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Re: Toroid Eddy Current?

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Ray,

I think there are three factors at work that diminish the shorted turn
effect for toroids.

1.  The coupling is not real high.  I used MandKV31 (coupling calculation
program*) to find the coupling for a 22 inch C-C toroid with an 8 inch cord
that was 10 inches above a 30 inch long 10.25 Dia. secondary with 1000
turns.  The coupling was only 0.028.


2.  Toroids are not real good conductors.  Corregated dryer pipe and other
aluminum materials are faily resistive to RF currents.  Not sure how much
difference that makes but...

3.  There is not much current near the top of the coil.  As Paul's TSSP
project and my tests have shown.**  Thus, there is not a lot of nearby
current to couple to the toroid.


I think all three of these have some affect and add up to only a small Eddy
current effect from the toroid.  The actual numbers and all are a bit fuzzy
but it could probably all be figured out with a fair amount of precision.



At 09:58 PM 5/13/2001 -0700, you wrote:
>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.