Re: Wire length,resonance, and Q (fwd)

---------- Forwarded message ----------
Date: Mon, 25 May 1998 09:13:02 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Wire length,resonance, and Q (fwd)

HI Bart,

> Date: Fri, 22 May 1998 04:50:06 -0500
> From: "Barton B. Anderson" <mopar-at-uswest-dot-net>
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Wire length,resonance, and Q (fwd)
> John and All,
> Backing up for second;
> I think most would agree that the 1/4 wave formula is not absolute for operation,
> but, just as Tesla used the 1/4 wave calculation as a guide, when answering
> questions for new coilers who are looking for the number of turns for a
> secondary, I would suggest the 1/4 wave calculation, as it does put them right
> into the operational ballpark. Would others agree on this?

You can do *much* better by using Medhurst's Cself and Wheeler's 
Lself. I think those old equations should be thrown away forever. I 
spent three months rooting out a formula for Cself and Medhurst was 
IT for a uniformly wound coil. OK, there are bones of contention about
the true nature of Cself and what it actually is (Corums have devoted 
a chapter to this in a forthcoming book) but I note with a degree of 
disdain that they have come up with the exact same figure the 
Medhurst calculation would yield by taking the secondary inductance 
as measured and the resonant frequency as measured and calculating C 
based on those figures. There is some inconsistency in their approach 
here. The point I would make is that whatever the truth, the two 
calculations I have suggested *always* yield a pretty accurate 
answer. I suspect that a lot of the "1/4 wave" formulae have been 
arrived at retrospectively for particular systems. None of them is 
applicable to all in the way that Medhurst and Wheeler are and an 
examination with a spreadsheet suggests some of them won't work for 
any coils. This was the starting point for my investigation.

 > Going forward;
> This thread is always interesting when it comes up from time to time. The big
> question which I keep asking myself is, "What are the optimum parameters?" as
> John hinted towards. I wonder if there is really is an optimum. It appears that
> each coils optimum setting is unique to the geometry, size, power levels, ground
> plane, and a host of other variables.
> Bart

They are pretty conflicting: A high secondary reactance to yield a 
high voltage, a low secondary reactance to yield a high current. 
Using a large top C removes the burden of the low reactance 
requirement from the resonator itself. However, Vout can only reach 
what Es and top C will allow.