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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 --