Current through coils
 

Cecil Moore wrote:
wrote:
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.

You demanded that I defend my measurements so I removed them
as evidence. Now I am requesting that you defend the use of a
signal without phase to measure phase through a coil. That's
a very simple request. If one refuses such a simple request
to defend one's methods, what is one to think?

I didn't demand anything. I asked what equipment and frequency you
used.
When you told me, it became very obvious you could have made a much
more reliable measurement.

I'm suprised you wouldn't want to learn more about measurements.

I don't see anything Roy said that disagrees with what I measured, so
that's a non-issue.

I take it you don't want to discuss how to make better measurements?

73 Tom

Current through coils
 

Cecil Moore wrote:

You could start by explaining the center graphic in the following:
http://www.qsl.net/w5dxp/3freq.gif

I don't understand what it is and how you "constructed" it. Maybe you
can explain.

Did you build one and verify the results? I've never seen a coil loaded
antenna work on three exactly even harmonics without special
manipulation of lengths. That would make an interesting antenna if you
could just make it any length and any coil and have it work on
harmonics.

73 Tom

Current through coils
 

Cecil Moore wrote:
wrote:

Just because EZnec agrees with the phase measurements it
doesn't mean the current measurement was even remotely

close to being correct.

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.

Doesn't the change in distance between a pair of current nodes (or
voltage nodes) in the standing wave pattern on a straight conductor
that straddle an inserted inductor show its effective electrical
length? I would think that as long as a fairly pure standing wave
could be arranged with the inductor inside it, this method would allow
the effective electrical length to be measured at arbitrary
frequencies that are not at all related to the coil's self resonant
frequency. It seems that this is nearly what you are demonstrating
with your EZNEC examples. Electrical length (propagation distance) is
collapsing into the inductor.

Current through coils
 

Cecil,

I have to admit I am mostly lost about the meaning in your post below.

However, nothing in my comments was intended in any way as support or
denial of the measurements presented by Tom, W8JI. They look proper to
me, but I am not an expert on such measurements.

This entire thread is quite bizarre in that all sorts of special cases
are being debated (Tesla coils????) while the simplest basic level of
standing wave behavior is overlooked and even challenged.

I suppose that's typical for RRAA.

73,
Gene
W4SZ

Cecil Moore wrote:
wrote:

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.


You demanded that I defend my measurements so I removed them
as evidence. Now I am requesting that you defend the use of a
signal without phase to measure phase through a coil. That's
a very simple request. If one refuses such a simple request
to defend one's methods, what is one to think?

I gave up on my measurements rather than defend them. If you
don't defend yours, are you automatically giving up on them?
If no, one might then wonder why you require me to defend my
measurements while you refuse to defend yours.

Gene says standing wave current doesn't carry any phase
information. I concur. Roy says EZNEC agrees with my possibly
flawed measurements. I concur. Since EZNEC disagrees with your
conclusions about your measurements, and agrees with my conclusion
about your measurements, could your conclusions possibly be
flawed? I'm sure many readers would be interested in a
detailed explanation of exactly how to use a signal with
unchanging phase to measure the phase shift through a coil.
I certainly would be more interested in that explanation
than a boring tutorial on measurement techniques. Heck, even
the IEEE would be interested in such a unique technique and
it might even be patentable.

You could start by explaining the center graphic in the following:

http://www.qsl.net/w5dxp/3freq.gif

One can't help but notice your absolute silence on that subject.

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


humor Reminds me of a T-shirt I saw. It read, "I'm from the
government. I'm here 'to help you'." /humor

Logical diversions are very transparent - they even have names.
That one is called "diverting the issue". The issue is not my
measurements since I have withdrawn them as evidence. Seems
that automatically makes your measurements the subject of the
discussion.

Current through coils
 

wrote:
I'm suprised you wouldn't want to learn more about measurements.

I'm surprised you wouldn't want to share your engineering
knowledge, e.g. is it really possible to use a phaseless
signal to measure phase shift? If so, please enlighten us.
I can't figure out how to do it. Since you apparently have
figured it out, please share your knowledge with us.

I don't see anything Roy said that disagrees with what I measured, so
that's a non-issue.

Roy and I have previously agreed with your measurements. It's
your conclusions about those measurements that he apparently
doesn't seem to understand and neither do I. I'm certainly not
speaking for Roy, but when he points out to you that my
measurements agree with EZNEC, one wonders what that means
in reality.

I take it you don't want to discuss how to make better measurements?

I take it you don't want to share you knowledge of how to
measure phase using a phaseless signal? Such a feat is
extremely more important than any measurement discussion.

Please just explain from a technical standpoint how a
signal without phase can be used to measure a phase
shift through a coil. That's an extremely simple request
and would be extremely useful to the entire group.

