Bill Turner wrote:

On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

__________________________________________________ _______

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

Say what???? You have two variables that satisfy the equation:
XsubL and F
The equation does not mean that L varies!!!!!!!!!!!





How could you possibly define it otherwise?

--
Bill, W6WRT

On Sun, 07 Dec 2003 16:14:16 -0800, Bill Turner
wrote:

I use the "sub" because ascii doesn't have a lower-case L. The XsubL is
merely the reactance of the inductor. If I was using Word or some other
word processor I would write capital X with a subscript L.

In plain English: The reactance of a coil is equal to 2 times pi times
the frequency in Hz times the inductance in henries.

Got it?

Yes, "got it." Unfortunately it doesn't explain your hair-brained
theory of variable inductance within a fixed inductor.
In fact the effect you've been trying to decribe appears to be no more
than an esoteric and practically-insignificant technicality - *if*
indeed it exists at all.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

On Sun, 07 Dec 2003 16:14:16 -0800, Bill Turner
wrote:

I use the "sub" because ascii doesn't have a lower-case L. The XsubL is
merely the reactance of the inductor. If I was using Word or some other
word processor I would write capital X with a subscript L.

In plain English: The reactance of a coil is equal to 2 times pi times
the frequency in Hz times the inductance in henries.

Got it?

Yes, "got it." Unfortunately it doesn't explain your hair-brained
theory of variable inductance within a fixed inductor.
In fact the effect you've been trying to decribe appears to be no more
than an esoteric and practically-insignificant technicality - *if*
indeed it exists at all.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

Bill Turner wrote:

On Sun, 07 Dec 2003 21:35:22 GMT, John Popelish
wrote:

You are projecting your limitations onto others.

__________________________________________________ _______

I do have one limitation: I don't take insults from people I'm trying
to have a discussion with.

Bye.

Bill, I sincerely apologize for hurting your feelings unintentionally
with my clumsy comment. I should have kept strictly to inductors and
away from anything that could have been interpreted as a personal
attack.

You may not have an impedance bridge (a limitation) but I and others
do have one and they separate the components of an impedance,
especially if you take two or more readings at different frequencies
and solve a bit of math.

--
John Popelish

Bill Turner wrote:

On Sun, 07 Dec 2003 21:35:22 GMT, John Popelish
wrote:

You are projecting your limitations onto others.

__________________________________________________ _______

I do have one limitation: I don't take insults from people I'm trying
to have a discussion with.

Bye.

Bill, I sincerely apologize for hurting your feelings unintentionally
with my clumsy comment. I should have kept strictly to inductors and
away from anything that could have been interpreted as a personal
attack.

You may not have an impedance bridge (a limitation) but I and others
do have one and they separate the components of an impedance,
especially if you take two or more readings at different frequencies
and solve a bit of math.

--
John Popelish

I read in sci.electronics.design that Paul Keinanen
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:
On Sun, 7 Dec 2003 19:13:36 +0000, John Woodgate
wrote:

Low-frequency iron-cored coils are quite another matter; the
inductance varies with frequency, voltage, temperature, previous history
and the state of the tide on Europa.

I assume that you are referring to DC biased iron cores (without an
air gap) or some high permeability ferrites with a strong DC bias
current. These do indeed show a variation of inductance depending on
the DC bias current.

Not only that, the inductance can vary with the AC voltage applied, most
notably when saturation is approached, but it can also happen with
silicon iron at very low inductions. Nickel-iron alloys don't normally
show this 'bottom bend' effect.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!

I read in sci.electronics.design that Paul Keinanen
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:
On Sun, 7 Dec 2003 19:13:36 +0000, John Woodgate
wrote:

Low-frequency iron-cored coils are quite another matter; the
inductance varies with frequency, voltage, temperature, previous history
and the state of the tide on Europa.

I assume that you are referring to DC biased iron cores (without an
air gap) or some high permeability ferrites with a strong DC bias
current. These do indeed show a variation of inductance depending on
the DC bias current.

Not only that, the inductance can vary with the AC voltage applied, most
notably when saturation is approached, but it can also happen with
silicon iron at very low inductions. Nickel-iron alloys don't normally
show this 'bottom bend' effect.
--
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!

In article , Bill Turner
writes:

On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

_________________________________________________ ________

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

How could you possibly define it otherwise?

Bill, I can get down to first principles if necessary, but that isn't
necessary, is it?

INDUCTANCE doesn't change over frequency...even above the
"self-resonance" due to distributed capacity between windings.
That's very basic and applies up into the region where the
frequency is so high the whole "coil" structure starts behaving
like a distributed-constant conglomeration of equivalent parts.
But, that's a specialty area and far above any practical
application of home-made coils for RF.

Reactance is a function of frequency and inductance. The
reactance of an inductor DOES change over frequency. That's
also very basic. For _practical_ home-made coils, the only
major concern is the distributed capacity of the coil structure.
Distributed capacity is the _equivalent_ of a fixed, parallel
capacitor across the pure inductor part of the coil. That L
and C will determine the "self resonance" of the structure.

To find the distributed capacity of an inductor (the equivalent of
a fixed parallel capacity connected across the inductor), the
method described in the "Reference Data for Radio Engineers,"
fourth edition, 1956, ITT (aka "Green Bible"), chapter 10, pp 268-
269 can be used as follows:

Using a Q Meter or other instrument with a calibrated variable
capacitor, resonate the parallel L-C with the capacitor at two
frequencies exactly an octave apart (1:2 ratio). Take the
difference of the two variable capacitor resonating values as
"deltac." Let "freqsq" be the _square_ of the highest of the two
frequencies used. For uHy, pFd, and MHz:

L = (19,000) / (freqsq x deltac)

Inductance L is the "true" inductance of the coil, separated from
the distributed capacity.

