Re: Quarter Wavelength Frequency

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Gerry Reynolds" <gerryreynolds-at-earthlink-dot-net> 

Hi DC,

This is very good information for all.  The problem I'm defining is not
overcoupling but out of tune.  I think I'm gaining some insight into this
from what you say by considering both the forced and natural resonses of the
coil.
Thankyou for your response.

Gerry R.

 > Original poster: "Dr. Resonance" <resonance-at-jvlnet-dot-com>
 >
 >
 > Racing sparks usually result from overcoupling.
 >
 > In coils with small toploads this can occur due to the fact two different
 > frequencies are in operation simultaneously.  This means a 1/4 wavelength
 > appears up the coil for each of the two different frequencies and the high
 > potential is developed at two different locations.  The two freqs beat
 > against each other and produce a third beatnote freq.  The beats also
 > develop due to the smaller resonances along the coil which can beat
against
 > the principle freq which again leads to uneven potentials developing along
 > the coil length.
 >
 > The best cure for these problems include using a large topload as the
large
 > capacitance forces max potential development at a single freq and helps to
 > minimize the small minor freqs.  Usually with proper coeff. of coupling
and
 > a topload at least twice the dia. of the sec inductor "racing sparks" do
not
 > develop.
 >
 > For 4-6 inch dia. coils with 1,200 to 1,400 turns the sec winding should
 > start approximately 1.5 - 2.0 inches above the primary horizontal plane.
 >
 > 10-12 inch coils should use 3.5 inch elevation while 7 inches work best
for
 > 18 inch dia. sec.
 >
 > A 24 inch dia. sec needs to have the winding start at 9 inches above the
pri
 > horizontal plane.
 >
 > Many experimenters have ignored this information or are unaware of it
which
 > leads to the "racing spark" problems that are usually associated with
 > overcoupling.
 >
 > Dr. Resonance
 >
 >  >
 >  > It did seem like he was saying there would be two resonances.  The "1/4
 >  > wave" resonance (if we choose to use this name) must then refer to what
 >  > resembles a standing wave in the distribution of currents and voltages
 > along
 >  > the length of the coil.  If the voltage profile (unloaded) is close to
 >  > sinusoidal, then the voltage gradient must look like the current
profile
 >  > (the greatest turn to turn stress at the bottom).
 >  >
 >  > Could you explain why the turn to turn stresses seem to go up and often
 >  > results in racing arcs at about the 2/3 point up from the bottom when
the
 >  > coil is run out of tune?
 >  >
 >  > Gerry R
 >  >
 >  >
 >  >  > Original poster: Paul Nicholson <paul-at-abelian.demon.co.uk>
 >  >  >
 >  >  > Gerry Reynolds wrote:
 >  >  >
 >  >  >  > There are a lot of experience folks on this list that have
 >  >  >  > said that 1/4 wave resonance does not come into play and
 >  >  >  > the resonance is determined by the effective LC parameters
 >  >  >  > of the coil (or coil and top load combo).
 >  >  >
 >  >  > There's no complaint with the '1/4 wave resonance' bit, it's
 >  >  > a perfectly good name for the fundamental resonance of a
 >  >  > structure clamped at one end and free at the other.  It is
 >  >  > equivalent to 'LC' resonance.
 >  >  >
 >  >  > Our point to Jared is that the frequency of this resonance
 >  >  > is set by the self and mutual reactances of the structure in
 >  >  > question, and not by the properties of the materials that
 >  >  > went into its construction.  To use a mechanical analogy,
 >  >  > one wouldn't expect a tuning fork to keep the same frequency
 >  >  > after it had been hammered and worked into a different shape.
 >  >  > Jared I think is saying that the tuning fork will ring not just
 >  >  > with its new frequency but also its old one too.
 >  >  > --
 >  >  > Paul Nicholson
 >  >  > --
 >  >  >
 >  >  >
 >  >
 >  >
 >  >
 >
 >