Re: More RFI filter testing...
I think you are up against the quantum nature of matter
> 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
> 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
Exactly so. You (and every other coiler) have a parasitic relaxation
oscillator in the primary. How to get rid of it: provide an unlimited
current once the gap discharge begins :)
> 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...
BTW, I think you associated an inductance figure of 20uH with the gap
in an earlier piece (correct me if I'm wrong). That figure is highly
suspect. I have a coil with about 12uH of real inductor in its
primary and it runs as if no (or minimal) other inductance is present.
Another BTW - I use a Sencore LC35 LC analyser for my
measurements and it comfortably goes down to 1uH (below if one
ignores the inherent inaccuracies). The only thing I have so got
bad answers on this machine on was measuring my MMC strings.
**Aside: I have strings of seven caps. Each cap is bridged by a 10M
Ohm resistor. The instrument appears to measure correctly up to five
in series but then goes wildly inaccurate. I finally resorted to
putting the strings in a tuned circuit to determine their real value.
I don't think the leakage current due to resistors played a part but
will try again without them. Otherwise, the machine has worked
The Sencore even detects a single shorted turn in transformer
windings with ease with its "Q" measurement.