Half-Wave Coils

To: tesla-at-poodle.pupman-dot-com
Subject: Half-Wave Coils
From: Tesla List <tesla-at-stic-dot-net>
Date: Mon, 05 May 1997 01:18:17 -0500
Approved: tesla-at-stic-dot-net
Subject:  Half-Wave Coils
  Date:   Sun, 4 May 1997 19:29:06 -0400
  From:   "Thomas McGahee" <tom_mcgahee-at-sigmais-dot-com>
    To:   "Tesla List" <tesla-at-pupman-dot-com>


I changed the Subject title to reflect the topic

> Subject:  Re: Core Material
>   Date:   Sat, 3 May 1997 19:59:25 -0500
>   From:   "Robert W. Stephens" <rwstephens-at-headwaters-dot-com>
>     To:   Tesla List <tesla-at-pupman-dot-com>
> 
> 
> > Subject:  Re: Core Material
> >   Date:  Thu, 1 May 1997 23:03:44 -0400 (EDT)
> >   From:  SSNSanders-at-aol-dot-com
> >     To:  tesla-at-pupman-dot-com
> > 
> > 
> > In a message dated 97-05-01 18:20:51 EDT, you write:
> > 
> > << 
> >  Also, I was thinking about half wave coils, not many people seem
to
> >  build 
> >  these.  Why is this?  
> >   >>
> > I think you will have break out at the 1/4 wave area as well as
the 1/2
> > at
> > top. Your coil will be breaking out about 1/2 the way up and at
the top.
> > The
> > same goes for 3/4 and full wave. On a full wave it would break
out at
> > 1/4-1/2-3/4 and at top.  Stephen S.
> > 
> > 
> Stephen,
> 
> The high voltage points along a resonator, or transmission line
follow a
> voltage 
> distribution just like in a sine wave.  If you have a 1 wavelength 
> long resonator, the voltage peaks will occur at only the 1/4 and
3/4 
> wave positions.  At 1/2 wave and full wave you are returned to a 
> voltage null point.
> 
> rwstephens

rwstephens is correct in what he says. I just want to mention, for
the sake of completeness, that while the above statement is true, it
assumes that one end is connected to RF ground. It doesn't HAVE to
be, though!

It should be noted that there are *so-called* 1/2 wave coils in which
the primary is CENTERED over the secondary coil. Of their very nature
they tend to be more tightly coupled than the normal Tesla coil. The
CENTER of the coil then becomes the initial node, and both ends are
1/4 wavelength, and also 180 degrees out of phase. 

In the arrangement where the secondary has NO ground connection at
all, it is imperative that the load at each end be identical. If the
loads are imbalanced, then sparking will occur to the primary. 

An interesting variation on this "1/2 wave" Tesla coil is one in
which the center of the secondary is connected to a good RF ground.
In this case you *actually* have a twin coil that shares a common
primary. Rather than thinking of these coils as 1/2 wave, it is
probably more correct to think of them as DUAL 1/4 wave. A *TRUE* 1/2
wave *base-referenced* Tesla secondary would NOT throw sparks from
its top, but rather it would break out at its center, which is where
it is 1/4 wave.

As rwstephens points out, only the ODD multiples of 1/4 wave will
give out high voltage. But even though a 3/4 wave would give you a
high voltage out, it does not appear that there is any real advantage
to it in Tesla coil work. 1/4 wave is what we strive for in standard
Tesla coil work.

Fr. Tom McGahee