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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 |
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