Re: Impedance match, was:Coil Efficiency (quenching)

From: 	FutureT-at-aol-dot-com[SMTP:FutureT-at-aol-dot-com]
Sent: 	Wednesday, July 30, 1997 3:01 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: Impedance match, was:Coil Efficiency (quenching)

<< snip>I was trying to encourage others (and particularly the 
> speculators) on the list to actually get a scope onto it and see for 
> themselves what happens. I hope as many as have access to 
> instrumentation do.
>      I'd just like to say that we are incredibly lucky in this day 
> and age to have access to tools and instruments that Nikola could 
> only have dreamed about. IMHO, full advantage should be taken of 
> those tools to really understand how coils operate. Greg is not 
> designing his new coil on pure but using a combination of measurement 
> and advance in theory (hope you don't mind me speaking on your behalf 
> Greg).
>      Thanks to my own experiments and an excellent post earlier this 
> year by Gary Weaver ("The Best Primary"), I am now designing some 
> experiments to examine coupling from a new angle. I have noticed that 
> for resonators with an H/D significantly above 2, some height is 
> required in the primary (i.e. a helix or saucer can work better than 
> a properly tuned flat spiral). I came up with a guideline for good 
> results that the height of a primary whose bottom turn starts at the 
> same height as the bottom turn of the secondary  should be between
> 5 to 10% of the height of the secondary with a mean diameter around 
> 2 to 3 times that of the secondary. That was the experimental result.

Hi Malcolm,

This is very interesting, and suggests that all "k"s of a particular value
are not equal.

>     The theory: Using easily accessible mechanical analogy of the 
> steel ruler in the vise and varying "coupling" height and noting 
> effects on ruler movement, and looking at the concept of link 
> coupling into a transmission line, it seems to me that what in effect 
> we are doing is _tapping_ into the line at some way along its length
> (this applies to 2 coil systems only). Now if you do this in a 
> transmission line, you are tapping into a particular impedance (with
> a particular impedance) since this is different along all portions of 
> the line.

Very interesting about "tapping" into the line at a certain impedance
point.  I had also been thinking that something like this may be 
occuring.  IMO, this effect, if it does exist, makes a 2 coil system more
like a magnifier (where the driver can provide an impedance matching 
role.)  At least regarding impedance matching.  The magnifier of course
is different in other ways.  In any case if this impedance tapping is 
occuring, it is important that we study it as you said since it would have
a significant impact on coil efficiency.  (of course you know this...I'm
mentioning it for the benefit of others, as you do)
>     Up to now, effects of coupling on coil behaviour have been rather 
> difficult to determine. I think this is because when we normally vary 
> k, we are varying at least two quantities at once! k can be varied in 
> many different ways. For example, varying the height of the primary 
> relative to the secondary is not only altering flux coupling but also 
> the tap point.

Good point, and this could be the key.

>To alter k alone while leaving the tap point intact 
> means increasing primary diameter while holding both primary height
> and vertical position constant relative to the secondary. k can also 
> be altered by reducing primary height and knocking a turn or two off 
> to keep inductance constant. Another is to reduce turns and keep 
> height constant while increasing Cp value to maintain tune.
>     There is a good reason why this possibility has not been explored 
> (as far as I know). Primaries are normally set in concrete as far as 
> physical construction goes which makes it fiendishly difficult to 
> change the diameter or the height at will.
>    The experiments: I want to explore the possibility that altering k 
> in different ways but just one parameter at a time will give 
> credence to or refute the above ideas. It seems like a nightmare at 
> first glance but I regard it as absolutely necessary to advance the 
> art. If anyone has ideas on a construction method that might allow 
> altering as few parameters as possible I would love to hear them. I 
> am lucky to get use of the lab as such opportunites are fast 
> disappearing here.

I think that Gary Weaver in his excellent Best Primaries posts, had
a suggestion for a mechanical device that would "stretch" the primary,
and this may be useful for varying it in the way you suggested.  Bert
Pool has also devised a mechanism for compressing and 
un-compressing a helical primary to change it's inductance.  That was
a height change I think. 

A friend of mine (not a coiler), suggested using a bunch of plastic
rollers that would allow the coil windings to "slide" relative to each
other, thereby widening and narrowing the coil.  
>     Any other thoughts on the above most welcome. I regard tables as 
> useful guidelines to building a coil, but nailing things down in 
> mathematical formulae gives a much deeper understanding of how it 
> works and in my opinion, puts design on an engineering platform.


In one experiment, I took the extra coil from a working magnifier, and 
placed it directly on top of the driver (so that it was now a classic TC).
The spark increased from 41" to 43" (had to retune "out" a little--as
expected).  The driver had widely spaced turns, whereas the extra coil
had closely spaced turns, so there would be a discontinuity between
the coil sections as far as inductance concentration.  Not sure what
the significance of all this is, but it seems related to the "tapping" 
concept you mentioned. 

John Freau
> Malcolm