First tesla coils I ever made were spark gaps using a 15,000 volt neon sign
transformer, large caps out of aluminum foil, xfrmr oil and polyethylene
sheeting... later on friends and I built units around 50Khz-150Khz which
used push-pull circuits to drive the primary coil of the tesla (no noise
from the spark gap which is almost deafening!)--I think the first used 811
(825's?) tubes from old gov't surplus equip (I remember the tubes were about
the size of coke bottles)....

Warmest regards,
John

"Frank" wrote in message
news:EWkje.7026$wr.338@clgrps12...

"John Smith" wrote in message
...
Shield the coil, the coronas effect is still as powerful on florescents,
vtvms detecting voltage... that voltage may well be inducing a magnetic
field as it is conducted by air/ether/ground... but it looks to me like
the voltage is the main force... rfi will tear up a neighborhood too...

Warmest regards,
John

Since I have never had experience with a Tesla coil, this is all
relatively new to me. After a little research I found the following
information, which may be of interest.

The Tesla coil design reference at
http://home.wtal.de/herbs_teslapage/design.html provides an Excel spread
sheet showing all the appropriate parameters. The spread sheet example
shows a single gap spark transmitter, of input power 375 W at a frequency
of 322 kHz. Since the wavelength is relatively long, at 932 m, the near
field/far field transition is very close to the radiating structure, which
will include the conductive arc plasma.

Near field/far field transition is approximated as (2D^2)/lambda, where D
is the largest dimension of the radiating structure, and lambda is the
wavelength.

The observable effects you mention are therefore most likely due to far
field effects. The E/H ratio is still a constant at 377 ohms. From the
above formula you can see that you would have to be very close to the
souce for any inductive or capacative coupling to occur.

Having heard of Tesla coils I never realized they were only simple spark
gap transmitters.

73,

Frank