Inductance and K

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "sundog by way of Terry Fritz <teslalist-at-qwest-dot-net>" <sundog-at-timeship-dot-net>

Hi All,

   Fiddling with my VTTC over the weekend, I remembered an old trick used 
by amateur radio operators to tune their setup.

   You have a length of PVC pipe, usually 8" or so.  There's 2 sets of 
windings on it, with ~1.25" spacing between them (center of the 8" 
form).  Inside the form, there's a shorter section of 4" PVC with windings 
on it also.  The inner coils are placed in series with the outer coils, and 
the whole thing is put in series with the circuit to be tuned.

   When the inside form is at 90 degrees to the windings, the mutual 
inductance is lowest, and as it approaches parallel to the outside 
windings, the mutual inductance is the greatest.

  My question...

    Suppose I put a 10 turn primary, tightly coupled to the 
secondary.  Then I put a similar variable inductor in series with it (off 
axis and away from the primary).  This will give me a lot of freedom to 
tune the system as it's running, but how does it affect K?  Will I have to 
move the primary physically closer to the secondary to get the same 
coupling if I add the off-axis variable inductor?  Will I see a change in K 
as I vary the inductance of the primary?

I ask this because it would seem to be a lot easier for VTTC coilers to 
build something along these lines vs obtaining a variable air cap and 
submerging it in oil.   I'm just wondering how the added inductance that's 
not coupled to the secondary will affect K.

Thanks!

Shad

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Shad (Sundog)
G-5 #1373
"Ever stop to think, and forget to start again?"
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