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Re: Wire Length

. . . I can understand why Tesla increased the inner spacing. . . .

We know that Tesla was using the flat spiral coil as a spread-spectrum wireless transmitter.  He may have increased the spacing of the inner turns in order to facilitate the occurance of harmonics.

20 Q. Was this transmitter in regular use in your laboratory
prior to May, 1899?

A. Yes, sir; it was in regular use for a number of years prior
to my going to Colorado, having been constructed, if I
remember rightly, sometime in 1895, but it was not used in
the manner described to produce two oscillations until a
much later date, I think sometime in 1898. [NIKOLA TESLA:
Anderson, Twenty First Century Books, 1998, p. 13.]

As for the means by which harmonics can be produced with a flat spiral coil,

89 x-Q. In your answer to Question 16, you say of the large
coil to which you have frequently referred, "This coil I excited
by a primary so proportioned that when the primary was
closed by the make-and-break disk which discharged the
condensers, the oscillations in the secondary were quick-
ened much above the rate which the secondary or spiral
vibrated when the primary was opened."  Please explain
this statement more fully.

A. In endeavoring to perfect my coil, and by this I refer to a
form of oscillatory apparatus which I have originated, I dis-
covered that at times I would get two oscillations, and I
soon found the cause.  The oscillation of the spiral coil in
this case was obviously dependent on its coefficient of self-
induction and was the slower the greater the inductance
which it possessed when in action.  Now the induction was
reduced when the primary or exciting circuit was closed
through mutual induction of the circuits.  This influence is
readily determinable in some forms of circuits and can be
calculated in advance with tolerable precision.  When I
stated here that the primary was proportioned so and so, I
meant that the primary effect was so adjusted that when
the primary was closed by the make-and-break disk, the
self-induction of the spiral coil was reduced to a certain
value which I desired to obtain.  This proportioning was
done generally by linking the primary circuit with the spiral
coil more or less, thus regulating by mutual induction the
self-induction of the coil so that I obtained two oscillations
which followed each other in extremely rapid succession.  I
wish to add that this was not the only way I graduated the
effect to obtain the desired result, for I adopted frequently
other expedients when they were convenient.  For instance,
I would vary the self-induction of the primary by adding to it
a few turns of a regulating self-induction coil, which I had
on hand.  It consisted of about 24 turns of stout wire wound
on a drum and permitted me to vary the self-induction from
a few to about 100,000 centimeters.  At times, I would modify
the self-induction of the primary or secondary in other ways,
many of which would, of course, suggest themselves to any
expert who would have concentrated himself with as much
energy as I did on becoming proficient in the manipulation
of tuned circuits. [Ibid, p. 63-65.]


Original poster: "Barton B. Anderson" <bartb@xxxxxxxxxxxxxxxx>

Thanks Gary, appreciate the references you give out. I can understand why Tesla increased the inner spacing. Hope I won't have to do the same, but easy enough if I do. I finished the form today, so now just a matter of installing the plexi standoff runners (which is inset into the provided grooves). Then it should be ready for wire!

Here's a photo of the form.
http://www.classictesla.com/flat/Img_3002fast.jpg (dial up)

http://www.classictesla.com/flat/Img_3002.jpg (original image, large file)

Take care,