Coiling myths

["Tesla list" <tesla@xxxxxxxxxx>]

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.)

* 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.)

* 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
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