Re: Coupling constant for 4.25" secondary

>>What I would like to ask is, for other coilers using 4.25" secondaries,
>>what values of k have you achieved?
>>Gary Lau
>>Waltham, MA USA

>Original Poster: "Dr. Resonance" <Dr.Resonance-at-next-wave-dot-net> 
>With small coils systems the best way to achieve a high coeff of coupling
>(0.18 to 0.20) is to use edge wound copper strap which allows for a very
>high density as opposed to copper tubing or wire.  We usually hit 0.18 with
>our smaller systems and this is with a flat spiral configuration using
>edgewound copper strap --- usually 5/8 inch wide.  It works for us.

Hi Dr. Resonance

Thanks for the tip.  This was something I was wondering about - primary
geometry vs coupling.  A while back, there was a brief thread about using
two-layer primaries.  It sounds like both the edge-wound and two layer
techniques achieve the same thing - concentrating the primary in a
smaller volume, and presumably, that achieves a higher k.  I assume that
some kind of insulation is necessary between strap turns, and that
varying the tap point is somewhat less straightforward than with tubing.
I may opt for the two-layer approach (since I don't have a source of
copper ribbon), and I'll probably make a dry run using just some 22AWG
wire to test the inductance and k before building the real thing.  I
assume wire gauge won't affect L and k if the spacing is like the final
version.  It may be a while before I get to this, but I'd be interested
if anyone has pictures on-line of either ribbon or two-layer primaries.

Gary Lau
Waltham, MA USA