Re: Capacitive transformer Tesla coil

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

Original poster: "Antonio Carlos M. de Queiroz by way of Terry Fritz <twftesla-at-qwest-dot-net>" <acmq-at-compuland-dot-com.br>

Tesla list wrote:
> 
> Original poster: "Jolyon Vater Cox by way of Terry Fritz
<twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>
> 
> Antonio,
> I have been thinking about those primary coils myself re. how much
> capacitance from the topload do they intercept -especially the wider flat
> "pancake" and "conical" types of primary.
> 
> Since with the CCTC the primary is replaced by the influence plane the
> coupling will be greater as the plane is made wider or more enclosing
> because it will intercept more of the topload capacitance increasing C2 and
> decreasing C3. Is this not also true with inductively-coupled TCs which use
> flat or conical primaries?

Things are more complex with inductive coupling. The distance between
the windings is important, but the covering of the ground plane by a
flat winding is not so. Flat primaries, with a constant number of 
turns, have maximum coupling for a certain diameter.
 
> Also with regard inductively-coupled TCs where if I am correct tuning and
> coupling are traditionally considered independent, is this really true, for
> instance, when tapped primaries are used with different capacitors to
> "match" the same secondary. Surely, as the number of primary turns changes
> so does the coupling ie. more turns= more coupling, fewer turns = less
> coupling, unless I am mistaken.

Yes, the tuning affects the coupling too. The coupling can be readjusted
by changing the height of the secondary (But this changes the
capacitance between primary and secondary, and changes the tuning a
bit).
It's easy to reach the correct point by successive adjustments.
 
> Would it not be possible to use a variable capacitor between C1-L1 and the
> influence plane to vary the coupling without affecting the frequency unduly?

Yes. The antenna in my prototype is a variable capacitor between the 
terminal and the induction plane, that is something equivalent. A
variable capacitor between L1-C1 and the plane would turn the effect
of the capacitance between the plane and the ground apparent, reducing
the coupling.

> Finally, as the topology of the influence plane is developed to minimise
> C3 -from a flat plane through a cone and finally a cylinder or sphere
> doesn't the plane become nore like a waveguide to some extent?

The involved frequencies are too small for the size of the apparatus.
The device would act as just a lumped capacitor.

Antonio Carlos M. de Queiroz