On Sun, 29 Apr 2007 06:52:17 -0500, "amdx" wrote:

I agree with your assertion that distributed winding capacitance
degrades efficiency.
My thoughts about this are ;
Assume a 10 turn loop, between each turn there is a capacitance,
so, you have a complete circuit, (L,C,R) there is current
flowing through this circuit that is not flowing through the entire 10
turn loop. (this happens in the other 9 turns also)
I think these extra currents flowing that don't make the entire 10
turn circuit increase the losses.

Hi Mike,

Capacitance does not bring loss. Loss ALWAYS resides in Resistance
and nothing else.

Between you and Bill, there appears to be a fixation on the loopS
(emphasis on there being more than one). If you are going to blame
them (that emphasis on there being more than one), and try to tie it
to loss (that emphasis being naturally in Resistance, not
Capacitance); then it follows it is in the natural increase in
conductor Resistance that occurs when wires are spaced closer than 3
or 4 wire diameters to each other. When wires (or loops in this case)
are in close proximity, the magnetic field of the near wire (or loop
in this case, and each loop in proximity to the next) FORCES the
current in that loop to the surface of the wire - INCREASING that
conductor's Skin Resistance. Loss thus increases by proximity.
Capacitance does too, but that is merely a correlating factor.
Remember (and this is good advice, especially suited to Newsgroup
rumors you may pick up): Correlation is NOT causality.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 29 Apr 2007 06:52:17 -0500, "amdx" wrote:

I agree with your assertion that distributed winding capacitance
degrades efficiency.
My thoughts about this are ;
Assume a 10 turn loop, between each turn there is a capacitance,
so, you have a complete circuit, (L,C,R) there is current
flowing through this circuit that is not flowing through the entire 10
turn loop. (this happens in the other 9 turns also)
I think these extra currents flowing that don't make the entire 10
turn circuit increase the losses.

Hi Mike,

Capacitance does not bring loss.

I'm not ready to give on that yet, but I could be convinced.
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.

Loss ALWAYS resides in Resistance and nothing else.

I agree, X/R=Q Lower Q means more loss.
(let's not get into radiation resistance right now)


Between you and Bill, there appears to be a fixation on the loopS
(emphasis on there being more than one). If you are going to blame
them (that emphasis on there being more than one), and try to tie it
to loss (that emphasis being naturally in Resistance, not
Capacitance); then it follows it is in the natural increase in
conductor Resistance that occurs when wires are spaced closer than 3
or 4 wire diameters to each other. When wires (or loops in this case)
are in close proximity, the magnetic field of the near wire (or loop
in this case, and each loop in proximity to the next) FORCES the
current in that loop to the surface of the wire - INCREASING that
conductor's Skin Resistance. Loss thus increases by proximity.
Capacitance does too, but that is merely a correlating factor.

Proximity effect could cause all of the additional losses.
Or it might just be part of the additional losses.

Why is it that when you get near self resonance of a coil the Q gets lower?
Note; to help clearify my question,
( as you get nearer and nearer resonance the capacitor you are using to tune
the inductor is getting smaller and smaller, and closer to equalling the
self
capacitance of the inductor)

Remember---Correlation is NOT causality.

If you measure reading skills in an elementary school you will find the
kids with big feet read better.

But then 5th graders usually have bigger feet than kindergarteners.

Thanks for the discussion____

Mike

"amdx" wrote in message
...

"Richard Clark" wrote in message
...
On Sun, 29 Apr 2007 06:52:17 -0500, "amdx" wrote:

I agree with your assertion that distributed winding capacitance
degrades efficiency.
My thoughts about this are ;
Assume a 10 turn loop, between each turn there is a capacitance,
so, you have a complete circuit, (L,C,R) there is current
flowing through this circuit that is not flowing through the entire 10
turn loop. (this happens in the other 9 turns also)
I think these extra currents flowing that don't make the entire 10
turn circuit increase the losses.

Hi Mike,

Capacitance does not bring loss.

I'm not ready to give on that yet, but I could be convinced.
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.

Loss ALWAYS resides in Resistance and nothing else.

I agree, X/R=Q Lower Q means more loss.
(let's not get into radiation resistance right now)


Between you and Bill, there appears to be a fixation on the loopS
(emphasis on there being more than one). If you are going to blame
them (that emphasis on there being more than one), and try to tie it
to loss (that emphasis being naturally in Resistance, not
Capacitance); then it follows it is in the natural increase in
conductor Resistance that occurs when wires are spaced closer than 3
or 4 wire diameters to each other. When wires (or loops in this case)
are in close proximity, the magnetic field of the near wire (or loop
in this case, and each loop in proximity to the next) FORCES the
current in that loop to the surface of the wire - INCREASING that
conductor's Skin Resistance. Loss thus increases by proximity.
Capacitance does too, but that is merely a correlating factor.

Proximity effect could cause all of the additional losses.
Or it might just be part of the additional losses.

