Hello, Yesterday, Walt K6WRU wrote "In analog filter design, you get to choose between good phase performance and good amplitude performance. You can't have both. If you want a flat passband and steep skirts, you'll get wonky phase." I suppose that is basically correct for the standard "off-the-shelf" filters available to the ham community.
However, filters can be produced that correct the group-delay. I have designed many such crystal-filters in my career spanning almost three decades. These filters were supplied to companies such as Harris for use in military equipment. A typical shape-factor 60dB/1dB would be less than 1.4. The corrected group-delay would be quite flat over perhaps 80% of the 1dB bandwidth. (For many years, one of my filter designs was part of the display in the lobby-area of Harris in Rochester NY; it may still be there for all I know.) Additionally, about the "Bessel" design, I would look first to either a" Gaussian to 6dB" or a "0.05 degree phase-ripple" approach. If I recall correctly, either choice can give sharper skirts than the Bessel and still have relatively flat group-delay. (I no longer have access to Zverev, my copy of which by the way was full of errors, especially in the band-reject section.) K6WRU wrote "There is no free lunch, it's physics." So true. Engineering is all about compromise; what do I have to give up to get what I still want. 73 Jerry KM3K ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
