To All, Once the phase noise of local oscillator has been addressed the IF filter becomes the next most important element in the receiving system for audio clarity. Having a flat amplitude response in the filter pass band gives a clear quality to the voice. Most ceramic filters and some crystal filters have poor pass band responses leaving the audio on the muddy side. Collins mechanical filters have for several decades been the benchmark for receiver IF filter technology.
SDR has eliminated the need for IF filtering at the expense of poor image responses in cases where high level signals are present in adjacent channels. SDR works best in satellite and cell phone environments where signal levels are controlled either by distance or minimum power necessary for communications. Amateur radios of the future may emulate cell phone power control technology, but until that is widely in use, a hybrid system with a roofing filter and SDR IF currently offers the best performance. Art, KC6UQH -----Original Message----- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Alan P. Biddle Sent: Saturday, May 30, 2009 12:29 AM To: amsat-bb@amsat.org Subject: [amsat-bb] Re: FT-847 vs IC-910 I would also strongly recommend better filters than the stock ceramic filters to do a comparison. When I bought FT-847 in 1998, Inrad did not have compatible filters, so I bought the Collins mechanical filters which were available. I did not do extensive testing, but the HF reception was remarkably better than the stock filters. Alan WA4SCA _______________________________________________ Sent via amsat...@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb __________ Information from ESET NOD32 Antivirus, version of virus signature database 4116 (20090529) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com __________ Information from ESET NOD32 Antivirus, version of virus signature database 4116 (20090529) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com _______________________________________________ Sent via amsat...@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
