Re: K Quiz

Subject:      Re: K Quiz
       Date:  Tue, 10 Jun 1997 11:41:13 +1200
       From:  "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Organization:  Wellington Polytechnic, NZ
         To:   tesla-at-pupman-dot-com

Hello Mark, all,
                 Following on from Mark's little quiz, I have the 
following query which might relate to something quite important 

> Hello coilers,
>         Here is a little food for thought.
>      "K" is the term applied to the degree of magnetic coupling between
> the
> primary and secondary coils of a conventional tesla coil (or the primary
> and
> driver
> coil in the magnifier configuration).  Typically, we aim for values
> between
> 0.1 and
> 0.25 or so for a conventional tesla coil, and 0.4 or higher for
> magnifier
> primary/driver coil systems.  "M" is the amount of mutual inductance
> between the
> primary and secondary coil.  We define:
> K = M / SQUARE_ROOT [ Lp x Ls ]
> where Lp is the primary inductance, Ls is the secondary inductance,  M
> is the
> mutual inductance, and K is the coefficient of coupling between the two
> coils.
<snip of quiz>

     k itself is relatively easy to measure and quantify. But as far 
as I know, the figure says nothing about _how_ the primary is 
coupling into the secondary. For example, I can score identical k's 
with a flat primary with the same outer dimension as that of the 
resonator when placed below the resonator as I can with a helical 
primary with the resonator sitting inside it (easy). Has anybody 
examined performance issues around the degree of coupling into say, 
just the bottom few turns vs a primary that loosely couples a long 
way up the secondary? I have a gut feeling that this may be a
significant determinant of system performance given the normal high 
secondary Q's and the fact that all else being equal, performance 
for a given power input varies so widely in different systems.