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Looking at a diagram of Tesla's "magnifying transmitter" I see something that looks like an antenna loading coil.  Do I have this right?

No, the second or third coil of the Tesla coil transmitter is not a loading coil.  This coil, which might take the form of a flat spiral, a conical spiral, or a solenoid, is actually a helical resonator.

A simplified diagram of an advanced Tesla wireless transmission-reception system.  The entire circuit consists of an advanced Tesla RF alternator powering a Tesla coil transmitter with a passive Tesla receiver standing out to the right.  Both the coil associated with the "High potential adjustable resonant secondary circuit" and the one labeled "Inductance" are helical resonators, not loading coils.

The purpose of a loading coil is to add inductance to an electrically short antenna that already has some inductance. This added inductance brings the radio-wave launching structure, that is to say the antenna, into tune, reducing the SWR, and allowing it to radiate more efficiently.

On the other hand, the purpose of a Tesla coil transmitter's helical resonator has nothing to do with increasing radiating efficiency. Quite to the contrary, the ultimate design objective is to suppress electromagnetic radiation. As for the small inductance of the straight conductor that connects the helical resonator's upper terminal to the elevated terminal, this can be eliminated by bringing the top turn of the helical resonator right up to the bottom of the elevated terminal. The sole purpose of the Tesla coil transmitter's helical resonator is to charge the elevated terminal to a high potential by VSWR and to create a strong a magnetic field.

It has been noted that Tesla's early transmitter circuits include what appears to be an antenna loading coil, and this is understandable.  In 1919 Nikola Tesla wrote,

     "The popular impression is that my wireless work was begun in 1893, but as a matter of fact I spent the two preceding years in investigations, employing forms of apparatus, some of which were almost like those of today. . . ."

A simple diagram of an early Tesla wireless transmitter, ca. 1891.  The circuit consists of an early Tesla RF alternator connected to an antenna through what might be described as a loading coil.

but he goes on to say,

      ". . . It was clear to me from the very start that the successful consummation could only be brought about by a number of radical improvements." [True Wireless]

The fact of the matter is that Tesla's early work was with radiating circuits, and he was transmitting radio waves.  This was only a prelude to subsequent work in which he developed the advanced wireless transmitter with which the emission of radio waves is almost entirely suppressed.  It is the performance of the advanced Tesla wireless transmitter and the requisite Tesla wireless receiver that is presently being investigated by a number of individuals and groups around the world.

Once again,

     ". . . This is the apparatus I had at 35 South Fifth Avenue and also Houston Street. . . . That is the way I had it for the production of current effects which were rather of damped character because, at that period, I used circuits of great activity which radiated rapidly. . . . a system of transmission, based on the same principle, . . . was a transmission by electromagnetic waves. . . ."

A Tesla radio transmitter incorporating a magnetic loop antenna.

And, he goes on to say,

     ". . . The solution lay in a different direction.  I am showing you this [diagram] simply as a typical form of apparatus of that period, and if you go over the literature of the present day you will find that the newest arrangements have nothing better to show." [Nikola Tesla On His Work With Alternating Currents . . ., p. 55-56]

So you can see that Tesla's early transmitters and the present day advanced Tesla transmitter design are radically different.  It is true that some of the early Tesla transmitters were in fact radio transmitters, but the later Tesla transmitters are not radio transmitters.  The reason the familiar diagram of a flat-spiral transmitter appearing on page 160 of Nikola Tesla On His Work With Alternating Currents . . . and other places does not show a loading coil is because no loading coil is present.  Keep in mind that all of these drawings represent the advanced Tesla wireless transmitter shown along side of a requisite Tesla wireless receiver as shown below.

As for the value of 1,000 cm capacity that some have assumed for the antenna of Tesla's early wireless transmitter, this is incorrect.  Tesla was speaking about a measurement technique and the precision he was able to achieve in 1916, not about specifics of his early wireless experiments.

     ". . . I used this machine in transmission of signals, particularly with the telephone, in a great many investigations, and I discovered a way, for instance, of measuring accurately capacities employing this machine. . . . With an antenna of 1,000 centimeters, I can very easily read half a centimeter.  There is no method known which would enable an expert to read as closely as that.  I used this machine in experiments as these. . . . In those years, of course, I was developing the principles.  I have shown that five steps had to be accomplished before wireless was an art, a real art that could be applied scientifically." [NTAC, p. 16-17]

Getting back to radio antenna loading coils and Tesla's development of the advanced wireless transmission-reception system in which radio waves are suppressed,

