That is why we built special test fixtures for us and INRAD to test strong signal IMD handling on all of our K3 filters.
73, Eric On 11/18/2010 4:49 AM, Geoffrey Mackenzie-Kennedy wrote: > Bruce, > > I believe that your suspicion is correct. The sticking point in the design > of a high performance up-conversion receiver at this time is the first LO, > whose phase noise must be suitably "low" and whose cost is acceptable. There > can be problems with VHF "Roofing" filters, but there are ways to overcome > these. > > Regarding the use of very narrow roofing filters (crystal) in a > down-conversion receiver, there is an underlying filter generated IMD > problem which might or might not affect the IMD performance of the overall > receiver - depending upon the "IMD performance" of those parts of the > receiver ahead of and behind the filter. The problem is that for any given > quality of quartz used in the crystals, the IMD performance of a crystal > filter can be shown to worsen as the filter's bandwidth narrows. I suspect > that the 6 kHz roofing filter used in Kenwood's TS-590S ahead of the IF > crystal filters is there to give some protection to the narrower IF filters. > > 73, > Geoff > GM4ESD > > > Bruce McLaughlin wrote on Wednesday, November 17, 2010, at 11:02 PM: > > >> 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. > <snip> > > > ______________________________________________________________ > 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
