Re: /4 wave theory/cite the variance?

["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>

I wrote:
> > The lowest frequency at which one end of an un-terminated solenoid
> > shows a purely resistive impedance.

dwp wrote:
> Errrr.
> There is a lower freq for the 'purely resistive impedance':
> (wait for it....) 0 Hz.

My mistake, I should have said '...resistive impedance between one
of the terminals and earth'.

At DC this impedance is almost a pure capacitive reactance.  I've
taken to calling this capacitance the 'bulk DC capacitance', since
it is the direct sum total of the coil's distributed external
capacitance.  It is fairly easy to measure, and its value can help
to inspire rough guess-timates of the actual effective capacitance at
resonance, eg by dividing it by two, say.

As the frequency goes up from DC, the impedance becomes less
capacitive, passes through zero reactance at the 1/4 wave, and then
becomes inductive until the next higher resonance, where it switches
back to capacitive, and so on.
--
Paul Nicholson
--