Current through coils
 

Current through coils
 

Tom Donaly wrote:
You load your antennas with a Tesla coil? Did you read the part
about a Tesla coil going to a lumped inductor when it was shortened?

A minimum Tesla coil is 1/4WL. My 75m bugcatcher coil
mounted on my pickup as a base-loaded coil with no
whip is 1/4WL on 6.6 MHz. Going from 6.6 Mhz to 4 MHz
is only 40% shortening. I think the lumped inductor
crossover point is probably pretty far below 4 MHz.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

John Popelish wrote:

I appreciate the correction. I am weak in the area of RF
instrumentation, but am learning fast. It is an area I have somehow
avoided for a long time, but am getting interested in it, lately.

Good. It is an interesting area of electronics. If you are comfortable
with RF circuitry, RF instrumentation is only a small additional step.

I would very much like to see a more complete report on the
measurements you have made, in relation to this thread.

The problem is always time. I'm at the busiest time of the year for me,
so everything that isn't a fore is sitting. I really swore I wouldn't
get involved in an ungoing three year debate, but here I am anyway. I
guess I needed a break from a constant string of projects all with
tight deadlines.

I am sure I
would learn from seeing that. I tried to find an operating manual or
application note on the network analyzer you used, but found little
that was helpful to teach me how it works, and how one applies it. It
seems to have 4 signal connectors (if I am interpreting what I have
found, correctly) and I can interpret your web account to mean several
possible things, so I am still under a bit of a cloud, here. Your
tutelage is much appreciated.

This is the closest manual I could find.

http://www.home.agilent.com/cgi-bin/...OUNTRY_CODE=US

For this:

http://www.home.agilent.com/USeng/na...881282/pd.html

Agilent seems to obsolete things after seven years.

I have some useful equipment. Including an Impedance test set I paid
about 20K for in the 90's. It directly measures almost anything you
would every want to know.

The nice thing about having test gear is being able to build almost
anything. I have it because of work. You can do a lot with almost
nothing except a vector voltmeter and a test fixture, but the automated
measurements save me time.

73 Tom

Current through coils
 

Tom, W9JI wrote:
"It is only after the voltages, one proportional to current and one
proportional to voltage, are added that the voltage is rectified and
used to drive the meter."

Obviously a power determination must use voltage and current samples
taken at the same place at the same time. We can`t use today`s voltage
and yesterday`s current nor can we use the voltage over here and the
current over there.

Everything happens simultaneously and at the same sampling point.

A single loop terminated in a diode is coupled to the center conductor
of the coax. Its magnetic coupling produces the current sample. Its
capacitive coupling produces the voltage sample. These are tweaked for
identical deflection of the power meter.

Best regards, Richard Harrison, KB5WZI

Current through coils
 

Cecil Moore wrote:

is only 40% shortening. I think the lumped inductor
crossover point is probably pretty far below 4 MHz.
73, Cecil http://www.qsl.net/w5dxp

There isn't any "crossover point". That point has been made several
times by different people.

There is a gradual transition over a very wide frequency range, and a
rapidly increasing change as self-resonace is approached.

Current through coils
 

chuck wrote:
I understand that on page 6, the reference qualifies the statement in
the abstract by saying that for heights " . . . less than 15 degrees . .
. one passes to the lumped element regime . . ."

I thought Cecil was drawing examples for heights greater than 15
degrees. Have I misunderstood?

You understand, Chuck, for example, my 75m bugcatcher coil, base-
mounted on my GMC pickup with no whip is 1/4WL self-resonant at
6.6 MHz, i.e. it is 90 degrees on 6.6 Mhz. By ratio and proportion,
the height on 4 MHz is 90(4/6.6) = ~54.5 degrees, 3.6 times the
transition height for passing to the lumped element regime. One
would have to divide the self-resonant frequency by 6 to get down
to the 15 degree maximum for the lumped element regime so 1.1 MHz
would be the highest frequency for which the lumped element regime
could be considered valid.

