Re: TC Inductance Formulas...

To: tesla-at-grendel.objinc-dot-com
Subject: Re: TC Inductance Formulas...
From: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
Date: Wed, 21 Feb 1996 09:46:20 +1200
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Hi everybody,
              Replying to Timothy Chandler on this topic...

<big snip>

> L:(Average)    (SUM)  0.166435839  166.43583937  166435.83937
>                (AVG)  0.027739307  27.739306562  27739.306562

<again> 

> L[m]:(Average) (SUM)  0.167945794  167.94579413  167945.79413
>                (AVG)  0.027990966  27.990965688  27990.965688

<and again>
  
> L[p]:(Average) (SUM)  0.166568649  166.56864907  166568.64907
>                (AVG)  0.027761442  27.761441511  27761.441511

I don't think you said what the measured inductance was (I may
have missed it.)
     Comment - I too like exactitude but in the real world this is
physically not possible. All the science I know quantifies the
degree of uncertainty or experimental error. For example, the "end 
effect" of a dipole aerial means that best tune is obtained with the 
less-than-ideally calculated element length. I suspect there are end 
effects associated with coils as well and any coil will couple 
however loosely into its surroundings. You will probably find that 
slightly different formulae are needed to get the closest values for 
different aspect ratios.
     Last comment - if you are after accuracy in resonance measurement
use NO resistance, series or shunting with the coil. The following is
the "real" resonance formula :

    fr = 1/(2xPI) x SQRT( 1/(LxC) - R^2/(4xL^2) )

I think I got that mouthful correct (I stand to be corrected). Anyhow,
by plugging the figures in you can see why the usual no-resistance
formula is generally good enough for a quick and dirty ballpark 
figure.
    Further comments welcome.
    
Malcolm