# re: 3/4 wavelength secondaries

Thanks to Richard Hull, Robert W. Stevens, and John H. Couture for their
answers to my query re the subject.

I have snipped all of the above responses since they virtually reiterate
the same ideas, ie., it should be possible to wind a 3/4 wave coil and
make it resonate somewhere near its 3/4 wave frequency, taking into
account its cself, etc.

Richard, I want to do this if its possible. I understand it "should break
out 1/3 of the way up the coil. If it is a standing wave, maybe it won't.

John, I have my own home-brewed program to design coils. It does
approximately what you suggest as far as satisfying the numerous
applicable equations. It uses Wheeler and various other accepted
equations for L, wavelength and frequency.

Robert, I have a coil in which the wire length is "fairly" close to the
1/4 wave resonant frequency. This coil will put out discharges exceeding
36" from a 4.5" insulator on top with only a 1/4-20 screw for the top
terminal. there is also a great amount of corona from the top several
turns of the secondary. Driving power is a 15kv 120ma neon.

Why did I bring this all up?

I have tried to design and wind both 1/4 and 3/4 wave coils to be run
with none or very little terminal capacitance with the idea that given
the same energy delivered to the terminal capacitance, and using the
energy equal to 1/2 cv^2...then decreasing the terminal cap should lead
to increasing the voltage. Although its been a couple of years since I
read Tesla's CSN, I believe he thought he was winding 1/4 wave coils and,
if memory serves, he used very small terminal caps. I understand about
corona and the fact that a toroid should build up the energy before
breakout, but is that really how a TC works? I should not be able to get
36" discharges from a 1/4-20 bolt if that assumption is true.

In any event I do not believe a 1/4 or 3/4 wave coil can be wound in any
"reasonable" configuration. In fact the resonant frequency of 1/4 wave
coils is always about 40% higher than the 1/4 wave wire length and a
toroid must be used to bring in the frequency even taking into account
the increase in cself due to ionization. The resonant frequency of a 3/4
wave coil is always lower than the 3/4 wave wire length so the 3/4 wave
coil cannot be tuned at all. I have tried configurations from 5" to 48"
in diameter and heights up to 190"(absurd, but the program allows it).
I have actually built coils up to 48"x48" just to prove the program and
the designs usually come in close to 10%.

I would certainly appreciate any comments to this and I would especially
like to hear from anyone who has built a 1/4 or 3/4 wave coil that comes
in close to the correct frequency.

Thanks for listening

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