If it pleases you to use DSP set wider than roofing filter - by all means, go for it.
I would not, however, clame objectivity based on my subjective experience or somebody's valuable opinion and simplistic explanation , I perefer measurements performed on good lab equipment. K8ZOA did some of the measurements on 500 Hz filter, but most of them probably applicable for the 1.8kHz filter. See report here: http://www.cliftonlaboratories.com/elecraft_k3_noise_blanker_and_crystal_dsp_filtering.htm In his measuremetns, setting DSP wider than the actual roofing filter actually degraded the total response in the stop band. 73, Igor, N1YX ----- Original Message ----- From: "Jim Brown" <[email protected]> To: [email protected] Sent: Tuesday, March 27, 2012 2:33:14 PM Subject: Re: [Elecraft] K3 Filter questions On 3/27/2012 11:12 AM, [email protected] wrote: > I am pretty sure the DSP filter is effective only if it is narrower than the > roofing filter. Not at all true. When reading K6LL's comments, bear in mind that he is a VERY good operator and engineer. I value anything he has to say. I posted yesterday that I had done almost the same thing -- told the K3 that my 1.8 kHz filter was a 2 kHz filter so that it switches in at 2 kHz -- and that I was pretty pleased with the result. When there are multiple filters in any signal chain their responses combine (the proper engineering term is "cascade") so that the total filtering capability is that of both added together. This is most pronounced when two filters have approximately the same bandwidth and are set to the same frequency. The way this works is that if filter #1 is rejecting by 6 dB at a given off-frequency point and filter #2 is attenuating by 4 dB, the combined rejection will be 10 dB. This is approximately what K6LL and I are doing. 73, Jim K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