The constant of "19,000" is a simple approximation considering
that 1956 was the age of slide rules and electromechanical four-
function calculators. If the parallel resonating capacitor is well-
calibrated, the "true inductance" formula works out well. If the
parallel resonating capacitor is not calibrated, forget the whole
thing; there are several C-meters on the market that can allow
rather precise +/- 0.1 pFd resolution calibration if anyone is into
home metrology.

Anyone wishing to play with simple algebra can figure out the
formula from basic resonance equation at two frequencies exactly
an octave apart. That will result in the true mathematical value of
the constant given in the Green Bible. :-)

Len Anderson
retired (from regular hours) electronic engineer person

In article , Bill Turner
writes:

On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

_________________________________________________ ________

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

How could you possibly define it otherwise?

Bill, I can get down to first principles if necessary, but that isn't
necessary, is it?

INDUCTANCE doesn't change over frequency...even above the
"self-resonance" due to distributed capacity between windings.
That's very basic and applies up into the region where the
frequency is so high the whole "coil" structure starts behaving
like a distributed-constant conglomeration of equivalent parts.
But, that's a specialty area and far above any practical
application of home-made coils for RF.

Reactance is a function of frequency and inductance. The
reactance of an inductor DOES change over frequency. That's
also very basic. For _practical_ home-made coils, the only
major concern is the distributed capacity of the coil structure.
Distributed capacity is the _equivalent_ of a fixed, parallel
capacitor across the pure inductor part of the coil. That L
and C will determine the "self resonance" of the structure.

To find the distributed capacity of an inductor (the equivalent of
a fixed parallel capacity connected across the inductor), the
method described in the "Reference Data for Radio Engineers,"
fourth edition, 1956, ITT (aka "Green Bible"), chapter 10, pp 268-
269 can be used as follows:

Using a Q Meter or other instrument with a calibrated variable
capacitor, resonate the parallel L-C with the capacitor at two
frequencies exactly an octave apart (1:2 ratio). Take the
difference of the two variable capacitor resonating values as
"deltac." Let "freqsq" be the _square_ of the highest of the two
frequencies used. For uHy, pFd, and MHz:

L = (19,000) / (freqsq x deltac)

Inductance L is the "true" inductance of the coil, separated from
the distributed capacity.

The constant of "19,000" is a simple approximation considering
that 1956 was the age of slide rules and electromechanical four-
function calculators. If the parallel resonating capacitor is well-
calibrated, the "true inductance" formula works out well. If the
parallel resonating capacitor is not calibrated, forget the whole
thing; there are several C-meters on the market that can allow
rather precise +/- 0.1 pFd resolution calibration if anyone is into
home metrology.

Anyone wishing to play with simple algebra can figure out the
formula from basic resonance equation at two frequencies exactly
an octave apart. That will result in the true mathematical value of
the constant given in the Green Bible. :-)

Len Anderson
retired (from regular hours) electronic engineer person

Bill Turner wrote:

On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.


Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

The formula is fine. Your understanding of it is wrong.
X is inductive reactance.
F is frequency.
L is inductance.

F is a variable, L is fixed and X (the reactance of L at
the frequency) varies as the frequency varies.



--
Bill, W6WRT

Bill Turner wrote:

On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.


Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

The formula is fine. Your understanding of it is wrong.
X is inductive reactance.
F is frequency.
L is inductance.

F is a variable, L is fixed and X (the reactance of L at
the frequency) varies as the frequency varies.



--
Bill, W6WRT

On Mon, 08 Dec 2003 19:46:43 -0800, Bill Turner
wrote:

On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

_________________________________________________ ________

I maintain it does. Otherwise the formula X=2piFL is invalid. Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

That is what everybody is trying to say.

It is like discussing is a candle _emitting_light_ into the room or is
the candle _absorbing_darkness_. This becomes quite apparent when the
wick of the candle is black when the candle has been put out, clearly
it has absorbed a lot of darkness :-).

In an incandescent lamp, the electric current will constantly renew
the filament, thus preventing a lot of darkness being concentrated on
the filament.

One could develop quite scientific methods to measure the amount of
darkness absorbed and predict the behaviour of other lamps. This can
also be debated successfully for a quite a while, until some serious
disagreeing measurements are brought into the discussion.

The disagreement here seems to depend on how one defines what inductance
is.

It has often been defined by the ability to store energy.

I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above.

L = Xl / (2 pi f) applies only to _pure_inductive Xl

It does _not_ apply to L = X / (2 pi f) in which X is some combination
of Xl and Xc !


Do you disagree with that?

That formula has been taught for decades. Are you saying it is wrong?

The formulas taught for decades a

Xl = 2 pi f L _and _ Xc = -1/(2 pi f C)

How do you arrive to the incorrect L = X / (2 pi f) from the
equations above ?

Please note, it is the magnitude of X what you are measuring with some
simple test gear, not Xl. Thus, the original claim is an artefact of
the measurement method.

Paul OH3LWR

On Mon, 08 Dec 2003 19:46:43 -0800, Bill Turner
wrote:

On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

_________________________________________________ ________

I maintain it does. Otherwise the formula X=2piFL is invalid. Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

That is what everybody is trying to say.

