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Re: Copper Banding?

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

On 28 Feb 2005, at 19:56, Tesla list wrote:

> Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>
> Tesla list wrote:
> >Original poster: Kurt Schraner <k.schraner@xxxxxxxxxxx>
> >Hi David, Scott D,
> >well, the effect is _real_, and not a matter of words only. Let me
> >remind a former posting, where a comparison of measured vs.
> >calculated L values has been shown, at:
> >http://www.pupman.com/listarchives/2004/October/msg00018.html I
> >didn't yet get an answer, explaining in easy to understand physical
> >reasoning, about the difference. Might be, it can be interpreted, by
> >way of a higher interturn capacitance in ribbon primaries, than
> >"wire" spirals of the same planar geometry, counteracting the
> >inductance? Regards,
> >           Kurt Schraner
> >Tesla list schrieb:
> >
> >>Original poster: "david baehr" <dfb25@xxxxxxxxxxx>
> >>
> >>In a previouse post, it was stated that a banded pri. would have
> >>less inductance than a copper tubing pri. Could someone explain this
> >>? IF YA got 50' of copper tubing , and 50' of banded pri. , wouldnt
> >>be about the same ????????////
> The reason is that a flat spiral made with tape acts as a stack of
> coupled filamental coils. If the coupling were unitary, the inductance
> would be the same of a single filament. But as the coupling between
> distant filaments is smaller than one, the inductance decreases.
> Consider for example two parallel filamental coils with inductance L.
> If they are at small distance, they act as a single coil with
> inductance L. If they are far apart, the coupling between them is
> insignificant, and the total inductance falls to L/2.
> Antonio Carlos M. de Queiroz

I recall a diagram from long ago when I researched the skin effect
which show the current density in a copper tape as being at a maximum
at the edges and a minimum in the centre. There is the separation of
the parallel inductors.