Nikola Tesla Books
Books written by or about Nikola Tesla
frequency than the vibrations of the voice. At any rate, there will be an arc, whether in the primary of the secondary which will be blown out, or the resistance of which will be enormously increased, rhythmically with the vibrations impressed by voice or otherwise, as the case may be. The control of the arc is effected by a jet of air or other gas issuing under pressure from an orifice the opening of which is controlled in some convenient way by the vibrations. An arrangement of such apparatus is illustrated in the diagram below, the arc controlled thus being in the secondary. The source of direct currents S charges a condenser C and the discharges of the same (a very great number) through a break d and primary p energize a secondary s with the usual connection in telegraphy as I have introduced. The air or gas under pressure is controlled by a diaphragm and valve v. The outlet pipe t can be screwed up as close to the diaphragm as is necessary for the best result. In this or a modified way a powerful apparatus may be controlled by very feeble undulations, as those of the human voice.
Colorado Springs
June 15, 1899
First experiments in the station were made today. The e.m.f. of the supply transformer was 200 volts only. The break on the disk, which was driven by a Crocker Wheeler motor, varied from 800 - 1200 per second. ω was found to be 800 approximately.
Under these conditions the secondary from the New York high tension transformer could only charge from 3 - 4 jars and it was impossible to obtain more than a harmonic of the vibration of the secondary system of the oscillator, which required many more jars.
The secondary was wound on a conical framework, there being 14 turns of an average length of 130 feet each, that is approximately.
The primary was formed by one turn of cable, used in New York laboratory for the same purpose, consisting of 37 wires No. 9 covered with rubber and breading. The details of construction are to be described later.
Note: Sparks went over the lightning arresters instead of going to the ground This made it necessary to change the connection to the ground, separating that of the secondary of the oscillator from the ground of the arresters. By connecting the secondary to a water pipe, and leaving the ground of the arrester as before, the sparks ceased. This indicates a bad ground on the arresters. The latter work exceedingly well. The ground connection was made by driving in a gas pipe about 12 feet deep and gammoning coke around it. This is the usual way as here practised.
The power taken in these first experiments was small, 1/2 - 3/4 H. P. only. The spark on the secondary was 5" long but very thick and noisy; indicates considerable capacity in the secondary. The variation of the length of the spark in the break did not produce much change. The weather was very stormy, hail, lightning.
36
June 14
The transmitter with the output power modulation by means of "regulating arc" represents the variation with "air" microphone. The oscillator scheme remained the same as the one of June 13. The remark on the advantage of supply from a direct current source is repeated (probably due to parasitic modulation which would be caused by an excitation generator of alternating low frequency current). Transmitter output power modulation is now performed in a secondary-antenna circuit, by means of an electric arc of which the intensity is varied with sound pressure variation rhythm. The sound is regulated by gas flow under the pressure of special valve v which is regulated by moving pipe t.
The amplitude modulation is achieved by carrier power variation around the average value at the rhythm of the modulated signal. Modulated signal is of small power and therefore this device as a whole could be made as an amplifier with frequency conversion.
June 15
This trial run of the new oscillator was Tesla's first step towards the implementation of his high-power generator. The secondary of the HF transformer was made conical in order to reduce the voltage between turns at the top of the coil. This feature is described as one of the alternatives in his “Electrical Transformer” patent(26). Tesla was the first to suggest using braided insulated wires instead of solid conductors in HF circuits in order to reduce eddy currents (see e.g. ref. 46, p. 60).
June 15
By starting the test operation of the newly constructed oscillator Tesla begins the work on a high power generator. The oscillator high frequency transformer secondary is conical in shape with 14 turns and with an average turn length of 40 meters. The primary consisted of one turn made of 37 stranded wires 2.9mm in diameter with rubber and cloth insulation.* Such a large transformer is dictated by the high voltage requirement. The secondary is of a conical shape in order to reduce voltage between turns at the top of the coil. A similar shape of the transformer is observed in Tesla patent "Electrical Transformer"(16) as one of the variations (it seems that Tesla favored the secondary in the shape of a flat spiral with the primary at the outside of the spiral, so that the common terminal of primary and secondary is grounded).
Fast primary capacitor discharge was performed by means of rotating interrupting device - 800 to 1200 times per second. The shape of oscillations therefore close to the one on Figure 2P.b (please see Appendix: Tesla's Oscillator). At this point, there is not sufficient data in order to accurately consider the operation of the oscillator and to understand all remarks on lightning arresters and grounding operation method.
* Tesla was the first who suggested the use of stranded insulated wires in circuits with high frequency currents instead of solid conductor for the purpose of reduction of eddy currents effect (please see reference No. 46, p. 60).