It is like discussing is a candle _emitting_light_ into the room or is
the candle _absorbing_darkness_. This becomes quite apparent when the
wick of the candle is black when the candle has been put out, clearly
it has absorbed a lot of darkness :-).

In an incandescent lamp, the electric current will constantly renew
the filament, thus preventing a lot of darkness being concentrated on
the filament.

One could develop quite scientific methods to measure the amount of
darkness absorbed and predict the behaviour of other lamps. This can
also be debated successfully for a quite a while, until some serious
disagreeing measurements are brought into the discussion.

The disagreement here seems to depend on how one defines what inductance
is.

It has often been defined by the ability to store energy.

I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above.

L = Xl / (2 pi f) applies only to _pure_inductive Xl

It does _not_ apply to L = X / (2 pi f) in which X is some combination
of Xl and Xc !


Do you disagree with that?

That formula has been taught for decades. Are you saying it is wrong?

The formulas taught for decades a

Xl = 2 pi f L _and _ Xc = -1/(2 pi f C)

How do you arrive to the incorrect L = X / (2 pi f) from the
equations above ?

Please note, it is the magnitude of X what you are measuring with some
simple test gear, not Xl. Thus, the original claim is an artefact of
the measurement method.

Paul OH3LWR

On Tue, 09 Dec 2003 04:59:29 GMT, wrote:



Bill Turner wrote:

On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.

That's right. You end up with X/2piF and X and F are inter-related;
they are not independent variables.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

On Tue, 09 Dec 2003 04:59:29 GMT, wrote:



Bill Turner wrote:

On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.

That's right. You end up with X/2piF and X and F are inter-related;
they are not independent variables.
--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

1) you guys are just arguing symantics. You both know what really happens.
".... "Inductance" vs. the total reactance measuring as inductive...." call
it what you like.

1a)
You are also both using (some might say mis-using) the term "linear" to mean
"varies linearly with..." rather than the more common meaning that
superposition applies. RLC sircuits are linear. Any given parameter may
not vary linearly as the frequency is varied. Also, this use of 'linear'
depends upon the type of scale being used--log or linear.

2) John,
You better re-think your last statement about the series equivalent of a
practical coil. It implies that there is some way to measure a low Z at the
resonance of the coil under discussion. You say:
"The series
equivalent [impedance ? Steve] goes down as the frequency increases,
and goes to zero at
resonance. "
While a series resonant LC exhibits this behavior, the series equivalent
of a practical coil does not do this. The series equivalent must do the
same thing as the parallel equivalent -- namely go to a high impedance at
resonance. That's why it is called *equivalent*--the total, or terminal
impedance is equal for the two representations (at a single frequency).

Pretty sure I got that right....
Steve
k]9]d]c]i


A practical coil usually goes to parallel resonance - at which the series
equivalent does not go to zero
"John Woodgate" wrote in message
...
I read in sci.electronics.design that Bill Turner
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:

Both statements are true and easily provable. A simple air core coil
which measures one microhenry at a low frequency may have an inductance
of several millihenries (or even henries) when near its self resonant
frequency.

This is what happens to the *parallel equivalent* inductance. The series
equivalent goes down as the frequency increases, and goes to zero at
resonance.
--
Regards, John Woodgate, OOO - Own Opinions Only.
http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go
to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!

1) you guys are just arguing symantics. You both know what really happens.
".... "Inductance" vs. the total reactance measuring as inductive...." call
it what you like.

1a)
You are also both using (some might say mis-using) the term "linear" to mean
"varies linearly with..." rather than the more common meaning that
superposition applies. RLC sircuits are linear. Any given parameter may
not vary linearly as the frequency is varied. Also, this use of 'linear'
depends upon the type of scale being used--log or linear.

2) John,
You better re-think your last statement about the series equivalent of a
practical coil. It implies that there is some way to measure a low Z at the
resonance of the coil under discussion. You say:
"The series
equivalent [impedance ? Steve] goes down as the frequency increases,
and goes to zero at
resonance. "
While a series resonant LC exhibits this behavior, the series equivalent
of a practical coil does not do this. The series equivalent must do the
same thing as the parallel equivalent -- namely go to a high impedance at
resonance. That's why it is called *equivalent*--the total, or terminal
impedance is equal for the two representations (at a single frequency).

Pretty sure I got that right....
Steve
k]9]d]c]i


A practical coil usually goes to parallel resonance - at which the series
equivalent does not go to zero
"John Woodgate" wrote in message
...
I read in sci.electronics.design that Bill Turner
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:

Both statements are true and easily provable. A simple air core coil
which measures one microhenry at a low frequency may have an inductance
of several millihenries (or even henries) when near its self resonant
frequency.

This is what happens to the *parallel equivalent* inductance. The series
equivalent goes down as the frequency increases, and goes to zero at
resonance.
--
Regards, John Woodgate, OOO - Own Opinions Only.
http://www.jmwa.demon.co.uk
Interested in professional sound reinforcement and distribution? Then go
to
http://www.isce.org.uk
PLEASE do NOT copy news posts to me by E-MAIL!

Gents,

Another practical consideration. Another area where caution is
advised--paralleling bypass caps. In solid state Power Amplifier design,
such a configuratin can cause problems because there is a point where one is
above self resonance and acts like an inductance in parallel with the other
cap which is still capacitive-- thus, resonance and no bypass. Been there,
done that. We put a small Z in between. Frequently a small bead or
resistor if possible.
Seems there is an equivalent problem with series inductors.

