Re: 8-9 RFI noise thoughts.

Hi Terry,

I think your trying to account for the wave effects with lumped parameters.

When the gap fires a wave probagates from each side of  the SP.  they will
have oppositer polarities. The waves will be partialy reflected at each
change of
impeadance.  SP to interconnection, interconnection to coil, coil to
interconnection etc.

If I remember correctly you primary is about 30m long.  The wave velocity
will be some were between a half c and c. If its half a wave (I now think)
then thats a frequency some where between 2.4MHz and 4.8MHZ.  The wave
should be at a maximum one quater from each end of the primary as the waves
will cancel at the SP and at the center of the primary.  Check it out.

Regards Alwyn Jones (FL)

-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Cc: R.E.Burnett <R.E.Burnett-at-newcastle.ac.uk>
Date: 10 August 1999 12:18
Subject: 8-9 RFI noise thoughts.

>Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>Hi All,
> I think I have identified the source of the waveforms I see on the scope
>from the primary circuit firing.  The waveform is composed of basically
>three separate mechanisms:
>1. The first wave form is simply our old friend the few hundred ampere
>primary decrement wave that powers our coils.  It is simply the ringdown of
>the primary capacitor and inductor.  No surprise there...
>2. There is a fairly powerful 5-30 MHz burst right after the gap fires that
>last around 100uS.  I think this is caused by the self-capacitance of the
>primary and the inductance of the primary wiring.  My coil seems to have
>about 39pF of self-capacitance on the primary and around 890nH of wiring
>inductance.  When this system is hit by the gap firing, it rings for a
>short time.  This is especially important in that it hits the lower
>television frequencies.  However, since this oscillation travels through
>the whole primary loop, there should be ways of filtering it.  Perhaps a
>small inductor or two in line with the primary would lower this frequency
>to where it would damp out before oscillating too much or simply be so low
>as not to be a problem.  I think the zero crossing bursts are basically
>this mechanism too.
>There may also be about a 5MHz signal too that may be formed by the primary
>inductor and it's self capacitance.  This signal gets a little lost in all
>the other fun but it should be there, but of fairly low power...
>3. The third noise source is the gap.  When the natural capacitance between
>the electrodes is suddenly shorted as conduction begins, wild things
>happen.  Although this is not a true circuit theory phenomenon, I can
>reproduce the noise in computer models with a cap and inductor across the
>gap.  Judging from my measurements and making some guesses,  the gap
>capacitance seems to be on the order of 20pF.  The inductance is around
>80nH with a series resistance of a fraction of an ohm.  If the gap is
>charged to 21kV the burst power is enormous.  3GHz at around 2000 amps for
>a 10nS burst!!  Note that 2000 x 21000 = 42 megawatts!!  The RMS power may
>be in the tens of watts.  I don't think this signal travels too far down
>the interconnect wiring but is rather an intense point source of RF.  It
>can easily spray into the surrounding area and affect nearby electronics
>(like fiber optic probes).  However, I would think such high frequency
>would not travel too far into the surrounding neighborhood (I really don't
>know that??).
> I will try ferrites at the gap tips when they come.  The frequency would
>suggest that the electrodes may carry some of this current and the ferrites
>may present a good load to this signal...  Otherwise, one may have to put
>the gap in on old microwave or something to "try" and stop this burst from
>getting out.  I think trying to contain this burst will be tricky at a
>wavelength of a few inches.  The normal shielding may just act like and
>antenna when hit with this RF.  May need some microwave expert advice on
>this one...
> I assume the real mechanism is some fancy plasma thing...  Probably
>nuclear bomb science... ;-)  Hopefully, it could pre prevented all
>together.  Shielded, at least...
>Soooo.  The ~27MHz stuff should be filterable without too much trouble.
>Hopefully this would be the majority of RF that could irritate the
>neighbors.  The 3GHz pulse may be really nasty to stop...  I have no doubt
>of its power.
>BTW - I messed up on yesterday's post.  It is not 3000000 amps, more like
>~5000...  Was "thinking" too fast there :-)  Of course, the field probe
>would react differently to such a source, so the real level can only said
>to be "high"...
> Terry