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

To: tesla-at-pupman-dot-com
Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)
From: Tesla List <mod1-at-pupman-dot-com>
Date: Sun, 19 Oct 1997 21:54:54 -0600 (MDT)
Approved: mod1-at-poodle.pupman-dot-com


---------- Forwarded message ----------
Date: Mon, 20 Oct 1997 09:49:29 +1200
From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)  

Terry,
        My apologies. I did transcribe the equation incorrectly. You 
are correct that the last term is typically 4 or 5 orders of 
magnitude less than the first (when done correctly :(. Experiment 
suggests that capacitive loading is by far the biggest bugbear of 
accurate F measurements for a resonator. The ESR is a very 
significant figure when it comes to measuring coil Q. I conduct most 
of my measurements using a source impedance of 7 Ohms (which still 
dips when feeding the base of a resonator at resonance).

Again, my apologies,
Malcolm

> From: terryf-at-verinet-dot-com
> To: Tesla List <tesla-at-pupman-dot-com>
> Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)   
> 
> At 03:21 PM 10/16/97 -0600, you wrote:
> >
> >
> >---------- Forwarded message ----------
> >Date: Fri, 17 Oct 1997 08:31:02 +1200
> >From: Malcolm Watts <MALCOLM-at-directorate.wnp.ac.nz>
> >To: tesla-at-pupman-dot-com
> >Subject: Re: Non-Linear Coil Winding Experiment. (and more tests!)  
> >
> >Hi Terry,
> >
> ><SNIP>
> >> high Z source the Q (bandwidth) should broaden as you describe but Fo should
> >> stay the same.  Of course with non-linear coils there may be unknown factors
> >> at work, but my results with different resistances did not show anything
> >> unusual.
> >> 
> >>         Terry
> >
> >Fo shouldn't stay exactly the same and measurement by myself and 
> >others show it doesn't. The popular 1/[2PI.SQRT(LC)] formula assumes 
> >zero resistance. The real formula 1/[2PI.SQRT(LC - R^2/4L^2)] takes
> >this resistance into account. The resistance is the Effective Series 
> >Resistance at the frequency being measured.
> >
> >Malcolm
> >
> >
> 
> If      L=10 mH
>         C=10 pF
>         R=50
> 
> I get:  LC = 10^(-13)     R^2 = 2500    4*(L^2) = 0.0004
> 
> Fo = 1/[2*pi*SQRT(10^(-13) - 2500/0.0004)] = 0 - 0.00006366i
> 
> Can you clarify this equation?  It isn't making sense to me.
> 
> The  R^2/4L^2  part must be different???
> 
> Ahhh...... perhaps you meant the frequency of a decaying impulse response of
> a coil.
> 
> Fo = SQRT(1/LC-(R/2L)^2)/(2*pi)  This equation is correct only for an
> impulse response (capacitive discharge).  My measurements were steady-state
> AC.  Trying the numbers:
> 
> 1/(2*pi*SQRT(L*C)) = 503292.546158 Hz
> 
> SQRT(1/LC-(R/2L)^2)/(2*pi) = 503292.38888 Hz
> 
> A difference of 0.157278 Hz
> 
> How would one measure such a subtle difference?   Perhaps, I have made an
> error or wrong assumption?
> 
>         Terry