More RFI filter testing...
I was trying different RFI filters tonight... Nothing worked... didn't
even effect it at all...
I tested the scope and probe equipment to be sure something screwy was not
going on there. Aside from pure RFI pickup on the case of the fiber-optic
transducer, the signals appear to be very real. I could switch transducers
off and disconnect optic cables and such and the signal will stop just like
it should. the signal was definitely being feed to the scope through the
Now get this... Frustrated, I stuck a 1K ohm resistor in series with the
primary circuit. The pulse did NOT change at all!!! Even stranger, I can
get the pulse by just turning the variac up to before the point it will
arc. There will be an occasional high power pulse with no normal arc!
As far as I can tell, the real meat of the pulse lasts about 20nS and is
composed of very high frequency and very high power signals.
My latest theory of the minute is....
The pulse seems completely unrelated to the primary coil or other primary
parts. It appears that the pulse is caused by the actual arc at the spark
gap. The heavy wiring in that area, just serves as an antenna to transmit
these 1GHz+ signals. I suspect the gap stores energy as capacitance across
the gap. When conduction starts, the arc becomes a super high power high
frequency transmitter for about 20nS. Apparently, this initial arc can
occur by itself without starting the primary circuit into conduction. Ie.
it can occur so fast the primary circuit will be unaffected by the fast
local arc of the gap. I must assume this is common to any spark gap system
and not just Tesla coils. This is good in that it may have more data about
it somewhere. Unfortunately, the power, speed, frequency, and connected
metal parts will make this thing bazaarly difficult to stop or even shield
So to make a long story short. It looks like the initial gap
capacitance's stored energy is going into the initial arc at the gap and
feeding a tremendous amount of power into the arc for about 20nS. That
power is being converted to very powerful, high-frequency RF. Since the
arc size is about 1/4 inch, I assume the frequency extends well into the
low number of GHz region...