Nikola Tesla Books
Books written by or about Nikola Tesla
be some distance apart and which are energized alternately by discharging condensers of suitable capacity through the corresponding primaries. In Figures 2. and 3. one sending circuit is arranged so that its period is altered by inserting some inductance as in 2., or by short-circuiting a part of the circuit periodically, by means of an automatic device. It is not necessary to use such a device; however, arrangements of this kind will be later illustrated. On the receiving station two synchronized circuits responding to the vibrations - each to one - of the sender. The receiver R responds only when both circuits I and II affect sensitive devices a a1. The diagrams are self-explanatory.
Colorado Springs
June 28, 1899
Approximate estimate of the secondary with 20 turns on tapering frame, before referred to, from data of the secondary with 36 turns on the same frame. In the latter the wires 3 notches apart, in the former 7 notches.
Roughly, the capacity of the secondary with 20 turns will be, if C be that of the secondary with 36 turns:
C1 = $! {20 \over 36} $! x $! {3 \over 7} $! C = $! {60 \over 252} $! C = $! {20 \over 84} $! C = $! {10 \over 42} $! C = $! {5 \over 21} $! C
and the self-induction L1 of the secondary with 20 turns compared with L - that of the secondary with 36 turns, will be
L1 = $! ({20 \over 36})^{2} $! x $! {{36 \times 3} \over {20 \times 7}} $! L = $! ({5 \over 9})^{2} $! x $! {27 \over 35} $! L = $! {675 \over 2835} $! L
Now L = 383 x 105 C = 1200 cm.
Therefore C1 = $! {5 \over 21} $! x 1200 = 290 cm. and L1 = $! {{383 \times 675} \over 2835} $! x 105 = 9 x 106 cm. From this T = $! { {{2 \pi} \over 10^{3}} {\sqrt { {290 \over {9 \times 10^{5}}} \times {{9 \times 10^{6}} \over 10^{9}} }} = {107 \over 10^{7}} } $! approx. as period of sec. system (roughly) and n = $! { 10^{7} \over 107} $! = 93,458 per sec. Now the length of wire for 20 turns, about 139 feet per turn, will be 139 x 20 feet. This gives λ = 11,120 feet or $! {λ \over 4} $! = 2780 feet and this would correspond to n = 90,000 approx.
Adding a ball of 38 cm. capacity would give a total capacity
290 + 38 = 328 $! {\sqrt{328}} $! = 18.11 $! {\sqrt{290}} $! = 17 approx.
hence by adding a ball the secondary vibration will be reduced by a ratio of: $! {17 \over 18.11} $! or it will be $! {17 \over 18.11} $! x 93,460 = 88,000 approx. This would be too quick a vibration to best suit the apparatus as then we would have only 4 jars on each side of the primary.
49
June 27
The transmitter (Figs. 1 and 2) and receiver (Fig. 3) having several tuned circuits, the transmitter generating several signals at different frequencies and the receiver responding only when all these signals act at the same time, were the subject of two patent applications filed 16 July 1900 (subsequently granted)(38).
This method allows much more selective reception than a single-frequency channel, and is much less sensitive to interference, and the signal can only be decoded by a special receiver. In his patent applications Tesla likens it to a lock which can only be opened when one knows the combination.
The entry of June 27th was subsequently brought in evidence in a dispute before the U.S. Patent Office about priority to the idea of a multi-frequency system(68). The back of the page bears the stamp âU.S. Patent Office, Nov. 1902".
June 27
The circuit of transmitter (Figure No. 1 and 2) and receiver (Figure No. 3) with more than one resonant circuit so that transmitter produces two or more signals of different frequencies, and the receiver reacts when all these signals act simultaneously, are patented in two patents submitted on July 16, 1900(38).
By use of this system, considerably better selection is possible on the receiving location than when signal with only one frequency is used. At the same time this system enables considerably better protection against outside disturbances and the signal is coded so that only special receivers can receive and decode the signal. Such system (Tesla mentioned patents) compares with a lock which can be opened only by knowing the combination*.
* On the back of the original Tesla text of June 27, 1899 there is the seal; U.S. PATENT OFFICE, Nov. 15, 1902, and text by typewriter; "Tesla Exhibit Colorado Sketch".
June 28
After four days he again continues the calculations related to transmitter. He calculates the capacitance and inductance of transformer secondary on coil frame with twenty turns on the basis of known values for a coil with 36 turns. Here it is seen that the secondary coil capacitance he considers is proportional to the number of turns and inversely proportional to the distance between turns. Therefore he obtains that the ratio between distributed capacitance of the new coil and distributed capacitance of the old coil is equal N1d/Nd1 (N is the number of turns and d is distance between turns).
The ratio of secondary coils' inductances at number of turns change is calculated from the relation
$! {{\left({N_{1} \over N}\right)^{2} {l \over l_{1}}} = {{\left({N_{1} \over N}\right)^{2}}{Nd \over N_{1}d_{1}}} = {N_{1} d \over Nd_{1}}} $!
Such ratio originates from the equation for an indefinitely long coil and the end result is the same as the one for the ratio of secondary distributed capacitances change.
Numerical data for old coil distributed capacitance appears here for the first time without any explanation. With calculated distributed capacitance and inductance for new coil, Tesla determines the oscillation period for the new secondary. This period (or its reciprocal value - frequency) compares with value obtained on the basis of the condition that wirelength in the secondary coil is equal to quarter of a wavelength. Then he adds the sphere capacitance to secondary and determines the reduction of resonant frequency. He concludes that vibration is high, because then small capacitance in primary circuit is required. In that case the source does not have to operate at full power. At the end, in series with the secondary he adds "additional coil", adds together all capacitances (obviously incorrectly) and by not taking into account the inductance of "additional coil", he determines the change of secondary resonant frequency.
