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RE: Frequency splitting and measuring Q


Hi Skip,

The frequency spliting that I have refered to is the classic splitting of 
the power points in the resonator into two frequencies about resonance and 
is due to over coupling.  Please do no confuse this with Q.  Q is a function 
of the quality of a coil and is related only to its internal inductance and 
the total loses dissapated within it.  Coupling and frequency spliting are 
related to the closeness of two coupled coils and their ability to 
faithfully transfer or produce a given fixed frequency output.  The quench 
time of a spark gap can also affect the coupling and, therefore, frequency 
splitting in many systems.

This is almost a non-issue where tesla coils are concerned.  We are not 
processing power for efficient single frequency  through-put or 
communicating on a fixed frequency as in radio, therefore we are not too 
worried about frequency splitting.  We are concerned about voltage output! 
  We could care less if our 10 foot streamers are a few khz apart in energy 
content!  I have long argued that we need to get this radio engineering 
mentality out of Tesla coiling.   We must fully understand it, but not apply 
it in every little detail as if we are running a radio station.   If we are 
ever shut down by the FCC, it will not be for frequency splitting!  It will 
be for operating a spark excited, multi-kilowatt RF source.  A real big 
no-no since the 1930's.

This not an invitation to get sloppy, however.   You need not be over 
concerned with this issue unless you just do something stupid like try and 
run a two coil system above k=.25 with a simple kludged up gap or something 
like that.  A nice helping of overcoupling is not the horror it is made out 
to be.  Gross over coupling is usually done by rank amateurs whose gap is 
terrible and who jam the primary right up aginst a tall slender secondary 
with a needlepoint electrode.  A classic sign of gross overcoupling is 
sparks racing up and down a coil's secondary.

I prefer to overcouple to the point of spark racing and then back off a bit. 
 This way you are sure that max power transfer for your system is taking 
place.  You are also sure that you are over coupled, have frequency 
splitting, and are getting the most bang for your electrical buck.    With a 
really superior gap (short quench time) we have coupled two coil systems up 
to k=.30.  "Nemesis" ran 10KW with K=.25 coupling!

In general, any split frequencies within the .707 bandpass will have little 
or no effect on system operation and the extra coupling will really kick 
butt!  So feel free to splatter your power over a range of frequencies 
provided your resonator doesn't complain.

Richard Hull, TCBOR


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From: tesla
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shu95mmc; stevej; twill19; yiorgos
Subject: Frequency splitting and measuring Q
Date: Monday, April 01, 1996 12:03PM