

In the example of a standing wave antenna the phase shift is zero, both
experimentally and theoretically. (Approximate. Real world conditions
might cause small non-zero shifts.)

If you place this same loading coil in a traveling wave antenna you can
undoubtedly measure some sort of phase shift. (Exact amount left as an
exercise for the student.)

Bottom line: Any characteristic, such as phase, that explicitly depends
on the wave nature of a signal needs to be referenced to that condition,
not some arbitrary setup.

It's likely that quite a number of people don't realize that there's no
phase shift of current or voltage along a short or open circuited
lossless transmission line -- except for, like on an antenna, periodic
polarity reversals.

Roy Lewallen, W7EL

Current through coils

"Gene Fuller" wrote:..
Your messages seem to imply that there is some sort of characteristic
"phase shift" in a loading coil. Ain't so.

Thanks, Gene. What was implied is what has been reported as fact
by others - that the zero phase shift on both ends of a loading coil
measures the delay through the coil to be close to zero.

In the example of a standing wave antenna the phase shift is zero, both
experimentally and theoretically. (Approximate. Real world conditions
might cause small non-zero shifts.)

Please note that the phase shift in the wire is also zero. That the phase
shift is measured to be zero in a coil or a wire in a standing wave
environment is not of any practical importance whatsoever.

If you place this same loading coil in a traveling wave antenna you can
undoubtedly measure some sort of phase shift. (Exact amount left as an
exercise for the student.)

That was the discussion involving Dr. Corum's papers and the VF of
large RF inductors, like a 75m bugcatcher coil.
--
73, Cecil, W5DXP

Current through coils

"Roy Lewallen" wrote:
It's likely that quite a number of people don't realize that there's no
phase shift of current or voltage along a short or open circuited
lossless transmission line -- except for, like on an antenna, periodic
polarity reversals.

If we have 45 degrees of transmission line and measure no phase
shift at each end of that 45 degrees, does that mean the transmission
line is really zero degrees long?

If we have an unknown number of degrees of coil and measure
no phase on each side of the coil, does that mean the coil is
really zero degrees long?
--
73, Cecil, W5DXP

Current through coils

Cecil,

You're a sly one, but not quite sly enough. 8-) 8-)

What is the meaning of "delay" in a standing wave antenna? Delay, like
phase, depends on the environment.

The measurement results reported by W8JI a few days ago stand on their
own. He described the setup and measurements adequately.

If you choose to make extrapolations to another environment, have at it.
Just don't expect anyone else to automatically agree with your
extrapolations.

As I recall, this three-year saga started with consideration of a loaded
mobile antenna, which I believe would be considered a standing wave
antenna. Have you since equipped your steed with a Beverage or rhombic?
Are phase shifts and delays now important?

73,
Gene
W4SZ

Cecil Moore wrote:
"Gene Fuller" wrote:..

Your messages seem to imply that there is some sort of characteristic
"phase shift" in a loading coil. Ain't so.

Thanks, Gene. What was implied is what has been reported as fact
by others - that the zero phase shift on both ends of a loading coil
measures the delay through the coil to be close to zero.

In the example of a standing wave antenna the phase shift is zero, both
experimentally and theoretically. (Approximate. Real world conditions
might cause small non-zero shifts.)

Please note that the phase shift in the wire is also zero. That the phase
shift is measured to be zero in a coil or a wire in a standing wave
environment is not of any practical importance whatsoever.

If you place this same loading coil in a traveling wave antenna you can
undoubtedly measure some sort of phase shift. (Exact amount left as an
exercise for the student.)

That was the discussion involving Dr. Corum's papers and the VF of
large RF inductors, like a 75m bugcatcher coil.
--
73, Cecil, W5DXP

Current through coils

Cecil Moore wrote:
What was the indicator? What was the coupling device?

I have an assortment of toroids of various materials from Amidon. I'm
at work right now and I don't remember if I used 43 or F material.

How did you construct the coupling transformer? How did you make it
immune to electric fields?

On six meters, it would take a darned small probe and indicator to not
greatly perturb the system.

They are small toroids. I chose 6m because the dipole area was
physically small.

They may be small toroids, but what do they connect to? What is the
common mode impedance of the indicator at 50MHz?

If I was going to test something like this, I'd use a small indicator
hanging from the antenna and do it on a low frequency.

