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0.5*C*V*V vaild? (Was Output Voltages and Voltage/Length)


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From:  Mark S. Rzeszotarski, Ph.D. [SMTP:msr7-at-po.cwru.edu]
Sent:  Monday, February 09, 1998 1:46 AM
To:  Tesla List
Subject:  Re: 0.5*C*V*V vaild?  (Was Output Voltages and Voltage/Length)

Hello All,
        I said in part:
<snip>
>  I have also built a series of tesla coils with back-to-back
>LED's placed every 2 inches along the length of the coil with various H/D
>configurations to examine the voltage rise in these rather heavily damped
>coil systems.  Several observations are notable:
>1.  The voltage distribution goes from a minimum at the base to a maximum at
>the top when tuned to the quarter wavelength of the coil system, even in a
>damped coil system.
        And yes, this means that the LED's are brightest at the base of the
coil, and dim or off at the top of the coil, indicating maximum current at
the base and minimum current at the top.  The LED's are connected
back-to-back and are current monitoring devices.  The primary voltage
induces a secondary current via the mutual inductance between the primary
and secondary coils.  This current at the base of the secondary coil is
hopefully a maximum.  If a standing wave is established on the secondary,
the current will be a maximum at the base, and a minimum at the top of the
coil.  The voltage distribution will be zero at the base (due to the RF
ground), and a maximum at the top of the coil if the coil is operated at its
electrical 1/4 wavelength.  
          The LED's are highly nonlinear, and drop the Q of the coil
significantly.  Nonetheless, the current distribution at resonance is easily
seen.  The voltage distribution must be inferred from the current
distribution.  One can demonstrate half wave and higher harmonic standing
waves with H/D ratios as low as 1:1, although it is better seen on the 3:1
or 4:1 coils.
        The 8.4 kV/inch rule of thumb comes from an average of several
literature references for RF voltage sources in the kilohertz range.  D.C.'s
8.6 kV/inch is close enough.
        The best sources on helical resonators are written by the Corum
brothers, but there are a few things left out of the analysis here and there.
Regards,
Mark S. Rzeszotarski, Ph.D.