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- To: tesla-at-pupman-dot-com
- Subject: Re: Why does top capacitance work? (fwd)
- From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
- Date: Mon, 10 Mar 1997 11:06:48 +1200
- Organization: Wellington Polytechnic, NZ
- Priority: normal
HI John, I have to take issue with some of the statements in this piece: <snip> > >I often wondered if a critically coupled classical coil would be superior > to other combinations. I do not believe a critically coupled coil has ever > been built. There are several parameters that have to be coordinated. Rp > would have to equal Rs and Lm = sqrt(RpRs)/(6.283 F). Also Lm = K > sqrt(LpLs). Note that critical coupling involves more than only a single > hump test. <snip> I thought a single peaked response *just* prior to splitting was axiomatic as far as critical coupling goes. Rp equalling Rs is a special case: the coils have identical L/Cs - never the case in TC. The strict definition of critical coupling (a la Terman et al) is that critical coupling is achieved when the resistance reflected back into the primary from the secondary matches the primary's own internal resistance. In the case of a step-up transformer (TC), Rp reflected << Rs. To make matters even more complex, the governing resistance in the primary is non-linear (spark gap) so critical coupling depends on a transformed secondary spark impedance equalling that of the gap. Coupling might get close to critical if the gap is alight while the secondary issues a discharge but if the gap can be put out, we can do far better than the max power transfer theorem suggests. We can get the bulk of the energy (minimizing gap losses) into the secondary and put the gap out in theory. People who have measured this though have found that it is easier said than done. Malcolm
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