--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On Sun, 7 Dec 2003 19:17:08 +0000, John Woodgate
wrote:

This is a 1920s problem. Just as you parallel capacitors of different
type, electrolytic, metallized foil and ceramic, to get a wideband
component, so you put inductors of different construction in series to
get a wide band component. You can wind them all on a bit of wax-
impregnated dowel if you like. (;-)

__________________________________________________ _______

That will work, no doubt. My point was that it takes some serious
engineering and careful testing; you can't just wrap some wire on a form
and expect it to work correctly across a wide range of frequencies.

--
Bill, W6WRT

Gents,

Another practical consideration. Another area where caution is
advised--paralleling bypass caps. In solid state Power Amplifier design,
such a configuratin can cause problems because there is a point where one is
above self resonance and acts like an inductance in parallel with the other
cap which is still capacitive-- thus, resonance and no bypass. Been there,
done that. We put a small Z in between. Frequently a small bead or
resistor if possible.
Seems there is an equivalent problem with series inductors.

--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On Sun, 7 Dec 2003 19:17:08 +0000, John Woodgate
wrote:

This is a 1920s problem. Just as you parallel capacitors of different
type, electrolytic, metallized foil and ceramic, to get a wideband
component, so you put inductors of different construction in series to
get a wide band component. You can wind them all on a bit of wax-
impregnated dowel if you like. (;-)

__________________________________________________ _______

That will work, no doubt. My point was that it takes some serious
engineering and careful testing; you can't just wrap some wire on a form
and expect it to work correctly across a wide range of frequencies.

--
Bill, W6WRT

You're still doing it. Paul (I think) said "measure" and Bill, no, looks
like Len (I think) said "finding", meaning "calculating".


"Avery Fineman" wrote in message
...
In article , Bill Turner
writes:

On Sun, 07 Dec 2003 13:55:35 +0200, Paul Keinanen
wrote:

.snip
Not only can you *not* measure them separately, they can not be
physically separated either, since the parasitic capacitance is always
present between adjacent windings....


Nonsense. General Radio had a nice little formula way back
before 1956 for finding the distributed capacity of an inductor.
Len Anderson
retired (from regular hours) electronic engineer person

You're still doing it. Paul (I think) said "measure" and Bill, no, looks
like Len (I think) said "finding", meaning "calculating".


"Avery Fineman" wrote in message
...
In article , Bill Turner
writes:

On Sun, 07 Dec 2003 13:55:35 +0200, Paul Keinanen
wrote:

.snip
Not only can you *not* measure them separately, they can not be
physically separated either, since the parasitic capacitance is always
present between adjacent windings....


Nonsense. General Radio had a nice little formula way back
before 1956 for finding the distributed capacity of an inductor.
Len Anderson
retired (from regular hours) electronic engineer person

OOPS Bill. By the formula, change F and Xl changes! Avery said below;
"reactance changes with frequency" and is correct. Also, if you change L
then Xl changes, but that is not what he said.

--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

__________________________________________________ _______

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

How could you possibly define it otherwise?
--
Bill, W6WRT

OOPS Bill. By the formula, change F and Xl changes! Avery said below;
"reactance changes with frequency" and is correct. Also, if you change L
then Xl changes, but that is not what he said.

--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 07 Dec 2003 18:25:51 GMT, (Avery Fineman) wrote:

Write on the whiteboard 100 times: Inductance does not change
with frequency...reactance changes with frequency.

__________________________________________________ _______

Not true. Inductance and reactance are related by the formula
XsubL = 2 pi F L. If XsubL has changed, then so has the inductance, and
vice versa.

How could you possibly define it otherwise?
--
Bill, W6WRT

Ahhhh! So there does seem to be a mis interpretation of the formula
here.-Steve

Bill,
I believe you are placing the dependant and independent variables in the
wrong place. The Xl is the dependant variable. Xl *depends upon* F and L,
not the other way around. That is, given an L and F you calculate the X.
X is the answer.
Only if you know there are no other contributing factors can the formula
be used the other way, because it does not factor them (the parasitic
capacitance) in. That is, Given an X measurement you can not tell the
inductance, only the *equivalent total* inductive reactance.


--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid. Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

--
Bill, W6WRT

Ahhhh! So there does seem to be a mis interpretation of the formula
here.-Steve

Bill,
I believe you are placing the dependant and independent variables in the
wrong place. The Xl is the dependant variable. Xl *depends upon* F and L,
not the other way around. That is, given an L and F you calculate the X.
X is the answer.
Only if you know there are no other contributing factors can the formula
be used the other way, because it does not factor them (the parasitic
capacitance) in. That is, Given an X measurement you can not tell the
inductance, only the *equivalent total* inductive reactance.


--
Steve N, K,9
d, c. i


"Bill Turner" wrote in message
...
On 08 Dec 2003 20:09:43 GMT, (Avery Fineman) wrote:

INDUCTANCE doesn't change over frequency

__________________________________________________ _______

I maintain it does. Otherwise the formula X=2piFL is invalid. Is that
what you're saying?

I understand what you're saying about the inductance of a coil being
fixed and the reactance is the net result of that fixed inductance plus
the effect of the parasitic capacitance between windings, vs frequency,
of course. If one chooses to *model* a coil that way, I have no
objection. You will no doubt arrive at the correct reactance for a
given frequency.

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

--
Bill, W6WRT

There'something sour here. Way down ...


