Re: Then what's the topload FOR?

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

Original poster: "Paul Nicholson by way of Terry Fritz <twftesla-at-qwest-dot-net>" <paul-at-abelian.demon.co.uk>

Hi Dave,

You're doing a grand job there!  Maybe I can clarify a point...

> In either the 'rf transformer' case or the '1/4 wave' case the
> voltage will rise to some large value.  In the rf transformer
> approach to modeling, cf turns ratio.  In the 1/4 wave
> approach, the math heads towards infinity...

Dave, you've got a false dichotomy on the go here.  First, turns
ratio is only a worthwhile consideration when the coupling
coefficient is very close to unity.  Then, the primary and
secondary fields completely intersect and the voltage transformation
ratio has no choice but to equal the turns ratio.  Currents will
flow as necessary in order to achieve this.  When k falls below 
unity, the turns ratio no longer describes the transformation. 

All is not lost however, because at low coupling, if you make the
primary and secondary resonant at about the same frequency, then the
peak voltage transformation ratio turns out to be the square root of
the self-inductance ratio, or equally, the inverse of the square
root of the capacitance ratio.  In this low-k realm, the k factor
affects only the time taken for the energy transfer to be completed.

The lumped LC circuit is an approximation to the behaviour of the
resonator and is adequate to describe, for most purposes, what's
going on. However for a thorough analysis of a resonating solenoid,
a distributed model must be used, in which the rather slow 
propagation of signals along the coil is taken account of.  The
distributed and lumped models are not contradictory, the former is
just a more detailed description, and the latter, a simpler, more
practically useful one.  To get the best of both worlds, you would
use the distributed model, eg E-Tesla6, to get accurate lumped
equivalents for the self-capacitance and self-inductance, and then
apply these in a simple lumped LCR model or circuit sim. 

Pardon me for butting in Dave, but your comment raised an opportunity
to address an often-heard confusion, caused no doubt by a certain
very misleading document which lurks out there on the Internet. 
--
Paul Nicholson
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