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Re: 3/4 wavelength secondaries

Tesla List wrote:
> 
> >From MALCOLM-at-directorate.wnp.ac.nzWed Jul 31 21:52:24 1996
> Date: Thu, 1 Aug 1996 13:33:07 +1200
> From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> To: tesla-at-pupman-dot-com
> Subject: Re: 3/4 wavelength secondaries
> 
> Hi Ed Phillips, all,
> 
> > Question: Why the interest in free-space wirelength?
> >     There have been a lot of listings here lately in
> > which it appears that the author thinks there is something
> > "magic" about having the coil operate near the free-space
> > quarter-wave resonant frequency of the winding.  I can't see
> > what difference this really makes, as long as the coil is
> > excited at the correct resonant frequency as determined by
> > self and lumped (top terminal) capacitance.  Am I missing
> > something?
> >     One other point.  Although I don't remember seeing
> > it expressed explicitly, the effects of a top toroid are
> > at least twofold:
> > 1. The L/C ratio of the secondary is lowered, reducing its
> > surge impedance and hence the loss of Q for a given power
> > lost in discharge.  Seems to me this should increase the current
> > when the discharge starts.
> > 2. The breakdown voltage is increased, increasing the formation
> > of the streamers which finally carry current when breakdown
> > occurs.  In the case of one of my small coils, this effect takes
> > seconds.
> 
> I think Skip said that he found he was getting longer and longer
> discharges the closer he got to matching the wirelength with
> fr. Am I right Skip? There is another possibility too. Skip, are the
> best coils the biggest? If so, it may be that you are also getting
> benefits from maximising the radius of curvature of the system. I
> know Tesla mentioned this frequently and I think stated that he could
> build coils with no corona leakage if the r.o.c. was maximised.
> 
> Justapossibility,
> Malcolm

Hi Ed, Malcolm and all

Yes, as my coils have grown in diameter, the discharge length has grown . 
I have attributed this to the increase in Lp and Cself which in effect 
lowers the resonant frequency of the secondary and brings it closer to 
the 1/4 wave wire length. I have tried to use a similar length of wire so 
the secondaries have also grown shorter. The most recent is only 30" high 
and I don't know what my next step will be. That is one of the major 
reasons I posted this whole 1/4,  3/4 business to the list. An obvious 
answer is to use a flat spiral secondary, as I believe Tesla envisioned, 
to raise the Lp to the highest value, but I can't figure out how to build 
it.

Oh well, tomorrow is another day

Skip