7/11/00                                                   

Helical Coil

I've been wondering, maybe someone can tell me the difference between the different configurations on primary coils. My original coil had a helical configuration. Most of the designs I see these days are Conical and most of the design programs include calculations for Flat coils. Is the Conical coil an attempt to 'focus' the magnetic field from the primary?

Another thing that has been bugging me is that with a conventional configuration: Helical Coil with primary at bottom, aren't we wasting half of the magnetic field from the primary? A little less than half of the field is below the coil and perhaps in the ground doing absolutely no good! Logic would dictate having the primary at the mid-point of the secondary, perhaps grounding a center tap on the secondary. If this were done, would we make the secondary 1/4 or 1/2 Wave of the resonant frequency? Wouldn't we get about twice the output from the same primary? Would RF interference be reduced as the opposite ends of the secondary are 180 degrees out of phase (and would tend to cancel at any distance)? 

Of course the mid-primary configuration would present mechanical problems for the coiler. First, I would think the easiest mounting would be horizontal but it would have to be mounted high off the ground to avoid arcs directly to ground. The most impressive thing to do would be to ground one end of the secondary and have the input power 'floating'. Of course, this would put the primary source at 1/2 of the Tesla coil output voltage!

Anyone have any thoughts on this?