From: Paul
Date: Thu, 05 Oct 2000 12:32:58 +0100
Subject: Re: [TSSP] Progress report 28th Sep 2000
Malcolm Watts wrote: > The obvious possibility is msmt error. I'm inclined to agree with you that the overall consistency of your set of measurements is encouraging. You have already highlighted the one doubtful reading. There is always the possibility of systematic error but I think that suggestion should be kept decidedly in reserve. > Therefore, I would be interested to know what an approach other > than Medhurst suggests and how Medhurst arrives at his result. I have doubts about the applicability of Medhurst's Q results to tesla resonators. Medhurst made his AC resistance measurements at frequencies well below the lowest self resonant frequency, by swamping Cself with large external capacitances. This forces the coil's current distribution to be almost uniform. Thus we might expect an additional factor to occur when considering coils operating near their bare self resonant frequency. This effect would be more pronounced in the absence of a topload, since then the current non-uniformity is highest. This discrepancy would not be noticed in the conventional applications for Medhurst AC resistance estimates, since most HF inductors work with circuit capacitances significantly higher than the self capacitance and therefore have uniform current. As a result I'm looking to find a way to calculate the effective AC resistance independently of Medhurst. On primary ringdown measurements, > The *relative* times and levels give all the information needed > to calculate differences in proportional losses on a per-cycle > basis. Your observed scale invariance of the ringdown (with respect presumably to bang energy and frequency) suggests to me that if the gap resistance is significant, then it must also be more or less constant with current and frequency. Alternatively, if the gap resistance is not constant (which I might reasonably expect to be the case) then it must be relatively small. > General rules can be derived such as constant (or nearly so) > voltage drop per gap etc. Presumably then the (nearly constant) grap volts drop is small. Would that indicate that the dominant factor in primary circuit loss is not the gap? > I think the major thing to come out of my secondary > research was that for non-output discharge applications, > secondary characteristics really matter but if one is > designing for long sparks, those considerations, while > important to a certain extent are relegated to the stalls, > because the emphasis now shifts to dealing with the > characteristics of ionized air and how best to make it do what > is required. Agreed. Terry has described satisfactory performance from his coil despite a low measured Q. Any predictions of voltage and current from our software model will only apply to small signal operation. We might hope that one day we will be able to predict Q, but will that help in optimising real world coils? Perhaps not. Regards, -- Paul Nicholson, Manchester, UK. --
Maintainer Paul Nicholson, paul@abelian.demon.co.uk.