Re: Why tesla coil is air-cored to operate efficiently at high freq?

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "D.C. Cox" <resonance@xxxxxxxxxx>


It's all about time.  It requires a finite period of time to 
magnetize an iron core, and at high frequencies this time period is 
too long, so RF coils work better without a core.  This effect will 
be covered in detail in my forthcoming book, "Tesla's Marvelous 
Transformer:  The Tesla Coil, which I am presently hard at work 
on.  It looks like approx 650 pages when I finish it with a lot of 
drawings, figures, and photographs.

I believe the "swinging" action you are referring to is the rapid 
transfer of charge from the capacitor to inductor in a tank 
circuit.  Another type of "swinging" transfer occurs between the 
primary and secondary circuits as energy is swapped back and 
forth.  This is indesireable and that's why efficient quenching (turn 
off) of the spark gap is necessary --- to prevent this type of 
action.  Ideally, all energy is transferred to the sec coil in the 
first burst.  In most classic TC oscillators it usually requires 2 to 
2.5 pri-sec swaps to get all the energy in the sec coil.  Energy is 
wasted. That's why the solid state coils are so much more efficient 
--- the IGBTs can turn off rapidly and trap the energy in the sec coil.

Dr. Resonance





> I have three theoretical questions here:
>
>
> I read this from a website: "A normal transformer users an iron core 
> in order to operate at low frequencies, whereas the Tesla Coil is 
> air-cored to operate efficiently at much higher frequencies".
>
>
>
> I understand that a normal transformer relies on turn ratios and the 
> air core is there to reinforce the magnetic flux.
>
>
>
> May I then ask, why is an iron core only required in low frequency 
> operation and why do we use an air-core for high frequency operation?
>
>
> Lastly, I read this from another website: " In the Tesla "swing", 
> the kick is supplied by the AC electrical current moving back and 
> forth". Can someone elaborate on this please? Is it actually 
> referring to the LC circuit - both the secondary and primary 
> operating at the same frequency that reinforce each other?
>
>
>
> Thank you very much for your kind attention.
>
>
> Regards
> Sam