Re: More RFI filter testing...

to: Terry

Good theory.  I suggest a test by enclosing your primary gap in some screen
material such as fine mesh screen automotive centers sell for fuel filters.
For this test it doesn't have to look good --- just surround the sparkgap
completely.  Ground it and repeat your test.  If the fine mesh Faraday cage
stops the signal then you know you found the culprit.



-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Sunday, August 08, 1999 3:33 AM
Subject: More RFI filter testing...

>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