RE: Bart's Coil

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

Original poster: "Malcolm Watts by way of Terry Fritz <twftesla-at-qwest-dot-net>" <m.j.watts-at-massey.ac.nz>

Hi John,
         Now I'm a little surprised:

On 28 Nov 2001, at 19:47, Tesla list wrote:

> Original poster: "John H. Couture by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <couturejh-at-mgte-dot-com>
> 
> 
> Malcolm -
> 
> The test frequency is not arbitrarily chosen. The bare secondary of Bart's
> coil has three "resonant" frequencies. One is the natural resonant frequency
> (114.56) with the coil self capacity that you can calculate or obtain using
> one of those famous TC Design programs. There are two other frequencies
> (68.493 and 69.444) that vary when the coupling between the secondary and
> primary is changed. There is much more to this unsolved TC problem that is
> not mentioned in any textbooks.

I would have expected the side-frequencies to be sitting either side 
of the 114.56kHz. They have been every time I've measured coupling 
that way. I'm not surprised there appears to be no relation between 
the side-frequencies and the 114.56kHz. I will have to revisit the 
posts on this topic to see how the tests were done. My fault for 
being lazy.
 
> My question - At the design stage the natural resonant frequency can be
> determined. How do you determine the other two frequencies at the design
> stage? What is the "theoretical"? relationship between these three
> frequencies? The secondary is unchanged for two of the frequencies, 114.56
> and 68.493, no toroids or shorts!

I believe you already gave the formula relating k and Fo to Fhi and 
Flo. That is the only relationship I'm aware of it. It's been known 
for decades.
 
> If you are going to make these tests use smaller coils and tighter
> couplings. The frequencies will be farther apart and easier to read. Refer
> to the graph mentioned in a previous post.

Will do.

Regards,
Malcolm