In article , Bill Turner
writes:

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

One can still argue that the inductance and inductive reactance are as
well as the capacitance and the capacitive reactance are still there
as separate entities, but we can not measure them separately from
terminals of the coil. Thus, this is an artefact of the measurement
method.

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. I would not call it an artifact of
the measurement method, but rather an artifact of the coil itself.

Nonsense. General Radio had a nice little formula way back
before 1956 for finding the distributed capacity of an inductor.
It was published in the Green Bible (ITT Reference Data for
Radio Engineers, small format, dark green hard cover). I used it
years ago and earlier this year and many times between.

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

Now if someone actually wants to WIND COILS, I have a little aid
for tiny ones wound on common screw thread forms that was
published in Ham Radio magazine. Has measured Qs over
frequency as well as basic inductance. I'll attach it to private e-mail
(PDF) to anyone that requests it.

Using common screw thread formers and solid wire allows a good
repeatability between bench and application. Forms can be anything
from a 4-40 bolt to a common screw-thread lamp base.

Folks in here are getting too wound up...and coiling to strike. :-)

Len Anderson
retired (from regular hours) electronic engineer person

I read in sci.electronics.design that Terry Pinnell terrypinDELETE@dial
..pipexTHIS.com wrote (in )
about 'Winding coils', on Sun, 7 Dec 2003:
John Devereux wrote:

Bill Turner writes:

On 6 Dec 2003 13:39:51 -0800, Winfield Hill
wrote:

We're talking a small air-coil here.

Doesn't matter what kind of coil; all coils have a non-linear plot of
either inductance vs frequency OR reactance vs frequency. ALL coils.

Well, just about anything is "non-linear" if you measure it accurately
enough! But is it really true that the *inductance* of a "small air
coil" is "dramatically" non-linear with frequency as you stated?

Intuitively I'd have thought the answer was plainly No, but I'm
certainly not technically savvy enough to be confident about that. But
I strongly suspect that the thread is already ovedue an unambiguous
definition of 'inductance'. Where's John Woodgate when you really need
him...g.

I'm here today, but I was away all last week. I don't think I can add
much; small air-cored coils have inductance independent of frequency up
to about half the self-resonant frequency, when deviation begins to be
noticeable. 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. Also, it comes in two varieties,
series equivalent and shunt equivalent, and you'd better get the right
one for your problem. As the inductor gets 'worse', at lower
frequencies, the shunt equivalent tends to infinity, which puzzles
students no end.
--
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 Terry Pinnell terrypinDELETE@dial
..pipexTHIS.com wrote (in )
about 'Winding coils', on Sun, 7 Dec 2003:
John Devereux wrote:

Bill Turner writes:

On 6 Dec 2003 13:39:51 -0800, Winfield Hill
wrote:

We're talking a small air-coil here.

Doesn't matter what kind of coil; all coils have a non-linear plot of
either inductance vs frequency OR reactance vs frequency. ALL coils.

Well, just about anything is "non-linear" if you measure it accurately
enough! But is it really true that the *inductance* of a "small air
coil" is "dramatically" non-linear with frequency as you stated?

Intuitively I'd have thought the answer was plainly No, but I'm
certainly not technically savvy enough to be confident about that. But
I strongly suspect that the thread is already ovedue an unambiguous
definition of 'inductance'. Where's John Woodgate when you really need
him...g.

I'm here today, but I was away all last week. I don't think I can add
much; small air-cored coils have inductance independent of frequency up
to about half the self-resonant frequency, when deviation begins to be
noticeable. 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. Also, it comes in two varieties,
series equivalent and shunt equivalent, and you'd better get the right
one for your problem. As the inductor gets 'worse', at lower
frequencies, the shunt equivalent tends to infinity, which puzzles
students no end.
--
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 Bill Turner
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:
Making a plate choke which covers all frequencies from 160
through 10 meters (including the WARC bands) with sufficient inductance
but without self-resonances in any ham band is difficult to the point of
being nearly impossible. Many amplifier designers give up trying to
design such a choke and simply switch part of the inductance in or out
of the circuit depending on which band is selected.

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. (;-)
--
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 Bill Turner
wrote (in ) about 'Winding
coils', on Sun, 7 Dec 2003:
Making a plate choke which covers all frequencies from 160
through 10 meters (including the WARC bands) with sufficient inductance
but without self-resonances in any ham band is difficult to the point of
being nearly impossible. Many amplifier designers give up trying to
design such a choke and simply switch part of the inductance in or out
of the circuit depending on which band is selected.

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. (;-)
--
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 John Devereux
wrote (in ) about 'Winding coils', on Sun,
7 Dec 2003:
I'm afraid you are using the word "inductance" in a
different way from everyone else

It would be better to say 'equivalent inductance', being the value L -
1/(w^2C). L = true (series equivalent) inductance, C = self-capacitance
(treated as lumped in parallel with L) and w = 2[pi]f = angular
frequency.

Resistance ignored, as irrelevant at this level.
--
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 John Devereux
wrote (in ) about 'Winding coils', on Sun,
7 Dec 2003:
I'm afraid you are using the word "inductance" in a
different way from everyone else

It would be better to say 'equivalent inductance', being the value L -
1/(w^2C). L = true (series equivalent) inductance, C = self-capacitance
(treated as lumped in parallel with L) and w = 2[pi]f = angular
frequency.

Resistance ignored, as irrelevant at this level.
--
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 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!

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!

Bill Turner wrote:

You are speaking in *practical* terms, which is fine. It's true that at
relatively low frequencies, well below the self-resonant point, coils
appear to have constant inductance. No argument there. The discussion
came about because someone asserted that inductance was a constant,
REGARDLESS of frequency, and that is just not true.

I disagree. The inductive component of the impedance remains
essentially constant through resonance. What is non ideal about the
inductor is that it does not exhibit just inductance, but a parallel
combination if inductance and capacitance. Ignoring the capacitance
and calling the effect variable inductance is just not as accurate a
way to describe what is going on.

--
John Popelish