Re: Spice simulation pictures

To: tesla-at-pupman-dot-com
Subject: Re: Spice simulation pictures
From: GE Leyh <lod-at-pacbell-dot-net>
Date: Sat, 14 Oct 1995 21:30:32 +0000
Skip wrote:


> Greg
> This discussion seems to infer that the length of the TC when using the
> transmission line analogy is something other than 1/4 wave long. My
> understanding of transmission lines is that he energy transmitted down
> the line continously transfers between the magnetic field and the e
> field. If the TC secondary is indeed 1/4 wave long then it appears to me
> that it would certainly be possible to have all of the energy in the
> transmission line concentrated at the top of the secondary in the
> e-field without the need for a large toroidal capacitance.

  But remember, a transmission line has capacitance evenly distributed 
along the line, and the voltage along any 1/4 wave section of the line
is _never_ concentrated in one spot, but is distributed in a 1/4 sine-wave
profile at any given instant.  This means that the energy must be distributed 
as well, where the energy at any given point will be 1/2 CV^2.
  A resonant transformer, on the other hand, lumps all of the capacitance
into one element, and the inductance into another.  In this case, the single
capacitor is the only device in the ckt that can store energy in an electric
field, so twice per cycle it contains the _entire_ energy of the secondary ckt.
Since there is no wave propagating in a resonant xfmr, it doesn't matter what 
the electrical length of the coil is, in the slightest.
  A standard TC without a toroid acts a lot like a tapered xmsn line, since
most of its C is distributed along its length, with more C closer to the ground.
Typical effective impedances for these xmsn lines are 15,000 to 40,000 ohms,
depending on the aspect ratio, and # of turns per inch.  A TC with a normal 
toroid is somewhere in between these two regimes, as a greater percentage 
of the total e-field is emerging from the toroid.  A TC with a _huge_ toroid
acts a resonant xfmr for the most part, since almost all of its e-field lines
originate from the toroid.  The currents along the secondary are all almost
in phase in this case, and most of the energy collects at the toroid.

  It would seem then, that any xmsn line characteristics that a TC might 
possess should be considered detrimental, and should be 'swamped out' by
adding sufficent C to the top of the coil.

-GL