Re: Tapered Secondary Coil

Tesla List wrote:
> > Subject: Tapered Secondary Coil
> >From bert.hickman-at-aquila-dot-comSat Nov 23 20:04:43 1996
> Date: Sat, 23 Nov 1996 09:35:07 -0800
> From: Bert Hickman <bert.hickman-at-aquila-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: Tapered Secondary Coil
> Tesla List wrote:
> >
> > >From scottb-at-aca.caFri Nov 22 20:30:34 1996
> > Date: Fri, 22 Nov 1996 15:37:04 -0500
> > From: scottb-at-aca.ca
> > To: tesla-at-pupman-dot-com
> > Subject: Tapered Secondary Coil
> >
> > I have seen some secondaries that are tapered, and some that are not.  What
> > (mathematically) is the difference, and what are the effects??
> >
> > /sb
> Scott,
> A tapered secondary (with the larger diameter at the bottom) has
> decreasing inductance per turn as you go higher up the coil. When used
> as a resonator with little or no top-loading (small discharge terminal),
> it exhibits a less well-defined resonant frequency (i.e., lower Q) than
> a constant diameter resonator. The characteristic impedance of a tapered
> resonator also varies with height, being higher Z at the botttom, and
> lower at the top. A tapered resonator also has substantially less
> "lumped" inductance than one with constant diameter (equal to the base).
> A tapered resonator will see less overall resonant rise than a
> constant-diameter resonator of the same height and base-diameter.
> However, it should also be less sensitive to detuning from stray
> capacitance. Because most of the inductance is concentrated in the lower
> half, the voltage stress at the bottom portion is greater than for a
> constant diameter coil.  Addition of significant top-loading capacitance
> should sharpen the tune somewhat, but the resonator will retain its
> distributed parameter (transmission-line) characteristics to a greater
> degree than a constant diameter resonator.
> There appears to be no marked performance advantage in using a tapered
> resonator versus a standard helix in a 2-coil system. However, it sure
> looks different...
> Safe coilin' to you!
> -- Bert --

Bert and all

Has anyone tried to build a tapered resonator and run it upside down,
ie., drive the thing at the small end. Couple of interesting
observations: the top of the coil is self shielding, no toroid is
necessary, the distributed parameters (inductance) may enhance the
voltage rise.

I will build one if someone can give me a reasonable way to do it.