     ". . . This form of apparatus . . . was installed on a large scale with four phases in my plant on Long Island with which I was to telephone around the world . . . I used the apparatus, yes, in connection with the antenna too, but this is from a patent drawing in which an antenna is shown; I mean, I used it in every connection.  [Fig. 38] illustrates an antenna with my transmitting circuit . . . I had different kinds of apparatus.  Then I had a sensibly damped wave because at that time I still was laboring under the same difficulties as some do this day--I had not learned how to produce a circuit which would give me, with very few fundamental impulses, a perfectly continuous wave.  That came with the perfection of the devices.  When I came to my experiments in Colorado, I could take my apparatus like that and get a continuous or undamped wave, almost without exception, between individual discharges." [NTAC, p. 61]

The reason Tesla was able to obtain an almost undamped wave was because very little energy was being dissipated in the form of radio waves from the entire "oscillating circuit" comprised of a resonance transformer that he called the "transmitting circuit," an elevated terminal that he sometimes called an "antenna," and a ground terminal (see NTAC, p. 60-61).  In NTAC the distinction made between an antenna alone, and the transformer secondary or resonator plus the elevated terminal plus the ground terminal can be unclear.  For example he says,

     ". . . this machine . . . was connected to the condensers, and these condensers were discharged through a primary which excited the secondary; the antenna was included in the secondary. . . ." (see NTAC, p. 65).

Notice that he says, "included in" rather than 'attached to.'  It's as if Tesla is viewing the entire "oscillating circuit" as comprising the launching structure rather than just the "antenna" alone, and this, indeed, is believed to be the case by some of us who have taken the extra step of replicating the advanced Tesla transmitting and receiving apparatus. 
Here is a second example of a seeming preference to use the term "oscillating circuit" in place of the term "antenna."

     "I would get, I should say, approximately 30 horsepower in the antenna; that is, I would get 30 horsepower in the oscillating circuit. . . ." (see NTAC, p. 67-68).

Getting back to the flat-spiral electrical resonator, it was an evolutionary step in the development of an advanced wireless transmission-reception system in which the energy propagates in a form other than that of radio waves.

     "This coil, which I have subsequently shown in my patents Nos. 645,576 and 649,621, in the form of a spiral, was, as you see, [earlier] in the form of a cone.  The idea was to put the coil, with reference to the primary, in an inductive connection which was not close--we call it now a loose coupling--but free to permit a great resonant rise.  That was the first single step, as I say, toward the evolution of an invention which I have called my "magnifying transmitter."  That means, a circuit connected to ground and to the antenna, of a tremendous electromagnetic momentum and small damping factor, with all the conditions so determined that an immense accumulation of electrical energy can take place." [NTAC, p. 72-73]

(This being said, it is suggested that one might wish to maintain an open mind as to the flat-spiral resonator's ongoing usefulness.)

In regards to Tesla's priority in the invention of radio, it is true that some historians credit Reginald Fessenden for making improvements to the early spark-gap transmitter design in 1900.  Other scholars say no, it was Ferdinand Braun who did this in an improvised demonstration in 1898.  In fact it was Nikola Tesla who developed the basic techniques for improving transmitter performance, allowing significantly higher levels of radio-frequency energy (five orders of magnitude) to be concentrated into a damped or partially damped wave of a single frequency.  This is an historical fact, documented by U.S. Patent No. 454,622, SYSTEM OF ELECTRIC LIGHTING, June 23, 1891.  The patent's drawing shows an energy storage capacitor and a discharger on the primary side of a resonance transformer.  This radio-frequency power supply circuit was used in wireless demonstrations starting in 1891, culminating in a demonstration of the world's first practical wireless transmitter at an 1893 meeting of the National Electric Light Association in St. Louis.

This circuit from U.S. Patent No. 454,622 shows the world's first practical radio-frequency alternating current power supply.

SYSTEM OF ELECTRIC LIGHTING was only the first in a series of wireless telecommunications patents.  MEANS FOR GENERATING ELECTRIC CURRENTS, No. 514,168 of February 6, 1894 describes a variation of this same circuit.  Between September 15, 1896 and November 18, 1898 no fewer than 17 additional patents were granted for equipment directly related to the production of powerful high-frequency electrical currents.  It was during that same period, on September 2, 1897, that Tesla filed his first application, which was directly related to wireless transmission and reception, resulting in two patents that were subsequently issued as SYSTEM OF . . . and APPARATUS FOR TRANSMISSION OF ELECTRICAL ENERGY, dated March 20 and May 15, 1900 respectively.  On July 1, 1898 another wireless-related application was filed for the radio-controlled boat resulting in the patent, "METHOD OF AND APPARATUS FOR CONTROLLING MECHANISM OF MOVING VESSELS OR VEHICLES issued November 8, 1898.

Created April 19, 2008 

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