Re: TC vs MAG

From: 	Malcolm Watts[SMTP:MALCOLM-at-directorate.wnp.ac.nz]
Sent: 	Monday, August 25, 1997 1:27 AM
To: 	tesla-at-pupman-dot-com
Subject: 	Re: TC vs MAG

Hi Jim,
          My answers for what they're worth....

> From:   bmack[SMTP:bmack-at-frontiernet-dot-net]
> Sent:   Sunday, August 24, 1997 10:37 PM
> To:     tesla list
> Subject:    TC vs MAG
> hello all
> I've been reading references here and there on the list to 
> magnifiers and secondary windings of TC's.
> To the best of my understanding, the difference between the 
> mag and the TC is that the mag uses tight HF transformer coupling
> (as tight as air core gets-that is) and uses an additional quarter wave
> resonator in series with the Hf transformer secondary.  This additional
> resonator should have as little  magnetic coupling as possible as to
> avoid damping. Right so far?

Yes. Except that in a sense, the resonator is coupled to the driving 
system as long as the gap is alight since the two are _electrically_ 
coupled. You can reach k > 0.9 in an air-cored transformer quite 

 > My questions are: > 
> 1) Is the mag secondary quarter wave resonant, or is the turns ratio 
> the main issue here?

Turns ratio. Ideally the driver is a voltage source. In practice, it 
never is because the primary cap is not a voltage source. For a 
tightly coupled driver, you can tune the primary to the resonator and 
virtually ignore the secondary.
> 2) If it is quarter wave, the sum length is half wave which should
> give poor results. Is there some phase abberation that makes this 
> work?

This is really only an issue in a loose coupled system where the two
secondaries appear to form a single resonator.  

> 3) Some coilers don't get seem to get too fussy about the actual
> wire length used, rather they use a "magic number" of 900 turns.
> Maybe I'm too theoretical, but I ALWAYS calculate the wire length
> to get a "ballpark" idea of free resonance, THEN go for optimal
> aspect ratio.  I would like your opinions on this.

The 900 - 1000 turn guide allows a fair amount of inductance without 
the wire become too small and hence excessively lossy. Wire length
is really a bygone era thing. I use the Lself and Cself of the 
resonator to calculate Fr. Works every time for every resonator I've 
ever built.

> 4) In some low power table tops I've built, it was noted that 
> the resonant freqency was very sensitive to the actual wire 
> length.
> In fact the secondary could be in two or more sections separated
> by about a foot (didn't try longer) and still maintained a  frequency
> realtionship to pure length! 

Well, it will to some extent. If you work through Wheeler's Lself 
formula you can see why. What you have done is to reduce the 
inductance by separating the winding into pieces but at the same 
time, you have increased Cself by maing the thing taller. 

> These models used small top capacitances. 
> Thus my confusion about the magnifier concept.

What k was the system running at?

> Thanks in advance,
> Jim M