If you use a larger capacitance resonance will naturally be at a lower
frequency so you will be measuring the Q there instead. Selectivity will be
higher, but when the bandwidth at the 3dB points is divided into the centre
frequency the Q will still come out at the right value, albeit at this new,
lower, freq.
Incidently, when measuring low Qs you should use the geometric centre
frequency in this calculation rather than the mid point between the two 3dB
points. ie. Fc = SQRT(Fu * Fl) where Fl and Fu are the 3dB frequencies.
It won't make much difference when the Q is in the hundreds, but will be
noticable when used on small coils.
Andy 'JNT
> Is this the right way of going about it? If I use a larger
> capacitor across
> the coil won't this give a sharper selectivity and improved
> apparent Q?
>
> Regards,
> Peter, G3LDO
>
> e-mail <[email protected]>
>
> Web <http://web.ukonline.co.uk/g3ldo>
