Re: More RFI filter testing...donuts
Try this, they work great for me. Get 2 ferrite donuts, mine have a 1.25"
diameter hole in the middle and they are 2.75" diameter on the outside, 1"
thick. I wrap 40 turns of #14 copper insulated house wire on each donut.
Be sure to use insulated wire. A piece of wire about 10' to 12' long will
give you 40 turns. I leave about 12" of wire sticking out on each end for
hook up. I use these on all my coils.
At 07:33 PM 8/7/99 -0600, you wrote:
>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
> 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...