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Re: Top Load Optimizing - Q?

Hi Jim,

> Original Poster: "Jim Firanzi" <teslacoiler-at-mad.scientist-dot-com> 
> 
> In a well-written article, Rodney posted the following:
> 
> "The main concept with top-load design is matching it to the secondary coil.
> With capacitive/reactive tuned circuits, the way to obtain zero impedance is
> to match your capacitive reactance with the inductive reactance."  The
> complete article may be viewed here:
> 
> http://www.geocities-dot-com/ResearchTriangle/Campus/9367/tuning.html
> 
> He goes on to calculate capacitive reactance of the torroid top load, and
> states that the goal is to design your top load so that this capacitive
> reactance cancells out the native inductive reactance of the secondary.  He
> goes on to make the following statement:

A comment:  Personally that "cancellation" bit rubs the wrong way 
with me. Why?  They only cancel at one frequency and that 
frequency can be anything below the self-resonant frequnecy that 
you choose.  Calculating the capacitance (or reactance at some 
particular frequency) of a topload as if it were isolated and then 
expecting that figure to match reality when it is mounted on a coil is 
utterly futile according to experiment. Even reason cannot sustain 
that view.
 
> "The secondary coil is best described as an air-core inductor ? for that
> matter, any coil of wire is known as an inductor. As capacitors have
> capacitive reactance, inductors have *inductive* reactance.  The formula for
> calculating the inductive reactance of your secondary coil is  X(L) = 2 * Pi
> *  F * L ..."

It is a resonant structure in its own right (i.e. it does possess a self 
capacitance). In calling a coil an inductor one is generally 
describing its properties way below its self-resonant frequency. 

> My question is this:  Programs like Wintesla calculate both the inductive
> reactance of a secondary AS WELL AS the native capacitance of that
> secondary.  Should I attempt to design my coil such that total capacitive
> reactance (secondary + toroid) cancells out the inductive reactance?  Or do
> we ignore the native capacitance of the secondary?

You can't - it's there to stay unfortunately.

Regards,
Malcolm
 
> It's not the size of the spark, it's the frequency.
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