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*To*: tesla-at-pupman-dot-com*Subject*: Re: Vortex gap loss measurements*From*: "Daniel Boughton" <daniel_boughton-at-yahoo-dot-com> (by way of Terry Fritz <twftesla-at-uswest-dot-net>)*Date*: Sun, 03 Sep 2000 19:01:10 -0600*Delivered-To*: fixup-tesla-at-pupman-dot-com-at-fixme

Bert: Excellent call to Morecroft (Terman the RF guru of Stanford defers to his(Morecroft on Spark Telegraphy) mastery of this subject that's how I discovered the book) and excellent summary too. Excellent points (gems)you brought up too: 1. The first current peak is responsible for burning open the channel and determines its resultant resistance. 2. Gap resistance is fairly stable for the remainder of the decrement. Thanks, Dan --- Tesla list <tesla-at-pupman-dot-com> wrote: > Original poster: "Bert Hickman" > <bert.hickman-at-aquila-dot-com> > > Gary, Dan, John, Jim and all.. :^) > > Excellent experiment! > > It turns out that introducing virtually any spark > gap into a single > (uncoupled) RLC circuit will induce > linearly-decrementing behavior > instead of the exponential decay seen with a classic > RLC circuit. It's > interesting to rediscover this, since it was > originally reported by Dr. > J. Zenneck almost 100 years ago (1904!). Because of > the linear > decrement, tank circuit energy goes to zero in a > sharply-defined period > of time. The waveform on Gary's site clearly shows > this happening in 295 > uSec for the Vortex Gap. An exponential decline will > asymptotically > approach zero but will never quite get there (at > least in theory). > > The spark gap's nonlinear, arc-like behavior is > characterized by a > relatively constant voltage drop (only tens of > volts) that's pretty much > independent of gap current. The actual voltage drop > is mostly a function > of the geometry, materials used in the gap, gas > pressure, and the type > of gas(es) and metal(s) that form the arc. The > instantaneous energy > that's lost in the gap is almost directly > proportional to tank circuit > current (E = V*I), and it's this characteristic that > actually drives the > linear decrement. > > John H. Morecroft devotes a fair section of his book > to the behavior of > spark gaps in RLC and coupled circuits in > "Principles of Radio > Communication" (in all three editions, but the 1921 > 1st edition is the > most thorough). Of particular interest is an > equation, originally > developed by Zenneck and Stone, which describes the > linearly > decrementing tank circuit current as a function of > the Effective Gap > Resistance (R): > > Section A: Section B: Section C: > ---------- ---------- ---------- > I = -E*Sqrt(C/L) * (1-(R*t)/(2*L)) * > sin(t/(Sqrt(LC)) > > While Sections A and C of the above equation simply > describe the peak > current and sinusoidal oscillations, section B > represents the linear > decrementing term that forms the "envelope" of the > waveform. If the > spark gap behaved as a pure resistor, section B > would instead be an > exponential function of time. The current envelope > declines to zero when > (R*t)/(2*L) = 1. > > This means that, if we know L and measure t, we can > solve for the > effective gap resistance R and use it to compare > different types of > gaps! Morecroft suggests that gap resistance was > actually governed by > the magnitude of the FIRST current maximum. > Apparently, the higher the > first current peak, the larger the initial plasma > channel, and the lower > the effective gap resistance for the remainder of > the decrement. This > also implied that there was relatively little > modulation of gap > resistance by the oscillating RF current inside the > envelope. > > Let's re-look at Gary's experiment now in the light > of the above > relationship. Gary's primary circuit resonated at > 138 kHz, and per his > coil specs, he was using a 0.021 uF tank cap. This > implies a tank > inductance of about 63 uH. The Vortex gap > decremented to zero in about > 295 uSec, while the vacuum gap did so about 17.5% > quicker, or in about > 243 uSec. This implies that the vacuum gap lost > energy more quickly, and > thus had a higher effective gap resistance. Solving > for the effective > gap resistances of the two gaps styles: > > RVortex = 2*L/t = (2*63e-6)/(295e-6) = 0.43 ohms > (lower = GOOD) > > and > > RVacuum = (2*63e-6)/(243e-6) = 0.52 ohms > > Conclusion: > The Vortex gap has significantly lower gap > resistance, possibly because > of the greater number of charge carriers available > at the higher > operating pressure. However, gap resistance is only > one parameter making > for an efficient gap. Another is its quenching > capability. Higher > pressure gaps often take longer to quench. However, > some of Gary's > earlier measurements seemed to indicate that the > vacuum gap was not > quenching very well, so it remains for another set > of experiments to > determine if the Vortex gap has better quenching > ability. > > Great job, Gary! > > Safe coilin' to you all! > > -- Bert -- > -- > Bert Hickman > Stoneridge Engineering > Email: bert.hickman-at-aquila-dot-com > Web Site: http://www.teslamania-dot-com > > Tesla list wrote: > > > > Original poster: "Lau, Gary" <Gary.Lau-at-compaq-dot-com> > > > > Today I found some time and performed a comparison > between the gap losses of > > my single vacuum gap, and my new single vortex > gap. To do so, I scoped the > > primary ringdown with no secondary in place. I > used a Terry Fritz fiber > > optic voltage probe across the primary coil and a > digital storage scope to > > record the results. I have not yet accurately > calibrated the voltage > > readout, so for now, the results are just relative > to each other. > > > > With no secondary in place, the ringdown is a > linearly decrementing > > waveform, not logarithmic. As such, the slope of > the ringdown indicates the > > losses in the circuit and is independent of the > gap firing voltage. I > > performed ringdown slope measurements at a variety > of gap widths to vary the > > initial voltage, but the ringdown slope is a > constant, independent of Vgap. > > > > The power to the blower motor is varied through a > lamp dimmer and I tried > > varying the motor speed to see what effect that > had. At very low speed, the > > linearly decrementing waveform became slightly > logarithmic-looking, but > > still predominantly linear. The gap breakdown > voltage appeared to change > > slightly at low speed, but this was hard to > measure as it was slight and the > > bang-to-bang gap breakdown voltage is not as > consistent as one might hope. > > > > The slope decrement figures are assuming that my > probe is accurately > > calibrated for voltage, though I suspect it may > not be, so the figures are > > useful only for relative comparison purposes. > > The pressurized vortex gap decremented at > 200V/usec. > > The vacuum gap decremented at 235V/usec (17.5% > faster). > > The vortex gap breakdown voltage is about 20% > higher than the vacuum gap at > > the same gap distance. > > > > Vortex gap web page: > > > > > http://people.ne.mediaone-dot-net/lau/tesla/vortexgap.htm > > > === message truncated === __________________________________________________ Do You Yahoo!? Yahoo! Mail - Free email you can access from anywhere! http://mail.yahoo-dot-com/

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