From: Paul
Date: Fri, 06 Oct 2000 08:51:44 +0100
Subject: Re: [TSSP] Progress report 28th Sep 2000
On Q factors, Malcolm Watts wrote: > I suspect that much previous research of this type was done > with radio applications in mind since tuning small inductors > with capacitors is the norm for those applications. Bare > resonators are out for such apps since the influence of the > confinements is much too great to be useful. Indeed. The only case I can think of from radio engineering is that of cavity and helical resonators, as used in narrow band filters. The helical resonator in particular looks and functions a lot like a tesla secondary. Years ago, when I worked for a telecomms consultancy, I had the job of designing a helical bandpass filter for VHF. At the time I could find no way to predict the bandwidth/Q factor of the helicals, in the end it came down to good old trial and error. The situation doesn't seem to have changed since! On gap losses, I won't go too far into this topic, since I don't know what I'm talking about! But just one question, perhaps gap conduction characteristics would be easier to measure in steady state conditions, using a CW source of a hundred watts or so, stepped up as necessary, by which the gap AC impedance could be measured more directly? A bridge arrangement perhaps? This might avoid some of the difficulties inevitable with the monitoring the transient ringdown and would eliminate the unknown losses of the impulsed primary L and C. On secondary behaviour, > Meanwhile, I am interested in focusing on the behaviour of the > resonator alone since its modelling is of great interest to me. Well you're in the right forum for that! > In particular, I am curious to know just how closely the Corum's > model and its consequent predictions of enormous voltages approaches > reality. I'm not familiar with their model. Perhaps you can tell us about it? In fact, this may be a good opportunity to ask all our tssp list members what they consider to be the outstanding mysteries (either for them personaly, or in general) surrounding secondary resonator operation. I've been reading back through some of the tesla list archives and noted plenty of confusion in the past. Puzzles about V and I distributions, that kind of thing. I'll start with my 'most wanted' list: 1/ How do we predict the AC resistance and therefore the Q factor and input impedance at resonance? 2/ How significant are ground conduction losses (both normal radial, and circular eddy)? 3/ How do we arrive at the optimum shape, turns, and wire size for max volts for a given power level or bang size? (I suspect that given an answer to (1), then (3) would be just a programming exercise). > I have seen some indications in low level tests that > left me flabbergasted and suspecting they might not be too far > wide of the mark. But is it realistically modelled by a > uniform transmission line? I'd like to hear and discuss more about the Corum's suggestions. Any net references available? > And just how close can one get to actually measuring the real > voltages produced by a non- toploaded resonator? Personaly, I prefer to measure secondary base current, which can be done quite accurately with a suitably calibrated current transformer. >From the current measurement one can get a pretty good estimate of the top voltage without going anywhere near it! Regards All, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.