# Re: Redesigning/tuning a coil

```Original poster: "john cooper" <tesla-at-tesla-coil-dot-com>

Maybe I've a poor understanding of this but I've been laboring under the
impression that the sloped primary allows for a stronger coupling of the
prim to sec as it reduces the distance from those outside turns to the
sec.  It seems to me that the sloped prim may also 'shape the field'
somewhat or better direct it towards the sec.  My memory tells me that the
electric field diminishes as an inverse square function with respect to
distance, and that mag fields fall at an inverse cubed or 4th?  If a
tighter coupling than a flat prim would provide is not beneficial to a
particular coil then I can see that it wouldn't be of much use.  Have I got
this all wrong, partly wrong?  I think I probably need to spend some
quality time with 'Electromagnetic Waves and Radiating Systems' by Edward
C. Jordan/Keith G. Balman to brush up on the basics.  Hmmmmm.

---------- Original Message ----------------------------------
From: "Tesla list" <tesla-at-pupman-dot-com>
Date:  Mon, 19 Apr 2004 21:31:13 -0600

>Original poster: "Antonio Carlos M. de Queiroz" <acmq-at-compuland-dot-com.br>
>
>Tesla list wrote:
> >
> > Original poster: "john cooper" <tesla-at-tesla-coil-dot-com>
> >
> > Regarding the primary angle:  I ran through that experiment on my largest
> > coil a few years ago and 18 degrees of slope was the maximum allowable
> > primary slope on that coil.  Primary is about 19 turns of 1/4" cu and I
> > believe it was tapped at 17 turns.  1 degree over that 18 and the primary
> > field wouldn't cover the top of the secondary and, believe me, you could
> > tell where it was hitting the secondary, an inch or two below the top
> > turn.
>
>(?!) This magnetic field is working in a quite unusual way. The
>exact distribution of the magnetic field along the secondary coil
>doesn't have any particular importance. What matters is
>the coupling between the coils. Excessive inclination can
>result in excessive proximity between the coils, and problems with
>the electric field along the secondary coil, causing "racing sparks"
>along the secondary coil and primary-secondary sparks. Nothing related
>directly with the magnetic field.
>
>I don't see any reason for the use of inclinated primary coils. A
>flat coil generates adequate coupling and is easier to build.
>
>Antonio Carlos M. de Queiroz
>

```