Re: Tesla coil formula

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: Steve Conner <steve@xxxxxxxxxxxx>

>you have to effectively introduce a fiddle factor

I agree. I spent a long time staring at Jared's wire length equations 
trying to figure out if they were saying something new. Eventually I 
came to the same conclusion as Malcolm did, about the fiddle factor.

What Jared does is to work out the quarter wave resonance frequency 
of a given length of wire. Of course, when he makes it into a Tesla 
resonator, it doesn't resonate anywhere near that frequency, so he 
adds terminal capacitance until it does. He then seems to claim that 
there is something magic about that terminal capacitance, and the 
alignment of the operating frequency with the quarter wave frequency 
of the straight wire, that makes good performance.

Both theory and experiment are against him on this count. We predict- 
and find in practice- that the best terminal capacitance to use is 
just the biggest that you can drive to about its breakout voltage, u 
sing the tank capacitors and power supply you have available. 
However, if you make the toroid too big compared to the secondary 
coil, the secondary will be overstressed by voltage and die from 
racing sparks and flashovers before you achieve the spark length you 
should be getting.

Finally, even a straight piece of wire doesn't resonate at exactly 
the frequency predicted by the "rope resonance" equation, using the 
speed of light as the wave velocity. When you make a wire antenna, it 
turns out the effective speed of "light" is slightly lower than "c" 
and you have to cut it slightly shorter for resonance. IIRC the 
required length of a half-wave dipole is about 468/f, for length in 
feet and frequency in megahertz.

Steve Conner
http://www.scopeboy.com/