Please feel free to make that measurement. W7EL just reported that
EZNEC agrees with my phase measurements. So does Kraus.

You may not have been measuring anything like you think, in particular
voltage. Just because EZnec agrees with the phase measurements it
doesn't mean the current measurement was even remotely close to being
correct.

So, tell us about the probe and indicator.

Similar to the ones W7EL used. They were calibrated within one turn
of each other. The signals at the ends of the coax lines were calibrated
for equality in magnitude and phase. Magnitudes are a relative measurement
but phase was not. I ran the experiment two ways.

I you hung coaxial lines off a current transformer on a 6-meter dipole
down to some test instrument, you wasted a lot of time. There isn't any
possible way you measured an unperturbed system.

You'd better reconfigure as a monopole, and do it on a lower frequency.

One was Lissajous figures on my 100 MHz Leader. The other was putting
the two samples in opposite phase to each other, i.e. phasor subtraction.
For small angles, the angle is equal to the sine of the angle so the
addition
of two coherent sine waves yields an amplitude proportional to the phase
difference when the phase difference is small. The phase difference was
so small it was virtually undetectable.

I wouldn't trust that system at all.

Even with the equipment I have and having build hunderds of sampling
systems, I'd never attempt a measurement like you just made.

You brought a pair of long coaxial lines that are grounded at the far
end up to within an inch of the antenna, hung what amounts to being a
capacitor between the high voltage high impedance side of the antenna
to ground, and presumed to measure voltage and current on six meters!

You can get away with a toroid on 80 or 40 meters if the test gear and
lines are all near ground potential along with the point of the antenna
you are measuring, but it is really off the wall to assume you can hang
a toroid on a dipole past a loading coil, have that toroid connect to a
cable hanging in air down to some test gear, and not severely perturb
the system. Worse yet, the test was done on 50MHz!

I used a very small floating probe with NO earth path and the indicator
right on the probe. I had to do that to not perturb the system on 40
and 80 meters. I can't imagine trying to do what I did on six meters,
I'd have needed an entire metering system the size of a half-dollar or
smaller.

Making a measurement at the base of a vertical on a low frequency like
Roy did allows the person making the measurement to get away with lots
of things, but I can tell you right now I'd NEVER be able to measure
anything in a short mobile antenna if I ran cables up to the probes, in
particular if I made the test on six meters!

73 Tom

Current through coils

Gene Fuller wrote:
What is the meaning of "delay" in a standing wave antenna?

Same as in a traveling wave antenna - the length of
time it takes a traveling wave signal to make it through
a coil or a wire. The lumped-circuit model assumes that
delay is equal to zero even for traveling wave antennas.

Delay, like phase, depends on the environment.

I defined what I meant by "delay" through a coil a few days
ago. It was the delay experienced by a traveling wave
flowing through a coil or 1/2 the delay experienced by
a traveling wave making a round trip to the end of a coil
and back based on the self-resonant frequency. That's what
the velocity factor calculations were all about. Does the
0.66 velocity factor disappear when RG-8 is used as a stub?
Then neither does the 0.0175 coil velocity factor disappear
when it is used in a standing wave environment.

The cos(kz)*cos(wt) nature of the standing wave current
prohibits that standing wave current from being used to
determine the velocity factor of a coil or of a wire. The
lumped-circuit model assumes the velocity factor through
any and every coil to be *greater than unity*.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils

Cecil Moore wrote:
I officially withdraw my measurements as evidence in this
debate and instead substitute the EZNEC results, provided
by W7EL, as evidence.

What does it mean that EZNEC agrees with my possibly
flawed phase measurements? What does it mean that EZNEC
agrees with my argument and disagrees with yours?

How does one use a signal with unchanging phase to measure
the phase shift through a coil or wire? Forgive me if I'm
wrong, but seems to me, you have claimed to have done
exactly that. Please explain how you did that so we can
judge whether your measurements were also flawed.

I expected you would want to discuss the problems of making a
measurement in the high impedance part of an antenna with a toroid
around the wire and a coaxial cable running down to a 100MHz scope on
50Mhz.

I see now you really only want to spew, and have no desire to learn
anything.

I took the time to carefully outline what Roy's measurements and mine
would be significantly more reliable, and I see you disregarded that
also.

I'm very disappointed in your reaction to the effort I made to help you
understand measurement techniques.

73 Tom

Current through coils