brainwagon "There is much pleasure in useless knowledge." — Bertrand Russell

12Dec/090

An Active Filter Design

Eldon, WA0UWH pointed out WA4DSY's website that features an active filter design applet. I was just waking up this morning, so I thought I might give it a try. I used LTSpice's universal op-amp node, and wired it for positive and negative voltage feeds. I specified a 2.2uH value for the caps, and a 800hz center frequency, with a bandwidth of 300hz. It is just a two pole filter, so you shouldn't expect much, but I suspect it would be useful. I am tempted to try to adjust the resistor values to nearby standard values, and see how it looks, but I think I'll need coffee before I do that.

2009-12-12_0932

Addendum: a little poking around, rounding the various values to their nearest 10% values resulted in a filter with approximately the same shape, but which had decreased gain in the bandpass region (roughly 3db down from the original). I suspect at the very least, you could compensate by adjusting the overall gain of the filter.