Current through coils
 

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.

Current through coils
 

Richard Clark wrote:
Having built nigh on an hundred, you are right - I don't have one now.
I don't plan to build anymore either as it would do nothing to lower
the text noise floor.

I've enjoyed the speculation tho'.

The two most humorous parts of this entire thing:

1.) RF current can stand still, yet cause current in a transformer
secondary.

2.) We have to use a "directional current coupler" to sort current
flowing one way from current floing the other, because of standing wave
current.

This entire thing has become almost laughable. It looks like the thread
has regressed to the point where people no longer understand
directional couplers or current transformers.

Anyone who knows how a directional coupler works is rolling around on
the floor laughing at the suggestion of sorting "forward current" from
"reflected current".

It appears this thread has reached the lowest level, where impossible
to build instrumentation is now demanded as the only acceptable proof.

What a trip!

73 Tom

Current through coils
 

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

Current through coils
 

Cecil and Roy, Please stop Ad Hominem.

Keep to the subject where we can disagree or agree. Hopefully, some of
us will learn.

Cecil Moore wrote:

Roy Lewallen wrote:

I believe it's relevant to the discussion at hand on this group, so
I'll share it here, ...


So you believe my personal feelings about you are relevant
to a technical discussion???? Exactly which technical
parameters are affected by my feelings about you?

Current through coils
 

wrote:
1.) RF current can stand still, yet cause current in a transformer
secondary.

Please provide a technical response to the following.

Hecht, in "Optics" says of standing waves of light in space:
"Its profile *DOES NOT MOVE* through space; it is clearly not
of the form f(x+vt). At any point x = x', the amplitude is a
constant equal to 2Eot*sin(kx') and E(x',t) [the electric
field] varies harmonically as cos(wt)." page 289, 4th edition.

The 'z' movement for a standing wave current magnitude
along a wire is completely divorced from the frequency of
the wave. Its profile *DOES NOT MOVE* through the wire.
Same as light standing waves above. It is not of the
form f(z+wt).

Since standing waves of light in space do not move, why is it
surprising that standing waves of RF on a wire do not move
for exactly the same reason since they have identical equations?
The standing wave energy in the H-field of RF standing waves
will certainly cause current in a transformer secondary just
as the standing wave light electric field will activate a
light detector.

2.) We have to use a "directional current coupler" to sort current
flowing one way from current flowing the other, because of standing wave
current.

There really may be humor in that statement which I never made.
I've never heard of a "directional current-only coupler". If
anyone knows of one, it sure would solve the measurement problem.

Anyone who knows how a directional coupler works is rolling around on
the floor laughing at the suggestion of sorting "forward current" from
"reflected current".

And I'm one of them. I've never said there existed such a device,
just that if it did exist, it would solve the measurement problem.
As it is, we haven't solved the measurement problem. The only means
I've seen of actually measuring the phase shift through a coil is
using the self-resonance method. Measuring the phase shift of
standing waves won't work because STANDING WAVES HAVE NO PHASE
SHIFT WHETHER THERE'S A COIL IN THE CIRCUIT OR NOT!

It appears this thread has reached the lowest level, where impossible
to build instrumentation is now demanded as the only acceptable proof.

It was a wish, not a demand. But we can indeed separate out the
forward wave from the reflected wave in a transmission line by
using a directional coupler calibrated for the Z0 of the line.
We can then carry those concepts over to a standing wave antenna,
according to Balanis.

So consider this experiment.

coil
source---50 ohm coax---X-////-Y---50 ohm coax---Load

We have directional couplers installed at 'X' and 'Y' and
we can in theory look at the phases of the forward and
reflected currents on each side of the coil. Will the
forward and reflected currents through the coil show
a phase shift or not? Seems we should start at a pretty
low frequency (low reactance) and work our way up. I
think the phase shift pattern would be clear.

Note that a cap to ground to the left of 'X' and a cap
to ground to the right of 'Y' would result in a pi-net
tuner. Wonder if there's any phase shift through the
coil in a pi-net tuner? Is a pi-net tuner a "phasing
network"?

How could the coil cause an arc on the Smith Chart
without changing the phase of the wave through the coil?
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Dave wrote:

Keep to the subject where we can disagree or agree.

Done! See my postings of today. I apologize for my
previous emotional outbursts.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

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

Current through coils
 

Anyone who knows how a directional coupler works is rolling around on
the floor laughing at the suggestion of sorting "forward current" from
"reflected current".

And I'm one of them. I've never said there existed such a device,
just that if it did exist, it would solve the measurement problem.
As it is, we haven't solved the measurement problem.

I've solved the measurement problem. I measured current and voltage
levels and phase of each.

I've measured time delay of current appearing at the coil output
compared to input.

We have directional couplers installed at 'X' and 'Y' and
we can in theory look at the phases of the forward and
reflected currents on each side of the coil. Will the
forward and reflected currents through the coil show
a phase shift or not?

With all the respect I can muster, here we go again Cecil.

Current is current. Voltage is voltage.

A traditional directional coupler works by comparing voltage across the
line at any one point to current in the line at that same point. The
current sampling device is summed at the operating frequency with the
voltage sampling device, and the resulting voltage is measured. When
voltage and current are in phase, the detected voltage levels add. When
they are fully out of phase they subtract.

Now we could build a transmission line system of measuring SWR that
would work the very same way (normally done at VHF). Or we could build
a line section that allows us to slide a probe along it and measure
voltage or current nodes and finding maximum and minimum calculate SWR.

In every single device we would be able to build, we would never be
able to sort reflected current from forward because current is current.
There really isn't any such thing as current traveling two directions
at one past one point in a system.

You have taken this argument to an absolute dead end, because you
insist current can flow two directions at the same time at one single
point in a system.

You are demanding a measurement method that uses a device that cannot
be built to measure something that does not exist. That is either
humorous, sad, or frustrating. It sure isn't science.

73 Tom

Current through coils
 

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

Current through coils
 

Tom,

Whenever Cecil gets in a total lather I am reminded of John Belushi in
Animal House. "Were you there when the Germans bombed Pearl Harbor?"

This entire saga has been greatly extended and quite thoroughly confused
by imprecise and flat-out-incorrect terminology. It probably won't get
better any time soon.

Currents, waves, and fields are used interchangeably as the mood
strikes. Phase shift can refer to almost anything, it seems. Free-space
optics are used as an analog to current in a wire. Descriptions that
almost certainly have little transferability from one human to another
abound, such as "superposed local RF phasors".

Oh well, it's entertaining, at least for a while.

73,
Gene
W4SZ

wrote:

With all the respect I can muster, here we go again Cecil.

Current is current. Voltage is voltage.

[snip]

In every single device we would be able to build, we would never be
able to sort reflected current from forward because current is current.
There really isn't any such thing as current traveling two directions
at one past one point in a system.

You have taken this argument to an absolute dead end, because you
insist current can flow two directions at the same time at one single
point in a system.

You are demanding a measurement method that uses a device that cannot
be built to measure something that does not exist. That is either
humorous, sad, or frustrating. It sure isn't science.

73 Tom