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Re: Notes on Terry's observations
Dr. Resonance wrote:
> The toroid reacts with the secondary distributed capacitance which is
> comprised of the many small series capacitances between turns. The
> harmonics are supported by the turn to turn capacitances, ie, distributed
> capacitances. This effect is what produces all the multiple harmonics you
> are observing. If you connect a super huge top load capacitance you will
> see only one fundamental with any multiple resonances produced attenuated
> down by 10-20 dB, and, in effect, do not become part of the active
> secondary circuit due to their attenuation. This is why TC tuners should
> always use a very large topload, ie, to prevent all the undesireable
> multiple harmonics that cause strange effects which some experimenters call
> "racing sparks" along the secondary coil. Use a huge topload and "racing
> sparks" will disappear altogether assuming the primary is in proper tune.
> Racing sparks are caused by too small topload and multiple series
> resonances with the distributed capacities along the secondary inductor
> reacting with the topload capacitance.
A large top load adds a large capacitive load at the end of the
transmission line (lets assume an uniform line as a reasonable
approximation for a vertical coil, what requires some optimism).
This shifts to lower frequency all the natural frequencies of the
system,
making it more and more like a system with the top terminal grounded as
the size of the top load is increased. Let f0 by the main resonance
frequency without any top load. The effect of a top load is that the
fundamental mode shifts to low frequency, and the other modes , that
were at 3f0, 5f0, 7f0, ... shift in the direction of 2f0, 4f0, 6f0, ...
If the coil is designed to operate with already some loss due
to skin effect and other losses that increase with frequency at
the resonance frequency with a large top load, the other resonances
will be at much higher frequency, and so will be heavily damped,
as you correctly point out.
About "racing sparks", I still believe that the reason is simply
the accumulation of static charges in the surface of the resonator.
Antonio Carlos M. de Queiroz