Joe et. al. Someone mentioned combining the Flex I/Q mixer with the roofing filters of the K3. I've noticed Icom started using the I/Q mixer with the IC-7800, IC-7700 and now the IC-7600. This seems to be how they can get by with only a broad skirted 3 kHz roofing filter and still have respectable performance. I'm wondering what it would be like if Elecraft did use a similar DSP but with narrow xtal filters ie. 200 Hz? It does sound like a good mix but I'm no expert on DSP. Steve N4LQ [email protected] ----- Original Message ----- From: "Joe Subich, W4TV" <[email protected]> To: <[email protected]> Sent: Thursday, August 06, 2009 11:47 PM Subject: Re: [Elecraft] HaroldZ, Variable bandwidth filter, etc
> >> What is the two tone dynamic range of the K3 when both >> signals are inside the roofing filter bandwidth? >> >> Close-in IMD measurements are virtually always done using a >> CW bandwidth filter. None of the published data (ARRL, >> Sherwood Engineering) tests IMD inside the DSP process >> without xtal filter selectivity. > > With roofing filters that are matched to the appropriate bandwidth > for the operating mode dynamic range inside the roofing filter is > not a consideration. Once the interfering signal gets inside the > roofing filter, it's interference and nothing is going to get rid > of it. > > For example, the point of a 200 Hz filter is not so much to reduce > IMD (remember the interfering signals need to be 200 Hz and 400 Hz > (or 300 Hz and 600 Hz, etc. away to cause IMD "on frequency") but > to prevent close in signals from effecting AGC, etc. As Rob Sherwood > has said many times, the problem with close in interference is just > as likely to be "dirty" signals (phase noise, key clicks, and > transmitter IMD) as it is to be receiver effects as long as the > dynamic range is 90 dB or more. > > 73, > > ... Joe, W4TV > > > >> -----Original Message----- >> From: [email protected] >> [mailto:[email protected]] On Behalf Of William Carver >> Sent: Thursday, August 06, 2009 9:56 PM >> To: [email protected] >> Subject: [Elecraft] HaroldZ, Variable bandwidth filter, etc >> >> >> What is the two tone dynamic range of the K3 when both >> signals are inside the roofing filter bandwidth? >> >> Close-in IMD measurements are virtually always done using a >> CW bandwidth filter. None of the published data (ARRL, >> Sherwood Engineering) tests IMD inside the DSP process >> without xtal filter selectivity. >> >> My experience with a homebrew K3-like topology, except a >> strong diode second mixer (instead of NE602-type mixer), is >> the limiting factor INSIDE THE ROOFING FILTER bandwidth can >> be the DSP performance. If you put a FLEX DSP processor >> behind a K3 2.8 KHz SSB filter you would have FLEX numbers >> close in, K3 numbers outside the roofing filter. The >> advantages of both. >> >> So rather than bandaid by buying more filters, or push for a >> variable filter, if the dynamic range inside the filter is >> not good enough one should concentrate on (1) strengthening >> the post-xtal-filter intercept of the receiver circuits and >> (2) reducing the close-in phase noise of the LO. >> >> Bill - W7AAZ >> >> >> >> >> >> >> ______________________________________________________________ >> 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 ______________________________________________________________ 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
