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Wireless Energy Transmission

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 terminls of radio transmitters,
the answer is not known because radio engineers assume it to be of
no practical interest.

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.  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.  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.

* * * * * * * * *


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 cn 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?

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.

In addition to the vertical electric field of the surace 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.  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.