30MHz Spark Gap Testing

From:  terryf-at-verinet-dot-com [SMTP:terryf-at-verinet-dot-com]
Sent:  Wednesday, April 08, 1998 7:06 PM
To:  Tesla List
Subject:  Re: 30MHz Spark Gap Testing 

Hi Dale,

Wow! lots of questions, but here goes.....

At 08:14 AM 4/8/98 -0500, you wrote:
>From:  Dale Hall [SMTP:Dale.Hall-at-trw-dot-com]
>Sent:  Tuesday, April 07, 1998 8:20 PM
>To:  Tesla List
>Subject:  RE>30MHz Spark Gap Testing 
>RE>30MHz Spark Gap Testing - Is this real??
>Terry & List,   Your scope observations are very interesting. Good
>Would like to see a detailed schematic dwg w/LRC values of set up, incldg  load
>equivalency the probes, where & how they are connected.
>Of particular interest is the value & number of interconnects - looks like
you may
>be using copper strapping everywhere - what lengths, widths, thickness' ?, 
>likewise about any RFC bypass caps to gnd (NST centertap). This portion of the
>circuit is the most likely to contain HF damped osc from the sparking impulse
>excitation ***.  The Tesla primary is a highly selective filter to all but the
>fundamental resonant frequency, turning any energy into a common resonant 
>sinusoid (effect of capacitive and inductive resonance at moderate
Q)....even with
>spark gap opening and closing in series with a previously stimulated  LC it
>would merely serve to add energy at the resonant freq to the resonating LC  -at- 
>f=1/(2PI*sqr(LC)). The placement of the gap changes little (parallel w/ NST or
>series w/ Lpri given the RFC's provide good isolation).

See http:/www.peakpeak-dot-com/~terryf/tesla/experiments/experiments.html and
look at the RC filter paper.  The test equipment and setup is identical with
the following exceptions:

The aluminum straps have been replaced with identical copper straps. 1.2 or
1.5 inches wide by about 12 inches by 5 mil thick.

The voltage probe is 5Meg ohms (but I don't use it because of noise.
Working on this.)

The current shunt shown in the paper (didn't work worth....) has been
replaced with ten parallel .1 ohm 1 watt SMT resistors connected to the
copper strap with as good of RF design as I knew how to do) for a resistance
of 0.01 ohm.  I think it is shown in the probe description paper.

The filter is as described.  The center tap of the neon is grounded.  I
think the paper left this out.

>Perform some Lrfc & Crfc calcs for likely activity around 50MHz. 
>Have you scoped the Igap alone ?, Current between RFC and gap (each side) ?,
>and the current between gap and Cpri ?  What was Cpri, Lpri for your tests ?

Haven't done this to the level you suggest.  I have played some with the
setup.  See "30MHz (now 40MHz) Probe Testing Update." post.  Cpri= 17.0nF

>For your 50 ohm terminated antenna test, can you describe it in more detail ?
>Are you using transmission line matching to antenna impedance ?
>(1/2 wave 50 MHz ~ 9.36',  1/2 wave 200kHz ~ 2340')

It is a Radio Shack scanner antenna (can't find part number at the moment)
that is connected to a 50ohm BNC terminator and then to the scope.  I can
see the effects on a simple wire antenna if I look closely but the
attenuation is high.

> I typically find ~2mHz oscillation after spark channel conduction in my coils.
>Next time I set things up I'll look closely at the gap = vacuum.
> I use TDS 540 usually BW limited to ~100MHz.

Can't visualize the 540 at the moment.  I think I have used every modern Tek
scope (blown a few up too :-)))).  Should work great.  Digital storage is
far superior for this stuff.

>*** sparking impulse excitation  Ref: HV Engr Fundamentals, Kuffel, Zaengl
pgs 375,6
> ISBN 0-08-024212-X  1986 Pergamon Press.  
> Fig 5.34 Trichel pulses: regular pulses before but close to each event of
gap breakdown
>Trichel studied this effect using static conditions for observation &
control for research..

I may be seeing the Trichel pulses.  50nS before the gap current fires, the
antenna voltage shows signs of activity.

I have been so busy I haven't thought much about the fundamentals behind the
bursts.  Probably more a fields and physics problem than a simple circuit
theory thing.  Malcolm has some ideas on this.

I have all 42 original scope pictures and original text notes at:


Sorry no html link.  The files are called 1-8.jpg, 9-16.jpg.....  The text
file is 1-42.txt