Re: coupling coefficient

Hi Dan,

> 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.
> [snip]
> All,
> I *should* know this, but I don't, so...
> What are the standard techniques for checking the coefficient of coupling?
> Thanks,
> Dan

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.