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Re: Coiling myths

Original poster: "Malcolm Watts" <m.j.watts@xxxxxxxxxxxx>

Hi Paul,
         I think there is a really nice way to directly calculate
what the actual speed of propagation along the wire in the solenoid
(for whatever reason) is:

On 4 Apr 2005, at 12:55, Tesla list wrote:

> Original poster: Paul Nicholson <paul@xxxxxxxxxxxxxxxxxxx>
> While I'm in the mood for summarising things, I thought I'd list
> some of the theoretical myths that seem to keep cropping up in
> Tesla coiling:-
> * Myth: Signals travel through a coil as if they were moving at
>          light speed through the wire.
> (They don't.  The effective velocity 'along the wire' of a solenoid
>   is given to within a few percent by ln(h/d)*0.39 + 1.19 times c.)

At its principal resonant frequency, the structure is acting as
though it is physically a quarter of a wavelength long (lets assume a
bare coil and no end effects - close). Then, the propagation time
along the coil length (height) is 1/4Fr. Dividing the length of the
resonator by that time gives the velocity and dividing that by the
number of turns and multiplying the result by the circumference gives
the effective propagation velocity in the wire.

> * Myth: Lumped operation is a different thing from distributed
>          operation.
> (These are just two levels of detail in the mathematical modelling
>   of coil resonance.)
> * Myth: Voltage magnification is much higher than the turns ratio
>          of secondary to primary, attributed to 'resonant rise'.
> (The voltage ratio is rather less than the turns ratio due to the
>   limited coupling between the two coils.)

I think that should be qualified by saying that this is not true for
CW drive or to be more succint, true for driving with a limited shot
of energy.


> * Myth: Current in the wire offers a different mechanism for energy
> transfer to the E and H fields.
> (It doesn't. Fields and currents are bound together, and a given
> energy flow (along a coil, say) can be described equivalently
> using either set of terms.)
> * Myth: The low frequency inductance, Ldc, as measured by an LCR
> meter or estimated by Wheeler, is the effective resonating
> inductance.
> (It isn't. It doesn't correctly represent either the stored energy or
> the ratio of top volts to base current, because it doesn't allow for
> the non-uniform current.)
> * Myth: The bulk capacitance of the coil, Cdc, (measured at uniform
> voltage by an LCR meter) is the effective resonating
> capacitance.
> (It isn't. It has the same defects as Ldc because it doesn't allow
> for the non-uniform voltage in the resonating coil.)
> * Myth: High Q factor is important for secondary coils fired from an
> initial charged primary cap.
> (Only a modest Q is required. Output voltage is not proportional to
> Q as some suggest, but is limited by energy conservation.)
> I've only listed the myths that I feel confident to discuss and
> refute. Perhaps others can add to the list from their fields of
> expertise? Let's not bother with the numerous myths about
> Tesla Himself, nor the inane core beliefs of the many modern techno-
> superstitions. -- Paul Nicholson --