Jim Brown-10 wrote:
>
> On Tue, 19 Aug 2008 11:18:54 -0700 (PDT), Bill W4ZV wrote:
>
>>You only need the two -6 dB points
>
> That's looking at the elephant through a pinhole. It can also be
> very useful to know what happens much further down the filter slope
> -- say at the -20 and -30 dB points.
>
Well why not the -60 to -80 dB points? :-) Two points are entirely
sufficient to **center** the filter's 6 dB bandwidth, which was the question
asked. Regarding Ed's comment about ripple, we'll never see 6 dB ripple
excursions unless there is a defective filter. The filters I've checked can
have a very slightly asymmetrical response (we're talking tenths of a dB)
but I set mine so that -6 dB points are equidistant from the center.
73, Bill
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