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On Light and Other High Frequency Phenomena (Digested)

This paper is based on the lecture presented by Nikola Tesla in 1892, and published in 1893. The original paper can be found here:

On Light and Other High Frequency Phenomena
[ pdf - full version(link down) | text - missing a few images ]

The following is just my interpretation of his words, for the section "On the Apparatus and Method of Conversion". For full reference please refer to the original lecture. Please feel free to critique my interpretation and leave comments if you have anything to contribute.


Nikola Tesla was working with High Frequency currents of a particular nature.
He had ways of obtaining them from continuous or low frequency alternating currents (figure 1).

The basic idea is to charge capacitors (preferably with a high voltage that can breakdown air easily), and discharge them "disruptively", and to maintain oscillation resulting from the impulse (as well known LC oscillations).

One method to produce this would be to use a DC generator of high voltage (high enough voltage to break through a small air space). This would be used to charge a capacitor to a certain potential where the air or insulating medium breaks down and a disruptive discharge occurs, exhausting a large portion of the built up energy in the capacitor. The power supply should not be able to charge the capacitor faster than the capacitor can discharge, or the capacitor can play no role. However if the power supply charges too slowly, the discharges will be infrequent. So ideally, for a capacitor charged from a DC source, the rate of charge should be as rapid as possible without exceeding the rate of discharge.

Generally the resulting impulses have oscillations, but if conditions are met to avoid those oscillations, this could be a means for producing a direct current of lower potential.

"This method of conversion is exceedingly interesting and I was much impressed by its beauty when I first conceived it. It is ideal in certain respects. It involves the employment of no mechanical devices of any kind, and it allows of obtaining currents of any desired frequency from an ordinary circuit, direct or alternating. The frequency of the fundamental discharges depending on the relative rates of supply and dissipation can be readily varied within wide limits, by simple adjustments of these quantities, and the frequency of the superimposed vibration by the determination of the capacity, self-induction and resistance of the circuit. The potential of the currents, again, may be raised as high as any insulation is capable of withstanding safely by combining capacity and self-induction or by induction in a secondary, which need have but comparatively few turns."

It seems often the case that it's difficult to keep discharges oscillating, as they tend to be hard to start, and once started are difficult to stop. So it's useful to use an interrupter with the discharge. Tesla used a magnetic field and an air blast for this purpose. The magnet is most useful when used with large direct currents, but if alternating currents are used, it's best if they are of high current and low frequency.

To be continued...