As the paper says: "Of course, the uniform current assumption
has no validity for coils operating anywhere near self-resonance."

Even the 100 uH test coil, 90 degrees self-resonant at 16 MHz,
when used on 4 MHz is 90(4/16) = ~22.5 degrees, still above
the 15 degree limit. One would have to go down to 2.7 MHz
for the lumped element regime to be valid for that 100 uH
coil and that is for an excellent coil with a Q of around 300.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

wrote:
John Popelish wrote:
(snip)

I would very much like to see a more complete report on the
measurements you have made, in relation to this thread.

The problem is always time. I'm at the busiest time of the year for me,
so everything that isn't a fore is sitting. I really swore I wouldn't
get involved in an ungoing three year debate, but here I am anyway. I
guess I needed a break from a constant string of projects all with
tight deadlines.

I can appreciate that. I have recently gotten sucked into a wide
ranging study of ferrite rod antenna basics, and am having trouble
finding time to go to work or to bed. Almost every preconceived
notion I had about them I have been able to disprove by direct
measurement. Very educational.


I am sure I
would learn from seeing that. I tried to find an operating manual or
application note on the network analyzer you used, but found little
that was helpful to teach me how it works, and how one applies it.
(snip)

This is the closest manual I could find.

http://www.home.agilent.com/cgi-bin/...OUNTRY_CODE=US

For this:

http://www.home.agilent.com/USeng/na...881282/pd.html

I'll take a good look at these.

Agilent seems to obsolete things after seven years.

I have some useful equipment. Including an Impedance test set I paid
about 20K for in the 90's. It directly measures almost anything you
would every want to know.
(snip)

So far, I am working with an RF volt meter, a signal generator or two,
and an antique Boonton 160A Q meter. But I am finding lots of ways to
put them to use. I would love to have a vector volt meter or vector
impedance meter. A network analyzer is way beyond my budget.

Current through coils
 

wrote:

Cecil Moore wrote:
is only 40% shortening. I think the lumped inductor
crossover point is probably pretty far below 4 MHz.

There isn't any "crossover point". That point has been made several
times by different people.

One of those people supporting a "crossover point" is Dr.
Corum in his IEEE peer reviewed paper at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf (page 6)

Dr. Corum is pretty clear about 15 degrees, i.e. 4% of a
wavelength, being the "crossover point". He considers 15
degrees to 90 degrees to require a distributed network
analysis while below 15 degrees, "one passes to the lumped-
element regime ..."

The "crossover point" would be the same rule as for a
transmission line. How long does a transmission line with
reflections have to be before it is no longer valid to
consider it a lumped piece of wire. 15 degrees is 4% of
a wavelength and sounds reasonable. However, under
the right conditions, one could arrange a current node
at the halfway point of that 15 degrees of feedline thus
causing current to flow into both ends of the feeline
at the same time. 1/2 cycle later, current would be
flowing out of both ends. How would a lumped-circuit
model handle those conditions?

The "crossover point" is obviously arbitrary but if one
locates it very far above 15 degrees, according to Dr.
Corum, one risks invalid analysis results such as have
been reported here.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Cecil,

(No smiley faces this time. No trolls or tricks either.)

The assertion that there is some important difference between a standing
wave and its component traveling waves has been made on a number of
occasions in this thread. Indeed, that concept seems pretty central to
the entire issue.

It may be worth examining the importance of this distinction further.

Basic assumptions:

* System is linear, with no diodes, saturating cores, etc.

* System is steady-state, with no startup transients.

* System is lossless, including a lack of radiation

* Superposition applies, i.e., scaling works and we can add subcomponent
functions without error. The whole is precisely equal to the sum of the
parts, no more and no less.

If any of these assumptions are not operative, then what follows may not
be correct.

