Re: Quarter Wavelength Frequency

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

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
 >  > --
 >  >
 >  >
 >
 >
 >