Bruce, there is a limit on the upper signal frequency based on the I.F. chosen and how good one can make the input filter in order to have adequate image frequency rejection while avoiding excessive filter loss.
AFAIK, "up conversion" became popular as a way to cover the VLF frequencies and avoid any tuning gaps (such as the K3 has between 8 and 9 MHz) by putting the first I.F. up above the highest tuning range. That wasn't practical in the past (esp. with vacuum tubes) because mixers and amplifiers with low noise figures needed more protection from very strong signals. But with more robust devices it became practical. Even so, the best performance occurs with down conversion as it always has. Ron AC7AC -----Original Message----- I suspect it is going to become the standard for many if not most of the new radios. As soon as it became apparent that effective roofing filters can really improve the close in IMD performance, it seems as if a low first IF frequency has become almost mandatory. I note that the Orion and the new Yaesu FT 5000 both use down conversion for the first IF and, therefore, have effective narrow roofing filters. I wonder when, or if, ICOM and the others will follow suit. Bruce-W8FU -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Wayne Burdick Sent: Tuesday, November 16, 2010 6:32 PM To: Elecraft Reflector Subject: Re: [Elecraft] Down-conversion ______________________________________________________________ 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