Why is it that when you get near self resonance of a coil the Q gets
lower?
Note; to help clearify my question,
( as you get nearer and nearer resonance the capacitor you are using to
tune
the inductor is getting smaller and smaller, and closer to equalling the
self
capacitance of the inductor)

Remember---Correlation is NOT causality.

If you measure reading skills in an elementary school you will find the
kids with big feet read better.

But then 5th graders usually have bigger feet than kindergarteners.

Thanks for the discussion____

Mike


Hi Mike

I am curious about how the comment in your post ---
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.
I would have thought that, when the circulating current increases when a
passive devce is introduced, the Q would have Increased.

Jerry

On Sun, 29 Apr 2007 14:30:29 -0500, "amdx" wrote:

Capacitance does not bring loss.

I'm not ready to give on that yet, but I could be convinced.
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.

Hi Mike,

This is then a characteristic of the Capacitor called D (dissipation).
Any increase in current tied to loss immediately goes to the bottom
line of resistance - it is a square law relationship, after all.

Loss ALWAYS resides in Resistance and nothing else.

I agree, X/R=Q Lower Q means more loss.
(let's not get into radiation resistance right now)

Why not? Small loops suffer by comparison, and multi-turn loops even
more so.

Proximity effect could cause all of the additional losses.
Or it might just be part of the additional losses.

For wire separations beyond 3 or 4 wire diameters, the increase in
skin effect is small. It might be noted that interwinding Capacitance
also falls.

Why is it that when you get near self resonance of a coil the Q gets lower?
Note; to help clearify my question,
( as you get nearer and nearer resonance the capacitor you are using to tune
the inductor is getting smaller and smaller, and closer to equalling the
self
capacitance of the inductor)

Again, the answer must reside in Resistance. There are many
characteristics (wavelength, solenoid diameter, length, pitch, wire
gauge, self-capacitance, distributed capacitance, balance,
connections, earth proximity, radiation resistance) being juggled with
small Loop antennas and some (even many) choices that can be made to
resonate the antenna do not lead to an efficient solution.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Sun, 29 Apr 2007 14:30:29 -0500, "amdx" wrote:

Capacitance does not bring loss.

I'm not ready to give on that yet, but I could be convinced.
It seems I could add capacitors across turns of a coil and increase
circulating currents that would show as a lower Q. But I haven't
built a coil to test this.

Hi Mike,

This is then a characteristic of the Capacitor called D (dissipation).
Any increase in current tied to loss immediately goes to the bottom
line of resistance - it is a square law relationship, after all.

So your saying yes, the thought experiment would show more loss,
but the loss is in the capacitor. The loss in a capacitor would be
dielectric
and loss in the plates right?


Loss ALWAYS resides in Resistance and nothing else.

I agree, X/R=Q Lower Q means more loss.
(let's not get into radiation resistance right now)

Why not? Small loops suffer by comparison, and multi-turn loops even
more so.

I figure it would only confuse the issue.
I was trying to stay away from radiation resistance because my experience of
the effect Bill ask about has been with small aircore inductors. But on
second thought
even those have Rr.

Proximity effect could cause all of the additional losses.
Or it might just be part of the additional losses.

For wire separations beyond 3 or 4 wire diameters, the increase in
skin effect is small. It might be noted that interwinding Capacitance
also falls.

Why is it that when you get near self resonance of a coil the Q gets
lower?
Note; to help clearify my question,
( as you get nearer and nearer resonance the capacitor you are using to
tune
the inductor is getting smaller and smaller, and closer to equalling the
self
capacitance of the inductor)



Again, the answer must reside in Resistance. There are many
characteristics (wavelength, solenoid diameter, length, pitch, wire
gauge, self-capacitance, distributed capacitance, balance,
connections, earth proximity, radiation resistance) being juggled with
small Loop antennas and some (even many) choices that can be made to
resonate the antenna do not lead to an efficient solution.

Richard, I don't think anyone would disagree that the losses are resistive.
You seem to have answered the question I posted by saying it's increased
resistance.
Yes I agree,
Why does the reistance go up near resonance?

Mike

On Apr 29, 4:52 am, "amdx" wrote:
"Bill Bowden" wrote in message

oups.com... Does anyone know why the distributed winding capacitance of a loop
antenna, or any inductor, degrades the efficiency?

-Bill

Hi Bill.
I agree with your assertion that distributed winding capacitance
degrades efficiency.
My thoughts about this are ;
Assume a 10 turn loop, between each turn there is a capacitance,
so, you have a complete circuit, (L,C,R) there is current
flowing through this circuit that is not flowing through the entire 10
turn loop. (this happens in the other 9 turns also)
I think these extra currents flowing that don't make the entire 10
turn circuit increase the losses.

Anyone care to run with that, or explain it more clearly, or shoot it
down.

Mike


I think you are right. Good explanation.

