Re: Toroid Eddy Current?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Ed Phillips by way of Terry Fritz <twftesla-at-uswest-dot-net>" <evp-at-pacbell-dot-net>

Tesla list wrote:
> 
> Original poster: "Ray Haynes by way of Terry Fritz <twftesla-at-uswest-dot-net>"
<ray.haynes-at-home-dot-com>
> 
> Doesn't the toroid form a single shorted turn that would dampen the
> secondary by lowering the Q? It seems that the toroid is close enough to the
> secondary to have an effect. An interesting test could be performed if
> someone had a working coil with an identical spare toroid. That spare toroid
> could be cut with a band saw radially toward the center stopping couple of
> inches from the middle. Probably 3 or 4 (maybe more) equally spaced cuts
> would be adequate and maybe dabs of epoxy to stabilize the cuts. Then
> install the modified toroid, retune the coil and compare the results with
> the original toroid.
> 
> Maybe I'm off base but I have never seen this discussed and if the Q of the
> material for the secondary coil form matters, seems this just might.
> 
> Ray

	I have measured the inductance and Q of several coils with and without
toroids on top, and the difference was unmeasurable (L<0.1%) with a good
1000 Hz inductance bridge.  Coupling to the "shorted turn" of the toroid
is too loose to make any difference.

Ed