Current through coils
 

On Wed, 15 Mar 2006 20:08:18 GMT, Cecil Moore wrote:

Richard Clark wrote:
Provide the Velocity Factor and Characteristic Impedance per the
formulas you offered:

Tom Donaly has graciously volunteered to provide those values.
Please stand by.

You have nothing to show of your own work employing your own
references?

I can do this myself, as certainly Tom can too; but it says nothing
about your well coming up dry when we ask you to carry your own water
in supporting your claims.

Current through coils
 

Richard Clark wrote:
.. I can do this myself, as certainly Tom can too; but it says nothing
about your well coming up dry when we ask you to carry your own water
in supporting your claims.

Pure humor with zero technical content follows:
So sue me for being lazy. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

On Wed, 15 Mar 2006 20:57:21 GMT, Cecil Moore wrote:
So sue me for being lazy. :-)

The legacy of Xerox research.

Current through coils
 

Richard Clark wrote:
Cecil Moore wrote:
So sue me for being lazy. :-)

The legacy of Xerox research.

Please remind us of the technical content of your posting.
Do you think experimental technical results depend upon
whom is doing the experiment? If I dropped dead, could
Tom's results change from valid to invalid?
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

On Wed, 15 Mar 2006 21:29:14 GMT, Cecil Moore wrote:
Do you think experimental technical results depend upon
whom is doing the experiment?
Clearly you have nothing to offer that conflicts in that respect.
If I dropped dead, could Tom's results change from valid to invalid?
are you asking would you be technically dead, or clinically dead, or
dead lazy? This appears to be a reverse progression question.

None of your work appears by your admitted laxity. None of your
testing appears by lack of its accomplishment.

No pulse can be discerned through the evidence of correspondence
(classic result of The Chinese Room Argument).

Diagnosis:
Xerox induced narcosis.

Current through coils
 

Cecil Moore wrote:
Richard Clark wrote:
Cecil Moore wrote:
So sue me for being lazy. :-)

The legacy of Xerox research.

Please remind us of the technical content of your posting.
Do you think experimental technical results depend upon
whom is doing the experiment? If I dropped dead, could
Tom's results change from valid to invalid?
73, Cecil http://www.qsl.net/w5dxp

Probably, since it appears you are the only one finding fault with
them.

It appears you have painted yourself into a corner by trying o apply a
paper about Tesla coils that specifically states it applies only to
inductors at self-resonance to inductors operating away from
self-resonance.

For example, if you look at this time-delay plot:

http://www.w8ji.com/inductor_current_time_delay.htm

you'll see time delay is essentially flat except near the 16MHz
self-resonant frequency and a higher-frequency resonance at 26 MHz.

If I coupled that inductor to a oscillator like a Telsa coil has, it
would indeed oscillate near the frequency where the inductor has
considerable time delay. That time delay is largely because the
inductor looks like a combination of shunt C and series L, and is
indeed in mode similar to what we find in a transmission line. It is a
narrow bandwidth effect because the resonance is high-Q. It does not
surprise me at all.

73 Tom

Current through coils
 

Richard Clark wrote:
None of your work appears by your admitted laxity. None of your
testing appears by lack of its accomplishment.

My testing results have been reported. Here are the results
of the VF calculation for my 75m bugcatcher coil.

The test for physical structure is met. The paper asserts
that the expression gives acceptable results with errors
less than 10%.

The VF of my 75m bugcatcher coil calculates out to be
VF = 0.0175 at 6.6 MHz where it measured to be self-
resonant. That self-resonant measurement included
a length of coax and a one foot bottom section so the
actual self-resonant frequency will be somewhat higher
than I measured. I could probably make a calculation
to adjust for the coax and bottom section.

The VF calculated directly from the too-low self-
resonant frequency was 0.015 which is 14% different
from Dr. Corum's equation. Given the uncertainly in
the exact self-resonant frequency in my measurements,
that's pretty reasonable. Ballpark is all we need
to understand the concepts.

Working backward, Dr. Corum's VF would make the
coil self-resonant at 7.7 MHz. There's probably
enough slop in my measurement configuration to
account for the 1.1 MHz difference.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Cecil, W5DXP wrote:
"How is it possible to use a signal (standing wave current) that is
known not to change phase, to measure the phase delay through a wire or
coil?"

Ignore it.

Lissajous figures result from applying signals to the vertical and
horizontal deflection circuits of an oscilloscope simultaneously. Phase
difference between signals of the same frequency make a distinctive
pattern.