As you have stated, including references from Hecht, it is customary to
mathematically show traveling waves in the form: cos (kz +/- wt)
Through straightforward addition and simple trigonometry is is seen that
the standing wave corresponding to the sum of equal magnitude forward
and reverse traveling waves has the form: cos (kz) * cos (wt)


The key question then becomes, what information has been lost in adding
the traveling waves to form a standing wave? All of the parameters and
variables are still in the standing wave equation, namely, k, z, w, t.
The numerical values and definitions for these terms have not changed.
One can add constant phase offsets in the traveling wave equations, but
those don't really add any new information, and in any case they are not
lost in converting to the standing wave format.

Are there some hidden variables that have not been considered? If so,
what are they, and where do they show up in the original traveling wave
equations? If not, why does the analysis and measurement of the
traveling wave components give one iota more information than the
analysis and measurement of the standing wave?

There is little doubt that real world conditions will violate some of
the assumptions, but that does not seem to be the issue in the debate at
this time.

Again, what extra information would be gained if somehow the traveling
wave components could be measured?

73,
Gene
W4SZ




Cecil Moore wrote:
wrote:

[snip]


Current is current.


On the contrary, one can look at the formula for standing wave
current and see that standing wave current is NOT like traveling
wave current. Traveling wave current is of the form f(z+wt) or
f(z-wt) depending upon the direction of travel. Standing wave
current is of the form f(z) + f(wt) so they are quite different
and therefore have *different* characteristics.

As you can see from the functions, magnitude and phase are
interlocked for a traveling wave. Magnitude and phase are
unlocked for a standing wave. With a phasor fixed at zero
degrees, how does a standing wave phasor manage to flow?

Current through coils
 

Gene Fuller wrote:
As you have stated, including references from Hecht, it is customary to
mathematically show traveling waves in the form: cos (kz +/- wt)
Through straightforward addition and simple trigonometry is is seen that
the standing wave corresponding to the sum of equal magnitude forward
and reverse traveling waves has the form: cos (kz) * cos (wt)

I see I made a typo and typed a '+' sign in my previous equation.
Of course, it should have been a '*' sign for multiply.

Are there some hidden variables that have not been considered?

Not a hidden variable, but there seems to be a hidden
mathematical concept, at least hidden from some individuals.

In case some might not know, 'z' is the position up and down
the wire, omega (w) is our old friend 2*pi*f, and 't' is, of
course, time.

In the traveling wave equation, cos(kz +/- wt), the position on
the wire and omega*time are added or subtracted *before* the cosine
function is taken. That means that the position on the wire and the
phase velocity are inter-related. One cannot have one without the
other. And that is indeed a characteristic of a traveling
wave. Physical position, frequency, and time all go into
making a traveling wave. It is modeled as a rotating phasor.

However, in the equation, cos(kz) * cos(wt), the physical position,
'z' is disconnected from the phase velocity, 'wt'. The standing wave
is no longer moving in the 'z' dimension. If you pick a 'z' and hold
it constant, i.e. choose a single point on the wire, the standing
wave becomes simply some constant times cos(wt). Thus at any fixed
point on the line, the standing wave is not moving - it is just
oscillating at the 'wt' rate and a current probe will certainly pick
up the H-field signal. The phase of the standing wave current is
everywhere, up and down the 1/2WL thin-wire, equal to zero. The sum
of the forward phasor and reflected phasor doesn't rotate. Its phase
doesn't change with position. Only its magnitude changes with position
and if the forward wave magnitude equals the reflected wave magnitude,
it is not flowing in the real sense that current flows. It is a
standing wave and it is just standing there.

The main thing to realize is that the standing wave equation
divorces the position of the standing wave from its phase
velocity such that the phase velocity is not active in the
'z' dimension, i.e. up and down the wire. The standing wave
current "pseudo phasor" is not rotating. The standing wave
is not going anywhere. It is not flowing along a wire or
through a coil. Measuring its phase is meaningless because
the phase is already known to be constant and unchanging from
tip to tip in a 1/2WL dipole or across a loading coil in a
mobile antenna.

Thinking that standing wave current flows from the middle of a
dipole to the ends is just a misconception. The equation for
a standing wave indicates that it doesn't flow. What is flowing
are the forward and reflected waves.
--
73, Cecil http://www.qsl.net/w5dxp