# RE: Flat coils & undamped waves (was Wire Length)

```Original poster: "David Thomson" <dwt@xxxxxxxxxxxx>

>      Answer to your question is that "inductors are inductors" no
> matter what the shape and flat spirals have no special and desireable
> electrical properties.

This is not my experience.  Wind a flat spiral coil to 300 kHz, then wind a
solenoid coil to 300 kHz.  Coat each coil with 1/8" epoxy.  The flat spiral
coil will rise in frequency, the solenoid will drop in frequency.  The
geometries definitely do make a difference.

Further, there are two separate Wheeler equations for calculating the
inductance of flat spirals and solenoids.  The reason there are two
different equations, rather than just one, is because the geometry *does*
make a difference in the coil's properties.

Also, flat spiral coils have a greater range of resonance than do solenoid
coils.  For the same amount of wire and same average radius, a flat spiral
coil will have an output with lower potential and higher current than a
solenoid will, thus, flat spirals make better secondaries in a magnifier
setup.

According to schematics of Wardencliffe obtained from the Belgrade museum
and published by Leland Anderson, Tesla's final Wardencliffe layout involved
a flat spiral secondary and tall solenoid extra coil.

I have built combination flat spiral and solenoid coils and the combination
works great for driving a very high frequency extra coil.  I'm presently
building a new combination setup and just wound the flat spiral, today.  In
my present system, the flat spiral and tall extra coil tune to the same
frequency.  However, I will build an alternative tall solenoid at three
times the flat spiral frequency.  When the tall solenoid is powered by a
flat spiral and tuned to a higher frequency, the output is an electric blue
flame at the top load, rather than the usual streamers.  Tesla described
similar results in his earlier experiments.  You can see a previous
incarnation of this coil setup at:

http://www.tesla-coil-builder.com/FlatSpiralSolenoidCombo.htm

When it comes to winding flat spirals with ribbon wire, there is no
advantage from the extra self-capacitance because the flat wire acts like
several coils wound in parallel, thus the inductance is decreased
accordingly.  Calculating the frequency of the flat spiral using the Wheeler
inductance formula for flat spirals made from round wire works the same for
flat spirals made from ribbon wire.

Dave

```