On Fri, 05 Dec 2003 08:38:18 -0800, Bill Turner
wrote:

As you may know, the inductance of a coil is not a fixed value, but
varies dramatically with frequency.

Er, you mean *reactance* of a coil varies dramatically with frequency,
don't you?
--

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

On Sat, 06 Dec 2003 13:09:02 -0800, Bill Turner wrote:

On Sat, 06 Dec 2003 18:39:18 +0000, Paul Burridge
wrote:

As you may know, the inductance of a coil is not a fixed value, but
varies dramatically with frequency.

Er, you mean *reactance* of a coil varies dramatically with frequency,
don't you?

_________________________________________________ ________

Er, no I don't. They both vary with frequency.

If the inductance did NOT vary with frequency, the X sub L vs F plot
would be linear. In reality, it is anything but linear.

X sub L is inductive reactance, yes that varies with freq.
L is the fixed value inductance.

though there is some parasitic capacitance between windings that does effect the
resonant freq. a bit. www.coilcraft.com gives guidelines to this.





Remove "HeadFromButt", before replying by email.

On Sat, 06 Dec 2003 13:09:02 -0800, Bill Turner wrote:

On Sat, 06 Dec 2003 18:39:18 +0000, Paul Burridge
wrote:

As you may know, the inductance of a coil is not a fixed value, but
varies dramatically with frequency.

Er, you mean *reactance* of a coil varies dramatically with frequency,
don't you?

_________________________________________________ ________

Er, no I don't. They both vary with frequency.

If the inductance did NOT vary with frequency, the X sub L vs F plot
would be linear. In reality, it is anything but linear.

X sub L is inductive reactance, yes that varies with freq.
L is the fixed value inductance.

though there is some parasitic capacitance between windings that does effect the
resonant freq. a bit. www.coilcraft.com gives guidelines to this.





Remove "HeadFromButt", before replying by email.

Bill Turner wrote...

Er, no I don't. They both vary with frequency.

If the inductance did NOT vary with frequency, the X sub L
vs F plot would be linear. In reality, it is anything but linear.

We're talking a small air-coil here. As SRF is approached the
reactance does depart from the expected linear plot, but that's
because one should have considered X_C as well. Say, you're not
talking about an exotic high-frequency region where the physical
diameter of a coil may drop slightly due to proximity effect?
Sheesh!

Thanks,
- Win

whill_at_picovolt-dot-com

Bill Turner wrote...

Er, no I don't. They both vary with frequency.

If the inductance did NOT vary with frequency, the X sub L
vs F plot would be linear. In reality, it is anything but linear.

We're talking a small air-coil here. As SRF is approached the
reactance does depart from the expected linear plot, but that's
because one should have considered X_C as well. Say, you're not
talking about an exotic high-frequency region where the physical
diameter of a coil may drop slightly due to proximity effect?
Sheesh!

Thanks,
- Win

whill_at_picovolt-dot-com

On Sat, 06 Dec 2003 13:09:02 -0800, Bill Turner
wrote:

On Sat, 06 Dec 2003 18:39:18 +0000, Paul Burridge
wrote:

As you may know, the inductance of a coil is not a fixed value, but
varies dramatically with frequency.

Er, you mean *reactance* of a coil varies dramatically with frequency,
don't you?

_________________________________________________ ________

Er, no I don't. They both vary with frequency.

If the inductance did NOT vary with frequency, the X sub L vs F plot
would be linear. In reality, it is anything but linear.

I'm still none the wiser. Unless you're taking into account stray
inductance from the leads, of course. But the *body* of the inductor
by itself must surely be of a fixed inductance. One does not come
across coils rated at "3uH @ 150Mhz.", for example!
Are you talking about the impact of stray L from the lead-lengths?

--

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

On Sat, 06 Dec 2003 13:09:02 -0800, Bill Turner
wrote:

On Sat, 06 Dec 2003 18:39:18 +0000, Paul Burridge
wrote:

As you may know, the inductance of a coil is not a fixed value, but
varies dramatically with frequency.

Er, you mean *reactance* of a coil varies dramatically with frequency,
don't you?

_________________________________________________ ________

Er, no I don't. They both vary with frequency.

If the inductance did NOT vary with frequency, the X sub L vs F plot
would be linear. In reality, it is anything but linear.

I'm still none the wiser. Unless you're taking into account stray
inductance from the leads, of course. But the *body* of the inductor
by itself must surely be of a fixed inductance. One does not come
across coils rated at "3uH @ 150Mhz.", for example!
Are you talking about the impact of stray L from the lead-lengths?

--

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

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?


--

John Devereux

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?


--

John Devereux

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.

--
Terry Pinnell
Hobbyist, West Sussex, UK