Re: RE: How do you measure filter offset

Posted by Bill W4ZV on Aug 19, 2008; 8:26pm
URL: http://elecraft.85.s1.nabble.com/How-do-you-measure-filter-offset-tp733034p734061.html

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