Re: Another toroid question

• To: tesla-at-pupman-dot-com
• Subject: Re: Another toroid question
• From: "Barton B. Anderson" <mopar-at-uswest-dot-net> (by way of Terry Fritz <twf-at-verinet-dot-com>)
• Date: Sat, 26 Dec 1998 12:20:58 -0700
• Approved: twf-at-verinet-dot-com

Jon and Ed,

> <big snip>
> Ed,
> Your reply got me thinking of a way to measure the capacitance change when I
> add the second toroid. I worked backwards through the formula, (using
> WinTesla), inputting the change in tuning to arrive at the change in the top
> load capacitance. This roughly gave me the following: When I added the 6 x19
> toroid on top of the 4 x 15.5 one the primary tap changed 1.3 turns. This
> works out to about a 9pf increase in capacitance, a total of 28pf. Does this
> seem right to you? I am going to try attaching the second toroid as you
> have.
> The coil was a big hit with all of our Christmas party guests, (inlaws),
> they were quite impressed!
>
> Jon

Jon, while you were thinking about how to measure, I was thinking about how to
calculate Ed's statement on double toroid capacitance. Ed, I think your right.
Since the upper and lower toroids are both loosing surface area when stacked,
both toroids are affected.  I did a quick calc and it agrees with Jon's
measurement.

Here's what I did (using Jon's data):
Toroid A:  4" x 15.5"
Toroid B:  6" x 19"

I combined cross section diameters and multiplied by 70% = (4 + 6) * 0.7 = 7"
I did the same with the outer diameters = (15.5 + 19) * 0.7 = 24.15"

I now have a simulated toroid of 7" x 24.15" which calculates to 27pF (quite
close to Jon's measurement of 28pF). It can't be this simple, can it?

Bart

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