[Lf] Calculating distributed C for inductors]

[Andre' Kesteloot]

Dave Brown wrote:

> The classic method for determining self capacitance of an inductor is to
> measure the resonant frequency (freq) with several values of parallel
> capacitance.(C)
>
> Making a plot of 1/(freq)squared on the vertical axis v. resonating
> capacitance on the horizontal axis yields a straight line(or should!!) that
> intersects the HORIZONTAL or capacitance axis at a negative C  value when
> extrapolated.
>  The negative C value is the self capacitance of the inductor in question.
> As well,  the slope of the straight line is a measure of the  TRUE
> inductance value of the coil and can be taken from the relation  L (henries)
> = 0.0253M, where M is the slope of the line.(freq in MHz and C in pF).
>
> A more practical method based on the above is the F/2F method where the
> inductor is resonated at an initial frequency, F1, the added parallel C
> value measured (C1). The inductor is then re-resonated at TWICE the first
> frequency, say F2, and again the resonating C measured(C2).
> The inductor self-capacitance is then given by
> Cself = (C1 - 4C2)/3.
>
> Measuring the inductance and then the parallel resonating capacitance and
> trying to predict the stray C from the required result correction will only
> give an approximate answer, as will direct measument of the self-resonant
> frequency (and thence to the self-C)  but for accurate work the F/2F method
> is better.
>
> 73
> Dave
> ZL3FJ