RE: Frequency splitting and measuring Q
To: tesla <tesla-at-grendel.objinc-dot-com>
Subject: RE: Frequency splitting and measuring Q
From: Richard Hull <whitlock-dot-com!RICHARDH-at-uucp-1.csn-dot-net>
Date: Mon, 01 Apr 96 16:28:00 PST
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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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Subject: Frequency splitting and measuring Q
Date: Monday, April 01, 1996 12:03PM