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
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
>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
>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
> ISBN 0-08-024212-X 1986 Pergamon Press.
> Fig 5.34 Trichel pulses: regular pulses before but close to each event of
>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