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Pickup Coils
A chunk of this was missing when it came back to me:
Another interesting use of the pickup coil is for experimenting
with transmission of electrical power through ground currents.
For obvious reasons I prefer to conduct these experiments with a
rather small, low power Tesla coil, usually 4 inches in diameter
or so. The reader who has followed some of my Tesla work will
begin to understand why I recommend such system parameters as
large (even huge) primary coils in Tesla coil design, not just
for efficiency, but also because it allows for tuning flexibility
to perform experiments such as this.
Take your small Tesla coil system, with the secondary coil
grounded to a dedicated RF ground, and load discharger onto the
coil until no spark allowed to break out. Then re-tune the coil.
HINTS: If you do not have an oscilloscope and frequency counter,
use a low pressure light, such as a neon or florescent tube
(brighter glow = closer in tune), or draw spark with a grounded
probe, as an indicator of system tune. If the primary on your
existing coil system is not large enough to allow the tank
circuit to tune with the new secondary configuration, lash on a
temporary primary extension, and keep in mind you will want
tighter coupling.
A normal 1/4 wave Tesla coil system with large discharger that is
not allowed to spark is called a "Tesla Transmitter". The system
energy is trapped in the resonator, and is forced to ground by
the high voltage on the discharger. Tesla transmitters pump ex-
ceptionally strong currents through the base wire and ground
path. They will "power up" or energize the RF ground to the point
that spark may be drawn off the ground with a key or other
conductor held in the hand. This condition of a "powered up"
ground is excellent for Tesla transmission experiments.
Once the Tesla coil system is top loaded and tuned for trans-
mission, wind and tune a pickup coil to match the new system
frequency. Using just the bare pickup coil connected to the
dedicated RF ground (or simply "system" ground); sparking from
the pickup coil will be so intense that the coil will be des-
troyed in short order. To get a sharp tune on the pickup coil
without frying it, it will sometimes be necessary to establish a
remote ground so that the coil can be brought into tune without
burning up. A simple remote ground for tuning purposes is easy to
establish: connect the pickup coil to a water pipe and subtract
turns until sparking or corona is detected, drive a short copper
clad ground rod some distance from system ground and connect the
pickup coil to this, or set up a small insulated counterpoise
over the system ground and connect the pickup coil to the
counterpoise.
Once the pickup coil is in sharp tune you may have an assistant
work the controls of the Tesla transmitter and you may take the
pickup coil into the field. I have been able to detect RF ground
currents by connecting the base wire of the pickup coil at the
following locations (objects): basement copper water pipe in the
neighbors houses (300 ft, 600 ft), galvanized storm culvert (500
ft), creek bed (connection to 50 foot AL flashing sunk in bottom,
1500 ft), 3 foot copper clad ground rod (200 ft). The input power
into the Tesla transmitter in this case was below 1.4 kVA into a
4 inch coil with 30 x 4 toroid. By using a high Q six inch coil
(wound with #21 magnet wire on a properly sealed coil form) tuned
to the transmitter frequency with a small toroid, I was able to
light florescent tubes at the creek bed ground connection 1/4
mile away from the transmitter.
Tesla transmitter performance is greatly dependant upon the spark
gaps. In Tesla's transmission experiments with small oscillators
he used a mercury break which produced a continuous wave
(undamped) signal (see: U.S. Patent No. 609,245, "Electrical-
Circuit Controller" ; U.S. Patent No. 568,179 "Method and
Apparatus for Producing Currents of High Frequency"; NIKOLA
TESLA: LECTURE BEFORE THE NEW YORK ACADEMY OF SCIENCES - APRIL 6,
1897, edited by Leland I. Anderson, 1994, Twenty First Century
Books, ISBN 0-9636012-7-X, pp74 fig 17 & 18. The next best thing
is a quench gap with closely spaced electrodes which are sealed
airtight, and lastly is the normal static and rotary gaps used by
most coilers which produce a highly damped signal.
Richard Quick
... If all else fails... Throw another megavolt across it!