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Re: Toroid = shorted turn ?
Hi Will,
> Original Poster: "Payne, Will E" <will.e.payne-at-lmco-dot-com>
>
> Most large top loads and especially toroids I have seen are conductive all
> the way 'round, which forms a shorted turn above the top of the coil. The
> induced EMF would create a repulsive field cancelling the ringup field, in
> effect "shading" the upper end of the secondary and wasting energy.
>
> Some coilers believe this is not a significant effect, but I remain
> skeptical. Coil behavior is pretty sensitive to the spacing between the top
> winding and the toroid, although I realize other effects are also at work
> here. I tried to insulate the joints of my stovepipe toroid and connect
> each section together at the center. The voltage at the joints would be no
> more than a hundred volts, I think. Since my joint insulation did not
> survive the assembly process, and I have plenty of more important things to
> optimize, my experiment may have to wait for the next toroid. However, I
> would like to hear from anyone else who has investigated this.
I have. If you measure the inductance of a coil with and without a
toroid on top the difference will be close to zilch. I once thought
the same as you. BTW, if the ring is a near perfect conductor, it
shouldn't absorb much energy at all. In fact, toploading the coil
does something even more dramatic, shorted turn or not. Up to a
certain size, it actually increases the Q of the coil as the top
turns are dragged into passing current. Now what was all that about
uniform coil currents??
You can gauge the effects of mutual coupling and its importance
or lack thereof for yourself by taking an unwanted resonator, cutting
the winding midway, and doing one of the standard tests for measuring
M and k. It is worth doing and gives some valuable insights into the
part coupling plays in resonator action.
Malcolm