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