Wire length,resonance, and Q (fwd)
From: Greg Leyh [SMTP:lod-at-pacbell-dot-net]
Sent: Thursday, May 28, 1998 7:17 AM
To: Tesla List
Subject: Re: Wire length,resonance, and Q (fwd)
Mark S Graalman wrote:
> I have to wonder here if there isn't a simple
> misunderstanding of 1/4 wave resonance, the fact
> that we are talking about an ELECTRICAL 1/4 wave
> and not a PHYSICAL 1/4 wave. That a 'monopole'
> tesla secondary is a ELECTRICAL 1/4 wave from
> the bottom to the top, and any situation where one
> has a current node at one end and a voltage node
> at the other is being operated as a 1/4 wave electrically
> regardless of its physical length.
This is true, and devices such as waveguide stubs and antennas
often operate in this 1/4 wave mode. However, a TC secondary
_does not_ behave in this way, for the following simple reason:
There is no actual voltage node (max V, min I) at the top.
Although there is a current node at the base (max I, min V),
the top winding carries both the maximum voltage _and_ nearly
the maximum current, just like in a standard HV transformer.
This current at the top simply goes into charging the top
electrode, which has a lumped capacitance back to ground.
The current going into the arc is typically only 30 to 40%
of the total current being delivered to the top electrode.
If you change the "electrical length" of the TC secondary,
this will still be the case.