"Paul Keinanen" wrote in message
...
[snip]
The problem with circuits containing both inductances and capacitances
is that in one kind of reactance, there is a +90 degree phase shift
and the other with -90 degree phase shift. Thus, when these are
combined, they partially cancel each other, producing different
magnitudes and some phase shift between -90 and +90 degrees. If only
the resultant magnitude is used (and the resultant phase is ignored),
this would give the false impression that the inductance changes with
frequency.

I don't quite follow where you are going here. below the self resonant
freq the angle will be +90 (minus a little for what ever resistance is
there).


The rest of this about measuring the energy from DC, I don't think is at all
practical.

[snip] the inductance could be measured in a different way.
... the energy
stored in the inductance is W = I*I*L/2. ...
...cut the DC current...dissipate the energy in some kind of
integrating load across L. Even if there is a significant
capacitance[snip]
...the energy would bounce back
between L and C, but finally it would be dissipated by the external
load. ...
Thus using this measurement method, the value of L would be the same
regardless if C is present or not....

Paul OH3LWR

OK. so then, how do you propose to measure this energy? I don't think
it is practical.


--
Steve N, K,9
d, c. i

There'something sour here. Way down ...


"Paul Keinanen" wrote in message
...
[snip]
The problem with circuits containing both inductances and capacitances
is that in one kind of reactance, there is a +90 degree phase shift
and the other with -90 degree phase shift. Thus, when these are
combined, they partially cancel each other, producing different
magnitudes and some phase shift between -90 and +90 degrees. If only
the resultant magnitude is used (and the resultant phase is ignored),
this would give the false impression that the inductance changes with
frequency.

I don't quite follow where you are going here. below the self resonant
freq the angle will be +90 (minus a little for what ever resistance is
there).


The rest of this about measuring the energy from DC, I don't think is at all
practical.

[snip] the inductance could be measured in a different way.
... the energy
stored in the inductance is W = I*I*L/2. ...
...cut the DC current...dissipate the energy in some kind of
integrating load across L. Even if there is a significant
capacitance[snip]
...the energy would bounce back
between L and C, but finally it would be dissipated by the external
load. ...
Thus using this measurement method, the value of L would be the same
regardless if C is present or not....

Paul OH3LWR

OK. so then, how do you propose to measure this energy? I don't think
it is practical.


--
Steve N, K,9
d, c. i

On Tue, 09 Dec 2003 09:19:23 -0800, Bill Turner
wrote:

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

Measurement errors? I don't know enough about your way of working to
say. But thanks for giving your worked example. It'll no doubt help to
pin down the exact area of disagreement between us.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

On Tue, 09 Dec 2003 09:19:23 -0800, Bill Turner
wrote:

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

Measurement errors? I don't know enough about your way of working to
say. But thanks for giving your worked example. It'll no doubt help to
pin down the exact area of disagreement between us.

--

"I expect history will be kind to me, since I intend to write it."
- Winston Churchill

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

--
Bill, W6WRT

The inductance is not changing. What you are measuring is not pure
inductance but the coil has a stray capacitance. That is what is making the
coil seof resonate.

YOu did not say what hapens at 110 mhz, 200 mhz, and 500 mhz, if you did ,
it would measuer capacitance reactance. How do you change a coil into a
capacitor ? You don't , but the effect of reactance has.

Look at it this from a totally differant angle. You stick the leads of a DV
voltmeter in the wall socket. It does not show any deflection other than
maybe the first jump when it is plugged in. Does that mean there is no
voltage or power in the circuit, I think not. Stick your fingers in it and
see what hapens :-)

Your method is flawed in the same way, you only measured inductance ( not
really that , but the inductive reactance at a given frequency, but did not
measuer capcitance. Where did the capacitance come from ? It is what makes
the coil selfresonante. If you measuer a circuit that has inductance,
capacitance and resistance, depending on if it is series or pareallel
resonate here is what will hapen. As the frequency is increaced the
inductance reactance will increace, it will measuer resistance at the
reosnant frequency , then a large capacitance reactance and then a small
capacitance reactance or else the reverse will hapen, capacitive reactance,
resisstance, inductive reactance. However none of the actual inductance,
capacitance or resistance values will change. YOu are confusing inductacne
and reactance.

YOu are only seeing one part of the big picture. YOu have to look at
several formulars to see what is going on in a circuit that has inductance
and capacitance.

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

--
Bill, W6WRT

The inductance is not changing. What you are measuring is not pure
inductance but the coil has a stray capacitance. That is what is making the
coil seof resonate.

YOu did not say what hapens at 110 mhz, 200 mhz, and 500 mhz, if you did ,
it would measuer capacitance reactance. How do you change a coil into a
capacitor ? You don't , but the effect of reactance has.

Look at it this from a totally differant angle. You stick the leads of a DV
voltmeter in the wall socket. It does not show any deflection other than
maybe the first jump when it is plugged in. Does that mean there is no
voltage or power in the circuit, I think not. Stick your fingers in it and
see what hapens :-)

Your method is flawed in the same way, you only measured inductance ( not
really that , but the inductive reactance at a given frequency, but did not
measuer capcitance. Where did the capacitance come from ? It is what makes
the coil selfresonante. If you measuer a circuit that has inductance,
capacitance and resistance, depending on if it is series or pareallel
resonate here is what will hapen. As the frequency is increaced the
inductance reactance will increace, it will measuer resistance at the
reosnant frequency , then a large capacitance reactance and then a small
capacitance reactance or else the reverse will hapen, capacitive reactance,
resisstance, inductive reactance. However none of the actual inductance,
capacitance or resistance values will change. YOu are confusing inductacne
and reactance.

