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Re: Non-Linear Coil Winding Experiment. (and more tests!)



---------- Forwarded message ----------
Date: Tue, 14 Oct 1997 09:53:12 -0400 (EDT)
From: "Mark S. Rzeszotarski, Ph.D." <msr7-at-po.cwru.edu>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!) 

Hello Terry and All,
        I find your results quite interesting and along the same line of
research I am investigating at present using coils wound with multiple gauge
wire sizes along the length of the coil (to achieve low Zbase and high
Zsurge simultaneously).  A few comments:
       You stated in part:
>The coils were driven from a sine wave generator with a 600 ohm output Z.
        I suggest winding a transformer to reduce the output impedance of
your signal generator to a more reasonable value.  I used a 50 ohm output
impedance signal generator and still found the coil severely affected by the
generator.  I wound a 150:1 transformer using a ferrite core to drop the
impedance, and then started getting results close to theory.  (Kudos to
Malcolm Watts for suggesting the idea originally!)   Make sure the ferrites
can work up to 2 MHz, or add a toroid to your coils to drop the resonant
frequency a bit.  The extra C might reduce variability in the measurements
as well.

>        I tested the coils in a reasonably open space on a hardwood floor 6
>inches above bare dirt.  I tried the coils in other locations at various
>distances from the surroundings the results don't change significantly
>unless I get within about 2 feet from something big.  As far as I can tell,
>everything is reasonably accurate.  The field mapping experiment obviously
>had some variability but the general results I feel are accurate.
        If things are not changing significantly two feet away, you are
loading down the Q of the coils significantly with your signal generator.  I
can change resonance significantly by waving my hand six feet from the coil.
This is easily seen on a vector impedance meter.  I assume your 'scope probe
is at least six feet away as well.  The steel re-rod in my basement floor
also affects things a lot.  I center my coils between the basement floor and
the floor above.  Even this is a tradeoff.

>        One thing that blew one of my pet theories to hell is that the
>quarter wavelength for a 235.6 foot long wire is 1043.7 kHz.  All these
>coils exceeded that frequency considerably (so much for worrying about wire
>length vs frequency).
        True.  But you still might want to design your coil to force that to
match.  (More on this some other time.)

>        I feel that the reduction in the self capacitance was due more to
>the field concentration in the #2 and #3 coils rather than the winding to
>winding capacitance. 
        Quite possible.  It is also quite possible that stray
capacitance/inductance in the signal generator is causing a shift in
resonant frequency.  If your coil capacitance is only 5 pF, any stray
capacitance is significant!  I will try to duplicate the experiment myself.

>If anyone with good equipment would like to examine these coils and
>verify my tests, these coils are small and light so I can mail them.
        I am interested.  Contact me via private E-mail.  
Regards,
Mark S. Rzeszotarski, Ph.D.