One can use coax lines with identical delays to couple the inputs with
phase sampling loops. Take samples of the currents at the two points
where the phase difference would be known. Amplitudes can be adjusted
for a suitable pattern. It will be destinctive.

Then take samples from the same source. Add a known delay to one channel
until you have reproduced the distinctive pattern you had observed when
testing the felay between the points that have the unknown phase
difference.

With a few elaborations, that`s how a phase monitor works.

Best regards, Richard Harrison, KB5WZI

Current through coils
 

wrote:
Probably, since it appears you are the only one finding fault with
them.

Tom Donaly hasn't even posted any results yet. How could I
possibly be finding fault with them?

It appears you have painted yourself into a corner by trying o apply a
paper about Tesla coils that specifically states it applies only to
inductors at self-resonance to inductors operating away from
self-resonance.

Quoting from the previously referenced paper: ".. is an approximation ...
appropriate for quarterwave resonance and is valid for helices with
(5*N*D^2)/lamda 1. N is the turns/inch, D is the diameter of the
coil, and lamda is the self-resonant frequency. That calculation
for my 75m bugcatcher coil is ~0.4 so it meets the criteria.

The VF calculation of 0.175 is therefore valid. There is no valid
reason to suspect that the VF wouldn't hold approximately down to
4 MHz and below. There is no warning of such abrupt shifts in the
VF anywhere in the article. And Dr. Corum's VF equation is close
enough to my rough earlier estimate of 0.15 to be acceptable.

you'll see time delay is essentially flat except near the 16MHz
self-resonant frequency and a higher-frequency resonance at 26 MHz.

But cos(kz)*cos(wt) is what is being measured. That signal has zero
phase shift from tip to tip in a 1/2WL thin-wire dipole. It cannot
be used to measure phase shift because it is incapable of a phase
shift through 180 degrees of wire or 180 degrees of coil. It only
changes phase every 180 degrees of a wire or coil.

What is happening in the above measurement is that when the coil
is more than 1/2WL, the phase of the standing wave current suddenly
reverses from close to zero to close to 180 degrees. This is all
explained in Kraus', "Antennas for All Applications", 3rd edition,
Figure 14-4 and is perfectly understandable. The phase of the standing
wave current changes from zero to 180 degrees every 1/2WL. I've seen
exactly the same thing in my experiments just as Kraus predicts and
it supports my side of the argument.

The standing wave current, which has unchanging phase, cannot be
used to determine the phase shift in a wire or coil. A
signal with a cos(kz)*cos(wt) equation doesn't change phase
with variations in 'z'. How can it possibly be used to detect
phase changes in the 'z' dimension?
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Richard Harrison wrote:
Cecil, W5DXP wrote:
"How is it possible to use a signal (standing wave current) that is
known not to change phase, to measure the phase delay through a wire or
coil?"

Ignore it.

Lissajous figures result from applying signals to the vertical and
horizontal deflection circuits of an oscilloscope simultaneously. Phase
difference between signals of the same frequency make a distinctive
pattern.

One can use coax lines with identical delays to couple the inputs with
phase sampling loops. Take samples of the currents at the two points
where the phase difference would be known. Amplitudes can be adjusted
for a suitable pattern. It will be destinctive.

Then take samples from the same source. Add a known delay to one channel
until you have reproduced the distinctive pattern you had observed when
testing the felay between the points that have the unknown phase
difference.

With a few elaborations, that`s how a phase monitor works.

Many analog scopes aren't capable of producing a meaningful Lissajous
figure at HF because of the limited bandwidth of the horizontal channel.
Significant phase delays occur at frequencies well below the nominal
cutoff frequency, which is often much lower than the vertical channel.
Before believing in the validity of any figure, you should look at the
figure you get when you apply the signal to both axes at the same time.
If it deviates significantly from a single diagonal line, you won't be
able to trust other patterns.

It would be a simple matter for a digital scope to present a good
Lissajous figure, since the bandwidth is determined solely by the input
samplers rather than a series of amplifiers and the CRT deflection
structure as in an analog scope. I haven't looked closely at digital
scopes lately, but I'd be surprised if most don't have the capability of
making a good Lissajous figure at HF. It would be simply a matter of
internal firmware programming.

Of course, a dedicated phase monitor would be designed for good phase
and amplitude match between channels at the frequencies it's specified
to be used at.

Roy Lewallen, W7EL