While you are at it, please explain the EZNEC results
in the middle graphic at: http://www.qsl.net/w5dxp/3freq.gif.
the request for which you seem to have forgotten about.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

wrote:

Cecil Moore wrote:
You could start by explaining the center graphic in the following:
http://www.qsl.net/w5dxp/3freq.gif

I don't understand what it is and how you "constructed" it. Maybe you
can explain.

I simulated a typical vertical base-loaded coil system using the
helical coil feature of EZNEC. I found the resonant frequency and
displayed the results in the left graphic. I then left everything
else alone while I multiplied the resonant frequency by 2 and
displayed the results in the middle graphic. I then multiplied the
resonant frequency 3 and displayed the results in the right graphic.
It's a no-brainer. Have you never done such with EZNEC?

Would someone, somewhere, please explain the ~0.2 amps at the
bottom of the coil in the middle configuration Vs the ~2.0
amps at the top of the coil? Is EZNEC reporting bogus results?
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

John Popelish wrote:
It seems
that this is nearly what you are demonstrating with your EZNEC
examples. Electrical length (propagation distance) is collapsing into
the inductor.

Please explain how that could be possible with constant
magnitude and phase of the currents through the coil.
The magnitude and phase is absolutely constant according
to the presuppositions of the lumped-circuit model. How
could it possibly collapse?
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Gene Fuller wrote:
However, nothing in my comments was intended in any way as support or
denial of the measurements presented by Tom, W8JI. They look proper to
me, but I am not an expert on such measurements.

How about his conclusions about those measurements?
Maybe you can help him out. How does one measure the
phase shift through a coil using a signal that doesn't
support phase? If there is a way, I and others would
certainly like to know about it. So far, I confess
that I haven't been able to figure it out.
--
73, Cecil http://www.qsl.net/w5dxp

Current through coils
 

Cecil Moore wrote:

Reg Edwards wrote:

A 100 turn coil, 10 inches long, 2 inches in diameter, has an
inductance of 102 microhenrys, a Q of aproximately 380 at F = 1.9 MHz,
and the self-resonant frequency is 12.0 MHz.


I'll bet the measured self-resonant frequency would be lower
if mounted as a base-loading coil on my pickup.

Seems the VF of the coil is 0.041 based on 10" being 1/4WL
at 12 MHz. Assuming that VF holds down to 1.9 MHz we
can calculate the electrical length of the coil on 1.9 MHz
which will be the same as the phase shift through the coil.

So I get about ~14 degrees of phase shift through that coil
at 1.9 MHz assuming the self-resonant frequency really
is 12 MHz at the spot where the coil is mounted.

If the coil were used on 3.8 MHz, the phase shift would
be ~28 degrees.

But my 75m bugcatcher coil shows to be self-resonant at
6.6 MHz while sitting there on my pickup being driven
by an MFJ-259B. It is 6.5" long. When 6.5" is 1/4WL
at 6.6 MHz, the VF = 0.0145, considerably lower than
the coil above and operating much closer to its self-
resonant frequency.

A length of 6.5" coil with a VF of 0.145 on 4 MHz is
~55 degrees of phase shift. And indeed the net current
at the top of the coil drops to about 2/3 of what it
is at the bottom.

Ok, I have had a thought. And I had to go back to where everyone,
starting with Cecil, was talking about or responding to a constant delay
through the coil.

Picking a nice round number, say 55 degrees, I would then need 35
degrees of whip above that coil to make a quarter wave resonant antenna,
correct?

So, it should work just as well, using Cecil's reasoning, if I displace
that coil to another position. He did measure the coil as a standalone
device which causes a fixed delay, correct?

Ok, so now I move that coil up the antenna, not much, say 2 degrees.
Now I have 2 degrees below the coil, and 33 above it. It will still be
resonant, right? Now I move it another 2, and another and another,
until it it at the top, with no stinger. With the reasoning I have
heard from Cecil, it will always be resonant.

tom
K0TAR

Current through coils
 

Cecil Moore wrote:
wrote:

Cecil Moore wrote:

You could start by explaining the center graphic in the following:
http://www.qsl.net/w5dxp/3freq.gif


I don't understand what it is and how you "constructed" it. Maybe you
can explain.


I simulated a typical vertical base-loaded coil system using the
helical coil feature of EZNEC. I found the resonant frequency and
displayed the results in the left graphic. I then left everything
else alone while I multiplied the resonant frequency by 2 and
displayed the results in the middle graphic. I then multiplied the
resonant frequency 3 and displayed the results in the right graphic.
It's a no-brainer. Have you never done such with EZNEC?

Would someone, somewhere, please explain the ~0.2 amps at the
bottom of the coil in the middle configuration Vs the ~2.0
amps at the top of the coil? Is EZNEC reporting bogus results?

It looks like various magnitudes that you would find at 2 points along
a standing wave, with various fractions of the wave in the inductor as
frequency changes. In spite of hitting these various magnitude
values, there are still only two phases, 0 or 180 anywhere outside the
coil. In some cases, the standing wave goes through a node, inside
the coil and reverses phase from one end of the coil to the other.