YOu are only seeing one part of the big picture. YOu have to look at
several formulars to see what is going on in a circuit that has inductance
and capacitance.

In article , Bill Turner
writes:

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

I'm saying that the student doesn't understand inductance.

Inductance does NOT vary over frequency for any coil of wire under
its self-resonance.

Reactance varies over frequency with inductance fixed...directly
proportional to frequency. Inductance doesn't vary.

Yes, you can FIND inductance in Henries if you measure its
reactance at a particular frequency. Inductance in Henries has NOT
changed by doing so. Inductance in Henries remains constant.

[feel free to quibble over the spelling of "Henries" v. "Henrys" :-) ]

If your reactance-measuring gizmo is not calibrated properly, then
its readings will show an APPARENT change in inductance. The
inductance still hasn't changed...only the calibration of the gizmo
is off.

Don't get all wound up and take a turn for the worse...

Len Anderson
retired (from regular hours) electronic engineer person

In article , Bill Turner
writes:

The disagreement here seems to depend on how one defines what inductance
is. I maintain that inductance of a coil is nothing more than the
reactance divided by 2piF, as derived from the formula above. Do you
disagree with that? That formula has been taught for decades. Are you
saying it is wrong?

I'm saying that the student doesn't understand inductance.

Inductance does NOT vary over frequency for any coil of wire under
its self-resonance.

Reactance varies over frequency with inductance fixed...directly
proportional to frequency. Inductance doesn't vary.

Yes, you can FIND inductance in Henries if you measure its
reactance at a particular frequency. Inductance in Henries has NOT
changed by doing so. Inductance in Henries remains constant.

[feel free to quibble over the spelling of "Henries" v. "Henrys" :-) ]

If your reactance-measuring gizmo is not calibrated properly, then
its readings will show an APPARENT change in inductance. The
inductance still hasn't changed...only the calibration of the gizmo
is off.

Don't get all wound up and take a turn for the worse...

Len Anderson
retired (from regular hours) electronic engineer person

Bill Turner wrote:

On Tue, 09 Dec 2003 04:59:29 GMT, wrote:

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.


__________________________________________________ _______

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

Here are your own words:
"At that self-resonant frequency, the coil is behaving like a
parallel resonant circuit, which of course it is, due to the
parasitic capacitance between each winding."

Your example ignores the capacitance, which you have stated
exists. There is nothing in your formula that addresses it.
You cannot use the formula or the math above (in your post) to
support your point of view, because it does not contain any
term for capacitance. The capacitance exists, and exhibits
a larger and larger affect on the circuit as the frequency
increases from 1 - 99 mHz.


This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

--
Bill, W6WRT

Bill Turner wrote:

On Tue, 09 Dec 2003 04:59:29 GMT, wrote:

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.


__________________________________________________ _______

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

Here are your own words:
"At that self-resonant frequency, the coil is behaving like a
parallel resonant circuit, which of course it is, due to the
parasitic capacitance between each winding."

Your example ignores the capacitance, which you have stated
exists. There is nothing in your formula that addresses it.
You cannot use the formula or the math above (in your post) to
support your point of view, because it does not contain any
term for capacitance. The capacitance exists, and exhibits
a larger and larger affect on the circuit as the frequency
increases from 1 - 99 mHz.


This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

--
Bill, W6WRT

In article ,
Paul Burridge wrote:

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

As Spock said to Kirk, "You proceed from a false assumption." Or, to
put it another way, the scenario you've just laid out contains an
inherent contradiction.

The inductance meter that you are using (or assuming) is not actually
measuring inductance. It's measuring reactance, and back-calculating
to what the inductance would be *if* it were measuring a "pure"
inductance.

However, as you recognize, the component that you are measuring is
*not* a pure inductance. Its actual reactance is the result of
interaction between its inductance, its inter-winding and distributed
capacitance, and its winding resistance (at any given frequency).

So, what you're observing can best be interpreted as follows:

- At low frequencies (well below resonance), the component's
reactance is dominated by its inductive component. It's a decent
approximation of a "pure" inductance. The inductance meter gives
accurate estimate of the inductive component.

- At high frequencies (well above resonance), the component's
reactance is dominated by its capacitive component. It becomes a
decent approximation of a "pure" capacitance at some point, I
suspect.

At these frequencies, your simple inductance meter lies through its
teeth. It "tells" you that the part's inductance is such-and-
such, but it's not telling you the truth. It's hiding from you
the fact that the reactance it's seeing isn't inductive at all (the
reactance decreases as frequency goes up, and exhibits a capacitive
phase angle).

So, I think, what you're facing here is the problem which occurs when
you try to force simplifying assumptions ("the component being
measured is a pure inductance" and "an inductance meter actually
measures inductance") outside the range in which these assumptions are
valid.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

In article ,
Paul Burridge wrote:

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.
At 2 MHz you find it to be 12.56 ohms.
At 10 MHz you find it to be 62.8 ohms.
So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.
At 95 MHz you would expect the reactance to be 6.28*95=596.6 ohms, but
much to your surprise, it measures 1000 ohms.
At 99 MHz, instead of the expected 6.28*99=621.72 ohms, it measures
50,000 ohms!!

All the above is perfectly normal and easily observable.

My point is that when a coil measures 50,000 ohms at 99 MHz, its
inductance HAS TO BE L=X/(2*pi*F), or 50,000/(6.28*99)=80.4 uH!

