Nikola Tesla Books
Books written by or about Nikola Tesla
Neglecting R2 we have ÏLp=0.206 and Lp=287,000 cm approx.
For secondary 14 turns on conical frame average length of turn 130 feet.
E = 57.7 $! {E \over I} $! = 4.57 Ï2L2 = 16.49 Ls = $! {4 \over 716} $! = 0.0056 henry approx.
I = 12.65
Ï = 716 ($! {E \over I} $!)2 = 20.98 ÏL = 4 approx. or Ls = 5,600,00 cm. approx.
R = 2.12 R2 = 4.49
Coefficient of mutual induction, 2 primary turns in series:
M = Ep/ÏIs = 6 x 109/716 x 10.7 = 783,300 cm.
- Ep = 6
- Is = 10.7 Ï = 716
This will reduce L. Reduction estimated from
L - $! {M^2 \over N} $! = L (I - $! {M^2 \over NL} $!) = L x 0.64
Colorado Springs
June 18, 1899
Experiments were continued with the oscillator showing that proper vibration does not take place, evidently owing to some cause which is still to be explained. To see whether the trouble is due to poor induction from the primary, a coil-wound on a drum of about 30" diam, 10" long, 500 turns approx. of No.26 wire, used in some experiments in New York - was connected to the free end of the secondary and with this coil a great rise was obtained, streamers about 12" long being obtained on the last free turn even with a small excitation of secondary. The trouble seems to be due to internal capacity. The total length of a quarter wave with coil was about 2400 feet, which agrees fairly with the calculation from the vibration of the primary circuit. The experiments with the coil show strikingly the advantage of an extra coil, as I call it, already noticed in experiments in New York; that is, a coil practically not inductively connected but merely used to raise the impressed electromotive force.
Measurements of inductance of the secondary as used: 12 turns on tapering frame 1 1/4" apart from center to center showed:
| Current through secondary | E.m.f. on terminals | Ï |
| 10.9 | 74 V | 710 |
from this L's was found = 9,500,000 cm.
Readings for mutual induction:
| Current through secondary | E.m.f. on primary (one turn) | Ï |
| 10.9 | 4.75 | 710 |
gave M' = $! {E \over IÏ} $! = 0.00062 H or 620,000 cm.
38
June 17
The repeated measurement of ground resistance between water pipe and grounded plate clearly shows that the terrain around the laboratory is poorly conductive. After a long period of ground moistening the resistance was reduced (probably the soil around the ground plate was moistened). The obvious ground resistance instability leads Tesla to think that grounding will cause difficulties in oscillator operation. The connection to water pipe as alternative grounding has, according to Tesla, disadvantages because this introduces the additional conductor in the oscillator circuit. Whether this is correct depends on a number of factors (e.g., on distance between water pipe and ground surface), but it is certain that the water pipe provides better grounding than the already mentioned grounding plate.*
The oscillator primary and secondary inductance Tesla measures on the basis of impedance module and known resistance. He determines the impedance from the ratio between voltage and current at a frequency of approximately 144 Hz. He indicates the coil's resistance, but he doesn't explain whether he determines them by measurement or by calculation.
Mutual primary and secondary inductance he determines from the ratio of no-load voltage in the secondary and excitation current in the primary multiplied by the circular frequency at which he performs the measurement.
The term "L-reduction" now is not clear. The term L - M2/N, corresponds to the primary inductance when the secondary coil is in short circuit. On the basis of mutual inductance and primary and secondary inductance it is found that the transformer link coefficient is approximately 0.6, which indicates a very good link.
* The experience with grounding in this period was small. On June 16 Tesla explains the grounding as "usually", and under this he probably considers the usual lightning grounding, The grounding for the purpose of telegraphy with one wire dates from 1838, when Stinheil demonstrated the use of the ground as a return conductor. In 1893 Tesla shows the plan for wireless transmission system(6), where the alternating current's source connects by "one terminal to ground (the water pipe is suitable as well) and the other terminal to a body of large surface P". The grounding is achieved by connection to a water pipe on receivers made by Popov in 1895(32), In about 1895 Marconi performs the experiments with Hertz apparatius, so that one inductor's arcing device terminal connects to ground, and the other is connected to the elevated conductor with the end capacitance(30). Detail analysis and measurements of grounding influence and types of ground were performed in about 1905 and later (please see ref. No. 19, p. 796).
June 18
The secondary circuit was modified by the addition of another coil, altering its response to the primary and the spectrum of the oscillations. Tesla had already found in experiments in New York that this âextra coilâ had a good effect. This coil was not inductively coupled to the transformer (some coupling probably existed, though weak).
June 18
So far Tesla didn't show the method by which to determine the oscillation frequency, but it is clear that he already had some results. When looking for the mismatch reason of measured and calculated value he tries one new modification of the high frequency transformer. He makes a new coil, which is connected by its one terminal to the open secondary terminal, and then a considerable voltage increase at the other terminal of the new coil is achieved.
By adding the coil in series with the secondary, Tesla changes the oscillator secondary circuit.- So the secondary reaction to the primary becomes different and changes the oscillations' spectrum. The effect of the "additional" is known to Tesla from his experiments in the New York laboratory. This coil is not in inductive link with the high frequency transformer (link probably exists, but poor).
The analysis of Tesla's oscillator with "additional coil" could not be performed according to Oberbeck Theory because the secondary circuit is changed. Instead of capacitance C2 (please see Appendix: Tesla's Oscillator) now the parasitic secondary coil capacitance exists with which in parallel is connected the series combination of "additional coil" with quite indefinite parasitic capacitances. For the purpose of orientation when determining the secondary circuit Tesla mentions that the secondary wire length has to amount to one quarter of a wavelength. This requirement appears in patents from 1897(13,14,15). Actually the wire will be shorter, because the speed of current propagation along the coil is lower than along the real conductor.
The measurement of oscillator circuit parameters he performs on a rewound secondary. He gives first capacitance measurements in primary oscillator circuit.
