# Extra coil

```Original poster: "Nebojsa Kovacevic by way of Terry Fritz <twftesla-at-qwest-dot-net>" <morfeus-at-EUnet.yu>

73
Hello All!

Most of the people are confused with the part of the Tesla coil which he
named "extra coil". In his lab we can clearly notice three separated
parts: primary circuit, secondary circuit and the thing that Tesla calls
"extra coil". Primary coil transforms the AC currents of 140Hz from the
primary transformer into the high frequency currents (radio frequency).
The purpose of the secondary coil is to on a specific frequency produce
energy for the helicoidal resonator. Complexe construction of the extra
coil makes the perfect conditions for using the possibilities of the
helicoidal windings as a slow wave resonator. This type of coil is now
days known as opened helicoidal resonator.
The configuration we are comonly using today is producing high voltage
only (high energy). But if we want to get high voltage and high
amperage, we should construct the system with tertiary coil.
Let`s take a look at the Tesla`s apparatus as a perfect example. He used
currents. Primary coil has very high inductive relation with the
secondary, which has the serial resonance of the same frequency as
adjusted helicoidal resonator from which Tesla emitts his streamers.
Many people are surprised that the secondary coil is adjusted on the
exact frequency as the primary coil. The real attention should be paid
on the extra coil which spectaculary dominating on the central part of
his lab.
Rotary break is the most important part in the constuctions with extra
coil. Before all, for a high power you need as many breaks as you can
acchieve per second. Everyone has to have in mind that high amperage in
the coil doesn`t mean very high voltage. The power which is transmitted
to the secondary coil is proportional to the number of the breaks in
second. Other usefull aspect of the break is the break duration which is
the key for a proper functioning of the primary and secondary coil. The
time duration of the spark in the break is the time in which the spark
really exists in the gap before it shuts down.
While the spark is in the gap, the system will oscillate on the two
frequencies (two line system so to call it). Spectral diference, or the
frequency diference is proportional to the magnetic relation between the
primary and the secondary circuits. To get the max. results, these two
frequencies should have the frequency diference DF.
All this means that with incresing the inductive relation between the
primary and the secondary, the time of the spark in the gap should be as
shorter as possible. But, in the case of critical relation between the
coils, DF is falling to zero, so the duration of the spark isn`t a
controll parameter any more.

The readers familiar with the problem must ask them selfs, why to build
an extra coil? Isn`t the finall goal we are all trying to acchieve,
generating a high potencial (energy)? This is true if we want to get
only high potencial. Hmm....our friend Tesla must have wanted more. In
Colorado, he wanted to get  high potencial and very high power.
We are all aware of the two frequencies that builds in the system with
very high inductive related coils(primary and secondary). The phenomenon
of two frequencies. This can be seen as a two frequency spectre on the
o-scopes with primary and secondary coils with concentrated parameters.
Extra coil should be noted as a diferent part of the system, comparing
to the one we have in the primary-secondary system. (When it is compared
with the secondary coil, it`smagnetic relation to the primary coil is
minor). Extra coil is infact 1/4 wave lenght helicoidal resonator.
Analise of the tertiary coil as a concentrated parameter circuitry is
absolutly unsuccessful.
In every way, the looses should be cut down in the tertiary coil.
Helicoidal resonator on lower frequencies is only a coil of the small
diameter with high number of turns of wire, placed above the ground.
Coil, with capacitor on the top acts as a 1/4 wave lenght "antenna"
which doesn`t emitts. Instead of the vertical tower a few thousands of
feets high - real aerial, Tesla had the resonating coil which doesn`t
emitts, and it`s hight was only a part of that hipotetic tower. The
nature of the slow waves in the coil is what makes all this possible. It
should be paid attention on a few things about the helicoidal
resonators:
The base or entry will have the characteristical low impendance, and on
the top (or the high frequency exit), will have high impendance. This
means that in the purpose of the activating the coil Tesla had to
connect a very high currents to the base of the extra coil. That way, as
much electricity you put in the base of the extra coil, with  properly
adjusted frequency, the more electricity you will get on the top of the
coil(terminal). The currents on the top depends on the high frequency
currents in the base of the extra coil, short wave voltage ratio, and
the characteristical impendance of the resonator. All these claims can
be measured and calculated very easily. Besides, as tertiary coil can be
used any 1/4 wave lenght resonator which doesn`t emitts - helicoidal
resonator, coaxial resonator, even microwave owen!
I am hoping that in this point, every reader is abble to see that the
combination of the primary and the secondary coils is, efectivly, only
one powerful oscillator of the high energy, which brings the currents of
the low voltage and high amperage in the base of the extra coil, in
order to build a high potencial high energy currents.

I think that we should add this coil in our constuctions finally......

Regards,
Nele

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