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Re: That secondary behaviour, E-Tesla5, and Corum's thing...

Hi Antonio,

At 11:56 PM 04/15/2000 -0300, you wrote:
>Hi:
>
>Apparently now we all agree that a lumped model models very well
>what happens up to the first resonance or a coil. 

I think we have pretty much decided that!  Whew!

>
>Since several of you are now playing with coil resonances, I can
>return to a topic that I mentioned a few times in the past:
>
>A long vertical coil is a rather nonuniform transmission line.
>An ideal transmission line would have resonances at frequencies
>f0, 3f0, 5f0, 7f0,... My experiments with coils indicate that
>the resonances of a typical coil appear shifted to low frequency
>in relation to what would appear in an ideal transmission line.
>Can someone verify this?

What height to width ratio would you be interested in?  My coils are pretty
conventional but perhaps I could dig something up.  I think the lower
harmonic frequencies are caused by the fact that the very top of the coil
looks like a capacitor since it charges the large area at the top of the
coil.  That's why the graph below is distorted at the top of the coil
(right side of the graph with height being the x axis:

http://users.better-dot-org/tfritz/VoltDistBare.jpg

E-Tesla5 used to have trouble with bare coils until I programmed in the
corresponding voltage distribution for this and that fixed it right up.

I would suspect that a very long thin (like 4 feet long 1 inch dia) coil
would have a very small top capacitance and hit the Fo, 3Fo, ...
frequencies much more accurately.  Is that what you are trying to check?

>
>Another curious experiment is to see what happens with the extra
>resonances with a terminal is added to the coil. The first resonance
>goes to lower frequency, as expected, but the other resonances also
>shift to lower frequency. In an ideal transmission line, they would
>approach 2f0, 4f0, 6f0,..., where f0 is the frequency of the first
>resonance without terminal. The reason is that the coil starts to
>behave as if the terminal end were grounded, by effect of the
>terminal capacitance.

I have some big terminals :-)  I'll see what I can come up with.  My
longest coil is only 6.14 aspect ratio.  Would that work or does it REALLY
need to be long and thin?

Cheers,

	Terry

>
>Antonio Carlos M. de Queiroz
>
References: