# Quarter Wave Calculations, HELP!!!

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From:  Barton B. Anderson [SMTP:mopar-at-mn.uswest-dot-net]
Sent:  Tuesday, April 14, 1998 11:01 PM
To:  Tesla List
Subject:  Re: Quarter Wave Calculations, HELP!!!

Joshua,

We want the highest voltage possible at the top of the coil (toroid). A quarter
wavelength design permits this (so does a 3/4 wavelength design but takes 3 times the
wire length among several other factors). At the start of a sinewave, we are at max
current and minimum voltage. At the wave's first peak we hit maximum voltage. There
are 4 basic points to a sinewave (2 peaks, 2 zero-crossings), the first peak is 1/4
of the sinewave. Why do we want this? Because of the maximum voltage at the peak. If
we wind our secondary to end at this peak of the tanks resonant frequency's sinewave,
we acheive maximum voltage at the top of the coil.

The length of the secondary winding is derived from the quarter wavelength of the
primary circuits resonant frequency. Wavelength is found by dividing the velocity of
the wave by the frequency of the wave. Since the velocity of a radio wave is the
speed of light or 300,000,000 meters/sec, and because you know your tank circuits
resonant frequency, you can simply divide the velocity by your tanks resonant
freqency and then divide by 4 to find the 1/4 wavelength.

Example:
(assuming a 100KHz resonant tank frequency):

L2 = Secondary Wire Length | V = 300,000,000 | F = 100KHz

L2 = (( V / F ) / 4 ) x 3.28
L2 = ( 300,000,000 / 100KHz ) / 4 ) x 3.28
L2 = 2460 ft

3.28 is a conversion factor for meters into feet.

Hope it helps more than it confuses,
|_Bart_|

Tesla List wrote:

> ----------
> From:  Joshua Resnick [SMTP:seraphim-at-WPI.EDU]
> Sent:  Tuesday, April 14, 1998 12:22 AM
> To:  Tesla List
> Subject:  Quarter Wave Calculations, HELP!!!
>
> List,
>
>         Does anybody have a formula (and the connected reasoning) for calculating
> the quarter wave frequency of a secondary and its associated top
> capacitance.  If you don't know why, I'm still interested in the formula.