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

As Spock said to Kirk, "You proceed from a false assumption." Or, to
put it another way, the scenario you've just laid out contains an
inherent contradiction.

The inductance meter that you are using (or assuming) is not actually
measuring inductance. It's measuring reactance, and back-calculating
to what the inductance would be *if* it were measuring a "pure"
inductance.

However, as you recognize, the component that you are measuring is
*not* a pure inductance. Its actual reactance is the result of
interaction between its inductance, its inter-winding and distributed
capacitance, and its winding resistance (at any given frequency).

So, what you're observing can best be interpreted as follows:

- At low frequencies (well below resonance), the component's
reactance is dominated by its inductive component. It's a decent
approximation of a "pure" inductance. The inductance meter gives
accurate estimate of the inductive component.

- At high frequencies (well above resonance), the component's
reactance is dominated by its capacitive component. It becomes a
decent approximation of a "pure" capacitance at some point, I
suspect.

At these frequencies, your simple inductance meter lies through its
teeth. It "tells" you that the part's inductance is such-and-
such, but it's not telling you the truth. It's hiding from you
the fact that the reactance it's seeing isn't inductive at all (the
reactance decreases as frequency goes up, and exhibits a capacitive
phase angle).

So, I think, what you're facing here is the problem which occurs when
you try to force simplifying assumptions ("the component being
measured is a pure inductance" and "an inductance meter actually
measures inductance") outside the range in which these assumptions are
valid.

--
Dave Platt AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

Bill Turner wrote:

On Tue, 9 Dec 2003 19:20:25 -0500, "Ralph Mowery"
wrote:

The inductance is not changing. What you are measuring is not pure
inductance but the coil has a stray capacitance. That is what is making the
coil seof resonate.

__________________________________________________ _______

I am well aware of that, but you are tap dancing around the relevance of
the formula X=2*pi*F*L.

Just answer this: If I have a coil of very high Q (no appreciable
resistance), and I apply 100 volts of 100 MHz AC to it, and measure a
current of 2 milliamps through it, then:

1. What is its reactance?
2. What is its inductance?

Its impedance has been measured to have a magnitude of 50,000 ohms.
If you have independent information that its Q is very high, you can
assume that this impedance is made up of some combination of inductive
reactance and capacitive reactance. With a single measurement such as
this, that is about all you can say.

It cannot be assumed to be all inductive reactance (or any particular
combination of inductive and capacitive reactances), just because
someone labeled the device as an inductor or because it looks like a
coil. Other measurements are needed to nail the details.

A parallel resonance with 50,000 ohms impedance (at some frequency) is
not the same thing as an inductance with 50,000 ohms of inductive
reactance (at the same frequency). They pass a similar magnitude of
current at that frequency for the same applied AC, but their current
phases do not match. And their reaction to nonsinusiodal waveforms is
very different.

--
John Popelish

Bill Turner wrote:

On Tue, 9 Dec 2003 19:20:25 -0500, "Ralph Mowery"
wrote:

The inductance is not changing. What you are measuring is not pure
inductance but the coil has a stray capacitance. That is what is making the
coil seof resonate.

__________________________________________________ _______

I am well aware of that, but you are tap dancing around the relevance of
the formula X=2*pi*F*L.

Just answer this: If I have a coil of very high Q (no appreciable
resistance), and I apply 100 volts of 100 MHz AC to it, and measure a
current of 2 milliamps through it, then:

1. What is its reactance?
2. What is its inductance?

Its impedance has been measured to have a magnitude of 50,000 ohms.
If you have independent information that its Q is very high, you can
assume that this impedance is made up of some combination of inductive
reactance and capacitive reactance. With a single measurement such as
this, that is about all you can say.

It cannot be assumed to be all inductive reactance (or any particular
combination of inductive and capacitive reactances), just because
someone labeled the device as an inductor or because it looks like a
coil. Other measurements are needed to nail the details.

A parallel resonance with 50,000 ohms impedance (at some frequency) is
not the same thing as an inductance with 50,000 ohms of inductive
reactance (at the same frequency). They pass a similar magnitude of
current at that frequency for the same applied AC, but their current
phases do not match. And their reaction to nonsinusiodal waveforms is
very different.

--
John Popelish

In article , Bill Turner
writes:

On Tue, 09 Dec 2003 04:59:29 GMT, wrote:

I maintain it does. Otherwise the formula X=2piFL is invalid.

NO! In the above equation, X varies when F varies. The equation
does NOT mean that L varies as F varies.

_________________________________________________ ________

Perhaps an example will make it clear.

Suppose you have a coil which measures 1 uH at 1 MHz. It is known to
have a self-resonant (parallel) frequency of 100 MHz.

OK, it has a distributed capacity of 2.533 pFd.

The circuit being measured is composed of a pure inductance
of 1.000 uHy and pure capacitance of 2.533 pFd in parallel.

We can neglect the losses in each one of those components
for the sake of illustration.

You measure its reactance at 1 MHz using the formula X=2*pi*F and find
it to be 6.28 ohms.

The inductive reactance is 6.28319 Ohms at 1 MHz and the
capacitive reactance is 62.8326 KOhms at 1 MHz.

In terms of susceptance, the B_sub_L is 0.159153 and
15.9153x10^-6 mhos, respectively. Total susceptance is then
0.159137 mhos or 6.28389 Ohms. [reactance meter probably isn't
calibrated that close to show the slight change due to distributed
capacity]

At 2 MHz you find it to be 12.56 ohms.

