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Re: Racing Sparks

Original poster: "Gerry  Reynolds" <gerryreynolds@xxxxxxxxxxxxx>

Hi Jared,

I think Paul Nickelson may have explained this phenomenum. With no topload, the ratio of the next higher resonant frequency to the fundamental is lower. As the topload is increased, the fundamental is reduced in frequency faster than the the next higher mode thus reducing the exitation of that higher frequency mode. It seems like racing arcs can occur for the following reasons (if my understanding and memory is correct):

1. Too much power for the coil size.

2. Too much coupling. The energy coupled into the coil is more concentrated in the lower turns and less spread out resulting in an energy wave propagating up the coil that causes too much stress between windings.

3. Out of tune. This can result in exitation of the higher resonant modes that can cause a voltage node at an intermediate position up the coil.

4. Topload is too small allowing for greater exitation of the higher resonant modes.

Gerry R..

Original poster: Jared E Dwarshuis <jdwarshui@xxxxxxxxx>

It is possible to get racing sparks without tight coupling. Larry and
I deliberatly made a 1.5 wave coil with a centered primary that had no
top end capacitors. What we found was racing sparks that existed only
at the quarter wave sections at the ends of the coil.(It looked like a
fiery Q-Tip).  When we added secondary capacitance the racing sparks
disapeared.  (Draw your own conclusion!)

I have noticed that tightly coupled coils are fussy about tuning. They
want the primary to be tapped in just the right place, and the spark
gap needs carefull tweaking. Lose coupled coils are more forgiving
about tuning.

Jared Dwarshuis