# Re: tuning question

```Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi,

At 10:39 PM 4/14/2001 -0400, you wrote:
>what does it mean to tune a tesla coil and how? what will i need to do this?
>waveform generators? oscilloscopes? LCR machines?
>

A Tesla coil has two main circuits.  The primary circuit composed of the
primary coil, primary capacitor and spark gap.  Then there is the secondary
circuit composed of the secondary coil and the coil and top load's
capacitance.  These two circuits are tuned inductor/capacitor circuits
which oscillate at a frequency given by:

Fo = 1 / (2 x pi x SQRT(L x C))

The coil starts out by charging the primary capacitor to a high voltage
around say 15000 volts.  The the spark gap will suddenly fire and complete
the primary circuit so the primary capacitor and primary inductor will
oscillate at their natural Fo frequency.  This creates a very power full
magnetic field which is magnetically coupled to the secondary coil and top
load capacitance.  This field will set up a similar oscillation in the
secondary but the voltage produced will be much higher roughly proportional to:

Vtop = 0.7 x Vpri x SQRT(Cp / Ctop)

When we talk of "tuning" a coil, we are adjusting the circuits so that they
operate at the same frequency.  This is normally done by changing the
position of the electrical connection on the primary coil which changes its
inductance to a value that will give the primary circuit an oscillating
frequency that matches the secondary system's operating frequency.

There are three methods used to tune a Tesla coil.

1.	Trial and error - If the coils will tune, you can usually simply try a
bunch of tap points until you get the longest streamers.  This should be
done at minimal power until you get close to the correct place.

2.	By calculation - There are a number of computer programs that will get
very close to the correct tap point.  One that comes to mind is a web based
on-line Java version at:

http://www.classictesla-dot-com/java/javatc.html

another is at:
http://home.att-dot-net/~couturejh/

There are also many others.

There are also a ton of equations and information at:

3.	Test equipment - You can us the usual test equipment for tuning too.
But it is usually far easier to use the computer programs to get the coil
designed right and then use trial and error.  A very simple project to
build a tuner is at:

http://hot-streamer-dot-com/TeslaCoils/Misc/TCT/TCT.htm

You can also use scopes, signal generators, frequency counters, and the
like but most people don't have these handy.

I am not sure how deeply you wanted to get into this, but this should get