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Re: Wireless Energy Transmission

Hi,

My comments, as they relate to Tesla coils (else the moderator reject my
post :-)) follow.  Of course, this is on subject because Dr. Tesla did not
arrive in Colorado Springs 100 years ago today to "start a fun high voltage
hobby".  He wanted to transmit energy to the masses without wires.  Thank
goodness the hobby part worked :-))

At 09:52 AM 5/18/99 -0400, you wrote:
>Dear Malcolm, Bert, and all:
>
>Henry M. Bradford sent me a copy of Part 2 of his excellent article
>on wireless energy transmission.  It appeared in the May edition of
>the Old Timer's Bulletin of the Antique Wireless Association at p.
>28.  Part I was in the February edition at p. 28.  I have reproduced
>some interesting portions of Part 2:
>
>The Tesla magnifying transmitter appears to be an ingenious means of
>injecting a large current into the ground from a single terminal.
>The key question was (and still is) how far from the ground terminal
>this current and its associated electrical disturbance can be
>detected at frequencies high enough for practical communications --
>a few metres, a few wavelengths, around the world?  Although the
>same phenomenon occurs at the ground terminals of radio transmitters,
>the answer is not known because radio engineers assume it to be of
>no practical interest.

Tesla coils do not produce giant secondary currents.  The big ones may push
100 amps into a ground terminal of the secondary.  Not "big" by any means.
Consider dropping a typical AC transmission line to the ground.  They carry
about 500 amps normally at say 220kV.  When they fall to the ground, the
currents are far greater than anything a Tesla coil could do.  Yet, the
ground effects after a few hundred feet are nil.  The losses at higher
frequencies than 60 Hz (say 50Khz) are enormous.  You would just heat the
ground near the coil.  In defense of radio engineers, most could talk about
earth grounding effects until your ears bleed... :-)

>
>At frequencies much smaller than the lowest whole earth resonant
>frequencies of several Hertz to several tens of Hertz, the charge
>from the ground terminal would obey the laws of electrostatics and
>spread uniformly over the surface of the whole earth.  

Well, not quite.  Since the terminal is charged, the opposite but equal
ground charges would stick around pretty much near the base of the coil.
The air between them would serve as a dielectric and the system would look
like a charged capacitor.  Not much would escape from the system at all.

>The current
>caused by the flow of this charge would decrease with distance, but
>its extent also would be worldwide. At the lower earth resonant
>frequencies, which Tesla calculated, one would expect global
>oscillations and standing waves as he described, if the resistance
>losses in the earth were small enough.  

Unfortunately, the earth losses are enormous.  Any oscillation would be
damped and would never make it very far.  If the Earth were high Q you may
have a chance.  Unfortunately, it is very low Q and that is not easy to fix
at this point :-))

>These oscillations likely
>would be modified somewhat by interaction with the spherical cavity
>between the earth and the ionosphere.  At much higher frequencies,
>the charge would still tend to flow to the surface of the earth, but
>the current would be confined to within tens of hundreds of metres
>of the surface by the "skin effect", and the range of the
>disturbance would be reduced by the I squared R losses.

The militaries of the world communicate with submarines with giant radio
antennas working in the tens of Hz range.  Long waves travel through the
earth well.  So well that these giant antennas are buried underground.  The
Earth just dissipates higher frequencies in the form of heating the ground
around the wire.  The Earth has three main electrical properties,
capacitance, inductance, and resistance.  The resistance is the real killer
here.  It just sucks up all the power very close to the source (like 50
feet).  The impulse response of lightning strikes would be a good indicator...

>
>* * * * * * * * *
>
>
>Radio transmitters with good antennas and real ground connections,
>not just ground screens or counterpoises, radiate both radio waves
>from their antennas and Tesla-type earth currents from their ground
>terminals.  They provide a useful means of comparing the
>effectiveness of the two types of wireless signal produced by the
>same source, provided that the signals can be distinguished from one
>another.  In particular, they raise the question:  if earth current
>signals travel far enough to have practical value, why have they not
>been received from the ground terminals of radio transmitters -- or
>have they?

I would respectfully submit that they don't go far and thus have not been
received.

>
>The answer may depend on which type of electrical disturbance
>associated with the earth current is being received.  (Tesla was
>never very clear about this aspect of the proposed receiver.)  For
>example, if it is the vertical electric field of the charge on the
>surface of the earth that flows from the transmitter's ground
>terminal, then either the sphere and ground of a Tesla receiver or
>the aerial and ground of a radio receiver should respond to it.  At
>frequencies above about 30 kilohertz, radio signals can be
>distinguished from possible earth signals because of the difference
>between day and night reception and other ionospheric effects.  In
>the very low frequency range the differences may not be so obvious,
>but we will assume here for purposes of discussion that over the
>years constant major deviations from expected radio signal strengths
>and characteristics would have been noted.  This implies that at
>large distances from low frequency radio transmitters the vertical
>electric field of their radio waves are stronger than those
>generated by the surface charge from their ground terminals.

Since the air has an intrinsic impedance of ~50 ohms.  Perhaps someone
knows the intrinsic impedance of the ground??  This would be a clue as to
how far such waves would travel.

>
>In addition to the vertical electric field of the surface charge, the
>current from the ground terminal would produce a horizontal
>potential gradient or electric field due to the resistance of the
>soil or water.  

The ground and water would affect a potential gradient in the form of
resistance.  It would turn it into local heat.

>At the receiver, this field would be parallel to the
>great circle joining the transmitter and receiver.  This is the
>direction in which James H. Rogers apparently obtained the best
>reception in experiments with underground antenna wires. ["America's
>Greates War Invention -- The Rogers Underground Wireless," by H.
>Winfield Secor, Electrical Experimenter, March 1919. Also reprinted
>in: Part II -- Reference Articles for Solutions to Tesla's Secrets,
>compiled by John T. Ratslaff; Tesla Book Co., Millbrae, Cal., (415)
>697-4903.  Probably available from 21st Century Books)  The
>underground antennas were intended to improve the signal-to-noise
>ratio by reducing atmospheric interference , and according to
>documented reports of long distance reception of low frequency radio
>stations around the time of World War I, they were quite
>successful.  The signals detected by these antennas may be evidence
>of a practical Tesla earth current mode of communications at low
>frequencies.  However, it should be noted that radio waves
>travelling over a conducting soil induce currents and voltages in
>the same direction.
>

Low frequency radio is a well developed science. Unfortunately, it is
mostly used by the military and they are not known for publishing all their
secrets :-)  However, tons leaks out and they draw much from the open
scientific community.  I would suggest you study the submarine
communications subjects.  This would cover most of this topic well.

Always a fun topic...

	Terry