Re: Tesla Coil RF Transmitter

["Tesla list" <tesla@xxxxxxxxxx>]

Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>

Tesla list wrote:
> Original poster: "Gary Peterson" <gary@xxxxxxxxxxxx
>
> > Original poster: "Antonio Carlos M. de Queiroz" <acmdq@xxxxxxxxxx>
> >
> > These may have been the ideas that Tesla had about radio transmission,
> > but both have serious problems, to not say that they are wrong:
> I believe it's too soon to say one way or the other whether Tesla's 
> ideas on the wireless transmission of electrical energy are entirely valid.
>
> > The idea of conducting current through the air is simply unworkable.
> I disagree.  An insulating gas such as air can be made conductive 
> through the process of atomic and molecular ionization, i.e., the 
> creation of plasma.   Charges flow more or less freely in plasma 
> depending on its strength or the degree of ionization.  By way of 
> practical example, say that we have two precisely attuned Tesla 
> coils each having independent ground connections and slightly 
> elevated toploads.  Next, space them far enough apart so sparks 
> cannot jump between the terminals.  The conditions now exist for the 
> creation of capacitively coupled discharge plasma between their 
> respective elevated terminals through which an electrical current 
> will flow. Current will also flow between the two ground 
> terminals.  BTW, this is the type-two transmitter configuration.

Charges don't flow freely in plasma. The resistivity is significant.
Note that the equivalent linear resistance of the spark gap in our
Tesla coils is easily of several Ohms, for distances of a few mm.
This improves with reduced pressures, but a wire can easily
conduct the same current with losses many orders of magnitude
smaller.
Capacitive coupling decreases very fast with distance. It's the
"local field" of the antenna. Remember that both coils have
capacitance to ground, and this does not change significantly
if the coils are moved apart, while the capacitance between
the terminals decreases fast. The capacitance to ground of the
receiving coil and the capacitance between the terminals form
a capacitive voltage divider of huge ratio for quite small
distances. If the distance is comparable to the wavelength of
the transmitted signal, we have electromagnetic waves, far field.

> > Tesla's idea of using a very elevated terminal is of completely
> > inviable construction, . . .
> I assume you're refering to U.S. Patents No. 645,576 and 649,621 
> where he makes reference to, "maintaining terminals at elevations of 
> fifteen miles or more above the level of the sea."   Read these 
> patents again and you'll see that he follows this up by saying, 
> "Through my discoveries before mentioned and the production of 
> adequate means, the necessity of maintaining terminals at such 
> inaccessible altitudes is obviated . . ."  Tesla also said, "when I 
> filed the applications of September 2, 1897, for the transmission of 
> energy in which this method was disclosed, it was already clear to 
> me that I did not need to have terminals at such high elevation . . 
> . I had already calculated and found that I did not need great 
> heights to apply this method. My patent says that I break down the 
> atmosphere "at or near" the terminal. . . . my experiments in 
> Colorado showed that at a height of 1 mile it is plenty enough 
> rarefied to break down under the stress and conduct the current to 
> the distant points. . . .

Many people live at more than a mile above sea level, and do not see
currents flowing trough the air...

> If my conducting atmosphere is 2 or 3 miles above the plant, I 
> consider this very near the terminal as compared to the distance of 
> my receiving terminal, which may be across the Pacific. . . . I have 
> constructed and patented a form of apparatus which, with a moderate 
> elevation of a few hundred feet, can break the air stratum 
> down.  You will then see something like an aurora borealis across 
> the sky, and the energy will go to the distant place. . . .

A few hundred feet away, except for the irradiated energy.

> > . . . and would not work anyway, because the line
> > going to the elevated terminal would work as an antenna, and irradiate
> > most of the power. . . .
>
> I agree the conductor that connects the resonator to the elevated 
> terminal would radiate.  One question to be answered is how much of 
> the power supply alternator's output would be lost as 
> electromagnetic radiation from this conductor.  A possible solution 
> is to use a higher aspect ratio extra coil and eliminate the 
> conducting cylinder altogether, as is suggested in APPARATUS FOR 
> TRANSMITTING ELECTRICAL ENERGY, U.S. Patent 1,119,732.

The shape of the conductor, straight or coiled, does not make significant
difference in the far field generated. The total height of the system is
the most important factor.

> A 25 kHz type-one transmitter would be expensive, but not extremely 
> hard to build.  Losses in the secondary and extra coil would be 
> minimized by use of heavy wire.  The 1936 improved elevated terminal 
> would be a requirement. Two of these machines have to be built for a 
> proper system analysis.

The wavelength would be 12 km. Something smaller than about 1 km would not
irradiate much. The local field would be usable up to a distance similar
to the height of the system. Receiving antennas would have to be of
similar size. Direct connections would use less wire...

> > . . . The high current going into the ground doesn't mean
> > anything. It just returns to the terminal by displacement current
> > after moving just a bit away from the ground connection, without
> > producing significant electromagentic waves. . . .
>
> This is only the case when there is no receiver.  As stated in my 
> previous post, a precisely tuned helical resonator type receiver has 
> to used for a type-one transmitter function as it is intended.  To 
> get the most meaningful results the transmitting and receiving 
> facilities should be of identical construction. . . .

How the transmitter would be aware of the existance of a far receiver?
People at that time may have been impressed by the analysis of the
basic double resonance system, where it is apparently possible to
transmit all the energy in a primary LC circuit to a secondary
LC circuit, no matter what is the coupling coefficient between the
coils. If the coupling is low, the transfer just takes more time.
But in practice, losses eat all the energy if the coupling is too
low, before it has time to accumulate at the receiver. And this
does not consider electromagnetic waves, that is what would
excite the receiver if the distance to the transmitter is large.
They add more dispersion, as irradiated energy that is not captured
by the receiver is lost, but produce far fields much larger than
the local field. The end is the radio systems that we use. Kilowatts
of transmitted energy for microwatts of received energy not very
far away.

Antonio Carlos M. de Queiroz