Re: LC and misc.

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Jared,

On 31 Jul 2005, at 20:36, Tesla list wrote:

> Original poster: Jared E Dwarshuis <jdwarshui@xxxxxxxxx>
>
> Hi: Gerry
> From: Jared
>
> I would agree that a coil with little or no top end would make a
> rather poor coil.
>
> There is a design compromise involved between maximizing inductance
> while still retaining a respectable top end. Mainly its the Medhurst
> capacitance that eats you alive with the stubby coils.
>
> Where is the perfect H/D for a quarter wave? I dont know!. But I would
> be willing to bet that Dr. Resonance has gotten pretty close to it by
> emperical means.

Knowing that you can use Medhurst and Wheeler as useful
approximations of the dynamic reactive components in a resonator you
can arrive at (mutually exclusive) optimal values depending on what
your target is. Conclusions I reached from doing the exercise for a
normal 1/4 wave upright resonator were:

- maximum inductance for a given length of wire; h/d = 0.6 or
thereabouts, closewound

- maximum resonator Q; h/d = 1, spacewound or Litz

- highest L/C ratio; h/d = 3, closewound

- best compromise for a TC secondary (where voltage standoff
matters); h/d = 5

Cmed hits a minimum for an aspect ratio of about or a bit less than 1
if coil diameter is held constant. It climbs fairly linearly for
2 < h/d < 5 and then climbs substantially faster and also climbs as
h/d drops below 1.

Malcolm