At 2 MHz, the inductive reactance is 12.5664 Ohms or 0.0795775
mhos while the distributed capacitance has 31.8306 mhos. The
total susceptance is 0.0795456 mhos or 12.5714 Ohms. That is
within 0.0907% of 12.56 Ohms and darn few reactance measuring
gizmos are calibrated that close...

At 10 MHz you find it to be 62.8 ohms.

Okay, at 10 MHz, the inductive susceptance is 0.0159155 mhos
and the capacitive susceptance is 159.153 x 10^-6 mhos, the
total being 0.0157563 mhos or 63.4665 Ohms reactance. That's
an error of 1.061% from 62.8 and still fairly reasonable for the error
of a reactance meter or whatever.

So far the reactance is changing linearly with respect to frequency.
(Actually it is not perfectly linear, but the difference at these
frequencies is small and probably would not be observed with run of the
mill test equipment.)

Okay, that's progress. We are agreed that test equipment can have
errors...he said with a grin having worked in metrology and a
standards lab for over 2 years in the past... :-)

But, as you approach 100 MHz, you find the change is obviously no longer
linear.

Ah, but you are measuring TWO things at the same time, the
parallel of the true inductor and its distributed capacity. Once you
are into measuring multiple elements, you need a test setup to
try to get a handle on the individual components. That is why I
brought up the "true inductance" two-frequency test on a Q meter
that has a calibrated tuning capacitor. That WILL establish the
equivalent pure capacitor due to distributed winding capacity in the
coil (the physical inductor form).

Once you KNOW the distributed capacity, its just a matter of some
button-pushing on a good scientific handheld calculator to derive
true inductance from the reactance readings of both inductance and
distributed capacity. [I recommend an HP 32 S II as an RPN fan]

The parallel capacitance will definitely exist as more picoFarads in
a circuit such as a FET gate which has a very high parallel resistance
(or very low conductance if you can think in terms of admittance).
That FET input capacitance will change the higher frequency resonance
even lower.

Offhand, I'd say that 2.533 pFd distributed capacity is rather high and
probably is around 1.0 pFd (solenoidal type, no core)...but a FET
gate input and its PCB traces to ground plane can be an additional
2.0 pFd. That's 3.0 pFd total and the self-resonance of that circuit is
now 91.888 MHz.

This is not an illusion. If you have an inductance meter which uses 99
MHz as a test frequency, it WILL MEASURE 80.4 uH.

That "inductance meter" is still measuring TWO THINGS AT THE
SAME TIME. The physical coil still has two components, the
pure inductance in parallel with a pure capacitance representing
the distributed capacity of the windings. Those are inseperable
unless you do something like the "true inductance" test at octave
separation frequencies or equivalent.

A Q Meter of any kind made today, last year, or back in the pre-
history before 1947, MEASURES THREE THINGS AT THE SAME
TIME! Yet the Q Meter is still accurate enough to derive the
equivalent parallel resistance, parallel inductance, and parallel
capacitance of the physical coil's windings. [it actually measures
conductance and susceptance as a total magnitude and relates
that to the Q or loss factor while the calibrated frequency setting
and calibrated variable capacitor allow separate "inductance"
measurement even though the Q Meter is "looking" at both L and
C_sub_d in parallel]

ANYONE using test equipment SHOULD be aware of what their
equipment does, how it works (in general), and what it really
measures. Since inductance does NOT change in a passive coil
(that isn't otherwise influenced by magnetic fields), what anyone
measures on a particular coil is THREE THINGS: The conductance
due to losses and the susceptance due to BOTH parallel inductance
and parallel capacitance. Conductance will change with frequency
depending on a lot of different factors (coil form, coil core, wire used,
shield used (if any), dielectric of the former material, core permittivity,
etc.). Susceptance will change with frequency because of the TWO
components...BUT THE INDUCTIVE COMPONENT DOES NOT
CHANGE.

And therefore, I maintain that inductance DOES vary with frequency.

How can it be otherwise?

The baseline taught in all textbooks (where I learned it first) and in
classes (where I learned it second) all agree that one MUST
separate the components into their "pure" form and THEN derive the
component parts by different tests. That is how it is perceived by
most other folks based on a lot of first-principle demonstration.

Inductance of a coil DOES NOT CHANGE WITH FREQUENCY.
Basic definition. First-principle stuff by definition.

You CAN say that APPARENT inductance changes if you are just
doing one kind of test. "Apparent" isn't going to work well when this
coil is dropped into a circuit thinking that "inductance changes with
frequency" and the circuit contains a lot of other sneaky little
components that can shoot the "apparent" reading way off. No one
successfully works with L-C and active-device networks using this
"apparent" reading. One separates the component parts first, then
combines them into manageable parallel-equivalent or series-equivalent
circuits.

The ILLUSION is from looking at an impedance- or admittance-measuring
instrument such as a Q Meter and thinking its calibrated inductance
dial "measures inductance." It doesn't...but it comes very close. That is
just the calibrated variable capacitor tuning to resonance at specific
frequencies...as a convenience to the user. The capacitance markings
will be accurate but any external coil that has significant parallel
capacitance from its windings will add to the calibrated capacity on the
dial. Some Q Meters allow variable frequency settings to do things
like the octave-separation-of-frequency measurement of the external
test parallel capacity.

An impedance or admittance bridge type of instrument can yield
different "errors" and "illusions" depending on their type/kind.

Len Anderson
retired (from regular hours) electronic engineer person