Re: Proposed capacitive transformer TC?

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

Original poster: "Jolyon Vater Cox by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jolyon-at-vatercox.freeserve.co.uk>

Is C1 formed between the electric induction plane and the ground plane -or
will supplementary capacitor need to be connected?

What is the function of L1 and why is it necessary-  is it  to resonate with
C1 perhaps? I am asking because  I envisaged the device I was describing as
a capacitive autotransformer like a pi-tank or the tank circuit of a
Colpitts oscillator (albeit without the feedback arrangements)

Coupling is capacitive. Would it not be possible -in theory at least- to
vary the coupling by varying the distance from the induction plane to the
ground plane and topload without changing the ratio of C1 to C2 -although I
surmise this would affect the resonant frequency somewhat.

Finally, could it be that the real advantages of this form of TC would be
towards the higher end of the RF spectrum when coils are much smaller and
more difficult to adjust than they are at low frequencies?

From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, July 28, 2002 4:26 AM
Subject: Re: Proposed capacitive transformer TC?


> 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>
>
> > I am aware that some sort of "feed plane" between the topload and ground
> plane
> > (and capacitively coupled to both) would be required and it would have
to be
> > designed so that it did not unduly interfere with the magnetic field
> generated
> > by the "secondary" coil (L1) -not a correct definition as there would be
no
> > "primary" and therefore no inductive coupling.
>
> Maybe just an insulated metal plate under the secondary coil, as a
> ground
> plane, but not connected to ground. The plate shall have a hole in the
> center for the base of the secondary (grounded), and may have a section
> cut away to avoid the formation of a single turn around (under) the
> secondary.
>
> > The feed plane would of course have to be fed with RF either from a
generator
> > or a from a spark-gap.
> >
> > I am thinking of starting small to test the concept without entailing
excess
> > cost e.g.. so am considering building a "mini-coil" using 40SWG wire on
a
> > plastic vitamin pill container for L1 and a flyback transformer to fire
a
> > spark-gap connected between the ground and the feed plane which might be
a
> > horizontally-mounted metal sheet a central hole big enough for the coil
to
> > stand vertically within it without actually touching the metal sheet. Or
> maybe
> > the feedplane could be a non-inductive coil surrounding L1 and connected
> > between the PSU and the spark-gap with the insulated wire double-backed
> so that
> > the magnetic fields cancel leaving only the electric field to interact
> with L1,
> > the output inductor.
> >
> > If the proposed device were constructed, is it at all likely that there
would
> > be enough capacitive coupling between the feedplane/ground capacitor C1
> and the
> > parallel-resonant circuit L1-C2-C1 to allow sufficient energy to be
> transferred
> > from the former to the latter for the production of sparks or streamers?
> >
> > Finally, would it permissible for me to submit *.jpeg or *.bmp images of
the
> > device to the TCML for further reference and comment?
>
> Use ascii art, or put the pictures somewhere in the web and post the
> links.
>
> The system can surely be built, but two coils are needed. The schematic
> diagram may be as:
>
>                      (=====) Terminal
>                         |
>                         L2
>                         |
>  o------+--L1--+-----===|=== Electric induction plane
>         o      |        |
> PSU    gap     C1       |
>         o      |        |
>  o------+------+--------+--o Ground
>
> L1 is not magnetically coupled (significantly) to L2. A
> capacitor C2 is formed between the induction plane and
> the body of L2 and the terminal.
> A lumped model for this circuit is:
>
>  o------+--L1--+--C2--+
>         o      |      |
> PSU    gap     C1     L2
>         o      |      |
>  o------+------+------+--o Ground
>
> Interchanging L1-C1 and L2-C2, what doesn't make diference
> once the gap fires, shows that the circuit is equivalent to the
> directly coupled Tesla coil that I described some days ago.
>
> I can easily modify my system to this configuration and see
> what happens.
>
> This system has an inconvenience: It's not possible to choose
> independently the equivalent of the coupling coefficient in
> a Tesla transformer and the voltage gain. The maximum voltage
> gain with reasonable coupling appears to be around 20. My system
> is tuned to 9.53, and works.
>
> Antonio Carlos M. de Queiroz
>
>
>
>
>