-Bill

"Bill Bowden" wrote in message
ups.com...
On Apr 29, 4:52 am, "amdx" wrote:
"Bill Bowden" wrote in message

oups.com... Does
anyone know why the distributed winding capacitance of a loop
antenna, or any inductor, degrades the efficiency?

-Bill

Hi Bill.
I agree with your assertion that distributed winding capacitance
degrades efficiency.
My thoughts about this are ;
Assume a 10 turn loop, between each turn there is a capacitance,
so, you have a complete circuit, (L,C,R) there is current
flowing through this circuit that is not flowing through the entire 10
turn loop. (this happens in the other 9 turns also)
I think these extra currents flowing that don't make the entire 10
turn circuit increase the losses.

Anyone care to run with that, or explain it more clearly, or shoot it
down.

Mike


I think you are right. Good explanation.

-Bill

Well Bill, That has been the theory I've been thinking with for 8 or 9
years now. However, if as Richard suggests the phenomena is caused
by proximity effect, the techniques I used to lower interwinding capacitance
and raise Q, would be the same I'd use to reduce proximity efect and raise
Q.
If there are circuilating currents caused by interwinding capacitance, it
seems
they would cause the proximity effect to be even stronger and pinch down the
current flow area even more and raise losses.

A question for all,
Does a basketweave winding reduce proximity effect?
Mike

Distributed capacitance may affect single-turn coils differently from
multiturn-coils. And those vary as their length to diameter ratio
varies.

Mike wrote:
"Anything that increases capacitance will reduce component Q. I believe
he was quoting W8JI.

Mike also wrote:
"What do you think?"

In 1999 Tom Bruhns was experimenting, trying to find the relationship
between coil Q and parasitic C. He picked up reports that helical
resonators weere superior to short coaxial resonators. Tom also wrote:
"Reg (Edwards,RJE) then thinks the internal coil capacitance is just
femanding extra extra coil current and loss as the result of its cyclic
charge and discharge."

Reg seems to have had a nice explanation for coil loss from parasitic
capacitance.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote in message
...
Distributed capacitance may affect single-turn coils differently from
multiturn-coils. And those vary as their length to diameter ratio
varies.

Mike wrote:
"Anything that increases capacitance will reduce component Q. I believe
he was quoting W8JI.

Mike also wrote:
"What do you think?"

In 1999 Tom Bruhns was experimenting, trying to find the relationship
between coil Q and parasitic C. He picked up reports that helical
resonators weere superior to short coaxial resonators. Tom also wrote:
"Reg (Edwards,RJE) then thinks the internal coil capacitance is just
femanding extra extra coil current and loss as the result of its cyclic
charge and discharge."

Reg seems to have had a nice explanation for coil loss from parasitic
capacitance.

Do you know where this explanation might be found?

Thanks, Mike

Bill Bowden wrote:
It would seem that a loop antenna with 100pF of winding capacitance in
parallel with a external capacitor of 200pF would resonate at the
same frequency as a antenna with no winding capacitance and a external
capacitor of 300pF, but apparently that's not the case.

The "100pF of winding capacitance" is NOT across the
entire coil as is the 200pF external capacitor. When
the operating frequency of a coil is more than ~15% of
the self-resonant frequency, the lumped circuit model
starts to fall apart. In your above example, the operating
frequency is ~60% of the self-resonant frequency so you
need to use the distributed network model (or Maxwell's
equations).

Quoting from an IEEE white paper about RF coils at:

http://www.ttr.com/TELSIKS2001-MASTER-1.pdf

"... lumped element circuit theory does not (and cannot)
accurately embody a world of second order partial
differential equations in space and time."

"The concept of coil 'self-capacitance' is an attempt
to circumvent transmission line effects on small coils
when the current distribution begins to depart from
its DC behavior. The notion has been developed by
starting with Maxwell's equations and using only the
first two terms in the Taylor series expansion for
the distributed current to obtain an expression for
the self-impedance of a generalized closed circuit.
Upon extracting Neumann's formula for the self inductance,
the remaining negative component of the reactance permits
an expression for the coil self-capacitance. These formulae
are valid for a PARALLEL combination of an inductance and
a capacitance when the operating frequency is well below
1/SQRT(L*CL). They permit a coil with a SLIGHTLY
nonuniform current distribution to be treated AS THOUGH THE
CURRENT WERE UNIFORM and the coil was shunted with a lumped
element capacitance."

The author shows how to estimate the VF and Z0 of a coil
that is operated at more than 15% of its self-resonant
frequency. It can thus be modeled as a transmission line.

The same author shows in his class notes at:

http://www.ttr.com/corum/index.htm

that the calculated self-resonant frequency of a particular
coil based on the measured self-capacitance was in error
by 65.2% when the "lumped-element assumption" was used.

The calculated self-resonant frequency based on the
transmission line distributed network model was within
5% of the measured self-resonant frequency.
--
73, Cecil http://www.w5dxp.com