Re: coupling coefficient
> Original Poster: Dan Kline <ntesla-at-ntesla.csd.sc.edu>
> >Original Poster: "D.C. Cox" <DR.RESONANCE-at-next-wave-dot-net>
> >to: Jim
> >Even with small coils any type of helix usually results in overcoupling.
> >We prefer a flat spiral and then check the coeff. of coupling using
> >standard techniques.
> I *should* know this, but I don't, so...
> What are the standard techniques for checking the coefficient of coupling?
Here are two I use: for a signal generator and scope check, sniff the
secondary with a probe positioned some distance away and feed the
primary with gap shorted with a signal generator with some series
resistance (to minimize shunting). The double-tuned response relies
on the primary being able to oscillate freely as it does in normal
operation. Note the two frequencies that the *system* rings at,
subtract one from the other and divide by the resonant frequency of
the resonator. This gives k. It assumes pri is tuned to sec.
The other is dynamic test: capture the beat envelope on the scope.
time the ringup to max secondary amplitude. This is Tdwell. Note the
resonant frequency. k = 1/2*Tdwell*Fr.
The derivation of this starts from the relation between the two
beat frequencies as measured in method 1 and the definition of dwell
time. Note that the presence of the beat envelope signals
overcoupling (highly useful since it also signals a complete energy
transfer minus losses from pri-sec). For both tests the primary must
be tuned to the secondary or the result will be in error.