Re: Best sparks (fwd)

---------- Forwarded message ----------
Date: Fri, 10 Jul 1998 09:43:36 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Best sparks (fwd)

Hi Greg, all,

> Date: Tue, 07 Jul 1998 09:31:45 -0700
> From: Greg Leyh <lod-at-pacbell-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Best sparks (fwd)
> DC wrote:
> > Terry listed an equation regarding the spectral emission from the arc
> > itself.  This equation listed the RC time constant as a source for the
> > generated frequency.  This is incorrect.  RC time constant is a dissipative
> > factor.  It will not store energy like an LC time constant value and does
> > not support resonance, in fact, tends to reduce or oppose any resonant
> > buildup.  
> Actually, Terry's equation is quite valid, and gives the 3dB freq 
> for a given RC circuit.  RC oscillators are actually quite common,
> too much so sometimes for someone trying to stabilize an amplifier!
> Energy storage is not a prerequisite for oscillation;  any gain
> mechanism with feedback shifted 180deg will oscillate nicely.
> Ever hear of a relaxation oscillator?  This is the primary mechanism
> at work in lightning strikes, for producing the whistlers and even
> the multiple strikes.  Anyone who has played around with HVDC is
> familiar with the distinct screechy whistle as a corona reaches out
> to a grounded screwdriver... an RC oscillator at work!
> The 2.5MHz component in Electrum's output power is undoubtedly an
> RC oscillation between the top C and the effective R of the arc
> channel, for the oscillation is quite erratic in amplitude, and 
> therefore very low Q in nature.

Also worth noting is that there is an inherent mechanism in a 
discharge which makes oscillations possible - the negative impedance 
characteristic. The arc is not a pure resistance.