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. 

Gary Weaver

At 07:33 PM 8/7/99 -0600, you wrote:
>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>Hi All,
>	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
>measurement equipment.
>	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...
>	Terry